A MEMS piezoresistive accelerometer and a method for manufacturing the same

Abstract

The embodiment of the present disclosure provides a MEMS piezoresistive accelerometer and a preparation method, the accelerometer includes: a lower substrate; a first substrate, arranged on the lower substrate, the first substrate is provided with a cavity running through its thickness; a second substrate and a passivation layer, the second substrate is arranged on the upper surface of the first substrate, and the passivation layer is arranged on the upper surface of the second substrate; wherein the second substrate and the passivation layer corresponding to the cavity together form a sensitive beam; a piezoresistor, embedded in the second substrate; the piezoresistor is electrically connected to a frame or a mass block composed of the first substrate, the second substrate and a support frame; at least one metal electrode is arranged on the piezoresistor; an extraction electrode is arranged on the passivation layer, and the extraction electrode is electrically connected to the metal electrode; a mass block is located in the cavity, and the mass block is arranged on the lower surface of the second substrate; a permanent magnet is arranged on the mass block; a support frame is arranged on the upper surface of the second substrate; and an upper substrate is covered and placed on the upper port of the support structure.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the technical field of accelerometers, and specifically relate to a MEMS (Micro-Electro-Mechanical System) piezoresistive accelerometer and a preparation method thereof. Background Art

[0002] MEMS piezoresistive accelerometer is an acceleration test sensor with piezoresistors on sensitive beams as sensitive elements. It is one of the main devices of inertial navigation and even inertial navigation systems. Due to its advantages of small size, low power consumption, easy integration and low cost, it is currently widely used in various fields such as transportation, aviation, and national defense.

[0003] However, due to the limitations of the piezoresistive accelerometer's own structure, its sensitivity and natural frequency restrict each other. That is, as the structural sensitivity increases, the stiffness coefficient of the elastic structure will inevitably decrease, resulting in a decrease in the structural natural frequency. This seriously restricts the development and application of MEMS piezoresistive accelerometers.

[0004] Therefore, how to solve the above problems has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art and provide a MEMS piezoresistive accelerometer and a method for preparing the same.

[0006] According to one aspect of an embodiment of the present disclosure, a MEMS piezoresistive accelerometer is provided, comprising:

[0007] lower basement;

[0008] A first substrate, disposed on the lower base, wherein the first substrate is provided with a cavity running through the thickness thereof;

[0009] A second substrate and a passivation layer, wherein the second substrate is disposed on the upper surface of the first substrate, and the passivation layer is disposed on the upper surface of the second substrate; wherein the second substrate and the passivation layer corresponding to the cavity together form a sensitive beam;

[0010] A varistor is embedded in the second substrate; the varistor is electrically connected to a frame or a mass block formed by the first substrate, the second substrate and a support frame;

[0011] At least one metal electrode arranged on the varistor;

[0012] An extraction electrode is disposed on the passivation layer, and the extraction electrode is electrically connected to the metal electrode;

[0013] A mass block is located in the cavity, and the mass block is arranged on the lower surface of the second substrate;

[0014] A permanent magnet is disposed on the mass block;

[0015] A support frame, disposed on the upper surface of the second substrate;

[0016] An upper substrate and a cover are placed on the upper port of the support structure.

[0017] Optionally, the metal electrode is in the shape of an elongated strip; the at least one metal electrode is multiple, and the multiple metal electrodes are arranged at intervals on the varistor.

[0018] Optionally, the varistor is connected to the frame or the mass block respectively via a Wheatstone bridge.

[0019] Optionally, a varistor region is provided on the second substrate; each varistor region is provided with at least two varistors.

[0020] Optionally, there are two of the at least two piezoresistors, and the two piezoresistors are arranged along the length direction of the sensitive beam; wherein one of the piezoresistors is electrically connected to the frame, and the other piezoresistors is electrically connected to the mass block.

[0021] Optionally, the material of the metal electrode includes Cu.

[0022] Optionally, there are two permanent magnets, which are symmetrically arranged and embedded in the lower surface of the mass block.

