Double-layer thin film surface acoustic wave device based on filling type structure and preparation method of double-layer thin film surface acoustic wave device

Abstract

The invention discloses a double-layer film surface acoustic wave device based on a filling type structure and a preparation method thereof. The double-layer film surface acoustic wave device comprises a substrate, a first piezoelectric film layer, a second piezoelectric film layer, a protective layer and an interdigital electrode, wherein the first piezoelectric film layer is superposed on the substrate, and the protective layer is superposed on the first piezoelectric film layer; two grooves are formed by etching the protective layer and the first piezoelectric film layer, and the bottoms of the grooves extend into the first piezoelectric film layer; the second piezoelectric film layer is superposed in the groove, and the thickness of the second piezoelectric film layer is consistent with the depth of the groove; and the interdigital electrode is overlapped on the second piezoelectric film layer, so that the double-layer film surface acoustic wave device with a high electromechanical coupling coefficient is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of MEMS (Micro - Electro - Mechanical System) processing, and particularly relates to a dual - layer thin - film surface acoustic wave device based on an embedding structure and a preparation method thereof. Background Art

[0002] In recent years, portable mobile communication devices have been widely applied in real life, promoting the rapid development of miniaturized devices. Among them, SAW (Surface Acoustic Wave) devices are key devices in the development of miniaturized devices. With the advent of the 5G era, higher requirements are imposed on the frequency, bandwidth, temperature compensation ability, etc. of filters. In addition, the frequency and bandwidth of SAW devices are mainly determined by the sound velocity and electromechanical coupling coefficient of piezoelectric materials. In SAW devices, the electromechanical coupling coefficient is the main parameter for measuring the performance of piezoelectric materials, representing the conversion efficiency between electrical energy and mechanical energy. Therefore, in order to apply SAW devices to more practical scenarios, it is necessary to improve the electromechanical coupling coefficient of the devices.

[0003] Among the piezoelectric thin - film materials of SAW devices, AlN (aluminum nitride) thin films have the advantages of high resistivity, high thermal conductivity, large sound velocity, better thermal stability, and compatibility with CMOS processes. Due to these characteristics, AlN thin films have broad application potential in SAW devices. However, AlN thin films also have obvious disadvantages, that is, their electromechanical coupling coefficient is very small, resulting in a small electromechanical coupling coefficient of SAW devices based on AlN thin films under traditional methods and structures, which limits the further improvement of their performance.

[0004] Therefore, how to provide a surface acoustic wave device with a high electromechanical coupling coefficient has become an important issue. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a dual - layer thin - film surface acoustic wave device based on an embedding structure and a preparation method thereof.

[0006] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0007] In a first aspect, the present invention provides a dual - layer thin - film surface acoustic wave device based on an embedding structure, and the dual - layer thin - film surface acoustic wave device includes:

[0008] A substrate;

[0009] A first piezoelectric thin - film layer stacked on the substrate;

[0010] A protective layer stacked on the first piezoelectric thin - film layer;

[0011] Two grooves; the two grooves are formed by etching the protective layer and the first piezoelectric thin film layer, and the bottom of the groove extends deep into the first piezoelectric thin film layer;

[0012] A second piezoelectric thin film layer stacked in the groove; the thickness of the second piezoelectric thin film layer is consistent with the depth of the groove;

[0013] Interdigital electrodes stacked on the second piezoelectric thin film layer.

[0014] Optionally, the bottom of the groove extends deep into the upper half of the first piezoelectric thin film layer.

[0015] Optionally, the depth range of the groove is 0.6um - 0.8um.

[0016] Optionally, the two grooves are arranged side by side, and the distance between them is consistent with the pitch of the interdigital electrodes.

[0017] Optionally, the material of the substrate is diamond.

[0018] Optionally, the material of the first piezoelectric thin film layer is AlN; the material of the protective layer is SiO2; the material of the second piezoelectric thin film layer is ZnO.

[0019] Optionally, the material of the interdigital electrodes is Al, Mo, Pt or Au.

