High-polarization piezoelectric composite film, preparation method and application thereof

Abstract

The application relates to a high-polarization piezoelectric composite film and a preparation method and application thereof, and belongs to the technical field of filters. The method comprises the following steps: providing a piezoelectric wafer for ion implantation to obtain a piezoelectric wafer implantation sheet; providing a first supporting substrate, depositing a metal film with Au, Al, Cu or Pt after RCA cleaning; performing RCA cleaning on the first supporting substrate and the piezoelectric wafer implantation sheet, bonding the first supporting substrate and the piezoelectric wafer implantation sheet to obtain a bonding body; performing heating annealing on the bonding body to obtain a first supporting substrate containing a thin film layer; applying an electric field to the thin film layer to polarize the thin film layer and obtain a high-polarization piezoelectric film; performing RCA cleaning on a second supporting substrate, bonding the second supporting substrate and the piezoelectric film; and removing the metal film to obtain a high-polarization piezoelectric composite film. The application can prepare a high-polarization, large-area and uniform single-domain hetero-composite piezoelectric wafer, and has important significance for promoting the industrialization of high-performance filters.

Description

Technical Field

[0001] This application relates to a highly polarized piezoelectric composite thin film, its preparation method, and its application, belonging to the field of filter technology. Background Technology

[0002] With the commercialization and widespread adoption of 5G technology, global data traffic has exploded, placing unprecedented demands on the performance of mobile communication terminal radio frequency (RF) front-ends. As a core component of the RF front-end, the market for surface acoustic wave (SAW) filters has experienced rapid growth. To meet the increasing availability of new frequency bands in 5G and future communication standards, the market has imposed more stringent comprehensive requirements on the performance of SAW filters: they must not only be smaller and consume less power, but also possess higher operating frequencies, wider passband bandwidth, greater power capacity, and excellent thermal stability and reliability.

[0003] To address these challenges, industry and research have turned their attention to heterogeneous composite substrates, such as piezoelectric on insulators (POIs), as next-generation acoustic wave devices. Compared to traditional solutions based on piezoelectric single-crystal substrates (such as lithium tantalate or lithium niobate), heterogeneous integration technology can combine high-performance piezoelectric single-crystal thin films with low-loss supporting substrates, theoretically achieving a leap in device performance and giving rise to entirely new acoustic wave operating modes. However, the core bottleneck of this technological path lies in the fabrication and domain engineering control of high-quality piezoelectric single-crystal thin films.

[0004] Currently, the mainstream process for fabricating such heterocomposite substrates is ion beam lift-off technology. While this technology can achieve the transfer of single-crystal thin films, its high-energy ion implantation process introduces a large number of point defects and lattice damage into the piezoelectric material lattice. These implantation defects directly lead to a serious consequence: the "multidomain formation" of the piezoelectric thin film. In an ideal piezoelectric single crystal, all domains should be aligned, which is the basis for obtaining optimal piezoelectric and acoustic performance. Multidomain structures significantly disrupt the electric field distribution and acoustic wave propagation characteristics of the device, leading to a sharp deterioration in performance.

[0005] Traditional methods for repairing damage caused by ion implantation involve high-temperature annealing. However, this repair process itself presents new and more challenging problems. A key characteristic of piezoelectric materials is that their coercive electric field decreases significantly with increasing temperature. This means that in a high-temperature annealing environment, the piezoelectric film is in an "electrically soft state," and its domain structure is extremely unstable. At this point, any minute and unavoidable disturbance to the electric field, such as static electricity within the device cavity, potential differences between substrates, or even the field generated by pyroelectric effects within the material, is sufficient to cause random flipping of the film's domains, leading to the re-formation of a multi-domain structure during annealing, rendering the repair work futile.

