Z-axis MEMS closed-loop accelerometer assembly and accelerometer

Abstract

The invention discloses a Z-axis MEMS closed-loop accelerometer assembly and an accelerometer, and relates to the technical field of MEMS accelerometers. The Z-axis MEMS closed-loop accelerometer adopts a closed-loop design, the structure comprises the substrate, the electrode layer and the movable structure layer, the detection mass blocks in the movable structure layer are symmetrically designed and manufactured to be poor in quality, and the detection mass blocks with large mass are used as the detection mass blocks and the driving mass blocks at the same time; according to the teeterboard structure, the occupied area of a driving mass block independently arranged in a traditional teeterboard structure is omitted, the space occupied by a movable structure layer is remarkably reduced, the effective detection area is increased, and therefore the detection sensitivity is improved.

Description

Technical Field

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

[0002] Micro - electro - mechanical systems (MEMS), as a miniaturized integrated system integrating micro - mechanical structures and micro - electronic technologies, have become one of the core technologies in the inertial sensing field due to their advantages of small size, low power consumption, and mass production. Among them, MEMS inertial sensors based on the capacitance detection principle play an important role in industrial control, automotive electronics, aerospace, and consumer electronics fields due to their high sensitivity and low - noise characteristics. As a typical representative, the capacitive accelerometer realizes signal conversion by detecting the capacitance change caused by acceleration, and its structural design and process optimization directly affect the performance and reliability of the device.

[0003] Currently, MEMS capacitive accelerometers mainly adopt three forms: comb - tooth structure, sandwich structure, and seesaw structure. The comb - tooth structure realizes in - plane (X / Y - axis) acceleration detection by changing the area or the distance, but its out - of - plane (Z - axis) detection ability is limited; although the sandwich structure has high signal - to - noise ratio and high precision, the complex multi - layer process leads to high manufacturing cost and low yield, making it difficult to meet the requirements of large - scale applications; the seesaw structure has strong process compatibility and has become the mainstream solution for Z - axis detection.

[0004] The seesaw structure supports a movable detection mass block through a torsion beam, and the change in the distance between the movable detection mass block and the fixed electrode forms a differential capacitance signal, and the acceleration detection is completed through the backend circuit. However, the seesaw structure requires an additional driving mass block, which is suspended on one side of the detection mass block, resulting in an overall too large chip area, and because of too many damping holes, its detection area becomes smaller and the sensitivity decreases.

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

[0006] The present invention provides a Z - axis MEMS closed - loop accelerometer component and an accelerometer to solve the problem that the existing Z - axis accelerometer has a reduced sensitivity and an overall too large area due to the driving mass block and too many damping holes occupying the detection area.

[0007] The present invention is realized through the following technical solutions: In the first aspect of the present invention, a Z - axis MEMS closed - loop accelerometer component is provided, including: A substrate; An electrode layer, including at least a pair of differential capacitance plates disposed on the substrate; A movable structure layer is disposed above the substrate and the electrode layer, and includes a detection mass and a torsion beam. The detection mass is bonded to the substrate through the torsion beam. When an acceleration signal is generated in the Z-axis direction, the detection mass moves out of the plane relative to the torsion beam to form a differential detection signal on the at least one pair of differential capacitor plates. Wherein, the detection mass is divided into a first detection mass and a second detection mass that are symmetric with respect to the torsion beam, and the mass of the first detection mass is greater than the mass of the second detection mass, so that the first detection mass is used as both a detection mass and a drive mass at the same time.

[0008] The Z-axis accelerometer component of the present invention can be used independently or in combination. By manufacturing the mass difference of the symmetric detection masses and using the larger mass as both the detection mass and the drive mass at the same time, the area occupied by the independently provided drive mass in the traditional seesaw structure is saved, the space occupied by the movable structure layer is significantly reduced, and the effective detection area is increased, improving the detection sensitivity. The symmetric design of the movable structure layer avoids the redundant layout of the single-sided mass while realizing the differential detection function, thereby reducing the overall area of the chip and meeting the requirements of high-density integration.

[0009] Preferably, the electrode layer includes differential force-applying capacitor plates and differential detection capacitor plates; The differential force-applying capacitor plates include a positive force-applying capacitor plate and a negative force-applying capacitor plate. The positive force-applying capacitor plate and the negative force-applying capacitor plate are respectively disposed below the first detection mass and the second detection mass and are symmetric with respect to the torsion beam; The differential detection capacitor plates include a positive detection capacitor plate and a negative detection capacitor plate. The positive detection capacitor plate and the negative detection capacitor plate are respectively disposed below the first detection mass and the second detection mass and are symmetric with respect to the torsion beam; The polarities of the capacitor plates on the same side of the torsion beam are the same.

