MEMS multifunctional sensor and preparation method thereof

Abstract

The invention provides an MEMS multifunctional sensor and a preparation method thereof.The MEMS multifunctional sensor comprises a first substrate, a second substrate and a sensor assembly, the first substrate comprises a sensor area and an annular bonding area, the annular bonding area is connected to the sensor area in the circumferential direction of the sensor area, a circumferential cavity is formed between the annular bonding area and the sensor area, and the annular bonding area is connected to the sensor area in the circumferential direction of the annular bonding area; the circumferential cavity is of an annular cavity structure, the annular bonding area is in bonding connection with the second substrate, an annular groove is formed in the end, making contact with the second substrate, of the annular bonding area, the annular groove of the annular bonding area is covered with the second substrate, an annular bonding cavity is formed, and the sensor assembly is arranged in the sensor area and used for sensing external pressure. The thermal stress transmitted from the bonding interface is offset by using the deformation of the circumferential cavity and the thin-layer medium around the bonding cavity, so that the bonding thermal stress at the position of the piezoresistor is effectively reduced, the zero output drift of the sensor caused by stress concentration is avoided, and the output precision of the sensor is improved.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application belong to the technical field of micro-electro-mechanical system (MEMS), and particularly relate to a MEMS multifunctional sensor and a preparation method thereof. BACKGROUND

[0002] MEMS sensors can be divided into piezoresistive, capacitive, resonant and piezoelectric types. Among them, MEMS piezoresistive sensors have high sensitivity, fast response, small size and low power consumption, and play an important role in this field. Generally, MEMS piezoresistive sensors work based on piezoresistive effect. When external physical quantity acts on the sensitive film, the film deforms, causing the resistance of the piezoresistive resistor to change, and the change is converted into an electrical signal output through a Wheatstone bridge.

[0003] Traditional MEMS piezoresistive sensors generally adopt a square prism sealed cavity structure, and use a "back" shaped bonding area to connect different substrates during the process of process wafer. However, due to the difference in thermal expansion coefficient between silicon substrate and glass substrate, and the temperature required by anodic bonding process is significantly higher than the working temperature, bonding thermal stress will be generated at the bonding interface, which is transmitted to the film surface and piezoresistive resistor through the silicon substrate medium above the bonding interface, thereby causing zero drift problem and affecting the measurement accuracy of the sensor. To solve this problem, low-temperature bonding process is usually used in the prior art, but this will also cause the bonding strength to decrease, affecting the service life of the sensor. SUMMARY

[0004] Embodiments of the present application aim to at least solve one of the technical problems existing in the prior art, and provide a MEMS multifunctional sensor and a preparation method thereof.

[0005] The first aspect of the present application provides a MEMS multifunctional sensor, which comprises: A first substrate, the first substrate comprises a sensor area and an annular bonding area, the annular bonding area is connected to the sensor area along the circumference of the sensor area, a circumferential cavity is formed between the annular bonding area and the sensor area, and the circumferential cavity is an annular cavity structure; A second substrate, the annular bonding area is bonded to the second substrate, one end of the annular bonding area in contact with the second substrate has an annular groove, and the second substrate covers the annular groove of the annular bonding area and forms an annular bonding cavity; A sensor assembly, the sensor assembly is arranged in the sensor area, and the sensor assembly is used for sensing external pressure.

[0006] In some embodiments of the present application, the circumferential cavity comprises a first annular cavity and a second annular cavity along a direction from the first substrate to the second substrate, the first annular cavity is in communication with the second annular cavity, and a radial thickness of the first annular cavity is greater than a radial thickness of the second annular cavity.

[0007] In some embodiments of the present application, the second annular cavity is in communication with the first annular cavity near an inner ring of the sensor region.

[0008] In some embodiments of the present application, a cross section of the annular groove is trapezoidal.

[0009] In some embodiments of the present application, an end cavity is formed between the sensor region and the second substrate, and the end cavity is in communication with the circumferential cavity.

[0010] In some embodiments of the present application, the sensor region has a thin film cavity, the thin film cavity is a cuboid cavity, a cross section of the cuboid cavity is square in a thickness direction perpendicular to the first substrate, and a portion of the sensor region corresponding to a side of the thin film cavity away from the second substrate is a sensitive thin film. The sensor assembly comprises four first piezoresistors, the four first piezoresistors are arranged on a side of the sensitive thin film away from the second substrate, the four first piezoresistors are respectively arranged at centers of four sides of the thin film cavity, and the four first piezoresistors constitute a first Wheatstone bridge. The sensor assembly comprises four pairs of first ohmic contacts, each pair of the first ohmic contacts is arranged at two ends of a corresponding one of the first piezoresistors.

