Low-noise MEMS accelerometer
The low-noise MEMS accelerometer addresses high noise issues by employing a large sensitive mass area, low resonant frequency, and E-shaped folded beam structure with triangular electrodes, enhancing sensitivity and reducing parasitic modes for high-precision tasks.
Patent Information
- Application Number
- CN202321915233.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2023-07-20
- Publication Date
- 2024-12-17
- Estimated Expiration
- Not applicable · inactive patent
AI Technical Summary
Existing MEMS accelerometers suffer from high background noise, which limits their application in high-precision tasks such as earthquake early warning and oil and gas exploration, and there is a lack of research on low-noise MEMS accelerometers capable of detecting microseismic signals.
A low-noise MEMS accelerometer design featuring a large sensitive mass area, low resonant frequency, and high quality factor, incorporating an E-shaped folded beam structure with an intermediate frame to reduce parasitic modes and cross-axis crosstalk, and a displacement-capacitance sensing array with triangular electrodes for improved sensitivity.
The design achieves low thermomechanical noise, suppresses parasitic mode influence, and enhances sensitivity through a compact electrode arrangement, making it suitable for high-precision applications.
Smart Images
Figure CN222181817U_ABST
Abstract
Description
Technical Field
[0001] The utility model belongs to the technical field of micro-electromechanical systems, and particularly relates to a low-noise MEMS accelerometer. Background Art
[0002] Micro-electromechanical systems (MEMS) include micro-sensors, micro-actuators and corresponding processing circuits. They are a new discipline developed on the basis of microelectronics and micromechanical technologies. They are manufactured using batch processing technology compatible with integrated circuits. The size of the components is in the range of millimeters to micrometers. Compared with traditional mechanical devices, they have the advantages of small size, light weight, high reliability, and easy integration, which greatly improves the automation, intelligence and reliability of the system. MEMS accelerometers are inertial instruments that use micro-machining technology to convert acceleration signals into inertial forces to complete physical quantity detection. Compared with traditional accelerometers, MEMS accelerometers have the advantages of small size, low cost, strong overload resistance, and batch processing and production. At present, MEMS accelerometers have not only become the core components of micro-inertial measurement combinations, but have also rapidly expanded to other civilian fields. Traditional MEMS accelerometers are mainly used in low-precision scenarios such as automotive electronics and commercial electronics. The device has a high background noise and cannot meet the requirements of high-precision tasks such as earthquake early warning and oil and gas exploration. As there is little research and development on low-noise MEMS accelerometers, how to design a low-noise MEMS accelerometer that can detect microseismic signals is a problem that needs to be solved at this stage. Utility Model Content
[0003] The purpose of the utility model is to provide a low-noise MEMS accelerometer, which realizes an overall structure of a large sensitive mass area, a low resonant frequency and a high quality factor, thereby reducing the thermal mechanical noise of the device; on the basis of a traditional serpentine folded beam, an E-shaped folded beam structure with an intermediate frame is realized, thereby reducing the influence of parasitic modes and suppressing cross-axis crosstalk; a displacement-capacitance sensing array based on triangular electrodes is proposed, and by cross-placing two groups of electrodes, the electrode arrangement is made more compact, thereby improving the capacitance detection sensitivity within the entire effective detection period.
[0004] The above technical objectives of the utility model are achieved through the following technical solutions:
[0005] A low-noise MEMS accelerometer comprises an upper glass layer with a U-shaped cavity, a mass-spring oscillator silicon layer, a lower glass layer with a large rectangular cavity and two groups of horseshoe magnets; the upper surface of the upper glass layer is provided with 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 comprises a large-size sensitive mass area, an E-shaped folded beam structure with an intermediate frame connected to the sensitive mass area and an oscillator outer frame connected to the folded beam; the upper surface of the oscillator silicon layer is provided with a metal layer structure, comprising 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 external pad; the horseshoe magnet comprises a yoke, a horseshoe magnet and a magnetic pole piece; the sensitive mass area, the E-shaped folded beam structure and the outer frame of the accelerometer have the same thickness and are all 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. The upper and lower glass substrate layers are both 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, and the metal upper electrode array is a rectangular electrode; 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; the metal layer 1 includes a zero potential layer and a signal routing; the 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 a signal routing.
[0006] The sensitive axis direction of the accelerometer is horizontal. When an acceleration signal is input in the direction of the sensitive axis, the sensitive mass area is displaced by the inertial force, and the E-shaped folded beam series structure is deformed accordingly, always stretching and compressing at the same time, forming an elastic force opposite to the inertial force, so that the mass-spring oscillator structure tends to be stable, and the input acceleration signal is converted into a displacement signal of the sensitive mass area.
