Z-axis MEMS closed-loop accelerometer assembly and accelerometer

Abstract

The present invention discloses a Z-axis MEMS closed-loop accelerometer assembly and accelerometer, relating to the technical field of micromechanical MEMS accelerometers. The Z-axis MEMS closed-loop accelerometer of the present invention adopts a closed-loop design, comprising a substrate, an electrode layer, and a movable structure layer. By symmetrically designing and manufacturing the detection mass blocks in the movable structure layer, the larger mass block is used as both the detection mass block and the driving mass block, eliminating the area occupied by the independently provided driving mass block in a traditional seesaw structure. This significantly reduces the space occupied by the movable structure layer, increases the effective detection area, and thus improves detection sensitivity.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-mechanical MEMS accelerometers, and in particular to a Z-axis MEMS closed-loop accelerometer component and an accelerometer. Background Art

[0002] Microelectromechanical systems (MEMS), miniaturized integrated systems that combine micromechanical structures and microelectronics, have become a core technology in the field of inertial sensing due to their small size, low power consumption, and mass production capabilities. MEMS inertial sensors, based on capacitance detection principles, hold a significant position in industrial control, automotive electronics, aerospace, and consumer electronics due to their high sensitivity and low noise. Capacitive accelerometers, a typical example, convert signals by detecting capacitance changes caused by acceleration. Their structural design and process optimization directly impact device performance and reliability.

[0003] Currently, MEMS capacitive accelerometers primarily utilize three configurations: comb-tooth, sandwich, and seesaw. The comb-tooth configuration achieves in-plane (X / Y axis) acceleration detection through variable area or spacing, but its out-of-plane (Z axis) detection capabilities are limited. While the sandwich configuration offers high signal-to-noise ratio and high precision, the complex multi-layer process leads to high manufacturing costs and low yield, making it difficult to meet the demands of large-scale applications. The seesaw configuration offers strong process compatibility and has become the mainstream solution for Z-axis detection.

[0004] The seesaw structure uses a torsion beam to support a movable detection mass. The change in spacing between the beam and the fixed electrode generates a differential capacitance signal, which is then used by the back-end circuitry to detect acceleration. However, the seesaw structure requires an additional drive mass suspended on one side of the detection mass, resulting in an excessively large chip area. Furthermore, the excessive number of damping holes reduces the detection area and sensitivity.

[0005] Therefore, there is an urgent need for a new Z-axis MEMS capacitive accelerometer that optimizes the detection area and sensitivity to meet the urgent demand for miniaturized and high-performance devices in the field of inertial sensing. Summary of the Invention

[0006] The present invention provides a Z-axis MEMS closed-loop accelerometer assembly and an accelerometer to solve the problems of existing Z-axis accelerometers, such as reduced sensitivity and excessively large overall area, caused by a driving mass block and excessive damping holes occupying the detection area.

[0007] The present invention is achieved through the following technical solutions:

[0008] A first aspect of the present invention provides a Z-axis MEMS closed-loop accelerometer assembly, comprising:

[0009] substrate;

[0010] an electrode layer comprising at least a pair of differential capacitor plates disposed on the substrate;

[0011] a movable structural layer, disposed above the substrate and the electrode layer, comprising a detection mass and a torsion beam, wherein the detection mass is bonded to the substrate via the torsion beam; when an acceleration signal is generated in the Z-axis direction, the detection mass moves out-of-plane relative to the torsion beam to form a differential detection signal on the at least one pair of differential capacitor plates;

[0012] Among them, the detection mass block is divided into a first detection mass block and a second detection mass block that are symmetrical relative to the torsion beam. The mass of the first detection mass block is greater than the mass of the second detection mass block, so that the first detection mass block can be used as both a detection mass block and a driving mass block.

[0013] The Z-axis accelerometer assembly of the present invention can be used as a standalone accelerometer or in combination. By creating a symmetrical mass difference between the detection masses, the larger mass is used as both the detection mass and the driving mass. This eliminates the area occupied by the independently installed driving mass in the traditional seesaw structure, significantly reducing the space occupied by the movable structure layer, increasing the effective detection area, and improving detection sensitivity. The symmetrical movable structure layer design achieves differential detection while avoiding the redundant layout of the mass blocks on one side, thereby reducing the overall chip area and meeting the requirements of high-density integration.

[0014] Preferably, the electrode layer includes a differential force capacitor plate and a differential detection capacitor plate;

[0015] The differential forcing capacitor plate includes a positive forcing capacitor plate and a negative forcing capacitor plate, the positive forcing capacitor plate and the negative forcing capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical relative to the torsion beam;

[0016] The differential detection capacitor plate includes a positive detection capacitor plate and a negative detection capacitor plate, and the positive detection capacitor plate and the negative detection capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical with respect to the torsion beam;

[0017] The capacitor plates located on the same side of the torsion beam have the same polarity.

