Low feedthrough MEMS resonant microgravity accelerometer

Abstract

The application discloses a low feed-through MEMS resonant microgravity accelerometer, which is composed of upper and lower layers, the upper layer is a single-crystal silicon made accelerometer micro-mechanical sensitive structure for sensing external acceleration, gold is deposited on the upper layer as an electrode for input and output of signals, and the lower layer is a glass substrate for supporting the micro-mechanical sensitive structure of the upper layer. The application carries out differential detection on the two beams of a tuning fork resonator through an increased detection electrode, suppresses the feed-through component in the resonator output signal, and solves the problem that the closed loop oscillation performance is difficult to improve due to the feed-through signal. The application solves the problem that a large mass block of the resonant microgravity accelerometer is prone to collapse by increasing auxiliary anchor points, improves the out-of-plane stiffness of the accelerometer without affecting the stiffness of the sensitive axis, and improves the impact resistance of the resonant microgravity accelerometer.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) technology, specifically relating to a low feedthrough MEMS resonant microgravity accelerometer. Background Technology

[0002] Microgravity measurement has significant practical implications for aerospace, geological exploration, and gravity navigation. Resonant accelerometers, due to their small size, low cost, high accuracy, and near-digital output, represent the future direction of high-precision accelerometer development and are highly favored and valued by researchers worldwide. However, the measurement accuracy of resonant accelerometers is affected by factors such as the topology of the sensor's sensing element, manufacturing process, and driving and detection principles. This can cause subtle changes in gravitational acceleration to be submerged in the background noise of the closed-loop oscillator, resulting in inaccurate measurement of microgravity changes. Therefore, microgravity measurement requires sensors with sufficiently high mechanical sensitivity.

[0003] The core sensing structure of a resonant accelerometer mainly includes a suspended mass, two symmetrically arranged micro-lever amplification mechanisms, and two symmetrically distributed sensitive resonators. The mass is suspended by a thin, flexible spring beam. Under the action of external acceleration, it generates inertial force, which is amplified by the micro-lever mechanisms and transmitted to the subsequent sensitive resonators. The frequency change of the sensitive resonator corresponds to the change in acceleration.

[0004] For resonant accelerometers, improving mechanical sensitivity requires a large mass and a spring beam with lower stiffness on the sensitive shaft. However, a larger sensitive mass is prone to collapse during microfabrication due to insufficient support stiffness, reducing the yield rate. The stiffness of the flexible support spring on the non-sensitive shaft also decreases as the stiffness of the sensitive shaft decreases. When the flexible support spring is too soft, insufficient out-of-plane stiffness will cause the mass to collapse when the sensor is subjected to out-of-plane impacts, reducing the device's impact resistance.

[0005] On the other hand, constructing high-performance MEMS oscillators is another key focus for improving resonant accelerometers. Resonant accelerometers typically employ capacitive sensing. Due to the lack of sufficient impedance between capacitive transducers, the excitation signal is directly transmitted to the output, causing crosstalk to the dynamic current of the response—a feedthrough effect. The feedthrough effect distorts the amplitude and phase frequency responses of the resonator. When the feedthrough component dominates, the true vibration signal of the resonator is masked, affecting the control accuracy based on closed-loop oscillation, deteriorating the oscillator's frequency stability, and consequently impacting the sensor's accuracy. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a low-feedthrough MEMS resonant microgravity accelerometer. This invention addresses the technical problems in existing resonant accelerometers, such as the sensor being subjected to out-of-plane impacts during the processing and operation of large-mass MEMS resonant microgravity accelerometers, leading to easy collapse of the mass block and the difficulty in improving closed-loop oscillation performance due to feedthrough effects. This invention improves the processing yield, impact resistance, and measurement accuracy of the resonant microgravity accelerometer output.

[0007] The present invention adopts the following technical solution:

[0008] A low feedthrough MEMS resonant microgravity accelerometer includes an upper monocrystalline silicon micromechanical sensing structure and a glass substrate disposed on the lower layer of the monocrystalline silicon micromechanical sensing structure. Gold electrodes are deposited on the surface of the monocrystalline silicon micromechanical sensing structure.

[0009] The single-crystal silicon micromechanical sensing structure includes a mass block, which is connected to a set of tuning fork resonators via two micro-lever amplification structures. The two sets of tuning fork resonators are symmetrically arranged to form a pair of differential sensing structures. A fourth support anchor point is set between the two sets of tuning fork resonators. Second support anchor points are set on both sides of the fourth support anchor point. The two sets of second support anchor points are connected to the mass block via corresponding second support springs. Third support anchor points are set on both sides of each tuning fork resonator. First support springs are set at the four corners of the mass block. Each first support spring is connected to a corresponding first support anchor point, which makes the mass block levitate.

[0010] Multiple auxiliary support anchors are spaced apart on the glass substrate, and gaps are set between the auxiliary support anchors and the single-crystal silicon micromechanical sensitive structure.

[0011] Preferably, the second support spring includes 2×m folding spring sections and m-1 frame beams, where m is a greater than integer; the frame beams are square frames and are connected to the connection points of the two folding spring sections, and the centroid of the frame beams coincides with the centroid of the corresponding second support anchor point.

[0012] Preferably, the 2×m-section folding springs are located on the upper and lower sides of the second support anchor point, with m sections on each side, and the upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point.

[0013] Preferably, the width of the frame beam is 5~10μm, and the width of the folding spring is 5~10μm.

[0014] Preferably, the tuning fork resonator is excited by a first excitation electrode plate or a second excitation electrode plate, and the vibration signal detected by the first fixed detection electrode and the second fixed detection electrode is output after passing through a differential amplifier.

