Low-feed-through MEMS resonant microgravity accelerometer

Abstract

The invention discloses a low-feed-through MEMS resonant microgravity accelerometer which is composed of an upper layer structure and a lower layer structure, the upper layer is an accelerometer micromechanical sensitive structure made of monocrystalline silicon and used for sensing external acceleration, and gold is deposited on the upper layer to serve as an electrode and used for signal input and output. The lower layer is a glass substrate and is used for supporting the micromechanical sensitive structure of the upper layer. According to the tuning fork resonator, differential detection is carried out on the two beams of the tuning fork resonator by adding the detection electrodes, and the feed-through component in the output signal of the resonator is suppressed, so that the problem that the closed-loop oscillation performance is difficult to improve due to the feed-through signal is solved. By adding the auxiliary anchor points, the problem that the resonant microgravity accelerometer has a large mass block and is easy to collapse during processing is solved; by designing the supporting spring with the frame, the out-of-plane rigidity of the accelerometer is improved under the condition that the rigidity of the sensitive shaft is not influenced, and the shock resistance of the resonant microgravity accelerometer is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a low-feedthrough MEMS resonant microgravity accelerometer. Background Art

[0002] Microgravity measurements are of vital practical significance to aerospace, geological exploration, and gravity navigation. Resonant accelerometers, with their advantages such as small size, low cost, high precision, and quasi-digital output, are the future direction of high-precision accelerometer development and are favored and valued by researchers worldwide. The measurement accuracy of resonant accelerometers is affected by factors such as the topology of the sensor's sensitive element, its processing technology, and its drive and detection principles. This results in the resonant frequency shift caused by slight changes in gravitational acceleration being drowned out by the closed-loop oscillator's background noise, making it impossible to accurately measure microgravity changes. Therefore, microgravity measurements require sensors with sufficiently high mechanical sensitivity.

[0003] The core sensitive structure of a resonant accelerometer consists of 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. The inertial force generated by external acceleration is amplified by the micro-lever mechanism and transmitted to the subsequent sensitive resonators. Frequency changes in the sensitive resonators correspond to changes in acceleration.

[0004] For resonant accelerometers, increasing mechanical sensitivity requires a larger mass and a spring beam with lower stiffness in the sensitive axis. However, during micromachining, larger sensitive masses are prone to collapse due to insufficient support stiffness, reducing yield. The stiffness of the non-sensitive axis of the flexible support spring also decreases as the stiffness of the sensitive axis decreases. If the flexible support spring is too soft, insufficient out-of-plane stiffness can cause the mass to collapse when the sensor is subjected to out-of-plane impact, reducing the device's shock resistance.

[0005] On the other hand, building high-performance MEMS oscillators is another key focus for improving resonant accelerometers. Resonant accelerometers generally use capacitive detection schemes. Due to the lack of sufficient impedance between capacitive transducers, the excitation signal is transmitted directly to the output, causing crosstalk with the corresponding dynamic current, a phenomenon known as the feedthrough effect. The presence of the feedthrough effect distorts the amplitude-frequency and phase-frequency responses of the resonator. When the feedthrough component dominates, the resonator's true vibration signal is obscured, affecting the control accuracy of the closed-loop oscillation, deteriorating the oscillator's frequency stability, and thus affecting the accuracy of the sensor. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the deficiencies in the above-mentioned prior art and provide a low-feedthrough MEMS resonant microgravity accelerometer, which is used to solve the technical problems in the existing resonant accelerometers, such as the sensor being subjected to out-of-plane impact during the processing and operation of the large-mass MEMS resonant microgravity accelerometer, the easy collapse of the mass block, and the difficulty in improving the closed-loop oscillation performance due to the feedthrough effect, thereby improving the processing yield, impact resistance and measurement accuracy of the resonant microgravity accelerometer output.

[0007] The present invention adopts the following technical solutions: A low-feedthrough MEMS resonant microgravity accelerometer comprises an upper single-crystal silicon micromechanical sensitive structure and a glass substrate disposed under the single-crystal silicon micromechanical sensitive structure, wherein a gold electrode is deposited on the surface of the single-crystal silicon micromechanical sensitive structure; The single-crystal silicon micromechanical sensitive structure includes a mass block, which is connected to a group of tuning fork resonators via two micro-lever amplification structures. The two groups of tuning fork resonators are symmetrically arranged to form a pair of differential sensitive structures. A fourth support anchor point is provided between the two groups of tuning fork resonators. Second support anchor points are provided on both sides of the fourth support anchor point. The two groups of second support anchor points are connected to the mass block via corresponding second support springs. A third support anchor point is provided on both sides of each tuning fork resonator. First support springs are provided at the four corners of the mass block. Each first support spring is connected to a corresponding first support anchor point to suspend the mass block. A plurality of auxiliary support anchor points are arranged at intervals on the glass substrate, and gaps are set between the auxiliary support anchor points and the single crystal silicon micromechanical sensitive structure.

[0008] Preferably, the second support spring includes 2×m folding springs and m-1 frame beams, where m is an integer greater than; the frame beam is a square frame and is connected to the connection between the two folding springs, and the centroid of the frame beam coincides with the centroid of the corresponding second support anchor point.

