CN116577523A - Acceleration sensor based on vibration microspheres and preparation method - Google Patents
Acceleration sensor based on vibration microspheres and preparation method Download PDFInfo
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- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 claims abstract description 49
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- 239000004952 Polyamide Substances 0.000 description 3
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 3
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- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 2
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/09—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B7/00—Microstructural systems; Auxiliary parts of microstructural devices or systems
- B81B7/02—Microstructural systems; Auxiliary parts of microstructural devices or systems containing distinct electrical or optical devices of particular relevance for their function, e.g. microelectro-mechanical systems [MEMS]
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
- B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
- B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2201/00—Specific applications of microelectromechanical systems
- B81B2201/02—Sensors
- B81B2201/0228—Inertial sensors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B81—MICROSTRUCTURAL TECHNOLOGY
- B81B—MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES
- B81B2203/00—Basic microelectromechanical structures
- B81B2203/01—Suspended structures, i.e. structures allowing a movement
- B81B2203/0118—Cantilevers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Pressure Sensors (AREA)
Abstract
The application belongs to the technical field of semiconductor device MEMS structure processes, relates to an acceleration sensor, and particularly relates to an acceleration sensor based on vibration microspheres and a preparation method thereof. The sensor is characterized in that a bonding process is adopted to bond a lithium niobate wafer and a silicon substrate at a low temperature, thinning and polishing are carried out, an electrode is prepared on the surface of the lithium niobate through a sputtering process and an IBE etching process, a deep silicon etching process is carried out on the back surface of the silicon substrate to realize release of a center mass ring and a cantilever beam with a composite structure, and then a microsphere is fixed at the center of a device through an ultraviolet curing adhesive, so that the piezoelectric vibration sensing device is prepared. Compared with the acceleration sensor with a mass block structure, the vibration microsphere acceleration sensor prepared by the application has higher output and wider frequency bandwidth, has higher output charge and higher sensitivity under the resonance frequency, and can meet the test requirement under the medium-low frequency micro-vibration environment.
Description
Technical Field
The application belongs to the technical field of semiconductor device MEMS structure processes, relates to an acceleration sensor, and particularly relates to an acceleration sensor based on vibration microspheres and a preparation method thereof.
Background
At present, in the fields of vehicle engineering, aerospace and the like, the detection and control of acceleration have become particularly common. However, the existing sensor still faces a great test in terms of improving the detection efficiency and the detection precision. One trend in the future is to optimize the performance of acceleration sensors based on the piezoelectric effect. Typical piezoelectric materials are PZT thin films, aluminum nitride (AluminumNitride, alN), and Lithium Niobate (LN). The PZT has the performance advantage of high piezoelectric coefficient, d 33 Can reach 300pC/N, d 31 Can reach more than 200 pC/N. However, the disadvantages of PZT are obvious, lead in PZT can pollute water source and affect environment, and the PZT does not accord with the green development concept. Aluminum nitride has a very low relative dielectric constant, so that AlN is characterized by low loss and high sensitivity, and is widely used in sensors and resonators. AlN has a significant disadvantage in that its piezoelectric coefficient is low, d 33 Only about 5 pC/N. This suggests that AlN is not sufficiently capable of interconverting electrical and mechanical energy. LN is a high Wen Tiedian resistant material with Curie temperatures up to 1210 ℃. The LN can accommodate most MEMS process temperatures. Therefore, it is almost unnecessary to consider when designing LN-based devicesDepolarization problems caused by process temperature variations. The MEMS device has small volume, and the size of the MEMS sensor is usually millimeter or even micrometer, and the MEMS sensor has the characteristics of light weight and low energy consumption. The miniaturized component has the advantages of small inertia, high resonant frequency, short response time and the like. The surface to volume ratio of the MEMS is also high the sensitivity of the sensor. The acceleration and the vibration intensity are closely related, so that a high-sensitivity piezoelectric vibration sensor needs to be designed to improve the performance of the sensor and realize accurate measurement of the acceleration.
Disclosure of Invention
The application aims to provide a novel structural design of an acceleration sensor based on vibration microspheres, which is characterized in that a vibration microsphere structure is designed and manufactured on the basis of a cantilever beam, so that the weight of a central mass block is increased, restraint and traction are increased by changing the design structure of the cantilever beam, deflection and torsion displacement are reduced, a transverse effect is reduced, so that the sensor has larger deformation rigidity and stability, and the output performance and sensitivity of the sensor are improved.
The application is realized by adopting the following technical scheme:
an acceleration sensor based on vibration microsphere comprises a Si substrate, wherein a layer of SiO grows on the surface of the Si substrate 2 Thin film and LiNbO 3 And the silicon-based lithium niobate bonding sheet is formed after bonding the wafers. The silicon-based lithium niobate bonding sheet forms a frame, a central mass ring and four composite cantilever beams through MEMS technology; each composite cantilever beam consists of a cross beam and a longitudinal beam which are vertically arranged, namely the composite cantilever beam is provided with three connecting ends, wherein two connecting ends are connected with the frame, and the other connecting end is connected with the central mass ring; the four composite cantilever beams are symmetrically arranged on two sides of the central mass ring in pairs; electrodes are uniformly distributed on the cross beam and the longitudinal beam; and microspheres are fixed on the central mass ring.
Further preferably, the outer circumference of the central mass ring is square, and the inner circumference is circular. The microsphere is fixed on the central mass ring through ultraviolet curing glue; the PA material is used as the microsphere, and compared with other materials, the PA material has better wear resistance and excellent shock resistance, and has the advantages of low density and high thermal stability.
