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Micromachines
Volume 10
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Micromachines, Volume 10, Issue 5 (May 2019) – 71 articles

Cover Story (view full-size image): Three-dimensional (3D) microfluidic channels simulate human tissues such as blood vessels and can be used in surgical simulator models to evaluate surgical devices and train novice surgeons. We established a novel method for fabricating microchannels within a spherical model such as an eyeball. We propose integrating the newly fabricated eye model with the membrane covered 3D microchannel to train novice surgeons to perform glaucoma surgery. View this paper
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16 pages, 10500 KiB  
Article
Robotic Micropipette Aspiration for Multiple Cells
by Yaowei Liu, Maosheng Cui, Jingjing Huang, Mingzhu Sun, Xin Zhao and Qili Zhao
Micromachines 2019, 10(5), 348; https://doi.org/10.3390/mi10050348 - 27 May 2019
Cited by 16 | Viewed by 6007
Abstract
As there are significant variations of cell elasticity among individual cells, measuring the elasticity of batch cells is required for obtaining statistical results of cell elasticity. At present, the micropipette aspiration (MA) technique is the most widely used cell elasticity measurement method. Due [...] Read more.
As there are significant variations of cell elasticity among individual cells, measuring the elasticity of batch cells is required for obtaining statistical results of cell elasticity. At present, the micropipette aspiration (MA) technique is the most widely used cell elasticity measurement method. Due to a lack of effective cell storage and delivery methods, the existing manual and robotic MA methods are only capable of measuring a single cell at a time, making the MA of batch cells low efficiency. To address this problem, we developed a robotic MA system capable of storing multiple cells with a feeder micropipette (FM), picking up cells one-by-one to measure their elasticity with a measurement micropipette (MM). This system involved the following key techniques: Maximum permissible tilt angle of MM and FM determination, automated cell adhesion detection and cell adhesion break, and automated cell aspiration. The experimental results demonstrated that our system was able to continuously measure more than 20 cells with a manipulation speed quadrupled in comparison to existing methods. With the batch cell measurement ability, cell elasticity of pig ovum cultured in different environmental conditions was measured to find optimized culturing protocols for oocyte maturation. Full article
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Figure 1
<p>The operation process of new micropipette aspiration (MA) process for batch cells. (<b>a</b>) Insert measuring micropipette (MM) into the feeder micropipette (FM). (<b>b</b>) Deliver the cells to the microscopic field and hold the target cell by the MM. (<b>c</b>) Draw back the adhesive cells with the calculated negative pressure. (<b>d</b>) Withdraw the FM and measure the Young’s modulus of the cell by MM.</p> Full article ">Figure 2
<p>Schematic: The tilted measuring micropipette (MM) is just able to insert into the tilted feeder micropipette (FM).</p> Full article ">Figure 3
<p>Schematic: The cell almost cannot be aspirated by the tilted measuring micropipette (MM).</p> Full article ">Figure 4
<p>The FM was tilted to 12.3°, and the MM was horizontal.</p> Full article ">Figure 5
<p>Tilt angle detection results. (<b>a</b>) A tilted feeder micropipette (FM). (<b>b</b>) A tilted measuring micropipette (MM). The red frames in (<b>a</b>,<b>b</b>) are the detected edges of the FM and MM. The width changes due to the defocusing along the length direction of the (<b>c</b>) feeder micropipette and (<b>d</b>) measuring micropipette.</p> Full article ">Figure 6
<p>The process of oocyte detection. (<b>a</b>) The region of interest (ROI) selection. (<b>b</b>) The image after morphological opening. (<b>c</b>) The binary image. (<b>d</b>) The number of black pixels in the binary image in ROI during the delivery process.</p> Full article ">Figure 7
<p>Schematic figure of force analysis when drawing back the other cell from the held cell.</p> Full article ">Figure 8
<p>Diagram of force analysis in the calibration experiment.</p> Full article ">Figure 9
<p>Automated aspiration of the oocyte. (<b>a</b>) Diagram of the shell model using to estimate the Young’s modulus of the zona pellucida of the oocyte. (<b>b</b>) The MA of porcine oocytes.</p> Full article ">Figure 10
<p>The operation flow of new MA process for batch cells.</p> Full article ">Figure 11
<p>NK-MR601 micro-operation system.</p> Full article ">Figure 12
<p>Oocyte aspiration. (<b>a</b>) Oocyte aspiration for measuring its Young’s modulus; (<b>b</b>) Oocyte edge position in the measuring process.</p> Full article ">Figure 13
<p>The relationship between the aspiration pressure and the elongation of the zona pellucida (ZP) when its Young’s modulus is detected as 22.80 kPa.</p> Full article ">
18 pages, 3841 KiB  
Review
Development of Bioelectronic Devices Using Bionanohybrid Materials for Biocomputation System
by Jinho Yoon, Taek Lee and Jeong-Woo Choi
Micromachines 2019, 10(5), 347; https://doi.org/10.3390/mi10050347 - 27 May 2019
Cited by 15 | Viewed by 4506
Abstract
Bioelectronic devices have been researched widely because of their potential applications, such as information storage devices, biosensors, diagnosis systems, organism-mimicking processing system cell chips, and neural-mimicking systems. Introducing biomolecules including proteins, DNA, and RNA on silicon-based substrates has shown the powerful potential for [...] Read more.
Bioelectronic devices have been researched widely because of their potential applications, such as information storage devices, biosensors, diagnosis systems, organism-mimicking processing system cell chips, and neural-mimicking systems. Introducing biomolecules including proteins, DNA, and RNA on silicon-based substrates has shown the powerful potential for granting various functional properties to chips, including specific functional electronic properties. Until now, to extend and improve their properties and performance, organic and inorganic materials such as graphene and gold nanoparticles have been combined with biomolecules. In particular, bionanohybrid materials that are composed of biomolecules and other materials have been researched because they can perform core roles of information storage and signal processing in bioelectronic devices using the unique properties derived from biomolecules. This review discusses bioelectronic devices related to computation systems such as biomemory, biologic gates, and bioprocessors based on bionanohybrid materials with a selective overview of recent research. This review contains a new direction for the development of bioelectronic devices to develop biocomputation systems using biomolecules in the future. Full article
(This article belongs to the Special Issue Emerging Memory and Computing Devices in the Era of Intelligent Machines)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Bioelectronic devices based on bionanohybrid materials to develop biomemory, biologic gates, and bioprocessors for biocomputation systems.</p> Full article ">Figure 2
<p>Multilevel biomemory device. (<b>A</b>) Schematic image demonstrating a multilevel biomemory device using metal ions states to control two different kinds of metalloprotein. (<b>B</b>) Cyclic voltammogram of a multilevel biomemory device composed of recombinant azurin and cytochrome c that shows two apparently distinguished reduction potential peaks and two oxidation potential peaks. (<b>C</b>) Memory performance of a multilevel biomemory device including writing, reading, and erasing steps by applying the potential values of reduction and oxidation potential peak values and the OCP values of metalloproteins. (Reproduced with permission from [<a href="#B43-micromachines-10-00347" class="html-bibr">43</a>], published by John Wiley and Sons, 2010).</p> Full article ">Figure 3
<p>Electrochemical signal enhanced biomemory device. (<b>A</b>) Schematic image of the biomemory device composed of Azu and gold nanoparticles (GNP). (<b>B</b>) Redox potential peak values for optimizing the GNP diameter. (<b>C</b>) Cyclic voltammogram of Azu–GNP and Azu. (<b>D</b>) memory performance of Azu–GNP and Azu. (Reproduced with permission from [<a href="#B17-micromachines-10-00347" class="html-bibr">17</a>], published by John Wiley and Sons, 2011).</p> Full article ">Figure 4
<p>Resistive biomemory device. (<b>A</b>) Schematic image of a resistive biomemory device composed of pRNA-3WJ and quantum dot (QD) on a gold substrate, (<b>B</b>) I–V curves of bare Au, pRNA-3WJ, QD and pRNA-3WJ, and QD. (<b>C</b>) Resistive switching function and stability test for a resistive biomemory device composed of MoS<sub>2</sub> and DNA on a gold substrate with apparently distinguished resistance states and long-term stability for 10 days. (Reproduced with permission from [<a href="#B50-micromachines-10-00347" class="html-bibr">50</a>], published by the American Chemical Society, 2015, and reproduced with permission from [<a href="#B52-micromachines-10-00347" class="html-bibr">52</a>], published by Elsevier, 2019).</p> Full article ">Figure 5
<p>Biologic gates. (<b>A</b>) Schematic image of a DNA-based biologic gate based on metal ions inserted inside mismatched DNA pairs and differential pulse voltammetry (DPV) results of this device by controlling output signals through Ag<sup>+</sup> and Hg<sup>2+</sup> ions inserted inside mismatched DNA pairs. (<b>B</b>) Schematic image of a protein/DNA-based biologic gate through the signal transduction of a protein-based biologic gate to a DNA-based biologic gate for the final outputted fluorescence signal (Reproduced with permission from [<a href="#B64-micromachines-10-00347" class="html-bibr">64</a>], published by John Wiley and Sons, 2013 and reproduced with permission from [<a href="#B65-micromachines-10-00347" class="html-bibr">65</a>], published by John Wiley and Sons, 2016).</p> Full article ">Figure 6
<p>Analog decision mimicking bioelectronic device. (<b>A</b>) Schematic image and theory of this bioelectronic device through the analogously processed output signals by two different external factors inputted (negative input and positive input) by electrochemical investigation. (<b>B</b>) Bionanohybrid material used for this device composed of metalloprotein used as signal generator, organic chemical linkers as signal controller, and inorganic materials used for signal modulation. (<b>C</b>) The plotted results of analog decision-making based on the analysis of electrochemical signal by defined external factors showed the decision variation of 12 persons based on the defined threshold values. (Reproduced with permission from [<a href="#B59-micromachines-10-00347" class="html-bibr">59</a>], the figures follow the terms of use under a Creative Commons Attribution 4.0 International License.).</p> Full article ">Figure 7
<p>Bioprocessors. (<b>A</b>) Schematic image and electrophoresis results of DNA-based bioprocessor composed of six stages, including the first stage as problem encoder, the second stage as DNA solution bay for converted DNA preparation, the third as mixing controller for mixing and ligase of appropriate DNA sequences to make the template of DNA duplexes, the fourth as solution purifier for isolation of optimal DNA template from impurities such as the incompletely hybridized oligonucleotides or enzymes, the fifth as PCR amplifier for amplification of optimal DNA template which is the optimal route, and the sixth as gel electrophoresis to acquire the final electrophoresis data for solving optimal-route-planning problems, (<b>B</b>) Schematic image of bioprocessor based on bionanohybrid materials to demonstrate the specific processing functions including the electrochemical signal reinforcement, regulation, and amplification. (Reproduced with permission from [<a href="#B82-micromachines-10-00347" class="html-bibr">82</a>], published by American Chemical Society, 2015, and reproduced with permission from [<a href="#B31-micromachines-10-00347" class="html-bibr">31</a>], published by John Wiley and Sons, 2013).</p> Full article ">
18 pages, 2232 KiB  
Article
The Matrix KV Storage System Based on NVM Devices
by Tao Cai, Fuli Chen, Qingjian He, Dejiao Niu and Jie Wang
Micromachines 2019, 10(5), 346; https://doi.org/10.3390/mi10050346 - 27 May 2019
Cited by 3 | Viewed by 3103
Abstract
The storage device based on Nonvolatile Memory (NVM devices) has high read/write speed and embedded processor. It is a useful way to improve the efficiency of Key-Value (KV) application. However it still has some limitations such as limited capacity, poorer computing power compared [...] Read more.
The storage device based on Nonvolatile Memory (NVM devices) has high read/write speed and embedded processor. It is a useful way to improve the efficiency of Key-Value (KV) application. However it still has some limitations such as limited capacity, poorer computing power compared with CPU, and complex I/O system software. Thus it is not an effective way to construct KV storage system with NVM devices directly. We analyze the characteristics of NVM devices and demands of KV application to design the matrix KV storage system based on NVM Devices. The group collaboration management based on Bloomfilter, intragroup optimization based on competition, embedded KV management based on B+-tree, and the new interface of KV storage system are presented. Then, the embedded processor in the NVM device and CPU can be comprehensively utilized to construct a matrix KV pair management system. It can improve the storage and management efficiency of massive KV pairs, and it can also support the efficient execution of KV applications. A prototype is implemented named MKVS (the matrix KV storage system based on NVM devices) to test with YCSB (Yahoo! Cloud System Benchmark) and to compare with the current in-memory KV store. The results show that MKVS can improve the throughput by 5.98 times, and reduce the 99.7% read latency and 77.2% write latency. Full article
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<p>The structure of MKVS.</p> Full article ">Figure 2
<p>Schematic diagram of the MKVS access interface.</p> Full article ">Figure 3
<p>The throughput of changing the number of KV pairs with Workloadb.</p> Full article ">Figure 4
<p>The throughput of changing the number of access operations with Workloadb.</p> Full article ">Figure 5
<p>The throughput of changing the number of KV pairs with Workloada.</p> Full article ">Figure 6
<p>The throughput of changing the number of access operations with Workloada.</p> Full article ">
2 pages, 149 KiB  
Editorial
Editorial for the Special Issue on AC Electrokinetics in Microfluidic Devices
by Antonio Ramos and Pablo García-Sánchez
Micromachines 2019, 10(5), 345; https://doi.org/10.3390/mi10050345 - 25 May 2019
Viewed by 2058
Abstract
The use of AC electric fields for manipulating and/or characterizing liquids and small particles in suspension is well-known [...] Full article
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices)
10 pages, 1831 KiB  
Article
Effects of Charge Transport Materials on Blue Fluorescent Organic Light-Emitting Diodes with a Host-Dopant System
by Neng Liu, Sijiong Mei, Dongwei Sun, Wuxing Shi, Jiahuan Feng, Yuanming Zhou, Fei Mei, Jinxia Xu, Yan Jiang and Xianan Cao
Micromachines 2019, 10(5), 344; https://doi.org/10.3390/mi10050344 - 25 May 2019
Cited by 79 | Viewed by 7373
Abstract
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including [...] Read more.
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N,N’-Di(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4’-diamine(NPB), 4,4’-Bis(N-carbazolyl)-1,1,-biphenyl (CBP) and molybdenum trioxide (MoO3), were selected to be HTLs, and the blue OLED with TAPC HTL exhibited a maximum luminance of 2955 cd/m2 and current efficiency (CE) of 5.75 cd/A at 50 mA/cm2, which are 68% and 62% higher, respectively, than those of the minimum values found in the device with MoO3 HTL. Fixing the hole transport material TAPC, the replacement of TPBi ETL with Bphen ETL can further improve the performance of the device, in which the maximum luminance can reach 3640 cd/m2 at 50 mA/cm2, which is 23% higher than that of the TPBi device. Furthermore, the lifetime of the device is also optimized by the change of ETL. These results indicate that the carrier mobility of transport materials and energy level alignment of different functional layers play important roles in the performance of the blue OLEDs. The findings suggest that selecting well-matched electron and hole transport materials is essential and beneficial for the device engineering of high-efficiency blue OLEDs. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) The schematic structure of our blue organic light-emitting diodes (OLEDs). (<b>b</b>) The energy level diagram of the blue OLEDs.</p> Full article ">Figure 2
<p>(<b>a</b>) Current density versus voltage curves, (<b>b</b>) luminance versus current density curves, (<b>c</b>) current efficiency versus current density curves of blue OLEDs with 2,2’,2″-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) electron transport layers (ETL) and four different hole transport layers (HTLs). (<b>d</b>) Luminance versus current density curves of blue OLEDs with TPBi ETL and N,N’-Di(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4’-diamine (NPB), 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), NPB/TAPC HTLs.</p> Full article ">Figure 3
<p>(<b>a</b>) Normalized electroluminescence spectra of OLEDs with TPBi ETL and four different HTLs. The inset is a luminescence image of the TAPC device at 50 mA/cm<sup>2</sup>. (<b>b</b>) Photoluminescence (PL) spectra of 30 nm mCP and BCzVBi films deposited on ITO substrates.</p> Full article ">Figure 4
<p>(<b>a</b>) Current density versus voltage curves, (<b>b</b>) luminance versus current density curves, (<b>c</b>) current efficiency versus current density curves, (<b>d</b>) normalized EL spectra of blue OLEDs with TAPC HTL and 4,7-Diphenyl-1,10-phenanthroline (Bphen), TPBi ETLs.</p> Full article ">Figure 5
<p>Evolution of the normalized luminance and voltage of blue OLEDs with Bphen and TPBi ETL stressed under 20 mA/cm<sup>2</sup>.</p> Full article ">
19 pages, 8224 KiB  
Article
The Effect of Displacement Constraints on the Failure of MEMS Tuning Fork Gyroscopes under Shock Impact
by Jiangkai Lian, Jianhua Li and Lixin Xu
Micromachines 2019, 10(5), 343; https://doi.org/10.3390/mi10050343 - 24 May 2019
Cited by 9 | Viewed by 3316
Abstract
Displacement constraints such as stops are widely used in engineering to improve the shock resistance of microelectromechanical system (MEMS) tuning fork gyroscopes. However, in practical applications, it has been found that unexpected breakage can occur on MEMS tuning fork gyroscopes with stops. In [...] Read more.
