A low-noise MEMS accelerometer

Abstract

The application discloses a low-noise MEMS accelerometer, which increases the sensitive mass, reduces the resonance frequency and improves the quality factor through a large-size mass block, multiple sets of series folded beams and upper and lower glass cover plate structures with cavities, so that the accelerometer with low thermal mechanical noise is realized; meanwhile, the displacement-capacitance sensing array based on the triangular electrode optimizes the electrode arrangement mode in unit area and improves the capacitance sensing sensitivity. The application realizes the mass-spring oscillator structure with low noise through deep reactive ion etching technology, realizes the sandwiched accelerometer structure of glass-silicon-glass through thermal compression bonding and glue bonding, and improves the performance of the MEMS accelerometer.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) technology, and specifically relates to a low-noise MEMS accelerometer. Background Technology

[0002] Micro-Electro-Mechanical Systems (MEMS) encompass microsensors, microactuators, and corresponding processing circuits, representing a new discipline developed based on microelectronics and micromechanical technologies. Manufactured using integrated circuit-compatible mass production techniques, the components are measured in millimeters to micrometers. Compared to traditional mechanical devices, they offer advantages such as small size, light weight, high reliability, and ease of integration, significantly improving the automation, intelligence, and reliability of systems. MEMS accelerometers are inertial instruments that utilize micromachining technology to convert acceleration signals into inertial forces for physical quantity detection. Compared to traditional accelerometers, MEMS accelerometers offer advantages such as small size, low cost, strong overload resistance, and mass production capability. Currently, MEMS accelerometers are not only becoming core components of miniature inertial measurement systems but are also rapidly expanding into other civilian applications. Traditional MEMS accelerometers are primarily used in low-precision scenarios such as automotive electronics and commercial electronics, but their high inherent noise level makes them unsuitable for high-precision tasks such as earthquake early warning and oil and gas exploration. Given the limited research and development of low-noise MEMS accelerometers, designing a low-noise MEMS accelerometer capable of detecting micro-vibration signals is a problem that needs to be solved at this stage. Summary of the Invention

[0003] The purpose of this invention is to provide a low-noise MEMS accelerometer that achieves an overall structure with a large sensitive mass region, low resonant frequency, and high quality factor, thereby reducing the thermomechanical noise of the device. Based on the traditional serpentine folded beam, an E-shaped folded beam structure with an intermediate frame is realized, which reduces the influence of parasitic modes and suppresses cross-axis crosstalk. A displacement-capacitance sensing array based on triangular electrodes is proposed. By placing two sets of electrodes in a cross pattern, the electrode arrangement is made more compact, which improves the capacitance detection sensitivity throughout the entire effective detection cycle.

[0004] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A low-noise MEMS accelerometer includes an upper glass layer with a U-shaped cavity, a mass-spring oscillator silicon layer, a lower glass layer with a large-area rectangular cavity, and two sets of horseshoe magnets. The upper glass layer has a metal upper electrode array, an upper internal pad, an upper metal sealing ring, and a solder layer for bonding the upper glass layer and the mass-spring oscillator structure. The mass-spring oscillator silicon layer includes a large-size sensitive mass region, an E-shaped folded beam structure with a middle frame connected to the sensitive mass region, and an outer frame of the oscillator connected to the folded beam. The upper surface of the oscillator silicon layer has a metal layer structure, including a triangular lower electrode array forming a displacement-capacitance sensor with the metal upper electrode array on the surface of the upper glass layer, a metal coil for electromagnetic feedback, a lower internal pad for signal transmission, a lower metal sealing ring, and an outer pad. The horseshoe magnets include a yoke, a horseshoe magnet, and magnetic pole pieces. The sensitive mass region, the E-shaped folded beam structure, and the outer frame of the accelerometer have the same thickness and are all located on the same upper surface. The structure of the low-noise MEMS accelerometer includes an upper glass substrate layer, an upper glass metal layer, an upper glass solder layer, a silicon substrate layer, an insulating layer 1, an ohmic contact layer, a metal layer 1, an insulating layer 2, a metal layer 2, and a lower glass substrate layer. Both the upper and lower glass substrate layers are borosilicate glass with cavities. The upper glass metal layer includes a metal upper electrode array, an upper internal pad, and an upper metal sealing ring. The upper glass solder layer is solder tin used for bonding the upper glass layer and the mass-spring oscillator structure layer. The silicon substrate layer includes a mass-spring oscillator structure and an outer frame. Metal layer 1 includes a zero-potential layer and signal traces. Metal layer 2 includes a triangular lower electrode array, a metal coil, a lower internal pad, a lower metal sealing ring, an outer pad, and signal traces.

