A 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor and preparation method thereof

Abstract

This application provides a 15 A model ferroelectric single crystal thin film piezoelectric vibration sensor and a preparation method thereof, wherein the bottom electrode / silicon dioxide layer / silicon substrate is bonded to a lithium niobate wafer, and then thinned, chemically mechanically polished and cleaned in sequence to obtain a lithium niobate single crystal thin film; alignment marks and surface electrodes are prepared on the wafer surface by magnetron sputtering and ion beam etching and stripping processes, and then the lithium niobate single crystal thin film is etched by ion beam etching to pattern it, and the silicon dioxide layer is etched by reactive ion etching to pattern it, and then the bottom electrode is etched by ion beam etching to pattern it, and finally a deep silicon etching process is used to prepare a cantilever beam and a mass block from the front of the silicon substrate and release the device from its back. The present application can well bond the ferroelectric single crystal lithium niobate thin film to the silicon wafer, and on this basis, a standard MEMS process is used to prepare a sensor device, with high process feasibility and repetition rate, and the prepared device has a wide frequency band and a very high output voltage.

Description

Technical Field

[0001] The present invention relates to the field of MEMS structure manufacturing technology, and more particularly to a method for 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor and its preparation method. Background Art

[0002] As the main monitoring parameter of the monitoring system, the effective extraction and monitoring of vibration signals in a diverse vibration environment poses a severe challenge to traditional vibration sensors. Piezoelectric vibration sensors based on piezoelectric materials have become the main development direction of vibration sensors in the future. At present, there are five major types of piezoelectric materials, such as piezoelectric crystals, piezoelectric ceramics, piezoelectric polymers, piezoelectric composites, and piezoelectric films. Although piezoelectric crystals, piezoelectric ceramics, piezoelectric polymers, and piezoelectric composites all have their own excellent performance, they all have the problem of incompatibility with MEMS processes.

[0003] For piezoelectric vibration sensors, the piezoelectric coefficient of the material plays a decisive role in the performance of the device. At present, piezoelectric vibration sensors mostly use ferroelectric thin films PZT, PMN-PT and lithium niobate. Among them, ferroelectric PZT film and relaxor ferroelectric PMN-PT film as piezoelectric materials have high energy density, excellent dielectric properties and PZT is easy to prepare and are widely used in the preparation of sensors and energy collectors. However, as a ferroelectric polycrystalline material, its performance is relatively unstable, and it contains lead elements that are not friendly to the human body and the environment.

[0004] There are three main working modes of piezoelectric vibration sensors based on ferroelectric films: 15 ,d 31 and d 33 The piezoelectric coefficient plays a decisive role in the performance of force-electric output, sensitivity and quality factor. Most cantilever beam vibration sensors usually use the upper and lower electrodes. 31 mode, and the piezoelectric coefficient d 31 The smaller the voltage output, the corresponding sensitivity and the device performance, the more important it is to design a new mode of piezoelectric vibration sensor with high output performance. Summary of the invention

[0005] In view of this, the present application provides a 15 The invention discloses a piezoelectric vibration sensor of a single-crystal ferroelectric film and a preparation method thereof, which can be used to manufacture a sensor device with a wide frequency band and a high output voltage, and can also improve the corresponding sensitivity of the device.

[0006] The specific technical solutions of this application are as follows:

[0007] This application provides a 15A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor comprises the following steps:

[0008] Step 1: clean the lithium niobate wafer and the silicon substrate respectively, deposit a silicon dioxide layer on the surface of the silicon substrate by plasma enhanced chemical vapor deposition, and magnetron sputter a bottom electrode on the surface of the silicon dioxide layer;

[0009] Step 2: bonding the lithium niobate wafer to the silicon substrate, and then sequentially thinning, chemical mechanical polishing and cleaning to obtain a lithium niobate single crystal film;

[0010] Step 3: Prepare the alignment mark by magnetron sputtering and ion beam etching process, and then prepare the surface electrode by magnetron sputtering and lift-off process in the developed pattern area;

[0011] Step 4: Use ion beam method to etch the lithium niobate single crystal film to pattern it, then use reactive ion etching method to etch the silicon dioxide layer to pattern it; finally, use ion beam method to etch the bottom electrode to pattern it.

[0012] Step 5: The cantilever beam and the mass block are prepared on the patterned lithium niobate surface by using a spray-photolithography-development-post-bake-deep silicon etching method, and the device is released from the back of the silicon substrate by using a spray-photolithography-development-post-bake-deep silicon etching method to obtain the d 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor.

