Common-film differential high-static-pressure resonant differential pressure sensor based on hot resistance driving

Abstract

The invention discloses a common-film differential high-static-pressure resonant differential pressure sensor based on hot resistance driving, and relates to a pressure sensor. The invention provides a novel sensor structure based on a thermal piezoresistive effect. The sensor adopts a thermal piezoresistive effect for driving and piezoresistive detection, and comprises a low-voltage side pressure sensing film, a bonding oxide layer, a structural layer, a buried oxide layer, a high-voltage side pressure film and a substrate layer, the low-voltage side pressure sensing film is made of a silicon material, the structural layer and the high-voltage side pressure film are made of SOI sheets, and the substrate layer is made of BF33 glass; the high-pressure side pressure film and the low-pressure side pressure film respectively sense high pressure and low pressure and sense a difference value between the high pressure and the low pressure through deformation of the pressure films, deflection deformation of the films generates tensile stress in a central area and pressure stress in an edge area, the double resonators sense opposite stress and generate opposite frequency deviation, and the difference between the two is used for representing a differential pressure value. The glass substrate is mainly used for isolating thermal stress of the packaging stainless steel base.

Description

Technical Field

[0001] The present invention relates to a pressure sensor, and in particular to a common-membrane differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive. Background Art

[0002] In the fields of industry, automobile, medical treatment, environmental monitoring, etc., pressure measurement components are increasingly required to meet the requirements of high precision, miniaturization and low power consumption. At the same time, they also have important strategic significance in national defense fields such as cabin pressure measurement of manned spacecraft, atmospheric data systems of aircraft, special vehicle carriers, etc.

[0003] Pressure sensors can be categorized as absolute, gauge, and differential pressure based on their reference pressure type. The first two types essentially have customizable reference pressures, and their errors are primarily caused by temperature and environmental variations. In contrast, differential pressure sensors introduce static pressure errors, significantly limiting pressure measurement accuracy. Balancing differential pressure measurement sensitivity with static pressure drift sensitivity is one of the primary challenges facing differential pressure sensors. Applications in medical, energy development, aerospace, and deep-sea exploration even require micro-differential pressure measurements under high static pressure, placing extremely high demands on the measurement capabilities of differential pressure sensors. Supported by MEMS (Micro-Electro-Mechanical Systems) technology, this type of sensor enables miniaturization, high precision, and low cost. Among the many sensitive types, resonant differential pressure sensors stand out for their high precision, high stability, and quasi-digital output, occupying a key position in the field of high-precision differential pressure measurement.

[0004] In recent years, some domestic research institutions and universities have entered the field of MEMS resonant pressure sensors and have made some progress in MEMS absolute pressure sensors. However, no substantial breakthroughs have been achieved in MEMS differential pressure resonant pressure sensors, particularly those capable of high-precision micro-differential pressure measurement under high static pressure conditions. The development of high-precision resonant differential pressure sensors presents numerous difficulties. Summary of the Invention

[0005] The present invention aims to achieve high-precision detection of small differential pressure ranges under high static pressure conditions. It provides a common-membrane differential high-static-pressure resonant differential pressure sensor based on thermal piezoresistive drive. This sensor utilizes the heat pump effect and small plate deflections to induce stress changes within the membrane, which in turn shift the resonator's resonant frequency, thereby representing the pressure value. The dual-resonator differential output amplifies pressure sensitivity, minimizing common-mode signals. The small resonator size and internal sensor cavity make it suitable for use in high static pressure scenarios.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] A common-film differential high-static-pressure resonant differential pressure sensor based on thermal piezoresistive drive, which consists of a low-pressure side pressure-sensing layer, a resonant structure layer, a high-pressure side pressure-sensing layer, and a glass substrate layer from top to bottom;

[0008] The high-voltage-side pressure-sensing layer and the resonant structure layer are fabricated from the same SOI wafer. The resonant structure layer is fabricated from the thinner device layer of the SOI wafer through a micromachining process and then subjected to a release process to form a movable structure. The high-voltage-side pressure-sensing film is fabricated on the thicker handle layer of the SOI wafer through a wet etching process. The low-voltage-side pressure-sensing layer is fabricated from another silicon wafer, and the SOI wafer and silicon wafer are bonded together through a silicon bonding process. The glass substrate layer is fabricated from BF33 glass and bonded to the SOI wafer through an anodic bonding process. During use, the low-voltage-side pressure-sensing layer and the high-voltage-side pressure-sensing layer are respectively connected to the lower and higher pressure ends of the differential pressure to be measured. Based on the pressure difference between the low-pressure and high-pressure sides, the principle of small plate deflection is used to generate tensile stress in the center region and compressive stress in the edge region of the resonant structure layer, thereby causing the natural frequencies of the two resonators arranged in different stress regions to change in opposite directions. The difference in the natural frequencies of the two resonators is used to represent the differential pressure to be measured. The glass substrate layer is primarily used to isolate thermal stress transmitted from the metal base to the core.

