A three-axis MEMS force sensor with self-calibration function

Abstract

The application discloses a three-axis MEMS force sensor with a self-calibration function, which comprises a glass substrate, a fixed electrode on the upper surface of the glass substrate and a device layer suspended above the glass substrate. The fixed electrode on the upper surface of the glass substrate comprises a fixed interdigital aluminum electrode, a fixed metal electrode, an electrode connecting line and a self-detection leading electrode. The device layer suspended above the glass substrate comprises a device anchor point, four L-shaped piezoelectric driving beams, an electrostatic suction module, a sensitive driving table and a capacitive three-axis force sensor. The fixed metal electrode is placed in correspondence with a center mass of the capacitive three-axis force sensor, and the electrostatic suction module is located between the piezoelectric driving beam and the sensitive driving table. The application suppresses the problem of cross-axis crosstalk, realizes cross-axis and normal three-axis driving, realizes real-time detection of cross-axis driving capacitance, and realizes switching between a force detection mode and a calibration mode through adjustment of the electrostatic suction module.

Description

Technical Field

[0001] This invention belongs to the field of triaxial force sensors and MEMS self-calibration devices, specifically relating to a triaxial MEMS force sensor with self-calibration function. Background Technology

[0002] Triaxial force sensors can be used to detect touch and are an important medium for intelligent robots to perceive human life. They play a crucial role in fields such as medical care, robotics, and wearable devices. Force sensors can be classified into capacitive, piezoelectric, piezoresistive, electromagnetic, and optical types according to their operating principles. Among them, capacitive sensors are widely used due to their advantages such as high sensitivity, high resolution, and good temperature stability.

[0003] Generally, differential detection capacitive sensors have higher sensitivity than non-differential detection sensors. Differential detection capacitors can be classified into tilted capacitors, grid capacitors, and comb-type capacitors. Tilted capacitors change capacitance through varying electrode spacing; when the upper electrode is subjected to external force, it tilts, causing one electrode to decrease in capacitance and the other to increase. However, tilted capacitors are currently typically calculated using complex integration algorithms. Grid capacitors change capacitance through varying electrode area, resulting in high output linearity. Comb-type capacitors change capacitance through both varying electrode area and spacing; the specifically distributed comb-shaped electrodes can reduce cross-axis interference. Grid and comb-type capacitors are simple in principle, have good performance, and are more widely used.

[0004] Currently, environmental changes and process design factors can lead to errors in sensor performance. Therefore, regular sensor calibration is crucial to ensure measurement accuracy. Current calibration techniques require sending the sensor to a factory calibration stage to simulate its operating conditions. However, in practical applications, sensors are soldered onto PCBs, making removal for calibration impractical. Furthermore, most current research focuses on providing calibration functions for inertial sensors, with very few methods specifically for force sensors. Therefore, to save on additional calibration costs, integrating a real-time self-calibration structure into the sensor design from the outset is extremely important.

[0005] During calibration, an essential structure is the drive stage used to simulate external excitation. Drive stages can be categorized by their operating principle into electrostatic drive, electromagnetic drive, and piezoelectric drive. Electrostatic drive is primarily based on the principle of electrostatic force between capacitors; the principle is simple and easy to understand, but it suffers from problems such as attraction effects and electrostatic plate contact effects. Electromagnetic drive is based on the principle of a current-carrying conductor experiencing Ampere force in a uniform magnetic field, which can generate large driving torque and offset, but it has disadvantages such as high energy consumption and heat generation. Piezoelectric drive is based on the principle of the piezoelectric effect of crystals; when pressure is applied, the piezoelectric material deforms and shifts. This method has advantages such as adjustable range, wide output range, and low driving voltage. Summary of the Invention

[0006] To overcome the shortcomings of the aforementioned background technology, this invention proposes a triaxial MEMS (microelectromechanical system) force sensor with self-calibration function. This invention integrates a calibration drive stage module, which can perform real-time calibration of cross-axis detection while realizing three-dimensional force detection.

[0007] The solution adopted by this invention to solve its technical problem is:

[0008] A triaxial MEMS force sensor with self-calibration function includes a glass substrate and a fixed electrode on its upper surface, and a device layer suspended above the glass substrate.

[0009] The fixed electrode on the upper surface of the glass substrate includes a fixed interdigitated aluminum electrode, a fixed metal electrode, an electrode connecting wire, and a self-detection lead-out electrode.

