CN116358764A - Triaxial MEMS force sensor with self-calibration function - Google Patents

Abstract

The invention discloses a triaxial 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 wire and a self-detection leading-out electrode. The device layer suspended above the glass substrate comprises a device anchor point, four L-shaped piezoelectric driving beams, an electrostatic attraction module, a sensitive driving table and a capacitive triaxial force sensor. The fixed metal electrode is correspondingly arranged with the central mass block of the capacitance type triaxial force sensor, and the electrostatic attraction module is arranged between the piezoelectric driving beam and the sensitive driving platform. The invention suppresses the problem of cross-axis crosstalk, realizes cross-axis and normal triaxial driving, realizes real-time detection of a cross-axis driving capacitor, and realizes switching of a force detection mode and a calibration mode by adjusting an electrostatic attraction module.

Description

Triaxial MEMS force sensor with self-calibration function

Technical Field

The invention belongs to the field of triaxial force sensors and MEMS self-calibration devices, and particularly relates to a triaxial MEMS force sensor with a self-calibration function.

Background

The three-axis force sensor can be used for detecting touch sense, is an important medium for the intelligent robot to sense human life, and plays a key role in the fields of medical care, robot industry, wearable devices and the like. The force sensor can be classified into a capacitive type, a piezoelectric type, a piezoresistive type, an electromagnetic type and an optical type according to the principle, wherein the capacitive sensor is widely used due to the advantages of high sensitivity, high resolution, good temperature stability and the like.

In general, a capacitive sensor employing differential detection has higher sensitivity than a sensor employing non-differential detection, and differential detection capacitance can be classified into a tilting type capacitance, a gate type capacitance, and a comb type capacitance. The inclined capacitor changes through changing the distance, the upper electrode is inclined when being subjected to external force, one corresponding capacitor is reduced, the other capacitor is increased, but the inclined capacitor is usually calculated through a relatively complex integration algorithm at present; the grid type capacitor causes the change of the capacitor through the change of the area, and the output linearity is higher; the comb-tooth type capacitor changes the capacitance through changing the area and the distance, and the comb-tooth electrodes with specific distribution can reduce cross-axis interference. The grid type capacitor and the comb type capacitor are simple in principle, have good performance and are widely applied.

At present, the sensor performance is error due to environmental change, process design and other factors, and in order to ensure the accuracy of the measurement result, it is very important to calibrate the sensor regularly. Current calibration techniques require the sensor to be sent to a calibration drive station in the factory to simulate the sensor's operating conditions. However, in practical applications, it is not practical to solder the sensor to the PCB and detach it for calibration. In addition, most of the current researches are to provide calibration functions for the inertial sensor, and few calibration methods for the force sensor are available. Therefore, to save additional calibration costs, it is extremely important to integrate a real-time self-calibration structure for the sensor at the beginning of the design.

In the calibration process, the driving table for simulating external excitation is an indispensable structure, and the driving table can be classified into electrostatic driving, electromagnetic driving, piezoelectric driving and the like according to principles. The electrostatic driving is mainly based on the electrostatic force principle between capacitors, the principle is simple and easy to understand, but the problems of attraction effect, electrostatic plate touch effect and the like exist; the electromagnetic drive is based on the principle that the electrified wire is acted by ampere force in a uniform magnetic field, and can generate larger driving moment and offset, but the electromagnetic drive has the disadvantages of high energy consumption and easy heating; the piezoelectric driving is based on the principle of crystal piezoelectric effect, and when pressure is applied, the piezoelectric material generates deformation and offset, and the mode has the advantages of adjustable range, large-range output, low driving voltage and the like.

Disclosure of Invention

In order to overcome the defects in the background technology, the invention provides a triaxial MEMS (micro electro mechanical system) force sensor with a self-calibration function.

The invention solves the technical problems by adopting the scheme that:

a triaxial MEMS force sensor with self-calibration function 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 wire and a self-detection extraction electrode.

The device layer suspended above the glass substrate comprises a device anchor point, four L-shaped piezoelectric driving beams, an electrostatic attraction module, a sensitive driving platform and a capacitive triaxial force sensor.

