Ultrasonic transducer and preparation method thereof

Abstract

The invention discloses an ultrasonic transducer and a preparation method thereof.The ultrasonic transducer comprises a conductive backing layer, a first metal electrode, a piezoelectric ceramic piece, a second metal electrode, a conductive matching layer, a packaging layer, a first bonding layer and a second bonding layer, and the conductive backing layer, the piezoelectric ceramic piece and the conductive matching layer are sequentially packaged in the packaging layer from bottom to top; a first metal electrode is arranged between the conductive backing layer and the piezoelectric ceramic piece, a second metal electrode is arranged between the piezoelectric ceramic piece and the conductive matching layer, a first bonding layer is arranged between the conductive backing layer and the first metal electrode, and a second bonding layer is arranged between the conductive matching layer and the second metal electrode. According to the invention, the damage rate of the piezoelectric ceramic piece is reduced through the processing sequence of bonding the piezoelectric ceramic piece and the conductive backing layer and then finely thinning the piezoelectric ceramic piece and a low-temperature bonding process. The obtained transducer is high in imaging resolution, high in yield and suitable for high-performance intravascular ultrasonic imaging.

Description

Technical Field

[0001] This invention relates to the field of medical device manufacturing technology, specifically to an ultrasonic transducer and its preparation method. Background Technology

[0002] Intravascular ultrasound (IVUS) is a core technology for intravascular imaging diagnosis and interventional treatment of coronary arteries. It uses a high-frequency miniature ultrasound probe at the tip of the interventional catheter to acquire high-resolution images of the cross-section of the blood vessel in real time. It can not only display the morphology of the blood vessel lumen, but also clearly reveal the microstructural information such as the thickness of the blood vessel wall and the composition of plaque (such as calcification, fibrosis, and lipid pools), providing key information for the assessment of critical stenosis, stent size selection, and postoperative prognosis.

[0003] The imaging quality and reliability of IVUS are highly dependent on the performance of the ultrasonic transducer, and the bandwidth, sensitivity, signal-to-noise ratio, and long-term stability of the transducer are all determined by the fabrication process. Currently, existing IVUS transducer fabrication processes face two major technological bottlenecks, severely restricting product quality and production efficiency:

[0004] Firstly, there is the mechanical damage and warping of thin piezoelectric ceramic sheets: Current technology involves grinding and thinning the piezoelectric ceramic sheet to 20-80 μm (the required thickness for high-frequency transducers), then depositing metal electrodes on both sides of the sheet, followed by coating a backing layer / matching layer and curing at 100-160℃. Due to the extremely low mechanical strength of the thin piezoelectric ceramic sheet, it is easily subjected to binder shrinkage stress and thermal stress at high temperatures, leading to warping, cracking, and even breakage. This results in a yield rate of less than 50% and poor batch consistency.

[0005] Secondly, interface defects and uncontrolled thickness: The backing layer / matching layer adopts manual or semi-automatic scraping / pouring process (composite slurry of epoxy resin and metal particles), which easily introduces bubbles, pores and delamination defects. This not only reduces the mechanical bonding strength, but also causes sound wave reflection and scattering, resulting in a decrease in sound coupling efficiency. Moreover, after high-temperature curing, the surface smoothness of the coating is poor, Ra≥1.0μm, and the thickness error exceeds ±20%, resulting in low subsequent grinding efficiency and further aggravating performance fluctuations. Summary of the Invention

[0006] The purpose of this invention is to provide an ultrasonic transducer and its manufacturing method to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for manufacturing an ultrasonic transducer, comprising the following steps:

[0008] Prepare conductive backing layer and conductive matching layer;

[0009] The piezoelectric ceramic sheet is pre-thinned to a thickness of 0.1~0.2 mm, and a first metal electrode is prepared on one side of the pre-thinned piezoelectric ceramic sheet;

[0010] A conductive backing layer and a piezoelectric ceramic sheet with a first metal electrode are bonded together using conductive adhesive to obtain a conductive backing layer-piezoelectric ceramic sheet bonding assembly. A first bonding layer is formed between the conductive backing layer and the surface of the piezoelectric ceramic sheet with the first metal electrode, and the thickness of the first bonding layer is 1~3μm.

[0011] The piezoelectric ceramic sheet of the conductive backing layer-piezoelectric ceramic sheet bonding assembly is thinned so that the thickness of the piezoelectric ceramic sheet is 1 / 2 of the length of the ultrasonic wave inside the piezoelectric ceramic at the target ultrasonic frequency.

[0012] A second metal electrode is fabricated on the exposed surface of the finely thinned piezoelectric ceramic sheet;

[0013] A conductive matching layer is bonded to a piezoelectric ceramic sheet with a second metal electrode using conductive adhesive to obtain a conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly. A second bonding layer is formed between the conductive matching layer and the surface of the piezoelectric ceramic sheet with the second metal electrode, and the thickness of the second bonding layer is 1~3μm.