[0010] The device layer suspended above the glass substrate includes device anchor points, four L-shaped piezoelectric drive beams, an electrostatic attraction module, a sensitive drive stage, and a capacitive triaxial force sensor.

[0011] There are four fixed interdigitated aluminum electrodes in total. The two horizontal fixed interdigitated aluminum electrodes serve as the lower electrodes of the horizontal drive detection capacitor, and the two vertical fixed interdigitated aluminum electrodes serve as the lower electrodes of the vertical drive detection capacitor. Each fixed interdigitated aluminum electrode is placed corresponding to a gate-type silicon electrode on the sensitive drive stage. The tangential drive capacitor is differentially detected by a variable area method, and the capacitance signal is led out along the electrode connection line through the self-detection lead-out electrode.

[0012] The fixed metal electrode is placed corresponding to the central mass block of the capacitive triaxial force sensor. The capacitance is detected by detecting the normal force through a variable-spacing method. The capacitance signal is led out along the electrode connection line through the self-detection lead-out electrode.

[0013] The device comprises 19 pairs of electrode connection lines and self-detection leads. Each fixed interdigitated aluminum electrode connects to two electrode connection lines and two self-detection leads to extract the tangential drive capacitor signal. One fixed metal electrode connects to one electrode connection line and one self-detection lead to extract the normal force detection capacitor signal. Eight tangential force detection anchor points connect to eight electrode connection lines and eight self-detection leads to extract the tangential force detection module signal. Two electrostatic attraction anchor points connect to two electrode connection lines and two self-detection leads to achieve electrostatic attraction and switch to force sensor detection mode.

[0014] The single L-shaped piezoelectric drive beam, from bottom to top, includes an L-shaped silicon beam, a lower drive electrode Pt covering the L-shaped silicon beam, a piezoelectric material PZT covering the lower drive electrode, and a distributed drive upper electrode Pt covering the piezoelectric material PZT. One end of each L-shaped piezoelectric drive beam is fixed to the device anchor point, and the other end is connected to the sensitive drive stage.

[0015] The electrostatic attraction module is located between the piezoelectric drive beam and the sensitive drive platform, and consists of two sets. Each set includes an electrostatic attraction anchor point, electrostatic attraction fixed comb teeth, electrostatic attraction movable comb teeth, a fixed attraction island, and a movable attraction block. The electrostatic attraction fixed comb teeth are fixed to the electrostatic attraction anchor point. The electrostatic attraction movable comb teeth are connected to the sensitive drive platform, located diagonally across the platform, and move with it, corresponding one-to-one with the electrostatic attraction fixed comb teeth. The movable attraction block is connected to the sensitive drive platform and positioned corresponding to the attraction fixed island. The distance between the movable attraction block and the fixed attraction island is less than the distance between the electrostatic attraction fixed comb teeth and the electrostatic attraction movable comb teeth.

[0016] The aforementioned sensitive driving stage includes a lateral sensitive unit and a longitudinal sensitive unit. The lateral sensitive unit consists of two horizontally arranged gate-type silicon electrodes, which serve as the upper electrode of the X-axis driving detection capacitor; the longitudinal sensitive unit consists of two vertically arranged gate-type silicon electrodes, which serve as the upper electrode of the Y-axis driving detection capacitor.

[0017] The capacitive triaxial force sensor includes a limiting block, a U-shaped beam, an inclined beam, a central mass block, and a tangential force detection module.

[0018] The central mass block of the capacitive triaxial force sensor is connected to the sensitive drive stage via a U-shaped beam and an inclined beam.

[0019] The limiting block is obtained by thinning the central mass block and is used for overload protection during normal force detection to prevent the normal force detection electrode from contacting.

[0020] The capacitive triaxial force sensor tangential force detection module includes a tangential force detection anchor point, movable tangential force detection comb teeth, and fixed tangential force detection comb teeth. The fixed tangential force detection comb teeth are fixed to the tangential force detection anchor point. There are a total of 8 sets of tangential force detection modules, symmetrically distributed around the central mass block, with 2 sets on each side. The 8 regions around the central mass block are connected to the same number of movable tangential force detection comb teeth, corresponding one-to-one with the fixed tangential force detection comb teeth. The spacing between them is greater than the spacing between the electrostatically attracted movable comb teeth and the electrostatically attracted fixed comb teeth.

