Low-temperature-drift MEMS piezoresistive pressure sensor and preparation method thereof

Abstract

The invention provides a low-temperature drift MEMS piezoresistive pressure sensor and a preparation method thereof. The pressure sensor comprises a first substrate, a second substrate, a first structural layer, a second structural layer and a piezoresistor strip, a first groove is formed in the lower surface of the first substrate, and the second substrate is fixed to the first substrate and seals the first groove; an annular second groove is formed in the periphery of the bottom surface of the first groove; a third groove is formed in the middle of the upper surface of the first substrate; the first structural layer is arranged in the third groove, and the second structural layer is arranged in the second groove; the first structure layer and the second structure layer are made of metal; the upper surface of the first substrate is provided with a plurality of piezoresistor strips surrounding the first structure layer, and the plurality of piezoresistor strips correspond to the second structure layer. The pressure sensor has the technical effect that the sensitivity and reliability of the pressure sensor are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of pressure sensors, and in particular relates to a low-temperature drift MEMS piezoresistive pressure sensor and a preparation method thereof. Background Art

[0002] MEMS (Micro-Electro-Mechanical System) pressure sensors have many advantages such as high sensitivity, small size, low power consumption, good consistency and easy mass production, and have been widely used in industrial production, automotive electronics, biomedicine, national defense and military, scientific research, and aerospace. The types of MEMS pressure sensors mainly include MEMS piezoresistive pressure sensors, MEMS capacitive pressure sensors, MEMS resonant pressure sensors, and MEMS piezoelectric pressure sensors. Among them, MEMS piezoresistive pressure sensors have become the most common pressure sensors on the market due to their good linearity and reliability. A typical MEMS piezoresistive pressure sensor is made by diffusion or ion implantation on the edge of a sensitive film. These four piezoresistors are then reasonably arranged and interconnected to form a Wheatstone bridge. When an external force forces the film to deform, the resistance of the piezoresistors changes under the stress and is converted into a corresponding electrical signal output through the Wheatstone bridge.

[0003] However, in actual applications, MEMS piezoresistive pressure sensors will produce significant sensitivity temperature drift and zero point temperature drift due to the temperature characteristics of the piezoresistance coefficient in the piezoresistive strip and the thermal stress (bonding thermal stress) generated by the anodic bonding process, which will reduce the measurement accuracy of the sensor. In order to deal with the above two temperature drift problems of MEMS piezoresistive pressure sensors, the traditional method is to increase the doping concentration of the piezoresistive strip and select an anodic bonding process with a lower bonding temperature when preparing the MEMS piezoresistive pressure sensor. However, with the increase of the doping concentration in the piezoresistive strip and the decrease of the bonding temperature in the anodic bonding process, the piezoresistive effect in the sensor piezoresistive strip and the strength of the anodic bonding interface will weaken rapidly, resulting in a rapid decrease in the sensitivity and reliability of the sensor. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art and provide a new technical solution for a low-temperature drift MEMS piezoresistive pressure sensor and a preparation method thereof.

[0005] According to a first aspect of the present invention, there is provided a low-temperature drift MEMS piezoresistive pressure sensor, comprising:

[0006] A first substrate and a second substrate, wherein a first groove is provided on the lower surface of the first substrate, and the second substrate is fixed to the first substrate and closes the first groove; an annular second groove is provided around the bottom surface of the first groove; the first substrate is made of single crystal silicon;

[0007] A first structural layer and a second structural layer, wherein a third groove is provided in the middle of the upper surface of the first substrate; the first structural layer is provided in the third groove, the second structural layer is provided in the second groove, and the second structural layer surrounds the outer side of the first structural layer; the first structural layer and the second structural layer are both made of metal;

[0008] A varistor strip, wherein a plurality of varistor strips are arranged on the upper surface of the first substrate around the first structural layer, and the plurality of varistor strips all correspond to the second structural layer;

[0009] The first structural layer, the second structural layer, the first substrate below the first structural layer, and the first substrate above the second structural layer together constitute a pressure sensitive film, and the multiple piezoresistive strips are all located in the pressure sensitive film and are used to measure pressure according to the deformation of the pressure sensitive film.

[0010] Optionally, the low temperature drift MEMS piezoresistive pressure sensor further includes a passivation layer;

[0011] The passivation layer is arranged around the upper surface of the first substrate and covers the varistor strip.

