Magnetic Polymeric Conduits in Biomedical Applications
Design and Study of a Novel P-Type Junctionless FET for High Performance of CMOS Inverter
An All-in-One Testing Chip for Simultaneous Measurement of Multiple Thermoelectric Parameters in Doped Polysilicon
Automatic Extraction and Compensation of P-Bit Device Variations in Large Array Utilizing Boltzmann Machine Training

Journal Description

Micromachines

Micromachines is a peer-reviewed, open access journal on the science and technology of small structures, devices and systems, published monthly online by MDPI. The Chinese Society of Micro-Nano Technology (CSMNT) is affiliated with Micromachines and its members receive discounts on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), PubMed, PMC, Ei Compendex, dblp, and other databases.
Journal Rank: JCR - Q2 (Physics, Applied) / CiteScore - Q2 (Mechanical Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 16.2 days after submission; acceptance to publication is undertaken in 1.8 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Testimonials: See what our editors and authors say about Micromachines.
Companion journal: Micro.

Impact Factor: 3.0 (2023); 5-Year Impact Factor: 3.0 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2072-666X

Latest Articles

24 pages, 4433 KiB

Open AccessReview

Towards Perfluoroalkyl and Polyfluoroalkyl Substance (PFAS)-Free Energy Harvesting: Recent Advances in Triboelectric Nanogenerators for Sports Applications

by Mónica P. S. Ferreira, Inês Ferreira, Vânia Pais, Liliana Leite, João Bessa, Fernando Cunha and Raúl Fangueiro

Micromachines 2025, 16(3), 313; https://doi.org/10.3390/mi16030313 (registering DOI) - 7 Mar 2025

Abstract

Triboelectric nanogenerators (TENGs) can convert the mechanical energy of physical activities into electricity. This is particularly useful in sports applications, where physical activity can power devices such as wearables that can provide real-time feedback on athletes’ performance or health. To work, a TENG usually needs tribopositive and tribonegative materials. Currently, the vast majority of TENGs use materials containing perfluoroalkyl and polyfluoroalkyl substances (PFAS) as tribonegative materials. However, these substances pose risks to humans and the environment, which has led the European Union to consider restrictions on these compounds. For this reason, PFAS-free alternatives, such as polydimethylsiloxane (PDMS) and MXenes, need to be better explored to replace PFAS materials while aiming to achieve equal efficiency. This review will explore some of the recent advances that have been developed in the field of PFAS-free TENGs, with an emphasis on sports applications. Full article

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13 pages, 2361 KiB

Open AccessArticle

Integrated Wastewater Remediation and Energy Production: Microfluidic Photocatalytic Fuel Cells Enabled by Dye Pollutants

by Youquan Zhou, Fangzhou Luo, Zhichao Wang, Jiayi Zhu and Hao Yang

Micromachines 2025, 16(3), 312; https://doi.org/10.3390/mi16030312 (registering DOI) - 7 Mar 2025

Abstract

Directly degrading the dyes in the wastewater is a missed opportunity. Herein, we propose a solution employing a microfluidic chip to construct a photocatalytic fuel cell (PFC) system, which can efficiently degrade tetracycline while generating electricity simultaneously under visible-light irradiation. This approach utilizes the photogenerated electrons from the dye Rhodamine B (RhB), which are effectively transferred through a gold layer to activate persulfate in water, leading to enhanced tetracycline degradation. Experimental results reveal that within one hour of reaction duration, the degradation efficiency of tetracycline within the PFC system was doubled. At a persulfate (PS) concentration of 2 mM, the system’s open-circuit voltage and short-circuit photocurrent density reached 0.26 V and 0.00239 mA·cm⁻² respectively, both exceeding the values detected at 0.5 mM PS. Additionally, the system’s power density was triple that at 0.5 mM PS. Notably, when the PS concentration in the system was elevated from 0.5 mM to 2 mM, the degradation efficiency of tetracycline witnessed a significant boost from 35.16% to 60.78%. This approach proffers a novel tactic for harnessing dye waste via microfluidic devices. The PFC system accomplishes not only the degradation of dyes and antibiotics but also the generation of electrical energy, substantially enhancing the energy utilization efficiency. Full article

(This article belongs to the Topic Advances in Microfluidics and Lab on a Chip Technology, 2nd Edition)

