Surface acoustic wave device

Abstract

The invention relates to a surface acoustic wave device, comprising: a substrate; the first piezoelectric film is arranged on the substrate; the second piezoelectric film is arranged on the first piezoelectric film; the first transducer electrode is arranged on the second piezoelectric film; the second transducer electrode is arranged on the second piezoelectric film and corresponds to the first transducer electrode in position; the crystal orientations of the first piezoelectric film and the second piezoelectric film are different, so that the electromechanical coupling coefficient and the energy flow angle of the surface acoustic wave device in the target acoustic mode are optimal. The surface acoustic wave device provided by the invention can meet the requirements of large bandwidth and low insertion loss at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of micro-electromechanical devices, and in particular to a surface acoustic wave device. Background Art

[0002] The surface acoustic wave delay line is one of the key components of the RF signal processing system. With the continuous development of RF communication technology, the acoustic delay line is required to work at a higher frequency band. In the case of limited reduction in feature size, it is necessary to use a sound wave mode with a higher sound speed. The existing technology will produce greater losses for the following reasons: The acoustic delay line of a traditional single-layer piezoelectric film has a long delay distance and obvious scattering in the length direction of the device. If the energy flow angle PFA is not 0, and there is an angle between the direction of the acoustic energy flow and the direction of the acoustic wave, the acoustic wave emitted by the input transducer may propagate beyond the transducer electrode area when reaching the output end, and cannot be received by the receiving transducer, resulting in additional losses. In the process of propagation of the acoustic wave signal of the traditional single-layer piezoelectric film acoustic delay line in the piezoelectric film, the acoustic energy leaks to the substrate seriously, thus also generating additional losses.

[0003] It can be seen that the delay line of the traditional single-layer piezoelectric film often compromises between the horizontal loss caused by beam deviation and the substrate loss and other losses caused by poor acoustic energy confinement ability, and cannot take both into account. At the same time, in the design of acoustic delay lines, the electromechanical coupling coefficient K 2 The limitation also makes it difficult for the traditional single-layer piezoelectric film delay line to simultaneously meet the requirements of larger bandwidth and lower insertion loss. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a surface acoustic wave device which can simultaneously meet the requirements of a larger bandwidth and a lower insertion loss.

[0005] The technical solution adopted by the present invention to solve the technical problem is: to provide a surface acoustic wave device, including: substrate; A first piezoelectric film is disposed on the substrate; A second piezoelectric film, disposed on the first piezoelectric film; a first transducer electrode, disposed on the second piezoelectric film; a second transducer electrode, disposed on the second piezoelectric film and corresponding to the position of the first transducer electrode; The first piezoelectric film and the second piezoelectric film have different crystal orientations, so that the electromechanical coupling coefficient and the energy flow angle of the surface acoustic wave device in a target acoustic mode are both optimized.

[0006] Furthermore, the crystal orientation angles of the first piezoelectric film and the second piezoelectric film are set to be optimal angles for the electromechanical coupling coefficient and the energy flow angle of the surface acoustic wave device in the target acoustic mode.

[0007] Furthermore, a crystal orientation angle between the first piezoelectric film and the second piezoelectric film is between 50° and 90°, or between 150° and 190°.

[0008] Furthermore, the crystal orientations of the first piezoelectric film and the second piezoelectric film are determined by the following method: Acquiring a crystal orientation that maximizes the electromechanical coupling coefficient of the first piezoelectric film in the target acoustic mode as its initial crystal orientation; Based on the initial crystal orientation, determining a crystal orientation range of the second piezoelectric film that makes the electromechanical coupling coefficient of the surface acoustic wave device in the target acoustic mode greater than a set value, and then calculating the angle range of the crystal orientation between the two piezoelectric films and selecting a plurality of target angles therefrom; For each of the target angles, a curve of the electromechanical coupling coefficient and energy flow angle of the surface acoustic wave device in the target acoustic mode changing with the crystal orientation of the first piezoelectric film is obtained, and then the target angle that optimizes the electromechanical coupling coefficient and energy flow angle is determined as the crystal orientation angle, as well as the crystal orientation of the first piezoelectric film, and the crystal orientation of the second piezoelectric film is calculated.

[0009] Furthermore, the crystal cut type of the first piezoelectric film is -X cut, and the crystal Euler angle is (-25°~-45°, -90°, 90°), and the crystal cut type of the second piezoelectric film is X cut, and the crystal Euler angle is (15°~45°, 90°, 90°); or, the crystal cut type of the first piezoelectric film is -X cut, and the crystal Euler angle is (-165°~5°, -90°, 90°), and the crystal cut type of the second piezoelectric film is X cut, and the crystal Euler angle is (-27.5°~2.5°, 90°, 90°).

