Topological MEMS capacitance triaxial accelerometer and preparation method thereof

Abstract

The invention relates to a topological MEMS capacitance triaxial accelerometer and a preparation method thereof, the topological MEMS capacitance triaxial accelerometer comprises a substrate B, an out-of-plane measurement structure, an in-plane measurement structure and a metal electrode plate, and the metal electrode plate is embedded in the upper surface of the substrate B; the out-of-plane mass block PM is arranged to be of a seesaw swing mode structure with the cantilever beam L as the fulcrum, and the out-of-plane mass block PM surrounds the periphery of the in-plane mass block M in a square shape. The in-plane measurement structure comprises an in-plane mass block M and a measurement unit; the in-plane mass block M comprises at least two hollow-out areas K arranged in a topology expansion array mode, each hollow-out area K is internally provided with a measuring unit, and each measuring unit comprises a pair of cantilever beams S, an anchor point A and two variable comb tooth capacitors; the variable comb capacitor is of a fixed tooth offset differential structure. According to the invention, not only can the sensitivity of the device be improved by increasing the topology of the array arrangement number, but also the simplicity and the fault tolerance of batch processing are improved through the geometric configuration, and the flexible adaptability design can be carried out for the requirements of different sizes through the array design.

Description

Technical Field

[0001] This invention relates to the field of microelectromechanical accelerometer technology, specifically to a topological MEMS capacitive triaxial accelerometer and its fabrication method. Background Technology

[0002] Micro-Electro-Mechanical Systems (MEMS) accelerometers are mechanical sensors fabricated using MEMS technology. They measure inertial parameters such as inertial force, vibration, and tilt angle through electrical signals. MEMS accelerometers offer advantages such as small size, low cost, low power consumption, high reliability, and ease of manufacturing, leading to their widespread application in fields like vehicle manufacturing, long-range guidance, industrial control, and instrument testing. MEMS accelerometers are categorized based on the type of sensitive signal used: piezoresistive, piezoelectric, capacitive, tunneling current, and resonant. Capacitive accelerometers, in particular, are widely used due to their high accuracy, low temperature sensitivity, low power consumption, wide dynamic range, and micromechanical structure. The main fabrication process for MEMS accelerometers is micromachining, including bulk micromachining, surface micromachining, and laser micromachining. Bulk micromachining further includes dry etching and wet etching. In addition, there are wafer bonding, LIGA process, SOI process, SOG process, microelectrode discharge process, and 3D lithography process.

[0003] From a mechanical perspective, a capacitive accelerometer can be viewed as a mass-spring-damped system, where acceleration acts as an inertial force through the mass. MEMS capacitive accelerometers offer advantages such as high sensitivity, good temperature stability, relatively simple structure, low power consumption, and good DC characteristics. Therefore, how to reduce the impact of the environment on accelerometer performance through reasonable accelerometer structural design, improve sensitivity, and effectively apply it to mass production is a problem that needs to be solved for high-performance MEMS accelerometers. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a topological MEMS capacitive triaxial accelerometer and its fabrication method. The triaxial accelerometer of this invention decomposes the measurement requirements of the three axes into in-plane and out-of-plane measurement structures. The in-plane measurement structure features accelerometers with different distributions of comb-tooth electrode plates and more rational external contours and perimeters. Simultaneously, through a topological extended array structure, X-axis and Y-axis measurement units are cross-distributed, and different measurement needs can be met by increasing or decreasing the number and arrangement of measurement units. The design of this invention's triaxial accelerometer also ensures that other measurement units can continue to perform measurements even if the anchor point of one measurement unit detaches, effectively improving the process tolerance during fabrication. The out-of-plane measurement structure is nested in a U-shape around the in-plane measurement structure, achieving out-of-plane motion detection through a seesaw-type capacitor, maximizing device area utilization. This effectively improves the sensitivity of the MEMS capacitive triaxial accelerometer and adapts to various measurement environments.

[0005] The working principle of the triaxial accelerometer of this invention is as follows: the acceleration, which is difficult to measure directly, is converted into a mechanical signal by an inertial mass block, and then converted into an electrical signal of capacitance change by a sensing device. Through analysis and integration by the back-end signal processing circuit, linear detection of acceleration is achieved.

[0006] On one hand, the present invention provides a topological MEMS capacitive triaxial accelerometer, which includes: a substrate B, an out-of-plane measurement structure, an in-plane measurement structure, and a metal electrode plate, wherein the metal electrode plate is embedded in the upper surface of the substrate B; The out-of-plane measurement structure includes: a fixed outer frame, an out-of-plane mass block PM, and a cantilever beam L; the in-plane measurement structure includes: an in-plane mass block M and a measurement unit. The out-of-plane mass block PM is located inside the fixed outer frame. Both ends of the out-of-plane mass block PM are connected to the fixed outer frame via cantilever beams L. The fixed outer frame is bonded and fixedly connected to the substrate B. The out-of-plane mass block PM is configured as a seesaw swinging structure with the cantilever beams L as the fulcrum. The out-of-plane mass block PM is divided into two weight parts with unequal weights along the straight line where the two cantilever beams L are located. The two weight parts and the metal electrode plate form parallel plate capacitors CZ1 and CZ2 respectively for out-of-plane motion detection. The out-of-plane mass block PM surrounds the outer periphery of the in-plane mass block M in a U-shape. The in-plane mass block M includes at least two hollow regions K arranged in a topologically extended array, and each hollow region K contains one measurement unit. The two adjacent measurement units are 90° centrally symmetrical. The measurement unit includes: a pair of cantilever beams S, an anchor point A, and two variable comb-tooth capacitors; the anchor point A is located at the center of the hollow area K, the variable comb-tooth capacitors are fixed-tooth bias differential structures, the variable comb-tooth capacitors are connected to the in-plane mass block M and the anchor point A, and the anchor point A is anoly bonded and fixedly connected to the substrate B; one end of each cantilever beam S is connected to the anchor point A, and the other end is connected to the inner frame of the hollow area K; the in-plane measurement structure performs in-plane motion detection.