[0005] The accelerometer's sensitive axis is horizontal. When an acceleration signal is input along the sensitive axis, the sensitive mass region is displaced by inertial force. The E-shaped folded beam series structure deforms accordingly, always stretching and compressing simultaneously, forming an elastic force opposite to the inertial force. This stabilizes the mass-spring oscillator structure and converts the input acceleration signal into a displacement signal of the sensitive mass region.

[0006] The spring beam structure comprises a series of E-shaped folding beams with an intermediate frame, symmetrical about the sensitive mass region. The E-shaped folding beam is an improvement on the traditional serpentine folding beam by adding an intermediate connecting beam. Multiple sets of folding beams are connected in series and linked by the intermediate frame to form the spring structure of the oscillator.

[0007] A triangular lower electrode array, employing a special triangular shape, is sputtered onto the upper surface of the sensitive mass region, comprising two sets of intersecting electrode arrays. A conventional rectangular upper electrode array is sputtered onto the upper surface of the upper glass. The upper and lower electrodes form a capacitive sensor based on the triangular electrodes, enabling displacement detection in the sensitive mass region.

[0008] The feedback driver uses electromagnetic feedback. Two sets of horseshoe magnets are set above and below the device to form an external magnetic circuit. Current is passed through the electromagnetic coil. Based on the principle that a conductive coil experiences the Lorentz force in a magnetic field, closed-loop electromagnetic feedback can be completed.

[0009] The fabrication process of low-noise MEMS accelerometers includes the following steps: S1: Fabricate a cavity, a metal top electrode array, and a solder layer on the front side of the upper glass wafer; S2: Create cavities and adhesive layers on the front side of the lower glass wafer; S3: Fabricate a triangular lower electrode array, metal coil, lower inner pad, lower metal seal ring, and outer pad on the front side of the silicon wafer; S4: Deep reactive ion etching is performed on the front side of the silicon wafer to form a mass-spring oscillator structure. S5: The bonding between the silicon wafer and the upper and lower glass wafers is achieved by using hot-press bonding and adhesive bonding methods, respectively.

[0010] In step S1, laser etching is performed on the upper glass wafer to create cavities and reduce the sliding damping of the device. Next, metal alignment marks are sputtered and aligned with the laser-etched cross marks for subsequent layout positioning. Then, a metal upper electrode array on the upper glass is formed by photolithography sputtering followed by peeling, which forms a capacitive sensor with the silicon layer triangular lower electrode array. Finally, a thick solder is formed by electroplating to create a capacitive gap between the upper and lower electrodes, preparing for subsequent signal transmission and thermo-bonding. Step S2 involves laser etching of the lower glass wafer to create cavities; then, metal alignment marks are sputtered; finally, photoresist is spin-coated to prepare for adhesive bonding between the lower glass and silicon. Step S3 includes the fabrication of alignment mark layer, insulating layer 1, ohmic contact layer, metal layer 1, insulating layer 2, and metal layer 2, which involves processes such as photolithography, RIE, PECVD, and sputtering. In step S4, deep reactive ion etching is performed on the silicon wafer. To avoid the edge-cutting effect and improve the etching rate, an aluminum thin film is first sputtered on the back of the silicon wafer. After etching to 2 / 3 of the depth, photoresist is used to continue etching until the entire wafer is etched through. Finally, the photoresist and aluminum layer are dissolved to release the silicon bulk structure.

