MEMS piezoresistive pressure sensor and preparation method thereof

Abstract

The invention provides an MEMS piezoresistive pressure sensor and a preparation method thereof. The pressure sensor comprises a first substrate, a first piezoresistor strip, a second piezoresistor strip, a second substrate, an upper polar plate and a lower polar plate, a first groove and a second groove are formed in the lower surface of the first substrate, the annular second groove is annularly formed in the outer side of the first groove, and an annular boss is formed between the first groove and the second groove; the first piezoresistor strip corresponds to the first groove, and the second piezoresistor strip corresponds to the second groove; the upper polar plate is arranged at the bottom of the annular boss; a lower polar plate is arranged at the top of the second substrate, and a bulge matched with the third groove is arranged at the top of the lower polar plate; and the upper surface of the second substrate is bonded with the lower surface of the first substrate. One technical effect of the invention is that not only the wide measuring range is realized, but also the high comprehensive performance can be maintained in the full measuring range.

Description

Technical Field

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

[0002] MEMS (Micro-Electro-Mechanical System) piezoresistive pressure sensors occupy an important position among many MEMS pressure sensors due to their advantages of high sensitivity, good frequency effect, low hysteresis and good stability, and are widely used in many important fields such as industrial production, medical health, aerospace, ocean exploration, and national defense and military. The common structures of MEMS piezoresistive pressure sensors can be roughly divided into two categories: square membrane structure and rectangular membrane structure according to the shape of the pressure-sensitive film. The square membrane structure is suitable for medium and low pressure application scenarios, while the rectangular membrane structure is suitable for medium and high pressure application scenarios. With the development of society, various fields not only put forward higher requirements on the performance of MEMS piezoresistive pressure sensors, but also hope that the sensors have a wider range.

[0003] However, the use of square diaphragm structures to design MEMS piezoresistive pressure sensors will lead to a rapid increase in nonlinearity when expanding high-pressure applications, while the use of rectangular diaphragm structures will significantly reduce sensitivity when expanding low-pressure applications. Therefore, these two commonly used structures have limitations in maintaining high performance and wide range at the same time. 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 MEMS piezoresistive pressure sensor and a method for preparing the same.

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

[0006] A first substrate, wherein a first groove and a second groove are provided on the lower surface of the first substrate, wherein the first groove is located in the middle of the lower surface of the first substrate, and the second groove is annularly arranged outside the first groove, and an annular boss is formed between the first groove and the second groove; wherein the depth of the first groove is greater than the depth of the second groove;

[0007] A plurality of first varistor strips and a plurality of second varistor strips, wherein the plurality of first varistor strips and the plurality of second varistor strips are both arranged on the upper surface of the first substrate, and the first varistor strips correspond to the first grooves, and the second varistor strips correspond to the second grooves; the plurality of first varistor strips form a first Wheatstone bridge, and the plurality of second varistor strips form a second Wheatstone bridge, and the first Wheatstone bridge and the second Wheatstone bridge are connected in series;

[0008] A second substrate, an upper electrode plate and a lower electrode plate, wherein the upper electrode plate is disposed at the bottom of the annular boss, and a third groove is provided at the bottom of the upper electrode plate; the lower electrode plate is disposed at the top of the second substrate, and a protrusion matching with the third groove is provided at the top of the lower electrode plate; the upper surface of the second substrate is bonded to the lower surface of the first substrate, and a part of the protrusion is embedded in the third groove, and the upper electrode plate can move downward relative to the lower electrode plate to a preset position;

[0009] The area above the second substrate and corresponding to the first groove forms a first pressure-sensitive thin film structure, and the area above the second substrate and corresponding to the first groove, the annular protrusion and the second groove together form a second pressure-sensitive thin film structure.

[0010] Optionally, the MEMS piezoresistive pressure sensor further includes a first ohmic contact and a second ohmic contact;

[0011] Two of the first ohmic contacts are respectively provided at both ends of the first piezoresistive strip and both ends of the second piezoresistive strip;

[0012] The second ohmic contact is provided on the upper surface of the first substrate, and the second ohmic contact is located between the first piezoresistive strip and the second piezoresistive strip and corresponds to the position of the annular boss.

