A MEMS piezoresistive pressure sensor and its fabrication method

Abstract

The application provides a MEMS piezoresistive pressure sensor and a preparation method thereof. The pressure sensor comprises a first substrate, a first piezoresistive strip, a second piezoresistive strip, a second substrate, an upper electrode plate and a lower electrode plate. A first groove and a second groove are arranged on the lower surface of the first substrate. The annular second groove is arranged outside the first groove, and an annular boss is formed between the first groove and the second groove. The first piezoresistive strip corresponds to the first groove, and the second piezoresistive strip corresponds to the second groove. The bottom of the annular boss is provided with the upper electrode plate. The top of the second substrate is provided with the lower electrode plate, and the top of the lower electrode plate is provided with a protrusion matched with the third groove. The upper surface of the second substrate and the lower surface of the first substrate are bonded. One technical effect of the application is that not only a wide range is obtained, but also a high comprehensive performance is maintained in the full range.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of piezoresistive pressure sensors, and particularly relates to a MEMS piezoresistive pressure sensor and a preparation method thereof. BACKGROUND

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

[0003] However, the use of the square film structure to design the MEMS piezoresistive pressure sensor will cause the nonlinearity to rapidly increase when expanding high pressure applications, and the use of the rectangular film structure will significantly reduce the sensitivity when expanding low pressure applications. Therefore, both of the two common structures have limitations in simultaneously maintaining high performance and wide range. SUMMARY

[0004] The application aims to at least solve one of the technical problems existing in the prior art, and provides a new technical solution of a MEMS piezoresistive pressure sensor and a preparation method thereof.

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

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

[0007] A plurality of first piezoresistive strips and a plurality of second piezoresistive strips are arranged on the upper surface of the first substrate, and the first piezoresistive strips correspond to the first recess and the second piezoresistive strips correspond to the second recess; the first piezoresistive strips form a first Wheatstone bridge, the second piezoresistive 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. 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 mating with the third groove is provided at the top of the lower electrode plate; the upper surface of the second substrate and the lower surface of the first substrate are bonded, and 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 double-square 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 both the first ohmic contact and the second ohmic contact is 3μm-6μm.

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

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

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

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

[0025] Step 1: Provide a single-crystal silicon wafer as the first substrate;

[0026] Step 2: Ion implantation of P-type impurities is performed on the upper surface of the single-crystal silicon wafer to form the first varistor strip and the second varistor strip;

[0027] Step 3: Ion implantation is performed on both ends of the first varistor strip and the second varistor strip to form a first ohmic contact, and ion implantation is performed on the upper surface of the first substrate to form a second ohmic contact.

[0028] Step 4: Perform 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 is performed on the lower surface of the single-crystal silicon wafer to form a square shallow trench;

[0030] Step 6: Dry etching is performed on 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 is performed on the inner side of the annular boss to form the first groove;

[0032] Step 8: Sputter metal onto the lower surface of the single-crystal silicon wafer to form a first metal layer, and etch the first metal layer;

[0033] Step 9: Etch the lower surface of the first metal layer to form a third groove in order to prepare the upper electrode plate;

[0034] Step 10: Photolithography is performed on the first passivation layer to form a first via; wherein the first via is provided above both the first ohmic contact and the second ohmic contact;

[0035] Step 11: Sputter metal onto the surface of the first passivation layer and etch it to form the interconnect unit in the first passivation layer;

[0036] Step 12: Perform chemical vapor deposition on the surface of the first passivation layer to form a second passivation layer, and perform photolithography on the second passivation layer to form a second via.

[0037] Step 13: Sputter metal onto the surface of the second passivation layer and etch it to form the interconnect unit in the second passivation layer;

[0038] Step 14: Provide a piece of borosilicate glass as a second substrate;

[0039] Step 15: Sputter and form a second metal layer on the upper surface of the second substrate, and etch the second metal layer;

[0040] Step 16: Etch the upper surface of the second metal layer to form protrusions to prepare the 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 sealed cavity to complete the fabrication 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] One technical advantage of this invention is that:

[0043] In this embodiment, the MEMS piezoresistive pressure sensor can maintain high overall performance while significantly expanding its range by reasonably switching between the first pressure-sensitive thin film structure and the second pressure-sensitive thin film structure when dealing with low and high pressure.