[0010] Preferably, the positive detection capacitor plate and the negative detection capacitor plate are close to the torsion beam, and the positive force-applying capacitor plate and the negative force-applying capacitor plate are far from the torsion beam.

[0011] Preferably, a recess is etched on the surface of the second detection mass facing away from the substrate, so that the mass of the first detection mass is greater than the mass of the second detection mass.

[0012] Preferably, damping holes or damping grooves are etched on the outer periphery of the detection mass.

[0013] Preferably, the movable structure layer further includes a plurality of buffer components and a plurality of convex columns; The buffer components are arranged on the outer periphery of the detection mass for in-plane movement limiting; The convex columns are arranged on the opposite surfaces of the detection mass and the substrate for out-of-plane movement limiting.

[0014] 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.

[0015] In a second aspect of the present invention, a Z-axis MEMS closed-loop accelerometer is provided, which includes two Z-axis MEMS closed-loop accelerometer components as described in any one of the first aspects of the present invention, and the two Z-axis MEMS closed-loop accelerometer components are centrosymmetric.

[0016] Preferably, the electrode layer includes a differential force-applying capacitor plate and a differential detection capacitor plate; The differential force-applying capacitor plate includes a positive force-applying capacitor plate and a negative force-applying capacitor plate. The positive force-applying capacitor plate and the negative force-applying capacitor plate are respectively arranged below the first detection mass and the second detection mass and are symmetric with respect 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 and the second detection mass and are symmetric with respect to the torsion beam; The polarities of the capacitor plates on the same side of the torsion beam are the same; The positive force-applying capacitor plate and the negative force-applying capacitor plate in different Z-axis MEMS closed-loop accelerometer components are connected, and the positive detection capacitor plate and the negative detection capacitor plate in different Z-axis MEMS closed-loop accelerometer components are connected.

[0017] Preferably, the Z-axis MEMS closed-loop accelerometer is vacuum packaged.

[0018] 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 provided driving mass block in the traditional seesaw structure is eliminated, significantly reducing the space occupied by the movable structure layer, increasing the effective detection area, and improving the detection sensitivity. Combining the design of symmetrically distributed first and second detection mass blocks, while realizing the differential detection function, it avoids the redundant layout of unilateral mass blocks, significantly reducing the overall chip area and meeting the requirements of high-density integration. In addition, the closed-loop control allows the device to work in a vacuum packaging environment. Through the closed-loop control system, the oscillation phenomenon caused by the vacuum packaging can be suppressed, achieving low noise and high sensitivity, and meeting the requirements of inertial navigation and vibration monitoring scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings. In the drawings: Figure 1 is a cross-sectional schematic view of a Z-axis MEMS closed-loop accelerometer assembly according to an embodiment of the present invention; Figure 2 is a top view of a movable structure layer according to an embodiment of the present invention; Figure 3 is a top view of a detection mass block according to an embodiment of the present invention; Figure 4 is a cross-sectional view of a movable structure layer according to an embodiment of the present invention; Figure 5 is a structural schematic view of a buffer component according to an embodiment of the present invention; Figure 6 is a schematic diagram of a five-electrode structure according to an embodiment of the present invention; Figure 7 is a schematic diagram of a three-electrode structure according to an embodiment of the present invention; Figure 8 is a measurement schematic diagram of a five-electrode structure accelerometer according to an embodiment of the present invention; Figure 9 is a measurement schematic diagram of a three-electrode structure accelerometer according to an embodiment of the present invention; Figure 10 is a top view of a Z-axis MEMS closed-loop accelerometer according to an embodiment of the present invention.

[0020] The drawings and the reference numerals are described as follows: 100 - Substrate, 101 - Bonding anchor, 200 - Electrode layer, 210 - Differential force - adding capacitor plate, 220 - Differential detection capacitor plate, 230 - First capacitor plate, 240 - Second capacitor plate, 300 - Movable structure layer, 310 - Torsion beam, 320 - Detection mass, 321 - First detection mass, 322 - Second detection mass, 3221 - Concave portion, 323 - Damping groove, 330 - Buffer member, 340 - Stud, 115a, 115b - L - shaped beam, 116a, 116b, 117a, 117b - T - shaped beam. Detailed implementation manners

[0021] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to embodiments and the accompanying drawings. The illustrative 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.

[0022] 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 inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily be limited to other steps or units inherent to the process, method, system, product or device.

[0023] The terms used in the various embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the various embodiments of the present invention. As used herein, the singular forms are also intended to include the plural forms unless the context clearly indicates otherwise. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the various embodiments of the present invention belong. The terms (such as those defined in a commonly used dictionary) will be interpreted as having the same meaning as the contextual meaning in the relevant technical field and will not be interpreted as having an idealized meaning or being overly formal unless clearly defined in the various embodiments of the present invention.