[0021] The beneficial effects of this invention are: It employs comb-tooth capacitance to detect multi-dimensional forces, and through a specific arrangement, it effectively suppresses the problem of cross-axis crosstalk. Furthermore, from the initial design of the capacitive triaxial force sensor structure, a piezoelectric sensitive driving stage structure is integrated. Unlike electrostatic driving, piezoelectric driving can achieve cross-axis and normal triaxial driving, and can generate large displacements under low-frequency conditions, thereby simulating the motion state of external excitation. Simultaneously, a gate-type silicon electrode is designed on the sensitive driving stage to achieve real-time detection of the cross-axis driving capacitance. During actual operation, the force detection mode and calibration mode are switched by adjusting the electrostatic attraction module, eliminating the need to remove the sensor and return it to the factory for calibration, thus saving calibration costs. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the sensor chip of the present invention;

[0023] Figure 2(a) is a magnified detail of the self-calibration module of the sensor device layer of the present invention;

[0024] Figure 2(b) is an enlarged detail view of the L-shaped piezoelectric drive beam of the sensor device layer of the present invention;

[0025] Figure 2(c) is a magnified detail of the layer force detection module of the sensor device of the present invention;

[0026] Figure 3 This is a schematic diagram of the electrode distribution on the glass substrate of the sensor of the present invention;

[0027] Figure 4(a) is a schematic diagram of the variable area detection capacitor pair structure of the sensitive driving stage;

[0028] Figure 4(b) is a schematic diagram of the capacitor pair formed by the fixed comb teeth and the movable comb teeth;

[0029] Figure 5 This is a process flow diagram of the sensor fabrication process of the present invention;

[0030] Figure 6(a) is a schematic diagram of the operation of the sensor of the present invention under the action of shear force + Fx;

[0031] Figure 6(b) is a schematic diagram of the operation of the sensor of the present invention under the action of normal force Fz;

[0032] Figure 6(c) is a schematic diagram of the sensor of the present invention performing tangential calibration;

[0033] Figure 6(d) is a schematic diagram of the normal calibration operation of the sensor of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0035] The overall structure of a triaxial MEMS force sensor with self-calibration function, from bottom to top, consists of a glass substrate layer 1 and a fixed electrode on its upper surface, and a device layer 2 suspended above the glass substrate. The overall structure is formed by silicon-glass bonding. Figure 1 As shown.

[0036] The device layer 2 of this invention includes device anchor points 3, four L-shaped piezoelectric drive beams (4.1, 4.2, 4.3, 4.4), a sensitive drive stage 5, electrostatic attraction anchor points (6.1, 6.2), electrostatic attraction fixed comb teeth (7.1, 7.2), electrostatic attraction movable comb teeth (8.1, 8.2), fixed attraction islands (9.1, 9.2), movable attraction blocks (10.1, 10.2), gate silicon electrodes (11.1, 11.2, 11.3, 11.4), and a capacitive triaxial force detection sensor 12, as shown in Figure 2(a). Each L-shaped piezoelectric drive beam is connected to the device anchor point 3 at one end and to the sensitive drive stage 5 at the other end, located on the center line of the sensitive drive stage, with the four L-shaped piezoelectric drive beams surrounding the entire sensitive drive stage. The electrostatic attraction fixed comb teeth (7.1, 7.2) are fixed on the electrostatic attraction anchor points (6.1, 6.2). The electrostatically attracted movable comb teeth (8.1, 8.2) are connected to the sensitive driving stage 5, located diagonally on the sensitive driving stage, and move with the sensitive driving stage, corresponding one-to-one with the electrostatically attracted fixed comb teeth. Movable attracting blocks are connected to the sensitive driving stage and placed correspondingly to the attracting fixed islands; the distance between the movable attracting blocks and the fixed attracting islands is less than the distance between the electrostatically attracted fixed comb teeth and the electrostatically attracted movable comb teeth. The movable attracting blocks and attracting fixed islands are used for overload protection to prevent contact between the comb tooth electrodes. Movable attracting blocks (10.1, 10.2) are connected to the sensitive driving stage and placed correspondingly to the attracting fixed islands (9.1, 9.2). The central mass block of the capacitive triaxial force sensor 12 is connected to the sensitive driving stage via a U-shaped beam and an inclined beam, located at the center of the device layer. The sensitive driving stage 5 includes a transverse sensitive unit and a longitudinal sensitive unit. The lateral sensing unit consists of two lateral gate silicon electrodes (11.1, 11.3), which serve as the upper electrode of the X-axis driving detection capacitor; the longitudinal sensing unit consists of two longitudinal gate silicon electrodes (11.2, 11.4), which serve as the upper electrode of the Y-axis driving detection capacitor.