Displacement constraints such as stops are widely used in engineering to improve the shock resistance of microelectromechanical system (MEMS) tuning fork gyroscopes. However, in practical applications, it has been found that unexpected breakage can occur on MEMS tuning fork gyroscopes with stops. In this paper, the effects of two displacement constraints on the failure mode of MEMS tuning fork gyroscopes are studied. The MEMS tuning fork gyroscope is simplified to a two-degree-of-freedom (2DOF) model, then finite element analysis (FEA) is used to study the effects of displacement constraint on the gyroscope. The analysis proves that even if the displacement constraint of direct contact with the weak connecting beam is not established, the equivalent stiffness of the gyroscope can be enhanced by limiting the displacement of the movable mass, thereby improving the shock resistance of the gyroscope. However, under the shock of high-g level, displacement constraint with insufficient spacing will cause multiple collisions of the small-stiffness oscillating frame and lead to an increase in stress. The cause of failure and shock resistance of a MEMS tuning fork gyroscope are verified by the shock test. By comparing the results, we can get a conclusion that is consistent with the theoretical analysis. Full article
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Figure 1
<p>A two-degree-of-freedom (2DOF) model of a microelectromechanical systems (MEMS) tuning fork gyroscope. (<b>a</b>) Simplified schematic of the two-degree-of-freedom (2DOF) model; (<b>b</b>) schematic view of motion and stress of the model when the system is impacted along the negative Z-axis; (<b>c</b>) schematic view of motion and stress of the model when the system is impacted along the positive Z-axis.</p> Full article ">Figure 2
<p>Model of a MEMS tuning fork gyroscope transformed from <a href="#micromachines-10-00343-f001" class="html-fig">Figure 1</a>c when the movable mass adheres to the substrate.</p> Full article ">Figure 3
<p>Comparison of two acceleration processes. A higher loading rate of shock impact means greater acceleration at each moment, which that means a higher velocity at the collision.</p> Full article ">Figure 4
<p>Schematic view of a MEMS tuning fork gyroscope.</p> Full article ">Figure 5
<p>Simplified model and refined parts.</p> Full article ">Figure 6
<p>The Z-axis shock pulses of four different durations and directions applied in the simulation.</p> Full article ">Figure 7
<p>First principal stress of the MEMS tuning fork gyroscope under two Z-axis shock pulses with shock pulse duration of 80 μs.</p> Full article ">Figure 8
<p>First principal stress of the MEMS tuning fork gyroscope under two Z-axis shock pulses with a shock pulse duration of 1 ms.</p> Full article ">Figure 9
<p>Deformation and weak positions under the impact of Shock Pulse 1 (the red arrows with ‘a’ indicate the direction of shock impact relative to the MEMS tuning fork gyroscope).</p> Full article ">Figure 10
<p>The X-axis shock pulses of Shock Pulses 5 and 6 applied in the simulation.</p> Full article ">Figure 11
<p>First principal stress of the MEMS tuning fork gyroscope and the deformation of weak position under the impact of Shock Pulse 5 (a<sub>0</sub> = 25,000 g, τ = 50 μs, the red arrows with ‘a’ indicate the shock direction relative to the MEMS tuning fork gyroscope).</p> Full article ">Figure 12
<p>First principal stress of the MEMS tuning fork gyroscope under the impact of Shock Pulse 6 (a<sub>0</sub> = 25,000 g, τ = 1 ms).</p> Full article ">Figure 13
<p>Schematic cross-section of the MEMS tuning fork gyroscope and fixture.</p> Full article ">Figure 14
<p>The fitted curves based on the measured acceleration pulses with different shock levels.</p> Full article ">Figure 15
<p>The experimental device and installation.</p> Full article ">Figure 16
<p>MEMS tuning fork gyroscope failures under positive Z-axis shock impact (a<sub>0</sub> = 20,000 g, τ = 80 μs).</p> Full article ">Figure 17
<p>MEMS tuning fork gyroscope failures under negative Z-axis shock impact (a<sub>0</sub> = 20,000 g, τ = 80 μs).</p> Full article ">Figure 18
<p>MEMS tuning fork gyroscope failures under X-axis shock impact (a<sub>0</sub> = 25,000 g, τ = 50 μs).</p> Full article ">
9 pages, 5088 KiB  
Article
Fan-Out Wafer and Panel Level Packaging as Packaging Platform for Heterogeneous Integration
by Tanja Braun, Karl-Friedrich Becker, Ole Hoelck, Steve Voges, Ruben Kahle, Marc Dreissigacker and Martin Schneider-Ramelow
Micromachines 2019, 10(5), 342; https://doi.org/10.3390/mi10050342 - 23 May 2019
Cited by 45 | Viewed by 13118
Abstract
Fan-out wafer level packaging (FOWLP) is one of the latest packaging trends in microelectronics. Besides technology developments towards heterogeneous integration, including multiple die packaging, passive component integration in packages and redistribution layers or package-on-package approaches, larger substrate formats are also targeted. Manufacturing is [...] Read more.
Fan-out wafer level packaging (FOWLP) is one of the latest packaging trends in microelectronics. Besides technology developments towards heterogeneous integration, including multiple die packaging, passive component integration in packages and redistribution layers or package-on-package approaches, larger substrate formats are also targeted. Manufacturing is currently done on a wafer level of up to 12”/300 mm and 330 mm respectively. For a higher productivity and, consequently, lower costs, larger form factors are introduced. Instead of following the wafer level roadmaps to 450 mm, panel level packaging (PLP) might be the next big step. Both technology approaches offer a lot of opportunities as high miniaturization and are well suited for heterogeneous integration. Hence, FOWLP and PLP are well suited for the packaging of a highly miniaturized energy harvester system consisting of a piezo-based harvester, a power management unit and a supercapacitor for energy storage. In this study, the FOWLP and PLP approaches have been chosen for an application-specific integrated circuit (ASIC) package development with integrated SMD (surface mount device) capacitors. The process developments and the successful overall proof of concept for the packaging approach have been done on a 200 mm wafer size. In a second step, the technology was scaled up to a 457 × 305 mm2 panel size using the same materials, equipment and process flow, demonstrating the low cost and large area capabilities of the approach. Full article
(This article belongs to the Special Issue Smart Miniaturised Energy Harvesting)
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<p>Existing wafer and panel sizes influencing fan-out panel level packaging developments.</p> Full article ">Figure 2
<p>Fan-out wafer/panel level packaging process flow options.</p> Full article ">Figure 3
<p>Fan-out wafer/panel level package structures from different process flow options.</p> Full article ">Figure 4
<p>Package layout; (<b>a</b>) daisy chain package, (<b>b</b>) functional.</p> Full article ">Figure 5
<p>Die and SMD assembly on the carrier; (<b>a</b>) 200 mm wafer, (<b>b</b>) detail of the 457 × 305 mm<sup>2</sup> panel.</p> Full article ">Figure 6
<p>Existing wafer and panel sizes influencing fan-out panel level packaging developments.</p> Full article ">Figure 7
<p>Processed fan-out panel; (<b>a</b>) panel detail, (<b>b</b>) panel overview with package detail (ASIC with SMD components).</p> Full article ">Figure 8
<p>Manufactured ASIC packages by FOWLP/PLP; (<b>a</b>) daisy chain package, (<b>b</b>) functional package.</p> Full article ">Figure 9
<p>Electrical test results of the daisy chain packages; (<b>a</b>) daisy chain resistance of chip to package interconnects, (<b>b</b>) capacity of integrated capacitors.</p> Full article ">Figure 10
<p>X-ray CT package analysis; (<b>a</b>) package overview, (<b>b</b>) package top layer; (<b>c</b>) virtual cross section through chip interconnects, (<b>d</b>) virtual cross section through SMD interconnects.</p> Full article ">Figure 10 Cont.
<p>X-ray CT package analysis; (<b>a</b>) package overview, (<b>b</b>) package top layer; (<b>c</b>) virtual cross section through chip interconnects, (<b>d</b>) virtual cross section through SMD interconnects.</p> Full article ">Figure 11
<p>Package cross section; ASIC with SMD component embedded in the molding compound and connected by a thin film redistribution layer.</p> Full article ">
12 pages, 5677 KiB  
Article
Scalable Fabrication and Testing Processes for Three-Layer Multi-Color Segmented Electrowetting Display
by Guisong Yang, Biao Tang, Dong Yuan, Alex Henzen and Guofu Zhou
Micromachines 2019, 10(5), 341; https://doi.org/10.3390/mi10050341 - 23 May 2019
Cited by 11 | Viewed by 4061
Abstract
Colorful electrowetting displays (EWD) present many challenges, such as scalability and electro-optical performance improvement (e.g., brightness, color gamut, and contrast ratio). The first full investigation of scalable fabrication and testing processes for multi-color segmented EWD with potentially unprecedented electro-optical performance is proposed. A [...] Read more.
Colorful electrowetting displays (EWD) present many challenges, such as scalability and electro-optical performance improvement (e.g., brightness, color gamut, and contrast ratio). The first full investigation of scalable fabrication and testing processes for multi-color segmented EWD with potentially unprecedented electro-optical performance is proposed. A three-layer architecture is employed to achieve colorful EWD, where the key components are three primary color layers (cyan, magenta, and yellow), switched independently. Unlike previous reports referred to herein, which used the same fabrication and testing processes for each layer, this architecture facilitates a uniform performance, improves yield, and simplifies the process for colorful EWD. With an aperture ratio greater than 80%, National Television Standards Committee (NTSC) color gamut area greater than 63%, switching speed lower than 12 ms, and DC driving voltage below 22V, the testing results of colorful EWD are proven successfully by using our proposed processes. The processes investigated in this paper have greatly improved efficiency, suitable for a high-volume of full-color EWD. Full article
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Figure 1
<p>Schematic of electrowetting display and images of a tested sample. (<b>a</b>) Without voltage applied, a homogeneous oil film is present, showing the colored off-state. (<b>b</b>) With voltage applied, the oil film contracts, showing the white on-state. (<b>c</b>,<b>d</b>) The corresponding top view micrographs demonstrate a typical oil relaxation and contraction of a pixel. The size of the square pixel is 200 μm × 200 μm.</p> Full article ">Figure 2
<p>A three-layer colorful segmented electrowetting display design. (<b>a</b>) Side view of three-layer architecture pixels with the principle of subtractive color mixing in a reflective display. (<b>b</b>) Top view of the segmented electrowetting display arrays and details of pixel design, with the square pixel grid and notch-patterned indium tin oxide (ITO) electrode.</p> Full article ">Figure 2 Cont.
<p>A three-layer colorful segmented electrowetting display design. (<b>a</b>) Side view of three-layer architecture pixels with the principle of subtractive color mixing in a reflective display. (<b>b</b>) Top view of the segmented electrowetting display arrays and details of pixel design, with the square pixel grid and notch-patterned indium tin oxide (ITO) electrode.</p> Full article ">Figure 3
<p>Schematic of scalable and efficient fabrication steps for a three-layer colorful segmented electrowetting display, including photos of some equipment.</p> Full article ">Figure 4
<p>Schematic of the electro-fluid display inspector system for scalable testing process.</p> Full article ">Figure 5
<p>Fabrication results characterization after insulator and lithography steps. (<b>a</b>) Optical micrograph of the edge of the homogeneous amorphous fluoropolymer Teflon AF1600X after the insulator step. (<b>b</b>) A micrograph of the patterned photoresist pixel grids with a 119.7° water contact angle on the hydrophobic fluoropolymer and 35.6° water contact angle on the hydrophilic photoresist after the lithography step. (<b>c</b>) Surface morphology data corresponding to the edge of the fluoropolymer in (<b>a</b>), measured by the stylus profiler. (<b>d</b>) Surface morphology data corresponding to pixel grids in (<b>b</b>), measured by the stylus profiler.</p> Full article ">Figure 6
<p>Photos of three color monochromatic segmented electrowetting display G2.5 size glass substrates after the oil/water filling and sealing of assembly step.</p> Full article ">Figure 7
<p>White area versus voltage curve for the fabricated three-layer colorful segmented electrowetting display, showing cyan, magenta, and yellow oil movement in pixels. Pixels are not activated from 0–9 V, threshold voltage for oil rupture is 10 V, ~50% aperture ratio is achieved at 15 V, and 80% aperture ratio at 22 V.</p> Full article ">Figure 8
<p>Pixel luminance change ratio due to oil motion as a function of time (switching speed) for each color layer (cyan, magenta, and yellow).</p> Full article ">Figure 9
<p>Electrowetting display color gamut demonstration, using scalable fabrication and testing processes. (<b>a</b>) A photo of a fabricated and tested three-layer segmented colorful electrowetting display. (<b>b</b>) Color gamut of the corresponding colorful segmented electrowetting display in (<b>a</b>), measured by an optical colorimeter (63% National Television Standards Committee (NTSC) in International Commission on Illumination (CIE) 1976).</p> Full article ">
3 pages, 163 KiB  
Editorial
Product/Process Fingerprint in Micro Manufacturing
by Guido Tosello
Micromachines 2019, 10(5), 340; https://doi.org/10.3390/mi10050340 - 22 May 2019
Cited by 8 | Viewed by 2691
Abstract
The continuous trend towards miniaturization and multi-functionality embedded in products and processes calls for an ever-increasing research and innovation effort in the development of micro components and related micro manufacturing technologies [...] Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
10 pages, 4358 KiB  
Article
Moiré-Based Alignment Using Centrosymmetric Grating Marks for High-Precision Wafer Bonding
by Boyan Huang, Chenxi Wang, Hui Fang, Shicheng Zhou and Tadatomo Suga
Micromachines 2019, 10(5), 339; https://doi.org/10.3390/mi10050339 - 22 May 2019
Cited by 6 | Viewed by 6510
Abstract
High-precision aligned wafer bonding is essential to heterogeneous integration, with the device dimension reduced continuously. To get the alignment more accurately and conveniently, we propose a moiré-based alignment method using centrosymmetric grating marks. This method enables both coarse and fine alignment steps without [...] Read more.
High-precision aligned wafer bonding is essential to heterogeneous integration, with the device dimension reduced continuously. To get the alignment more accurately and conveniently, we propose a moiré-based alignment method using centrosymmetric grating marks. This method enables both coarse and fine alignment steps without requiring additional conventional cross-and-box alignment marks. Combined with an aligned wafer bonding system, alignment accuracy better than 300 nm (3σ) was achieved after bonding. Furthermore, the working principle of the moiré-based alignment for the backside alignment system was proposed to overcome the difficulty in bonding of opaque wafers. We believe this higher alignment accuracy is feasible to satisfy more demanding requirements in wafer-level stacking technologies. Full article
(This article belongs to the Special Issue Heterogeneous Integration for Optical Micro and Nanosystems)
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<p>(<b>a</b>) Layout of the centrosymmetric grating mark for moiré-based alignment, (<b>b</b>) the top grating mark turns over and are superimposed onto the identical bottom grating mark, the moiré fringes are therefore formed during alignment and bonding processes in (<b>c</b>).</p> Full article ">Figure 2
<p>(<b>a</b>) Moiré fringes generated by the superimposing two line gratings (<span class="html-italic">L</span><sub>1</sub> and <span class="html-italic">L</span><sub>2</sub>) with slightly different pitches (<span class="html-italic">p</span><sub>1</sub> and <span class="html-italic">p</span><sub>2</sub>); (<b>b</b>) the intensity distribution (red line) of superimposed grating image along <span class="html-italic">x</span>-direction, from which a sinusoidal envelop curve (black line) can be derived to address the peaks of moiré fringes more clearly.</p> Full article ">Figure 3
<p>(<b>a</b>) Moiré fringe pattern with a small misalignment by Δ<span class="html-italic">x</span> (≠0), which will lead to a moiré shift (Δ<span class="html-italic">X</span>) in the <span class="html-italic">x</span>-direction between the two rows of moiré fringes; (<b>b</b>) the moiré shift can be determined by detecting the phase difference between two digital moiré fringes, i.e., <span class="html-italic">I</span>(<span class="html-italic">x</span>) and <span class="html-italic">I</span><sub>shift</sub>(<span class="html-italic">x</span>).</p> Full article ">Figure 4
<p>Moiré fringe patterns with various misalignments as examples: (<b>a</b>) Δ<span class="html-italic">x</span> = Δ<span class="html-italic">y</span> = 0; (<b>b</b>) Δ<span class="html-italic">x</span> = 1 μm, Δ<span class="html-italic">y</span> = 2 μm; (<b>c</b>) Δ<span class="html-italic">x</span> = Δ<span class="html-italic">y</span> = 0 with a small angular error (<span class="html-italic">δ</span> = 0.5°).</p> Full article ">Figure 5
<p>Moiré fringe patterns with large misalignments beyond the moiré measurement range: (<b>a</b>) Δ<span class="html-italic">x</span> = 50 μm, Δ<span class="html-italic">y</span> = 0; (<b>b</b>) Δ<span class="html-italic">x</span> = Δ<span class="html-italic">y</span> = 200 μm; (<b>c</b>) Δ<span class="html-italic">x</span> = Δ<span class="html-italic">y</span> = 200 μm with an angular error (<span class="html-italic">δ</span> = 3°).</p> Full article ">Figure 6
<p>Schematic illustration of the aligned wafer bonding system and the moiré-based alignment process using centrosymmetric grating marks.</p> Full article ">Figure 7
<p>The aligned wafer bonding system used in this study: (<b>a</b>) photograph, the schematic diagrams of (<b>b</b>) the parallel adjustment and (<b>c</b>) the infrared (IR) alignment systems.</p> Full article ">Figure 8
<p>(<b>a</b>) Scanning electron microscope (SEM) image of the centrosymmetric grating mark fabricated on the Si wafer; (<b>b</b>) IR image of the moiré fringe pattern for the Si/Si wafer bonding; (<b>c</b>) the intensity distribution as a function of position along <span class="html-italic">x</span>-direction in the blue rectangular region; (<b>d</b>) the moiré shift in <span class="html-italic">x</span>-direction (Δ<span class="html-italic">X</span>, the average value of Δ<span class="html-italic">X</span><sub>1</sub><span class="html-italic">~</span>Δ<span class="html-italic">X</span><sub>4</sub><span class="html-italic">)</span> was measured by analysis of the moiré fringes after fast Fourier transform (FFT) and low pass filter.</p> Full article ">Figure 9
<p>The alignment errors in <span class="html-italic">x</span>- and <span class="html-italic">y</span>- directions after bonding: (<b>a</b>) alignment using the cross-and-box marks; (<b>b</b>) alignment using the moiré-based centrosymmetric grating marks.</p> Full article ">Figure 10
<p>The working principle of moiré-based alignment for the backside alignment system: (<b>a</b>) the calibration between the computer-generated and the captured actual images; (<b>b</b>) detecting the top grating mark positions; (<b>c</b>) detecting the bottom grating mark positions and aligning two wafers by restoring the top and bottom mark positions.</p> Full article ">
11 pages, 4812 KiB  
Article
Effects of UV Irradiation on the Sensing Properties of In2O3 for CO Detection at Low Temperature
by Lucio Bonaccorsi, Angela Malara, Andrea Donato, Nicola Donato, Salvatore Gianluca Leonardi and Giovanni Neri
Micromachines 2019, 10(5), 338; https://doi.org/10.3390/mi10050338 - 22 May 2019
Cited by 10 | Viewed by 2943
Abstract
In this study, UV irradiation was used to improve the response of indium oxide (In2O3) used as a CO sensing material for a resistive sensor operating in a low temperature range, from 25 °C to 150 °C. Different experimental [...] Read more.