[0024] In the first aspect of the present invention, a Z - axis MEMS closed - loop accelerometer assembly is provided, which can be used as an independent Z - axis accelerometer.

[0025] Please refer to Figure 1Schematic cross-sectional view of the Z-axis MEMS closed-loop accelerometer assembly shown, which includes a substrate 100, an electrode layer 200, and a movable structure layer 300 from bottom to top. Among them, the electrode layer 200 adopts a differential capacitor plate structure and is arranged on the substrate 100 as a detection electrode. The electrode layer 200 includes at least a pair of differential capacitor plates. A pair of differential capacitor plates means a pair of positive and negative capacitor plates. When measuring the Z-direction acceleration signal, a differential capacitance signal is formed on the positive and negative capacitor plates, and the Z-axis acceleration can be calculated by the backend detection circuit according to the differential capacitance signal.

[0026] The movable structure layer 300 is arranged above the substrate and includes a torsion beam 310 and a detection mass 320. The detection 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 detection mass 320 is bonded to the substrate 100 through the torsion beam 310. When an acceleration signal is generated in the Z-axis direction, the detection mass 320 moves out of the plane with the torsion beam 310, forming a distance difference with at least a pair of differential capacitor plates in the electrode layer, and a differential detection signal is formed on at least a pair of differential capacitor plates.

[0027] Please refer to Figure 2 The top view of the movable structure layer shown. The detection mass 320 is divided into a first detection mass 321 and a second detection mass 322 on the left and right sides with the connected torsion beam 310 as the boundary. The first detection mass 321 and the second detection mass 322 are symmetric with respect to the torsion beam 310, and there is a mass difference between the first detection mass and the second detection mass. The positions of the first detection mass 321 and the second detection mass 322 can be interchanged, that is, the mass of the first detection mass is greater than the mass of the second detection mass, or the mass of the second detection mass is greater than the mass of the first detection mass. The side with the larger mass is used as both the detection mass and the driving mass at the same time. In the following description, the first detection mass 321 and the second detection mass 322 are collectively referred to as the detection mass. By sharing the detection mass and the driving mass, the chip size is reduced.

[0028] In a preferred embodiment, refer to Figure 8 、 Figure 9 As shown, a bonding anchor 101 is set at the center position of the substrate 100. The two ends of the torsion beam 310 are respectively connected to the bonding anchor 101 and the center of the movable structure layer. The bonding anchor is set at the center position, no longer on both sides of the central axis, and there is only one, reducing the bonding area, thereby reducing the thermal stress generated during bonding, and arranging the movable structure layer directly above the substrate.

[0029] The torsion beam 310 can adopt a double-beam structure to increase the spring stiffness and change the resonant frequency.

[0030] In the preferred embodiment, refer toFigure 3 The top view of the detection mass block shown, a recess 3221 is etched on one side surface of the second detection mass block 322.

[0031] By etching a recess on the surface of the detection mass block on one side of the torsion beam, a mass difference exists between the inspection mass blocks on both sides. For example, a recess 3221 is etched on the upper surface of the second detection mass block 322 (i.e., the side facing away from the electrode plate), so that the mass of the second detection mass block 322 is less than the mass of the first detection mass block 321. The first detection mass block 321 serves as both the detection mass block and the drive mass block at the same time; or a recess is etched on the upper surface of the first detection mass block 321, so that the mass of the first detection mass block 321 is less than the mass of the second detection mass block 322. The second detection mass block 322 serves as both the detection mass block and the drive mass block at the same time. When there is an acceleration signal in the Z-axis direction, the drive mass block moves out-of-plane along with the torsion beam.

[0032] The recess 3221 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 cross-sectional shape of the recess is not limited, and can be a quadrilateral, a square, a circle, an ellipse, a triangle, etc., and can be one or more.

[0033] In a preferred embodiment, please refer to Figure 3 、 Figure 4 shown, Figure 4 Shown is a cross-sectional view of the movable structure layer. The movable structure layer 300 further includes a buffer member 330 and a convex post 340.

[0034] A plurality of buffer members 330 are arranged on the outer periphery of the detection mass block, serving as an in-plane stop structure for limiting the in-plane (XY plane) movement of the detection mass block. A plurality of convex posts 340 are arranged on the opposite surfaces of the detection mass block and the substrate 100, and are located in the outer frame. There is no metal electrode under the convex posts, serving as an out-of-plane stop structure for limiting the out-of-plane (Z-axis) movement of the detection mass block. By simultaneously setting corresponding stop structures in the X / Y / Z three directions, the anti-overload ability and reliability of the device are improved.

