Preparation method of internal acoustic reflection layer of piezoelectric material and acoustic filter

Abstract

This invention provides a method for preparing an acoustic reflection layer within a piezoelectric material and an acoustic filter, relating to the field of acoustics. The method for preparing the acoustic reflection layer includes: providing a piezoelectric initial substrate; implanting light elements into the piezoelectric initial substrate through at least one ion implantation to obtain a piezoelectric substrate and an implantation layer located on the surface of the piezoelectric substrate, the implantation layer comprising at least one implantation element-rich layer and at least one implantation surface layer, the at least one implantation element-rich layer and at least one implantation surface layer being alternately arranged, with the implantation surface layer being the layer furthest from the piezoelectric substrate; and annealing the piezoelectric substrate and the implantation layer to obtain the acoustic reflection layer and the piezoelectric functional surface layer. This method not only effectively reduces costs, but also results in an acoustic impedance difference between the obtained acoustic reflection layer and the piezoelectric substrate material that is close to the acoustic impedance difference between the piezoelectric substrate material and air, greatly improving the acoustic reflectivity of the interface and achieving the localization of sound wave energy in the near-surface layer.

Description

Technical Field

[0001] This invention relates to the field of acoustics, specifically to a method for preparing an internal acoustic reflective layer of a piezoelectric material and an acoustic filter. Background Technology

[0002] With the development of new application scenarios relying on wireless communication networks, such as vehicle-to-everything (V2X) and intelligent transportation, human society has placed new demands on radio frequency (RF) filtering modules, including high frequency, large bandwidth, low loss, and good temperature stability. To meet these requirements, filter developers have proposed methods such as piezoelectric on insulator (POI) structures, film bulk acoustic resonators (FBARs), and solid-mounted resonators (SMRs) to design acoustic reflection layers, thereby achieving localization of acoustic wave energy and excitation of resonant modes.

[0003] As can be seen from formulas (1.1) and (1.2), in order to increase the acoustic reflectivity at the interface, the acoustic impedance difference between the two sides of the interface needs to be increased as much as possible.

[0004] Z = ρ·c(1.1) Z is the acoustic characteristic impedance, in Pa·s / m; ρ is the density of the medium, in kg / m³; c is the speed of sound in the medium, in m / s.

[0005]

[0006] Sound intensity reflectivity, The absolute value of sound pressure reflectivity. and The acoustic characteristic impedance of the first and second media is given in Pa·s / m.

[0007] Due to the significant difference in density and sound velocity, solid-gas interfaces can achieve an acoustic reflectivity close to 1, making them the preferred acoustic reflection surface for high-performance filters. For example, the acoustic reflectivity at the AlN-air interface can reach 99.995%. However, while this design approach can achieve localized sound wave energy and resonant modes, the industry has yet to find a low-cost method for inserting acoustic reflection layers. For instance, the fabrication process for FBAR devices requires complex technology and is costly. Summary of the Invention

[0008] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a method for preparing an acoustic reflective layer, which can simply and effectively prepare an acoustic reflective layer with high reflectivity.

[0009] In one aspect of the present invention, a method for preparing an acoustic reflective layer is provided. According to an embodiment of the present invention, the method for preparing an acoustic reflective layer includes: providing a piezoelectric initial substrate; implanting a light element into the piezoelectric initial substrate through at least one ion implantation to obtain a piezoelectric substrate and an implanted layer located on the surface of the piezoelectric substrate, the implanted layer comprising at least one implanted element-rich layer and at least one implanted surface layer, the at least one implanted element-rich layer and the at least one implanted surface layer being alternately arranged, the implanted surface layer being the layer furthest from the piezoelectric substrate; and annealing the piezoelectric substrate and the implanted layer to obtain the acoustic reflective layer and the piezoelectric functional surface layer. Thus, by implanting a light element into the piezoelectric initial substrate through ion implantation and using annealing technology to achieve the diffusion of implanted ions and the growth of bubbles, the acoustic wave energy is localized in the near-surface layer. The above-described preparation method not only effectively reduces costs, but also improves the acoustic impedance difference between the prepared acoustic reflective layer and the piezoelectric substrate material to a level close to the acoustic impedance difference between the piezoelectric substrate material and air, thereby greatly improving the acoustic reflectivity of the interface.

