Three-axis MEMS accelerometer

Abstract

The invention discloses a three-axis MEMS (Micro Electro Mechanical System) accelerometer, relates to the field of inertial sensors, and aims to solve the problems of poor temperature drift and relatively low closed-loop range of a multi-axis accelerometer. The array substrate comprises a substrate, an insulating layer, an electrode layer and a structural layer which are designed layer by layer, the structural layer comprises an X-axis structural layer, a Y-axis structural layer and a Z-axis structural layer; the Z-axis structure layer comprises a hollow Z-axis sensitive mass block and a first anchor point located in the center of the Z-axis sensitive mass block, the Z-axis sensitive mass block is connected with the first anchor point through a torsion beam, and the masses of the Z-axis sensitive mass block on the two sides of the torsion beam are not equal; the X-axis structural layer and the Y-axis structural layer are located on the two sides of the torsion beam and in a hollow area of the Z-axis sensitive mass block respectively. Sensitive mass blocks of the detection structures and the stress application structures of the X-axis structure layer and the Y-axis structure layer are not shared, and the resonant frequencies of the detection structures and the stress application structures are the same. According to the invention, the temperature drift and the closed-loop range are optimized, and the chip area of the multi-axis sensor is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of inertial sensors, and in particular to a three-axis MEMS accelerometer. Background Art

[0002] A MEMS (Micro Electro-Mechanical System) inertial sensor refers to a complete device formed by system integration or in-package integration of a MEMS and an ASIC (Application Specific Integrated Circuit).

[0003] MEMS inertial sensors are generally categorized as MEMS accelerometers and MEMS gyroscopes, both of which are primarily used in inertial space. Accelerometers measure the displacement and acceleration of a moving object, while gyroscopes determine its position and track its posture. In recent years, with the rapid advancement of microelectronics and micromechanical technologies, MEMS accelerometers have become increasingly widely used, encompassing numerous fields. Therefore, they hold significant research value and market potential.

[0004] Traditional accelerometers are mostly single-axis accelerometers with single-vector detection. However, with the development of various fields, the application demand for dual-axis and tri-axis accelerometers is constantly increasing, and single-axis accelerometers can no longer meet application needs. The current solution is to assemble multiple single-axis accelerometers into dual-axis or tri-axis accelerometers through special packaging, and then cooperate with gyroscopes to form an IMU module. However, such modules are often large in size, high in cost, and the packaging process introduces large orthogonality errors, making them unsuitable for mass production. Multi-axis accelerometers designed based on the design concept of single-axis accelerometers have problems such as poor open-loop nonlinearity, low closed-loop range, poor temperature drift, and poor overload resistance, which cannot meet the needs of many fields. Summary of the Invention

[0005] The object of the present invention is to provide a three-axis MEMS accelerometer to address all or part of the above-mentioned problems, so as to improve the temperature drift difference and low closed-loop range problems of multi-axis accelerometers.

[0006] The technical solution adopted in the present invention is as follows: A three-axis MEMS accelerometer includes a substrate, an insulating layer, an electrode layer, and a structural layer designed layer by layer; the structural layers include an X-axis structural layer, a Y-axis structural layer, and a Z-axis structural layer; the Z-axis structural layer includes a hollow Z-axis sensitive mass block and a first anchor point located at the center of the Z-axis sensitive mass block, the Z-axis sensitive mass block being connected to the first anchor point via a torsion beam, and the masses of the Z-axis sensitive mass block on either side of the torsion beam being unequal; the X-axis structural layer and the Y-axis structural layer are respectively located on either side of the torsion beam and within the hollow region of the Z-axis sensitive mass block; the X-axis structural layer and the Y-axis structural layer do not share the sensitive mass blocks of the detection structure and the force-applying structure, and the detection structure and the force-applying structure have the same resonant frequency.

[0007] Furthermore, the Z-axis sensitive mass block includes a positive mass block and a negative mass block located on both sides of the torsion beam, and a suspended mass block connected to the positive mass block; and a damping hole is provided on the suspended mass block.

[0008] Furthermore, the electrode layer includes a Z-axis positive force electrode and a Z-axis positive detection electrode located below the positive mass block, and a Z-axis negative force electrode and a Z-axis negative detection electrode located below the negative mass block; the Z-axis positive force electrode and the Z-axis negative force electrode are respectively located on both sides of the torsion beam.

[0009] Furthermore, the X-axis structural layer includes an X-axis detection mass block and an X-axis force mass block; the Y-axis structural layer includes a Y-axis detection mass block and a Y-axis force mass block; the X-axis detection mass block and the X-axis force mass block have the same structure and are orthogonally arranged; the Y-axis detection mass block and the Y-axis force mass block have the same structure and are orthogonally arranged; the X-axis detection mass block and the Y-axis detection mass block are isolated from each other, and the X-axis force mass block and the Y-axis force mass block are isolated from each other.

[0010] Furthermore, the X-axis force-applying mass block is provided with holes.