[0007] The spring beam structure includes a series of E-shaped folded beams with an intermediate frame symmetrical about the sensitive mass area. The E-shaped folded beam is improved by adding an intermediate connecting beam on the basis of the traditional serpentine folded beam. Multiple groups of folded beams are connected in series and connected through the intermediate frame to form a spring structure of the vibrator.
[0008] The upper surface of the sensitive mass area is sputtered with a triangular lower electrode array, which adopts a special triangular shape and contains two sets of cross-placed electrode arrays. The upper surface of the upper glass is sputtered with a traditional rectangular upper electrode array. The upper and lower electrodes form a capacitive sensor based on triangular electrodes to realize displacement detection of the sensitive mass area.
[0009] The feedback driver uses electromagnetic feedback. Two groups of horseshoe magnets are respectively set at the upper and lower parts of the device to form an external magnetic circuit. Current is passed through the electromagnetic coil. According to the principle that the conductive coil is subjected to the Lorentz force in the magnetic field, the electromagnetic closed-loop feedback can be completed.
[0010] The processing technology of low-noise MEMS accelerometer includes the following steps:
[0011] S1: Fabricate the cavity, metal upper electrode array and solder layer on the front side of the upper glass wafer;
[0012] S2: making a cavity and a bonding layer on the front side of the lower glass wafer;
[0013] S3: fabricating a triangular lower electrode array, a metal coil, a lower inner pad, a lower metal sealing ring and an outer pad on the front side of the silicon wafer;
[0014] S4: performing deep reactive ion etching on the front side of the silicon wafer to form a mass-spring oscillator structure;
[0015] S5: Bonding the silicon wafer to the upper glass wafer and the lower glass wafer respectively by means of thermal compression bonding and adhesive bonding.
[0016] In step S1, the upper glass wafer is laser etched to etch out a cavity to reduce the sliding film damping of the device; then a metal alignment mark is sputtered to align with the laser-etched cross mark for subsequent layout positioning; then, a metal upper electrode array of the upper glass is formed by photolithography sputtering and peeling, and a capacitive sensor is formed with the triangular lower electrode array of the silicon layer; finally, a thick solder is formed by electroplating to form a capacitive gap between the upper and lower electrodes, and to prepare for subsequent signal transmission and hot pressing bonding;
[0017] Step S2: laser etching the lower glass wafer to etch out a cavity; then sputtering metal alignment marks; and finally spin coating photoresist to prepare for adhesive bonding between the lower glass and silicon.
[0018] Step S3 includes the production of an alignment mark layer, an insulating layer 1, an ohmic contact layer, a metal layer 1, an insulating layer 2, and a metal layer 2, which involves processes such as photolithography, RIE, PECVD, and sputtering;
[0019] In step S4, the silicon wafer is subjected to deep reactive ion etching. To avoid the edge trimming effect and increase the etching rate, a layer of aluminum film is first sputtered on the back of the silicon wafer. After etching to 2 / 3 of the depth, etching is continued using a photoresist patch until it is completely etched through. Finally, the photoresist and aluminum layer are dissolved to release the silicon body structure.
[0020] Step S5 includes two wafer-level bondings. Since the adhesive bonding temperature is relatively low, the upper glass wafer and the silicon wafer are firstly thermally pressed and then the silicon wafer and the lower glass wafer are adhesively bonded.
[0021] After the above steps, the low-noise MEMS accelerometer is completed.
