Preparation method of x-cut single crystal lithium niobate-based miniature transverse wave piezoelectric micromechanical ultrasonic transducer and transverse wave probe

Abstract

The invention relates to the technical field of electronic materials and devices, in particular to a preparation method of a miniature transverse wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate and a transverse wave probe, and the method comprises the following steps: carrying out growth and x cutting on lithium niobate crystals to obtain a self-polarized lithium niobate wafer; carrying out graphical processing on the self-polarized lithium niobate wafer; cutting the self-polarized lithium niobate wafer subjected to graphical processing based on a preset tangential angle to obtain lithium niobate wafer slices at different tangential angles; and preparing the transverse wave probe by using the lithium niobate wafer slices at different tangential angles. The invention aims to realize preparation of a PMUT transverse wave device and solve the limitation that a traditional transverse wave probe is large in size and difficult to array and integrate.

Description

Technical Field

[0001] The invention relates to the technical field of electronic materials and devices, and in particular to a preparation method of a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate and a shear wave probe. Background Art

[0002] Ultrasonic waves are mechanical waves with a frequency higher than 20KHz. They have unique acoustic properties due to their high frequency and short wavelength, and are extremely valuable in the field of solid structure defect detection. Ultrasonic body waves include longitudinal waves and transverse waves. Longitudinal waves oscillate along the propagation direction and can propagate in a variety of media. The particle vibration is parallel to the wave propagation direction. They have strong penetration but fast high-frequency attenuation. They are suitable for detecting defects parallel to the workpiece surface. Transverse waves oscillate perpendicular to the propagation direction and only exist in solids. Their particle vibration is perpendicular to the wave propagation direction. They have the characteristics of low wave velocity, shorter wavelength and significant attenuation. They are suitable for near-surface inclined defect detection. The longitudinal wave probe of traditional ultrasonic probes is usually based on the bulk piezoelectric ceramic d31 or d33 mode, and the shear wave probe mostly uses the bulk piezoelectric ceramic d15 or d24 mode. Although bulk piezoelectric ceramics have the advantages of high sensitivity, stability and energy conversion efficiency, their processing relies on mechanical cutting, and their size reaches the centimeter level. They are difficult to integrate in an array and have poor consistency. At the same time, their preparation process is complex, involving model filling, polarization and high-temperature treatment, and the cost is high.

[0003] At present, with the advancement of micro-electromechanical system technology, PMUT (Piezoelectric Micromachined Ultrasonic Transducer) has overcome many defects of traditional bulk piezoelectric ceramics, and has the characteristics of miniaturization, excellent consistency, strong reliability and easy integration, and is a very promising ultrasonic transducer device. However, PMUT has a special structure. If the piezoelectric ceramic film is used as the diaphragm, it only generates and receives longitudinal waves in the d31 bending vibration mode. Due to the difficulty of micro-machining technology for the processing of the side electrodes of conventional piezoelectric films, it is impossible to prepare PMUT shear wave devices, and it is difficult to break through the limitations of traditional shear wave probes that are large in size and difficult to integrate in arrays, and it is impossible to meet the needs of high-resolution and near-surface tilt defect detection for shear wave devices. Summary of the invention

[0004] The purpose of the present invention is to realize the preparation of PMUT shear wave devices, solve the limitations of traditional shear wave probes that are large in size and difficult to integrate in arrays, and provide a preparation method and a shear wave probe of a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate. The technical solutions adopted are as follows:

[0005] The technical solution of the first aspect of the present invention provides a method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate, the method comprising:

[0006] Growing and x-cutting lithium niobate crystals to obtain self-polarized lithium niobate wafers;

[0007] Patterning of self-polarized lithium niobate wafers;

[0008] Cutting the patterned self-polarized lithium niobate wafer based on a preset tangential angle to obtain lithium niobate wafer slices at different tangential angles;

[0009] Shear wave probes were prepared by slicing lithium niobate wafers at different tangential angles.

[0010] Furthermore, the self-polarized lithium niobate wafer is patterned by:

[0011] A first metal layer and a second metal layer are respectively deposited on both sides of a self-polarized lithium niobate wafer, and the first metal layer and the second metal layer are respectively patterned.