[0011] Step S5 includes two wafer-level bonding operations. Since the adhesive bonding temperature is relatively low, thermo-press bonding is first performed between the upper glass wafer and the silicon wafer, followed by adhesive bonding between the silicon wafer and the lower glass wafer.

[0012] After the above steps, the low-noise MEMS accelerometer is fabricated.

[0013] The beneficial effects of this invention are as follows: This solution designs a low-noise MEMS accelerometer that achieves low thermomechanical noise. Low noise is achieved through a large sensitive mass region, low resonant frequency, and high quality factor. The large sensitive mass region is achieved through a large-size silicon mass block; the low resonant frequency is achieved through multiple sets of series-connected folded beams; and the high quality factor is achieved by etching cavities in the upper and lower glass cover plates. The mass-spring oscillator structure is fabricated using deep reactive ion etching to form the mass block and series-connected folded beam structure, while the upper and lower glass cover plates are fabricated using laser etching to form large-area, deep cavities. Compared to traditional MEMS accelerometers, the low-noise MEMS accelerometer of this invention also implements an E-shaped folded beam structure with a central frame, improving the parasitic mode suppression ratio, reducing the influence of parasitic modes, and suppressing cross-axis crosstalk. Furthermore, this invention implements a displacement-capacitance sensing array based on triangular electrodes, which can increase the electrode density and improve sensitivity throughout the entire detection cycle. Attached Figure Description

[0014] Figure 1a is a cross-sectional schematic diagram of the low-noise MEMS accelerometer of the present invention; Figure 1b is a 3D diagram showing the top glass layer of the low-noise MEMS accelerometer of the present invention. Figure 1c is a 3D diagram of the silicon layer separation of the low-noise MEMS accelerometer of the present invention; Figure 1d is a 3D view of the lower glass layer of the low-noise MEMS accelerometer of the present invention; Figure 2a is a schematic diagram of the E-beam oscillator structure with a middle frame of the low-noise MEMS accelerometer of the present invention. Figure 2b is a schematic diagram of the displacement-capacitance sensing array based on triangular electrodes for the low-noise MEMS accelerometer of the present invention. Figures 3a-3i are flowcharts of the upper glass wafer fabrication process for the low-noise MEMS accelerometer of the present invention; Figures 4a-4e are flowcharts of the lower glass wafer fabrication process for the low-noise MEMS accelerometer of the present invention; Figures 5a-5t are flowcharts of the intermediate silicon wafer fabrication process for the low-noise MEMS accelerometer of the present invention; Figures 6a-6b are flowcharts of the three-layer wafer bonding process for the low-noise MEMS accelerometer of the present invention; Figure 7a is an explanatory diagram of the materials used in Figures 3a-3i, 4a-4e and 6a-6b of the present invention; Figure 7b is an explanatory diagram of the materials used in Figures 5a-5t and 6a-6b of this invention.

[0015] Reference numerals: 1. Upper glass layer; 2. Silicon layer; 3. Lower glass layer; 4. Horseshoe magnet; 5. Upper electrode array; 6. Upper internal pad; 7. Upper metal sealing ring; 8. Solder layer; 9. Sensitive mass area; 10. E-shaped folded beam structure; 11. Outer frame; 12. Triangular lower electrode array; 13. Metal coil; 14. Lower internal pad; 15. Lower metal sealing ring; 16. External pad; 17. Magnetic yoke; 18. Magnet body; 19. Magnetic pole piece; 101. Upper glass substrate layer; 102. Upper glass metal layer; 103. Upper glass solder layer; 201. Silicon substrate layer; 202. Insulating layer 1; 203. Ohmic contact layer; 204. Metal layer 1; 205. Insulating layer 2; 206. Metal layer 2; 301. Lower glass substrate layer. Detailed Implementation

[0016] The following description is merely a preferred embodiment of the present invention, and the scope of protection is not limited to this embodiment. All technical solutions falling within the scope of the present invention should be protected by the present invention. Identical components are indicated by the same reference numerals.