[0018] Preferably, the positive detection capacitor plate and the negative detection capacitor plate are close to the torsion beam, and the positive force capacitor plate and the negative force capacitor plate are far away from the torsion beam.

[0019] Preferably, a recessed portion is etched on a surface of the second detection mass block facing away from the substrate, so that the mass of the first detection mass block is greater than the mass of the second detection mass block.

[0020] Preferably, damping holes or damping grooves are etched on the outer periphery of the detection mass block.

[0021] Preferably, the movable structural layer further comprises a plurality of buffer components and a plurality of convex columns;

[0022] The buffer component is arranged on the outer periphery of the detection mass block and is used for limiting the in-plane motion;

[0023] The convex column is arranged on the opposite surface of the detection mass block and the substrate, and is used for limiting out-of-plane motion.

[0024] Preferably, an insulating layer is deposited on the surface of the substrate, and the insulating layer is used to isolate the electrode layer from the substrate.

[0025] A second aspect of the present invention provides a Z-axis MEMS closed-loop accelerometer, comprising two Z-axis MEMS closed-loop accelerometer assemblies as described in any one of the first aspects of the present invention, wherein the two Z-axis MEMS closed-loop accelerometer assemblies are centrally symmetrical.

[0026] Preferably, the electrode layer includes a differential force capacitor plate and a differential detection capacitor plate;

[0027] The differential forcing capacitor plate includes a positive forcing capacitor plate and a negative forcing capacitor plate, the positive forcing capacitor plate and the negative forcing capacitor plate being respectively disposed below the first detection mass block and the second detection mass block and symmetrically relative to the torsion beam;

[0028] The differential detection capacitor plate includes a positive detection capacitor plate and a negative detection capacitor plate, the positive detection capacitor plate and the negative detection capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical with respect to the torsion beam;

[0029] The capacitor plates on the same side of the torsion beam have the same polarity;

[0030] The positive forcing capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative forcing capacitor plate, and the positive detection capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative detection capacitor plate.

[0031] Preferably, the Z-axis MEMS closed-loop accelerometer is vacuum packaged.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects: by using the first detection mass block as both the detection mass block and the driving mass block, the independently arranged driving mass block in the traditional seesaw structure is eliminated, the space occupied by the movable structure layer is significantly reduced, and the effective detection area is increased, thereby improving the detection sensitivity. Combined with the design of the symmetrically distributed first and second detection masses, the redundant layout of the single-sided mass block is avoided while achieving the differential detection function, significantly reducing the overall chip area and meeting the requirements of high-density integration. In addition, the closed-loop control allows the device to operate in a vacuum packaging environment. The closed-loop control system can suppress the oscillation phenomenon caused by the vacuum packaging, achieve low noise and high sensitivity, and meet the requirements of inertial navigation and vibration monitoring scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the examples. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be considered as limiting the scope. A person of ordinary skill in the art can also derive other relevant drawings based on these drawings without inventive effort. In the drawings:

[0034] Figure 1 is a cross-sectional schematic diagram of a Z-axis MEMS closed-loop accelerometer assembly according to an embodiment of the present invention;

[0035] Figure 2 is a top view of a movable structural layer according to an embodiment of the present invention;

[0036] Figure 3 is a top view of a detection mass block according to an embodiment of the present invention;

[0037] Figure 4 is a cross-sectional view of a movable structural layer according to an embodiment of the present invention;

[0038] Figure 5 This is a schematic structural diagram of a buffer component according to an embodiment of the present invention;

[0039] Figure 6 is a schematic diagram of a five-electrode structure according to an embodiment of the present invention;

[0040] Figure 7 1 is a schematic diagram of a three-electrode structure according to an embodiment of the present invention;

[0041] Figure 8 1 is a measurement schematic diagram of a five-electrode structure accelerometer according to an embodiment of the present invention;

[0042] Figure 9 1 is a measurement schematic diagram of a three-electrode structure accelerometer according to an embodiment of the present invention;

[0043] Figure 10 FIG. 4 is a top view of a Z-axis MEMS closed-loop accelerometer according to an embodiment of the present invention.

[0044] Description of the accompanying drawings and reference numerals is as follows:

[0045] 100 - substrate, 101 - bonding anchor point, 200 - electrode layer, 210 - differential force capacitor plate, 220 - differential detection capacitor plate, 230 - first capacitor plate, 240 - second capacitor plate, 300 - movable structural layer, 310 - torsion beam, 320 - detection mass block, 321 - first detection mass block, 322 - second detection mass block, 3221 - recessed portion, 323 - damping groove, 330 - buffer component, 340 - boss, 115a, 115b - L-shaped beams, 116a, 116b, 117a, 117b - T-shaped beams. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0047] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to other steps or units inherent in the device.