[0012] Furthermore, the self-polarized lithium niobate wafer after the patterning process is cut based on a preset tangential angle to obtain lithium niobate wafer slices at different tangential angles, including:

[0013] Construct a three-dimensional simulation model of d15 lithium niobate;

[0014] The optimal polarization angle that maximizes the shear wave displacement amplitude is extracted using a three-dimensional simulation module;

[0015] The lithium niobate wafer is cut based on the optimal polarization angle and the initial self-polarization direction of the d15 type lithium niobate.

[0016] Further, preparing a shear wave probe by slicing lithium niobate wafers at different tangential angles includes:

[0017] Using lithium niobate wafer slices with a target tangential angle as the piezoelectric layer;

[0018] The top of the piezoelectric layer uses a viscous solid coupling material as a matching layer;

[0019] The bottom of the piezoelectric layer is connected to the packaging substrate through conductive glue.

[0020] Furthermore, preparing a shear wave probe by slicing lithium niobate wafers at different tangential angles also includes:

[0021] Based on the laser etching process, the shear wave array probe is prepared by using lithium niobate wafer slices with a target tangential angle.

[0022] The technical solution of the second aspect of the present invention provides a shear wave probe, which adopts the preparation method of the miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate described in the technical solution of the first aspect of the present invention. The shear wave probe includes a PCB packaging board, and the top of the PCB packaging board is sequentially provided with a conductive glue, a first electrode, a piezoelectric layer, a second electrode and a matching layer, and the piezoelectric layer adopts a self-polarized lithium niobate wafer.

[0023] Furthermore, the shear wave probe includes a plurality of shear wave sub-probes, and the plurality of shear wave sub-probes are arranged at equal intervals.

[0024] Furthermore, the shear wave probe includes a shear wave transmitting unit and a shear wave receiving unit; the shear wave transmitting unit is configured so that the piezoelectric layer converts the electrical signal into a mechanical signal through the inverse piezoelectric effect; the shear wave receiving unit is configured so that the piezoelectric layer converts the mechanical signal into an electrical signal through the direct piezoelectric effect.

[0025] The technical solution of the third aspect of the present invention provides an electronic device, comprising: a processor and a memory communicatively connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the steps of the method for preparing a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate as described in the technical solution of the first aspect of the present invention.

[0026] The technical solution of the fourth aspect of the present invention provides a computer-readable storage medium, on which is stored a program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate. The program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate is executed by a processor to implement the steps of the method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate described in the technical solution of the first aspect of the present invention.

[0027] The present invention has the following beneficial effects:

[0028] The present invention provides a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate. The method grows and x-cuts lithium niobate crystals to obtain self-polarized lithium niobate wafers to replace traditional bulk piezoelectric ceramics and conventional piezoelectric films. The self-polarized lithium niobate wafers are then patterned to extract electrodes to generate shear waves. The lithium niobate is also laser-etched to obtain an integrated array. Based on the self-polarization characteristics of lithium niobate, there is no need to separately process the polarization of side electrodes, and there is no need to add wedge blocks for waveform conversion, thereby overcoming the problems of large size of traditional shear wave probes, difficulty in array integration, and inability of conventional PMUTs to generate and receive shear waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A method flow chart of a method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate provided by one embodiment of the present invention;

[0031] Figure 2 A schematic diagram of the process flow of a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate provided by one embodiment of the present invention;

[0032] Figure 3 A schematic diagram of a curve showing a variation of the shear wave amplitude ratio in the x and y directions in a plane with the tangential angle provided by an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of different mechanical cutting and scribing angles provided by an embodiment of the present invention;

[0034] Figure 5 A schematic structural diagram of a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate provided by one embodiment of the present invention;

[0035] Figure 6 A schematic diagram of an LN shear wave PMUT ultrasonic transmission and reception test provided by an embodiment of the present invention;

[0036] Figure 7 A schematic diagram of a self-transmitting and self-receiving waveform of an LN shear wave device provided by an embodiment of the present invention;

[0037] Figure 8 A process flow for preparing a LN shear wave PMUT array provided by an embodiment of the present invention;

[0038] Icon: 100-PCB packaging board; 200-conductive adhesive, 300-first electrode, 400-piezoelectric layer, 500-second electrode, 600-matching layer. DETAILED DESCRIPTION

[0039] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the preparation method and shear wave probe of a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate proposed by the present invention, its specific implementation method, structure, characteristics and effects as follows in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0040] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0041] The following specifically describes a method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate and a specific scheme of a shear wave probe provided by the present invention in conjunction with the accompanying drawings.

