CN110531114A - A kind of MEMS three-axis piezoresistance formula accelerometer chip of purely axial deformation and preparation method thereof - Google Patents

Abstract

The invention discloses a MEMS triaxial piezoresistive accelerometer chip with pure axial deformation and a preparation method thereof. The X measuring unit, the Y measuring unit and the Z measuring unit in the sensor are respectively used to measure the X direction, the Y direction and the The acceleration in the Z direction realizes the separate measurement of the acceleration in the three directions; each measurement unit includes a mass block, a support beam and a sensitive beam. No matter which measurement unit it is, the support beam and the sensitive beam are set separately through the mass block, and the support beam supports the mass. The block moves, and the stress is mainly concentrated on the sensitive beam, so that the resistance of the piezoresistor strip on the sensitive beam changes, and the two perform their own duties, which greatly weakens the direct coupling relationship between sensitivity and resonance frequency; The synchronous movement of the quality block and the two ends of the fixed sensitive beam also move synchronously, so that the sensitive beam always meets the pure axial deformation condition. Under the same resonance frequency, the sensitivity of the sensor is optimal, so that the sensor chip has good performance indicators .

Description

A MEMS triaxial piezoresistive accelerometer chip with pure axial deformation and its preparation method

【Technical field】

The invention belongs to the field of micromechanical electronic system sensor measurement, and in particular relates to a MEMS triaxial piezoresistive accelerometer chip with pure axial deformation and a preparation method thereof.

【Background technique】

The output of MEMS acceleration sensor is the mechanical measurement sensor second only to the pressure sensor, and it is one of the most widely used MEMS devices at present. MEMS piezoresistive acceleration sensor has simple structure, small appearance and superior performance, especially suitable for the measurement of low frequency acceleration. In addition to being used in aerospace for various overload and vibration parameter measurements such as aircraft wind tunnel tests and flight tests, it can also be used for testing vibration parameters at various stages of engine test benches in industry.

There are many measurement principles used in MEMS acceleration sensors, mainly piezoresistive, piezoelectric, capacitive, thermal convection, tunnel, fiber optic and resonant. Compared with other types of MEMS acceleration sensors, MEMS piezoresistive acceleration sensors have the advantages of wide measurement range, simple processing technology, can measure dynamic and static signals, good dynamic response, convenient testing, simple follow-up processing circuit, and low cost. be widely used.

For the three-axis piezoresistive acceleration sensor, it is used to measure the acceleration in three directions. No matter which direction it is, the sensitivity and working bandwidth of the acceleration sensor are always its most important working indicators. Therefore, these two parameters are often used in the design process. Design the accelerometer structure as an optimization target. However, there is a mutually restrictive relationship between the natural frequency and the sensitivity, which affects the further improvement of the acceleration sensor. In the design of the acceleration sensor, it is very important to weaken the mutual constraint relationship between the sensitivity of the acceleration sensor and the natural frequency, and to obtain the optimal value of the sensitivity and the natural frequency at the same time. When the acceleration sensor measures the acceleration in the z direction, since the acceleration is perpendicular to the chip, it is particularly important to adjust the sensitivity and natural frequency of the measurement unit.

【Content of invention】

The purpose of the present invention is to overcome the shortcoming of above-mentioned prior art, provide a kind of MEMS triaxial piezoresistive accelerometer chip of pure axial deformation and preparation method thereof; The earth weakens the direct coupling relationship between the sensitivity and the resonant frequency, and at the same resonant frequency, the sensitivity of the sensor is optimal, so that the sensor chip has a good performance index.

In order to achieve the above object, the present invention adopts the following technical solutions to achieve:

A MEMS triaxial piezoresistive accelerometer chip with pure axial deformation, comprising: X measuring unit, Y measuring unit and Z measuring unit fixedly arranged in the chip outer frame, the three measuring units are isolated by the chip outer frame; Z The vertical centerline of the measurement unit is parallel to the vertical centerline of the X measurement unit, and the vertical centerline of the Y measurement unit is perpendicular to the vertical centerline of the Z measurement unit; the outer frame of the chip is bonded on the bottom glass plate; The Z measurement unit includes a third mass block and a fourth mass block, and the outer sides of the third mass block and the fourth mass block are connected to the outer frame of the chip through a second support beam; the inner side of the third mass block is set There is a first protrusion, and a first groove is respectively arranged on both sides of the first protrusion; a second groove is arranged on the inner side of the fourth mass block, and a first groove is respectively arranged on both sides of the second groove. Two protrusions; the first protrusion is engaged in the second groove, and each second protrusion is engaged in a second groove; each second protrusion is connected to the first protrusion through the third sensitive beam; the second The two outer ends of the inner sides of the third mass block and the fourth mass block are respectively connected by a second sensitive beam;

The piezoresistors on the second sensitive beam and the third sensitive beam are connected through metal leads to form a Wheatstone full bridge.

A further improvement of the present invention is:

Preferably, the plane of the second support beam is parallel to the XY plane, and the plane of the second support beam is set at the center line of the third mass block or the fourth mass block in the z direction; the second support beam is fixedly provided with a serpentine beam.

Preferably, the serpentine beam includes several serpentine units; each serpentine unit is fixedly arranged between the third mass block and the chip outer frame, or is fixedly arranged between the fourth mass block and the chip outer frame; The serpentine unit includes a first plane and a second plane perpendicular to each other, the first plane is parallel to the transverse centerline of the Z measurement unit, the second plane is parallel to the vertical centerline of the Z measurement unit, and the two sides of each first plane The ends are respectively connected with a second plane.

Preferably, the first protrusion includes a first connecting segment and a first protruding end integrally connected, the first connecting segment integrally connects the third mass body and the first protruding end, and the width of the first protruding end is greater than The width of the first connecting section; the second protrusion includes a second connecting section and a second protruding end, the second connecting section connects the fourth quality block main body and the second protruding end, and the width of the second protruding end is greater than that of the second protruding end The width of the connecting section; each second protruding end is connected to the first protruding end through a third sensitive beam.

Preferably, the two second sensitive beams are respectively arranged on the outside of a second connecting section.