[0012] Optionally, the low temperature drift MEMS piezoresistive pressure sensor further includes an ohmic contact;

[0013] Two ends of the varistor strip are respectively provided with ohmic contacts, and the ohmic contacts are used to realize electrical connection between the varistor strip and the lead wire.

[0014] Optionally, a projection of the first structure layer on the upper surface of the first substrate does not overlap with a projection of the second structure layer on the upper surface of the first substrate;

[0015] The sum of a projection area of ​​the first structure layer on the upper surface of the first substrate and a projection area of ​​the second structure layer on the upper surface of the first substrate is the same as a projection area of ​​the bottom surface of the first groove on the upper surface of the first substrate.

[0016] Optionally, the material of the first structural layer is the same as that of the second structural layer, and is at least one of lead, gold, zinc, magnesium, aluminum and copper.

[0017] Optionally, the first structural layer has four arc corners, and adjacent arc corners are connected by arc lines.

[0018] Optionally, the thickness of the first structural layer and the second structural layer are both half of the thickness of the pressure sensitive film.

[0019] Optionally, the thickness of the varistor strip is 1 μm-3 μm, and the thickness of the ohmic contact is 1 μm-3 μm.

[0020] Optionally, the passivation layer is made of at least one of silicon oxide and silicon nitride, and has a thickness of 0.1 μm-5 nm.

[0021] According to a second aspect of the present invention, a method for preparing a low-temperature drift MEMS piezoresistive pressure sensor is provided, comprising the following steps:

[0022] Step S1, preparing a single crystal silicon wafer as a first substrate;

[0023] Step S2, performing P-type doping on the upper surface of the single crystal silicon wafer to form a varistor;

[0024] Step S3, performing P-type heavy doping at both ends of the varistor to form an ohmic contact region;

[0025] Step S4, depositing a silicon dioxide layer on the upper surface of the single crystal silicon wafer;

[0026] Step S5, photolithography the silicon dioxide layer to expose the single crystal silicon wafer; wherein the silicon dioxide layer after photolithography serves as a passivation layer;

[0027] Step S6, performing photolithography on the upper surface of the single crystal silicon wafer to form a third groove;

[0028] Step S7, sputtering metal in the third groove and performing photolithography to prepare a first structural layer;

[0029] Step S8, etching the lower surface of the single crystal silicon wafer to form a first groove;

[0030] Step S9, etching the periphery of the bottom surface of the first groove to form a second groove;

[0031] Step S10, performing magnetron sputtering and photolithography in the second groove to prepare a second structural layer;

[0032] Step S11, bonding the lower surface of the single crystal silicon wafer to the surface of the glass substrate to form a closed cavity between the single crystal silicon wafer and the glass substrate; wherein the glass substrate serves as a second substrate.

[0033] A technical effect of the present invention is:

[0034] In the embodiment of the present application, the pressure-sensitive film of the low-temperature drift MEMS piezoresistive pressure sensor adopts a first structural layer and a second structural layer whose elastic modulus changes significantly with temperature, thereby compensating for the sensitivity temperature drift of the pressure sensor caused by the temperature characteristics of the piezoresistive coefficient when the temperature changes, thereby ultimately enabling the pressure sensor to obtain more accurate detection results.

[0035] Moreover, the thermal expansion coefficient of the metal materials in the first structural layer and the second structural layer is relatively large. When these two parts of the structure shrink (expand) due to temperature, they can offset the bonding thermal stress on the varistor strips in the pressure sensor, thereby compensating for the zero-point temperature drift of the pressure sensor caused by the bonding thermal stress, thereby further improving the measurement accuracy of the sensor.

[0036] In addition, the pressure sensitive film is respectively composed of a first structural layer and a second structural layer made of metal materials, a first substrate below the first structural layer, and a first substrate above the second structural layer. When the pressure sensitive film is subjected to the overload pressure of the pressure sensor, the first structural layer and the second structural layer can effectively bear the deformation by virtue of the ductility of the metal material, thereby significantly enhancing the overload resistance of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A cross-sectional view of a low-temperature drift MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0038] Figure 2 This is a structural cross-sectional view corresponding to preparation step 1 in an embodiment of the present invention;

[0039] Figure 3 This is a structural cross-sectional view corresponding to preparation step 2 in an embodiment of the present invention;

[0040] Figure 4 It is a top view of the structure corresponding to preparation step 2 in an embodiment of the present invention;

