Preparation method of interdigital transducer chip based on zinc oxide piezoelectric film

Abstract

The invention discloses a preparation method of an interdigital transducer chip based on a zinc oxide piezoelectric film, belongs to the technical field of ultrasonic control, and solves the problems that a traditional rigid piezoelectric substrate material is thick, heavy, high in rigidity and difficult to bend, and application of the traditional rigid piezoelectric substrate material in flexible and wearable devices is limited. According to the preparation method of the interdigital transducer chip based on the zinc oxide piezoelectric film, the zinc oxide film is prepared on a silicon substrate through a magnetron sputtering technology, and the performance of the zinc oxide piezoelectric film is represented and analyzed through instruments such as an X-ray diffraction analyzer and a scanning electron microscope. Compared with a common rigid piezoelectric single crystal substrate, the thickness of the zinc oxide film prepared through the method is far smaller than that of a rigid material, compared with rigid piezoelectric single crystals, the zinc oxide film can bear higher input power, meanwhile, the chip can control cells through the sound tweezers technology, and the chip can be developed into flexible wearable equipment to be applied to multiple fields.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic manipulation, and particularly relates to a preparation method of an interdigital transducer chip based on zinc oxide piezoelectric thin film. Background Art

[0002] Acoustic tweezer technology refers to a technology that uses acoustic radiation force to suspend and move micro-particles. The two key components in acoustic tweezer technology are a piezoelectric substrate and an interdigital transducer. An interdigital transducer is a device that can convert an electrical signal into a sound wave or convert a sound wave into an electrical signal. It is usually composed of multiple pairs of intersecting metal strips, forming an interdigital structure. When a voltage is applied, these two metal strips will vibrate, thus generating a sound wave; a piezoelectric substrate is a material with piezoelectric effect. The piezoelectric effect means that when a voltage or strain is applied to this material, it will generate mechanical strain or displacement; conversely, when mechanical strain or displacement is applied, it will generate a voltage. Commonly used piezoelectric single crystal materials include lithium niobate, lithium tantalate, quartz, etc. These materials usually have good mechanical properties, such as high hardness, good fatigue resistance, etc. Piezoelectric single crystal materials can achieve high quality factor and frequency stability, and have wide applications in electro-acoustic devices, sensors, filters, resonators and other fields.

[0003] Rigid piezoelectric substrate materials have inconveniences in some applications, that is: rigid piezoelectric substrate materials are usually relatively thick, which limits the compactness and flexibility of the interdigital transducer; moreover, the weight of rigid piezoelectric substrate materials is relatively large, and for some applications with lightweight design, the applicability is poor; at the same time, due to the high stiffness of rigid piezoelectric substrate materials, it is difficult to bend, so its application in flexible and wearable devices is limited. However, piezoelectric thin film materials have the advantages of light weight, low energy consumption, good biocompatibility, etc. The mechanically adjustable characteristics can be applied to the human body, and flexible piezoelectric thin films can be attached to different parts of the body to monitor health parameters such as heart rate, body temperature, blood pressure, respiration, sweat and blood components, which can provide new technical means for flexible wearable ultrasonic devices. Therefore, it is necessary to improve the manufacturing method of flexible piezoelectric thin film interdigital transducer chips. Summary of the Invention

[0004] The present invention prepares zinc oxide thin film on a silicon substrate by magnetron sputtering technology, and characterizes and analyzes the performance of zinc oxide piezoelectric thin film through instruments such as X-ray diffractometer and scanning electron microscope; for devices with good performance, the thin film piezoelectric material has the advantages of being bendable and high-temperature resistant; it provides strong support for the application of flexible piezoelectric thin films in the field of surface acoustic wave devices, and provides new ideas and methods for the research and application of wearable ultrasonic devices.