[0009] Furthermore, the silicon wafer may be a P-type single crystal silicon wafer with a thickness of 300 μm.

[0010] Furthermore, four centrally symmetrically distributed electrode holes are arranged on the low-voltage side pressure-sensitive film, including two driving electrode holes and two detection / grounding electrode holes, which correspond to the driving and detection end electrodes of the central resonator and the edge resonator respectively. The low-voltage side pressure-sensitive film is polished by a chemical mechanical polishing process to ensure that the film thickness is uniform, and the deviation can be controlled within 5%.

[0011] Furthermore, the resonant structure layer is composed of a central resonator, an edge resonator, a central resonator driving electrode, a central resonator detection electrode, an edge resonator driving electrode, an edge resonator detection electrode and an outer frame. The central resonator is connected to the central resonator driving electrode and the central resonator detection electrode through four supporting sensitive beams. The connection form is that the two supporting sensitive beams on the left are connected to the central resonator driving electrode, and the two supporting sensitive beams on the right are connected to the central resonator detection electrode. The edge resonator is also connected to the edge resonator driving electrode and the edge resonator detection electrode through its four supporting sensitive beams, and the connection form is the same as that of the central resonator; the central resonator driving electrode, the central resonator detection electrode, the edge resonator driving electrode, the edge resonator detection electrode and the frame are not connected.

[0012] Furthermore, the central resonator and the edge resonator have the same components, both including a dual-mass plate, four supporting beams and a micron piezoresistive beam connected to the dual-mass plate. The dual-mass plate is connected to the electrode through four supporting sensitive beams. The micron piezoresistive beam runs across the center of the dual-mass plate and forms a Wheatstone bridge structure. The central resonator is located in the tensile stress area when the pressure membrane is deformed, and the edge resonator is located in the compressive stress area when the pressure membrane is deformed. Through the different position distributions of the central resonator and the edge resonator, the two produce opposite frequency changes under the action of differential pressure, the frequency of the tensile stress area increases, and the frequency of the compressive stress area decreases. After differential circuit processing, the output signal is multiplied and common-mode interference is suppressed.

[0013] Furthermore, the thermal piezoresistive drive is generated by the heat pump effect of a micronized piezoresistive beam connected to a dual-mass plate when energized. The specific process is as follows: Joule heating generated by the current causes the piezoresistive beam to expand, resulting in a decrease in resistance. This resistance change causes current fluctuations, which in turn causes the piezoresistive beam's temperature to cyclically vary, ultimately forming thermal oscillations that match the mechanical vibration frequency. Absorbing energy from a DC source without the need for AC current can break the resonator's mechanical Q limit, theoretically achieving an infinite Q value.

[0014] Furthermore, the high-pressure side pressure-sensitive membrane is square in shape and is centered in the center area of ​​the core body to ensure that the thickness of the membrane layer is evenly distributed.

[0015] Furthermore, during actual use, a certain amount of static pressure will be introduced into the low-pressure side pressure-sensing layer and the high-pressure side pressure-sensing layer on both sides at the same time (the static pressure range of this design is 0Mpa~30Mpa). On this basis, the high-pressure side pressure-sensing layer will be connected to a certain value of differential pressure (the range of this design is 300KPa). Ideally, the pressure core is only sensitive to the differential pressure and is not sensitive to the static pressure introduced. Based on the difference between the total pressure (static pressure + differential pressure) introduced into the high-pressure side pressure-sensing layer and the total pressure (static pressure) introduced into the low-pressure side pressure-sensing layer, tensile stress is generated in the central area of ​​the resonant structure layer and compressive stress is generated in the edge area through the principle of small deflection deformation of the thin plate, thereby causing the natural frequencies of the two resonators arranged in different stress zones to change in opposite directions. The difference between the frequency change (positive value) of the resonator arranged in the tensile stress area under the action of pressure and the frequency change (negative value) of the resonator arranged in the compressive stress area is used to characterize the size of the differential pressure to be measured, which can amplify the sensitivity of the differential pressure.

[0016] Furthermore, the substrate layer is made of BF33 glass with a thermal expansion coefficient similar to that of single crystal silicon material, and has a penetrating air guide hole for transmitting pressure to the high-pressure side pressure-sensitive membrane. The air guide hole is centrally located on the glass base, corresponding to the center of the high-pressure side pressure-sensitive membrane, so as to ensure the symmetry and efficiency of the pressure conduction path and realize distortion-free transmission of the pressure signal to be measured to the high-pressure side pressure-sensitive membrane.

[0017] Furthermore, the fundamental resonant frequency of the central resonator should be higher than the fundamental resonant frequency of the edge resonator. The frequency difference is achieved by adjusting the size of the supporting beam (including beam length, beam width and beam thickness, etc.), and ensuring that there is no crossover in the frequency response curves of the dual resonators within the pressure test range to avoid measurement signal confusion and errors.