[0020] Optionally, the thickness range of the substrate is 100μm - 120μm; the thickness range of the first piezoelectric thin film layer is 0.8μm - 1μm; the thickness range of the protective layer is 0.35um - 0.55um; the thickness range of the second piezoelectric thin film layer is 0.6um - 0.8um; the thickness range of the interdigital electrodes is 30nm - 80nm.

[0021] In a second aspect, the present invention provides a method for manufacturing a double-layer thin film surface acoustic wave device based on an embedded structure, the manufacturing method comprising:

[0022] Select a substrate;

[0023] Grow a first piezoelectric thin film layer on the substrate;

[0024] Grow a protective layer on the first piezoelectric thin film layer;

[0025] Using electron beam lithography technology, etch from the upper surface of the protective layer downward to form two grooves extending deep into the first piezoelectric thin film layer;

[0026] Grow a second piezoelectric thin film layer with a thickness consistent with the depth of the groove in the groove;

[0027] The interdigital electrodes are grown on the second piezoelectric thin film layer by an electron beam evaporation coating method.

[0028] Optionally, before growing the first piezoelectric thin film layer on the substrate, the preparation method further includes:

[0029] Processing the substrate by an ion bombardment method.

[0030] In a double-layer thin film surface acoustic wave device based on an embedding structure provided by the present invention, a protective layer stacked on the first piezoelectric thin film layer can suppress the downward dissipation of the surface acoustic wave. By etching the protective layer and the first piezoelectric thin film layer, the bottoms of two grooves penetrate deep into the first piezoelectric thin film layer, and the second piezoelectric thin film layer is stacked in the grooves. This partially embedded structure can enable the surface acoustic wave device to be excited more effectively, thereby improving the energy conversion efficiency of the interdigital transducer and the electromechanical coupling coefficient of the device.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings. Description of the Drawings

[0032] Figure 1 is a cross-sectional view of a double-layer thin film surface acoustic wave device based on an embedding structure provided by an embodiment of the present invention;

[0033] Figure 2 is a Rayleigh mode displacement distribution diagram of a traditional surface acoustic wave device structure at the resonant frequency;

[0034] Figure 3 is a Rayleigh mode displacement distribution diagram of the double-layer thin film surface acoustic wave device provided by an embodiment of the present invention at the resonant frequency;

[0035] Figure 4 is a schematic diagram of the relationship between the groove depth and the ZnO layer thickness and the electromechanical coupling coefficient;

[0036] Figure 5 is a schematic flow diagram of a preparation method of a double-layer thin film surface acoustic wave device based on an embedding structure provided by an embodiment of the present invention.

[0037] Reference numerals: 1, substrate; 2, first piezoelectric thin film layer; 3, protective layer; 4, second piezoelectric thin film layer; 5, interdigital electrodes. Detailed Embodiments

[0038] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0039] To address the technical problem of the relatively small electromechanical coupling coefficient of existing surface acoustic wave devices, an embodiment of the present invention provides a double-layer thin-film surface acoustic wave device based on an embedding structure. Refer to Figure 1 , Figure 1 which is a cross-sectional view of a double-layer thin-film surface acoustic wave device based on an embedding structure provided by an embodiment of the present invention. The double-layer thin-film surface acoustic wave device includes a substrate 1, a first piezoelectric thin-film layer 2, a second piezoelectric thin-film layer 4, a protective layer 3, and interdigital electrodes 5.

[0040] In the embodiment of the present invention, the substrate 1 serves as the support of the device. The material of the substrate 1 can be diamond, and its thickness range can be 100 μm - 120 μm. Diamond has excellent electrical properties, optical properties, and chemical stability. Selecting a diamond substrate can improve the performance and reliability of the device.

[0041] In the embodiment of the present invention, the first piezoelectric thin-film layer 2 is stacked on top of the substrate 1. The first piezoelectric thin-film layer 2 can achieve the conversion between electrical signals and acoustic wave signals through the piezoelectric effect. The first piezoelectric thin-film layer 2 is made of a material with excellent piezoelectric properties. Among them, the material of the first piezoelectric thin-film layer 2 can be AlN, and its thickness range can be 0.8 μm - 1 μm.