[0005] The technical solution adopted by the present invention is: the preparation method of the interdigital transducer chip based on zinc oxide piezoelectric thin film includes the following steps: Step 1: Preparation of zinc oxide piezoelectric thin film; Use a 4-inch Si with a thickness of 500 μm as the substrate, and there is a layer of SiO2 with a thickness of 475 nm on its surface. Use a dual-target magnetron sputtering instrument to prepare a zinc oxide thin film on the silicon through magnetron sputtering technology; Step 2: Lithography of interdigital pattern on the zinc oxide piezoelectric thin film; After obtaining the zinc oxide piezoelectric thin film, prepare an interdigital transducer on its surface. The width of the interdigital fingers and the width between fingers are designed to be 5 μm, the corresponding acoustic wave wavelength is 20 μm, and the number of interdigital pairs is 40. Process the designed interdigital pattern on a Cr mask plate; Step 3: Gold plating of interdigital; After lithography, gold plate the interdigital pattern; The interdigital material is gold, and magnetron sputtering technology is still used for gold plating; Step 4: Stripping, cutting and chip processing; Put the gold-plated zinc oxide material into acetone liquid, use acetone to dissolve the excess photoresist, and strip the excess part on the surface except the interdigital structure; Seal and store. After 5 hours of soaking, the interdigital pattern remains on the zinc oxide thin film of the silicon substrate. After taking it out, rinse the acetone with absolute ethanol, and then put the transducer into deionized water for cleaning; Fix each interdigital transducer on the designed PCB board, use a wire bonding machine to connect the interdigital electrodes to the PCB board through metal wires, and then weld the SMA interface to the PCB board. The preparation of the interdigital transducer chip is completed; Step 5: Scanning electron microscope and X-ray diffraction test; Observe the internal structure through a scanning electron microscope, and judge whether the prepared zinc oxide thin film has a good structure through scanning X-ray diffraction; Step 6: Loss test of interdigital transducer; Use a network analyzer to measure the insertion loss and return loss. These data can help determine the transmission efficiency and anti-interference performance of the surface acoustic wave device, and guide the design and optimization of the use of the surface acoustic wave device; Step 7: Chip drive application test; Verify the drive performance of the chip using microparticles and cells.

[0006] In the said Step 1, during the sputtering process, first put the silicon wafer into the cavity, close the chamber door and evacuate for 3 hours, then open the argon and oxygen gas valves, set the argon gas flux to 48 Sccm, the oxygen gas flux to 4 Sccm, the pressure to 1.5 Pa, the power to 180 W, the bias power supply to -75 V, and the tray rotation speed to 10 r / min. After starting the sputtering, confirm whether the chamber is lit through the baffle; The sputtered atoms or molecules fly away from the target surface at high speed, and after a certain distance, they are deposited on the negative film or substrate to form a zinc oxide thin film; The sputtering time for each cycle is 1 h, with a 15-min interval, and the sputtering is repeated in this cycle; after a total sputtering time of 4 h, a zinc oxide thin film with a thickness of 3.83 μm can be prepared; then it is placed in an oven and heat-annealed at 300 °C for 1 h to release stress and improve the stability of the thin film.

[0007] In the second step, photoresist is spin-coated. The zinc oxide substrate is placed on the internal suction cup, and the vacuum value is below 15 to ensure that the material will not be thrown off during spin coating; the rotation speed is set to 500 r / min, and after 10 s, the rotation speed is increased to 3000 r / min for 30 s to ensure that the photoresist is evenly spread on the zinc oxide substrate; after spin coating, the material is placed on a constant-temperature heating plate and baked at 115 °C for 2 min to cure the photoresist. Before lithography using lithography equipment, after the mercury lamp is turned on for 8 min, the designed mask plate is placed in the lithography machine. The interdigital pattern is engraved on the substrate through the difference in the ultraviolet light penetration between the mask plate with and without the interdigital pattern. The ultraviolet exposure dose in this process is set to 30 mJ / cm², and the distance between the substrate and the mask plate is 10 μm; after exposure, it is taken out after developing in the developer for 100 s with tweezers. After confirming under the microscope that the width of the interdigital structure is uniform and undamaged and the spacing is equal, the subsequent gold plating operation can be carried out.