[0042] See also Figure 1 and Figure 2 As shown, it shows a method flow chart and a process flow diagram of a method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate provided by the present invention, and the method comprises:

[0043] Step S100: growing and x-cutting lithium niobate crystals to obtain self-polarized lithium niobate wafers; specifically, growing lithium niobate (LN) crystals directly in air by using a Czochralski growth method, the LN crystals are pulled in the x-direction, the crystals are kept in equal diameter during the growth process, and then the grown lithium niobate single crystal rods are cut by x-cutting to obtain x-cut LN wafers of target size, preferably 6-inch, 0.5 mm thick x-cut LN wafers; it should be noted that during the cutting process, it is necessary to accurately control the cutting thickness and the diameter of the wafer, and then cut the single crystal rods into sizes that meet the requirements, so as to provide a suitable material basis for subsequent processing and application, and after obtaining the x-cut LN wafers, subsequent grinding and polishing are required to ensure indicators such as surface flatness and roughness;

[0044] In this embodiment, the lithium niobate wafer obtained by the pulling method and x-cutting has a self-polarization characteristic, so there is no need to separately process the side electrode polarization, and there is no need to add a wedge block for waveform conversion. By sputtering metal electrodes on the upper and lower surfaces of the prepared x-cut LN wafer, it can be made to work in the thickness shear mode to directly generate shear waves, which solves the problem that the prior art needs to use a longitudinal wave probe and a wedge block to generate shear waves, and there are impedance mismatch, limited energy transmittance and complex propagation path calculation after adding the wedge block; on the other hand, compared with the conventional piezoelectric film in the PMUT of the prior art, its polarization direction is the same as the electric field excitation direction, and in the micromachining process, only the upper and lower metal electrodes need to be deposited and led out, but the prior art can only generate longitudinal waves. If shear waves are to be generated, the side electrodes of the piezoelectric film must be polarized to make it work in the shear mode, and this process cannot be achieved at present; the present invention utilizes the self-polarization of LN, and there is no need to separately process the side electrode polarization. It can generate shear waves while avoiding the limitations of conventional processes, thereby solving the problem that the current PMUT device cannot generate shear waves.

[0045] Step S200: performing patterning processing on the self-polarized lithium niobate wafer;

[0046] Step S200 specifically includes:

[0047] Step S210: depositing a first metal layer and a second metal layer on both sides of the self-polarized lithium niobate wafer, and performing graphic processing on the first metal layer and the second metal layer respectively; specifically, using magnetron detection technology to deposit the first metal layer and the second metal layer on both sides of the self-polarized lithium niobate wafer, prepare a clean self-polarized lithium niobate wafer, and place it on a base in a vacuum chamber of a magnetron sputtering device to ensure that the wafer is fixed firmly and the position is accurate; for depositing the first metal layer, set the process parameters of magnetron sputtering so that metal atoms are evenly deposited on one side of the lithium niobate wafer to form a continuous first metal layer with a thickness that meets the requirements. Next, following the same operating procedure, a second metal layer is deposited on the other side of the wafer to ensure that the quality and thickness uniformity of the metal layers on both sides are good; the magnetron sputtering metal electrode layer is preferably Cr combined with Au, with Cr being sputtered first and then Au being sputtered; after the metal layer deposition is completed, the wafer with the metal layer is transferred to an etching process equipment, and the first metal layer and the second metal layer are patterned according to a pre-designed electrode pattern, and are converted into a first electrode and a second electrode, respectively; at the same time, when etching the electrode pattern, it is necessary to reserve a device dicing spacing, which is based on the maximum edge collapse size in the subsequent dicing process. Reserving this spacing can effectively avoid the adverse effects of edge collapse caused during dicing on device performance, thereby ensuring that each device finally obtained has good integrity and performance stability.