[0048] The terms used in various embodiments of the present invention are only used to describe the purpose of specific embodiments and are not intended to limit the various embodiments of the present invention. As used herein, the singular form is intended to also include the plural form, unless the context clearly indicates otherwise. Unless otherwise limited, all terms used here (including technical terms and scientific terms) have the same meaning as those of ordinary skill in the art generally understood by the various embodiments of the present invention. The terms (such as those defined in generally used dictionaries) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having idealized meaning or too formal meaning, unless clearly defined in various embodiments of the present invention.

[0049] A first aspect of the present invention provides a Z-axis MEMS closed-loop accelerometer assembly that can be used as an independent Z-axis accelerometer.

[0050] See Figure 1The cross-sectional schematic diagram of a Z-axis MEMS closed-loop accelerometer assembly shown in FIG. From bottom to top, it includes a substrate 100, an electrode layer 200, and a movable structure layer 300. The electrode layer 200, which utilizes a differential capacitor plate structure and is disposed on the substrate 100, serves as a detection electrode. The electrode layer 200 includes at least one pair of differential capacitor plates, i.e., a pair of positive and negative capacitor plates. When measuring the Z-direction acceleration signal, a differential capacitance signal is generated on the positive and negative capacitor plates. The Z-axis acceleration can then be calculated based on the differential capacitance signal via the back-end detection circuit.

[0051] The movable structural layer 300 is disposed above the substrate and includes a torsion beam 310 and a proof mass 320. The proof mass 320 is connected to one end of the torsion beam 310, and the other end of the torsion beam 310 is connected to the substrate. The proof mass 320 is bonded to the substrate 100 via the torsion beam 310. When an acceleration signal is generated in the Z-axis direction, the proof mass 320 moves out-of-plane with the torsion beam 310, creating a distance difference between the proof mass 320 and at least one pair of differential capacitor plates in the electrode layer, generating a differential detection signal on the at least one pair of differential capacitor plates.

[0052] See Figure 2 In the top view of the movable structural layer shown, the detection mass block 320 is divided into a first detection mass block 321 and a second detection mass block 322 on the left and right sides by the connected torsion beam 310. The first detection mass block 321 and the second detection mass block 322 are symmetrical relative to the torsion beam 310, and there is a mass difference between the first detection mass block and the second detection mass block. The positions of the first detection mass block 321 and the second detection mass block 322 are interchangeable, that is, the mass of the first detection mass block is greater than the mass of the second detection mass block, or the mass of the second detection mass block is greater than the mass of the first detection mass block, and the side with larger mass is used as both the detection mass block and the driving mass block. In the following description, the first detection mass block 321 and the second detection mass block 322 are collectively referred to as the detection mass block. By sharing the detection mass block and the driving mass block, the chip size is reduced.

[0053] In a preferred embodiment, see Figure 8 、 Figure 9 As shown, a bonding anchor 101 is positioned at the center of substrate 100, with the ends of torsion beam 310 connected to bonding anchor 101 and the center of the movable structural layer, respectively. This central location, rather than having only one bonding anchor, reduces the bonding area and, consequently, the thermal stress generated during bonding, while also positioning the movable structural layer directly above the substrate.

[0054] The torsion beam 310 may adopt a double-beam structure to increase the spring stiffness and change the resonant frequency.

[0055] In a preferred embodiment, see Figure 3 In the top view of the detection mass block shown, a recessed portion 3221 is etched on one side surface of the second detection mass block 322 .

[0056] By etching a recessed portion on the surface of the proof mass on one side of the torsion beam, a mass difference between the two proof masses is achieved. For example, by etching a recessed portion 3221 on the upper surface of the second proof mass 322 (i.e., the side facing away from the electrode plate), the mass of the second proof mass 322 is reduced to that of the first proof mass 321, allowing the first proof mass 321 to serve as both a proof mass and a driving mass. Alternatively, by etching a recessed portion on the upper surface of the first proof mass 321, the mass of the first proof mass 321 is reduced to that of the second proof mass 322, allowing the second proof mass 322 to serve as both a proof mass and a driving mass. When an acceleration signal is applied in the Z-axis direction, the driving mass moves out of plane via the torsion beam.

[0057] The recessed portion 3221 includes a plurality of uniform shallow grooves, the thickness of which is less than the thickness of the detection mass block. The cross-sectional shape of the recess is not limited and can be quadrilateral, square, circle, ellipse, triangle, etc., or one or more.