The preparation method of the acceleration sensor based on the vibration microsphere comprises the following steps:
step S1: preparation of silicon-based lithium niobate bonding sheet
Cleaning a Y-cut lithium niobate wafer and a silicon substrate, growing a silicon dioxide layer on the surface of the silicon substrate by adopting a PECVD method, bonding the silicon substrate with an oxide layer and a lithium niobate single crystal film at a low temperature, and then obtaining a silicon-based lithium niobate bonding sheet through thinning and polishing processes;
step S2: preparation of marking patterns and surface electrodes
Cleaning a silicon-based lithium niobate bonding sheet, and preparing an alignment mark and a surface electrode on a composite cantilever beam of a sensor by adopting a magnetron sputtering and etching process;
step S3: etching the lithium niobate single crystal film by using an IBE process, and etching the silicon dioxide film layer by using an RIE process, so that the lithium niobate film layer and the silicon dioxide film layer are patterned;
step S4: preparing a cantilever beam and a central mass ring on the front surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching;
the release of the composite cantilever beam and the central mass ring is completed on the back surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching;
step S5: after the ultraviolet light curing adhesive is coated on the surfaces of the microspheres, the microspheres are placed at the inner circumference of the central mass ring and are irradiated by ultraviolet lamps to cure the ultraviolet light curing adhesive;
and finally, preparing the acceleration sensor based on the vibration microsphere.
Further preferably, step S1 is specifically that a Y-cut lithium niobate wafer and a silicon substrate are firstly subjected to acid washing at an ambient temperature of 150 ℃, then subjected to alkali washing by hydrogen peroxide and ammonia water, then sequentially subjected to ultrasonic washing by acetone and absolute ethyl alcohol, then subjected to ultrasonic washing by deionized water to wash surface impurities and organic matters, and dried by nitrogen to blow-dry the surface; growing a silicon dioxide layer with the thickness of 1-3 mu m on the surface of the silicon substrate by adopting a PECVD method; bonding the Y-cut lithium niobate wafer and the silicon substrate at the bonding temperature of 80-120 ℃ and the bonding pressure of 1000-3000N, and then annealing for 3h at the temperature of 120-150 ℃; the silicon-based lithium niobate bonding sheet was thinned and polished, wherein the thickness of the lithium niobate layer was 5 μm.
Further preferably, step S2 is specifically that the designed alignment mark pattern and the metal electrode pattern are customized onto a mask plate in advance, a layer of chromium/gold is sputtered on the silicon-based lithium niobate by a magnetron sputtering method, then photoresist AZ6130 is used, a photoresist homogenizer is used for homogenizing at a low speed of 500r/min for 10 seconds, a photoresist homogenizer is used for homogenizing at a high speed of 3000r/min for 30 seconds, a hot plate is used for pre-baking for 60 seconds at a temperature of 100 ℃, a photoetching device is an EVG610 photoetching machine, and the exposure dose is 100J/cm 2 Developing with developing solution AZ400K and water in a ratio of 1:4, flushing the film with plasma water after developing, drying with nitrogen, removing photoresist with an oxygen plasma photoresist remover, and post-drying at 120 ℃ for 15min; the unwanted metal layer is then removed by IBE etching. Wherein, the thickness ratio of the surface electrode and the alignment mark manufactured by magnetron sputtering is 10nm/50nm.
Further preferably, in step S3, the spin speed of the spin coater is set to 1000r/min, AZ4620 is used for photoresist, then a hot plate is used for baking for 180S, the photolithography is performed by using a photolithography machine EVG610, and the exposure dose is set to 400mJ/cm 2 Mixing the developing solution AZ400k with water in a ratio of 1:3, developing the pattern, removing the residual primer after the development by using oxygen plasma, and finally hardening the film on a hot plate at 120 ℃ for 15 minutes; and (3) etching by adopting an IBE process, and checking etching conditions every half an hour until patterning of the lithium niobate single crystal film is completed. And then etching the silicon dioxide layer by adopting an RIE process to complete the patterning of the silicon dioxide layer.
Further preferably, step S4 is specifically that a deep silicon etching process is used to etch and prepare a silicon-based cantilever beam and a central mass ring on a bonding sheet, wherein the etching thickness is 100 mu m; and respectively carrying out ultrasonic treatment on the etched bonding sheet by using acetone, absolute ethyl alcohol and deionized water, then washing the surface by using deionized water, and drying the surface by using nitrogen. Spraying positive photoresist AZ4620 with a photoresist sprayer at the back of the bonding sheet, spraying the photoresist 16 times with thickness of 60 μm, pre-baking at 100deg.C for 2min, and photoetching at exposure dose of 800mJ/cm 2 Then developing by using a developing solution AZ400k and water in a ratio of 1:3, and removing residues by using oxygen plasma after the isograph is completely developedCoating the residual primer on a hot plate at 120 ℃ for 20min after removing the primer; bonding the front surface of the bonding sheet and the silicon wafer by adopting pump oil, and etching the deep silicon with the thickness of 400 mu m to release the composite cantilever beam and the central mass ring; and (3) soaking and washing the pumping oil on the surface of the structure by using absolute ethyl alcohol, and then washing for a plurality of times by using deionized water, and naturally evaporating the water.
In summary, according to the novel structural design of the acceleration sensor based on the vibration microsphere and the preparation method thereof provided by the application, through bonding lithium niobate with a silicon substrate with a silicon dioxide layer at a low temperature, preparing an alignment mark and a surface electrode on a lithium niobate film by adopting methods of sputtering, etching, IBE etching and the like, etching a lithium niobate single crystal film to pattern the lithium niobate single crystal film, adopting RIE to complete patterning of a silicon oxide layer, adopting a deep silicon etching process to etch a silicon substrate front surface to prepare a center mass ring and a cantilever beam, etching the silicon substrate back surface, coating a trace amount of ultraviolet curing adhesive on the microsphere surface, then placing the microsphere surface at a middle joint, and irradiating the ultraviolet curing adhesive by using ultraviolet lamps to cure the ultraviolet curing adhesive, thus obtaining the acceleration sensor based on the microsphere. Compared with a four-cantilever sensor, the composite Liang Weiqiu sensor has higher output and widens the frequency bandwidth. Compared with a mass block structure, the center microsphere structure of the sensor has higher output charge and higher sensitivity under the resonance frequency, and can meet the test requirement under the medium-low frequency micro-vibration environment.