[0011] In some embodiments of the present application, the sensor region has four block cavities, the four block cavities correspond to four corners of the thin film cavity, each block cavity is in communication with the thin film cavity and the end cavity, a portion of the sensor region between two adjacent block cavities forms a bridge, and a portion of the sensor region between the four block cavities forms a mass block, the mass block is arranged at a center of the thin film cavity. The sensor assembly comprises four second piezoresistors, the four second piezoresistors are respectively arranged on a side of each of the four bridges away from the thin film cavity, and the four second piezoresistors constitute a second Wheatstone bridge. The sensor assembly comprises four pairs of second ohmic contacts, each pair of the second ohmic contacts is arranged at two ends of a corresponding one of the second piezoresistors.

[0012] In some embodiments of the present application, each second piezoresistor is arranged at an end of the bridge close to the mass block.

[0013] In some embodiments of the present application, the MEMS multifunctional sensor further comprises an insulating layer covering the surface of the first substrate away from the second substrate.

[0014] The second aspect of the present application provides a preparation method of a MEMS multifunctional sensor, which is used for preparing the MEMS multifunctional sensor of any one of the above-mentioned embodiments, and the method comprises: Step one: selecting an N-type single crystal silicon wafer with a 100 crystal face as the first substrate; Step two: preparing a silicon dioxide thin layer at the shallow layer on the upper surface of the first substrate by oxygen injection isolation technology, to prepare for the subsequent preparation of a thin film cavity and a circumferential cavity; Step three: forming a ring cavity shape required for bonding cavity by wet etching on the outside of the bottom of the first substrate; Step four: forming a cylindrical end cavity by photolithography and deep reactive ion etching on the inside area of the bottom of the first substrate; Step five: again preparing a cavity and a ring-shaped narrow slot by photolithography and deep reactive ion etching on the central and peripheral areas of the bottom of the first substrate, so as to expose the mass block and the lower half of the bridge structure, and ensure that the silicon dioxide thin layer at the shallow layer on the upper surface of the silicon wafer is in communication; Step six: removing the silicon dioxide thin layer by wet etching on the shallow layer on the upper surface of the first substrate through the cavity and the ring-shaped narrow slot, to form a thin film cavity, a sensitive thin film, a circumferential cavity, a mass block and a bridge; the thin film cavity is in communication with the four block cavities around the mass block; Step seven: forming a first piezoresistor and a second piezoresistor by P-type doping on the surface and back of the silicon wafer; Step eight: forming a first ohmic contact and a second ohmic contact by P-type heavy doping on both ends of the first piezoresistor and the second piezoresistor; Step nine: forming an insulating layer by depositing a silicon dioxide layer on the surface of the silicon wafer; Step ten: selecting a glass wafer, and anodically bonding the ring-shaped bonding area on the back of the silicon wafer with the surface of the glass substrate to realize the sealing of the cavity and form a second substrate, thereby completing the preparation of the sensor.

[0015] Compared with the prior art, the present application has the following advantages: 1. The MEMS multifunctional sensor of the present application can uniformly and quickly transmit the bonding thermal stress upward by adopting the special structure of the ring-shaped bonding area and the end cavity, and can offset part of the thermal stress transmitted from the bonding interface by the deformation of the thin layer medium around the circumferential cavity and the bonding cavity, thereby effectively reducing the bonding thermal stress at the position of the piezoresistor, avoiding the zero point output drift of the sensor caused by stress concentration, and improving the output precision of the sensor.

[0016] 2. The MEMS multifunctional sensor of the present application realizes the preparation of the accelerometer mass and the bridge by stacking the medium under the sensitive film of the pressure sensor, thereby realizing device integration, improving the space utilization, and realizing the compatibility of both the land area and the preparation process optimization by optimizing the cavity release process, simplifying the processing flow, reducing the production cost.