[0023] Optionally, the material of the permanent magnet includes CoNiMnP alloy or Permalloy.

[0024] Furthermore, it also includes:

[0025] A support beam is disposed between the mass block and the first substrate, and is used to support the mass block.

[0026] A second aspect of an embodiment of the present disclosure provides a method for preparing a MEMS piezoresistive accelerometer, comprising:

[0027] providing a first substrate;

[0028] Performing patterning on the first substrate to form a mass block body and a first groove surrounding the mass block body;

[0029] forming a second groove on the lower surface of the first substrate;

[0030] forming a second substrate on the upper surface of the first substrate;

[0031] Etching the lower surface of the first substrate to form a support beam;

[0032] forming a third groove on the lower surface of the mass block body;

[0033] forming a permanent magnet in the third groove;

[0034] forming a lower base on the lower surface of the first substrate;

[0035] performing a thinning process on the second substrate;

[0036] Performing patterning on the second substrate to form a sensitive beam and a mass block;

[0037] forming a varistor in a varistor region of the second substrate;

[0038] forming a metal electrode on the varistor;

[0039] forming a passivation layer on the upper surface of the second substrate;

[0040] Performing patterning on the passivation layer to expose four sides of the upper surface of the second substrate;

[0041] forming a support layer on the second substrate and the passivation layer;

[0042] Removing the support layer to form a support frame and exposing the passivation layer;

[0043] forming an extraction electrode on the passivation layer;

[0044] An upper substrate is provided and connected to the support frame.

[0045] The beneficial effects of the embodiments of the present disclosure include:

[0046] The present invention introduces the magnetoresistance effect, embeds a plurality of parallel long metal electrodes in the traditional varistor, and divides the varistor into many small areas with a much larger width than length, which is equivalent to connecting a plurality of resistors with a very small aspect ratio in series, so as to increase the magnetoresistance sensitivity of the resistor. At the same time, symmetrical permanent magnets are added on both sides of the varistor, and the change amount △R of the resistance under the action of acceleration is effectively increased through the magnetoresistance effect, thereby improving the output of the Wheatstone bridge and thus improving the sensitivity of the accelerometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of the arrangement of piezoresistors and permanent magnets on the upper surface of the MEMS piezoresistive accelerometer disclosed in the present invention;

[0048] Figure 2 The MEMS piezoresistive accelerometer disclosed in the present invention is Figure 1 Sectional view along the A-A' direction;

[0049] Figure 3 The MEMS piezoresistive accelerometer disclosed in the present invention is Figure 1 Cross-section along the B-B' direction;

[0050] Figure 4 A schematic diagram of a Wheatstone bridge connection of a piezoresistor of a MEMS piezoresistive accelerometer disclosed in the present invention;

[0051] Figure 5 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 1 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0052] Figure 6 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 2 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0053] Figure 7 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 3 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0054] Figure 8 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 4 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0055] Fig. 9 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 5 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0056] Fig.10 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 6 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0057] Fig.11 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 7 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0058] Fig.12 This is a schematic diagram of the magnetic field direction of the permanent magnet obtained in step 7 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0059] Fig.13 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 8 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0060] Fig.14 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 9 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0061] Fig.15 It is a schematic diagram of the structure cross section along the A-A' direction obtained in step 10 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0062] Fig.16 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 11 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0063] Fig.17 A top view of the structure obtained in step 12 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0064] Fig.18 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 13 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0065] Fig.19 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 14 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0066] Fig. 20 It is a schematic diagram of the structural cross-section along the AA' direction obtained in step 15 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention.

[0067] Fig.21 It is a schematic diagram of the structural cross-section in the A-A' direction obtained in step 16 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention;

[0068] Fig. 22 It is a schematic diagram of the structural cross-section along the AA' direction obtained in step 17 of preparing the MEMS piezoresistive accelerometer disclosed in the present invention.