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(a) The schematic diagram of the PFC, (b) the internal structure of the microchannel, (c) the design of the glass substrate with gold-plated electrodes, and (d) the prepared PFC device. Full article ">Figure 2
(a) Schematic diagram of the test system, (b) physical diagram of the test system, and (c) the reaction mechanisms of PFC systems. Full article ">Figure 3
(a) The degradation of TC by the photoexcited RhB/PS system, (b) the absorption spectra of the solution before and after the reaction, and degradation efficiency of tetracycline at different (c) flow rates, (d) light intensities, (e) PS concentrations, and (f) sodium sulfate concentrations in a microfluidic chip. Full article ">Figure 4
The polarization curve of the system under different (a) flow rate, (c) light intensities, (e) PS concentrations, and (g) sodium sulfate concentrations, and the power density curve of the system under different (b) flow rates, (d) light intensities, (f) PS concentrations, and (h) sodium sulfate concentrations. Full article ">Figure 5
Open-circuit voltage–time plot. Full article ">

23 pages, 9429 KiB

Open AccessReview

An Overview of Hot Carrier Degradation on Gate-All-Around Nanosheet Transistors

by Huimei Zhou

Micromachines 2025, 16(3), 311; https://doi.org/10.3390/mi16030311 - 6 Mar 2025

Abstract

Gate-All-Around (GAA) Nanosheet (NS) transistors have been identified as the device architecture for 3 nm and beyond as they provide additional scaling benefits. The Hot Carrier (HC) effect cannot be ignored in the development of metal oxide semiconductor field effect transistors (MOSFETs). In this article, we present a comprehensive review of Hot Carrier Degradation (HCD) studies on GAA NS transistors including geometry dependencies, surface orientation impacts, corner effects, characterization methodologies, process impacts and self-heating impacts from different researchers, together with the challenges and outlook, providing an insightful and valuable HCD reliability discussion and review on the cutting-edge technology in continuous MOSFET scaling. Full article

(This article belongs to the Special Issue Multifunctional Transistors: Outlooks and Challenges)

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18 pages, 11650 KiB

Open AccessArticle

Optimization of Cutting Parameters to Minimize Wall Deformation in Micro-Milling of Thin-Wall Geometries

by Ahmet Hasçelik, Kubilay Aslantas and Bekir Yalçın

Micromachines 2025, 16(3), 310; https://doi.org/10.3390/mi16030310 - 6 Mar 2025

Abstract

Thin-walled micro-structures are a critical component of micro-devices, and their precise manufacture has a direct impact on product performance. Micro-milling is an effective manufacturing method that enables the production of micro-thin-walled structures with high precision and performance. Wall deformation is an undesirable problem in the production of parts with complex geometries and high aspect ratios, particularly when the height-to-thickness ratio (h/t) exceeds 20. In the micro-milling process, cutting parameters are the main factors affecting wall deformation. Therefore, optimising the cutting parameters is critical for the accuracy and precision of the cutting process. In this study, thin walls of 50 µm thickness, 1 mm height and 10 mm length were machined from an Al6061-T6 alloy using a tungsten carbide cutting tool with a diameter of 1 mm. The effects of feed rate, spindle speed and depth of cut cutting parameters (control parameters) used in the micro-milling process on the cutting forces and wall deformation (outputs) were investigated. A Taguchi L18 orthogonal design was used to optimise the cutting parameters. During the micro-milling experiments, the cutting forces were recorded, and the amount of deformation occurring in the thin wall was accurately determined using an optical profilometer with a motorised measuring system. Taguchi and ANOVA analyses were performed on the measured values of F_x tangential force, F_y feed force and thin-wall deformation to determine the effect of the control parameters on the outputs and to determine the most suitable cutting parameters to minimise deformation and keep the cutting forces under control. As a result of this study, the cutting parameter with the highest effect on the tangential force F_x was the depth of cut, with 56.94%, while the most effective cutting parameter on the feed force F_y was the feed rate, with 45.3%. The most effective parameter on the machined thin-wall deformation was the feed rate, with 87.36%. This study on the optimisation of cutting parameters in micro-thin-walled structures covers a unique topic that has been addressed in limited numbers in the literature. Full article

(This article belongs to the Special Issue Micro-Manufacturing and Applications, 5th Edition: Materials and High-Precision Micromachining)