[0009] Preferably, 2×m sections of 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.

[0010] Preferably, the width of the frame beam is 5-10 μm, and the width of the folding spring is 5-10 μm.

[0011] Preferably, the tuning fork resonator is excited by the first excitation electrode plate or the 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.

[0012] Preferably, the tuning fork resonator includes a first vibration beam and a second vibration beam, and the first vibration beam and the second vibration beam are arranged in parallel.

[0013] 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.

[0014] Preferably, the distance between the first vibration beam and the second vibration beam is 200-500 μm.

[0015] 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.

[0016] Preferably, the gap between the auxiliary support anchor point and the single crystal silicon micromechanical sensitive structure is 10-50 μm.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention discloses a low-feedthrough MEMS resonant microgravity accelerometer. The symmetrical tuning fork resonator generates a reverse frequency offset when subjected to acceleration, thereby offsetting the same-direction drift caused by temperature / vibration. The auxiliary anchor point supports the large mass block during processing, thereby reducing the collapse rate. After release, there is no contact, thereby ensuring sensitivity. The independent detection electrode differential output offsets the capacitive feedthrough signal with the same phase, thereby resolving the pain point in the background technology where the real signal is obscured by the parasitic signal. The folded spring structure with a frame beam is used to achieve stiffness decoupling, thereby effectively resolving the contradiction between the triple requirements of the microgravity sensor in improving the sensitivity of the sensitive axis, enhancing the anti-collapse capability of the anchor point, and achieving stiffness decoupling, and high precision, impact resistance, and high yield. Furthermore, the square frame beams are connected to the folded spring nodes to optimize stress distribution and avoid fracture caused by stress concentration.

[0018] 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 rate. Furthermore, the folding beam width is 5~10μm to achieve low stiffness of the sensitive axis, and the frame beam width is 5~10μm to improve the out-of-plane stiffness, thereby solving the problem of easy damage to the sensor structure caused by insufficient out-of-plane stiffness. Furthermore, the signals of the two detection electrodes are processed differentially to effectively suppress parasitic signals and eliminate the problem of feedthrough effect masking the real motion signal of the resonator.

[0019] Furthermore, the beam spacing is set within the range of 200 to 500 μm, which optimizes the layout space of the excitation electrodes and the detection electrodes.

[0020] Furthermore, the maximum spacing between the auxiliary support anchors is less than 2000 μm, ensuring sufficient support force to prevent the mass block from collapsing.

[0021] Furthermore, the gap of 10 to 50 μm separates the anchor point from the sensitive structure and prevents the release of etching solution residue, thus reducing the overall process difficulty.

[0022] In summary, the present invention has the characteristics of simple structure and good impact resistance, and can be applied to fields such as aerospace, geological exploration and military applications.

[0023] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings to be used in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 This is a schematic diagram of the sensitive chip; Figure 2 Schematic diagram of a low feedthrough MEMS resonant microgravity accelerometer; Figure 3 Schematic diagram of support spring with frame beam; Figure 4 Schematic diagram of a low-feedthrough tuning fork resonator and detection scheme; Figure 5 It is the amplitude-frequency response diagram corresponding to before and after the difference; Figure 6 It is the phase-frequency response diagram corresponding to before and after the difference; Figure 7 This is a diagram showing the influence of different frame beam widths on the equivalent stiffness of the microspring in the X, Y, and Z directions.

[0026] Among them: 1. Mass block; 2. Micro-lever amplification structure; 3. Tuning fork resonator; 3a. First vibration beam; 3b. Second vibration 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 drive electrode 11-1; First fixed detection electrode 11-2; Second fixed drive electrode 11-3; Second fixed detection electrode 11-4; 12. Differential amplifier. DETAILED DESCRIPTION

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "one side", "one end", "one side" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0029] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0030] It will be understood that when used in this specification and the appended claims, the terms “comprises” and “comprising” indicate the presence of described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0031] It should also be understood that the terms used in the present specification are only for the purpose of describing particular embodiments and are not intended to limit the present invention. As used in the present 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.

[0032] It should be further understood that the term "and / or" used in the present description and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0033] The accompanying drawings illustrate various schematic diagrams of structures according to embodiments disclosed herein. These figures are not drawn to scale; for clarity, some details are exaggerated and some details may be omitted. The shapes of the various regions and layers shown in the figures, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Those skilled in the art may design regions / layers with different shapes, sizes, and relative positions as needed.

[0034] This invention provides a low-feedthrough MEMS resonant microgravity accelerometer. A symmetrical tuning fork resonator operates differentially under acceleration (one pull, one compress), with differential detection via independent electrodes, simultaneously suppressing common-mode interference and feedthrough noise. Auxiliary anchors are embedded in the mass with a spacing of less than 2000μm, providing support (to prevent collapse) during machining and detaching with a gap of 10-50μm after release. The first support spring has a low stiffness in the sensitive axis to ensure sensitivity. The second support spring utilizes a frame beam + folded spring combination, increasing the accelerometer's out-of-plane stiffness without affecting the stiffness in the sensitive axis, thereby improving the resonant microgravity accelerometer's impact resistance. This effectively balances high precision, impact resistance, and high yield. By adding detection electrodes to differentially detect the two vibration beams of the tuning fork resonator, the feedthrough component in the resonator's output signal is suppressed, addressing the difficulty of improving closed-loop oscillation performance due to feedthrough. The addition of auxiliary anchors addresses the problem of large masses in resonant microgravity accelerometers, which are prone to collapse during machining.