[0048] Step S300: cutting the patterned self-polarized lithium niobate wafer based on a preset tangential angle to obtain lithium niobate wafer slices at different tangential angles; specifically, slicing is performed by mechanical cutting, specifically, placing the patterned self-polarized lithium niobate wafer on a workbench of a high-precision mechanical cutting device, and ensuring that the wafer is placed stably and accurately positioned; then, according to the preset tangential angle, the cutting knife angle of the cutting device is accurately adjusted to make it completely consistent with the preset cutting direction. After starting the cutting device, the slicing knife cuts into the wafer along the preset tangential angle, and finally completes the wafer cutting operation to obtain different cutting directions. Slices of lithium niobate wafers at different tangential angles can be accurately obtained by mechanically cutting and slicing based on a preset tangential angle in step S300. Slices at different tangential angles can meet the diverse design requirements of ultrasonic transducers, and expand the performance control range of ultrasonic transducers based on lithium niobate materials. Slices with appropriate tangential angles can be selected according to specific detection scenarios and requirements for shear wave characteristics to optimize the performance of ultrasonic transducers in transmitting and receiving shear waves, thereby improving the pertinence and effectiveness of ultrasonic transducers in applications such as different solid structure defect detection, and enhancing the accuracy and applicability of overall ultrasonic detection.

[0049] Step S300 specifically includes:

[0050] Step S310: construct a three-dimensional simulation model of d15 lithium niobate; specifically, based on the finite element analysis software COMSOL, modeling is performed according to the actual geometric shape and size characteristics of lithium niobate. For example, according to the conventional shapes of its crystals such as a cuboid or a cube, by inputting the corresponding length, width, and height parameters, a three-dimensional geometric solid model representing lithium niobate is created; then the material corresponding to the created geometric model is set to d15 lithium niobate;

[0051] Step S320: Use the three-dimensional simulation module to extract the optimal polarization angle that maximizes the shear wave displacement amplitude; specifically, based on the constructed d15 type lithium niobate three-dimensional simulation model, enter the COMSOL solver setting interface and configure the time step and convergence criterion parameters for the solution; then, perform time domain simulation on lithium niobate cut at different angles x, and change the polarization angle within the LN plane by modulating the Euler angle in the software to simulate the electric field distribution, stress and strain conditions, and shear wave generation and propagation characteristics inside the lithium niobate crystal at different polarization angles; after each simulation calculation is completed, use the post-processing function of the software to extract the shear wave amplitude-related data in the x and y directions within the plane, organize the corresponding shear wave amplitude data at these different angles, and use the software's own data visualization tools or export the data to professional drawing software to draw the shear wave amplitude ratio in the x and y directions within the plane as a function of the tangential angle, observe the trend of the amplitude ratio changing with the angle, and find the tangential angle corresponding to the maximum amplitude ratio, which is the optimal polarization angle. Figure 3 As shown, from Figure 3 It can be understood that the shear wave displacement amplitude ratio in the x and y directions in the plane at 10 mm in the far field is the largest, reaching 45.6. At this time, this angle is determined to be the optimal angle. Then, when the LN wafer is mechanically cut and sliced ​​later, the dicing knife is made to form a certain angle with the initial x-cut LN wafer self-polarization direction P according to this optimal angle for dicing, and finally the x-cut LN shear slice at this angle is obtained. By constructing a three-dimensional simulation model of d15 lithium niobate and using it to extract the optimal polarization angle that maximizes the shear wave displacement amplitude ratio, the optimal tangential angle can be accurately determined from a theoretical level, providing a scientific basis for the cutting of lithium niobate wafers in the subsequent actual preparation of ultrasonic transducers, and helping to obtain lithium niobate slices with the best performance in specific application scenarios, so that the prepared ultrasonic transducer can realize shear wave propagation of particle vibration completely along a single direction, greatly improving its sensitivity and resolution in detecting tiny defects in a specific direction inside a solid structure, and optimizing the pertinence and accuracy of ultrasonic transducers in detecting different defects.

