CN104907568B - Piezoresistive thick film pressure sensor manufacturing method based on femtosecond laser composite technology - Google Patents

Abstract

The invention discloses a preparation method of a piezoresistive thick film pressure sensor based on femtosecond laser composite technology. The laser is used as the original laser for scanning sintering and melting. Then, according to the real-time monitoring feedback, choose to use picosecond or femtosecond laser to finish the specific area. According to the actual needs of piezoresistive thick film pressure sensor processing, real-time monitoring can be dimension detection, crystal phase structure detection, surface morphology detection, composition detection, etc. The invention can realize more precise size control and resistance value control, saves the subsequent process of repairing resistance, and can achieve the precision that can be used without compensation. At the same time, it also saves the cleaning, polishing and other processes required after the completion of traditional 3D printing, effectively solving the problems of powder blowing, high residual stress, and low strength.

Description

Fabrication method of piezoresistive thick film pressure sensor based on femtosecond laser recombination technology

technical field

The invention belongs to the technical field of pressure sensor chips, and in particular relates to a preparation method of a piezoresistive thick film pressure sensor based on femtosecond laser composite technology.

Background technique

Thick film pressure sensor is the product of the combination of thick film technology and sensor technology. It integrates thick film technology and pressure sensor technology. It is insensitive to temperature, simple in process, good in repeatability, suitable for harsh environments, high in reliability and low in cost. Etc. The piezoresistive thick-film pressure sensor is the most widely used thick-film pressure sensor. It generally uses ceramics (such as alumina) and metals (such as stainless steel) as elastomers, and glass glaze containing metal oxides as resistors. It is printed layer by layer by screen printing process and then sintered. Since the thickness of the sintered resistance film in the silk screen manufacturing process is about 10 microns, it is difficult to accurately control the resistance value after sintering, and the error is often between 5-10%, which makes it very difficult to adjust and compensate in batches, resulting in deviation of the accuracy of the thick film pressure sensor. Low, often need to repair resistance.

3D printing technology is an additive manufacturing method that uses powder materials to build up products layer by layer through selective laser sintering or melting. Compared with traditional manufacturing technology, it can easily manufacture complex and difficult products that are difficult to produce with traditional technology. However, the surface of 3D printed parts often shows shortcomings such as low strength, powder blowing, spheroidization, high residual stress, and high surface roughness. It is necessary to remove slag and polish the molded parts. In the current 3D printing process, only visual monitoring is used to control the size. Without the real-time monitoring function of microstructure and composition, we have no way of knowing the microstructure of parts, and we cannot better control their mechanical properties.

In recent years, short-pulse lasers (such as nanosecond lasers, picosecond lasers, and femtosecond lasers) have attracted much attention in the field of precision processing due to their small thermal influence and high processing accuracy. The pulse width of nanosecond laser is nanosecond (10 ^-9 seconds) level, and its repetition frequency is generally hundreds of kHz, up to 10MHz, so it can achieve high processing efficiency. Picosecond (10 ^-12 seconds) lasers are sufficient to avoid thermal diffusion of energy and achieve the peak energy density required for these ablation critical processes, which can provide high average power (10 W) and good beam quality (M2 < 1.5), Can be focused into a 10μm or smaller spot within the effective working distance. Femtosecond laser (10 ^-15 seconds) avoids the existence of thermal diffusion during the duration of each laser pulse interacting with matter, and fundamentally eliminates the melting zone and heat affected zone similar to long pulse processing. The impact of shock waves and other effects on surrounding materials and thermal damage greatly reduces the space involved in the processing process, thereby improving the accuracy. The beam diameter can be focused to within 1 μm, and the accuracy can reach within 100nm. up to 0.1nm.

Nanosecond/picosecond/femtosecond laser composite technology can integrate the advantages of processing speed, precision and cost, and apply it to the sintering and micromachining of sensors, which can quickly and effectively avoid the powder blowing that occurs in the current laser sintering process, For complex problems such as residual stress, the compensation step can be omitted. There are no 3D printed sensor products using this technology yet.