[0042] In the embodiment of the present invention, the protective layer 3 is stacked on top of the first piezoelectric thin-film layer 2. The protective layer 3 can function to provide protection for the structure located below it, prevent the structure located below it from being affected by the external environment, and the protective layer 3 can suppress the downward dissipation of surface acoustic waves and increase the temperature stability of the device. The protective layer 3 can be made of an insulating material. Among them, the material of the protective layer 3 can be SiO2 (silicon dioxide), and its thickness range is 0.35 μm - 0.55 μm.

[0043] In the embodiment of the present invention, two grooves are formed by etching the protective layer 3 and the first piezoelectric thin-film layer 2. The bottom of the grooves penetrates into the first piezoelectric thin-film layer 2; the second piezoelectric thin-film layer 4 is stacked in the grooves, and the thickness of the second piezoelectric thin-film layer 4 is the same as the depth of the grooves.

[0044] Similarly, the second piezoelectric thin-film layer 4 can also achieve the conversion between electrical signals and acoustic wave signals through the piezoelectric effect. The second piezoelectric thin-film layer 4 is made of a material with excellent piezoelectric properties. Among them, the material of the second piezoelectric thin-film layer 4 can be ZnO (zinc oxide), and its thickness range is 0.6 μm - 0.8 μm.

[0045] In an embodiment of the present invention, the bottom of the groove extends deep into the first piezoelectric film layer 2, and the second piezoelectric film layer 4 is superimposed in the groove. This partially filled structure can achieve effective regulation of surface acoustic waves while maintaining the overall integrity of the first piezoelectric film layer 2. It can form a stronger charge accumulation and produce a more drastic displacement on the surface of the first piezoelectric film layer 2 and the second piezoelectric film layer 4, so that the surface acoustic wave device can be more effectively excited, thereby improving the energy conversion efficiency of the interdigital transducer and the electromechanical coupling coefficient of the device.

[0046] Furthermore, the bottom of the groove extends deep into the upper half of the first piezoelectric film layer 2. By limiting the bottom of the groove to the upper half of the first piezoelectric film layer 2, interference with the underlying substrate 1 can be avoided, while maximizing the piezoelectric properties of the first piezoelectric film, reducing the energy loss of the surface acoustic wave during propagation, and improving the overall performance and efficiency of the device.

[0047] Specifically, the depth of the groove may range from 0.6 um to 0.8 um.

[0048] In an embodiment of the present invention, the thickness of the second piezoelectric film layer 4 is consistent with the depth of the groove, which can avoid exposing the second piezoelectric film layer 4 directly to the external environment and causing it to be physically damaged, chemically corroded or contaminated. It also helps to maintain the flatness of the device surface, providing a good foundation for subsequent process steps.

[0049] In the embodiment of the present invention, two grooves are arranged in parallel, and the distance between the two grooves is consistent with the spacing between the interdigital electrodes 5 .

[0050] In the embodiment of the present invention, the interdigital electrodes 5 are superimposed on the second piezoelectric film layer 4. The interdigital electrodes 5 are usually made of a highly conductive material, such as Al (aluminum), Mo (molybdenum), Pt (platinum) or Au (gold).

[0051] Specifically, Au is preferably used as the material of the interdigital electrode 5. Au has extremely low resistivity, can effectively reduce energy loss during signal transmission, and also has excellent anti-oxidation and anti-corrosion properties, and can maintain long-term stable electrical properties under complex environmental conditions. In addition, Au also has good ductility and adhesion, and can form a firm interface contact with the second piezoelectric film layer 4, thereby ensuring efficient energy coupling between the electrode and the piezoelectric film.

[0052] In one implementation, the thickness of the interdigital electrode 5 may be 30 nm-80 nm.

[0053] In an embodiment of the present invention, the protective layer 3 superimposed on the first piezoelectric thin film layer 2 can suppress the downward dissipation of surface acoustic waves. By etching the protective layer 3 and the first piezoelectric thin film layer 2, the bottoms of two grooves penetrate deep into the first piezoelectric thin film layer 2, and the second piezoelectric thin film layer 4 is superimposed in the grooves. This partially filled structure can enable the surface acoustic wave device to be excited more effectively, thereby improving the energy conversion efficiency of the interdigital transducer and the electromechanical coupling coefficient of the device.