[0015] Preferably, the tuning fork resonator includes a first vibrating beam and a second vibrating beam, which are arranged in parallel.

[0016] Preferably, the first vibration beam includes a first fixed driving electrode and a first fixed detection electrode, and the second vibration beam includes a second fixed driving electrode and a second fixed detection electrode; the first fixed driving electrode, the first fixed detection electrode, the second fixed driving electrode and the second fixed detection electrode are respectively connected to the glass substrate through anchor points.

[0017] Preferably, the distance between the first vibrating beam and the second vibrating beam is 200~500μm.

[0018] Preferably, the minimum straight-line distance between any auxiliary support anchor points, or between any first support anchor point, second support anchor point, third support anchor point, and fourth support anchor point, is less than 2000 μm.

[0019] Preferably, the gap between the auxiliary support anchor point and the single-crystal silicon micromechanical sensitive structure is 10~50μm.

[0020] Compared with the prior art, the present invention has at least the following beneficial effects:

[0021] This invention discloses a low-feedthrough MEMS resonant microgravity accelerometer. A symmetrical tuning fork resonator generates a reverse frequency shift under acceleration, offsetting the same-direction drift caused by temperature / vibration. An auxiliary anchor point supports a large mass block during processing, reducing the collapse rate. After release, there is no contact, ensuring sensitivity. Independent detection electrodes provide differential output, canceling in-phase capacitive feedthrough signals and addressing the problem of parasitic signals masking the true signal in previous technologies. A folded spring structure with a frame beam achieves stiffness decoupling, effectively resolving the contradiction between the three requirements of improving sensitivity of the sensitive axis, enhancing the anchor point's anti-collapse capability, and achieving stiffness decoupling in microgravity sensors, as well as high precision, impact resistance, and high yield.

[0022] Furthermore, the rectangular beam is connected to folded spring nodes to optimize stress distribution and avoid fractures caused by stress concentration.

[0023] Furthermore, by arranging the springs on both sides of the support anchor point in a centrally symmetrical manner, the out-of-plane torque that may be caused by the process or stress is reduced, thereby optimizing the processing stability and yield.

[0024] Furthermore, the folded beam is 5~10μm wide to achieve low stiffness of the sensitive axis, and the frame beam is 5~10μm wide to improve out-of-plane stiffness, thereby solving the problem of easy damage to the sensor structure caused by insufficient out-of-plane stiffness.

[0025] Furthermore, the signals from the two detection electrodes are processed differentially to effectively suppress parasitic signals and eliminate the problem of feedthrough effect masking the true motion signal of the resonator.

[0026] Furthermore, the beam spacing was set within the range of 200~500μm, optimizing the arrangement space of the excitation electrode and the detection electrode.

[0027] Furthermore, the maximum spacing between the auxiliary support anchor points is less than 2000μm to ensure sufficient support force and prevent the mass block from collapsing.

[0028] Furthermore, the gap of 10~50μm separates the anchor point from the sensitive structure and prevents the release of residual etching solution, thus reducing the overall process difficulty.

[0029] In summary, this invention features a simple structure and good impact resistance, making it suitable for applications in aerospace, geological exploration, and military fields.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the following description of the relative embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of a sensitive chip;

[0033] Figure 2 Schematic diagram of a low feedthrough MEMS resonant microgravity accelerometer;

[0034] Figure 3 A schematic diagram of a support spring for a frame beam;

[0035] Figure 4 A schematic diagram of a low-feedthrough tuning fork resonator and its detection scheme;

[0036] Figure 5 The amplitude-frequency response diagrams are shown before and after the differential conversion.

[0037] Figure 6 The phase frequency response diagrams are shown before and after the differential operation.

[0038] Figure 7 The diagram shows the effect of different frame beam widths on the equivalent stiffness of the microspring in the X, Y, and Z directions.

[0039] The components include: 1. mass block; 2. micro-lever amplification structure; 3. tuning fork resonator; 3a. first vibrating beam; 3b. second vibrating beam; 4. first support spring; 5. second support spring; 5a. folding spring; 5b. frame beam; 6. first support anchor point; 7. second support anchor point; 8. third support anchor point; 9. fourth support anchor point; 10. auxiliary support anchor point; first fixed driving electrode 11-1; first fixed detection electrode 11-2; second fixed driving electrode 11-3; second fixed detection electrode 11-4; 12. differential amplifier. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "one side," "one end," and "one side," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0042] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0043] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0044] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0045] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0046] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0047] This invention provides a low-feedthrough MEMS resonant microgravity accelerometer. A symmetrical tuning fork resonator operates differentially under acceleration (one pull, one compression), with differential detection via independent electrodes, simultaneously suppressing common-mode interference and feedthrough noise. Auxiliary anchor points are embedded in the mass block at <2000μm intervals, providing support during fabrication (preventing collapse) and disengaging with a 10-50μm gap after release. The first support spring has low sensitive shaft stiffness to ensure sensitivity. The second support spring uses a combination of frame beams and folding springs, increasing the out-of-plane stiffness of the accelerometer without affecting the sensitive shaft stiffness, thus improving the shock resistance of the resonant microgravity accelerometer. This effectively balances the contradiction between high precision, shock resistance, and high yield. By adding detection electrodes to perform differential detection on the two vibrating beams of the tuning fork resonator, the feedthrough component in the resonator output signal is suppressed, solving the problem of feedthrough signals hindering the improvement of closed-loop oscillation performance. The addition of auxiliary anchor points addresses the problem of the large mass block in the resonant microgravity accelerometer being prone to collapse during fabrication.