[0011] Furthermore, the X-axis detection mass block is provided with a first comb tooth unit arranged along the X-axis direction, a second anchor point, a third anchor point located at the center of the X-axis detection mass block, a first spring and a first beam structure; the first comb tooth unit includes first fixed comb teeth and first movable comb teeth that match each other; the first fixed comb teeth are connected to the second anchor point, and the first movable comb teeth are connected to the X-axis detection mass block; the first spring is located on both sides of the third anchor point, the inner side of the first spring is connected to the third anchor point through the first beam structure, and the outer side of the first spring is connected to the X-axis detection mass block.

[0012] Furthermore, the X-axis force mass block is provided with a second comb tooth unit arranged along the X-axis direction, a fourth anchor point, a fifth anchor point located at the center of the X-axis force mass block, a second spring and a second beam structure; the second comb tooth unit includes second fixed comb teeth and second movable comb teeth that match each other; the second fixed comb teeth are connected to the fourth anchor point, and the second movable comb teeth are connected to the X-axis force mass block; the second spring is located on both sides of the fifth anchor point, the inner side of the second spring is connected to the fifth anchor point through the second beam structure, and the outer side of the second spring is connected to the X-axis force mass block.

[0013] Furthermore, the comb tooth gap of the second comb tooth unit is smaller than the comb tooth gap of the first comb tooth unit; the number of comb tooth pairs of the second comb tooth unit is greater than the number of comb tooth pairs of the first comb tooth unit; the comb tooth facing area of the second comb tooth unit is greater than the comb tooth facing area of the first comb tooth unit.

[0014] Furthermore, the edges of the sensitive mass blocks of the detection structure and the force-applying structure of the X-axis structural layer and the Y-axis structural layer, as well as the inside of the hollow area of the Z-axis sensitive mass block, are all provided with limit stop structures; some or all of the limit stop structures of the X-axis structural layer, the Y-axis structural layer and the Z-axis structural layer are shared.

[0015] Furthermore, the position limiting stop structure includes a stop block, and a first protrusion is provided on the side wall of the stop block.

[0016] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: The three-axis MEMS accelerometer designed in this application sets the X-axis structural layer and the Y-axis structural layer in the hollow area of the Z-axis structural layer. The structural layers of the three axes can be processed simultaneously on the same single chip, which saves costs and reduces the chip area. In addition, the anchor point of the Z-axis structural layer is shared with the limit stop structure of the X / Y-axis structural layer, further reducing the chip area. The accelerometer adopts a hollow structure design, and the central anchor point is far away from the sensitive mass block, which can release the thermal stress generated during bonding, reduce the detection error caused by thermal stress in the entire temperature zone, and optimize the temperature drift. The sensitive mass blocks of the detection structure and the force structure of the accelerometer in the X-axis structural layer and the Y-axis structural layer are no longer shared, and the sensitive mass size of the detection structure and the force structure can be adjusted separately, thereby optimizing the sensitivity index and improving the closed-loop range. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 This is an overall structural diagram of the three-axis MEMS accelerometer provided in an embodiment of the present application.

[0018] Figure 2 It is a structural diagram of the Z-axis structural layer in an embodiment of the present application.

[0019] Figure 3 It is a structural diagram of the X-axis structural layer and the Y-axis structural layer in the embodiment of the present application.

[0020] Figure 4 It is a structural diagram of the limit stop structure in an embodiment of the present application.

[0021] In the figure, 10 is a suspended mass block, 11 is a damping hole, 12 is a Z-axis positive force electrode, 13 is an X-axis force mass block, 14a is a first Z-axis positive detection electrode, 14b is a second Z-axis positive detection electrode, 15 is a first anchor point, 16a is a first Z-axis negative detection electrode, 16b is a second Z-axis negative detection electrode, 17 is a Y-axis detection mass block, 18 is a Z-axis negative force electrode, 19 is a negative mass block, 20 is a Y-axis force mass block, 21 is a torsion beam, 22 is an X-axis detection mass block, 23 is a positive mass block, 24 is a first movable comb tooth module, 25 is a first fixed comb tooth module, 26 is a second movable comb tooth module, 27 is a second fixed comb tooth module, 28 is a second limit stop structure, 29 is a first limit stop structure, and 30 is a fifth movable comb tooth module. Tooth module, 31 is the fifth fixed comb tooth module, 32 is the sixth movable comb tooth module, 33 is the sixth fixed comb tooth module, 34 is a hole, 35 is a second spring, 36 is a first beam structure, 37 is a second anchor point, 38 is a third anchor point, 39 is a third movable comb tooth module, 40 is a third fixed comb tooth module, 41 is a fourth movable comb tooth module, 42 is a fourth fixed comb tooth module, 43 is a seventh movable comb tooth module, 44 is a seventh fixed comb tooth module, 45 is an eighth movable comb tooth module, 46 is an eighth fixed comb tooth module, 47 is a first protrusion, 48 is a fourth anchor point, 49 is a fifth anchor point, 50 is a second beam structure, and 51 is a first spring. DETAILED DESCRIPTION

[0022] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0023] Any feature disclosed in this specification (including any appended claims and abstract), unless otherwise stated, may be replaced by other equivalent or similar features. In other words, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0024] In response to the common problems of poor temperature drift and low closed-loop range in current multi-axis accelerometers, the embodiments of the present application propose a three-axis MEMS accelerometer, which aims to improve the problems of poor temperature drift and low closed-loop range in multi-axis accelerometers.