[0069] In the figure, 1, first substrate; 2, second substrate; 3, support beam; 4, permanent magnet; 5, lower substrate; 6, sensitive beam; 7, mass block; 8, varistor; 9, metal electrode; 10, passivation layer; 11, support frame; 12, lead-out electrode; 13, upper substrate; 14, first groove; 15, second groove; 16, third groove. DETAILED DESCRIPTION

[0070] In order to enable those skilled in the art to better understand the technical solution of the present disclosure, the present disclosure is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0071] like Figure 1-4As shown, a MEMS piezoresistive accelerometer includes: a lower substrate 5, a first substrate 1, a second substrate 2, a passivation layer 10, a piezoresistor 8, a metal electrode 9, an extraction electrode 12, a mass block 7, a permanent magnet 4, a support frame 11 and an upper substrate 13. The first substrate 1 is arranged on the lower substrate 5, and the first substrate 1 is provided with a cavity running through its thickness. The second substrate 2 and the passivation layer 10, the second substrate 2 is arranged on the upper surface of the first substrate 1, and the passivation layer 10 is arranged on the upper surface of the second substrate 2. Among them, the second substrate 2 and the passivation layer 10 corresponding to the cavity together form a sensitive beam 6. The piezoresistor 8 is embedded in the second substrate 2. The piezoresistor 8 is electrically connected to the frame or mass block 7 composed of the first substrate 1, the second substrate 2 and the support frame 11. At least one metal electrode 9 is arranged on the piezoresistor 8. The extraction electrode 12 is arranged on the passivation layer 10, and the extraction electrode 12 is electrically connected to the metal electrode 9. The mass block 7 is located in the cavity, and the mass block 7 is arranged on the lower surface of the second substrate 2. The permanent magnet 4 is disposed on the mass block 7. The support frame 11 is disposed on the upper surface of the second substrate 2. The upper base 13 is disposed on the upper port of the support structure.

[0072] In some embodiments, the lower substrate 5 and the upper substrate 13 are both made of glass. In some embodiments, the lower substrate 5 and the upper substrate 13 are made of Pyrex#7740 glass, and the thickness is 200-400 μm. In the present disclosure, the materials of the lower substrate 5 and the upper substrate 13 have relatively close physical properties to silicon materials, which can reduce the error caused by the mismatch of physical parameters, and can also be used as a micromechanical limit structure to provide overload protection for the accelerometer.

[0073] In some embodiments, the first substrate 1 is made of single crystal silicon and has a thickness of 400-600 μm.

[0074] In some embodiments, there are two permanent magnets 4 , which are symmetrically arranged and embedded in the lower surface of the mass block 7 .

[0075] Specifically, the permanent magnets 4 are symmetrically distributed on both sides of the bottom of the mass block 7 and arranged in a straight line with the four varistors 8 to provide a stable magnetic field for the varistors 8. In some embodiments, the material of the permanent magnets 4 is CoNiMnP alloy or Permalloy.

[0076] In some embodiments, the support beam 3 is disposed between the mass block 7 and the first substrate 1 to support the mass block 7. In some embodiments, the lower surface of the support beam 3 and the bottom surface of the mass block 7 are located in the same plane and are arranged in a central symmetric manner, and the thickness is 40-80 μm.

[0077] Further, specific reference Figure 1The mass block 7 is located in the center of the structure, and its left and right sides are connected to the frame through a support beam 3, and its upper and lower ends are connected to the frame through a sensitive beam 6. Among them, the first substrate 1, the second substrate 2 and the support frame 11 together constitute a frame. Further, when the first substrate 1, the second substrate 2 and the support frame 11 are made of silicon-based materials, they together constitute a silicon-based frame. In some embodiments, the cross-sectional area of ​​the sensitive beam 6 is much smaller than the cross-sectional area of ​​the support beam 3.

[0078] In some embodiments, the second substrate 2 is made of single crystal silicon and has a thickness of 200-400 μm.