[0010] According to embodiments of the present invention, the light element includes one or more of hydrogen ions, helium ions, nitrogen ions, oxygen ions, fluoride ions, neon ions, and argon ions.

[0011] According to an embodiment of the present invention, the ion implantation energy is 15~1000 keV, and the ion implantation dose is 1×10⁻⁶. 14 ~5×10 17 ions / cm 2 When performing the ion implantation multiple times, the dose and energy of the ion implantation are gradually reduced.

[0012] According to an embodiment of the present invention, the annealing temperature is 80-1400 °C, the annealing time is 0.5-150 h, and the annealing atmosphere is vacuum, air, carbon monoxide, carbon dioxide, oxygen, nitrogen, or an inert gas.

[0013] According to an embodiment of the present invention, the annealing process can be a single annealing or multiple annealing processes.

[0014] According to an embodiment of the present invention, the thickness of the acoustic reflective layer is 1 nanometer to 2 micrometers.

[0015] According to an embodiment of the present invention, the thickness of the piezoelectric functional surface layer is 80 nanometers to 6 micrometers.

[0016] According to embodiments of the present invention, the piezoelectric initial substrate comprises one or more of perovskite-structured compounds, oxides, nitrides, borates, and silicates. Optionally, the perovskite-structured compound comprises one or more of lithium niobate, lithium tantalate, barium titanate, barium tantalate, and sodium niobate; the oxide comprises one or more of zinc oxide and quartz; the nitride comprises one or more of gallium nitride, aluminum nitride, scandium nitride, aluminum gallium nitride, and aluminum scandium nitride; the borate comprises one or more of lithium tetraborate, calcium lanthanum borate, and yttrium calcium borate; and the silicate comprises one or more of gallium lanthanum silicate, gallium tantalum silicate, gallium niobium silicate, yttrium gallium silicate, and lutetium gallium silicate. The thickness of the piezoelectric initial substrate is 100 nanometers to 1000 micrometers.

[0017] In another aspect, the present invention provides an acoustic filter. According to an embodiment of the invention, the acoustic filter is prepared based on the method described above. The acoustic filter includes a piezoelectric substrate, an acoustic reflection layer, a piezoelectric functional surface layer, and a metal electrode arranged sequentially. The acoustic reflection layer includes a piezoelectric material and air bubbles dispersed within the piezoelectric material. Therefore, the acoustic impedance difference between the acoustic reflection layer and the piezoelectric substrate material is close to the level of the acoustic impedance difference between the piezoelectric substrate material and air, which helps to greatly improve the acoustic reflectivity of the interface, thereby improving the performance of the acoustic filter.

[0018] According to an embodiment of the present invention, the acoustic filter includes a surface acoustic wave filter and / or a bulk acoustic wave filter.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of a method for preparing an acoustic reflective layer in one embodiment of the present invention; Figure 2 This is a flowchart illustrating the fabrication process of the acoustic reflector layer in one embodiment of the present invention; Figure 3 This is a flowchart illustrating the fabrication of the acoustic reflector layer in another embodiment of the present invention; Figure 4 This is a schematic diagram of the structure of a surface acoustic wave filter in one embodiment of the present invention; Figure 5 This is a transmission electron microscope image of the acoustic reflection layer test in Example 1; Figure 6 This is a simulated test diagram of the surface acoustic wave filter based on the acoustic reflection layer in Comparative Example 1; Figure 7 This is a simulated test diagram of the surface acoustic wave filter based on the acoustic reflection layer in Example 1. Detailed Implementation

[0021] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0022] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0023] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0024] In one aspect of the invention, a method for preparing an acoustic reflective layer is provided. According to an embodiment of the invention, referring to... Figure 1 , Figure 2 (Single ion implantation) and Figure 3 (Multiple ion implantations) The method for preparing the acoustic reflective layer includes: S100: Provides piezoelectric initial substrate.