[0018] Furthermore, the resonator mass plate is provided with a wet release hole, which is rectangular in shape, to ensure the consistency of the release rate of each movable area during the release process of the structural layer, thereby improving the stability and yield of the resonator structure release process.

[0019] Furthermore, movable structural grooves are provided on the low-pressure side pressure-sensing layer corresponding to the installation positions of the central resonator and the edge resonator. The movable structural grooves are used for the mobility of the resonator and as storage space for the getter. The Ti getter can be filled through the packaging process to maintain a long-term high vacuum environment inside the sensor, thereby ensuring the stability and reliability of the resonator performance.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) Simplify the sensor closed-loop process: Based on the thermal piezoresistive effect, by applying a DC current to the micron piezoresistive beam and utilizing the coupling of the current thermal effect and the piezoresistive effect, when the DC current reaches a certain value, the resonator can achieve self-oscillation under DC excitation. When the DC current reaches a specific threshold, the Joule heat generated by the micron piezoresistive beam causes the structure to expand thermally, thereby changing its resistance value, forming a positive feedback mechanism that matches the mechanical vibration and achieving stable oscillation. This driving method does not require complex AC signal modulation and feedback control circuits, simplifies the sensor closed-loop process, reduces the number of components in the sensor detection circuit and the circuit board area, and significantly reduces the complexity of circuit design and manufacturing costs.

[0022] 2) High Static Pressure Range: This invention utilizes a thermal piezoresistive drive system. Its micron-scale piezoresistive beam and miniaturized resonator structure significantly reduce the effective cavity volume within the pressure core. This smaller cavity significantly reduces the impact of medium compression on sensor performance under high-pressure environments, increasing the sensor's static pressure range to 30 MPa and improving its overall static pressure resistance.

[0023] 3) Improved pressure sensitivity: The present invention utilizes a dual-resonator differential structure, placing the central resonator and the edge resonator in the tensile stress zone and compressive stress zone, respectively, when the pressure membrane is deformed. Under the action of differential pressure, the two resonators produce frequency changes in opposite directions. The output frequencies of the two resonators are processed by a differential circuit, which increases the frequency output by approximately 2 times compared to a single-resonator structure. Simulations have shown that within the differential pressure measurement range of 0Pa to 300kPa, the pressure sensitivity of the sensor of the present invention reaches 25 Hz / Pa, which is approximately 100% higher than the differential pressure sensitivity of two separate resonators designed in the present invention. This enables high-precision detection of small differential pressure signals under high static pressure backgrounds.

[0024] 4) Excellent Temperature Characteristics: The dual resonators in this invention utilize the same material and structural design and are arranged on the same pressure membrane. Temperature changes affect both resonators equally, resulting in a common-mode signal. The differential output effectively suppresses common-mode errors caused by temperature changes. Simulations have demonstrated that the sensor's temperature drift coefficient is as low as 0.16 Hz / °C over a wide temperature range of -40°C to 80°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the overall structure of an embodiment of the present invention.

[0026] Figure 2 This is an exploded view of the three-dimensional structure of an embodiment of the present invention.

[0027] Figure 3 This is a front view of the overall structure of the structural layer of an embodiment of the present invention.

[0028] Figure 4 This is a front view of the overall structure of the resonator according to an embodiment of the present invention.

[0029] Figure 5 A front view of the high-voltage side pressure-sensing layer according to an embodiment of the present invention

[0030] Figure 6 This is a front view of the low-pressure side pressure-sensitive membrane according to an embodiment of the present invention.

[0031] Figure 7 This is a front view of the oxide layer according to an embodiment of the present invention.

[0032] Figure 8 This is a differential pressure-sensitive deformation cloud diagram of an embodiment of the present invention (magnified 500 times).

[0033] Figure 9 This is a deformation cloud diagram of the static pressure effect of an embodiment of the present invention (magnified 500 times).

[0034] Figure 10 This is a temperature thermal expansion deformation cloud diagram of an embodiment of the present invention (magnified 500 times).

[0035] Figure 11 : This is the simulated differential pressure sensitivity of the embodiment of the present invention.

[0036] Figure 12 This is the simulated static pressure sensitivity at room temperature without differential pressure according to an embodiment of the present invention.

[0037] Figure 13 This is the temperature sensitivity of the simulation without adding differential pressure and static pressure in the embodiment of the present invention.

[0038] Figure 14 FIG. 1 is a schematic diagram of core loading according to an embodiment of the present invention (the glass substrate layer is not shown).