[0025] The three MEMS accelerometers proposed in this application are designed layer by layer from bottom to top: a substrate, an insulating layer, an electrode layer, and a structural layer. The insulating layer is deposited on the substrate to shield parasitic capacitance. The electrode layer is deposited on the insulating layer via evaporation or sputtering and primarily serves as a detection / force electrode for out-of-plane (Z-axis) detection. The structural layers include X-axis, Y-axis, and Z-axis structural layers, enabling three-dimensional acceleration detection.

[0026] The Z-axis structural layer includes a Z-axis sensitive mass, shared by both the detection and force-applying structures. The Z-axis sensitive mass is hollow, with a first anchor point 15 located at its center. This first anchor point 15 is connected to the Z-axis sensitive mass via torsion beams 21 on either side. The hollow structure of the Z-axis structural layer allows the first anchor point 15, at the bonding location, to be positioned away from the Z-axis sensitive mass, thereby optimizing the accelerometer's temperature drift.

[0027] The Z-axis sensitive mass has an unequal mass on either side of the torsion beam 21, resulting in a mass difference. The unbalanced mass on either side of the first anchor point 15 (above and below) provides a torsional torque to the Z-axis structural layer when acceleration is applied, causing the Z-axis sensitive mass to twist around the torsion beam 21. The Z-axis sensitive mass forms a plate capacitor with the electrode layer beneath it. When acceleration is applied, the distance between the Z-axis sensitive mass and the electrode layer changes, causing the capacitance on either side of the first anchor point 15 to increase and decrease, forming a differentially varying capacitor. The change in differential capacitance reflects the magnitude of the input acceleration.

[0028] In addition, in order to cope with the stress concentration phenomenon caused by the torsional force on the torsion beam 21, in some feasible implementations, the root of the torsion beam 21 is chamfered to play a reinforcing role and prevent stress concentration.

[0029] The X-axis structural layer and the Y-axis structural layer are respectively located on both sides of the torsion beam 21 and in the hollow area of the Z-axis sensitive mass block. Figure 1 In the hollow areas adjacent to the upper and lower parts of the middle torsion beam 21, Figure 1 The X-axis structural layer is located within the hollow sub-region above the torsion beam 21, while the Y-axis structural layer is located within the hollow sub-region below the torsion beam 21. The first anchor point 15 serves as a stop for both the X-axis and Y-axis structural layers. The three-axis structural layers share the same first anchor point 15, which reduces the bonding area and thermal stress generated by bonding, thereby improving temperature drift.

[0030] The X-axis and Y-axis layers share a common sensing mass for the detection and force structures, and the resonant frequencies of the detection and force structures are the same. That is, the X-axis layer has the same resonant frequency for the detection and force structures, and the Y-axis layer has the same resonant frequency for the detection and force structures.

[0031] like Figure 2 As shown in FIG. 1 , as an optional embodiment, the Z-axis sensitive mass includes a positive mass 23 located above the torsion beam 21 and a negative mass 19 located below the torsion beam 21. A suspended mass 10 is connected to the positive mass 23, for example, connected to the outside of the positive mass 23. The suspended mass 10 can increase the mass of the positive mass 23, thereby generating a mass difference on both sides of the first anchor point 15.

[0032] In some feasible embodiments, damping holes 11 are provided on the suspended mass 10 . The damping holes 11 are, for example, densely distributed small holes or integrally formed holes. The purpose of designing the damping holes 11 is to reduce the damping of the suspended mass 10 .

[0033] As mentioned above, the main function of the electrode layer is to serve as the detection / force electrode of the Z-axis structure layer. As an optional embodiment, Figure 2 As shown, the electrode layer includes a Z-axis positive force electrode 12 and a Z-axis positive detection electrode located below the positive mass block 23. The Z-axis positive detection electrodes are distributed on both sides of the Z-axis positive force electrode 12. Figure 2 In the embodiment, the first Z-axis positive detection electrode 14a and the second Z-axis positive detection electrode 14b are respectively located on the left and right sides of the Z-axis positive detection electrode. The electrode layer also includes a Z-axis negative force electrode 18 and a Z-axis negative detection electrode located below the negative mass block 19. The Z-axis negative detection electrodes are distributed on both sides of the Z-axis negative force electrode 18, as shown in FIG. Figure 2 In the diagram, the first Z-axis negative detection electrode 16a and the second Z-axis negative detection electrode 16b are located on the left and right sides of the Z-axis negative detection electrode, respectively. The Z-axis positive force electrode 12 and the Z-axis negative force electrode 18 are located on the upper and lower sides of the torsion beam 21, respectively. Each electrode can be in the form of a long strip.