The number of the fixed interdigital aluminum electrodes is 4, the 2 transverse fixed interdigital aluminum electrodes are used as lower electrodes of the transverse driving detection capacitor, and the 2 longitudinal fixed interdigital aluminum electrodes are used as lower electrodes of the longitudinal driving detection capacitor. Each fixed interdigital aluminum electrode is correspondingly arranged with one grid-type silicon electrode on the sensitive driving platform, tangential driving capacitance is detected in a differential mode through a variable area method, and capacitance signals are led out along an electrode connecting line through a self-detection leading-out electrode.

The fixed metal electrode is correspondingly arranged with the central mass block of the capacitive triaxial force sensor, the capacitance is detected through the variable-interval detection normal force, and capacitance signals are led out along the electrode connecting line through the self-detection leading-out electrode.

The electrode connecting wires and the self-detection leading-out electrodes are 19 pairs in total, wherein each fixed interdigital aluminum electrode is connected with 2 electrode connecting wires and 2 self-detection leading-out electrodes, so that tangential driving capacitance signals are led out; the 1 fixed metal electrode is connected with 1 electrode connecting wire and 1 self-detection extraction electrode, so that signals of the normal force detection capacitor are extracted; the 8 tangential force detection anchor points are connected with 8 electrode connecting lines and 8 self-detection extraction electrodes, so that signals of the tangential force detection module are extracted; the 2 electrostatic attraction anchor points are connected with 2 electrode connecting lines and 2 self-detection leading-out electrodes, so that electrostatic attraction is realized, and the detection mode is switched to a force sensor detection mode.

The single L-shaped piezoelectric driving beam comprises an L-shaped silicon beam, a driving lower electrode Pt covered on the L-shaped silicon beam, piezoelectric materials PZT covered on the driving lower electrode and distributed driving upper electrodes Pt covered on the piezoelectric materials PZT from bottom to top, one end of each L-shaped piezoelectric driving beam is fixed on a device anchor point, and the other end of each L-shaped piezoelectric driving beam is connected with a sensitive driving platform.

The electrostatic attraction module is positioned between the piezoelectric driving beam and the sensitive driving platform, and comprises two groups, wherein each group comprises an electrostatic attraction anchor point, electrostatic attraction fixed comb teeth, electrostatic attraction movable comb teeth, a fixed attraction island and a movable attraction module. The static attraction fixed comb teeth are fixed on static attraction anchor points, the static attraction movable comb teeth are connected with the sensitive driving table, are positioned at the diagonal positions of the sensitive driving table, move along with the sensitive driving table and correspond to the static attraction fixed comb teeth one by one. The movable attraction block is connected with the sensitive driving table and is placed corresponding to the attraction fixed island, and the distance between the movable attraction block and the fixed attraction island is smaller than the distance between the static attraction fixed comb teeth and the static attraction movable comb teeth.

The sensitive driving platform comprises a transverse sensitive unit and a longitudinal sensitive unit. The transverse sensitive unit consists of two transverse grid-type silicon electrodes which are used as upper electrodes of the X-axis driving detection capacitor; the longitudinal sensitive unit consists of two longitudinal grid-type silicon electrodes which are used as an upper electrode of the Y-axis driving detection capacitor.

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

The central mass block of the capacitive triaxial force sensor is connected with the sensitive driving platform through a U-shaped beam and an inclined beam.

The limiting block is obtained by thinning the central mass block and is used for overload protection during normal force detection and preventing normal force detection electrodes from contacting.

The tangential force detection module of the capacitive triaxial force sensor comprises a tangential force detection anchor point, a movable comb tooth for tangential force detection and a fixed comb tooth for tangential force detection. The fixed broach of tangential force detection is fixed on the fixed anchor point of tangential force detection, and 8 sets of tangential force detection module altogether, the symmetric distribution is around central mass piece, every limit 2 sets. The 8 areas around the central mass block are connected with the same number of movable comb teeth for detecting tangential force and correspond to the fixed detection comb teeth for detecting tangential force one by one, and the interval between the movable comb teeth for electrostatic attraction and the fixed comb teeth for electrostatic attraction is larger than the interval between the movable comb teeth for electrostatic attraction and the fixed comb teeth for electrostatic attraction.