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20 pages, 11640 KiB

Open AccessArticle

The Influence of Sample Microfabrication and Annealing on the Mechanical Strain–Stress Behavior of Stainless Steels and Corrosion Resistant Aluminum Alloys in Micro-Tensile Tests

by Janko Auerswald, Joel Tenisch, Christoph Fallegger and Markus Seifert

Micromachines 2025, 16(3), 309; https://doi.org/10.3390/mi16030309 - 6 Mar 2025

Abstract

Miniaturized components for enhanced integrated functionality or thin sheets for lightweight applications often consist of face-centered cubic metals. They exhibit good strength, corrosion resistance, formability and recyclability. Microfabrication technologies, however, may introduce cold work or detrimental heat-induced lattice defects into the material, with consequences for the mechanical properties. Austenitic stainless steels (1.4310, 1.4301) and aluminum alloys (EN AW-5005-H24, EN AW-6082-T6) were selected for this study. The influence of pulsed fiber laser cutting, microwaterjet cutting, and annealing on the strain–stress behavior was investigated. The micro-tensile test setup comprised a flex-structure force sensor, a laser extensometer, and a dedicated sample holder. Fiber laser cut 1.4310 samples exhibited early failure at low fracture strain in narrow shear band zones. The shear band zones were detectable on the sample surface, in the laser extensometer images, in the horizontal sections of the stress–strain curves, and in the microstructure. Inside the shear band zones, grains were strongly elongated and exhibited numerous parallel planar defects. Heat-induced chromium carbides, in combination with low stacking fault energy (SFE) and elevated carbon content, favored shear band zone formation in 1.4310. In contrast, microwaterjet cut high SFE materials EN AW-5005-H24 and EN AW-6082-T6, as well as low-carbon austenitic stainless steel 1.4301, exhibited uniform plastic deformation. Full article

(This article belongs to the Section D：Materials and Processing)

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11 pages, 1999 KiB

Open AccessArticle

Optimized Quasi-Optical Mode Converter for TE_33,12 in 210 GHz Gyrotron

by Hamid Sharif, Muhammad Haris Jamil and Wenlong He

Micromachines 2025, 16(3), 308; https://doi.org/10.3390/mi16030308 - 6 Mar 2025

Abstract

This article discusses the design of a high-performance quasi-optical mode converter for the

T E_{33, 12}

mode at 210 GHz. The conversion process is challenging due to a caustic-to-cavity radius ratio of approximately 0.41. The mode converter employs an optimized dimpled [...] Read more.

This article discusses the design of a high-performance quasi-optical mode converter for the

T E_{33, 12}

mode at 210 GHz. The conversion process is challenging due to a caustic-to-cavity radius ratio of approximately 0.41. The mode converter employs an optimized dimpled wall launcher, analyzed using coupling mode theory with twenty-five coupled modes, compared to the usual nine modes and optimized reflector systems, to effectively address the conversion challenge.Electromagnetic field analysis within the launcher wall was optimized using MATLAB R2021b. The radiation fields from the launcher were analyzed in free space using Gaussian optics and vector diffraction theory. The mirror system consists of a quasi-elliptical mirror, an elliptical mirror, and phase-corrected parabolic mirrors. Following phase correction, the output window achieved a scalar Gaussian mode content of 99.0% and a vector Gaussian mode content of 97.4%. Full article

(This article belongs to the Special Issue Optoelectronic Fusion Technology)

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4 pages, 170 KiB

Open AccessEditorial

Microfluidic Paper-Based Devices

by Lung-Ming Fu

Micromachines 2025, 16(3), 307; https://doi.org/10.3390/mi16030307 - 6 Mar 2025

Abstract

Since their development by Whitesides’ group in 2007 [...] Full article

12 pages, 281 KiB

Open AccessArticle

Scattering Theory in an N-Pole Semiconductor Quantum Device: The Unitarity of the Current S-Matrix and Current Conservation

by Jan Kučera, Ulrich Wulf and George Alexandru Nemnes

Micromachines 2025, 16(3), 306; https://doi.org/10.3390/mi16030306 - 5 Mar 2025

Abstract

In a number of previous publications, scattering theory for N-pole semiconductor quantum devices was developed. In the framework of the Landauer–Büttiker formalism, an S-matrix was constructed with the aid of an R-matrix providing a mapping of the in-going waves onto the out-going waves. These waves include propagating waves and evanescent waves, the latter of which decay exponentially in the leads which are connected to the active region of the N-pole device. In order to formulate the current conservation in the N-pole device, it is necessary to define the current S-matrix schematically as

\tilde{S} = k^{1 / 2} S k^{- 1 / 2}

, where k contains the information about the k-vectors of the mentioned in- and out-going waves. In this paper, we show how the complete current S-matrix is calculated including the coupling between the propagating and evanescent components and coupling to the bound states in the active device region. One then finds a sub-matrix of