[0048] Please see Figure 1The present invention discloses a low feedthrough MEMS resonant microgravity accelerometer, comprising an upper and lower two-layer structure. The upper layer structure is an accelerometer micromechanical sensing structure made of single-crystal silicon, used to sense external acceleration, and gold is deposited on it as electrodes for signal input and output.

[0049] The lower structure is a borosilicate glass substrate, which is used to support the micromechanical sensitive structure of the upper layer; the auxiliary support anchor point 10 is not connected to other structures in the upper layer, and the gap is 10~50μm.

[0050] Please see Figure 2 The micromechanical sensing structure of the accelerometer includes: a mass block 1, a micro-lever amplification structure 2, a first tuning fork resonator 3-1, a second tuning fork resonator 3-2, a first support spring 4, a second support spring 5, a first support anchor point 6, a second support anchor point 7, a third support anchor point 8, a fourth support anchor point 9, and an auxiliary support anchor point 10.

[0051] A coordinate system is established with the center point of the MEMS accelerometer sensor's sensing structure as the origin, and the horizontal and vertical axes as the X and Y axes, respectively, with the sensing axis being the Y-axis. The mass block 1 is connected to two sets of tuning fork resonators 3 via four micro-lever amplification structures 2. The two sets of tuning fork resonators 3 have identical structures and are symmetrical about the X-axis. When an external acceleration input is received, the natural frequency of one of the two tuning fork resonators 3 increases under tension, while the natural frequency of the other decreases under pressure, forming a pair of differential sensing structures to eliminate common-mode interference.

[0052] Four sets of first support springs 4 are arranged at the four corners of the mass block 1 and connected to the first support anchor points 6, so that the mass block 1 is suspended.

[0053] Two sets of second support anchor points 7 are connected to the mass block 1 through two sets of second support springs 5, providing sufficient support stiffness for the suspended mass block 1.

[0054] The auxiliary support anchor points 10 include multiple auxiliary support anchor points 10, which are evenly distributed within the mass block 1. The minimum straight-line distance between any auxiliary support anchor point 10 or between any first support anchor point 6, second support anchor point 7, third support anchor point 8 and fourth support anchor point 9 is less than 2000μm.

[0055] There are 8 auxiliary support anchor points 10.

[0056] Please see Figure 3 Each set of second support springs 5 ​​contains 2×m sections of folding springs 5a and m-1 frame beams 5b, where m is an integer greater than 2; the width of the frame beams 5b is 5~10μm, and the width of the folding springs 5a is 3~5μm.

[0057] Two m-section folding springs 5a are located on the upper and lower sides of the second support anchor point 7, with m sections on each side. The upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point 7.

[0058] The frame beam 5b is a square frame that is connected to the two folded springs 5a. Its centroid coincides with the centroid of the corresponding second support anchor point 7, which makes the mass distribution of the entire support spring uniform, reduces the out-of-plane torque that may be caused by the process or stress, and thus optimizes the processing stability and yield.

[0059] Please see Figure 4 Each tuning fork resonator 3 includes a first vibrating beam 3a and a second vibrating beam 3b, with a distance of 200~500μm between the first vibrating beam 3a and the second vibrating beam 3b.

[0060] The first vibrating beam 3a includes a first fixed driving electrode 11-1 and a first fixed detection electrode 11-2, and the second vibrating beam 3b includes a second fixed driving electrode 11-3 and a second fixed detection electrode 11-4; the first fixed driving electrode 11-1, the second fixed driving electrode 11-3, the first fixed detection electrode 11-2, and the second fixed detection electrode 11-4 are all connected to the glass substrate by anchor points.

[0061] The tuning fork resonator 3 is excited by the first excitation electrode plate or the second excitation electrode plate. The vibration signal detected by the first detection electrode plate and the second detection electrode plate is output after passing through the differential amplifier 12. The feedthrough component in the differential detection signal is suppressed, and a pure motion signal is obtained.

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0063] Example 1

[0064] In existing technologies, the field of microgravity measurement has long faced the technical dilemma of balancing sensor mechanical sensitivity and structural reliability. Traditional resonant accelerometers employ a single resonator structure, which, while increasing the inertial force of the mass block, reduces the stiffness of the sensitive shaft supporting the spring, making it prone to manufacturing collapse. This structural defect of insufficient out-of-plane stiffness makes the device susceptible to impact damage during transportation or operation, hindering the practical application of high-precision sensors. In a case involving a geological exploration device operating underground, the sensor support structure became unstable, causing the resonant frequency to drift and resulting in systematic deviations in the measurement data.

[0065] To address these issues, the research team identified optimizing structural stiffness distribution and stress transmission paths as key areas for improvement. By analyzing the inertial force transmission mechanism of the mass block, they discovered that the symmetrical arrangement of the micro-lever amplification mechanism and resonators can improve signal output stability. Further research revealed that the multi-point distribution of support springs can effectively disperse stress concentration. Based on this, they proposed introducing a differential resonator array into the sensitive structure and constructing a composite support system to balance stiffness requirements.

[0066] Therefore, this application proposes a structural scheme comprising an upper monocrystalline silicon micromechanical sensing structure and a lower glass substrate, with gold electrodes deposited on the surface of the sensing structure. The structure includes a mass block connected by micro-levers and a symmetrical tuning fork resonator assembly, with a fourth support anchor point and second support anchor points on both sides. The second support anchor points are connected to the mass block via support springs, and third support anchor points are located on both sides of the tuning fork resonators. The mass block is suspended at its four corners by first support springs connected to anchor points, and the glass substrate has intermittent auxiliary support anchor points.