[0037] An L-shaped piezoelectric drive beam is formed by stacking an L-shaped silicon beam 13, a driving lower electrode Pt14, a piezoelectric material PZT15, and a distributed driving upper electrode Pt16, as shown in Figure 2(b). As shown in Figures 2(c) and 6(c), the capacitive triaxial force sensor 12 includes a limiting block 28, inclined beams (17.1, 17.2, 17.3, 17.4), a U-shaped beam (18.1, 18.2, 18.3, 18.4), tangential force detection anchor points (19.1, 19.2, 19.3, 19.4, 19.5, 19.6, 19.7, 19.8), movable comb teeth for tangential force detection (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8), fixed comb teeth for tangential force detection (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8), and a central mass block 22. The fixed comb teeth (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8) for tangential force detection are fixed on the fixed anchor points for tangential force detection and are distributed around the central mass block. The movable comb teeth (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8) for tangential force detection move together with the central mass block 22 and correspond one-to-one with the fixed comb teeth for tangential force detection. The U-shaped beam (18.1, 18.2, 18.3, 18.4) and the inclined beam (17.1, 17.2, 17.3, 17.4) connect the central mass block 22 to the sensitive drive stage 5.

[0038] The glass substrate layer of the present invention includes a glass substrate 23 and fixed interdigitated aluminum electrodes (24.1, 24.2, 24.3, 24.4), fixed metal electrodes 25, and electrode connecting wires (26.1, 26.2, 26.3, 26.4, 26.5, 26.6, 26.7, 26.8, 26.9, 26.10, 26.11, 26.12, 26.13, 26.14, 26.5, 26.14, 26.6) on its upper surface. .15, 26.16, 26.17, 26.18, 26.19), self-test lead-out electrodes (27.1, 27.2, 27.3, 27.4, 27.5, 27.6, 27.7, 27.8, 27.9, 27.10, 27.11, 27.12, 27.13, 27.14, 27.15, 27.16, 27.17, 27.18, 27.19), such as Figure 3As shown, each gate silicon electrode of the device layer suspended on the glass substrate is placed correspondingly to each fixed interdigitated aluminum electrode, forming a variable-area tangential drive capacitor detection unit, resulting in four sets of drive capacitor detection units. Electrode connection lines (26.2, 26.3, 26.6, 26.7, 26.12, 26.13, 26.16, 26.17) and self-detection lead-out electrodes (27.2, 27.3, 27.6, 27.7, 27.12, 27.13, 27.16, 27.17) are connected accordingly to extract the tangential drive capacitor signal. A fixed metal electrode 25 forms the lower electrode for normal force detection, and the detection signal is extracted through electrode connection line 26.10 and self-detection lead-out electrode 27.10. The electrode connection lines (26.8, 26.18) and the self-test lead-out electrodes (27.8, 27.18) constitute a switch for switching between force detection mode and calibration mode, and are used to provide voltage to the electrostatic attraction module.

[0039] Figure 4(a) shows the principle of variable area capacitance detection. The gray electrode is a silicon electrode in the grid electrode, and the black electrode is a pair of electrodes in the fixed interdigitated aluminum electrode. The silicon electrode and the pair of aluminum electrodes form two capacitors. The two capacitors have the same initial cross-sectional area, i.e., l1 = l2, and the differential capacitance is 0. When switching to calibration mode and driving the sensor tangentially, the cross-sectional area of ​​one capacitor increases and the cross-sectional area of ​​the other decreases, resulting in one capacitor value increasing and the other decreasing, thus changing the differential capacitance value. Furthermore, the length of the upper silicon electrode is greater than the length of the lower interdigitated aluminum electrode. Taking the X-axis drive as an example, the lateral sensing unit generates differential capacitance output through variable area, while the longitudinal sensing unit has no capacitance output because its cross-sectional area remains unchanged. The Y-axis drive is similar, thus realizing the cross-axis decoupling function. Figure 4(b) shows the principle of comb-tooth capacitance detection, where the gray part is the movable comb tooth and the black part is the fixed comb tooth. The tangential detection unit of the capacitive triaxial force sensor of this invention employs biased comb teeth, with movable and fixed comb teeth arranged alternately. The distances between one movable comb tooth and two fixed comb teeth are d1 and d2, respectively, and d1 is much smaller than d2. Therefore, the capacitance value on the d2 side is negligible compared to the capacitance value on the d1 side. When the movable comb tooth moves longitudinally, the capacitance on the d1 side increases or decreases, thereby achieving differential capacitance detection.