[0008] In the third step, during the gold plating process, first, the surface of the substrate is subjected to plasma cleaning for 5 min and then placed in a magnetron sputtering device to pump vacuum for 2 h; the argon gas cylinder is opened, and chromium plating is used to increase the adhesion between gold and the substrate. The power is set to 60 W, the argon gas flux is set to 20 Sccm, and the sputtering time is 1 min. After starting, check whether the chamber is ignited through the baffle; after this operation, a gold target is used, the power is set to 70 W, the argon gas flux is set to 20 Sccm, and the sputtering time is 4 min. After starting, check whether the chamber is ignited through the baffle. After gold plating, the argon gas is closed and the pressure is maintained for 10 min, and then the zinc oxide is taken out.

[0009] In the fourth step, to improve the chip preparation efficiency, there are usually multiple interdigital transducers on one mask plate. After the stripping operation, it can be cut into blocks according to the interdigital pattern.

[0010] In the sixth step, for an ideal zinc oxide piezoelectric thin film, the Rayleigh wave velocity is 2650 m / s, and the surface wave propagation velocity on silicon is 4680 m / s. The surface acoustic wave velocity of the device is calculated by the product of the frequency and the wavelength and is between 2650 m / s and 4680 m / s. This is because the designed interdigital wavelength is greater than the zinc oxide film thickness, so that a part of the surface acoustic wave propagates in the zinc oxide thin film, and the other part propagates in the silicon and silicon dioxide media.

[0011] In Step 7, mix 5-micron fluorescent microspheres and PBS solution at a ratio of 1:10. Take 0.2 μl of the liquid drop and place it on the interdigital transducer. Set the frequency of the signal generator to 195 MHz, set the input amplitude to 200 mV, connect it to a 30 W power amplifier, and the amplified signal is connected to the surface acoustic wave chip to generate acoustic waves. The particles in the liquid drop generate vortices under the drive of the transducer and gather at the center after 20 seconds.

[0012] In Step 7, the chip can also enrich human lymphocytes. First, stain the lymphocytes in the opti-mem medium with 1% Calcein-AM for 5 minutes, then mix them with PBS solution at a ratio of 1:8. Take 0.2 μl of the liquid drop with lymphocytes and place it on the interdigital electrode; set the frequency of the signal generator to 195 MHz, set the input amplitude to 300 mV, connect it to a 30 W power amplifier, and a vortex phenomenon occurs in the liquid drop with cells. After 17 s, the lymphocytes in the vortex gradually enrich to the center of the vortex.

[0013] Advantages of the present invention: The preparation method of the interdigital transducer chip based on zinc oxide piezoelectric thin film uses magnetron sputtering method to prepare zinc oxide piezoelectric thin film on a silicon substrate. By adjusting process parameters and preparation methods, the thin film structure and piezoelectric properties of zinc oxide are optimized. At the same time, further test results show that the zinc oxide prepared by this method has good z-direction growth under a scanning electron microscope. And on this basis, an interdigital transducer with a frequency of 195 MHz prepared on the surface of zinc oxide as a piezoelectric substrate has a return loss of -1.8 dB and an insertion loss of -33.8 dB, with good performance. Compared with common rigid piezoelectric single crystal substrates such as lithium niobate, the thickness of the zinc oxide thin film prepared by the method of the present invention is much smaller than that of rigid materials, and it can withstand higher input power compared with rigid piezoelectric single crystals such as lithium niobate. At the same time, this chip can use acoustic tweezers technology to manipulate cells and can be developed into a flexible wearable device for applications in multiple fields. Description of the Drawings

[0014] Figure 1 is the processing flow chart of the zinc oxide device of the present invention.

[0015] Figure 2 is the morphology diagram of the zinc oxide layer scanned by SEM electron microscope.

[0016] Figure 3 is the XRD scan result diagram.

[0017] Figure 4 is the test result diagram of the network analyzer of S11 and S21 of the zinc oxide device.

[0018] Figure 5It is a fluorescence field map for verifying the driving performance of the chip using microparticles.

[0019] Figure 6 It is a fluorescence field map for verifying the driving performance of the chip using cells.