The application has reasonable design, adopts the composite cantilever beam microsphere structure, can reduce the transverse effect, improves the sensitivity of the sensor output charge, and has good practical application and popularization value.
Drawings
In order to more clearly illustrate the embodiments of the application or the prior art solutions, the drawings which are used in the description of the embodiments or the prior art will be presented, it being obvious that the drawings in the description below are only some embodiments of the application and that other drawings can be obtained from them without inventive effort for a person skilled in the art.
FIG. 1 shows a flow chart of a preparation method of a vibration microsphere acceleration sensor based on a lithium niobate ferroelectric film.
Fig. 2 shows a schematic structural diagram of a silicon-based lithium niobate ferroelectric single crystal film with a silicon dioxide layer obtained after the bonding process in the present application.
Fig. 3 shows a flow chart of sensor alignment marks and metal electrode preparation.
Fig. 4 shows a sensor functional layer and oxide layer patterning flow chart.
FIG. 5 shows a process flow diagram of the cantilever beam preparation process of the vibrating microsphere acceleration sensor.
Fig. 6 shows a graph of the output charge of the composite Liang Weiqiu sensor according to the present application compared with the output charge of the four-beam microsphere sensor, the four-beam mass sensor, and the composite beam mass sensor under the same simulation of the COMSOL software.
Fig. 7 shows a schematic diagram of a composite Liang Weiqiu sensor according to the application.
Reference numerals in fig. 7: 1-frame, 2-center mass ring, 3-composite cantilever beam, 301-cross beam, 302-longitudinal beam, 4-electrode and 5-microsphere.
Fig. 8 shows a graph of the simulated analysis data of the usable frequency band of the composite Liang Weiqiu sensor according to the present application.
Figure 9 shows the displacement distribution of the device at the cross section of the composite Liang Weiqiu sensor according to the application under the input of an excitation acceleration signal.
Fig. 10 shows a schematic diagram of a composite beam mass sensor structure.
Reference numerals in fig. 10: 1-frame, 3-composite cantilever beam, 4-electrode and 6-mass block.
FIG. 11 shows a graph of simulated analysis data for the usable frequency band of a composite beam mass sensor.
FIG. 12 shows the device displacement distribution at the cross section of a composite beam mass sensor under an input excitation acceleration signal.
FIG. 13 shows a schematic diagram of a four-beam microsphere sensor.
Reference numerals in fig. 13: 1-frame, 2-center mass ring, 4-electrode, 7-single cantilever beam.
FIG. 14 shows a graph of simulated analysis data for the usable frequency bands of a four-beam microsphere sensor.
FIG. 15 shows the device displacement distribution at the cross section of a four-beam microsphere sensor under the input of an excitation acceleration signal.
Fig. 16 shows a schematic diagram of a four-beam proof-mass sensor structure.
Reference numerals in fig. 16: 1-frame, 4-electrode, 6-mass block and 7-single cantilever beam.
Fig. 17 shows a graph of simulated analysis data for the usable frequency bands of a four-beam mass sensor.
Fig. 18 shows the device displacement distribution of the four-beam mass sensor at the cross section under the input of an excitation acceleration signal.
Detailed Description
Referring to fig. 1, a flowchart of a method for preparing a vibration microsphere acceleration sensor according to an embodiment of the present application is shown.
The preparation method of the vibration microsphere acceleration sensor based on the novel structural design of the MEMS technology comprises the following specific steps:
step S1: preparation of silicon-based lithium niobate bonding sheet
As shown in fig. 2, the Y-cut lithium niobate wafer and the silicon substrate are cleaned, a silicon dioxide layer is grown on the surface of the silicon substrate by adopting a PECVD method, the silicon substrate with an oxide layer is bonded with the lithium niobate single crystal film at a low temperature, and then the silicon-based lithium niobate bonding sheet is prepared by thinning and polishing processes.
Wherein the cleaning solution comprises acetone, isopropanol, absolute ethyl alcohol, concentrated sulfuric acid, hydrogen peroxide and ammonia water. The bonding pressure is 1000-3000N, and the bonding temperature is 80-120 ℃.
Step S2: preparation of marking patterns and surface electrodes
As shown in fig. 3, the silicon-based lithium niobate bonding pad is cleaned, and an alignment mark and a surface electrode are prepared on the composite cantilever of the sensor by adopting a magnetron sputtering and etching process.
The cleaning of the silicon-based lithium niobate film is to remove surface organic matters and other impurities, and prepare for the preparation of the alignment marks and the surface electrodes. The magnetron sputtering power is 300-600W, and the surface electrode is chromium/gold.
Step S3: as shown in fig. 4, the lithium niobate single crystal thin film is etched using an IBE process, and the silicon dioxide thin film layer is etched using an RIE process, so that the lithium niobate thin film layer and the silicon dioxide thin film layer are patterned.
The IBE and RIE processes need to use the photoresist AZ4620 as a mask, the thickness of the mask is 8-15 mu m, and the developing solution AZ400k and water are mixed according to the proportion of 1:3 for developing.
Step S4: as shown in fig. 5, the composite cantilever beam and the central mass ring are prepared on the front surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching.
As shown in fig. 5, the release of the composite cantilever beam and the central mass ring is completed on the back surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching.
Wherein the spray glue is photoresist AZ4620 glue, the spray thickness is 30-60 μm, and the developing solution AZ400K is mixed with water in a ratio of 1:3 for developing.