[0044] Furthermore, when the MEMS piezoresistive pressure sensor is subjected to low pressure, the primary pressure-sensitive film structure, which plays a secondary role, also causes multiple primary piezoresistive strips to form a first Wheatstone bridge to generate an output voltage, contributing to the final output voltage of the MEMS piezoresistive pressure sensor. Similarly, when the MEMS piezoresistive pressure sensor is subjected to high pressure, the secondary pressure-sensitive film structure, after the annular protrusion ends its suspended state, also plays a secondary role, continuing to cause multiple secondary piezoresistive strips to form a second Wheatstone bridge to generate an output voltage, contributing to the final output voltage of the MEMS piezoresistive pressure sensor. This effectively improves the sensitivity of the MEMS piezoresistive pressure sensor within its full-scale range.

[0045] Moreover, during the testing process, the upper and lower plates of the MEMS piezoresistive pressure sensor have the same potential, which creates an electrostatic repulsion between them. The third groove on the upper plate and the protrusion on the lower plate further enhance this electrostatic repulsion, thereby preventing the upper and lower plates from sticking together and causing the MEMS piezoresistive pressure sensor to fail. This significantly improves the reliability of the MEMS piezoresistive pressure sensor.

[0046] In addition, the annular protrusion on the first substrate of the MEMS piezoresistive pressure sensor can function as both a mass block in the stress concentration area of ​​the second pressure-sensitive thin film structure and a beam below the non-stress concentration area of ​​the second pressure-sensitive thin film structure, thereby effectively improving the sensitivity and linearity of the MEMS piezoresistive pressure sensor. Attached Figure Description

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

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

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

[0050] Figure 4 This is a cross-sectional view corresponding to step 1 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

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

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

[0053] Figure 7 This is a cross-sectional view corresponding to step 3 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

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

[0055] Figure 9 This is a cross-sectional view corresponding to step 4 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0056] Figure 10This is a cross-sectional view corresponding to step 5 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0057] Figure 11 This is a bottom view corresponding to step 5 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0058] Figure 12 This is a cross-sectional view corresponding to step 6 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0059] Figure 13 This is a bottom view corresponding to step 6 of the method for fabricating a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0060] Figure 14 This is a cross-sectional view corresponding to step 7 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0061] Figure 15 This is a bottom view corresponding to step 7 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0062] Figure 16 This is a cross-sectional view corresponding to step 8 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0063] Figure 17 This is a bottom view corresponding to step 8 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0064] Figure 18 This is a cross-sectional view corresponding to step 9 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0065] Figure 19 This is a top view corresponding to step 10 of the method for fabricating a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0066] Figure 20 This is a cross-sectional view corresponding to step 11 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0067] Figure 21 This is a top view corresponding to step 11 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0068] Figure 22 This is a cross-sectional view corresponding to step 12 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0069] Figure 23 This is a top view corresponding to step 12 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0070] Figure 24 This is a cross-sectional view corresponding to step 13 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0071] Figure 25 This is a top view corresponding to step 13 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention;

[0072] Figure 26 This is a cross-sectional view corresponding to step 14 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0073] Figure 27 This is a cross-sectional view corresponding to step 15 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0074] Figure 28 This is a top view corresponding to step 15 of the fabrication method of a MEMS piezoresistive pressure sensor according to an embodiment of the present invention.

[0075] Figure 29 This is a cross-sectional view corresponding to step 16 of the fabrication method of 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 thin film structure; 10. Sealed cavity; 11. Second pressure-sensitive thin film structure; 12. Lower electrode plate; 13. Second substrate. Detailed Implementation

[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, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0078] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0079] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0080] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0081] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0082] According to a first aspect of the invention, see Figure 1 This paper presents a MEMS piezoresistive pressure sensor that not only has a wide measurement range but also maintains high overall performance across the entire measurement range.

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

[0084] A first substrate 5 has a first groove and a second groove on its lower surface. The first groove is located in the middle of the lower surface of the first substrate 5, and the annular second groove is arranged around the outside of the first groove. An annular boss 7 is formed between the first groove and the second groove. The depth of the first groove is greater than the depth of the second groove.