[0017] This invention designs a low-noise MEMS accelerometer, as shown in Figure 1a, comprising an upper glass layer with a U-shaped cavity, a mass-spring oscillator silicon layer, a lower glass layer with a large-area rectangular cavity, and two sets of horseshoe magnets; the upper surface of the upper glass layer has a metal upper electrode array, an upper internal pad, an upper metal sealing ring, and a solder layer for bonding the upper glass layer and the mass-spring oscillator structure layer; the mass-spring oscillator silicon layer includes a large-size sensitive mass region, an E-shaped folded beam structure with a middle frame connected to the sensitive mass region, and an oscillator outer frame connected to the folded beam; the upper surface of the oscillator silicon layer has a metal layer structure, including a triangular lower electrode array that forms a displacement-capacitance sensor with the metal upper electrode array on the surface of the upper glass layer, a metal coil for electromagnetic feedback, a lower internal pad for signal transmission, a lower metal sealing ring, and an outer pad; the horseshoe magnets include a yoke, a magnet body, and magnetic pole pieces. The structure of the low-noise MEMS accelerometer includes an upper glass substrate layer, an upper glass metal layer, an upper glass solder layer, a silicon substrate layer, an insulating layer 1, an ohmic contact layer, a metal layer 1, an insulating layer 2, a metal layer 2, and a lower glass substrate layer. The specific breakdown is shown in Figures 1b, 1c, and 1d. Both the upper and lower glass substrate layers are borosilicate glass with cavities. The upper glass metal layer includes a metal upper electrode array, an upper internal pad, and an upper metal sealing ring. The upper glass solder layer is solder used for bonding the upper glass layer and the mass-spring oscillator structure layer. The silicon substrate layer includes a mass-spring oscillator structure and an outer frame. Metal layer 1 includes a zero-potential layer and signal traces. Metal layer 2 includes a triangular lower electrode array, a metal coil, a lower internal pad, a lower metal sealing ring, an external pad, and signal traces.

[0018] The mass oscillator-spring structure of the low-noise MEMS accelerometer includes a large sensitive mass block, three sets of series-connected E-shaped folded beams, and a central frame. The sensitive mass block, the E-shaped folded beam structure, and the outer frame of the accelerometer have the same thickness and are all located on the same upper surface. The series-connected E-shaped folded beams on the left and right sides are symmetrical about the sensitive mass block; the central frame connects the series-connected E-shaped folded beams; the E-shaped beams are an improvement on the traditional serpentine folded beams by adding a central connecting beam, as shown in Figure 2a. The sensitive axis direction of the accelerometer is shown in the figure. x Axial direction.

[0019] A triangular lower electrode array is sputtered on the upper surface of the sensitive mass region. It adopts a special triangular shape and contains two sets of adjacent and intersecting electrode arrays. Different electrode arrays are selected for output according to the displacement of different mass blocks, which can improve the sensitivity of capacitive sensing. A traditional rectangular upper electrode array is sputtered on the upper surface of the upper glass. After flipping the upper glass, the upper and lower electrodes form a displacement-capacitance sensing array based on triangular electrodes, as shown in Figure 2b, to realize displacement detection of the sensitive mass region.

[0020] Two sets of horseshoe magnets are respectively set above and below the device to form an external magnetic circuit; a metal coil is sputtered on the upper surface of the sensitive mass region; when current is applied, the metal coil is subjected to Lorentz force in the magnetic field formed by the horseshoe magnets, thus completing the closed-loop feedback of the electromagnetic method.