[0013] Optionally, the MEMS piezoresistive pressure sensor further includes a first passivation layer and a second passivation layer;

[0014] The first passivation layer is disposed on the upper side of the first substrate and covers the first piezoresistive strip and the second piezoresistive strip; the second passivation layer is disposed on the upper side of the first passivation layer.

[0015] Optionally, the MEMS piezoresistive pressure sensor further includes a connection unit;

[0016] The connection unit is provided on both the first passivation layer and the second passivation layer, and the connection unit is used for electrically connecting to the first piezoresistive strip and the second piezoresistive strip.

[0017] Optionally, the shape of the annular boss is a square frame shape.

[0018] Optionally, the materials of the first piezoresistive strip, the second piezoresistive strip, the first ohmic contact and the second ohmic contact are all single-crystalline silicon.

[0019] Optionally, the thicknesses of both the first piezoresistive strip and the second piezoresistive strip are 1 μm - 3 μm;

[0020] The thickness of the first ohmic contact and the second ohmic contact are both 3 μm-6 μm.

[0021] Optionally, the first substrate is made of single crystal silicon, and has a thickness of 500 μm.

[0022] Optionally, the upper plate is electrically connected to the first substrate, and the lower plate is electrically connected to the first substrate;

[0023] When a bias voltage is applied to the first substrate, an electrostatic repulsive force is formed between the upper plate and the lower plate.

[0024] According to a first aspect of the present invention, a method for preparing a MEMS piezoresistive pressure sensor is provided, comprising the following steps:

[0025] Step 1, providing a single crystal silicon wafer as a first substrate;

[0026] Step 2, performing ion implantation of P-type impurities on the upper surface of the single crystal silicon wafer to form a first varistor strip and a second varistor strip;

[0027] Step 3, respectively performing ion implantation on both ends of the first varistor strip and the second varistor strip to form a first ohmic contact, and performing ion implantation on the upper surface of the first substrate to form a second ohmic contact;

[0028] Step 4, performing chemical vapor deposition on the upper surface of the single crystal silicon wafer to form a first passivation layer; wherein the first passivation layer covers the first varistor strip and the second varistor strip;

[0029] Step 5, dry etching the lower surface of the single crystal silicon wafer to form a square shallow groove;

[0030] Step 6, dry-etching the bottom of the square shallow groove to form an annular boss; wherein a second groove is formed on the outer side of the annular boss;

[0031] Step 7, dry etching the inner side of the annular boss to form a first groove;

[0032] Step 8, sputtering metal on the lower surface of the single crystal silicon wafer to form a first metal layer, and etching the first metal layer;

[0033] Step 9, etching the lower surface of the first metal layer and forming a third groove to prepare an upper electrode plate;

[0034] Step 10, performing photolithography on the first passivation layer to form a first through hole; wherein the first through hole is disposed above the first ohmic contact and the second ohmic contact;

[0035] Step 11, sputtering metal on the surface of the first passivation layer and etching to form a connection unit in the first passivation layer;

[0036] Step 12, performing chemical vapor deposition on the surface of the first passivation layer to form a second passivation layer, and performing photolithography on the second passivation layer to form a second through hole;

[0037] Step 13, sputtering metal on the surface of the second passivation layer and etching to form a connection unit in the second passivation layer;

[0038] Step 14, providing a piece of borosilicate glass as a second substrate;

[0039] Step 15: sputtering and forming a second metal layer on the upper surface of the second substrate, and etching the second metal layer;

[0040] Step 16: etching the upper surface of the second metal layer and forming a protrusion to prepare a lower electrode plate;

[0041] Step 17: Bond the upper surface of the second substrate to the lower surface of the first substrate to form a closed cavity to complete the preparation of the pressure sensor; wherein a portion of the protrusion of the lower electrode plate is embedded in the third groove of the upper electrode plate.

[0042] A technical effect of the present invention is:

[0043] In the embodiment of the present application, the MEMS piezoresistive pressure sensor can reasonably switch between the first pressure-sensitive film structure and the second pressure-sensitive film structure when dealing with low pressure and high pressure, thereby significantly expanding the range of the MEMS piezoresistive pressure sensor while still maintaining a high overall performance.