The beneficial effects of the invention are as follows: the comb tooth capacitor is adopted to detect multidimensional force, and the problem of cross-axis crosstalk can be well restrained through specific arrangement. In addition, at the beginning of the structural design of the capacitive triaxial force sensor, a piezoelectric sensitive driving platform structure is integrated for the capacitive triaxial force sensor, and the piezoelectric driving is different from electrostatic driving, so that the cross axis and normal triaxial driving can be realized, and larger displacement can be generated under the low-frequency condition, thereby simulating the motion state of external excitation. Meanwhile, a grid type silicon electrode is designed on the sensitive driving platform, so that real-time detection of the cross-axis driving capacitor can be realized. When the sensor is in actual work, the force detection mode and the calibration mode are switched by adjusting the electrostatic attraction module, and the sensor is not required to be taken down to be brought back to factory calibration, so that the calibration cost is saved.

Drawings

FIG. 1 is a schematic diagram showing the overall structure combination of a sensor chip according to the present invention;

FIG. 2 (a) is an enlarged detail view of a sensor device layer self-calibration module of the present invention;

FIG. 2 (b) is an enlarged detail view of the L-shaped piezoelectric actuator beam of the sensor device layer of the present invention;

FIG. 2 (c) is an enlarged detail view of the sensor device layer force detection module of the present invention;

FIG. 3 is a schematic diagram showing the distribution of electrodes on a glass substrate of a sensor according to the present invention;

FIG. 4 (a) is a schematic diagram of a structure of a variable area detection capacitor of a sensitive drive stage;

FIG. 4 (b) is a schematic diagram of the capacitance pair formed by the fixed comb teeth and the movable comb teeth;

FIG. 5 is a process flow diagram of the sensor preparation of the present invention;

FIG. 6 (a) is a schematic diagram showing the operation of the sensor of the present invention under the action of shear force +Fx;

FIG. 6 (b) is a schematic diagram illustrating the operation of the sensor of the present invention under normal force Fz;

FIG. 6 (c) is a schematic diagram illustrating the operation of the sensor of the present invention to achieve tangential calibration;

fig. 6 (d) is a schematic diagram of the operation of the sensor of the present invention to achieve normal calibration.

Detailed Description

The invention is further illustrated by the following examples and the accompanying drawings:

the whole structure of the triaxial MEMS force sensor with the self-calibration function is formed by sequentially arranging a glass substrate layer 1, a fixed electrode on the upper surface of the glass substrate layer and a device layer 2 suspended above the glass substrate from bottom to top, and forming the whole structure through silicon-glass bonding, as shown in figure 1.

The device layer 2 comprises a device anchor point 3, four L-shaped piezoelectric driving beams (4.1, 4.2, 4.3 and 4.4), a sensitive driving table 5, electrostatic attraction anchor points (6.1 and 6.2), electrostatic attraction fixed comb teeth (7.1 and 7.2), electrostatic attraction movable comb teeth (8.1 and 8.2), fixed attraction island (9.1 and 9.2), movable attraction blocks (10.1 and 10.2), grid-type silicon electrodes (11.1 and 11.2, 11.3 and 11.4) and a capacitive triaxial force detection sensor 12, as shown in fig. 2 (a). One end of each L-shaped piezoelectric driving beam is connected with a device anchor point 3, one end of each L-shaped piezoelectric driving beam is connected with a sensitive driving table 5, the L-shaped piezoelectric driving beams are positioned on the central line of the sensitive driving table, and four L-shaped piezoelectric driving beams encircle the whole sensitive driving table. The static attraction fixed comb teeth (7.1, 7.2) are fixed on static attraction anchor points (6.1, 6.2). The static attraction movable comb teeth (8.1, 8.2) are connected with the sensitive driving table 5, are positioned at the diagonal line position of the sensitive driving table, move along with the sensitive driving table and correspond to the static attraction fixed comb teeth one by one. The movable attraction block is connected with the sensitive driving table and is placed corresponding to the attraction fixed island, and the distance between the movable attraction block and the fixed attraction island is smaller than the distance between the static attraction fixed comb teeth and the static attraction movable comb teeth. The movable actuation block and the actuation fixed island are used for overload protection, the comb electrode is prevented from contacting, the movable actuation block (10.1, 10.2) is connected with the sensitive driving platform, and the movable actuation block and the actuation fixed island (9.1, 9.2) are correspondingly placed. The central mass block of the capacitive triaxial force sensor 12 is connected with the sensitive driving platform through a U-shaped beam and an inclined beam and is positioned at the central position of the device layer. The sensitive drive table 5 comprises a transverse sensitive unit and a longitudinal sensitive unit. The transverse sensitive unit consists of two transverse grid-type silicon electrodes (11.1 and 11.3) which are used as upper electrodes of the X-axis drive detection capacitor; the longitudinal sensitive unit consists of two longitudinal grid-type silicon electrodes (11.2 and 11.4) which are used as upper electrodes of the Y-axis driving detection capacitor.

