A MEMS capacitive accelerometer and a method of manufacturing the same

Abstract

The application discloses a MEMS capacitive accelerometer, which comprises a cover plate, a structure layer and a substrate, the structure layer comprises a fixed frame and a mass block, an acceleration release groove one is arranged in the middle of the fixed frame, the mass block can be displaced along the X axis and the Y axis in the acceleration release groove one, the fixed frame is arranged between the cover plate and the substrate through four-edge clamping packaging, the mass block comprises a detection unit one, a detection unit two, a detection unit three and a detection unit four which are arranged in sequence in a counterclockwise method from the left lower corner and correspond to four corners, the detection unit one and the detection unit two and the detection unit three and the detection unit four are respectively symmetrically arranged along the Y axis to form an X axis acceleration detection differential structure, and the detection unit one and the detection unit four and the detection unit two and the detection unit three are respectively symmetrically arranged along the X axis to form a Y axis acceleration detection differential structure. The application designs a differential fixed-tooth bias detection structure, improves linearity and sensitivity, eliminates interference caused by a non-sensitive axis and reduces cross-coupling degree.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of accelerometers, in particular to a MEMS capacitive accelerometer and a manufacturing method thereof. BACKGROUND

[0002] As one of key applications of micro-electro-mechanical system (MEMS) technology, an accelerometer is an inertial sensor for measuring single-axis, double-axis or three-axis acceleration. The accelerometer has a wide application in many fields such as consumer electronics, automotive systems, medical applications and aerospace, and occupies an important position in modern science and technology.

[0003] The accelerometer can be divided into piezoelectric type, piezoresistive type, capacitive type, tunnel type, optical type and electromagnetic type, and the capacitive accelerometer gradually develops into a mainstream product in the field of MEMS accelerometers due to its advantages of high sensitivity, low power consumption, low noise, wide frequency response and strong reliability. The detection principle of the capacitive accelerometer is mainly based on the change of capacitance. In the capacitive accelerometer, one electrode is fixed, and the other electrode connected with a mass block is movable. When acceleration acts on the sensor, the mass block is displaced, the distance between the two electrodes is changed, the capacitance value is changed, and the size of the acceleration is detected.

[0004] The capacitive accelerometer includes important technical indexes such as range, measurement accuracy, impact resistance, cross-axis sensitivity and bandwidth. However, due to the limitations of factors such as vibration, temperature change, material property difference and structure contact collision, the capacitive accelerometer has problems such as poor linearity, difficult sensitivity suppression of non-sensitive axes and lack of protection structure and insufficient impact resistance. SUMMARY

[0005] The application aims to at least solve one of the technical problems in the related art. To this end, one object of the application is to provide a MEMS capacitive accelerometer and a manufacturing method thereof, which solves the problems of large cross-coupling, poor linearity and poor impact resistance of the existing accelerometer through optimization of structure design and adoption of a three-layer full-silicon process.

[0006] In a first aspect, the application provides a MEMS capacitive accelerometer, which comprises a cover plate, a structure layer and a substrate for wiring to introduce an electrical signal to the structure layer. The structure layer comprises a fixed frame and a mass block. An acceleration release slot one is formed in the middle of the fixed frame. The mass block is arranged inside the acceleration release slot one, and the mass block can be displaced in the X-axis and Y-axis directions along the acceleration release slot one. The fixed frame is arranged between the cover plate and the substrate through four-edge clamping packaging.

[0007] The mass block comprises detection unit one, detection unit two, detection unit three and detection unit four arranged in sequence in counterclockwise direction from the lower left corner, and the detection unit one and the detection unit two, the detection unit three and the detection unit four are respectively symmetrically arranged along the Y axis to form an X axis acceleration detection differential structure, and the detection unit one and the detection unit four, the detection unit two and the detection unit three are respectively symmetrically arranged along the X axis to form a Y axis acceleration detection differential structure.

[0008] Preferably, the mass block is composed of an inner frame and an outer frame, the outer frame is provided with an acceleration release slot two in the middle, the inner frame is provided with four groups of acceleration release slots three at the corresponding four corners, the outer side of the inner frame is connected with the acceleration release slot two through four groups of Y axis support beams at the corresponding four corners, the four groups of Y axis support beams are symmetrically arranged along the X axis and the Y axis, and the four groups of Y axis support beams are connected with the edges of the inner frame parallel to the X axis, the detection unit one comprises a first Y axis acceleration detection mechanism and a second Y axis acceleration detection mechanism, the first Y axis acceleration detection mechanism and the second Y axis acceleration detection mechanism are arranged at the edges of the inner frame parallel to the Y axis near the Y axis support beams, the first Y axis acceleration detection mechanism is arranged inside the acceleration release slot two, and the second Y axis acceleration detection mechanism is arranged inside the acceleration release slot three, Y axis comb electrodes are arranged at positions corresponding to the first Y axis acceleration detection mechanism and the second Y axis acceleration detection mechanism, and the Y axis comb electrodes are connected with the cover plate and the substrate through bonding on the upper and lower sides.

