MEMS capacitive accelerometer and manufacturing method thereof

Abstract

The MEMS capacitive accelerometer comprises a cover plate, a structural layer and a substrate, the structural layer comprises a fixed frame and a mass block, a first acceleration release groove is formed in the middle of the fixed frame, the mass block can move in the X-axis direction and the Y-axis direction along the first acceleration release groove, and the fixed frame is arranged between the cover plate and the substrate in a four-edge clamping and packaging mode; the mass block comprises a first detection unit, a second detection unit, a third detection unit and a fourth detection unit which correspond to the four corners and are sequentially arranged anticlockwise from the lower left corner, and the first detection unit, the second detection unit, the third detection unit and the fourth detection unit form an X-axis acceleration detection differential structure symmetrically along the Y axis. The first detection unit, the fourth detection unit, the second detection unit and the third detection unit form a Y-axis acceleration detection differential structure symmetrically along the X axis. The differential fixed tooth offset detection structure is designed, the linearity and the sensitivity are improved, interference caused by a non-sensitive axis is eliminated, and the cross coupling degree is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of accelerometers, and in particular to a MEMS capacitive accelerometer and a manufacturing method thereof. Background Art

[0002] Accelerometers, a key application of microelectromechanical systems (MEMS) technology, are inertial sensors used to measure uniaxial, biaxial, or triaxial acceleration. Accelerometers are widely used in a wide range of fields, including consumer electronics, automotive systems, medical applications, and aerospace, and play a vital role in modern technology.

[0003] Accelerometers can be categorized into various types, including piezoelectric, piezoresistive, capacitive, tunnel, optical, and electromagnetic. Capacitive accelerometers have gradually become the mainstream in the MEMS accelerometer field due to their high sensitivity, low power consumption, low noise, wide-band response, and strong reliability. The detection principle of capacitive accelerometers is primarily based on changes in capacitance. In a capacitive accelerometer, one electrode is fixed, while the other, connected to a proof mass, is movable. When acceleration acts on the sensor, the proof mass shifts, causing the distance between the two electrodes to change, resulting in a change in capacitance, which in turn detects the magnitude of the acceleration.

[0004] Capacitive accelerometers include key technical specifications such as range, measurement accuracy, shock resistance, cross-axis sensitivity, and bandwidth. However, due to limitations such as vibration, temperature changes, differences in material properties, and structural contact and collision, capacitive accelerometers suffer from problems such as poor linearity, difficulty in suppressing sensitivity along non-sensitive axes, and insufficient shock resistance due to a lack of protective structures. Summary of the Invention

[0005] The present invention aims to address, at least to a certain extent, one of the technical problems in the related art. To this end, one object of the present invention is to provide a MEMS capacitive accelerometer and a method for manufacturing the same. By optimizing the structural design and employing a three-layer all-silicon process, the present invention addresses the problems of existing accelerometers, such as high cross-coupling, poor linearity, and poor shock resistance.

[0006] In a first aspect, the present invention provides a MEMS capacitive accelerometer comprising a cover plate, a structural layer, and a substrate for wiring to introduce electrical signals into the structural layer. The structural layer comprises a fixed frame and a mass block. An acceleration release slot 1 is defined in the middle of the fixed frame. The mass block is disposed within the acceleration release slot 1 and is capable of displacement along the acceleration release slot 1 in the X-axis and Y-axis directions. The fixed frame is disposed between the cover plate and the substrate via a four-side clamping package.

[0007] The mass block includes detection unit one, detection unit two, detection unit three and detection unit four, which are arranged in sequence counterclockwise 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 respectively form an X-axis acceleration detection differential structure symmetrically along the Y axis. The detection unit one and the detection unit four, the detection unit two and the detection unit three respectively form a Y-axis acceleration detection differential structure symmetrically along the X axis.