Contents of the invention

Aiming at the defects in the manufacturing process of the piezoresistive thick film pressure sensor, such as low precision and the decrease of interface strength due to excessive bonding materials, the present invention combines nanosecond-picosecond-femtosecond laser composite technology to propose a femtosecond-based Preparation method of piezoresistive thick film pressure sensor with second laser composite technology.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

The piezoresistive thick-film pressure sensor preparation method based on femtosecond laser composite technology is to prepare the piezoresistive thick-film pressure sensor layer by layer from top to bottom or from bottom to top. When the elastomer is a metal elastomer, the piezoresistive The thick-film pressure sensor consists of an elastomer layer, a dielectric layer, a resistive layer, and a protective layer from bottom to top. The protective layer is passed through by electrodes connected to the resistive layer; when the elastomer is an insulating ceramic elastomer, piezoresistive thick-film The pressure sensor consists of an elastomer layer, a resistive layer, and a protective layer from bottom to top, and the protective layer is passed through by electrodes connected to the resistive layer;

The production steps of each layer are as follows:

(1) In a vacuum environment, load the current layer of raw material powder on the workbench and preheat it;

(2) Determine the original laser according to the accuracy requirements of the current layer, and use the original laser to scan, sinter, melt and solidify the raw materials; the selection principle of the original laser is: choose a laser with a shorter pulse for the current layer with high precision requirements, and use a laser with a lower precision requirement The current layer of the current layer uses a laser with a longer pulse; based on the above selection principles combined with experience and experimental verification, the original laser used to make the current layer is determined among nanosecond lasers, picosecond lasers and femtosecond lasers;

(3) Real-time detection and analysis of one or more of the size, crystal phase structure, surface morphology and composition of the currently formed layer, and feedback the analysis results to the control center;

(4) Compare the analysis result received by the control center with the preset target, if the analysis result reaches the preset target, end and start to make the next layer; otherwise, execute step (5);

(5) Use the finishing laser to finish the specific area of the formed current layer, and then perform step (3); the specific area refers to the area where the analysis result does not reach the preset target, and the selection principle of the finishing laser It is: (a) picosecond laser or femtosecond laser; at the same time, (b) its processing accuracy is higher than that of the original laser.

The above-mentioned original laser and finishing laser are all provided by multi-wavelength integrated fiber lasers. The multi-wavelength integrated fiber lasers include controllers, nanosecond laser probes, picosecond laser probes and femtosecond laser probes, nanosecond laser probes, picosecond laser probes, and picosecond laser probes. Both the laser probe and the femtosecond laser probe are connected with the controller, and the controller is used to control the emission and shutdown of the nanosecond laser, the picosecond laser and the femtosecond laser.

In step (3), a real-time monitoring system is used for real-time detection and analysis. The real-time monitoring system includes a control drive system and a detection instrument. The detection instrument is connected to the control drive system. The detection instrument includes a size detection instrument, a crystal phase structure One or more of testing instruments, surface morphology testing instruments, and component testing instruments.

The detection instrument includes one or more of a scanning electron microscope, an X-ray diffractometer, an infrared camera and a mass spectrometer.

As preferred: the raw material of the elastomer layer is stainless steel, zirconia or aluminum oxide; the raw material of the dielectric layer is aluminum oxide; the raw material of the resistance layer is glass based on ruthenium oxide or ruthenate; the raw material of the electrode is gold, platinum , silver, palladium, copper or nickel.

The nanosecond-picosecond-femtosecond laser composite technology adopted in the present invention is realized by using a multi-wavelength integrated fiber laser that can provide nanosecond laser, picosecond laser and femtosecond laser at the same time. First, according to the accuracy requirements of each layer of the piezoresistive pressure sensor, a nanosecond, picosecond or femtosecond laser is selected as the original laser for scanning sintering and melting. Then, according to the real-time monitoring feedback, choose to use picosecond or femtosecond laser to finish the specific area. According to the actual needs of piezoresistive pressure sensor processing, real-time monitoring can be size detection, crystal phase structure detection, surface morphology detection, composition detection, etc.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

It can achieve more precise size control and resistance value control, eliminating the need for subsequent repair and other processes, and can achieve the accuracy that can be used without compensation. At the same time, it also saves the cleaning, polishing and other processes required after the completion of traditional 3D printing, effectively solving the problems of powder blowing, high residual stress, and low strength.