[0009] Preferably, the outer side of the outer frame is connected with the acceleration release slot one through four groups of X axis support beams at the corresponding four corners, the four groups of X axis support beams are symmetrically arranged along the X axis and the Y axis, and the four groups of X axis support beams are connected with the edges of the outer frame parallel to the Y axis, the detection unit one comprises a first X axis detection mechanism, the first X axis detection mechanism is arranged at the edges of the outer frame parallel to the X axis near the X axis support beams, the first X axis detection mechanism is arranged inside the acceleration release slot two, an X axis comb electrode is arranged at the position of the first X axis detection mechanism, and the X axis comb electrode is connected with the cover plate and the substrate through bonding on the upper and lower sides.

[0010] Preferably, the detection unit one further comprises a second X axis detection mechanism and a third X axis detection mechanism, the second X axis detection mechanism and the third X axis detection mechanism are respectively connected with the two edges of the inner frame inside the acceleration release slot three and parallel to the X axis, the second X axis detection mechanism and the third X axis detection mechanism are stacked along the X axis, and X axis comb electrodes are arranged at positions corresponding to the second X axis detection mechanism and the third X axis detection mechanism.

[0011] Preferably, the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism each comprise a plurality of groups of Y-axis movable combs equidistantly arranged along the X-axis in parallel, the Y-axis comb electrode is provided with a plurality of groups of Y-axis fixed combs equidistantly arranged at the positions of the Y-axis movable combs, and the plurality of groups of Y-axis fixed combs are alternately and spacedly arranged with the plurality of groups of Y-axis movable combs; the first X-axis detection mechanism, the second X-axis detection mechanism and the third X-axis detection mechanism each comprise a plurality of groups of X-axis movable combs equidistantly arranged along the Y-axis in parallel, the X-axis comb electrode is provided with a plurality of groups of X-axis fixed combs equidistantly arranged at the positions of the X-axis movable combs, and the plurality of groups of X-axis fixed combs are alternately and spacedly arranged with the plurality of groups of X-axis movable combs.

[0012] Preferably, in the initial state, the distance between the Y-axis movable comb and its adjacent Y-axis fixed comb is different, and the distance between the X-axis movable comb and its adjacent X-axis fixed comb is different.

[0013] Preferably, the potentials on the mass block are all equal to potential one, the potentials of all the X-axis comb electrodes in the detection unit one and the detection unit four are all equal to potential two, the potentials of all the X-axis comb electrodes in the detection unit two and the detection unit three are all equal to potential three, the potential one, the potential two and the potential three are all different, the potentials of all the Y-axis comb electrodes in the detection unit one and the detection unit two are all equal to potential four, the potentials of all the Y-axis comb electrodes in the detection unit three and the detection unit four are all equal to potential five, and the potential one, the potential four and the potential five are all different.

[0014] Preferably, the four corners of the mass block are provided with acceleration release grooves four, the acceleration release grooves four are provided with a blocking block for limiting excessive displacement of the mass block, and the upper and lower sides of the blocking block are connected with the cover plate and the substrate through bonding, respectively.

[0015] Preferably, the surface of the mass block is provided with a plurality of groups of damping holes penetrating up and down.

[0016] In a second aspect, the application provides a manufacturing method of an accelerometer, which comprises any one of the above-mentioned MEMS capacitive accelerometers, and the manufacturing method is as follows:

[0017] S1: selecting a double-side polished N-type single crystal silicon wafer as the base material of the cover plate, and generating a uniform silicon dioxide insulating layer on the surface thereof through a thermal oxidation process;

[0018] S2: etching the surface silicon dioxide at the preset positions to form a bonding boss pattern;

[0019] S3: locally etching the silicon wafer at the preset positions to form a suspended cavity of the sensitive mass block, and completing the preparation of the cover plate;

[0020] S4: bonding the cover plate with the SOI wafer;

[0021] S5: thinning the SOI base silicon by grinding and chemical mechanical polishing, and removing the insulating layer by a wet etching process to release the SOI top silicon structure as the base material of the structure layer;

[0022] S6: sequentially depositing Ti as an adhesion layer and Au as a bonding layer at predetermined positions on the surface of the structure layer, and then forming a metal bonding ring through a photolithography and etching process;

[0023] S7: etching the structure layer by a deep reactive ion etching process to form a movable structure for release and complete the preparation of the structure layer;

[0024] S8: taking a second double-side polished N-type single crystal silicon wafer as the base material of the substrate, repeating steps S1-S3, and then generating a silicon dioxide insulating layer by a thermal oxidation process for subsequent electrode isolation;