[0017] 3. The MEMS multifunctional sensor of the present application increases the bonding strength at the bonding interface by bonding the single crystal silicon medium on both sides of the cavity, and uses the double-layer cavity structure of the end cavity and the bonding cavity to maintain the internal vacuum environment, ensures the long-term air tightness, prolongs the service life of the device, at the same time, reduces the damping coefficient of the accelerometer, improves the quality factor and sensitivity of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a top view schematic diagram of the pressure sensor pressure sensitive resistor arrangement in the MEMS multifunctional sensor of the present application; Figure 2 It is a top view schematic diagram of the acceleration sensor pressure sensitive resistor arrangement in the MEMS multifunctional sensor of the present application; Figure 3 It is a sectional view of the MEMS multifunctional sensor of the present application along the A-A' direction; Figure 1 Figure 4 It is a structure sectional view corresponding to the preparation step one in the embodiment of the present application; Figure 5 It is a structure sectional view corresponding to the preparation step two in the embodiment of the present application; Figure 6 It is a structure sectional view corresponding to the preparation step two shown in the figure; Figure 5 Figure 7 It is a structure sectional view corresponding to the preparation step three in the embodiment of the present application; Figure 8 It is a structure sectional view corresponding to the preparation step three shown in the figure; Figure 7 Figure 9 It is a structure sectional view corresponding to the preparation step four in the embodiment of the present application; Figure 10 It is a structure sectional view corresponding to the preparation step four shown in the figure; Figure 9 Figure 11 It is a structure sectional view corresponding to the preparation step five in the embodiment of the present application; Figure 12 It is a structure sectional view corresponding to the preparation step five shown in the figure; Figure 11 Figure 13 ​​​​​This is a cross-sectional view of the structure corresponding to step six in this embodiment of the invention; Figure 14 for Figure 13 The diagram shows the B-B' cross-sectional view of the structure corresponding to preparation step six; Figure 15 for Figure 13 The bottom view of the structure corresponding to preparation step six is ​​shown; Figure 16 This is a cross-sectional view of the structure corresponding to step seven in this embodiment of the invention; Figure 17 for Figure 16 The top view of the structure corresponding to preparation step seven is shown; Figure 18 for Figure 16 The bottom view of the structure corresponding to preparation step seven is shown; Figure 19 This is a cross-sectional view of the structure corresponding to step eight in this embodiment of the invention; Figure 20 for Figure 19 The top view of the structure corresponding to preparation step eight is shown; Figure 21 for Figure 19 The bottom view of the structure corresponding to preparation step eight is shown. Figure 22 This is a cross-sectional view of the structure corresponding to step nine in this embodiment of the invention; Figure 23 This is a cross-sectional view of the structure corresponding to step nine in this embodiment of the invention.

[0019] The labels in the attached diagram are as follows: 1. Insulating layer; 2. First substrate; 3. First varistor; 4. First ohmic contact; 5. Thin film cavity; 6. Sensitive thin film; 7. Circumferential cavity; 8. Mass block; 9. Second varistor; 10. Second ohmic contact; 11. Bridge; 12. Second substrate; 13. End cavity; 14. Bonding cavity; 15. Annular bonding region; 16. Sensor region. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit disclosure. The described embodiments are some, but not all, of the embodiments of the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0021] like Figures 1 to 3As shown, the first aspect of the present application provides a MEMS multifunctional sensor, which comprises a first substrate 2, a second substrate 12 and a sensor assembly. The sensor assembly is arranged in a sensor area 16 of the first substrate 2 (as shown in Figure 3 Specifically, the first substrate 2 comprises the sensor area 16 and a ring-shaped bonding area 15 connected to the sensor area 16 along the circumference of the sensor area 16. A circumferential cavity 7 is formed between the ring-shaped bonding area 15 and the sensor area 16, and the circumferential cavity 7 has a ring-shaped cavity structure. The ring-shaped bonding area 15 is bonded to the second substrate 12. The end of the ring-shaped bonding area 15 in contact with the second substrate 12 has a ring-shaped groove. The second substrate 12 covers the ring-shaped groove of the ring-shaped bonding area 15 and forms a ring-shaped bonding cavity 14.