[0010] Furthermore, the materials of the first piezoelectric film and the second piezoelectric film include lithium niobate and lithium tantalate.

[0011] Furthermore, a ratio between the sum of the thicknesses of the first piezoelectric film and the second piezoelectric film and the wavelength of the target surface acoustic wave is less than 1.

[0012] Furthermore, a ratio between the thickness of the first piezoelectric film and the thickness of the second piezoelectric film is between 3 / 7 and 7 / 3.

[0013] Furthermore, the first transducer electrode and the second transducer electrode are SPUDT electrodes.

[0014] Furthermore, the material of the first transducer electrode and the second transducer electrode includes aluminum, copper, gold, titanium, nickel, platinum, and molybdenum.

[0015] Furthermore, the material of the substrate includes silicon carbide, diamond, and sapphire.

[0016] Beneficial Effects Due to the adoption of the above-mentioned technical scheme, the present invention has the following advantages and positive effects compared with the prior art: the present invention improves the leakage of acoustic energy by setting two layers of piezoelectric films with different crystal orientations, while ensuring that other performance indicators of the delay line remain basically unchanged, reducing insertion loss and propagation loss, and expanding the use scenarios of the surface acoustic wave delay line; and there is performance improvement for different acoustic modes, and the performance improvement brought by the delay line with relatively high loss by adopting the structure designed by the present invention is greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic cross-sectional structure diagram of an embodiment of the present invention; Figure 2 is a schematic cross-sectional structure diagram of a transducer electrode unit according to an embodiment of the present invention; Figure 3 Schematic diagram of a method for determining a crystal orientation angle between two piezoelectric films in S0 mode according to an embodiment of the present invention; Figure 4 is the K corresponding to different crystal orientation angles of the S0 mode in the embodiment of the present invention 2 and the curve of PFA changing with crystal orientation; Figure 5 is a comparison diagram of insertion loss (IL) and 3-dB bandwidth (3dB-FBW) of a delay line at different ratios of the thickness of a double-layer piezoelectric film in the S0 mode of an embodiment of the present invention and a delay line of a traditional single-layer piezoelectric film; Figure 6 Schematic diagram of a method for determining a crystal orientation angle between two piezoelectric films in an SHO mode according to an embodiment of the present invention; Figure 7 is the K corresponding to different crystal orientation angles of the SHO mode of the embodiment of the present invention 2 and the curve of PFA changing with crystal orientation; Figure 8 is a comparison diagram of insertion loss (IL) and 3-dB bandwidth (3dB-FBW) of a delay line of a conventional single-layer piezoelectric film in a SH0 mode with different ratios of thickness of a double-layer piezoelectric film according to an embodiment of the present invention; Fig. 91 is a comparison diagram of the response and loss of the S0 mode surface acoustic wave delay line of the double-layer piezoelectric film of Example 1 according to the embodiment of the present invention and the S0 mode surface acoustic wave delay line of the single-layer piezoelectric film of Comparative Example 1; Fig.10 This is a comparison diagram of the response and loss of the SH0 mode surface acoustic wave delay line of the double-layer piezoelectric film of Example 2 of the implementation mode of the present invention and the SH0 mode surface acoustic wave delay line of the single-layer piezoelectric film of Comparative Example 2. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0019] An embodiment of the present invention relates to a surface acoustic wave delay line, such as Figure 1 As shown, from bottom to top, there are a supporting substrate 1, a first piezoelectric film 2, a second piezoelectric film 3, a first transducer electrode array 4, and a second transducer electrode array 5.

[0020] Among them, this embodiment mainly discusses the horizontal shear surface acoustic wave SH mode (SH0 mode) or the symmetric Lamb wave S mode (S0 mode), but the embodiments of the present invention are not limited thereto.

[0021] The ratio of the sum of the thickness of the first piezoelectric film 1 and the second piezoelectric film 2 to the wavelength of the excited elastic wave is less than 1, and both are made of lithium niobate or lithium tantalate.

[0022] The supporting substrate is one of silicon carbide, diamond, sapphire and the like.

[0023] The first transducer electrode and the second transducer electrode are made of one or more metal alloys of aluminum, copper, gold, titanium, nickel, platinum, and molybdenum, and adopt a distributed acoustic reflection transducer (DART) or electrode width control transducer (EWC) structural design to achieve unidirectional energy propagation.