[0020] Figure 7 It is a physical picture of the product of the zinc oxide interdigital transducer chip on a silicon substrate fabricated by the method of the present invention. Detailed implementation manners

[0021] Zinc oxide is a material with a relatively high piezoelectric effect. It can convert mechanical stress into an electrical signal and also convert an electrical signal into mechanical stress. This property enables it to be widely used in piezoelectric applications such as sensors and actuators. Zinc oxide piezoelectric materials have excellent chemical stability and heat resistance, and can maintain stable performance at high temperatures and in harsh environments. Moreover, the piezoelectric properties of zinc oxide piezoelectric materials can be adjusted by controlling their microstructure and composition to meet the requirements of different applications. In addition, compared with other piezoelectric materials, the cost of zinc oxide piezoelectric materials is relatively low, so it has certain advantages in mass production and is suitable as the piezoelectric thin film of the interdigital transducer.

[0022] In addition, as a flexible material, the zinc oxide piezoelectric thin film can exist in a relatively thin form, usually in the range of a few micrometers to dozens of micrometers. This makes the interdigital transducer more compact and flexible to adapt to various application requirements. Moreover, due to its light weight, the zinc oxide piezoelectric thin film can play a role in applications where it is necessary to reduce the overall mass of the device. At the same time, the zinc oxide piezoelectric thin film has good flexibility and bending performance, and can adapt to applications with curved surfaces, bends or irregular shapes. This enables the interdigital transducer to better combine with various devices and improve the flexibility and adaptability of the system.

[0023] The specific steps of the present invention are described in detail. The preparation method of the interdigital transducer chip based on zinc oxide piezoelectric thin film includes: Step 1, preparation of the zinc oxide (ZnO) piezoelectric thin film. Use a 4-inch Si with a thickness of 500 μm as the substrate, and there is a layer of SiO2 with a thickness of 475 nm on its surface. Use a DM-250 dual-target magnetron sputtering instrument to prepare the zinc oxide thin film on the silicon by magnetron sputtering technology. Use a pure zinc target with a purity of 99.995% and a specification of φ50*5 mm.

[0024] During the sputtering process, first place the silicon wafer into the chamber. After closing the chamber door and evacuating the vacuum for 3 hours, open the argon and oxygen gas valves. Set the argon gas flux to 48 Sccm, the oxygen gas flux to 4 Sccm, the pressure to 1.5 Pa, the power to 180 W, the bias power supply to -75 V, and the tray rotation speed to 10 r / min. After starting the sputtering, confirm whether the chamber lights up through the baffle. Based on the ion bombardment and sputtering effects, add a magnetic field and an electric field in the vacuum chamber to form a magnetron electron gun. By applying a high voltage, electrons are emitted from the cathode and pass through an acceleration device to form a high-speed electron beam. The high-speed electron beam collides with gas molecules in the gas, releasing a large number of electrons. These free electrons interact with the magnetic field to form a ring-shaped electron cloud. By setting the magnetic field, the ring-shaped electron cloud is confined near the target, and the electron beam is turned into a spiral shape. Under the action of the electron vortex, the high-speed electrons collide with the atoms on the surface of the target. The collision transfers energy and momentum, causing the target atoms to dissociate and sputter. The sputtered atoms or molecules fly away from the surface of the target at high speed. After traveling a certain distance, they are deposited on the negative film or substrate to form a zinc oxide thin film.

[0025] Each sputtering time is 1 hour, with an interval of 15 minutes, and sputtering is repeated in this cycle. After a total sputtering time of 4 hours, a zinc oxide thin film with a thickness of 3.83 μm can be prepared. Then place it in an oven and perform heat annealing treatment at 300 °C for 1 hour to release stress and improve the stability of the thin film.

[0026] Step two, lithograph the interdigital pattern on the zinc oxide piezoelectric thin film. After obtaining the zinc oxide piezoelectric thin film, prepare an interdigital transducer on its surface. The width of the interdigital fingers and the width between the fingers are designed to be 5 μm, the corresponding acoustic wavelength is 20 μm, and the number of interdigital pairs is 40. Process the designed interdigital pattern on a Cr mask plate.