[0013] Preferably, the thickness of the silicon dioxide layer and the oxide layer is 1-3 μm, the thickness of the bottom electrode is 100-350 nm, the thickness of the lithium niobate single crystal film is 5-10 μm, and the thickness of the mass block and the cantilever beam is 60-100 μm.

[0014] Preferably, the cleaning solutions in step 1 are acetone, isopropanol, anhydrous ethanol and deionized water in sequence.

[0015] Preferably, the power of the magnetron sputtering in step 1 is 300-600W, and the bottom electrode is chromium / gold.

[0016] Preferably, the bonding pressure in step 2 is 1000-3000N, and the bonding temperature is 80-120°C.

[0017] Preferably, the thinning and chemical mechanical polishing in step 2 are specifically as follows: first, a 1-20 μm Al 2 O 3 Grinding, and finally polishing pressure 40 ~ 50N and 500nm SiO 2 Polishing is performed.

[0018] Preferably, the preparation of the alignment mark and the surface electrode in step 3 uses reverse photoresist AZ5214, and the positive photoresist parameters are: pre-baking on a hot plate at 95°C for 2 minutes, and the exposure dose is 65mJ / cm 2 , 110℃ hot plate post-bake for 2 minutes; negative photoresist parameters: plate pre-bake at 95℃ for 2 minutes, exposure dose 45mJ / cm 2 , 110℃ hot plate drying for 90s, flood exposure 540mJ / cm 2

[0019] Preferably, the ion beam etching and reactive ion etching method in step 4 uses a positive photoresist AZ4620, and the spin coating thickness is 8 μm to 15 μm.

[0020] Preferably, the spray glue in step five is positive resist AZ4620, the spray glue thickness is 30 μm to 60 μm, and the developer is developed with a ratio of developer to water of 1:2.

[0021] The present application also provides a 15 mode ferroelectric single crystal thin film piezoelectric vibration sensor, composed of the d 15 The method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor is used to prepare it.

[0022] In summary, the present application provides a 15 A mode ferroelectric single crystal thin film piezoelectric vibration sensor and a preparation method thereof, wherein the bottom electrode / silicon dioxide layer / silicon substrate is bonded to a lithium niobate wafer, and then thinned, chemically mechanically polished and cleaned in sequence to obtain a lithium niobate single crystal thin film; alignment marks and surface electrodes are prepared on the wafer surface by magnetron sputtering, ion beam etching and stripping processes, and then the lithium niobate single crystal thin film is etched by ion beam etching to pattern it, and the silicon dioxide layer is etched by reactive ion etching to pattern it, and then the bottom electrode is etched by ion beam etching to pattern it, and finally a deep silicon etching process is used to prepare a cantilever beam and a mass block from the front of the silicon substrate and release the device from its back. The present application can well bond the ferroelectric single crystal lithium niobate thin film to the silicon wafer, realize the heterogeneous integration of the silicon oxide baseband bottom electrode and the ferroelectric single crystal thin film, and then complete the preparation of components with wide-band and high-voltage output, with high process feasibility and repetition rate, providing a good theoretical and process basis for the development and preparation of high-frequency micro-vibration devices. The present application utilizes a ferroelectric single crystal lithium niobate thin film d 15 The model improves the principle of voltage output and sensitivity. The product has high electromechanical conversion efficiency, and the performance decreases very little in low temperature environment, which is environmentally friendly and provides a guarantee for the preparation of sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0024] Figure 1 In the embodiment of this application, 15 Flow chart of the preparation method of the mode ferroelectric single crystal thin film piezoelectric vibration sensor;

[0025] Figure 2 This is a cross-sectional view of a lithium niobate single crystal thin film structure with a bottom electrode / silicon dioxide layer / silicon as a substrate in an embodiment of the present application;

[0026] Figure 3 In the embodiment of this application, 15 Schematic diagram of the structure of the mode ferroelectric single crystal thin film piezoelectric vibration sensor. DETAILED DESCRIPTION

[0027] Reference Figure 1 , Figure 1 In the embodiment of this application, 15 Flow chart of the preparation method of mode ferroelectric single crystal thin film piezoelectric vibration sensor.