[0040] The fabrication process of a capacitive triaxial force sensor with self-calibration function is as follows: Figure 5 As shown from top to bottom, the specific process flow is as follows:

[0041] (a) A driving lower electrode Pt layer, a piezoelectric material PZT thin film layer and a driving upper electrode Pt layer are sequentially deposited on an SOI silicon wafer.

[0042] (b) Using photolithography and dry etching processes, the bulk silicon outside the anchor points on the back of the silicon wafer and the area where the comb electrodes are fixed is thinned by 10 to 30 μm for the first time to expose the height of the limiting block, remove the adhesive and clean the silicon wafer.

[0043] (c) Using photolithography and dry etching processes, the bulk silicon outside the anchor point, fixed comb electrode and limiting block area on the back of the silicon wafer is thinned to 200-350μm for the second time to expose the height of the central mass block, remove the resist and clean the silicon wafer.

[0044] (d) Using photolithography and dry etching processes, the bulk silicon outside the areas of the back anchor point, fixed comb electrode, limiting block and central mass block of the silicon wafer is thinned to 100-150μm for the third time to expose the height of the upper silicon electrode, remove the resist and clean the silicon wafer.

[0045] (e) The upper metal electrode is etched and patterned by ion beam etching to form a distributed driving upper electrode of an L-shaped piezoelectric driving beam.

[0046] (f) Etch and pattern the driving lower electrode Pt layer to expose the top silicon device layer.

[0047] (g) The top silicon is etched on the front side to form the driving platform structure, gate structure and movable comb structure, and etched through them.

[0048] (h) Prepare a glass plate, clean it according to standard, and form a groove on the glass substrate through photolithography. Then, fabricate a metal thin film on the glass substrate as the lower electrode of the capacitor through sputtering.

[0049] (i) A fixed metal electrode layer is prepared on a glass substrate using photolithography, and the resist is removed and the substrate is cleaned.

[0050] (j) Align and bond the back side of the silicon wafer and the front side of the glass, etch to release the comb structure, clean the bonded wafer, and dicing and encapsulate.

[0051] Figure 6(a) shows a schematic diagram of the operation of the sensor of the present invention when subjected to +Fx in force detection mode. A large voltage is applied between the electrostatically attracted fixed comb teeth (7.1, 7.2) and the electrostatically attracted movable comb teeth (8.1, 8.2). The fixed attracted islands (9.1, 9.2) and the movable attracted blocks (10.1, 10.2) are attracted together, fixing the sensitive drive stage 5. At this time, the sensitive drive stage is equivalent to the anchor point of the capacitive triaxial force sensor. All the applied external force is applied to the central mass block 22. The two U-shaped beams on the left (18.1, 18.4) are stretched, and the two U-shaped beams on the right (18.2, 18.3) are compressed. The central mass block is shifted in the direction of the applied force. The total capacitance Cx1 decreases, and the total capacitance Cx2 increases. The differential capacitance in the X-axis is not zero. The total capacitances of capacitors Cy1 and Cy2 remain unchanged, so the differential capacitance in the Y-axis is zero. Since the spacing between the normal force detection capacitors is almost unchanged, there is no output in the Z direction. At this time, the sensor is used as a triaxial force decoupling sensor.

[0052] Figure 6(b) shows a schematic diagram of the sensor's operation in calibration mode for +X direction calibration. After releasing the voltage between the electrostatically engaged fixed comb teeth (7.1, 7.2) and the electrostatically engaged movable comb teeth (8.1, 8.2), the system switches to calibration mode. The sensitive drive stage 5, connected to the central mass block 22 via U-shaped beams (18.1, 18.2, 18.3, 18.4) and inclined beams (17.1, 17.2, 17.3, 17.4), applies the voltage shown in the figure to the distributed upper electrodes Pt on the L-shaped piezoelectric beam. The darker upper electrodes are applied with a positive voltage, while the lighter upper electrodes are applied with a negative voltage. This drives the sensitive drive stage and causes the central mass block to simulate the motion state under +Fx conditions. The X-direction drive capacitor is detected by the transverse grid capacitors (11.2, 11.4) on the sensitive drive stage. Since the cross-sectional area of ​​the longitudinal grid capacitors (11.1, 11.3) remains unchanged, there is no Y-direction drive capacitor output. At this time, the comb capacitor of the tangential force detection unit also generates a differential capacitor output. The variable area differential capacitor output of the sensitive drive stage is compared with the differential capacitor output of the force sensor comb, thereby realizing real-time calibration of the sensor's tangential detection characteristics.

