MEMS capacitive triaxial accelerometer and detection system

Abstract

The invention discloses an MEMS capacitive triaxial accelerometer and a detection system, the triaxial accelerometer comprises an X-axis accelerometer, a Y-axis accelerometer and a Z-axis accelerometer, the X-axis accelerometer and the Y-axis accelerometer are nested in the Z-axis accelerometer, the Z-axis accelerometer is connected with a central anchor point through an upper torsion beam and a lower torsion beam, and the X-axis accelerometer and the Y-axis accelerometer are connected with the central anchor point through an upper torsion beam and a lower torsion beam. The central anchor point is fixedly connected with outer frames of the X-axis accelerometer and the Y-axis accelerometer at the same time, an eccentric mass block is designed at one end of the Z-axis accelerometer, the X-axis accelerometer and the Y-axis accelerometer are the same in structure and are orthogonally arranged, the X-axis accelerometer, the Y-axis accelerometer and the Z-axis accelerometer are mutually independent in structure and function, and independent detection of input acceleration in the X direction and the Y direction is achieved respectively. And out-of-plane capacitance detection in the vertical direction. According to the invention, the detection units in the X, Y and Z directions are integrated on the single-layer silicon wafer, so that a three-axis acceleration detection scheme which is compact in structure, independent in detection, high in sensitivity and high in process compatibility is formed.

Description

Technical Field

[0001] The present invention belongs to the field of micro-electromechanical systems (MEMS) and micro-inertial measurement technology, and in particular relates to a MEMS capacitive three-axis accelerometer and a detection system. Background Art

[0002] Microelectromechanical systems (MEMS) technology, a revolutionary breakthrough in micro-nano manufacturing at the end of the 20th century, achieved miniaturization, integration, and cost-effectiveness in sensor devices by integrating mechanical structures and electronic circuits on silicon-based chips. Since its commercialization in the 1980s, MEMS technology has gradually transitioned from laboratory research to large-scale industrial applications. Its core advantage lies in the use of semiconductor processes to mass-produce micron-scale movable structures, combined with integrated circuits for signal detection and processing. This significantly reduces device size, power consumption, and manufacturing costs while retaining traditional sensor functions.

[0003] MEMS accelerometers are a typical application of MEMS technology in the field of inertial sensing. Their basic principle is to obtain external acceleration information by detecting the inertial displacement of a mass under acceleration. Compared with traditional mechanical accelerometers, MEMS accelerometers offer advantages such as small size, light weight, ease of integration, high reliability, and a wide measurement range. As a result, MEMS accelerometers have been widely used in automotive electronics, smartphones, drones, wearable devices, and other fields.

[0004] The current mainstream MEMS three-axis accelerometers mostly use a single-mass three-dimensional detection structure or an in-plane multi-axis coupling design. Although they can realize the simultaneous measurement of XYZ three-axis acceleration, they still face many technical bottlenecks in practical applications: In order to realize the three-axis detection function, the existing design usually requires the sensitive structures of different axes to be arranged in different areas in the chip plane, resulting in a large overall device volume, which is not conducive to miniaturization and integration. At the same time, due to the physical connection or signal path interference between the structures of each detection axis, inter-axis coupling is easily generated, affecting the independent detection accuracy of acceleration in each direction. In addition, the planar layout of the multi-axis sensitive structure causes the Z-axis detection sensitivity to be significantly lower than the X / Y axis, which restricts the accuracy balance of three-dimensional acceleration measurement. Therefore, how to achieve a MEMS three-axis accelerometer structure with a compact structure, independent axial decoupling, high sensitivity and high reliability while ensuring detection accuracy has become a key technical problem that needs to be solved in this field. Summary of the Invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a MEMS capacitive triaxial accelerometer with a coplanar nested structure, which has a compact structure, independent detection, high sensitivity and strong process compatibility.