Step S5: the microsphere surface is coated with ultraviolet light curing adhesive and then is placed at the inner circumference of the central mass ring, and ultraviolet light is used for irradiating the ultraviolet light curing adhesive.
Wherein, the microsphere is made of PA (polyamide), the radius of the microsphere is 2000 μm, and the radius of the inner circle of the center mass ring for placing the microsphere is 1321 μm.
The bonding technology of the ferroelectric single crystal lithium niobate thin film and the silicon substrate with the silicon dioxide layer is mature, and the preparation of broadband and strong signal output components can be well completed. Finally prepared acceleration sensor based on vibration microsphere and LiNbO 3 The thickness of the film is 5 mu m, the thickness of the silicon dioxide layer is 1-3 mu m, the thickness of the silicon substrate is 500 mu m, the thickness of the surface electrode is 100-350 nm, and the thickness of the central mass ring and the composite cantilever beam is 60-100 mu m.
In order to make the objects, features and advantages of the present application more obvious and understandable, the technical solutions of the embodiments of the present application are clearly and completely described, and it is apparent that the embodiments described below are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, are intended to fall within the scope of the present application. The reagents and raw materials used in the examples of the application are all commercially available or self-made.
Example 1
A preparation method of an acceleration sensor based on vibration microspheres comprises the following steps:
step 1, preparing a silicon-based lithium niobate bonding sheet
1a, carrying out acid washing on a Y-cut lithium niobate wafer and a silicon substrate at the environmental temperature of 150 ℃, then carrying out alkali washing by using hydrogen peroxide and ammonia water, then carrying out ultrasonic washing by using acetone and absolute ethyl alcohol in sequence for 5min, then carrying out ultrasonic washing by using deionized water for 5min to wash surface impurities and organic matters, and drying the surface by using nitrogen.
1b, growing a silicon dioxide layer with the thickness of 2 mu m on the surface of the silicon substrate by adopting a PECVD method.
1c, bonding the lithium niobate wafer and the silicon substrate at a bonding temperature of 80 ℃ and a bonding pressure of 1000N, and then annealing for 3 hours at a temperature of 120 ℃.
1d, thinning and polishing the silicon-based lithium niobate bonding sheet to make the thickness of the bonding sheet be 5 mu m.
Step 2, repeating the step 1a to clean the silicon-based lithium niobate bonding sheet, and preparing an alignment mark and a metal electrode, wherein the method comprises the following steps:
2a, pre-customizing a designed alignment mark pattern and a metal electrode pattern on a mask plate, sputtering a layer of chromium/gold on silicon-based lithium niobate by adopting a magnetron sputtering method, then using a photoresist AZ6130, homogenizing the photoresist for 10 seconds at a low speed of 500r/min by a photoresist homogenizing machine, homogenizing the photoresist for 30 seconds at a high speed of 3000r/min, pre-baking for 60 seconds under a hot plate at 100 ℃, and adopting an EVG610 photoetching machine by photoetching equipment, wherein the exposure dose is 100J/cm 2 Developing with developing solution AZ400K and water in a ratio of 1:4, flushing the film with plasma water after developing, drying with nitrogen, removing the photoresist for 2 minutes with an oxygen plasma photoresist remover, and post-drying for 15 minutes at 120 ℃ under a hot plate. And then etching to remove the unnecessary metal layer by using an IBE process.
Wherein, the thickness ratio of chromium/gold used for the surface electrode and the alignment mark manufactured by magnetron sputtering is 10nm/50nm, and the metal chromium has the function of enabling the gold electrode to be well adhered on the lithium niobate wafer as an adhesion layer.
And 2b, removing the photoresist on the surface by using acetone, ethanol and deionized water after etching.
And 2c, observing the finished product of the preparation process by using a microscope, wherein a group of electrodes are arranged on the cross beam and the longitudinal beam of each composite cantilever beam.
And 3, etching and patterning the silicon-based lithium niobate, wherein the method comprises the following steps of:
3a, repeating the operation of 1a cleaning the surface of the bonding sheet.
3b, setting the rotating speed of a photoresist homogenizing machine to be 1000r/min for homogenizing photoresist, using AZ4620 as photoresist, then baking for 180s by a hot plate, photoetching by adopting a photoetching machine EVG610, and setting the exposure dose to be 400mJ/cm 2 Developing solution AZ400k and water are mixed for 1:3, the residual primer after development is removed by oxygen plasma after pattern development, and finally, the film is hardened on a hot plate at 120 ℃ for 15 minutes.
And 3c, etching by using an IBE process, and checking etching conditions every half an hour until patterning of the lithium niobate single crystal film is completed.
And 3d, etching by adopting an RIE process to complete the patterning of the silicon dioxide layer.
And 4, preparing a silicon-based cantilever beam and a silicon-based central mass ring and releasing a device, wherein the preparation method specifically comprises the following steps of:
4a, etching the front surface of the bonding sheet by using a deep silicon etching process to prepare a silicon-based cantilever beam and a central mass ring, wherein the etching thickness is 100 mu m.
4b, respectively carrying out ultrasonic treatment on the etched bonding sheet by using acetone, absolute ethyl alcohol and deionized water for 5 minutes, cleaning the surface by using deionized water, and drying the surface by using nitrogen.
4c, spraying positive photoresist AZ4620 on the back of the bonding sheet by a photoresist sprayer, spraying the positive photoresist AZ4620 for 16 circles with the thickness of 60 mu m, then pre-baking for 2min at the temperature of 100 ℃, and then carrying out photoetching process, wherein the exposure dose is 800mJ/cm 2 And then developing by using a developing solution AZ400k and water in a ratio of 1:3, removing residual primer by using oxygen plasma after the complete development of the pattern, and hardening the film on a hot plate at 120 ℃ for 20min after photoresist removal.