[0054] See Figure 2 and Figure 3 , Figure 2 is the Rayleigh mode displacement distribution diagram of the traditional surface acoustic wave device structure at the resonant frequency, Figure 3 is the Rayleigh mode displacement distribution diagram of the double-layer thin film surface acoustic wave device provided by the embodiment of the present invention at the resonant frequency. As Figure 2 and Figure 3 shown, most of the energy is confined to the surface of the SAW device and rapidly decreases with depth. The displacement of the double-layer thin film surface acoustic wave device provided by the embodiment of the present invention is more intense, and stronger charge accumulation is more likely to form on the surface. The surface acoustic wave can be excited more effectively, effectively improving the electromechanical coupling coefficient.

[0055] See Figure 4 , Figure 4 is a schematic diagram of the relationship between the groove depth and the ZnO layer thickness and the electromechanical coupling coefficient. When the groove depth and the ZnO layer thickness are preferably 750 nm, the electromechanical coupling coefficient is the highest.

[0056] Based on the same inventive concept, the embodiment of the present invention also provides a preparation method of a double-layer thin film surface acoustic wave device based on a filled-in structure. See Figure 5 , Figure 5 is a schematic flow chart of a preparation method of a double-layer thin film surface acoustic wave device based on a filled-in structure provided by the embodiment of the present invention, which specifically includes the following steps:

[0057] Step S501, select a substrate.

[0058] Prepare substrate 1, and the material of substrate 1 can be diamond. The substrate 1 is cleaned using a standard cleaning process, and the specific process is as follows:

[0059] Fix the substrate 1 on the cleaning rack, and then alternately place it in acetone, ethanol, and deionized water for ultrasonic cleaning for 10 min - 15 min, and the ultrasonic frequency is set to 80 W - 100 W. Then, the substrate 1 after surface ultrasonic cleaning treatment is dried with a nitrogen gun for later use. After the above steps of cleaning, dust, organic impurities, etc. on the sample surface can be removed. Among them, the thickness range of the substrate 1 is 100 μm - 120 μm.

[0060] In one implementation, before growing the first piezoelectric thin film layer 2 on the substrate 1, the preparation method further includes: treating the substrate 1 using an ion bombardment method to remove surface contaminants of the substrate 1. The treatment conditions are: the radio frequency power is 50 W, the argon gas flow rate ranges from 64 sccm, and the duration is 300 s.

[0061] Step S502, grow a first piezoelectric thin film layer on the substrate.

[0062] In the embodiment of the present invention, the first piezoelectric thin film layer 2 can be grown on the substrate 1 by magnetron sputtering. The material of the first piezoelectric thin film layer 2 can be AlN, and the thickness range of the first piezoelectric thin film layer 2 is 0.8 μm - 1 μm. Specifically, an Al target with a purity of 99.9995% is used as the sputtering target for growing the first piezoelectric thin film layer 2, and direct current source sputtering is used for growth. The substrate 1 is placed in the magnetron sputtering chamber. After the vacuum degree reaches the set 1*10 -5 Pa, high-purity N2 (nitrogen) and high-purity Ar with a nitrogen-argon ratio of 1.5:1 are introduced. After the gas flow rate is stable, the sputtering power of the target is set. The Al target power ranges from 120 W to 160 W. After pre-sputtering the Al target, the temperature is raised to 450 °C, and then the AlN thin film material is sputtered. The sputtering duration is 5 h, and the preparation of the first piezoelectric thin film layer 2 is completed.

[0063] Among them, the magnetron sputtering method can be replaced by MOCVD (Metal-organic Chemical Vapor Deposition, metal-organic chemical vapor deposition method) or chemical vapor deposition method.

[0064] Step S503, grow a protective layer on the first piezoelectric thin film layer.