[0035] See also Figure 1 The present invention discloses a low-feedthrough MEMS resonant microgravity accelerometer, comprising an upper and lower structure. The upper structure is a micromechanical sensitive structure of the accelerometer, made of single-crystal silicon, and is used to sense external acceleration. Gold is deposited on the upper structure as electrodes for signal input and output. 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 of the upper layer, and the gap is 10~50μm.

[0036] See also Figure 2 The accelerometer micromechanical sensitive structure 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 and a fourth support anchor point 9, and an auxiliary support anchor point 10.

[0037] A coordinate system is established with the center point of the MEMS accelerometer sensor's sensitive structure as the origin, and the horizontal and vertical axes as the X and Y axes, respectively, with the Y axis as the sensitive axis. The mass 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 are identical in structure and symmetrical about the X axis. When an external acceleration input is applied, the natural frequency of one tuning fork resonator 3 increases due to tension, while the natural frequency of the other decreases due to compression, forming a differential sensing pair to eliminate common-mode interference.

[0038] Four groups 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 to suspend the mass block 1 .

[0039] The two groups of second support anchor points 7 are connected to the mass block 1 through the two groups of second support springs 5 ​​, providing sufficient support stiffness for the suspended mass block 1 .

[0040] The auxiliary support anchor points 10 include multiple auxiliary support anchor points 10, which are evenly distributed in the mass block 1. The minimum straight-line distance between any auxiliary support anchor points 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.

[0041] The number of auxiliary support anchor points 10 is 8.

[0042] See also Figure 3 Each group of second support springs 5 ​​contains 2×m folding springs 5a and m-1 frame beams 5b, where m is an integer greater than 2; the width of the frame beam 5b is 5~10μm, and the width of the folding spring 5a is 3~5μm.

[0043] 2×m sections of folding springs 5a are located on the upper and lower sides of the second support anchor point 7, with m sections on each side, and the upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point 7.

[0044] The frame beam 5b is a square frame, which is connected to the connection point of the two folding springs 5a. Its centroid coincides with the centroid of the corresponding second support anchor point 7, so that the mass of the entire support spring is evenly distributed, reducing the out-of-plane torque that may be caused by the process or stress, thereby optimizing the processing stability and yield. See also Figure 4 Each tuning fork resonator 3 includes a first vibration beam 3a and a second vibration beam 3b, and the distance between the first vibration beam 3a and the second vibration beam 3b is 200-500 μm.

[0045] The first vibration beam 3a includes a first fixed driving electrode 11-1 and a first fixed detection electrode 11-2, and 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 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 through anchor points.

[0046] The tuning fork resonator 3 is excited by the first excitation electrode plate or the second excitation electrode plate, and 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 will be suppressed to obtain a pure motion signal.

[0047] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0048] Example 1 In the existing technology, the field of microgravity measurement has long faced the technical contradiction of finding a balance between the mechanical sensitivity of sensors and the reliability of their structures. Traditional resonant accelerometers use a single resonator structure. While increasing the inertial force of the mass block, the stiffness of the sensitive axis of the supporting spring is reduced, which can easily lead to processing collapse. The structural defect of insufficient out-of-plane stiffness makes the device susceptible to impact damage during transportation or operation, restricting the practical application of high-precision sensors. When a certain type of geological exploration equipment was operating underground, the resonant frequency drifted due to the instability of the sensor support structure, resulting in systematic deviations in the measurement data.

[0049] To address these issues, the R&D team identified optimizing the structural stiffness distribution and stress transfer paths as key areas for improvement. By analyzing the inertial force transmission mechanism of the mass block, they found that a symmetrical layout of the micro-lever amplification mechanism and resonators could improve signal output stability. Further research revealed that a multi-point distribution of support springs effectively dispersed stress concentration. Based on this, they proposed introducing a differential resonator array within the sensitive structure and constructing a composite support system to balance stiffness requirements.

[0050] Therefore, this application proposes a structural solution comprising an upper monocrystalline silicon micromechanical sensitive structure and a lower glass substrate, with gold electrodes deposited on the surface of the sensitive structure. This structure comprises a mass block and a symmetrical tuning fork resonator group connected by a microlever, with a fourth support anchor point and second support anchor points on either side. The second support anchor points are connected to the mass block via support springs, and third support anchor points are provided on either side of the tuning fork resonator. The four corners of the mass block are suspended by connecting anchor points via the first support springs, and interstitial auxiliary support anchor points are provided on the glass substrate.