\tilde{S}

which is unitary and which is restricted to the space of the propagating components. We demonstrate that current conservation is associated with the unitarity just of this sub-matrix. Full article

(This article belongs to the Special Issue Wide-Bandgap Semiconductor Devices: Materials, Fabrication, and Applications)

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18 pages, 5207 KiB

Open AccessArticle

Misalignment in Mechanical Interlocking Heterogeneous Integration: Emergent Behavior and Geometry Optimization

by Matthew Nakamura, Corrisa Heyes, Ethan Rocheville, Kirsten Peterson and Joseph J. Brown

Micromachines 2025, 16(3), 305; https://doi.org/10.3390/mi16030305 - 4 Mar 2025

Abstract

This paper addresses the challenge of misalignment in cantilever-based mechanical interlocking structures used for the heterogeneous integration of integrated circuits (ICs). As IC applications expand into flexible and multi-functional platforms, precise alignment becomes critical to maintaining optimal mechanical and electrical performance. We investigate the effects of X and Y misalignment on snap-through forces in cantilever arrays, focusing on their impact on mechanical integrity. The experimental results demonstrate that for X-axis misalignments below 15%, the increase in the required snap-through force is less than 5%. In contrast, Y-axis misalignment shows an even more negligible impact, with less than a 5% reduction in force for up to 20% misalignment. Additionally, through polynomial fits of the model across a range of cantilever angles, this study provides a design template for future exploration of cantilever interactions using nonlinear mechanics while minimizing computational load. These findings offer valuable insights for optimizing misalignment tolerance and improving the design of interlocking structures for IC integration, contributing to the development of robust systems for next-generation IC devices. Full article

(This article belongs to the Special Issue Advanced Packaging Technology for MEMS Devices)

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9 pages, 2321 KiB

Open AccessArticle

Gallium Nitride High Electron Mobility Transistor Device with Integrated On-Chip Array Junction Temperature Monitoring Unit

by Yukuan Chang, Yue Su, Mingke Xiao, Jiatao Wu, Xu Zhang and Hongda Chen

Micromachines 2025, 16(3), 304; https://doi.org/10.3390/mi16030304 - 4 Mar 2025

Abstract

Herein, we present a novel method for junction temperature monitoring of GaN HEMT devices to achieve real-time temperature perception at different locations on the device surface. Through sputtering patterned Ti/Pt thermistor strips on the surface of a GaN HEMT device to construct an on-chip array junction temperature monitoring unit, the thermal distribution of the device during operation is fully reflected. The developed temperature monitoring unit exhibited a desirable temperature coefficient of resistance of 0.183%/°C in the range of 25 °C to 205 °C. Comparison with the thermal imager shows that the integrated temperature monitoring unit can accurately reflect the real-time temperature with a monitoring accuracy of more than 95%, which helps to improve the long-term reliability of GaN power devices under actual application conditions of high frequency and high power density. Full article

(This article belongs to the Special Issue Wide-Bandgap Semiconductor Devices: Materials, Fabrication, and Applications)

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(a) The cross-sectional structure of GaN-HEMT power device cell with integrated temperature monitoring unit. (b) Photograph of the GaN power device with an embedded temperature sensing unit taken by a digital camera. (b’) A magnified view of the temperature sensing unit. (c) Schematic of the preparation procedure for GaN power devices with integrated distributed junction temperature monitoring unit. (Arrows denote the sequential direction of the fabrication steps). Full article ">Figure 2
Transfer characteristics of the fabricated GaN-HEMT at VDS = 3 V. Full article ">Figure 3
Output characteristics of the fabricated GaN-HEMT. Full article ">Figure 4
Relative resistance changes versus the applied temperature of the sensing unit at different positions, corresponding to the left (a), middle (b), and right (c) positions, respectively. Full article ">Figure 5
(a–d) Thermal images of the GaN-HEMT power device with integrated temperature monitoring unit under different drain current conditions, corresponding to constant currents of 0.0 A (a), 0.5 A (b), 1.0 A (c), and 1.5 A (d). (e) Comparison of the temperatures measured by the infrared imager and the temperature monitoring units at different locations under normal working conditions of the device. (Arrows associate the data curves with their vertical axes). Full article ">