[0022] According to the MEMS multifunctional sensor of the present application, the first substrate 2, the second substrate 12 and the sensor assembly are provided. The first substrate 2 comprises the sensor area 16 and the ring-shaped bonding area 15 connected to the sensor area 16 along the circumference of the sensor area 16. The sensor area 16 is provided with the sensor assembly for sensing external pressure. The sensor area 16 is not in contact with the second substrate 12. The ring-shaped bonding area 15 is bonded to the second substrate 12 to connect the first substrate 2 and the second substrate 12. The closed ring-shaped bonding cavity 14 formed between the ring-shaped bonding area 15 and the second substrate 12 reduces the contact area of the ring-shaped bonding area 15 and the second substrate 12, thereby reducing the thermal stress generated by the bonding of the ring-shaped bonding area 15 and the second substrate 12, and reducing the thermal stress transmitted from the ring-shaped bonding area 15 to the sensor area 16. The thermal stress generated by the bonding of the ring-shaped bonding area 15 and the second substrate 12 is transmitted along the thickness direction of the first substrate 2 from the end of the ring-shaped bonding area 15 close to the second substrate 12 to the end of the ring-shaped bonding area 15 away from the second substrate 12. The circumferential cavity 7 of the sensor area 16 blocks the transmission of the thermal stress of the ring-shaped bonding area 15 to the sensor area 16. The double effects of the ring-shaped bonding cavity 14 and the axial cavity can reduce the influence of the bonding thermal stress on the sensor area 16 and the sensor assembly arranged in the sensor area 16, avoid the sensor zero-point output drift caused by the stress concentration of the sensor area 16 and the sensor assembly, improve the accuracy of the sensor output, and ensure the service life of the sensor.

[0023] In some embodiments of the present application, the MEMS multifunctional sensor further comprises an insulating layer 1 covering the surface of the side of the first substrate 2 away from the second substrate 12. Specifically, the insulating layer 1 completely covers the upper surface of the first substrate 2 to isolate and protect the piezoresistor of the sensor area 16. The material of the insulating layer 1 is at least one of silicon dioxide and silicon nitride. The thickness of the insulating layer 1 is 100-500 nm.

[0024] In some embodiments of the present application, the first substrate 2 includes a sensor region 16 and an annular bonding region 15 connected along the circumference of the sensor region 16, the sensor region 16 is not in contact with the second substrate 12 and forms a cavity along the thickness direction of the first substrate 2, and the annular bonding region 15 is bonded to the second substrate 12 at one end close to the second substrate 12. Specifically, the sensor region 16 has a cylindrical structure as a whole, the inner ring of the annular bonding region 15 is a circular ring, and the outer ring of the annular bonding region 15 is a positive direction ring, that is, the inner ring of the circular annular bonding region 15 is connected to the outer wall of the sensor region 16 along the circumference of the cylindrical sensor region 16, and the end of the annular bonding region 15 away from the second substrate 12 is connected to the sensor region 16. The annular groove of the annular bonding region 15 is a circular groove, and the annular bonding cavity 14 formed by the annular groove is a circular cavity structure. The sensor region 16 and the annular bonding region 15 are integrally formed, and the material of the sensor region 16 and the annular bonding region 15 is the same. The material of the first substrate 2 is single crystal silicon, that is, the material of the sensor region 16 and the annular bonding region 15 is single crystal silicon, and the thickness of the first substrate 2 is 300-500 μm.

[0025] Specifically, the annular bonding region 15 has oppositely arranged first and second ends, wherein the first end is bonded to the second substrate 12, and the first end is provided with an annular groove, and the second end is connected to the sensor region 16 along the circumference of the sensor region 16.

[0026] In some embodiments of the present application, along the direction from the first substrate 2 to the second substrate 12, the circumferential cavity 7 includes a first annular cavity and a second annular cavity, the first annular cavity and the second annular cavity are in communication, and the radial thickness of the first annular cavity is greater than the radial thickness of the second annular cavity. By setting the radial thickness of the first annular cavity to be greater than the radial thickness of the second annular cavity, the distance between the second end of the annular bonding region 15 and the sensor region 16 is greater than the distance between other positions of the annular bonding region 15 and the sensor region 16, thereby further reducing the transmission of thermal stress.

[0027] In some embodiments of the present application, the second annular cavity communicates with the inner ring of the first annular cavity close to the sensor region 16. Specifically, the circumferential cavity extends along the radial direction of the sensor region 16 from the outer wall of the cylindrical sensor region 16 to the inner wall of the annular bonding region 15, that is, the first annular cavity and the second annular cavity are both formed by extending from the outer wall of the cylindrical sensor region 16 to the inner wall of the annular spacing region, therefore, the wall thickness of the annular bonding region 15 corresponding to the first annular cavity is smaller than the wall thickness of the annular bonding region 15 corresponding to the second annular cavity, by reducing the wall thickness of the second end of the annular bonding region 15 connected to the sensor region 16, the heat dissipation of the second end of the annular bonding region 15 can be improved, thereby reducing the thermal stress transmitted from the annular bonding region 15 to the sensor region 16.