[0051] Among them, the single-crystal silicon micromechanical sensitive structure refers to a movable component formed through micromachining, which can be achieved through deep reactive ion etching (DRE) and is used to convert inertial force into mechanical deformation. The gold electrode refers to a metal conductive layer, which can be formed through sputtering deposition and is used to convert electrical signals. The mass block refers to an inertial force sensing element, which can be implemented as a rectangular silicon structure and is used to concentrate inertial force. The microlever amplification structure refers to a force transmission mechanism, which can be implemented as a hinged beam structure and is used to amplify inertial force. The tuning fork resonator refers to a vibration frequency sensitive element, which can be implemented as a dual-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 through silicon glass anodic bonding and is used to provide structural support. The support spring refers to an elastic connecting component, which can be implemented as 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 with a discrete distribution to prevent machining collapse.

[0052] Specifically, when the mass block is displaced by inertial force, the displacement is amplified by the micro-lever structures on both sides and then transmitted to the tuning fork resonator. The two symmetrically arranged sets of resonators generate differential frequency signals, and the support system formed by the fourth support anchor and the second support anchor stabilizes the transmission path. The first support spring forms symmetrical supports at the four corners, keeping the mass block in a balanced and suspended state. The auxiliary support anchors of the glass substrate maintain an appropriate gap with the upper structure, providing temporary support to prevent structural collapse during processing, and not affecting the freedom of the movable parts when the device is operating. The differential output of the two sets of tuning fork resonators eliminates common-mode interference through the signal processing circuit, thereby improving detection sensitivity.

[0053] Compared to existing technologies, the differential resonator layout effectively suppresses frequency drift caused by ambient temperature changes, and the symmetrical support structure ensures more uniform stress distribution. The composite support system maintains low stiffness in the sensitive axis while improving out-of-plane stiffness through multi-directional support points. The interstitial auxiliary support design overcomes the limitations of traditional fixed support methods on movable structures, providing necessary support during processing without affecting performance.

[0054] Through the above-mentioned technical solution, this application achieves the coordinated optimization of mechanical sensitivity and structural reliability. Differential signal processing effectively reduces the impact of feedthrough effects on detection accuracy. The composite support system enables the sensitive structure to maintain low stiffness while also possessing impact resistance. The auxiliary support design significantly improves the micromachining yield rate. This structural solution solves the technical problem of high-sensitivity sensors being prone to collapse while ensuring the accuracy of microgravity detection.

[0055] Example 2 The present application further proposes that the second support spring includes 2×m folding springs and m-1 frame beams, where m is an integer greater than 2; the frame beam is a square frame and is connected to the connection between the two folding springs, and the centroid of the frame beam coincides with the centroid of the corresponding second support anchor point.

[0056] The folding spring is an elastic structure formed by multiple curved beam segments connected in series. This can be achieved using a U-shaped or V-shaped zigzag configuration. This reduces stiffness along the sensitive axis by increasing the effective beam length. The frame beam is a rigid support structure surrounding the folding spring connection. This can be achieved using a rectangular ring beam. Aligning its centroid with the support anchor point balances stress distribution and enhances structural stability.

[0057] Specifically, when the mass is displaced by acceleration, the second support spring transmits the amplified inertial force through the elastic deformation of the folding spring. The folding spring has 2×m sections, corresponding to m-1 frame beams. This configuration ensures low stiffness in the sensitive axis while enhancing out-of-plane stiffness through the constraining effect of the frame beams. The connection between the frame beam and the folding spring forms a rigid node, which suppresses parasitic vibrations along the non-sensitive axis and prevents unintended deformation of the support structure.

[0058] Compared with existing technologies, traditional support springs often use single-section straight beams or simple folding structures, which make it difficult to simultaneously reduce the stiffness of the sensitive axis and maintain out-of-plane stiffness. This solution, through the alternating combination of multi-section folding springs and frame beams, maintains low stiffness along the sensitive axis while leveraging the geometric constraints of the frame beams to enhance out-of-plane deformation resistance. This solves the problem of mass collapse caused by insufficient out-of-plane stiffness in traditional structures.

[0059] Through the above technical solution, this application achieves the coordinated optimization of the support spring's high compliance along the sensitive axis and high stiffness along the non-sensitive axis, ensuring the mechanical sensitivity of acceleration measurement while improving the structure's impact resistance. The design of the centroid of the frame beam and the support anchor point aligning effectively disperses stress concentration, avoids localized fracture failure, and enhances the reliability of the device.

[0060] Example 3 The present application further proposes that the folding spring is located on the upper and lower sides of the second support anchor point, with m sections set on each side, and the upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point.

[0061] The folding spring is an elastic structure formed by multiple curved beam segments connected in series. It can be fabricated using single-crystal silicon through micromachining. Periodic bending creates a compressible or tensile deformation path, which transmits mass displacement and cushions external impacts. The centroidal symmetry of the second support anchor means that the folding springs on the upper and lower sides are mirror images relative to the anchor's geometric center. This symmetric layout can be achieved using photolithography mask layout design. This symmetry results in complementary deformation of the two springs under load, offsetting coupled displacement along the non-sensitive axis.