[0022] The beneficial effects of the utility model are as follows: the scheme designs a low-noise MEMS accelerometer, which can achieve low thermomechanical noise, and the low noise is achieved through a large sensitive mass area, a low resonant frequency, and a high quality factor. The large sensitive mass area is achieved by a large-sized silicon mass block; the low resonant frequency is achieved by multiple groups of series-connected folded beams; and the high quality factor is achieved by etching cavities in the upper and lower glass cover plates. The processing of the mass-spring oscillator structure forms a mass block and a series-connected folded beam structure by deep reactive ion etching, and the processing of the upper and lower glass cover plates forms a large-area, deep-sized cavity by laser etching. Compared with traditional MEMS accelerometers, the low-noise MEMS accelerometer involved in the utility model also realizes an E-shaped folded beam structure with an intermediate frame, which improves the parasitic mode suppression ratio, reduces the parasitic mode influence, and suppresses cross-axis crosstalk. In addition, the utility model realizes a displacement-capacitance sensing array based on triangular electrodes, which can increase the electrode arrangement density and improve the sensitivity within the entire detection cycle. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 It is a cross-sectional schematic diagram of the low-noise MEMS accelerometer of the utility model;
[0024] Figure 2 This is a 3D diagram of the upper glass layer of the low-noise MEMS accelerometer of the utility model;
[0025] Figure 3 This is a 3D diagram of the silicon layer splitting of the low-noise MEMS accelerometer of the utility model;
[0026] Figure 4 It is a 3D diagram of the lower glass layer of the low-noise MEMS accelerometer of the utility model;
[0027] Figure 5 It is a schematic diagram of the structure of an E-shaped beam vibrator with an intermediate frame of the low-noise MEMS accelerometer of the utility model;
[0028] Figure 6 It is a schematic diagram of a displacement-capacitance sensing array based on triangular electrodes of the utility model low-noise MEMS accelerometer;
[0029] Figure 7 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0030] Figure 8 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0031] Fig. 9 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0032] Fig.10 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0033] Fig.11 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0034] Fig.12 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0035] Fig.13 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0036] Fig.14 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0037] Fig.15 This is a flow chart of glass wafer processing for the low-noise MEMS accelerometer of the utility model;
[0038] Fig.16 This is the process flow chart of the glass wafer processing of the low-noise MEMS accelerometer of this utility model.
[0039] Fig.17 This is the process flow chart of the glass wafer processing of the low-noise MEMS accelerometer of this utility model.
[0040] Fig.18 This is the process flow chart of the glass wafer processing of the low-noise MEMS accelerometer of this utility model.
[0041] Fig.19 This is the process flow chart of the glass wafer processing of the low-noise MEMS accelerometer of this utility model.
[0042] Fig. 20 This is a process flow chart of the lower glass wafer of the low-noise MEMS accelerometer of the utility model;
[0043] Fig.21 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0044] Fig. 22 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0045] Fig.23 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0046] Fig.24 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0047] Fig.25 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0048] Fig.26 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0049] Fig. 27 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0050] Fig.28 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0051] Fig.29 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0052] Fig.30 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0053] Fig.31 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0054] Fig.32 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0055] Fig.33 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0056] Fig.34 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0057] Fig.35 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0058] Fig.36 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0059] Fig.37This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0060] Fig.38 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0061] Fig.39 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0062] Fig.40 This is a process flow chart of the intermediate silicon wafer of the low-noise MEMS accelerometer of the utility model;
[0063] Fig.41 It is a three-layer wafer bonding flow chart of the low-noise MEMS accelerometer of the utility model;
[0064] Fig.42 It is a three-layer wafer bonding flow chart of the low-noise MEMS accelerometer of the utility model;
[0065] Fig.43 This utility model Figure 7-Figure 15 , Figure 16-Figure 20 and Figure 41-42 Illustration of the materials used;
[0066] Fig.44 This utility model Figure 21-Figure 40 and Figure 41-42 Illustration of the materials used.
[0067] Figure 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; 11. outer frame; 12. triangular lower electrode array; 13. metal coil; 14. lower internal pad; 15. lower metal sealing ring; 16. external pad; 17. yoke; 18. magnet body; 19. pole piece; 101. upper glass substrate layer; 102. upper glass metal layer; 103. upper glass solder layer; 201. silicon substrate layer; 202. insulating layer one; 203. ohmic contact layer; 204. metal layer one; 205. insulating layer two; 206. metal layer two; 301. lower glass substrate layer. DETAILED DESCRIPTION
[0068] The following is only a preferred embodiment of the present invention, and the protection scope is not limited to this embodiment. All technical solutions under the concept of the present invention should belong to the protection scope of the present invention. The same parts are represented by the same reference numerals.
[0069] The utility model designs a low-noise MEMS accelerometer, such as Figure 1 , including 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 groups of horseshoe magnets; the upper surface of the upper glass layer is provided with 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 area, an E-shaped folded beam structure with an intermediate frame connected to the sensitive mass area and an oscillator outer frame connected to the folded beam, the upper surface of the oscillator silicon layer is provided with 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 external pad; the horseshoe magnet includes a yoke, a magnet body and a pole piece. 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 split effect is as follows: Figure 2 , Figure 3 and Figure 4 As shown. The upper and lower glass substrate layers are both 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; the metal layer 1 includes a zero potential layer and a signal routing; the 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 a signal routing.