22 pages, 1604 KiB

Open AccessArticle

Maximum Correntropy Criterion Kalman/Allan Variance-Assisted FIR Integrated Filter for Indoor Localization

by Manman Li, Lei Deng, Yide Zhang, Yuan Xu and Yanli Gao

Micromachines 2025, 16(3), 303; https://doi.org/10.3390/mi16030303 - 4 Mar 2025

Abstract

To obtain more accurate information on using an inertial navigation system (INS)-based integrated localization system, an integrated filter with maximum correntropy criterion Kalman filter (mccKF) and finite impulse response (FIR) is proposed for the fusion of INS-based multisource sensor data in this work. In the realm of medical applications, precise localization is crucial for various aspects, such as tracking the movement of a medical instrument within the human body or monitoring its position in the human body during procedures. This study uses ultra-wideband (UWB) technology to rectify the position errors of the INS. In this method, the difference between the positions of the INS and UWB is used as the measurement of the filter. The main data fusion filter in this study is the mccKF, which utilizes the maximum correntropy criterion (mcc) method to enhance the robustness of the Kalman filter (KF). This filter is used for fusing data from multiple sources, including the INS. Moreover, we use the Mahalanobis distance to verify the performance of the mccKF. If the performance of the mccKF is lower than the preset threshold, the Allan Variance-assisted FIR filter is used to replace the mccKF, which is designed in this work. This adaptive approach ensures the resilience of the system in demanding medical environments. Two practical experiments were performed to evaluate the effectiveness of the proposed approach. The findings indicate that the mccKF/FIR integrated method reduces the localization error by approximately 32.43% and 37.5% compared with the KF and mccKF, respectively. These results highlight the effectiveness of the proposed approach. Full article

(This article belongs to the Special Issue Artificial Intelligence for Micro Inertial Sensors)

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13 pages, 4271 KiB

Open AccessArticle

Experimental Study on Ultrasonic Vibration-Assisted Grinding of SiCp/Al Composites Grinding

by Jinghao Jin, Jian Mao, Rong Wang and Mengyang Cui

Micromachines 2025, 16(3), 302; https://doi.org/10.3390/mi16030302 - 4 Mar 2025

Abstract

Aluminum matrix composites reinforced with silicon carbide particles (SiCp/Al) are widely used in aerospace fields with excellent properties, such as high specific strength, high specific stiffness, and high thermal conductivity. Due to the heterogeneous structure, its microstructure is one of the determinants of workpiece life, and ultrasonic vibration can improve the surface quality after grinding. Therefore, in this study, ultrasonic vibration-assisted grinding (UVAG) orthogonal tests were designed to study the surface morphology of SiCp/Al and the form of SiC particle removal under different machining parameters based on the SEM observation of the material surface, and to analyze the percentage of different kinds of grinding forces. The results show that the existence of particle fracture force depends on the relative sizes of the maximum undeformed chip thickness and the critical chip thickness. Through surface roughness testing and analysis, the influence of processing parameters on the surface roughness of the material is explored, and it is found that the application of ultrasound reduces the surface roughness of the material, which can be used as a guideline for the surface quality of the grinding process and the optimization of the process parameters. Full article

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5 pages, 888 KiB

Open AccessEditorial

The Integration of Artificial Intelligence with Micro–Nano-Systems: Perspectives, Challenges and Future Prospects

by Juvenal Rodríguez-Reséndiz, Marcos Aviles and José M. Álvarez-Alvarado

Micromachines 2025, 16(3), 301; https://doi.org/10.3390/mi16030301 - 4 Mar 2025

Abstract

Technological advances have allowed various systems to be developed on a small scale [...] Full article

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25 pages, 11067 KiB

Open AccessReview

Applications and Recent Advances of Low-Temperature Multicomponent Solders in Electronic Packaging: A Review

by Guodong Wu, Jingfang Shen, Ding Zhou, Muhammad Khairi Faiz and Yew Hoong Wong

Micromachines 2025, 16(3), 300; https://doi.org/10.3390/mi16030300 - 3 Mar 2025

Abstract

Flexible wearable devices and solar flexible units often use thermally sensitive organic materials as substrates, which are prone to thermal damage during the bonding process in 3D packaging, leading to chip deformation or failure. Multicomponent solders, with well-designed multicomponent metallic elements, exhibit unique low-melting-point characteristics. The application of low-temperature multicomponent solders in electronic packaging can significantly reduce bonding temperatures and minimize thermal damage to chips. This paper reviews the wettability and preparation methods of low-temperature multicomponent solders, and concludes the effect of different metallic elements on the solders. Additionally, this paper discusses the research on interfacial reactions, mechanical properties of low-temperature multicomponent solder joints, providing valuable insights for future research and development in this field. Full article