[0067] Among them, the single-crystal silicon micromechanical sensing structure refers to a movable component formed by micromachining, which can be realized using deep reactive ion etching (DRIE) technology, and is used to convert inertial force into mechanical deformation. The gold electrode refers to a conductive metal layer, which can be formed using sputtering deposition technology, and is used for electrical signal conversion. The mass block refers to an inertial force sensing element, which can be realized using a rectangular silicon structure, and is used to concentrate inertial force. The micro-lever amplification structure refers to a force transmission mechanism, which can be realized using a hinged beam structure, and is used to amplify the effect of inertial force. The tuning fork resonator refers to a vibration frequency sensing element, which can be realized using a double-beam coupling structure, and is used to convert mechanical deformation into a frequency signal. The support anchor point refers to a structural fixing point, which can be formed using silicon glass anodic bonding technology, and is used to provide structural support. The support spring refers to an elastic connecting component, which can be realized using a folded beam structure, and is used to balance stiffness and deformation requirements. The auxiliary support anchor point refers to an auxiliary fixing point, which can be designed in a discrete manner to prevent processing collapse.

[0068] Specifically, when the mass block is displaced by inertial force, the displacement is amplified and transmitted to the tuning fork resonators through the micro-lever structures on both sides. Two symmetrically arranged sets of resonators generate a differential frequency signal, and the support system formed by the fourth and second support anchor points stabilizes the transmission path. The first support springs form symmetrical supports at the four corners, keeping the mass block in a balanced, suspended state. The auxiliary support anchor points of the glass substrate maintain an appropriate gap with the upper structure, providing temporary support during processing to prevent structural collapse, and not affecting the degrees of freedom of moving parts during device operation. The differential output of the two sets of tuning fork resonators eliminates common-mode interference through signal processing circuitry, improving detection sensitivity.

[0069] Compared to existing technologies, the differential resonator layout effectively suppresses frequency drift caused by changes in ambient temperature, and the symmetrical support structure ensures a more uniform stress distribution. The composite support system, while maintaining low stiffness of the sensitive shaft, enhances out-of-plane stiffness through multi-directional support points. The intermittent auxiliary support design overcomes the limitations of traditional fixed support methods on movable structures, providing necessary support during the manufacturing stage without affecting performance.

[0070] Through the above technical solutions, this application achieves synergistic optimization of mechanical sensitivity and structural reliability, and differential signal processing effectively reduces the impact of feedthrough effect on detection accuracy. The composite support system enables the sensitive structure to maintain low stiffness while possessing impact resistance, and the auxiliary support design significantly improves the yield of microfabrication products. This structural solution solves the technical problem of high-sensitivity sensors being prone to collapse while ensuring microgravity detection accuracy.

[0071] Example 2

[0072] This application further proposes that the second support spring includes 2×m folded spring sections and m-1 frame beams, where m is an integer greater than 2; the frame beams are square frames and are connected to the connection points of the two folded spring sections, and the centroid of the frame beams coincides with the centroid of the corresponding second support anchor point.

[0073] Among them, the folded spring refers to an elastic structure formed by multiple curved beam segments connected in series. Specifically, it can be implemented using a U-shaped or V-shaped zigzag configuration, and the stiffness in the sensitive axis direction is reduced by increasing the effective beam length. The frame beam refers to the rigid support structure surrounding the connection of the folded spring. Specifically, it can be implemented using a rectangular ring beam, and its centroid is aligned with the support anchor point to balance the stress distribution and enhance the structural stability.

[0074] Specifically, when the mass block is displaced by acceleration, the second support spring transmits the amplified inertial force through the elastic deformation of the folding spring. The number of folding spring sections is set to 2×m sections, corresponding to m-1 frame beams. This configuration ensures low-sensitivity axis stiffness while enhancing out-of-plane stiffness through the constraint effect of the frame beams. The connection between the frame beams and the folding springs forms a rigid node, which can suppress parasitic vibrations in non-sensitivity axis directions and prevent unexpected deformation of the support structure.

[0075] Compared to existing technologies, traditional support springs often employ single-section straight beams or simple folded structures, making it difficult to balance out-of-plane stiffness while reducing the stiffness of the sensitive axis. This solution, through an alternating combination of multi-section folded springs and frame beams, maintains low stiffness on the sensitive axis while leveraging the geometric constraints of the frame beams to enhance out-of-plane deformation resistance, thus solving the problem of mass block collapse caused by insufficient out-of-plane stiffness in traditional structures.

[0076] Through the above technical solution, this application achieves a synergistic optimization of high compliance of the support spring in the sensitive axis direction and high stiffness in the non-sensitive axis direction, which not only ensures the mechanical sensitivity of acceleration measurement but also improves the impact resistance of the structure. The centroidal coincidence design of the frame beam and the support anchor point effectively disperses stress concentration, avoids local fracture failure, and enhances the reliability of the device.

[0077] Example 3

[0078] This application further proposes that the folding spring is located on the upper and lower sides of the second support anchor point, with m sections on each side, and the upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point.

[0079] The folded spring refers to an elastic structure formed by multiple connected curved beam segments. It can be made of single-crystal silicon using microfabrication techniques. Through periodic bending, it forms a compressible or stretchable deformation path to transmit mass displacement and buffer external impacts. The centroidal symmetry of the second support anchor point means that the folded springs on the upper and lower sides are mirror images of the anchor point's geometric center. This symmetrical layout can be achieved using photolithographic mask design. This symmetry allows the springs on both sides to undergo complementary deformation under stress, canceling out coupling displacements in non-sensitive axis directions.