[0006] Technical solution: The present invention describes a MEMS capacitive three-axis accelerometer comprising an X-axis accelerometer, a Y-axis accelerometer, and a Z-axis accelerometer. The X-axis accelerometer and the Y-axis accelerometer are nested within the Z-axis accelerometer. The Z-axis accelerometer is connected to a central anchor point using upper and lower torsion beams. The central anchor point is also fixedly connected to the outer frames of the X-axis accelerometer and the Y-axis accelerometer. An eccentric mass block is designed at one end of the Z-axis accelerometer. The X-axis accelerometer and the Y-axis accelerometer have identical structures and are arranged orthogonally. The X-axis, Y-axis, and Z-axis accelerometers are independent in structure and function, respectively, and independently detect input accelerations in the X and Y directions, as well as out-of-plane capacitance detection in the vertical direction.

[0007] Optionally, the Z-axis accelerometer also includes: a Z-axis accelerometer frame, a Z-axis accelerometer stress relief hole, and positive and negative external detection electrodes of the Z-axis accelerometer. The Z-axis accelerometer stress relief hole is set on the Z-axis accelerometer frame, and the central anchor point is set in the central area of the Z-axis accelerometer frame. The area enclosed by the Z-axis accelerometer frame is divided into a left half and a right half. The Y-axis accelerometer and the X-axis accelerometer are respectively set in the left half and the right half. The positive and negative external detection electrodes of the Z-axis accelerometer are respectively set on the upper surfaces of the left and right ends of the Z-axis accelerometer frame.

[0008] Optionally, the Z-axis accelerometer stress relief hole includes upper and lower stress relief holes of the Z-axis accelerometer, which are respectively arranged at the upper and lower ends of the Z-axis accelerometer frame.

[0009] Optionally, the Z-axis accelerometer adopts a differential capacitance detection structure.

[0010] Optionally, the Y-axis accelerometer structure includes: a Y-axis accelerometer outer frame, a Y-axis accelerometer frame, upper and lower serpentine beams of the Y-axis accelerometer, a Y-axis accelerometer stress relief hole, upper and lower anchor points of the Y-axis accelerometer, a fixed electrode of the Y-axis accelerometer, a central crossbeam of the Y-axis accelerometer, and a synovial capacitance detection structure. The Y-axis accelerometer stress relief hole is arranged on the Y-axis accelerometer frame, the central crossbeam of the Y-axis accelerometer divides the area enclosed by the Y-axis accelerometer frame into an upper half and a lower half, and the Y-axis accelerometer fixed electrodes are respectively arranged in the middle area of the upper half and the lower half. The Y-axis accelerometer frame is elastically connected to the upper and lower anchor points of the Y-axis accelerometer through the upper and lower serpentine beams of the Y-axis accelerometer, and the synovial capacitance detection structure is arranged in the areas on both sides of the fixed electrode of the Y-axis accelerometer, and its two ends are respectively connected to the Y-axis accelerometer frame and the fixed electrode of the Y-axis accelerometer.

[0011] Optionally, the synovial capacitance detection structure includes a movable comb tooth frame, movable comb teeth, a fixed comb tooth frame and fixed comb teeth, the movable comb teeth are attached to the movable comb tooth frame, the fixed comb teeth are attached to the fixed comb tooth frame, the movable comb teeth and the fixed comb teeth are staggered, the movable comb tooth frame is connected to the Y-axis accelerometer frame, and the fixed sparse tooth frame is connected to the fixed electrode of the Y-axis accelerometer.

[0012] Optionally, the Y-axis accelerometer stress relief holes include upper and lower stress relief holes of the Y-axis accelerometer and left and right stress relief holes of the Y-axis accelerometer, which are respectively arranged at the upper and lower ends and left and right ends of the Y-axis accelerometer frame.

[0013] Optionally, both the Y-axis accelerometer and the X-axis accelerometer are differentially detected.

[0014] Optionally, the three-axis accelerometer is integrated on a single-layer silicon wafer.

[0015] The detection system of the present invention includes the MEMS capacitive three-axis accelerometer.