[0006] Traditional polarization, with its inherent high breakdown risk and insurmountable uniformity issues, has become a key bottleneck in the manufacturing of advanced acoustic wave filters. Existing technologies cannot meet the requirements of high performance, high consistency, and high reliability for devices in the 5G era. For heterogeneous integrated substrates such as POI with multilayer stacked structures, applying a high-voltage electric field to such a complex structure results in a very complex electric field distribution, which easily leads to breakdown at the interlayer interfaces, making traditional polarization methods difficult to apply.

[0007] Therefore, how to fabricate highly polarized, large-area, and uniform single-domain heterogeneous composite piezoelectric wafers is of great significance for further promoting the industrialization of high-performance filters. Summary of the Invention

[0008] To address the aforementioned issues, this application provides a highly polarized piezoelectric composite thin film, its preparation method, and its applications. The method provided in this application can prepare highly polarized, large-area, and uniform single-domain heterogeneous composite piezoelectric wafers, which is of great significance for promoting the industrialization of high-performance filters.

[0009] This application provides a method for preparing a highly polarizable piezoelectric composite thin film, the method comprising the following steps: 1) Provide a piezoelectric wafer, perform ion implantation to obtain a piezoelectric wafer implantation sheet including a thin film layer, an implantation layer and a residual material layer; 2) Provide a first support substrate, perform RCA cleaning, and then deposit a metal thin film on it; 3) After performing RCA cleaning on the first support substrate and the piezoelectric wafer implantation wafer, the metal layer of the first support substrate is bonded to the thin film layer of the piezoelectric wafer implantation wafer to obtain a bonded body; 4) The bond body is heated and annealed to separate the thin film layer from the residual layer, thereby removing the piezoelectric wafer and obtaining a first support substrate containing the thin film layer; 5) Apply an electric field to the thin film layer to polarize it, thereby obtaining a highly polarized piezoelectric thin film; 6) Provide a second support substrate, perform RCA cleaning, and then bond the second support substrate to the piezoelectric thin film; 7) Remove the metal film to remove the first supporting substrate, thereby obtaining the highly polarized piezoelectric composite film; The metal thin film is made of one or more of Au, Al, Cu, and Pt.

[0010] Optionally, the thickness of the metal thin film is 10~100nm.

[0011] Optionally, step 5) of applying an electric field to polarize the thin film layer includes: using a salt solution to cover the peeled piezoelectric thin film as the upper electrode, the metal thin film as the bottom electrode, applying a high voltage DC electric field of 10~40kV / mm, and a polarization time of 60~1000s.

[0012] Unlike existing metal hard electrode contact polarization processes, the surface of the nanoscale thin film after peeling is rough. If traditional solid electrodes are used, insulating air gaps will form at these rough ripples, which will not only severely weaken the polarization electric field, but may even cause field-induced tip discharge at sharp protrusions and break down the film. However, the solution in this application introduces a conductive salt solution with controlled concentration as the upper electrode. By utilizing the surface tension and fluidity of the liquid, a fully covered micro-nanoscale conformal contact is achieved, which makes the conductive liquid build a flat equipotential surface on the piezoelectric film surface, greatly homogenizing the electric field distribution and eliminating the risk of interlayer electrical breakdown caused by air gaps.

[0013] Optionally, the salt solution is a conductive salt solution with a concentration of 0.1~1.0 mol / L.

[0014] The concentration of the conductive solution directly determines the ionic strength and resistivity of the liquid electrode. This application has conducted experiments and screening on the concentration of the conductive solution used: if the solution concentration is too low, its high resistance characteristics will cause strong Joule heating under high pressure, which will cause the liquid to boil and vaporize, and will also cause the piezoelectric film to undergo secondary depolarization or lattice thermal stress damage due to local overheating; if the solution concentration is too high, under the micro Joule heating generated by polarization high pressure or long-term exposure, solvent evaporation will easily cause salt microcrystals to crystallize on the film surface, and these solid microcrystals will create local electric field distortion points on the equipotential surface, affecting product quality.

[0015] Optionally, the conductive salt solution is an aqueous solution of lithium chloride, a calcium chloride solution, or a mixed solution of potassium nitrate and lithium nitrate.