[0014] The conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly is encapsulated with Pyrelin to obtain an ultrasonic transducer.

[0015] Further, the piezoelectric ceramic sheet is pre-thinned to a thickness of 0.1~0.15mm, which includes: first grinding the piezoelectric ceramic sheet to a thickness of 0.15~0.20mm, and then polishing the piezoelectric ceramic sheet to a thickness of 0.1~0.15mm, and making the surface flatness Ra 0.3~0.4μm.

[0016] Furthermore, the thinning process includes: first grinding the piezoelectric ceramic with an 800-1000# grinding wheel to a thickness of 60-90 μm; then grinding the piezoelectric ceramic sheet with a 2000-2500# grinding wheel to a thickness of 50-80 μm; and finally wet polishing the piezoelectric ceramic sheet to a thickness of 30-70 μm, with a surface flatness Ra of 0.1-0.2 μm.

[0017] Furthermore, the conductive adhesive is a vacuum-degassed epoxy conductive adhesive; the bonding parameters are: pressure 0.3~0.5MPa, pressure rise rate 0.05~0.10MPa / s, temperature 35~50℃, heating rate 2~5℃ / min, and heat and pressure holding time 20~30 minutes.

[0018] Furthermore, the preparation of the conductive matching layer includes: thinning the conductive matching layer, wherein the thickness of the thinned conductive matching layer is 1 to 1.5 times the length of the ultrasonic wave inside the conductive matching layer at the target ultrasonic frequency, and the surface flatness Ra is ≤ 0.2 μm.

[0019] Furthermore, before the Piriton is packaged, the surface of the conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly is treated with O2 plasma. The treatment parameters are: O2 flow rate 10~40 sccm, cavity pressure 0.1~0.5 Torr, radio frequency power 5~30W, and treatment time 30~60s.

[0020] Furthermore, the pyrelin encapsulation includes depositing a pyrelin film on the surface of the conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly, wherein the thickness of the pyrelin film is 3~10μm.

[0021] A second aspect of the present invention provides an ultrasonic transducer prepared by the above method, comprising a conductive backing layer, a first metal electrode, a piezoelectric ceramic sheet, a second metal electrode, a conductive matching layer, an encapsulation layer, a first bonding layer, and a second bonding layer. The conductive backing layer, the piezoelectric ceramic sheet, and the conductive matching layer are sequentially encapsulated in the encapsulation layer from bottom to top. A first metal electrode is disposed between the conductive backing layer and the piezoelectric ceramic sheet, and a second metal electrode is disposed between the piezoelectric ceramic sheet and the conductive matching layer. A first bonding layer is disposed between the conductive backing layer and the first metal electrode, and a second bonding layer is disposed between the conductive matching layer and the second metal electrode.

[0022] Furthermore, the thickness of both the first bonding layer and the second bonding layer is 1~2μm, and the thickness of the piezoelectric ceramic sheet is 30~70μm.

[0023] Furthermore, the thickness of both the first bonding layer and the second bonding layer is 1 μm, and the thickness of the piezoelectric ceramic sheet is 49 μm or 67 μm.

[0024] Beneficial effects:

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. Reducing the breakage rate of piezoelectric ceramic sheets during thinning and improving the yield rate of ultrasonic sensors: By adopting a sequence of first bonding the conductive backing layer and the piezoelectric ceramic sheet, and then finely thinning the piezoelectric ceramic sheet, on the one hand, the overall structure of the bonding component provides mechanical strength support to the piezoelectric ceramic sheet during the thinning process, breaking through its own thinning thickness limit. It can reliably thin it to 30~70μm without damaging its surface integrity. On the other hand, the low-temperature bonding process (≤50℃) avoids the thin piezoelectric ceramic sheet directly bearing the thermal stress and shrinkage stress caused by the existing high-temperature curing process (100-160℃), effectively preventing its warping and cracking. Experiments show that the method of this invention can reduce the breakage rate of piezoelectric ceramic sheets to ≤5%, significantly improving the yield rate and product consistency.

[0027] 2. Achieving ultra-thin, defect-free interface bonding to improve acoustic performance: By employing epoxy conductive adhesive and precision bonding technology, the bonding layer thickness can be precisely controlled within 1~3μm, far smaller than traditional bonding processes (>10μm), greatly reducing sound wave reflection and scattering losses at the interface. Furthermore, replacing the existing mixed slurry casting process with a pure adhesive layer bonding process effectively eliminates interface bubbles and delamination defects, improving the mechanical bonding strength and acoustic matching efficiency of the interface.