[0007] Furthermore, in the topological MEMS capacitive triaxial accelerometer of the present invention, the variable comb capacitor includes a movable comb electrode C and a fixed comb electrode E; one end of the movable comb electrode C is connected to the inner frame of the hollow area K of the in-plane mass block M and extends inward; the electrode base of the fixed comb electrode E is fixedly connected to the anchor point A; the comb teeth of the fixed comb electrode E extend towards the movable comb electrode C; the variable comb capacitors are 180° centrally symmetrical.

[0008] Furthermore, in the topological MEMS capacitive triaxial accelerometer of the present invention, in the three-dimensional rectangular coordinate system XYZ, the coordinate axes parallel to the substrate B include the X-axis and the Y-axis, and the coordinate axis perpendicular to the substrate B and pointing from the substrate B to the out-of-plane mass block PM is the Z-axis; the measurement sensitive coordinate axes of the in-plane measurement structure include the X-axis and the Y-axis, and the measurement sensitive coordinate axis of the out-of-plane measurement structure is the Z-axis.

[0009] In this invention, the number of hollowed-out areas K is preferably 4, 6, 8, 9, or 16 to ensure the symmetry of the overall in-plane measurement structure.

[0010] In this invention, anchor point A is connected to base B for support, and the anchor point is located at the center of each hollow structure, achieving a high degree of balance from a mechanical perspective.

[0011] In this invention, preferably, the masses of both the in-plane mass block M and the out-of-plane mass block PM can be adjusted by processes such as drilling and counterweighting.

[0012] In this invention, each hollow region K is provided with one measurement unit, and the hollow regions K are arranged in the form of a topological extended array; preferably, the capacitance can be adjusted by adding or removing measurement units to optimize the overall performance of the topological MEMS capacitive triaxial accelerometer.

[0013] The topological MEMS capacitive triaxial accelerometer of this invention decomposes the measurement requirements of the three axes into in-plane and out-of-plane measurements. Through a topological extended array structure, X-axis and Y-axis measurement units are cross-distributed. Different measurement needs can be met by increasing or decreasing the number and arrangement of measurement units. This design can also ensure that other measurement units can still perform measurements normally even if the anchor point of a certain measurement unit falls off, effectively improving the process tolerance during manufacturing.

[0014] In this invention, the out-of-plane measurement structure is nested in a U-shape around the in-plane measurement structure, and out-of-plane motion detection is achieved through a seesaw-type capacitor, thereby maximizing the utilization of the device area.

[0015] In this invention, preferably, both the in-plane fixed comb electrode plate base and the out-of-plane seesaw electrode plate base are provided with limiting devices to prevent electrostatic adsorption between the movable electrode plate and the fixed electrode plate after the device is subjected to an impact exceeding the range.

[0016] Furthermore, in the topological MEMS capacitive triaxial accelerometer of the present invention, the X-axis measurement unit and the Y-axis measurement unit in the in-plane measurement structure are arranged alternately. The movable comb electrode C and the fixed comb electrode E of the X-axis measurement unit are both perpendicular to the X-axis, and the movable comb electrode C and the fixed comb electrode E of the Y-axis measurement unit are both perpendicular to the Y-axis.

[0017] Furthermore, in the topological MEMS capacitive triaxial accelerometer described in this invention, the interlacing area of ​​the movable comb electrode C and the fixed comb electrode E should be less than 70% of the area of ​​the opposite sides of the comb teeth. This is to prevent the in-plane mass electrode from contacting the base of the sensing comb electrode during peak sensing mode.

[0018] In this invention, the relative lateral area of ​​the comb teeth refers to the core effective area of ​​capacitance detection formed by the corresponding movable comb electrode C and fixed comb electrode E of the variable comb capacitor in the MEMS capacitive triaxial accelerometer, which is equivalent to the area of ​​the electrode plate.

[0019] Furthermore, in the topological MEMS capacitive triaxial accelerometer of the present invention, the distance ratio between the comb teeth of the movable comb electrode C and the comb teeth of the adjacent fixed comb electrodes E is less than or equal to 1:3.

[0020] Furthermore, in the topological MEMS capacitive triaxial accelerometer described in this invention, the cantilever beam S is a folded beam structure composed of a combination of a serpentine beam and a crab-shaped beam, and the cantilever beam L is a tuning fork-type spring beam structure.

[0021] Furthermore, in the topological MEMS capacitive triaxial accelerometer described in this invention, the elastic coefficient k of the folded beam is calculated using the following formulas (1) to (4): (1) (2) (3) (4) Among them, L b and L t For the strength of the folded beam parallel to the x-axis and y-axis, wt Let n be the width of the folded beam, n be the number of times the beam is folded, and E be the width of the folded beam. b I is the elastic modulus of the folded beam material. z,b and I z,t These are the moments of inertia of the corresponding parts of the folded beam.

[0022] Furthermore, in the topological MEMS capacitive triaxial accelerometer described in this invention, the in-plane mass block M and the cantilever beam S are the same functional layer, and the material of the functional layer is silicon.

[0023] On the other hand, the present invention provides a method for fabricating a topological MEMS capacitive triaxial accelerometer, wherein the topological MEMS capacitive triaxial accelerometer is any one of the topological MEMS capacitive triaxial accelerometers described above; the fabrication method includes: obtaining the topological MEMS capacitive triaxial accelerometer by processing it using a silicon-on-glass substrate fabrication process.