[0058] In a preferred embodiment, see Figure 3 、 Figure 4 As shown, Figure 4 The movable structure layer 300 further includes a buffer component 330 and a protrusion 340 .

[0059] Multiple buffer components 330 are arranged around the periphery of the proof mass, acting as in-plane stops to limit the proof mass's in-plane motion (XY plane). Multiple protrusions 340 are positioned on the outer frame, on the opposing surface of the proof mass and substrate 100. Without metal electrodes beneath them, these protrusions act as out-of-plane stops to limit the proof mass's out-of-plane motion (Z axis). By providing corresponding stop structures in all three directions (X, Y, and Z), the device's overload resistance and reliability are enhanced.

[0060] In a preferred embodiment, see Figure 5 The buffer component 330 includes a dummy beam and a bonding area with the substrate ( Figure 5 The dummy beams (shown in black in the middle) consist of an L-shaped beam and a T-shaped beam. The T-shaped beam is connected to one side of the proof mass, while the L-shaped beam and T-shaped beam are connected to the buffer component. The dummy beams on the proof mass and the buffer component are electrically connected to the same potential and nested with equal spacing. The short ends of the L-shaped and T-shaped beams are nested and constrained to form a set of limit units, acting as a stop for the in-plane motion of the proof mass.

[0061] See Figure 5 As shown, an L-shaped beam 115 is connected to one side of the buffer component. a , 115 b , and T-beam 116 a , 116 b , a T-beam 117 is connected to the outer corner of the detection mass block side a , 117 b , L-beam 115 a With T-beam 116 a , 117 a Nested together, forming a set of limit units, as the stop structure in the X direction, L-shaped beam 115 b With T-beam 116 b , 117 b Nested together, they form a set of limit units that act as a stop in the Y direction. These two sets of limit units operate in a variable-area manner in the Z direction, generating sliding film damping that helps reduce thermal noise. They also provide a limit function in the interference direction, providing overload protection and improving the overall reliability and overload resistance of the device.

[0062] In a preferred embodiment, there are four buffer components 330 , which are respectively disposed at the four corners of the detection mass block.

[0063] In a preferred embodiment, damping holes are etched on the periphery of the detection mass. The damping holes are set on the outer frame of the detection mass, which does not occupy the area facing the detection mass and the capacitor plate, thereby increasing the plate capacitance and further improving the overall detection sensitivity.

[0064] In a preferred embodiment, see Figure 3 As shown, a damping groove 323 is etched on the periphery of the detection mass. A plurality of damping holes are connected to form a damping groove to reduce mechanical thermal damping.

[0065] Damping holes or damping grooves can also be etched around the connection between the detection mass block and the torsion beam to release the thermal stress generated during bonding.

[0066] Furthermore, a step is etched on the surface of the proof mass facing the substrate 100. The step at the center serves as a bonding anchor point with the substrate 100. The step height is preferably 2-3 μm. The step, recess, and protrusion can be pre-etched multiple times on the proof mass using a double-sided photolithography process.

[0067] In one embodiment, the substrate 100 and the proof mass are both made of silicon material, ensuring that the thermal expansion coefficients of the two are the same, thereby solving the thermal adaptation problem in high and low temperature environments.

[0068] In a preferred embodiment, the electrode layer adopts a five-electrode structure. Figure 6 As shown, Figure 6 Figure 2 shows a schematic diagram of a five-electrode structure, where the electrode layer includes a differential forcing capacitor plate 210 and a differential detection capacitor plate 220. The differential forcing capacitor plate 210 includes a positive forcing capacitor plate and a negative forcing capacitor plate, which are respectively disposed below a first detection mass block 321 and a second detection mass block 322. This means that each of the first detection mass block 321 and the second detection mass block 322 corresponds to a corresponding forcing capacitor plate, and the positive and negative forcing capacitor plates are symmetrical relative to the torsion beam 310. The differential detection capacitor plates 220 include a positive detection capacitor plate and a negative detection capacitor plate, which are respectively disposed below the first detection mass 321 and the second detection mass 322. That is, one detection capacitor plate corresponds to each of the first detection mass 321 and the second detection mass 322, and the positive detection capacitor plates and the negative detection capacitor plates are symmetrical with respect to the torsion beam 310. The capacitor plates located on the same side of the torsion beam have the same polarity. That is, the positive force capacitor plate and the positive detection capacitor plate are located on the same side of the torsion beam, and the negative force capacitor plate and the negative detection capacitor plate are located on the same side of the torsion beam.

[0069] The detection capacitor plate and the force capacitor plate respectively face the detection mass block above to form the corresponding detection capacitor and force capacitor. By reasonably adjusting the area distribution of the detection electrode plate and the force electrode plate, the design requirements of the sensitivity index and the closed-loop range index are achieved.