Description of drawings

In order to illustrate the method of the present invention more clearly, the accompanying drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, In other words, other drawings can also be obtained from these drawings on the premise of not paying creative work.

Fig. 1 is a sectional front view of a metal elastomer piezoresistive thick film pressure sensor. In the figure, 101-support ring, 102-sensing diaphragm, 103-dielectric layer, 104-protective layer, 105-resistive layer, 106-conductive layer, 107 - cavity;

Fig. 2 is the cross-sectional front view of the insulating elastomer piezoresistive thick film pressure sensor, in the figure, 201-support ring, 202-sensing diaphragm, 204-resistive layer, 205-protective layer, 206-conductive layer, 207-empty Cavity;

Fig. 3 is a flowchart of a specific embodiment of the method of the present invention.

detailed description

The piezoresistive thick film pressure sensor includes an integrated elastic body, which is divided into metal elastic body and insulating elastic body. The sensing diaphragm of the metal elastic body is made of a dielectric layer and then a resistive layer, as shown in Figure 1. On the sensing diaphragm of the insulating elastomer, a resistive layer is directly made to monitor the strain, as shown in Figure 2.

As shown in Fig. 1, the metal elastic body pressure sensor mainly includes a protective layer (104), a conductive layer (106), a resistive layer (105), a dielectric layer (103) and an elastic body. The dielectric layer (103) is disposed on the elastic body, the resistance layer (105) and the conductive layer (106) are disposed on the dielectric layer (103), and the protective layer (104) is disposed on the resistance layer (105) and the conductive layer (106) The upper part is used to protect the resistance layer (105) and the conductive layer (106). The conductive layer (106) communicates with the resistance layer (105), and leads the signal of the resistance layer (105) out of the protection layer (104).

The elastic body is the main body of the pressure sensor, which is composed of a supporting ring (101) and a sensing diaphragm (102). The upper end of the supporting ring (101) is sealed by the sensing diaphragm (102), and the lower end is open, that is, the supporting ring (101) and the sensing diaphragm The sheet (102) forms a cavity (107). The support ring (101) is used to support the sensing diaphragm (102), the protective layer (104), the conductive layer (106) and the resistance layer (105), and the sensing diaphragm (102) is a time-strained layer for sensing external pressure, Its thickness is determined by performance indicators such as the range and sensitivity of the pressure sensor. The supporting ring (101) and the sensing diaphragm (102) are made of the same material, which can be stainless steel or other metal materials.

The dielectric layer (103) is used as the insulating layer of the resistance layer (105) and the elastic body, and its material may be aluminum oxide, and is connected. The resistive layer (105) is composed of four resistors arranged at different positions on the sensing diaphragm (102) to form a Wheatstone bridge of the pressure sensor, and its material is glass ruthenium oxide or ruthenate-based. The conductive layer (106) is connected to the four resistors of the resistance layer (105), and the material of the conductive layer (106) can be gold, platinum, silver, palladium, copper, nickel and other metals.

As shown in Figure 2, the elastomer in the insulated elastomer pressure sensor is a ceramic insulating material, mainly including a protective layer (205), a conductive layer (206), a resistive layer (204) and an elastomer, a conductive layer (206) and a resistive layer ( 204) is directly printed on the elastic body, and the protective layer (205) is arranged on the conductive layer (206) and the resistive layer (204) to protect the conductive layer (206) and the resistive layer (204). The conductive layer (206) communicates with the resistance layer (204), and leads the signal of the resistance layer (204) out of the protection layer (205).