[0024] In this invention, preferably, the fabrication method of the topological MEMS capacitive triaxial accelerometer includes the following steps: Step 1: Create anchor points A silicon wafer is selected, and photolithography and dry etching are performed sequentially to obtain the bonding anchor point A. After dry etching, resist removal and cleaning are performed. The silicon wafer has a thickness of 300 μm and is p-type. <100> Si, resistivity <0.0015 Ω·cm.

[0025] Step 2: Fabrication of substrate B and metal electrode plate Borosilicate glass sheet is selected as substrate B. The borosilicate glass sheet is etched to obtain metal trace grooves. Using lift-off technology, Ti-Al metal is deposited in the grooves to form the metal electrode plate to complete the conductivity of the entire device. Step 3: Wafer bonding and thinning The silicon wafer and the borosilicate glass sheet are bonded together using anodic bonding technology; then, the silicon wafer is thinned to a thickness of 120-130 μm using a thinning machine. Step 4: Device Molding and Interconnection Aluminum electrodes are grown on the thinned silicon surface using magnetron sputtering for ASIC circuit connection. Then, deep silicon etching technology is used to etch the silicon except for anchor point A according to the structure of the out-of-plane measurement structure and the in-plane measurement structure to complete the fabrication of the structural layer, thus obtaining the topological MEMS capacitive triaxial accelerometer of the present invention.

[0026] The beneficial effects of this invention are: Compared to traditional parallel electrode plate accelerometers, the topological MEMS capacitive triaxial accelerometer of this invention significantly improves sensitivity during operation due to its more rational geometry, resulting in a more accurate theoretical calculation of the original induced voltage. The array design allows for flexible adaptation to different size requirements, achieving the best performance among various microelectromechanical accelerometer structures. Traditional accelerometer structures are based on a mass block with comb teeth extending from it to both sides. This results in limited device size and application scenarios, and manufacturing yield is constrained by the relationship between the number of anchor points and the mass block's mass. In contrast, the topological design of this invention makes the device more flexible in application and significantly improves manufacturing yield. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the topological MEMS capacitive triaxial accelerometer of the present invention; Figure 2 The pattern structure of the in-plane measurement structure in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the in-plane measurement structure from the yz plane perspective in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the in-plane measurement structure from the xz plane perspective in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram illustrating the principle of the in-plane measurement structure for detecting acceleration input along the x-axis and y-axis in Embodiment 1 of the present invention. Figure 6 The in-plane measurement structure of Embodiment 1 of the present invention is a pattern structure of a single topological unit; Figure 7 The pattern structure is the out-of-plane measurement structure of Embodiment 1 of the present invention. Detailed Implementation

[0028] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described in detail with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the detailed embodiments, conventional conditions or conditions provided by the manufacturer shall apply.

[0029] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. Specific Implementation Method 1

[0030] The present invention discloses a topological MEMS capacitive triaxial accelerometer, comprising: a substrate B, an out-of-plane measurement structure, an in-plane measurement structure, and a metal electrode plate, wherein the metal electrode plate is embedded on the upper surface of the substrate B. The above-mentioned out-of-plane measurement structure includes: a fixed outer frame, an out-of-plane mass block PM, and a cantilever beam L; the above-mentioned in-plane measurement structure includes: an in-plane mass block M and a measurement unit. The out-of-plane mass block PM is located inside the fixed outer frame. Both ends of the out-of-plane mass block PM are connected to the fixed outer frame via cantilever beams L. The fixed outer frame is bonded and fixedly connected to the aforementioned base B. The out-of-plane mass block PM is configured as a seesaw swinging structure with the cantilever beams L as the fulcrum. The out-of-plane mass block PM is divided into two weight parts with unequal weights along the straight line where the two cantilever beams L are located. The two weight parts and the metal electrode plate respectively form a parallel plate capacitor CZ1 and a parallel plate capacitor CZ2 for out-of-plane motion detection. The out-of-plane mass block PM surrounds the aforementioned in-plane mass block M in a U-shape. The in-plane mass block M includes at least two hollow regions K arranged in a topologically extended array. Each hollow region K contains one of the aforementioned measurement units, and two adjacent measurement units are centrally symmetrical at 90°. The aforementioned measurement unit includes: a pair of cantilever beams S, an anchor point A, and two variable comb-tooth capacitors; the anchor point A is located at the center of the hollow area K, the variable comb-tooth capacitors are fixed-tooth bias differential structures, the variable comb-tooth capacitors are connected to the in-plane mass block M and the anchor point A, and the anchor point A is anoly bonded and fixedly connected to the aforementioned substrate B; one end of each cantilever beam S is connected to the anchor point A, and the other end is connected to the inner frame of the hollow area K; the aforementioned in-plane measurement structure performs in-plane motion detection.

[0031] In some implementations, the number of hollowed-out areas K is preferably 4, 6, 8, 9, 16, etc., to maintain the overall structure symmetry.

[0032] In some embodiments, the variable comb-tooth capacitor includes a movable comb-tooth electrode C and a fixed comb-tooth electrode E; one end of the movable comb-tooth electrode C is connected to the inner frame of the hollow area K of the in-plane mass block M and extends inward; the electrode base of the fixed comb-tooth electrode E is fixedly connected to the anchor point A; the comb teeth of the fixed comb-tooth electrode E extend toward the movable comb-tooth electrode C; the variable comb-tooth capacitors are 180° centrally symmetrical.

