Based on MEMS piezoresistive high-precision multi-point thin-film pressure distribution sensor

Abstract

This invention relates to the field of monitoring sensor technology, specifically to a high-precision multi-point thin-film pressure distribution sensor based on MEMS piezoresistive technology. The sensor employs a three-layer sandwich structure, comprising a thin-film layer, a MEMS piezoresistive layer, and a PET protective layer from bottom to top. This application utilizes a MEMS piezoresistive absolute pressure sensor as the sensing unit, employing a silicon diaphragm and a micro-machined piezoresistive bridge for pressure conversion. This effectively improves accuracy and reduces errors, particularly the 24-hour time drift error, solving the numerical failure problem caused by material creep in traditional sensors. Due to the excellent thermomechanical stability of the MEMS sensing element, the influence of temperature drift is reduced. Combined with the thin-film layer and PET protective layer, the sensor maintains stable output under different thermal environments. Through micron-level measurement point size design, extremely high spatial distribution density is achieved, effectively improving the resolution limit and enabling the capture of minute pressure fluctuations, providing a data foundation for the synthesis of high-precision pressure cloud maps.

Description

Technical Field

[0001] This invention relates to the field of monitoring sensor technology, and in particular to a high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive technology. Background Technology

[0002] Pressure distribution measurement technology has wide applications in aerospace, automotive seat comfort evaluation, foot pressure analysis, and industrial precision assembly. To enable pressure monitoring of complex curved surfaces or confined spaces, flexible thin-film pressure distribution sensors have emerged. These sensors typically consist of two flexible substrates sandwiching a sensing material, and acquire two-dimensional pressure distribution information of the contact surface through a sensing array.

[0003] Existing conventional piezoresistive thin-film pressure distribution sensors suffer from severe temperature and time drift due to the susceptibility of organic sensing materials to environmental temperature, humidity, and creep under long-term load. This results in poor stability, and the measurement results often only provide qualitative trend analysis, rather than high-precision quantitative measurement. In addition, the processing consistency of traditional materials is poor, making it difficult to guarantee the uniformity and resolution limit between measurement points under large-area distribution. Summary of the Invention

[0004] The main objective of this invention is to provide a high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive technology to solve the problems raised in related technologies.

[0005] To achieve the above objectives, according to one aspect of the present invention, a high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type is provided. The sensor adopts a three-layer sandwich structure, which includes a thin film layer, a Mems piezoresistive layer and a PET protective layer from bottom to top.

[0006] The Mems piezoresistive layer is a sensing component, consisting of multiple ultra-thin absolute pressure sensors. These ultra-thin absolute pressure sensors are distributed in an array on the thin film layer, forming multiple independent pressure measurement points. Each ultra-thin absolute pressure sensor has an overload capacity of five times.

[0007] Preferably, the thin film layer is made of either PI or PET material.

[0008] Preferably, the PI material is an electronic-grade PI film with a thickness of 25μm-75μm. The preparation method of the PI film layer is as follows:

[0009] Surface pretreatment: The thin film surface is activated using plasma at a power of 300W for 60 seconds to enhance the adhesion of the metal layer.

[0010] Circuit fabrication: Nano silver paste inkjet printing or screen printing is used. After printing, the circuit is placed in an oven and cured at 230℃ for 60 minutes to form a conductive circuit with a thickness of 5μm-10μm.

[0011] Insulation layer printing: A layer of UV-curable insulating ink is printed in the non-pad area and instantaneously cured using a UV exposure machine with an energy of 1200mJ / cm².

[0012] Preferably, the PET material used is high-transparency optical-grade PET with a thickness of 50μm-125μm. The preparation method of the PET film layer is as follows:

[0013] Surface pretreatment: The thin film surface is activated using plasma at a power of 300W for 60 seconds to enhance the adhesion of the metal layer.

[0014] Circuit fabrication: Nano silver paste inkjet printing or screen printing is used. After printing, the circuit is placed in an oven and cured at 150°C for 30 minutes to form a conductive circuit with a thickness of 5μm-10μm.

[0015] Insulation layer printing: A layer of UV-curable insulating ink is printed in the non-pad area and instantaneously cured using a UV exposure machine with an energy of 1200mJ / cm².

[0016] Preferably, the thin film layer is the bottom base support layer, used to provide support for the upper structure and carry circuit traces.