[0085] Multiple first varistor strips 31 and multiple second varistor strips 32 are disposed on the upper surface of the first substrate 5, with the first varistor strips 31 corresponding to the first groove and the second varistor strips 32 corresponding to the second groove; the multiple first varistor strips 31 form a first Wheatstone bridge and the multiple second varistor strips 32 form a second Wheatstone bridge, with the first Wheatstone bridge and the second Wheatstone bridge connected in series;

[0086] The second substrate 13, the upper electrode plate 8, and the lower electrode plate 12 are provided. The upper electrode plate 8 is disposed at the bottom of the annular protrusion 7, and the bottom of the upper electrode plate 8 is provided with a third groove. The lower electrode plate 12 is disposed at the top of the second substrate 13, and the top of the lower electrode plate 12 is provided with a protrusion that cooperates with the third groove. The upper surface of the second substrate 13 and the lower surface of the first substrate 5 are bonded together, and part of the protrusion is embedded in the third groove. The upper electrode plate 8 can be moved downward relative to the lower electrode plate 12 to a preset position.

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

[0088] In this embodiment, the MEMS piezoresistive pressure sensor can maintain high overall performance while significantly expanding its range by reasonably switching between the first pressure-sensitive thin film structure 9 and the second pressure-sensitive thin film structure 11 when dealing with low and high pressure.

[0089] Furthermore, when the MEMS piezoresistive pressure sensor is subjected to low pressure, the first pressure-sensitive thin film structure 9, which plays a secondary role, also causes multiple first piezoresistive strips 31 to form a first Wheatstone bridge to generate an output voltage, contributing to the final output voltage of the MEMS piezoresistive pressure sensor. Similarly, when the MEMS piezoresistive pressure sensor is subjected to high pressure, the second pressure-sensitive thin film structure 11 also plays a secondary role after the annular boss 7 ends its suspended state, continuing to cause multiple second piezoresistive strips 32 to form a second Wheatstone bridge to generate an output voltage, contributing to the final output voltage of the MEMS piezoresistive pressure sensor, thereby effectively improving the sensitivity of the MEMS piezoresistive pressure sensor within its full-scale range.

[0090] Moreover, during the testing process, the upper electrode plate 8 and the lower electrode plate 12 of this MEMS piezoresistive pressure sensor have the same potential, which creates an electrostatic repulsion between them. The third groove of the upper electrode plate 8 and the protrusion of the lower electrode plate 12 further enhance this electrostatic repulsion, thereby preventing the upper electrode plate 8 and the lower electrode plate 12 from sticking together and causing the MEMS piezoresistive pressure sensor to fail, thus significantly improving the reliability of the MEMS piezoresistive pressure sensor.

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

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

[0093] For example, the upper surface of the second substrate 13 is sealed to the outer bottom region of the first substrate 5, thereby forming a vacuum-sealed cavity 1010. Both the first substrate 5 and the second substrate 13 are made of borosilicate glass with a thickness of 500μm-1000μm.

[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 and applied to the surface of the MEMS piezoresistive pressure sensor, the annular protrusion 7 is in a suspended state, which puts the second pressure-sensitive thin film structure 11 into its main working state, and makes... Figure 3 The first piezoresistive strips 31, numbered R1, R2, R3, and R4 respectively, are located in the stress concentration area (square film), thereby causing the second Wheatstone bridge formed by R1, R2, R3, and R4 to generate an output voltage. As the pressure applied to this MEMS piezoresistive pressure sensor further increases, the annular protrusion 7 will continue to move downwards until the upper electrode 8 and the lower electrode 12 come into contact with each other, finally ending the suspended state. This allows the first pressure-sensitive thin film structure 9 to take over the second pressure-sensitive thin film and enter the main working state, thus enabling... Figure 3 The first piezoresistive strip 31, composed of R5, R6, R7 and R8, is located in a new stress concentration area (rectangular film), thereby causing the first Wheatstone bridge connected by R5, R6, R7 and R8 to generate an output voltage, thus completing the full-range pressure measurement of the MEMS piezoresistive pressure sensor of the present invention.

[0096] Based on the above, it can be seen that the MEMS piezoresistive pressure sensor of the present invention can reasonably switch between square and rectangular film structures when dealing with low and high pressures, thereby meeting the requirement of significantly expanding the measurement range of the MEMS piezoresistive pressure sensor while maintaining high performance. Furthermore, during operation, the MEMS piezoresistive pressure sensor applies a certain voltage bias to the first substrate 5, making the potentials of the upper electrode 8 and the lower electrode 12 the same. This generates electrostatic repulsion between the two electrodes. The third groove at the bottom of the upper electrode 8 and the protrusion at the top of the lower electrode 12 increase the relative surface area between the upper electrode 8 and the lower electrode 12, making the electrostatic repulsion more significant. This design effectively prevents the upper electrode 8 and the lower electrode 12 from sticking together, causing pressure sensor failure, thereby improving the reliability of the pressure sensor.