[0025] According to some embodiments of the present invention, the material of the piezoelectric initial substrate can be a single crystal, polycrystalline, or other epitaxially grown material on a substrate. In some specific embodiments, the material of the piezoelectric initial substrate includes one or more of perovskite-structured compounds, oxides, nitrides, borates, and silicates. In some specific embodiments, the perovskite-structured compounds include one or more of lithium niobate, lithium tantalate, barium titanate, barium tantalate, and sodium niobate; the oxides include one or more of zinc oxide and quartz; the nitrides include one or more of gallium nitride, aluminum nitride, scandium nitride, aluminum gallium nitride, and aluminum scandium nitride; the borates include one or more of lithium tetraborate, calcium lanthanum borate, and yttrium calcium borate; and the silicates include one or more of gallium lanthanum silicate, gallium tantalum silicate, gallium niobium silicate, yttrium gallium silicate, and lutetium gallium silicate. Therefore, the requirement of preparing acoustic reflection layers from multiple different materials can be met, reducing the application limitations of the preparation method of the present invention.

[0026] According to some embodiments of the present invention, the thickness of the piezoelectric initial substrate is 100 nanometers to 1000 micrometers, such as 100 nanometers, 500 nanometers, 1 micrometer, 5 micrometer, 10 micrometer, 50 micrometer, 100 micrometer, 500 micrometer, 800 micrometer, 1000 micrometer, etc.

[0027] S200: Light elements are implanted into the piezoelectric initial substrate through at least one ion implantation to obtain a piezoelectric substrate 100 and an implanted layer located on the surface of the piezoelectric substrate 100. The implanted layer includes at least one implanted element-rich layer 200 and at least one implanted surface layer 300, which are alternately arranged. The implanted surface layer 300 is the layer furthest from the piezoelectric substrate 100. Figure 2 (Ion implantation sequentially forms only a monolayer of element-rich implanted layer 200 and a monolayer of implanted surface layer 300) and Figure 3 As shown ( Figure 3 (Taking triple ion implantation as an example). Thus, in this step, light elements are implanted onto the surface portion of the piezoelectric initial substrate via ion implantation, thereby forming a piezoelectric substrate (i.e., the portion of the initial substrate not implanted with light elements) and an implantation layer on its surface. The implantation layer includes an implantation element-rich layer 200 and an implantation surface layer 300. The implantation element-rich layer 200 is the main concentrated distribution area of ​​light elements, and the implantation surface layer 300 is the surface portion containing a small amount of residual light elements.

[0028] According to some embodiments of the present invention, with reference to Figure 3 When multiple ion implantations are performed, a multi-layered and alternately arranged implantation element-rich layer 200 and implantation surface layer 300 are formed. After subsequent annealing, a multi-layered and alternately arranged acoustic reflection layer 210 and piezoelectric functional surface layer 310 will also be formed.

[0029] In some embodiments, during multiple ion implantations, the dose and energy of the ion implantation are gradually reduced, so that with each ion implantation, the corresponding implantation element-rich layer 200 and implantation surface layer 300 formed are closer to the surface of the overall structure.

[0030] According to some embodiments of the present invention, the light element includes one or more of hydrogen ions, helium ions, nitrogen ions, oxygen ions, fluoride ions, neon ions, and argon ions. Implantation with the aforementioned light element ions can effectively form bubbles during subsequent annealing, which facilitates the formation of the acoustic reflection layer.

[0031] According to some embodiments of the present invention, the ion implantation energy is 15~1000keV (e.g., 15keV, 20keV, 50keV, 100keV, 200keV, 300keV, 400keV, 500keV, 600keV, 700keV, 800keV, 900keV, 1000keV, etc.), and the ion implantation dose is 1×10⁻⁶. 14 ~5×10 17 ions / cm 2 Therefore, the aforementioned energy and injection dosage can effectively achieve ion injection.

[0032] S300: Annealing is performed on the piezoelectric substrate 100 and the implanted layer to obtain an acoustic reflection layer 210 and a piezoelectric functional surface layer 310. The acoustic reflection layer 210 is located between the piezoelectric substrate 100 and the piezoelectric functional surface layer 310. In this step, reverse gradient diffusion of implanted ions and bubble growth are achieved by using annealing technology. That is, the acoustic reflection layer 210 has bubbles formed by light elements distributed in it. The acoustic reflection layer with these bubbles can reflect sound waves, thereby localizing the sound wave energy in the near-surface layer (i.e., the piezoelectric functional surface layer 310). During the annealing process, the implanted ions migrate to the grain boundaries and large vacancy clusters, and cause bubbles to be generated in the implanted element-rich layer 200, or to grow the bubbles as much as possible, thus obtaining the acoustic reflection layer 210. After annealing, the implanted surface layer 300 forms the piezoelectric functional surface layer 310, effectively realizing electroacoustic coupling.