[0034] In order to limit the displacement of the Z-axis sensitive mass block and improve the overload resistance of the Z-axis structural layer, as an optional implementation method, a limited stop structure is provided inside the hollow area of the Z-axis sensitive mass block, at least in the diagonal direction. This limited stop structure can limit the mechanical displacement of the Z-axis sensitive mass block under large impact.

[0035] In some possible implementations, such as Figure 2As shown, first position-limiting stop structures 29 are designed at the four corners of the hollow sub-regions on both sides of the torsion beam 21 to limit the in-plane motion of the Z-axis sensitive mass. Furthermore, because the X-axis and Y-axis structural layers are respectively arranged within the hollow sub-regions on the upper and lower sides of the torsion beam 21, the first position-limiting stop structures 29 provided inside the Z-axis sensitive mass can also limit the movement of the X-axis and Y-axis structural layers in the sensitive direction, limiting their mechanical displacement under severe impact.

[0036] In some feasible embodiments, the edges of the sensitive mass blocks of the detection structures and force-applying structures of the X-axis and Y-axis structural layers are also provided with limit stop structures to limit the mechanical displacement of the X-axis and Y-axis structural layers. Alternatively, all or part of the first limit stop structures 29 provided on the inner side of the Z-axis sensitive mass block can be reused as the limit stop structures provided on the edges of the sensitive mass blocks of the detection structures and force-applying structures of the X-axis and Y-axis structural layers, allowing some or all of the limit stop structures to be shared across the X-axis, Y-axis, and Z-axis structural layers. This effectively reduces the bonding area, thereby alleviating thermal stress and improving temperature drift.

[0037] For example, in some optional embodiments, such as Figure 3 As shown, the X-axis structural layer includes an X-axis detection mass 22 and an X-axis force mass 13; the Y-axis structural layer includes a Y-axis detection mass 17 and a Y-axis force mass 20. The X-axis detection mass 22 and the X-axis force mass 13 have the same structure and are arranged orthogonally; the Y-axis detection mass 17 and the Y-axis force mass 20 have the same structure and are arranged orthogonally. The X-axis detection mass 22 and the Y-axis detection mass 17 are isolated from each other, while the X-axis force mass 13 and the Y-axis force mass 20 are isolated from each other, so that the X-axis detection mass 22 and the Y-axis detection mass 17 are diagonally distributed in the hollow area of the Z-axis sensitive mass, and the X-axis force mass 13 and the Y-axis force mass 20 are diagonally distributed in the hollow area of the Z-axis sensitive mass.

[0038] In some optional embodiments, a hole 34 is provided on the X-axis force mass 13 (the Y-axis force mass 20 has the same structure). This hole 34 serves two functions: first, to release thermal stress during bonding, thereby reducing temperature drift; second, the sensitive mass of the X-axis force mass 13 can be adjusted by adjusting the hole. Adjusting the sensitive mass of the X-axis force mass 13 ensures that the X-axis force mass 13 meets closed-loop requirements, significantly improving closed-loop feedback capabilities and increasing closed-loop range. The hole 34 can take various forms, including a single hole or an array.

[0039] like Figure 3As shown, second position-limiting stop structures 28 are provided at the four corners of the X-axis force mass block 13, the X-axis detection mass block 22, the Y-axis force mass block 20, and the Y-axis detection mass block 17, wherein the first anchor point 15 serves as the second position-limiting stop structure 28 common to the four mass blocks, which can effectively save chip area. Figure 3 As shown, the second limit stop structure 28 provided on the right edge of the X-axis force mass block 13 and the Y-axis detection mass block 17 is shared with the first limit stop structure 29 on the right side of the Z-axis structural layer, and the second limit stop structure 28 provided on the left edge of the X-axis detection mass block 22 and the Y-axis force mass block 20 is shared with the first limit stop structure 29 on the left side of the Z-axis structural layer. Figure 1 In the example, the limit stop structures at the common position are all marked with the first limit stop structure 29. Therefore, Figure 1 Only the upper right corner of the X-axis detection mass block 22, the upper left corner of the X-axis force mass block 13, the lower right corner of the Y-axis force mass block 20 and the lower left corner of the Y-axis detection mass block 17 are marked with the second limit stop structure 28.

[0040] The first limit stop structure 29 and the second limit stop structure 28 have the same structure. Figure 4 As shown, in some feasible embodiments, the first position-limiting stop structure 29 (the second position-limiting stop structure 28 has the same structure) includes a stop block with a first protrusion 47 disposed on its sidewall. The first protrusion 47 can be, for example, a small bump etched around the periphery of the stop block. The stop block with the first protrusion 47 is used on one side to limit the movement of the sensitive mass blocks of the X / Y-axis structural layer, and on the other side to limit the movement of the sensitive mass block of the Z-axis. This ensures that the chip's mechanical structure is not damaged under high impact loads, thereby improving the accelerometer's overall overload resistance. Furthermore, the stop block with the first protrusion 47 can also form a groove on its edge to relieve thermal stress during bonding and improve temperature drift.