[0041] Figure 5 It is a top view of the structure corresponding to preparation step 3 in an embodiment of the present invention;

[0042] Figure 6 It is a structural cross-sectional view corresponding to preparation step 4 in an embodiment of the present invention;

[0043] Figure 7 It is a structural cross-sectional view corresponding to preparation step 5 in an embodiment of the present invention;

[0044] Figure 8 It is a top view of the structure corresponding to preparation step 5 in an embodiment of the present invention;

[0045] Fig. 9 It is a structural cross-sectional view corresponding to preparation step 6 in an embodiment of the present invention;

[0046] Fig.10 It is a structural cross-sectional view corresponding to preparation step 7 in an embodiment of the present invention;

[0047] Fig.11 It is a top view of the structure corresponding to preparation step 7 in an embodiment of the present invention;

[0048] Fig.12 It is a structural cross-sectional view corresponding to preparation step 8 in an embodiment of the present invention;

[0049] Fig.13 A bottom view of the structure corresponding to preparation step 8 in an embodiment of the present invention;

[0050] Fig.14 It is a structural cross-sectional view corresponding to preparation step 9 in an embodiment of the present invention;

[0051] Fig.15 A bottom view of the structure corresponding to preparation step 9 in an embodiment of the present invention;

[0052] Fig.16 It is a structural cross-sectional view corresponding to the preparation step 10 in the embodiment of the present invention;

[0053] Fig.17 A bottom view of the structure corresponding to preparation step 10 in an embodiment of the present invention;

[0054] Fig.18 It is a structural cross-sectional view corresponding to preparation step 11 in an embodiment of the present invention.

[0055] In the figure: 1. passivation layer; 2. first substrate; 3. varistor strip; 4. ohmic contact; 5. first structural layer; 6. second structural layer; 7. pressure sensitive film; 8. closed cavity; 9. second substrate. DETAILED DESCRIPTION

[0056] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0057] The embodiments of the present application will be described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and should not be construed as limitations on the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

[0058] The term "first" or "second" in the specification and claims of this application may include one or more of the features explicitly or implicitly. In the description of this application, unless otherwise specified, "plurality" means two or more. In addition, "and / or" in the specification and claims means at least one of the connected objects, and the character " / " generally means that the objects connected before and after are in an "or" relationship.

[0059] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0060] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0061] According to a first aspect of the present invention, see Figure 1 , provides a low-temperature drift MEMS piezoresistive pressure sensor, which can significantly reduce the sensitivity temperature drift of the pressure sensor in the prior art caused by the temperature characteristics of the piezoresistive coefficient, and can also reduce the zero point temperature drift caused by bonding thermal stress, thereby effectively improving the measurement accuracy of the pressure sensor.

[0062] Specifically, the low temperature drift MEMS piezoresistive pressure sensor comprises:

[0063] A first substrate 2 and a second substrate 9, wherein a first groove is provided on the lower surface of the first substrate 2, the second substrate 9 is fixed to the first substrate 2 and closes the first groove, and a closed cavity 8 is formed between the first substrate 2 and the second substrate 9; an annular second groove is provided around the bottom surface of the first groove; the material of the first substrate 2 is single crystal silicon; illustratively, the maximum thickness of the first substrate 2 is 500 μm;

[0064] A first structural layer 5 and a second structural layer 6, a third groove is provided in the middle of the upper surface of the first substrate 2; the first structural layer 5 is provided in the third groove, the second structural layer 6 is provided in the second groove, and the second structural layer 6 surrounds the outer side of the first structural layer 5; the first structural layer 5 and the second structural layer 6 are both made of metal;

[0065] A varistor strip 3, wherein a plurality of varistor strips 3 are arranged on the upper surface of the first substrate 2 around the first structural layer 5, and the plurality of varistor strips 3 correspond to the second structural layer 6; wherein the varistor strip 3 may be P-type doped single crystal silicon;

[0066] The first structural layer 5, the second structural layer 6, the first substrate 2 below the first structural layer 5, and the first substrate 2 above the second structural layer 6 together constitute a pressure sensitive film 7, and the multiple piezoresistive strips 3 are all located on the pressure sensitive film 7 and are used to measure pressure according to the deformation of the pressure sensitive film 7.