[0062] Specifically, when the mass block is displaced by acceleration, the displacement is transmitted to the second support spring through the micro-lever amplification structure. The folding springs on the upper and lower sides are based on a centrally symmetrical layout, and produce symmetrical deformation responses when subjected to tension or pressure. When the mass block moves along the sensitive axis, the folded beam sections of the upper and lower springs bend synchronously to form a linear stiffness characteristic; when subjected to out-of-plane impact, the symmetrically arranged springs offset the lateral displacement component through reverse deformation, thereby suppressing the non-sensitive axis movement of the mass block. The number of sections m of the folding spring can be adjusted according to the stiffness requirements. For example, when m is 3, a six-section folding structure is formed, which reduces the equivalent stiffness in the sensitive axis direction while ensuring the support stiffness.

[0063] Compared to existing technologies, traditional support springs employ a unilateral arrangement or asymmetric folding structures, which can easily introduce torsional torque when transmitting displacement and result in asymmetric stress distribution in the resonator. This solution utilizes a centrally symmetrical folding spring layout to balance the deformation of the upper and lower springs, eliminating stress concentration caused by structural asymmetry and reducing the motion deviation of the micro-lever amplification mechanism, thereby reducing the noise component in the resonator's detection signal.

[0064] Through the above technical solution, this application achieves a highly linear response of the support spring along the sensitive axis while suppressing the interference of displacement along the non-sensitive axis on the resonator. The symmetrically arranged folded springs offset lateral coupling errors through complementary deformation, improving the accuracy of displacement transmission by the micro-lever mechanism and, in turn, enhancing the signal-to-noise ratio of the acceleration detection signal, providing a structural foundation for the precise measurement of weak gravity changes.

[0065] Example 4 The present application further proposes that the width of the frame beam is 5 to 10 microns, and the width of the folding spring is 5 to 10 microns.

[0066] The width of the frame beam refers to the transverse dimension of the horizontal or vertical beams that comprise the rectangular frame. It can be formed using photolithography and deep reactive ion etching processes. Its width is determined by balancing support stiffness with structural stability requirements. The width of the frame beam directly affects the support structure's ability to resist deformation and its ability to constrain the folding spring.

[0067] The width of the folding spring refers to the lateral dimension of the spring beam. This can be controlled by adjusting the mask pattern size. The width range is selected based on the relationship between the stiffness of the sensitive axis and the out-of-plane impact resistance. The folding spring width works in conjunction with the frame beam to suppress displacement interference in non-sensitive directions.

[0068] Specifically, when the width of the frame beam is limited to 5 to 10 microns, it can provide sufficient constraint stiffness for the folding spring, preventing the micro-lever amplification structure from deforming in non-sensitive directions under acceleration loads. The width of the folding spring is also set to 5 to 10 microns, giving it low stiffness in the sensitive axis direction to transmit the amplified inertial force, while maintaining high stiffness in the non-sensitive axis direction to resist external impact. The matching width design of the frame beam and the folding spring ensures the stability of the support structure while avoiding the risk of mass collapse due to overly soft springs.

[0069] Compared to existing technologies, traditional designs often use a single fixed value or an undefined range for the width of the frame beam and folding spring, making it difficult to balance support stiffness and sensitivity. By limiting the width range of both, this solution improves mechanical sensitivity along the sensitive axis while enhancing impact resistance along the non-sensitive axis, thus resolving the problem of structural collapse caused by insufficient support stiffness during processing.

[0070] 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 the micromachining process and the risk of device failure.

[0071] Example 5 The present application further proposes that the tuning fork resonator is excited by the first excitation electrode plate or the 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.

[0072] Among them, the tuning fork resonator refers to a resonant unit composed of two parallel vibrating beams, which can be specifically realized by electrostatic drive, and the vibrating beams are caused to produce periodic deformation by applying an alternating voltage.

[0073] The first excitation electrode plate and the second excitation electrode plate refer to driving electrodes arranged on both sides of the vibration beam, which can be implemented by a metal thin film deposition process, and the resonant motion of the vibration beam is excited by alternately applying driving voltages.

[0074] Among them, the differential amplifier refers to a circuit module used to process two detection signals. Specifically, an operational amplifier can be used to form a differential input structure to extract the effective vibration signal by offsetting the common-mode noise.

[0075] Specifically, when external acceleration acts on the mass, the inertial force is amplified by a microlever and transmitted to the tuning fork resonator, causing its resonant frequency to shift. The first and second fixed detection electrodes respectively capture the displacement signals of the vibrating beam. Due to the differential structure, the two signals exhibit opposite phase shifts. A differential amplifier subtracts the two signals, eliminating environmental interference and circuit noise while retaining the effective signal component related to acceleration.

[0076] Compared with existing technologies, traditional resonant accelerometers use single-ended detection, where the excitation and detection signals share a common electrode, leading to significant feedthrough. This solution separates the excitation and detection paths through a differential detection structure, while also utilizing a differential amplifier to suppress common-mode interference, effectively reducing direct coupling during signal transmission.