[0028] 3. Modular design and precise thickness control enhance process flexibility: The conductive backing layer and conductive matching layer can be independently optimized in terms of material ratio and thickness, and can be independently processed to the target thickness through precision grinding. This enables precise control of the thickness of each functional layer of the transducer, ensuring that they all operate at the optimal acoustic thickness. This modular design facilitates rapid adaptation and customized production for different high-frequency requirements such as 30-40MHz, significantly improving process flexibility and production efficiency.

[0029] 4. Significantly Improved Transducer Imaging Performance: The ultrasonic transducer fabricated in this invention, thanks to its ultra-thin piezoelectric ceramic sheet, high-precision bonding layer, and matching layer, can operate at a maximum frequency of 40MHz and achieve an image resolution of up to 37μm, clearly displaying the structure of each layer of the blood vessel wall and the morphology of the lumen. Compared with existing technologies, the bandwidth and imaging resolution of the transducer are significantly improved. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the fabrication process of the acoustic transducer of the present invention;

[0031] Figure 2 This is a diagram showing the thinning effect of the bonded composite piezoelectric ceramic sheet;

[0032] Figure 3 This is an image showing the thinning effect of a single piezoelectric ceramic sheet.

[0033] Figure 4 This is a schematic diagram of the ultrasonic transducer structure of the present invention;

[0034] Figure 5 Comparison table of ultrasonic transducer parameters of the present invention with those of existing technologies;

[0035] Figure 6 for Figure 5 Pulse excitation performance test spectrum of Sample 1.

[0036] Wherein: 1-Piezoelectric ceramic sheet; 2-Conductive matching layer; 3-Conductive backing layer; 4-Metal electrode; 5-Encapsulation layer; 6-Bonding layer. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0039] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0040] Please refer to Figures 1-2 This invention provides a method for fabricating an ultrasonic transducer. The ultrasonic transducer fabricated by this invention is used in routine coronary / peripheral artery stenosis assessment scenarios, requiring a balance between imaging depth and resolution. The piezoelectric ceramic sheet uses the mature PZT-5H piezoelectric ceramic material, and the specific fabrication steps are as follows:

[0041] S1. Preparation of conductive backing layer 3

[0042] Material ratio: Tungsten powder, silver powder, and epoxy resin are mixed in a mass ratio of 75:5:20; wherein, the tungsten powder is high acoustic attenuation tungsten powder with a particle size of 5~10μm; the silver powder is conductive reinforced silver powder with a particle size of 1-3μm; and the epoxy resin is E-51 type low shrinkage silver powder.

[0043] It should be noted that the conductive backing layer of the present invention is not limited to the above-described mixture of tungsten powder, silver powder, and epoxy resin. In other embodiments, the conductive backing layer may be made by mixing epoxy resin with at least one metal powder selected from tungsten powder, silver powder, and gold powder. Further, the mass ratio of epoxy resin to metal powder may be 6:4 to 9:1, preferably 8:2.

[0044] Molding and curing: After mixing the above materials, stir at 1500 rpm for 30 minutes using a planetary mixer; degas under vacuum for 5 minutes with a vacuum degree of -0.095 MPa; pour into a mold with a bottom surface flatness Ra≤0.1μm and an initial slurry thickness of 8mm; place the mold in a high-temperature furnace and heat to 120℃ at a heating rate of 5℃ / min and cure for 2 hours to avoid stress concentration.

[0045] Grinding and Testing: After curing, a diamond grinding wheel was used to grind the upper and lower surfaces to a thickness of 6mm using 400# grit, and then finely ground to a thickness of 5mm using 1000# grit. The acoustic impedance was measured to be 20±2Mrayl, the acoustic attenuation coefficient to be 25±5dB / mm, and the volume resistivity to be ≤5×10⁻⁶. -4 Ω・cm; After passing the test, the thickness was reduced to 0.27mm by grinding with 400#, 1000# and 2000# grinding wheels in sequence, and polished until the surface flatness Ra≤0.1μm. Then, it was placed in isopropanol and deionized water for ultrasonic rinsing in sequence, and then dried at 40~60℃ to ensure that there is no residual solvent and moisture on the surface.

[0046] It should be noted that the present invention is not limited to the above grinding parameters. The conductive backing layer can be ground to a thickness of 0.15~0.3mm, polished to a surface flatness Ra≤0.2μm, and then ultrasonically rinsed and dried to ensure that there is no residual solvent and moisture on the surface.

[0047] S2, Preparation of conductive matching layer 2

[0048] Material ratio: Silver powder and epoxy resin are mixed at a mass ratio of 75:25; wherein the silver powder is highly conductive silver powder with a particle size of 0.5~1μm, and the epoxy resin is EPO-TEK301-2 type high-flow epoxy resin.