[0033] In some embodiments, in the three-dimensional rectangular coordinate system XYZ, the coordinate axes parallel to the base B include the X-axis and the Y-axis, and the coordinate axis perpendicular to the base B and pointing from the base B to the out-of-plane mass block PM is the Z-axis; the measurement sensitive coordinate axes of the in-plane measurement structure include the X-axis and the Y-axis, and the measurement sensitive axis of the out-of-plane measurement structure is the Z-axis.

[0034] In some embodiments, the X-axis measurement unit and the Y-axis measurement unit in the above-described in-plane measurement structure are arranged alternately. The movable comb electrode C and the fixed comb electrode E of the X-axis measurement unit are both perpendicular to the X-axis, and the movable comb electrode C and the fixed comb electrode E of the Y-axis measurement unit are both perpendicular to the Y-axis.

[0035] In some embodiments, the cross-area of ​​the movable comb electrode C and the fixed comb electrode E should be less than 70% of the area of ​​the opposite sides of the comb teeth; the area of ​​the opposite sides of the comb teeth is the area of ​​the electrode plate. The purpose is to prevent the in-plane mass block electrode from touching the base of the sensing comb electrode during the peak of the sensing mode.

[0036] In some embodiments, the ratio of the distance between the teeth of the movable comb electrode C and the teeth of the adjacent fixed comb electrodes E is less than or equal to 1:3.

[0037] In some embodiments, the ratio of the distance between the teeth of the movable comb electrode C and the teeth of the adjacent fixed comb electrodes E is 1:3.

[0038] In some embodiments, the cantilever beam S is a folded beam structure composed of a combination of a serpentine beam and a crab-shaped beam, and the cantilever beam L is a tuning fork type spring beam structure.

[0039] In some embodiments, the elastic coefficient k of the folded beam is calculated using the following formulas (1) to (4): (1) (2) (3) (4) Among them, L b and L t For the strength of the folded beam parallel to the x-axis and y-axis, w t Let n be the width of the folded beam, n be the number of times the beam is folded, and E be the width of the folded beam. b I is the elastic modulus of the folded beam material. z,b and I z,t These are the moments of inertia of the corresponding parts of the folded beam.

[0040] In some implementations, the in-plane mass block M and the cantilever beam S are the same functional layer.

[0041] In some embodiments, the aforementioned functional layer material is silicon. Specific Implementation Method Two

[0042] On the other hand, the present invention provides a method for fabricating a topological MEMS capacitive triaxial accelerometer, wherein the topological MEMS capacitive triaxial accelerometer is any one of the topological MEMS capacitive triaxial accelerometers described in Specific Embodiment 1; the fabrication method includes: obtaining the topological MEMS capacitive triaxial accelerometer by processing it using a silicon on a glass substrate fabrication process.

[0043] In some embodiments, the fabrication method of the above-mentioned topological MEMS capacitive triaxial accelerometer includes the following steps: Step 1: Create anchor points A silicon wafer was selected, and a first photolithography and dry etching were performed sequentially to obtain bonding anchor points A. After dry etching, resist removal and cleaning were carried out. The silicon wafer has a thickness of 300 μm and a p-type... <100> Si, resistivity <0.0015 Ω·cm.

[0044] Step 2: Fabrication of substrate B and metal electrode plate A borosilicate glass sheet is selected as substrate B. The borosilicate glass sheet is etched to obtain metal trace grooves. Using lift-off technology, Ti-Al metal is deposited in the grooves to form the metal electrode plate, thereby completing the conductivity of the entire device.

[0045] Step 3: Wafer bonding and thinning The silicon wafer and the borosilicate glass sheet are bonded together using anodic bonding technology; then, the silicon wafer is thinned to a thickness of 120~130um using a thinning machine.

[0046] Step 4: Device Molding and Interconnection Aluminum electrodes are grown on the thinned silicon surface using magnetron sputtering for ASIC circuit connection. Then, deep silicon etching technology is used to etch the silicon except for anchor point A according to the structure of the out-of-plane measurement structure and the in-plane measurement structure to complete the fabrication of the structural layer, thus obtaining the topological MEMS capacitive triaxial accelerometer of the present invention.

[0047] The present invention will be further described in detail below with reference to specific embodiments.

[0048] Example 1: like Figures 1-7 As shown, a topological MEMS capacitive triaxial accelerometer of the present invention includes: a substrate B, an out-of-plane measurement structure, an in-plane measurement structure, and a metal electrode plate, wherein the metal electrode plate is embedded on the upper surface of the substrate B. The out-of-plane measurement structure includes: a fixed outer frame, an out-of-plane mass block PM, and a cantilever beam L; the in-plane measurement structure includes: an in-plane mass block M and a measurement unit. The out-of-plane mass block PM is located inside the fixed outer frame. Both ends of the out-of-plane mass block PM are connected to the fixed outer frame through cantilever beams L. The fixed outer frame is bonded and fixedly connected to the base B. The out-of-plane mass block PM is configured as a seesaw swinging structure with the cantilever beams L as the fulcrum. The out-of-plane mass block PM is divided into two weight parts with unequal weights with the straight line where the two cantilever beams L are located as the axis. The two weight parts and the metal electrode plate respectively form a parallel plate capacitor CZ1 and a parallel plate capacitor CZ2 for out-of-plane motion detection. The out-of-plane mass block PM surrounds the in-plane mass block M in a U-shape. The in-plane mass block M includes 6 hollow regions K arranged in a topologically extended array. Each hollow region K contains a measurement unit, and two adjacent measurement units are 90° centrally symmetrical. The measurement unit includes: a pair of cantilever beams S, an anchor point A, and two variable comb-tooth capacitors; the anchor point A is located at the center of the hollow area K, and the variable comb-tooth capacitors are fixed-tooth bias differential structures. The variable comb-tooth capacitors are connected to the in-plane mass block M and the anchor point A, and the anchor point A is anoly bonded and fixedly connected to the substrate B; one end of each cantilever beam S is connected to the anchor point A, and the other end is connected to the inner frame of the hollow area K; the in-plane measurement structure performs in-plane motion detection. In this embodiment 1, the pair of cantilever beams S are S1 and S2.