[0077] Through the above technical solution, the present application can reduce the influence of the feedthrough effect on the resonator output, improve the signal-to-noise ratio of the vibration signal, thereby improving the control accuracy and frequency stability of the closed-loop oscillator, and ultimately achieve high-sensitivity measurement of microgravity acceleration.

[0078] Example 6 The present application further proposes that the tuning fork resonator includes a first vibration beam and a second vibration beam, and the first vibration beam and the second vibration beam are arranged in parallel.

[0079] The first vibration beam refers to the core vibration unit that constitutes the tuning fork resonator. Specifically, it can be realized by using single-crystal silicon material through micromachining to form a slender beam structure, and its two ends are fixed to the substrate by anchor points. The second vibration beam refers to a vibration unit arranged symmetrically with the first vibration beam. Specifically, it can be formed into a parallel structure using the same material and process as the first vibration beam. The two constitute a differential detection pair. The parallel arrangement means that the axes of the two vibration beams are equidistant and in the same direction. Specifically, it can be achieved by controlling the pattern spacing through photolithography. This layout causes the two beams to produce opposite deformations when loaded.

[0080] Specifically, when the mass is displaced by acceleration, a microlever amplification structure transmits the displacement to the tuning fork resonator. The parallel first and second vibration beams undergo symmetrical tensile or compressive deformation under the action of inertial forces, causing the resonant frequencies of the two beams to shift in opposite directions. By detecting the differential frequency signal of the two beams, common-mode interference is eliminated and the effective signal is amplified. The parallel arrangement ensures consistency in the vibration modes of the two beams, avoiding detection errors caused by structural asymmetry and enhancing the resonator's resistance to environmental interference.

[0081] Compared to existing technologies, traditional resonant accelerometers often use a single vibrating beam structure, where parasitic currents between the drive and detection electrodes can easily lead to feedthrough. This solution utilizes a parallel, symmetrical dual vibrating beam design, creating a natural differential pair between the drive and detection signals, effectively canceling out the common-mode component of the feedthrough current. Unlike existing technologies where non-parallel resonators can cause phase mismatch in the detection signals due to differences in vibration modes, this solution ensures perfect matching of the vibration characteristics of the two beams through precise parallel control.

[0082] Through the above technical solution, this application significantly reduces the feedthrough noise in capacitance detection, allowing the effective vibration signal of the resonator to be fully extracted. The differential detection mechanism of the parallel dual beams improves the sensitivity of acceleration measurement while suppressing the impact of environmental factors such as temperature drift on detection accuracy. This structural design ensures the long-term stability of the resonator in microgravity measurements and avoids systematic errors caused by the failure of a single beam structure.

[0083] Example 7 The present 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.

[0084] Among them, the fixed driving electrode refers to a metal structure used to apply an alternating voltage to generate an electrostatic force to drive the vibration beam to vibrate. Specifically, it can be implemented by an array of interdigitated electrodes, and the vibration beam is induced to generate bending vibrations through the periodically changing electric field force. The fixed detection electrode refers to a metal structure used to pick up the displacement change of the vibration beam. Specifically, it can be implemented by a parallel plate capacitor structure that is spatially isolated from the driving electrode, and the vibration amplitude is reflected by detecting the change in capacitance between the vibration beam and the electrode. The anchor point refers to a supporting structure that mechanically connects the vibration beam to the substrate and electrically conducts the vibration. Specifically, it can be implemented by a silicon pillar structure formed by deep reactive ion etching, which establishes a stable electrical path while ensuring the freedom of the vibration beam.

[0085] Specifically, the driving electrode and the detection electrode are spatially separated and arranged on different vibration beams, so that the driving signal and the detection signal form independent transmission paths. When the driving electrode applies an excitation voltage, the vibration beam generates forced vibration and changes the capacitance value of the detection electrode, while the parasitic capacitance formed by the physical isolation between the driving signal and the detection signal is effectively suppressed. The anchor point fixes the potential reference of each electrode to the glass substrate, avoiding the potential drift caused by the difference in the displacement of the vibration beam and further reducing the coupling strength of the stray capacitance between the electrodes.

[0086] Compared to existing technologies, traditional solutions often employ coplanar arrangements of drive and detection electrodes or share the same vibration beam, causing the excitation signal to leak directly to the detection terminal through inter-electrode capacitance. This solution distributes the drive and detection functions to independent vibration beams and establishes a potential reference at the substrate, enhancing the physical isolation of the signal transmission path and minimizing the distribution parameters of stray capacitance.

[0087] Through the above technical solution, this application can effectively suppress the direct feedthrough of the drive 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 true vibration response during closed-loop control, providing a stable frequency modulation reference for the subsequent signal processing system, and ultimately achieving improved acceleration measurement accuracy.

[0088] Example 8 The present application further proposes that the distance between the first vibration beam and the second vibration beam is 200-500 μm.

[0089] The distance between the first and second vibration beams refers to the vertical spacing between their central axes when the two beams are arranged in parallel. This can be achieved by controlling the positional accuracy of the beam structure through photolithography. This distance range balances signal detection sensitivity and structural stability. The spacing between the vibration beams is determined by the interaction between capacitive coupling and mechanical coupling effects, specifically by adjusting the matching degree between the electrode layout area and the vibration mode. This spacing range effectively suppresses direct feedthrough interference between the drive signal and the detection signal.