[0027] Use AZ5214 photoresist and apply the photoresist through a spin coater (WS-650Mz-23NP PB). Place the zinc oxide substrate on the internal suction cup, with the vacuum value below 15 to ensure that the material will not be thrown off during spin coating. Set the rotation speed to 500 r / min. After 10 s, increase the rotation speed to 3000 r / min for 30 s to ensure that the photoresist is evenly spread on the zinc oxide substrate. After spin coating, place the material on a constant temperature heating plate and bake it at 115 °C for 2 min to cure the photoresist.

[0028] The lithography equipment used is the EVG610 lithography machine. After turning on the mercury lamp for 8 minutes before lithography, the designed mask is placed in the lithography machine. The interdigital pattern is engraved on the substrate by the difference in the penetration of ultraviolet light through the mask with and without the interdigital pattern. The ultraviolet exposure dose in this process is set to 30 mJ / cm², and the distance between the substrate and the mask is 10 μm. After exposure, it is developed in 300 MIF developer for 100 s and then taken out with tweezers. After confirming under the microscope that the width of the interdigital structure is uniform and undamaged and the spacing is equal, the subsequent gold plating operation can be carried out.

[0029] Step 3: Interdigital gold plating. After lithography is completed, the interdigital pattern is gold-plated; the interdigital material is gold, and magnetron sputtering technology is still used for gold plating. First, the surface of the substrate is subjected to plasma cleaning for 5 minutes and then put into the magnetron sputtering equipment to evacuate for 2 hours; the argon gas cylinder is opened, and chromium plating is used to increase the adhesion between gold and the substrate. The power is set to 60 W, the argon gas flux is set to 20 Sccm, and the sputtering time is 1 minute. After starting, check whether the chamber is ignited through the baffle; after this operation, a gold target is used, the power is set to 70 W, the argon gas flux is set to 20 Sccm, and the sputtering time is 4 minutes. After starting, check whether the chamber is ignited through the baffle. After gold plating, the argon gas is closed and the pressure is maintained for 10 minutes, and then the zinc oxide is taken out.

[0030] Step 4: Stripping, cutting and chip processing. The gold-plated zinc oxide material is put into acetone liquid, and the excess photoresist is dissolved by acetone to strip the excess part on the surface except the interdigital structure. It is sealed and stored. After soaking for 5 hours, the interdigital pattern remains on the zinc oxide thin film on the silicon substrate. After taking it out, it is rinsed with anhydrous ethanol to remove acetone, and then the transducer is put into deionized water for cleaning. In order to improve the chip preparation efficiency, there are usually multiple interdigital transducers on one mask. After the stripping operation, it can be cut into blocks according to the interdigital pattern.

[0031] Each interdigital transducer is fixed on the designed PCB (Printed Circuit Board). The interdigital electrodes are connected to the PCB by metal wires using a wire bonding machine, and the SMA interface is soldered to the PCB by a soldering iron. The preparation of the interdigital transducer chip is completed.

[0032] Step 5: Scanning electron microscope and X-ray diffraction testing.

[0033] SEM (Scanning Electron Microscope) is a microscope that uses a high-energy electron beam to scan and image samples. SEM uses an electron gun to generate a high-energy electron beam, and then focuses the electron beam to a very small beam spot through a focusing system. The scanning electron beam forms an electron radial scan on the sample surface, while measuring the signal reflected from the sample surface. These reflected signals are collected and converted into images. By controlling the focus of the electron beam, very clear and detailed sample surface morphology and structural information can be obtained. SEM can observe the sample surface in real time, which is very suitable for observing the dynamic process of materials, such as the observation of biological samples, or studying real-time reactions on the surface of materials.

[0034] In the present invention, a zinc oxide thin film with a thickness of 3.83 μm was prepared, and the internal structure was observed by a scanning electron microscope (SEM). Figure 2 The morphology of the zinc oxide layer is shown, showing that it is uniformly columnar. It can be seen that the zinc oxide film is composed of highly oriented columnar nanocrystals perpendicular to the substrate and has good z-direction growth.