[0008] Preferably, the mass block is composed of an inner frame and an outer frame, an acceleration release groove 2 is opened in the middle of the outer frame, and four groups of acceleration release grooves 3 are opened at the corresponding four corners of the inner frame. The outer side of the inner frame is connected to the acceleration release groove 2 through four groups of Y-axis support beams at the corresponding four corners. The four groups of Y-axis support beams are symmetrical along the X-axis and the Y-axis and the four groups of Y-axis support beams are connected to the edge of the inner frame parallel to the X-axis. The detection unit 1 includes 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 edge of the inner frame close to the Y-axis support beam parallel to the Y-axis. The first Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 2, and the second Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 3. Y-axis comb teeth electrodes are provided at the positions corresponding to 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 teeth electrode are respectively connected to the cover plate and the substrate by bonding.

[0009] Preferably, the four corresponding corners of the outer side of the outer frame are connected to the acceleration release slot one through four groups of X-axis support beams, the four groups of X-axis support beams are symmetrical along the X-axis and the Y-axis, and the four groups of X-axis support beams are connected to the edge of the outer frame parallel to the Y-axis. The detection unit one includes a first X-axis detection mechanism, which is arranged at the edge of the outer frame close to the X-axis support beam parallel to the X-axis. The first X-axis detection mechanism is arranged inside the acceleration release slot two, and an X-axis comb electrode is provided at the position of the first X-axis detection mechanism. The upper and lower sides of the X-axis comb electrode are respectively connected to the cover plate and the substrate by bonding.

[0010] Preferably, the detection unit one also includes a second X-axis detection mechanism and a third X-axis detection mechanism, and the second X-axis detection mechanism and the third X-axis detection mechanism are respectively connected to the two sides of the inner frame located inside the acceleration release slot 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 X-axis comb electrodes are provided at the 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 include a plurality of groups of Y-axis movable comb teeth arranged at equal intervals parallel to the X-axis, and the Y-axis comb tooth electrodes are provided with a plurality of groups of Y-axis fixed comb teeth at equal intervals at positions corresponding to the Y-axis movable comb teeth, and the plurality of groups of Y-axis fixed comb teeth and the plurality of groups of Y-axis movable comb teeth are alternately arranged at intervals. The first X-axis detection mechanism, the second X-axis detection mechanism and the third X-axis detection mechanism each include a plurality of groups of X-axis movable comb teeth at equal intervals parallel to the Y-axis, and the X-axis comb tooth electrodes are provided with a plurality of groups of X-axis fixed comb teeth at equal intervals at positions corresponding to the X-axis movable comb teeth, and the plurality of groups of X-axis fixed comb teeth and the plurality of groups of X-axis movable comb teeth are alternately arranged at intervals.

[0012] Preferably, in the initial state, the distances between the Y-axis movable comb teeth and their adjacent Y-axis fixed comb teeth are different, and the distances between the X-axis movable comb teeth and their adjacent X-axis fixed comb teeth are different.

[0013] Preferably, the potentials on the mass blocks are all the same, which is potential one; the potentials of all the X-axis comb-tooth electrodes located in the detection unit one and the detection unit four are equal to potential two; the potentials of all the X-axis comb-tooth electrodes located in the detection unit two and the detection unit three are equal to potential three; the potential one, potential two and potential three are not equal; the potentials of all the Y-axis comb-tooth electrodes located in the detection unit one and the detection unit two are equal to potential four; the potentials of all the Y-axis comb-tooth electrodes located in the detection unit three and the detection unit four are equal to potential five; the potential one, potential four and potential five are not equal.

[0014] Preferably, four acceleration release grooves are provided at the four corners of the mass block, and a blocking block for limiting excessive displacement of the mass block is provided in the acceleration release groove. The upper and lower sides of the blocking block are respectively connected to the cover plate and the substrate by bonding.

[0015] Preferably, a plurality of groups of damping holes running vertically through the surface of the mass block are provided.