[0044] Furthermore, when the MEMS piezoresistive pressure sensor faces low pressure, the first pressure-sensitive film structure, which plays a secondary role, will also cause the multiple first piezoresistance strips to form a first Wheatstone bridge to generate an output voltage, and contribute to the MEMS piezoresistive pressure sensor generating a final output voltage; similarly, when the MEMS piezoresistive pressure sensor faces high pressure, the second pressure-sensitive film structure will also play a secondary role after the annular boss ends its suspended state, continuing to cause the multiple second piezoresistance strips to form a second Wheatstone bridge to generate an output voltage, and contribute to the MEMS piezoresistive pressure sensor generating a final output voltage, thereby effectively improving the sensitivity of the MEMS piezoresistive pressure sensor within the full-scale range.

[0045] Moreover, during the test of the MEMS piezoresistive pressure sensor, the upper plate and the lower plate have the same electric potential, so that an electrostatic repulsion is formed between the two. The cooperation between the third groove of the upper plate and the protrusion of the lower plate further enhances the electrostatic repulsion, thereby preventing the upper plate and the lower plate from sticking to each other and causing the MEMS piezoresistive pressure sensor to fail, significantly improving the reliability of the MEMS piezoresistive pressure sensor.

[0046] In addition, the annular boss of the first substrate of the MEMS piezoresistive pressure sensor can play the role of both a mass block in the stress concentration area of ​​the second pressure-sensitive film structure and a beam below the non-stress concentration area of ​​the second pressure-sensitive film structure, thereby effectively improving the sensitivity and linearity of the MEMS piezoresistive pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A cross-sectional view of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0048] Figure 2 A top view of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0049] Figure 3 A top view of a first substrate of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0050] Figure 4 A cross-sectional view corresponding to step 1 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0051] Figure 5 A cross-sectional view corresponding to step 2 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0052] Figure 6 A top view corresponding to step 2 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0053] Figure 7 A cross-sectional view corresponding to step 3 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0054] Figure 8 A top view corresponding to step 3 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0055] Fig. 9 A cross-sectional view corresponding to step 4 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0056] Fig.10A cross-sectional view corresponding to step 5 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0057] Fig.11 A bottom view corresponding to step 5 of the method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0058] Fig.12 A cross-sectional view corresponding to step 6 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0059] Fig.13 A bottom view corresponding to step 6 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0060] Fig.14 A cross-sectional view corresponding to step 7 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0061] Fig.15 A bottom view corresponding to step 7 of the method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0062] Fig.16 A cross-sectional view corresponding to step 8 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0063] Fig.17 A bottom view corresponding to step 8 of the method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0064] Fig.18 A cross-sectional view corresponding to step 9 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0065] Fig.19 A top view corresponding to step 10 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0066] Fig. 20 A cross-sectional view corresponding to step 11 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0067] Fig.21 A top view corresponding to step 11 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0068] Fig. 22 A cross-sectional view corresponding to step 12 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0069] Fig.23 A top view corresponding to step 12 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0070] Fig.24 A cross-sectional view corresponding to step 13 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0071] Fig.25 A top view corresponding to step 13 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0072] Fig.26 A cross-sectional view corresponding to step 14 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0073] Fig. 27 A cross-sectional view corresponding to step 15 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0074] Fig.28 A top view corresponding to step 15 of a method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0075] Fig.29 It is a cross-sectional view corresponding to step 16 of the method for preparing a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0076] In the figure: 1, connecting unit; 21, first passivation layer; 22, second passivation layer; 31, first varistor strip; 32, second varistor strip; 4, first ohmic contact; 5, first substrate; 6, second ohmic contact; 7, annular boss; 8, upper electrode plate; 9, first pressure-sensitive film structure; 10, closed cavity; 11, second pressure-sensitive film structure; 12, lower electrode plate; 13, second substrate. DETAILED DESCRIPTION

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] According to a first aspect of the present invention, see Figure 1 , provides a MEMS piezoresistive pressure sensor, which not only has a wider range, but also maintains high comprehensive performance within the full range.