[0035] XRD stands for X-ray diffraction, which is a technique for analyzing the crystal structure of materials. Its principle is based on the fact that the lattice structure of the material crystal can scatter the incident X-rays, generate different scattered waves, and form diffraction patterns. The phase difference and amplitude difference between these scattered waves depend on the lattice structure and the distance and array between atoms. When X-rays pass through the crystal, they are scattered by the electron cloud of the crystal atoms, forming a three-dimensional periodic vibration mode, that is, a scattered wave, including reflection, interference and scattering. The position, phase and amplitude differences of these peaks and troughs are all determined by the crystal structure and the distance between atoms.

[0036] When a beam of X-rays enters a crystal, it will undergo a series of scattering effects. At a certain angle, these scattered waves will form a strong diffraction signal through constructive interference, forming a diffraction peak. This angle corresponds to certain structural parameters such as spacing, lattice and crystal plane direction, so the structure of the crystal can be determined by observing the position of the diffraction peak. XRD scanning records a series of diffraction patterns by rotating the sample and detector, and then uses data processing software to convert these patterns into information such as the position, intensity and width of the diffraction peak. Finally, the structure of the sample is determined by comparing the experimental data with the standard crystal database.

[0037] Scanning X-ray diffraction (XRD) revealed that the prepared zinc oxide exhibited a good (002) phase. The results obtained are as follows: Figure 3 As shown, it indicates that the prepared zinc oxide film has a good structure.

[0038] Step 6, Interdigital Transducer Loss Test.

[0039] Insertion loss and return loss are two important indicators for evaluating the performance of surface acoustic wave devices. Insertion loss refers to the amount of attenuation introduced when a signal passes through a surface acoustic wave device. A lower insertion loss means that the surface acoustic wave device attenuates the signal less and can transmit the signal more effectively. Insertion loss can be measured by comparing the power of the input and output signals.

[0040] Return loss refers to the amount of attenuation caused when a signal returns from the output end to the input end. A higher return loss means that the surface acoustic wave device can better suppress signal echoes, reducing signal interference and reflection. Return loss can be measured by injecting an input signal into the surface acoustic wave device and then measuring the power of the signal returned to the input end.

[0041] When evaluating the performance of surface acoustic wave devices, professional instruments are needed to measure insertion loss and return loss. Here, a network analyzer is used to measure insertion loss and return loss. These data can help determine the transmission efficiency and anti-interference performance of surface acoustic wave devices and guide the design and optimization of the use of surface acoustic wave devices. The measurement results are as Figure 4 shown.

[0042] From the test results of the network analyzer, it can be seen that the S11 and S21 of this device produce obvious resonances around 195 MHz, and there are resonant peaks around. S11 is -1.8 dB and S21 is -33.8 dB. For an ideal zinc oxide piezoelectric thin film, the Rayleigh wave velocity is 2650 m / s, and the propagation velocity of the surface wave on silicon is 4680 m / s. By calculating the product of the frequency and wavelength, the surface acoustic wave velocity of the device is 3900 m / s, which is between 2650 m / s and 4680 m / s. This is because the designed interdigital wavelength is 20 μm, which is greater than the zinc oxide film thickness of 3.83 μm, causing a part of the surface acoustic wave to propagate in the zinc oxide thin film and another part to propagate in the silicon and silicon dioxide media.

[0043] Step 7, Chip Driving Application Test. The driving performance of the chip is verified using microparticles and cells.

[0044] Mix 5-micron fluorescent microspheres with PBS solution at a ratio of 1:10. Take 0.2 μl of the liquid drop and place it on the interdigital transducer. Set the frequency of the signal generator to 195 MHz, the input amplitude to 200 mV, connect a 30 W power amplifier, and connect the amplified signal to the surface acoustic wave chip to generate sound waves. The microparticles in the liquid drop generate vortices under the drive of the transducer and gather at the center after 20 seconds. The fluorescence field pattern is as Figure 5 shown.