The elastic body is composed of a supporting ring (201) and a sensing diaphragm (202), the upper end of the supporting ring (201) is sealed by the sensing diaphragm (202), and the lower end is open, that is, the supporting ring (201) and the sensing diaphragm (202) form cavity (207). The support ring (201) is used to support the sensing diaphragm (202), the protective layer (205), the conductive layer (206) and the resistance layer (204), and the sensing diaphragm (202) is a time-strained layer for sensing external pressure, Its thickness is determined by performance indicators such as the range and sensitivity of the pressure sensor. The supporting ring (201) and the sensing diaphragm (202) are made of the same material, which can be ceramic insulating materials such as alumina and zirconia.

The insulated elastomer pressure sensor and the metal elastomer pressure sensor have the following differences: (1) The elastomer materials are different, the elastomer in the insulated elastomer pressure sensor is insulating ceramics, and the elastomer in the metal elastomer pressure sensor is metal; (2) There is no dielectric layer in the insulating elastic body pressure sensor, and the conductive layer and the resistive layer are printed directly on the elastic body; in the metal elastic body pressure sensor, the dielectric layer is arranged on the elastic body, and the conductive layer and the resistive layer are printed on the dielectric layer. Apart from the above differences, other features of the insulating elastomer pressure sensor and the metal elastomer pressure sensor are the same.

Fig. 3 is the concrete flowchart of the method of the present invention, and the present invention carries out following steps layer by layer:

(1) In a vacuum environment, load the current layer of raw material powder on the workbench and preheat it.

(2) Determine the original laser according to the accuracy requirements of the current layer, and use the original laser to scan, sinter, melt and solidify the raw materials. The original laser is a nanosecond laser, picosecond laser or femtosecond laser.

According to the piezoresistive pressure sensor structure of the present invention, the piezoresistive pressure sensor is molded layer by layer to make the piezoresistive pressure sensor. The accuracy requirements of different layers may be different, so the original lasers selected for different layers are also different. The selection principle of the original laser is: the current layer that requires high precision can choose a laser with a shorter pulse as the original laser, such as picosecond laser or femtosecond laser; the current layer that requires low precision can choose a laser with a longer pulse as the original laser. laser. This step is based on the above selection principles combined with experience and experimental verification to determine the original laser used to prepare the current layer.

(3) Use a real-time monitoring system to detect and analyze one or more of the size, crystal phase structure, surface morphology, and composition of the currently formed layer in real time, and feed back the analysis results to the control center.

The real-time monitoring system includes a control drive system and a detection instrument. The detection instrument is connected to the control drive system. The detection instrument includes one or more of a size detection instrument, a crystal phase structure detection instrument, a surface morphology detection instrument, and a component detection instrument. kind. In a specific implementation, the detection instrument includes a scanning electron microscope, an X-ray diffractometer, an infrared camera and a mass spectrometer.

(4) Compare the analysis result received by the control center with the preset target, if the analysis result reaches the preset target, proceed to step (6); otherwise, execute step (5).

(5) Use the finishing laser to finish the specific area of the formed current layer, and then perform step (3). The specific area refers to the area where the analysis result does not reach the preset target. Finishing lasers are generally chosen with shorter pulses than the original laser.

(6) Repeat steps (1)~(5) to complete the molding of the next layer.

According to the layered structure of the piezoresistive thick film pressure sensor, the order of 3D printing can be from top to bottom or from bottom to top.

In specific implementation, both the original laser and the finishing laser are provided by a multi-wavelength integrated fiber laser, and the multi-wavelength integrated fiber laser includes a controller, a nanosecond laser probe, a picosecond laser probe and a femtosecond laser probe, and the nanosecond laser probe , the picosecond laser probe and the femtosecond laser probe are all connected to the controller, and the controller is used to control the emission and shutdown of the nanosecond laser, the picosecond laser and the femtosecond laser.