[0083] Specifically, the MEMS piezoresistive pressure sensor includes:

[0084] A first substrate 5, wherein a first groove and a second groove are provided on the lower surface of the first substrate 5, wherein the first groove is located in the middle of the lower surface of the first substrate 5, and the second groove is annularly arranged on the outer side of the first groove, and an annular boss 7 is formed between the first groove and the second groove; wherein the depth of the first groove is greater than the depth of the second groove;

[0085] A plurality of first varistor strips 31 and a plurality of second varistor strips 32, wherein the plurality of first varistor strips 31 and the plurality of second varistor strips 32 are both arranged on the upper surface of the first substrate 5, and the first varistor strips 31 correspond to the first grooves, and the second varistor strips 32 correspond to the second grooves; the plurality of first varistor strips 31 form a first Wheatstone bridge, and the plurality of second varistor strips 32 form a second Wheatstone bridge, and the first Wheatstone bridge and the second Wheatstone bridge are connected in series;

[0086] A second substrate 13, an upper electrode plate 8 and a lower electrode plate 12, wherein the upper electrode plate 8 is arranged at the bottom of the annular boss 7, and a third groove is arranged at the bottom of the upper electrode plate 8; a lower electrode plate 12 is arranged at the top of the second substrate 13, and a protrusion matching the third groove is arranged at the top of the lower electrode plate 12; the upper surface of the second substrate 13 is bonded to the lower surface of the first substrate 5, and part of the protrusion is embedded in the third groove, and the upper electrode plate 8 can move downward to a preset position relative to the lower electrode plate 12;

[0087] The area above the second substrate 13 and corresponding to the first groove constitutes a first pressure-sensitive film structure 9, and the area above the second substrate 13 and corresponding to the first groove, the annular protrusion, and the second groove together constitute a second pressure-sensitive film structure 11. The first pressure-sensitive film structure 9 includes the upper middle area of ​​the first substrate 5 corresponding to the first groove and the first piezoresistive strip 31; the first pressure-sensitive film structure 9 includes the annular protrusion, the second piezoresistive strip 32, the upper peripheral area of ​​the first substrate 5 corresponding to the second groove and the annular protrusion, and the first pressure-sensitive film structure 9.

[0088] In the embodiment of the present application, the MEMS piezoresistive pressure sensor can reasonably switch between the first pressure-sensitive film structure 9 and the second pressure-sensitive film structure 11 when dealing with low pressure and high pressure, thereby significantly expanding the range of the MEMS piezoresistive pressure sensor while still maintaining a high overall performance.

[0089] Furthermore, when the MEMS piezoresistive pressure sensor faces low pressure, the first pressure-sensitive film structure 9, which plays a secondary role, will also cause the multiple first piezoresistance strips 31 to form a first Wheatstone bridge to generate an output voltage, and contribute to the final output voltage generated by the MEMS piezoresistive pressure sensor; similarly, when the MEMS piezoresistive pressure sensor faces high pressure, the second pressure-sensitive film structure 11 will also play a secondary role after the annular boss 7 ends its suspended state, and continue to cause the multiple second piezoresistance strips 32 to form a second Wheatstone bridge to generate an output voltage, and contribute to the final output voltage generated by the MEMS piezoresistive pressure sensor, thereby effectively improving the sensitivity of the MEMS piezoresistive pressure sensor within the full-scale range.

[0090] Moreover, during the test of the MEMS piezoresistive pressure sensor, the upper electrode 8 and the lower electrode 12 have the same electric potential, so that an electrostatic repulsion is formed between the two. The cooperation between the third groove of the upper electrode 8 and the protrusion of the lower electrode 12 further enhances the electrostatic repulsion, thereby preventing the upper electrode 8 and the lower electrode 12 from adhering to each other and causing the MEMS piezoresistive pressure sensor to fail, thereby significantly improving the reliability of the MEMS piezoresistive pressure sensor.

[0091] In addition, the annular boss 7 of the first substrate 5 of the MEMS piezoresistive pressure sensor can play the role of a mass block in the stress concentration area of ​​the second pressure-sensitive film structure 11, and can also play the role of a beam below the non-stress concentration area of ​​the second pressure-sensitive film structure 11, thereby effectively improving the sensitivity and linearity of the MEMS piezoresistive pressure sensor.