[0070] The mass oscillator-spring structure of the low-noise MEMS accelerometer includes a large-sized sensitive mass block, three sets of series-connected E-shaped folded beams and an intermediate frame. The thickness of the sensitive mass area, E-shaped folded beam structure and outer frame of the accelerometer are the same and are all on the same upper surface. The series-connected E-shaped folded beams on the left and right sides are symmetrical about the sensitive mass area; the intermediate frame is connected between the series-connected E-shaped folded beams; the E-shaped beam is improved by adding an intermediate connecting beam on the basis of the traditional serpentine folded beam, such as Figure 5 The sensitive axis direction of the accelerometer is the x-axis direction in the figure.
[0071] The upper surface of the sensitive mass area is sputtered with a triangular lower electrode array, which adopts a special triangular shape and includes two sets of adjacent cross-placed electrode arrays. Different electrode array outputs are selected according to different mass block displacements to improve the sensitivity of capacitive sensing; the upper surface of the upper glass is sputtered with a traditional rectangular upper electrode array. After the upper glass is turned over, the upper and lower electrodes form a displacement-capacitive sensing array based on triangular electrodes, such as Figure 6 , to achieve displacement detection in sensitive mass areas.
[0072] Two groups of horseshoe magnets are respectively arranged at the upper and lower parts of the device to form an external magnetic circuit; a metal coil is sputtered on the upper surface of the sensitive mass area; when current is passed through, the metal coil is subjected to the Lorentz force in the magnetic field formed by the horseshoe magnet, completing the electromagnetic closed-loop feedback.
[0073] When acceleration is input in the direction of the sensitive axis, the sensitive mass area is displaced by the inertial force, and the E-shaped folded beam series structure is deformed accordingly, always stretching and compressing at the same time, forming an elastic force in the opposite direction of the inertial force, making the mass-spring oscillator structure stable, and finally it can be obtained Among them, x is the displacement of the mass block, m is the mass of the vibrator, k is the vibrator stiffness coefficient, a is the magnitude of the input acceleration, and ω0 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.
[0074] The principle of the displacement-capacitance sensing array based on triangular electrodes is to input the positive and negative voltage intervals into the electrode array on the upper surface of the upper glass cover. After the upper glass cover is turned upside down, the triangular lower electrode array on the upper surface of the sensitive mass area and the two left and right rectangular upper electrode plate arrays on the upper surface of the upper glass cover form differential capacitors C1 and C2 respectively. When there is no input acceleration, the area facing the lower electrode array and the two upper electrode arrays is equal, then For the triangular electrode, when the lower electrode moves the distance When the capacitance difference is Among them, n is the number of electrode plates in each group of lower electrode arrays, ε is the dielectric constant, l is the height of the triangular electrode plate, w is the bottom width of the triangular electrode plate, and d is the distance between the lower electrode plate and the two upper electrode plates. The change in displacement of the mass block causes the change in the capacitance difference. By detecting the charge change of the electrode plate through the subsequent circuit, the magnitude of the input acceleration can be obtained.
[0075] The specific processing steps for low-noise MEMS accelerometers include:
[0076] a. Make the cavity, metal upper electrode array and solder layer on the front side of the upper glass wafer
[0077] b. Making a cavity and a bonding layer on the front side of the lower glass wafer;
[0078] c. Fabricate a triangular lower electrode array, a metal coil, a lower inner pad, a lower metal sealing ring and an outer pad on the front side of the silicon wafer;
[0079] d. Perform deep reactive ion etching on the front side of the silicon wafer to form a mass-spring oscillator structure;
[0080] e. Bonding the silicon wafer to the upper glass wafer and the lower glass wafer respectively by means of thermal compression bonding and adhesive bonding;
[0081] The upper glass wafer in step a is manufactured by laser etching, sputtering, electroplating and other processing steps, and the specific steps include:
[0082] S1: The upper glass wafer 1 is a 1 mm thick BF33 glass, used as the upper cover plate, such as Figure 7 ;
[0083] S2: Etch a 40μm deep alignment mark and a 500μm deep U-shaped cavity on the upper glass wafer by laser processing, such as Figure 8 ;
[0084] S3: Spray photoresist on the front side of the upper glass wafer and pattern it, such as Fig. 9 ;
[0085] S4: Sputter 100nm of Cr on the front side of the upper glass wafer and strip the photoresist to use as alignment marks and scribe lines, such as Fig.10 ;
[0086] S5: Spray photoresist on the front side of the upper glass wafer and pattern it, such as Fig.11 ;
[0087] S6: Sputter 50nmTiW, 80nmNi, 400nmAu on the front of the upper glass wafer, and strip the photoresist to use as the metal upper electrode array, signal routing, upper internal pads and upper metal sealing ring, such as Fig.12 ;
[0088] S7: Sputter a 100nm metal seed layer Al on the front side of the upper glass wafer so that the entire surface can be conductive, such as Fig.13 ;
[0089] S8: Spray photoresist on the front side of the upper glass wafer four times, expose and develop respectively, finally form a 20μm thick photoresist and pattern it, and remove the unprotected Al with aluminum etching solution, such as Fig.14 ;
[0090] S9: Electroplate 17μm Sn solder on the metal sealing ring and the upper inner pad on the front side of the upper glass wafer for thermocompression bonding. Use acetone and ultrasound to remove the photoresist, and use aluminum etching solution to remove the remaining Al, such as Fig.15 .