[0024] like Figure 2 As shown, the first transducer and the second transducer composed of the ground electrode or the suspended electrode are both single-phase unidirectional transducers (SPUDTs), and the acoustic reflectors constructed therein and arranged asymmetrically relative to the signal electrode realize unidirectional propagation of the signal and reduce the loss.

[0025] The commonly used structures of SPUDT are Figure 2 (a) Distributed Acoustic Reflection Transducer (DART) and Figure 2(b) Electrode width controlled transducer (EWC). Both structures achieve unidirectional propagation by modulating the reflection characteristics by utilizing the asymmetry in the structure. The only difference between the two structures is the width of the electrode.

[0026] The first transducer electrode and the second transducer electrode of DART or EWC are Figure 1 They are located on the left and right sides of the second piezoelectric film and are placed face to face. The distance between the two sets of transducer electrode arrays is the delay distance of the delay line. The electrode on one side is selected as the input transducer, and the electrode on the other side is the output transducer.

[0027] By selecting the target acoustic mode and designing the crystal orientation of the first piezoelectric film and the second piezoelectric film in the acoustic mode, the double-layer piezoelectric film delay line can ensure low horizontal loss while the substrate loss and other losses are also low, thus greatly reducing the overall loss. The specific method is as follows: determining the target acoustic mode; Get the electromechanical coupling coefficient K of the first piezoelectric film in the target acoustic mode 2 The change curve of the crystal orientation is used to determine the electromechanical coupling coefficient K. 2 Maximum crystal orientation; According to the determined crystal orientation, the electromechanical coupling coefficient K of the double-layer piezoelectric film delay line in the same acoustic mode is obtained. 2 The curve of the change of the crystal orientation of the second piezoelectric film is used to determine the electromechanical coupling coefficient K 2 A larger range of crystal orientation values ​​is determined, thereby determining the range of crystal orientation angles between the two layers of piezoelectric films; Select multiple crystal orientation angles to obtain the K values ​​corresponding to different crystal orientation angles. 2 and multiple curves of PFA changing with the crystal orientation of the first piezoelectric film, thereby determining the electromechanical coupling coefficient K 2 The crystal orientation angle of the energy flow angle PFA and the crystal orientation of the first piezoelectric film; The crystal orientation of the second piezoelectric film is calculated according to the crystal orientation of the first piezoelectric film and the angle between the films.

[0028] When determining the crystal orientation, the crystal orientation of the second piezoelectric film may be determined first and then the crystal orientation of the first piezoelectric film may be calculated. Figure 3 As shown, taking the crystal orientation of the second piezoelectric film of the upper layer as an example, further explanation is given for the horizontal shear surface acoustic wave SH mode (SH0 mode) and the symmetric Lamb wave S mode (S0 mode).

[0029] Figure 3 (a) is the electromechanical coupling coefficient K of the S0 mode delay line of a single-layer piezoelectric film 2Curve of change with the crystal orientation of the upper film. Generally speaking, the electromechanical coupling coefficient of the target acoustic mode should be as large as possible. Therefore, if it is a delay line of a single-layer piezoelectric film, the crystal orientation α should be in the range of 25°~45°.

[0030] Figure 3 (b) The electromechanical coupling coefficient K of the double-layer piezoelectric film S0 mode delay line 2 If a double-layer piezoelectric film structure is used and the crystal orientation of the upper film is temporarily set to the angle with the largest electromechanical coupling coefficient (i.e., α_up=35°), and the crystal orientation of the lower film α_down is changed within the range of 0°~360°, then Figure 3 (b) K 2 The curve of the change of the crystal orientation α_down of the lower film. In order to obtain a larger electromechanical coupling coefficient, α_down should be in the range of -25°~-45°. Therefore, the range of the crystal orientation angle β between the double-layer films is 50°~90°.

[0031] Figure 4 In the case of the double-layer piezoelectric film of the present invention, the target acoustic mode is the S0 mode and the crystal orientation angle β is 50°, 70° and 90° respectively, corresponding to the K values ​​of different crystal orientations. 2 And PFA change curve.

[0032] The crystal orientation of the second piezoelectric film is α_up, the crystal orientation of the first piezoelectric film is α_down, and the crystal orientation difference is fixed to β (β=α_up–α_down).