[0033] In some embodiments, refer to Figure 3 During multiple ion implantations, a multi-layered, alternating layer of implanted element-rich material 200 and implanted surface layer 300 are formed. After subsequent annealing, a multi-layered, alternating acoustic reflection layer 210 and piezoelectric functional surface layer 310 are formed. This can further form a Bragg-like acoustic reflection layer.

[0034] Furthermore, after ion implantation, piezoelectric materials may suffer damage, which can be repaired by annealing.

[0035] The bubbles distributed in the acoustic reflective layer 210 are formed by injected ions. If the injected ions are helium ions, then the bubbles are helium gas.

[0036] According to some embodiments of the present invention, the annealing temperature is 80-1400℃ (e.g., 80℃, 100℃, 200℃, 400℃, 500℃, 600℃, 800℃, 1000℃, 1200℃, 1400℃, etc.), and the annealing time is 0.5-150h (e.g., 0.5h, 1h, 5h, 10h, 20h, 40h, 50h, 80h, 100h, 110h, 120h, 140h, 150h, etc.). Under the above annealing conditions, reverse gradient diffusion of implanted ions and bubble growth are effectively achieved, resulting in an acoustic reflective layer with high acoustic reflectivity, thereby localizing acoustic energy in the near-surface layer. Those skilled in the art can flexibly select the annealing temperature and time according to different piezoelectric materials.

[0037] In some embodiments, the annealing process can be a single annealing or multiple annealing processes, and the annealing time mentioned above is the total annealing time.

[0038] The annealing atmosphere should be a vacuum, air, carbon monoxide, carbon dioxide, oxygen, nitrogen, or an inert gas. This can improve annealing efficiency.

[0039] According to some embodiments of the present invention, the thickness of the acoustic reflective layer is 1 nanometer to 2 micrometers, such as 1 nanometer, 10 nanometer, 50 nanometer, 100 nanometer, 200 nanometer, 400 nanometer, 500 nanometer, 800 nanometer, 1 micrometer, 1.2 micrometer, 1.5 micrometer, 1.8 micrometer, 2 micrometer, etc.

[0040] According to some embodiments of the present invention, the thickness of the piezoelectric functional surface layer is 80 nanometers to 6 micrometers, such as 80 nanometers, 100 nanometers, 200 nanometers, 400 nanometers, 500 nanometers, 800 nanometers, 1 micrometer, 1.5 micrometers, 2 micrometers, 4 micrometers, 5 micrometers, 6 micrometers, etc.

[0041] According to an embodiment of the present invention, light elements are implanted into a piezoelectric initial substrate by ion implantation, and annealing technology is used to achieve diffusion of implanted ions and growth of bubbles, thereby localizing the acoustic energy in the near-surface layer. The above preparation method can not only effectively reduce costs, but also improve the acoustic impedance difference between the prepared acoustic reflection layer and the piezoelectric substrate material to a level close to the acoustic impedance difference between the piezoelectric substrate material and air, thereby greatly improving the acoustic reflectivity of the interface.

[0042] In another aspect, the present invention provides an acoustic filter. According to an embodiment of the invention, this acoustic filter is prepared based on the method described above, referring to… Figure 4 The acoustic filter comprises a piezoelectric substrate 100, an acoustic reflection layer 210, a piezoelectric functional surface layer 310, and a metal electrode 400 arranged sequentially. The acoustic reflection layer 210 includes a piezoelectric material and air bubbles dispersed within the piezoelectric material. Therefore, the acoustic impedance difference between the acoustic reflection layer and the piezoelectric substrate material is close to the level of the acoustic impedance difference between the piezoelectric substrate material and air, which helps to greatly improve the acoustic reflectivity of the interface, thereby enhancing the performance of the acoustic filter.

[0043] In some embodiments, the materials of the metal electrodes include, but are not limited to, conductive metal materials such as aluminum, copper, silver, and titanium.

[0044] In some embodiments, the acoustic filter described above may be a single resonator or an acoustic filter obtained by connecting multiple resonators in series.