[0021] When an acceleration is input along the sensitive axis, the sensitive mass region is displaced by inertial force. The E-shaped folded beam series structure deforms accordingly, constantly stretching and compressing simultaneously, creating an elastic force opposite to the inertial force. This stabilizes the mass-spring oscillator structure, ultimately leading to... ;in, Let be the displacement of the mass block. For the mass of the oscillator, The oscillator stiffness coefficient is... Input the magnitude of the acceleration. This is the undamped natural angular frequency of the system. If the relative displacement of the mass block can be detected, the magnitude of the input acceleration can be detected.

[0022] The principle of the displacement-capacitance sensing array based on triangular electrodes is to input positive and negative voltages alternately into the electrode array on the upper surface of the upper glass cover. After the upper glass cover is flipped up and down, the triangular lower electrode array on the upper surface of the sensitive mass region and the two left and right rectangular upper electrode plate arrays on the upper surface of the upper glass cover respectively form differential capacitances. and When there is no input acceleration, the areas of the lower electrode array and the two upper electrode arrays facing each other are equal. For a triangular electrode, the distance the current electrode moves... ( When the capacitance difference is ), ;in, This represents the number of electrode plates in each lower electrode array group. Where is the dielectric constant. The height of the triangular electrode plate. The width of the bottom of the triangular electrode plate. The distance between the lower electrode plate and the two upper electrode plates is denoted as . The change in the displacement of the mass block causes a change in the capacitance difference. By detecting the change in charge on the electrode plates in the subsequent circuit, the magnitude of the input acceleration can be obtained.

[0023] The specific fabrication steps for low-noise MEMS accelerometers include: a. Fabricate cavities, metal electrode arrays, and solder layers on the front side of the upper glass wafer. b. Fabricate cavities and adhesive layers on the front side of the lower glass wafer; c. Fabricate a triangular lower electrode array, metal coil, lower inner pad, lower metal sealing ring, and outer pad on the front side of the silicon wafer; d. Perform deep reactive ion etching on the front side of the silicon wafer to form a mass-spring oscillator structure; e. Bonding of silicon wafers to upper and lower glass wafers is achieved by thermo-press bonding and adhesive bonding, respectively. The upper glass wafer in step a is manufactured through laser etching, sputtering, electroplating, and other processing steps. Specific steps include: S1: The upper glass wafer 1 is made of 1mm thick BF33 glass and is used as the upper cover plate, as shown in Figure 3a; S2: 40mm etched onto the upper glass wafer using laser processing. Deep alignment marks and 500 A deep, U-shaped cavity, as shown in Figure 3b; S3: Photoresist is sprayed onto the front side of the upper glass wafer and patterned, as shown in Figure 3c; S4: Sputter 100nm of Cr on the front side of the upper glass wafer and strip the photoresist to use as alignment marks and dicing grooves, as shown in Figure 3d; S5: Spray photoresist onto the front side of the upper glass wafer and pattern it, as shown in Figure 3e; S6: Sputter 50nm TiW, 80nm Ni, and 400nm Au on the front side of the upper glass wafer and strip the photoresist to use as the metal upper electrode array, signal traces, upper internal pads, and upper metal sealing ring, as shown in Figure 3f; S7: A 100nm metal seed layer Al is sputtered on the front side of the upper glass wafer to make the entire surface conductive, as shown in Figure 3 g. S8: Photoresist is sprayed four times onto the front side of the upper glass wafer, and then exposed and developed separately to finally form a 20-layer... Thick photoresist is applied and patterned, and the unprotected Al is removed using aluminum etching solution, as shown in Figure 3h; S9: Electroplating 17 on the metal sealing ring and upper internal pads on the front side of the upper glass wafer. Sn solder was used for thermoforming. The photoresist was removed with acetone and ultrasonication, and the remaining Al was removed with aluminum etching solution, as shown in Figure 3i.

