Mem s resonant accelerometer with etch protection and impact protection structure

Abstract

The application discloses a MEMS resonant accelerometer with etching protection and anti-impact structure and belongs to the field of micro electro mechanical inertial sensors. The device comprises fixed anchor points, a center detection mass, four groups of double-stage micro levers, two groups of differential double-end tuning fork resonant units, a same-layer etching protection frame, a decoupling beam and two groups of flexible stop structures. The protection frame is connected with the main anchor points through folding beams and blocks sputtering particles in a deep silicon etching process to protect a functional area. The flexible stop structure is an elastic cantilever beam plus a cross boss structure, realizes bidirectional anti-impact, amplifies inertial force through the micro lever, completes force-frequency conversion through the resonant unit and reduces cross-axis coupling through the decoupling beam. The protection structure is prepared in the same layer, does not need additional masks and processes and has zero additional cost, and is suitable for high-precision inertial measurement scenes.

Description

Technical Field

[0001] This invention belongs to the field of micro-electro-mechanical systems (MEMS) inertial sensor technology, specifically relating to a resonant accelerometer comprising an etched protective structure and a flexible shock-resistant stop. Background Technology

[0002] MEMS accelerometers are among the most commercially successful and highest-volume MEMS sensors. Based on different detection principles, they can be categorized into several types, including capacitive, piezoresistive, piezoelectric, thermal convection, and resonant accelerometers. Among these, resonant accelerometers detect the magnitude of input acceleration by sensing changes in the natural frequency of a sensitive resonator. The output signal is a quasi-digital frequency signal, offering significant advantages such as strong anti-interference capabilities, good long-term stability, high sensitivity, high resolution, and simple interface circuitry. It is one of the mainstream technologies for high-precision MEMS accelerometers and has irreplaceable application value in the mid-to-high-end inertial measurement field.

[0003] The double-ended tuning fork resonator is a widely used force-sensitive unit in resonant accelerometers. Its typical structure consists of two parallel, slender resonant beams fixed at both ends. During operation, the two beams vibrate in opposite phase planes. In this vibration mode, the forces at the anchor points cancel each other out, resulting in minimal energy loss at the anchor points and thus exhibiting a very high quality factor and excellent stability. To improve the sensitivity of acceleration detection, existing designs typically introduce a micro-lever mechanism between the inertial mass and the double-ended tuning fork resonator. This lever principle amplifies the weak inertial force generated by the mass before applying it to the resonant beams, thereby achieving higher detection sensitivity within a limited chip area.

[0004] In the fabrication of MEMS accelerometers, structural protection is crucial for ensuring process stability. On one hand, in deep reactive ion etching (DRIE) based on silicon-glass bonding, sputtered particles move randomly within the high aspect ratio gaps of the structure. Due to the obstruction of anchor points, these sputtered particles accumulate towards the central mass block, causing the photoresist on the mass block surface to be penetrated or damaged. This leads to over-etching of the mass block structure in subsequent etching processes, severely affecting structural integrity and device performance consistency, and reducing wafer yield. Adding additional metal mask layers or adjusting etching parameters increases process costs or sacrifices etching quality. On the other hand, accelerometers may be subjected to external impacts in the complex environments of transportation, assembly, and actual operation. When the impact acceleration exceeds the structural tolerance limit, the mass block will experience excessive displacement, causing collisions between device structures. This can lead to the fracture of delicate beam structures such as resonant beams and flexible support beams, resulting in functional failure. Rigid stops have high stiffness; during impact, the mass block collides hard with the rigid stop, generating extremely high impact stress at the moment of impact, which can still easily cause beam structure fracture or stop structure damage, indicating limited impact resistance. Summary of the Invention

[0005] The purpose of this invention is to address the challenges faced by MEMS accelerometers by providing a MEMS resonant accelerometer with etching protection and shock resistance structure. Through structural co-design, it achieves deep silicon etching process protection and bidirectional shock resistance without increasing the photomask, changing the standard process flow, or significantly increasing the chip area.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a MEMS resonant accelerometer with etching protection and impact resistance structure, comprising a fixed anchor point group, a central detection mass block, four sets of two-stage micro-lever mechanisms, two sets of differential double-ended tuning fork resonant units, an integrated etching protection structure, two transverse axis decoupling beams, and two sets of flexible stop structures.