[0028] The present application embodiment provides a 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor comprises the following steps:

[0029] S1: clean the lithium niobate wafer and silicon substrate respectively, deposit a silicon dioxide layer on the surface of the silicon substrate by plasma enhanced chemical vapor deposition, and magnetron sputter the bottom electrode on the surface of the silicon dioxide layer;

[0030] S2: bonding the lithium niobate wafer to the silicon substrate, and then sequentially thinning, chemical mechanical polishing and cleaning to obtain a lithium niobate single crystal film;

[0031] S3: preparing alignment marks by magnetron sputtering and ion beam etching, and then preparing surface electrodes in the developed pattern area by magnetron sputtering and lift-off process;

[0032] S4: etching the lithium niobate single crystal film by ion beam method to pattern it, then etching the silicon dioxide layer by reactive ion etching method to pattern it; finally etching the bottom electrode by ion beam method to pattern it;

[0033] S5: The cantilever beam and the mass block are prepared on the patterned lithium niobate surface by using methods such as spraying-photolithography-development-post-bake-deep silicon etching, and the device is released from the back of the silicon substrate by using methods such as spraying-photolithography-development-post-bake-deep silicon etching to obtain the d 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor.

[0034] It should be noted that the polarization direction of the lithium niobate single crystal film and the force direction of the ferroelectric film used in the embodiment of the present application are perpendicular to the electrode direction, and the piezoelectric coefficient d is calculated by using the Bond matrix and MATLAB software. 15 The largest tangential piezoelectric coefficient of lithium niobate is d 15 The maximum value is approximately d 31 100 times, using the piezoelectric coefficient d 15 The performance of the piezoelectric cantilever vibration sensor can be effectively improved.

[0035] It should be noted that cleaning the lithium niobate wafer and silicon substrate in S1 can remove organic matter and impurities on the surface, ensure that the silicon substrate and lithium niobate surface remain clean, and complete the growth of the silicon substrate surface oxide layer and the bottom electrode to obtain a process surface capable of direct bonding process. Thinning, chemical mechanical polishing and cleaning are performed in sequence in S2 to obtain a lithium niobate single crystal film. Alignment marks and surface electrode preparation are completed in S3. Ion beam etching and reactive ion etching are used in S4 to pattern the lithium niobate, silicon dioxide layer and bottom electrode layer. In S5, the silicon substrate is etched from the front of the silicon substrate using deep silicon etching to form the required mass block and cantilever beam thickness, and then the device is released from the back of the silicon substrate using deep silicon etching to complete the preparation of the vibration sensor. The preparation method of the embodiment of the present application can well bond the ferroelectric single crystal lithium niobate film to the SOI wafer, realize the heterogeneous integration of the silicon substrate with bottom electrode oxide and the ferroelectric single crystal film, and on this basis, the standard MEMS process is used to complete the preparation of the device, with high process feasibility and repetition rate.

[0036] According to the embodiment of the present application, the thickness of the silicon dioxide layer is 1 to 3 μm, the thickness of the bottom electrode is 100 to 350 nm, the thickness of the lithium niobate single crystal film is 5 to 10 μm, and the thickness of the mass block and the cantilever beam is 60 to 100 μm.

[0037] According to an embodiment of the present application, the cleaning solutions described in S1 are acetone, isopropanol, anhydrous ethanol and deionized water, respectively.

[0038] According to an embodiment of the present application, the power of the magnetron sputtering in S1 is 300-600 W, and the bottom electrode is chromium / gold.

[0039] According to an embodiment of the present application, the bonding pressure in S2 is 1000-3000N, and the bonding temperature is 80-120°C.

[0040] It should be noted that the bonding method of the embodiment of the present application avoids problems such as debonding and structural cracking caused by thermal mismatch and other problems, can improve the bonding effect of ferroelectric single crystal lithium niobate film and silicon wafer, and solve the shortcomings of the prior art.

[0041] According to the embodiment of the present application, the thinning and chemical mechanical polishing in S2 are specifically as follows: first, a 1-20 μm Al2O3 layer is formed under a pressure of 40-50 N. 2 O 3 Grinding, and finally polishing pressure 40 ~ 50N and 500nm SiO 2 Polishing is performed.

[0042] It should be noted that the thinning and chemical mechanical polishing methods have achieved the preparation of high-quality, large-area, low-stress ferroelectric single crystal films.

[0043] According to the embodiment of the present application, the preparation of the alignment mark and the surface electrode described in S3 uses reverse photoresist AZ5214, and the positive photoresist parameters are: pre-baking on a hot plate at 95°C for 2 minutes, and the exposure dose is 65mJ / cm 2 , 110℃ hot plate post-bake for 2 minutes; negative photoresist parameters: plate pre-bake at 95℃ for 2 minutes, exposure dose 45mJ / cm 2 , 110℃ hot plate drying for 90s, flood exposure 540mJ / cm 2 Bake on a hot plate at 90-120°C for 90-120 seconds.