[0016] In a second aspect, the present invention provides a method for manufacturing an accelerometer, including any one of the above-mentioned MEMS capacitive accelerometer solutions, and the manufacturing method is as follows:

[0017] S1: A double-sided polished N-type single crystal silicon wafer is selected as the substrate of the cover plate, and a uniform silicon dioxide insulating layer is formed on its surface through a thermal oxidation process;

[0018] S2: etching the preset position to remove the silicon dioxide on the surface to form a bonding platform pattern;

[0019] S3: Locally etch the preset position of the silicon wafer to form a suspended cavity of the sensitive mass block and complete the cover plate preparation;

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

[0021] S5: Thinning the SOI substrate silicon by grinding and chemical mechanical polishing, and then removing the insulating layer by wet etching to release the SOI top silicon structure as the substrate for the structural layer;

[0022] S6: Ti as an adhesion layer and Au as a bonding layer are sequentially deposited at a preset position on the surface of the structural layer, and then a metal bonding ring is formed by photolithography and etching processes;

[0023] S7: The structural layer is etched using a deep reactive ion etching process to form a movable structure to complete the release and complete the preparation of the structural layer;

[0024] S8: Take a second double-sided polished N-type single crystal silicon wafer as the substrate, repeat steps S1-S3, and then generate a silicon dioxide insulating layer through a thermal oxidation process for subsequent electrode isolation;

[0025] S9: Based on step S8, a layer of Al is deposited on the surface, and a wiring layer connected to the metal electrode is formed by dry etching;

[0026] S10: Based on step S9, a silicon dioxide insulating layer is deposited 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 a predetermined position to expose an electrode contact area;

[0028] S12: Repeat the process of step S6, and on the basis of step S11, prepare a metal bonding ring symmetrical to the structural layer and a bonding pad at the same time, thereby completing the substrate preparation;

[0029] S13: Align the substrate and the structural layer and implement packaging using a thermocompression bonding process;

[0030] S14: After etching away the cover plate and the silicon at the preset position of the structural layer, the individual chips are separated through the wafer dicing process, and the substrate pads are exposed to complete the device preparation.

[0031] The beneficial effects of the present invention are:

[0032] (1) A single-mass dual-axis accelerometer is proposed. Compared with the multi-axis accelerometer constructed by placing mutually orthogonal single-axis accelerometers, the use of a single mass helps to improve the overall performance and reduce the size, while also reducing Brownian noise.

[0033] (2) At the specific structural level, twelve groups of X-axis comb teeth structures constitute a differential capacitance detection structure for detecting X-axis acceleration, and eight groups of Y-axis comb teeth structures constitute a differential capacitance detection structure for detecting Y-axis acceleration. Through the reasonable arrangement of positions, the comb teeth structure for detecting acceleration is set to the maximum extent. At the same time, the capacitance changes caused by the non-sensitive axis will offset each other. Such a differential capacitance detection structure can greatly improve linearity and eliminate cross-coupling interference.

[0034] (3) A folded beam is used as the support structure of the accelerometer. Compared with L-shaped beams and serpentine beams, it has advantages such as low cross-sensitivity and strong anti-interference ability. By studying the influence of the length, width and thickness of the folded beam on the displacement and resonant frequency of the accelerometer, and combining the process conditions, the size of the accelerometer is determined. This design makes up for the defects of the existing dual-axis accelerometer with a small range and the sensitivity that cannot meet the requirements of the detection circuit at a large range;

[0035] (4) Stop blocks are set at the four corners of the sensitive mass block to prevent the mass block from colliding with the fixed comb structure when it is subjected to large impact or strong vibration, thereby avoiding physical damage that may lead to structural failure and improving the impact resistance of the accelerometer;

[0036] (5) In the three-layer all-silicon process of the capacitive accelerometer, the combination of silicon-silicon dioxide bonding (cover plate and structural layer) and gold-gold bonding (structural layer and substrate) shows significant advantages. Silicon-silicon dioxide bonding has the characteristics of thermal expansion matching, high airtightness and high mechanical strength. It can reduce the stress caused by temperature changes, provide reliable environmental isolation, and protect the internal sensitive structure from humidity and particle contamination. At the same time, the bonding interface is strong and suitable as a support for the cover plate and the structural layer. Gold-gold bonding has the advantages of excellent conductivity, low temperature process, flexibility to compensate for stress and high reliability. It ensures low-resistance electrical connection and improves the efficiency of capacitive signal transmission. It is usually completed at a lower temperature to avoid high temperature damage to the formed structure. The ductility of gold can alleviate the thermal mismatch stress between silicon and substrate and reduce the risk of interface cracking. Metal bonding provides stable ohmic contact and is suitable for high-frequency signal transmission and grounding requirements. This combined bonding strategy complements the packaging advantages of silicon-silicon dioxide with the electrical advantages of gold-gold bonding. While ensuring high airtightness and mechanical strength, it optimizes signal transmission and stress management, significantly improving the environmental adaptability, long-term stability and detection accuracy of the accelerometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In the attached figure:

[0038] Figure 1 This is an exploded diagram of a MEMS capacitive accelerometer proposed in the present invention.

[0039] Figure 2 This is a schematic structural diagram of the structural layer proposed in the present invention.

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

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

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

[0043] Figure 6 Schematic diagram of step S3 in the manufacturing method proposed by the present invention.

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

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

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

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

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

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

[0050] Figure 13 Schematic diagram of step S10 in the manufacturing method proposed by the present invention.

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

[0052] Figure 15 Schematic diagram of step S12 in the manufacturing method proposed by the present invention.

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

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

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

[0056] Figure 19 This is a graph showing the relationship between the Y-axis comb capacitance and acceleration proposed by the present invention.

[0057] Figure 20 This is the X-axis harmonic response curve proposed by the present invention.

[0058] Figure 21 This is the Y-axis harmonic response curve proposed by the present invention.

[0059] Figure 22 This is the stress diagram of a 500g load in the X-axis direction proposed by the present invention.

[0060] Figure 23 This is the stress diagram of a 500g load in the Y-axis direction proposed by the present invention.

[0061] In the figure: 1-cover plate, 2-structural 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 teeth, 13-X-axis movable comb teeth, 14-Y-axis fixed comb teeth, 15-Y-axis movable comb teeth, 16-adhesion layer, 17-bonding layer, 18-wiring layer, 19-soldering pad. DETAILED DESCRIPTION

[0062] Reference Figure 1 and Figure 2 A MEMS capacitive accelerometer includes a cover plate 1, a structural layer 2, and a substrate 3 for wiring to introduce electrical signals to the structural layer 2. The structural layer 2 includes a fixed frame 9 and a mass 4. An acceleration release slot 1 is defined in the middle of the fixed frame 9. The mass 4 is disposed within the acceleration release slot 1 and can move along the acceleration release slot 1 in the X-axis and Y-axis directions. The fixed frame 9 is sandwiched between the cover plate 1 and the substrate 3 via a four-side package.

[0063] The mass block 4 includes detection unit 1, detection unit 2, detection unit 3 and detection unit 4, which are arranged in a counterclockwise manner starting from the lower left corner and corresponding to the four corners. Detection unit 1 and detection unit 2, detection unit 3 and detection unit 4 are symmetrical along the Y axis to form an X-axis acceleration detection differential structure, and detection unit 1 and detection unit 4, detection unit 2 and detection unit 3 are symmetrical along the X axis to form a Y-axis acceleration detection differential structure.

[0064] Obviously, based on the above, by setting 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 achieved.

[0065] In this embodiment, referring to Figure 2 and Figure 3The mass block 4 is composed of an inner frame and an outer frame. An acceleration release groove 2 is opened in the middle of the outer frame, and four groups of acceleration release grooves 3 are opened at the corresponding four corners of the inner frame. The outer side of the inner frame is connected to the acceleration release groove 2 through four groups of Y-axis support beams 8 at the corresponding four 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 all connected to the edge of the inner frame parallel to the X-axis. The detection unit 1 includes 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 edge of the inner frame close to the Y-axis support beam 8 parallel to the Y-axis. The first Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 2, and the second Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 3. Y-axis comb electrodes 6 are provided at the positions corresponding to the first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism. The upper and lower sides of the Y-axis comb electrode 6 are respectively connected to the cover plate 1 and the substrate 3 by bonding.