And 4d, bonding the front surface of the bonding sheet and the silicon wafer by adopting oil pumping, and etching the deep silicon to a thickness of 400 mu m to release the composite cantilever beam and the central mass ring.
4e, soaking and washing the pump oil on the surface of the structure by using absolute ethyl alcohol, and then washing for a plurality of times by using deionized water, and naturally evaporating the water.
Step 5, adhesion installation of the central microsphere, specifically:
and (3) after a trace of ultraviolet light curing adhesive is coated on the surface of the microsphere, placing the microsphere at the joint of the central mass ring, and irradiating the microsphere for 5min by using an ultraviolet lamp to cure the ultraviolet light curing adhesive, so as to obtain the piezoelectric vibration sensor. Wherein the microsphere is made of PA (polyamide), the radius of the microsphere is 2000 μm, and the radius of a mass ring for placing the microsphere is 1321 μm.
The structure of the acceleration sensor (composite Liang Weiqiu sensor) prepared through the steps is shown in fig. 7, and the silicon-based lithium niobate bonding sheet forms a frame 1, a central mass ring 2 and four composite cantilever beams 3 through an MEMS (micro electro mechanical systems) process, wherein the outer periphery of the central mass ring 2 is square, and the inner periphery of the central mass ring 2 is round. Each composite cantilever beam 3 is composed of a cross beam 301 and a longitudinal beam 302 which are vertically arranged, namely, the composite cantilever beam 3 is provided with three connecting ends, wherein two connecting ends are connected with the frame 1, and the other connecting end is connected with the central mass ring 2 (namely, two connecting ends of the longitudinal beam 302 are respectively connected with the frame 1 and the central mass ring 2, and one connecting end of the cross beam 301 is connected with the frame 1); the four composite cantilever beams 3 are symmetrically arranged on the upper side and the lower side of the central mass ring 2 (of course, the four composite cantilever beams can also be symmetrically arranged on the left side and the right side of the central mass ring); a group of electrodes 4 are arranged on the cross beam 301 and the longitudinal beam 302; the microsphere 5 is fixed on the central mass ring 2. Wherein the thickness of the silicon substrate is 500 mu m, the thickness of the silicon dioxide layer is 3 mu m, and LiNbO 3 The thickness of the film is 5 mu m, the thickness of the electrode is 100-350 nm, and the thickness of the central mass ring and the composite cantilever beam are 70 mu m. The microsphere radius was 2000 μm and the inner circumference radius of the central mass ring was 1321 μm.
As shown in fig. 6, four different structures of the sensor were simulated by compounding Liang Weiqiu (application), four-beam microspheres, four-beam mass, compound-beam mass, and the like. The data shown in fig. 6 is plotted by analyzing and comparing the maximum output charge of each structure at different accelerations. The electrostatic fields of all the structures and the parameter settings of the solid mechanical field are the same, and only the acceleration is changed to simulate the output of different structures. As shown in fig. 6, under the same condition of the center structure, the cantilever sensor of the composite structure has a larger charge output value than the four cantilever sensors, and the increment of the output charge is larger as the acceleration increases. In contrast, when the cantilever beam structures are identical, the sensor with the microsphere in the center structure has higher output charge and sensitivity than the sensor with the center mass structure.
The stress distribution at the resonant frequency (first third order) of the composite Liang Weiqiu sensor prepared in example 1 (as shown in fig. 7) was examined; wherein: first order natural frequency isf osc1 = 1533.1Hz, which shows bending modes, with a tendency to move up and down amplitude; natural frequencies of the second order and the third order are respectivelyf osc2 =2513 Hz sumf osc3 = 4228.1Hz, which shows a twisting mode with a tendency to cantilever overturning.
As shown in FIG. 8, the maximum displacement generated by the device prepared in example 1 of the present application is shown in the simulated analysis data graph of the usable frequency band of the composite Liang Weiqiu sensorfThe maximum displacement of the cantilever beam is the maximum at the moment of being= 1533.1Hz, and the method can be used for detecting vibration signals in a medium-low frequency range.
As shown in fig. 9, the composite Liang Weiqiu sensor has a device displacement distribution at the cross section under an input excitation acceleration signal. At the cross section, the displacement distribution under excitation signals of different frequencies was studied, whose vibration displacement has a displacement value in the measured frequency band range that is much smaller than the displacement value at the natural frequency. The transverse vibration displacement changes gently, and the service life of the sensor can be prolonged under the condition of ensuring larger output charges.
The structure of the existing composite beam mass block sensor is shown in fig. 10, and four composite cantilever beams 3 are symmetrically arranged on two sides of a mass block 6 in pairs and are connected with a frame 1; a set of electrodes 4 are arranged on the cross member 301 and the longitudinal member 302. The application detects the stress distribution of the composite beam mass sensor at the resonance frequency (the first third order); wherein: first order inherentThe frequency isf osc1 = 3533.8Hz, which shows bending modes, with a tendency to move up and down amplitude; natural frequencies of the second order and the third order are respectivelyf osc2 =2513 Hz sumf osc3 = 4228.1Hz, which shows a twisting mode with a tendency to cantilever overturning.
As shown in FIG. 11, the usable frequency band of the composite beam-mass sensor is simulated and analyzed to obtain a data graph, and the composite beam-mass sensor is used as a control device in embodiment 1 of the present application, which generates a maximum displacement infThe maximum displacement of the cantilever beam is maximum at 3533.8Hz, but the vibration displacement value is smaller than that of fig. 8, and the output charge due to the smaller stress on the piezoelectric crystal is also smaller due to the piezoelectric effect.