[0049] The variable comb-tooth capacitor includes a movable comb-tooth electrode C and a fixed comb-tooth electrode E; one end of the movable comb-tooth electrode C is connected to the inner frame of the hollow area K of the in-plane mass block M and extends inward; the electrode base of the fixed comb-tooth electrode E is fixedly connected to the anchor point A; the comb teeth of the fixed comb-tooth electrode E extend towards the movable comb-tooth electrode C; the variable comb-tooth capacitors are 180° centrally symmetrical.

[0050] In the three-dimensional rectangular coordinate system XYZ, the coordinate axes parallel to the base B include the X-axis and Y-axis, and the coordinate axis perpendicular to the base B and pointing from the base B to the out-of-plane mass block PM is the Z-axis; the measurement sensitive coordinate axes of the in-plane measurement structure include the X-axis and Y-axis, and the measurement sensitive axis of the out-of-plane measurement structure is the Z-axis.

[0051] Anchor point A is connected to base B for support, and the anchor point is located at the center of each hollow structure, achieving a high degree of balance from a mechanical point of view.

[0052] The mass of both the in-plane mass block M and the out-of-plane mass block PM can be adjusted through processes such as drilling and counterweighting.

[0053] The overall performance of the topological MEMS capacitive triaxial accelerometer can be optimized by adjusting the capacitance by adding or removing measurement units.

[0054] Measurement units are cross-distributed along the X and Y axes.

[0055] The out-of-plane measurement structure is nested in a U-shape around the in-plane measurement structure. Out-of-plane motion detection is achieved through a seesaw-type pendulum capacitor, maximizing the utilization of the device area.

[0056] Both the in-plane fixed comb electrode plate base and the out-of-plane seesaw electrode plate base are equipped with limiting devices to prevent electrostatic adsorption between the movable electrode plate and the fixed electrode plate after the device is subjected to an impact exceeding the range.

[0057] In the in-plane measurement structure, the X-axis measurement unit and the Y-axis measurement unit are arranged alternately. The movable comb electrode C and the fixed comb electrode E of the X-axis measurement unit are both perpendicular to the X-axis, and the movable comb electrode C and the fixed comb electrode E of the Y-axis measurement unit are both perpendicular to the Y-axis.

[0058] The intersecting area of ​​the movable comb electrode C and the fixed comb electrode E should be less than 70% of the area of ​​their opposite sides. The area of ​​their opposite sides is the area of ​​the electrode plate. This is to prevent the in-plane mass electrode from touching the base of the sensing comb electrode during peak induction mode.

[0059] The ratio of the distance between the teeth of the movable comb electrode C and the teeth of the adjacent fixed comb electrodes E is 1:3.

[0060] The cantilever beam S is a folded beam structure composed of a combination of serpentine and crab-shaped beams, while the cantilever beam L is a tuning fork-type spring beam structure.

[0061] In a topological MEMS capacitive triaxial accelerometer, the elastic coefficient k of the folded beam is calculated using the following formulas (1) to (4): (1) (2) (3) (4) Among them, L b and L t For the strength of the folded beam parallel to the x-axis and y-axis, w t Let n be the width of the folded beam, n be the number of times the beam is folded, and E be the width of the folded beam. b I is the elastic modulus of the folded beam material. z,b and I z,t These are the moments of inertia of the corresponding parts of the folded beam.

[0062] The in-plane mass block M and the cantilever beam S are in the same functional layer, and the material of the functional layer is silicon.

[0063] The in-plane mass block M is connected to the folded beam structure S at the corresponding position, which restricts the movable direction of the in-plane mass block M, so that the in-plane mass block M can only translate in a direction parallel to the XY plane.

[0064] like Figure 5 As shown, Figure 5 for Figure 1 The diagram shows the principle of a topological MEMS capacitive triaxial accelerometer for detecting acceleration input along an in-plane sensitive axis. The sensitive axis detection capacitor includes a capacitor detection group CX1 composed of a fixed comb electrode E1 and a movable comb electrode C1, and a capacitor detection group CX2 composed of a fixed comb electrode E2 and a movable comb electrode C2.

[0065] When a topological capacitive accelerometer detects acceleration input along an in-plane sensitive axis, an in-plane mass block M moves parallel to the Y-axis, such as... Figure 5 As shown by the middle arrow, the first detection capacitor group CX1 and the second detection capacitor group CX2 have changes with the same amplitude but opposite directions. The detection circuit detects the difference between the change in the first detection capacitor group CX1 (ΔCX1) and the change in the second detection capacitor group CX2 (ΔCX2), and calculates the acceleration input along the sensitive axis. That is, the detection circuit measures the magnitude of the differential signal ΔCX1-ΔCX2, and by reverse calculation, the acceleration information of the input sensitive axis can be obtained.

[0066] The movable part PM is connected to the cantilever beam structure L at the corresponding position, which restricts the movable part PM's direction of movement, so that the movable part PM can only swing around the X-axis as the rotation axis.

[0067] When a topological capacitive accelerometer detects acceleration input along an out-of-plane sensitive axis, the movable part PM oscillates perpendicularly to the Z-axis with the X-axis as its rotation axis. The first detection capacitor group CZ1 and the second detection capacitor group CZ2 exhibit changes in amplitude but opposite directions. The detection circuit measures the difference between the change in the first detection capacitor group CZ1 (ΔCZ1) and the change in the second detection capacitor group CZ2 (ΔCZ2), and calculates the acceleration input along the sensitive axis. In other words, the detection circuit measures the magnitude of the differential signal ΔCZ1 - ΔCZ2, and by reverse calculation, the acceleration information of the input sensitive axis can be obtained.