[0066] Obviously, based on the above, when acceleration in the Y-axis direction is generated, the inner frame can be displaced 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 both be displaced along the Y-axis. It should be noted that due to the symmetrical relationship between the detection unit 1, the detection unit 2, the detection unit 3 and the detection unit 4, the structure of the detection unit 1 is disclosed, and the detection unit 2, the detection unit 3 and the detection unit 4 can also be directly obtained, such as Figure 2 As shown, when acceleration in the Y-axis direction is generated, the Y-axis acceleration detection differential structure can be driven to move by the displacement of the inner frame to detect the Y-axis acceleration.

[0067] In this embodiment, referring to Figure 2 and Figure 3 The four corresponding corners of the outer side of the outer frame are connected to the acceleration release slot 1 through four groups of X-axis support beams 7. The four groups of X-axis support beams 7 are symmetrical along the X-axis and Y-axis and the four groups of X-axis support beams 7 are connected to the edge of the outer frame parallel to the Y-axis. The detection unit 1 includes a first X-axis detection mechanism, which is arranged at the edge of the outer frame close to the X-axis support beam 7 parallel to the X-axis. The first X-axis detection mechanism is arranged inside the acceleration release slot 2. An X-axis comb electrode 5 is provided at the position of the first X-axis detection mechanism. The upper and lower sides of the X-axis comb electrode 5 are respectively connected to the cover plate 1 and the substrate 3 by bonding.

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

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

[0070] In this embodiment, referring to Figure 2 and Figure 3 The detection unit 1 also includes 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 to the two sides of the inner frame located inside the acceleration release slot 3 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 5 are provided at the positions corresponding to the second X-axis detection mechanism and the third X-axis detection mechanism.

[0071] Obviously, based on the above, when acceleration is generated in the X-axis direction, the inner frame is displaced, and the second X-axis detection mechanism and the third X-axis detection mechanism are also displaced. Therefore, through reasonable position setting, the comb structure for detecting acceleration is set to the maximum extent to detect acceleration.

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

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

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

[0075] Obviously, based on the above, the distances between the movable comb teeth and their adjacent fixed comb teeth are different, forming a fixed-tooth biased comb tooth structure, which makes the initial capacitance of the structure larger and achieves high-sensitivity detection.

[0076] In this embodiment, referring to Figure 2 and Figure 3 , the potentials on the mass block 4 are all the same, which is potential one; the potentials of all X-axis comb-tooth electrodes 5 located in the detection unit 1 and the detection unit 4 are equal, which is potential two; the potentials of all X-axis comb-tooth electrodes 5 located in the detection unit 2 and the detection unit 3 are equal, which is potential three; potential one, potential two, and potential three are all unequal; the potentials of all Y-axis comb-tooth electrodes 6 located in the detection unit 1 and the detection unit 2 are all equal, which is potential four; the potentials of all Y-axis comb-tooth electrodes 6 located in the detection unit 3 and the detection unit 4 are all equal, which is potential five; potential one, potential four, and potential five are all unequal.

[0077] Obviously, based on the above, by introducing the corresponding potential signal, the acceleration can be detected by the change of the comb capacitance.

[0078] In this embodiment, referring to Figure 2 and Figure 3 Four acceleration release grooves are provided at the four corners of the mass block 4. The acceleration release grooves are provided with blocking blocks 10 for limiting excessive displacement of the mass block 4. The upper and lower sides of the blocking block 10 are respectively connected to the cover plate 1 and the substrate 3 by bonding.

[0079] Obviously, based on the above, there is a gap between the acceleration release slot four and the blocking block 10, and the gap is smaller than the distance required for the movable comb teeth and the fixed comb teeth to collide. The setting of the blocking block 10 prevents the mass block 4 from colliding with the fixed comb tooth structure when it is subjected to a large impact or strong vibration, thereby avoiding physical damage that leads to structural failure and improving the impact resistance of the accelerometer.

[0080] In this embodiment, referring to Figure 2 and Figure 3 The surface of the mass block 4 is provided with a plurality of damping holes 11 running through the surface of the mass block 4 up and down.