[0035] In a preferred embodiment, refer to Figure 5 the schematic structural diagram of the buffer member shown, the buffer member 330 includes a dummy beam and a bonding area with the substrate ( Figure 5 shown as the black area in), the dummy beam includes an L-shaped beam and a T-shaped beam. The T-shaped beam is connected to one side of the detection mass block, and the L-shaped beam and the T-shaped beam are connected to one side of the buffer member. The dummy beams on the detection mass block and the buffer member are set to the same potential when electrically connected, and they are nested with each other and have equal spacing. The short ends of the L-shaped beam and the T-shaped beam are nested and constrained with each other, forming a set of limiting units, serving as a stop structure for the in-plane movement of the detection mass block.

[0036] Please refer to Figure 5 as shown, an L-shaped beam 115 is connected to one side of the buffer component a 、115 b , and a T-shaped beam 116 a 、116 b , a T-shaped beam 117 is connected to the outer circumferential corner on the side of the detection mass a 、117 b , the L-shaped beam 115 a and the T-shaped beam 116 a 、117 a are nested with each other to form a set of limiting units, serving as a stop structure in the X direction. The L-shaped beam 115 b and the T-shaped beam 116 b 、117 b are nested with each other to form a set of limiting units, serving as a stop structure in the Y direction. These two sets of limiting units are in a similar variable area manner in the Z direction, generating synovial damping, which is beneficial to reducing thermal noise. At the same time, they have a limiting function in the interference direction, realizing overload protection and improving the overall reliability and overload resistance of the device.

[0037] In a preferred embodiment, there are four buffer components 330, which are respectively arranged at the four corners of the detection mass.

[0038] In a preferred embodiment, damping holes are etched on the outer periphery of the detection mass. The damping holes are arranged on the outer frame of the detection mass and do not occupy the facing area between the detection mass and the capacitor plates, thereby increasing the flat capacitor and further improving the overall detection sensitivity In a preferred embodiment, please refer to Figure 3 as shown, a damping groove 323 is etched on the outer periphery of the detection mass. Multiple damping holes are connected to form a damping groove to reduce mechanical thermal damping.

[0039] Damping holes or damping grooves can also be etched around the connection between the detection mass and the torsion beam to release the thermal stress generated during bonding.

[0040] Furthermore, steps are etched on the opposite surface of the detection mass and the substrate 100, and the step at the center position is used as a bonding anchor point with the substrate 100. Among them, the height of the step is preferably 2-3 um, and the steps, recesses and protrusions can be completed by multiple etching processes on the detection mass through double-sided lithography.

[0041] In one embodiment, the substrate 100 and the detection mass are both made of silicon material to ensure the same thermal expansion coefficient of the two, and solve the thermal adaptation problem in high and low temperature environments.

[0042] In a preferred embodiment, the electrode layer adopts a five-electrode structure. Please refer toFigure 6 As shown Figure 6 As shown is a schematic diagram of a five - electrode structure. The electrode layer includes differential force - adding capacitor plates 210 and differential detection capacitor plates 220. Among them, the differential force - adding capacitor plates 210 include a positive force - adding capacitor plate and a negative force - adding capacitor plate. The positive force - adding capacitor plate and the negative force - adding capacitor plate are respectively disposed below the first detection mass 321 and the second detection mass 322. That is, each of the first detection mass 321 and the second detection mass 322 corresponds to one force - adding capacitor plate, and the positive force - adding capacitor plate and the negative force - adding capacitor plate are symmetric with respect to the torsion beam 310. The differential detection capacitor plates 220 include a positive detection capacitor plate and a negative detection capacitor plate. The positive detection capacitor plate and the negative detection capacitor plate are respectively disposed below the first detection mass 321 and the second detection mass 322. That is, each of the first detection mass 321 and the second detection mass 322 corresponds to one detection capacitor plate, and the positive detection capacitor plate and the negative detection capacitor plate are symmetric with respect to the torsion beam 310. The polarities of the capacitor plates on the same side of the torsion beam are the same. That is, the positive force - adding capacitor plate and the positive detection capacitor plate are on the same side of the torsion beam, and the negative force - adding capacitor plate and the negative detection capacitor plate are on the same side of the torsion beam.

[0043] The detection capacitor plates and the force - adding capacitor plates respectively form corresponding detection capacitors and force - adding capacitors with the detection masses directly above them. By reasonably adjusting the area distribution of the detection electrode plates and the force - adding electrode plates, the design requirements of the sensitivity index and the closed - loop range index are achieved.