Because the pressure sensor is a multi-layer structure, including a protective layer, a conductive layer, a resistive layer, an elastomer layer, etc., different layers have different requirements for accuracy, so the lasers selected for different layers are also different. Generally, lasers with shorter second pulses such as picosecond lasers or femtosecond lasers can be used for layers that require higher precision. In addition, the actual processing effect is also different from the preset effect, so the actual processing effect can be obtained in real time through the real-time monitoring system, and the laser used can be further adjusted according to the actual processing effect, so as to realize the precise processing of the product.

In each molding process, the three lasers of the multi-wavelength integrated fiber laser and the multiple detection methods of the real-time monitoring system are not all required. Generally, the appropriate original laser, finishing laser and detection methods are selected according to the requirements of the pressure sensor. However, a variety of lasers and a variety of detection means make the present invention versatile, and can realize point-by-point control of the pressure sensor, and realize online control of any scale, shape, composition and microstructure.

Claims (7)

1. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique, it is characterised in that:

According to preparing pressure resistance type thick film pressure transducer from top to bottom or the most successively, when elastomer is metal elastic gonosome Time, pressure resistance type thick film pressure transducer is followed successively by elastomer layer, dielectric layer, resistive layer, protective layer from top to bottom, protection Layer has the electrode being connected with resistive layer to pass；When elastomer is insulating ceramics elastomer, pressure resistance type thick film pressure transducer Being followed successively by elastomer layer, resistive layer, protective layer from top to bottom, protective layer has the electrode being connected with resistive layer to pass；

The making step of each layer is as follows:

(1), in vacuum environment, load current layer raw material powder on the table and preheat；

(2) determine original laser according to the required precision of current layer, use original laser that raw material is scanned sintering Fusing and solidification；The selection principle of original laser is: the current layer that required precision is high is selected the laser that pulse is shorter, right The low current layer of required precision then selects the laser that pulse is longer；Based on above-mentioned selection principle and incorporate experience into, verification experimental verification Nanosecond laser, picosecond laser and femtosecond laser determine and makes the original laser that current layer is used；

(3) detect in real time and analyze in the size of molded current layer, crystal phase structure, surface morphology and composition one Or multinomial, and analysis result is fed back to control centre；

(4) analysis result control centre received and goal-selling comparison, if analysis result reaches goal-selling, then Terminate and start from next layer；Otherwise, step (5) is performed；

(5) use polish laser that the specific region of molded current layer is carried out polish, then perform step (3)； Described specific region refers to that analysis result is not up to the region of goal-selling, and described polish laser selection principle is: (a) For picosecond laser or femtosecond laser；Meanwhile, (b) its machining accuracy is higher than original laser.

2. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 1, It is characterized in that:

Described original laser and polish laser are provided by multi-wavelength integrated fiber lasers, and described multi-wavelength is integrated Optical fiber laser includes that controller, nanosecond laser probe, picosecond laser probe and femtosecond laser are popped one's head in, nanosecond laser probe, Picosecond laser probe and femtosecond laser probe be all connected with controller, controller for control nanosecond laser, picosecond laser and The transmitting of femtosecond laser and closedown.

3. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 1, It is characterized in that:

Using real-time monitoring system detect in real time and analyze in step (3), described real-time monitoring system includes control Drive system processed and detecting instrument, detecting instrument is connected with controlling drive system, and described detecting instrument includes size detection One or more in instrument, crystal phase structure detecting instrument, surface profile measurement instrument, composition detection instrument.

4. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 3, It is characterized in that:

Described detecting instrument includes the one in scanning electron microscope, X-ray diffractometer, infrared video camera and mass spectrograph or many Kind.

5. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 1, It is characterized in that:

The raw material of elastomer layer is rustless steel, zirconium oxide or aluminium oxide.

6. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 1, It is characterized in that:

The raw material of dielectric layer is aluminium oxide.

7. pressure resistance type thick film pressure transducer preparation method based on femtosecond laser complex technique as claimed in claim 1, It is characterized in that:

The raw material of electrode is gold, platinum, silver, palladium, copper or nickel.