[0081] As another embodiment of the present application, this embodiment provides a method for manufacturing an accelerometer, including any of the above-mentioned MEMS capacitive accelerometer solutions, and the manufacturing method is as follows:

[0082] S1: Select a double-sided polished N-type single crystal silicon wafer as the base material of the cover plate 1, and generate a uniform silicon dioxide insulation layer on its surface through a thermal oxidation process, such as Figure 4 As shown;

[0083] S2: Etching the preset position to remove the silicon dioxide on the surface to form a bonding platform pattern, such as Figure 5 As shown;

[0084] S3: Perform local etching on the preset position of the silicon wafer to form a suspended cavity of the sensitive mass block, and complete the preparation of the cover plate 1, such as Figure 6 As shown;

[0085] S4: Bond the cover plate 1 to the SOI wafer, as shown in Figure 7 As shown;

[0086] S5: Thin the SOI base silicon by grinding and chemical mechanical polishing, and then remove the insulating layer by wet etching process to release the SOI top silicon structure as the substrate of the structural layer 2, such as Figure 8 As shown;

[0087] S6: Ti as an adhesion layer 16 and Au as a bonding layer 17 are sequentially deposited at a preset position on the surface of the structural layer 2, and then a metal bonding ring is formed by photolithography and etching processes, such as Figure 9 As shown;

[0088] S7: Use deep reactive ion etching process to etch the structural layer 2 to form a movable structure to complete the release and complete the preparation of the structural layer 2, such as Figure 10 As shown;

[0089] S8: Take a second double-sided polished N-type single crystal silicon wafer as the base material of substrate 3, repeat steps S1-S3, and generate a silicon dioxide insulation layer through a thermal oxidation process for subsequent electrode isolation, such as Figure 11 As shown;

[0090] S9: Based on step S8, a layer of Al is deposited on the surface, and a wiring layer 18 connected to the metal electrode is formed by dry etching, such as Figure 12 As shown;

[0091] S10: Based on step S9, a silicon dioxide insulating layer is deposited on the surface by chemical vapor deposition to cover the electrode area to prevent short circuit, such as Figure 13 As shown;

[0092] S11: Etching the silicon dioxide insulating layer at a predetermined position to expose the electrode contact area, such as Figure 14 As shown;

[0093] S12: Repeat step S6. On the basis of step S11, prepare a metal bonding ring symmetrical to the structure layer 2 and prepare a pad 19 at the same time, and complete the preparation of the substrate 3. Figure 15 As shown;

[0094] S13: Align the substrate 3 with the structural layer 2 and implement packaging using a thermocompression bonding process, such as Figure 16 As shown;

[0095] S14: After etching away the silicon at the preset position of the cover plate 1 and the structure layer 2, separate the individual chips through the wafer scribing process and expose the substrate pad 19 to complete the device preparation, such as Figure 17 shown.

[0096] Obviously, based on the above, the three-layer all-silicon process has good temperature characteristics and can suppress the zero drift and scale factor drift caused by the thermal mismatch stress of the material, thereby improving the temperature stability of the accelerometer; the use of wafer-level packaging has little effect on the performance of the accelerometer due to the stress caused, and can simplify the overall process flow, improve production efficiency, and reduce manufacturing costs; the use of the top silicon of the SOI silicon wafer as the structural layer can reduce parasitic capacitance and accurately control the thickness of the structural layer.

[0097] In order to more clearly illustrate the scheme and effect of this implementation, the following examples are provided with reference to the accompanying drawings:

[0098] Reference Figure 18 and Figure 19 , Figure 18 This is the relationship between the X-axis comb capacitance and acceleration. Figure 19 The following graph shows the relationship between the Y-axis comb capacitance and acceleration, demonstrating the effect of acceleration in different directions on the X- and Y-axis comb capacitances. Within the 500g range, the sensitive axis exhibits excellent linearity, while acceleration in the non-sensitive axis has minimal, almost negligible effect on the X- and Y-axis comb capacitances, significantly reducing cross-coupling.