[0052] Step S330: Cut the lithium niobate wafer based on the optimal polarization angle and the initial self-polarization direction of d15 lithium niobate; specifically, perform angle calibration and adjustment on the cutting equipment according to the optimal polarization angle determined by simulation analysis and other means in step S320 and the known initial self-polarization direction of d15 lithium niobate (0°x cut LN as a reference angle); use the angle adjustment function of the cutting equipment to make the cutting direction of the cutting tool form a corresponding angle relationship with the initial self-polarization direction; for example, in the case of obtaining a 36°x cut LN shear piece, the tool needs to be rotated to an angle position of 36° counterclockwise to the initial self-polarization direction to ensure the accuracy of the cutting angle. See also Figure 4 As shown, Figure 4The figure shows a schematic diagram of 6-inch x-cut LN wafer layout scribing. The red arrow line is the area dividing line. Numbers 1-12 are 12 scribing areas with different angles, corresponding to x-cut LN shear pieces with different angles. P is the self-polarization direction of the initial x-cut LN wafer, that is, 0° x-cut LN, which is used as a reference angle. Since LN is in-plane polarized, x-cut LN with different angles can be obtained by scribing at different angles counterclockwise. Area 2 is 36° x-cut LN, and the final packaged shear wave probe uses LN shear pieces at the square optimal polarization angle.

[0053] Step S330 can accurately obtain lithium niobate shear slices of different angles that meet the expected performance requirements by cutting the lithium niobate wafer based on the optimal polarization angle and the initial self-polarization direction, thereby providing basic materials for the subsequent packaging of high-performance shear wave probes; for example, by using specific angle slices such as 58°x-cut LN shear slices, the packaged shear wave probe can better utilize the polarization characteristics of the lithium niobate material at this angle, achieve better quality shear wave generation and propagation effects, and effectively improve the resolution and accuracy of the probe when detecting internal defects in solid structures.

[0054] Step S400: preparing a shear wave probe by using lithium niobate wafer slices at different tangential angles.

[0055] See also Figure 5 As shown, step S400 specifically includes:

[0056] Step S410: using lithium niobate wafer slices with a target tangential angle to form a piezoelectric layer; specifically, selecting slices with a target tangential angle from lithium niobate wafer slices with different tangential angles obtained by cutting as piezoelectric layer materials; then depositing a first metal layer and a second metal layer on both sides of the piezoelectric layer, respectively, and patterning the first metal layer and the second metal layer, respectively, to obtain a first electrode and a second electrode;

[0057] Step S420: A viscous solid coupling material is used as a matching layer on the top of the piezoelectric layer; specifically, a matching layer is prepared on the top of the piezoelectric layer (i.e., lithium niobate slice) after the electrode is prepared. In this embodiment, AB glue is preferably used as the matching layer material; a high-precision dispensing device or coating tool is used to evenly coat the prepared AB glue on the top surface of the piezoelectric layer. By controlling the coating thickness and coating area and other parameters, the matching layer finally formed is preferably 0.3 mm. At the same time, it is ensured that the matching layer and the piezoelectric layer can fit closely to avoid partial uncovering or uneven glue layer thickness, so as to achieve the function of better coupling shear waves and reducing shear wave attenuation between the device and the solid carrier structure;

[0058] Step S430: the bottom of the piezoelectric layer is connected to the packaging substrate through a conductive glue; specifically, in this embodiment, a conductive silver paste is selected as the conductive glue, and a proper amount of the conductive silver paste is applied to the bottom of the piezoelectric layer; then the piezoelectric layer coated with the conductive silver paste is accurately placed at a corresponding position on the pre-prepared packaging substrate, and the piezoelectric layer and the packaging substrate are tightly fitted by applying appropriate pressure to ensure that the conductive silver paste forms a good conductive path between the two; finally, the structure of the packaged LN shear wave PMUT device is, from top to bottom, a matching layer, a first electrode, a LN piezoelectric layer, a second electrode, a conductive silver paste, and a packaging substrate;