Preferably, the X measurement unit and the Y measurement unit have the same structure, and are each composed of two first measurement blocks, each first measurement block includes a first mass block and a second mass block, and the first mass block and the second mass block The outer sides of the blocks are connected to the outer frame of the chip through a first support beam, and the inner sides of the first mass block and the second mass block are connected to the first sensitive beam through hinge beams;

The piezoresistors on the first sensitive beam in the X measurement unit are connected through metal leads to form a Wheatstone half bridge; the piezoresistors on the first sensitive beam in the Y measurement unit are connected through metal leads to form a Wheatstone half bridge.

Preferably, the inner sides of the first mass block and the second mass block are provided with first notches, and the two first notches are arranged symmetrically with respect to the transverse centerline of the first measuring block; the two ends of the hinge beam are respectively connected to the two The inner end surface of the first notch is fixedly connected; the hinge beam is arranged on the vertical center line of the first measuring block.

Preferably, the inner sides of the first mass block and the second mass block are connected by two first sensitive beams, and the two first sensitive beams are respectively arranged on both sides of the first notch, and the two first sensitive beams are opposite to the hinge The beam is symmetrical.

Preferably, the outer sides of the first mass block and the second mass block are provided with second gaps; one end of each first support beam is fixedly connected to the outer frame of the chip, and the other end is fixedly connected to the inner end surface of the second gap; the first The support beam is arranged on the vertical centerline of the first measuring block.

A method for preparing the above-mentioned MEMS triaxial piezoresistive accelerometer chip of pure axial deformation, comprising the following steps:

1) Perform double-sided thermal oxidation on the SOI silicon wafer, and form a layer of thermal oxygen silicon dioxide layer on the upper surface and the lower surface of the SOI silicon wafer, respectively, the thermal oxygen silicon dioxide layer on the upper surface and the thermal oxygen dioxide layer on the lower surface silicon layer;

2) Using a lightly doped plate, remove the upper surface thermal oxygen silicon dioxide layer in the lightly doped region on the upper surface of the SOI by photolithography and reactive ion etching, and after doping boron ions in the lightly doped region, a lightly doped silicon dioxide layer is formed. Doped area;

3) using a heavily doped plate, removing the thermal oxygen silicon dioxide layer on the upper surface in the heavily doped region by photolithography and reactive ion etching, and performing heavy doping in the heavily doped region to form an ohmic contact region;

4) Deposit a Ti/Al layer on the front side of the SOI silicon wafer by physical vapor deposition, and perform photolithography through the metal pad and the wire plate to form the metal lead and pad structure;

5) Depositing a layer of silicon dioxide layer by vapor phase deposition on the back side of the thermal oxygen silicon dioxide layer on the lower surface, and the thermal oxygen silicon dioxide layer and the silicon dioxide layer on the lower surface form a double mask layer;

6) remove the double mask layer in the deeply etched area on the back of the SOI silicon wafer by the reactive ion etching method, so that the substrate silicon in the deeply etched area of the SOI silicon wafer is exposed; etch the substrate silicon by the deep reactive ion etching method, and Eroding away a part of the lower part of the first support beam and the hinge beam in the X measurement unit and the Y measurement unit, and a part of the lower part of the first mass block and the second mass block;

7) Remove the double mask layer of the second support beam and the serpentine beam backside etching area in the Z measurement unit by photolithography; continue etching by deep reactive ion etching method to form the lower part of the second support beam, the serpentine beam The lower part of the beam, the lower part of the first support beam, the lower part of the hinge beam, and the base layer structure of all masses;

8) performing a photoresist mask on the bottom glass plate by moving the gap pattern, and performing wet etching by KOH to form a hollow area on the bottom glass plate;

9) Etching the remaining double mask layer on the back of the SOI silicon wafer by a deep reactive ion etching method, so that the substrate silicon of the SOI silicon wafer is exposed; the substrate silicon region is encapsulated on the bottom glass plate by anodic bonding;

10) Etching and removing the thermal oxygen silicon dioxide layer on the upper surface of the SOI silicon wafer by reactive ion etching, coating a layer of photoresist, and then etching by inductively coupled plasma etching until the buried oxide layer stops, forming the first The support beam, the hinge beam, the sensitive beam and the upper parts of all mass blocks form the second support beam and the device layer part of the serpentine beam.

11) Remove the device layer and buried oxide layer on the upper surface of the second support beam by reactive ion etching, and then etch off the device layer and buried oxide layer in the upper region of the serpentine beam by reactive deep ion etching, and the second support beam and the upper part of the serpentine beam are etched;

12) Spray the photoresist on the front side of the etched SOI silicon wafer for protection, remove the photoresist in the corresponding buried oxide layer area, and then use the buffer solution to etch the remaining buried oxide layer on the front side of the SOI silicon wafer to clean the SOI silicon wafer Dry the front side naturally, and finally remove the photoresist on the front side of the SOI silicon wafer;

13) The SOI silicon wafer is processed by low-temperature annealing process, and the MEMS three-axis piezoresistive accelerometer chip with pure axial deformation is fabricated.

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

The invention discloses a MEMS three-axis piezoresistive accelerometer chip with pure axial deformation. The X measuring unit, the Y measuring unit and the Z measuring unit in the sensor are respectively used to measure the acceleration in the X direction, the Y direction and the Z direction , can realize the separate measurement of acceleration in three directions; the Z unit includes a mass block, a support beam and a sensitive beam; the support beam and the sensitive beam are set separately through the mass block, the support beam supports the movement of the mass block, and the stress is mainly concentrated on the sensitive beam, so that The resistance of the piezoresistor strip on the sensitive beam changes, and the two perform their duties, which greatly weakens the direct coupling relationship between the sensitivity and the resonance frequency; at the same time, due to the synchronous movement of the two mass blocks, the two The ends also move synchronously, so that the sensitive beam always meets the pure axial deformation condition. Under the same resonant frequency, the sensitivity of the sensor is optimal, so that the sensor chip has good performance indicators; the inner sides of the third mass block and the fourth mass block The connecting part is set as a matching and meshing structure to increase the firmness of the connection between the two; because one of the second sensitive beam and the third sensitive beam is directly connected to the inner side of the third mass block and the fourth mass block, the other It is the fitting part of the connection, so that when the chip is subjected to acceleration in the Z direction, one of the second sensitive beam and the third sensitive beam is subjected to a tensile force, and the other is subjected to a compressive force, thereby forming a Wheatstone full bridge. Through this structure The Wheatstone full bridge can be formed in one structure, which simplifies the structure and improves the output sensitivity. Compared with the traditional half-bridge design, the sensitivity is doubled; the sensor chip can realize the three-axis acceleration below 100g. separate measurements.