[0099] Reference Figure 20 and Figure 21 , Figure 20 is the X-axis harmonic response curve, Figure 21 The Y-axis harmonic response curve shows the harmonic response curves of the accelerometer along the X and Y axes. Analysis shows that the accelerometer's resonant frequency is significantly higher than the required frequency range for actual operation, effectively avoiding damage to the accelerometer due to structural resonance and fatigue damage, thereby significantly improving the accelerometer's reliability.

[0100] Reference Figure 22 and Figure 23 , Figure 22 is the stress diagram of 500g load in the X-axis direction, Figure 23 This is the stress diagram for a 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, both of which are far less than the ultimate strength of silicon material. Therefore, the designed accelerometer has strong shock resistance.

Claims

1. A MEMS capacitive accelerometer, characterized in that: The invention comprises a cover plate (1), a structural layer (2), and a substrate (3) for wiring to realize the introduction of electrical signals into the structural layer (2); the structural layer (2) comprises a fixed frame (9) and a mass block (4); an acceleration release groove (1) is provided in the middle of the fixed frame (9); the mass block (4) is arranged inside the acceleration release groove (1), and the mass block (4) can be displaced in the X-axis and Y-axis directions along the acceleration release groove (1); the fixed frame (9) is arranged between the cover plate (1) and the substrate (3) by four-side clamping packaging; The mass block (4) comprises a detection unit 1, a detection unit 2, a detection unit 3 and a detection unit 4 which are arranged in a counterclockwise manner in correspondence with the four corners starting from the lower left corner. The detection unit 1 and the detection unit 2, the detection unit 3 and the detection unit 4 respectively form an X-axis acceleration detection differential structure symmetrically along the Y axis. The detection unit 1 and the detection unit 4, the detection unit 2 and the detection unit 3 respectively form a Y-axis acceleration detection differential structure symmetrically along the X axis.

2. A MEMS capacitive accelerometer according to claim 1, characterized in that: The mass block (4) is composed of an inner frame and an outer frame, an acceleration release groove 2 is opened in the middle of the outer frame, four groups of acceleration release grooves 3 are opened at the corresponding four corners of the inner frame, and the outer side of the inner frame is connected to the acceleration release groove 2 through four groups of Y-axis support beams (8) at the corresponding four 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 to the edge of the inner frame parallel to the X-axis. The detection unit 1 includes a first Y-axis acceleration detection mechanism and a second Y-axis acceleration detection mechanism. The first Y-axis The acceleration detection mechanism and the second Y-axis acceleration detection mechanism are arranged at the edge of the inner frame body close to the Y-axis support beam (8) parallel to the Y-axis, the first Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 2, and the second Y-axis acceleration detection mechanism is arranged inside the acceleration release groove 3. Y-axis comb teeth electrodes (6) are provided at the positions corresponding to 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 teeth electrode (6) are respectively connected to the cover plate (1) and the substrate (3) by bonding.

3. The MEMS capacitive accelerometer according to claim 2, wherein: The four corresponding corners of the outer side of the outer frame are connected to the acceleration release groove one through four groups of X-axis support beams (7), 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 to the edge of the outer frame parallel to the Y-axis. The detection unit one includes a first X-axis detection mechanism, which is arranged at the edge of the outer frame close to the X-axis support beam (7) parallel to the X-axis, and is arranged inside the acceleration release groove two. An X-axis comb electrode (5) is provided at the position of the first X-axis detection mechanism, and the upper and lower sides of the X-axis comb electrode (5) are respectively connected to the cover plate (1) and the substrate (3) by bonding.

4. The MEMS capacitive accelerometer according to claim 3, wherein: The detection unit 1 further includes a second X-axis detection mechanism and a third X-axis detection mechanism, wherein the second X-axis detection mechanism and the third X-axis detection mechanism are respectively connected to two sides of the inner frame located inside the acceleration release slot 3 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 X-axis comb electrodes (5) are provided at positions corresponding to the second X-axis detection mechanism and the third X-axis detection mechanism.