[0033] From the energy loss mechanism of a single-layer delay line, it can be seen that when designing a delay line, the energy flow angle PFA should be kept as close to 0 as possible and the electromechanical coupling coefficient K 2 Larger, combined with different crystal orientation angles K 2 From the PFA curve, we can see that the crystal orientation of the upper film α_up should be in the range of 15°~45° (i.e. Figure 4 Once the crystal orientation and crystal orientation angle of the second piezoelectric film on the upper layer are determined, the crystal orientation α_down of the first piezoelectric film on the lower layer can be calculated (α_down=α_up-β).

[0034] It can be seen that the delay line electromechanical coupling coefficient K of the double-layer piezoelectric film proposed in the present invention is 2 The maximum corresponding crystal orientation is very close to the crystal orientation corresponding to the energy flow angle PFA of 0, which can simultaneously ensure K 2 The delay line K of the traditional single-layer piezoelectric film is 2The crystal orientations with maximum and PFA 0 are quite different, so it is impossible to satisfy K at the same time. 2 Optimal and PFA optimal, the double-layer piezoelectric film delay line of the present invention just avoids such problems.

[0035] Keeping the total thickness of the double-layer piezoelectric film unchanged, by changing the ratio of the thickness of the second piezoelectric film to the total thickness, the performance indicators of the corresponding delay line are also different. The lower the loss of the delay line, the better, while the larger the bandwidth, the better. Therefore, if Figure 5 As shown, in order to obtain a low-loss and wide-bandwidth surface acoustic wave delay line, the thickness of the second piezoelectric film should be in the range of 30% to 70% ( Figure 5 The middle gray area shows that the loss of the S0 mode acoustic delay line based on the double-layer piezoelectric film is greatly reduced, while the bandwidth is improved compared with the S0 mode acoustic delay line based on the single-layer piezoelectric film.

[0036] Figure 6 (a) is the electromechanical coupling coefficient K of the single-layer piezoelectric film SH0 mode delay line 2 The curve changes with the crystal orientation of the upper film. If it is a delay line of a single-layer piezoelectric film, the crystal orientation α should be in the range of -15°~5°.

[0037] Figure 6 (b) The electromechanical coupling coefficient K of the double-layer piezoelectric film SH0 mode delay line 2 If a double-layer piezoelectric film structure is used and the crystal orientation of the upper film is temporarily set to the angle that maximizes the electromechanical coupling coefficient (i.e., α_up=-5°), and the crystal orientation of the lower film α_down is changed within the range of 0°~360°, then Figure 3 (b) K 2 The curve of the change of the crystal orientation α_down of the lower film. In order to obtain a larger electromechanical coupling coefficient, α_down should be in the range of -165°~5°. Therefore, the range of the crystal orientation angle β between the double-layer films is 150°~190°.

[0038] Figure 7 is the K corresponding to different crystal orientations when the target acoustic mode is the SH0 mode and the angle β between the two layers is 150°, 170° and 190° respectively when the double-layer piezoelectric film is used in the present invention. 2 And PFA change curve.

[0039] The crystal orientation of the second piezoelectric film is α_up, the crystal orientation of the first piezoelectric film is α_down, and the angle between the two layers is fixed at β (β=α_up–α_down).

[0040] From the energy loss mechanism of a single-layer delay line, it can be seen that when designing a delay line, the energy flow angle PFA should be kept as close to 0 as possible and the electromechanical coupling coefficient K 2 Larger, combined with different angles K 2 From the PFA curve, we can see that the crystal orientation of the upper film α_up should be in the range of -27.5°~2.5° (i.e. Figure 7 Once the crystal orientation of the second piezoelectric film and the crystal orientation angle between the two layers of piezoelectric films are determined, the crystal orientation α_down of the first piezoelectric film can be calculated (α_down=α_up-β).

[0041] Similar to the S0 mode surface acoustic wave delay line, the SH0 mode delay line of the double-layer piezoelectric film of the present invention can simultaneously meet the K 2 Optimal and PFA Optimal.

[0042] The design concept is the same as that of the S0 mode SAW delay line, such as Figure 8 As shown, in order to obtain a low-loss and wide-bandwidth surface acoustic wave delay line, the thickness of the second piezoelectric film should be in the range of 30% to 70% ( Figure 8 The middle gray area shows that the loss of the SH0 mode delay line based on the double-layer piezoelectric film is greatly reduced, while the bandwidth is improved compared with the SH0 mode delay line based on the single-layer piezoelectric film.

[0043] The present embodiment is further described below through two comparative examples.

[0044] Fig. 9 This is a comparison chart of the response and loss of the S0 mode surface acoustic wave delay line of the double-layer piezoelectric film of Example 1 of the present invention and the S0 mode surface acoustic wave delay line of the single-layer piezoelectric film of Comparative Example 1.