[0049] It should be noted that the conductive matching layer of the present invention is not limited to the above-mentioned mixing scheme of silver powder and epoxy resin. In other embodiments, the conductive matching layer can be made by mixing epoxy resin with at least one metal powder selected from tungsten powder, silver powder, and gold powder. Further, the mass ratio of epoxy resin to metal powder can be 5:5 to 9:1, preferably 7:3.

[0050] Molding and curing: Stir the above material at 1200 rpm for 20 minutes; after vacuum degassing for 3 minutes, pour it into the mold with an initial thickness of 6 mm; heat to 100°C at a heating rate of 3°C / min and cure for 1.5 hours.

[0051] Grinding and Testing: Grind to a thickness of 5mm, and test its acoustic impedance as 4.8±0.5 MTayl and volume resistivity as ≤1×10⁻⁶. -2Ω・cm; After passing the test, the surface is thinned to 100μm by grinding with 400#, 1000# and 2000# grinding wheels in sequence, and polished until the surface flatness Ra≤0.1μm. Then, it is placed in isopropanol and deionized water for ultrasonic rinsing in sequence, and then dried at 40-60℃ to ensure that there is no residual solvent and moisture on the surface.

[0052] It should be noted that the present invention is not limited to the above-mentioned grinding parameters. The conductive matching layer can be ground thinned to 1-1.5 times the length of the internal ultrasonic waves at the target ultrasonic frequency, such as 80-150μm at 30MHz. After polishing, the surface flatness Ra≤0.2μm is achieved. Then, ultrasonic rinsing and drying are performed to ensure that there is no residual solvent and moisture on the surface.

[0053] S3. Pre-thinning the piezoelectric ceramic sheet and preparing the first metal electrode.

[0054] Substrate selection: 0.3mm thick PZT-5H piezoelectric ceramic sheet was selected, with a longitudinal piezoelectric strain constant d33=590pC / N. PZT-5H is a typical formulation of lead zirconate titanate series piezoelectric ceramics with high electromechanical coupling and high sensitivity. It belongs to soft piezoelectric ceramics and has advantages such as ultra-high piezoelectric constant and high dielectric constant. However, it has low mechanical strength, weak bending strength and compressive strength, and poor impact resistance. If subjected to excessive mechanical stress during assembly or use, it is prone to cracking and breakage.

[0055] Pre-thinning treatment: Using a precision grinding machine, the piezoelectric ceramic sheet is first ground to a thickness of 0.2mm under a pressure of 5N and a speed of 100rpm, and then polished to a thickness of 0.15mm with a 2000# grinding wheel, with a surface flatness Ra=0.4μm.

[0056] Electrode plating: One side of the piezoelectric ceramic sheet was plasma cleaned at a power of 50W for 30 seconds to remove surface oil. A silver electrode was then plated using magnetron sputtering with a target purity of 99.99%, a sputtering power of 100W, a time of 60 seconds, and an electrode thickness of 100nm. After plating, the electrode was placed in a petri dish for later use. This electrode is the first metal electrode.

[0057] It should be noted that the present invention is not limited to the above-described implementation details. Other metal electrodes, such as gold electrodes and gold-silver hybrid electrodes, can also be prepared by magnetron sputtering or electroplating. Pre-thinning can also reduce the thickness of the piezoelectric ceramic sheet to 0.15~0.20mm, so that its surface flatness Ra=0.3~0.4μm.

[0058] When thinning a single piezoelectric ceramic sheet, cracking is highly likely to occur after thinning to 0.1 mm, leading to thinning failure. This invention only pre-thinns the piezoelectric ceramic sheet within a thickness range less prone to cracking (≥0.1 mm) to obtain a flat surface, facilitating subsequent electrode plating and bonding processes. (Refer to...) Figure 3The single piezoelectric ceramic sheet did not show any surface structure damage when polished to a thickness of 0.15mm. After pre-thinning, the structure was intact and the surface was flat.

[0059] S4, bonded conductive backing layer and piezoelectric ceramic sheet

[0060] Cleaning and activation: The conductive backing layer and the piezoelectric ceramic sheet were ultrasonically cleaned with isopropanol for 10 minutes at 300W and ultrasonically cleaned with deionized water for 5 minutes. They were then dried with hot air at 50℃ to avoid water stains. The two were then placed in an ion cleaning furnace and O2 plasma was introduced at a flow rate of 30sccm. The furnace was treated for 45s at a chamber pressure of 0.2Torr and a radio frequency power of 80W to introduce -OH groups into the surface and improve the wettability of the adhesive layer.

[0061] Bonding adhesive preparation: Esolder3022 epoxy conductive adhesive was used as the bonding adhesive. Its A / B components were mixed at a mass ratio of 100:8 and stirred evenly. Vacuum degassing was performed for 3-5 minutes.