In this study, UV irradiation was used to improve the response of indium oxide (In2O3) used as a CO sensing material for a resistive sensor operating in a low temperature range, from 25 °C to 150 °C. Different experimental conditions have been compared, varying UV irradiation mode and sensor operating temperature. Results demonstrated that operating the sensor under continuous UV radiation did not improve the response to target gas. The most advantageous condition was obtained when the UV LED irradiated the sensor in regeneration and was turned off during CO detection. In this operating mode, the semiconductor layer showed an apparent “p-type” behavior due to the UV irradiation. Overall, the effect was an improvement of the indium oxide response at 100 °C toward low CO concentrations (from 1 to 10 ppm) that showed higher results than in the dark, which is promising to extend the detection of CO with an In2O3-based sensor in the sub-ppm range. Full article
(This article belongs to the Special Issue Nanostructure Based Sensors for Gas Sensing: from Devices to Systems)
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<p>Diagram showing the experimental conditions used.</p> Full article ">Figure 2
<p>Scanning Electron Microscopy (SEM) image of the prepared In<sub>2</sub>O<sub>3</sub>.</p> Full article ">Figure 3
<p>XR diffractogram of the calcined indium oxide powder.</p> Full article ">Figure 4
<p>Transient response of the indium oxide sensor to 5 ppm CO at different operating temperatures.</p> Full article ">Figure 5
<p>Transient sensor response at T = 100 °C and different CO concentrations.</p> Full article ">Figure 6
<p>In<sub>2</sub>O<sub>3</sub> sensor response at different CO concentrations and temperatures in “UV Off” (<b>a</b>) and “UV On” (<b>b</b>) mode. Error bars are calculated on the average of 5 runs.</p> Full article ">Figure 7
<p>Transient sensor response at T = 100 °C and different CO concentrations in “UV On in air” mode.</p> Full article ">Figure 8
<p>Sensor response to (<b>a</b>) 10 ppm; (<b>b</b>) 5 ppm and (<b>c</b>) 1 ppm of CO at different operating temperatures and different UV irradiation modes. Error bars are calculated on the average of five runs.</p> Full article ">Figure 9
<p>(<b>a</b>) Calibration curve showing the sensor response to different CO concentrations under the “UV On in air” method; (<b>b</b>) calibration curve plotted in log-log scale.</p> Full article ">Figure 10
<p>Transient sensor response in “UV Off” mode and “UV On in air” mode. (T = 100 °C, 10 ppm CO).</p> Full article ">
20 pages, 13135 KiB  
Article
Development of Piezo-Actuated Two-Degree-of-Freedom Fast Tool Servo System
by Yamei Liu, Yanping Zheng, Yan Gu, Jieqiong Lin, Mingming Lu, Zisu Xu and Bin Fu
Micromachines 2019, 10(5), 337; https://doi.org/10.3390/mi10050337 - 22 May 2019
Cited by 15 | Viewed by 4163
Abstract
Fast tool servo (FTS) machining technology is a promising method for freeform surfaces and machining micro-nanostructure surfaces. However, limited degrees of freedom (DOF) is an inherent drawback of existing FTS technologies. In this paper, a piezo-actuated serial structure FTS system is developed to [...] Read more.
Fast tool servo (FTS) machining technology is a promising method for freeform surfaces and machining micro-nanostructure surfaces. However, limited degrees of freedom (DOF) is an inherent drawback of existing FTS technologies. In this paper, a piezo-actuated serial structure FTS system is developed to obtain translational motions along with z and x-axis directions for ultra-precision machining. In addition, the principle of the developed 2-DOF FTS is introduced and explained. A high-rigidity four-bar (HRFB) mechanism is proposed to produce motion along the z-axis direction. Additionally, through a micro-rotation motion around flexible bearing hinges (FBHs), bi-directional motions along the x-axis direction can be produced. The kinematics of the mechanism are described using a matrix-based compliance modeling (MCM) method, and then the static analysis and dynamic analysis are performed using finite element analysis (FEA). Testing experiments were conducted to investigate the actual performance of the developed system. The results show that low coupling, proper travel, and high natural frequency are obtained. Finally, a sinusoidal wavy surface is uniformly generated by the mechanism developed to demonstrate the effectiveness of the FTS system. Full article
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<p>The mechanical structure of the 2-DOF (degrees of freedom) fast tool servo (FTS).</p> Full article ">Figure 2
<p>Schematic of the designed 2-DOF FTS.</p> Full article ">Figure 3
<p>Schematic of moving principles of the high-rigidity four bar (HRFB) mechanism.</p> Full article ">Figure 4
<p>Schematic of moving principles of the flexible bearing hinges (FBHs) mechanism.</p> Full article ">Figure 5
<p>The coordinate system of (<b>a</b>) leaf spring flexible hinges and (<b>b</b>) right circular flexible hinges.</p> Full article ">Figure 6
<p>Schematic of module I and II.</p> Full article ">Figure 7
<p>Schematic of the module V.</p> Full article ">Figure 8
<p>Schematic of the module VI.</p> Full article ">Figure 9
<p>Input compliance model of the HRFB in the y-axis direction. (<b>a</b>) Equivalent spring model of the HRFB; (<b>b</b>) The simplified model of the HRFB.</p> Full article ">Figure 9 Cont.
<p>Input compliance model of the HRFB in the y-axis direction. (<b>a</b>) Equivalent spring model of the HRFB; (<b>b</b>) The simplified model of the HRFB.</p> Full article ">Figure 10
<p>The simplified model of the input compliance in the x-axis direction.</p> Full article ">Figure 11
<p>Stress simulation of the FTS.</p> Full article ">Figure 12
<p>The first four modes of the mechanism.</p> Full article ">Figure 13
<p>The first four modes of FTS assembly.</p> Full article ">Figure 14
<p>Experimental setup for performance testing.</p> Full article ">Figure 15
<p>Experimental results of (<b>a</b>) motion stroke of the z-axis, (<b>b</b>) the coupling motion along the x-axis.</p> Full article ">Figure 16
<p>Experimental results of (<b>a</b>) motion stroke of the x-axis, (<b>b</b>) the coupling motion along the z-axis.</p> Full article ">Figure 17
<p>Dynamic responses along (<b>a</b>) z-axis and (<b>b</b>) x-axis.</p> Full article ">Figure 18
<p>Resolutions of the mechanism along (<b>a</b>) z-axis and (<b>b</b>) x-axis.</p> Full article ">Figure 19
<p>Step responses along (<b>a</b>) z-axis and (<b>b</b>) x-axis.</p> Full article ">Figure 20
<p>Hysteresis characteristic curve: (<b>a</b>) z-axis direction; (<b>b</b>) x-axis direction.</p> Full article ">Figure 21
<p>Experimental setup for the cutting.</p> Full article ">Figure 22
<p>(<b>a</b>) Simulated sinusoidal wavy surface. (<b>b</b>) The sinusoidal wavy surface machined by the FTS mechanism.</p> Full article ">Figure 23
<p>Sinusoidal wavy surface morphology.</p> Full article ">
11 pages, 5556 KiB  
Article
100 Gb/s Silicon Photonic WDM Transmitter with Misalignment-Tolerant Surface-Normal Optical Interfaces
by Beiju Huang, Zanyun Zhang, Zan Zhang, Chuantong Cheng, Huang Zhang, Hengjie Zhang and Hongda Chen
Micromachines 2019, 10(5), 336; https://doi.org/10.3390/mi10050336 - 22 May 2019
Cited by 4 | Viewed by 4369
Abstract
A 4 × 25 Gb/s ultrawide misalignment tolerance wavelength-division-multiplex (WDM) transmitter based on novel bidirectional vertical grating coupler has been demonstrated on complementary metal-oxide-semiconductor (CMOS)-compatible silicon-on-insulator (SOI) platform. Simulations indicate the bidirectional grating coupler (BGC) is widely misalignment tolerant, with an excess coupling [...] Read more.
A 4 × 25 Gb/s ultrawide misalignment tolerance wavelength-division-multiplex (WDM) transmitter based on novel bidirectional vertical grating coupler has been demonstrated on complementary metal-oxide-semiconductor (CMOS)-compatible silicon-on-insulator (SOI) platform. Simulations indicate the bidirectional grating coupler (BGC) is widely misalignment tolerant, with an excess coupling loss of only 0.55 dB within ±3 μm fiber misalignment range. Measurement shows the excess coupling loss of the BGC is only 0.7 dB within a ±2 μm fiber misalignment range. The bidirectional grating structure not only functions as an optical coupler, but also acts as a beam splitter. By using the bidirectional grating coupler, the silicon optical modulator shows low insertion loss and large misalignment tolerance. The eye diagrams of the modulator at 25 Gb/s don’t show any obvious deterioration within the waveguide-direction fiber misalignment ranger of ±2 μm, and still open clearly when the misalignment offset is as large as ±4 μm. Full article
(This article belongs to the Special Issue Silicon Photonics Bloom)
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<p>(<b>a</b>) Schematic diagram of the bidirectional grating coupler (BGC)-based wavelength-division-multiplex (WDM) optical interconnect tested with fiber array. (<b>b</b>) The schematic diagram of the proposed WDM transmitter.</p> Full article ">Figure 2
<p>(<b>a</b>) The normalized optical power of different directions with perfectly vertical fiber incidence (inset picture shows the schematic of the BGC). (<b>b</b>) The wavelength-dependent grating split ratio with different fiber incident positions.</p> Full article ">Figure 3
<p>(<b>a</b>) The calculated coupling efficiency variation of a unidirectional grating coupler (GC) with fiber misalignment. (<b>b</b>) The calculated coupling efficiency variation of a bidirectional GC with fiber misalignment.</p> Full article ">Figure 4
<p>Schematic of demonstrated ultrawide misalignment tolerance modulator with bidirectional grating couplers.</p> Full article ">Figure 5
<p>(<b>a</b>) Optical micrograph of the WDM transmitter with surface-normal optical interfaces. (<b>b</b>) The zoom-in picture of the MR Multiplexer. (<b>c</b>) The zoomed-in picture of the directional coupler. (<b>d</b>) The zoom-in picture of the bidirectional grating coupler-based surface-normal optical interface.</p> Full article ">Figure 6
<p>(<b>a</b>) The coupling efficiency spectra with waveguide-direction fiber misalignment for a conventional GC. (<b>b</b>) The coupling efficiency spectra with waveguide-direction fiber misalignment for a bidirectional GC.</p> Full article ">Figure 7
<p>Static characteristics of the modulator: (<b>a</b>) Spectra response of modulator with 2.4 nm FSR, (<b>b</b>) Spectra response of modulator at different reversed voltages.</p> Full article ">Figure 8
<p>Normalized optical spectra of microring multiplexer before and after thermal tuning with a channel space of 2.4 nm.</p> Full article ">Figure 9
<p>25 Gb/s eye diagram of WDM transmitter with different wavelengths: (<b>a</b>) 1554 nm, (<b>b</b>) 1556.4 nm, (<b>c</b>) 1558.8 nm, (<b>d</b>) 1561.2 nm.</p> Full article ">Figure 10
<p>25 Gb/s eye diagram of WDM transmitter at different fiber offset from the central position of the grating coupler along the horizontal direction of waveguide: (<b>a</b>) +2 μm offset, (<b>b</b>) −2 μm offset, (<b>c</b>) +4 μm offset, (<b>d</b>) −4 μm offset.</p> Full article ">
11 pages, 5430 KiB  
Article
Analysis of the Downscaling Effect and Definition of the Process Fingerprints in Micro Injection of Spiral Geometries
by Antonio Luca and Oltmann Riemer
Micromachines 2019, 10(5), 335; https://doi.org/10.3390/mi10050335 - 22 May 2019
Cited by 7 | Viewed by 2904
Abstract
Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process [...] Read more.
Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process window. Moreover, the small cavity dimensions represent a limit for process monitoring due to the inability to install in-cavity sensors. Therefore, new solutions must be found. In this study, the downscaling effect was investigated by means of three spiral geometries with different cross sections, considering the achievable flow length as a response variable. Process indicators, called “process fingerprints”, were defined to monitor the process in-line. In the first stage, a relationship between the achievable flow length and the process parameters, as well as between the process fingerprints and the process parameters, was established. Subsequently, a correlation analysis was carried out to find the process indicators that are mostly related to the achievable flow length. Full article
(This article belongs to the Special Issue Product/Process Fingerprint in Micro Manufacturing)
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<p>Spirals with different cross sections.</p> Full article ">Figure 2
<p>Changeable mould unit including a central ejector for spiral geometries with a cross section of 1 × 1 mm<sup>2</sup>. (<b>A</b>) Bottom view; (<b>B</b>) top view; (<b>C</b>) side view.</p> Full article ">Figure 3
<p>Quadrants of the flow spiral.</p> Full article ">Figure 4
<p>Example of measurements of the angle α for three different spiral parts with cross sections of (<b>A</b>) 0.5 × 0.5 mm<sup>2</sup>, flow length: 28.83 mm; (<b>B</b>) 1 × 1 mm<sup>2</sup>, flow length: 62.86 mm and (<b>C</b>) 0.25 × 0.25 mm<sup>2</sup>, flow length: 11.21 mm.</p> Full article ">Figure 5
<p>Working principle of FormicaPlast 2K [<a href="#B16-micromachines-10-00335" class="html-bibr">16</a>].</p> Full article ">Figure 6
<p>Achievable flow lengths for spiral geometries with different cross sections and for different process parameters.</p> Full article ">Figure 7
<p>Main effect plot for spiral geometries with (<b>a</b>) 1 × 1 mm<sup>2</sup>, (<b>b</b>) 0.5 × 0.5 mm<sup>2</sup> and (<b>c</b>) 0.25 × 0.25 mm<sup>2</sup> cross sections.</p> Full article ">Figure 8
<p>Main effect plot for maximum injection pressure.</p> Full article ">Figure 9
<p>Main effect plot for mean injection speed.</p> Full article ">Figure 10
<p>Main effect plot for mean injection pressure.</p> Full article ">Figure 11
<p>Values of the coefficient of correlation calculated between the flow length and the process fingerprints.</p> Full article ">
12 pages, 4353 KiB  
Article
A Rapid Thermal Nanoimprint Apparatus through Induction Heating of Nickel Mold
by Xinxin Fu, Qian Chen, Xinyu Chen, Liang Zhang, Aibin Yang, Yushuang Cui, Changsheng Yuan and Haixiong Ge
Micromachines 2019, 10(5), 334; https://doi.org/10.3390/mi10050334 - 21 May 2019
Cited by 15 | Viewed by 5126
Abstract
Thermal nanoimprint lithography is playing a vital role in fabricating micro/nanostructures on polymer materials by the advantages of low cost, high throughput, and high resolution. However, a typical thermal nanoimprint process usually takes tens of minutes due to the relatively low heating and [...] Read more.
Thermal nanoimprint lithography is playing a vital role in fabricating micro/nanostructures on polymer materials by the advantages of low cost, high throughput, and high resolution. However, a typical thermal nanoimprint process usually takes tens of minutes due to the relatively low heating and cooling rate in the thermal imprint cycle. In this study, we developed an induction heating apparatus for the thermal imprint with a mold made of ferromagnetic material, nickel. By applying an external high-frequency alternating magnetic field, heat was generated by the eddy currents and magnetic hysteresis losses of the ferromagnetic nickel mold at high speed. Once the external alternating magnetic field was cut off, the system would cool down fast owe to the small thermal capacity of the nickel mold; thus, providing a high heating and cooling rate for the thermal nanoimprint process. In this paper, nanostructures were successfully replicated onto polymer sheets with the scale of 4-inch diameter within 5 min. Full article
(This article belongs to the Section D：Materials and Processing)
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<p>Experimental setup for rapid thermal NIL (T-NIL): (<b>a</b>) schematic diagram of the rapid imprint apparatus; (<b>b</b>) cross-section view of the chamber and imprint materials stack during the imprint process; and (<b>c</b>) photograph of the home-made imprint apparatus.</p> Full article ">Figure 2
<p>(<b>a</b>) Photograph of the customer-made induction coil panel; and (<b>b</b>) schematic illustration of induction heating for nickel mold.</p> Full article ">Figure 3
<p>(<b>a</b>) Schematic illustrations of thermal nanoimprint process on polymer sheet; and (<b>b</b>) sequence of heating and pressing during the thermal nanoimprint process.</p> Full article ">Figure 4
<p>(<b>a</b>) Plot of the depth of imprinted poly(methyl methacrylate) (PMMA) nanoholes vs imprint pressure under the imprint temperature of 120 °C; and (<b>b</b>) plot of the depth of imprinted PMMA nanoholes vs imprint temperature under the imprint pressure of 0.5 MPa. The height of nanopillars on the mold is 250 nm.</p> Full article ">Figure 5
<p>(<b>a</b>) Plot of measured temperature at different locations vs imprint time during a typical imprint process; and (<b>b</b>) infrared radiation (IR) thermal image of the nickel mold at one moment in the heating process (the unit for the axis in <a href="#micromachines-10-00334-f005" class="html-fig">Figure 5</a>b is °C).</p> Full article ">Figure 6
<p>(<b>a</b>) Photograph of the 4-inch diameter nickel mold (right) and nanopatterned PMMA sheet fabricated through our rapid imprint apparatus (left); (<b>b</b>) top-viewed scanning electron microscope (SEM) image of the nickel mold; (<b>c</b>) tilted-viewed SEM image of the nickel mold; (<b>d</b>) top-viewed SEM images of the imprinted PMMA sheet; and (<b>e</b>) tilted-viewed SEM images of the imprinted PMMA sheet’s cross section.</p> Full article ">Figure 7
<p>(<b>a</b>) Top-viewed SEM image of the anodic aluminum oxide (AAO) mold; and (<b>b</b>) top-viewed SEM image of the imprinted PMMA layer on polyethylene terephthalate (PET) substrate.</p> Full article ">
17 pages, 11166 KiB  
Article
A New Time–Frequency Feature Extraction Method for Action Detection on Artificial Knee by Fractional Fourier Transform
by Tianrun Wang, Ning Liu, Zhong Su and Chao Li
Micromachines 2019, 10(5), 333; https://doi.org/10.3390/mi10050333 - 20 May 2019
Cited by 7 | Viewed by 2944
Abstract
With the aim of designing an action detection method on artificial knee, a new time–frequency feature extraction method was proposed. The inertial data were extracted periodically using the microelectromechanical systems (MEMS) inertial measurement unit (IMU) on the prosthesis, and the features were extracted [...] Read more.