[0039] exist Figures 1 to 7 In the , each mark is:

[0040] 1. Electrode hole; 2. Bonding oxide layer electrode through hole; 3. Low-voltage side pressure-sensitive film; 4. Bonding oxide layer; 5. Structural layer; 6. Buried oxide layer; 7. High-voltage side pressure-sensitive layer; 8. Substrate layer; 9. Driving electrode; 10. Edge resonator; 11. Center resonator; 12. Detection electrode; 13. Support sensitive beam; 14. Release hole; 15. Inertial mass plate; 16. Micron piezoresistive beam; 17. High-voltage side pressure-sensitive film; 18. Anodic bonding frame; 19. Bonding oxide layer movable structure release groove; 20. Buried oxide layer movable structure release groove; 21. Structural layer frame; DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the following embodiments will be further described in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Referring to Figures 1-7 , the differential pressure sensor core of the present embodiment primarily comprises a high-pressure-side pressure-sensing membrane 17 and a low-pressure-side pressure-sensing membrane 3. In actual use, the high-pressure-side pressure-sensing membrane 17 is connected to the high-pressure vent of the package housing, and the low-pressure-side pressure-sensing membrane 3 is connected to the low-pressure vent of the package housing. The difference in pressure between the two is the differential pressure. The core design of this invention is to reduce the volume of the cavity within the core, thereby being able to withstand high static pressure while sensing a small difference between the two.

[0043] like Figure 2 An exploded view of the differential pressure sensor core designed for this embodiment shows, from right to left, the low-pressure side pressure-sensing layer (including the low-pressure side pressure-sensing film 3), the bonding oxide layer 4, the structural layer 5, the buried oxide layer 6, the high-pressure side pressure-sensing layer 7 (including the high-pressure side pressure-sensing film), and the glass substrate layer 8.

[0044] The preparation of the low-voltage side pressure-sensitive layer is to first etch electrode through-holes and grooves, then silicon bond, and then CMP thinning to a predetermined thickness. Specifically, an additional 300μm thick P-type single-crystal silicon wafer is used as a raw material to make the low-voltage side pressure-sensitive film 3. Before bonding with the SOI wafer on which the movable resonant structure layer 5 is made and HF released, four centrally symmetrically distributed electrode through-holes 1 are first prepared on the bonding surface of the low-voltage side pressure-sensitive film 3 by a dry etching process. The electrode through-holes 1 are square through-holes. In this embodiment, the side length of the hole can be (200±1)μm; then, a groove (depth of about 3μm) corresponding to the bonding oxide layer movable structure release groove 19 is etched by a dry etching process. The bonding oxide layer movable structure release groove 19 corresponds to the groove etched on the low-voltage side pressure-sensitive film 3. During the sensor packaging process, these grooves are used to accommodate Ti getter. The design and fabrication of the release groove 19 for the movable structure of the bonding oxide layer ensures the structural integrity of the bonding oxide layer 4 while providing space for the edge resonators 10 and the center resonator 11 to move and a storage space for the Ti getter. During the sensor packaging process, the Ti getter absorbs residual gas, ensuring that the edge resonators 10 and the center resonator 11 are always in a high vacuum environment, thereby ensuring the high quality factor and stable operating performance of the resonator. The structure is then bonded to the pre-fabricated SOI wafer through a silicon bonding process. During the bonding process, the bonding temperature is controlled between 300°C and 400°C, the bonding pressure is between 5 MPa and 10 MPa, and the bonding time is maintained for 30 to 60 minutes to ensure the strength and sealing of the bonding interface. After bonding, the low-pressure side pressure-sensing layer is thinned to the desired thickness (specifically, the thickness in this embodiment is (20 ± 0.5) μm) through a CMP (chemical mechanical polishing) process. The low-pressure side pressure-sensing membrane 3 is relatively thin, allowing for small deflections to ensure sensor sensitivity.

[0045] The embedded oxide layer's movable structure release groove 20 is fabricated via an HF wet release process. Its primary function is to ensure the oscillator's mobility. During the release process, by controlling the specific HF solution concentration and etching time, the embedded oxide layer 6 material is precisely removed, avoiding damage to critical structures such as the oscillator, thereby enabling the oscillator and other structures in the structural layer 5 to achieve mobility. The embedded oxide layer 6 is part of the SOI wafer structure. During sensor manufacturing, it serves as an isolation layer between the structural layer 5 and the high-voltage pressure-sensing layer 7. This design anticipates a thickness of 3μm.