[0091] The lower glass wafer in step b is manufactured by laser etching, sputtering and other processing steps, and the specific steps include:
[0092] S10: The lower glass wafer 3 is a BF33 glass with a thickness of 1 mm, and is used as a lower cover plate. Fig.16 ;
[0093] S11: 40 μm deep alignment marks and 500 μm deep large area cavities are etched on the lower glass wafer by laser processing, such as Fig.17 ;
[0094] S12: Spray photoresist on the front side of the lower glass wafer and pattern it, such as Fig.18 ;
[0095] S13: 100 nm of Cr is sputtered on the front side of the lower glass wafer and the photoresist is stripped off to be used as alignment marks and scribe lines, as shown in FIG. Fig.19 ;
[0096] S14: Spin-coat 10 μm photoresist on the front side of the lower glass wafer for adhesive bonding, such as Fig. 20 .
[0097] In step c, the silicon wafer is subjected to processes such as photolithography, RIE, PECVD, and sputtering. The specific steps include:
[0098] S15: Silicon wafer 2 has a thickness of 525 μm and a crystal orientation of 100, and is used as the most important functional layer and structural layer of the device, such as Fig.21 ;
[0099] S16: Spin-coat photoresist on both sides of the silicon wafer and pattern it, such as Fig. 22 ;
[0100] S17: Etch 2μm on both sides of the silicon wafer by RIE and remove the resin to use as alignment marks and scribe grooves, such as Fig.23 ;
[0101] S17: 500nm thick silicon oxide is deposited on the front side of the silicon wafer by PECVD to serve as an insulating layer, such as Fig.24 ;
[0102] S18: Spin-coat and pattern photoresist on the front side of the silicon wafer, such as Fig.25 ;
[0103] S19: Etch 500nm on the insulating layer 1 on the front side of the silicon wafer by RIE to leave a window for ohmic contact, such as Fig.26 ;
[0104] S20: 50nm TiW, 60nm Pt, and 500nm Au are sputtered in sequence on the front side of the silicon wafer by magnetron sputtering, and the metal outside the window is stripped by acetone immersion and ultrasonication, and ohmic contact is completed by annealing. Fig. 27 ;
[0105] S21: Spin-coat and pattern photoresist on the front side of the silicon wafer, such as Fig.28 ;
[0106] S22: 50nm TiW, 60nm Pt, and 400nm Au are sequentially sputtered on the front side of the silicon wafer by magnetron sputtering, and the excess metal is stripped by acetone immersion and ultrasonication, and the metal layer 1 is annealed. Fig.29 ;
[0107] S23: 650nm thick silicon oxide is deposited on the front side of the silicon wafer by PECVD, such as Fig.30 ;
[0108] S24: Spin-coat and pattern photoresist on the front side of the silicon wafer, such as Fig.31 ;
[0109] S25: 650nm of silicon oxide is etched on the front side of the silicon wafer by RIE, and the photoresist is dissolved with acetone to complete the second insulating layer, such as Fig.32 ;
[0110] S26: Spin coating and photolithography on the front side of the silicon wafer and patterning, such as Fig.33 ;
[0111] S27: 50nm TiW, 80nm Ni, and 400nm Au are sequentially sputtered on the front side of the silicon wafer by magnetron sputtering, and the metal layer 2 is completed after stripping and annealing. Fig.34 ;
[0112] In step d, deep reactive ion etching is performed on the silicon wafer, and the specific steps include:
[0113] S28: Sputter 500nm of Al on the back of the silicon wafer, such as Fig.35 ;
[0114] S29: Spin-coat and pattern thick photoresist on the front side of the silicon wafer, e.g. Fig.36 ;
[0115] S30: Etching 500nm on the front side of the silicon wafer by RIE to etch the silicon oxide of the insulating layer 1, such as Fig.37 ;
[0116] S31: The silicon wafer is transferred to the SPTS 601E equipment to complete the Bosch process cycle and perform deep reactive ion etching (DRIE), such as Fig.38 ;
[0117] S32: When etching reaches a depth of about 420 μm, the wafer is taken out of the etcher, 8 μm thick photoresist is spin-coated on the back, and it is glued to another operating wafer (for support). It is naturally cured for 3-4 days, and DRIE is continued until the entire structure is etched through. Fig.39 ;
[0118] S33: Use acetone to dissolve the photoresist, and use aluminum etching solution to remove the back Al layer to release the silicon wafer, such as Fig.40 ;