[0016] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows: (1) The overall coplanar integrated structure is adopted, and the detection structures of the X-axis and Y-axis are located in the central area of the device, respectively including symmetrically arranged movable comb teeth and fixed electrodes, forming a comb-tooth differential capacitance detection structure; the X-axis and Y-axis accelerometer frames are elastically connected to the fixed anchor point through a folding beam to achieve sensitive response to the acceleration in the plane; the two groups of structures above and below the beam are symmetrically arranged about the center of the device, further suppressing common-mode interference and enhancing the signal decoupling capability; the detection structure in the Z-axis direction is surrounded by the outer side of the X-axis and Y-axis structures in the form of an outer frame, and is elastically connected to the central anchor point through a torsion beam, thereby achieving high-sensitivity out-of-plane capacitance in the vertical direction Detection; (2) In terms of structural design, a nested layout is adopted to integrate the X and Y axis accelerometers into the Z axis structure, which greatly reduces the size of the device and makes the overall structure more compact; at the same time, differential detection is adopted in the three axes of X, Y and Z, which not only improves the sensitivity and linearity, but also effectively reduces the noise interference of the signal; in order to enhance the structural strength and dynamic stability of the device, a transverse rigid connecting beam is set in the middle of the accelerometer frame in the X / Y direction, which can improve the overall structural rigidity and suppress torsional interference; in addition, a number of stress release holes are designed in key areas such as the connection between the accelerometer frame and the elastic beam to release residual stress during chip packaging or temperature changes, thereby improving the stability and long-term reliability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the structure of the three-axis accelerometer of the present invention;

[0018] Figure 2 Schematic diagram of the structure of the Y-axis accelerometer of the present invention;

[0019] Figure 3 Schematic diagram of the synovial capacitance detection structure of the Y-axis accelerometer of the present invention;

[0020] In the figure: 1-Z-axis accelerometer frame, 2-Y-axis accelerometer outer frame, 3a-Z-axis accelerometer upper stress relief hole, 3b-Z-axis accelerometer lower stress relief hole, 4a-Z-axis accelerometer upper torsion beam, 4b-Z-axis accelerometer lower torsion beam, 5-X-axis accelerometer, 6-Z-axis accelerometer eccentric mass, 7-X-axis accelerometer outer frame, 8-Z-axis accelerometer central anchor point, 9-Y-axis accelerometer, 10-Y-axis accelerometer frame, 11a-Y-axis accelerometer upper serpentine beam, 11b-Y-axis Accelerometer lower serpentine beam, 12a-Y-axis accelerometer upper stress relief hole, 12b-Y-axis accelerometer lower stress relief hole, 13a-Y-axis accelerometer upper anchor point, 13b-Y-axis accelerometer lower anchor point, 14a and 14b are the positive and negative fixed electrodes of the Y-axis accelerometer respectively, 15-Y-axis accelerometer central beam, 16a-Y-axis accelerometer left stress relief hole, 16b-Y-axis accelerometer right stress relief hole, 17-movable comb tooth frame, 18-movable comb teeth, 19-fixed comb tooth frame, 20-fixed comb teeth. DETAILED DESCRIPTION

[0021] The following will describe the MEMS capacitive triaxial accelerometer structure proposed in the present invention in detail with reference to the accompanying drawings. It should be understood that the embodiments of the present invention are only used to illustrate the principles of the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0022] A MEMS accelerometer is a miniature sensor based on Newton's second law. It uses microelectromechanical systems (MEMS) technology to convert tiny physical changes into electrical signals, thereby detecting an object's acceleration. Multi-axis MEMS accelerometers can simultaneously measure acceleration in multiple directions, typically providing acceleration data along three axes, enabling precise monitoring of an object's motion. This invention, based on this fundamental principle, enhances the sensitivity and accuracy of triaxial detection through the coordinated design of structural optimization and capacitive detection mechanisms.

[0023] The present invention proposes a MEMS capacitive three-axis accelerometer, which integrates detection units in the X, Y, and Z directions on a single-layer silicon chip to form a three-axis acceleration detection solution with a compact structure, independent detection, high sensitivity, and strong process compatibility. Figure 1As shown, the overall structure adopts a nested layout, consisting of a set of Z-axis accelerometers surrounding two sets of X-axis accelerometers 5 and Y-axis accelerometers 9. The X-axis and Y-axis accelerometers are identical in structure and are arranged orthogonally to independently detect input acceleration in the X and Y directions, respectively. Because the Z-axis accelerometer, X-axis accelerometer, and Y-axis accelerometer are structurally and functionally isolated modules, with no mechanical connections or signal interference paths between them, cross-axis coupling is effectively avoided, improving the independence of the three-axis signals and measurement accuracy.