[0046] As shown in Figure 5, the high-voltage pressure-sensing layer 7 is etched primarily through a wet silicon etching process to create a high-voltage pressure-sensing film 17. The thickness is calculated as the thickness of the SOI substrate minus the etching depth. This thickness should be thicker than the low-voltage pressure-sensing film 3 to produce the deflection shown in Figure 8 when the pressure applied to this side is higher than that on the low-voltage side. In the wet silicon etching process, a KOH solution can be used as the etching solution, with a concentration of 20-30wt% and an etching temperature of 70-80°C. The thickness of the high-voltage pressure-sensing film can be precisely controlled by controlling the etching time. The anodic bonding frame 18 requires a certain width to ensure sufficient strength in the anodic bonding area with the glass substrate layer 8. This ensures the strength and sealing of the anodic bonding area between the high-voltage pressure-sensing layer 7 and the glass substrate layer 8. During the anodic bonding process, a voltage of 500-1000V, a temperature of 300-400°C, and a pressure of 50-150N are applied, causing a chemical reaction in the materials in the anodic bonding frame 18 area, achieving a strong bond between the high-voltage pressure-sensitive layer 7 and the glass substrate layer 8. This ensures the stability of the sensor's internal structure during use, prevents external environmental interference with the sensor's sensitive structure, and ensures that the pressure signal can be accurately transmitted from the glass substrate layer 8 to the high-voltage pressure-sensitive film 17. The circular through-holes in the glass substrate layer 8 serve primarily as air guides.

[0047] The bonding oxide layer electrode through-hole 2 is used to realize the electrical connection between the electrodes. During the preparation of the bonding oxide layer 4, it is formed by processes such as photolithography and etching to ensure the transmission of electrical signals between the low-voltage side pressure-sensitive film 3, the structural layer 5 and other layers, and to ensure the effective connection between the driving electrode 9, the detection electrode 12 and the external circuit, so that the sensor can work normally.

[0048] The bonding oxide layer 4 primarily serves as an insulation and bonding aid. During the bonding process between the low-voltage-side pressure-sensitive layer and the SOI wafer, the bonding oxide layer 4 enhances the stability and reliability of the bonding interface and isolates the conductive structures of different layers to prevent short circuits. The bonding oxide layer electrode via 2 is located within the bonding oxide layer 4.

[0049] The structure is etched on the SOI (Silicon-On-Insulator) device layer through a dry etching process to form Figure 3 In the structural layer 5 shown, the fundamental frequencies of the edge resonators 10 and the center resonator 11 are designed to have a certain difference, with the frequency of the center resonator 11 being higher than that of the edge resonator 10, to ensure that the frequency response curves after differentiation do not cross. Both resonators are connected to the corresponding drive electrodes 9 and detection electrodes 12 via four supporting sensitive beams 13 to ensure electrical connection of the resonators. An insulating isolation zone is formed between the electrodes and the structural layer frame 21 to prevent signal short circuits.

[0050] The two resonators have the same structure, consisting of a dual inertial mass plate 15, four supporting sensitive beams 13, and a micron piezoresistive beam 16. The difference is that the width of the sensitive support beam 13 of the central resonator 11 is larger than that of the edge resonator to ensure the fundamental frequency interval. In this embodiment, the length and width of the release hole 14 of the central resonator 11 (20 μm × 8.75 μm) are 1 μm larger than the release hole of the edge resonator (19 μm × 7.75 μm). That is, the overall mass of the dual inertial mass plate 15 of the edge resonator is greater than that of the dual inertial mass plate of the central resonator, which leads to the fundamental frequency of the central resonator (about 2.092×10 6 Hz) than the fundamental frequency of the edge resonator (about 2.086×10 6 ) high 6~8Khz, to ensure the fundamental frequency interval, the sensitive support beam 13 occurs in the core Figure 8 When the deflection shown in the figure is deformed, tensile stress is generated in the central area and compressive stress is generated in the edge area. When compressive stress or tensile stress is felt, the frequency of the resonator changes accordingly. This is because a resonator is composed of four supporting sensitive beams 13, two inertial mass plates 15 and a micron piezoresistive beam 16. The main stiffness contribution to its resonant frequency comes mainly from the four supporting sensitive beams 13 and the one micron piezoresistive beam 16. The mass plate mainly provides motion inertia to ensure the vibration continuity of the resonator. When the four supporting sensitive beams 13 feel the stress change, the stiffness of the entire resonator changes, thereby changing the frequency, thereby indicating the pressure magnitude. At the same time, the central resonator located in the tensile stress area has its supporting sensitive beam 13 tensed, resulting in an increase in structural stiffness and an increase in the resonant frequency; the edge resonator located in the compressive stress area has its supporting sensitive beam 13 compressed, resulting in a decrease in structural stiffness and a decrease in the resonant frequency. Then, by subtracting the frequency change of the central resonator (increase is a positive value) from that of the edge resonator (decrease is a negative value), a frequency change approximately twice that of a single resonator is obtained. That is, under the same differential pressure, the differential pressure sensitivity of the dual resonators after differentiation is approximately twice that of a single resonator.