[0025] S9: on the basis of step S8, depositing a layer of Al on the surface and forming a wiring layer connected with the metal electrode through dry etching;

[0026] S10: on the basis of step S9, depositing a silicon dioxide insulating layer on the surface by chemical vapor deposition to cover the electrode area to prevent short circuit;

[0027] S11: etching the silicon dioxide insulating layer at predetermined positions to expose the electrode contact area;

[0028] S12: repeating the process of step S6, on the basis of step S11, preparing a metal bonding ring symmetric to the structure layer and preparing a pad at the same time to complete the preparation of the substrate;

[0029] S13: aligning the substrate with the structure layer and realizing packaging by a thermal compression bonding process;

[0030] S14: etching to remove the cover plate and the silicon at predetermined positions of the structure layer, separating individual chips by wafer dicing, and exposing the substrate pad to complete the preparation of the device.

[0031] The beneficial effects in the present application are:

[0032] (1) a single mass double-axis accelerometer is proposed, compared with the way of placing mutually orthogonal single-axis accelerometers to construct a multi-axis accelerometer, using a single mass helps to improve the overall performance and reduce the size, and reduces the Brownian noise;

[0033] (2) In the specific structure layer, twelve groups of X-axis comb tooth structures constitute a differential capacitance detection structure for detecting X-axis acceleration, and the other eight groups of Y-axis comb tooth structures constitute a differential capacitance detection structure for detecting Y-axis acceleration. Through reasonable arrangement of positions, the comb tooth structures for detecting acceleration are maximally set. At the same time, the capacitance changes caused by non-sensitive axes are all offset. Through such a differential capacitance detection structure, the linearity and cross-coupling interference can be well improved.

[0034] (3) The folded beam is used as the support structure of the accelerometer, which has the advantages of low cross-sensitivity, strong anti-interference ability and the like compared with L-shaped beam and snake-shaped beam. The influence of the length, width and thickness of the folded beam on the displacement and resonance frequency of the accelerometer is studied, and the size of the accelerometer is determined in combination with the process conditions. This design makes up for the defects that the existing dual-axis accelerometer has a small range and the sensitivity cannot meet the requirements of the detection circuit in a large range;

[0035] (4) The blocking block is arranged at the four corners of the sensitive mass block, so that the mass block is prevented from colliding with the fixed comb tooth structure when the mass block is subjected to a large impact or strong vibration, thereby avoiding physical damage and structural failure, and the impact resistance of the accelerometer is improved;

[0036] (5) In the three-layer full-silicon process of the capacitive accelerometer, the combination of silicon-silicon dioxide bonding (cover plate and structure layer) and gold-gold bonding (structure layer and substrate) is adopted, which has obvious advantages. The silicon-silicon dioxide bonding has the characteristics of thermal expansion matching, high airtightness and mechanical strength, can reduce the stress caused by temperature change, provides reliable environmental isolation, protects the internal sensitive structure from humidity and particle pollution, and the bonding interface is firm, which is suitable for supporting the cover plate and the structure layer. Gold-gold bonding has the advantages of excellent electrical conductivity, low temperature process, flexibility stress compensation and high reliability, which ensures low resistance electrical connection, improves the efficiency of capacitive signal transmission, is usually completed at a lower temperature to avoid damage to the formed structure caused by high temperature, the ductility of gold can relieve the thermal mismatch stress between silicon and substrate, reduce the risk of interface cracking, and metal bonding provides stable ohmic contact, which is suitable for high-frequency signal transmission and grounding requirements. This combined bonding strategy complements the packaging advantages of silicon-silicon dioxide and the electrical advantages of gold-gold bonding, ensuring high airtightness and mechanical strength while optimizing signal transmission and stress management, significantly improving the environmental adaptability, long-term stability and detection accuracy of the accelerometer. BRIEF DESCRIPTION OF DRAWINGS

[0037] In the drawings:

[0038] Figure 1 An exploded view of a MEMS capacitive accelerometer according to the present application is shown.

[0039] Figure 2 A structure diagram of a structure layer according to the present application is shown.

[0040] Figure 3 The present invention proposes Figure 2 A magnified view of a portion of point A (detection unit 1).

[0041] Figure 4 This is a schematic diagram of step S1 in the manufacturing method proposed in this invention.

[0042] Figure 5 This is a schematic diagram of step S2 in the manufacturing method proposed in this invention.

[0043] Figure 6 This is a schematic diagram of step S3 in the manufacturing method proposed in this invention.

[0044] Figure 7 This is a schematic diagram of step S4 in the manufacturing method proposed in this invention.

[0045] Figure 8 This is a schematic diagram of step S5 in the manufacturing method proposed in this invention.

[0046] Figure 9 This is a schematic diagram of step S6 in the manufacturing method proposed in this invention.