[0024] This triaxial accelerometer structure utilizes coplanar integration, enabling single-step fabrication on a single silicon wafer. This greatly simplifies the manufacturing process and significantly improves integration. Through a nested layout, the X- and Y-axis accelerometer structures are embedded within the Z-axis accelerometer structure, significantly improving silicon wafer area utilization. This allows the overall structure to achieve triaxial functionality while occupying a smaller footprint. Compared to traditional multi-layer stacked structures, this significantly reduces chip size, offering greater integration and miniaturization advantages.

[0025] The Z-axis accelerometer is connected to the anchor point using a torsion beam structure, and the anchor point is fixedly connected to the outer frame of the X-axis and Y-axis accelerometers at the same time to limit the displacement of the movable structure of the X-axis and Y-axis, avoid collision between microstructures under overload conditions, and enhance the stability and reliability of the overall structure. An eccentric mass block 6 is designed at one end of the Z-axis accelerometer. When the external environment generates vertical acceleration input, the Z-axis accelerometer frame 1 undergoes out-of-plane angular displacement under the action of the inertial torque. The Z-axis detection structure adopts an out-of-plane capacitance detection form. The detection electrodes are arranged on the upper surface of the two ends of the outer frame of the Z-axis accelerometer. When the Z-axis accelerometer frame undergoes angular displacement, the distance between it and the upper detection electrode changes, causing a change in capacitance. Because the structure adopts a nested layout, the movable frame portion corresponding to the detection electrode is far away from the torsion fulcrum. When the Z-axis accelerometer undergoes the same angular displacement, the movable frame produces a larger out-of-plane displacement, thereby significantly improving the capacitance sensitivity in the out-of-plane direction. The Z-axis accelerometer also uses a differential capacitance detection structure, which effectively suppresses interference signals from the circuit or packaging process and offsets common-mode interference caused by temperature changes, thereby improving the detection signal-to-noise ratio and stability. By detecting the change in capacitance and combining it with known structural parameters, the magnitude of the acceleration in the Z-axis direction can be derived.

[0026] like Figure 1As shown, the Z-axis accelerometer includes a Z-axis accelerometer frame 1, upper and lower stress relief holes 3a and 3b, upper and lower torsion beams 4a and 4b, an eccentric mass 6, a central anchor point 8, and positive and negative external detection electrodes. The upper and lower stress relief holes 3a and 3b are located at the upper and lower ends of the Z-axis accelerometer frame 1, respectively. The eccentric mass 6 is located at one end of the Z-axis accelerometer frame 1. The central anchor point 8 is located in the center of the Z-axis accelerometer frame 1, dividing the Z-axis accelerometer frame 1 into a left and right half. The Y-axis accelerometer 9 and the X-axis accelerometer 5 are located in the left and right halves, respectively, with the Y-axis accelerometer 9 and the X-axis accelerometer 5 being arranged orthogonally. The central anchor point 8 is connected to the Y-axis accelerometer outer frame 2 and the X-axis accelerometer outer frame 7 on both sides. The upper and lower ends of the Z-axis accelerometer central anchor point 8 are connected to the Z-axis accelerometer frame 1 through the upper and lower torsion beams 4a and 4b respectively. The positive and negative external detection electrodes of the Z-axis accelerometer are also set on the upper surfaces of the left and right ends of the Z-axis accelerometer frame 1.