[0068] In the in-plane measurement structure of Embodiment 1, the working principle is explained using the Y-axis detection unit as an example. The sensitive in-plane mass block M is suspended from the anchor point A via a spring beam structure. When the accelerometer of Embodiment 1 is subjected to an acceleration impact, the sensitive in-plane mass block M moves due to inertia. The movable and fixed comb teeth distributed on both sides of the in-plane mass block M form a variable comb-tooth capacitor. When the in-plane mass block M moves, the spacing between the comb teeth also changes, thereby changing the capacitance value.

[0069] The variable comb-tooth capacitor is designed as a fixed-tooth bias differential structure. The fixed comb-tooth electrodes, fixed on the stator base, are connected to the same substrate area via anchor points. The distances between the movable comb-tooth electrode C and the adjacent fixed comb-tooth electrodes E are unequal, with a distance ratio of approximately 1:4 on both sides. Therefore, the capacitance on the side with the larger distance is ignored. Furthermore, the variable comb-tooth capacitors on both sides of the in-plane mass block M are connected in parallel to form a differential pair, which serves as the input signal for the subsequent detection circuit.

[0070] The initial capacitance of a variable comb capacitor Writing style (1-1): (1-1) In equation (1-1), The vacuum permittivity, The relative permittivity, , , These are the overlap length of the comb teeth between the movable comb tooth electrode and the fixed comb tooth electrode, the thickness of the comb teeth, and the distance between the comb teeth, respectively. Equation (1-1) yields the capacitance change of a variable comb capacitor when a small displacement occurs between the comb teeth. Writing style (1-2): (1-2) In equation (1-2), the new amount , These represent the changes in overlap length and the changes in comb tooth spacing, respectively.

[0071] When the accelerometer is subjected to an accelerometer action along the positive Y direction, the variable comb capacitor formed by the movable comb teeth on both sides and the fixed comb teeth undergoes opposite changes. The variable comb capacitor can be represented as follows: (1-3) (1-4) The differential capacitance at this time is: (1-5) Differential detection can double the capacitance change, thus improving detection accuracy.

[0072] The differential capacitance signal is linearly related to the minute displacement of the in-plane mass block M along the Y direction, meaning it is linearly related to the external input acceleration along the Y direction. Therefore, by using the differential capacitance signal as the input signal of the back-end differential capacitance detection circuit, the value of the external input acceleration signal can be measured.

[0073] In the out-of-plane measurement structure of this embodiment 1, the cantilever beam L of the Z-axis out-of-plane mass block PM is a tuning fork-type spring beam. The two ends of the Z-axis out-of-plane mass block PM have unequal weights, and it will rotate around the tuning fork beam axis when subjected to out-of-plane acceleration impact. The Z-axis out-of-plane mass block PM and the electrode plate above it form a parallel plate capacitor.

[0074] When the accelerometer is not subjected to acceleration in the Z direction, the capacitances of the two parallel plates formed by the Z-axis mass block and the electrode plates are both static capacitances, which can be expressed as: (2-1) in Let be the dielectric constant, S be the area of ​​the electrode and the mass block facing each other, and z be the distance between the mass block and the electrode in the initial state. When the sensor is subjected to Z-axis acceleration, the Z-axis mass block rotates around the axis, changing the distance between the mass block and the electrode plate, thereby altering the capacitance value. Since the capacitance on one side of the Z-axis increases while the other side decreases, let the change be denoted as... , The capacitance value decreases. The capacitance value increases: (2-2) (2-3) Differential capacitors can be obtained as follows: (2-4) (2-5) Let the distance between the center of the electrode plate and the torsional axis of the mass block be... Because the electrode spacing Z is relative to Very small It can be approximated by the torsion angle θ and Conclusion: (2-6) (2-7) The topological MEMS capacitive triaxial accelerometer of this embodiment 1 is used for a range of ±50g and has strong shock resistance. Its sensitivity reaches 30mV / g per axis, which is 10% higher than that of traditional triaxial accelerometers.

[0075] Example 2: The fabrication method of a topological MEMS capacitive triaxial accelerometer in Example 1 includes: obtaining the above-mentioned topological MEMS capacitive triaxial accelerometer by silicon fabrication process on a glass substrate.

[0076] Example 3: Example 1 describes a method for fabricating a topological MEMS capacitive triaxial accelerometer, comprising the following steps: Step 1: Create anchor points A silicon wafer was selected, and photolithography and dry etching were performed sequentially to obtain bonding anchor points A. After dry etching, resist removal and cleaning were carried out. The silicon wafer has a thickness of 300 μm and is p-type. <100> Si, resistivity <0.0015 Ω·cm.

[0077] Step 2: Fabrication of substrate B and metal electrode plate A borosilicate glass sheet is selected as substrate B. The borosilicate glass sheet is etched to obtain metal trace grooves. Using lift-off technology, Ti-Al metal is deposited in the grooves to form the metal electrode plate, thereby completing the conductivity of the entire device.

[0078] Step 3: Wafer bonding and thinning The silicon wafer and the borosilicate glass sheet are bonded together using anodic bonding technology; then, the silicon wafer is thinned to a thickness of 120~130um using a thinning machine.

[0079] Step 4: Device Molding and Interconnection Aluminum electrodes are grown on the thinned silicon surface using magnetron sputtering for ASIC circuit connection. Then, deep silicon etching technology is used to etch the silicon except for anchor point A according to the structure of the out-of-plane measurement structure and the in-plane measurement structure to complete the fabrication of the structural layer, thus obtaining the topological MEMS capacitive triaxial accelerometer of the present invention.