[0092] In a specific implementation, see Figure 2 , the first pressure-sensitive film structure 9 is a rectangular film structure; and the second pressure-sensitive film structure 11 is a square film structure.

[0093] Exemplarily, the upper surface of the second substrate 13 is sealed to the outer area of ​​the bottom of the first substrate 5 to form a vacuum closed cavity 1010. The first substrate 5 and the second substrate 13 are both made of borosilicate glass with a thickness of 500 μm-1000 μm.

[0094] It should be noted that the working principle of the MEMS piezoresistive pressure sensor of the present invention is as follows:

[0095] When the input pressure is low pressure and applied to the surface of the MEMS piezoresistive pressure sensor, the annular boss 7 is in a suspended state, which makes the second pressure sensitive film structure 11 in the main working state and makes Figure 3 The first piezoresistors 31 numbered R1, R2, R3 and R4 are in the stress concentration area (square film), so that the second Wheatstone bridge connected by R1, R2, R3 and R4 generates an output voltage. As the pressure applied to the MEMS piezoresistive pressure sensor increases further, the annular boss 7 will continue to move downward until the upper plate 8 and the lower plate 12 contact each other and finally end the suspended state, so that the first pressure sensitive film structure 9 replaces the second pressure sensitive film in the main working state, and makes Figure 3 The first piezoresistive resistor strip 31 numbered R5, R6, R7 and R8 is located in the new stress concentration area (rectangular membrane), so that the first Wheatstone bridge connected by R5, R6, R7 and R8 generates an output voltage, thereby completing the measurement of the full-scale pressure of the MEMS piezoresistive pressure sensor of the present invention.

[0096] Based on the above content, it can be known that the MEMS piezoresistive pressure sensor of the present invention can reasonably switch between the square membrane structure and the rectangular membrane structure when dealing with low pressure and high pressure, thereby meeting the need for the MEMS piezoresistive pressure sensor to significantly expand the range while maintaining high performance. In addition, during operation, the MEMS piezoresistive pressure sensor applies a certain voltage bias to the first substrate 5 so that the upper electrode 8 and the lower electrode 12 have the same potential, and electrostatic repulsion is generated between the two electrodes. The third groove at the bottom of the upper electrode 8 and the convex design at the top of the lower electrode 12 increase the relative surface area between the upper electrode 8 and the lower electrode 12, thereby making the electrostatic repulsion more significant. Such a design can effectively prevent the upper electrode 8 and the lower electrode 12 from adhering to each other and causing the pressure sensor to fail, thereby improving the reliability of the pressure sensor.

[0097] Optionally, the MEMS piezoresistive pressure sensor further includes a first ohmic contact 4 and a second ohmic contact 6;

[0098] Two first ohmic contacts 4 are respectively disposed at two ends of the first varistor strip 31 and two ends of the second varistor strip 32;

[0099] The second ohmic contact 6 is disposed on the upper surface of the first substrate 5 , and the second ohmic contact 6 is located between the first varistor strip 31 and the second varistor strip 32 and corresponds to the position of the annular boss 7 .

[0100] In the above embodiment, the electrical connection between the first varistor strip 31 and the second varistor strip 32 can be stably achieved through the first ohmic contact 4 and the second ohmic contact 6 .

[0101] Optionally, the MEMS piezoresistive pressure sensor further includes a first passivation layer 21 and a second passivation layer 22;

[0102] The first passivation layer 21 is disposed on the upper side of the first substrate 5 and covers the first varistor strip 31 and the second varistor strip 32 ; the second passivation layer 22 is disposed on the upper side of the first passivation layer 21 .

[0103] In the above embodiment, the first passivation layer 21 and the second passivation layer 22 can better protect the first piezoresistor strip 31 and the second piezoresistor strip 32, and at the same time, a double-layer wiring design is adopted in the first passivation layer 21 and the second passivation layer 22 to ensure the stability of the electrical connection of the MEMS piezoresistive pressure sensor.

[0104] Exemplarily, the materials of the first passivation layer 21 and the second passivation layer 22 are at least one of silicon oxide or silicon nitride, and the thickness is 100 nm-5000 nm.