[0044] It should be noted that the use of reverse glue AZ5214 avoids the difficulty of metal stripping using positive photoresist, reduces the metal line width, and improves the stripping accuracy. At the same time, the use of AZ5214 reverse glue and flood exposure makes it form an inverted trapezoid, which is more conducive to the stripping of the metal electrode. The use of IBE to etch lithium niobate avoids the problems of slow etching rate and etching angle of the RIE process, and combines the deep silicon etching process to prepare a shear mode cantilever beam piezoelectric vibration sensor. The devices prepared by this MEMS process have a high yield rate and high repeatability, and can obtain sensors with excellent performance, providing a good foundation for high-frequency micro-vibration components.

[0045] According to the embodiment of the present application, the ion beam etching and reactive ion etching described in S4 both use positive photoresist AZ4620 with a coating thickness of 8 μm to 15 μm.

[0046] According to an embodiment of the present application, the spray glue described in S5 is AZ4620 glue, the spraying thickness is 30μm to 60μm, and the development is performed using a developer and water ratio of 1:2.

[0047] Reference Figures 2-3 , Figure 2is a cross-sectional view of a lithium niobate single crystal thin film structure with a bottom electrode / silicon dioxide layer / silicon as a substrate in an embodiment of the present application, Figure 3 In the embodiment of this application, 15 Schematic diagram of the structure of the mode ferroelectric single crystal thin film piezoelectric vibration sensor.

[0048] The present application also provides a 15 mode ferroelectric single crystal thin film piezoelectric vibration sensor, composed of the d 15 The method for preparing a ferroelectric single crystal thin film piezoelectric vibration sensor is used to prepare the sensor. It should be noted that the d 15 The piezoelectric vibration sensor of the ferroelectric single crystal thin film is based on the Bond matrix and small deflection deformation theory. The piezoelectric coefficient d is calculated using the Bond matrix. 15 The maximum lithium niobate cut is achieved, and the appropriate lithium niobate cut is selected, and bonding, thinning, polishing, etching, developing, and patterning are performed in sequence. The product obtained in the embodiment of the present application has high electromechanical conversion efficiency and output voltage, and the performance decreases little in low temperature environment, and is suitable for applications in low temperature extreme environments.

[0049] In order to make the purpose, features, and advantages of this application more obvious and easy to understand, the technical solutions in the embodiments of this application are clearly and completely described. Obviously, the embodiments described below are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0050] The reagents and raw materials used in the examples of this application are all commercially available or homemade.

[0051] Example 1

[0052] Step 1: Prepare a lithium niobate single crystal thin film with a bottom electrode / silicon dioxide layer / silicon as a substrate. The specific method is as follows:

[0053] a. The lithium niobate wafer and silicon substrate were ultrasonically treated with acetone, isopropyl ketone, anhydrous ethanol and deionized water for 5 minutes respectively, rinsed with deionized water, and dried with nitrogen to remove organic matter and impurities on the surface;

[0054] b A 2 μm thick silicon dioxide layer was grown on a silicon substrate using plasma enhanced chemical vapor deposition;

[0055] c. magnetron sputtering a bottom electrode on the surface of the silicon dioxide layer. The power of the magnetron sputtering equipment is 500W. 20nm of metal chromium is sputtered on the surface of the silicon dioxide layer as an adhesion layer and 200nm of gold is sputtered as a bottom electrode to obtain a process surface capable of performing a direct bonding process;

[0056] d. Repeat step (a) to clean the silicon substrate again;

[0057] First, the lithium niobate wafer and the silicon substrate are pre-bonded in air, and the wafer bonding system is evacuated to 10 - 5 Pa, pre-bonding and annealing for 3 h at a bonding pressure of 2000 N and a bonding temperature of 100 °C to complete the bonding;

[0058] f bonded wafer was thinned by Logitech-LP50 system at a plate speed of 40r / min and a thinning pressure of 40N using 20μm Al 2 O 3 Grinding;

[0059] The g bond wafer was polished to 5 μm by a Logitech-LP50 polishing system at a disk speed of 40 r / min, an arm swing amplitude of 70%, and a polishing pressure of 40 N. The bond wafer was cleaned again to complete the thinning polishing process.