[0044] Furthermore, the differential force - adding capacitor plates 210 are located on the outside, and the differential detection capacitor plates 220 are 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 force - adding capacitor plate and the negative force - adding capacitor plate are far from the torsion beam. That is, on the substrate 100, the order of the capacitor plates arranged in sequence is the positive force - adding capacitor plate, the positive detection capacitor plate, the negative detection capacitor plate, the negative force - adding capacitor plate, or the negative force - adding capacitor plate, the negative detection capacitor plate, the positive detection capacitor plate, the positive force - adding capacitor plate.

[0045] In a preferred embodiment, the electrode layer adopts a three - electrode structure. Please refer to Figure 7 As shown Figure 7Shown is a schematic diagram of a three - electrode structure. 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 disposed below the first detection mass 321 and the second detection mass 322, that is, each of the first detection mass 321 and the second detection mass 322 corresponds to a capacitor plate. The polarities of the first capacitor plate and the second capacitor plate are opposite and symmetric with respect to the torsion beam. Compared with the five - electrode structure in this embodiment, the force - applying electrode and the detection electrode are no longer independent but share each other, that is, the positive - electrode force - applying capacitor plate is also the positive - electrode detection capacitor plate, and the negative - electrode force - applying capacitor plate is also the negative - electrode detection capacitor plate, meeting the adaptability of the ASIC chip. And the metal electrodes are prepared by MEMS deposition process or sputtering process. Using aluminum metal can greatly reduce the production cost.

[0046] The working principle of the accelerometer of the present invention is as follows: When there is an external acceleration signal input, a differential structure is formed between the positive and negative detection capacitor plates in the electrode layer, converting the measured accelerometer signal into a capacitance signal, and then analyzing it through a backend detection circuit (such as the C2V module inside the ASIC chip). A feedback voltage is applied to the force - applying electrode through a closed - loop control system. At this time, the inertial force is replaced by the electrostatic force, so that the detection mass returns to the initial position, and the voltage is used as the output signal to realize the measurement of the acceleration signal.

[0047] Please refer to Figure 6 、 Figure 8 shown in Figure 8 is a schematic diagram of acceleration measurement of a five - electrode structure. It is defined that Figure 6 the capacitor plate on the right side in θ is the positive electrode, and the capacitor plate on the left side is the negative electrode. The detection mass moves out - of - plane through the torsion beam. When the tilt angle of the right - hand detection mass is θ , the tilt angle of the left - hand detection mass is - ;

[0048] where represents the size of the positive - electrode detection capacitor, is the vacuum permittivity, 、 are the closest and farthest distances from the detection electrode to the torsion beam, 、 are the upper and lower edges of the positive - electrode detection capacitor in the XY plane, d is the distance between the detection mass and the metal electrode (detection capacitor plate), represents integration with respect to the X - axis, represents integration with respect to the Y - axis, represents the change in the distance between the detection mass and the capacitor plate.

[0049] The magnitude of the positive electrode boosting capacitor is: ; In the formula, represents the magnitude of the positive electrode boosting capacitor, is the vacuum permittivity, , are the closest and farthest distances from the boosting electrode to the torsion beam, , are the upper and lower side lines of the positive electrode boosting capacitor in the XY plane, d is the distance between the detection mass and the metal electrode, represents the integration with respect to the X-axis, represents the integration with respect to the Y-axis, represents the change in the distance between the detection mass and the capacitor plate.

[0050] Then there is: ;

[0051] Among them, represents the horizontal distance from the torsion beam to the capacitor plate, is the tilt angle of the right detection mass.

[0052] Under normal circumstances, the parallel plate capacitor is symmetric about the X-axis, so it can be obtained that , and the above formula is simplified to: ; ;

[0053] Since the masses on the left and right sides are rigidly connected, when the tilt angle of the right detection mass is , the tilt angle of the left detection mass is , so the magnitude of the negative electrode detection capacitor can be obtained as: ;

[0054] Among them, represents the magnitude of the negative electrode detection capacitor, is the vacuum permittivity, , are the closest and farthest distances from the detection electrode to the torsion beam, is the upper side line of the capacitor plate in the XY plane, is the tilt angle of the right detection mass, d is the distance between the detection mass and the metal electrode, represents the horizontal distance from the torsion beam to the capacitor plate, represents the integration with respect to the Y-axis.

[0055] The magnitude of the negative electrode boosting capacitor is: ;

[0056] In the formula, represents the magnitude of the negative electrode boosting capacitance, is the vacuum permittivity, , are the nearest and farthest distances from the boosting electrode to the torsion beam, is the upper edge line of the capacitor plate in the XY plane, is the tilt angle of the right-side detection mass, d is the distance between the detection mass and the metal electrode, represents the horizontal distance from the torsion beam to the capacitor plate, represents the integration with respect to the Y axis.