[0079] In some embodiments, the upper surface of the sensitive beam 6 and the top of the mass block 7 are in the same plane, and the sensitive beam 6 is 10-20 μm thick, 20-40 μm wide, and 40-60 μm long.

[0080] In some embodiments, the second substrate 2 has a varistor region, and each varistor region is provided with at least two varistors 8 .

[0081] In some embodiments, there are two piezoresistors 8, and the two piezoresistors 8 are arranged along the length direction of the sensitive beam 6. One piezoresistors 8 is electrically connected to the frame, and the other piezoresistors 8 is electrically connected to the mass block 7. Further, the piezoresistors 8 are respectively connected to the frame or the mass block 7 through a Wheatstone bridge.

[0082] Specifically, the varistor 8 is located on the upper surface of the sensitive beam 6 and is connected to the frame or the mass block 7 respectively. They are arranged in the same direction and symmetrically positioned, and are connected in a Wheatstone bridge manner through leads.

[0083] In some embodiments, there are multiple metal electrodes 9 , and the multiple metal electrodes 9 are arranged on the varistor 8 at intervals.

[0084] Specifically, the metal electrodes 9 are regularly laid in the varistor 8, dividing the varistor 8 into many small areas whose width is much larger than their length. The above arrangement is equivalent to connecting multiple resistors with very small aspect ratios in series to increase the resistance magnetoresistance sensitivity. In some embodiments, the material of the metal electrode 9 includes Cu.

[0085] In some embodiments, the metal electrode 9 is in the shape of a long strip.

[0086] In some embodiments, the second substrate 2 is made of silicon dioxide or silicon nitride, and has a thickness of 100-200 nm.

[0087] Furthermore, the passivation layer 10 has a contact hole formed by photolithography, and a lead electrode 12 is disposed in the contact hole. In some embodiments, the lead electrode 12 is made of metal, preferably at least one of aluminum, copper, platinum, titanium, gold, etc., with a thickness of 100-500 nm.

[0088] In some embodiments, the support frame 11 is connected to the upper substrate 13 by anodizing bonding, and at the same time serves as a step to support the upper substrate 13 to form a vacuum cavity, thereby providing a movable space for the mass block 7 .

[0089] In some embodiments, the support frame 11 is made of amorphous silicon.

[0090] The working principle of the MEMS piezoresistive accelerometer disclosed in the present invention is as follows:

[0091] When the piezoresistive accelerometer is subjected to an upward acceleration, the mass block 7 moves downward, driving the sensitive beam 6 to bend downward. The piezoresistors 8 on the surface of the sensitive beam 6 are subjected to stress and produce resistance changes in the opposite direction. At the same time, the distance between the piezoresistors 8 far from the mass block 7 and the center of the permanent magnet 4 changes, and the magnetic field strength changes. Under the influence of the magnetoresistance effect, the resistance value further changes. Since the magnetic field strength at both ends of the permanent magnet 4 is much smaller than the magnetic field strength at the center, under the action of acceleration, the distance between R1 and R2 and the center of the permanent magnet 4 increases, and the resistance value decreases due to the magnetoresistance effect, which is the same as the change trend of the piezoresistive effect. The distance between R1' and R2' and the center of the permanent magnet 4 remains basically unchanged, resulting in a larger output of the Wheatstone bridge, thereby increasing the sensitivity of the MEMS piezoresistive accelerometer without affecting the natural frequency. In addition, when the accelerometer is working normally, the temperature increase will cause the resistance of the varistor 8 to decrease, thereby causing the accelerometer output to decrease. In the present disclosure, the temperature increase will also increase the resistance of the metal electrode 9, compensating for the resistance of the varistor 8, and vice versa, thereby suppressing the temperature drift of the accelerometer to a certain extent.