[0060] Step 2: Prepare the alignment mark, surface electrode, lithium niobate piezoelectric layer and bottom electrode patterning of the lithium niobate single crystal film. The specific method is as follows:

[0061] a Repeat step 1(a) to clean the substrate again;

[0062] b. Use magnetron sputtering surface electrode, the sputtering machine frequency is 500W, grow 10 nanometers of metal chromium as the adhesion layer, grow 50 nanometers of metal gold as the alignment mark layer;

[0063] c The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the developer AZ238 is used for development, and the residual primer after development is removed by oxygen plasma, and the film is hardened by post-baking at 110℃ on the hot plate for 2 minutes, and then the IBE etching process is used to complete the preparation of alignment marks;

[0064] d. The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the hot plate is baked at 110℃ for 90s. The photolithography equipment EVG610 performs flood exposure, and the developer AZ238 is used for development. The oxygen plasma is used for 2 minutes to remove the residual primer after development;

[0065] e. Use magnetron sputtering surface electrode, the sputtering machine frequency is 500W, grow 20 nanometers of metal chromium as the adhesion layer, grow 200 nanometers of metal gold as the surface electrode, soak in acetone for 2 hours, ultrasonicate for 2 minutes, rinse the surface with deionized water, blow dry the surface with nitrogen, and complete the surface metal stripping;

[0066] f. Use positive photoresist 4620, and use a photoresist machine at a speed of 1000 rpm for photoresist, pre-bake for 2 minutes at a hot plate at 100°C, then use a photolithography machine EVG610 for photolithography, use developer AZ400K for development, use oxygen plasma for 2 minutes to remove the residual primer after development, and finally use a hot plate at 120°C for hardening;

[0067] g Use IBE plasma etcher to etch for about 4 hours, check the etching status of lithium niobate film every half hour, complete the patterning of lithium niobate single crystal film, use reactive ion etcher to etch for about 1.5 hours, complete the patterning of silicon dioxide layer, and finally use plasma etcher to etch for about 4 minutes, check the etching status of metal layer every half minute, and complete the bottom electrode etching process.

[0068] Step 3: Preparation and release of silicon substrate mass block and cantilever beam, the specific method is as follows:

[0069] a. Use acetone, anhydrous ethanol and deionized water to perform ultrasonic treatment for 5 minutes respectively, then rinse the surface with deionized water and blow dry the surface with nitrogen to complete the cleaning of the silicon-based lithium niobate single crystal film;

[0070] b. Use positive photoresist AZ4620, spray glue process, spray coating thickness of 15um, pre-bake at 100℃ for 2 minutes on hot plate, then use photolithography machine EVG610 for photolithography, use developer AZ400k ratio 1:3 for development, run oxygen plasma for 4 minutes to remove the residual primer after development, and finally harden the film at 120℃ for 20 minutes on hot plate;

[0071] c. A 60 μm thick silicon layer is etched using deep silicon etching equipment to prepare a mass block and cantilever beam structure;

[0072] d. Ultrasonicate in acetone and anhydrous ethanol for 5 minutes respectively, rinse with deionized water, and blow dry with nitrogen to remove the remaining glue and impurities on the surface of the silicon substrate;

[0073] e. Spray 8 circles of 4620 glue on the back of the silicon substrate with a glue sprayer, bake on a hot plate at 100°C for 4 minutes, use a photolithography device EVG610 for overlay, develop with developer AZ400K in a ratio of 1:2, remove the residual primer after development with oxygen plasma, and finally heat the plate at 120°C for 30 minutes to harden the film;

[0074] g. Pump oil is used to bond it to the silicon wafer, and the deep silicon etcher continues to etch the silicon to a thickness of 440 μm, thereby releasing the cantilever beam and the mass block;

[0075] h Soak in anhydrous ethanol for 30 minutes to remove the pump oil on the surface of the structure, release the cantilever beam stress, complete the preparation of the surface mass block and the cantilever beam, and obtain the product.

[0076] Tests show that the frequency range of the product obtained in this embodiment reaches 20 Hz to 2000 Hz, and the sensitivity of the output voltage reaches 28.4 mV / g, so that the sensor can sensitively sense vibration signals in the environment within a wide frequency band.

[0077] Example 2

[0078] Step 1: Prepare a lithium niobate single crystal thin film with a bottom electrode / silicon dioxide layer / silicon as a substrate. The specific method is as follows:

[0079] a. The lithium niobate wafer and silicon substrate were ultrasonically treated with acetone, isopropyl ketone, anhydrous ethanol and deionized water for 5 minutes respectively, rinsed with deionized water, and dried with nitrogen to remove organic matter and impurities on the surface;

[0080] b A 1 μm thick silicon dioxide layer was grown on a silicon substrate using plasma enhanced chemical vapor deposition;

[0081] c. magnetron sputtering a bottom electrode on the surface of the silicon dioxide layer. The power of the magnetron sputtering equipment is 400W. 10nm of metal chromium is sputtered on the surface of the silicon dioxide layer as an adhesion layer and 100nm of gold is sputtered as an electrode to obtain a process surface capable of performing a direct bonding process.