[0047] Figure 10 This is a schematic diagram of step S7 in the manufacturing method proposed in this invention.

[0048] Figure 11 This is a schematic diagram of step S8 in the manufacturing method proposed in this invention.

[0049] Figure 12 This is a schematic diagram of step S9 in the manufacturing method proposed in this invention.

[0050] Figure 13 This is a schematic diagram of step S10 in the manufacturing method proposed in this invention.

[0051] Figure 14 This is a schematic diagram of step S11 in the manufacturing method proposed in this invention.

[0052] Figure 15 This is a schematic diagram of step S12 in the manufacturing method proposed in this invention.

[0053] Figure 16 This is a schematic diagram of step S13 in the manufacturing method proposed in this invention.

[0054] Figure 17 This is a schematic diagram of step S14 in the manufacturing method proposed in this invention.

[0055] Figure 18 This is a graph showing the relationship between the X-axis comb capacitance and acceleration proposed in this invention.

[0056] Figure 19 The Y-axis comb tooth capacitance and acceleration change relation diagram proposed in the application.

[0057] Figure 20 The X-axis harmonic response curve diagram proposed in the application.

[0058] Figure 21 The Y-axis harmonic response curve diagram proposed in the application.

[0059] Figure 22 The stress diagram of 500g load in the X-axis direction proposed in the application.

[0060] Figure 23 The stress diagram of 500g load in the Y-axis direction proposed in the application.

[0061] In the figure: 1-cover plate, 2-structure layer, 3-substrate, 4-mass block, 5-X-axis comb tooth electrode, 6-Y-axis comb tooth electrode, 7-X-axis support beam, 8-Y-axis support beam, 9-fixed frame, 10-blocking block, 11-damping hole, 12-X-axis fixed comb tooth, 13-X-axis movable comb tooth, 14-Y-axis fixed comb tooth, 15-Y-axis movable comb tooth, 16-adhesion layer, 17-bonding layer, 18-wiring layer, 19-solder pad. DETAILED DESCRIPTION

[0062] Reference Figure 1 and Figure 2 A MEMS capacitive accelerometer, comprising a cover plate 1, a structure layer 2 and a substrate 3 for wiring to realize the introduction of electrical signals to the structure layer 2, the structure layer 2 comprising a fixed frame 9 and a mass block 4, the fixed frame 9 having an acceleration release groove one in the middle, the mass block 4 being arranged inside the acceleration release groove one and being capable of displacement in X-axis and Y-axis directions along the acceleration release groove one, the fixed frame 9 being arranged between the cover plate 1 and the substrate 3 through four-edge clamping packaging.

[0063] The mass block 4 comprises detection unit one, detection unit two, detection unit three and detection unit four arranged in turn in a counterclockwise manner from the lower left corner corresponding to the four corners, the detection unit one and the detection unit two, the detection unit three and the detection unit four being respectively symmetrical along the Y-axis to form an X-axis acceleration detection differential structure, and the detection unit one and the detection unit four, the detection unit two and the detection unit three being respectively symmetrical along the X-axis to form a Y-axis acceleration detection differential structure.

[0064] Obviously, based on the above, through the arrangement of the X-axis acceleration detection differential structure and the Y-axis acceleration detection differential structure, acceleration detection in the X-axis direction and the Y-axis direction can be realized.

[0065] In this embodiment, reference is made to Figure 2 and Figure 3, the mass 4 is composed of an inner frame and an outer frame, the outer frame is provided with an acceleration release slot two in the middle, the inner frame is provided with four groups of acceleration release slots three at the corresponding corners, the outer side of the inner frame is connected with the acceleration release slot two through four groups of Y-axis support beams 8 at the corresponding corners, the four groups of Y-axis support beams 8 are symmetrical along the X-axis and the Y-axis, and the four groups of Y-axis support beams 8 are connected with the edges of the inner frame parallel to the X-axis, the detection unit one comprises a first Y-axis acceleration detection mechanism and a second Y-axis acceleration detection mechanism, the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism are arranged at the edges of the inner frame parallel to the Y-axis support beam 8 along the Y-axis, the first Y-axis acceleration detection mechanism is arranged in the acceleration release slot two, the second Y-axis acceleration detection mechanism is arranged in the acceleration release slot three, Y-axis comb electrodes 6 are arranged at the positions of the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism, and the upper and lower sides of the Y-axis comb electrodes 6 are connected with the cover plate 1 and the substrate 3 through bonding respectively.

[0066] Obviously, based on the above, when the acceleration in the Y-axis direction is generated, the inner frame can displace along the Y-axis under the action of the Y-axis support beam 8, so that the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism can displace along the Y-axis, and it should be noted that, due to the symmetrical relationship between the detection unit one, the detection unit two, the detection unit three and the detection unit four, the structure of the detection unit one is disclosed, and the detection unit two, the detection unit three and the detection unit four can also be directly obtained, as shown in Figure 2 Thus, when the acceleration in the Y-axis direction is generated, the displacement of the Y-axis acceleration detection differential structure can be driven by the displacement of the inner frame to detect the Y-axis acceleration.