With the aim of designing an action detection method on artificial knee, a new time–frequency feature extraction method was proposed. The inertial data were extracted periodically using the microelectromechanical systems (MEMS) inertial measurement unit (IMU) on the prosthesis, and the features were extracted from the inertial data after fractional Fourier transform (FRFT). Then, a feature vector composed of eight features was constructed. The transformation results of these features after FRFT with different orders were analyzed, and the dimensions of the feature vector were reduced. The classification effects of different features and different orders are analyzed, according to which order and feature of each sub-classifier were designed. Finally, according to the experiment with the prototype, the method proposed above can reduce the requirements of hardware calculation and has a better classification effect. The accuracies of each sub-classifier are 95.05%, 95.38%, 91.43%, and 89.39%, respectively; the precisions are 78.43%, 98.36%, 98.36%, and 93.41%, respectively; and the recalls are 100%, 93.26%, 86.96%, and 86.68%, respectively. Full article
(This article belongs to the Special Issue MEMS for Aerospace Applications)
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<p>Results of Multiorder fractional Fourier transform (FRFT) with single action (order: 0–1).</p> Full article ">Figure 2
<p>Results of Multiorder FRFT with single action in 3D (order: 0–1).</p> Full article ">Figure 3
<p>(<b>a</b>) The results of FRFT of walking in 0.7 order. (<b>b</b>) The results of FRFT of different actions in 0.7 order.</p> Full article ">Figure 4
<p>The Order–Amplitude figures of different features of 40 groups for the walk action. (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math>, (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>v</mi> <mi>a</mi> <mi>r</mi> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math>, (<b>e</b>) <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math>, (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>, (<b>g</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> and (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>.</p> Full article ">Figure 5
<p>Standard deviation and mean of eight features of the walk action. (<b>a</b>) The standard deviation of each feature, (<b>b</b>) The mean of each feature.</p> Full article ">Figure 6
<p>The Order–Amplitude figures of different features of 40 groups for the upstairs action. (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math>, (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>v</mi> <mi>a</mi> <mi>r</mi> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math>, (<b>e</b>) <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math>, (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>, (<b>g</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> and (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>.</p> Full article ">Figure 7
<p>Standard deviation and mean of eight features of the upstairs action. (<b>a</b>) The standard deviation of each feature, (<b>b</b>) The mean of each feature.</p> Full article ">Figure 8
<p>The Order–Amplitude figures of different features of 40 groups for the dwstairs action. (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math>, (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>v</mi> <mi>a</mi> <mi>r</mi> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math>, (<b>e</b>) <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math>, (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>, (<b>g</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> and (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>.</p> Full article ">Figure 9
<p>Standard deviation and mean of eight features of the dwstairs action. (<b>a</b>) The standard deviation of each feature, (<b>b</b>) The mean of each feature.</p> Full article ">Figure 10
<p>The Order–Amplitude figure of different features of 40 groups for the run action. (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math>, (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>v</mi> <mi>a</mi> <mi>r</mi> </mrow> </semantics></math>, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math>, (<b>e</b>) <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math>, (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>, (<b>g</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> and (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>.</p> Full article ">Figure 11
<p>Standard deviation and mean of eight features of the run action. (<b>a</b>) The standard deviation of each feature, (<b>b</b>) The mean of each feature.</p> Full article ">Figure 12
<p>The effect of classification. (<b>a</b>) walk and dwstairs with the features <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math> when Order = 0.67; (<b>b</b>) walk and dwstairs with the features <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math> when Order = 0.20; (<b>c</b>) walk and dwstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> when Order = 0.67; (<b>d</b>) dwstairs and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math> when Order = 0.64; (<b>e</b>) dwstairs and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math> when Order = 0.20; (<b>f</b>) dwstairs and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math> when Order = 0.64; (<b>g</b>) walk and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> when Order = 0.71; (<b>h</b>) walk and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> when Order = 0.20; (<b>i</b>) walk and upstairs with the features <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math> when Order = 0.71; (<b>j</b>) all the actions with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> when Order = 0.75; (<b>k</b>) all the actions with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math> when Order = 0.75; (<b>l</b>) all the actions with the features <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>M</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math> when Order = 0.75.</p> Full article ">Figure 13
<p>The effect of classification with two features extracted directly in the time domain without FRFT. (<b>a</b>) walk and dwstairs with the features <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>; (<b>b</b>) dwstairs and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>; (<b>c</b>) walk and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>; (<b>d</b>) all the actions with the features <math display="inline"><semantics> <mrow> <mi>v</mi> <mi>a</mi> <mi>r</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>I</mi> <mi>Q</mi> <mi>R</mi> </mrow> </semantics></math>.</p> Full article ">Figure 14
<p>The structure and process of the classifier. As different orders and feature vectors are needed to classify walk, upstairs and dwstairs, one can distinguish walk and dwstairs first, and then separate upstairs from walk and dwstairs, respectively, then separate upstairs from walk and dwstairs, respectively.</p> Full article ">Figure 15
<p>The artificial knee. The position of the pneumatic cylinder, servo motor and control circuit with inertial measurement unit (IMU) have been pointed out.</p> Full article ">Figure 16
<p>MEMS (microelectromechanical systems)-IMU, the position of IMU and barometer have been pointed out.</p> Full article ">Figure 17
<p>The results of each sub-classifier. (<b>a</b>) run and other actions with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>; (<b>b</b>) walk and dwstairs with the features <math display="inline"><semantics> <mrow> <mi>s</mi> <mi>t</mi> <mi>d</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>; (<b>c</b>) walk and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>m</mi> <mi>e</mi> <mi>a</mi> <mi>n</mi> </mrow> </semantics></math>; (<b>d</b>) dwstairs and upstairs with the features <math display="inline"><semantics> <mrow> <mi>r</mi> <mi>a</mi> <mi>n</mi> <mi>g</mi> <mi>e</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mi>p</mi> <mi>k</mi> <mi>s</mi> <mi>N</mi> <mi>u</mi> <mi>m</mi> </mrow> </semantics></math>.</p> Full article ">
18 pages, 5183 KiB  
Article
A Nanomechanical Analysis of Deformation Characteristics of 6H-SiC Using an Indenter and Abrasives in Different Fixed Methods
by Jisheng Pan, Qiusheng Yan, Weihua Li and Xiaowei Zhang
Micromachines 2019, 10(5), 332; https://doi.org/10.3390/mi10050332 - 18 May 2019
Cited by 10 | Viewed by 4369
Abstract
The super-precise theory for machining single crystal SiC substrates with abrasives needs to be improved for its chemical stability, extremely hard and brittle. A Berkovich indenter was used to carry out a systematic static stiffness indentation experiments on single crystal 6H-SiC substrates, and [...] Read more.
The super-precise theory for machining single crystal SiC substrates with abrasives needs to be improved for its chemical stability, extremely hard and brittle. A Berkovich indenter was used to carry out a systematic static stiffness indentation experiments on single crystal 6H-SiC substrates, and then these substrates were machined by utilizing fixed, free, and semi-fixed abrasives, and the nanomechanical characteristics and material removal mechanisms using abrasives in different fixed methods were analyzed theoretically. The results indicated that the hardness of C faces and Si faces of single crystal 6H-SiC under 500 mN load were 38.596 Gpa and 36.246 Gpa respectively, and their elastic moduli were 563.019 Gpa and 524.839 Gpa, respectively. Moreover, the theoretical critical loads for the plastic transition and brittle fracture of C face of single crystal 6H-SiC were 1.941 mN and 366.8 mN, while those of Si face were 1.77 mN and 488.67 mN, respectively. The 6H-SiC materials were removed by pure brittle rolling under three-body friction with free abrasives, and the process parameters determined the material removal modes of 6H-SiC substrates by grinding with fixed abrasives, nevertheless, the materials were removed under full elastic-plastic deformation in cluster magnetorheological finishing with semi-fixed abrasives. Full article
(This article belongs to the Special Issue SiC based Miniaturized Devices)
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<p>Principle of workpiece rotation grinding.</p> Full article ">Figure 2
<p>Experimental apparatus for cluster MR effect in plane polishing.</p> Full article ">Figure 3
<p>Surface topography of nanoindentation.</p> Full article ">Figure 4
<p>Test results of Single crystal 6H-SiC substrates under small loads (<b>a</b>) Load and depth curve in small loads of C face and (<b>b</b>) Load and depth curve in small loads of Si face.</p> Full article ">Figure 5
<p>Test results of Single crystal 6H-SiC substrates under large loads (<b>a</b>) Load and depth curve in large loads of C face and (<b>b</b>) Load and depth curve in large loads of Si face.</p> Full article ">Figure 6
<p>Schematic diagram of fixation abrasive grinding.</p> Full article ">Figure 7
<p>Morphology of Single crystal 6H-SiC substrates ground with different grades of grit (<b>a</b>) No.1 (Ra 0.303 μm), (<b>b</b>) No.2 (Ra 0.029 μm), (<b>c</b>) No.3 (Ra 0.015 μm) and (<b>d</b>) No.4 (Ra 0.002 μm).</p> Full article ">Figure 8
<p>Three-Body and two-body abrasion.</p> Full article ">Figure 9
<p>Morphology of single crystal 6H-SiC substrates after lapping. (<b>a</b>) After lapping by W14 diamond. (<b>b</b>) After lapping by W1.5 diamond.</p> Full article ">Figure 10
<p>Contact state diagram of the abrasives, workpiece, and lapping plate. (<b>a</b>) Ideal contact state. (<b>b</b>) Actual contact state.</p> Full article ">Figure 11
<p>Scanning electron microscope (SEM) morphology of Single crystal 6H-SiC wafer polishing belt. (<b>a</b>) Schematic diagram of polishing, (<b>b</b>) schematic diagram of the polishing belt, (<b>c</b>) SEM morphology of entrance and (<b>d</b>) SEM morphology of exit.</p> Full article ">
13 pages, 9326 KiB  
Article
Fabrication and Characteristic of a Double Piezoelectric Layer Acceleration Sensor Based on Li-Doped ZnO Thin Film
by Chunpeng Ai, Xiaofeng Zhao, Sen Li, Yi Li, Yinnan Bai and Dianzhong Wen
Micromachines 2019, 10(5), 331; https://doi.org/10.3390/mi10050331 - 17 May 2019
Cited by 13 | Viewed by 3345
Abstract
In this paper, a double piezoelectric layer acceleration sensor based on Li-doped ZnO (LZO) thin film is presented. It is constituted by Pt/LZO/Pt/LZO/Pt/Ti functional layers and a Si cantilever beam with a proof mass. The LZO thin films were prepared by radio frequency [...] Read more.
In this paper, a double piezoelectric layer acceleration sensor based on Li-doped ZnO (LZO) thin film is presented. It is constituted by Pt/LZO/Pt/LZO/Pt/Ti functional layers and a Si cantilever beam with a proof mass. The LZO thin films were prepared by radio frequency (RF) magnetron sputtering. The composition, chemical structure, surface morphology, and thickness of the LZO thin film were analyzed. In order to study the effect of double piezoelectric layers on the sensitivity of the acceleration sensor, we designed two structural models (single and double piezoelectric layers) and fabricated them by using micro-electro-mechanical system (MEMS) technology. The test results show that the resonance frequency of the acceleration sensor was 1363 Hz. The sensitivity of the double piezoelectric layer was 33.1 mV/g, which is higher than the 26.1 mV/g of single piezoelectric layer sensitivity, both at a resonance frequency of 1363 Hz. Full article
(This article belongs to the Section A：Physics)
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<p>Basic structure of proposed acceleration sensor in two models: (<b>a</b>) Model I; (<b>b</b>) model II.</p> Full article ">Figure 2
<p>The ANSYS simulation curve between resonance frequency and length of cantilever beam.</p> Full article ">Figure 3
<p>Operating principle of proposed acceleration sensor: (<b>a</b>) Deformation of cantilever beam under the action of <span class="html-italic">F</span>; (<b>b</b>) operating principle of double piezoelectric layer; (<b>c</b>) equivalent circuit of double piezoelectric layer.</p> Full article ">Figure 4
<p>Main fabrication process of the chip: (<b>a</b>) Growing SiO<sub>2</sub>; (<b>b</b>) depositing Ti/Pt; (<b>c</b>) sputtering Li-doped ZnO (LZO) I; (<b>d</b>) depositing Pt; (<b>e</b>) sputtering LZO II; (<b>f</b>) depositing Pt; (<b>g</b>) etching on the top side; (<b>h</b>) releasing cantilever beam.</p> Full article ">Figure 5
<p>Photograph of packaged acceleration sensor chip.</p> Full article ">Figure 6
<p>XRD spectra of the LZO thin film (inset shows (002) peaks of pure ZnO and 5 wt % LZO).</p> Full article ">Figure 7
<p>XPS spectra of the LZO thin film: (<b>a</b>) Full range; (<b>b</b>) narrow scan.</p> Full article ">Figure 8
<p>Atomic force microscopy (AFM) images of the LZO thin film: (<b>a</b>) Surface morphology; (<b>b</b>) 3D surface topography.</p> Full article ">Figure 9
<p>Scanning electron microscope (SEM) cross-section image of the sensor.</p> Full article ">Figure 10
<p>Piezoelectric characteristic of pure ZnO and 5 wt % LZO.</p> Full article ">Figure 11
<p>Testing system of acceleration sensor.</p> Full article ">Figure 12
<p>Relationship curve between output voltage and excitation frequency: (<b>a</b>) resonant frequency; (<b>b</b>) quality factor.</p> Full article ">Figure 13
<p>Output voltage of sensor working in model I and model II.</p> Full article ">Figure 14
<p>Output voltage of the sensor below resonance frequency.</p> Full article ">Figure 15
<p>Sensitivity of the sensor in the range from 1355 Hz to 1363 Hz.</p> Full article ">
28 pages, 3095 KiB  
Review
Synthesis and Applications of Silver Nanowires for Transparent Conductive Films
by Yue Shi, Liang He, Qian Deng, Quanxiao Liu, Luhai Li, Wei Wang, Zhiqing Xin and Ruping Liu
Micromachines 2019, 10(5), 330; https://doi.org/10.3390/mi10050330 - 16 May 2019
Cited by 47 | Viewed by 9162
Abstract
Flexible transparent conductive electrodes (TCEs) are widely applied in flexible electronic devices. Among these electrodes, silver (Ag) nanowires (NWs) have gained considerable interests due to their excellent electrical and optical performances. Ag NWs with a one-dimensional nanostructure have unique characteristics from those of [...] Read more.