[0017] Preferably, the planar dimensions of a single measuring point are either 0.4mm×0.4mm or 0.6mm×0.6mm, and the thickness of a single measuring point is 0.4mm~0.5mm.

[0018] Preferably, each measurement point of the Mems piezoresistive layer is connected to a conductive trace on the thin film layer (100) via an electrode pin.

[0019] Preferably, the PET protective layer covers the Mems piezoresistive layer, and its edges and gaps are sealed to the bottom film layer by an adhesive layer.

[0020] Preferably, the Mems piezoresistive layer uses a 4-inch or 6-inch SOI wafer as the substrate and lightly doped polycrystalline silicon or monocrystalline silicon doped with boron ions as the piezoresistive bridge. The fabrication method is as follows: a 300nm silicon dioxide insulating layer is grown on the SOI wafer by low-pressure chemical vapor deposition, and boron is doped using an ion implantation process at an energy of 40keV and a dose of 2×10¹. 5The silicon wafer is then rapidly thermally annealed at 1000℃ for 30 seconds to activate impurities. Deep reactive ion etching is used to thin the wafer from the back side, controlling the remaining silicon film thickness to 15μm-25μm to form a pressure-sensing film. Vacuum bonding is used to bond the silicon wafer to the cover plate to form an absolute pressure cavity. Finally, it is laser-cut into independent micro-sensing units of 0.4mm×0.4mm.

[0021] Preferably, the PET protective layer is made of flexible PET film with a thickness of 30μm-50μm, and the inner side is coated with a modified acrylic pressure-sensitive adhesive or hot melt adhesive film with a thickness of 20μm; the processing method is as follows: the protective layer is visually aligned with the base plate of the welded sensing unit with high precision, and a vacuum hot press is used to hold it for 120s in an environment of 120℃ and 0.5MPa.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This application employs a MEMS piezoresistive absolute pressure sensor as the sensing unit, and utilizes a silicon diaphragm and a micro-machined piezoresistive bridge circuit for pressure conversion, which can effectively improve accuracy and reduce error. At the same time, it reduces 24-hour time drift error and solves the problem of numerical failure caused by material creep in traditional sensors.

[0024] Because MEMS sensing elements have good thermomechanical stability, the effect of temperature drift is reduced. Combined with thin film layer and PET protective layer, the sensor can maintain stable output under different thermal environments, improving reliability in complex application scenarios.

[0025] This application achieves extremely high spatial distribution density through a micrometer-level measurement point size design, which can effectively improve the resolution limit and capture minute pressure fluctuations, providing a data foundation for the synthesis of high-precision pressure cloud maps.

[0026] The sensing element has a five-fold overload capacity, and with the buffering and sealing effect of the 300 PET protective layer, it effectively prevents physical damage to the internal MEMS chip from transient impacts, thus extending the service life of the sensor. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall invention.

[0028] Figure label:

[0029] 100, Thin film layer; 200, Mems piezoresistive layer; 300, PET protective layer. Detailed Implementation

[0030] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0031] Please see Figure 1 This embodiment provides a high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive technology. Its overall structure is in the form of a flexible thin film. This structural characteristic allows it to be bent or folded according to the shape of the object to be measured, thereby attaching to the surface of a flat or complex curved object to collect pressure distribution data in real time.

[0032] The sensor comprises, from bottom to top, a thin film layer 100, a Mems piezoresistive layer 200, and a PET protective layer 300. The Mems piezoresistive layer 200, as the core sensing layer, is sandwiched and encapsulated between the thin film layer 100 and the PET protective layer 300. Through the design of the three-layer sandwich structure, physical protection and electrical insulation of the internal micro sensing elements are achieved.

[0033] The thin film layer 100 serves as the base support layer, its main function being to provide support for the upper structure and carry circuit traces. Depending on the thermal stability requirements of the actual application environment, this layer can be made of polyethylene terephthalate or polyimide. Pre-set conductive lines are provided on the upper surface of the thin film layer 100; these lines are fabricated using precision printing or etching processes to transmit electrical signals from the sensing points to the external acquisition interface.

[0034] The thin film layer 100 is made of either PI (polyimide) or PET (polyethylene terephthalate). The PI material is an electronic-grade PI film with a thickness of 25μm-75μm, suitable for applications requiring welding temperatures above 250℃. The PET material is a high-transparency optical-grade PET with a thickness of 50μm-125μm, suitable for cost-sensitive applications and applications with operating temperatures below 80℃.