[0057] Please refer to Figure 7 , Figure 9 , Figure 9 The schematic diagram of the three-electrode structure acceleration measurement is shown. The detection mass moves out of the plane through the torsion beam. When the tilt angle of the right-side mass is , the tilt angle of the left-side mass is . Define Figure 7 The right-side capacitor plate in

[0058] The magnitude of the positive electrode detection capacitance / positive electrode boosting capacitance is: ; Among them, represents the magnitude of the positive electrode boosting capacitance, represents the magnitude of the positive electrode detection capacitance, , are respectively the nearest and farthest distances from the positive electrode detection capacitance plate / positive electrode boosting capacitance plate to the torsion beam 310.

[0059] Since the masses on the left and right sides are rigidly connected, the tilt angle of the right-side mass is , and the tilt angle of the left-side mass is . Therefore, the magnitude of the negative electrode detection capacitance / negative electrode boosting capacitance can be obtained as: ;

[0060] In the formula, represents the magnitude of the negative electrode boosting capacitance, represents the magnitude of the negative electrode detection capacitance, , are respectively the nearest and farthest distances from the positive electrode detection capacitance plate / positive electrode boosting capacitance plate to the torsion beam. Compared with the parameters in the five-electrode structure, , so the sensitivity and closed-loop feedback ability of the three-electrode structure are better than those of the five-electrode structure.

[0061] In the solution of this application, the vertical distance between the detection mass and the detection electrode plate d is much smaller than the lateral distance between the detection electrode plate and the torsion beam or , so the maximum tilt angle is: ;

[0062] In the formula, represents the maximum tilt angle of the detection mass, is the distance between the detection mass and the detection electrode plate, is the lateral distance between the detection electrode plate and the torsion beam, and due to the pull-in effect, the working range of the seesaw structure is usually much smaller than , so the actual displacement can be defined as: ; In the formula, 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 and the metal electrode.

[0063] When the swing angle of the accelerometer is very small, the detection mass and the detection electrode can be approximately equivalent to a parallel-plate capacitor, so the calculation method of the parallel-plate capacitor can be used to calculate the capacitance value, which is expressed as: ;

[0064] In the formula, represents the equivalent parallel-plate capacitor, is the vacuum permittivity, is the relative permittivity, is the facing area between the detection mass and the detection electrode plate, d is the distance between the detection mass and the detection electrode plate. When there is an external acceleration, the detection mass will twist, the capacitance on one side increases, and the capacitance on the other side decreases. Therefore, the differential capacitance change is: ;

[0065] Among them, is the differential capacitance, is the vacuum permittivity, is the relative permittivity, is the facing area between the mass and the metal electrode, d is the distance between the detection mass and the metal electrode, represents the displacement change, , respectively represent the changes at both ends of the differential detection capacitor plate.

[0066] When , there is: ; ; ;

[0067] Among them, differential capacitance, represents the equivalent parallel-plate capacitance, is the vacuum permittivity, is the relative permittivity, is the facing area between the mass block and the metal electrode, d is the distance between the detection mass block and the metal electrode, represents the rotational elastic modulus, is the torque coefficient, represents the moment of inertia, L represents the horizontal distance between the center of the detection capacitor plate and the torsion beam, represents acceleration, represents the displacement change, from which we can obtain: ;

[0068] In the formula, represents acceleration, represents the rotational elastic modulus, is the torque coefficient, represents the moment of inertia, is the tilt angle of the detection mass block, d is the distance between the detection mass block and the metal electrode, represents the rotational elastic modulus, is the torque coefficient, is the differential capacitance, is the basic capacitance, L is the horizontal distance between the center of the detection capacitor plate and the torsion beam. By measuring the capacitance change, the magnitude of the external acceleration can be calculated.

[0069] For the five-electrode structure, the sensitivity can be expressed as: ; Among them, represents the acceleration sensitivity of the five-electrode structure, is the differential capacitance, is the torque coefficient, represents the moment of inertia, d is the distance between the detection mass block and the metal electrode, is the acceleration, is the detected capacitance.

[0070] For the three - electrode structure, the sensitivity can be expressed as: ;

[0071] where, represents the sensitivity of the three - electrode structure accelerometer, is the differential capacitance, is the torque coefficient, represents the moment of inertia, d is the distance between the detection mass and the metal electrode, is the acceleration, is the size of the force - applying capacitance, is the size of the detected capacitance.

[0072] Thus, when the chip size and the process - manufacturing capabilities are limited, the detection electrode and the force - applying electrode can be combined for use, that is, the three - electrode structure is adopted to improve the sensitivity.