[0080] Specifically, when the mass block is displaced by acceleration, the displacement is transmitted to the second support spring through a micro-lever amplification structure. The folded springs on the upper and lower sides are based on a centrally symmetrical layout, producing a symmetrical deformation response when subjected to tension or compression. When the mass block moves along the sensitive axis, the folded beam segments of the upper and lower springs bend synchronously, forming a linear stiffness characteristic; when subjected to out-of-plane impact, the symmetrically arranged springs counteract the lateral displacement component through reverse deformation, suppressing the movement of the mass block along non-sensitive axes. The number of folded spring segments m can be adjusted according to stiffness requirements. For example, when m is 3, a six-segment folded structure is formed, which reduces the equivalent stiffness in the sensitive axis direction while ensuring support stiffness.

[0081] Compared to existing technologies, traditional support springs, which employ a single-sided arrangement or asymmetrical folding structure, are prone to introducing torsional torque when transmitting displacement, resulting in asymmetrical stress distribution in the resonator. This solution, through a centrally symmetrical folding spring layout, balances the deformation of the springs on both sides, eliminating stress concentration caused by structural asymmetry, reducing motion deviation of the micro-lever amplification mechanism, and thus reducing noise components in the resonator's detection signal.

[0082] Through the above technical solution, this application achieves high linearity response of the support spring in the sensitive axis direction, while suppressing the interference of non-sensitive axis displacement on the resonator. The symmetrically arranged folding spring cancels out lateral coupling error through complementary deformation, improves the accuracy of displacement transmission by the micro-lever mechanism, and thus enhances the signal-to-noise ratio of the acceleration detection signal, providing a structural basis for the accurate measurement of weak gravity changes.

[0083] Example 4

[0084] This application further proposes that the width of the frame beam is 5 to 10 micrometers and the width of the folding spring is 5 to 10 micrometers.

[0085] The width of the frame beam refers to the lateral dimension of the transverse or longitudinal beams that constitute the rectangular frame. It can be formed using photolithography and deep reactive ion etching processes, and its width range is determined by balancing the requirements of support stiffness and structural stability. The width of the frame beam directly affects the deformation resistance of the supporting structure and the constraint effect on the folding springs.

[0086] The width of the folded spring refers to the lateral dimension of the spring beam, which can be controlled by adjusting the size of the mask pattern. Its width range is selected based on the matching relationship between the sensitive shaft stiffness and out-of-plane impact resistance. The synergistic effect of the folded spring width and the frame beam can suppress displacement disturbances in non-sensitive directions.

[0087] Specifically, limiting the width of the frame beam to 5 to 10 micrometers provides sufficient constraint stiffness for the folding spring, preventing deformation in non-sensitive directions of the micro-lever amplified structure under acceleration loads. The width of the folding spring is also set to 5 to 10 micrometers, ensuring lower stiffness in the sensitive axis direction to transmit the amplified inertial force, while maintaining higher stiffness in the non-sensitive axis direction to resist external impacts. This matching design of the frame beam and folding spring widths ensures the stability of the supporting structure while avoiding the risk of mass block collapse due to excessively soft springs.

[0088] Compared to existing technologies, traditional designs typically use a single fixed value or an undefined range for the width of the frame beams and folding springs, making it difficult to balance support stiffness and sensitivity. This solution, by limiting the width range of both, improves mechanical sensitivity along the sensitive axis while enhancing impact resistance along non-sensitive axes, thus resolving the structural collapse problem caused by insufficient support stiffness during manufacturing.

[0089] Through the above technical solution, this application realizes the differentiated stiffness design of the support spring in the sensitive axis and non-sensitive axis directions, which not only meets the high sensitivity requirements of microgravity measurement, but also improves the structural reliability of the sensor under complex working conditions, while reducing the difficulty of microfabrication process and the risk of device failure.

[0090] Example 5

[0091] This application further proposes that a tuning fork resonator is excited by a first excitation electrode plate or a second excitation electrode plate, and the vibration signal detected by the first fixed detection electrode and the second fixed detection electrode is output after passing through a differential amplifier.

[0092] Among them, the tuning fork resonator refers to a resonant unit composed of two parallel vibrating beams, which can be implemented by electrostatic driving, by applying an alternating voltage to cause the vibrating beams to undergo periodic deformation.

[0093] The first excitation electrode plate and the second excitation electrode plate refer to the driving electrodes set on both sides of the vibrating beam. Specifically, they can be realized by metal thin film deposition process. The resonant motion of the vibrating beam is excited by alternately applying driving voltage.

[0094] Among them, the differential amplifier refers to the circuit module used to process two detection signals. Specifically, it can be constructed using operational amplifiers to form a differential input structure, thereby extracting the effective vibration signal by canceling common-mode noise.

[0095] Specifically, when external acceleration acts on the mass block, the inertial force is amplified by a micro-lever and transmitted to the tuning fork resonator, causing a change in its resonant frequency. The first and second fixed detection electrodes capture the displacement signal of the vibrating beam, and the two signals exhibit opposite phase changes due to the differential structure. A differential amplifier subtracts the two signals to eliminate environmental interference and circuit noise, retaining the effective signal component related to acceleration.

[0096] Compared to existing technologies, traditional resonant accelerometers use a single-ended detection method, and the shared electrode for the excitation and detection signals leads to a significant feedthrough effect. This solution separates the excitation and detection paths through a differential detection structure, and simultaneously utilizes a differential amplifier to suppress common-mode interference, effectively reducing direct coupling during signal transmission.

[0097] Through the above technical solution, this application can reduce the impact of feedthrough effect on resonator output, improve the signal-to-noise ratio of vibration signal, thereby improving the control accuracy and frequency stability of closed-loop oscillator, and ultimately achieve high-sensitivity measurement of microgravity acceleration.