[0051] The drive electrode 9 is used to provide DC excitation to the micron piezoresistive beam 16. When energized, it undergoes thermal expansion and displacement. The SOI structural layer 5 should be constructed of low-resistance N-type silicon to impart a negative piezoresistive coefficient. The thermal expansion of the piezoresistive beam 16 generates displacement that maintains its motion through the inertial mass plate 15. This negative piezoresistive coefficient causes the piezoresistive beam to decrease in resistance when subjected to tension, reducing the current flowing through it and the temperature, causing it to contract and drive the inertial mass plate 15 in the opposite direction. The negative piezoresistive beam then begins to be compressed, causing its resistance to increase. This increases the current flowing through it and the temperature, causing it to expand and drive the inertial mass plate 15 in the opposite direction. This cycle repeats, generating a vibration signal. This process requires the DC current to exceed a certain threshold and the dimensions of the piezoresistive beam 16 to be sufficiently small. Since the mechanical frequency has a first-order relationship with the three-dimensional dimensions, while the thermal frequency has a second-order relationship with the three-dimensional dimensions, as the dimensions of the piezoresistive beam 16 decrease, the thermal frequency increases at a higher rate than the mechanical frequency. Consequently, self-oscillation occurs when the DC current reaches a certain threshold. The structure layer frame 21 is mainly used to isolate the electrodes from the outer surface of the core to prevent short circuits, breakdown and other problems during actual use. The structure layer frame 21 adopts a ring structure design with a width of 300μm and is directly formed on the device layer through an etching process.

[0052] The embedded oxide layer movable structure release groove 20 is prepared by HF wet release process, and its main function is to ensure the mobility of the resonator. In the release process, the embedded oxide layer movable structure release groove 20 can accurately remove the embedded oxide layer 6 material by controlling the specific HF solution concentration and etching time, avoiding damage to key structures such as the resonator. Figure 5 As shown, the high-pressure side pressure-sensitive film 17 is etched mainly by wet silicon etching process. The thickness is the thickness of the SOI substrate layer minus the etching depth. It should be thicker than the low-pressure side pressure-sensitive film 3 to form a pressure higher than the low-pressure side when the pressure on this side is higher than that on the low-pressure side. Figure 8 The deflection deformation shown in the figure requires that the anodic bonding frame 18 has a certain width to ensure sufficient strength of the anodic bonding area with the glass substrate layer 8. The anodic bonding frame 18 is used to ensure the strength and sealing of the anodic bonding area between the high-voltage side pressure-sensitive layer 7 and the glass substrate layer 8. During the anodic bonding process, by applying a certain voltage and temperature, the material in the area of ​​the anodic bonding frame 18 undergoes a chemical reaction, thereby achieving a firm bond between the high-voltage side pressure-sensitive layer 7 and the glass substrate layer 8. This ensures the stability of the internal structure of the sensor during use, prevents the external environment from interfering with the sensitive structure inside the sensor, and ensures that the pressure signal can be accurately transmitted from the glass substrate layer 8 to the high-voltage side pressure-sensitive film 17. The circular through holes on the glass substrate layer 8 are mainly used as air guide holes.

[0053] The above-mentioned layers of structure are combined through corresponding process steps to form a MEMS resonant differential pressure sensor that can withstand large static pressure and is sensitive to micro differential pressure. Its core advantage lies in the extremely small internal cavity design. By compressing the effective volume inside the sensor to 15% of the traditional structure, the compressibility of the gas or liquid medium under the action of static pressure is significantly reduced, thereby reducing the stress transmitted by static pressure to the resonator. Under the static pressure on both sides, the stress transmitted to the resonator is small, and the static pressure frequency response is low. The device is loaded with pressure as shown in the figure below. Figure 14 ,exist Figure 14 In the figure, the differential pressure P1 is the pressure difference to be measured, which is introduced from the bottom vent. The static pressure P2 is introduced from the vents on both sides. Under the static pressure of only 30Mpa on both sides, it is verified by experiments that the core shows uniform axial compression deformation, and the deformation is as follows: Figure 9 As shown, magnified 500 times, from Figure 9 It can be seen that the core produces an effect similar to up and down squeezing without lateral deformation, and the stress cloud map has the same color. Therefore, the stress transmitted to the resonator is very small. By reasonably setting the thickness of the low-pressure side pressure-sensitive film 3, the thickness of the high-pressure side pressure-sensitive film 17, and the arrangement position of the central resonator 11 and the edge resonator 10, the additional stress actually borne by the resonator is less than 0.01% of the total static pressure, and finally the static pressure sensitivity after differentiation is as low as 0.7517Hz / MPa ( Figure 12 ), which is 2 orders of magnitude higher than the traditional structure. When differential pressure is applied to the core, the core produces Figure 8 The deformation effect shown in the figure, the blue in the center represents tensile stress, and the red at the edge represents compressive stress. By placing the resonator at the center and the edge, the differential pressure sensitivity is amplified after sensing different stresses. Figure 11 The differential pressure sensitivity of the MEMS resonant differential pressure sensor in the present invention at different temperatures is demonstrated. Figure 11 In the figure, the horizontal axis is the differential pressure (kPa), the left side of the vertical axis is the frequency (Hz), and the right side is the frequency after differentiation (Hz). Figure 11 It can be seen that at different temperatures (such as -40℃, -80℃, 20℃, 80℃, etc.), the "differential" curve is relatively stable, indicating that the differential output can effectively reduce the interference of temperature on the measurement. The linear fitting formula is y=25.526x+6237.3, R 2 = 1. A highly linear relationship was observed between differential pressure and differential frequency at different temperatures. That is, for every 1 kPa change in differential pressure, the differential frequency changed by approximately 25.526 Hz. This further demonstrates that the sensor of the present invention has good consistency and accuracy in differential pressure measurement under different temperature environments, at approximately 25 Hz / kPa. Compared to the frequency change caused by static pressure, this is approximately 33,000 times greater. This indicates that the designed differential pressure sensor is insensitive to static pressure but sensitive to differential pressure. This verifies the sensor's highly selective response to differential pressure signals and its ability to reliably detect small differential pressure signals even under high static pressure.