[0062] Precision bonding: Five dots of adhesive are evenly applied to the upper surface of the conductive backing layer using a dispensing machine. The dots are arranged in a regular pentagonal pattern with a spacing of 0.5 mm and a single dot volume of 0.005 μL. The conductive backing layer is fixed on the lower stage of the bonding machine and vacuum adsorption is used. The piezoelectric ceramic sheet electrode surface obtained by S3 is fixed on the upper stage with the lower part facing down. Alignment is achieved using a 40x microscope with an alignment accuracy of ±5 μm. An initial contact force of 0.03 N is applied first, and the diffusion state of the adhesive layer is observed. After alignment is completed, the pressure is gradually increased to 0.4 MPa at a pressure rise rate of 0.05 MPa / s and maintained for 4 seconds to expel interfacial air and form a uniform thin adhesive layer. At the same time, the temperature is heated to 50°C at a heating rate of 2°C / min and held at the same temperature and pressure for 20 minutes. After natural cooling to room temperature, the pressure is released after about 30 minutes. The conductive backing layer-piezoelectric ceramic sheet bonded assembly is obtained. The bonding layer thickness is measured to be 2 μm, and there are no bubbles or delamination.

[0063] It should be noted that the present invention is not limited to the above-described implementation details. During precision bonding, pressure can also be applied to 0.3~0.5MPa, with the pressure rise rate controlled at 0.05~0.1MPa / s, and maintained for 3~5 seconds to expel interfacial air and form a uniform thin adhesive layer. At the same time, the temperature is heated to 35~50℃, with the heating rate controlled at 2~5℃ / min, and the temperature and pressure are maintained for 20~30 minutes. After naturally cooling to room temperature for about 20~30 minutes, the pressure is released, and the conductive backing layer-piezoelectric ceramic sheet bonding assembly is removed. The bonding layer thickness can be controlled to 1~3μm.

[0064] This invention reduces the bubble content of the bonding adhesive by using pure Esolder3022 epoxy conductive adhesive and performing vacuum degassing. Then, by bonding the conductive backing layer and the piezoelectric ceramic sheet with the bonding adhesive under slow pressure, the interfacial air can be further discharged, which helps to reduce the bubble rate of the bonding layer and build a thin, uniform and stable bonding layer, thereby improving the overall stability of the ultrasonic transducer.

[0065] The maximum heat treatment temperature of the piezoelectric ceramic sheet in this invention is only 50°C, which is only 1 / 3 of the high-temperature curing temperature (100-160°C) of the prior art. This can effectively prevent the piezoelectric ceramic sheet from warping, cracking or even breaking at high temperature, and create conditions for its subsequent safe thinning.

[0066] S5, Precision Thin Piezoelectric Ceramic Sheet

[0067] Fixing and supporting: The conductive backing layer side of the conductive backing layer-piezoelectric ceramic sheet bonding assembly prepared by S4 is fixed on a stainless steel grinding jig with paraffin wax, and then the piezoelectric ceramic sheet side of the assembly is placed on the grinding disc with the grinding surface facing.

[0068] Stepwise grinding and thinning: First, use an 800# grinding wheel for coarse grinding, and thin to 90μm under 3N pressure and 50rpm speed, leaving a polishing allowance; during the grinding process, continuously spray an ethanol-water mixture with a volume ratio of 1:1 and cool down; then use a 2000# grinding wheel for fine grinding to 80μm; finally, use a diamond polishing slurry with a particle size of 0.5μm for wet polishing to 67μm. This thickness is 1 / 2 of the ultrasonic wave length inside the piezoelectric ceramic at the target ultrasonic frequency, so that the surface flatness Ra=0.2μm.

[0069] It should be noted that the present invention is not limited to the above-described implementation details. Depending on the target polishing thickness of the piezoelectric ceramic sheet for this component (30-70 μm), the thinning process can be achieved through stepwise grinding. First, coarse grinding with an abrasive wheel can be used to achieve a thickness of 60-90 μm, followed by fine grinding with an abrasive wheel to achieve a thickness of 50-80 μm, and finally wet polishing to the target thickness of 30-70 μm, while maintaining a surface flatness Ra of 0.1-0.2 μm. For example, when the target polishing thickness is 30 μm, grinding can be done first to a thickness of 60 μm, then to a thickness of 50 μm, and finally wet polishing to a thickness of 30 μm; when the target polishing thickness is 50 μm, grinding can be done first to a thickness of 80 μm, then to a thickness of 70 μm, and finally wet polishing to a thickness of 50 μm.