[0059] The working principle of the device prepared by the preparation method of the micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate is as follows: LN, as a piezoelectric material, has a reversible piezoelectric effect, that is, there are two interrelated physical processes, namely, the positive piezoelectric effect and the inverse piezoelectric effect; when subjected to an external electric field, according to the inverse piezoelectric effect, the lattice structure inside the LN will change due to the influence of the electric field force, thereby causing the material to produce mechanical deformation on its surface, such as thickness changes; on the contrary, when LN is subjected to external mechanical stress, based on the positive piezoelectric effect, the electric dipole moment inside the crystal will change accordingly, thereby generating charges on the surface of the material. This characteristic provides the core physical basis for the transducer to realize the mutual conversion between electrical signals and mechanical signals; the transmission working mode principle of the LN shear wave PMUT device is as follows: in the transmission working mode, the inverse piezoelectric effect is used to realize the conversion of electrical signals to mechanical signals (shear waves); specifically, for the in-plane polarization thickness in the present invention, A shear-type LN structure is constructed, and voltage excitation is applied to the upper and lower metal electrodes. At this time, an electric field perpendicular to the in-plane polarization direction is generated inside the LN. Due to the piezoelectric properties of LN and its crystal structure characteristics, this electric field will induce transverse shear stress in the LN along the thickness direction. Under the action of this shear stress, the LN material produces shear deformation, and this shear vibration is the source of the shear wave. The generated shear wave can then propagate with the help of the surrounding medium, thereby realizing the emission of the shear wave to the outside world. This process converts the electrical drive signal into a shear wave signal that can be used for detection, opening the signal emission link in ultrasonic detection. The principle of the receiving working mode of the LN shear wave PMUT device is as follows: when in the receiving working mode, the situation is the opposite, relying on the positive piezoelectric effect to achieve the conversion of mechanical signals (shear waves) to electrical signals. When the external shear wave is transmitted to the LN piezoelectric layer through the medium, it will exert transverse shear stress on the LN, causing the lattice structure of the LN to be subjected to external force and produce corresponding strain. Based on the positive piezoelectric effect, this strain will cause the electric dipole moment inside the LN crystal to be redistributed, thereby generating charges on its surface, thereby converting the incoming shear wave mechanical signal into an electrical signal that can be detected and processed by subsequent circuits, completing the shear wave reception process and providing a key signal source for the entire ultrasonic detection system to obtain feedback information.

[0060] In summary, the miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate prepared by the preparation method utilizes the piezoelectric effect of LN and realizes the effective mutual conversion between electrical signals and shear-wave mechanical signals in the transmitting and receiving working modes, which provides strong technical support for the detection of internal defects of solid structures in ultrasonic detection applications.

[0061] In order to test the ultrasonic working characteristics of the LN shear wave PMUT device prepared by this preparation method, we selected the LN shear wave PMUT device obtained by the above preparation method and placed the device in the ultrasonic transmission and reception test system; see Figure 6 The schematic diagram of the LN shear wave PMUT ultrasonic transmission and reception test shown in the figure is that the LN shear wave PMUT is firstly pasted on the surface of the PS block using a shear wave coupling agent, and the thickness of the PS block is about 2 cm; then, the LN shear wave PMUT device is connected to a high-frequency pulse generator and excited by a 30Vpp voltage pulse signal, the excitation frequency is 1.5MHz, and the signal output end is connected to an oscilloscope to display the received time domain voltage pulse signal, and the receiving gain is 20dB; finally, the spontaneously transmitted and received waveforms of the LN shear wave PMUT device are measured as follows Figure 7 shown; from Figure 7 It can be understood that the shear wave echo time received by the LN shear wave PMUT is about 36μs, and the round-trip propagation distance in the PS block is 4cm. After calculation, the shear wave speed in the PS block is about 1100m / s; it can be seen that the micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate can generate shear waves as expected, and the shear waves can be effectively propagated in the set medium (PS block), which verifies that the device is feasible and effective in the shear wave generation and propagation mechanism, indicating that it has ultrasonic working ability. The entire experiment is realized from the electrical signal excitation to generate shear waves (inverse piezoelectric effect), to the echo being received and converted into electrical signals after the shear wave propagates (positive piezoelectric effect), which fully verifies that the working principle of the micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate based on positive and negative piezoelectric effects is feasible, and verifies the rationality and effectiveness of the designed device structure and the adopted preparation method in realizing the function of the ultrasonic transducer.