[0007] The fixed anchor point group includes two main anchor points and multiple auxiliary anchor points. The two main anchor points are U-shaped structures, symmetrically arranged vertically, and fully bonded to the substrate at the bottom, providing the main support force. The auxiliary anchor points are distributed around the functional structure and are small rectangular structures used to fix the lever fulcrum, the fixed end of the resonant unit, and the cantilever beam of the stop structure. All anchor points are firmly bonded to the substrate.

[0008] The central sensing mass block is located at the geometric center of the entire structural layer, symmetrical about the X and Y axes. It is the core inertial unit for sensing acceleration. When there is an external acceleration input, the mass block generates displacement, converting the acceleration signal into inertial force.

[0009] Four sets of dual-stage micro-lever structures are symmetrically arranged along the Y-axis, with two sets at the top and two at the bottom. Each double-ended tuning fork resonator unit is connected to two sets of dual-stage micro-levers. Each dual-stage micro-lever mechanism includes a parallel-arranged secondary lever and a primary lever. One end of the secondary lever is connected to the mass block via an input connecting beam, and the other end is connected to an auxiliary anchor point via a secondary fulcrum beam. One end of the intermediate connecting beam is connected to the secondary lever, and the other end is connected to the primary lever. The primary lever is connected to the auxiliary anchor point via a primary fulcrum beam, and to the double-ended tuning fork resonator unit via an output connecting beam. By rotating the two-stage levers at small angles, the inertial force generated by the mass block is amplified in two stages and then transmitted to the resonator unit. This achieves a greater amplification factor than a single-stage lever with the same chip area, while also reducing the lever's length, making it less prone to bending, and lowering mechanical nonlinearity.

[0010] Two sets of double-ended tuning fork resonant units are symmetrically arranged on both sides of the central detection mass block along the Y-axis. Each set of resonant units includes two parallel resonant beams, end bases, a driving electrode plate, and a detection electrode plate. The two resonant beams extend parallel to each other along the Y-axis, with identical structural dimensions. Each end is fixed to one of the two bases, one connected to the output end of the micro-lever, and the other fixed to an auxiliary anchor point. The driving electrode plate and the detection electrode plate are arranged on both sides of the resonant beams, maintaining a uniform gap between them to form a parallel plate driving and detection capacitor. During operation, a DC bias voltage and an AC driving voltage are applied to the driving electrode plate, and the same DC bias voltage is applied to the detection electrode plate. Electrostatic excitation causes the two resonant beams to vibrate in-plane in opposite phases. In this mode, the reaction forces at the anchor points cancel each other out, resulting in low energy loss and a high quality factor. When inertial force is applied axially to the end of the resonant unit through a micro-lever, the resonant beam is subjected to axial stress, causing a change in its natural frequency: under tensile stress, the beam's equivalent stiffness increases, and the resonant frequency rises; under compressive stress, the beam's equivalent stiffness decreases, and the resonant frequency decreases. Two sets of symmetrical resonant units, one under tension and the other under compression, experience equal and opposite frequency changes under acceleration. By detecting the frequency difference between the two sets of resonant units, the magnitude of the input acceleration can be obtained. This differential detection method effectively suppresses common-mode interference such as temperature changes and residual stress in the packaging, improving detection stability.

[0011] The etching protection structure is a one-piece closed silicon frame surrounding all functional structures. The frame is connected to the main anchor point via multiple folded flexible beams, each composed of multiple straight beams, similar to a planar spring structure. This allows the protective frame to be suspended and fixed on the anchor point, while also releasing residual stress in the anchor point structure through flexible deformation of the beams. A uniformly sized process gap is reserved between the frame and the internal detection mass block. The frame does not mechanically contact any functional structure; therefore, during normal device operation, the protective frame will not interfere with the movement of the mass block, levers, or resonant beams, and will not affect the device's detection function. During deep silicon etching, due to the geometric shielding of the anchor point, sputtered particles generated by reactive ion etching will scatter towards the detection mass block and deposit on the photoresist surface of the central functional area, causing photoresist damage and leading to over-etching of the device structure. The folded beams create more gaps, providing a channel for particle discharge. The closed protective frame acts as a physical barrier, preventing particles moving from the outer anchor point area to the central functional area from directly damaging the photoresist in the functional area, thus achieving self-protection during the etching process. Since the protective frame and other functional structures are fabricated simultaneously in the same photolithography and etching steps, no additional photomask or process steps are required. It is fully compatible with standard SOG MEMS processes and will not increase process costs.