[0045] According to some embodiments of the present invention, acoustic filters include surface acoustic wave filters and / or bulk acoustic wave filters.

[0046] According to an embodiment of the present invention, the method for preparing the above-mentioned acoustic filter includes the steps of preparing the acoustic reflection layer (i.e., steps S100, S200 and S300) and preparing the metal electrode 400 on the surface of the piezoelectric functional surface layer 310.

[0047] Example Example 1 Step 1: Provide a piezoelectric single crystal wafer made of lithium niobate with a thickness of 500µm.

[0048] Step 2: Perform a one-time ion implantation of the piezoelectric single crystal wafer using helium ions. The implantation energy is 120 keV, and the ion implantation dose is 5 × 10⁻⁶. 15 ions / cm 2 .

[0049] Step 3: The ion-implanted piezoelectric single crystal wafer is placed in an annealing furnace and subjected to a two-step annealing process in an air atmosphere. The first annealing temperature is 250°C and the annealing time is 15 hours; the second annealing temperature is 450°C and the annealing time is 4 hours, resulting in a piezoelectric substrate, an acoustic reflection layer and a piezoelectric functional surface layer that are sequentially arranged. A metallic aluminum electrode is formed on the surface of the piezoelectric functional layer to obtain a surface acoustic wave (SAW) filter. The SAW filter is then tested using transmission electron microscopy (TEM). Figure 5 As shown, multiple helium bubbles are distributed in the acoustic reflection layer.

[0050] Example 2 Step 1: Provide an epitaxially grown piezoelectric initial substrate, the substrate being a sapphire substrate, the epitaxial piezoelectric material being zinc oxide, the substrate thickness being 550µm, and the epitaxial thickness being 1µm.

[0051] Step 2: Perform a single-stage ion implantation of the piezoelectric initial substrate using helium ions at an implantation energy of 90 keV and an ion implantation dose of 6E15 ions / cm². 2 .

[0052] Step 3: The ion-implanted piezoelectric single crystal wafer is placed in an annealing furnace and subjected to a two-step annealing process in an air atmosphere. The first annealing temperature is 300℃ and the annealing time is 18 hours; the second annealing temperature is 600℃ and the annealing time is 4 hours, to obtain a piezoelectric substrate, an acoustic reflection layer and a piezoelectric functional surface layer arranged sequentially. A metallic aluminum electrode is formed on the surface of the piezoelectric functional layer to obtain a surface acoustic wave filter.

[0053] Example 3 Step 1: Provide a piezoelectric single crystal wafer made of lithium niobate with a thickness of 550µm.

[0054] Step 2: Perform multiple ion implantations on the piezoelectric single crystal wafer using helium ions. The first implantation is at 300 keV, and the ion implantation dose is 7E15 ions / cm. 2 The target depth of the He-rich layer was 900 nm, the second implantation energy was 160 keV, and the ion implantation dose was 6E15 ions / cm². 2 The target depth of the He-rich layer was 600 nm, the energy of the third ion implantation was 60 keV, and the ion implantation dose was 5E15 ions / cm. 2 The target depth of the He-rich layer is 300 nm, forming a Bragg acoustic reflector layer.

[0055] Step 3: The ion-implanted piezoelectric single crystal wafer is placed in an annealing furnace and subjected to a two-step annealing process in an air atmosphere. The first annealing temperature is 250°C and the annealing time is 15 hours; the second annealing temperature is 450°C and the annealing time is 4 hours, resulting in a piezoelectric substrate, an acoustic reflection layer and a piezoelectric functional surface layer that are sequentially arranged. A metallic aluminum electrode is formed on the surface of the piezoelectric functional layer to obtain a surface acoustic wave filter, as shown in the structural diagram below. Figure 3 As shown.

[0056] Comparative Example 1 Piezoelectric single-crystal wafers are directly used as surface acoustic wave filters. The material is lithium niobate with a thickness of 500µm.

[0057] Comparative Example 2 The piezoelectric initial substrate obtained by epitaxial growth is directly used as the surface acoustic wave filter. The substrate is a sapphire substrate, the epitaxial piezoelectric material is zinc oxide, the substrate thickness is 550µm, and the epitaxial thickness is 1µm.