Flexible transparent conductive electrodes (TCEs) are widely applied in flexible electronic devices. Among these electrodes, silver (Ag) nanowires (NWs) have gained considerable interests due to their excellent electrical and optical performances. Ag NWs with a one-dimensional nanostructure have unique characteristics from those of bulk Ag. In past 10 years, researchers have proposed various synthesis methods of Ag NWs, such as ultraviolet irradiation, template method, polyol method, etc. These methods are discussed and summarized in this review, and we conclude that the advantages of the polyol method are the most obvious. This review also provides a more comprehensive description of the polyol method for the synthesis of Ag NWs, and the synthetic factors including AgNO3 concentration, addition of other metal salts and polyvinyl pyrrolidone are thoroughly elaborated. Furthermore, several problems in the fabrication of Ag NWs-based TCEs and related devices are reviewed. The prospects for applications of Ag NWs-based TCE in solar cells, electroluminescence, electrochromic devices, flexible energy storage equipment, thin-film heaters and stretchable devices are discussed and summarized in detail. Full article
(This article belongs to the Special Issue New Perspectives in Nanowires: From Growth and Characterization to Technological Applications)
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<p>Properties and applications of recently developed devices based on Ag NWs TCE. “Heat management”, reproduced with permission [<a href="#B14-micromachines-10-00330" class="html-bibr">14</a>]. Copyright 2015, ACS Nano. “Heat TCF” means “Heat Transparent conductive film”, reproduced with permission [<a href="#B15-micromachines-10-00330" class="html-bibr">15</a>]. Copyright 2019, ACS Applied Materials &amp; Interfaces. “Organic light emitting diode (OLED)”, reproduced with permission [<a href="#B16-micromachines-10-00330" class="html-bibr">16</a>]. Copyright 2017, Nanotechnology. “Stretchable LED”, reproduced with permission [<a href="#B17-micromachines-10-00330" class="html-bibr">17</a>]. Copyright 2017, Current Applied Physics. “Solar cell”, reproduced with permission [<a href="#B18-micromachines-10-00330" class="html-bibr">18</a>]. Copyright 2016, Journal of Materials Chemistry A. “TCF”, reproduced with permission [<a href="#B19-micromachines-10-00330" class="html-bibr">19</a>]. Copyright 2016, Solar Energy Materials and Solar Cells. “TCE”, reproduced with permission [<a href="#B20-micromachines-10-00330" class="html-bibr">20</a>]. Copyright 2017, Solar Energy Materials and Solar Cells. “Heater”, reproduced with permission [<a href="#B21-micromachines-10-00330" class="html-bibr">21</a>]. Copyright 2018, Nanoscale.</p> Full article ">Figure 2
<p>Synthesis of Ag NWs and some influencing factors: (<b>a</b>) Diameters and lengths of the Ag NWs as a function of the molar ratio of PVP/AgNO<sub>3</sub> and transmission electron microscope (TEM) image of Ag nanostructures obtained with 0.5 mL of Ag seeds added [<a href="#B45-micromachines-10-00330" class="html-bibr">45</a>]. Copyright 2004, Crystal Growth. (<b>b</b>) Schematic representation of the polyol synthesis of Ag NWs [<a href="#B58-micromachines-10-00330" class="html-bibr">58</a>]. Copyright 2016, Materials Chemistry and Physics. (<b>c</b>) Schematic of the different concentrations of AgNO<sub>3</sub> for synthesis of Ag NWs with different diameters [<a href="#B54-micromachines-10-00330" class="html-bibr">54</a>]. Copyright 2014, Solid State Chemistry. (<b>d</b>) Schematic illustration of template synthesis procedures for obtaining the AgI/Ag heterojunction structures [<a href="#B84-micromachines-10-00330" class="html-bibr">84</a>]. Copyright 2007, Advanced Functional Materials.</p> Full article ">Figure 3
<p>The schematic illustration of the preparation of Ag NWs/ZnO composite TCE and the sheet resistance, transmittance at 550 nm and figure of merit for the Ag NWs TCEs with different spin-coating cycles of ZnO, respectively [<a href="#B91-micromachines-10-00330" class="html-bibr">91</a>]. Copyright 2018, Journal of Alloys and Compounds.</p> Full article ">Figure 4
<p>Two preparation methods of Ag NWs TCE. (<b>a</b>) Fabrication processes of the hybrid electrode on a photopolymer substrate [<a href="#B98-micromachines-10-00330" class="html-bibr">98</a>]. Copyright 2017, Organic Electronics. (<b>b</b>) Schematic illustration of the RTR fabrication process for the embedded Ag NWs TCE on PET film [<a href="#B102-micromachines-10-00330" class="html-bibr">102</a>]. Copyright 2017, Organic Electronics.</p> Full article ">Figure 5
<p>Solutions to the problems of high junction resistance, poor mechanical stability and poor thermal/environmental stability in Ag NWs TCE preparation: (<b>a</b>) SEM images of pristine Ag NWs, NaAlg/Ag NWs composite film, NaAlg/Ag NWs composite film after mechanical pressing and NaAlg/Ag NWs composite film after mechanical pressing and CaCl<sub>2</sub> treatment and the schematic diagrams of junction between Ag NWs corresponding to SEM images, and the schematic illustration of a possible mechanism of crack renovation [<a href="#B104-micromachines-10-00330" class="html-bibr">104</a>]. Copyright 2017, ACS Applied Materials and Interfaces. (<b>b</b>) Schematic of moisture treatment for capillary-force-induced cold welding of Ag NWs [<a href="#B103-micromachines-10-00330" class="html-bibr">103</a>]. Copyright 2017, Nano Letters. (<b>c</b>) The 3D (left) and sectional (right) schematic peel-assembly-transfer (PAT) procedure for the insertion of the PEI/PAA adhesion multilayer between Ag NWs and PET substrates. (<b>d</b>) The prepared Ag NWs TCF on PET substrate indicating that the film is transparent and flexible, and the transmittance spectra of the Ag NWs network before and after PAT process [<a href="#B109-micromachines-10-00330" class="html-bibr">109</a>]. Copyright 2017, Langmuir.</p> Full article ">Figure 6
<p>Some applications of the Ag NWs TCE. (<b>a</b>) Schematic illustration showing the preparation process of NC LDH NSs@Ag@CC by a single-step electrochemical deposition (ECD) process [<a href="#B115-micromachines-10-00330" class="html-bibr">115</a>]. Copyright 2017, Nano Energy. (<b>b</b>) Preparation of the conductive and scattering flexible substrates [<a href="#B119-micromachines-10-00330" class="html-bibr">119</a>]. Copyright 2017, Organic Electronics. (<b>c</b>) Photographs of the light emission of the Ru-based ECL displays with a Ag NWs electrode (top), PEDOT:PSS/Ag NWs hybrid electrode (middle), and T-PEDOT:PSS/Ag NWs hybrid electrode (bottom) and the ECL spectra of the flexible Ru-based ECL displays with the three types of electrodes and the relative change in the intensity of the flexible Ru-based ECL displays with the three types of electrodes as a function of bending cycles [<a href="#B118-micromachines-10-00330" class="html-bibr">118</a>]. Copyright 2017, Chemical Communications. (<b>d</b>) Fabrication and properties of Ag NFs ECSW [<a href="#B124-micromachines-10-00330" class="html-bibr">124</a>]. Copyright 2017, Advanced Material.</p> Full article ">
19 pages, 3663 KiB  
Review
Wettability Manipulation by Interface-Localized Liquid Dielectrophoresis: Fundamentals and Applications
by Jitesh Barman, Wan Shao, Biao Tang, Dong Yuan, Jan Groenewold and Guofu Zhou
Micromachines 2019, 10(5), 329; https://doi.org/10.3390/mi10050329 - 16 May 2019
Cited by 19 | Viewed by 4791
Abstract
Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a [...] Read more.
Electric field-based smart wetting manipulation is one of the extensively used techniques in modern surface science and engineering, especially in microfluidics and optofluidics applications. Liquid dielectrophoresis (LDEP) is a technique involving the manipulation of dielectric liquid motion via the polarization effect using a non-homogeneous electric field. The LDEP technique was mainly dedicated to the actuation of dielectric and aqueous liquids in microfluidics systems. Recently, a new concept called dielectrowetting was demonstrated by which the wettability of a dielectric liquid droplet can be reversibly manipulated via a highly localized LDEP force at the three-phase contact line of the droplet. Although dielectrowetting is principally very different from electrowetting on dielectrics (EWOD), it has the capability to spread a dielectric droplet into a thin liquid film with the application of sufficiently high voltage, overcoming the contact-angle saturation encountered in EWOD. The strength of dielectrowetting depends on the ratio of the penetration depth of the electric field inside the dielectric liquid and the difference between the dielectric constants of the liquid and its ambient medium. Since the introduction of the dielectrowetting technique, significant progress in the field encompassing various real-life applications was demonstrated in recent decades. In this paper, we review and discuss the governing forces and basic principles of LDEP, the mechanism of interface localization of LDEP for dielectrowetting, related phenomenon, and their recent applications, with an outlook on the future research. Full article
(This article belongs to the Special Issue Optofluidics 2018)
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<p>Schematic representation of (<b>A</b>) Pellat’s classic experiment of dielectric liquid actuation against gravity by a non-homogeneous electric field, and (<b>B</b>) dielectric siphon.</p> Full article ">Figure 2
<p>(<b>A</b>) Schematic representation of the closed surface integral <math display="inline"><semantics> <mi mathvariant="sans-serif">Σ</mi> </semantics></math> and corresponding area for calculation of net vertical force of electrical origin on the liquid between insulator-coated electrodes. The choice of closed surface integral is reduced to a simple summation of six discrete areas denoted by 2 for the contribution of air, 5 for the contribution from liquid, and 1 and 3, and 4 and 6 for the contribution from the dielectrics above and below the air–liquid interface, respectively. (<b>B</b>) Schematic representation of the equivalent resistor/capacitor (RC) circuit model for determination of the electric field in different regions. Images are reproduced from Reference [<a href="#B30-micromachines-10-00329" class="html-bibr">30</a>] with the permission of the American Chemical Society.</p> Full article ">Figure 3
<p>Highly insulating liquid actuation by liquid dielectrophoresis (LDEP) forces using co-planar micro electrodes. (<b>A</b>) Cross-sectional view of a dielectric liquid drop sitting on co-planar microelectrodes, and the top view of the spreading of the liquid, stretching like a liquid finger along the gap between the electrodes. (<b>B</b>) Sequence of the snapshots of the video micrographs demonstrating water transportation by LDEP force along the patterned electrode gap. Images are adopted from Reference [<a href="#B31-micromachines-10-00329" class="html-bibr">31</a>] with the permission of Elsevier.</p> Full article ">Figure 4
<p>(<b>A</b>) Schematic of diletcrowetting experiment (ambient air) depicting the cross-sectional view of a dielectric droplet sitting on a substrate without voltage, and the top view of a spreading droplet on linear interdigitated electrodes (IDEs). (<b>B</b>) Optical images of the top and side views of a spreading droplet under different dielectrowetting voltages. (<b>C</b>) Apparent contact angle of a stripe-shaped droplet of propylene glycol as a function of applied voltage. Open circles represent the increasing voltage half cycle, and filled squares represent the decreasing voltage half cycle. Inset: linear fit to the cosine of the apparent contact angle versus applied voltage squared. Images are reproduced from Reference [<a href="#B21-micromachines-10-00329" class="html-bibr">21</a>] with the permission of the American Physical Society.</p> Full article ">Figure 5
<p>(<b>A</b>) Schematic representation of the experimental open microfluidics device with a large IDE pad for a reservoir and smaller IDE pads for various microfluidics operations. (<b>B</b>) Series of snapshots explaining the droplet splitting (<b>a</b>–<b>d</b>) and transporting (<b>e</b>–<b>g</b>) operations. Scale bars are 2 mm. (<b>C</b>) Droplet generation on the device by dielectrowetting. Scale bars are 2 mm. Images are reproduced from Reference [<a href="#B41-micromachines-10-00329" class="html-bibr">41</a>] with the permission of the Royal Society of Chemistry.</p> Full article ">Figure 6
<p>(<b>A</b>) Schematic representation of the working principle of the optical switch based on dielectrowetting spreading of liquid drop. (<b>B</b>) Liquid crystal droplet-based optical switches in the off and on (78 V) state. The left droplet shows a black color and the right one shows red. Images are reproduced from Reference [<a href="#B66-micromachines-10-00329" class="html-bibr">66</a>] with permission of the Royal Society of Chemistry.</p> Full article ">
2 pages, 3092 KiB  
Correction
Correction: Shen, X. et al. Research on the Disc Sensitive Structure of a Micro Optoelectromechanical System (MOEMS) Resonator Gyroscope. Micromachines, 2019, 10, 264
by Xiang Shen, Liye Zhao and Dunzhu Xia
Micromachines 2019, 10(5), 328; https://doi.org/10.3390/mi10050328 - 16 May 2019
Viewed by 2397
Abstract
In the published paper [...] Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application, Volume II)
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<p>The photo of the fabricated micro optoelectromechanical system resonator gyroscope (MOEMS-RG).</p> Full article ">
31 pages, 9481 KiB  
Review
Recent Progress in the Voltage-Controlled Magnetic Anisotropy Effect and the Challenges Faced in Developing Voltage-Torque MRAM
by Takayuki Nozaki, Tatsuya Yamamoto, Shinji Miwa, Masahito Tsujikawa, Masafumi Shirai, Shinji Yuasa and Yoshishige Suzuki
Micromachines 2019, 10(5), 327; https://doi.org/10.3390/mi10050327 - 15 May 2019
Cited by 116 | Viewed by 9592
Abstract
The electron spin degree of freedom can provide the functionality of “nonvolatility” in electronic devices. For example, magnetoresistive random access memory (MRAM) is expected as an ideal nonvolatile working memory, with high speed response, high write endurance, and good compatibility with complementary metal-oxide-semiconductor [...] Read more.
The electron spin degree of freedom can provide the functionality of “nonvolatility” in electronic devices. For example, magnetoresistive random access memory (MRAM) is expected as an ideal nonvolatile working memory, with high speed response, high write endurance, and good compatibility with complementary metal-oxide-semiconductor (CMOS) technologies. However, a challenging technical issue is to reduce the operating power. With the present technology, an electrical current is required to control the direction and dynamics of the spin. This consumes high energy when compared with electric-field controlled devices, such as those that are used in the semiconductor industry. A novel approach to overcome this problem is to use the voltage-controlled magnetic anisotropy (VCMA) effect, which draws attention to the development of a new type of MRAM that is controlled by voltage (voltage-torque MRAM). This paper reviews recent progress in experimental demonstrations of the VCMA effect. First, we present an overview of the early experimental observations of the VCMA effect in all-solid state devices, and follow this with an introduction of the concept of the voltage-induced dynamic switching technique. Subsequently, we describe recent progress in understanding of physical origin of the VCMA effect. Finally, new materials research to realize a highly-efficient VCMA effect and the verification of reliable voltage-induced dynamic switching with a low write error rate are introduced, followed by a discussion of the technical challenges that will be encountered in the future development of voltage-torque MRAM. Full article
(This article belongs to the Special Issue Emerging Memory and Computing Devices in the Era of Intelligent Machines)
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<p>Reported writing energy for toggle magnetoresistive random-access memory (MRAM) (red dots) and spin-transfer torque-based switching (STT-MRAM) (blue dots) as a function of magnetic tunnel junctions (MTJ) cell size and the target area for voltage-torque MRAM.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic illustration of sample stack used for the first demonstration of the voltage-controlled magnetic anisotropy (VCMA) effect in an all-solid state structure, and (<b>b</b>) applied bias voltage dependence of the polar-magneto-optical Kerr effect (MOKE) hysteresis curves for a 0.58 nm-thick Fe<sub>80</sub>Co<sub>20</sub> layer.</p> Full article ">Figure 3
<p>Example of applied electric-field dependence of <span class="html-italic">K</span><sub>PMA</sub><span class="html-italic">t</span><sub>free</sub> observed in an MgO-based MTJ structure. Reprinted figure with permission from [<a href="#B48-micromachines-10-00327" class="html-bibr">48</a>], Copyright 2010 by the AIP Publishing LLC.</p> Full article ">Figure 4
<p>Conceptual diagram of voltage-induced dynamic switching for a perpendicularly-magnetized film. The in-plane bias magnetic field, <span class="html-italic">H</span><sub>bias</sub>, which determines the axis of the precessional dynamics, is applied in the +<span class="html-italic">x</span> direction. (<b>a</b>) initial state (point S), (<b>b</b>) precessional switching process induced by an application of pulse voltage (from point S to point M), and (<b>c</b>) relaxation process (from point M to point E).</p> Full article ">Figure 5
<p>Experimental demonstration of voltage-induced dynamic switching. (<b>a</b>) Schematic of the sample structure of a voltage-controlled perpendicularly-magnetized MTJ and observed bi-stable switching between parallel and antiparallel magnetization configurations induced by successive pulse voltage applications. (<b>b</b>) Pulse width dependence of switching probability, <span class="html-italic">P</span><sub>SW</sub>. Due to the precessional dynamics, <span class="html-italic">P</span><sub>SW</sub> exhibits oscillatory behavior depending on the pulse width.</p> Full article ">Figure 6
<p>Microscopic origin of the VCMA effect. (<b>a</b>) Orbital magnetic moment mechanism. (<b>b</b>) Electric quadrupole mechanism. (<b>c</b>) Schematic of the nonlinear electric field at the interface between the dielectrics and the ferromagnet, which induces a charge redistribution-induced VCMA effect.</p> Full article ">Figure 7
<p>Diagram of the electronic states related to X-ray absorption spectroscopy and X-ray magnetic circular dichroism (XAS/XMCD) measurements at the <span class="html-italic">L</span>-edges of transition metals.</p> Full article ">Figure 8
<p>Voltage-induced changes to the magnetic moment of Co in the Fe/Co/MgO system. (<b>a</b>) Schematic of the sample structure. (<b>b</b>) Typical XAS/XMCD results around the Co-absorption edges. (<b>c</b>) Voltage-induced change to the orbital magnetic moment in Co. (<b>d</b>) Voltage-induced changes to the effective spin magnetic moment (<span class="html-italic">m</span><sub>S</sub> − 7<span class="html-italic">m</span><sub>T</sub>) in Co. Reprinted figure with permission from [<a href="#B113-micromachines-10-00327" class="html-bibr">113</a>], Copyright 2017 by the American Physical Society.</p> Full article ">Figure 9
<p>Voltage-induced changes to the magnetic moment of Pt in the Fe/Pt/MgO system. (<b>a</b>) Schematic of the sample structure and its high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image. (<b>b</b>) Typical XAS/XMCD results around the Pt-absorption edges. (<b>c</b>) Voltage-induced change to the orbital magnetic moment in Pt. (<b>d</b>) Voltage-induced changes to the effective spin magnetic moment (<span class="html-italic">m</span><sub>S</sub> − 7<span class="html-italic">m</span><sub>T</sub>) in Pt. Reproduced from [<a href="#B116-micromachines-10-00327" class="html-bibr">116</a>]. CC BY 4.0.</p> Full article ">Figure 10
<p>Scalability issue for voltage-torque MRAMs. The dependence of the required <span class="html-italic">K</span><sub>PMA</sub><span class="html-italic">t</span><sub>free</sub> and VCMA coefficient on the diameter of the MTJ was estimated for each thermal stability factor (Δ<sub>0</sub>).</p> Full article ">Figure 11
<p>(<b>a</b>) Bias voltage dependence of normalized tunnel magnetoresistance (TMR) curves measured under in-plane magnetic fields for an orthogonally magnetized MTJ consisting of Cr/ultrathin Fe (0.44 nm)/MgO/Fe (10 nm). The inset shows a cross-sectional TEM image of the MTJ. (<b>b</b>) Applied electric-field dependence of <span class="html-italic">K</span><sub>PMA</sub><span class="html-italic">t</span><sub>Fe</sub> values. The inset displays an example of a normalized <span class="html-italic">M</span>-<span class="html-italic">H</span> curve. <span class="html-italic">K</span><sub>PMA</sub> was evaluated from the yellow-colored area with the saturation magnetization value that was obtained by a SQUID measurement. Reprinted figure with permission from [<a href="#B133-micromachines-10-00327" class="html-bibr">133</a>], Copyright 2017 by the American Physical Society.</p> Full article ">Figure 12
<p>Fe thickness dependence of the VCMA coefficient observed in a Cr/ultrathin Fe(<span class="html-italic">t</span><sub>Fe</sub>)/MgO/Fe structure. A large VCMA coefficient with nonlinear behavior was found in the thinner Fe thickness range, <span class="html-italic">t</span><sub>Fe</sub> &lt; 0.6 nm (blue dots). Reprinted figure with permission from [<a href="#B133-micromachines-10-00327" class="html-bibr">133</a>], Copyright by the American Physical Society.</p> Full article ">Figure 13
<p>(<b>a</b>) HAADF-STEM images of a multilayer structure of Cr/ultrathin Ir-doped Fe/MgO. Inter-diffused Ir atoms can be identified by atomic-scale Z-contrast HAADF-STEM imaging as indicated by the yellow arrows. (<b>b</b>) Comparison of the polar MOKE hysteresis curves for pure Fe (1 nm)/MgO and Fe (1 nm)/Ir (0.1 nm)/MgO structures. (<b>c</b>) Dependence of the intrinsic interface magnetic anisotropy energy, K<sub>i,0</sub>, on the thickness of the Ir layer. Reproduced from [<a href="#B35-micromachines-10-00327" class="html-bibr">35</a>]. CC BY 4.0.</p> Full article ">Figure 14
<p>(<b>a</b>) Bias voltage dependence of normalized TMR curves measured under in-plane magnetic fields for an orthogonally-magnetized MTJ consisting of Cr/Ir-doped Fe(0.82 nm)/MgO/Fe(10 nm). (<b>b</b>) Applied electric-field dependence of <span class="html-italic">K</span><sub>PMA</sub><span class="html-italic">t</span><sub>FeIr</sub>. The inset shows an example of voltage-induced FMR excitation measured by a homodyne detection technique, which proves the high speed responsiveness of the observed VCMA effect. Reproduced from [<a href="#B35-micromachines-10-00327" class="html-bibr">35</a>]. CC BY 4.0.</p> Full article ">Figure 15
<p>First principles calculations of the electric-field induced magnetic anisotropy energy change in an Ir-doped Fe/MgO system. (<b>a</b>) Supercell structure used for the calculation, consisting of MgO (5 ML)/FeIr (5 ML)/MgO (5 ML). (<b>b</b>) Atomic-resolved magnetic anisotropy energies (MAE) change induced by an electric-field of 0.1 V/nm in MgO. The Ir concentration was maintained at about 6% in the FeIr layer. (<b>c</b>) The electric-field induced MAE arising from second-order perturbation of the spin-orbit coupling for Ir atoms in layers 1 and 2. Reproduced from [<a href="#B35-micromachines-10-00327" class="html-bibr">35</a>]. CC BY 4.0.</p> Full article ">Figure 16
<p>Spin polarized local density of states of Ir-5<span class="html-italic">d</span> orbitals and magnetic anisotropy energy as a function of the band energy in layer 2.</p> Full article ">Figure 17
<p>(<b>a</b>) Experimental setup for evaluating the WER of an MTJ. (<b>b</b>) Pulsed-voltage-driven magnetization switching in a p-MTJ. (<b>c</b>) WER as a function of Δ obtained from numerical simulations.</p> Full article ">Figure 18
<p>Example of the optimized WER as a function of <span class="html-italic">t</span><sub>pulse</sub> observed in a perpendicularly-magnetized MTJ consisting of Ta/(Co<sub>50</sub>Fe<sub>50</sub>)<sub>80</sub>B<sub>20</sub>/MgO/reference layer. The blue and red symbols represent the WER of parallel (P) to antiparallel (AP) and AP to P switching, respectively. Reprinted figure with permission from [<a href="#B109-micromachines-10-00327" class="html-bibr">109</a>], Copyright 2019 by the IOP Publishing Ltd.</p> Full article ">Figure 19
<p>(<b>a</b>) Contour plot of energy density in the absence of a bias voltage. (<b>b</b>) Appearance of a local peak in the WER observed in an MTJ consisting of Ta/(Co<sub>30</sub>Fe<sub>70</sub>)<sub>80</sub>B<sub>20</sub> (1.1 nm)/MgO/reference layer. The filled circles and the lines represent experimental data and numerical simulations, respectively. Reprinted figure with permission from [<a href="#B107-micromachines-10-00327" class="html-bibr">107</a>], Copyright 2018 by the American Physical Society.</p> Full article ">Figure 20
<p>(<b>a</b>)–(<b>c</b>) Effects of pulse shaping on magnetization trajectory. The red and green lines represent the magnetization trajectory during and after application of the pulse, <span class="html-italic">t</span><sub>pulse</sub>, respectively. (<b>d</b>), (<b>e</b>) WER minimum as a function of rise time (blue symbols) and fall time (red symbols). (<b>d</b>) experimental results; (<b>e</b>) numerical simulation results. Reprinted figure with permission from [<a href="#B108-micromachines-10-00327" class="html-bibr">108</a>], Copyright 2019 by the American Physical Society.</p> Full article ">Figure 21
<p>(<b>a</b>) Comparison of write pulse sequence in conventional and inverse bias methods. (<b>b</b>) Numerically obtained WER as a function of Δ using two different methods.</p> Full article ">
25 pages, 4775 KiB  
Review
TiO2 Based Nanostructures for Photocatalytic CO2 Conversion to Valuable Chemicals
by Abdul Razzaq and Su-Il In
Micromachines 2019, 10(5), 326; https://doi.org/10.3390/mi10050326 - 15 May 2019
Cited by 49 | Viewed by 6588
Abstract
Photocatalytic conversion of CO2 to useful products is an alluring approach for acquiring the two-fold benefits of normalizing excess atmospheric CO2 levels and the production of solar chemicals/fuels. Therefore, photocatalytic materials are continuously being developed with enhanced performance in accordance with [...] Read more.