[0012] Two sets of flexible stop structures are symmetrically arranged along the X-axis. Each set of flexible stop structures includes two elastic cantilever beams and a cross-shaped stop boss. The length of the elastic cantilever beam is along the X-axis, the beam width is uniform, and the thickness is consistent with the structural layer. One end is fixed to an auxiliary anchor point, and the other end is a free end that is suspended. The cross-shaped stop boss is a cross-shaped structure composed of two orthogonal beams, which serve as stop structures in the Y and X directions, respectively. The Y-direction stop beam is located between the two elastic cantilever beams, parallel to the length of the cantilever beams, and the distance between it and the two cantilever beams is the stop gap. The stop gap is less than the minimum gap of the movable structure of the device. During normal operation, the cross-shaped stop boss does not contact the elastic cantilever beams and does not affect the normal detection of the device. When the device is subjected to a large impact acceleration, the displacement of the mass block exceeds the stop gap. The cross-shaped stop boss contacts the free end of the elastic cantilever beam. The continued movement of the mass block will push the elastic cantilever beam to undergo in-plane bending deformation. The bending of the cantilever beam generates an elastic restoring force in the opposite direction of the mass block's movement. The deformation of the beam absorbs the impact energy, limiting the maximum displacement of the mass block within the design range and preventing structural damage caused by collision. The cross-shaped structure can simultaneously achieve bidirectional stopping in both sensitive and non-sensitive axis directions. Unlike the hard impact of traditional rigid stops, the flexible deformation of the elastic cantilever beam can prolong the impact time, reduce the peak impact stress, avoid structural damage caused by the impact itself, and improve the impact resistance reliability of the device.

[0013] Two transverse decoupling beams are arranged symmetrically along the X-axis. Each decoupling beam consists of multiple flexible beams connected end to end. The stiffness is smaller along the Y-axis and larger along the X-axis. The two ends are connected to the central detection mass block and the auxiliary anchor point, respectively, to achieve motion decoupling in non-sensitive axis directions and reduce cross-axis coupling error.

[0014] The overall structure of this invention adopts a symmetrical design with differential symmetrical arrangement, which can effectively reduce the drift error introduced by changes in the external environment and improve the stability of the device. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of the MEMS resonant accelerometer described in this invention;

[0016] Figure 2 This is a schematic diagram of the structure of the two-stage micro-lever mechanism described in this invention;

[0017] Figure 3 This is a schematic diagram of the structure of the double-ended tuning fork resonator unit described in this invention;

[0018] Figure 4 This is a partially enlarged schematic diagram of the etching protection structure described in this invention;

[0019] Figure 5 This is a schematic diagram of the flexible stop structure described in this invention;

[0020] Figure 6 This is a schematic diagram of the transverse axis decoupling beam described in this invention;

[0021] Explanation of reference numerals in the attached figures:

[0022] 1-Main anchor point, 2-Auxiliary anchor point, 3-Central detection mass block, 4-Dual-stage micro-lever mechanism, 5-Dual-end tuning fork resonant unit, 6-Etched protective frame, 7-Folded flexible beam, 8-Elastic cantilever beam, 9-Cross stop boss, 10-Secondary lever, 11-Primary lever, 12-Secondary fulcrum beam, 13-Primary fulcrum beam, 14-Input connecting beam, 15-Intermediate connecting beam, 16-Output connecting beam, 17-Resonant beam, 18-Drive electrode plate, 19-Detection electrode plate, 20-End base, 21-Decoupling beam. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0024] The X-axis and Y-axis mentioned in this embodiment are only reference directions for conveniently describing the relative position of the structure and do not constitute a limitation on the arrangement direction in the actual application of the present invention. The Y-axis is the acceleration sensitive axis and the X-axis is the normal to the sensitive axis.

[0025] The MEMS resonant accelerometer with etching protection and shock resistance structure described in this embodiment is symmetrical about the X-axis and Y-axis.