[0105] Optionally, the MEMS piezoresistive pressure sensor further includes a connection unit 1;

[0106] Both the first passivation layer 21 and the second passivation layer 22 are provided with the connection unit 1, and the connection unit 1 is used for electrically connecting the first piezoresistive strip 31 and the second piezoresistive strip 32. Exemplarily, the connection unit 1 is a lead and a pad.

[0107] In the above embodiment, a first through hole is provided in the first passivation layer 21, and a second through hole is provided in the second passivation layer 22. The leads in the first through hole and the second through hole can electrically connect the first piezoresistive strip 31 and the second piezoresistive strip 32 to the pads on the surface of the second passivation layer 22.

[0108] Exemplarily, the material of the connection unit 1 is at least one of aluminum, copper, platinum, titanium, and gold, and the thickness is 50 nm - 500 nm.

[0109] In a specific embodiment, referring to Figure 3 、 Figure 6 and Figure 8 , the piezoresistive strips are respectively divided and named into two categories, R1, R2, R3 and R4 (i.e., the second piezoresistive strip 32) and R5, R6, R7 and R8 (i.e., the first piezoresistive strip 31), according to whether their arrangement positions belong to the stress concentration area of the second pressure-sensitive thin film structure 11 or the first pressure-sensitive thin film structure 9. Multiple first piezoresistive strips 31 can form a first Wheatstone bridge through leads and pads, and multiple second piezoresistive strips 32 can form a second Wheatstone bridge through leads and pads. The output ends of the first Wheatstone bridge and the second Wheatstone bridge are then serially output through the leads and pads. The second ohmic contact 6 has two, and their top views are rectangular and are arranged vertically between the P-type piezoresistive strips numbered R1 and R5 and between the P-type piezoresistive strips numbered R4 and R8.

[0110] Both the first piezoresistive strip 31 and the second piezoresistive strip 32 are P-type piezoresistive strips. The first ohmic contact 4 is a P-type ohmic contact; the second ohmic contact 6 is an N-type ohmic contact.

[0111] Optionally, the shape of the annular boss 7 is a double-square shape. This helps to ensure the stability of the downward movement of the second pressure-sensitive thin film structure 11.

[0112] Optionally, the materials of the first piezoresistive strip 31, the second piezoresistive strip 32, the first ohmic contact 4, and the second ohmic contact 6 are all single-crystalline silicon. This makes the performance of the MEMS piezoresistive pressure sensor relatively stable and helps to stably measure the pressure.

[0113] Optionally, the thickness of the first varistor strip 31 and the second varistor strip 32 are both 1 μm-3 μm;

[0114] The thickness of the first ohmic contact 4 and the second ohmic contact 6 are both 3 μm-6 μm, which helps to stably realize the electrical connection between the first varistor strip 31 and the second varistor strip 32 .

[0115] Optionally, the first substrate 5 is made of single crystal silicon, and the thickness of the first substrate 5 is 500 μm, which makes the performance and structure of the first substrate 5 relatively stable.

[0116] Optionally, the upper electrode plate 8 is electrically connected to the first substrate 5, and the lower electrode plate 12 is electrically connected to the first substrate 5;

[0117] When a bias voltage is applied to the first substrate 5 , an electrostatic repulsive force is formed between the upper electrode plate 8 and the lower electrode plate 12 .

[0118] In the above embodiment, it can be effectively ensured that the first pressure-sensitive film structure 9 and the second pressure-sensitive film structure 11 cause the upper electrode plate 8 to adhere to the lower electrode plate 12 during the movement process, thereby better ensuring the working stability of the pressure sensor.