The L-shaped silicon beam 13, the driving lower electrode Pt14, the piezoelectric material PZT15, and the distributed driving upper electrode Pt16 are stacked to form an L-shaped piezoelectric driving beam, as shown in fig. 2 (b). As shown in fig. 2 (c) and 6 (c), the capacitive triaxial force detection sensor 12 includes a stopper 28, oblique beams (17.1, 17.2, 17.3, 17.4), U-beams (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), tangential force detection movable combs (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7, 20.8), tangential force detection fixed combs (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7, 21.8), and a center mass 22. The fixed comb teeth (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7 and 21.8) for tangential force detection are fixed on fixed anchor points for tangential force detection, distributed around the central mass block, and the movable comb teeth (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7 and 20.8) for tangential force detection move along with the central mass block 22 and are in one-to-one correspondence with the fixed comb teeth for tangential force detection. U-beams (18.1, 18.2, 18.3, 18.4), diagonal beams (17.1, 17.2, 17.3, 17.4) connect the central mass 22 with the sensitive drive table 5.

The glass substrate layer of the present invention comprises a glass substrate 23 and fixed interdigital aluminum electrodes (24.1, 24.2, 24.3, 24.4) on the upper surface thereof, fixed metal electrodes 25, electrode connecting lines (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, 26.15, 26.16, 26.17, 26.18, 26.19), self-detection extraction 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), as shown in fig. 3. Each grid type silicon electrode of the device layer suspended on the glass substrate and each fixed interdigital aluminum electrode are correspondingly placed to form a variable-area tangential driving capacitance detection unit, and four groups of driving capacitance detection units are formed in a conformal mode. The electrode connecting wires (26.2, 26.3, 26.6, 26.7, 26.12, 26.13, 26.16, 26.17) are correspondingly connected with the self-detection extraction electrodes (27.2, 27.3, 27.6, 27.7, 27.12, 27.13, 27.16, 27.17) for extracting tangential driving capacitance signals. The fixed metal electrode 25 forms a normal force detection lower electrode, and the detection signal is led out through an electrode connecting line 26.10 and a self-detection lead-out electrode 27.10. Electrode connecting wires (26.8, 26.18) and self-detection extraction electrodes (27.8, 27.18) form a switch for switching between a force detection mode and a calibration mode, and are used for providing voltage for the electrostatic attraction module.

Fig. 4 (a) is a schematic diagram of driving capacitance area-variable detection, the gray electrode is one silicon electrode in the gate electrode, the black electrode is a group of electrode pairs in the fixed interdigital aluminum electrode, one silicon electrode and a group of aluminum electrode pairs form two capacitors, the initial cross-sectional areas of the two capacitors are the same, i.e. l1=l2, and the differential capacitance is 0. When the sensor is driven tangentially by switching to the calibration mode, one cross-sectional area of the two capacitors is increased, one cross-sectional area is decreased, one capacitor value is increased, the other capacitor value is decreased, and the differential capacitance value is changed. The length of the upper silicon electrode is longer than that of the lower interdigital aluminum electrode, and by taking X-axis driving as an example, the transverse sensitive unit generates differential capacitance output through variable area, the longitudinal sensitive unit has no capacitance value output due to unchanged cross section area, and Y-axis driving is the same, so that the cross-axis decoupling function is realized. Fig. 4 (b) is a schematic diagram of comb capacitance detection, in which the gray part is a movable comb and the black part is a fixed comb. The tangential detection unit of the capacitive triaxial force sensor adopts offset comb teeth, the movable comb teeth and the fixed comb teeth are arranged in a crossed mode, the distance between one movable comb tooth and the two fixed comb teeth is d1 and d2 respectively, d1 is far smaller than d2, and therefore the capacitance value of the d2 side is negligible compared with that of the d1 side. When the movable comb teeth longitudinally move, the capacitance on the d1 side is increased or decreased, so that differential capacitance detection is realized.