[0092] Compared with the traditional MEMS piezoresistive accelerometer, the present invention has the following advantages:

[0093] 1. The present disclosure introduces the magnetoresistance effect, embeds a plurality of parallel long strip metal electrodes 9 in the traditional varistor 8, and divides the varistor 8 into many small areas with a much larger width than length, which is equivalent to connecting a plurality of resistors with a very small aspect ratio in series, so as to increase the magnetoresistance sensitivity of the resistor. At the same time, symmetrical permanent magnets 4 are added on both sides of the varistor 8, and the magnetoresistance effect effectively increases the change △R of the resistance under the action of acceleration, thereby improving the output of the Wheatstone bridge and thus improving the sensitivity of the accelerometer.

[0094] 2. The present invention embeds a plurality of parallel long metal electrodes 9 in a traditional varistor 8. When the sensor works normally, an increase in temperature will cause the resistance of the varistor 8 to decrease, thereby causing the sensor output to decrease. However, an increase in temperature will also increase the resistance of the metal electrode 9, compensating for the resistance of the varistor 8, and vice versa, thereby suppressing the temperature drift of the sensor to a certain extent.

[0095] 3. This disclosure is prepared using MEMS technology, and the sensor has the advantages of small size, high precision, good consistency, easy mass production, and low cost.

[0096] Based on the same inventive concept, the embodiments of this disclosure also provide a MEMS piezoresistive accelerometer and a preparation method thereof. The structure of the MEMS piezoresistive accelerometer can refer to the relevant descriptions above and will not be elaborated here.

[0097] A MEMS piezoresistive accelerometer and a preparation method thereof, comprising:

[0098] Step 1: Provide a first substrate 1.

[0099] Specifically, as Figure 5 shown, a 400-μm-thick N-type (100) silicon wafer is selected as the first substrate 1.

[0100] Step 2: Pattern the first substrate 1 to form the main body of the mass 7 and the first groove 14 surrounding the main body of the mass 7.

[0101] Specifically, as Figure 6 shown, the first groove 14 is formed on the upper surface of the first substrate 1 by photolithography and DRIE (Deep Reactive Ion Etching), and the main body of the mass 7 is constructed.

[0102] In some embodiments, the cross-sectional width of the first groove 14 is 50 μm and the depth is 350 μm, and its shape is "square".

[0103] Step 3: Form a second groove 15 on the lower surface of the first substrate 1.

[0104] Specifically, as Figure 7 shown, the second groove 15 for the movement of the mass 7 is etched on the lower surface of the first substrate 1 by photolithography and DRIE. In some embodiments, the depth of the second groove 15 is 10 μm.

[0105] Step 4: Form a second substrate 2 on the upper surface of the first substrate 1.

[0106] Specifically, as Figure 8 shown, the second substrate 2 is closely attached to the upper surface of the first substrate 1 by anodic bonding.

[0107] In some embodiments, a 200-μm-thick N-type (100) silicon wafer is selected as the second substrate 22.

[0108] Step 5: Etch the lower surface of the first substrate 1 to form the support beam 3.

[0109] Specifically, as Fig. 9As shown, the support beam 3 is formed on the lower surface of the first substrate 1 by etching through photolithography and DRIE.

[0110] Step 6: forming a third groove 16 on the lower surface of the main body of the mass block 7.

[0111] Specifically, Fig.10 As shown, a third groove 16 is formed on the lower surface of the first substrate 1 by photolithography and DRIE.

[0112] In some embodiments, a third groove with a length of 15 μm, a width of 5 μm, and a depth of 200 μm is etched on the left and right sides of the lower surface of the first substrate 1 by photolithography and DRIE.

[0113] Step 7: forming a permanent magnet 4 in the third groove 16 .

[0114] In some embodiments, a barrier layer is formed in the third groove 16, a seed layer is prepared on the barrier layer, and the groove is filled under a magnetic field of a certain direction and its magnetic field direction is determined to form the permanent magnet 4. In some other embodiments, the permanent magnet 4 is a CoNiMnP permanent magnet.