Photocatalytic conversion of CO2 to useful products is an alluring approach for acquiring the two-fold benefits of normalizing excess atmospheric CO2 levels and the production of solar chemicals/fuels. Therefore, photocatalytic materials are continuously being developed with enhanced performance in accordance with their respective domains. In recent years, nanostructured photocatalysts such as one dimensional (1-D), two dimensional (2-D) and three dimensional (3-D)/hierarchical have been a subject of great importance because of their explicit advantages over 0-D photocatalysts, including high surface areas, effective charge separation, directional charge transport, and light trapping/scattering effects. Furthermore, the strategy of doping (metals and non-metals), as well as coupling with a secondary material (noble metals, another semiconductor material, graphene, etc.), of nanostructured photocatalysts has resulted in an amplified photocatalytic performance. In the present review article, various titanium dioxide (TiO2)-based nanostructured photocatalysts are briefly overviewed with respect to their application in photocatalytic CO2 conversion to value-added chemicals. This review primarily focuses on the latest developments in TiO2-based nanostructures, specifically 1-D (TiO2 nanotubes, nanorods, nanowires, nanobelts etc.) and 2-D (TiO2 nanosheets, nanolayers), and the reaction conditions and analysis of key parameters and their role in the up-grading and augmentation of photocatalytic performance. Moreover, TiO2-based 3-D and/or hierarchical nanostructures for CO2 conversions are also briefly scrutinized, as they exhibit excellent performance based on the special nanostructure framework, and can be an exemplary photocatalyst architecture demonstrating an admirable performance in the near future. Full article
(This article belongs to the Special Issue Nanostructures for Photocatalysis)
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Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Proposed mechanism of photocatalytic CO<sub>2</sub> conversion to CH<sub>3</sub>OH employing CdS and Bi<sub>2</sub>S<sub>3</sub> TNT photocatalysts (taken with permission from [<a href="#B47-micromachines-10-00326" class="html-bibr">47</a>]). (<b>b</b>) Production yield of CO and CH<sub>4</sub> from Pt-MgO-covered TNN films (taken with permission from [<a href="#B48-micromachines-10-00326" class="html-bibr">48</a>]).</p> Full article ">Figure 2
<p>Schematic of the mechanism involved in the photocatalytic conversion of CO<sub>2</sub> into: (<b>a</b>) CH<sub>4</sub> employing Cu<sub>2</sub>O NP-incorporating TNT (taken with permission from [<a href="#B50-micromachines-10-00326" class="html-bibr">50</a>]), and (<b>b</b>) CH<sub>3</sub>OH using Cu-modified TNF films (taken with permission from [<a href="#B51-micromachines-10-00326" class="html-bibr">51</a>]).</p> Full article ">Figure 3
<p>(<b>a</b>) Synthesis procedure for hydrogenated TiO<sub>2</sub> nanotubes CoOx photocatalyst. (<b>b</b>) Photocatalytic CO and CH<sub>4</sub> yield employing the AB-H-CoOx sample using photocatalytic and photothermal catalytic approaches (taken with permission from [<a href="#B53-micromachines-10-00326" class="html-bibr">53</a>]).</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic presentation of the proposed photocatalytic conversion of CO<sub>2</sub> into CO, CH<sub>4</sub>, CH<sub>3</sub>OH and other value-added chemicals employing Au-TNW (taken with permission from [<a href="#B54-micromachines-10-00326" class="html-bibr">54</a>]). (<b>b</b>) Z-scheme proposed for ZnFe<sub>2</sub>O<sub>4</sub>-TNB for CO<sub>2</sub> conversion to its respective products (taken with permission from [<a href="#B59-micromachines-10-00326" class="html-bibr">59</a>]).</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic view of photocatalytic conversion of CO<sub>2</sub> into CH<sub>4</sub> on rGO-TNT (taken with permission from [<a href="#B30-micromachines-10-00326" class="html-bibr">30</a>]). (<b>b</b>) Production rate of CO and CH<sub>4</sub> from GR-TNR with varied concentrations of graphene (taken with permission from [<a href="#B60-micromachines-10-00326" class="html-bibr">60</a>]).</p> Full article ">Figure 6
<p>(<b>a</b>) Schematic overview of the synthesis procedure for FANT, and (<b>b</b>) the proposed mechanism for photocatalytic conversion of CO<sub>2</sub> into CH<sub>4</sub> employing the FANT photocatalyst (taken with permission from [<a href="#B61-micromachines-10-00326" class="html-bibr">61</a>]).</p> Full article ">Figure 7
<p>(<b>a</b>) TEM image showing the loading of N-TiO<sub>2</sub> nanoparticles onto g-C<sub>3</sub>N<sub>4</sub> nanosheets, and (<b>b</b>) proposed scheme involved in photocatalytic CO<sub>2</sub> conversion (taken with permission from [<a href="#B62-micromachines-10-00326" class="html-bibr">62</a>]). (<b>c</b>) TEM image showing the 2-D nanostructure of TiO<sub>2</sub> nanosheets coupled with g-C<sub>3</sub>N<sub>4</sub> nanosheets, and (<b>d</b>) schematic view of the interfacial charge transfer within TNS-CNN with the proposed photocatalytic CO<sub>2</sub> conversion mechanism (taken with permission from [<a href="#B63-micromachines-10-00326" class="html-bibr">63</a>]).</p> Full article ">Figure 8
<p>(<b>a</b>) SEM image of a representative TiO<sub>2−x</sub>/g-C<sub>3</sub>N<sub>4</sub> sample displaying sheet-type g-C<sub>3</sub>N<sub>4</sub> embedded with TiO<sub>2−x</sub> nanoparticles, and (<b>b</b>) schematic of the electronic structure of TiO<sub>2−x</sub>/g-C<sub>3</sub>N<sub>4</sub> with the proposed mechanism of photocatalytic CO<sub>2</sub> conversion (taken with permission from [<a href="#B64-micromachines-10-00326" class="html-bibr">64</a>]).</p> Full article ">Figure 9
<p>(<b>a</b>) SEM image of the TiO<sub>2</sub>-Octylamine hybrid nanostructure, and (<b>b</b>) schematic view of photocatalytic conversion of CO<sub>2</sub> into formate product using ultrathin TiO<sub>2</sub> nanosheets (taken with permission from [<a href="#B65-micromachines-10-00326" class="html-bibr">65</a>]). Schematic view of (<b>c</b>) unsaturation of ultrathin nanosheets with the appearance of oxygen vacancies, and (<b>d</b>) photocatalytic CO<sub>2</sub> conversion to CH<sub>4</sub> with water vapors employing ultrathin TiO<sub>2</sub> nanosheets with highly dispersed Pt nanoparticles (taken with permission from [<a href="#B66-micromachines-10-00326" class="html-bibr">66</a>]).</p> Full article ">Figure 10
<p>(<b>a</b>) Schematic view of the band energy diagram for Cu<sub>2</sub>O-loaded TiO<sub>2</sub> pillared photocatalysts for conversion of CO<sub>2</sub> into value-added chemicals (taken with permission from [<a href="#B68-micromachines-10-00326" class="html-bibr">68</a>]). (<b>b</b>) FESEM image for TT550 sample displaying the layered structure of MXenes loaded with TiO<sub>2</sub> nanoparticles, and (<b>c</b>) the proposed mechanism of photogenerated charge transfer within the TiO<sub>2</sub>-Ti<sub>3</sub>C<sub>2</sub> 2-D nanostructure (taken with permission from [<a href="#B69-micromachines-10-00326" class="html-bibr">69</a>]).</p> Full article ">Figure 11
<p>SEM images of (<b>a</b>) solid MS, (<b>b</b>) yolk/shell MS, and (<b>c</b>) hollow MS. (<b>d</b>) CO production rate for various samples via photocatalytic CO<sub>2</sub> conversion (taken with permission from [<a href="#B73-micromachines-10-00326" class="html-bibr">73</a>]).</p> Full article ">Figure 12
<p>Image of <span class="html-italic">camellia</span> leaf, SEM image of artificial leaf displaying a porous structure, and the production rate of CO and CH<sub>4</sub> via the photocatalytic conversion of CO<sub>2</sub> and water vapors (taken with permission from [<a href="#B74-micromachines-10-00326" class="html-bibr">74</a>]).</p> Full article ">Figure 13
<p>(<b>a</b>) Photocatalytic CH<sub>4</sub> evolution and (<b>b</b>) production rate employing various samples with varied ratios of ZnIn<sub>2</sub>S<sub>4</sub> to TiO<sub>2</sub> (taken with permission from [<a href="#B75-micromachines-10-00326" class="html-bibr">75</a>]). (<b>c</b>) SEM image of Cu<sub>2</sub>O/S-TiO<sub>2</sub>/CuO p-n-p nanostructure, and (<b>d</b>) band gap diagram with the mechanism involved in the conversion of CO<sub>2</sub> to CH<sub>4</sub> (taken with permission from [<a href="#B76-micromachines-10-00326" class="html-bibr">76</a>]).</p> Full article ">Figure 14
<p>Proposed mechanism of photocatalytic CO<sub>2</sub> conversion with water vapors employing (<b>a</b>) AuPd-3DOM TiO<sub>2</sub> photocatalyst (taken with permission from [<a href="#B77-micromachines-10-00326" class="html-bibr">77</a>]), and (<b>b</b>) Au-3DOM TiO<sub>2</sub> photocatalyst (taken with permission from [<a href="#B78-micromachines-10-00326" class="html-bibr">78</a>]).</p> Full article ">
11 pages, 1924 KiB  
Article
Modeling and Analysis of the Noise Performance of the Capacitive Sensing Circuit with a Differential Transformer
by Yafei Xie, Ji Fan, Chun Zhao, Shitao Yan, Chenyuan Hu and Liangcheng Tu
Micromachines 2019, 10(5), 325; https://doi.org/10.3390/mi10050325 - 15 May 2019
Cited by 12 | Viewed by 3630
Abstract
Capacitive sensing is a key technique to measure the test mass movement with a high resolution for space-borne gravitational wave detectors, such as Laser Interferometer Space Antenna (LISA) and TianQin. The capacitance resolution requirement of TianQin is higher than that of LISA, as [...] Read more.
Capacitive sensing is a key technique to measure the test mass movement with a high resolution for space-borne gravitational wave detectors, such as Laser Interferometer Space Antenna (LISA) and TianQin. The capacitance resolution requirement of TianQin is higher than that of LISA, as the arm length of TianQin is about 15 times shorter. In this paper, the transfer function and capacitance measurement noise of the circuit are modeled and analyzed. Figure-of-merits, including the product of the inductance L and the quality factor Q of the transformer, are proposed to optimize the transformer and the capacitance measurement resolution of the circuit. The LQ product improvement and the resonant frequency augmentation are the key factors to enhance the capacitance measurement resolution. We fabricated a transformer with a high LQ product over a wide frequency band. The evaluation showed that the transformer can generate a capacitance resolution of 0.11 aF/Hz1/2 at a resonant frequency of 200 kHz, and the amplitude of the injection wave would be 0.6 V. This result supports the potential application of the proposed transformer in space-borne gravitational wave detection and demonstrates that it could relieve the stringent requirements for other parameters in the TianQin mission. Full article
(This article belongs to the Special Issue Advances in Capacitive Sensors)
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<p>Block diagram of the capacitive sensing circuit with a differential transformer.</p> Full article ">Figure 2
<p>(<b>a</b>) The front-end circuit model with a differential transformer and (<b>b</b>) its equivalent circuit. <span class="html-italic">C<sub>t</sub></span><sub>1</sub> and <span class="html-italic">C<sub>t</sub></span><sub>2</sub> are resonant frequency tuning capacitors. They consist of both the internal stray capacitors of the transformer primary windings and the other capacitors used there. <span class="html-italic">C</span><sub>11</sub> and <span class="html-italic">C</span><sub>12</sub> are much larger than other capacitors in the circuit. Combining <span class="html-italic">C</span><sub>11</sub> and <span class="html-italic">C</span><sub>12</sub> with <span class="html-italic">R<sub>f</sub></span><sub>1</sub> and <span class="html-italic">R<sub>f</sub></span><sub>2</sub>, the lattice is used to limit the DC gain, and thus prevents the amplifiers from saturation.</p> Full article ">Figure 3
<p>The schematic diagram of the front-end circuit for noise calculation.</p> Full article ">Figure 4
<p>Measured <span class="html-italic">LQ</span> product of our transformer and the <span class="html-italic">LQ</span> production in Reference [<a href="#B25-micromachines-10-00325" class="html-bibr">25</a>].</p> Full article ">Figure 5
<p>Minimum current noise and capacitance resolution of the front-end circuit limited by the transformer. (<b>a</b>) Noises from 10 kHz to 200 kHz. (<b>b</b>) More details of the curves in the frequency band between 100 kHz and 200 kHz. The blue curves represent the minimum current noise calculated with Equation (14). The red curves represent the minimum capacitance resolution calculated with Equation (20).</p> Full article ">
18 pages, 7203 KiB  
Article
Dynamic Analysis of a Micro Beam-Based Tactile Sensor Actuated by Fringing Electrostatic Fields
by Zhichong Wang, Qichang Zhang, Wei Wang and Jianxin Han
Micromachines 2019, 10(5), 324; https://doi.org/10.3390/mi10050324 - 14 May 2019
Cited by 2 | Viewed by 2859
Abstract
A new kind of fringing electrostatic actuation mode is developed. In this new actuation mode, the expression of fringing electrostatic force is found. The nonlinear dynamic analysis of this new actuation mode is presented by using the Method of Multiple Scales. An experiment [...] Read more.