[0026] The anchor point group includes two main anchor points 1 and multiple auxiliary anchor points 2. All anchor points are bonded and fixed to the substrate on their lower surfaces, with no relative movement. The two main anchor points 1 are U-shaped structures arranged symmetrically vertically, with openings facing each other, semi-enclosing the central functional area. The main anchor points have high structural rigidity and a large bonding area, providing primary support for the entire device and also serving as fixing points for the etching protection frame. The auxiliary anchor points 2 are smaller rectangular silicon structures distributed around the functional structure, serving as fulcrums for the bi-stage micro-lever, fixing ends for the double-ended tuning fork resonator unit, fixing ends for the elastic cantilever beam, and fixing ends for the decoupling beam, respectively. All auxiliary anchor points are designed to correspond to the dimensions of the object being fixed, ensuring fixing strength.

[0027] The central detection mass block 3 is located at the geometric center of the structure and is a centrally symmetrical movable inertial structure. When there is an external acceleration input, the mass block generates displacement and converts the acceleration signal into inertial force.

[0028] Two decoupling beams 21 are provided, symmetrically arranged on both sides of the mass block along the X-axis. Each decoupling beam is a folded structure composed of multiple flexible beams connected end to end, exhibiting high stiffness along the X-axis and lower stiffness along the Y-axis. One end of the decoupling beam is connected to the central detection mass block 3, and the other end is fixedly connected to the corresponding auxiliary anchor point 2. When the mass block is subjected to disturbance force along the X-axis, the high stiffness of the decoupling beam restricts the displacement of the mass block in the X-axis direction, reducing cross-axis coupling; when the mass block moves along the Y-axis, the low stiffness of the decoupling beam does not affect the normal inertial displacement of the mass block, achieving decoupling of the non-sensitive axis. The two decoupling beams have identical structural dimensions and are symmetrically arranged to ensure symmetrical stiffness.

[0029] The dual-stage micro-lever mechanism 4 consists of four sets, arranged symmetrically along the center, with two sets positioned vertically and two vertically along the Y-axis. Each double-ended tuning fork resonant unit is connected to two sets of dual-stage micro-levers. Each set of dual-stage micro-lever mechanisms includes a parallel-arranged secondary lever 10 and a primary lever 11, as well as a secondary fulcrum beam 12, a primary fulcrum beam 13, an input connecting beam 14, an intermediate connecting beam 15, and an output connecting beam 16. The input end of the secondary lever 10 is connected to the central detection mass block 3 via the input connecting beam 14, which is a slender, flexible beam extending along the Y-axis with a width of 10 μm. The secondary lever 10 is connected to the corresponding auxiliary anchor point 2 via the secondary fulcrum beam 12, forming a secondary rotation fulcrum. The secondary fulcrum beam 12 is also a slender, flexible beam extending along the Y-axis with a width of 10 μm, allowing the lever to rotate around the fulcrum at a small angle. The output end of the secondary lever 10 is connected to the input end of the primary lever 11 via an intermediate connecting beam 15. The intermediate connecting beam 15 is a slender, flexible beam extending along the Y-axis with a width of 10 μm, enabling force transmission between the two levers. The primary lever 11 is connected to the corresponding auxiliary anchor point 2 via a primary fulcrum beam 13, forming a primary rotation fulcrum. The primary fulcrum beam 13 is also a slender, flexible beam extending along the Y-axis with a width of 10 μm. The output end of the primary lever 11 is connected to the end base 20 of the corresponding double-ended tuning fork resonator unit 5 via an output connecting beam 16. The output connecting beam 16 is also a slender, flexible beam extending along the Y-axis with a width of 10 μm, transmitting the amplified inertial force axially to the resonator unit.

[0030] When there is an acceleration input along the Y-axis, the central detection mass block 3 is displaced along the Y-axis by inertial force. This displacement is caused by the input connecting beam 14, which drives the input end of the secondary lever 10 to move. The secondary lever rotates around the fulcrum at a small angle, amplifying the force in the first stage. This force is then amplified by the intermediate connecting beam 15, which drives the input end of the primary lever 11 to move. The primary lever rotates around the fulcrum at a small angle, amplifying the force in the second stage. This force is then transmitted to the double-ended tuning fork resonator unit through the output connecting beam 16, thus achieving two-stage amplification of the inertial force.