The processing process flow of the capacitive triaxial force sensor with the self-calibration function is shown from top to bottom in fig. 5, and the specific process flow is as follows:

(a) And a driving lower electrode Pt layer, a piezoelectric material PZT thin film layer and a driving upper electrode Pt layer are sequentially deposited on the SOI silicon wafer.

(b) And (3) adopting photoetching and dry etching processes to thin bulk silicon outside the anchor points on the back surface of the silicon wafer and the fixed comb electrode regions for the first time by 10-30 mu m, exposing the height of the limiting block, removing photoresist and cleaning the silicon wafer.

(c) And (3) adopting photoetching and dry etching processes to thin bulk silicon outside the anchor points on the back surface of the silicon wafer, the fixed comb electrodes and the limited block areas to 200-350 mu m for the second time, exposing the height of the central mass block, removing photoresist and cleaning the silicon wafer.

(d) And (3) adopting photoetching and dry etching processes to thin bulk silicon outside the anchor points on the back of the silicon wafer, the fixed comb electrodes, the limiting block and the central mass block area to 100-150 mu m for the third time, exposing the height of the upper silicon electrode, removing photoresist and cleaning the silicon wafer.

(e) And etching and patterning the upper metal electrode by adopting an ion beam to form the distributed driving upper electrode of the L-shaped piezoelectric driving beam.

(f) And etching and patterning the Pt layer of the driving lower electrode to expose the top silicon device layer.

(g) And etching the top silicon on the front surface to form a driving platform structure, a grid structure and a movable comb structure, and etching the driving platform structure, the grid structure and the movable comb structure thoroughly.

(h) Preparing a glass sheet, standard cleaning, forming a groove on a glass substrate through a photoetching process, and manufacturing a layer of metal film serving as a lower electrode of the capacitor on the glass substrate through a sputtering process.

(i) And preparing a fixed metal electrode layer of the glass substrate by adopting a photoetching process, removing photoresist and cleaning.

(j) And (3) performing alignment bonding on the back surface of the silicon wafer and the front surface of the glass, etching to release the comb tooth structure, cleaning the bonding piece, and scribing and packaging.

A schematic diagram of the operation of the sensor of the present invention when subjected to + Fx in the force sensing mode is shown in fig. 6 (a). A larger voltage is added between static attraction fixed comb teeth (7.1 and 7.2) and static attraction movable comb teeth (8.1 and 8.2), fixed attraction islands (9.1 and 9.2) are attracted with movable attraction blocks (10.1 and 10.2) to fix a sensitive driving table 5, the sensitive driving table is equivalent to an anchor point of a capacitance type triaxial force sensor, the applied external force is all added to a central mass block 22, two U-shaped beams (18.1 and 18.4) on the left side are stretched, two U-shaped beams (18.2 and 18.3) on the right side are compressed, the central mass block is deviated in the force application direction, the total capacitance of Cx1 is reduced, the total capacitance of Cx2 is increased, and the differential capacitance of X axis is not 0; the total capacitance of the capacitors Cy1 and Cy2 is unchanged, so that the differential capacitance in the Y axis direction is 0; because the normal force detection capacitance distance is almost unchanged, no Z-direction output exists, and the sensor is used as a triaxial force decoupling sensor.

A schematic diagram of the operation of the sensor of the present invention to achieve +x calibration in calibration mode is shown in fig. 6 (b). The voltage between static attraction fixed comb teeth (7.1, 7.2) and static attraction movable comb teeth (8.1, 8.2) is released, the static attraction fixed comb teeth are switched to a calibration mode, a sensitive driving table 5 is integrated with a central mass block 22 through U-shaped beams (18.1, 18.2, 18.3 and 18.4) and inclined beams (17.1, 17.2, 17.3 and 17.4), voltage shown in the drawing is applied to a distributed upper electrode Pt on the L-shaped piezoelectric beam, wherein positive voltage is applied to a dark part upper electrode, negative voltage is applied to a light part upper electrode, so that a sensitive driving table can be driven, the central mass block is driven to simulate a motion state when being subjected to +Fx, an X-direction driving capacitor is detected through transverse grid capacitors (11.2 and 11.4) on the sensitive driving table, and Y-direction driving capacitor output is avoided because the cross sectional area of the longitudinal grid capacitors (11.1 and 11.3) is unchanged. At the moment, the comb tooth capacitance of the tangential force detection unit also generates differential capacitance output, and the variable area differential capacitance output of the sensitive driving platform is compared with the force sensor comb tooth differential capacitance output, so that the tangential detection characteristic of the sensor is calibrated in real time.