[0082] d. Repeat step (a) to clean the silicon substrate again;

[0083] First, the lithium niobate wafer and the silicon substrate are pre-bonded in air, and the wafer bonding system is evacuated to 10 - 5 Pa, pre-bonding and annealing for 3 h at a bonding pressure of 1000 N and a bonding temperature of 80 °C to complete the bonding;

[0084] f bonded wafer was thinned by Logitech-LP50 system at a plate speed of 70r / min and a thinning pressure of 40N using 9μm Al 2 O 3 Grinding;

[0085] The g bond wafer was polished to 8 μm by a Logitech-LP50 polishing system at a disk speed of 70 r / min, an arm swing amplitude of 70%, and a polishing pressure of 40 N. The bond wafer was cleaned again to complete the thinning polishing process.

[0086] Step 2: Prepare alignment marks, surface electrodes and bottom electrode patterns of lithium niobate single crystal thin films. The specific method is as follows:

[0087] a Repeat step 1(a) to clean the substrate again;

[0088] b. The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the developer AZ238 is used for development, and the residual primer after development is removed by oxygen plasma, and the film is hardened by post-baking at 110℃ on the hot plate for 2 minutes, and then the IBE etching process is used to complete the preparation of the alignment mark;

[0089] c The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the hot plate is baked at 110℃ for 90s. The photolithography equipment EVG610 performs flood exposure, and the developer AZ238 is used for development. The oxygen plasma is used for 2 minutes to remove the residual primer after development;

[0090] d. Use magnetron sputtering surface electrode, the sputtering machine frequency is 400W, grow 10 nanometers of metal chromium as the adhesion layer, grow 100 nanometers of metal gold as the surface electrode, soak in acetone for 2 hours, ultrasonicate for 2 minutes, rinse the surface with deionized water, blow dry the surface with nitrogen, and complete the surface metal stripping;

[0091] e. Use positive photoresist 4620, and use a photoresist machine at a speed of 1000 rpm for photoresist, pre-bake for 2 minutes at a hot plate at 100°C, then use a photolithography machine EVG610 for photolithography, use developer AZ400K for development, use oxygen plasma for 2 minutes to remove the residual primer after development, and finally use a hot plate at 120°C for hardening;

[0092] f Use IBE plasma etcher to etch for about 5 hours, check the etching status of lithium niobate film every half hour, complete the patterning of lithium niobate single crystal film, use reactive ion etcher to etch for about 1 hour, complete the patterning of silicon dioxide layer, and finally use plasma etcher to etch for about 2 minutes, check the etching status of metal layer every half minute, and complete the bottom electrode etching process.

[0093] Step 3: Prepare a silicon substrate mass block and a cantilever beam. The specific method is as follows:

[0094] a. Use acetone, anhydrous ethanol and deionized water to perform ultrasonic treatment for 5 minutes respectively, then rinse the surface with deionized water and blow dry the surface with nitrogen to complete the cleaning of the silicon-based lithium niobate single crystal film;

[0095] b. Use positive photoresist AZ4620, spray glue process, spray coating thickness of 30um, pre-bake at 100℃ for 2 minutes on hot plate, then use photolithography machine EVG610 for photolithography, use developer AZ400k ratio 1:3 for development, run oxygen plasma for 4 minutes to remove the residual primer after development, and finally harden the film at 120℃ for 25 minutes on hot plate;

[0096] c. A 80 μm thick silicon layer is etched using deep silicon etching equipment to prepare a mass block and cantilever beam structure;

[0097] d. Ultrasonicate in acetone and anhydrous ethanol for 5 minutes respectively, rinse with deionized water, and blow dry with nitrogen to remove the remaining glue and impurities on the surface of the silicon substrate;

[0098] e. Spray 8 circles of 4620 glue on the back of the silicon substrate with a glue sprayer, bake on a hot plate at 100°C for 5 minutes, use a photolithography device EVG610 for overlay, develop with a developer AZ400K at a ratio of 1:2, remove the residual primer after development with oxygen plasma, and finally heat the plate at 120°C for 30 minutes to harden the film;

[0099] g. Pump oil is used to bond it to the silicon wafer, and the deep silicon etcher continues to etch the silicon to a thickness of 420 μm, thereby releasing the cantilever beam and the mass block;

[0100] h Soak in anhydrous ethanol for 30 minutes to remove the pump oil on the surface of the structure, release the cantilever beam stress, complete the preparation of the surface mass block and the cantilever beam, and obtain the product.

[0101] Tests show that the frequency range and output voltage sensitivity of the product obtained in this embodiment are similar to those of the product in Example 1, and there is no obvious performance difference.