5. The MEMS capacitive accelerometer according to claim 4, wherein: The first Y-axis acceleration detection mechanism and the second Y-axis acceleration detection mechanism each include a plurality of groups of Y-axis movable comb teeth (15) arranged at equal intervals along the X-axis in parallel, the Y-axis comb tooth electrodes (6) are provided with a plurality of groups of Y-axis fixed comb teeth (14) at equal intervals at positions corresponding to the Y-axis movable comb teeth (15), and the plurality of groups of Y-axis fixed comb teeth (14) and the plurality of groups of Y-axis movable comb teeth (15) are arranged alternately at intervals, and the first X-axis detection mechanism, the second X-axis detection mechanism and the third X-axis detection mechanism each include a plurality of groups of X-axis movable comb teeth (13) at equal intervals along the Y-axis in parallel, the X-axis comb tooth electrodes are provided with a plurality of groups of X-axis fixed comb teeth (12) at positions corresponding to the X-axis movable comb teeth (13), and the plurality of groups of X-axis fixed comb teeth (12) and the plurality of groups of X-axis movable comb teeth (13) are arranged alternately at intervals.

6. The MEMS capacitive accelerometer according to claim 5, wherein: In the initial state, the distance between the Y-axis movable comb teeth (15) and the adjacent Y-axis fixed comb teeth (14) is different, and the distance between the X-axis movable comb teeth (13) and the adjacent X-axis fixed comb teeth (12) is different.

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

8. The MEMS capacitive accelerometer according to claim 1, wherein: Four acceleration release slots are provided at the four corners of the mass block (4), and a blocking block (10) for limiting excessive displacement of the mass block (4) is provided in the four acceleration release slots. The upper and lower sides of the blocking block (10) are respectively connected to the cover plate (1) and the substrate (3) by bonding.

9. The MEMS capacitive accelerometer according to claim 1, wherein: The surface of the mass block (4) is provided with a plurality of groups of damping holes (11) penetrating vertically.

10. A method for manufacturing an accelerometer, characterized in that: The MEMS capacitive accelerometer according to any one of claims 1 to 9 is manufactured by the following method: S1: A double-sided polished N-type single crystal silicon wafer is selected as the substrate of the cover plate (1), and a uniform silicon dioxide insulating layer is formed on its surface through a thermal oxidation process; S2: etching the preset position to remove the silicon dioxide on the surface to form a bonding platform pattern; S3: Locally etch the preset position of the silicon wafer to form a suspended cavity of the sensitive mass block, completing the preparation of the cover plate (1); S4: bonding the cover plate (1) to the SOI wafer; S5: Thinning the SOI substrate silicon by grinding and chemical mechanical polishing, and then removing the insulating layer by wet etching to release the SOI top silicon structure as the substrate for the structural layer (2); S6: Ti as an adhesion layer (16) and Au as a bonding layer (17) are sequentially deposited at a preset position on the surface of the structural layer (2), and then a metal bonding ring is formed by photolithography and etching processes; S7: etching the structural layer (2) using a deep reactive ion etching process to form a movable structure to complete the release, thereby completing the preparation of the structural layer (2); S8: taking a second double-sided 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 a thermal oxidation process for subsequent electrode isolation; S9: Based on step S8, a layer of Al is deposited on the surface, and a wiring layer (18) connected to the metal electrode is formed by dry etching; S10: Based on step S9, a silicon dioxide insulating layer is deposited on the surface by chemical vapor deposition to cover the electrode area to prevent short circuit; S11: etching the silicon dioxide insulating layer at a predetermined position to expose an electrode contact area; S12: Repeat the process of step S6, and on the basis of step S11, prepare a metal bonding ring symmetrical to the structural layer (2) and prepare a pad (19) at the same time, thereby completing the preparation of the substrate (3); S13: aligning the substrate (3) and the structural layer (2), and implementing packaging by a thermocompression bonding process; S14: After etching away the silicon at the preset position of the cover plate (1) and the structural layer (2), the individual chips are separated by a wafer scribing process, and the substrate pad (19) is exposed, thereby completing the device preparation.

Images