[0080] Example 4: The only difference between Example 4 and Example 1 is the setting: the number of in-plane mass blocks M and the number of hollow areas K are 6, the hollow areas K are arranged in a topological 2×3 array, the overall size is 1.2mm×0.8mm, and the material is silicon ( <100> Crystal orientation).

[0081] Measurement unit: Each hollow area K contains 2 variable comb capacitors, adjacent measurement units are 90° centrally symmetrical, and the X / Y axis units are staggered.

[0082] Comb electrode (C / E): Movable comb tooth C has a width of 5μm and a thickness of 60μm; fixed comb tooth E has a width of 5μm and a thickness of 60μm. Interlacing area = 65% (<70%).

[0083] Comb tooth pitch ratio = 1:3, cantilever beam S (serpentine + crab folded beam): Lb=300μm, Lt=20μm, wt=8μm, n=4 folds.

[0084] Cantilever beam L (tuning fork type): arm length 100μm, width 10μm.

[0085] Out-of-plane mass block PM: a square-shaped ring (inner diameter 1.3mm × 0.9mm, outer diameter 2.2mm × 1.2mm), with a weight ratio of 2:1 at both ends and a thickness of 60μm.

[0086] Substrate and electrode: Substrate B = borosilicate glass (500 μm thick); Metal electrode plate = Ti-Al (20 nm Ti layer + 100 nm Al layer), embedded on the upper surface of the substrate.

[0087] Anchor point A: Diameter 30μm, anodic bonding pressure 1MPa, temperature 380℃.

[0088] The working state of this embodiment 4: acceleration can be detected normally on the X / Y / Z axes, with a measurement range of ±50g; core performance: X / Y axis sensitivity = 30mV / g, Z axis sensitivity = 34mV / g; process qualification rate = 86%; XY axis crosstalk = ±3.1%; key verification: after the anchor point of a single measurement unit fails, the overall sensitivity only decreases by 17% (proving the advantage of process tolerance).

[0089] Example 5: The only difference between Example 5 and Example 4 is that the comb tooth gap ratio is adjusted to 1:5, so that more comb tooth electrodes can be arranged in each hollow area, thus increasing the total capacitance, increasing the capacitance sensitivity by 46%, and optimizing the crosstalk to ±2.7%.

[0090] Example 6: The only difference between Example 6 and Example 4 is that the number of hollow areas K is 9, the topology is arranged in a 3×3 array, the size of the in-plane mass block is 1.2mm×1.2mm, and the density of the unit measurement unit per unit area is kept consistent with that of Example 1.

[0091] The adaptability of this embodiment 4: the sensitivity can be adjusted to 52mV / g by increasing or decreasing the number of arrays (9) (to meet the needs of different scenarios); area utilization: the chip area of ​​9 array units is only 50% larger than that of embodiment 1, but the sensitivity is improved by 73%, which proves the synergistic advantages of the topology array.

[0092] Comparative Example 1: The only difference between Comparative Example 1 and Example 4 is that the design is as follows: the in-plane mass block M has no "topology extension array" hollow area K, and only one hollow measurement unit is set (no multiple array units).

[0093] Comparative Example 1 uses only one hollow area measurement unit. Although the total size of the device is small, it results in a low mass of the in-plane sensitive mass block, which severely reduces the in-plane measurement sensitivity. Furthermore, since the in-plane measurement structure has only one central anchor point, the device is prone to entering a torsional state during operation. This not only affects the measurement accuracy of the measurement axis but also damages the comb structure of the device due to excessive torsion. In addition, the single anchor point is very prone to detachment due to stress and external impact during the manufacturing process, leading to device failure.

[0094] Comparative Example 2: The only difference between Comparative Example 2 and Example 4 is that the variable comb capacitor adopts a "symmetrical spacing design", with the distance ratio from the movable comb to the fixed comb on both sides being 1:1, instead of the 1:2.5-3.5 range of the present invention; the comb tooth interlacing area is 85% (≥70%, without avoiding the risk of contact).

[0095] When Comparative Example 2 adopts a symmetrical spacing design, due to the relationship between capacitance and displacement, a fixed-tooth evenly placed structure is required for the comb electrode plate design. That is, each movable comb tooth corresponds to two fixed comb teeth. This limits the number of comb electrode plates that can be arranged in a single hollow area, and the total capacitance value decreases compared to the fixed-tooth bias structure used in this invention. When the comb tooth interlacing area is greater than 70%, there is a risk of collision when the device is subjected to a large instantaneous displacement or torsion due to impact, which may damage the device structure.

[0096] Comparative Example 3: The only difference between Comparative Example 3 and Example 4 is that the design is as follows: In the out-of-plane measurement structure, the out-of-plane mass block PM does not adopt the "U-shaped surround of the in-plane mass block", but is arranged side by side with the in-plane mass block (the total chip area is consistent with the present invention); the cantilever beam L adopts the traditional "straight beam structure" (non-tuning fork type); in the in-plane measurement structure, the cantilever beam S adopts the traditional "single serpentine beam" (non-serpentine + crab folding beam).

[0097] When the in-plane and out-of-plane mass blocks of Comparative Example 3 do not use a nested structure, the dimensions of both the in-plane and out-of-plane measurement structures will be significantly reduced when the total area of ​​the device is the same. The total capacitance, capacitance sensitivity, and range of the device will all decrease accordingly, resulting in a serious deterioration in device performance. When the cantilever beam L is a straight beam, the mass block of the out-of-plane measurement structure will not only experience torsional displacement during operation, but also a large translation perpendicular to the Z-axis, which will affect the measurement accuracy of the measurement axis. When the in-plane measurement structure uses a traditional serpentine beam, the in-plane mass block is prone to torsion when the device is subjected to an external force in the in-plane torsional direction, causing large inter-axis crosstalk and affecting the linearity of the device.