[0067] In the embodiment, referring to Figure 2 and Figure 3 , the outer side of the outer frame is connected with the acceleration release slot one through four groups of X-axis support beams 7 at the corresponding corners, the four groups of X-axis support beams 7 are symmetrical along the X-axis and the Y-axis, and the four groups of X-axis support beams 7 are connected with the edges of the outer frame parallel to the Y-axis, the detection unit one comprises a first X-axis detection mechanism, the first X-axis detection mechanism is arranged at the edges of the outer frame parallel to the X-axis support beam 7 along the X-axis, the first X-axis detection mechanism is arranged in the acceleration release slot two, an X-axis comb electrode 5 is arranged at the position of the first X-axis detection mechanism, and the upper and lower sides of the X-axis comb electrode 5 are connected with the cover plate 1 and the substrate 3 through bonding respectively.

[0068] Obviously, based on the above, when the acceleration in the X-axis direction is generated, the inner frame and the outer frame can displace along the X-axis under the action of the X-axis support beam 7, and the X-axis acceleration detection differential structure can displace, so that the X-axis acceleration can be detected through the displacement of the X-axis acceleration detection differential structure.

[0069] In the embodiment, referring to Figure 2 and Figure 3The X-axis support beam 7 and the Y-axis support beam 8 are both folding beams.

[0070] In the embodiment, referring to Figure 2 and Figure 3 The detection unit one further comprises a second X-axis detection mechanism and a third X-axis detection mechanism, which are respectively connected to the two sides of the inner frame body inside the acceleration release groove three and parallel to the X-axis, and the second X-axis detection mechanism and the third X-axis detection mechanism are stacked along the X-axis, and the X-axis comb teeth electrode 5 is arranged at the positions of the second X-axis detection mechanism and the third X-axis detection mechanism.

[0071] Obviously, based on the above, when the acceleration in the X-axis direction occurs, the inner frame body generates displacement, and the second X-axis detection mechanism and the third X-axis detection mechanism also generate displacement, thereby, through reasonable position setting, the comb tooth structure for detecting acceleration is maximally set to detect acceleration.

[0072] In the embodiment, referring to Figure 2 and Figure 3 The first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism each comprise a plurality of groups of Y-axis movable combs 15 which are arranged in parallel along the X-axis at equal intervals, and the Y-axis comb electrode 6 is provided with a plurality of groups of Y-axis fixed combs 14 at positions corresponding to the Y-axis movable combs 15, and the plurality of groups of Y-axis fixed combs 14 are alternately and spacedly arranged with the plurality of groups of Y-axis movable combs 15, and the first X-axis detection mechanism, the second X-axis detection mechanism and the third X-axis detection mechanism each comprise a plurality of groups of X-axis movable combs 13 which are arranged in parallel along the Y-axis at equal intervals, and the X-axis comb electrode is provided with a plurality of groups of X-axis fixed combs 12 at positions corresponding to the X-axis movable combs 13, and the plurality of groups of X-axis fixed combs 12 are alternately and spacedly arranged with the plurality of groups of X-axis movable combs 13.

[0073] Obviously, based on the above, when there is displacement in the Y-axis direction, the Y-axis movable comb 15 can displace, so that the distance between the Y-axis movable comb 15 and the Y-axis fixed comb 14 changes, thereby causing the capacitance between the Y-axis movable comb 15 and the Y-axis fixed comb 14 to change, and the Y-axis acceleration is detected by the change of the internal capacitance of the Y-axis acceleration detection differential structure, and similarly, when there is displacement in the X-axis direction, the X-axis movable comb 13 can displace, so that the distance between the X-axis movable comb 13 and the X-axis fixed comb 12 changes, thereby causing the capacitance between the X-axis movable comb 13 and the X-axis fixed comb 12 to change, and the X-axis acceleration is detected by the change of the internal capacitance of the X-axis acceleration detection differential structure.

[0074] In the embodiment, referring to Figure 2 and Figure 3, the distance between the movable Y-axis comb teeth 15 and its adjacent Y-axis fixed comb teeth 14 is different, and the distance between the movable X-axis comb teeth 13 and its adjacent X-axis fixed comb teeth 12 is different.

[0075] Obviously, based on the above, the distance between the movable comb teeth and its adjacent fixed comb teeth is different, which constitutes the tooth offset comb structure, so that the initial capacitance of the structure is larger, and high sensitivity detection is realized.