[0065] In the embodiment of the present invention, the protective layer 3 can be grown on the first piezoelectric thin film layer 2 by magnetron sputtering. The material of the protective layer 3 can be SiO2, and the thickness range of the protective layer 3 is 0.35 um - 0.55 um. Specifically, a silicon target is used as the sputtering target for growing the SiO2 thin film, and direct current source sputtering is used for growth. The sample is placed in the magnetron sputtering chamber. After the vacuum degree reaches the set 1*10 -5 Pa, high-purity O2 (oxygen) and high-purity Ar with an oxygen-argon ratio of 1.5:1 are introduced. After the gas flow rate is stable, the sputtering power of the target is set. The silicon target power ranges from 600 W to 700 W. After pre-sputtering the silicon target, the SiO2 layer is sputtered. The sputtering duration is 40 min - 60 min, and the preparation of the protective layer 3 is completed.

[0066] Step S504, using electron beam lithography technology, etch downward from the upper surface of the protective layer to form two grooves that penetrate into the first piezoelectric thin film layer.

[0067] In an embodiment of the present invention, a photoresist is coated on the upper surface of the protective layer 3. Using electron beam lithography technology, a device pattern is obtained on the photoresist. An inductively coupled plasma etching (ICP) process or other etching technology is used for etching to obtain two grooves arranged at intervals and penetrating into the first piezoelectric thin film layer 2. The depth range of the grooves is 0.6 um - 0.8 um.

[0068] Step S505: Grow a second piezoelectric thin film layer with a thickness consistent with the groove depth in the grooves.

[0069] In an embodiment of the present invention, the second piezoelectric thin film layer 4 can be grown by magnetron sputtering. The material of the second piezoelectric thin film layer 4 can be ZnO, and the thickness range of the second piezoelectric thin film layer 4 is 0.6 um - 0.8 um. Specifically, after etching the first piezoelectric thin film layer 2 and the protective layer 3, the second piezoelectric thin film layer 4 is grown in the grooves by magnetron sputtering, and the growth thickness of the second piezoelectric thin film layer 4 is the same as the groove depth. A ZnO ceramic target is used as the sputtering target for growing the second piezoelectric thin film layer 4. The target uses a radio frequency source. After cleaning the etched sample, it is placed in the magnetron sputtering chamber. After the vacuum degree reaches 1*10 -5 Pa, high-purity N2 and high-purity O2 with an argon-oxygen ratio of 1:3 are introduced. After the gas flow rate is stable, the sputtering power of the target is set, and the power range is 130W - 150W. After pre-sputtering the ZnO target, the temperature is raised to 300 °C, and the ZnO thin film is sputtered. The sputtering duration is 3h - 4h, and the preparation of the second piezoelectric thin film layer 4 is completed.

[0070] Step S506: Grow interdigital electrodes on the second piezoelectric thin film layer by electron beam evaporation coating.

[0071] In an embodiment of the present invention, the interdigital electrodes 5 are usually made of highly conductive materials such as Al, Mo, Pt, or Au. The thickness range of the interdigital electrodes 5 is 30 nm - 80 nm. Specifically, by using electron beam evaporation coating, an Au layer is grown on the second piezoelectric thin film layer 4 through an electron beam evaporation platform. The sample is attached to the mask plate and placed in the tray, and then sent into the vacuum reaction chamber, where the pressure is 3*10 -5 Pa, the power is 200W, and the evaporation duration is 2h - 3h to complete the preparation of the interdigital electrodes 5.

[0072] After the electrode deposition is completed, the sample is peeled off through the lift-off technique, and the preparation of the device is completed.

[0073] In the embodiments of the present invention, the manufacturing process involved in the double-layer thin film surface acoustic wave device is simple, the material cost is relatively low, and the manufacturing process is environmentally friendly and safe. The film forming methods such as magnetron sputtering method and electron beam evaporation method involved in the manufacturing method are common methods in the semiconductor CMOS (Complementary Metal Oxide Semiconductor) process, and can be effectively integrated with the existing CMOS process. On the basis of ensuring the excellent performance of the device, the production cost can be effectively reduced, which conforms to the development law of Moore's Law. Moreover, both the first piezoelectric thin film layer 2 and the second piezoelectric thin film layer 4 are compatible with semiconductor process technologies and can be fabricated on various substrates.