[0058] Comparative Example 3 Piezoelectric single-crystal wafers are directly used as surface acoustic wave filters. The material is lithium niobate with a thickness of 550µm.

[0059] COMSOL simulation tests were performed on the acoustic reflection layers of the surface acoustic wave filters prepared in Examples 1-3 and Comparative Example 1. The simulation test results are shown in Table 1. The admittance ratio data in Table 1 are the differences between the highest and lowest points on the vertical axis of the test graph. The simulation test graph for Comparative Example 1 can be found in [reference needed]. Figure 6 The simulation test diagram of Example 1 can be found here. Figure 7 .

[0060] Table 1

[0061] By comparing Example 1 with Comparative Example 1, Comparative Example 2 with Comparative Example 2, and Comparative Example 3 with Comparative Example 3, it can be seen that the surface acoustic wave filter prepared by the present invention has a high admittance ratio, that is, the corresponding acoustic reflection layer of the surface has a high acoustic reflectivity, which can effectively reflect the acoustic wave energy leaking to the piezoelectric functional surface layer back to the piezoelectric functional surface layer for electro-acoustic coupling, thereby realizing the localization of acoustic wave energy in the piezoelectric functional surface layer and improving the energy utilization rate.

[0062] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0063] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of making an acoustic reflector, characterized by, include: Provide piezoelectric initial substrate; Light elements are implanted into the piezoelectric initial substrate by at least one ion implantation to obtain a piezoelectric substrate and an implantation layer on the surface of the piezoelectric substrate. The implantation layer includes at least one implantation element-rich layer and at least one implantation surface layer, which are alternately arranged. The implantation surface layer is the one furthest from the piezoelectric substrate. Annealing is performed on the piezoelectric substrate and the injection layer to obtain the acoustic reflection layer and the piezoelectric functional surface layer.

2. The method of claim 1, wherein, The light elements include one or more of the following: hydrogen ions, helium ions, nitrogen ions, oxygen ions, fluoride ions, neon ions, and argon ions.

3. The method of claim 1, wherein, The ion implantation energy is 15~1000 keV. The ion implantation dose is 1 x 10 14 5 x 10 17 ions / cm 2 ; As the ion implantation is performed multiple times, the dose and energy of the ion implantation are gradually reduced.

4. The method of claim 1, wherein, The annealing temperature is 80-1400 ℃, and the annealing time is 0.5-150 h. The annealing process is carried out in a vacuum, air, carbon monoxide, carbon dioxide, oxygen, nitrogen, or an inert gas atmosphere.

5. The method of claim 1, wherein, The annealing process can be a single annealing or multiple annealing processes.

6. The method of any one of claims 1-5, wherein, The thickness of the acoustic reflective layer is 1 nanometer to 2 micrometers.

7. The method of any one of claims 1-5, wherein, The thickness of the piezoelectric functional surface layer is 80 nanometers to 6 micrometers.

8. The method of any one of claims 1-5, wherein, The piezoelectric initial substrate includes one or more of perovskite-structured compounds, oxides, nitrides, borates, and silicates. The perovskite structure compound includes one or more of lithium niobate, lithium tantalate, barium titanate, barium tantalate, and sodium niobate; the oxide includes one or more of zinc oxide and quartz; the nitride includes one or more of gallium nitride, aluminum nitride, scandium nitride, aluminum gallium nitride, and aluminum scandium nitride; the borate includes one or more of lithium tetraborate, calcium lanthanum borate, and yttrium calcium borate; the silicate includes one or more of gallium lanthanum silicate, gallium tantalum silicate, gallium niobium silicate, yttrium gallium silicate, and lutetium gallium silicate, and the thickness of the piezoelectric initial substrate is 100 nanometers to 1000 micrometers.

9. An acoustic filter, characterized in that, The acoustic filter is prepared by the method according to any one of claims 1 to 8, comprising a piezoelectric substrate, an acoustic reflection layer, a piezoelectric functional surface layer and a metal electrode arranged sequentially, wherein the acoustic reflection layer comprises a piezoelectric material and bubbles dispersed in the piezoelectric material.

10. The acoustic filter of claim 9, wherein, The acoustic filter includes a surface acoustic wave filter and / or a bulk acoustic wave filter.

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