A new kind of fringing electrostatic actuation mode is developed. In this new actuation mode, the expression of fringing electrostatic force is found. The nonlinear dynamic analysis of this new actuation mode is presented by using the Method of Multiple Scales. An experiment is designed to observe the dynamic behaviors of this structure. It is observed that the resonance frequency rises with the increase of the initial displacement and the decrease of the slit gap; a smaller slit gap makes marked change of the resonance frequency in the same range of the initial displacement; the increase of the vibration amplitude is linear with the increase of the initial displacement; the fringing electrostatic force has a larger impact on the frequency response of the nonlinear vibration when the initial displacement, the beam length and the actuated voltage are larger. This new fringing electrostatic actuation mode can be used in a micro tactile sensor. The results of dynamic analysis can provide support for sensor design. Based on the dynamic investigations into the micro cantilevered beam actuated by fringing electrostatic force; three usage patterns of the sensor are introduced as follows. Firstly, measuring resonance frequency of the micro beam can derive the initial displacement. Second, the initial displacement can be derived from vibration amplitude measurement. Third, jump phenomenon can be used to locate the initial displacement demand. Full article
(This article belongs to the Section A：Physics)
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<p>Concept structure of the tactile sensor.</p> Full article ">Figure 2
<p>Schematic illustration of cantilevered beam and electrode. (<b>a</b>) Structure size. (<b>b</b>) Simplified model.</p> Full article ">Figure 3
<p>Equipotential lines around the beam and the electrodes assuming <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mi>e</mi> </msub> <mo>=</mo> <mn>1</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math> and (<b>a</b>) for <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>0</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>, (<b>b</b>) for <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>0.02</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>, (<b>c</b>) for <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>0.04</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>, (<b>d</b>) for <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>0.06</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 4
<p>Data points and fitted curves of electrostatic force responding to initial displacement under different electrode thickness.</p> Full article ">Figure 5
<p>Fitted curves of electrostatic force based on different fit function.</p> Full article ">Figure 6
<p>Primary resonance’s frequency response curve under different initial displacement when <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>DC</mi> </mrow> </msub> <mo>=</mo> <mn>30</mn> <mtext> </mtext> <mi>V</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>AC</mi> </mrow> </msub> <mo>=</mo> <mn>0.5</mn> <mtext> </mtext> <mi>V</mi> </mrow> </semantics></math>.</p> Full article ">Figure 7
<p>Primary resonance’s resonance frequency versus initial displacement under different slit gap.</p> Full article ">Figure 8
<p>Primary resonance’s vibration amplitude versus initial displacement under different slit gap.</p> Full article ">Figure 9
<p>Vibration amplitude which is solved by using Method of Multiple Scales (MMS) and RK4 when <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>DC</mi> </mrow> </msub> <mo>=</mo> <mn>300</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>AC</mi> </mrow> </msub> <mo>=</mo> <mn>5</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 10
<p>Primary resonance’s vibration amplitude versus initial displacement under different excitation frequency ratio.</p> Full article ">Figure 11
<p>Phase trajectory.</p> Full article ">Figure 12
<p>Primary resonance’s frequency response curve under different initial displacement when the beam is made of steel, brass and aluminum.</p> Full article ">Figure 13
<p>Primary resonance’s frequency response curve under different initial displacement when <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>6</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 14
<p>Primary resonance’s frequency response curve under different initial displacement (<b>a</b>) when <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>DC</mi> </mrow> </msub> <mo>=</mo> <mn>350</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>AC</mi> </mrow> </msub> <mo>=</mo> <mn>5</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math> (<b>b</b>) when <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>DC</mi> </mrow> </msub> <mo>=</mo> <mn>300</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>v</mi> <mrow> <mi>AC</mi> </mrow> </msub> <mo>=</mo> <mn>10</mn> <mrow> <mtext> </mtext> <mi mathvariant="normal">V</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 15
<p>Experimental setup.</p> Full article ">Figure 16
<p>Resonance frequency versus initial displacement (linear region magnification).</p> Full article ">Figure 17
<p>Frequency response curve when the beam is near the end of the electrode in the thickness direction.</p> Full article ">Figure 18
<p>Vibration amplitude versus initial displacement base on MMS and TEST.</p> Full article ">Figure 19
<p>Frequency response curve when <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mi>b</mi> </msub> <mo>=</mo> <mn>100</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>d</mi> <mi>g</mi> </msub> <mo>=</mo> <mn>0.3</mn> <mrow> <mtext> </mtext> <mi>mm</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">
14 pages, 5843 KiB  
Article
An Electrothermal Cu/W Bimorph Tip-Tilt-Piston MEMS Mirror with High Reliability
by Liang Zhou, Xiaoyang Zhang and Huikai Xie
Micromachines 2019, 10(5), 323; https://doi.org/10.3390/mi10050323 - 14 May 2019
Cited by 26 | Viewed by 6441
Abstract
This paper presents the design, fabrication, and characterization of an electrothermal MEMS mirror with large tip, tilt and piston scan. This MEMS mirror is based on electrothermal bimorph actuation with Cu and W thin-film layers forming the bimorphs. The MEMS mirror is fabricated [...] Read more.
This paper presents the design, fabrication, and characterization of an electrothermal MEMS mirror with large tip, tilt and piston scan. This MEMS mirror is based on electrothermal bimorph actuation with Cu and W thin-film layers forming the bimorphs. The MEMS mirror is fabricated via a combination of surface and bulk micromachining. The piston displacement and tip-tilt optical angle of the mirror plate of the fabricated MEMS mirror are around 114 μm and ±8°, respectively at only 2.35 V. The measured response time is 7.3 ms. The piston and tip-tilt resonant frequencies are measured to be 1.5 kHz and 2.7 kHz, respectively. The MEMS mirror survived 220 billion scanning cycles with little change of its scanning characteristics, indicating that the MEMS mirror is stable and reliable. Full article
(This article belongs to the Special Issue Optical MEMS)
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<p>Various bimorph structures: (<b>a</b>) A single cantilever bimorph. (<b>b</b>) A lateral-shift-free (LSF) bimorph actuator; (<b>c</b>) A scanning electron micrograph (SEM) of a Cu/W LSF bimorph actuator; (<b>d</b>) An SEM of a Cu/W mirror with LSF design; (<b>e</b>) An inverted-series-connected (ISC) bimorph actuator. b1, b2, b3: bimorph segment #1, #2, and #3; m1, m2: multimorph segment #1 and #2.</p> Full article ">Figure 1 Cont.
<p>Various bimorph structures: (<b>a</b>) A single cantilever bimorph. (<b>b</b>) A lateral-shift-free (LSF) bimorph actuator; (<b>c</b>) A scanning electron micrograph (SEM) of a Cu/W LSF bimorph actuator; (<b>d</b>) An SEM of a Cu/W mirror with LSF design; (<b>e</b>) An inverted-series-connected (ISC) bimorph actuator. b1, b2, b3: bimorph segment #1, #2, and #3; m1, m2: multimorph segment #1 and #2.</p> Full article ">Figure 2
<p>Schematic of a microelectromechanical (MEMS) mirror based on Cu/W ISC actuators.</p> Full article ">Figure 3
<p>The modal simulation of the Cu/W mirror. (<b>a</b>) First resonant mode, piston, at the frequency of 1.493 kHz; (<b>b</b>) Second resonant mode, tip-tilt, at the frequency of 2.518 kHz.</p> Full article ">Figure 4
<p>Fabrication process flow of the MEMS mirror.</p> Full article ">Figure 5
<p>SEM of a fabricated MEMS mirror.</p> Full article ">Figure 6
<p>The vertical displacement (solid line), and the corresponding consumed power (dash line) versus the applied voltage. The errors for the displacement measurement were about ± 2 µm resulting from the errors of the microstage position reading and the focal point determination of the optical microscope.</p> Full article ">Figure 7
<p>The optical scan angle (solid line), and the corresponding center displacement (dash line) versus the applied voltage.</p> Full article ">Figure 8
<p>The frequency response of the micromirror from 1 Hz to 10 kHz.</p> Full article ">Figure 9
<p>(<b>a</b>) Step response of one actuator of the MEMS Mirror; (<b>b</b>) zoom-in rise edge; (<b>c</b>) zoom-in fall edge.</p> Full article ">Figure 10
<p>(<b>a</b>) Long-term frequency shift; (<b>b</b>) long-term scan angle change at the corresponding tip-tilt resonant frequency.</p> Full article ">Figure 11
<p>SEM pictures of the MEMS mirror after long-term actuation under the tip-tilt resonant frequency. (<b>a</b>) The full device; (<b>b</b>) a zoom-in SEM picture of the actuated bimorph near overlap between inversed bimorphs; (<b>c</b>) a zoom-in SEM picture of the actuated bimorph near a corner.</p> Full article ">
26 pages, 8703 KiB  
Review
Epitaxy of III-Nitrides on β-Ga2O3 and Its Vertical Structure LEDs
by Weijiang Li, Xiang Zhang, Ruilin Meng, Jianchang Yan, Junxi Wang, Jinmin Li and Tongbo Wei
Micromachines 2019, 10(5), 322; https://doi.org/10.3390/mi10050322 - 13 May 2019
Cited by 30 | Viewed by 6431
Abstract
β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially [...] Read more.
β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially ultra violet LEDs (light emitting diodes). Large efforts have been made to improve the quality of III-Nitrides epilayers on β-Ga2O3. Furthermore, the fabrication of vertical blue LEDs has been preliminarily realized with the best result that output power reaches to 4.82 W (under a current of 10 A) and internal quantum efficiency (IQE) exceeds 78% by different groups, respectively, while there is nearly no demonstration of UV-LEDs on β-Ga2O3. In this review, with the perspective from materials to devices, we first describe the basic properties, growth method, as well as doping of β-Ga2O3, then introduce in detail the progress in growth of GaN on (1 0 0) and (−2 0 1) β-Ga2O3, followed by the epitaxy of AlGaN on gallium oxide. Finally, the advances in fabrication and performance of vertical structure LED (VLED) are presented. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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<p>(<b>a</b>) Transformation relationships among Ga<sub>2</sub>O<sub>3</sub> in different crystalline phases and their hydrates. (<b>b</b>) Structural schematic illustration of the β-Ga<sub>2</sub>O<sub>3</sub> unit cell, manifesting the two gallium locations and three oxygen locations. (<b>c</b>) Cleavage nature of single crystal β-Ga<sub>2</sub>O<sub>3</sub>. Reprinted with permission from reference [<a href="#B64-micromachines-10-00322" class="html-bibr">64</a>]. Copyright 2014 SPIE.</p> Full article ">Figure 2
<p>Schematic illustrations of melt growth of β-Ga<sub>2</sub>O<sub>3</sub>: (<b>a</b>) Verneuil method; (<b>b</b>) floating zone method; (<b>c</b>) vertical Bridgeman method; (<b>d</b>) Czochralski method; (<b>e</b>) edge-defined film-fed growth method.</p> Full article ">Figure 3
<p>(<b>a</b>) Hall free carrier concentration versus the dopant (Si and Sn) concentration obtained by secondary ion mass spectrometry (SIMS). Reprinted with permission from reference [<a href="#B89-micromachines-10-00322" class="html-bibr">89</a>]. Copyright 2017 The Electrochemical Society. (<b>b</b>) Transmittance spectra of β-Ga<sub>2</sub>O<sub>3</sub> single crystals prepared by the Czochralski (CZ) method with different concentrations of electrons. Reprinted with permission from Reference [<a href="#B77-micromachines-10-00322" class="html-bibr">77</a>]. Copyright 2014 Elsevier.</p> Full article ">Figure 4
<p>(<b>a</b>) Projection of β-Ga<sub>2</sub>O<sub>3</sub> atomic structure perpendicular to the <span class="html-italic">a</span>-plane, showing the hexagonal-like arrangement of the Ga atoms bonded to O<sub>(3)</sub>, and (<b>b</b>) schematic illustration for the epitaxial relationship between <span class="html-italic">c</span>-plane h-GaN and <span class="html-italic">a</span>-plane β-Ga<sub>2</sub>O<sub>3</sub>.</p> Full article ">Figure 5
<p>(<b>a</b>) Initial observation of epitaxial relationship between <span class="html-italic">c</span>-plane wurtzite GaN and (1 0 0) plane β-Ga<sub>2</sub>O<sub>3</sub>. (<b>b</b>) Refined model of epitaxial relationship between <span class="html-italic">c</span>-plane wurtzite GaN and (1 0 0) plane β-Ga<sub>2</sub>O<sub>3</sub> with a stressed and reoriented GaN at the interface, the lattice mismatch (LM) minimum of 2.6% is given at a 1° tilted angle with respect to case (a). (<b>c</b>) The projection of β-Ga<sub>2</sub>O<sub>3</sub> atomic structure perpendicular to the (−2 0 1) plane, showing the hexagonal-like arrangement of oxygen atoms. (<b>d</b>) Full width half maximum (FWHM) of HR-XRD rocking curves around the (0 0 0 2) Bragg reflection for GaN grown on Al<sub>2</sub>O<sub>3</sub> (2580 arcsec), and on β-Ga<sub>2</sub>O<sub>3</sub> (1020 arcsec). Reprinted with permission from Reference [<a href="#B105-micromachines-10-00322" class="html-bibr">105</a>]. Copyright 2012. The Royal Society of Chemistry.</p> Full article ">Figure 6
<p>Temperature transients (temperature from EpiTT) and reflectance (405 nm) of (−2 0 1) β-Ga<sub>2</sub>O<sub>3</sub> heated under (<b>a</b>) H<sub>2</sub>, (<b>b</b>) N<sub>2</sub>, and (<b>c</b>) N<sub>2</sub> plus NH<sub>3</sub> atmosphere with corresponding optical images of the resulting surfaces in (<b>d</b>), (<b>e</b>), and (<b>f</b>) and SEM images in (<b>g</b>), (<b>h</b>), and (<b>i</b>). Reprinted with permission from reference [<a href="#B108-micromachines-10-00322" class="html-bibr">108</a>]. Copyright 2017 Elsevier.</p> Full article ">Figure 7
<p>(<b>a</b>) Schematic illustration of GaN growth using N<sub>2</sub> and H<sub>2</sub> as carrier gases. (<b>b</b>) Top-view SEM micrograph and (<b>c</b>) double-crystal X-ray diffractometry (DC XRD) pattern of GaN deposited on Ga<sub>2</sub>O<sub>3</sub> via MOCVD under an H<sub>2</sub> atmosphere. (<b>d</b>) DC XRD of rocking curve at the (0 0 0 2) plane of the GaN/Ga<sub>2</sub>O<sub>3</sub>/sapphire fabricated under an N<sub>2</sub> atmosphere and of GaN/sapphire fabricated under N<sub>2</sub> and H<sub>2</sub> atmospheres. Reprinted with permission from Reference [<a href="#B107-micromachines-10-00322" class="html-bibr">107</a>]. Copyright 2011. The Electrochemical Society.</p> Full article ">Figure 8
<p>Field emission scanning electron microscope (FESEM) images of surface morphology and cross section of deposited GaN layers as a function of the nitridation pressure. Reprinted with permission from Reference [<a href="#B98-micromachines-10-00322" class="html-bibr">98</a>]. Copyright 2006 Elsevier.</p> Full article ">Figure 9
<p>Procedure of HT-GaN regrowth method.</p> Full article ">Figure 10
<p>(<b>a</b>) Structural diagram of GaN on β-Ga<sub>2</sub>O<sub>3</sub> via atmosphere switch and two-step growth. (<b>b</b>) The XRC of GaN (0 0 0 2) reflection peak for GaN grown on (−2 0 1) β-Ga<sub>2</sub>O<sub>3</sub> substrate with GaN buffer layer and AlN buffer layer. (<b>c</b>) PL spectra of GaN grown on (−2 0 1) β-Ga<sub>2</sub>O<sub>3</sub> substrate with a GaN buffer layer at 8 K. Reprinted with permission from Reference [<a href="#B103-micromachines-10-00322" class="html-bibr">103</a>]. Copyright 2016 Springer Nature.</p> Full article ">Figure 11
<p>(<b>a</b>) Cross-sectional SEM image of the sample and (<b>b</b>) the etch-pit distribution observed by SEM image for the regrowth GaN epilayer grown on Ga<sub>2</sub>O<sub>3</sub>/Eco-GaN template. (<b>c</b>) The etch-pit distribution observed by SEM image for the u-GaN grown on sapphire. (<b>d</b>) XRD rocking curve of (0 0 0 2) reflection. Reprinted with permission from Reference [<a href="#B120-micromachines-10-00322" class="html-bibr">120</a>]. Copyright 2015 Elsevier.</p> Full article ">Figure 12
<p>(<b>a</b>) Timing charts of growth temperatures of GaN using facet layers. Plan-view SEM images of (<b>b</b>) facet-Al<sub>0.08</sub>Ga<sub>0.92</sub>N and (<b>c</b>) Al<sub>0.08</sub>Ga<sub>0.92</sub>N grown on facet-Al<sub>0.08</sub>Ga<sub>0.92</sub>N layer at 1080 °C. (<b>d</b>) XRC FWHM and (<b>e</b>) PL spectra of Al<sub>0.08</sub>Ga<sub>0.92</sub>N without and with facet-Al<sub>0.08</sub>Ga<sub>0.92</sub>N layer. Reprinted with permission from Reference [<a href="#B111-micromachines-10-00322" class="html-bibr">111</a>]. Copyright 2012 Wiley.</p> Full article ">Figure 13
<p>(<b>a</b>) Structural schematic of the samples. (<b>b</b>) Symmetric (0 0 4) and skew symmetric (1 0 4) XRD RCs. Reprinted with permission from reference [<a href="#B121-micromachines-10-00322" class="html-bibr">121</a>]. Copyright 2018 AIP Publishing.</p> Full article ">Figure 14
<p>(<b>a</b>) Schematic structure of InGaN/GaN MQW vertical structure light emitting diodes (VLED). (<b>b</b>) I−V curve from InGaN/GaN MQWs VLED grown on β-Ga<sub>2</sub>O<sub>3</sub> substrate (image of EL emission at 20 mA is shown in the inset). (<b>c</b>) EL spectra as a function of the injection current for the VLED. (<b>d</b>) EL intensity and IQE as functions of the injection current for the VLED. Reprinted with permission from reference [<a href="#B102-micromachines-10-00322" class="html-bibr">102</a>]. Copyright 2017 American Chemical Society.</p> Full article ">Figure 15
<p>(<b>a</b>) Schematic of a blue-LED based on an InGaN-MQW deposited on a β-Ga<sub>2</sub>O<sub>3</sub> substrate. Photograph of the initially demonstrated blue emission by vertical current injection in comparison with a current chip. (<b>b</b>) I–V characteristic of a blue-LED on β-Ga<sub>2</sub>O<sub>3</sub> substrate. (<b>c</b>) Radiant flux as a function of the vertical current flow for two different chip areas, 300 µm (left-down black coordinates) and 2 mm (up-right red coordinates), respectively. The radiant fluxes were measured with an integrating sphere. Reprinted with permission from Reference [<a href="#B64-micromachines-10-00322" class="html-bibr">64</a>]. Copyright 2014 SPIE.</p> Full article ">Figure 16
<p>(<b>a</b>) Schematic diagram of the chemical lift-off (CLO) process for InGaN/GaN based vertical structure LEDs. (<b>b</b>) Current-voltage curves of the LED devices before and after performing the CLO process. (<b>c</b>) Light output powers as a function of the injection current for the LED devices before and after performing the CLO process. The inset shows the light emission image at 5 mA of the vertical-type LED (after CLO process) with an emission wavelength of 460 nm. Reprinted with permission from Reference [<a href="#B120-micromachines-10-00322" class="html-bibr">120</a>]. Copyright 2015 Elsevier.</p> Full article ">
16 pages, 4148 KiB  
Article
Separation of Nano- and Microparticle Flows Using Thermophoresis in Branched Microfluidic Channels
by Tetsuro Tsuji, Yuki Matsumoto, Ryo Kugimiya, Kentaro Doi and Satoyuki Kawano
Micromachines 2019, 10(5), 321; https://doi.org/10.3390/mi10050321 - 12 May 2019
Cited by 9 | Viewed by 4073
Abstract
Particle flow separation is a useful technique in lab-on-a-chip applications to selectively transport dispersed phases to a desired branch in microfluidic devices. The present study aims to demonstrate both nano- and microparticle flow separation using microscale thermophoresis at a Y-shaped branch in microfluidic [...] Read more.