[0098] Example 6

[0099] This application further proposes a tuning fork resonator including a first vibrating beam and a second vibrating beam, wherein the first vibrating beam and the second vibrating beam are arranged in parallel.

[0100] The first vibrating beam is the core vibrating unit constituting the tuning fork resonator. It can be made of single-crystal silicon material and formed into a slender beam structure through micromachining, with both ends fixed to the substrate via anchor points. The second vibrating beam is a vibrating unit symmetrically arranged with the first vibrating beam. It can be formed into a parallel structure using the same material and process as the first vibrating beam, and the two form a differential detection pair. Parallel arrangement means that the axes of the two vibrating beams are equidistant and oriented in the same direction. This can be achieved by controlling the pattern spacing through photolithography. This layout causes the two beams to deform in opposite directions under load.

[0101] Specifically, when the mass block is displaced by acceleration, the micro-lever amplification structure transmits the displacement to the tuning fork resonator. The parallel first and second vibrating beams undergo symmetrical tensile or compressive deformation under inertial force, causing their resonant frequencies to shift in opposite directions. By detecting the differential frequency signals of the two beams, common-mode interference can be eliminated and the effective signal amplified. The parallel arrangement ensures consistency in the vibration modes of the two beams, avoiding detection errors caused by structural asymmetry, and simultaneously enhancing the resonator's resistance to environmental interference.

[0102] Compared to existing technologies, traditional resonant accelerometers often employ a single vibrating beam structure, where parasitic currents between the driving and sensing electrodes can easily lead to feedthrough effects. This solution utilizes a parallel and symmetrical dual-vibrating beam design, creating a natural differential pair between the driving and sensing signals of the two beams, effectively canceling the common-mode component of the feedthrough current. In existing technologies, non-parallel resonators cause phase mismatch in the sensing signal due to differences in vibration modes; however, this solution ensures perfect matching of the vibration characteristics of the two beams through precise parallel control.

[0103] Through the above technical solutions, this application significantly reduces feedthrough noise in capacitance detection, enabling the complete extraction of the effective vibration signal of the resonator. The differential detection mechanism of the parallel double beams improves the sensitivity of acceleration measurement while suppressing the influence of environmental factors such as temperature drift on detection accuracy. This structural design ensures the long-term stability of the resonator in microgravity measurements, avoiding systematic errors caused by the failure of a single beam structure.

[0104] Example 7

[0105] This application further proposes that the first vibration beam includes a first fixed driving electrode and a first fixed detection electrode, and the second vibration beam includes a second fixed driving electrode and a second fixed detection electrode; the first fixed driving electrode, the first fixed detection electrode, the second fixed driving electrode and the second fixed detection electrode are respectively connected to the glass substrate through anchor points.

[0106] The fixed driving electrode refers to the metal structure used to apply alternating voltage to generate electrostatic force to drive the vibration beam. Specifically, it can be implemented using an interdigitated electrode array, inducing bending vibration in the beam through a periodically changing electric field. The fixed detection electrode refers to the metal structure used to pick up changes in the vibration beam's displacement. Specifically, it can be implemented using a parallel-plate capacitor structure spatially isolated from the driving electrode, reflecting the vibration amplitude by detecting changes in capacitance between the vibration beam and the electrode. The anchor point refers to the support structure that mechanically connects the vibration beam to the substrate and provides electrical conductivity. Specifically, it can be implemented using a silicon pillar structure formed by deep reactive ion etching, establishing a stable electrical path while ensuring the vibration beam's degrees of freedom.

[0107] Specifically, the driving electrode and the detection electrode are spatially separated and positioned on different vibrating beams, allowing the driving signal and the detection signal to form independent transmission paths. When an excitation voltage is applied to the driving electrode, the vibrating beam undergoes forced vibration, changing the capacitance value of the detection electrode. The parasitic capacitance formed between the driving signal and the detection signal due to physical isolation is effectively suppressed. Anchor points uniformly fix the potential reference of each electrode to the glass substrate, avoiding potential drift caused by differences in the displacement of the vibrating beam, and further reducing the coupling strength of stray capacitance between the electrodes.

[0108] Compared to existing technologies, traditional solutions typically employ a coplanar arrangement of the driving and detection electrodes or share the same vibrating beam, causing the excitation signal to leak directly to the detection end through inter-electrode capacitance. This solution, by distributing the driving and detection functions to independent vibrating beams and establishing a potential reference at the substrate, enhances the physical isolation of the signal transmission path and controls the stray capacitance distribution parameters to a lower level.

[0109] Through the above technical solution, this application can effectively suppress the direct feedthrough of the driving signal to the detection end, reduce the interference intensity of background noise in the detection circuit, and thus improve the signal-to-noise ratio of the vibration signal. This design enables the resonator to accurately capture the real vibration response during closed-loop control, providing a stable frequency modulation reference for the subsequent signal processing system, and ultimately improving the accuracy of acceleration measurement.

[0110] Example 8

[0111] This application further proposes that the distance between the first and second vibrating beams is 200~500μm.

[0112] The distance between the first and second vibrating beams refers to the vertical spacing between their central axes when arranged in parallel. This spacing can be achieved by controlling the positional accuracy of the beam structure through photolithography. This distance range balances the relationship between signal detection sensitivity and structural stability. The spacing between the vibrating beams is determined based on the interaction of capacitive and mechanical coupling effects, and can be achieved by adjusting the matching degree between the electrode arrangement area and the vibration mode. This spacing range effectively suppresses direct feedthrough interference between the driving signal and the detection signal.