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

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

[0099] The upper surface of the first substrate 5 is provided with the second ohmic contact 6, 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 protrusion 7.

[0100] In the above embodiments, the electrical connection between the first ohmic contact 4 and the second ohmic contact 6 can be achieved relatively stably.

[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 embodiments, the first passivation layer 21 and the second passivation layer 22 can better protect the first piezoresistive strip 31 and the second piezoresistive strip 32. 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] For example, the first passivation layer 21 and the second passivation layer 22 are both made of at least one of silicon oxide or silicon nitride, and have a thickness of 100nm-5000nm.

[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 pad 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 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 connected in series 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 crystal 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 both the first varistor strip 31 and the second varistor strip 32 is 1μm-3μm;

[0114] The thickness of both the first ohmic contact 4 and the second ohmic contact 6 is 3μm-6μm. This helps to stabilize 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. This 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 repulsion is formed between the upper electrode 8 and the lower electrode 12.

[0118] In the above embodiments, it is possible to effectively ensure that the upper electrode 8 and the lower electrode 12 stick together during the movement of the first pressure-sensitive thin film structure 9 and the second pressure-sensitive thin film structure 11, thereby better ensuring the working stability of the pressure sensor.

[0119] According to a first aspect of the invention, see Figures 1 to 29 A method for fabricating a MEMS piezoresistive pressure sensor is provided, comprising the following steps:

[0120] Step 1: Provide an N-type single-crystal silicon wafer as the 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 the first varistor strip 31 and the second varistor strip 32;

[0122] Step 3: High-concentration P-type impurity ion implantation is performed on both ends of the first varistor strip 31 and the second varistor strip 32 to form the first ohmic contact 4, and N-type heavily doped ion implantation is performed on the upper surface of the first substrate 5 to form the second ohmic contact 6.

[0123] Step 4: Perform 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: Perform shallow dry etching on the lower surface of the single-crystal silicon wafer to form a square shallow trench.

[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: Deep dry etching is performed on the inner side of the annular boss 7 to form the first groove;

[0127] Step 8: Sputter metal onto the lower surface of the single-crystal silicon wafer to form a first metal layer, and etch the first metal layer to form a "U"-shaped metal layer;

[0128] Step 9: Etch the lower surface of the first metal layer (i.e., the "U"-shaped metal layer) to form a third groove in order to prepare the 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 provided above both the first ohmic contact 4 and the second ohmic contact 6;

[0130] Step 11: Sputter metal onto the surface of the first passivation layer 21 and etch it to form the connection unit 1 in the first passivation layer 21;

[0131] Step 12: Perform chemical vapor deposition on the surface of the first passivation layer 21 to form a second passivation layer 22, and perform photolithography on the second passivation layer 22 to form a second via.

[0132] Step 13: Sputter metal onto the surface of the second passivation layer 22 and etch it to form the connection unit 1 in the second passivation layer 22;

[0133] Step 14: Provide a piece of borosilicate glass as a second substrate 13;

[0134] Step 15: Sputter and form a second metal layer on the upper surface of the second substrate 13, and etch the second metal layer to form a "U"-shaped metal layer;

[0135] Step 16: Etch the upper surface of the second metal layer (i.e., the "U"-shaped metal layer) to form protrusions, in order to prepare the lower electrode plate 12;

[0136] Step 17: The upper surface of the second substrate 13 and the lower surface of the first substrate 5 are bonded together to form a sealed cavity 10 to complete the fabrication 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 embodiments, the fabrication method of the MEMS piezoresistive pressure sensor is reasonably designed, and the fabricated MEMS piezoresistive pressure sensor not only has a wide range, but also maintains high comprehensive performance across the entire range.