[0016] This application also verifies a variety of usable conductive salt solutions: lithium chloride aqueous solution can be polarized at room temperature and at medium to high temperatures; saturated calcium dichloride solution is suitable for environments below 400K; and a binary salt mixture of potassium nitrate and lithium nitrate is suitable for high-temperature environments up to 520K, and can maintain sufficient conductivity and stable liquid-phase contact at both room temperature and high temperature.

[0017] Optionally, the salt solution is a saturated aqueous lithium chloride solution.

[0018] Experiments and verifications have revealed significant technical advantages of using lithium chloride aqueous solutions: Unlike traditional hard metal electrodes (such as deposited nickel or chromium, which generate extremely high density of nucleation sites at the contact surface), LiCl aqueous solution electrodes do not induce additional and uncontrollable nucleation sites on the film surface; if the nucleation site density is too low or the distribution is random, it will lead to uneven polarization patterns; while LiCl solution can provide a uniform equipotential surface, which helps to control the smooth movement of domain walls and prevent excessive growth of local domains; compared with sodium chloride (NaCl), lithium chloride (LiCl) solution can provide superior lithium ion concentration (Li... + This increases the mobility of ions, thereby significantly improving the ionic conductivity of the thin film surface. During polarization, ions with high mobility can accumulate more rapidly on the thin film surface, compensating for the depolarization field generated during ferroelectric domain flipping in real time.

[0019] Optionally, step 7) of removing the metal film can be done by chemical etching or mechanical removal.

[0020] Optionally, the ions implanted are one or both of hydrogen ions and helium ions; Optionally, the piezoelectric wafer is made of one or more of lithium niobate, lithium tantalate, lithium tetraborate, lead magnesium niobate-lead titanate, quartz, potassium sodium tartrate, or lanthanum gallium silicate. Optionally, the first and second support substrates are made of one or more of silicon, sapphire, SiO2 / Si composite substrate, SiC, GaN, AlN, and diamond.

[0021] Optionally, the ion implantation energy is 50~500 keV, and the ion implantation dose is 3×10⁻⁶. 15 ~5×10 18 ions / cm 2 .

[0022] Optionally, the piezoelectric wafer, the first supporting substrate, and the second supporting substrate have diameters of 4 to 12 inches and initial thicknesses of 100 to 1000 μm.

[0023] Optionally, the etching of the metal film to separate the piezoelectric film from the first temporary support substrate is performed by immersion in an etching solution. Optionally, heating can be performed during the corrosion process to accelerate the reaction.

[0024] Optionally, the heating temperature is 40~60℃.

[0025] Optionally, the etching solution is a mixture of cerium ammonium nitrate and acetic acid; Optionally, the corrosive solution is a mixture of hydrochloric acid and hydrogen peroxide.

[0026] This application provides a high-polarity piezoelectric composite film obtained by the above-described method for preparing a high-polarity piezoelectric composite film.

[0027] This application provides the application of the aforementioned highly polarized piezoelectric composite thin film in acoustic filters.

[0028] The beneficial effects of this application include, but are not limited to: 1. Based on the high-polarization piezoelectric composite thin film, its preparation method, and its application, this application creatively designs and introduces a 10-100 nm metal thin film as the first supporting bonding layer and temporary bottom electrode. Combined with a conductive solution, the thin film layer can be polarized, thereby enabling the preparation of highly polarized, large-area, and uniform single-domain heterogeneous composite piezoelectric wafers. Furthermore, when applying liquid for polarization, due to the presence of the metal layer, the high-voltage electric field is precisely applied only to the piezoelectric thin film itself, completely confined between the upper and lower electrodes, avoiding outward diffusion that could cause breakdown of the supporting layer. This effectively ensures the safety of the thin film and guarantees the high quality of the prepared product.