[0113] Specifically, in the design of the vibration beam configuration of a tuning fork resonator, when the distance between the two vibration beams is too small, the edge electric field coupling between the driving electrode and the detection electrode will exacerbate signal crosstalk; when the distance is too large, the symmetry of the resonator will be compromised due to manufacturing errors. By controlling the distance between 200 and 500 μm, both the differential detection principle can be used to cancel common-mode interference and the symmetrical vibration modes of the vibration beams can be maintained. In practical implementation, a deep reactive ion etching process can be used to form a precise beam spacing, and the effective transfer of vibration energy can be ensured through anchor point layout.

[0114] Compared to existing technologies, the spacing between the vibrating beams in traditional resonant accelerometers is usually not optimized, posing a risk of signal distortion due to random spacing settings. This solution establishes a correlation mechanism between structural parameters and electrical performance by defining the physical boundaries of the vibrating beam spacing, overcoming the feedthrough noise problem caused by improper spacing design in existing technologies.

[0115] Through the above technical solution, this application effectively reduces the direct coupling interference of the driving signal to the detection circuit, ensuring that the change in resonant frequency can be accurately extracted. The setting of this spacing range allows the resonator to maintain high mechanical sensitivity while significantly improving the signal-to-noise ratio of signal detection, providing a reliable frequency reference for the precise measurement of microgravity acceleration.

[0116] Example 9

[0117] This application further proposes that the minimum straight-line distance between any auxiliary support anchor points, or between any first support anchor point, second support anchor point, third support anchor point, and fourth support anchor point, is less than 2000 micrometers.

[0118] The auxiliary support anchor points refer to support structures spaced apart on the glass substrate, maintaining a gap with the single-crystal silicon micromechanical sensing structure. They provide additional support in non-sensitive axis directions and can be made of the same glass material as the substrate through photolithography and etching processes. The minimum straight-line distance refers to the shortest spatial interval between the center points of any two anchor points, which can be achieved by adjusting the mask pattern layout. This distance limit is used to control the distribution density of the support system and avoid insufficient support stiffness in local areas.

[0119] Specifically, in the manufacturing process of single-crystal silicon micromechanical sensitive structures, the spatial arrangement between auxiliary support anchor points and main support anchor points is constrained within a specific distance range. When the anchor point spacing exceeds a critical value, the increased span of the support beam leads to a decrease in out-of-plane stiffness, potentially causing structural collapse. By limiting the minimum straight-line distance, the distribution density of the support system is optimized, effectively suppressing displacement in non-sensitive axis directions when the mass block moves along the sensitive axis, while simultaneously reducing yield losses due to structural deformation during processing.

[0120] In some specific implementations, auxiliary support anchors can be arranged in an array around the main support anchor, for example, using a honeycomb or grid distribution pattern, to balance the support force transmission path. The spacing between the auxiliary support anchors and the main support anchors can be adjusted according to the size of the sensitive structure, for example, using a denser anchor arrangement in the edge area of ​​the mass block.

[0121] Compared to existing technologies, traditional MEMS accelerometers typically employ a sparse support anchor point layout to reduce manufacturing complexity, but this can easily lead to excessively large support beam spans and insufficient out-of-plane stiffness. This solution constructs a high-density distributed support network by limiting the minimum spacing between anchor points. While ensuring flexibility along the sensitive axis, it significantly improves the constraint capability along non-sensitive axes, solving the dual problems of structural collapse during manufacturing and insufficient impact resistance during use.

[0122] Through the above technical solution, this application achieves precise control of the stiffness of the support system, which not only avoids the collapse of the mass block due to insufficient support, but also maintains the low stiffness characteristics in the sensitive axis direction, thereby improving the yield while ensuring the mechanical sensitivity of the sensor.

[0123] Example 10

[0124] This application further proposes that the gap between the auxiliary support anchor point and the single-crystal silicon micromechanical sensitive structure is 10~50μm.

[0125] The auxiliary support anchor points refer to the support structures spaced apart on the glass substrate, used to provide auxiliary support in the non-sensitive axis direction. Specifically, they can be achieved by forming protruding structures on the surface of the glass substrate using photolithography. By limiting the gap distance between this structure and the sensitive structure, it avoids restricting the degrees of freedom of the mass block's motion while enhancing the out-of-plane stiffness of the sensitive structure.

[0126] The gap setting refers to the physical isolation space formed between the auxiliary support anchor point and the single-crystal silicon micromechanical sensitive structure, which can be achieved by controlling the etching depth of the silicon-glass bonding process. This gap range can balance the contradiction between the support effect and motion disturbance. When the gap is less than 10μm, it may cause the anchor point to contact the sensitive structure, while it exceeds 50μm and cannot effectively restrict out-of-plane displacement.

[0127] Specifically, the auxiliary support anchors are arranged at intervals on the surface of the glass substrate, with their top planes maintaining a preset distance from the bottom surface of the single-crystal silicon micromechanical sensing structure. When the sensor is subjected to out-of-plane impact loads, the auxiliary support anchors, through the limiting space formed by the gaps, constrain the sensing structure, preventing the mass block from collapsing due to insufficient stiffness of the support springs. Simultaneously, this gap range ensures that under normal measurement conditions, the auxiliary support anchors will not come into contact with the sensing structure, avoiding the introduction of additional frictional resistance or parasitic capacitance interference.

[0128] Compared to existing technologies, traditional sensors lack auxiliary support anchor points or use fixed connections, making the sensitive structure prone to deformation during processing due to insufficient support stiffness. This solution, by limiting the gap range, preserves the degree of freedom of movement of the sensitive structure in the sensitive axis direction, while enhancing out-of-plane stiffness through a non-contact support design, thus resolving the contradiction between processing collapse and impact resistance.