Further, the second support beam is arranged at the center line of the third mass or the fourth mass in the z direction, so that the third mass or the fourth mass and the chip frame can be evenly connected by the support beam force; the second support beam is provided with a serpentine beam, the serpentine beam is a circuitous structure, the serpentine beam can lead out the wire without increasing the stiffness of the support beam; when the chip is accelerated in the z direction, the unique circuitous mass end The external structure can reduce the limiting force of the chip outer frame on the third mass block or the fourth mass block when the Z measurement unit is subjected to the acceleration in the z direction. The frame can be firmly connected, and at the same time, there are both tension-sensitive beams and compression-sensitive beams on the Z measurement unit, thereby forming a Wheatstone full bridge to improve output sensitivity; the snake-shaped beam is set on the supporting beam, and the It ensures that the mass block and the chip frame can be firmly connected, thereby improving the sensitivity of the acceleration sensor and reducing the cross-sensitivity of the sensor, while ensuring the connection force between the mass block and the chip frame; the snake-shaped beam is equipped with multiple snake-shaped units , which can ensure that the metal leads can be evenly distributed and drawn out.

Further, the Z measuring unit is provided with connecting sections and protruding ends with different widths, so that a fitting structure can be formed.

Further, two second sensitive beams are arranged near the edge to improve the sensitivity.

Further, in the X measurement unit and the Y measurement unit, both the support beam and the sensitive beam are set separately through the mass block, the support beam supports the movement of the mass block, and the stress is mainly concentrated on the sensitive beam, so that the resistance of the piezoresistor strip on the sensitive beam changes, the two perform their own duties, which greatly weakens the direct coupling relationship between the sensitivity and the resonance frequency; at the same time, due to the synchronous movement of the two mass blocks, the two ends of the fixed sensitive beam also move synchronously, so that the sensitive beam always satisfies Pure axial deformation condition.

Further, for the X measurement unit or the Y measurement unit, the hinge beam is arranged on the center line of each measurement block, and the first sensitive beam is symmetrical to the hinge beam; when receiving an acceleration in the x direction or the y direction, due to the two mass The block will move synchronously under the action of acceleration, so that the two ends of the fixed sensitive beam move the same at any time, the axial displacement of the two ends of the sensitive beam is opposite, and the lateral displacement cancels out, and because the sensitive beam is thin enough, the mass blocks at both ends The bending moment of the sensitive beam is so small that it can be ignored, so the sensitive beam always meets the condition of pure axial deformation, and the strain energy of the sensitive beam is concentrated on the axial deformation, which greatly increases the sensitivity of the sensor.

Further, the gap structure on the mass block can increase the distance between the mass blocks, or between the mass block and the outer frame of the chip, extend the length of the hinge beam or the support beam, and strengthen the space between the mass blocks or between the mass block and the chip outer frame. connection force.

The invention also discloses a method for preparing a MEMS triaxial piezoresistive accelerometer chip with pure axial deformation. , using reactive ion etching method, plasma-enhanced chemical vapor deposition method, deep reactive ion etching method and other methods to prepare chips in multiple steps; since the Z unit support beam is in the middle of the chip thickness direction (direction), for the MEMS process The processing is very challenging. The present invention adopts the double mask layer on the back, and divides deep reactive ion etching in two steps to etch grooves with different depths on the back, so that the structure of the lower half of the Z support beam and the mass blocks and supports The structure of the lower half of the beam and the hinge beam is formed at the same time. At the same time, the device layer is first etched on the front side, then the buried oxide layer, and finally the base layer on the upper part of the Z-axis support beam is etched to form the overall structure of the support beam.

【Description of drawings】

Fig. 1 is the overall structure schematic diagram of the present invention;

Fig. 2 is an enlarged schematic diagram of part A in Fig. 1;

Fig. 3 is an enlarged schematic diagram of part B in Fig. 1;

FIG. 4 is an enlarged schematic diagram of part C in FIG. 1;

Fig. 5 is a working principle diagram of the measuring unit in the x and y directions of the sensor;

Fig. 6 is a working principle diagram of the z-direction measuring unit of the sensor;

7 is a schematic diagram of the preparation structure of the sensor chip;

Wherein, (a) the figure is step 1); (b) the figure is step 2); (c) the figure is step 3); (d) the figure is step 4); (e)

The figure is step 5); (f) the figure is step 6); (g) the figure is step 7); (h) the figure is step 8); (i) the figure is step 9); (j) the figure is step 10) (k) the figure is step 11); (l) the figure is step 12);

Fig. 8 is a flow chart of the preparation structure of the sensor chip;

Among them: 1-first supporting beam; 2-first measuring block; 3-hinge beam; 4-sensitive beam; 5-chip frame; 6-second measuring block; 7-serpentine beam; 8-second support beam; 9-thermal oxygen silicon dioxide layer; 10-buried oxide layer; 11-device layer; 12-substrate silicon; 13-lightly doped region; 14-photoresist; 15-ohm contact region; 16-metal Lead wire; 17-pad structure; 18-silicon dioxide layer; 19-bottom glass plate; 20-Cu/Ar layer; 21-empty groove area; 2-1-first mass block; 2-2 second mass block ; 2-3-the first gap; 2-4-the second gap; 4-1-the first sensitive beam; 4-2 the second sensitive beam; 4-3 the third sensitive beam; 6-1-the third mass block ; 6-2 the fourth mass block; 6-3- the first protrusion; 6-4- the first groove; 6-5- the second protrusion; 6-6- the second groove; 6-3-1 - the first connecting section; 6-3-2- the first protruding end; 6-5-1- the second connecting section; 6-5-2- the second protruding end; 6-6-1- the front groove ; 6-6-2-rear end groove; 7-1-serpentine unit; 7-2-first plane; 7-3-second plane; 9-1-thermal oxygen silicon dioxide layer on the upper surface; 9 -2- Lower surface thermal oxygen silica layer.

【Detailed ways】

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" etc. The indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, or in a specific orientation. construction and operation, and therefore cannot be construed as limiting the present invention; the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be construed as indicating or implying relative importance; in addition, unless otherwise Clearly stipulated and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be directly connected or indirectly connected through an intermediary, Can be a communication within two elements. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention in specific situations.