[0070] This invention provides a method for precisely thinning the piezoelectric ceramic sheet in a conductive backing layer-piezoelectric ceramic sheet bonding assembly. Because the conductive backing layer acts as a support, it provides mechanical strength to the fragile piezoelectric ceramic sheet, effectively overcoming its inherent low mechanical strength. This significantly reduces the requirements for the thinning process while ensuring the structural integrity after thinning. Comparative tests show that the success rate of thinning the piezoelectric ceramic sheet in the conductive backing layer-piezoelectric ceramic sheet bonding assembly, i.e., the bonded composite piezoelectric ceramic sheet, is greater than 95%; while the success rate of thinning a single piezoelectric ceramic sheet without bonding under the same conditions is less than 50%. The thickness of the pre-thinned piezoelectric ceramic sheet in this invention is 0.15 mm. Figure 2 (a) The surface is smooth; the thickness of the finely thinned piezoelectric ceramic sheet is 67 μm, as shown in the reference. Figure 2 (b) The structure remains intact and the surface is smooth, with no cracks or defects. (Referencing) Figure 3 (b) The control piezoelectric ceramic sheet began to show wear when thinned to 80 μm. Figure 3 (c) When the thickness was reduced to 70 μm, large-area defects appeared, and the thinning failed.

[0071] This invention thins the piezoelectric ceramic sheet in a conductive backing layer-piezoelectric ceramic sheet bonding assembly. The overall thickness of the assembly enhances the mechanical strength of the piezoelectric ceramic sheet, effectively overcoming the shortcomings of PZT-5H piezoelectric ceramics, such as weak bending and compressive strength, poor impact resistance, and susceptibility to cracking and breakage under excessive mechanical stress during assembly or use. This reduces the requirements for the piezoelectric ceramic sheet thinning process. The thinned conductive backing layer-piezoelectric ceramic sheet bonding assembly exhibits high structural integrity, a smooth and flat surface, and no thinning cracks or defects. This thinning treatment effectively reduces the risk of piezoelectric ceramic sheet breakage, ensuring its mechanical integrity and durability. Furthermore, the step-by-step grinding thinning further reduces potential microscopic defects caused by thinning, minimizing the risk of breakage during subsequent processing and use with the ultrasonic sensor.

[0072] S6. Prepare a second metal electrode on the other side of the piezoelectric ceramic sheet.

[0073] Surface treatment: The exposed surface of the composite piezoelectric ceramic sheet obtained by S5 is cleaned with O2 plasma at a power of 40W for 20s to remove grinding residue.

[0074] Electrode plating: A silver electrode is plated on the other side of the piezoelectric ceramic sheet using magnetron sputtering. The parameters are the same as those for the metal electrode preparation in S3. The electrode covers the entire surface of the piezoelectric ceramic sheet, and the distance between the electrode edge and the conductive backing layer is 0.1 mm to avoid short circuits. This electrode is the second metal electrode.

[0075] S7, bonded conductive matching layer and piezoelectric ceramic sheet

[0076] Cleaning and activation: The conductive matching layer and the conductive backing layer-piezoelectric ceramic sheet assembly obtained in S6 after the preparation of the second metal electrode are processed according to the cleaning and activation parameters in S4.

[0077] Precision bonding: Four dispensing sites were applied to the second metal electrode using a dispensing machine, with the sites arranged in a square pattern. The amount of adhesive applied at each site was 0.003 μL. The alignment accuracy between the conductive matching layer and the piezoelectric ceramic sheet was controlled using a bonding machine to be ±5 μm. An initial contact force of 0.03 N was applied first. After alignment was completed, the pressure was gradually increased to 0.4 MPa and maintained for 4 seconds to expel interfacial air and form a uniform thin adhesive layer. At the same time, the temperature was raised to 50°C and maintained at the same temperature and pressure for 20 minutes. After natural cooling to room temperature, the pressure was released to avoid thermal release that could cause the component to stretch or warp. The sample was then removed, and the bonding layer thickness was measured to be 2 μm.

[0078] Grinding and thinning: The conductive matching layer is ground to a thickness of 17μm using a 1000# grinding wheel. This thickness is 1 / 4 wavelength at the target ultrasonic frequency of 30MHz. The surface is then polished to a flatness of Ra=0.3μm to ensure a thickness error of ±0.5μm.

[0079] It should be noted that the present invention is not limited to the above-described implementation details. In this step, the conductive matching layer can be ground to a thickness of 15~20μm and polished to a surface flatness Ra≤0.3μm; the bonding can also be pressurized to 0.3~0.5MPa, with the pressure rise rate controlled at 0.05~0.10MPa / s, and maintained for 3~5 seconds to expel interfacial air and form a uniform thin adhesive layer. At the same time, it is heated to 40~50℃, with the heating rate controlled at 2~5℃ / min, and held at temperature and pressure for 20~30 minutes; after naturally cooling to room temperature for about 30 minutes, the pressure is released, and the thickness of the bonding layer is controlled at 1~3μm to obtain a conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly.