[0027] like Figure 2 As shown, the Y-axis accelerometer 9 mainly includes a Y-axis accelerometer outer frame 2, a Y-axis accelerometer frame 10, upper and lower serpentine beams 11a and 11b of the Y-axis accelerometer, upper and lower stress release holes 12a and 12b of the Y-axis accelerometer, upper and lower anchor points 13a and 13b of the Y-axis accelerometer, fixed electrodes 14a and 14b of the Y-axis accelerometer, a central crossbeam 15 of the Y-axis accelerometer, left and right stress release holes 16a and 16b of the Y-axis accelerometer, and a synovial capacitance detection structure. Figure 3 As shown, the synovial capacitance detection structure includes a movable comb frame 17, movable comb teeth 18, a fixed comb frame 19, and fixed comb teeth 20. The movable comb teeth are attached to the movable comb frame, and the fixed comb teeth are attached to the fixed comb frame. The movable comb teeth and the fixed comb teeth are arranged in an alternating pattern. There is no connection between the Y-axis accelerometer outer frame 2 and the Y-axis accelerometer frame 10. The Y-axis accelerometer outer frame 2 is primarily used to limit the displacement of the Y-axis accelerometer frame 10 and the movable comb teeth 18, preventing collisions between the Y-axis accelerometer frame 10 and the Z-axis accelerometer frame 1, between the movable comb teeth 18 and the fixed comb frame 19, and between the fixed comb teeth 20 and the movable comb frame 17 in the event of an overload.

[0028] The upper and lower stress relief holes 12a and 12b of the Y-axis accelerometer are respectively provided at the upper and lower ends of the Y-axis accelerometer frame 10. The central crossbeam 15 of the Y-axis accelerometer divides the Y-axis accelerometer frame 10 into an upper and lower portion. A Y-axis accelerometer fixed electrode 14a is provided in the middle of the upper portion. An upper anchor point 13a is provided above the fixed electrode 14a. The upper end of the Y-axis accelerometer frame 10 is elastically connected to the upper anchor point 13a via an upper serpentine beam 11a. A Y-axis accelerometer fixed electrode 14b is provided in the middle of the lower portion. A lower anchor point 13b is provided below the fixed electrode 14b. The lower end of the Y-axis accelerometer frame 10 is elastically connected to the lower anchor point 13b via a lower serpentine beam 11b. The serpentine structure can effectively extend the equivalent beam length and reduce the cantilever stiffness, thereby improving the structure's response sensitivity to small acceleration inputs. The Y-axis accelerometer frame 10, corresponding to the two ends of the Y-axis accelerometer's central crossbeam 15, is provided with left and right stress relief holes 16a and 16b, respectively. The synovial capacitance detection structure is provided in the areas on both sides of the Y-axis accelerometer's fixed electrodes 14a and 14b. The two ends of the synovial capacitance detection structure are connected to the Y-axis accelerometer frame 10 and the Y-axis accelerometer's fixed electrodes 14a or 14b, respectively. The movable comb rack 17 is connected to the Y-axis accelerometer frame 10, and the fixed sparse tooth rack 19 is connected to the Y-axis accelerometer's fixed electrodes 14a or 14b. When the Y-axis accelerometer is displaced under acceleration, the overlapping area between the comb teeth changes, causing the capacitance value to change. At the same time, the capacitance of the upper and lower halves of the Y-axis accelerometer's central crossbeam 15 have opposite capacitance changes, thereby achieving differential detection, effectively suppressing common-mode interference, and achieving high-precision acceleration detection.

[0029] Through the above-mentioned structural design, the present invention not only realizes decoupled detection and high-sensitivity output in three-axis directions, but also has the advantages of compact structure, friendly processing technology, and high area utilization. It is suitable for a variety of micro inertial measurement system application scenarios with high requirements on spatial size and detection performance.

[0030] The triaxial accelerometer of this invention utilizes a nested layout structure and a compact design. The X / Y axes employ a serpentine folded beam design, a sliding membrane comb structure with differential detection, and an eccentric mass and torsion beam design for the Z-axis. This nested design allows the movable frame portion corresponding to the detection electrodes to be positioned away from the torsion fulcrum. This allows for greater out-of-plane displacement and capacitance sensitivity when the Z-axis accelerometer experiences the same angular displacement. The Z-axis utilizes out-of-plane differential capacitance detection, stress relief holes, and a rigid central connecting beam for the X and Y-axis accelerometers. The entire structure can be fabricated on a single silicon wafer.

[0031] The detection system of the present invention includes the MEMS capacitive three-axis accelerometer.