As shown in fig. 12, the composite beam mass sensor has a device displacement distribution at the cross section under the input of an excitation acceleration signal. At the cross section, the displacement distribution under excitation signals of different frequencies was studied, whose vibration displacement has a displacement value in the measured frequency band range that is much smaller than the displacement value at the natural frequency. The change of the transverse vibration displacement is relatively gentle, but the displacement value is smaller than that of the embodiment 1 of the application, and the corresponding output signal is smaller.
The structure of the four-beam microsphere sensor is shown in fig. 13, four single cantilever beams 7 are symmetrically arranged in four directions of a central mass ring 2 and are connected with a frame 1, and microspheres 5 are fixed on the central mass ring 2; a group of electrodes 4 are arranged on each single cantilever beam 7. The application detects the stress distribution cloud picture of the four-beam microsphere sensor at the resonance frequency (the first third order); wherein: first order natural frequency isf osc1 = 1400.6Hz, which shows bending modes, with a tendency to move up and down amplitude; natural frequencies of the second order and the third order are respectivelyf osc2 = 3301.3Hz sumf osc3 = 3307.1Hz, which shows a twisting mode with a tendency to cantilever overturning.
As shown in FIG. 14, the usable frequency band simulation analysis data graph of the four-beam microsphere sensor, which is the control device in example 1 of the present application, is the most generatedLarge displacement atf= 1400.6Hz, where the maximum displacement of the cantilever beam is maximum, but the usable frequency band is narrower than in fig. 8, which can only be used for testing in some low frequency environments.
As shown in fig. 15, the four-beam microsphere sensor has device displacement distribution conditions at the cross section under the input of an excitation acceleration signal. At the cross section, the displacement distribution under excitation signals of different frequencies was studied, whose vibration displacement has a displacement value in the measured frequency band range that is much smaller than the displacement value at the natural frequency. The transverse vibration displacement changes rapidly, and the service life of the sensor is reduced under the condition that the output charge is lower than that of the embodiment 1 of the application.
The structure of the existing four-beam mass sensor is shown in fig. 16, four single cantilever beams 7 are symmetrically arranged in four directions of a mass block 6 and are connected with a frame 1, and a group of electrodes 4 are uniformly distributed on each single cantilever beam 7. The application detects the stress distribution cloud image of the four-beam mass sensor at the resonance frequency (the first third order); wherein: first order natural frequency isf osc1 = 3363.3Hz, which shows bending modes, with a tendency to move up and down amplitude; natural frequencies of the second order and the third order are respectivelyf osc2 = 8427.7Hz sumf osc3 = 8432.5Hz, which shows a twisting mode with a tendency to cantilever overturning.
As shown in FIG. 17, the four-beam mass sensor, which is used as a control device in embodiment 1 of the present application, generates a maximum displacement in the following rangefThe maximum displacement of the cantilever beam is maximum at 3363.3Hz, but the vibration displacement value is smaller than that of fig. 8, and the output charge due to the smaller stress on the piezoelectric crystal is also smaller due to the piezoelectric effect.
As shown in fig. 18, the four-beam mass sensor has a device displacement distribution in the cross section under the input of an excitation acceleration signal. At the cross section, the displacement distribution under excitation signals of different frequencies was studied, whose vibration displacement has a displacement value in the measured frequency band range that is much smaller than the displacement value at the natural frequency. The transverse vibration displacement of the sensor changes rapidly, and the service life of the sensor can be reduced under the condition of small output charge.
Example 2
A preparation method of an acceleration sensor based on vibration microspheres comprises the following steps:
step 1, preparing a silicon-based lithium niobate bonding sheet, which comprises the following steps:
1a, acid washing and alkali washing a lithium niobate wafer and a silicon substrate, firstly, acid washing at the environmental temperature of 150 ℃, then alkali washing with hydrogen peroxide and ammonia water, then ultrasonic cleaning for 5min by sequentially using acetone and absolute ethyl alcohol, then ultrasonic cleaning for 5min by using deionized water to wash surface impurities and organic matters, and drying the surface by using nitrogen.
1b, growing a silicon dioxide layer with the thickness of 1 mu m on the surface of the silicon substrate by adopting a PECVD method.
1c, bonding the lithium niobate wafer and the silicon substrate at a bonding temperature of 120 ℃ and a bonding pressure of 2000N, and then annealing at a temperature of 150 ℃ for 3 hours.
1d, thinning and polishing the silicon-based lithium niobate bonding sheet to make the thickness of the bonding sheet be 1 mu m.
Step 2, repeating the step 1a to clean the silicon-based lithium niobate bonding sheet, and preparing an alignment mark and a metal electrode, wherein the method comprises the following steps:
2a, pre-customizing a designed alignment mark pattern and a metal electrode pattern on a mask plate, sputtering a layer of chromium/gold on silicon-based lithium niobate by adopting a magnetron sputtering method, then using a photoresist AZ6130, homogenizing the photoresist for 10 seconds at a low speed of 500r/min by a photoresist homogenizing machine, homogenizing the photoresist for 30 seconds at a high speed of 3000r/min, pre-baking for 60 seconds under a hot plate at 100 ℃, and adopting an EVG610 photoetching machine by photoetching equipment, wherein the exposure dose is 100J/cm 2 Developing with developing solution AZ400K and water in a ratio of 1:4, flushing the film with plasma water after developing, drying with nitrogen, removing photoresist for 2 minutes with an oxygen plasma photoresist remover, and post-drying for 15 minutes at 120 ℃ under a hot plate; the unwanted metal layer is then etched away using an IBE process.
Wherein, the thickness ratio of chromium/gold used for the surface electrode and the alignment mark manufactured by magnetron sputtering is 10nm/50nm, and the metal chromium has the function of enabling the gold electrode to be well adhered on the lithium niobate wafer as an adhesion layer.