[0041] Take the X-axis detection mass block 22 as an example, Figure 3As shown in the figure, as an optional embodiment, it is provided with a first comb unit arranged along the X-axis direction, a second anchor point 37, a third anchor point 38 located at the center of the X-axis proof mass 22, a first spring 51, and a first beam structure 36. The first comb unit includes matching first fixed comb teeth and first movable comb teeth. The first fixed comb teeth are connected to the second anchor point 37. The number of second anchor points 37 is the same as the number of first fixed comb teeth in the first comb unit. The second anchor point 37 connects the first fixed comb teeth to the base plate. The first movable comb teeth are connected to the X-axis proof mass 22 and move synchronously with the X-axis proof mass 22 in the sensitive direction (X-axis direction), thereby changing the capacitance of the first comb unit. The first spring 51 is located on both sides of the third anchor point 38. The inner side of the first spring 51 is connected to the third anchor point 38 via the first beam structure 36, and the outer side of the first spring 51 is connected to the X-axis proof mass 22.

[0042] For example, if Figure 3 As shown, in the first comb tooth unit, the third anchor point 38 is located at the center of the X-axis detection mass 22. With the third anchor point 38 as the origin, a second anchor point 37 is provided in each of the first, second, third, and fourth quadrants. Each second anchor point 37 is connected to a set of first fixed comb teeth, while four sets of first movable comb teeth are connected to corresponding positions inside the X-axis detection mass 22. The first fixed comb teeth and the first movable comb teeth in the second and third quadrants each constitute a set of positive detection comb teeth units, for example, the first movable comb tooth module 24 and the first fixed comb tooth module 25 constitute a set of positive detection comb teeth units. Similarly, the first fixed comb teeth and the first movable comb teeth in the first and fourth quadrants each constitute a set of negative detection comb teeth units, for example, the second movable comb tooth module 26 and the second fixed comb tooth module 27 constitute a set of negative detection comb teeth units.

[0043] Taking into account the accelerometer's nonlinear performance, chip size, and utilization, some feasible implementations design the first comb unit with a variable gap structure, with the ratio of the smaller gap to the larger gap between the first movable comb teeth and the first fixed comb teeth on the left and right sides being 1:3 to 1:5. When acceleration is input, the positive and negative detection capacitors form a differential signal, increasing the capacitance change. The back-end circuit converts the capacitance into a voltage, completing the output measurement of the acceleration signal.

[0044] The first beam structure 36 is bilaterally symmetrical about the third anchor point 38 and includes a dummy beam adjacent to the first spring 51. Furthermore, a corresponding second protrusion, such as a small etched bump, is designed on the dummy beam based on the minimum line width of the processing technology. This serves to protect the first spring 51 by preventing the stress generated at the base of the first spring 51 from exceeding the yield strength of the material under high impact loads, thereby improving overload resistance.

[0045] The structure of the Y-axis detection mass block 17 is the same as that of the X-axis detection mass block 22. The only difference is that the Y-axis detection mass block 17 and the X-axis detection mass block 22 are orthogonal to each other. That is, the X-axis detection mass block 22 is rotated 90 degrees as a whole. Then, the first comb unit on the Y-axis detection mass block 17 is arranged along the Y-axis direction. The sensitive direction of the first movable comb on the Y-axis detection mass block 17 is the Y-axis direction. For the convenience of distinction, as shown in FIG. Figure 3 As shown, on the Y-axis detection mass block 17, the third movable comb module 39 and the third fixed comb module 40 constitute a group of positive detection comb units, and the fourth movable comb module 41 and the fourth fixed comb module 42 constitute a group of negative detection comb units.

[0046] Take the X-axis force mass block 13 as an example, Figure 3 As shown in the figure, as an optional embodiment, it is equipped with a second comb unit arranged along the X-axis, a fourth anchor point 48, a fifth anchor point 49 located at the center of the X-axis force mass 13, a second spring 35, and a second beam structure 50. The second comb unit includes matching second fixed comb teeth and second movable comb teeth. The second fixed comb teeth are connected to the fourth anchor point 48. The number of fourth anchor points 48 is the same as the number of fixed comb modules in the second comb unit. The fourth anchor point 48 connects the second fixed comb teeth to the base plate. The second movable comb teeth are connected to the X-axis force mass 13 and move synchronously with the X-axis force mass 13 in the sensitive direction (X-axis), thereby changing the capacitance of the second comb unit. The second spring 35 is located on both sides of the fifth anchor point 49. The inner side of the second spring 35 is connected to the fifth anchor point 49 via the second beam structure 50, and the outer side of the second spring 35 is connected to the X-axis force mass 13.