Particle flow separation is a useful technique in lab-on-a-chip applications to selectively transport dispersed phases to a desired branch in microfluidic devices. The present study aims to demonstrate both nano- and microparticle flow separation using microscale thermophoresis at a Y-shaped branch in microfluidic channels. Microscale thermophoresis is the transport of tiny particles induced by a temperature gradient in fluids where the temperature variation is localized in the region of micrometer order. Localized temperature increases near the branch are achieved using the Joule heat from a thin-film micro electrode embedded in the bottom wall of the microfluidic channel. The inlet flow of the particle dispersion is divided into two outlet flows which are controlled to possess the same flow rates at the symmetric branches. The particle flow into one of the outlets is blocked by microscale thermophoresis since the particles are repelled from the hot region in the experimental conditions used here. As a result, only the solvent at one of outlets and the residual particle dispersion at the other outlet are obtained, i.e., the separation of particles flows is achieved. A simple model to explain the dynamic behavior of the nanoparticle distribution near the electrode is proposed, and a qualitative agreement with the experimental results is obtained. The proposed method can be easily combined with standard microfluidic devices and is expected to facilitate the development of novel particle separation and filtration technologies. Full article
(This article belongs to the Special Issue Selected Papers from the 9th Symposium on Micro-Nano Science and Technology on Micromachines)
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<p>(<b>a</b>) Schematic of the test section. The branched microfluidic channel has a rectangular cross-section in the <math display="inline"><semantics> <mrow> <mi>y</mi> <mi>z</mi> </mrow> </semantics></math> plane with a height <math display="inline"><semantics> <mrow> <mi>h</mi> <mo>=</mo> <mn>17.2</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m and a width <math display="inline"><semantics> <mrow> <mi>w</mi> <mo>=</mo> <mn>450</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m. The inlet flow is divided into two outlet flows <math display="inline"><semantics> <mi>α</mi> </semantics></math> and <math display="inline"><semantics> <mi>β</mi> </semantics></math>. A thin-film electrode heater is fabricated at the entrance of the outlet flow <math display="inline"><semantics> <mi>α</mi> </semantics></math>. Flow profiles of the inlet and outlets are schematically drawn based on the analytical solution of the Poiseuille flow in a rectangular channel [<a href="#B58-micromachines-10-00321" class="html-bibr">58</a>]. (<b>b</b>) Overview of the experimental setup. EF: emission filter. AF: absorption filter. DM: dichroic mirror. OL: objective lens. PC: personal computer.</p> Full article ">Figure 2
<p>Flow field at the test section without Joule heating for <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>1</mn> <mo>×</mo> <msup> <mn>10</mn> <mrow> <mo>−</mo> <mn>2</mn> </mrow> </msup> </mrow> </semantics></math> Pa. The inlet flow is equally separated into two outlet flows. (<b>a</b>) Experimental result obtained by the particle image velocimetry (PIV) analysis. (<b>b</b>) Numerical result at <math display="inline"><semantics> <mrow> <mi>z</mi> <mo>=</mo> <mi>h</mi> <mo>/</mo> <mn>2</mn> </mrow> </semantics></math> obtained by the simulation using a finite element method.</p> Full article ">Figure 3
<p>(<b>a</b>–<b>g</b>) Time series of the particle flow separation induced by microscale thermophoresis for the case with a particle diameter <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>1.0</mn> </mrow> </semantics></math> Pa. At <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> s, the heating by electrode is initiated. Particle flow from the inlet is separated at the Y-shaped branch. Because the thermophoresis is directed to the colder region, the PS particles cannot enter the outlet <math display="inline"><semantics> <mi>α</mi> </semantics></math>.</p> Full article ">Figure 4
<p>Time-development for fluorescence intensity of microparticles in the regions A, B, C, and D indicated in <a href="#micromachines-10-00321-f003" class="html-fig">Figure 3</a>a. The pressure difference <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math> is set to 1.0 Pa.</p> Full article ">Figure 5
<p>(<b>a</b>) Schematic figure of the test section and the positions of region A, B, C, and D analyzed in <a href="#micromachines-10-00321-f006" class="html-fig">Figure 6</a>; (<b>b</b>–<b>g</b>) Time series of the nanoparticle fluorescence. The particle flow separation is induced by microscale thermophoresis for the case with a particle diameter <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math> nm and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>1.0</mn> </mrow> </semantics></math> Pa. At <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> s, the heating by the electrode is initiated. Particle flow from the inlet is separated at the Y-shaped branch. Because the thermophoresis is directed to the colder region, the PS particles cannot enter the outlet <math display="inline"><semantics> <mi>α</mi> </semantics></math>. (<b>h</b>) Magnified figures of (<b>b</b>–<b>g</b>) for a rectangular region indicated in (<b>b</b>).</p> Full article ">Figure 6
<p>Time-development for fluorescence intensity of nanoparticles in the regions A, B, C, and D indicated in <a href="#micromachines-10-00321-f005" class="html-fig">Figure 5</a>a. The pressure difference <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math> is set to 1.0 Pa.</p> Full article ">Figure 7
<p>(<b>a</b>) Schematic figure of the test section and the positions of region A, B, C, and D analyzed in <a href="#micromachines-10-00321-f008" class="html-fig">Figure 8</a>; (<b>b</b>–<b>h</b>) Time series of the nanoparticle fluorescence. The particle flow separation is induced by microscale thermophoresis for the case with a particle diameter <math display="inline"><semantics> <mrow> <mi>d</mi> <mo>=</mo> <mn>100</mn> </mrow> </semantics></math> nm and <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> <mo>=</mo> <mn>0.5</mn> </mrow> </semantics></math> Pa. At <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> s, the heating by electrode is initiated. Particle flow from the inlet is separated at the Y-shaped branch. Because the thermophoresis is directed to the colder region, the PS particles hardly enter the outlet <math display="inline"><semantics> <mi>α</mi> </semantics></math>.</p> Full article ">Figure 8
<p>Time-development for fluorescence intensity of nanoparticles in regions A, B, C, and D indicated in <a href="#micromachines-10-00321-f007" class="html-fig">Figure 7</a>a. The pressure difference <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>P</mi> </mrow> </semantics></math> is set to 0.5 Pa.</p> Full article ">Figure 9
<p>(<b>a</b>) Schematic of the numerical model on the concentration increase at the branch. (<b>b</b>) Numerical results regarding the time-development for fluorescence intensity of nanoparticles in the regions A (<math display="inline"><semantics> <mrow> <mi>Y</mi> <mo>≈</mo> <mn>0</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m), B (<math display="inline"><semantics> <mrow> <mi>Y</mi> <mo>≈</mo> <mo>−</mo> <mn>72</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m), C (<math display="inline"><semantics> <mrow> <mi>Y</mi> <mo>≈</mo> <mo>−</mo> <mn>144</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m), and D (<math display="inline"><semantics> <mrow> <mi>Y</mi> <mo>≈</mo> <mo>−</mo> <mn>198</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m), shown in panel (<b>a</b>) and corresponding to <a href="#micromachines-10-00321-f006" class="html-fig">Figure 6</a>, where <math display="inline"><semantics> <mrow> <mi>Y</mi> <mo>=</mo> <mn>0</mn> </mrow> </semantics></math> <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math>m is placed at the center of the outlet <math display="inline"><semantics> <mi>α</mi> </semantics></math> in the <span class="html-italic">Y</span> direction.</p> Full article ">
13 pages, 1571 KiB  
Article
Tangential Flow Microfiltration for Viral Separation and Concentration
by Yi Wang, Keely Keller and Xuanhong Cheng
Micromachines 2019, 10(5), 320; https://doi.org/10.3390/mi10050320 - 12 May 2019
Cited by 12 | Viewed by 6147
Abstract
Microfluidic devices that allow biological particle separation and concentration have found wide applications in medical diagnosis. Here we present a viral separation polydimethylsiloxane (PDMS) device that combines tangential flow microfiltration and affinity capture to enrich HIV virus in a single flow-through fashion. The [...] Read more.
Microfluidic devices that allow biological particle separation and concentration have found wide applications in medical diagnosis. Here we present a viral separation polydimethylsiloxane (PDMS) device that combines tangential flow microfiltration and affinity capture to enrich HIV virus in a single flow-through fashion. The set-up contains a filtration device and a tandem resistance channel. The filtration device consists of two parallel flow channels separated by a polycarbonate nanoporous membrane. The resistance channel, with dimensions design-guided by COMSOL simulation, controls flow permeation through the membrane in the filtration device. A flow-dependent viral capture efficiency is observed, which likely reflects the interplay of several processes, including specific binding of target virus, physical deposition of non-specific particles, and membrane cleaning by shear flow. At the optimal flow rate, nearly 100% of viral particles in the permeate are captured on the membrane with various input viral concentrations. With its easy operation and consistent performance, this microfluidic device provides a potential solution for HIV sample preparation in resource-limited settings. Full article
(This article belongs to the Special Issue Micro- and Nanofluidics for Bionanoparticle Analysis)
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<p>Schematics of the working principle of the device used in this work. The device is comprised of two flat channels separated vertically by a polycarbonate (PC) nanoporous membrane (pore size of 50 nm). The membrane is functionalized with NeutrAvidin to capture the biotinylated virus, with nonspecific binding blocked by bovine serum albumin. (<b>a</b>) When there is no cross-membrane flow, the virus primarily flows through the top channel. (<b>b</b>) When filtration is promoted using a resistance channel connected to the top channel, fluid enters the device through the top channel inlet and exits from both top (retentate) and bottom (permeate) outlets of the filtration device. The virus is pushed onto the membrane and captured by affinity binding. The arrows in the channels indicate local fluid velocity magnitude and direction.</p> Full article ">Figure 2
<p>Schematic and photograph of the device. (<b>a</b>) A schematic showing the filtration device. A nanoporous PC membrane (50 nm pores) was assembled between two PDMS slabs containing molded microfluidic channels. The inlet in the top channel and outlets of both channels are labeled together with channel dimensions. The bottom right inset shows a top view of the molded PDMS posts which are regularly distributed in the bottom channel to physically support the membrane. (<b>b</b>) Photograph of the filtration device connected to a 65 mm long resistance channel. The devices are filled with food dye for visualization.</p> Full article ">Figure 3
<p>Magnitude profile of +<span class="html-italic">x</span> velocity and permeation percentage in the device from COMSOL simulation. (<b>a</b>) The top view of the simulated device and profiles of the axial velocity in <span class="html-italic">y</span>-<span class="html-italic">z</span> cross sections of the channel at different distances from the inlet. The simulated geometry contains a filtration device (region I) of two channels separated by a porous membrane and a 65-mm-long resistance channel (region II). The top channel of the filtration device is connected to the resistance channel, while the bottom channel is open to air at the outlet. The velocity profiles correspond to positions of different cross sections along the +<span class="html-italic">x</span> direction. These positions are labeled on the left of the velocity profiles in values (mm) and also as dashed lines in the <span class="html-italic">x</span>-<span class="html-italic">y</span> view of the simulated device (top). Axial flow is along the +<span class="html-italic">x</span> direction and the average inlet velocity is 2.4 mm/s. The left color legend of velocity magnitudes corresponds to the filtration device (region I) and right color legend corresponds to the resistance channel (region II). The magnitude of the axial velocity is observed to decrease in the top channel, but increase gradually in the bottom channel from the inlet to the outlet. (<b>b</b>) Fluid fraction permeating through the membrane and inlet pressure as a function of the resistance channel length. The blue solid circles correspond to the left <span class="html-italic">y</span>-axis and empty orange circles correspond to the right <span class="html-italic">y</span>-axis. The lines are to guide the eyes. The cross-sectional area of the resistance channel is constant. The average flow velocity at the inlet is 2.4 mm/s in all cases.</p> Full article ">Figure 4
<p>Fluid fraction permeating through the membrane as a function of (<b>a</b>) different flow rates and (<b>b</b>) inlet viral concentrations. In (<b>b</b>) the white bars are results from filtration devices connected with 65-mm-length resistance channels, while black bars are results from devices without. Error bars represent the standard deviation from at least 3 independent tests under the same condition. * indicates statistical difference based on two-tailed Student’s t-test at a 95% confidence interval.</p> Full article ">Figure 5
<p>Viral capture yield as a function of (<b>a</b>) sample flow rates and (<b>b</b>) viral concentrations. Viral concentration used in (<b>a</b>) was 5 × 10<sup>6</sup> particles/mL. The flow rate applied in (<b>b</b>) was 2400 µL/h. The white bars are results from filtration devices connected with the 65 mm resistance channel, while black bars are results from devices without. Error bars represent the standard deviation from at least 3 devices under the same conditions. Statistical analysis was conducted for (<b>b</b>) by applying an independent Student’s t-test at a 95% confidence interval and no statistically significant difference is observed among the white bars.</p> Full article ">
13 pages, 7053 KiB  
Article
PMMA-Based Wafer-Bonded Capacitive Micromachined Ultrasonic Transducer for Underwater Applications
by Mansoor Ahmad, Ayhan Bozkurt and Omid Farhanieh
Micromachines 2019, 10(5), 319; https://doi.org/10.3390/mi10050319 - 11 May 2019
Cited by 7 | Viewed by 4715
Abstract
This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. [...] Read more.
This article presents a new wafer-bonding fabrication technique for Capacitive Micromachined Ultrasonic Transducers (CMUTs) using polymethyl methacrylate (PMMA). The PMMA-based single-mask and single-dry-etch step-bonding device is much simpler, and reduces process steps and cost as compared to other wafer-bonding methods and sacrificial-layer processes. A low-temperature (< 180 ∘ C ) bonding process was carried out in a purpose-built bonding tool to minimize the involvement of expensive laboratory equipment. A single-element CMUT comprising 16 cells of 2.5 mm radius and 800 nm cavity was fabricated. The center frequency of the device was set to 200 kHz for underwater communication purposes. Characterization of the device was carried out in immersion, and results were subsequently validated with data from Finite Element Analysis (FEA). Results show the feasibility of the fabricated CMUTs as receivers for underwater applications. Full article
(This article belongs to the Section A：Physics)
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<p>Top (<b>left</b>) and cross-sectional (<b>right</b>) views of the proposed Capacity Micromachined Ultrasonic Transducer (CMUT), showing device dimensions.</p> Full article ">Figure 2
<p>Process steps for CMUT fabrication: (<b>a</b>) pattern lithography and developing, (<b>b</b>) oxide etching and cleaning, (<b>c</b>) polymethyl methacrylate (PMMA) coating, (<b>d</b>) membrane and cavity alignment and bonding, (<b>e</b>) final structure.</p> Full article ">Figure 3
<p>Device during fabrication stages: (<b>a</b>) before bonding, (<b>b</b>) final device, and (<b>c</b>) schematic of final device.</p> Full article ">Figure 4
<p>Thermocompression bonding tool: schematic (<b>left</b>), and actual (<b>right</b>).</p> Full article ">Figure 5
<p>Setup for pitch–catch experiment.</p> Full article ">Figure 6
<p>Output signal of RX-CMUT for a tone burst of 15 cycles at 200 kHz (<b>left</b>), normalized magnitude for a frequency sweep from 100 to 300 kHz (<b>right</b>).</p> Full article ">Figure 7
<p>Comparison of experimental and analytical unamplified output signal (<b>left</b>), corresponding acoustic pressure (<b>right</b>).</p> Full article ">Figure 8
<p>Simulated RX-CMUT output with varying bias voltage (<b>left</b>); associated sensitivity (<b>right</b>).</p> Full article ">Figure A1
<p>Side view (with reduced element count) and top view of FEA model.</p> Full article ">
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