[0035] The preparation method of thin film layer 100 is as follows:

[0036] Surface pretreatment: The thin film surface is activated using plasma at a power of 300W for 60 seconds to enhance the adhesion of the metal layer.

[0037] Circuit fabrication: Nano silver paste inkjet printing or screen printing is used. After printing, the circuit is placed in an oven and cured at 150°C for 30 minutes (PET substrate) or at 230°C for 60 minutes (PI substrate) to form a conductive circuit with a thickness of 5μm-10μm.

[0038] Insulation layer printing: A layer of UV-curable insulating ink is printed in the non-pad area and instantaneously cured using a UV exposure machine with an energy of 1200mJ / cm².

[0039] The piezoresistive layer 200 is the sensing component of this device, and its sensing element consists of multiple ultra-thin absolute pressure sensors. These ultra-thin absolute pressure sensors are distributed in an array on the thin film layer 100, forming multiple independent pressure measurement points. To achieve high-resolution distributed measurement, the planar dimensions of a single measurement point are designed to be on the micrometer scale, for example, 0.4mm × 0.4mm or 0.6mm × 0.6mm. This design allows for the integration of a larger number of sensing units per unit area. To maintain the overall thinness of the sensor, the thickness of a single measurement point is strictly controlled between 0.4mm and 0.5mm.

[0040] Within each sensing element of the Mems piezoresistive layer 200, a micro-machined silicon diaphragm and a piezoresistive bridge are integrated. When external pressure is applied to the PET protective layer 300 and transmitted to the Mems piezoresistive layer 200, the silicon diaphragm inside the sensing element undergoes a slight deformation. This deformation causes a change in the resistance value in the piezoresistive bridge, thereby linearly converting the mechanical pressure signal into an electrical signal. To adapt to different industrial scenarios, the Mems piezoresistive layer 200 can be configured with different measuring ranges, including but not limited to 100kPa, 200kPa, 700kPa, 1MPa, 1.5MPa, and 2MPa. Furthermore, the sensing element has a five-fold overload capacity, protecting the internal silicon diaphragm from rupture even under instantaneous impact forces exceeding its measuring range.

[0041] In terms of electrical connectivity, each measurement point of the Mems piezoresistive layer 200 is connected to a conductive trace on the thin film layer 100 via an electrode pin. The connection can be achieved through surface mount soldering or conductive adhesive bonding. The sensor supports standard supply voltages of 2.5V, 3.3V, or 5V and is directly compatible with conventional microcontrollers or signal conditioning circuits.

[0042] Mems piezoresistive layer 200 uses a 4-inch or 6-inch SOI wafer as the substrate and lightly doped polycrystalline silicon or monocrystalline silicon with boron ions as the piezoresistive bridge.

[0043] The fabrication method is as follows: A 300nm silicon dioxide insulating layer is grown on the SOI wafer by low-pressure chemical vapor deposition. Boron is doped using an ion implantation process at an energy of 40keV and a dose of 2×10¹. 5The silicon wafer is then rapidly thermally annealed at 1000℃ for 30 seconds to activate impurities. Deep reactive ion etching is used to thin the wafer from the back side, precisely controlling the remaining silicon film thickness to 15μm-25μm to form a pressure-sensing film. Vacuum bonding is used to bond the silicon wafer to the cover plate to form an absolute pressure cavity. Finally, it is laser-cut into independent micro-sensing units of 0.4mm×0.4mm.

[0044] A PET protective layer 300 covers the Mems piezoresistive layer 200, and its edges and gaps are sealed to the underlying thin film layer 100 by an adhesive layer, thus completely sealing the Mems piezoresistive layer 200 inside. The PET protective layer 300 not only serves as insulation, dustproofing, and waterproofing, but also functions as the pressure transmission medium. Due to the good flexibility of the PET protective layer 300, when an external load is applied to its surface, it can produce a small local displacement, uniformly and effectively transmitting pressure to the sensing diaphragm of the underlying Mems piezoresistive layer 200, ensuring measurement accuracy.

[0045] The PET protective layer 300 uses a flexible PET film with a thickness of 30μm-50μm, and the inner side is coated with a modified acrylic pressure-sensitive adhesive or hot melt adhesive film with a thickness of 20μm.