And 2b, removing the photoresist on the surface by using acetone, ethanol and deionized water after etching.
And 2c, observing the finished product of the preparation process by using a microscope, wherein a group of electrodes are arranged on the cross beam and the longitudinal beam of each composite cantilever beam.
Step 3, etching and patterning of silicon-based lithium niobate, which comprises the following steps:
3a, repeating the operation of 1a cleaning the surface of the bonding sheet.
3b, setting the rotating speed of a photoresist homogenizing machine to be 1000r/min for homogenizing photoresist, using AZ4620 as photoresist, then baking for 180s by a hot plate, photoetching by adopting a photoetching machine EVG610, and setting the exposure dose to be 400mJ/cm 2 Developing solution AZ400k and water are mixed for 1:3, the residual primer after development is removed by oxygen plasma after pattern development, and finally, the film is hardened on a hot plate at 120 ℃ for 15 minutes.
And 3c, etching by using an IBE process, and checking etching conditions every half an hour until patterning of the lithium niobate single crystal film is completed.
And 3d, etching by adopting an RIE process to complete the patterning of the silicon dioxide layer.
And 4, preparing a silicon-based cantilever beam and a silicon-based center mass ring and releasing a device, wherein the preparation and device release process specifically comprises the following steps of:
4a, etching the front surface of the bonding sheet by using a deep silicon etching process to prepare a silicon-based cantilever beam and a central mass ring, wherein the etching thickness is 80 mu m.
4b, respectively carrying out ultrasonic treatment on the etched bonding sheet by using acetone, absolute ethyl alcohol and deionized water for 5 minutes, cleaning the surface by using deionized water, and drying the surface by using nitrogen.
4c, spraying positive photoresist AZ4620 on the back of the bonding sheet by a photoresist sprayer, spraying the positive photoresist AZ4620 for 8 circles with the thickness of 30 mu m, then pre-baking for 2min at the temperature of 100 ℃, and then carrying out photoetching process, wherein the exposure dose is 800mJ/cm 2 And then developing by using a developing solution AZ400k and water in a ratio of 1:3, removing residual primer by using oxygen plasma after the complete development of the pattern, and hardening the film on a hot plate at 120 ℃ for 20min after photoresist removal.
And 4d, bonding the bonding piece and the silicon wafer by adopting oil pumping, and etching the deep silicon to a thickness of 420 mu m to release the cantilever beam and the central mass ring.
4e, pumping oil on the surface of the structure by using absolute ethyl alcohol, and then flushing the structure for a plurality of times by using deionized water, and naturally evaporating the water.
Step 5, adhesion installation of the central microsphere, specifically:
and (3) after a trace of ultraviolet light curing adhesive is coated on the surface of the microsphere, placing the microsphere at the joint of the central mass ring, and irradiating the microsphere for 5min by using an ultraviolet lamp to cure the ultraviolet light curing adhesive, so as to obtain the piezoelectric vibration sensor. Wherein the microsphere is made of PA (polyamide), the radius of the microsphere is 2000 μm, and the radius of a mass ring for placing the microsphere is 1321 μm.
The acceleration sensor (composite Liang Weiqiu sensor) is prepared through the steps, the designed vibration sensor is smaller in designed size on the basis of COMSOL theoretical simulation, the natural frequency is basically consistent with that of the embodiment 1, and the designed vibration sensor also has a larger charge output value.
In a word, compared with the composite beam mass block sensor, the four-beam microsphere sensor and the four-beam mass block sensor, the composite Liang Weiqiu sensor prepared by the application widens the application frequency band of the device, reduces the transverse sensitivity and improves the sensitivity of vibration signal collection in the Z-axis direction.
Finally, it should be noted that the above-mentioned embodiments are merely for illustrating the technical solution of the present application and not for limiting the same, and although the detailed description is given with reference to the embodiments of the present application, it should be understood by those skilled in the art that the technical solution of the present application may be modified or substituted without departing from the spirit and scope of the technical solution of the present application, and it should be covered by the scope of the claims of the present application.
Claims (10)
1. An acceleration sensor based on vibration microsphere comprises a Si substrate, wherein a layer of SiO grows on the surface of the Si substrate 2 Thin film and LiNbO 3 After bonding the wafers, forming a silicon-based lithium niobate bonding sheet;
the method is characterized in that: the silicon-based lithium niobate bonding sheet forms a frame (1), a central mass ring (2) and four composite cantilever beams (3) through an MEMS process;
each composite cantilever beam (3) is composed of a cross beam (301) and a longitudinal beam (302) which are vertically arranged, namely, the composite cantilever beam (3) is provided with three connecting ends, wherein two connecting ends are connected with a frame (1), and the other connecting end is connected with a central mass ring (2);
the four composite cantilever beams (3) are symmetrically arranged on two sides of the central mass ring (2) in pairs;
electrodes (4) are arranged on the cross beam (301) and the longitudinal beam (302) respectively;
and microspheres (5) are fixed on the central mass ring (2).
2. An acceleration sensor based on vibrating microspheres according to claim 1, characterized in that: the periphery of the center mass ring (2) is square, and the inner periphery of the center mass ring is round.
3. An acceleration sensor based on vibrating microspheres according to claim 1 or 2, characterized in that: the thickness of the silicon substrate is 500 mu m, the thickness of the silicon dioxide layer is 1-3 mu m, and LiNbO 3 The thickness of the film is 5 mu m, the thickness of the electrode is 100-350 nm, and the thickness of the central mass ring and the composite cantilever beam is 60-100 mu m.
4. An acceleration sensor based on vibrating microspheres according to claim 3, characterized in that: the radius of the microsphere (5) is 2000 mu m, and the radius of the inner circumference of the central mass ring is 1321 mu m.