[0031] Two sets of double-ended tuning fork resonant units 5 are arranged symmetrically on both sides of the mass block along the Y-axis, forming a differential detection structure. Each set of double-ended tuning fork resonant units includes two parallel resonant beams 17, two end bases 20, a driving electrode plate 18, and a detection electrode plate 19. The two resonant beams 17 extend parallel to each other along the Y-axis, with identical structural dimensions: 1100 μm long and 8 μm wide. Both ends are fixed to the two end bases 20; one end base 20 is connected to the output end of the micro-lever, serving as a movable input end, while the other end base 20 is fixed to an auxiliary anchor point, serving as a fixed end. The driving electrode plate 18 and the detection electrode plate 19 are rectangular flat plate structures, respectively positioned on both sides of the resonant beams, maintaining a uniform gap of 4 μm between them to form a parallel plate capacitor. During operation, the driving electrode plate applies an electrical signal, exciting the two resonant beams to vibrate; when axial force acts on the resonant beams, the natural frequency of the resonant beams changes with stress, and the acceleration value can be obtained by detecting the frequency change of the resonant unit through the detection electrode plate.

[0032] The etching protection structure is an integrated structure, comprising an etching protection frame 6 and multiple folded flexible beams 7. The etching protection frame 6 is a rectangular closed silicon frame surrounding all functional structures, with a frame thickness consistent with the structural layer thickness. A uniform 20μm process gap is maintained between the frame and the detection mass block, ensuring no contact with any functional structure and preventing interference with normal device operation. The multiple folded flexible beams 7 connect the frame sides to the main anchor point 1. Each folded beam consists of multiple straight beams folded back at right angles, with a beam width of 20μm. This fold not only suspends and fixes the frame but also releases residual stress through flexible deformation. Simultaneously, the gaps between the beams provide a discharge channel for etching byproducts and sputtered particles. When DRIE etching reaches the substrate interface, the frame acts as a physical barrier, blocking sputtered particles rebounding from the anchor point region, preventing particle damage to the photoresist in the central functional area, and reducing over-etching defects. The protection structure is etched and formed in the same layer as other functional structures in a single process, without adding masks or process steps, and is compatible with standard processes.

[0033] Two sets of flexible stop structures are arranged symmetrically along the X-axis. Each set of flexible stop structures includes two elastic cantilever beams 8 and one cross-shaped stop boss 9. The two elastic cantilever beams 8 are arranged in parallel, with their length direction along the X-axis. The beams are 20 μm wide and 200 μm long, with a thickness consistent with the structural layer. One end is fixed to the auxiliary anchor point 2, and the other end is a free end. The cross-shaped stop boss 9 is a cross-shaped structure, located on the side of the mass block, including orthogonal Y-direction stops and X-direction stops. The boss is located between the two elastic cantilever beams, with a uniform stop gap of 5 μm between the boss and the two cantilever beams. The stop gap is smaller than the minimum gap of the device structure. During normal operation, the displacement of the mass block is less than the stop gap, and the boss does not contact the cantilever beam, thus not affecting the normal detection of the device. Under a large impact, when the displacement of the mass block exceeds the stop gap, the cross boss contacts the cantilever beam, pushing the cantilever beam to bend and deform. The impact energy is absorbed through the elastic deformation of the beam, limiting the maximum displacement of the mass block and preventing the thin beam from breaking. The cross structure simultaneously achieves bidirectional stopping in both the Y and X directions. The flexible cantilever beam extends the collision time, reduces collision stress, and improves impact resistance.

[0034] This embodiment adopts a fully symmetrical design, with all symmetrical structures having consistent dimensions. This design can offset common-mode interference such as residual stress and temperature deformation, thereby improving device stability. Through structural collaborative design, this invention addresses SOG process etching sputtering defects via a co-layer etching protection structure without increasing process costs. Simultaneously, a cross-shaped flexible stop provides bidirectional impact resistance, enhancing the device's structural reliability.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A MEMS resonant accelerometer with etching protection and shock resistance structure, characterized in that, The accelerometer includes a fixed anchor point group, a central sensing mass block, four sets of double-stage micro levers, two sets of double-ended tuning fork resonant units, an etched protective structure, two decoupling beams, and two sets of flexible stop structures. The fixed anchor point group includes main anchor points and auxiliary anchor points. The main anchor points are two symmetrically arranged U-shaped structures that semi-enclose the central functional structure, while the auxiliary anchor points are distributed around the functional structure. The central sensing mass block is located at the geometric center of the structure and is a centrally symmetrical movable inertial structure. The double-stage micro levers are symmetrically arranged, with two sets arranged vertically along the Y-axis. Each double-ended tuning fork resonant unit is connected to two sets of double-stage micro levers. The input end of each set of double-stage micro levers is connected to the mass block via an input connecting beam, and the output end is connected to the end of a set of double-ended tuning fork resonant units via an output connecting beam. The double-ended tuning fork resonant units are symmetrically arranged along the Y-axis and fixed at both ends. The etched protective structure is a closed frame surrounding all functional structures. The frame is connected to the main anchor point via folded flexible beams. A uniform process gap is set between the frame and the detection mass block to prevent mechanical contact with the functional structures. The decoupling beam consists of multiple flexible beams connected end to end. The beams have lower stiffness along the Y-axis and higher stiffness along the X-axis. The two ends of the decoupling beam are connected to the central detection mass block and the auxiliary anchor point, respectively, to achieve decoupling in the non-sensitive axis direction. The flexible stop structure is arranged along the X-axis. Each set of flexible stops includes two elastic cantilever beams and a cross stop boss. One end of the elastic cantilever beam is fixed to the fixed anchor point, and the other end is a free end. The cross stop boss is positioned opposite the free end of the elastic cantilever beam, with a stop gap reserved between them. The stop gap is smaller than the minimum gap between the movable structures of the device.