A schematic of the operation of the sensor of the present invention when subjected to Fz in the force sensing mode is shown in fig. 6 (c). The electrostatic attraction module is used for fixing the sensitive driving platform 5, the sensitive driving platform is equivalent to an anchor point of the capacitive triaxial force sensor, the applied external force is totally applied to the central mass block 22, the normal force is detected by parallel plate capacitance formed by the central mass block 22 and the fixed metal 25 on the glass substrate 23, and when the normal force acts, the capacitance interval is reduced and the capacitance is increased. A bump positioned below the U-shaped beam is used as a limiting block 28 and is firstly contacted with the glass substrate, so that the short circuit caused by the contact of the upper electrode and the lower electrode is prevented. And when the center mass moves downwards, the heights of the movable comb teeth electrodes (20.1, 20.2, 20.3, 20.4, 20.5, 20.6, 20.7 and 20.8) on the periphery are smaller than those of the fixed comb teeth electrodes (21.1, 21.2, 21.3, 21.4, 21.5, 21.6, 21.7 and 21.8), so that the cross sectional areas of the comb teeth electrodes are not changed, and tangential output is not generated.

A schematic diagram of the operation of the sensor of the present invention to achieve normal calibration in calibration mode is shown in fig. 6 (d). And releasing the voltage of the electrostatic attraction module and switching to a calibration mode. A specific voltage is applied to the distributed upper electrode Pt on each L-shaped piezoelectric beam, wherein negative voltage is applied to four upper electrodes at one end connected with a sensitive driving platform, positive voltage is applied to the other four upper electrodes, so that the sensitive driving platform can be driven to move in the Z direction to drive the central mass block 22 to simulate the motion state when Fz is received, at the moment, the distance between the grid-type silicon electrodes (11.1, 11.2, 11.3 and 11.4) and the interdigital aluminum electrode 24 fixed on the glass substrate is reduced, the driving detection capacitance is increased, the distance between the central mass block and the fixed metal electrode 25 fixed in the center of the glass substrate is reduced, the normal force detection capacitance is increased, and normal calibration is realized by comparing the increase multiples of the two capacitances.

The decoupling principle of the capacitive triaxial force detection sensor is as follows:

when the sensor is subjected to Fx, the Cx1 distance is increased, and the capacitance value is reduced; the Cx2 pitch becomes smaller and the capacitance becomes larger; since the left side capacitance cross-sectional area is reduced and the right side capacitance cross-sectional area is increased, the overall capacitance values Cy1, cy2 are unchanged. The same applies when the sensor is subjected to-Fx action.

When the sensor is subjected to Fy, the Cy1 interval is reduced, and the capacitance value is increased; the Cy2 interval is increased, and the capacitance value is reduced; since the upper side capacitance cross-sectional area increases and the lower side capacitance cross-sectional area decreases, the overall capacitance values Cx1, cx2 are unchanged. The same applies when the sensor is subjected to-Fy.

When the sensor is subjected to Fz, the fixed comb tooth heights are higher than the movable comb tooth heights, so that the capacitance values of Cx1, cx2, cy1 and Cy2 are unchanged; as the center mass becomes less spaced from the fixed metal electrode, the Cz capacitance value will increase.

In summary, the coupling problem between the multi-dimensional force detection can be eliminated by the specially distributed comb electrodes.