[0115] Specifically, Fig.11 , 12 As shown, Ti is prepared as a barrier layer in the third groove 16 by magnetron sputtering, Cu is prepared as a seed layer on the barrier layer, and CoNiMnP permanent magnet 4 is electroplated under a magnetic field in a certain direction to fill the groove and determine its magnetic field direction to form a permanent magnet 44, and then the excess alloy is removed by CMP (Chemical Mechanical Polishing) process.

[0116] Step 8: forming a lower base 5 on the lower surface of the first substrate 1 .

[0117] Specifically, Fig.13 As shown, the first substrate 1 and the glass substrate are tightly bonded together by anodic bonding.

[0118] Step 9: Thinning the second substrate 2.

[0119] In some embodiments, such as Fig.14 As shown, the second substrate 2 is thinned to 30 μm.

[0120] Step 10: Perform patterning on the second substrate 2 to form the sensitive beam 6 and the mass block 7.

[0121] In some embodiments, the second substrate 2 is etched and thinned by photolithography and DRIE.

[0122] Specifically, Fig.15As shown, the second substrate 2 is etched to 10 μm by photolithography and DRIE, and the sensitive beam 6 and the mass block 7 are formed by etching.

[0123] Step 11: forming a varistor 8 in the varistor region of the second substrate 2.

[0124] In some embodiments, a varistor region is formed on the upper surface of the second substrate 2 , and the varistor 8 on the upper surface of the second substrate 2 is formed by photolithography and ion implantation.

[0125] Specifically, Fig.16 As shown, four varistors 8 are prepared in the varistor region on the upper surface of the second substrate 2 by photolithography and boron ion implantation.

[0126] Step 12: forming a metal electrode 9 on the varistor 8.

[0127] In some embodiments, at least two metal electrodes 9 arranged at an interval are formed on the varistor 8 .

[0128] In some embodiments, an electrode groove is formed on the varistor 8, a barrier layer is prepared in the electrode groove, a seed layer is prepared on the barrier layer, and a metal electrode 9 is made in the electrode groove.

[0129] Specifically, Fig.17 As shown, three rows of evenly distributed electrode grooves with a width of 3 μm and a depth of 6 μm are etched on the four varistors 8 by photolithography and DRIE, Ti is prepared as a barrier layer in the electrode groove by magnetron sputtering, Cu is prepared as a seed layer on the barrier layer, and the electrode groove is filled by electroplating Cu to form a metal electrode 9, and then the excess Cu is removed by CMP process.

[0130] Step 13: forming a passivation layer 10 on the upper surface of the second substrate 2 .

[0131] In some embodiments, the material of the passivation layer 10 includes silicon nitride.

[0132] Specifically, Fig.18 As shown, silicon nitride is deposited on the upper surface of the second substrate 2 by PECVD (Plasma Enhanced Chemical Vapor Deposition) to prepare the passivation layer 10.

[0133] Step 14: patterning the passivation layer 10 to expose four sides of the upper surface of the second substrate 2 .

[0134] Specifically, Fig.19As shown, the passivation layer 10 is etched on four sides of the upper surface of the second substrate 2 by photolithography and RIE (Reactive Ion Etching) until the second substrate 2 is exposed.

[0135] Step 15: forming a support layer on the second substrate 2 and the passivation layer 10.

[0136] Specifically, Fig. 20 As shown, a 6 μm thick support layer is prepared by PECVD on the second substrate 2 and the upper surface of the passivation layer 10. In some embodiments, the material of the support layer is amorphous silicon.

[0137] Step 16: remove the support layer to form a support frame 11 and expose the passivation layer 10.

[0138] Specifically, Fig.21 As shown, the support layer above the passivation layer 10 is etched by photolithography and DRIE to form a support frame 11 and expose the passivation layer 10 , so that the support frame 11 is formed on four sides of the upper surface of the second substrate 2 .

[0139] Step 17: forming an extraction electrode 12 on the passivation layer 10 .

[0140] Specifically, Fig. 22 As shown, a contact hole is formed on the upper surface of the passivation layer 10 by photolithography and RIE, and Au is prepared thereon as the electrode layer 12 by magnetron sputtering.