[0070] Furthermore, the differential forcing capacitor plate 210 is located on the outside, and the differential detection capacitor plate 220 is located on the inside, that is, the positive detection capacitor plate and the negative detection capacitor plate are close to the torsion beam, and the positive forcing capacitor plate and the negative forcing capacitor plate are away from the torsion beam. In other words, on the substrate 100, the order of the capacitor plates arranged in sequence is positive forcing capacitor plate, positive detection capacitor plate, negative detection capacitor plate, negative forcing capacitor plate, or negative forcing capacitor plate, negative detection capacitor plate, positive detection capacitor plate, positive forcing capacitor plate.

[0071] In a preferred embodiment, the electrode layer adopts a three-electrode structure. Figure 7 As shown, Figure 7The figure shows a schematic diagram of a three-electrode structure, in which the electrode layer includes a first capacitor plate 230 and a second capacitor plate 240. The first capacitor plate 230 and the second capacitor plate 240 are respectively arranged below the first detection mass block 321 and the second detection mass block 322, that is, the first detection mass block 321 and the second detection mass block 322 each correspond to a capacitor plate. The polarity of the first capacitor plate and the second capacitor plate are opposite, and they are symmetrical relative to the torsion beam. Compared with the five-electrode structure, the force electrode and the detection electrode in this embodiment are no longer independent, but are shared with each other, that is, the positive force capacitor plate is also the positive detection capacitor plate, and the negative force capacitor plate is also the negative detection capacitor plate, which meets the adaptability of the ASIC chip. The metal electrode is prepared by MEMS deposition process or sputtering process, and the use of metal aluminum can greatly reduce production costs.

[0072] The accelerometer of the present invention works as follows: when an external acceleration signal is input, a differential structure is formed between the positive and negative detection capacitor plates of the electrode layer, converting the measured accelerometer signal into a capacitance signal. This signal is then analyzed by a back-end detection circuit (such as the C2V module within the ASIC chip). A feedback voltage is applied to the force electrode through a closed-loop control system. At this time, the inertial force is replaced by an electrostatic force, causing the detection mass block to return to its initial position. The voltage is used as the output signal to achieve measurement of the acceleration signal.

[0073] See Figure 6 、 Figure 8 As shown, Figure 8 This is a schematic diagram of acceleration measurement using a five-electrode structure. Figure 6 The capacitor plate on the right is positive, and the capacitor plate on the left is negative. The detection mass moves out of the torsion beam. When the tilt angle of the right detection mass is θ When , the tilt angle of the left detection mass block is - θ , then the size of the positive detection capacitor is:

[0074] ;

[0075] in, Indicates the size of the positive electrode detection capacitor, is the dielectric constant of vacuum, 、 To detect the shortest and longest distances between the electrode and the torsion beam, 、 are the upper and lower edges of the positive detection capacitor in the XY plane, d is the distance between the detection mass and the metal electrode (detection capacitor plate), represents the integral about the X axis, represents the integration on the Y axis, Indicates the change in the distance between the detection mass and the capacitor plates.

[0076] The size of the positive electrode capacitor is:

[0077] ;

[0078] Where, Indicates the size of the positive electrode capacitor. is the dielectric constant of vacuum, 、 is the shortest and longest distance between the force electrode and the torsion beam, , are the upper and lower edges of the positive electrode capacitor in the XY plane, d To detect the distance between the mass block and the metal electrode, represents the integral about the X axis, represents the integration on the Y axis, Indicates the change in the distance between the detection mass and the capacitor plates.

[0079] Then we have:

[0080] ;

[0081] in, represents the horizontal distance from the torsion beam to the capacitor plate, is the tilt angle of the right detection mass block.

[0082] Normally, the flat plate capacitor is symmetrical about the X axis, so we can get , the above formula is simplified to:

[0083] ;

[0084] ;

[0085] Since the mass blocks on the left and right sides are rigidly connected, when the tilt angle of the right detection mass block is When , the tilt angle of the left detection mass block is , so the negative electrode detection capacitor size can be obtained as:

[0086] ;

[0087] in, Indicates the size of the negative electrode detection capacitor, is the dielectric constant of vacuum, 、 To detect the shortest and longest distances between the electrode and the torsion beam, is the upper edge of the capacitor plate in the XY plane, is the tilt angle of the right detection mass block, dTo detect the distance between the mass block and the metal electrode, represents the horizontal distance from the torsion beam to the capacitor plate, Indicates integration about the Y axis.

[0088] The negative electrode capacitance is:

[0089] ;

[0090] Where, Indicates the size of the negative electrode capacitance. is the dielectric constant of vacuum, 、 is the shortest and longest distance between the force electrode and the torsion beam, is the upper edge of the capacitor plate in the XY plane, is the tilt angle of the right detection mass block, d To detect the distance between the mass block and the metal electrode, represents the horizontal distance from the torsion beam to the capacitor plate, Indicates integration about the Y axis.