[0053] Figure 6(c) shows a schematic diagram of the sensor of this invention operating under the force detection mode when subjected to Fz. The sensitive driving stage 5 is fixed using an electrostatic attraction module. At this time, the sensitive driving stage acts as the anchor point of the capacitive triaxial force sensor. All applied external force is applied to the central mass block 22. The normal force is detected by the parallel plate capacitor formed by the central mass block 22 and the fixed metal 25 on the glass substrate 23. When subjected to the normal force, the capacitor spacing decreases, and the capacitance increases. A protrusion located below the U-shaped beam acts as a limiting block 28, which contacts the glass substrate first to prevent short circuits caused by contact between the upper and lower electrodes. Furthermore, when the central mass block moves downwards, the cross-sectional area of ​​the comb electrodes does not change because the height of the movable comb electrodes (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8) is smaller than the height of the fixed comb electrodes (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8), and therefore no tangential output is generated.

[0054] Figure 6(d) shows a schematic diagram of the normal calibration operation of the sensor in calibration mode. The voltage of the electrostatic attraction module is released, and the system switches to calibration mode. A specific voltage is applied to the distributed upper electrodes Pt on each L-shaped piezoelectric beam. A negative voltage is applied to the four upper electrodes connected to the sensitive driving stage, and a positive voltage is applied to the other four upper electrodes. This drives the sensitive driving stage to move in the Z direction, causing the central mass block 22 to simulate the motion state under the influence of Fz. At this time, the distance between the gate silicon electrodes (11.1, 11.2, 11.3, 11.4) and the interdigitated aluminum electrodes 24 fixed on the glass substrate decreases, increasing the driving detection capacitance. The distance between the central mass block and the fixed metal electrode 25 fixed in the center of the glass substrate decreases, increasing the normal force detection capacitance. Normal calibration is achieved by comparing the increase factors of these two capacitances.

[0055] The decoupling principle of the capacitive triaxial force sensor is as follows:

[0056] When the sensor is subjected to an Fx, the spacing between Cx1 increases, and the capacitance decreases; the spacing between Cx2 decreases, and the capacitance increases. Since the cross-sectional area of ​​the capacitor on the left decreases and the cross-sectional area of ​​the capacitor on the right increases, the overall capacitance values ​​Cy1 and Cy2 remain unchanged. The same principle applies when the sensor is subjected to a -Fx.

[0057] When the sensor is subjected to Fy, the spacing of Cy1 decreases and the capacitance increases; the spacing of Cy2 increases and the capacitance decreases. Since the cross-sectional area of ​​the upper capacitor increases and the cross-sectional area of ​​the lower capacitor decreases, the overall capacitance values ​​Cx1 and Cx2 remain unchanged. The same principle applies when the sensor is subjected to -Fy.

[0058] When the sensor is subjected to Fz, since the height of the fixed comb teeth is higher than that of the movable comb teeth, the capacitance values ​​of Cx1, Cx2, Cy1, and Cy2 remain unchanged; however, since the distance between the central mass block and the fixed metal electrode becomes smaller, the capacitance value of Cz will increase.

[0059] In summary, the coupling problem between multidimensional force detections can be eliminated by using comb-tooth electrodes with a specific distribution.