2. The MEMS resonant accelerometer according to claim 1, characterized in that, Each set of dual-stage micro-lever mechanisms includes a secondary lever, a primary lever, a secondary fulcrum beam, a primary fulcrum beam, and an intermediate connecting beam; the secondary lever and the primary lever are arranged in parallel, and the force transmission direction is consistent with the Y-axis direction; one end of the secondary lever is connected to the mass block through the input connecting beam, and the other end is connected to the auxiliary anchor point through the secondary fulcrum beam to form a secondary rotation fulcrum; One end of the intermediate connecting beam is connected to the secondary lever, and the other end is connected to the primary lever; the primary lever is connected to the auxiliary anchor point through the primary fulcrum beam to form a primary rotation fulcrum, and the primary lever is connected to the end of the double-ended tuning fork resonator unit through the output connecting beam.

3. The MEMS resonant accelerometer according to claim 2, characterized in that, The input connecting beam, intermediate connecting beam, output connecting beam, and each level of support beam are all slender and flexible beam structures. The length direction of each beam is along the Y-axis, allowing the lever to rotate at a small angle around the fulcrum.

4. The MEMS resonant accelerometer according to claim 1, characterized in that, The double-ended tuning fork resonator unit is arranged in two groups, symmetrically distributed along the Y-axis; each group of double-ended tuning fork resonator unit includes two parallel resonator beams, a driving electrode plate, a detection electrode plate and two end bases; the two resonator beams extend parallel to each other along the Y-axis, have completely identical structural dimensions, and are fixed at both ends to the bases, one base is connected to the micro lever output end, and the other base is fixed to the auxiliary anchor point; The driving electrode plate and the detection electrode plate are respectively set on both sides of the resonant beam, with a fixed gap between the electrode plates and the resonant beam, and the opposite surfaces form a parallel plate capacitor.

5. The MEMS resonant accelerometer according to claim 4, characterized in that, The two resonant beams are mechanically coupled through end bases and vibrate in opposite phases in plane during operation. When there is an acceleration input along the Y-axis, one set of double-ended tuning fork resonant units is subjected to axial tensile stress, and the resonant frequency increases, while the other set is subjected to axial compressive stress, and the resonant frequency decreases. The acceleration value is obtained by detecting the frequency difference between the two sets of resonant units.

6. The MEMS resonant accelerometer according to claim 1, characterized in that, The etching protection structure has a closed frame with a frame thickness consistent with the device structure thickness; each segment of the folded flexible beam has a uniform width, with one end connected to the frame and the other end connected to the main anchor point.

7. The MEMS resonant accelerometer according to claim 1, characterized in that, The length of the elastic cantilever beam is along the X-axis, and its thickness is consistent with the thickness of the device structure layer. The cross-shaped stop boss has a cross-shaped structure, including a Y-direction stop and an X-direction stop. The Y-direction stop is located between the two elastic cantilever beams, parallel to the elastic cantilever beams, and has an equal stop gap with the two cantilever beams. The X-direction stop is perpendicular to the elastic cantilever beams and combines with the Y-direction stop to form a cross shape. When the displacement of the mass block exceeds the stop gap, the cross-shaped stop boss comes into complete contact with the free end of the cantilever beam, and the cantilever beam undergoes in-plane bending deformation.

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