Claims

1. A MEMS capacitive three-axis accelerometer, characterized in that: include: The X-axis accelerometer, Y-axis accelerometer and Z-axis accelerometer are nested inside the Z-axis accelerometer. The Z-axis accelerometer is connected to the central anchor point using upper and lower torsion beams. The central anchor point is also fixedly connected to the outer frames of the X-axis accelerometer and Y-axis accelerometer. An eccentric mass block is designed at one end of the Z-axis accelerometer. The X-axis accelerometer and Y-axis accelerometer have the same structure and are arranged orthogonally. The X-axis, Y-axis and Z-axis accelerometers are independent of each other in structure and function, respectively realizing independent detection of input acceleration in the X and Y directions, as well as out-of-plane capacitance detection in the vertical direction.

2. The MEMS capacitive three-axis accelerometer according to claim 1, characterized in that: The Z-axis accelerometer also includes: a Z-axis accelerometer frame, a Z-axis accelerometer stress relief hole, and positive and negative external detection electrodes of the Z-axis accelerometer. The Z-axis accelerometer stress relief hole is set on the Z-axis accelerometer frame, and the central anchor point is set in the central area of the Z-axis accelerometer frame, dividing the area enclosed by the Z-axis accelerometer frame into a left half and a right half. The Y-axis accelerometer and the X-axis accelerometer are respectively set in the left half and the right half. The positive and negative external detection electrodes of the Z-axis accelerometer are respectively set on the upper surfaces of the left and right ends of the Z-axis accelerometer frame.

3. The MEMS capacitive three-axis accelerometer according to claim 1, wherein: The Z-axis accelerometer stress relief hole includes an upper and lower stress relief hole of the Z-axis accelerometer, which are respectively arranged at the upper and lower ends of the Z-axis accelerometer frame.

4. The MEMS capacitive three-axis accelerometer according to claim 1, wherein: The Z-axis accelerometer uses a differential capacitance detection structure.

5. The MEMS capacitive triaxial accelerometer according to claim 1, wherein: The Y-axis accelerometer structure includes: a Y-axis accelerometer outer frame, a Y-axis accelerometer frame, upper and lower serpentine beams of the Y-axis accelerometer, a Y-axis accelerometer stress relief hole, upper and lower anchor points of the Y-axis accelerometer, a fixed electrode of the Y-axis accelerometer, a central crossbeam of the Y-axis accelerometer, and a synovial capacitance detection structure. The Y-axis accelerometer stress relief hole is set on the Y-axis accelerometer frame. The central crossbeam of the Y-axis accelerometer divides the Y-axis accelerometer frame into an upper half and a lower half. The Y-axis accelerometer fixed electrodes are respectively set in the middle area of the upper half and the lower half. The Y-axis accelerometer frame is elastically connected to the upper and lower anchor points of the Y-axis accelerometer through the upper and lower serpentine beams of the Y-axis accelerometer. The synovial capacitance detection structure is set in the area on both sides of the Y-axis accelerometer fixed electrode, and its two ends are respectively connected to the Y-axis accelerometer frame and the Y-axis accelerometer fixed electrode.

6. The MEMS capacitive three-axis accelerometer according to claim 5, characterized in that: The synovial capacitance detection structure includes a movable comb tooth frame, movable comb teeth, a fixed comb tooth frame and fixed comb teeth. The movable comb teeth are attached to the movable comb tooth frame, the fixed comb teeth are attached to the fixed comb tooth frame, the movable comb teeth and the fixed comb teeth are arranged alternately, the movable comb tooth frame is connected to the Y-axis accelerometer frame, and the fixed comb tooth frame is connected to the fixed electrode of the Y-axis accelerometer.

7. The MEMS capacitive three-axis accelerometer according to claim 5, characterized in that: The Y-axis accelerometer stress relief holes include upper and lower stress relief holes and left and right stress relief holes, which are respectively arranged at the upper and lower ends and left and right ends of the Y-axis accelerometer frame.

8. The MEMS capacitive three-axis accelerometer according to claim 5, characterized in that: The Y-axis accelerometer and the X-axis accelerometer are both differential detection.

9. The MEMS capacitive three-axis accelerometer according to claim 1, wherein: The three-axis accelerometer is integrated on a single-layer silicon chip.

10. A detection system, characterized in that: The MEMS capacitive three-axis accelerometer comprises the one described in any one of claims 1 to 9.

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