In the present invention, for a separate measuring unit, its center is set as the inner side of the measuring unit, its periphery is set as the outer side, the vertical centerline refers to the centerline along the length direction, and the transverse centerline is perpendicular to the vertical centerline , is the centerline along the width direction; see Figure 1, set the two adjacent sides of the accelerometer chip, one along the x direction and the other along the y direction, the accelerometer chip is on the xoy plane, and the one perpendicular to the xoy plane is The z direction; no matter which measurement unit follows this rule, no further elaboration will be given.

Referring to Fig. 1, the present invention discloses a MEMS triaxial piezoresistive accelerometer chip with pure axial deformation, the sensor chip is made of SOI silicon chip, and the sensor consists of X measuring unit, Y measuring unit, Z measuring unit and chip outer frame 5 components, each measurement unit is set in the chip frame 5, and fixedly connected with the chip frame 5, the chip frame 5 is bonded on the bottom glass plate 20; the vertical centerline of the Z measurement unit is parallel to the X measurement The vertical centerline of the unit, the vertical centerline of the Y measurement unit is perpendicular to the vertical centerline of the Z measurement unit; the vertical centerline of the Z measurement unit is parallel to the y direction, and the vertical centerline of the Y measurement unit is parallel to y direction, the entire chip is on the xoy plane, and the direction perpendicular to the chip is the z direction; each measurement unit includes its own mass block, support beam and sensitive beam, and the three measurement units are used to measure x, y, and z respectively. direction of acceleration.

Referring to Fig. 1 and Fig. 2, the structure of the X measuring unit and the Y measuring unit is the same, and each is composed of two first measuring blocks 2 measuring blocks, and the two first measuring blocks 2 in one measuring unit are arranged in parallel, that is, the two first measuring blocks 2 The vertical axes of a measurement block 2 are parallel, and each first measurement block 2 is fixedly connected to the chip frame 5; each first measurement block 2 includes two mass blocks, which are respectively the first mass block 2-1 and the second mass block. Two mass blocks 2-2, the first mass block 2-1 and the second mass block 2-2 are provided with a first gap 2-3 at the intersection of its vertical center line and the inner side, and at the intersection of its vertical center line The intersection with the outer side is provided with a second gap 2-4, the first gap 2-3 and the second gap 2-4 are rectangular structures, the first mass block 2-1 and the second mass block 2-2 The first gaps 2-3 are arranged oppositely, and the two first gaps 2-3 are connected by a hinge beam 3, so that the inner side of the first mass block 2-1 and the inner side of the second mass block 2-2 pass through The hinged beam 3 is fixedly connected; along the transverse direction of the measuring unit, the two ends of the hinged beam 3 are respectively located at the center of the first mass block 2-1 and the second mass block 2-2; the first mass block 2-1 and the second mass block The inner edge of the block 2-2 except for the notch is connected by the first sensitive beam 4-1. In this embodiment, a first sensitive beam 4-1 is respectively provided on both sides of the first notch 2-3, and The two first sensitive beams 4-1 are symmetrical with respect to the hinged beam 3 and at the same time symmetrical with respect to the vertical centerline of the first measuring unit 2, the distance between the first mass 2-1 and the second mass 2-2 That is, the length of the first sensitive beam 4-1.

The outer sides of the first mass block 2-1 and the second mass block 2-2 are respectively connected to the chip frame 5 through the first support beam 1, and the two first support beams 1 are both on the vertical centerline of the first measurement block 2 Above, one end of each first support beam 1 is fixedly connected to the chip frame 5, and the other end is fixedly arranged on the second notch 2-4 of the first mass block 2-1 or the second notch of the second mass block 2-2 2-4 on the inner end face.

For the X measurement unit, the two first measurement blocks 2 are used to measure the acceleration in the x direction, and for the Y measurement unit, the two first measurement blocks 2 are used to measure the acceleration in the y direction; each of the X measurement unit or the Y measurement unit is first Both sensitive beams 4-1 are provided with piezoresistors; the piezoresistors on the two first sensitive beams 4-1 in the X measurement unit are connected by metal leads 16 and pads to form a semi-open-loop Wheatstone full bridge Circuit: The piezoresistors on the two first sensitive beams 4-1 in the Y measuring unit are connected through metal leads 16 and pads to form a semi-open-loop Wheatstone full-bridge circuit.

Referring to Fig. 3, the Z measuring unit is a second measuring block 6, the second measuring block 6 includes a third mass block 6-1 and a fourth mass block 6-2, the third mass block 6-1 and the fourth mass block 6 The inner side of -2 is connected by the second sensitive beam 4-2 and the third sensitive beam 4-3; the inner side of the third mass block 6-1 is provided with a first protrusion 6-3 and a first groove 6-4, the first protrusion 6-3 is arranged at the vertical centerline of the second measuring block 6, and the first protrusion 6-3 includes the integrally connected first connecting section 6-3-1 and the first protrusion end 6-3-2, the first connecting section 6-3-1 integrally connects the main part of the third mass block 6-1 and the first protruding end 6-3-2, and the first protruding end 6 - The width of 3-2 is greater than the width of the first connecting section 6-3-1, and the self-structure of the first protruding end 6-3-2 and the self-structure of the first connecting section 6-3-1 are both relative to the second The vertical centerline of the measuring block 6 is symmetrical; two first grooves 6-4 are formed between the two sides of the first protrusion 6-3 and the side edges of the second measuring block 6, and the two first grooves 6 -4 has the same structure and is symmetrical with respect to the vertical center line of the second measuring block 6; the fourth mass block 6-2 includes a second protrusion 6-5 and a second groove 6-6, and the second groove 6- 6 is arranged at the vertical center line of the second measuring block 6, and the second groove 6-6 includes a front groove 6-6-1 and a rear groove 6-6-2 connected with different widths, and the rear groove The first protruding end 6-3-2 is placed in the groove 6-6-2, the first connecting section 6-3-1 is placed in the front groove 6-6-1; the two ends of the second groove 6-6 There are two second protrusions 6-5 on the side, and the two second protrusions 6-5 are symmetrical with respect to the second groove 6-2, that is, symmetrical with respect to the center line of the second measuring block 6, and each second protrusion The riser 6-5 includes a second connecting section 6-5-1 and a second protruding end 6-5-2, and the width of the second protruding end 6-5-2 is greater than the width of the second connecting section 6-5-1 , the outer edge of the second protruding end 6-5-2 is flush with the outer edge of the second connecting section 6-5-1, so the inner edge of the second protruding end 6-5-2 is relatively The inner sides of the two connecting sections 6-5-1 protrude toward the inside of the second measuring block 6; a second protrusion 6-5 is placed in a first groove 6-4. It can be seen from the above description that the third mass 6-1 and the fourth mass 6-2 of the second measuring block 6 are in a state of relative mating engagement at the center of the second measuring mass 6, that is, the first protrusion 6-3 and The second groove 6-6 is mated and engaged, and the first groove 6-4 and the second protrusion 6-5 are mated and engaged. The protruding part of each second protrusion 6-5 to the vertical centerline of the second measuring block 6 is connected with the first protruding end 6-3-2 through the third sensitive beam 4-3, so the two first The two protrusions 6-5 are respectively connected to the first protruding end 6-3-2 through a third sensitive beam 4-3, and each end of the inner side of the fourth mass block 6-2 is respectively passed through a second sensitive beam 4 -2 is connected to one end of the inner side of the third quality block 6-1; the two third sensitive beams 4-3 are symmetrical to the vertical center line of the second measuring block 6, and the two second sensitive beams 4-2 are opposite It is symmetrical to the vertical centerline of the second measuring block 6 .