[0047] like Figure 3 As shown, in the second comb tooth unit, a fifth anchor point 49 is located at the center of the X-axis force mass 13. With the fifth anchor point 49 as the origin, a fourth anchor point 48 is provided in each of the first, second, third, and fourth quadrants. Each fourth anchor point 48 is connected to a set of second fixed comb teeth, while four sets of second movable comb teeth are connected to corresponding positions inside the X-axis force mass 13. The second fixed comb teeth and second movable comb teeth in the second and third quadrants each constitute a set of positive force comb tooth units, for example, the fifth movable comb tooth module 30 and the fifth fixed comb tooth module 31 constitute a set of positive force comb tooth units. Similarly, the second fixed comb teeth and second movable comb teeth in the first and fourth quadrants each constitute a set of negative force comb tooth units, for example, the sixth movable comb tooth module 32 and the sixth fixed comb tooth module 33 constitute a set of negative force comb tooth units.

[0048] Similarly, in some optional embodiments, the second comb tooth unit also adopts a variable gap structure, and the ratio of the smaller gap to the larger gap between the second movable comb teeth and the second fixed comb teeth on the left and right sides is designed to be 1:3~1:5.

[0049] The second beam structure 50 is bilaterally symmetrical about the fifth anchor point 49 and also includes a dummy beam adjacent to the second spring 35. Furthermore, corresponding second protrusions, such as small etched bumps, are also designed on the dummy beam based on the minimum line width of the processing technology. This serves to protect the second spring 35 by preventing the stress generated at the base of the second spring 35 from exceeding the yield strength of the material under high impact loads, thereby improving overload resistance.

[0050] The structure of the Y-axis force mass block 20 is the same as that of the X-axis force mass block 13. The only difference is the direction of the arrangement. The Y-axis force mass block 20 and the X-axis force mass block 13 are orthogonal to each other. That is, the X-axis force mass block 13 is rotated 90 degrees as a whole. Then, the second comb tooth units on the Y-axis force mass block 20 are arranged along the Y-axis direction. The sensitive direction of the second movable comb teeth on the Y-axis force mass block 20 is the Y-axis direction. For the convenience of distinction, as shown in FIG. Figure 3 As shown, on the Y-axis force-applying mass block 20 , a group of positive force-applying comb tooth units is formed by the seventh movable comb tooth module 43 and the seventh fixed comb tooth module 44 , and a group of negative force-applying comb tooth units is formed by the eighth movable comb tooth module 45 and the eighth fixed comb tooth module 46 .

[0051] The detection structure and the force-applying structure consider different centers of gravity. The tooth distribution of the first comb unit of the detection structure mainly considers the sensitivity index and nonlinear index to ensure that the sensitivity index and nonlinear index meet the project requirements under open-loop conditions. The tooth distribution of the second comb unit of the force-applying structure mainly considers the closed-loop capability and overall stability. Therefore, the tooth structure distribution of the first comb unit and the second comb unit is usually different, including differences in the number of comb tooth pairs, comb tooth gaps, and comb tooth facing areas. As an optional embodiment, the comb tooth gap of the second comb unit is smaller than the comb tooth gap of the first comb unit; the number of comb tooth pairs of the second comb unit is greater than the number of comb tooth pairs of the first comb unit; and the comb tooth facing area of the second comb unit is greater than the comb tooth facing area of the first comb unit. The purpose of this design is to maximize the force-applying capacitance and improve the closed-loop range. When the closed-loop feedback is in effect, the electrostatic force balances the inertial force, keeping the force-applying mass block in a balanced position.

[0052] As an optional embodiment, the first beam structure 36 and the second beam structure 50 can be connected in parallel or in series. By synchronously adjusting the mechanical stiffness of the spring and the sensitive mass of the force-applying mass, the resonant frequencies of the detection structure and the force-applying structure are ensured to be the same, so that they can move in the same direction when an acceleration input is applied.

[0053] The calculation formula of resonant frequency f is It can be seen that the magnitude of the resonant frequency is related to the mechanical stiffness k of the spring and the size of the sensitive mass m of the sensitive mass block. Taking the X-axis structural layer as an example, the resonant frequencies of the X-axis detection structure and the force structure are the same, and since the sensitive masses of the X-axis detection mass block 22 and the X-axis force mass block 13 are different, the mechanical stiffness of the first spring 51 and the second spring 35 are also different. The holes set on the X-axis force mass block 13 can adjust the sensitive mass size of the X-axis force mass block 13. The above-mentioned first spring 51 and second spring 35, as an optional embodiment, can be connected in parallel or in series. By synchronously adjusting the mechanical stiffness of the first spring 51 and the second spring 35, as well as the sensitive mass size of the X-axis force mass block 13, it is possible to ensure that the resonant frequencies of the detection structure and the force structure are the same, and when there is acceleration input, the two can move in the same direction.

[0054] For the X-axis structure layer, there are: , Where, Respectively represent the resonant frequencies of the detection structure and the force-applying structure in the X-axis structural layer, They represent the mechanical stiffness of the first spring 51 and the mechanical stiffness of the second spring 35 in the X-axis structural layer, They respectively represent the sensitive mass of the X-axis detection mass block 22 and the sensitive mass of the X-axis force mass block 13 in the X-axis structural layer.