[0029] 2. According to the high-polarization piezoelectric composite thin film, its preparation method and application, the entire process can ensure the convenient and rapid preparation of highly polarized, large-area, uniform single-domain heterogeneous composite piezoelectric wafers. The process steps are reasonably designed, and subsequent steps will not affect the polarization product quality. By peeling off the metal thin film as a temporary substrate and polarizing it with liquid, and then restoring it to a perfect "single domain" before transferring it to the final working substrate in a closed-loop process, the polarization process of the high-voltage conductive liquid is completely completed on the temporary carrier. All electric field impacts and micro-stresses are completely physically isolated from the final high-value substrate, thereby greatly improving the overall consistency and yield of the final composite thin film wafer.

[0030] 3. According to the high polarization piezoelectric composite thin film, its preparation method and application, by adopting the conformal liquid polarization method, the breakdown and microscopic non-adhesion problems of traditional solid electrodes can be overcome, making the film polarization uniform. In addition, the salt solution has a large wetting tension on the film, thus exhibiting a very small contact angle, which allows the liquid electrode to completely conform to and fill the micro-nano-scale roughness and undulations on the film surface caused by the peeling process. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of the preparation method of the highly polarized piezoelectric composite thin film involved in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the frequency response involved in Embodiment 1 of this application; Figure 3 This is a schematic diagram of the frequency response involved in Comparative Example 1 of this application.

[0032] List of attached images and labels: 100 piezoelectric wafer; 110 wafer implantation layer; 1101 thin film layer; 1102 implantation layer; 1103 residual material layer; 120 First support substrate; 130 metal layers; 140 Second support layer. Detailed Implementation

[0033] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials and reagents in the embodiments of the present application are all purchased through commercial channels.

[0034] The present application solution will be specifically described below through specific embodiments.

[0035] Example 1 This embodiment provides a method for preparing a highly polarized piezoelectric composite thin film, such as... Figure 1 As shown: 1) H-type process for lithium tantalate piezoelectric single-crystal wafers + Ion implantation, implantation energy 250 keV, dose 4 × 10⁻⁶ 17 ions / cm², to obtain a first wafer implantation wafer that sequentially comprises a thin film layer, an implantation layer and a residual layer; 2) The first support substrate (using Si as a temporary substrate) is subjected to RCA cleaning, and a 50nm high conductivity Pt metal thin film is deposited using CVD process. After the film deposition is completed, chemical mechanical polishing is performed to make its surface roughness less than 1nm. 3) After cleaning the polished metal film, the metal layer on the surface of the first support substrate is directly bonded to the thin film layer of the first wafer implantation wafer to form the first bond. The bonding process is as follows: the surface to be bonded is activated using an Ar ion source for 35 seconds and the bonding is performed at 150°C. 4) The first bond is heated and annealed to peel the wafer along the injection layer to obtain the first support substrate and the piezoelectric single crystal film on its metal layer. The annealing adopts the distributed heating annealing method: heating at 140°C for 8 hours and then heating at 240°C for 6 hours. 5) Using the metal thin film layer on the first supporting substrate as the bottom electrode, a saturated lithium chloride aqueous solution is uniformly covered on the uneven surface of the peeled piezoelectric film as a flexible conformal top electrode; a high-voltage DC electric field of 25 kV / mm is applied for 500 s. At this time, the high-voltage electric field perfectly penetrates the piezoelectric film layer vertically through the liquid, reaching the bottom metal grounding layer, achieving uniform single-domain polarization with full coverage. After polarization, the salt solution is removed by rinsing with deionized water. The specific steps include the following: 5.1) Sample pretreatment: The sample was ultrasonically cleaned with acetone, ethanol and deionized water for 8 min in sequence to remove surface grease and particulate contaminants; 5.2) Solution filtration: After the saturated lithium chloride solution is prepared, it is filtered through a 0.22μm microporous membrane to remove undissolved crystals and impurity particles; 5.3) Conducted in a Class 100 cleanroom, with relative humidity controlled at 50%; 5.4) Polarization process: The voltage increases linearly from zero to the set value, and the liquid thickness is controlled at 20 times the thickness of the piezoelectric film; 5.5) After power off, wait 15 seconds, remove the sample, and rinse it repeatedly with deionized water 3 times; then anneal at 450℃ for 1.5 hours to lock the polarization orientation. 6) The highly polarized piezoelectric thin film is bonded to the second support substrate (SiC). The bonding process is as follows: the surface to be bonded is activated using an Ar ion source for 35 seconds and the bonding is performed at 150°C. The first temporary support substrate and its attached metal film sacrificial layer are removed mechanically. The mechanical method involves mechanical thinning of the first temporary support substrate and the metal film using a 2000-mesh grinding wheel. Finally, the highly polarized piezoelectric composite thin film is obtained.