[0076] In this embodiment, referring to Figure 2 and Figure 3 , the potential on the mass block 4 is the same as the potential one, the potentials of all X-axis comb tooth electrodes 5 located in the detection unit one and the detection unit four are equal to the potential two, the potentials of all X-axis comb tooth electrodes 5 located in the detection unit two and the detection unit three are equal to the potential three, the potential one, the potential two and the potential three are all different, the potentials of all Y-axis comb tooth electrodes 6 located in the detection unit one and the detection unit two are equal to the potential four, the potentials of all Y-axis comb tooth electrodes 6 located in the detection unit three and the detection unit four are equal to the potential five, and the potential one, the potential four and the potential five are all different.

[0077] Obviously, based on the above, the corresponding potential signal is introduced, and the acceleration can be detected through the change of the comb capacitance.

[0078] In this embodiment, referring to Figure 2 and Figure 3 , four acceleration release grooves four are formed in the four corners of the mass block 4, a blocking block 10 for limiting excessive displacement of the mass block 4 is arranged in the acceleration release groove four, and the upper and lower sides of the blocking block 10 are connected with the cover plate 1 and the substrate 3 respectively through bonding.

[0079] Obviously, based on the above, there is a gap between the acceleration release groove four and the blocking block 10, and the gap is smaller than the distance required for the displacement collision between the movable comb teeth and the fixed comb teeth, so that the collision between the mass block 4 and the fixed comb structure is prevented when the mass block 4 is subjected to a large impact or strong vibration, thereby avoiding physical damage and structural failure, and the impact resistance of the accelerometer is improved.

[0080] In this embodiment, referring to Figure 2 and Figure 3 , a plurality of groups of damping holes 11 penetrating through the upper and lower surfaces of the mass block 4 are formed.

[0081] As another embodiment of the present application, the present embodiment proposes a manufacturing method of an accelerometer, which contains any one of the above-mentioned MEMS capacitive accelerometer schemes, and the manufacturing method is as follows:

[0082] S1: Select a double-side polished N-type single crystal silicon wafer as the base material of the cover plate 1, generate a uniform silicon dioxide insulating layer on the surface thereof through a thermal oxidation process, such asFigure 4 as shown in FIG. 2;

[0083] S2: Etching the pre-set position to remove the surface silicon dioxide and form the bonding boss pattern, as shown in FIG. 3; Figure 5

[0084] S3: Local etching the pre-set position of the silicon wafer to form the suspended cavity of the sensitive mass, and complete the preparation of the cover plate 1, as shown in FIG. 4; Figure 6

[0085] S4: Bonding the cover plate 1 with the SOI wafer, as shown in FIG. 5; Figure 7

[0086] S5: Thinning the SOI base silicon by grinding and chemical mechanical polishing, and then removing the insulating layer by wet etching process to release the SOI top layer silicon structure as the base material of the structure layer 2, as shown in FIG. 6; Figure 8

[0087] S6: Depositing Ti as the adhesion layer 16 and Au as the bonding layer 17 on the surface of the structure layer 2 at the pre-set position in sequence, and then forming the metal bonding ring through the photoetching and etching process, as shown in FIG. 7; Figure 9

[0088] S7: Etching the structure layer 2 by deep reactive ion etching process to form the movable structure and complete the release, and complete the preparation of the structure layer 2, as shown in FIG. 8; Figure 10

[0089] S8: Taking a second double-side polished N-type single crystal silicon wafer as the base material of the substrate 3, repeating steps S1-S3, and then generating a silicon dioxide insulating layer by thermal oxidation process for subsequent electrode isolation, as shown in FIG. 9; Figure 11

[0090] S9: On the basis of step S8, depositing a layer of Al on the surface and forming the wiring layer 18 connected with the metal electrode through dry etching, as shown in FIG. 10; Figure 12

[0091] S10: On the basis of step S9, depositing a silicon dioxide insulating layer on the surface by chemical vapor deposition to cover the electrode area to prevent short circuit, as shown in FIG. 11; Figure 13

[0092] S11: Etching the pre-set position to expose the electrode contact area, as shown in FIG. 12; Figure 14

[0093] S12: Repeating the step S6 process, on the basis of step S11, preparing the metal bonding ring symmetric to the structure layer 2 and preparing the pad 19 at the same time, and completing the preparation of the substrate 3, as shown in FIG. 13; Figure 15

[0094] ​​​​​​​​​​​S13: Aligning the substrate 3 with the structure layer 2, and realizing the packaging by using the thermal pressure bonding process, as shown in Figure 16 ;

[0095] S14: Etching to remove the cover plate 1 and the structure layer 2 at the preset position, and separating the single chip by the wafer slicing process, and exposing the substrate pad 19, and completing the device preparation, as shown in Figure 17 .