[0055] Assume that the first comb unit on the X-axis detection mass block 22 has two teeth on the left and right sides of the third anchor point 38. For the detection comb teeth, the smaller gap and the larger gap on both sides of the first movable comb tooth and the first fixed comb tooth are defined as and , the initial capacitance value is: , Where, They represent the initial capacitance value of the first comb tooth unit, the comb tooth facing area in the first comb tooth unit, and the relative dielectric constant, respectively.

[0056] When there is an acceleration a input in the sensitive direction, due to inertia, the sensitive mass block of the X-axis detection structure (i.e., the X-axis detection mass block 22) will produce a displacement x, and the capacitance change is: , Where, They represent capacitance change, positive detection capacitance change, and negative detection capacitance change, respectively.

[0057] Ignoring the high-order terms in the formula, the open-loop sensitivity of the X-axis structure layer can be obtained for: .

[0058] It can be seen that appropriately increasing the sensitive mass of the X-axis detection mass block 22 is helpful to improve the sensitivity of the accelerometer.

[0059] On the X-axis force-applying mass block 13, the electrostatic force applied to the positive force-applying comb unit is: , The electrostatic force applied to the negative force comb unit is: , Where, They represent the electrostatic forces applied to the positive force comb unit and the negative force comb unit, respectively. Respectively represent the smaller gap and the larger gap on both sides of the second movable comb teeth and the second fixed comb teeth in the second comb tooth unit, represents the number of comb tooth pairs of the second comb tooth unit on the left and right sides of the fifth anchor point 49, represent the preload DC voltage and feedback voltage respectively, and x still represents the displacement of the sensitive mass block (i.e., the X-axis force mass block 13). It represents the area of the comb teeth facing each other in the second comb tooth unit.

[0060] Then the electrostatic force on the X-axis force mass block 13 is for: .

[0061] During electrostatic force feedback, the sensitive mass is maintained at an equilibrium position, so ignoring high-order terms yields: .

[0062] The maximum range in closed loop is: .

[0063] It can be seen from the above formula that, under the condition that the back-end feedback voltage capability is constant and other structural parameters remain unchanged, appropriately reducing the sensitive mass of the X-axis force-applying mass block 13 is helpful to improve the closed-loop range.

[0064] For the Y-axis structure layer, there are: , Where, Respectively represent the resonant frequencies of the detection structure and the force-applying structure in the Y-axis structural layer, They represent the mechanical stiffness of the first spring 51 and the mechanical stiffness of the second spring 35 in the Y-axis structure layer, They respectively represent the sensitive mass of the Y-axis detection mass block 17 and the sensitive mass of the Y-axis force mass block 20 in the Y-axis structural layer.

[0065] Assume that the first comb unit on the Y-axis detection mass block 17 has two teeth on the left and right sides of the third anchor point 38. For the detection comb teeth, the smaller gap and the larger gap on both sides of the first movable comb tooth and the first fixed comb tooth are defined as and , the initial capacitance value is: , Where, Indicates the initial capacitance value of the first comb unit.

[0066] When there is an acceleration a input in the sensitive direction, due to inertia, the sensitive mass block of the Y-axis detection structure (i.e., the Y-axis detection mass block 17) will produce a displacement y, and the capacitance change is: , Where, They represent capacitance change, positive detection capacitance change, and negative detection capacitance change, respectively.

[0067] Ignoring the high-order terms in the formula, the open-loop sensitivity of the Y-axis structure layer can be obtained for: .

[0068] It can be seen that appropriately increasing the sensitive mass of the Y-axis detection mass block 17 is helpful to improve the sensitivity of the accelerometer.

[0069] On the Y-axis force-applying mass block 20, the electrostatic force applied to the positive force-applying comb unit is: , The electrostatic force applied to the negative force comb unit is: , Where, They represent the electrostatic forces applied to the positive force comb unit and the negative force comb unit, respectively. Respectively represent the smaller gap and the larger gap on both sides of the second movable comb teeth and the second fixed comb teeth in the second comb tooth unit, represents the number of comb tooth pairs of the second comb tooth unit on the left and right sides of the fifth anchor point 49, and y still represents the displacement of the sensitive mass block (ie, the Y-axis force-applying mass block 20).

[0070] Then the electrostatic force on the Y-axis force mass block 20 is for: .

[0071] During electrostatic force feedback, the sensitive mass is maintained at an equilibrium position, so ignoring high-order terms yields: , Where, It represents the sensitive mass of the Y-axis force-applying mass block 20.

[0072] The maximum range in closed loop is: .

[0073] It can be seen from the above formula that, under the condition that the back-end feedback voltage capability is constant and other structural parameters remain unchanged, appropriately reducing the sensitive mass of the Y-axis force-applying mass block 20 is helpful to improve the closed-loop range.

[0074] Because the X-axis and Y-axis structural layers are equal in size, independent of each other, and arranged orthogonally, they can reduce orthogonality errors, significantly improve cross-axis interference resistance, and enhance detection accuracy. Furthermore, the sensing mass of the sensing and force-applying structures is no longer shared, and adjusting the sensitive mass of the force-applying mass improves closed-loop feedback capabilities.