[0028] In some embodiments of the present application, the cross section of the annular groove is trapezoidal. The single crystal silicon medium inside the bonding cavity 14 deforms under the action of bonding thermal stress, thereby releasing the bonding thermal stress and reducing the stress transmitted to the sensitive thin film 6. In addition, the area of the second end of the annular bonding area 15 in contact with the second substrate 12 is small, and the cross section of the annular groove gradually decreases in the direction away from the second substrate 12, so that the annular bonding area 15 has sufficient rigidity. The single crystal silicon medium on both sides of the bonding cavity 14 serves to increase the anodic bonding strength and the internal vacuum degree of the cavity.

[0029] In some embodiments of the present application, the sensor area 16 is in a non-contact state with the second substrate 12, and an end cavity 13 is formed between the sensor area 16 and the second substrate 12. The end surface of the sensor area 16 close to the second substrate 12, the end surface of the second substrate 12 close to the first substrate 2, and the circular inner wall of the annular bonding area 15 jointly form a cylindrical end cavity 13. The end cavity 13 is in communication with the circumferential cavity 7 and the thin film cavity 5, respectively. The end cavity 13 is located in the center of the surface of the first substrate 2 close to the second substrate 12. The generated bonding thermal stress can be uniformly transmitted to the sensor surface through the end cavity 13.

[0030] In some embodiments of the present application, the sensor area 16 has a thin film cavity 5. The thin film cavity 5 is a cuboid cavity, and the cross section of the cuboid cavity is a square perpendicular to the thickness direction of the first substrate 2. The corresponding part of the sensor area 16 on the side away from the second substrate 12 is the sensitive thin film 6. Further, the circumferential cavity 7 is located outside the same height of the thin film cavity 5, that is, the minimum distance between the circumferential cavity and the insulating layer 1 is the same as the minimum distance between the thin film cavity 5 and the insulating layer 1. The cross section of the circumferential cavity 7 along the thickness direction of the first substrate 2 is a rectangular ring. The thin film connected by the annular bonding area 15 above the circumferential cavity 7 and the sensor area 16 deforms under the action of bonding thermal stress, thereby releasing the bonding thermal stress and reducing the stress transmitted to the sensitive thin film 6.

[0031] The sensor assembly comprises four first piezoresistors 3. The four first piezoresistors 3 are arranged on the side of the sensitive thin film 6 away from the second substrate 12, and the four first piezoresistors 3 correspond to the centers of the four edges of the thin film cavity 5, respectively. The four first piezoresistors 3 constitute a first Wheatstone bridge. Specifically, the four first piezoresistors 3 are located on the lower surface of the insulating layer 1. The first piezoresistors 3 can be arranged in the groove on the surface of the sensitive thin film 6. The four first piezoresistors 3 are arranged in parallel at the center positions of the four edges of the sensitive thin film 6 and face the edge centers of the thin film cavity, so as to arrange the piezoresistors at the maximum stress position of the sensitive thin film 6 and constitute the first Wheatstone bridge. The material of the first piezoresistor 3 is P-type doped single crystal silicon, and the thickness of the first piezoresistor 3 is 0.1-3 μm. The length and width are determined according to the design index.

[0032] The sensor assembly comprises four pairs of first ohmic contacts 4, each pair of first ohmic contacts 4 being arranged at two ends of a corresponding first piezoresistor 3. Specifically, the first ohmic contacts 4 are arranged at two ends of the first piezoresistor 3 to achieve good electrical interconnection between the first piezoresistor 3 and the lead wire, the material of the first ohmic contacts 4 is P-type heavily doped monocrystalline silicon, the thickness of the first ohmic contacts 4 is the same as that of the first piezoresistor 3, and the shape of the first ohmic contacts 4 is determined by the specific layout.

[0033] In some embodiments of the present application, the sensor region 16 has four block cavities corresponding to four corners of the thin film cavity 5, each block cavity being in communication with the thin film cavity 5 and the end cavity 13, the part of the sensor region 16 between two adjacent block cavities forming a bridge 11, and the part of the sensor region 16 between the four block cavities forming a mass block 8 corresponding to the center of the thin film cavity 5. Specifically, the mass block 8 and the four bridges 11 are formed by monocrystalline silicon medium directly below the thin film cavity, the mass block 8 is located at the center of the first substrate 2, and the thickness of the mass block 8 is 100-200 μm. The four bridges 11 are symmetrically arranged on the center lines of the four edges of the mass block 8 to achieve the connection of the mass block 8 and the surrounding monocrystalline silicon medium, and the width and height of the bridge 11 are both smaller than those of the mass block 8.