[0067] In the embodiment of the present application, the pressure sensitive film 7 of the low-temperature drift MEMS piezoresistive pressure sensor adopts a first structural layer 5 and a second structural layer 6 whose elastic modulus changes significantly with temperature, so that when the temperature changes, the sensitivity temperature drift of the pressure sensor caused by the temperature characteristics of the piezoresistive coefficient can be compensated, and finally the pressure sensor can obtain more accurate detection results.

[0068] Moreover, the thermal expansion coefficient of the metal materials in the first structural layer 5 and the second structural layer 6 is relatively large. When these two parts of the structure shrink (expand) due to temperature, they can offset the bonding thermal stress on the varistor strip 3 in the pressure sensor, thereby compensating for the zero-point temperature drift of the pressure sensor caused by the bonding thermal stress, further improving the measurement accuracy and reliability of the sensor.

[0069] In addition, the pressure sensitive film 7 is respectively composed of a first structural layer 5 and a second structural layer 6 made of metal materials, and a first substrate 2 below the first structural layer 5 and a first substrate 2 above the second structural layer 6. When the pressure sensitive film 7 is subjected to the overload pressure of the pressure sensor, the first structural layer 5 and the second structural layer 6 can effectively bear the deformation by virtue of the ductility of the metal material, thereby significantly enhancing the overload resistance of the sensor.

[0070] It should be noted that the working principle of the low temperature drift MEMS piezoresistive pressure sensor is as follows:

[0071] When the input pressure acts on the pressure sensitive film 7 of the low temperature drift MEMS piezoresistive pressure sensor, a compressive stress region is formed at the first structure layer 5 and the second structure layer 6, and a tensile stress region is formed at other positions of the pressure sensitive film 7. In the present invention, the material of the first structure layer 5 and the second structure layer 6 is metal, and the material of other positions of the pressure sensitive film 7 is still single crystal silicon. Therefore, when the ambient temperature of the working pressure sensor increases (decreases), the elastic modulus of the metal material in the first structural layer 5 and the second structural layer 6 in the compressed state will significantly decrease (increase), so that the compression deformation of the first structural layer 5 and the second structural layer 6 will significantly increase (decrease), and the first structural layer 5 and the second structural layer 6 will drive the tensile deformation of other positions of the pressure sensitive film 7 to increase (decrease), so that the stress of the piezoresistor strip 3 located on the pressure sensitive film 7 will increase (decrease) proportionally within the full range, and finally the sensitivity of the low-temperature drift MEMS piezoresistive pressure sensor of the present invention will increase (decrease) as the ambient temperature increases (decreases), and then the sensitivity temperature drift caused by the decrease (increase) of the piezoresistance coefficient in the piezoresistor strip 3 as the ambient temperature increases (decreases) can be compensated.

[0072] In addition, since the thermal expansion coefficient of the metal material in the first structure layer 5 and the second structure layer 6 is larger than that of the single crystal silicon medium in other positions of the pressure sensitive film 7, when the first structure layer 5 and the second structure layer 6 are placed at room temperature from the sputtering temperature, they will shrink and drive other positions of the pressure sensitive film 7 to stretch, and generate stress on the varistor strip 3 that is opposite to the bonding thermal stress, thereby reducing or even eliminating the influence of the bonding thermal stress on the zero point temperature drift of the pressure sensor.

[0073] Optionally, the low temperature drift MEMS piezoresistive pressure sensor further includes a passivation layer 1;

[0074] The passivation layer 1 is arranged around the upper surface of the first substrate 2 and covers the varistor strip 3 .

[0075] In the above embodiment, the passivation layer 1 can provide better isolation and protection for the varistor strip 3 .

[0076] Optionally, the low temperature drift MEMS piezoresistive pressure sensor further includes an ohmic contact 4;

[0077] Ohmic contacts 4 are respectively provided at both ends of the varistor strip 3 , and the ohmic contacts 4 are used to realize electrical connection between the varistor strip 3 and the lead wire.

[0078] In the above embodiment, the ohmic contacts 4 are located at both ends of the varistor strip 3 to achieve good electrical interconnection between the varistor strip 3 and the lead wire. Exemplarily, the material of the ohmic contacts 4 is P-type heavily doped single crystal silicon with a thickness of 1 μm-3 μm, and its shape is determined by the specific layout and wiring.