[0129] Through the above technical solution, this application effectively improves the structural stability of the sensitive structure in microfabrication processes, avoiding the problem of decreased yield due to insufficient support stiffness. Simultaneously, the gap design of the auxiliary support anchor points enhances out-of-plane stiffness without interfering with the vibration transmission path along the sensitive axis, ensuring the mechanical sensitivity of the sensor in microgravity measurements.

[0130] Differential feedthrough suppression effect

[0131] Please see Figure 5 The test results show that differential detection significantly improves the resonator's response amplitude: the response amplitude after differential detection is 2.1 times that before differential detection, greatly improving the detectability of the real vibration signal. Corresponding phase frequency response analysis shows that the phase angle at the resonant frequency of the in-phase mode increases from approximately 135° before differential detection to 180°, and the overall slope of the phase frequency curve increases significantly. This indicates that feedthrough parasitic signal components are effectively suppressed, making closed-loop oscillation easier to achieve and providing crucial support for the realization of stable, high-performance closed-loop circuits.

[0132] Spring stiffness simulation:

[0133] Please see Figure 6 and Figure 7 Simulation results show that the equivalent stiffness of the structure in the X, Y, and Z directions increases with the increase of the frame beam width, with the sensitive axis being the Y-axis. When the beam width exceeds 12 μm, the increase in stiffness in the Y and Z directions slows down. With a beam width of 12 μm, compared to the frameless structure: the stiffness in the X direction increases by approximately 167%; the stiffness in the Y direction (sensitive axis) increases by 26%; and the stiffness in the Z direction increases by 76.6%. This indicates that using a frame beam + folding spring combination to slightly increase the stiffness of the sensitive axis (26%) significantly enhances the stiffness in the non-sensitive axis (X, Z) directions (reaching 167% and 76.6%, respectively), effectively suppressing cross-sensitivity.

[0134] In summary, this invention provides a low-feedthrough MEMS resonant microgravity accelerometer. A differential tuning fork combined with differential detection synchronously suppresses common-mode interference and feedthrough parasitic signals. The auxiliary anchor point provides sufficient support during the silicon wafer thinning and polishing steps in the microfabrication process, preventing the collapse of the movable structure and improving the processing yield. The support spring uses a combination of frame beams and folding springs, which increases the out-of-plane stiffness of the accelerometer without affecting the stiffness of the sensitive shaft, thus improving the shock resistance of the resonant microgravity accelerometer.

[0135] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A low-feedthrough MEMS resonant microgravity accelerometer, characterized in that, It includes an upper monocrystalline silicon micromechanical sensing structure and a glass substrate disposed under the monocrystalline silicon micromechanical sensing structure. Gold electrodes are deposited on the surface of the monocrystalline silicon micromechanical sensing structure. The single-crystal silicon micromechanical sensing structure includes a mass block (1), which is connected to a set of tuning fork resonators through two micro-lever amplification structures (2). The two sets of tuning fork resonators are symmetrically arranged to form a pair of differential sensing structures. A fourth support anchor point (9) is set between the two sets of tuning fork resonators. A second support anchor point (7) is set on both sides of the fourth support anchor point (9). The two sets of second support anchor points (7) are connected to the mass block (1) through corresponding second support springs (5). A third support anchor point (8) is set on both sides of each tuning fork resonator. A first support spring (4) is set at each of the four corners of the mass block (1). Each first support spring (4) is connected to the corresponding first support anchor point (6) so that the mass block (1) is suspended. The tuning fork resonator (3) is excited by the first excitation electrode plate or the second excitation electrode plate. The vibration signal detected by the first fixed detection electrode (11-2) and the second fixed detection electrode (11-4) is output after passing through the differential amplifier (12). The tuning fork resonator (3) includes a first vibration beam (3a) and a second vibration beam (3b). The first vibration beam (3a) and the second vibration beam (3b) are arranged in parallel. The first vibration beam (3a) includes a first fixed driving electrode (11-1) and a first fixed detection electrode (11-2). The second vibration beam (3b) includes a second fixed driving electrode (11-3) and a second fixed detection electrode (11-4). The first fixed driving electrode (11-1), the first fixed detection electrode (11-2), the second fixed driving electrode (11-3), and the second fixed detection electrode (11-4) are respectively connected to the glass substrate through anchor points. The second support spring (5) includes 2×m folding springs (5a) and m-1 frame beams (5b), where m is an integer greater than 2. The frame beams (5b) are square frames and are connected to the connection points of the two folding springs (5a). The centroid of the frame beams (5b) coincides with the centroid of the corresponding second support anchor point (7). The 2×m folding springs (5a) are located on the upper and lower sides of the second support anchor point (7), with m sections on each side. The upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point (7). Multiple auxiliary support anchors (10) are spaced apart on the glass substrate, and the auxiliary support anchors (10) are spaced apart from the single-crystal silicon micromechanical sensitive structure.

2. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, characterized in that, The width of the frame beam (5b) is 5~10μm, and the width of the folding spring (5a) is 5~10μm.

3. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, characterized in that, The distance between the first vibrating beam (3a) and the second vibrating beam (3b) is 200~500μm.

4. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, characterized in that, The minimum straight-line distance between any auxiliary support anchor point (10) or between any first support anchor point (6), second support anchor point (7), third support anchor point (8) and fourth support anchor point (9) is less than 2000 μm.

5. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, characterized in that, The gap between the auxiliary support anchor point (10) and the single-crystal silicon micromechanical sensitive structure is 10~50μm.

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