[0091] See Figure 7 、 Figure 9 , Figure 9 The figure shows the schematic diagram of acceleration measurement of the three-electrode structure. The detection mass block moves out of the torsion beam. When the tilt angle of the right mass block is When , the inclination angle of the left mass block is ,definition Figure 7 The capacitor plate on the right side is the positive electrode, and the capacitor electrode on the left side is the negative electrode. According to the derivation of the above five-capacitor scheme, the force capacitor and the detection capacitor can be directly calculated.

[0092] The positive electrode detection capacitor / positive electrode force capacitor size is:

[0093] ;

[0094] in, Indicates the size of the positive electrode capacitor. Indicates the size of the positive electrode detection capacitor, 、 They are respectively the closest and farthest distances between the positive detection capacitor plate / the positive force capacitor plate and the torsion beam 310.

[0095] Since the mass blocks on the left and right sides are rigidly connected, the inclination angle of the mass block on the right is , the inclination angle of the left mass block is , so the negative electrode detection capacitance / negative electrode force capacitance can be obtained as:

[0096] ;

[0097] Where, Indicates the size of the negative electrode capacitance. Indicates the size of the negative electrode detection capacitor, 、 are the closest and farthest distances between the positive detection capacitor plate / positive force capacitor plate and the torsion beam, respectively. Compared with the parameters in the five-electrode structure, Therefore, the sensitivity and closed-loop feedback capability of the three-electrode structure are better than those of the five-electrode structure.

[0098] In this application, the vertical distance between the detection mass block and the detection electrode plate is d It is much smaller than the lateral distance between the detection electrode plate and the torsion beam or Therefore, the maximum tilt angle is:

[0099] ;

[0100] Where, represents the maximum tilt angle of the proof mass, is the distance between the detection mass block and the detection electrode plate, In order to detect the lateral distance between the electrode plate and the torsion beam, and due to the attraction effect, the working range of the seesaw structure is usually much smaller than , so the actual displacement can be defined as:

[0101] ;

[0102] Where, represents the horizontal distance from the torsion beam to the capacitor plate, is the tilt angle of the detection mass, d is the distance between the detection mass block and the metal electrode.

[0103] When the accelerometer's swing angle is very small, the detection mass and the detection electrode can be approximately equivalent to a flat plate capacitor. Therefore, the flat plate capacitor calculation method can be used to calculate the capacitance value, which is expressed as:

[0104] ;

[0105] Where, represents the equivalent flat plate capacitor, is the dielectric constant of vacuum, is the relative dielectric constant, is the area between the detection mass block and the detection electrode plate, d is the distance between the detection mass block and the detection electrode plate. When there is external acceleration, the detection mass block will twist, the capacitance on one side will increase, and the capacitance on the other side will decrease. Therefore, the change in differential capacitance is:

[0106] ;

[0107] in, is the differential capacitance, is the dielectric constant of vacuum, is the relative dielectric constant, is the area between the mass block and the metal electrode, d To detect the distance between the mass block and the metal electrode, represents the displacement change, 、 They respectively represent the changes at both ends of the differential detection capacitor plates.

[0108] when When:

[0109] ;

[0110] ;

[0111] ;

[0112] in, Differential capacitance, represents the equivalent flat plate capacitor, is the dielectric constant of vacuum, is the relative dielectric constant, is the area between the mass block and the metal electrode, d To detect the distance between the mass block and the metal electrode, represents the rotational elastic modulus, is the torque coefficient, represents the moment of inertia, L Indicates the horizontal distance between the center of the detection capacitor plate and the torsion beam, Indicates acceleration, represents the displacement change, from which we can get:

[0113] ;

[0114] Where, represents acceleration, represents the rotational elastic modulus, is the torque coefficient, represents the moment of inertia, To detect the tilt angle of the mass block, d To detect the distance between the mass block and the metal electrode, represents the rotational elastic modulus, is the torque coefficient, is the differential capacitance, As basic capacitor, L In order to detect the horizontal distance between the center of the capacitor plate and the torsion beam, the magnitude of the external acceleration can be calculated by measuring the change in capacitance.

[0115] For the five-electrode structure, the sensitivity can be expressed as:

[0116] ;

[0117] in, represents the sensitivity of the five-electrode structure accelerometer, is the differential capacitance, is the torque coefficient, represents the moment of inertia, d To detect the distance between the mass block and the metal electrode, is the acceleration, To detect the capacitance.