[0046] The processing method is as follows: The protective layer is visually aligned with the substrate of the welded sensing unit with high precision, and then held for 120 seconds using a vacuum hot press at a temperature of 120℃ and a pressure of 0.5MPa. This process ensures that the adhesive fully fills the gaps between the sensing elements, eliminates air bubbles, and achieves a fully sealed encapsulation.

[0047] In practical implementation, by arranging matrix-style scanning traces on the thin film layer 100, all measuring points in the Mems piezoresistive layer 200 can be connected to one or more unified signal acquisition interfaces. The system acquires real-time pressure values ​​at various coordinate points on the sensor surface through line-by-line scanning or parallel acquisition. After signal conditioning and algorithm processing, these data can be synthesized into a high-precision two-dimensional pressure distribution cloud map, which intuitively reflects the pressure distribution details of the contact surface.

[0048] Example 1: PI thin film substrate, 0.4mm Mems piezoresistive unit.

[0049] Example 2: PET film substrate, 0.6mm Mems piezoresistive unit.

[0050] Comparative Example 1: A conventional piezoresistive thin-film pressure distribution sensor is used, without MEMS structure.

[0051] Comparative Example 2: The same Mems sensing unit is used, but it is arranged on a 1.6mm thick rigid FR-4 PCB board.

[0052] To verify the technical advantages of the present invention, the above embodiments and comparative examples were subjected to the following tests:

[0053] Linearity and hysteresis test: A universal testing machine was used to perform loading and unloading cycles (0-100%FS) on a single measuring point of the sensor, and the output voltage change was recorded. The maximum deviation between the fitted curve and the actual curve was calculated.

[0054] Overload test: Apply an instantaneous impact force of 10MPa to the sensor with a range of 2MPa, observe the offset of the zero point output of the sensor after the pressure is removed, and observe the integrity of the silicon diaphragm with a microscope.

[0055] Fatigue test: Alternating pressure at a frequency of 2Hz was applied for 100,000 cycles to detect the change in the sensor sensitivity coefficient before and after the test.

[0056] Distribution uniformity test: The sensor is attached to a cylindrical curved surface with a diameter of 50 mm, uniform air pressure is applied, and the consistency of the values ​​at different measuring points in the array is compared.

[0057] Test metrics and results data

[0058] Test environment: 25℃, pressure range 0-1MPa, bending radius R=10mm

[0059] linearity 0.2%FS 0.35%FS 5.0%-8.0%FS 0.15%FS Hysteresis 0.15%FS 0.2%FS 10%-15%FS 0.1%FS Minimum bending radius 2mm (non-destructive) 3 mm (non-destructive) 5mm (easily broken wire) Unable to bend Overload capacity 500% (lossless) 500% (lossless) 150% (resulting in permanent deformation) 500% (lossless) Measurement point consistency <1.5% <2% >12% <1%

[0060] Based on the above test results, the present invention has the following outstanding technical effects compared with the prior art.

[0061] High precision and high linearity (Comparison Example 1):

[0062] Comparative Example 1 (traditional FSR) relies on changes in the material contact area, resulting in a hysteresis of over 10%, and is greatly affected by environmental humidity. This invention improves linearity by approximately 25-40 times and reduces hysteresis by nearly 100 times through the microscopic deformation of MEMS silicon films combined with piezoresistive bridge circuits, enabling better quantitative precision measurement rather than fuzzy tactile perception.

[0063] Excellent flexibility and adaptability to curved surfaces (Comparative Example 2):

[0064] While Comparative Example 2 offers high precision, its rigid substrate prevents its application to curved surfaces such as human joints and the inner walls of car tires. The sensor of this invention has an overall thickness of only about 0.5 mm, allowing it to operate stably even under extreme bending with a radius of 2 mm (R=2 mm). Furthermore, the micron-sized MEMS unit minimizes stress during bending, ensuring undistorted measurement accuracy under complex deformations.

[0065] Environmental tolerance and overload protection:

[0066] The three-layer packaging structure employed in this invention, combined with a 5x overload design for MEMS sensors, solves the problem of traditional thin-film sensors easily "crushing" or experiencing sensitivity drift under high-pressure impacts. Even under instantaneous impacts exceeding several times the measurement range, the internal silicon diaphragm remains intact due to the buffering protection and limiting design of the protective layer.