Claims (10)

1. The triaxial MEMS force sensor with the self-calibration function is characterized by comprising 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 wire and a self-detection extraction electrode;

the device layer suspended above the glass substrate comprises a device anchor point, four L-shaped piezoelectric driving beams, an electrostatic attraction module, a sensitive driving table and a capacitive triaxial force sensor;

the fixed interdigital aluminum electrode is correspondingly arranged with the grid-type silicon electrode on the sensitive driving table, the tangential driving capacitor is detected in a differential mode through a variable area method, and a capacitance signal is led out along an electrode connecting line through a self-detection leading-out electrode;

the fixed metal electrode is correspondingly arranged with a central mass block of the capacitive triaxial force sensor, the capacitance is detected through a variable-interval detection normal force, and a capacitance signal is led out along an electrode connecting line through a self-detection leading-out electrode;

the electrostatic attraction module is positioned between the piezoelectric driving beam and the sensitive driving platform, and comprises two groups, wherein each group comprises an electrostatic attraction anchor point, electrostatic attraction fixed comb teeth, electrostatic attraction movable comb teeth, a fixed attraction island and a movable attraction module; the static attraction fixed comb teeth are fixed on static attraction anchor points, the static attraction movable comb teeth are connected with the sensitive driving table, are positioned at the diagonal positions of the sensitive driving table, move along with the sensitive driving table and correspond to the static attraction fixed comb teeth one by one; the movable attraction block is connected with the sensitive driving platform and is placed corresponding to the attraction fixed island;

the sensitive driving platform comprises a transverse sensitive unit and a longitudinal sensitive unit;

the capacitive triaxial force sensor comprises a limiting block, a U-shaped beam, an inclined beam, a central mass block and a tangential force detection module, wherein the central mass block is connected with the sensitive driving platform through the U-shaped beam and the inclined beam;

the tangential force detection module of the capacitive triaxial force sensor comprises a tangential force detection anchor point, a tangential force detection movable comb tooth and a tangential force detection fixed comb tooth; the fixed broach of tangential force detection is fixed on the fixed anchor point of tangential force detection, and eight sets of tangential force detection module altogether, the symmetric distribution is around central mass piece, two sets of every limit.

2. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein the L-shaped piezoelectric driving beam comprises an L-shaped silicon beam, a driving lower electrode Pt covered on the L-shaped silicon beam, a piezoelectric material PZT covered on the driving lower electrode, and a distributed driving upper electrode Pt covered on the piezoelectric material PZT.

3. The triaxial MEMS force sensor with self-calibration function according to claim 2, wherein one end of each L-shaped piezoelectric driving beam is fixed on a device anchor point, and the other end is connected with a sensitive driving stage.

4. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein the electrode connection wires and the self-detection extraction electrodes are nineteen pairs in total;

each fixed interdigital aluminum electrode is connected with two electrode connecting wires and two self-detection extraction electrodes, so that tangential driving capacitance signals are extracted;

a fixed metal electrode is connected with an electrode connecting wire and a self-detection extraction electrode, so that signals of the normal force detection capacitor are extracted;

eight tangential force detection anchor points are connected with eight electrode connecting lines and eight self-detection extraction electrodes, so that signals of the tangential force detection module are extracted;

the two electrostatic attraction anchor points are connected with the two electrode connecting wires and the two self-detection leading-out electrodes, so that electrostatic attraction is realized, and the detection mode of the force sensor is switched.

5. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein a distance between the movable actuation block and the fixed actuation island is smaller than a distance between the electrostatic actuation fixed comb teeth and the electrostatic actuation movable comb teeth.

6. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein four fixed interdigital aluminum electrodes are used, two fixed interdigital aluminum electrodes in the transverse direction are used as the lower electrode of the transverse driving detection capacitor, and two fixed interdigital aluminum electrodes in the longitudinal direction are used as the lower electrode of the longitudinal driving detection capacitor.

7. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein the limiting block is thinned by a central mass block, and is located below the U-shaped beam for overload protection during normal force detection, so as to prevent contact of a normal force detection electrode.

8. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein a distance between the movable actuation block and the fixed actuation island is smaller than a distance between the electrostatic actuation fixed comb teeth and the electrostatic actuation movable comb teeth.

9. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein the lateral sensitive unit is composed of two lateral grid-type silicon electrodes, which are used as the upper electrode of the X-axis driving detection capacitor;

the longitudinal sensitive unit consists of two longitudinal grid-type silicon electrodes which are used as an upper electrode of the Y-axis driving detection capacitor.

10. The triaxial MEMS force sensor with self-calibration function according to claim 1, wherein eight areas around the central mass block are connected with the same number of movable comb teeth for detecting tangential force and are in one-to-one correspondence with the fixed detection comb teeth for detecting tangential force, and a gap between the movable comb teeth for electrostatic attraction is larger than a gap between the fixed comb teeth for electrostatic attraction.

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