[0074] It should be noted that the terms "first", "second", etc. are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances so that the embodiments of the present invention described herein can be implemented in an order different from those illustrated or described herein. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present invention.

[0075] In the description of this specification, the description referring to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0076] Although the present invention has been described in conjunction with various embodiments herein, however, in the process of implementing the claimed invention, those skilled in the art can understand and achieve other variations of the disclosed embodiments by viewing the accompanying drawings and the disclosure. In the description of the present invention, the term "comprising" does not exclude other components or steps, the term "a" or "one" does not exclude a plurality of cases, and the meaning of "a plurality" is two or more unless otherwise specifically defined. In addition, certain measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0077] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0078] In the present invention, unless otherwise clearly defined and limited, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or may also include the first and second features not being in direct contact but being in contact through additional features therebetween. Moreover, the first feature being "above", "over" and "on" the second feature includes the first feature being directly above and obliquely above the second feature, or merely indicating that the horizontal height of the first feature is higher than that of the second feature. The first feature being "below", "beneath" and "under" the second feature includes the first feature being directly below and obliquely below the second feature, or merely indicating that the horizontal height of the first feature is lower than that of the second feature.

[0079] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A double-layer thin-film surface acoustic wave device based on an inserted structure, characterized in that The double-layer thin film surface acoustic wave device includes: a substrate; a first piezoelectric thin film layer stacked on the substrate; a protective layer stacked on the first piezoelectric thin film layer; two grooves; the two grooves are formed by etching the protective layer and the first piezoelectric thin film layer, and the bottom of the groove penetrates into the first piezoelectric thin film layer; a second piezoelectric thin film layer stacked in the groove; the thickness of the second piezoelectric thin film layer is the same as the depth of the groove; interdigital electrodes stacked on the second piezoelectric thin film layer.

2. The double-layer thin film surface acoustic wave device according to claim 1, wherein The bottom of the groove penetrates into the upper half of the first piezoelectric thin film layer.

3. The double-layer thin-film surface acoustic wave device according to claim 1, characterized in that, The depth range of the groove is 0.6um - 0.8um.

4. The double-layer thin film surface acoustic wave device according to claim 1, characterized in that The two grooves are arranged side by side, and the distance between them is the same as the pitch of the interdigital electrodes.

5. The double-layer thin film surface acoustic wave device according to claim 1, characterized in that, The material of the substrate is diamond.

6. The double-layer thin-film surface acoustic wave device according to claim 1, wherein The material of the first piezoelectric thin film layer is AlN; the material of the protective layer is SiO2; the material of the second piezoelectric thin film layer is ZnO.

7. The double-layer thin film surface acoustic wave device according to claim 1, characterized in that, The material of the interdigital electrodes is Al, Mo, Pt or Au.

8. The double-layer thin-film surface acoustic wave device according to claim 1, wherein The thickness range of the substrate is 100μm - 120μm; the thickness range of the first piezoelectric thin film layer is 0.8μm - 1μm; the thickness range of the protective layer is 0.35um - 0.55um; the thickness range of the second piezoelectric thin film layer is 0.6um - 0.8um; the thickness range of the interdigital electrodes is 30nm - 80nm.

9. A preparation method of a double-layer thin film surface acoustic wave device based on an embedded structure, characterized in that, The preparation method includes: selecting a substrate; growing a first piezoelectric thin film layer on the substrate; growing a protective layer on the first piezoelectric thin film layer; using electron beam lithography technology to etch downward from the upper surface of the protective layer to form two grooves penetrating into the first piezoelectric thin film layer; growing a second piezoelectric thin film layer with a thickness the same as the depth of the groove in the groove; growing interdigital electrodes on the second piezoelectric thin film layer by electron beam evaporation coating method.

10. The preparation method according to claim 9, characterized in that, Before growing the first piezoelectric thin film layer on the substrate, the preparation method further includes: processing the substrate by ion bombardment method.

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