[0102] Example 3

[0103] Step 1: Prepare a lithium niobate single crystal thin film with a bottom electrode / silicon dioxide layer / silicon as a substrate. The specific method is as follows:

[0104] a. The lithium niobate wafer and silicon substrate were ultrasonically treated with acetone, isopropyl ketone, anhydrous ethanol and deionized water for 5 minutes respectively, rinsed with deionized water, and dried with nitrogen to remove organic matter and impurities on the surface;

[0105] b A 3 μm thick silicon dioxide layer was grown on a silicon substrate using plasma enhanced chemical vapor deposition;

[0106] c. magnetron sputtering a bottom electrode on the surface of the silicon dioxide layer. The power of the magnetron sputtering equipment is 300W. 30nm of metal chromium is sputtered on the surface of the silicon dioxide layer as an adhesion layer and 300nm of gold is sputtered as an electrode to obtain a process surface capable of performing a direct bonding process.

[0107] d. Repeat step (a) to clean the silicon substrate again;

[0108] First, the lithium niobate wafer and the silicon substrate are pre-bonded in air, and the wafer bonding system is evacuated to 10 - 5 Pa, pre-bonding and annealing for 3 h at a bonding pressure of 3000 N and a bonding temperature of 120 °C to complete the bonding;

[0109] f bonded wafer was thinned by Logitech-LP50 system at a plate speed of 70r / min and a thinning pressure of 40N using 3μm Al 2 O 3 Grinding;

[0110] The g bond wafer was polished to 10 μm by a Logitech-LP50 polishing system at a disk speed of 70 r / min, an arm swing amplitude of 70%, and a polishing pressure of 40 N. The bond wafer was cleaned again to complete the thinning polishing process.

[0111] Step 2: Prepare alignment marks, surface electrodes and bottom electrode patterns of lithium niobate single crystal thin films. The specific method is as follows:

[0112] a Repeat step 1(a) to clean the substrate again;

[0113] b. The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the developer AZ238 is used for development, and the residual primer after development is removed by oxygen plasma, and the film is hardened by post-baking at 110℃ on the hot plate for 2 minutes, and then the IBE etching process is used to complete the preparation of the alignment mark;

[0114] c The surface of lithium niobate single crystal film is coated with reverse glue AZ5214, and the coating machine is used for coating at a speed of 4000, and the hot plate is pre-baked for 2 minutes at 95℃, and then the photolithography machine EVG610 is used for photolithography, and the hot plate is baked at 110℃ for 90s. The photolithography equipment EVG610 performs flood exposure, and the developer AZ238 is used for development. The oxygen plasma is used for 2 minutes to remove the residual primer after development;

[0115] d. Use magnetron sputtering surface electrode, the sputtering machine frequency is 300W, grow 30 nanometers of metal chromium as the adhesion layer, grow 300 nanometers of metal gold as the surface electrode, soak in acetone for 3 hours, ultrasonicate for 4 minutes, rinse the surface with deionized water, blow dry the surface with nitrogen, and complete the surface metal stripping;

[0116] e. Use positive photoresist 4620, and use a photoresist machine at a speed of 1000 rpm for photoresist, pre-bake for 2 minutes at a hot plate at 100°C, then use a photolithography machine EVG610 for photolithography, use developer AZ400K for development, use oxygen plasma for 2 minutes to remove the residual primer after development, and finally use a hot plate at 120°C for hardening;

[0117] f Use IBE plasma etcher to etch for about 6 hours, check the etching status of lithium niobate film every half hour, complete the patterning of lithium niobate single crystal film, use reactive ion etcher to etch for about 2 hours, complete the patterning of silicon dioxide layer, and finally use plasma etcher to etch for about 4 minutes, check the etching status of metal layer every half minute, and complete the bottom electrode etching process.

[0118] Step 3: Prepare a silicon substrate mass block and a cantilever beam. The specific method is as follows:

[0119] a. Use acetone, anhydrous ethanol and deionized water to perform ultrasonic treatment for 5 minutes respectively, then rinse the surface with deionized water and blow dry the surface with nitrogen to complete the cleaning of the silicon-based lithium niobate single crystal film;

[0120] b. Use positive photoresist AZ4620, spray glue process, spray coating thickness of 60um, pre-bake at 100℃ for 2 minutes on hot plate, then use photolithography machine EVG610 for photolithography, use developer AZ400k ratio 1:3 for development, run oxygen plasma for 6 minutes to remove the residual primer after development, and finally harden the film at 120℃ for 30 minutes on hot plate;

[0121] c. A 90 μm thick silicon layer is etched using deep silicon etching equipment to prepare a mass block and cantilever beam structure;

[0122] d. Ultrasonicate in acetone and anhydrous ethanol for 5 minutes respectively, rinse with deionized water, and blow dry with nitrogen to remove the remaining glue and impurities on the surface of the silicon substrate;