[0073] In one embodiment, an insulating layer is deposited on the surface of the substrate 100. The insulating layer is used to isolate the electrode layer 200 from the substrate 100 to shield the parasitic capacitance. The insulating layer can be made of silicon nitride or silicon dioxide.

[0074] In one embodiment, the Z - axis MEMS closed - loop accelerometer assembly is vacuum - packaged and used as an independent accelerometer. A certain degree of vacuum is used for packaging to reduce the mechanical thermal noise.

[0075] The accelerometer of the present invention does not have a damping hole on the detection mass opposite to the metal electrode, aiming to ensure high sensitivity. However, there is a squeeze - film damping between the detection mass and the metal electrode, which will increase the thermal noise. One of the parameters affecting the mechanical thermal noise is the damping coefficient. Therefore, by selecting vacuum packaging during packaging, the effective gas viscosity coefficient in the chamber can be changed, further reducing the damping coefficient to achieve overall low noise.

[0076] The calculation formula for the thermomechanical noise of the MEMS accelerometer is: ;

[0077] In the formula, represents the thermomechanical noise, is the Boltzmann constant, is the thermodynamic temperature, is the damping coefficient, is the mass of the mass block. In the present invention, damping holes are provided on the outer frame of the mass block. At the same time, the damping comb teeth are of sliding film damping in the moving direction. Compared with squeeze film damping, the damping coefficient of sliding film damping is much smaller, which is beneficial to reducing mechanical thermal noise.

[0078] The accelerometer of the present invention adopts a closed-loop structure, which can improve the nonlinear problem existing in the planar capacitor. And the oscillation phenomenon caused by vacuum packaging is solved through a closed-loop control system. The overall structure of the invention is compact, with high sensitivity, and is a closed-loop structure, which is beneficial to improving the overall nonlinearity.

[0079] In the second aspect of the present invention, there is provided a Z-axis MEMS closed-loop accelerometer used in combination with the Z-axis MEMS closed-loop accelerometer assembly of Embodiment 1. Refer to Figure 10 the top view of the Z-axis MEMS closed-loop accelerometer shown. It includes two Z-axis MEMS closed-loop accelerometer assemblies that are centrosymmetric. Each accelerometer assembly includes a substrate 100, an electrode layer 200, and a movable structure layer 300 from bottom to top. The electrode layer 200 includes at least a pair of differential capacitance plates provided on the substrate 100. The movable structure layer 300 includes a detection mass block 320 and a torsion beam 310, which are provided above the substrate 100. One end of the torsion beam 310 is connected to the detection mass block 320, and the other end is connected to the substrate 100.

[0080] Among them, the detection mass block 320 is divided into a first detection mass block 321 and a second detection mass block 322 that are symmetric with respect 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 is used as both a detection mass block and a driving mass block at the same time.

[0081] In a preferred embodiment, the electrode layer adopts a five-electrode structure, including differential force-applying capacitance plates and differential detection capacitance plates. Among them, the differential force-applying capacitance plates include a positive force-applying capacitance plate and a negative force-applying capacitance plate. The positive force-applying capacitance plate and the negative force-applying capacitance plate are respectively provided below the first detection mass block 321 and the second detection mass block 322, and are symmetric with respect to the torsion beam 310; the differential detection capacitance plates include a positive detection capacitance plate and a negative detection capacitance plate. The positive detection capacitance plate and the negative detection capacitance plate are respectively provided below the first detection mass block 321 and the second detection mass block 322, and are symmetric with respect to the torsion beam 310, and the capacitance polarities on the same side of the torsion beam are the same. The positive force-applying capacitance plates and the negative force-applying capacitance plates in different Z-axis MEMS closed-loop accelerometer assemblies are connected, and the positive detection capacitance plates and the negative detection capacitance plates in different Z-axis MEMS closed-loop accelerometer assemblies are connected.

[0082] In a preferred embodiment, the electrode layer adopts a three-electrode structure. The electrode layer includes a first capacitor plate and a second capacitor plate, which are respectively disposed below the first detection mass 321 and the second detection mass 322. The polarities of the first capacitor plate and the second capacitor plate are opposite and symmetric with respect to the torsion beam 310. Wherein, the first capacitor plate and the second capacitor plate in different Z-axis MEMS closed-loop accelerometer components are connected.

[0083] The functions of the various parts on the mass of the three-electrode structure are the same as those of the various parts on the mass of the five-electrode structure. The only difference is the electrode distribution. In the three-electrode structure, the force-applying electrode and the detection electrode are no longer independent of each other, but share each other. The positive detection electrode plate is also the positive force-applying electrode plate, and the negative detection electrode is also the negative force-applying electrode plate. After the force-applying electrode and the detection electrode share each other, the detection capacitance or the force-applying capacitance can be increased, and at the same time, it is adapted to the three-electrode closed-loop ASIC, further improving the overall sensitivity of the device and the closed-loop feedback ability.