[0096] Obviously, based on the above, the three-layer full-silicon process has good temperature characteristics, can inhibit the zero drift and scale factor drift caused by the material thermal mismatch stress, and thus improves the temperature stability of the accelerometer; the wafer-level packaging has little influence on the performance of the accelerometer caused by the stress, and can simplify the overall process flow, improve the production efficiency, and reduce the manufacturing cost; the top layer silicon of the SOI wafer is used as the structure layer, which can reduce the parasitic capacitance and accurately control the thickness of the structure layer.

[0097] In order to more clearly illustrate the embodiments and effects of the present application, examples are combined with the accompanying drawings to illustrate:

[0098] Referring to Figure 18 and Figure 19 , Figure 18 is a change relationship diagram of the X-axis comb tooth capacitance and acceleration, Figure 19 is a change relationship diagram of the Y-axis comb tooth capacitance and acceleration, which shows the influence of the acceleration in different directions on the X-axis and Y-axis comb tooth capacitances. Within the range of 500g, the sensitive axis has good linearity, and the acceleration in the non-sensitive axis direction has little influence on the X-axis and Y-axis comb tooth capacitances, which can be almost ignored, which significantly reduces the cross-coupling degree.

[0099] Referring to Figure 20 and Figure 21 , Figure 20 is an X-axis direction harmonic response curve diagram, Figure 21 is a Y-axis direction harmonic response curve diagram, which shows the harmonic response curves of the X-axis and Y-axis directions of the accelerometer. Analysis shows that the resonance frequency of the accelerometer is significantly higher than the frequency range required for actual work, which effectively avoids the harm to the accelerometer caused by structural resonance and fatigue damage, thereby significantly improving the reliability of the accelerometer.

[0100] Referring to Figure 22 and Figure 23 , Figure 22 is a stress diagram of 500g load in the X-axis direction, Figure 23 is a stress diagram of 500g load in the Y-axis direction, the maximum stress in the X-axis direction is 18.9MPa, and the maximum stress in the Y-axis direction is 16.9MPa, which are far less than the ultimate strength of the silicon material, so the designed accelerometer has strong impact resistance.

Claims

1. A MEMS capacitive accelerometer, characterized by: The application relates to a structure layer (2) comprising a cover plate (1), a substrate (3) for wiring to introduce electric signals into the structure layer (2), a fixed frame (9) and a mass block (4), wherein the fixed frame (9) is provided with an acceleration release groove one in the middle part, the mass block (4) is arranged in the acceleration release groove one, and the mass block (4) can be displaced along the acceleration release groove one in the X-axis and Y-axis directions. The mass block (4) comprises detection unit one, detection unit two, detection unit three and detection unit four arranged in the anticlockwise method in sequence from the left lower corner, the detection unit one and the detection unit two, the detection unit three and the detection unit four are respectively symmetrically arranged along the Y-axis to form X-axis acceleration detection differential structures, and the detection unit one and the detection unit four, the detection unit two and the detection unit three are respectively symmetrically arranged along the X-axis to form Y-axis acceleration detection differential structures. The mass block (4) is composed of an inner frame body and an outer frame body, the outer frame body is provided with an acceleration release groove two in the middle part, the inner frame body is provided with four groups of acceleration release grooves three at the corresponding four corners, the outer side of the inner frame body is connected with the acceleration release groove two through four groups of Y-axis support beams (8) at the corresponding four corners, the four groups of Y-axis support beams (8) are symmetrically arranged along the X-axis and the Y-axis, and the four groups of Y-axis support beams (8) are connected with the edges of the inner frame body parallel to the X-axis, the detection unit one comprises a first Y-axis acceleration detection mechanism and a second Y-axis acceleration detection mechanism, the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism are arranged at the edges of the inner frame body parallel to the Y-axis near the Y-axis support beams (8), the first Y-axis acceleration detection mechanism is arranged in the acceleration release groove two, the second Y-axis acceleration detection mechanism is arranged in the acceleration release groove three, Y-axis comb electrodes (6) are arranged at the positions of the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism, and the Y-axis comb electrodes (6) are connected with the cover plate (1) and the substrate (3) through bonding on the upper and lower sides. The outer side of the outer frame body is connected with the acceleration release groove one through four groups of X-axis support beams (7) at the corresponding four corners, the four groups of X-axis support beams (7) are symmetrically arranged along the X-axis and the Y-axis, and the four groups of X-axis support beams (7) are connected with the edges of the outer frame body parallel to the Y-axis, the detection unit one comprises a first X-axis detection mechanism, the first X-axis detection mechanism is arranged at the edges of the outer frame body parallel to the X-axis near the X-axis support beams (7), the first X-axis detection mechanism is arranged in the acceleration release groove two, an X-axis comb electrode (5) is arranged at the position of the first X-axis detection mechanism, and the X-axis comb electrode (5) is connected with the cover plate (1) and the substrate (3) through bonding on the upper and lower sides. The detection unit one further comprises a second X-axis detection mechanism and a third X-axis detection mechanism, which are respectively connected to the two sides of the inner frame body inside the acceleration release slot three and parallel to the X-axis, and are stacked along the X-axis, and X-axis comb electrodes (5) are arranged at positions corresponding to the second X-axis detection mechanism and the third X-axis detection mechanism. The first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism each comprise a plurality of groups of Y-axis movable combs (15) arranged in parallel along the X-axis at equal intervals, and the Y-axis comb electrodes (6) are provided with a plurality of groups of Y-axis fixed combs (14) at positions corresponding to the Y-axis movable combs (15), and the plurality of groups of Y-axis fixed combs (14) and the plurality of groups of Y-axis movable combs (15) are alternately and spacedly arranged, and the first X-axis detection mechanism, the second X-axis detection mechanism and the third X-axis detection mechanism each comprise a plurality of groups of X-axis movable combs (13) arranged in parallel along the Y-axis at equal intervals, and the X-axis comb electrodes are provided with a plurality of groups of X-axis fixed combs (12) at positions corresponding to the X-axis movable combs (13), and the plurality of groups of X-axis fixed combs (12) and the plurality of groups of X-axis movable combs (13) are alternately and spacedly arranged. In the initial state, the distance between the Y-axis movable comb (15) and its adjacent Y-axis fixed comb (14) is different, and the distance between the X-axis movable comb (13) and its adjacent X-axis fixed comb (12) is different.