[0036] Example 2 This embodiment is basically the same as Embodiment 1, except that the material of the metal film is replaced with Au.

[0037] Example 3 This embodiment is basically the same as Embodiment 1, except that the material of the metal film is replaced with Al.

[0038] Example 4 This embodiment is basically the same as Embodiment 1, except that the material of the metal film is replaced with Cu.

[0039] Example 5 This embodiment is basically the same as Embodiment 1, except that the saturated lithium chloride aqueous solution is replaced with a saturated calcium dichloride solution.

[0040] Example 6 This embodiment is basically the same as Example 1, except that the saturated lithium chloride aqueous solution is replaced with a binary salt mixture of potassium nitrate and lithium nitrate, with the potassium nitrate concentration being 0.3 mol / L and the lithium nitrate concentration being 0.2 mol / L.

[0041] Comparative Example 1 In existing fabrication processes that do not involve polarization treatment, the damage caused by ion implantation is not repaired.

[0042] Comparative Example 2 Polarization using a metal hard electrode instead of a non-conductive salt solution presents challenges such as complex processes and low yield.

[0043] Comparative Example 3 The difference between this comparative example and Example 1 is that the saturated lithium chloride aqueous solution is replaced with a saturated sodium chloride aqueous solution.

[0044] Comparative Example 4 The difference between this comparative example and Example 1 is that a high-voltage DC electric field of 8kV / mm was applied and the polarization time was 1500s.

[0045] Comparative Example 5 The difference between this comparative example and Example 1 is that a high-voltage DC electric field of 50kV / mm was applied and the polarization time was 50s.

[0046] Comparative Example 6 The difference between this comparative example and Example 1 is that the thickness of the metal film is 5 nm.

[0047] Comparative Example 7 The difference between this comparative example and Example 1 is that the thickness of the metal film is 120 nm.

[0048] like Figure 2 and Figure 3 The figures show the frequency response diagrams for Example 1 and Comparative Example 1, respectively. According to the results, at the same frequency, the admittance ratio of Example 1 is 75.2 dB, which is significantly higher than the admittance ratio of Comparative Example 1 (66.1 dB) without polarization treatment. The increase in the admittance ratio significantly improves the performance of the device.

[0049] Test Example 1 The researchers tested and compared the products obtained from the preparation processes of the examples and comparative examples, as well as the advantages of the processes. The results are shown in Table 1 below.

[0050] The testing methods include: piezoelectric strain constant : Related to the square of the polarization intensity (P), by measuring the piezoelectric thin film The value thus provides feedback on the magnitude of the polarization intensity. The lower the value, the weaker the polarization intensity; the higher the value, the stronger the polarization intensity. Furthermore, the admittance ratio of the resonator prepared from the piezoelectric composite film was measured. This ratio is the ratio of the admittance maximum to the admittance minimum in the anti-resonance state of the piezoelectric composite film. The piezoelectric constant d... 33 The higher the value, the greater the amplitude of mechanical deformation induced by the electric field, the more significant the difference in admittance between the resonant and non-resonant states, and the higher the admittance ratio. A high admittance ratio is a direct reflection of high-quality polarization effect. The admittance ratio is one of the core indicators for evaluating the polarization effect and device performance of piezoelectric thin films. Its value directly reflects the electroacoustic conversion efficiency of piezoelectric thin films. The lower the value, the smaller the polarization intensity, and the higher the value, the higher the polarization intensity. The product yield of the examples and comparative examples was also statistically analyzed. The number of wafers prepared in each example or comparative example was 100. The product yield of the advanced piezoelectric composite substrate was statistically analyzed. Product yield = 1 - (number of fragments / 100) × 100%.