[0079] Optionally, a projection of the first structure layer 5 on the upper surface of the first substrate 2 and a projection of the second structure layer 6 on the upper surface of the first substrate 2 do not overlap;

[0080] The sum of the projection area of ​​the first structure layer 5 on the upper surface of the first substrate 2 and the projection area of ​​the second structure layer 6 on the upper surface of the first substrate 2 is the same as the projection area of ​​the bottom surface of the first groove on the upper surface of the first substrate 2 .

[0081] In the above embodiment, the design of the first structure layer 5 and the second structure layer 6 is relatively reasonable, which helps to ensure the sensitivity and reliability of the pressure sensor.

[0082] Exemplarily, the first structural layer 5 is located in the middle of one side surface (i.e., the front side) of the pressure sensitive film 7 and is in the shape of a four-leaf rose line, wherein the specific shape of the four-leaf rose line needs to be determined according to the simulated stress cloud diagram of the specific pressure sensitive film 7. The second structural layer 6 is located at the edge of the other side surface (i.e., the back side) of the pressure sensitive film 7, and its shape is the area of ​​the pressure sensitive film 7 minus the area projection of the first structural layer 5 on the pressure sensitive film 7 The shape corresponds to the remaining area.

[0083] Optionally, the material of the first structural layer 5 is the same as that of the second structural layer 6, and is at least one of lead, gold, zinc, magnesium, aluminum and copper. This makes the elastic modulus of the first structural layer 5 and the second structural layer 6 have a relatively stable elastic modulus.

[0084] Optionally, the first structural layer 5 has four arc angles, and adjacent arc angles are connected by arc lines. The first structural layer 5 is reasonably designed, which helps the first structural layer 5 and the second structural layer 6 to cooperate to ensure the stability and reliability of the pressure sensor.

[0085] Optionally, the thickness of the first structure layer 5 and the second structure layer 6 are both half of the thickness of the pressure sensitive film 7. This enables the pressure sensitive film 7 to better compensate for the temperature drift of the pressure sensor caused by the temperature characteristics of the piezoresistance coefficient when the temperature changes.

[0086] Optionally, the thickness of the varistor strip 3 is 1 μm-3 μm, and the thickness of the ohmic contact 4 is 1 μm-3 μm. This helps the varistor strip 3 to stably achieve electrical connection with the lead wire through the ohmic contact 4 .

[0087] Optionally, the passivation layer 1 is made of at least one of silicon oxide and silicon nitride, and has a thickness of 0.1 μm-5 nm.

[0088] In the above embodiment, the passivation layer 1 is thin and made of a reasonable material, which not only improves the isolation and protection effect of the passivation layer 1 on the varistor strip 3, but also helps to reduce the quality of the piezoresistive pressure sensor.

[0089] Exemplarily, the second substrate 9 is located directly below the first substrate 2 , and is made of borosilicate glass with a thickness of 500 μm.

[0090] According to a second aspect of the present invention, a method for preparing a low-temperature drift MEMS piezoresistive pressure sensor is provided, comprising the following steps:

[0091] Step S1, prepare a single crystal silicon wafer as a first substrate 2, see Figure 2 ; For example, the thickness of the single crystal silicon wafer is 500 μm, and it is an N-type single crystal silicon wafer;

[0092] Step S2, P-type doping is performed on the upper surface of the single crystal silicon wafer to form a varistor, see Figure 3 and Figure 4 ;

[0093] Step S3, performing P-type heavy doping at both ends of the varistor to form an ohmic contact 4 region, see Figure 5 ;

[0094] Step S4, depositing a silicon dioxide layer on the upper surface of the single crystal silicon wafer, see Figure 6 ;

[0095] Step S5, photolithography is performed on the silicon dioxide layer to expose the single crystal silicon wafer; wherein the silicon dioxide layer after photolithography is used as a passivation layer 1, see Figure 7 and Figure 8 ;

[0096] Step S6, photolithography is performed on the upper surface of the single crystal silicon wafer to form a third groove, see Fig. 9 ;

[0097] Step S7, sputtering metal in the third groove and performing photolithography to prepare the first structure layer 5, see Fig.10 and Fig.11 ;

[0098] Step S8, etching the lower surface of the single crystal silicon wafer to form a first groove, see Fig.12 and Fig.13 ;

[0099] Step S9, etching the periphery of the bottom surface of the first groove to form a second groove, see Fig.14 and Fig.15 ; For example, the etching method may be wet etching;

[0100] Step S10, magnetron sputtering and photolithography are performed in the second groove to prepare the second structure layer 6, see Fig.16 and Fig.17 ;

[0101] Step S11, bonding the lower surface of the single crystal silicon wafer to the surface of the glass substrate to form a closed cavity 8 between the single crystal silicon wafer and the glass substrate; wherein the glass substrate serves as the second substrate 9, see Fig.18 .