[0090] Specifically, in the vibration beam configuration design of the tuning fork resonator, when the spacing between the two vibration beams is too small, the fringe electric field coupling between the driving electrode and the detection electrode will aggravate signal crosstalk; when the spacing is too large, the symmetry of the resonator will be damaged due to processing errors. By controlling the spacing within the range of 200-500μm, the differential detection principle can be used to offset common-mode interference while maintaining the symmetrical vibration mode of the vibration beam. In the specific implementation process, a deep reactive ion etching process can be used to form a precise beam spacing, and the anchor point layout can be used to ensure the effective transmission of vibration energy.

[0091] Compared to existing technologies, the spacing between the vibration beams in traditional resonant accelerometers is typically not optimized, leading to the risk of signal distortion due to random spacing. This solution establishes a correlation between structural parameters and electrical performance by defining the physical boundaries of the vibration beam spacing, overcoming the feedthrough noise issue caused by improper spacing design in existing technologies.

[0092] Through the above technical solution, this application effectively reduces the direct coupling interference of the drive signal on the detection circuit, ensuring that the resonant frequency change can be accurately extracted. Setting 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 accurate measurement of microgravity acceleration.

[0093] Example 9 The present 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 microns.

[0094] Auxiliary support anchors are support structures spaced apart on the glass substrate, maintaining a gap between them and the single-crystal silicon micromechanical sensitive structure to provide additional support along the non-sensitive axis. Specifically, they can be fabricated using the same glass material as the substrate through photolithography and etching processes. The minimum straight-line distance, defined as the shortest spatial separation between the centers of any two anchors, 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.

[0095] Specifically, during the fabrication of single-crystal silicon micromechanical sensitive structures, the spatial arrangement between the auxiliary support anchors and the main support anchors is constrained to a specific distance range. When the anchor spacing exceeds a critical value, the span of the support beam increases, resulting in a decrease in out-of-plane stiffness, which may cause structural collapse. By limiting the minimum straight-line distance, the distribution density of the support system is optimized, effectively suppressing displacement along the non-sensitive axis when the mass moves along the sensitive axis, while also reducing yield losses caused by structural deformation during processing.

[0096] In some embodiments, the auxiliary support anchors can be arranged in an array around the primary support anchors, for example, in a honeycomb or grid pattern, to balance the force transmission path. The spacing between the auxiliary support anchors and the primary support anchors can be adjusted based on the size of the sensitive structure, for example, by using a denser anchor arrangement at the edge of the mass.

[0097] Compared with existing technologies, traditional MEMS accelerometers typically use a sparse support anchor layout to reduce process complexity, but this can easily lead to excessive support beam spans and insufficient out-of-plane stiffness. This solution, by limiting the minimum spacing between anchor points, constructs a high-density distributed support network. While maintaining flexibility along the sensitive axis, it significantly improves the restraint capability along the non-sensitive axis, resolving the dual issues of structural collapse during processing and insufficient impact resistance during use.

[0098] Through the above technical solution, the present 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 direction of the sensitive axis, thereby improving the yield while ensuring the mechanical sensitivity of the sensor.

[0099] Example 10 The present application further proposes that the gap between the auxiliary support anchor point and the single crystal silicon micromechanical sensitive structure is 10 to 50 μm.

[0100] Auxiliary support anchors are spaced apart on the glass substrate to provide auxiliary support along the non-sensitive axis. These are achieved by forming raised structures on the glass substrate using a photolithographic process. By limiting the gap distance from the sensitive structure, these structures not only avoid constraining the freedom of motion of the proof-mass but also enhance the out-of-plane stiffness of the sensitive structure.

[0101] The gap setting refers to the physical isolation space between the auxiliary support anchor and the single-crystal silicon micromechanical sensitive structure. This can be achieved by controlling the etching depth of the silicon-glass bonding process. This gap range can balance the contradiction between support effect and motion interference. When the gap is less than 10μm, the anchor may contact the sensitive structure, while exceeding 50μm will not effectively limit out-of-plane displacement.

[0102] Specifically, the auxiliary support anchors are spaced apart 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 sensitive structure. When the sensor is subjected to out-of-plane impact loads, the auxiliary support anchors create a limited space between them, constraining the sensitive structure and preventing the mass block from collapsing due to insufficient support spring stiffness. Furthermore, this gap ensures that under normal measurement conditions, the auxiliary support anchors do not come into contact with the sensitive structure, avoiding the introduction of additional frictional resistance or parasitic capacitance interference.

[0103] Compared to existing technologies, traditional sensors lack auxiliary support anchors or employ fixed connections, which can easily cause deformation of the sensitive structure during machining due to insufficient support stiffness. This solution, by limiting the gap range, preserves the freedom of movement of the sensitive structure along the sensitive axis while enhancing out-of-plane stiffness through a non-contact support design, resolving the conflict between machining collapse and impact resistance.