[0118] For the three-electrode structure, the sensitivity can be expressed as:

[0119] ;

[0120] in, represents the sensitivity of the three-electrode structure accelerometer, is the differential capacitance, is the torque coefficient, represents the moment of inertia, d To detect the distance between the mass block and the metal electrode, is the acceleration, is the size of the boost capacitor, To detect the capacitance.

[0121] Therefore, when the chip size and process processing capability are limited, the detection electrode and the force electrode can be used together, that is, a three-electrode structure can be adopted to improve sensitivity.

[0122] In one embodiment, an insulating layer is deposited on the surface of the substrate 100 to isolate the electrode layer 200 from the substrate 100 to shield parasitic capacitance. The insulating layer can be made of silicon nitride or silicon dioxide.

[0123] In one embodiment, the Z-axis MEMS closed-loop accelerometer assembly is vacuum packaged and used as a standalone accelerometer, with a certain degree of vacuum being used to reduce mechanical thermal noise.

[0124] The accelerometer of this invention does not have damping holes in the proof mass directly opposite the metal electrode to ensure high sensitivity. However, squeeze-film damping is provided between the proof mass and the metal electrode, which increases thermal noise. A major parameter affecting mechanical thermal noise is the damping coefficient. Therefore, by using vacuum packaging, the effective gas viscosity coefficient within the chamber can be changed, further reducing the damping coefficient and achieving overall low noise.

[0125] The calculation formula for the thermomechanical noise of MEMS accelerometer is:

[0126] ;

[0127] Where, represents the thermomechanical noise, is the Boltzmann constant, is the thermodynamic temperature, is the damping coefficient, In the present invention, damping holes are provided on the outer frame of the mass block, and the damping comb teeth are synovial damping in the direction of motion. Compared with squeeze film damping, the damping coefficient of synovial damping is much smaller, which is beneficial to reducing mechanical thermal noise.

[0128] The accelerometer of this invention utilizes a closed-loop structure to mitigate the nonlinearity issues inherent in plate capacitors. A closed-loop control system also mitigates oscillations caused by vacuum packaging. The invention boasts a compact overall structure, high sensitivity, and a closed-loop structure, which helps mitigate overall nonlinearity.

[0129] The second aspect of the present invention provides a Z-axis MEMS closed-loop accelerometer used in combination with the Z-axis MEMS closed-loop accelerometer assembly of Example 1. Figure 10 The top view of the Z-axis MEMS closed-loop accelerometer shown in FIG. 1 includes two centrosymmetric Z-axis MEMS closed-loop accelerometer assemblies. Each accelerometer assembly comprises, from bottom to top, a substrate 100, an electrode layer 200, and a movable structural layer 300. The electrode layer 200 includes at least one pair of differential capacitor plates disposed on the substrate 100. The movable structural layer 300 includes a proof mass 320 and a torsion beam 310, disposed above the substrate 100. One end of the torsion beam 310 is connected to the proof mass 320, and the other end is connected to the substrate 100.

[0130] Among them, the detection mass block 320 is divided into a first detection mass block 321 and a second detection mass block 322 symmetrical relative to the torsion beam 310. The mass of the first detection mass block 321 is greater than the mass of the second detection mass block 322, so that the first detection mass block 321 can be used as both a detection mass block and a driving mass block.

[0131] In a preferred embodiment, the electrode layer adopts a five-electrode structure, including a differential force capacitor plate and a differential detection capacitor plate. The differential force capacitor plate includes a positive force capacitor plate and a negative force capacitor plate, which are respectively arranged below the first detection mass block 321 and the second detection mass block 322 and are symmetrical relative to the torsion beam 310; the differential detection capacitor plate includes a positive detection capacitor plate and a negative detection capacitor plate, which are respectively arranged below the first detection mass block 321 and the second detection mass block 322 and are symmetrical relative to the torsion beam 310, and the capacitor polarity on the same side of the torsion beam is the same. The positive force capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative force capacitor plate, and the positive detection capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative detection capacitor plate.

[0132] In a preferred embodiment, the electrode layer adopts a three-electrode structure, comprising a first capacitor plate and a second capacitor plate, which are respectively disposed below the first proof mass 321 and the second proof mass 322. The first capacitor plate and the second capacitor plate have opposite polarities and are symmetrical with respect to the torsion beam 310. The first capacitor plate and the second capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies are connected.

[0133] The functions of each part on the three-electrode structure mass block are the same as those on the five-electrode structure mass block. The only difference is the electrode distribution. In the three-electrode structure, the force electrode and the detection electrode are no longer independent of each other, but shared with each other. The positive detection electrode plate is also the positive force electrode plate, and the negative detection electrode is also the negative force electrode plate. When the force electrode and the detection electrode are shared, the detection capacitance or the force capacitance can be increased, and at the same time, the three-electrode closed-loop ASIC is adapted to further improve the overall sensitivity and closed-loop feedback capability of the device.