[0138] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled 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 by, The application relates to a pressure sensor, which comprises the following parts: a first substrate, a lower surface of the first substrate being provided with a first groove and a second groove, the first groove being located in the middle of the lower surface of the first substrate, the second groove being annular and being located outside the first groove, and a ring-shaped boss being formed between the first groove and the second groove; the depth of the first groove is greater than that of the second groove; a plurality of first pressure-sensitive resistors and a plurality of second pressure-sensitive resistors, the first pressure-sensitive resistors and the second pressure-sensitive resistors being arranged on the upper surface of the first substrate, the first pressure-sensitive resistors corresponding to the first groove, and the second pressure-sensitive resistors corresponding to the second groove; the first pressure-sensitive resistors form a first Wheatstone bridge, and the second pressure-sensitive resistors form a second Wheatstone bridge, the first Wheatstone bridge and the second Wheatstone bridge being connected in series; a second substrate, an upper plate and a lower plate, the bottom of the ring-shaped boss being provided with the upper plate, the bottom of the upper plate being provided with a third groove; the top of the second substrate being provided with the lower plate, the top of the lower plate being provided with a protrusion matched with the third groove; the upper surface of the second substrate and the lower surface of the first substrate are bonded, and part of the protrusion is embedded in the third groove; the upper plate can be moved downward to a preset position relative to the lower plate; the area above the second substrate and corresponding to the first groove forms a first pressure-sensitive diaphragm structure, and the area above the second substrate and corresponding to the first groove, the ring-shaped boss and the second groove jointly form a second pressure-sensitive diaphragm structure.

2. The MEMS piezoresistive pressure sensor of claim 1, wherein, the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; 3. The MEMS piezoresistive pressure sensor of claim 2, wherein, the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; 4. The MEMS piezoresistive pressure sensor of claim 3, wherein, the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; 5. The MEMS piezoresistive pressure sensor of claim 1, wherein, the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss.

6. The MEMS piezoresistive pressure sensor of claim 4, wherein, the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; 7. The MEMS piezoresistive pressure sensor of claim 2, wherein, the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; 8. The MEMS piezoresistive pressure sensor of claim 1, wherein, the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss.

9. The MEMS piezoresistive pressure sensor of claim 1, wherein, the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss.

10. A method of fabricating a MEMS piezoresistive pressure sensor, characterized by, the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of the ring-shaped boss. the first pressure-sensitive resistors and the second pressure-sensitive resistors are respectively provided with two first ohmic contacts at two ends thereof; the upper surface of the first substrate is provided with the second ohmic contacts, and the second ohmic contacts are located between the first pressure-sensitive resistors and the second pressure-sensitive resistors and correspond to the position of Step 1, providing a single crystal silicon wafer as a first substrate; Step 2, ion implanting P-type impurities on the upper surface of the single crystal silicon wafer to form a first piezoresistor strip and a second piezoresistor strip; Step 3, ion implanting on both ends of the first piezoresistor strip and the second piezoresistor strip respectively to form a first ohmic contact, and ion implanting on the upper surface of the first substrate to form a second ohmic contact; Step 4, 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 piezoresistor strip and the second piezoresistor strip; Step 5, dry etching on the lower surface of the single crystal silicon wafer to form a square shallow groove; Step 6, dry etching on the groove bottom of the square shallow groove to form a ring-shaped boss; wherein the outer side of the ring-shaped boss forms a second groove; Step 7, dry etching on the inner side of the ring-shaped boss to form a first groove; Step 8, sputtering metal on the lower surface of the single crystal silicon wafer and forming a first metal layer, and etching the first metal layer; Step 9, etching on the lower surface of the first metal layer and forming a third groove to prepare an upper electrode plate; Step 10, photoetching on the first passivation layer to form a first through hole; wherein the first ohmic contact and the second ohmic contact are both provided with the first through hole above; Step 11, sputtering metal on the surface of the first passivation layer and etching to form a connecting unit in the first passivation layer; Step 12, chemical vapor deposition on the surface of the first passivation layer to form a second passivation layer, and photoetching 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 connecting unit in the second passivation layer; Step 14, providing a piece of borosilicate glass as a second substrate; Step 15: sputtering on the upper surface of the second substrate and forming a second metal layer, and etching the second metal layer; Step 16: etching on the upper surface of the second metal layer and forming a protrusion to prepare a lower electrode plate; Step 17: bonding the upper surface of the second substrate with the lower surface of the first substrate and forming a sealed cavity to complete the preparation of the pressure sensor; wherein part of the protrusion of the lower electrode plate is embedded in the third groove of the upper electrode plate.

Images