[0084] In one embodiment, a recess is etched on one side surface of the second detection mass, so that the mass of the first detection mass is greater than the mass of the second detection mass.

[0085] In one embodiment, damping holes or damping grooves are etched on the outer periphery of the detection mass.

[0086] In one embodiment, the movable structure layer further includes a plurality of buffer components and a plurality of convex columns; the buffer components are disposed on the outer periphery of the detection mass and are used for in-plane motion limiting; the convex columns are disposed on the opposite surfaces of the detection mass and the substrate and are used for out-of-plane motion limiting.

[0087] 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.

[0088] In one embodiment, the Z-axis MEMS closed-loop accelerometer adopts vacuum packaging.

[0089] The above specific embodiments further elaborate on the purpose, technical solution and beneficial effects of the present invention. It should be understood that the above are only the specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A Z-axis MEMS closed-loop accelerometer component, characterized in that, Comprising: A substrate; An electrode layer, including at least a pair of differential capacitance plates disposed on the substrate; A movable structure layer disposed above the substrate, including a detection mass block and a torsion beam, the detection mass block being bonded to the substrate through the torsion beam; when an acceleration signal is generated in the Z-axis direction, the detection mass block moves out-of-plane relative to the torsion beam to form a differential detection signal on the at least a pair of differential capacitance plates; Wherein, the detection mass block is divided into a first detection mass block and a second detection mass block that are symmetric with respect 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 is used as both a detection mass block and a driving mass block.

2. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, wherein The electrode layer includes differential force application capacitance plates and differential detection capacitance plates; The differential force application capacitance plates include a positive force application capacitance plate and a negative force application capacitance plate, the positive force application capacitance plate and the negative force application capacitance plate are respectively disposed below the first detection mass block and the second detection mass block, and are symmetric with respect to the torsion beam; The differential detection capacitance plates include a positive detection capacitance plate and a negative detection capacitance plate, the positive detection capacitance plate and the negative detection capacitance plate are respectively disposed below the first detection mass block and the second detection mass block, and are symmetric with respect to the torsion beam; The polarities of the capacitance plates on the same side of the torsion beam are the same.

3. The Z-axis MEMS closed-loop accelerometer assembly according to claim 2, characterized in that, The positive detection capacitance plate and the negative detection capacitance plate are close to the torsion beam, and the positive force application capacitance plate and the negative force application capacitance plate are far from the torsion beam.

4. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, characterized in that, A recessed portion is etched on the 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.

5. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, wherein Damping holes or damping grooves are etched on the outer periphery of the detection mass block.

6. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, characterized in that, The movable structure layer further includes a plurality of buffer components and a plurality of convex columns; The buffer components are disposed on the outer periphery of the detection mass block for in-plane movement limiting; The convex columns are disposed on the opposite surfaces of the detection mass block and the substrate for out-of-plane movement limiting.

7. The Z-axis MEMS closed-loop accelerometer assembly according to claim 1, characterized in that, 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.

8. A Z-axis MEMS closed-loop accelerometer, characterized in that, Including two Z-axis MEMS closed-loop accelerometer components as described in any one of claims 1-7, and the two Z-axis MEMS closed-loop accelerometer components are centrosymmetric.

9. The Z-axis MEMS closed-loop accelerometer according to claim 8, wherein The electrode layer includes differential force application capacitance plates and differential detection capacitance plates; The differential force application capacitance plates include a positive force application capacitance plate and a negative force application capacitance plate, the positive force application capacitance plate and the negative force application capacitance plate are respectively disposed below the first detection mass block and the second detection mass block, and are symmetric with respect to the torsion beam; The differential detection capacitance plates include a positive detection capacitance plate and a negative detection capacitance plate, the positive detection capacitance plate and the negative detection capacitance plate are respectively disposed below the first detection mass block and the second detection mass block, and are symmetric with respect to the torsion beam; The polarities of the capacitance plates on the same side of the torsion beam are the same; The positive force application capacitor plates in different Z-axis MEMS closed-loop accelerometer components are connected to the negative force application capacitor plates, and the positive detection capacitor plates in different Z-axis MEMS closed-loop accelerometer components are connected to the negative detection capacitor plates.

10. The Z-axis MEMS closed-loop accelerometer according to any one of claims 8-9, characterized in that, The Z-axis MEMS closed-loop accelerometer uses vacuum packaging.

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