[0141] Step 18: Provide an upper substrate 13 and connect the upper substrate 13 to the supporting frame 11 .

[0142] In some embodiments, the material of the upper substrate 13 includes glass.

[0143] Specifically, Figure 2 , Figure 3 As shown, the support frame 11 and the upper substrate 13 are tightly attached to each other by anodic bonding, thereby completing the preparation of the above-mentioned MEMS piezoresistive accelerometer.

[0144] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure 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 substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A MEMS piezoresistive accelerometer, characterized in that: include: lower basement; A first substrate, disposed on the lower base, wherein the first substrate is provided with a cavity running through the thickness thereof; A second substrate and a passivation layer, wherein the second substrate is disposed on the upper surface of the first substrate, and the passivation layer is disposed on the upper surface of the second substrate; wherein the second substrate and the passivation layer corresponding to the cavity together form a sensitive beam; A varistor is embedded in the second substrate; the varistor is electrically connected to a frame or a mass block formed by the first substrate, the second substrate and a support frame; At least one metal electrode arranged on the varistor; An extraction electrode is disposed on the passivation layer, and the extraction electrode is electrically connected to the metal electrode; A mass block is located in the cavity, the mass block is arranged on the lower surface of the second substrate, and the upper and lower ends of the mass block are respectively connected to the frame through a sensitive beam; A permanent magnet is disposed on the mass block; A support frame, disposed on the upper surface of the second substrate; An upper base cover is placed on the upper port of the support frame; The metal electrode is in the shape of a long strip; There are multiple at least one metal electrode, and the multiple metal electrodes are arranged in parallel and at intervals on the varistor; wherein the multiple metal electrodes are laid in the varistor, dividing the varistor into multiple areas with a width dimension greater than a length dimension; There are two permanent magnets, which are symmetrically arranged and embedded in the lower surface of the mass block; wherein the two permanent magnets are symmetrically distributed on both sides of the bottom of the mass block, and the two permanent magnets and the varistor are arranged in a straight line; Two piezoresistors are arranged on each sensitive beam; the two piezoresistors are arranged along the length direction of the sensitive beam; wherein one piezoresistors is connected to the frame, and the other piezoresistors is connected to the mass block.

2. The accelerometer according to claim 1, characterized in that The varistor is connected to the frame or the mass block respectively through a Wheatstone bridge.

3. The accelerometer according to claim 1, characterized in that The second substrate has a varistor area; each of the varistor areas is provided with at least two varistors.

4. The accelerometer according to claim 1, characterized in that The material of the metal electrode includes Cu.

5. The accelerometer according to claim 1, characterized in that The material of the permanent magnet includes CoNiMnP alloy or Permalloy.

6. The accelerometer according to claim 1, characterized in that Also includes: A support beam is disposed between the mass block and the first substrate, and is used to support the mass block.

7. A method for preparing a MEMS piezoresistive accelerometer, the method being implemented according to a MEMS piezoresistive accelerometer according to any one of claims 1 to 6, characterized in that: include: providing a first substrate; Performing patterning on the first substrate to form a mass block body and a first groove surrounding the mass block body; forming a second groove on the lower surface of the first substrate; forming a second substrate on the upper surface of the first substrate; Etching the lower surface of the first substrate to form a support beam; forming a third groove on the lower surface of the mass block body; forming a permanent magnet in the third groove; forming a lower base on the lower surface of the first substrate; performing a thinning process on the second substrate; Performing patterning on the second substrate to form a sensitive beam and a mass block; forming a varistor in a varistor region of the second substrate; forming a metal electrode on the varistor; forming a passivation layer on the upper surface of the second substrate; Performing patterning on the passivation layer to expose four sides of the upper surface of the second substrate; forming a support layer on the second substrate and the passivation layer; Removing the support layer to form a support frame and exposing the passivation layer; forming an extraction electrode on the passivation layer; An upper substrate is provided and connected to the support frame.

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