2. The MEMS capacitive accelerometer of claim 1, wherein: The potentials on the mass block (4) are all equal to potential one, the potentials of all the X-axis comb electrodes (5) located in the detection unit one and the detection unit four are all equal to potential two, the potentials of all the X-axis comb electrodes (5) located in the detection unit two and the detection unit three are all equal to potential three, the potential one, the potential two and the potential three are all different, the potentials of all the Y-axis comb electrodes (6) located in the detection unit one and the detection unit two are all equal to potential four, the potentials of all the Y-axis comb electrodes (6) located in the detection unit three and the detection unit four are all equal to potential five, and the potential one, the potential four and the potential five are all different.

3. The MEMS capacitive accelerometer of claim 1, wherein: Four corners of the mass block (4) are provided with an acceleration release slot four, and the acceleration release slot four is provided with a blocking block (10) for limiting excessive displacement of the mass block (4), and the blocking block (10) is connected with the cover plate (1) and the substrate (3) through bonding on the upper and lower sides.

4. The MEMS capacitive accelerometer of claim 1, wherein: A plurality of groups of damping holes (11) are formed on the surface of the mass block (4).

5. A method of manufacturing an accelerometer, characterized by: The MEMS capacitive accelerometer according to any one of claims 1-4 is manufactured by the following method: S1: selecting a double-side polished N-type single crystal silicon wafer as a base material of the cover plate (1), and generating a uniform silicon dioxide insulating layer on the surface thereof by a thermal oxidation process; S2: etching the surface of the preset position to remove the silicon dioxide, and forming a bonding boss pattern; S3: locally etching the preset position of the silicon wafer to form a suspended cavity of the sensitive mass block, and completing the preparation of the cover plate (1). S4: Bonding the cover plate (1) with the SOI wafer; S5: Thinning the SOI substrate silicon by grinding and chemical mechanical polishing, and then removing the insulating layer by wet etching process to release the SOI top layer silicon structure as the base material of the structure layer (2); S6: Depositing Ti as the adhesion layer (16) and Au as the bonding layer (17) on the surface of the structure layer (2) at the preset position in sequence, and then forming a metal bonding ring by photolithography and etching process; S7: Etching the structure layer (2) by deep reactive ion etching process to form a movable structure for release, and completing the preparation of the structure layer (2); S8: Taking a second double-side polished N-type single crystal silicon wafer as the base material of the substrate (3), repeating steps S1-S3, and then generating a silicon dioxide insulating layer by thermal oxidation process for subsequent electrode isolation; S9: On the basis of step S8, depositing a layer of Al on the surface and forming a wiring layer (18) connected with the metal electrode by dry etching; S10: On the basis of step S9, depositing a silicon dioxide insulating layer on the surface by chemical vapor deposition to cover the electrode area to prevent short circuit; S11: Etching the silicon dioxide insulating layer at the preset position to expose the electrode contact area; S12: Repeating the step S6 process, on the basis of step S11, preparing a metal bonding ring symmetric to the structure layer (2) and a pad (19) at the same time to complete the preparation of the substrate (3); S13: Aligning the substrate (3) with the structure layer (2) and realizing packaging by hot-press bonding process; S14: Etching to remove the silicon at the preset position of the cover plate (1) and the structure layer (2), separating individual chips by wafer dicing process, exposing the substrate pad (19), and completing the preparation of the device.

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