[0123] e. Spray 8 circles of 4620 glue on the back of the silicon substrate with a glue sprayer, bake on a hot plate at 100°C for 6 minutes, use a photolithography device EVG610 for overlay, develop with a developer AZ400K at a ratio of 1:2, remove the residual primer after development with oxygen plasma, and finally heat the plate at 120°C for 30 minutes to harden the film;

[0124] g. Pump oil is used to bond it to the silicon wafer, and the deep silicon etcher continues to etch the silicon to a thickness of 410 μm, thereby releasing the cantilever beam and the mass block;

[0125] h Soak in anhydrous ethanol for 30 minutes to remove the pump oil on the surface of the structure, release the cantilever beam stress, complete the preparation of the surface mass block and the cantilever beam, and obtain the product.

[0126] Tests show that the frequency range and output voltage sensitivity of the product obtained in this embodiment are similar to those of the product in Example 1, and there is no obvious performance difference.

[0127] In summary, the preparation method of the embodiment of the present application can well bond the ferroelectric single crystal lithium niobate film to the silicon wafer, realize the heterogeneous integration of the silicon oxide baseband bottom electrode and the ferroelectric single crystal film, and then complete the preparation of components with wide-band and high-voltage output. The product prepared in the embodiment of the present application has high electromechanical conversion efficiency and output performance, and the performance degradation in low-temperature environment is very small, and it is environmentally friendly, which provides a guarantee for the preparation of sensors.

[0128] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The steps include: Step 1: clean the lithium niobate wafer and the silicon substrate respectively, deposit a silicon dioxide layer on the surface of the silicon substrate by plasma enhanced chemical vapor deposition, and magnetron sputter a bottom electrode on the surface of the silicon dioxide layer; Step 2: bonding the lithium niobate wafer to the silicon substrate, and then sequentially thinning, chemical mechanical polishing and cleaning to obtain a lithium niobate single crystal film; Step 3: Prepare the alignment mark by magnetron sputtering and ion beam etching process, and then prepare the surface electrode by magnetron sputtering and lift-off process in the developed pattern area; Step 4: using an ion beam method to etch the lithium niobate single crystal film to pattern it, and then using a reactive ion etching method to etch the silicon dioxide layer to achieve patterning; Finally, the bottom electrode is etched by ion beam method to make it patterned; Step 5: The cantilever beam and the mass block are prepared on the patterned lithium niobate surface by using a spray-photolithography-development-post-bake-deep silicon etching method, and the device is released from the back of the silicon substrate by using a spray-photolithography-development-post-bake-deep silicon etching method to obtain the d 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor.

2. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The thickness of the silicon dioxide layer is 1-3 μm, the thickness of the bottom electrode is 100-350 nm, the thickness of the lithium niobate single crystal film is 5-10 μm, and the thickness of the mass block and the cantilever beam is 60-100 μm.

3. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The cleaning solutions in step 1 are acetone, isopropanol, anhydrous ethanol and deionized water in sequence.

4. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The power of the magnetron sputtering in step 1 is 300-600W, and the bottom electrode is chromium / gold.

5. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The bonding pressure in step 2 is 1000-3000N, and the bonding temperature is 80-120°C.

6. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The thinning and chemical mechanical polishing in step 2 are specifically as follows: first grinding with 1-20 μm Al2O3 at a pressure of 40-50 N, and finally polishing with 500 nm SiO2 at a polishing pressure of 40-50 N.

7. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The alignment marks and surface electrodes described in step 3 were prepared using reverse photoresist AZ5214. The positive photoresist parameters were: pre-baking on a hot plate at 95°C for 2 minutes and an exposure dose of 65 mJ / cm 2 , 110℃ hot plate post-bake for 2 minutes; negative photoresist parameters: plate pre-bake at 95℃ for 2 minutes, exposure dose 45mJ / cm 2 , 110℃ hot plate drying for 90s, flood exposure 540mJ / cm 2 .

8. According to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The cured film used in the ion beam etching and reactive ion etching methods in step 4 is positive resist AZ4620, and the spin coating thickness is 8 μm to 15 μm.

9. The method according to claim 1 15 A method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that: The spray glue in step 5 is positive resist AZ4620, the spray glue thickness is 30μm~60μm, and the developer is developed with a ratio of developer to water of 1:

2.

10. A 15 Mode ferroelectric single crystal thin film piezoelectric vibration sensor, characterized in that, The d according to any one of claims 1 to 9 15 The method for preparing a mode ferroelectric single crystal thin film piezoelectric vibration sensor is used to prepare it.

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