[0034] The sensor assembly comprises four second piezoresistors 9, each of which is arranged on a side of the four bridges 11 away from the thin film cavity 5, and the four second piezoresistors 9 form a second Wheatstone bridge. Specifically, the four second piezoresistors 9 are arranged in parallel on the lower surface of the bridge 11 close to the mass block 8, so as to arrange the piezoresistors at the maximum stress position of the sensitive thin film 6 and form a second Wheatstone bridge, the material of the second piezoresistor 9 is P-type doped monocrystalline silicon, the thickness of the second piezoresistor 9 is 0.1-3 μm, and the length and width thereof are determined according to the design index.

[0035] The sensor assembly comprises four pairs of second ohmic contacts 10, each pair of second ohmic contacts 10 being arranged at two ends of a corresponding second piezoresistor 9. Specifically, the second ohmic contacts 10 are arranged at two ends of the second piezoresistor 9 to achieve good electrical interconnection between the second piezoresistor 9 and the lead wire, the material of the second ohmic contacts 10 is P-type heavily doped monocrystalline silicon, the thickness of the second ohmic contacts 10 is the same as that of the second piezoresistor 9, and the shape of the second ohmic contacts 10 is determined by the specific layout.

[0036] Further, the second substrate 12 is arranged directly below the first substrate 2, the surface thereof is sealed and connected together with the outer side annular bonding region 15 of the back surface of the first substrate 2 to achieve environmental sealing of the annular bonding cavity 14. Specifically, the material of the second substrate 12 is at least one of monocrystalline silicon or glass, the thickness of the second substrate 12 is 400-1000 μm, and the annular bonding region 15 functions to reduce the bonding thermal stress of the sensor surface.

[0037] The working principle of the MEMS multifunctional sensor of the present application is as follows: When the sensor is subjected to external pressure, the sensitive film 6 deforms, so that stress and strain are generated at the first piezoresistor 3, based on the piezoresistive effect, the resistance of the piezoresistor changes accordingly, and an output voltage is generated through the first Wheatstone bridge; when the sensor is subjected to external vertical acceleration, the bridge 11 deforms, so that stress and strain are generated at the second piezoresistor 9, based on the piezoresistive effect, the resistance of the piezoresistor changes accordingly, and an output voltage is generated through the second Wheatstone bridge. Among them, since the anodic bonding is carried out by using the annular bonding area 15, and the transmission is carried out through the single crystal silicon medium around the lower half of the cylindrical cavity of the end cavity 13, compared with the traditional "back" bonding area and the square prism sealed cavity structure, the thermal stress is uniformly distributed and quickly transmitted upward to the surface of the sensor, effectively reducing the bonding thermal stress at the position of the piezoresistor. In this process, the single crystal silicon medium inside the bonding cavity 14 and the thin layer medium above the circumferential cavity 7 both offset part of the thermal stress transmitted from the bonding interface through deformation, further reducing the bonding thermal stress transmitted to the first piezoresistor 3 and the second piezoresistor 9, thereby reducing the influence of the bonding thermal stress on the zero drift of the sensor and improving the measurement accuracy.