[0024] The lower glass wafer in step b is fabricated through laser etching, sputtering, and other processing steps. Specific steps include: S10: The lower glass wafer 3 is 1mm thick BF33 glass, used as the lower cover plate, as shown in Figure 4a; S11: 40mm etched onto the lower glass wafer using laser processing. Deep alignment marks and 500 A deep, large-area cavity, as shown in Figure 4b; S12: Photoresist is sprayed onto the front side of the lower glass wafer and patterned, as shown in Figure 4c; S13: Sputter 100nm of Cr on the front side of the lower glass wafer and strip the photoresist to use as alignment marks and dicing grooves, as shown in Figure 4d; S14: Spin-coat 10μm of photoresist on the front side of the lower glass wafer for adhesive bonding, as shown in Figure 4e.

[0025] Step c involves performing photolithography, RIE, PECVD, sputtering, and other processes on the silicon wafer. Specific steps include: S15: Silicon wafer 2 has a thickness of 525 μm and a crystal orientation of 1 0 0. It is used as the most important functional and structural layer of the device, as shown in Figure 5a. S16: Spin-coat photoresist and pattern it on both sides of the silicon wafer, as shown in Figure 5b; S17: Etching 2 on both sides of the silicon wafer using RIE. And remove the glue, which is used as alignment marks and scribe grooves, as shown in Figure 5c; S17: A 500nm thick silicon oxide layer is deposited on the front side of the silicon wafer by PECVD as insulating layer 1, as shown in Figure 5d; S18: Spin-coat photoresist and pattern it on the front side of the silicon wafer, as shown in Figure 5e; S19: Etch 500nm on insulating layer 1 on the front side of the silicon wafer using RIE to create a window for ohmic contacts, such as... Figure 5f ; S20: 50nm TiW, 60nm Pt, and 500nm Au are sequentially sputtered on the front side of a silicon wafer by magnetron sputtering. The metal outside the window is removed by immersion in acetone and ultrasonication. Ohmic contact is completed by annealing, as shown in Figure 5 g. S21: Spin-coat photoresist and pattern it on the front side of the silicon wafer, as shown in Figure 5h; S22: 50nm TiW, 60nm Pt and 400nm Au are sequentially sputtered on the front side of the silicon wafer by magnetron sputtering. Excess metal is removed by acetone immersion and ultrasonication. Metal layer 1 is completed by annealing, as shown in Figure 5i. S23: A 650nm thick silicon oxide is deposited on the front side of the silicon wafer by PECVD, as shown in Figure 5j; S24: Spin-coat photoresist and pattern it on the front side of the silicon wafer, as shown in Figure 5k; S25: Etch 650nm silicon oxide on the front side of the silicon wafer using RIE, dissolve the photoresist with acetone, and complete the insulating layer 2, as shown in Figure 5 l; S26: Spin-coating and patterning the front side of the silicon wafer, as shown in Figure 5m; S27: 50nm TiW, 80nm Ni and 400nm Au are sequentially sputtered on the front side of the silicon wafer by magnetron sputtering. After lift-off and annealing, metal layer 2 is completed, as shown in Figure 5n. Step d involves deep reactive ion etching of the silicon wafer, specifically including the following steps: S28: Sputter 500nm Al on the back side of a silicon wafer, as shown in Figure 5. S29: Spin-coat a thick photoresist on the front side of the silicon wafer and pattern it, as shown in Figure 5p; S30: Etch 500nm on the front side of the silicon wafer using RIE to etch the silicon oxide of insulating layer 1, as shown in Figure 5 q; S31: The silicon wafer is transferred to the SPTS 601E equipment to complete the Bosch process cycle and perform deep reactive ion etching (DRIE), as shown in Figure 5 r; S32: When etched to approximately 420 At depth, the wafer is removed from the etching machine, and a thick layer of photoresist is spin-coated onto the back side. It is attached to another working wafer (to provide support), cured naturally for 3-4 days, and then DRIE is continued until the entire structure is etched through, as shown in Figure 5s; S33: Dissolve the photoresist with acetone and remove the back Al layer with aluminum etching solution to release the silicon wafer, as shown in Figure 5t; Step e involves wafer-level bonding of the three-layer structure, and the specific steps include: S33: Flip the upper glass wafer upside down so that the metal layer of the upper glass wafer is directly above the silicon layer. Align it with the cross mark and apply pressure with a fixture at 280°C for 60 minutes to complete the thermo-press bonding, as shown in Figure 6a. S34: After spin-coating a thick photoresist onto the lower glass wafer, bond the lower glass wafer to the silicon wafer and bake it at 120°C for 30 minutes, as shown in Figure 6b. After the bonding process, the low-noise MEMS accelerometer structure was fully fabricated.