[0134] In one embodiment, a recess is etched on one side surface of the second detection mass block, so that the mass of the first detection mass block is greater than the mass of the second detection mass block.

[0135] In one embodiment, damping holes or damping grooves are etched on the outer circumference of the proof mass.

[0136] In one embodiment, the movable structural layer further includes a plurality of buffer components and a plurality of bosses; the buffer components are arranged on the periphery of the detection mass block for limiting in-plane motion; the bosses are arranged on the opposite surfaces of the detection mass block and the substrate for limiting out-of-plane motion.

[0137] In one embodiment, an insulating layer is deposited on the surface of the substrate, and the insulating layer is used to isolate the electrode layer from the substrate.

[0138] In one embodiment, the Z-axis MEMS closed-loop accelerometer is vacuum packaged.

[0139] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A Z-axis MEMS closed-loop accelerometer assembly, characterized in that: include: substrate; an electrode layer comprising at least a pair of differential capacitor plates disposed on the substrate; a movable structural layer, disposed above the substrate, comprising a detection mass and a torsion beam, wherein the detection mass is bonded to the substrate via the torsion beam; when an acceleration signal is generated in the Z-axis direction, the detection mass moves out-of-plane relative to the torsion beam to form a differential detection signal on the at least one pair of differential capacitor plates; The detection mass block is divided into a first detection mass block and a second detection mass block that are symmetrical relative to the torsion beam, and the mass of the first detection mass block is greater than the mass of the second detection mass block, so that the first detection mass block can be used as both a detection mass block and a driving mass block; A recessed portion is etched on a surface of the second detection mass block on a side facing away from the substrate, so that the mass of the first detection mass block is greater than the mass of the second detection mass block; the recessed portion includes a plurality of uniform shallow grooves, and the thickness of the shallow grooves is less than the thickness of the detection mass block; The outer periphery of the detection mass block is etched with a damping hole or a damping groove, and the damping hole or the damping groove does not occupy the detection mass block. The area facing the differential capacitor plates.

2. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, wherein: The electrode layer includes a differential force capacitor plate and a differential detection capacitor plate; The differential forcing capacitor plate includes a positive forcing capacitor plate and a negative forcing capacitor plate, the positive forcing capacitor plate and the negative forcing capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical relative to the torsion beam; The differential detection capacitor plate includes a positive detection capacitor plate and a negative detection capacitor plate, and the positive detection capacitor plate and the negative detection capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical with respect to the torsion beam; The capacitor plates located on the same side of the torsion beam have the same polarity.

3. The Z-axis MEMS closed-loop accelerometer assembly according to claim 2, wherein: The positive detection capacitor plate and the negative detection capacitor plate are close to the torsion beam, and the positive force capacitor plate and the negative force capacitor plate are far away from the torsion beam.

4. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, wherein: The movable structural layer further includes a plurality of buffer components and a plurality of convex columns; The buffer component is arranged on the outer periphery of the detection mass block and is used for limiting the in-plane motion; The convex column is arranged on the opposite surface of the detection mass block and the substrate, and is used for limiting out-of-plane motion.

5. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, wherein: An insulating layer is deposited on the surface of the substrate, and the insulating layer is used to isolate the electrode layer from the substrate.

6. A Z-axis MEMS closed-loop accelerometer, characterized in that: It comprises two Z-axis MEMS closed-loop accelerometer assemblies according to any one of claims 1 to 5, wherein the two Z-axis MEMS closed-loop accelerometer assemblies are centrally symmetrical.

7. The Z-axis MEMS closed-loop accelerometer according to claim 6, characterized in that: The electrode layer includes a differential force capacitor plate and a differential detection capacitor plate; The differential forcing capacitor plate includes a positive forcing capacitor plate and a negative forcing capacitor plate, the positive forcing capacitor plate and the negative forcing capacitor plate being respectively disposed below the first detection mass block and the second detection mass block and symmetrically relative to the torsion beam; The differential detection capacitor plate includes a positive detection capacitor plate and a negative detection capacitor plate, the positive detection capacitor plate and the negative detection capacitor plate are respectively arranged below the first detection mass block and the second detection mass block, and are symmetrical with respect to the torsion beam; The capacitor plates on the same side of the torsion beam have the same polarity; The positive forcing capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative forcing capacitor plate, and the positive detection capacitor plate in different Z-axis MEMS closed-loop accelerometer assemblies is connected to the negative detection capacitor plate.

8. The Z-axis MEMS closed-loop accelerometer according to any one of claims 6 to 7, characterized in that: The Z-axis MEMS closed-loop accelerometer is vacuum packaged.

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