[0038] The second aspect of the present application provides a preparation method of a MEMS multifunctional sensor, which is used for preparing the MEMS multifunctional sensor of any one of the above embodiments, and the method comprises the following steps: Step one: select an N-type single crystal silicon wafer with a thickness of 500 μm and a crystal face of (100) as the first substrate 2, as shown in Figure 4 ; Step two: prepare a silicon dioxide thin layer on the shallow layer of the upper surface of the first substrate 2 by SIMOX (Separation by Implanted Oxygen), and the silicon dioxide thin layer corresponds to the positions of the thin film cavity 5 and the circumferential cavity 7, which prepares the first annular cavity for the subsequent preparation of the thin film cavity 5 and the circumferential cavity 7, as shown in Figure 5 and Figure 6 ; Step three: form the annular groove with a trapezoidal cross section required for the bonding cavity 14 by wet etching on the outside of the bottom of the first substrate 2, as shown in Figure 7 and Figure 8 ; Step four: form the cylindrical end cavity 13 at one end of the sensor area 16 close to the annular groove by photolithography and DRIE (Deep Reactive Ion Etching) on the inside of the bottom of the first substrate 2, as shown in Figure 9 andFigure 10 as shown in Fig. 6; Step five: four block cavities and a ring-shaped narrow slot are prepared at the center and the periphery of the bottom of the first substrate 2 by lithography and DRIE again, the ring-shaped narrow slot is a second ring-shaped cavity of the circumferential cavity, so as to expose the mass block 8 and the lower half of the bridge 11 structure, and ensure that the silicon dioxide thin layer at the shallow layer of the upper surface of the silicon wafer is communicated, that is, the four block cavities respectively extend to the silicon dioxide thin layer corresponding to the thin film cavity, and the second ring-shaped cavity extends to the silicon dioxide thin layer corresponding to the first ring-shaped cavity of the circumferential cavity, as shown in Fig. 7; Figure 11 as shown in Fig. 8; Figure 12 as shown in Fig. 9; Step six: the silicon dioxide thin layer is removed by wet etching the shallow layer of the upper surface of the first substrate 2 through the cavity and the ring-shaped narrow slot, so as to form the thin film cavity 5, the sensitive thin film 6, the first ring-shaped cavity of the circumferential cavity 7, the mass block 8 and the bridge 11, and the four block cavities around the thin film cavity 5 and the mass block 8 are communicated, as shown in Fig. 10; Figure 13 as shown in Fig. 11; Figure 14 as shown in Fig. 12; Figure 15 as shown in Fig. 13; Step seven: the first piezoresistor 3 and the second piezoresistor 9 are formed by P-type doping the surface and the back of the silicon material first substrate, and the thicknesses of the two piezoresistors are both 2 μm, as shown in Fig. 14; Figure 16 as shown in Fig. 15; Figure 17 as shown in Fig. 16; Figure 18 as shown in Fig. 17; Step eight: the first ohmic contact 4 and the second ohmic contact 10 are formed by P-type heavy doping at both ends of the first piezoresistor 3 and the second piezoresistor 9, as shown in Fig. 18; Figure 19 as shown in Fig. 19; Figure 20 as shown in Fig. 20; Figure 21 as shown in Fig. 21; Step nine: the insulating layer 1 is formed by depositing a silicon dioxide layer on the surface of the silicon material first substrate, and the thickness of the insulating layer 1 is 100 nm, as shown in Fig. 22; Figure 22 as shown in Fig. 23; Step ten: a 500 μm thick BF33 type glass sheet is selected, the ring-shaped bonding area 15 at the back of the silicon wafer is anodically bonded with the surface of the glass substrate, the cavity is sealed, the second substrate 12 is formed, and the preparation of the sensor is completed, as shown in Fig. 24. Figure 23 as shown in Fig. 25.

[0039] The MEMS multifunctional sensor prepared by the preparation method of the MEMS multifunctional sensor according to the embodiment of the present application utilizes the deformation of the thin layer medium around the circumferential cavity 7 and the bonding cavity 14 to offset the thermal stress transmitted from the bonding interface, effectively reduces the bonding thermal stress at the position of the piezoresistor, avoids the sensor zero point output drift caused by stress concentration, and improves the output precision of the sensor.

[0040] Compared with the prior art, the present application has the following advantages: 1. The MEMS multifunctional sensor of the present application can evenly and quickly reduce the bonding thermal stress upward by adopting the special structure of the annular bonding area 15 and the end cavity 13, and can effectively reduce the bonding thermal stress at the position of the piezoresistor by using the circumferential cavity 7 and the thin layer medium deformation around the bonding cavity 14 to offset part of the thermal stress transmitted from the bonding interface, thereby avoiding the sensor zero output drift caused by stress concentration and improving the sensor output precision.

[0041] 2. The MEMS multifunctional sensor of the present application can realize device integration, improve space utilization, and realize the compatibility of land area and preparation process optimization by stacking, using the medium below the pressure sensor sensitive film 6 to realize the preparation of the accelerometer mass block 8 and the bridge 11, and optimizing the cavity release process to simplify the processing flow and reduce the production cost.

[0042] 3. The MEMS multifunctional sensor of the present application can increase the bonding strength at the bonding interface by the single crystal silicon medium on both sides of the bonding cavity 14, and can ensure long-term air tightness, prolong the service life of the device, and reduce the damping coefficient of the accelerometer by using the double-cavity structure of the end cavity 13 and the bonding cavity 14 to maintain the internal vacuum environment, thereby improving the sensor quality factor and sensitivity.

[0043] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present application, but the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered to be within the protection scope of the present application.

Claims

1. A MEMS multifunctional sensor, characterized in that, The MEMS multifunctional sensor includes: A first substrate includes a sensor region and an annular bonding region. The annular bonding region is connected to the sensor region circumferentially along the sensor region. A circumferential cavity is formed between the annular bonding region and the sensor region. The circumferential cavity is an annular cavity structure. The second substrate has the annular bonding region bonded to it. One end of the annular bonding region that contacts the second substrate has an annular groove. The second substrate covers the annular groove of the annular bonding region and forms an annular bonding cavity. A sensor assembly, located in the sensor area, is used to sense external pressure.