[0119] In step e, wafer-level bonding of the three-layer structure is performed, and the specific steps include:
[0120] S33: Turn the upper glass wafer upside down so that the metal layer of the upper glass wafer is located directly above the silicon layer, align it through the cross mark, and apply pressure through the fixture at a temperature of 280°C for 60 minutes to complete the thermal compression bonding. Fig.41 ;
[0121] S34: After spin coating thick photoresist on the lower glass wafer, bond the lower glass wafer to the silicon wafer and post-bake at 120° C. for 30 minutes. Fig.42 ;
[0122] After the bonding process, the low-noise MEMS accelerometer structure is fully processed.
[0123] The specific embodiments described above further illustrate the technical problems, technical solutions and beneficial effects solved by the present invention. It should be understood that the above are only 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 in 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 groups of horseshoe magnets (4), It is characterized in that The upper glass layer (1) is provided with a U-shaped cavity, the lower glass layer (3) is provided with a rectangular cavity, the silicon layer (2) is a mass-spring oscillator silicon layer (2), A metal upper electrode array (5) is provided on the upper surface of the upper glass layer (1), and an upper internal solder pad (6), an upper metal sealing ring (7) and a solder layer (8) are also provided on the upper glass layer (1), and the solder layer (8) is used to bond the upper glass layer (1) and the mass-spring oscillator silicon layer (2); The mass-spring oscillator silicon layer (2) comprises a large-sized sensitive mass region (9), an E-shaped folded beam (10) structure with an intermediate frame connected to the sensitive mass region (9), and an oscillator outer frame (11) connected to the E-shaped folded beam (10) structure; The upper surface of the mass-spring oscillator silicon layer (2) has a metal layer structure, the metal layer structure 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 internal pad (14) for signal transmission, a lower metal sealing ring (15) and an external pad (16); The horseshoe magnet (4) comprises a yoke (17), a magnet body (18) and a magnetic pole piece (19); The sensitive mass area (9), the E-shaped folded beam (10) structure and the vibrator outer frame (11) have the same thickness, and the sensitive mass area (9), the E-shaped folded beam (10) structure and the vibrator outer frame (11) are all located on the same upper surface.
2. A low noise MEMS accelerometer according to claim 1, It is characterized in that The sensitive axis direction of the sensitive mass area (9) is horizontal.
3. A low noise MEMS accelerometer according to claim 1, It is characterized in that The E-shaped folded beam (10) structure comprises an E-shaped folded beam (10) with an intermediate frame which is symmetrical about the sensitive mass area (9), the E-shaped folded beam (10) comprising a serpentine folded beam and an intermediate connecting beam, and a plurality of groups of the E-shaped folded beams (10) are connected in series and connected through the intermediate frame to form a spring structure of the vibrator.
4. A low noise MEMS accelerometer according to claim 3, It is characterized in that The lower electrode array is located on the upper surface of the sensitive mass area (9), and two groups of cross-placed electrode arrays are arranged in the lower electrode array. The metal upper electrode array (5) is a rectangular electrode. The rectangular metal upper electrode array (5) cooperates with the triangular lower electrode array to form a capacitive sensor based on triangular electrodes, and the capacitive sensor is used to detect the displacement of the sensitive mass area (9).
5. The low noise MEMS accelerometer according to claim 1, It is characterized in that The upper glass layer (1), the silicon layer (2) and the lower glass layer (3) are combined into a feedback driver, the feedback driver adopts an electromagnetic feedback method, and the two groups of horseshoe magnets (4) are respectively arranged above and below the feedback driver to form an external magnetic circuit.
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Low-noise MEMS accelerometer
CN116835521A
A low-noise MEMS accelerometer
CN116835521B