(This article belongs to the Special Issue Micro/Nano Manufacturing of Electronic Devices)

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4 pages, 157 KiB

Open AccessEditorial

Transforming Drug Discovery with Miniaturized Predictive Tissue Models

by Mohsen Akbari

Micromachines 2025, 16(3), 299; https://doi.org/10.3390/mi16030299 - 3 Mar 2025

Abstract

Drug development is a lengthy and expensive process that involves screening thousands of potential candidates in vitro, followed by pre-clinical efficacy, pharmacokinetic, and pharmacodynamic studies in relevant animal models, before evaluating the safety and efficacy of a drug in clinical trials [...] Full article

(This article belongs to the Section B2: Biofabrication and Tissue Engineering)

27 pages, 4500 KiB

Open AccessArticle

Low Capillary Elastic Flow Model Optimization Using the Lattice Boltzmann Method and Non-Dominated Sorting Genetic Algorithm

by Yaqi Hou, Wei Zhang, Jiahua Hu, Feiyu Gao and Xuexue Zong

Micromachines 2025, 16(3), 298; https://doi.org/10.3390/mi16030298 - 28 Feb 2025

Abstract

In simulations of elastic flow using the lattice Boltzmann method (LBM), the steady-state behavior of the flow at low capillary numbers is typically poor and prone to the formation of bubbles with inhomogeneous lengths. This phenomenon undermines the precise control of heat transfer, mass transfer, and reactions within microchannels and microreactors. This paper establishes an LBM multiphase flow model enhanced by machine learning. The hyperparameters of the machine learning model are optimized using the particle swarm algorithm. In contrast, the non-dominated sorting genetic algorithm (NSGA-II) is incorporated to optimize bubble lengths and stability. This results in a coupled multiphase flow numerical simulation model that integrates LBM, machine learning, and the particle swarm algorithm. Using this model, we investigate the influence of elastic flow parameters on bubble length and stability in a T-shaped microchannel. The simulation results demonstrate that the proposed LBM multiphase flow model can effectively predict bubble elongation rates under complex conditions. Furthermore, multi-objective optimization determines the optimal gas–liquid two-phase inlet flow rate relationship, significantly mitigating elastic flow instability at low capillary numbers. This approach enhances the controllability of the elastic flow process and improves the efficiency of mass and heat transfer. Full article

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10 pages, 3090 KiB

Open AccessArticle

A Method for Fabricating Cavity-SOI and Its Verification Using Resonant Pressure Sensors

by Han Xue, Xingyu Li, Yulan Lu, Bo Xie, Deyong Chen, Junbo Wang and Jian Chen

Micromachines 2025, 16(3), 297; https://doi.org/10.3390/mi16030297 - 28 Feb 2025

Abstract

Cavity silicon on insulator (Cavity-SOI) offers significant design flexibility for microelectromechanical systems (MEMS). Notably, the shape and depth of the cavity can be tailored to specific requirements, facilitating the realization of intricate multi-layer structural designs. The novelty of the proposed fabrication methodology is manifested in its employment of a micromachining process flow, which integrates dry etching, wafer level Au–Si eutectic bonding, and chemical mechanical polishing (CMP) to create Cavity-SOI. This innovative approach substantially mitigates the complexity of fabrication, and the implementation of wafer-level gold–silicon eutectic bonding and vacuum packaging can be achieved, representing a distinct advantage over conventional methods. To evaluate the technical viability, a MEMS resonant pressure sensor (RPS) was designed. Experimental findings demonstrate that during the formation of Cavity-SOI, dry etching can accurately fabricate cavities of predefined dimensions, wafer-level Au–Si eutectic bonding can achieve efficient sealing, and CMP can precisely regulate the depth of cavities, thus validating the feasibility of the Cavity-SOI formation process. Additionally, when implementing Cavity-SOI in the fabrication of MEMS RPS, it enables the spontaneous release of resonators, effectively circumventing the undercut and adhesion issues commonly encountered with hydrofluoric acid (HF) release. The sensors fabricated using Cavity-SOI exhibit a sensitivity of 100.695 Hz/kPa, a working temperature range spanning from −10–60 °C, a pressure range of 1–120 kPa, and a maximum error of less than 0.012% full scale (FS). The developed micromachining process for Cavity-SOI not only streamlines the fabrication process but also addresses several challenges inherent in traditional MEMS fabrication. The successful fabrication and performance validation of the MEMS RPS confirm the effectiveness and practicality of the proposed method. This breakthrough paves the way for the development of high-performance MEMS devices, opening up new possibilities for various applications in different industries. Full article