[0098] This invention has been described through the specific embodiments described above. Those skilled in the art should understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Parts not described in detail in this specification are well-known to those skilled in the art. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from the scope of this application. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims of this invention.

Claims

1. A topological MEMS capacitive triaxial accelerometer, characterized in that, include: The substrate B, the out-of-plane measurement structure, the in-plane measurement structure, and the metal electrode plate, wherein the metal electrode plate is embedded on the upper surface of the substrate B; The out-of-plane measurement structure includes: a fixed outer frame, an out-of-plane mass block PM, and a cantilever beam L; the in-plane measurement structure includes: an in-plane mass block M and a measurement unit. The out-of-plane mass block PM is located inside the fixed outer frame. Both ends of the out-of-plane mass block PM are connected to the fixed outer frame via cantilever beams L. The fixed outer frame is bonded and fixedly connected to the substrate B. The out-of-plane mass block PM is configured as a seesaw swinging structure with the cantilever beams L as the fulcrum. The out-of-plane mass block PM is divided into two weight parts with unequal weights along the straight line where the two cantilever beams L are located. The two weight parts and the metal electrode plate form parallel plate capacitors CZ1 and CZ2 respectively for out-of-plane motion detection. The out-of-plane mass block PM surrounds the outer periphery of the in-plane mass block M in a U-shape. The in-plane mass block M includes at least two hollow regions K arranged in a topologically extended array, and each hollow region K contains one measurement unit. The two adjacent measurement units are 90° centrally symmetrical. The measurement unit includes: a pair of cantilever beams S, an anchor point A, and two variable comb-tooth capacitors; the anchor point A is located at the center of the hollow area K, the variable comb-tooth capacitors are fixed-tooth bias differential structures, the variable comb-tooth capacitors are connected to the in-plane mass block M and the anchor point A, and the anchor point A is anoly bonded and fixedly connected to the substrate B; one end of each cantilever beam S is connected to the anchor point A, and the other end is connected to the inner frame of the hollow area K; the in-plane measurement structure performs in-plane motion detection.

2. The topological MEMS capacitive triaxial accelerometer according to claim 1, characterized in that, The variable comb-tooth capacitor includes a movable comb-tooth electrode C and a fixed comb-tooth electrode E; one end of the movable comb-tooth electrode C is connected to the inner frame of the hollow area K of the in-plane mass block M and extends inward; the electrode base of the fixed comb-tooth electrode E is fixedly connected to the anchor point A; the comb teeth of the fixed comb-tooth electrode E extend towards the movable comb-tooth electrode C; the variable comb-tooth capacitors are 180° centrally symmetrical.

3. The topological MEMS capacitive triaxial accelerometer according to claim 2, characterized in that, In the three-dimensional rectangular coordinate system XYZ, the coordinate axes parallel to the base B include the X-axis and Y-axis, and the coordinate axis perpendicular to the base B and pointing from the base B to the out-of-plane mass block PM is the Z-axis; the measurement sensitive coordinate axes of the in-plane measurement structure include the X-axis and Y-axis, and the measurement sensitive coordinate axis of the out-of-plane measurement structure is the Z-axis.

4. The topological MEMS capacitive triaxial accelerometer according to claim 3, characterized in that, In the in-plane measurement structure, the X-axis measurement unit and the Y-axis measurement unit are arranged alternately. The movable comb electrode C and the fixed comb electrode E of the X-axis measurement unit are both perpendicular to the X-axis, and the movable comb electrode C and the fixed comb electrode E of the Y-axis measurement unit are both perpendicular to the Y-axis.

5. The topological MEMS capacitive triaxial accelerometer according to claim 1, characterized in that, The area of ​​the intersecting comb teeth of the movable comb electrode C and the fixed comb electrode E should be less than 70% of the area of ​​the opposite sides of the comb teeth.

6. The topological MEMS capacitive triaxial accelerometer according to claim 1, characterized in that, The ratio of the distance between the teeth of the movable comb electrode C and the teeth of the adjacent fixed comb electrodes E is less than or equal to 1:

3.

7. The topological MEMS capacitive triaxial accelerometer according to claim 1, characterized in that, The cantilever beam S is a folded beam structure composed of a combination of serpentine and crab-shaped beams, and the cantilever beam L is a tuning fork type spring beam structure.

8. The topological MEMS capacitive triaxial accelerometer according to claim 7, characterized in that, The elastic coefficient k of the folded beam is calculated using the following formulas 1) to 4): 1） 2） 3） 4） Among them, L b and L t For the strength of the folded beam parallel to the x-axis and y-axis, w t Let n be the width of the folded beam, n be the number of times the beam is folded, and E be the width of the folded beam. b I is the elastic modulus of the folded beam material. z,b and I z,t These are the moments of inertia of the corresponding parts of the folded beam.

9. The topological MEMS capacitive triaxial accelerometer according to claim 1, characterized in that, The in-plane mass block M and the cantilever beam S are in the same functional layer, and the material of the functional layer is silicon.

10. A method for fabricating a topological MEMS capacitive triaxial accelerometer, characterized in that, The topological MEMS capacitive triaxial accelerometer is the topological MEMS capacitive triaxial accelerometer as described in any one of claims 1 to 9; the fabrication method includes: obtaining the topological MEMS capacitive triaxial accelerometer by processing it using a silicon-on-glass substrate fabrication process.

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