[0119] According to a first aspect of the present invention, see Figures 1 to 29 , provides a method for preparing a MEMS piezoresistive pressure sensor, comprising the following steps:

[0120] Step 1, providing an N-type single crystal silicon wafer as a first substrate 5;

[0121] Step 2, ion implantation of P-type impurities is performed on the upper surface of the single crystal silicon wafer to form a first varistor strip 31 and a second varistor strip 32;

[0122] Step 3, respectively perform ion implantation of high-concentration P-type impurities on both ends of the first varistor strip 31 and the second varistor strip 32 to form a first ohmic contact 4, and perform N-type heavily doped ion implantation on the upper surface of the first substrate 5 to form a second ohmic contact 6;

[0123] Step 4, performing chemical vapor deposition on the upper surface of the single crystal silicon wafer to form a first passivation layer 21; wherein the first passivation layer 21 covers the first varistor strip 31 and the second varistor strip 32;

[0124] Step 5, performing shallow dry etching on the lower surface of the single crystal silicon wafer to form a square shallow groove;

[0125] Step 6, deep dry etching is performed on the bottom of the square shallow groove to form an annular boss 7; wherein a second groove is formed on the outer side of the annular boss 7;

[0126] Step 7, performing deep dry etching on the inner side of the annular boss 7 to form a first groove;

[0127] Step 8, sputtering metal on the lower surface of the single crystal silicon wafer to form a first metal layer, and etching the first metal layer to form a "return" shaped metal layer;

[0128] Step 9, etching the lower surface of the first metal layer (ie, the “return” type metal layer) and forming a third groove to prepare an upper electrode plate 8;

[0129] Step 10, photolithography is performed on the first passivation layer 21 to form a first through hole; wherein the first through hole is disposed above the first ohmic contact 4 and the second ohmic contact 6;

[0130] Step 11, sputtering metal on the surface of the first passivation layer 21 and etching to form a connection unit 1 in the first passivation layer 21;

[0131] Step 12, performing chemical vapor deposition on the surface of the first passivation layer 21 to form a second passivation layer 22, and performing photolithography on the second passivation layer 22 to form a second through hole;

[0132] Step 13, sputtering metal on the surface of the second passivation layer 22 and etching to form a connection unit 1 in the second passivation layer 22;

[0133] Step 14, providing a piece of borosilicate glass as a second substrate 13;

[0134] Step 15: sputtering and forming a second metal layer on the upper surface of the second substrate 13, and etching the second metal layer to form a “return”-shaped metal layer;

[0135] Step 16: etching the upper surface of the second metal layer (ie, the “return” type metal layer) to form a protrusion to prepare the lower electrode plate 12;

[0136] Step 17: Bond the upper surface of the second substrate 13 to the lower surface of the first substrate 5 to form a closed cavity 10 to complete the preparation of the pressure sensor; wherein a portion of the protrusion of the lower electrode plate 12 is embedded in the third groove of the upper electrode plate 8.

[0137] In the above-mentioned implementation manner, the preparation method of the MEMS piezoresistive pressure sensor is reasonably designed, and the prepared MEMS piezoresistive pressure sensor not only has a wider measuring range, but also can maintain a high comprehensive performance within the full measuring range.

[0138] 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 MEMS piezoresistive pressure sensor, characterized in that: include: A first substrate, wherein a first groove and a second groove are provided on the lower surface of the first substrate, wherein the first groove is located in the middle of the lower surface of the first substrate, and the second groove is annularly arranged outside the first groove, and an annular boss is formed between the first groove and the second groove; wherein the depth of the first groove is greater than the depth of the second groove; A plurality of first varistor strips and a plurality of second varistor strips, wherein the plurality of first varistor strips and the plurality of second varistor strips are both arranged on the upper surface of the first substrate, and the first varistor strips correspond to the first grooves, and the second varistor strips correspond to the second grooves; the plurality of first varistor strips form a first Wheatstone bridge, and the plurality of second varistor strips form a second Wheatstone bridge, and the first Wheatstone bridge and the second Wheatstone bridge are connected in series; A second substrate, an upper electrode plate and a lower electrode plate, the upper electrode plate is arranged at the bottom of the annular boss, and a third groove is arranged at the bottom of the upper electrode plate; a lower electrode plate is arranged at the top of the second substrate, and a protrusion is arranged on the top of the lower electrode plate to match the third groove; the upper surface of the second substrate is bonded to the lower surface of the first substrate, and part of the protrusion is embedded in the third groove, and the upper electrode plate can be moved downward to a preset position relative to the lower electrode plate; The area above the second substrate and corresponding to the first groove constitutes a first pressure-sensitive film structure, and the area above the second substrate and corresponding to the first groove, the annular protrusion, and the second groove together constitute a second pressure-sensitive film structure.