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The schematic diagram of the structure. (a) Standard SOI, (b) Cavity-SOI. Full article ">Figure 2
Fabrication steps of Cavity-SOI. (i) Clean the silicon wafer. (ii) Growth of an oxide layer as an insulating layer on the cleaned silicon wafer surface, followed by evaporation of a layer of Cr (50 nm) as an adhesive layer, a layer of Au (500 nm) as the bonding material, and spin coating of a layer of photoresist (PR) as a patterned mask. (iii) The cavities were etched on the surface of the silicon wafer with a depth of 10 μm. (iv) Clean the surface photoresist with acetone, alcohol, and deionized water. (v) Bond another silicon wafer at temperature of 390 °C and pressure of 2000 mbar. (vi) Thin the bonded silicon wafer to a predetermined thickness through CMP method. Full article ">Figure 3
Characterization of CMP and bonding quality. (a) Measurement results of surface roughness, ranging from 0.54 to 0.97 nm. (b) Test results of the bonding using an ultrasonic scanning microscope. The light-colored areas represent unbonded regions. (c) Scanning electron microscope image of the bonding interface. (d) Testing of the bonding shear force using a push–pull tester. (e) Shear force test results. The bonding can withstand a shear force of over 50 kgf. Full article ">Figure 4
Design of the pressure sensor. (a) Schematic diagram of the overall structure of the sensor, which consists of a glass cover plate and a Cavity-SOI from top to bottom. (b) Schematic diagram of the sensor structure; the cavity is located directly below the resonator (c) Schematic diagram of the device layer, where resonators are located at different positions on the device layer and connected to the pads at the edges through silicon wires. (d) Schematic diagram of the substrate layer. Full article ">Figure 5
(a) Schematic diagram of the fabrication process of the sensor. (i) Clean the Cavity-SOI fabricated in <a href="#micromachines-16-00297-f002" class="html-fig">Figure 2</a> using acetone, anhydrous ethanol, and deionized water. (ii) Etch the pressure-sensitive diaphragm in the center to a depth of 180 μm and the holes through the substrate layer at the edges on the back of the Cavity-SOI. (iii) Etch the resonators and other structures on the device layer. The resonators are positioned directly above the cavities. (iv) The BF33 glass is cleaned with concentrated sulfuric acid and deionized. (v) Evaporation of a layer of Cr/Au on the cleaned glass surface, followed by spin-coating of a layer of photoresist on the Cr/Au surface. (vi) Use the gold etching solution and chromium etching solution to etch the BF3 glass to a depth of 5 μm. (vii) Clean the glass, and remove the photoresist and Cr/Au. (viii) Bond the Cavity-SOI made in step (iii) and the glass cover made in step (vii) by anodic bonding. (b) Chip dimensions: approximately 10 mm in length and width, with a glass cover on the front and a pressure-sensitive diaphragm and lead holes on the back. And the package of the sensor. Full article ">Figure 6
(a) SEM photo of the resonator profile, with the cavity located directly below the resonator. (b) At the edge of the gold–silicon eutectic bonding interface, compared with (c), there is no undercut caused by HF release. Full article ">Figure 7
Test results of the sensor. (a) Test results of open-loop of microsensor under room temperature and atmosphere pressure, with a resonator Q value of 18,143. (b) In the temperature range of −10–60 °C, for the pressure of 1–120 kPa, the sensor is calibrated at different temperatures and pressures, and the error is less than 14 Pa. (c) The sensitivity of the side resonator for pressure is 51.02 Hz/kPa with a linearity of 0.999997 and the central resonator’s sensitivity to pressure is −49.675 Hz/kPa with a linearity of 0.999994. (d) The temperature sensitivity of the side resonator is 18.155 Hz/°C and the temperature sensitivity of the central resonator is 19.573 Hz/°C. Full article ">