[0054] Regarding the temperature effect, since the sensor core is composed of multiple materials (including single crystal silicon, SiO2 buried oxide layer, BF33 glass, etc.), the thermal expansion coefficient of single crystal silicon material is 2.6×10 -6 / ℃, the thermal expansion coefficient of BF33 glass is 3.25×10 -6 / ℃, the thermal expansion coefficient of silicon oxide is 0.5×10 -6 / ℃, but since the total thickness of the oxide layer designed in this embodiment (about 5μm) is almost negligible compared with the total thickness of the device (about 1350μm), the main thermal stress is caused by the difference in thermal expansion coefficients between single crystal silicon and BF33 glass, which is 0.65×10 -6 / ℃, which causes the core to produce Figure 10 As shown in the stress effect diagram, the stress distribution color of the entire core is relatively consistent. Therefore, through differential frequency output and a suitable dual-resonator arrangement, more than 95% of common-mode temperature interference can be effectively offset. Simulation verification shows that the temperature sensitivity of the differential pressure sensor designed in this embodiment is approximately 0.16 Hz / °C, which is much lower than the traditional single-resonator structure (typical value >10 Hz / °C). This is an extremely low level and can meet industrial-grade high-precision measurement requirements without the need for additional temperature compensation circuits.

[0055] Figure 13 The simulated temperature characteristics of the sensor in the embodiment of the present invention are shown. The horizontal axis is temperature (°C), the left side of the vertical axis is frequency (Hz), and the right side is the differential frequency (Hz). There are three curves in the figure: the "pressure" curve: represents the change in frequency of the edge resonator, that is, the resonator that senses compressive stress, with temperature. Its fitting formula is y=3.3031x+2E+06, R 2 =1, indicating that the frequency is linearly related to temperature. For every 1°C change in temperature, the frequency changes by about 3.3031Hz. The "pull" curve represents the frequency change of the central resonator, that is, the resonator that feels tensile stress, with temperature. The fitting formula is y=3.466x+2E+06, R 2 =1, that is, when the temperature changes by 1°C, the frequency changes by about 3.466Hz. The "differential" curve shows the change of frequency with temperature after differential processing. The fitting formula is y=0.163x+6212.5, R 2=0.9992, indicating that for every 1°C change in temperature, the frequency changes by approximately 0.163Hz after differentiation. Because the sensor core is composed of multiple materials with varying thermal expansion coefficients, temperature fluctuations generate stress that affects the frequency. However, the dual-resonator differential output design ensures that temperature affects both resonators similarly. This differentiation effectively reduces common-mode signal interference, resulting in an extremely low sensor temperature sensitivity of approximately 0.163Hz / °C. This maintains stable measurement accuracy across diverse temperature environments, enhancing environmental adaptability and reliability. This differential design is a key advantage of this sensor in terms of temperature characteristics, effectively overcoming measurement errors caused by differences in material thermal expansion coefficients.

[0056] The above embodiments are only preferred embodiments of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent of the present invention.

Claims

1. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive, characterized in that From top to bottom, it includes the low-pressure side pressure-sensitive layer, the resonant structure layer, the high-pressure side pressure-sensitive layer and the glass substrate layer; The high-voltage side pressure-sensing layer and the resonant structure layer are fabricated from the same SOI wafer, wherein the resonant structure layer is fabricated from the thinner device layer of the SOI wafer by a micromachining process and then formed into a movable structure by a release process; the high-voltage side pressure-sensing film is fabricated on the thicker handle layer of the SOI wafer by a wet etching process; The low-voltage side pressure-sensitive layer is prepared from another silicon wafer, and the SOI wafer and the silicon wafer are bonded by a silicon bonding process; The glass substrate layer is made of BF33 glass and bonded to the SOI wafer through an anodic bonding process; The low-pressure side pressure-sensitive layer and the high-pressure side pressure-sensitive layer are respectively connected to the lower pressure end and the larger pressure end of the differential pressure to be measured. Based on the pressure difference, tensile stress is generated in the central area of ​​the resonant structure layer and compressive stress is generated in the edge area through the principle of small deflection deformation of the thin plate, so that the natural frequencies of the two resonators arranged in different stress areas change in opposite directions, and the difference in the natural frequencies of the two resonators is used to represent the differential pressure to be measured; the glass substrate layer is used to isolate the thermal stress transmitted from the metal base to the core.

2. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive according to claim 1, characterized in that The low-voltage side pressure-sensitive film is provided with four centrally symmetrically distributed electrode holes, including two driving electrode holes and two detection / grounding electrode holes, which correspond to the driving and detection end electrodes of the central resonator and the edge resonator respectively. The low-voltage side pressure-sensitive film is polished by a chemical mechanical polishing process to ensure that the film thickness is uniform, and the deviation is controlled within 5%.

3. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive according to claim 1, characterized in that The resonant structure layer consists of a central resonator, an edge resonator, a central resonator driving electrode, a central resonator detection electrode, an edge resonator driving electrode, an edge resonator detection electrode, and an outer frame; the central resonator is connected to the central resonator driving electrode and the central resonator detection electrode through four supporting sensitive beams, the two supporting sensitive beams on the left are connected to the central resonator driving electrode, and the two supporting sensitive beams on the right are connected to the central resonator detection electrode; The edge resonator is connected to the edge resonator driving electrode and the edge resonator detection electrode through four supporting sensitive beams, and the connection form is the same as that of the central resonator; the central resonator driving electrode, the central resonator detection electrode, the edge resonator driving electrode, the edge resonator detection electrode are not connected to the frame.

4. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive as claimed in claim 1, characterized in that The central resonator and the edge resonator both include a dual-mass plate, four supporting beams, and a micron piezoresistive beam connecting the dual-mass plate; the dual-mass plate is connected to the electrode through four supporting sensitive beams, and the micron piezoresistive beam runs across the center of the dual-mass plate and forms a Wheatstone bridge structure; the central resonator is located in the tensile stress area when the pressure membrane is deformed, and the edge resonator is located in the compressive stress area when the pressure membrane is deformed.

5. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive as claimed in claim 1, characterized in that The thermal piezoresistive drive is generated by the heat pump effect of a micron-piezoresistive beam connected to a dual-mass plate when power is applied. The Joule heat generated by the current causes the piezoresistive beam to expand, resulting in a decrease in resistance. The change in resistance causes current fluctuations, which in turn causes the temperature of the piezoresistive beam to change periodically, forming thermal oscillations that match the mechanical vibration frequency. This absorbs energy from a DC source without the need for AC power, breaking through the mechanical Q value limit of the resonator.

6. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive as claimed in claim 1, characterized in that The high-pressure side pressure-sensitive membrane is square in shape and is centrally located in the center area of ​​the core body, and the thickness of the membrane layer is evenly distributed.

7. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive according to claim 1, characterized in that When the low-pressure side pressure-sensitive layer and the high-pressure side pressure-sensitive layer are in use, a static pressure of 0 MPa to 30 MPa is applied to both sides, and the high-pressure side pressure-sensitive layer is then subjected to a differential pressure of 300 KPa. Based on the difference between the total pressure applied to the high-pressure side pressure-sensitive layer and the total pressure applied to the low-pressure side pressure-sensitive layer, tensile stress is generated in the central area of ​​the resonant structure layer and compressive stress is generated in the edge area. The difference in frequency between the resonator change in the tensile stress area and the resonator change in the compressive stress area is used to represent the differential pressure to be measured.

8. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive as claimed in claim 1, characterized in that The substrate layer is made of BF33 glass with a thermal expansion coefficient close to that of single crystal silicon material, and has a through-hole for transmitting pressure to the high-pressure side pressure-sensitive film. The hole is centrally located on the glass base, corresponding to the center of the high-pressure side pressure-sensitive film.

9. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive as claimed in claim 1, characterized in that The basic resonant frequency of the central resonator is higher than the basic resonant frequency of the edge resonator. The frequency difference is achieved by adjusting the beam length, beam width and beam thickness of the support beam to ensure that there is no crossover in the frequency response curves of the dual resonators within the pressure test range.

10. A common-film differential high static pressure resonant differential pressure sensor based on thermal piezoresistive drive according to claim 1, characterized in that The resonator mass plate is provided with a rectangular wet release hole to ensure that the release rate of each movable area is consistent during the release process of the structural layer; the low-pressure side pressure-sensitive layer is provided with a movable structural groove corresponding to the installation position of the central resonator and the edge resonator, which is used for the mobility of the resonator and as a storage space for the degassing agent. The movable structural groove is filled with Ti degassing agent through a packaging process.

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