2. The MEMS multifunctional sensor according to claim 1, characterized in that, Along the direction from the first substrate to the second substrate, the circumferential cavity includes a first annular cavity and a second annular cavity, the first annular cavity and the second annular cavity are in communication, and the radial thickness of the first annular cavity is greater than the radial thickness of the second annular cavity.

3. The MEMS multifunctional sensor according to claim 2, characterized in that, The second annular cavity is connected to the inner ring of the first annular cavity near the sensor area.

4. The MEMS multifunctional sensor according to claim 1, characterized in that, The cross-section of the annular groove is trapezoidal.

5. The MEMS multifunctional sensor according to claim 1, characterized in that, An end cavity is formed between the sensor area and the second substrate, and the end cavity is in communication with the circumferential cavity.

6. The MEMS multifunctional sensor according to claim 5, characterized in that, The sensor region has a thin-film cavity, which is a cuboid cavity perpendicular to the thickness direction of the first substrate. The cross-section of the cuboid cavity is square. The portion of the thin-film cavity facing away from the second substrate constitutes the sensor region, which is a sensitive thin film. The sensor assembly includes: Four first varistors are disposed on the side of the sensitive film away from the second substrate. The four first varistors correspond to the four center sides of the film cavity, and the four first varistors form a first Wheatstone bridge. Four pairs of first ohmic contacts, each pair of first ohmic contacts being located at both ends of a corresponding first varistor.

7. The MEMS multifunctional sensor according to claim 6, characterized in that, The sensor region has four block cavities, which correspond to the four corners of the thin-film cavity. Each block cavity connects the thin-film cavity and the end cavity. The portion of the sensor region between two adjacent block cavities forms a bridge. The portion of the sensor region between the four block cavities forms a mass block, which is located at the center of the thin-film cavity. The sensor assembly includes: Four second varistors are respectively disposed on the side of the four bridges away from the thin film cavity, and the four second varistors constitute a second Wheatstone bridge. Four pairs of second ohmic contacts, each pair of second ohmic contacts being disposed at both ends of a corresponding second varistor.

8. The MEMS multifunctional sensor according to claim 7, characterized in that, Each of the second varistors is located at one end of the bridge near the mass block.

9. The MEMS multifunctional sensor according to claim 1, characterized in that, The MEMS multifunctional sensor also includes an insulating layer that covers the surface of the first substrate on the side opposite to the second substrate.

10. A method for fabricating a MEMS multifunctional sensor, the method being used to fabricate the MEMS multifunctional sensor according to any one of claims 1 to 9, characterized in that, The method includes: Step 1: Select an N-type single-crystal silicon wafer with a crystal plane of 100 as the first substrate; Step 2: A thin layer of silicon dioxide is prepared on the shallow surface of the first substrate using oxygen injection isolation technology to prepare for the subsequent preparation of thin film cavities and circumferential cavities; Step 3: Wet etching is performed around the bottom outer perimeter of the first substrate to form the annular cavity shape required for the bonding cavity; Step 4: A cylindrical end cavity is formed by photolithography and deep reactive ion etching in the inner region of the bottom of the first substrate; Step 5: The cavity and the annular narrow groove are fabricated again in the center and the surrounding area of ​​the bottom of the first substrate by photolithography and deep reactive ion etching, respectively, so as to expose the mass block and the lower half of the bridge structure, and ensure that they are connected to the thin silicon dioxide layer in the shallow layer on the upper surface of the silicon wafer. Step 6: Wet etching is performed on the shallow layer on the upper surface of the first substrate through cavities and annular narrow grooves to remove the silicon dioxide thin layer, forming a thin film cavity, a sensitive thin film, a circumferential cavity, a mass block, and a bridge; the thin film cavity is connected to the four block cavities around the mass block; Step 7: Form the first varistor and the second varistor by performing P-type doping on the surface and back of the silicon wafer; Step 8: Form a first ohmic contact and a second ohmic contact by performing P-type heavy doping on both ends of the first varistor and the second varistor; Step 9: An insulating layer is formed by depositing a silicon dioxide layer on the surface of the silicon wafer; Step 10: Select a glass plate and perform anodic bonding between the annular bonding area on the back of the silicon wafer and the surface of the glass substrate to seal the cavity and form a second substrate, thereby completing the fabrication of the sensor.

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