[0075] The present invention is not limited to the aforementioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A three-axis MEMS accelerometer, characterized in that: The invention comprises a substrate, an insulating layer, an electrode layer and a structural layer designed layer by layer; the structural layer comprises an X-axis structural layer, a Y-axis structural layer and a Z-axis structural layer; the Z-axis structural layer comprises a hollow Z-axis sensitive mass block and a first anchor point (15) located at the center of the Z-axis sensitive mass block, the Z-axis sensitive mass block is connected to the first anchor point (15) via a torsion beam (21), and the masses of the Z-axis sensitive mass block on both sides of the torsion beam (21) are unequal; the X-axis structural layer and the Y-axis structural layer are respectively located on both sides of the torsion beam (21) and in the hollow area of the Z-axis sensitive mass block; the sensitive mass blocks of the detection structure and the force-applying structure of the X-axis structural layer and the Y-axis structural layer are not shared, and the resonance frequencies of the detection structure and the force-applying structure are the same.

2. The three-axis MEMS accelerometer according to claim 1, wherein: The Z-axis sensitive mass block comprises a positive mass block (23) and a negative mass block (19) located on both sides of the torsion beam (21), and a suspended mass block (10) connected to the positive mass block (23); a damping hole (11) is provided on the suspended mass block (10).

3. The three-axis MEMS accelerometer according to claim 2, wherein: The electrode layer includes a Z-axis positive force electrode (12) and a Z-axis positive detection electrode (14a, 14b) located below the positive mass block (23), and a Z-axis negative force electrode (18) and a Z-axis negative detection electrode (16a, 16b) located below the negative mass block (19); the Z-axis positive force electrode (12) and the Z-axis negative force electrode (18) are respectively located on both sides of the torsion beam (21).

4. The three-axis MEMS accelerometer according to claim 1, wherein: The X-axis structural layer includes an X-axis detection mass block (22) and an X-axis force mass block (13); the Y-axis structural layer includes a Y-axis detection mass block (17) and a Y-axis force mass block (20); the X-axis detection mass block (22) and the X-axis force mass block (13) have the same structure and are arranged orthogonally; the Y-axis detection mass block (17) and the Y-axis force mass block (20) have the same structure and are arranged orthogonally; the X-axis detection mass block (22) and the Y-axis detection mass block (17) are isolated from each other, and the X-axis force mass block (13) and the Y-axis force mass block (20) are isolated from each other.

5. The three-axis MEMS accelerometer according to claim 4, wherein: The X-axis force-applying mass block is provided with holes.

6. The three-axis MEMS accelerometer according to claim 4, wherein: The X-axis detection mass block (22) is provided with a first comb tooth unit arranged along the X-axis direction, a second anchor point (37), a third anchor point (38) located at the center of the X-axis detection mass block (22), a first spring (51) and a first beam structure (36); the first comb tooth unit includes a first fixed comb tooth and a first movable comb tooth that match each other; the first fixed comb tooth is connected to the second anchor point (37), and the first movable comb tooth is connected to the X-axis detection mass block (22); the first spring (51) is located on both sides of the third anchor point (38), the inner side of the first spring (51) is connected to the third anchor point (38) through the first beam structure (36), and the outer side of the first spring (51) is connected to the X-axis detection mass block (22).

7. The three-axis MEMS accelerometer according to claim 6, wherein: The X-axis force mass block (13) is provided with a second comb tooth unit arranged along the X-axis direction, a fourth anchor point (48), a fifth anchor point (49) located at the center of the X-axis force mass block (13), a second spring (35) and a second beam structure (50); the second comb tooth unit includes a second fixed comb tooth and a second movable comb tooth that match each other; the second fixed comb tooth is connected to the fourth anchor point (48), and the second movable comb tooth is connected to the X-axis force mass block (13); the second spring (35) is located on both sides of the fifth anchor point (49), the inner side of the second spring (35) is connected to the fifth anchor point (49) through the second beam structure (50), and the outer side of the second spring (35) is connected to the X-axis force mass block (13).

8. The three-axis MEMS accelerometer according to claim 7, wherein: The comb tooth gap of the second comb tooth unit is smaller than the comb tooth gap of the first comb tooth unit; the number of comb tooth pairs of the second comb tooth unit is greater than the number of comb tooth pairs of the first comb tooth unit; the comb tooth facing area of the second comb tooth unit is larger than the comb tooth facing area of the first comb tooth unit.

9. The three-axis MEMS accelerometer according to claim 1, wherein: The edges of the sensitive mass blocks of the detection structure and the force-applying structure of the X-axis structural layer and the Y-axis structural layer, as well as the inside of the hollow area of the Z-axis sensitive mass block, are all provided with limit stop structures; some or all of the limit stop structures of the X-axis structural layer, the Y-axis structural layer and the Z-axis structural layer are shared.

10. The three-axis MEMS accelerometer according to claim 9, wherein: The position limiting stop structure comprises a stop block, and a first protrusion (47) is provided on a side wall of the stop block.

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