[0051] The test results are shown in Table 1. Table 1. Test results of the processes in the examples and comparative examples.

[0052] According to the data in Table 1, the piezoelectric strain constants of Examples 1 to 6 are all between 18.3 and 18.9 pm / V, the admittance ratio is between 73.9 and 75.2 dB, and the product yield reaches 92% to 96%. All three indicators are excellent and stable.

[0053] In contrast, the performance of Comparative Examples 1 to 7 was generally low or had obvious defects: the piezoelectric strain constants of Comparative Examples 1, 5, and 7 were only 14.3 to 16.1 pm / V, the admittance ratio was 66.1 to 67.2 dB, and the yield was 72% to 90%; the strain constants (17.1 to 17.6 pm / V) and admittance ratios (68.5 to 69.2 dB) of Comparative Examples 3 and 4 were slightly higher than those of the other comparative examples, but were still significantly lower than those of the examples; in particular, Comparative Example 6 could not be prepared due to process problems.

[0054] Comparative Example 1 did not polarize the prepared thin film, resulting in poor polarization of the piezoelectric thin film, which significantly reduced its piezoelectric strain constant and the admittance ratio of the device. Comparative Example 3, compared to Example 1, used a NaCl salt solution as the upper electrode for polarization. +The migration rate of the piezoelectric ions is lower than that of the metal ions in the examples, thereby reducing the ionic conductivity of the film surface and weakening the polarization effect of the piezoelectric film, resulting in a decrease in its piezoelectric strain constant and the admittance ratio of the device. In Comparative Example 4, the applied electric field strength is relatively small, and the polarization time is relatively increased. The domain orientation dynamics of the piezoelectric material are exponentially dependent on the electric field strength, and it is difficult to compensate for the insufficient electric field by extending the polarization time. The measured piezoelectric strain constant and admittance ratio are reduced. In Comparative Example 5, the applied electric field strength is relatively large, and the polarization time is relatively reduced, leading to dielectric breakdown, depolarization, or thermal stress cracking of the piezoelectric film, which in turn leads to a significant decrease in the measured piezoelectric strain constant and admittance ratio. The yield of the fabricated films decreased significantly. Comparative Example 6 used a thinner metal film, which had a limited effective contact area at the interface when bonding with the piezoelectric film, resulting in a significant decrease in bonding strength. This led to peeling and cracking at the bonding interface, making film fabrication impossible. Comparative Example 7 used a thicker metal film. As the film thickness increased, the thermal stress accumulated during annealing also increased, leading to increased wafer warpage. This resulted in cracking at the bonding interface and breakage of the piezoelectric film. The excessively thick metal left a recast layer or damage layer on the surface of the piezoelectric film after removal, affecting the device performance of the piezoelectric film. Consequently, the measured piezoelectric strain constant and admittance ratio decreased significantly, resulting in a substantial decrease in the fabrication yield.

[0055] Existing technologies for polarization treatment are all aimed at bulk wafers (thickness exceeding 10 cm), employing dual solid electrodes and applying a high-voltage electric field. Currently, no methods have been found to apply an electric field to thin films (thickness at the nm level) to achieve polarization and optimize ion implantation damage. In this application, the inventors, through repeated exploration and research, discovered that simply using dual solid electrode polarization for bulk wafers to polarize thin films results in two problems: firstly, the polarization electric field is severely weakened, potentially leading to field-induced tip discharge at sharp protrusions and causing film breakdown; secondly, the fabrication process is complex and yields low efficiency. Therefore, this application uses a combination of a metal thin film and a conductive salt solution to polarize the thin film, optimizing single-domain damage introduced by ion implantation. Through repeated experiments and verification, it was found that when using a conductive salt solution as an electrode in conjunction with a metal thin film for polarization, the composition and concentration of the conductive salt solution, as well as the applied voltage and polarization time, all affect the polarization effect of the thin film. Finally, after repeated experiments and exploration, an embodiment with excellent results was obtained.