[0067] High-resolution distributed acquisition:

[0068] By designing measurement points at the micrometer level, this invention increases the sensor density integrated within the same area by about 4-10 times compared to traditional technologies, enabling the capture of more subtle pressure gradient changes and thus synthesizing more detailed and realistic pressure cloud maps.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type, characterized in that: The sensor adopts a three-layer sandwich structure, which includes a thin film layer (100), a Mems piezoresistive layer (200) and a PET protective layer (300) from bottom to top. The Mems piezoresistive layer (200) is a sensing component, consisting of multiple ultra-thin absolute pressure sensors. The ultra-thin absolute pressure sensors are distributed in an array on the thin film layer (100) to form multiple independent pressure measurement points. The ultra-thin absolute pressure sensors have an overload factor of five times.

2. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The thin film layer (100) is made of either PI material or PET material.

3. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 2, characterized in that, The PI material used is an electronic-grade PI film with a thickness of 25μm-75μm. The preparation method of the PI film layer (100) is as follows: Surface pretreatment: The thin film surface is activated using plasma at a power of 300W for 60 seconds to enhance the adhesion of the metal layer. Circuit fabrication: Nano silver paste inkjet printing or screen printing is used. After printing, the circuit is placed in an oven and cured at 230℃ for 60 minutes to form a conductive circuit with a thickness of 5μm-10μm. Insulation layer printing: A layer of UV-curable insulating ink is printed in the non-pad area and instantaneously cured using a UV exposure machine with an energy of 1200mJ / cm².

4. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 2, characterized in that, The PET material used is high-transparency optical-grade PET with a thickness of 50μm-125μm. The preparation method of the PET film layer (100) is as follows: Surface pretreatment: The thin film surface is activated using plasma at a power of 300W for 60 seconds to enhance the adhesion of the metal layer. Circuit fabrication: Nano silver paste inkjet printing or screen printing is used. After printing, the circuit is placed in an oven and cured at 150°C for 30 minutes to form a conductive circuit with a thickness of 5μm-10μm. Insulation layer printing: A layer of UV-curable insulating ink is printed in the non-pad area and instantaneously cured using a UV exposure machine with an energy of 1200mJ / cm².

5. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The thin film layer (100) is the bottom base support layer, used to provide support for the upper structure and carry circuit traces.

6. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The planar dimensions of a single measuring point are either 0.4mm×0.4mm or 0.6mm×0.6mm, and the thickness of a single measuring point is 0.4mm~0.5mm.

7. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, Each measurement point of the Mems piezoresistive layer (200) is connected to a conductive trace on the thin film layer (100) via an electrode pin.

8. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The PET protective layer (300) covers the Mems piezoresistive layer (200), and its edges and gaps are sealed to the bottom film layer (100) by an adhesive layer.

9. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The Mems piezoresistive layer (200) uses a 4-inch or 6-inch SOI wafer as the substrate and lightly doped polycrystalline silicon or monocrystalline silicon doped with boron ions as the piezoresistive bridge. The fabrication method is as follows: a 300nm silicon dioxide insulating layer is grown on the SOI wafer by low-pressure chemical vapor deposition, and boron is doped using an ion implantation process at an energy of 40keV and a dose of 2×10¹. 5 The silicon wafer is then rapidly thermally annealed at 1000℃ for 30 seconds to activate impurities. Deep reactive ion etching is used to thin the wafer from the back side, controlling the remaining silicon film thickness to 15μm-25μm to form a pressure-sensing film. Vacuum bonding is used to bond the silicon wafer to the cover plate to form an absolute pressure cavity. Finally, it is laser-cut into independent micro-sensing units of 0.4mm×0.4mm.

10. The high-precision multi-point thin-film pressure distribution sensor based on Mems piezoresistive type according to claim 1, characterized in that, The PET protective layer (300) is made of flexible PET film with a thickness of 30μm-50μm, and coated with a modified acrylic pressure-sensitive adhesive or hot melt adhesive film with a thickness of 20μm on the inner side; the processing method is as follows: the protective layer is visually aligned with the substrate of the welded sensing unit with high precision, and a vacuum hot press is used to hold it for 120s in an environment of 120℃ and 0.5MPa.

Images