5. The vibrating microsphere-based acceleration sensor of claim 4, wherein: the microsphere (5) is made of PA;
the microsphere is fixed on the central mass ring (2) through ultraviolet light curing glue.
6. A preparation method of an acceleration sensor based on vibration microspheres is characterized by comprising the following steps: the method comprises the following steps:
step S1: preparation of silicon-based lithium niobate bonding sheet
Cleaning a Y-cut lithium niobate wafer and a silicon substrate, growing a silicon dioxide layer on the surface of the silicon substrate by adopting a PECVD method, bonding the silicon substrate with an oxide layer and a lithium niobate single crystal film at a low temperature, and then obtaining a silicon-based lithium niobate bonding sheet through thinning and polishing processes;
step S2: preparation of marking patterns and surface electrodes
Cleaning a silicon-based lithium niobate bonding sheet, and preparing an alignment mark and a surface electrode on a composite cantilever beam of a sensor by adopting a magnetron sputtering and etching process;
step S3: etching the lithium niobate single crystal film by using an IBE process, and etching the silicon dioxide film layer by using an RIE process, so that the lithium niobate film layer and the silicon dioxide film layer are patterned;
step S4: preparing a cantilever beam and a central mass ring on the front surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching;
the release of the composite cantilever beam and the central mass ring is completed on the back surface of the silicon-based lithium niobate bonding sheet through the processes of glue spraying, photoetching, developing, post-baking and deep silicon etching;
step S5: the microsphere surface is coated with ultraviolet light curing adhesive and then is placed at the inner circumference of the central mass ring, and ultraviolet light is used for irradiation to cure the ultraviolet light curing adhesive.
7. The method for preparing the acceleration sensor based on the vibration microsphere according to claim 6, wherein the method comprises the following steps: step S1, carrying out acid washing on a Y-cut lithium niobate wafer and a silicon substrate at an ambient temperature of 150 ℃, then carrying out alkali washing by using hydrogen peroxide and ammonia water, then carrying out ultrasonic washing by using acetone and absolute ethyl alcohol in sequence, then carrying out ultrasonic washing by using deionized water to wash surface impurities and organic matters, and drying the surface by using nitrogen; growing a silicon dioxide layer with the thickness of 1-3 mu m on the surface of the silicon substrate by adopting a PECVD method; bonding the Y-cut lithium niobate wafer and the silicon substrate at the bonding temperature of 80-120 ℃ and the bonding pressure of 1000-3000N, and then annealing for 3h at the temperature of 120-150 ℃; the silicon-based lithium niobate bonding sheet was thinned and polished so that the thickness of the lithium niobate layer was 5 μm.
8. The method for preparing the acceleration sensor based on the vibration microsphere according to claim 7, wherein the method comprises the following steps: step S2, the designed alignment mark pattern and the metal electrode pattern are customized on a mask plate in advance, a layer of chromium/gold is sputtered on the silicon-based lithium niobate by a magnetron sputtering method, then photoresist AZ6130 is used, a photoresist homogenizer is used for homogenizing the photoresist for 10 seconds at a low speed of 500r/min, a photoresist homogenizer is used for homogenizing the photoresist for 30 seconds at a high speed of 3000r/min, a hot plate is used for pre-baking for 60 seconds at a temperature of 100 ℃, and a photolithography device is an EVG610 photoetching machine, wherein the exposure dose is 100J/cm 2 Developing with developing solution AZ400K and water in a ratio of 1:4, flushing the film with plasma water after developing, drying with nitrogen, removing photoresist with an oxygen plasma photoresist remover, and post-drying at 120 ℃ for 15min; etching to remove the unnecessary metal layer by using an IBE process;
wherein, the thickness ratio of the surface electrode and the alignment mark manufactured by magnetron sputtering is 10nm/50nm.
9. The method for preparing the acceleration sensor based on the vibration microsphere according to claim 8, wherein the method comprises the following steps: step S3 is specifically to set the spin speed of a spin coater to 1000r/min for spin coating, AZ4620 is used for photoresist, then a hot plate is used for baking for 180S, a photoetching machine EVG610 is used for photoetching, and the exposure dose is set to 400mJ/cm 2 Mixing the developing solution AZ400k with water in a ratio of 1:3, developing the pattern, removing the residual primer after the development by using oxygen plasma, and finally hardening the film on a hot plate at 120 ℃ for 15 minutes; etching by adopting an IBE (ion beam etching) process, checking etching conditions every half an hour until patterning of the lithium niobate single crystal film is completed;
and then etching the silicon dioxide layer by adopting an RIE process to complete the patterning of the silicon dioxide layer.
10. The method for preparing the acceleration sensor based on the vibration microsphere according to claim 9, wherein the method comprises the following steps: step S4, etching and preparing a silicon-based cantilever beam and a central mass ring by using a deep silicon etching process, wherein the etching thickness is 100 mu m; respectively carrying out ultrasonic treatment on the etched bonding sheet by using acetone, absolute ethyl alcohol and deionized water, then washing the surface by using deionized water, and drying the surface by using nitrogen;
spraying positive photoresist AZ4620 with a photoresist sprayer at the back of the silicon substrate for 16 circles with the thickness of 60 μm, pre-baking at 100deg.C for 2min, and photoetching at exposure dose of 800mJ/cm 2 Then developing by using a developing solution AZ400k and water in a ratio of 1:3, removing residual primer by using oxygen plasma after the complete development of the pattern, and hardening the film on a hot plate at 120 ℃ for 20min after photoresist removal; bonding the front surface of the bonding sheet and the silicon wafer by adopting pump oil, and etching the deep silicon to a thickness of 400 mu m to release the cantilever beam and the central mass ring; and (3) soaking and washing the pumping oil on the surface of the structure by using absolute ethyl alcohol, and then washing for a plurality of times by using deionized water, and naturally evaporating the water.
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