Referring to Fig. 4, the outer sides of the third mass block 6-1 and the fourth mass block 6-2 are respectively connected to the chip frame 5 through a second support beam 8, the plane of the second support beam 8 is parallel to the XY plane, and the first At the center of the thickness of the three-mass block 6-1 or the fourth mass block 6-2 along the Z direction; the second support beam 8 is provided with a serpentine beam 7, and the plane of the serpentine beam 7 is perpendicular to the plane of the second support beam 8 ; One end of the serpentine beam 7 is connected to the outer edge of the third mass block 6-1 or the fourth mass block 6-2, and the other end is connected to the chip frame 5; the plane of the serpentine beam 7 is on the third mass block 6 -1 and the outer chip frame 5, or between the fourth mass 6-2 and the outer chip frame 5; the serpentine beam 7 includes several serpentine units 7-1, the serpentine unit 7-1 Arranged along the x direction between the proof mass and the chip frame 5, each serpentine unit 7-1 includes a first plane 7-2 and a second plane 7-3 perpendicular to each other, and the first plane 7-2 is parallel On the horizontal centerline of the Z measurement unit, i.e. the x direction, the second plane 7-3 is parallel to the vertical centerline of the Z measurement unit, and in the y direction, two ends of each first plane 7-2 are respectively connected to a second plane 7-2. Plane 7-3; the length of the first plane 7-2 in a serpentine unit 7-1 is not required, and can be set according to actual needs; the serpentine beam 7 is used to lead out the wire 16 without increasing the stiffness of the second support beam 8 , so that when the Z measurement unit is deformed by acceleration, the outer side of the third mass block 6-1 connected by the serpentine beam 7 and the chip frame 5 can be deformed along with the third mass mass block 6-1, and at the same time reduce the It is directly connected with the chip frame 5 to increase the deformation resistance of the third mass block 6-1; the same is true for the fourth mass block 6-2. All piezoresistors are fixedly arranged on each of the second sensitive beam 4-2 and the third sensitive beam 4-3, and all piezoresistors on the Z measurement unit are connected to the pads through metal leads 16, because on the Z measurement unit , when subjected to z-direction acceleration, there are both compression sensitive beams and tension sensitive beams, so that the piezoresistors on the sensitive beams can form a Wheatstone full bridge. The serpentine beam 7 on the Z-direction measuring unit enables the pure axial deformation of the second sensitive beam 4-2 to be realized, and at the same time, the function that there are both tension sensitive beams and compression sensitive beams on the same structure is realized, and then A Wheatstone full bridge is formed on a structure to improve the output sensitivity of the sensor. The sensor chip can realize the separate measurement of three-axis acceleration below 100g.

The size of the chip of this embodiment sensor is as follows:

The overall size of the sensor chip is: length × width × thickness = 6900 μm × 6900 μm × 410 μm;

The dimensions of the first support beam 1 in the X and Y measurement units are: length×width×thickness=300 μm×40 μm×410 μm;

The size of the second support beam 8 in the Z measuring unit is: length×width×thickness=1860 μm×290 μm×70 μm;

The size of the hinge beam of the X and Y measuring units is: length × width × thickness = 500 μm × 20 μm × 410 μm;

X, Y, Z measuring unit sensitive beams (including the first sensitive beam 4-1, the second sensitive beam 4-2 and the third sensitive beam 4-3) size: length × width × thickness = 70 μm × 10 μm × 5 μm;

The dimensions of the first mass block 2-1 and the second mass block 2-2 in the X and Y measurement units are: length×width×thickness=1530 μm×1000 μm×410 μm;

The dimensions of the third mass block 6-1 and the fourth mass block 6-2 in the Z measuring unit are: length×width×thickness=2800 μm×1860 μm×410 μm;

Lead width: 30μm;

The pad area is: 200μm×200μm.

The working principle of the sensor chip is:

Referring to Fig. 5, by Newton's second law F=ma, when the sensor chip is subjected to the acceleration a _x in the in-plane x direction, the mass blocks in the two first measuring blocks 2 in the X measuring unit are due to inertia In-plane movement occurs, causing deformation of the first support beam 1, thereby causing deformation of the first sensitive beam 4-1. According to the piezoresistive effect of silicon, the piezoresistor on the first sensitive beam 4-1 is under stress When the resistance value changes, the relationship between the resistance value change rate and the stress it receives is as follows:

Where: R is the initial resistance of the varistor;

π is the piezoresistive coefficient of the varistor;

σ is the stress of the varistor;

ΔR is the resistance change of the piezoresistor.

At this time, the semi-open-loop Wheatstone full bridge composed of four piezoresistors in the same working direction loses balance, and outputs an electrical signal proportional to the external acceleration _ax to realize the detection of acceleration. The relationship between the sensitivity S of the sensor and the external acceleration _ax is as follows:

Where: U _out is the output voltage of the Wheatstone bridge;

E is the Young's modulus of silicon;

π is the piezoresistive coefficient;

U _apply is the supply voltage of the Wheatstone bridge;

ε is the strain of the piezoresistive microbeam;

π ₄₄ is the shear piezoresistive coefficient;

l is the length of the sensitive beam;

Δl——the axial deformation of the sensitive beam;

When the sensor chip is subjected to the acceleration a _y of the in-plane y direction, the first mass 2-1 and the second mass 2-2 of the two first measurement blocks 2 in the Y measurement unit at this time occur due to inertia For in-plane movement, the working principle and sensitivity calculation method of the sensor chip are the same as when the sensor chip is subjected to the acceleration a _x , and will not be repeated here.