[0045] The chip can also enrich human lymphocytes. First, we stain lymphocytes in the opti-mem medium with 1% Calcein-AM for 5 minutes, then mix them with PBS solution at a ratio of 1:8, and take 0.2 μl of the liquid drop with lymphocytes and drop it on the interdigital electrode; set the frequency of the signal generator to 195 MHz, set the input amplitude to 300 mV, connect a 30 W power amplifier, and a vortex phenomenon occurs in the liquid drop with cells. After 17 seconds, the lymphocytes in the vortex gradually enrich to the center of the vortex, and the fluorescence field map is as shown in Figure 6 shown. The radius of the liquid drop before enrichment is 386 μm, and it shrinks to 52 μm after enrichment. After enrichment, the concentration of lymphocytes is increased by 55 times.

Claims

1. A preparation method of an interdigital transducer chip based on a zinc oxide piezoelectric thin film, characterized in that, It includes the following steps: Step 1, preparation of zinc oxide piezoelectric thin film: Use a 4-inch Si with a thickness of 500 μm as the substrate, which has a 475-nm SiO2 layer on its surface. Use a dual-target magnetron sputtering instrument to prepare a zinc oxide thin film on the silicon through magnetron sputtering technology; Step 2, lithography of interdigital patterns on the zinc oxide piezoelectric thin film; After obtaining the zinc oxide piezoelectric thin film, prepare an interdigital transducer on its surface. The width of the interdigital fingers and the width between fingers are designed to be 5 μm, the corresponding acoustic wave wavelength is 20 μm, and the number of interdigital pairs is 40. Process the designed interdigital pattern on a Cr mask plate; Step 3, gold plating of interdigital fingers: After lithography, gold plate the interdigital pattern; the material of the interdigital fingers is gold, and magnetron sputtering technology is still used for gold plating; Step 4, stripping, cutting and chip processing: Put the gold-plated zinc oxide material into acetone liquid, use acetone to dissolve the excess photoresist, and strip the excess part on the surface except the interdigital structure; seal and store. After soaking for 5 h, the interdigital pattern remains on the zinc oxide thin film on the silicon substrate. After taking it out, rinse the acetone with absolute ethanol, and then put the transducer into deionized water for cleaning; Fix each interdigital transducer on the designed PCB board, use a wire bonding machine to connect the interdigital electrodes to the PCB board through metal wires, and then weld the SMA interface to the PCB board. The preparation of the interdigital transducer chip is completed; Step 5, scanning electron microscope and X-ray diffraction test: Observe the internal structure through a scanning electron microscope, and judge whether the prepared zinc oxide thin film has a good structure through scanning X-ray diffraction; Step 6, loss test of interdigital transducer; Use a network analyzer to measure the insertion loss and return loss. These data can help determine the transmission efficiency and anti-interference performance of the surface acoustic wave device, and guide the design and optimization of the use of the surface acoustic wave device; Step 7, chip drive application test; Verify the driving performance of the chip using microparticles and cells.

2. The method for fabricating an interdigital transducer chip based on zinc oxide piezoelectric thin film according to claim 1, wherein: In the said Step 1, during the sputtering process, first put the silicon wafer into the cavity, close the chamber door and evacuate for 3 h, then open the argon and oxygen gas valves, set the argon gas flux to 48 Sccm, the oxygen gas flux to 4 Sccm, the pressure to 1.5 Pa, the power to 180 W, the bias power supply to -75 V, and the tray rotation speed to 10 r / min. After starting sputtering, confirm whether the cavity is ignited through the baffle; the sputtered atoms or molecules fly away from the target surface at high speed, and after a certain distance, they are deposited on the negative film or substrate to form a zinc oxide thin film; Each sputtering time is 1 h, with an interval of 15 min, and sputtering is repeated in this cycle; after a total sputtering time of 4 h, a zinc oxide thin film with a thickness of 3.83 μm can be prepared; then put it into an oven and heat-anneal it at 300 °C for 1 h to release stress and improve the stability of the thin film.