[0080] Similar to S4, the low-temperature bonding process in this step also avoids damage to the already thinned piezoelectric ceramic sheet caused by high-temperature curing, thus ensuring the integrity of the final component structure.

[0081] S8, Encapsulated conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly

[0082] Pretreatment: The conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly prepared by S7 was ultrasonically cleaned with isopropanol for 5 minutes, ultrasonically cleaned with deionized water for 3 minutes, and dried at 50°C for 20 minutes. With the bottom surface of the conductive backing layer as the bonding surface, it was fixed to a stainless steel sheet with a size of 5 mm × 3 mm and a thickness of 0.1 mm with paraffin wax.

[0083] Plasma treatment: The fixed conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly is placed in an ion cleaning furnace and subjected to low-power O2 plasma treatment. The O2 flow rate is 20 sccm, the chamber pressure is 0.3 Torr, the radio frequency power is 15W, and the treatment time is 40s, which is used to improve the adhesion of the Piriton membrane.

[0084] Pyrelin deposition: A stainless steel sheet is placed in the vacuum chamber of a Pyrelin deposition machine and evacuated to 0.001 Torr. The Pyrelin monomer is heated to 150°C for evaporation and 680°C for pyrolysis. The deposition is carried out at a deposition temperature of 25°C for 30 minutes to form a Pyrelin film with a thickness of 5~8μm, preferably 5μm, on the surface of the conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly.

[0085] The ultrasonic transducer obtained by the above method, as shown in Figure 4, includes: a conductive backing layer 3, a first metal electrode, a piezoelectric ceramic sheet 1, a second metal electrode, a conductive matching layer 2, an encapsulation layer 5, a first bonding layer, and a second bonding layer. The conductive backing layer, the piezoelectric ceramic sheet, and the conductive matching layer are sequentially encapsulated in the encapsulation layer from bottom to top. A first metal electrode is provided between the conductive backing layer and the piezoelectric ceramic sheet, and a second metal electrode is provided between the piezoelectric ceramic sheet and the conductive matching layer. A first bonding layer is provided between the conductive backing layer and the first metal electrode, and a second bonding layer is provided between the conductive matching layer and the second metal electrode.

[0086] The conductive backing layer 3 has a thickness of 0.2~0.3mm, preferably 0.27mm, and is made of epoxy resin mixed with at least one metal powder selected from tungsten powder, silver powder, and gold powder. This thickness design provides sufficient structural support and effectively absorbs reverse acoustic waves without excessively increasing the volume, thus meeting miniaturization requirements. The piezoelectric ceramic sheet 1 has a thickness of 20~70μm, preferably 67μm, and uses PZT-5H type piezoelectric ceramic with d33=590pC / N. This thickness range allows it to operate in the mid-to-high frequency range, balancing detection resolution and depth. The conductive matching layer 2 has a thickness of 15~20μm, preferably 17μm, and is made of epoxy resin mixed with metal powder. This optimized thickness enables acoustic impedance matching between the piezoelectric ceramic sheet and the detection medium, improving signal transmission efficiency. The metal electrode 4 is a magnetron sputtered silver-plated electrode with a thickness of 100nm. This thickness meets conductivity requirements without affecting the vibration performance of the piezoelectric ceramic sheet. The bonding layer 6 has a thickness of 1~3μm and is made of Esolder3022 epoxy conductive adhesive. This ultra-thin bonding layer ensures strong adhesion between adjacent components and efficient electrical signal conduction.

[0087] Performance testing:

[0088] The ultrasonic transducer was subjected to quality inspection: Observation under an optical microscope revealed no bubbles or cracks in the film layer. Its imaging resolution, operating frequency, bandwidth, and other performance characteristics were tested; the results are shown below. Figure 5 and Figure 6 The test results show that the piezoelectric ceramic sheet of sample 1 of this invention has a thickness of 67 μm, an operating frequency of 30 MHz, and an imaging resolution of 45.02 μm. Compared with the prior art, the transducer bandwidth is improved by 19.2%, and the imaging resolution is improved by 16.1%. Sample 2 has a piezoelectric ceramic sheet thickness of 49 μm, an operating frequency of 40 MHz, and an imaging resolution of 37.40 μm. Compared with the prior art, the transducer bandwidth is improved by 7.5%, and the imaging resolution is improved by 30.3%, significantly improving the imaging performance of the ultrasonic transducer.

[0089] In summary, this invention, through its unique process sequence and low-temperature precision bonding technology, has successfully solved long-standing technical problems such as the fragility of thin piezoelectric ceramic sheets, numerous interface defects, and difficulty in thickness control, thus achieving reliable fabrication of high-performance ultrasonic transducers and possessing extremely high industrial application value.