Referring to Fig. 6, the working principle of the Z axis is basically the same as that of the X and Y axes, the difference is that when subjected to the acceleration of the Z axis, the inner sides of the third mass 6-1 and the fourth mass 6-2 pass along the The up and down deflection in the z direction deforms the sensitive beams, and due to the roundabout end of the mass block, the deformation states of the middle two groups of sensitive beams are opposite to those of the outer two groups of sensitive beams; when the second sensitive beams of the outer two groups are 4- 2 When it is in a compressed state, the middle two groups of third sensitive beams 4-3 are in an elongated state; the four groups of sensitive beams form a Wheatstone bridge through wires.

The main technical indicators that the chip can achieve are as follows:

Range: 0 ~ 100g (three-axis acceleration);

Sensitivity: ≥1.6mV/g/3V;

Natural frequency: ≥10kHz;

Working temperature: -40℃～130℃.

The sensitivity and natural frequency of the chip designed in this embodiment are much higher than that of conventional accelerometer chips.

With reference to Fig. 7 and Fig. 8, the letter in the block diagram in Fig. 8 represents the sequence among Fig. 7, and the preparation method of chip among the present invention comprises the following steps:

1) Referring to (a) in FIG. 7, select raw materials, and use N-type (100) crystal plane double-sided polished SOI silicon wafer. The SOI silicon wafer includes substrate silicon 12 and buried oxide layer 10 stacked in sequence from bottom to top. and the device layer 11; the bottom glass plate 20 is made of BF33 glass; the SOI silicon wafer is cleaned, and double-sided thermal oxidation is performed at 900°C-1200°C to obtain a layer of thermal oxygen silicon dioxide layer 9 on the upper and lower surfaces of the silicon wafer respectively , including a thermal oxygen silicon dioxide layer 9-1 on the upper surface and a thermal oxygen silicon dioxide layer 9-2 on the lower surface, as a lightly doped mask layer, and at the same time improve the uniformity of ion implantation.

2) Referring to (b) in Figure 7, using a lightly doped plate, the first photolithography patterned the front side of the thermal oxygen silicon dioxide layer 9-1 on the upper surface, and removed the front side using a reactive ion etching (RIE) process The thermal oxygen silicon dioxide layer 9 in the lightly doped region 13, and the thermal oxygen silicon dioxide layer 9 in the remaining regions serve as a mask, and then lightly doped with boron ions to form a lightly doped region 13 in the device layer 11, so The above-mentioned lightly doped region 13 is the above-mentioned sensitive resistor, and each sensitive resistor is fixedly arranged on a sensitive beam, and the sensitive resistors on all sensitive beams are prepared through this step; The impurity concentration is uniformly distributed throughout the SOI device layer 11 .

3) Referring to the (c) figure in Figure 7, a layer of photoresist 14 is coated on the front side, the purpose is to protect the lightly doped region 13 from being affected in the next heavy doping step; using a heavily doped version, The second photolithography and reactive ion etching (RIE) process realizes the patterning of the silicon dioxide layer and removes the upper surface thermal oxygen silicon dioxide layer 9-1 and photoresist 14 in the front heavily doped region, and the photoresist 14 in the remaining regions Resist 14 acts as a mask, and then heavy doping of boron ions is performed to form a low-resistance ohmic contact region 15 in device layer 11; a redistribution diffusion annealing process is performed, and then a redistribution well push diffusion annealing process is performed to make the sensitive resistance The impurity concentration in the ohmic contact region 15 is evenly distributed to ensure stable contact between the next metal lead 16 and the piezoresistor on the sensitive beam.

4) Referring to (d) in Figure 7, a Ti/Al layer is formed on the entire front surface of the SOI silicon wafer using physical vapor deposition (PVD) technology, and then the third photolithography is performed using the metal pad and the wire plate, and then Etching the metal layers in other areas except the metal leads to form the metal leads 16 and the pad structure 17, and performing alloying process at high temperature.

5) Referring to (e) figure in FIG. 7, a silicon dioxide layer 18 is formed on the back side of the SOI silicon wafer using a PECVD process, and the silicon dioxide layer 18 is arranged on the back side of the thermal oxygen silicon dioxide layer 9-2 on the lower surface, At the same time, the thermal oxide silicon dioxide layer 9-2 on the lower surface and the silicon dioxide layer 18 are combined as a double mask layer for subsequent backside etching.

6) See (f) in Figure 7, the first etched plate on the back, and the fourth photolithography is in the back etching area of the SOI silicon wafer, and the RIE process is used to remove the thermal oxygen on the lower surface in the deep etching area on the back Silicon dioxide layer 9-2 and silicon dioxide layer 18, the lower surface of the rest of the region is thermally oxidized silicon dioxide layer 9-2 and silicon dioxide layer 18 as a mask; in the next etching step in order to ensure that the formed The supporting beam, the hinge beam 3 and the mass block have good edge verticality and aspect ratio, and are etched using deep reactive ion etching (Deep Reactive Ion Etching, DRIE); through this step, the X measurement unit and the A part of the lower part of the first supporting beam 1 and the hinge beam 3 in the Y measuring unit, and a part of the lower part of the first mass block 2-1 and the second mass block 2-2.

7) Referring to (g) in Figure 7, the second etching plate on the back, the fifth photolithography is to etch the area on the back of the SOI silicon wafer photolithography, and remove the second support beam 8 and the serpentine in the Z measurement unit The thermal silicon dioxide layer 9-2 and the silicon dioxide layer 18 on the lower surface of the etching region on the back side of the beam 7 as a mask layer, and the mask layer in the rest of the region serve as a mask; this step uses the DRIE process to etch the substrate silicon 12 , forming the lower part of the second support beam 8, the base layer structure of the third mass 6-1 and the fourth mass 6-2, the lower part of the serpentine beam 7, the lower part of the first support beam 1, the hinge beam 3, and the base layer structure of the first mass 2-1 and the second mass 2-2.