2. The MEMS piezoresistive pressure sensor according to claim 1, characterized in that: Also included is a first ohmic contact and a second ohmic contact; Two first ohmic contacts are respectively disposed at two ends of the first varistor strip and two ends of the second varistor strip; The second ohmic contact is disposed on the upper surface of the first substrate, and the second ohmic contact is located between the first varistor strip and the second varistor strip and corresponds to the position of the annular boss.

3. The MEMS piezoresistive pressure sensor according to claim 2, characterized in that: Also comprising a first passivation layer and a second passivation layer; The first passivation layer is disposed on the upper side of the first substrate and covers the first varistor strip and the second varistor strip; the second passivation layer is disposed on the upper side of the first passivation layer.

4. The MEMS piezoresistive pressure sensor according to claim 3, characterized in that: Also included is a connection unit; The first passivation layer and the second passivation layer are both provided with the connection unit, and the connection unit is used to electrically connect the first varistor strip and the second varistor strip.

5. The MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The shape of the annular boss is a Chinese-shaped circle.

6. The MEMS piezoresistive pressure sensor according to claim 4, characterized in that: The first varistor strip, the second varistor strip, the first ohmic contact, and the second ohmic contact are all made of single crystal silicon.

7. The MEMS piezoresistive pressure sensor according to claim 2, characterized in that: The thickness of the first varistor strip and the second varistor strip are both 1 μm-3 μm; The thickness of the first ohmic contact and the second ohmic contact are both 3 μm-6 μm.

8. The MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The material of the first substrate is single crystal silicon, and the thickness of the first substrate is 500 μm.

9. The MEMS piezoresistive pressure sensor according to claim 1, characterized in that: The upper electrode plate is electrically connected to the first substrate, and the lower electrode plate is electrically connected to the first substrate; When a bias voltage is applied to the first substrate, an electrostatic repulsive force is formed between the upper plate and the lower plate.

10. A method for preparing a MEMS piezoresistive pressure sensor, characterized in that: The steps include: Step 1, providing a single crystal silicon wafer as a first substrate; Step 2, performing ion implantation of P-type impurities on the upper surface of the single crystal silicon wafer to form a first varistor strip and a second varistor strip; Step 3, respectively performing ion implantation on both ends of the first varistor strip and the second varistor strip to form a first ohmic contact, and performing ion implantation on the upper surface of the first substrate to form a second ohmic contact; Step 4, performing chemical vapor deposition on the upper surface of the single crystal silicon wafer to form a first passivation layer; wherein the first passivation layer covers the first varistor strip and the second varistor strip; Step 5, dry etching the lower surface of the single crystal silicon wafer to form a square shallow groove; Step 6, dry-etching the bottom of the square shallow groove to form an annular boss; wherein a second groove is formed on the outer side of the annular boss; Step 7, dry etching the inner side of the annular boss to form a first groove; Step 8, sputtering metal on the lower surface of the single crystal silicon wafer to form a first metal layer, and etching the first metal layer; Step 9, etching the lower surface of the first metal layer and forming a third groove to prepare an upper electrode plate; Step 10, performing photolithography on the first passivation layer to form a first through hole; wherein the first through hole is disposed above the first ohmic contact and the second ohmic contact; Step 11, sputtering metal on the surface of the first passivation layer and etching to form a connection unit in the first passivation layer; Step 12, performing chemical vapor deposition on the surface of the first passivation layer to form a second passivation layer, and performing photolithography on the second passivation layer to form a second through hole; Step 13, sputtering metal on the surface of the second passivation layer and etching to form a connection unit in the second passivation layer; Step 14, providing a piece of borosilicate glass as a second substrate; Step 15: sputtering and forming a second metal layer on the upper surface of the second substrate, and etching the second metal layer; Step 16: etching the upper surface of the second metal layer and forming a protrusion to prepare a lower electrode plate; Step 17: Bond the upper surface of the second substrate to the lower surface of the first substrate to form a closed cavity to complete the preparation of the pressure sensor; wherein a portion of the protrusion of the lower electrode plate is embedded in the third groove of the upper electrode plate.

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