[0104] Through the above technical solution, this application effectively improves the structural stability of the sensitive structure during micromachining, avoiding the problem of reduced yield due to insufficient support stiffness. Furthermore, 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, thus ensuring the mechanical sensitivity of the sensor in microgravity measurements.

[0105] Differential feedthrough suppression effect See also Figure 5 The test results show that differential detection significantly improves the response amplitude of the resonator: the response amplitude after differentiation reaches 2.1 times that before differentiation, greatly improving the detectability of the real vibration signal. The corresponding phase-frequency response analysis shows that the phase angle at the resonant frequency of the in-phase mode increases from approximately 135° before differentiation to 180°, and the overall slope of the phase-frequency curve increases significantly. This shows that the feedthrough parasitic signal components are effectively suppressed, making closed-loop oscillation easier to achieve, providing key support for the realization of a stable, high-performance closed-loop circuit. Spring stiffness simulation: See also Figure 6 and Figure 7 Simulation results show that the equivalent stiffness of the structure in the X, Y, and Z directions increases with increasing frame beam width, with the Y axis being the most sensitive. When the beam width exceeds 12μm, the increase in stiffness in the Y and Z directions slows. With a beam width of 12μm, 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 while the stiffness in the sensitive axis is slightly increased (by 26%) using the frame beam + folded spring combination, the stiffness in the non-sensitive axes (X and Z) is significantly enhanced (by 167% and 76.6%, respectively), effectively suppressing cross-sensitivity.

[0106] In summary, the present invention presents a low-feedthrough MEMS resonant microgravity accelerometer. A differential tuning fork coupled with differential detection simultaneously suppresses common-mode interference and feedthrough parasitic signals. Auxiliary anchor points provide sufficient support for silicon wafer thinning and polishing during micromachining, preventing collapse of the movable structure and improving machining yield. The support spring utilizes a frame beam combined with a folded spring, increasing the accelerometer's out-of-plane stiffness without compromising the stiffness of the sensitive axis, thereby enhancing the resonant microgravity accelerometer's impact resistance.

[0107] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A low feedthrough MEMS resonant microgravity accelerometer, characterized in that: The invention comprises an upper single-crystal silicon micromechanical sensitive structure and a glass substrate arranged under the single-crystal silicon micromechanical sensitive structure, wherein a gold electrode is deposited on the surface of the single-crystal silicon micromechanical sensitive structure; The single crystal silicon micromechanical sensitive structure includes a mass block (1), the mass block (1) is connected to a group of tuning fork resonators through two micro-lever amplification structures (2), the two groups of tuning fork resonators are symmetrically arranged to form a pair of differential sensitive structures, a fourth support anchor point (9) is provided between the two groups of tuning fork resonators, second support anchor points (7) are provided on both sides of the fourth support anchor point (9), the two groups of second support anchor points (7) are connected to the mass block (1) through corresponding second support springs (5), and third support anchor points (8) are provided on both sides of each tuning fork resonator; first support springs (4) are provided at the four corners of the mass block (1), and each first support spring (4) is connected to the corresponding first support anchor point (6) so that the mass block (1) is suspended; A plurality of auxiliary support anchor points (10) are arranged at intervals on the glass substrate, and gaps are provided between the auxiliary support anchor points (10) and the single crystal silicon micromechanical sensitive structure.

2. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, characterized in that: The second support spring (5) includes 2×m sections of folding springs (5a) and m-1 frame beams (5b), where m is an integer greater than (2); the frame beam (5b) is a square frame and is connected to the connection point of the two sections of folding springs (5a), and the centroid of the frame beam (5b) coincides with the centroid of the corresponding second support anchor point (7).

3. The low feedthrough MEMS resonant microgravity accelerometer according to claim 2, characterized in that: 2×m sections of folding springs (5a) are located on the upper and lower sides of the second support anchor point (7), with m sections on each side, and the upper and lower sides are symmetrical about the centroid of the corresponding second support anchor point (7).

4. The low feedthrough MEMS resonant microgravity accelerometer according to claim 2, wherein: The width of the frame beam (5b) is 5 to 10 μm, and the width of the folding spring (5a) is 5 to 10 μm.

5. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, wherein: The tuning fork resonator (3) is excited by the first excitation electrode plate or the second excitation electrode plate, and 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).

6. The low feedthrough MEMS resonant microgravity accelerometer according to claim 5, characterized in that: The tuning fork resonator (3) comprises a first vibration beam (3a) and a second vibration beam (3b), and the first vibration beam (3a) and the second vibration beam (3b) are arranged in parallel.

7. The low feedthrough MEMS resonant microgravity accelerometer according to claim 6, characterized in that: The first vibration beam (3a) includes a first fixed driving electrode (11-1) and a first fixed detection electrode (11-2), and 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.

8. The low feedthrough MEMS resonant microgravity accelerometer according to claim 6, wherein: The distance between the first vibration beam (3a) and the second vibration beam (3b) is 200-500 μm.

9. The low feedthrough MEMS resonant microgravity accelerometer according to claim 1, wherein: The minimum straight-line distance between any auxiliary support anchor points (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.

10. 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 10-50 μm.

Images