[0045] Embodiment 1: The first piezoelectric film is a single crystal lithium niobate with an X-cut and a crystal orientation of -38° (Euler angles of (-38°, -90°, 90°)), and the second piezoelectric film is a single crystal lithium niobate with an X-cut and a crystal orientation of 32° (Euler angles of (32°, 90°, 90°)). At this time, the first piezoelectric film and the second piezoelectric film are both 300nm thick and have an angle of 70°, and the substrate is silicon carbide. The first transducer electrode and the second transducer electrode are 70nm aluminum, the electrode period is 4.6um, and the DART unidirectional transducer design is adopted.

[0046] Comparative Example 1: An S0 mode solid-state assembled LN / SiC delay line designed with a single-layer X-cut, 600nm thick single-crystal lithium niobate with a crystal orientation of 40° (Euler angles of (40°, 90°, 90°)) as the piezoelectric layer. The design of the electrode and substrate is exactly the same as in Example 1.

[0047] Fig. 9 The figure shows the comparison of S21 parameters, insertion loss and group delay of the S0 mode surface acoustic wave delay line of single and double-layer lithium niobate piezoelectric film with delay distances of 10λ~80λ (λ is the electrode period) in Example 1 and Comparative Example 1.

[0048] Fig. 9 (a) is the simulated S21 parameter curve of comparative example 1. When the delay distance is 10λ, the resonance frequency of the 0th-order Lamb wave (i.e., S0 mode) excited by the structure of comparative example 1 is 1.864 GHz, the 3-dB bandwidth is 4.02%, and the insertion loss (IL) is 7.97 dB.

[0049] Fig. 9 (b) is a simulated S21 parameter curve of Example 1 of the present application. The resonant frequency of the S0 mode excited by the double-layer lithium niobate piezoelectric film structure provided in Example 1 is basically the same as that of the single layer when the delay distance is 10λ, while the 3-dB bandwidth is increased from 4.02% of the single layer to 4.29%, and the insertion loss is reduced from 7.97dB of the single layer to 5.83dB. At other delay distances, the performance of the delay line of Example 1 is also improved to varying degrees compared with that of Comparative Example 1.

[0050] Fig. 9 (c) and Fig. 9 (d) shows the variation of insertion loss IL and group delay with delay distance of comparative example 1 and embodiment 1. The lower the insertion loss, the smaller the attenuation of the signal by the device. Therefore, the lower the insertion loss at the same delay distance, the better. The slope of the curve obtained by fitting the variation of insertion loss with different delay distances is the propagation loss PL. The propagation loss indicates the loss generated by the signal during propagation. The lower the propagation loss, the better.

[0051] It can be seen that the delay line using the rotated double-layer lithium niobate structure has a propagation loss of 1.39dB / mm from 4.82dB / mm of a single layer while the group delay remains basically unchanged, and the passband becomes smoother and more rectangular, the high-frequency stray mode passband is suppressed, and the low-frequency stray mode is reduced. Therefore, in overall comparison, the use of the piezoelectric layer of the rotated double-layer lithium niobate has made a breakthrough in the performance of the acoustic delay line of the LN / SiC solid-state assembly structure.

[0052] Under the premise that the signal delay performance remains unchanged, the insertion loss and propagation loss of the delay line of the present invention are significantly reduced, and the bandwidth is improved.

[0053] Fig.10 This is a comparison diagram of the response and loss of the SH0 mode surface acoustic wave delay line of the double-layer piezoelectric film of Example 2 of the present invention and the SH0 mode surface acoustic wave delay line of the single-layer piezoelectric film of Comparative Example 2.

[0054] Embodiment 2: The first piezoelectric film is a single crystal lithium niobate with an X-cut and a crystal orientation of -182.5° (i.e., 177.5°) (Euler angles of (177.5°, -90°, 90°)), and the second piezoelectric film is a single crystal lithium niobate with an X-cut and a crystal orientation of -12.5° (Euler angles of (-12.5°, 90°, 90°)). At this time, the first piezoelectric film and the second piezoelectric film are both 235nm thick and have an angle of 170°, and the substrate is silicon carbide. The first transducer electrode and the second transducer electrode are 70nm aluminum, the electrode period is 4um, and the DART unidirectional transducer design is adopted.