[0062] See also Figure 8As shown, the present invention also provides a preferred technical solution, and the preparation of shear wave probes using lithium niobate wafer slices at different tangential angles also includes: based on a laser etching process, preparing a shear wave array probe using lithium niobate wafer slices at a target tangential angle; specifically, according to the specific design requirements of the shear wave array probe to be prepared, such as the unit size, spacing, shape and other parameters of the array, selecting a suitable laser etching device and a designed array pattern, and importing the corresponding graphic data into the control system of the etching device; placing the processed lithium niobate wafer slices on the workbench of the laser etching device, starting the laser etching device, and scanning and etching the lithium niobate slices with a laser beam according to the preset graphic data and parameters, and gradually processing the lithium niobate slices into a shear wave array probe with multiple unit structures by controlling the path of the laser beam; for example Figure 8 As shown in , for the strip array, the strip LN shear wave device units are etched out at equal intervals along the corresponding direction; the process flow and packaging process of the lithium niobate shear wave array device are: the first laser etching, sticking the blocking isolation tape and encapsulating the matching layer, sticking the conductive silver glue to the PCB board, the second laser etching, and electrode bonding; the preferred technical solution uses the laser etching process to prepare the shear wave array probe and design and prepare LN shear wave devices of different thicknesses and sizes. On the one hand, it expands the functions of ultrasonic transducers based on lithium niobate materials in applications such as imaging. The shear wave array probe can realize the coordinated work of multiple units, improve the resolution, contrast and detection range of ultrasonic imaging, and provide an effective technical means for more accurate detection of complex defects inside solid structures and obtaining more detailed internal structure information;

[0063] In summary, the method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate provided by the present invention has the following beneficial effects:

[0064] 1. The present invention sequentially performs double-sided magnetron sputtering metal deposition, etching, dicing and other MEMS processes on x-cut LN wafers, and designs and prepares a micro shear wave PMUT device for the first time, filling the gap in the current miniaturized shear wave MEMS devices; at the same time, under the d15 thickness shear working mode, the micro shear wave PMUT device has a high electromechanical coupling coefficient and low dielectric loss, achieving high sensitivity and large bandwidth;

[0065] 2. Compared with the existing shear wave straight probe or wedge-shaped oblique probe, single crystal lithium niobate has the characteristic of self-polarization. The present invention does not require side electrodes, so it has the advantages of miniaturization, large-scale processing, and easy integration with circuits;

[0066] 3. When preparing x-cut LN wafers, the present invention can select different tangent angles to improve the performance of LN shear wave PMUT devices; in addition, the size and shape of LN can be optimized to further improve the shear wave transmission and reception performance; the LN wafer can be sliced ​​by rotating it counterclockwise at a specific angle to obtain shear slices with different tangent angles; the tangent angle can be specifically selected for specific applications, especially when performing specific types of solid defect detection, the appropriate tangent angle can be selected according to the size and direction of the defect to achieve the best detection effect.

[0067] See also Figure 2 , which shows a schematic structural diagram of a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate provided by an embodiment of the present invention. The technical solution of the second aspect of the present invention provides a shear-wave probe, and adopts the preparation method of the miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate described in the technical solution of the first aspect of the present invention. The shear-wave probe includes a PCB packaging board 100, and a conductive glue 200, a first electrode 300, a piezoelectric layer 400, a second electrode 500 and a matching layer 600 are sequentially arranged on the top of the PCB packaging board 100, and the piezoelectric layer 400 adopts a self-polarized lithium niobate wafer.

[0068] Preferably, the shear wave probe includes a plurality of shear wave sub-probes, and the plurality of shear wave sub-probes are equidistantly spaced apart from each other.