[0056] In summary, the process route adopted in this application is superior to the comparative examples in terms of overall performance in terms of piezoelectric response, electrical properties and manufacturing yield, indicating that it has significant technical advantages and repeatability. No existing technology has found a solution to repair the damage caused by ion implantation in a thin film by using deposited metal thin film in combination with conductive liquid. Therefore, the solution disclosed in this application has important application value and significance.

[0057] The above description is merely an embodiment of this application, and the scope of protection of this application is not limited to these specific embodiments, but is determined by the claims of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the technical concept and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing a highly polarized piezoelectric composite thin film, characterized in that, The preparation method includes the following steps: 1) Provide a piezoelectric wafer, perform ion implantation to obtain a piezoelectric wafer implantation sheet including a thin film layer, an implantation layer and a residual material layer; 2) Provide a first support substrate, perform RCA cleaning, and then deposit a metal thin film on it; 3) After performing RCA cleaning on the first support substrate and the piezoelectric wafer implantation wafer, the metal layer of the first support substrate is bonded to the thin film layer of the piezoelectric wafer implantation wafer to obtain a bonded body; 4) The bond body is heated and annealed to separate the thin film layer from the residual layer, thereby removing the piezoelectric wafer and obtaining a first support substrate containing the thin film layer; 5) Polarizing the thin film layer by applying an electric field, including: using a salt solution to cover the peeled piezoelectric thin film as the upper electrode, the metal thin film as the bottom electrode, applying a high voltage DC electric field of 10~40kV / mm, and a polarization time of 60~1000s to obtain a highly polarized piezoelectric thin film. 6) Provide a second support substrate, perform RCA cleaning, and then bond the second support substrate to the piezoelectric thin film; 7) Remove the metal film to remove the first supporting substrate, thereby obtaining the highly polarized piezoelectric composite film; The metal thin film is made of one or more of Au, Al, Cu, and Pt, and the thickness of the metal thin film is 10~100nm.

2. The method for preparing a highly polarized piezoelectric composite thin film according to claim 1, characterized in that, The salt solution is a conductive salt solution with a concentration of 0.1~1.0 mol / L.

3. The method for preparing a highly polarized piezoelectric composite thin film according to claim 2, characterized in that, The salt solution is a saturated aqueous solution of lithium chloride.

4. The method for preparing a highly polarized piezoelectric composite thin film according to claim 1, characterized in that, Step 7) involves removing the metal film using either chemical etching or mechanical removal methods.

5. The method for preparing a highly polarized piezoelectric composite thin film according to claim 1, characterized in that, The ions implanted are one or both of hydrogen ions and helium ions; and / or, The piezoelectric wafer is made of one or more of lithium niobate, lithium tantalate, lithium tetraborate, lead magnesium niobate-lead titanate, quartz, potassium sodium tartrate, or lanthanum gallium silicate; and / or, The first and second support substrates are made of one or more of the following materials: silicon, sapphire, SiO2 / Si composite substrate, SiC, GaN, AlN, and diamond.

6. The method for preparing a highly polarized piezoelectric composite thin film according to claim 1, characterized in that, The ion implantation energy is 50~500 keV, and the ion implantation dose is 3×10⁻⁶. 15 ~5×10 18 ions / cm 2 .

7. The high-polarization piezoelectric composite film obtained by the preparation method of the high-polarization piezoelectric composite film according to any one of claims 1 to 6.

8. The application of the highly polarized piezoelectric composite thin film as described in claim 7 in acoustic wave filters.

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