[0102] In the above-mentioned embodiments, the method for preparing the low-temperature drift MEMS piezoresistive pressure sensor is relatively reasonable, and is helpful for simply and quickly preparing the above-mentioned pressure sensor.

[0103] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A low temperature drift MEMS piezoresistive pressure sensor, characterized in that: include: A first substrate and a second substrate, wherein a first groove is provided on a lower surface of the first substrate, and the second substrate is fixed to the first substrate and closes the first groove; A second annular groove is arranged around the bottom surface of the first groove; the first substrate is made of single crystal silicon; A first structural layer and a second structural layer, wherein a third groove is provided in the middle of the upper surface of the first substrate; the first structural layer is provided in the third groove, the second structural layer is provided in the second groove, and the second structural layer surrounds the outer side of the first structural layer; the first structural layer and the second structural layer are both made of metal; A varistor strip, wherein a plurality of varistor strips are arranged on the upper surface of the first substrate around the first structural layer, and the plurality of varistor strips all correspond to the second structural layer; The first structural layer, the second structural layer, the first substrate below the first structural layer, and the first substrate above the second structural layer together constitute a pressure sensitive film, and the multiple piezoresistive strips are all located in the pressure sensitive film and are used to measure pressure according to the deformation of the pressure sensitive film.

2. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: Also including a passivation layer; The passivation layer is arranged around the upper surface of the first substrate and covers the varistor strip.

3. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: It also includes ohmic contacts; Two ends of the varistor strip are respectively provided with ohmic contacts, and the ohmic contacts are used to realize electrical connection between the varistor strip and the lead wire.

4. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: A projection of the first structure layer on the upper surface of the first substrate does not overlap with a projection of the second structure layer on the upper surface of the first substrate; The sum of a projection area of ​​the first structure layer on the upper surface of the first substrate and a projection area of ​​the second structure layer on the upper surface of the first substrate is the same as a projection area of ​​the bottom surface of the first groove on the upper surface of the first substrate.

5. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The material of the first structural layer is the same as that of the second structural layer and is at least one of lead, gold, zinc, magnesium, aluminum and copper.

6. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The first structural layer has four arc corners, and adjacent arc corners are connected by arc lines.

7. The low temperature drift MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The thickness of the first structural layer and the second structural layer are both half of the thickness of the pressure sensitive film.

8. The low temperature drift MEMS piezoresistive pressure sensor according to claim 3, characterized in that: The thickness of the varistor strip is 1 μm-3 μm, and the thickness of the ohmic contact is 1 μm-3 μm.

9. The low temperature drift MEMS piezoresistive pressure sensor according to claim 2, characterized in that: The material of the passivation layer is at least one of silicon oxide and silicon nitride, and the thickness is 0.1 μm-5 nm.

10. A method for preparing a low temperature drift MEMS piezoresistive pressure sensor, characterized in that: The steps include: Step S1, preparing a single crystal silicon wafer as a first substrate; Step S2, performing P-type doping on the upper surface of the single crystal silicon wafer to form a varistor; Step S3, performing P-type heavy doping at both ends of the varistor to form an ohmic contact region; Step S4, depositing a silicon dioxide layer on the upper surface of the single crystal silicon wafer; Step S5, photolithography the silicon dioxide layer to expose the single crystal silicon wafer; wherein the silicon dioxide layer after photolithography serves as a passivation layer; Step S6, performing photolithography on the upper surface of the single crystal silicon wafer to form a third groove; Step S7, sputtering metal in the third groove and performing photolithography to prepare a first structural layer; Step S8, etching the lower surface of the single crystal silicon wafer to form a first groove; Step S9, etching the periphery of the bottom surface of the first groove to form a second groove; Step S10, performing magnetron sputtering and photolithography in the second groove to prepare a second structural layer; Step S11, bonding the lower surface of the single crystal silicon wafer to the surface of the glass substrate to form a closed cavity between the single crystal silicon wafer and the glass substrate; wherein the glass substrate serves as a second substrate.

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