10 pages, 4488 KiB

Open AccessArticle

A MEMS Pirani Vacuum Gauge Based on Porous Silicon

by Yuzhe Lin, Zichao Zhang, Jifang Tao and Lianggong Wen

Micromachines 2025, 16(3), 296; https://doi.org/10.3390/mi16030296 - 28 Feb 2025

Abstract

Vacuum gauges based on Micro-Electro-Mechanical System (MEMS) technology have the advantages of small size, high reliability, and low cost, so they are widely used in semiconductor, chemical, laboratory, and aerospace. In this paper, a high-reliability MEMS Pirani vacuum gauge based on a porous silicon platform is designed, fabricated, and characterized. The repeatability within 4~10⁵ Pa has been tested. The porous silicon acting as a support material achieved a porosity of 68% and a thermal conductivity of 3.5 W/(m·K), and the surface morphology of the porous silicon is smooth. The proposed MEMS Pirani vacuum gauge containing no suspended thin-film structures has good mechanical stability and is unaffected by mechanical shock and vibration in operation. Full article

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19 pages, 3887 KiB

Open AccessArticle

The Effect of MoS₂ and Si₃N₄ in Surface Plasmon Resonance Biosensors for HIV DNA Hybridization Detection: A Numerical Study

by Talia Tene, Diana Coello-Fiallos, María de Lourdes Palacios Robalino, Fabián Londo and Cristian Vacacela Gomez

Micromachines 2025, 16(3), 295; https://doi.org/10.3390/mi16030295 - 28 Feb 2025

Abstract

This study presents a numerical investigation of surface plasmon resonance (SPR) biosensors incorporating silicon nitride (Si₃N₄) and molybdenum disulfide (MoS₂) for HIV DNA hybridization detection. By optimizing the thickness of Ag and Si₃N₄ and the number of MoS₂ layers, two configurations, Sys₂ (Ag-Si₃N₄) and Sys₃ (Ag-Si₃N₄-MoS₂), were selected for comparative analysis. Performance metrics, including the resonance angle shift, sensitivity, detection accuracy, and quality factor, demonstrated that Sys₂ achieved the highest sensitivity of 210.9°/RIU and an enhanced figure of merit (86.98 RIU⁻¹), surpassing state-of-the-art SPR sensors. Although Sys₃ exhibited a lower sensitivity of 158.1°/RIU due to MoS₂-induced optical losses, it provided a lower limit of detection, suggesting a trade-off between sensitivity and spectral broadening. Compared to previous SPR biosensors, the proposed configurations achieve superior sensitivity while maintaining stability and selectivity, positioning them as promising candidates for next-generation nucleic acid detection platforms. Full article

(This article belongs to the Special Issue Innovative Plasmonic Nanostructures: Integrating 2D Materials, Advanced Sensing, and Theoretical Modeling)

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16 pages, 20095 KiB

Open AccessArticle

Finite Element Analysis of Soft-Pad Moldless Stamping of Bistable Circular Micro Shells

by Mark M. Kantor, Asaf Asher, Rivka Gilat and Skava Krylov

Micromachines 2025, 16(3), 294; https://doi.org/10.3390/mi16030294 - 28 Feb 2025

Abstract

Bistable microstructures are promising for implementation in many mictroelectromechanical system (MEMS)-based applications due to their ability to stay in several equilibrium states, high tunability and unprecedented sensitivity to external stimuli. As opposed to the extensively investigated one-dimensional curved beam-type devices of this kind, microfabrication of non-planar two-dimensional bistable structures, such as plates or shells, represents a remarkable challenge. Recently reported by us, a new moldless stamping procedure, based on pressing a soft stamp over a thin suspended metallic film, was demonstrated to be a feasible direction for the fabrication of initially curved micro plates. However, reliable implementation of this fabrication paradigm and its further development requires better understanding of the role of the process parameters, and of the effect of both the plate and the stamp material properties on the shape of the formed shell and on the postfabrication residual stresses, and therefore on the shell behavior. The need for an appropriate choice of these parameters requires the development of a systematic modeling approach to the stamping process. Here, we report on a finite element (FE)-based methodology for modeling the processing sequences of a successfully fabricated aluminum (Al) micro shell of realistic geometry. The model accounts for the elasto-plastic behavior of the plate material, the nonlinear material behavior of the foam and the contact between them. It was found that the stamping pressure and the plate material parameters are the key parameters affecting the residual shell curvature as well as its shape. Consistently with previously presented experimental results, we show that the fabrication procedure partially relieves the prestresses emerging during preceding fabrication steps, leaving a nontrivial distribution of residual stresses in the formed shell. The presented analysis approach and results provide tools for designers and manufacturers of systems including micro structural elements of shell type. Full article

(This article belongs to the Special Issue MEMS Nano/Micro Fabrication, 2nd Edition)

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