3. The method for preparing an interdigital transducer chip based on a zinc oxide piezoelectric thin film according to claim 1, characterized in that: In the second step, spin-coat photoresist. Place the zinc oxide substrate on the internal suction cup with a vacuum value below 15 to ensure that the material will not be thrown off during spin-coating. Set the rotation speed to 500 r / min. After 10 s, increase the rotation speed to 3000 r / min for 30 s to ensure that the photoresist is evenly spread on the zinc oxide substrate. After spin-coating, place the material on a constant-temperature heating plate and bake it at 115 °C for 2 min to cure the photoresist. Before lithography using lithography equipment, after the mercury lamp is turned on for 8 min, place the designed mask plate into the lithography machine. The interdigital pattern is engraved on the substrate through the difference in the penetration of ultraviolet light by the mask plate with interdigital patterns and without interdigital patterns. In this process, the ultraviolet exposure dose is set to 30 mJ / cm², and the distance between the substrate and the mask plate is 10 μm. After exposure, put it into the developer for 100 s and then take it out with tweezers. After confirming under the microscope that the width of the interdigital structure is uniform and undamaged and the spacing is equal, the subsequent gold plating operation can be carried out.

4. The preparation method of the interdigital transducer chip based on zinc oxide piezoelectric thin film according to claim 1, characterized in that: In the third step, during the gold plating process, first perform plasma cleaning on the substrate surface for 5 min and then put it into the magnetron sputtering equipment to evacuate for 2 h. Open the argon gas cylinder and increase the adhesion between gold and the substrate by chromium plating. Set the power to 60 W, the argon gas flux to 20 Sccm, and the sputtering time to 1 min. After starting, confirm whether the chamber is ignited through the baffle. After this operation, use a gold target, set the power to 70 W, the argon gas flux to 20 Sccm, and the sputtering time to 4 min. After starting, confirm whether the chamber is ignited through the baffle. After gold plating, close the argon gas and keep the pressure for 10 min, then take out the zinc oxide.

5. The method for preparing an interdigital transducer chip based on a zinc oxide piezoelectric thin film according to claim 1, wherein: In the fourth step, in order to improve the chip preparation efficiency, there are usually multiple interdigital transducers on one mask plate. After the stripping operation, it can be cut into blocks according to the interdigital pattern.

6. The method for fabricating an interdigital transducer chip based on a zinc oxide piezoelectric thin film according to claim 1, characterized in that: In the sixth step, for an ideal zinc oxide piezoelectric thin film, the Rayleigh wave velocity is 2650 m / s, and the propagation velocity of the surface wave on silicon is 4680 m / s. The surface acoustic wave velocity of the device is calculated by the product of the frequency and the wavelength and is between 2650 m / s and 4680 m / s. This is because the designed interdigital wavelength is greater than the thickness of the zinc oxide film, so that a part of the surface acoustic wave propagates in the zinc oxide thin film and another part propagates in the silicon and silicon dioxide media.

7. The method for fabricating an interdigital transducer chip based on zinc oxide piezoelectric thin film according to claim 1, wherein: In the seventh step, mix 5-micron fluorescent microspheres and PBS solution at a ratio of 1:

10. Take 0.2 μl of the liquid drop and drop it on the interdigital transducer. Set the frequency of the signal generator to 195 MHz, the input amplitude to 200 mV, connect it to a 30-W power amplifier, and the amplified signal is connected to the surface acoustic wave chip to generate acoustic waves. The particles in the liquid drop generate vortices under the drive of the transducer and gather at the center after 20 s.

8. The method for preparing an interdigital transducer chip based on a zinc oxide piezoelectric thin film according to claim 1, wherein: In step seven, the chip can also enrich human lymphocytes. First, we stain the lymphocytes in the opti-mem medium with Calcein-AM at a concentration of 1% for 5 minutes, then mix them with PBS solution at a ratio of 1:8, and take 0.2 μl of the liquid drop with lymphocytes and drop it on the interdigital electrode. Set the frequency of the signal generator to 195 MHz, set the input amplitude to 300 mV, and connect it to a 30 W power amplifier. The liquid drop with cells generates a vortex phenomenon. After 17 seconds, the lymphocytes in the vortex gradually enrich to the center of the vortex.

Images