[0090] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method of making an ultrasonic transducer, characterized by, Includes the following steps: Prepare conductive backing layer and conductive matching layer; The piezoelectric ceramic sheet is pre-thinned to a thickness of 0.1~0.2 mm, and a first metal electrode is prepared on one side of the pre-thinned piezoelectric ceramic sheet; A conductive backing layer and a piezoelectric ceramic sheet with a first metal electrode are bonded together using conductive adhesive to obtain a conductive backing layer-piezoelectric ceramic sheet bonding assembly. A first bonding layer is formed between the conductive backing layer and the surface of the piezoelectric ceramic sheet with the first metal electrode, and the thickness of the first bonding layer is 1~3μm. The piezoelectric ceramic sheet of the conductive backing layer-piezoelectric ceramic sheet bonding assembly is thinned so that the thickness of the piezoelectric ceramic sheet is 1 / 2 of the length of the ultrasonic wave inside the piezoelectric ceramic at the target ultrasonic frequency. A second metal electrode is fabricated on the exposed surface of the finely thinned piezoelectric ceramic sheet; A conductive matching layer is bonded to a piezoelectric ceramic sheet with a second metal electrode using conductive adhesive to obtain a conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly. A second bonding layer is formed between the conductive matching layer and the surface of the piezoelectric ceramic sheet with the second metal electrode, and the thickness of the second bonding layer is 1~3μm. The conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly is encapsulated with Pyrelin to obtain an ultrasonic transducer.

2. The method according to claim 1, characterized in that, The process of thinning the piezoelectric ceramic sheet to a thickness of 0.1~0.15mm includes: first grinding the piezoelectric ceramic sheet to a thickness of 0.15~0.20mm, then polishing the piezoelectric ceramic sheet to a thickness of 0.1~0.15mm, and making the surface flatness Ra 0.3~0.4μm.

3. The method according to claim 1, characterized in that, The thinning process includes: first, grinding the piezoelectric ceramic with an 800-1000# grinding wheel to a thickness of 60-90 μm; then, grinding the piezoelectric ceramic sheet with a 2000-2500# grinding wheel to a thickness of 50-80 μm; and finally, wet polishing the piezoelectric ceramic sheet to a thickness of 30-70 μm, with a surface flatness Ra of 0.1-0.2 μm.

4. The method according to claim 1, characterized in that, The conductive adhesive is a vacuum-degassed epoxy conductive adhesive; the bonding parameters are: pressure 0.3~0.5MPa, pressure rise rate 0.05~0.10MPa / s, temperature 35~50℃, heating rate 2~5℃ / min, and holding time 20~30 minutes.

5. The method according to claim 1, characterized in that, The preparation of the conductive matching layer includes: thinning the conductive matching layer, wherein the thickness of the thinned conductive matching layer is 1 to 1.5 times the length of the ultrasonic wave inside the conductive matching layer at the target ultrasonic frequency, and the surface flatness Ra is ≤ 0.2 μm.

6. The method according to claim 1, characterized in that, Before the Piriton is packaged, the surface of the conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly is treated with O2 plasma. The treatment parameters are: O2 flow rate 10~40 sccm, cavity pressure 0.1~0.5 Torr, radio frequency power 5~30W, and treatment time 30~60s.

7. The method according to claim 1, characterized in that, The pyrelin encapsulation includes depositing a pyrelin film on the surface of the conductive backing layer-piezoelectric ceramic sheet-conductive matching layer bonding assembly, wherein the thickness of the pyrelin film is 3~10μm.

8. An ultrasonic transducer, prepared by the method according to any one of claims 1 to 7, comprising a conductive backing layer, a first metal electrode, a piezoelectric ceramic sheet, a second metal electrode, a conductive matching layer, an encapsulation layer, a first bonding layer, and a second bonding layer, wherein the conductive backing layer, the piezoelectric ceramic sheet, and the conductive matching layer are sequentially encapsulated in the encapsulation layer from bottom to top, characterized in that... A first metal electrode is provided between the conductive backing layer and the piezoelectric ceramic sheet, and a second metal electrode is provided between the piezoelectric ceramic sheet and the conductive matching layer. A first bonding layer is provided between the conductive backing layer and the first metal electrode, and a second bonding layer is provided between the conductive matching layer and the second metal electrode.

9. The ultrasonic transducer according to claim 8, characterized in that, The thickness of the first bonding layer and the second bonding layer is 1~2μm, and the thickness of the piezoelectric ceramic sheet is 30~70μm.

10. The ultrasonic transducer according to claim 9, characterized in that, The thickness of the first bonding layer and the second bonding layer is 1 μm, and the thickness of the piezoelectric ceramic sheet is 49 or 67 μm.

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