[0026] The specific embodiments described above further illustrate the technical problems, technical solutions, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-noise MEMS accelerometer, comprising an upper glass layer (1), a silicon layer (2), a lower glass layer (3), and two sets of horseshoe magnets (4), characterized in that, The upper glass layer (1) has a U-shaped cavity, the lower glass layer (3) has a rectangular cavity, and the silicon layer (2) is a mass-spring oscillator silicon layer (2). The upper surface of the upper glass layer (1) is provided with a metal upper electrode array (5); the upper glass layer (1) is also provided with an upper internal pad (6), an upper metal sealing ring (7) and a solder layer (8), the solder layer (8) being used to bond the upper glass layer (1) and the mass-spring oscillator silicon layer (2). The mass-spring oscillator silicon layer (2) includes a sensitive mass region (9), an E-shaped folded beam structure (10) with an intermediate frame connected to the sensitive mass region (9), and an oscillator outer frame (11) connected to the E-shaped folded beam structure (10). The E-shaped folding beam structure (10) includes an E-shaped beam with an intermediate frame that is symmetrical about the sensitive mass region (9). The E-shaped beam includes a serpentine folding beam and an intermediate connecting beam. Multiple sets of the E-shaped beams are connected in series and connected by the intermediate frame to form a spring structure of the oscillator. The upper surface of the mass-spring oscillator silicon layer (2) has a metal layer structure, which includes a triangular lower electrode array. The lower electrode array and the metal upper electrode array (5) on the surface of the upper glass layer (1) form a displacement-capacitance sensor. The metal layer structure also includes a metal coil (13) for electromagnetic feedback, a lower inner pad (14) for signal transmission, a lower metal sealing ring (15) and an outer pad (16). The horseshoe magnet (4) includes a yoke (17), a magnet body (18), and magnetic pole pieces (19); The sensitive mass region (9), the E-shaped folded beam structure (10) and the oscillator outer frame (11) have the same thickness, and the sensitive mass region (9), the E-shaped folded beam structure (10) and the oscillator outer frame (11) are all located on the same upper surface; The sensitive axis of the sensitive mass region (9) is horizontal; The lower electrode array is located on the upper surface of the sensitive mass region (9). The lower electrode array contains two sets of intersecting electrode arrays. The upper metal electrode array (5) is a rectangular electrode. The rectangular upper metal electrode array (5) cooperates with the triangular lower electrode array to form a capacitive sensor based on the triangular electrode. The capacitive sensor is used to detect the displacement of the sensitive mass region (9).

2. The low-noise MEMS accelerometer according to claim 1, characterized in that, The upper glass layer (1), silicon layer (2) and lower glass layer (3) are combined to form a feedback driver. The feedback driver adopts an electromagnetic feedback method. Two sets of horseshoe magnets (4) are respectively arranged above and below the feedback driver to form an external magnetic circuit.

3. A method for fabricating a low-noise MEMS accelerometer, characterized in that, Includes the following steps: S1: Fabricate cavities, metal electrodes, and solder layers on the front side of the upper glass wafer; S2: Create cavities and adhesive layers on the front side of the lower glass wafer; S3: Fabricate a triangular lower electrode array, metal coil, lower inner pad, lower metal seal ring, and outer pad on the front side of the silicon wafer; S4: Deep reactive ion etching is performed on the front side of the silicon wafer to form a mass-spring oscillator structure. S5: The bonding between the silicon wafer and the upper and lower glass wafers is achieved by using hot-press bonding and adhesive bonding methods, respectively.

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