Claims

1. A triaxial MEMS force sensor with self-calibration function, characterized in that, Includes a glass substrate and fixed electrodes on its upper surface, and a device layer suspended above the glass substrate; The fixed electrode on the upper surface of the glass substrate includes a fixed interdigitated aluminum electrode, a fixed metal electrode, an electrode connecting wire, and a self-detection lead-out electrode; The device layer suspended above the glass substrate includes device anchor points, four L-shaped piezoelectric drive beams, an electrostatic attraction module, a sensitive drive stage, and a capacitive triaxial force sensor. The fixed interdigitated aluminum electrode is placed corresponding to the gate-type silicon electrode on the sensitive driving stage. The tangential driving capacitor is differentially detected by the variable area method. The capacitance signal is led out along the electrode connection line through the self-detection lead-out electrode. The fixed metal electrode is placed corresponding to the central mass block of the capacitive triaxial force sensor. The capacitance is detected by detecting the normal force through a variable-spacing method. The capacitance signal is led out along the electrode connection line through the self-detection lead-out electrode. The electrostatic attraction module is located between the piezoelectric drive beam and the sensitive drive platform. There are two sets in total. Each set includes an electrostatic attraction anchor point, an electrostatic attraction fixed comb tooth, an electrostatic attraction movable comb tooth, a fixed attraction island, and a movable attraction block. The electrostatic attraction fixed comb tooth is fixed on the electrostatic attraction anchor point. The electrostatic attraction movable comb tooth is connected to the sensitive drive platform and is located at the diagonal position of the sensitive drive platform. It moves with the sensitive drive platform and corresponds one-to-one with the electrostatic attraction fixed comb tooth. The movable attraction block is connected to the sensitive drive platform and is placed correspondingly to the attraction fixed island. The sensitive drive stage includes a lateral sensitive unit and a longitudinal sensitive unit; The capacitive triaxial force sensor includes a limiting block, a U-shaped beam, an inclined beam, a central mass block, and a tangential force detection module. The central mass block is connected to the sensitive drive stage through the U-shaped beam and the inclined beam. The capacitive triaxial force sensor tangential force detection module includes a tangential force detection anchor point, a movable tangential force detection comb tooth, and a fixed tangential force detection comb tooth; the fixed tangential force detection comb tooth is fixed on the fixed tangential force detection anchor point, and there are a total of eight sets of tangential force detection modules, symmetrically distributed around the central mass block, with two sets on each side.

2. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The L-shaped piezoelectric drive beam includes an L-shaped silicon beam, a lower drive electrode Pt covering the L-shaped silicon beam, a piezoelectric material PZT covering the lower drive electrode, and a distributed upper drive electrode Pt covering the piezoelectric material PZT.

3. A triaxial MEMS force sensor with self-calibration function according to claim 2, characterized in that, One end of each L-shaped piezoelectric drive beam is fixed to the device anchor point, and the other end is connected to the sensitive drive stage.

4. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The aforementioned electrode connection wires and self-test lead-out electrodes comprise a total of nineteen pairs; Each fixed interdigitated aluminum electrode is connected to two electrode connection lines and two self-detection lead-out electrodes, thereby leading out the tangential drive capacitor signal; A fixed metal electrode is connected to an electrode connection wire and a self-detection lead-out electrode to extract the signal of the normal force detection capacitor. Eight tangential force detection anchor points are connected to eight electrode connection lines and eight self-detection lead-out electrodes to lead out the signal from the tangential force detection module; Two electrostatic attraction anchor points connect two electrode connection lines and two self-detection lead-out electrodes to achieve electrostatic attraction and switch to force sensor detection mode.

5. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The distance between the movable suction block and the fixed suction island is less than the distance between the electrostatic suction fixed comb teeth and the electrostatic suction movable comb teeth.

6. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, There are four fixed interdigitated aluminum electrodes in total. The two horizontal fixed interdigitated aluminum electrodes serve as the lower electrodes of the horizontal driving detection capacitor, and the two vertical fixed interdigitated aluminum electrodes serve as the lower electrodes of the vertical driving detection capacitor.

7. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The limiting block is obtained by thinning the central mass block and is located below the U-shaped beam. It is used for overload protection during normal force detection to prevent the normal force detection electrode from contacting.

8. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The lateral sensing unit consists of two lateral gate-type silicon electrodes, which serve as the upper electrode of the X-axis drive detection capacitor; The longitudinal sensing unit consists of two vertical gate-type silicon electrodes, which serve as the upper electrode of the Y-axis driving detection capacitor.

9. A triaxial MEMS force sensor with self-calibration function according to claim 1, characterized in that, The eight regions surrounding the central mass block are connected to the same number of movable comb teeth for tangential force detection, and correspond one-to-one with the fixed comb teeth for tangential force detection. The spacing between them is greater than the spacing between the movable comb teeth for electrostatic attraction and the fixed comb teeth for electrostatic attraction.

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