[0055] Comparative Example 2: A SH0 mode solid-state assembled LN / SiC delay line designed with a single-layer X-cut, -5° crystal orientation (Euler angles of (-5°, 90°, 90°)) 470nm thick single-crystal lithium niobate as the piezoelectric layer. The design of the electrodes and substrate is exactly the same as in Example 2.

[0056] Fig.10 The figure shows the comparison of S21 parameters, insertion loss and group delay of the SH0 mode surface acoustic wave delay line of single and double-layer lithium niobate piezoelectric film with delay distances of 10λ~80λ (λ is the electrode period) in Example 2 and Comparative Example 2.

[0057] Fig.10 (a) is the simulated S21 parameter curve of comparative example 2. When the delay distance is 10λ, the resonance frequency of the 0th-order horizontal shear wave (i.e., SH0 mode) excited by the structure of comparative example 2 is 1.501 GHz, the 3-dB bandwidth is 3.60%, and the insertion loss (IL) is 3.757 dB.

[0058] Fig.10 (b) is a simulated S21 parameter curve of Example 2 of the present application. The resonant frequency of the SH0 mode excited by the double-layer lithium niobate piezoelectric film structure provided in Example 2 is basically the same as that of the single layer when the delay distance is 10λ, while the 3-dB bandwidth is increased from 3.60% of the single layer to 4.19%, and the insertion loss is reduced from 3.757dB of the single layer to 2.635dB. At other delay distances, the performance of the delay line of Example 2 is also improved to varying degrees compared with that of Comparative Example 2.

[0059] Fig.10 (c) and Fig.10 (d) shows the variation of insertion loss IL and group delay of comparative example 2 and embodiment 2 with delay distance.

[0060] It can be seen that the delay line using the rotated double-layer lithium niobate structure has a propagation loss reduced from 0.90dB / mm of a single layer to 0.47dB / mm while the group delay remains basically unchanged, and the passband becomes smoother. Therefore, under the premise of unchanged signal delay performance, the insertion loss and propagation loss of the delay line of the present invention are significantly reduced, and the bandwidth is improved.

Claims

1. A surface acoustic wave device, characterized in that: include: substrate; A first piezoelectric film is disposed on the substrate; A second piezoelectric film, disposed on the first piezoelectric film; a first transducer electrode, disposed on the second piezoelectric film; a second transducer electrode, disposed on the second piezoelectric film and corresponding to the position of the first transducer electrode; The first piezoelectric film and the second piezoelectric film have different crystal orientations, so that the electromechanical coupling coefficient and the energy flow angle of the surface acoustic wave device in a target acoustic mode are both optimized.

2. The method according to claim 1, characterized in that: The crystal orientation angle between the first piezoelectric film and the second piezoelectric film is set to an angle that optimizes the electromechanical coupling coefficient and the energy flow angle of the surface acoustic wave device in a target acoustic mode.

3. The method according to claim 1, characterized in that: The crystal orientation angle between the first piezoelectric film and the second piezoelectric film is between 50° and 90°, or between 150° and 190°.

4. The surface acoustic wave device according to claim 1, characterized in that: The crystal cut type of the first piezoelectric film is -X cut, and the crystal Euler angle is ((-25°~-45°), -90°, 90°), and the crystal cut type of the second piezoelectric film is X cut, and the crystal Euler angle is ((15°~45°), 90°, 90°); or, the crystal cut type of the first piezoelectric film is -X cut, and the crystal Euler angle is ((-165°~5°), -90°, 90°), and the crystal cut type of the second piezoelectric film is X cut, and the crystal Euler angle is ((-27.5°~2.5°), 90°, 90°).

5. The surface acoustic wave device according to claim 1, characterized in that: The materials of the first piezoelectric film and the second piezoelectric film include lithium niobate and lithium tantalate.

6. The surface acoustic wave device according to claim 1, characterized in that: A ratio between a sum of thicknesses of the first piezoelectric film and the second piezoelectric film and a target surface acoustic wave wavelength is less than 1.

7. The surface acoustic wave device according to claim 1, characterized in that: The ratio of the thickness of the first piezoelectric film to the thickness of the second piezoelectric film is between 3 / 7 and 7 / 3.

8. The surface acoustic wave device according to claim 1, characterized in that: The first transducer electrode and the second transducer electrode are SPUDT electrodes.

9. The surface acoustic wave device according to claim 1, characterized in that: The materials of the first transducer electrode and the second transducer electrode include aluminum, copper, gold, titanium, nickel, platinum, and molybdenum.

10. The surface acoustic wave device according to claim 1, characterized in that: The substrate is made of silicon carbide, diamond, and sapphire.

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