8) Referring to (h) in FIG. 7 , use the movement gap layout, the sixth photolithography, and perform photoresist masking on the bottom glass plate 19, and perform wet etching with KOH to form the cavity area 21 to ensure the acceleration The sensor can move normally under working conditions; the hollow area 21 is used to match the supporting beam, hinge beam, sensitive beam, and mass block area in the acceleration chip; sputtering Cr on the empty slot area 21 in the bottom glass plate 19 /Au layer 20 to prevent electrostatic adsorption.

9) Referring to (i) figure in Fig. 7, use the RIE process to etch the thermal silicon dioxide layer 9-2 and the silicon dioxide layer 18 on the lower surface of the SOI silicon wafer as a mask to expose the SOI silicon wafer back The substrate silicon 12 in the chip is then encapsulated on the bottom glass plate 19 by anodic bonding.

10) Referring to (j) in Figure 7, the seventh photolithography, using the first etching plate on the front, photolithographically etches the front etching area, and uses the reactive ion etching (RIE) process to remove the upper surface in the front etching area. The surface is thermally oxidized silicon dioxide layer 9-1, and then coated with a layer of photoresist to protect the metal lead 16 and pad structure 17, and etched to the buried surface by using Inductively Coupled Plasma (ICP) etching technology. The oxygen layer 10 is stopped to form the first support beam 1 , the hinge beam 3 , the sensitive beam 4 and the upper half of all mass blocks, forming the second support beam 8 and the device layer part of the serpentine beam 7 .

11) Referring to (k) in Figure 7, the eighth photolithography, using the second etching plate on the front, photolithographically etches the area of the second support beam 8 on the front, and uses the reactive ion etching (RIE) process to remove the second support The buried oxide layer 10 in the region of the beam 8 does not remove the photoresist, and serves to protect the metal lead and pad structure 16 . In the next etching step, in order to ensure that the formed serpentine beam 7 has good edge verticality and aspect ratio, deep reactive ion etching (DRIE) technology (Deep Reactive Ion Etching, DRIE) is used here to etch, etch away The buried oxide layer 10 in the upper region of the serpentine beam 7; so far the etching of the upper part of the second support beam 8 and the serpentine beam 7 is completed.

12) Referring to (l) in FIG. 7, spray photoresist on the front side of the etched SOI silicon wafer for protection, and then use the third etching plate on the front side to remove the corresponding buried oxide layer 10 for the tenth photolithography. The photoresist in the area, and then use buffer solution HF acid to etch the buried oxide layer 10 from the front side, rinse with deionized water and acetone respectively, and then dry naturally, and finally remove the photoresist on the front side;

13) In order to further release and alleviate the residual stress (including: mechanical stress, film internal stress, thermal stress, etc.) of the integrated sensor chip during processing, a low-temperature annealing process is used for processing.

The preparation of the MEMS triaxial piezoresistive accelerometer chip with pure axial deformation is completed.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (10)