[0069] Preferably, the shear wave probe includes a shear wave transmitting unit and a shear wave receiving unit; the shear wave transmitting unit is configured so that the piezoelectric layer 400 converts the electrical signal into a mechanical signal through the inverse piezoelectric effect; the shear wave receiving unit is configured so that the piezoelectric layer 400 converts the mechanical signal into an electrical signal through the direct piezoelectric effect.

[0070] The technical solution of the third aspect of the present invention provides an electronic device, comprising: a processor and a memory communicatively connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the steps of the method for preparing a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate as described in the technical solution of the first aspect of the present invention.

[0071] The technical solution of the fourth aspect of the present invention provides a computer-readable storage medium, on which is stored a program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate. The program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate is executed by a processor to implement the steps of the method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate described in the technical solution of the first aspect of the present invention.

[0072] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0073] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. A method for preparing a micro shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate, characterized in that: The method comprises: Growing and x-cutting lithium niobate crystals to obtain self-polarized lithium niobate wafers; Patterning of self-polarized lithium niobate wafers; Cutting the patterned self-polarized lithium niobate wafer based on a preset tangential angle to obtain lithium niobate wafer slices at different tangential angles; Shear wave probes were prepared by slicing lithium niobate wafers at different tangential angles.

2. The preparation method according to claim 1, characterized in that Patterning of self-polarized lithium niobate wafers includes: A first metal layer and a second metal layer are respectively deposited on both sides of a self-polarized lithium niobate wafer, and the first metal layer and the second metal layer are respectively patterned.

3. The preparation method according to claim 1, characterized in that: The self-polarized lithium niobate wafer after patterning is cut based on a preset tangential angle, and the lithium niobate wafer slices at different tangential angles include: Construct a three-dimensional simulation model of d15 lithium niobate; The optimal polarization angle that maximizes the shear wave displacement amplitude is extracted using a three-dimensional simulation module; The lithium niobate wafer is cut based on the optimal polarization angle and the initial self-polarization direction of the d15 type lithium niobate.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The preparation of shear wave probes using lithium niobate wafer slices at different tangential angles includes: Using lithium niobate wafer slices with a target tangential angle to form a piezoelectric layer; The top of the piezoelectric layer uses a viscous solid coupling material as a matching layer; The bottom of the piezoelectric layer is connected to the packaging substrate through conductive glue.

5. The preparation method according to claim 4, characterized in that: The preparation of shear wave probes using lithium niobate wafer slices at different tangential angles also includes: Based on the laser etching process, the shear wave array probe is prepared by using lithium niobate wafer slices with a target tangential angle.

6. Shear wave probe, characterized in that, The method for preparing a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate according to any one of claims 1 to 5 is adopted, wherein the shear wave probe includes a PCB packaging board, and a conductive glue, a first electrode, a piezoelectric layer, a second electrode and a matching layer are sequentially arranged on the top of the PCB packaging board, and the piezoelectric layer adopts a self-polarized lithium niobate wafer.

7. The shear wave probe according to claim 6, characterized in that: The shear wave probe comprises a plurality of shear wave sub-probes, and the plurality of shear wave sub-probes are arranged at equal intervals.

8. The shear wave probe according to claim 6, characterized in that: The shear wave probe includes a shear wave transmitting unit and a shear wave receiving unit; the shear wave transmitting unit is configured so that the piezoelectric layer converts the electrical signal into a mechanical signal through the inverse piezoelectric effect; the shear wave receiving unit is configured so that the piezoelectric layer converts the mechanical signal into an electrical signal through the direct piezoelectric effect.

9. An electronic device, characterized in that: The electronic device includes: a processor and a memory communicatively connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the steps of the method for preparing a miniature shear wave piezoelectric micromechanical ultrasonic transducer based on x-cut single crystal lithium niobate as described in any one of claims 1 to 5.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate. The program for implementing a method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate is executed by a processor to implement the steps of the method for preparing a miniature shear-wave piezoelectric micromechanical ultrasonic transducer based on x-cut single-crystal lithium niobate as described in any one of claims 1 to 5.

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