1. A MEMS triaxial piezoresistive accelerometer chip of pure axial deformation, is characterized in that, comprises: X measurement unit, Y measurement unit and Z measurement unit that are fixedly arranged in chip outer frame (5), three The measurement unit is isolated by the chip outer frame (5); the vertical centerline of the Z measurement unit is parallel to the vertical centerline of the X measurement unit, and the vertical centerline of the Y measurement unit is perpendicular to the vertical centerline of the Z measurement unit; The chip outer frame (5) is bonded on the bottom glass plate (19); the Z measurement unit includes the third mass block (6-1) and the fourth mass block (6-2), the third mass block (6-1 ) and the outer side of the fourth mass block (6-2) are connected by a second support beam (8) and the chip frame (5); the inner side of the third mass block (6-1) is provided with The first protrusion (6-3), the two sides of the first protrusion (6-3) are respectively provided with a first groove (6-4); on the inner side of the fourth mass block (6-2) A second groove (6-6) is provided, and a second protrusion (6-5) is respectively arranged on both sides of the second groove (6-6); the first protrusion (6-3) engages with the In the two grooves (6-6), each second protrusion (6-5) is engaged in a second groove (6-6); each second protrusion (6-5) passes through the third sensitive The beam (4-3) is connected to the first protrusion (6-3); the two outer ends of the inner sides of the third mass block (6-1) and the fourth mass block (6-2) pass through a first mass block (6-2) respectively. Two sensitive beams (4-2) are connected; The piezoresistors on the second sensitive beam (4-2) and the third sensitive beam (4-3) are connected through metal leads (16) to form a Wheatstone full bridge. 2. the MEMS triaxial piezoresistive accelerometer chip of a kind of pure axial deformation according to claim 1, is characterized in that, the plane of described second support beam (8) is parallel to XY plane, and the second support beam The plane of (8) is set at the center line of the third mass block (6-1) or the fourth mass block (6-2) in the z direction; the second support beam (8) is fixedly provided with a serpentine beam (7) . 3. a kind of MEMS triaxial piezoresistive accelerometer chip of pure axial deformation according to claim 2, is characterized in that, described serpentine beam (7) comprises several serpentine units (7-1); Each serpentine unit (7) is fixedly arranged between the third mass block (6-1) and the chip outer frame (5), or fixedly arranged between the fourth mass block (6-2) and the chip outer frame (5) between; the serpentine unit (7-1) includes a first plane (7-2) and a second plane (7-3) perpendicular to each other, and the first plane (7-2) is parallel to the lateral direction of the Z measuring unit The centerline, the second plane (7-3) is parallel to the vertical centerline of the Z measuring unit, and the two ends of each first plane (7-2) are respectively connected with a second plane (7-3). 4. a kind of MEMS triaxial piezoresistive type accelerometer chip of pure axial deformation according to claim 1, is characterized in that, described first protrusion (6-3) comprises the first connecting section ( 6-3-1) and the first protruding end (6-3-2), the first connecting section (6-3-1) connects the main body of the third mass (6-3) and the first protruding end (6 -3-2) Integral connection, the width of the first protruding end (6-3-2) is greater than the width of the first connection section (6-3-1); the second protrusion (6-5) includes the second connection segment (6-5-1) and the second protruding end (6-5-2), the second connecting segment (6-5-1) connects the main body of the fourth mass block (6-4) and the second protruding end (6-5-2) connection, the width of the second protruding end (6-5-2) is greater than the width of the second connection section (6-5-1); each second protruding end (6-5- 2) Connect with the first protruding end (6-3-2) through a third sensitive beam (4-3). 5. the MEMS triaxial piezoresistive accelerometer chip of a kind of pure axial deformation according to claim 4, is characterized in that, two second sensitive beams (4-2) are respectively arranged on a second connecting section ( 6-5-1) outside. 6. the MEMS triaxial piezoresistive accelerometer chip of a kind of pure axial deformation according to claim 1, is characterized in that, the structure of X measurement unit and Y measurement unit is identical, respectively by two first measurement pieces ( 2) Composition, each first measuring block (2) includes a first mass block (2-1) and a second mass block (2-2), the first mass block (2-1) and the second mass block ( 2-2) The outer side of the first mass block (2-1) and the inner side of the second mass block (2-2) are connected by a first support beam (1) and the chip outer frame (5). Connected with the first sensitive beam (4-1) through the hinge beam (3); The piezoresistors on the first sensitive beam (4-1) in the X measurement unit are connected by metal leads (16) to form a Wheatstone half bridge; the piezoresistors on the first sensitive beam (4-1) in the Y measurement unit The sensitive resistors are connected through metal leads (16) to form a Wheatstone half bridge. 7. a kind of MEMS triaxial piezoresistive accelerometer chip of pure axial deformation according to claim 6, is characterized in that, the first mass block (2-1) and the second mass block (2-2) First gaps (2-3) are arranged on the inner sides, and the two first gaps (2-3) are arranged symmetrically with respect to the transverse center line of the first measuring block (2); the two ends of the hinge beam (3) are respectively It is fixedly connected with the inner end surfaces of the two first notches (2-3); the hinge beam (3) is arranged on the vertical center line of the first measuring block (2). 8. a kind of MEMS triaxial piezoresistive accelerometer chip of pure axial deformation according to claim 6, is characterized in that, the first mass block (2-1) and the second mass block (2-2) The inner sides are connected by two first sensitive beams (4-1), and the two first sensitive beams (4-1) are respectively arranged on both sides of the first notch (2-3), and the two first sensitive beams ( 4-1) It is symmetrical with respect to the hinge beam (3). 9. a kind of MEMS triaxial piezoresistive accelerometer chip of pure axial deformation according to claim 6, is characterized in that, the first mass block (2-1) and the second mass block (2-2) The outside is provided with a second gap (2-4); one end of each first support beam (1) is fixedly connected to the chip outer frame (5), and the other end is fixedly connected to the inner end surface of the second gap (2-4) ; The first support beam (1) is arranged on the vertical center line of the first measuring block (2). 10. a method for preparing the MEMS triaxial piezoresistive accelerometer chip of pure axial deformation according to claim 1, is characterized in that, comprises the following steps: 1) Carry out double-sided thermal oxidation to the SOI silicon wafer, and form a layer of thermal oxygen silicon dioxide layer (9) on the upper surface and the lower surface of the SOI silicon wafer respectively, which are respectively the upper surface thermal oxygen silicon dioxide layer (9-1 ) and the lower surface thermal oxygen silicon dioxide layer (9-2); 2) Using a lightly doped plate, remove the upper surface thermal oxygen silicon dioxide layer (9-1) in the lightly doped region of the SOI upper surface by photolithography and reactive ion etching, and dope boron in the lightly doped region After the ions, a lightly doped region (13) is formed; 3) Using a heavily doped plate, remove the upper surface thermal oxygen silicon dioxide layer (9-1) in the heavily doped region by photolithography and reactive ion etching, and perform heavy doping in the heavily doped region to form an ohmic contact zone (15); 4) Depositing a Ti/Al layer on the front side of the SOI silicon wafer by physical vapor deposition, and performing photolithography through the metal pad and the wire plate to form the metal lead (16) and the pad structure (17); 5) Deposit a layer of silicon dioxide layer (18) by vapor deposition on the back side of the lower surface thermal oxygen silicon dioxide layer (9-2), the lower surface thermal oxygen silicon dioxide layer (9-2) and the silicon dioxide layer (18) forming a double mask layer; 6) Remove the double mask layer in the deep etching area on the back of the SOI silicon wafer by reactive ion etching, so that the substrate silicon (12) in the deep etching area of the SOI silicon wafer is exposed; etch the substrate by deep reactive ion etching Silicon (12), etch away a part of the lower part of the first support beam (1) and the hinge beam (3) in the X measurement unit and the Y measurement unit, and the first mass block (2-1) and the second mass block (2-1) -2) part of the lower part; 7) Remove the double mask layer in the etching area of the second support beam (8) and the serpentine beam (7) in the Z measurement unit by photolithography; continue etching by deep reactive ion etching method to form the second support beam The lower part of (8), the lower part of the serpentine beam (7), the lower part of the first support beam (1), the lower part of the hinge beam (3), and the base layer structure of all mass blocks; 8) performing a photoresist mask on the bottom glass plate (19) by moving the gap pattern, and performing wet etching by KOH to form a cavity area (21) on the bottom glass plate (19); 9) Etching the remaining double mask layer on the back of the SOI silicon wafer by deep reactive ion etching, so that the substrate silicon (12) of the SOI silicon wafer is exposed; the substrate silicon (12) area is encapsulated by anodic bonding on the bottom glass plate (19); 10) Etching and removing the thermal oxygen silicon dioxide layer (9-1) on the upper surface of the SOI silicon wafer by reactive ion etching, coating a layer of photoresist, and then etching to the buried oxide layer by inductively coupled plasma etching (10) stop, form the upper part of the first support beam (1), hinge beam (3), sensitive beam (4) and all masses, form the second support beam (8), and the serpentine beam (7) Device layer part; 11) Removing the device layer and buried oxide layer (10) on the upper surface of the second support beam (8) by reactive ion etching, and then etching away the device layer on the upper region of the serpentine beam (7) by reactive deep ion etching and the buried oxide layer (10), the etching of the upper part of the second support beam (8) and the serpentine beam (7) is completed; 12) Spray photoresist on the front side of the etched SOI silicon wafer for protection, remove the photoresist in the corresponding buried oxide layer (10) region, and then use buffer to etch the remaining buried oxide layer (10) on the front side of the SOI silicon wafer ), after cleaning the front side of the SOI silicon wafer, dry it naturally, and finally remove the photoresist on the front side of the SOI silicon wafer; 13) The SOI silicon wafer is processed by low-temperature annealing process, and the MEMS three-axis piezoresistive accelerometer chip with pure axial deformation is fabricated.