A structure for suppressing spurious responses of SAW devices

Abstract

The present application provides a structure for suppressing the spurious response of a SAW device, wherein the SAW device comprises a first piezoelectric substrate layer, a second piezoelectric substrate layer, and an IDT layer; wherein the second piezoelectric substrate layer is placed on the first piezoelectric substrate layer, and the IDT layer is placed on the second piezoelectric substrate layer; and the IDT layer is composed of a first electrode and a second electrode. Conventional single-layer longitudinal leakage SAW devices inevitably generate some spurious responses caused by Rayleigh waves and horizontal shear waves during operation, which can easily cause a decrease in the quality factor of the SAW device, and deteriorate the insertion loss and in-band ripple; however, by adopting the structure provided by the present application, by adjusting the Euler angle of the second piezoelectric substrate layer and then comparing the admittance frequency response under different thicknesses of the second piezoelectric substrate layer, a suitable thickness of the second piezoelectric substrate layer is selected, thereby achieving good suppression of the spurious response of the SAW device while maintaining the electromechanical coupling coefficient of the SAW device unchanged.

Description

Technical Field

[0001] The present invention relates to the technical field of surface acoustic wave devices, and more particularly to a structure for suppressing spurious responses of SAW devices. Background Art

[0002] In recent decades, surface acoustic wave (SAW) devices have been favored by the RF front-end market due to their excellent performance and low manufacturing cost. With the popularization and development of 5G technology, higher and more requirements are placed on SAW devices in the RF front-end market, such as high frequency, high bandwidth, high out-of-band suppression and low insertion loss. However, due to the limitations of the interdigital transducer (IDT) process level and the wave velocity of the piezoelectric substrate material of the SAW device itself, traditional SAW devices find it difficult to achieve high electromechanical coupling coefficients at high frequencies. It can be said that the new era of 5G has brought new opportunities and challenges to SAW devices.

[0003] SAW devices made with lithium niobate or lithium tantalate piezoelectric substrates, represented by XY cuts, are longitudinal leaky SAW (LLSAW) devices. Their phase velocity is approximately 1.5-2 times that of traditional SAW devices, far exceeding the wave velocity of SAW devices whose main modes are Rayleigh waves and horizontal shear waves. This provides new ideas for the application of SAW devices in high frequencies. However, longitudinal leaky SAW devices inevitably produce some spurious responses caused by Rayleigh waves and horizontal shear waves during operation. The spurious response generated by horizontal shear waves is particularly large, which has an adverse effect on SAW devices whose main mode is longitudinal leakage waves, easily causing a decrease in the quality factor of the SAW device, and deterioration of insertion loss and in-band ripple. It can be said that spurious responses have seriously restricted the development of SAW devices. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned existing technical problems and proposes a structure for suppressing the stray response of SAW devices: the traditional single-layer piezoelectric substrate SAW device is converted into a double-layer piezoelectric substrate SAW device, and the Euler angle of the second piezoelectric substrate layer is adjusted according to the cutting angle of the first piezoelectric substrate layer, and then the ratio of the thickness of the second piezoelectric substrate layer to the entire piezoelectric substrate layer is adjusted. Finally, by comparing the admittance frequency response under different second piezoelectric substrate layer thicknesses, the appropriate second piezoelectric substrate layer thickness is selected, while achieving good suppression of the SAW device stray response while keeping the electromechanical coupling coefficient of the SAW device unchanged.

[0005] In order to achieve the above object, the specific scheme of the present invention is as follows:

[0006] A SAW device is designed, which includes a first piezoelectric substrate layer, a second piezoelectric substrate layer, and an IDT layer; the second piezoelectric substrate layer is placed on the first piezoelectric substrate layer, and the IDT layer is placed on the second piezoelectric substrate layer; the IDT layer is composed of a first electrode and a second electrode.

[0007] Furthermore, the first piezoelectric substrate layer and the second piezoelectric substrate layer are made of the same material, which may be lithium niobate or lithium tantalate.

[0008] Furthermore, the material of the IDT layer includes Al, Cu or Au, and optionally, the thickness thereof is 0.01*λ, where λ is the period length of the SAW device.

[0009] Furthermore, the first electrode and the second electrode have the same shape, and the distance between the first electrode and the left periodic boundary of the SAW device is the same as the distance between the second electrode and the right periodic boundary of the SAW device.

[0010] Furthermore, the length of the first electrode is d, and the distance between the first electrode and the left periodic boundary of the SAW device is f, wherein the value range of d is 0<d<0.5*λ, and f=λ / 4-d / 2.

[0011] Furthermore, the first electrode is set as the terminal 1V, and the second electrode is set as the ground terminal.

[0012] Furthermore, the first piezoelectric substrate layer is an X-cut material, and the rotation angle of the first piezoelectric substrate layer material is expressed by Euler angles as (α, -90°, 90°), wherein the value range of α is -180°≤α≤0°.

[0013] Furthermore, the second piezoelectric substrate layer is also made of X-shaped cut material, and the rotation angle of the second piezoelectric substrate layer material expressed by Euler angles is (-α, 90°, 90°).

[0014] Furthermore, the sum of the heights of the first piezoelectric substrate layer and the second piezoelectric substrate layer is b. Optionally, b=0.1*λ.

[0015] Furthermore, the height of the second piezoelectric substrate layer is c, and the height of the first piezoelectric substrate layer is bc, wherein the value range of c is 0<c<b.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] With the continuous popularization and development of 5G technology, longitudinal leakage SAW devices made of lithium niobate or lithium tantalate piezoelectric substrates represented by XY cut have a wave speed far exceeding that of traditional SAW devices, which provides new ideas for the application of SAW devices in high frequencies. However, longitudinal leakage SAW devices will inevitably produce some spurious responses caused by Rayleigh waves and horizontal shear waves during operation, especially the spurious responses generated by horizontal shear waves are relatively large, which have an adverse effect on SAW devices whose main mode is longitudinal leakage waves, and easily cause a decrease in the quality factor of SAW devices, and deterioration of insertion loss and in-band ripple, which seriously restricts the development of SAW devices. Therefore, the present invention provides a structure for suppressing the spurious response of SAW devices. The SAW device under this structure can suppress the spurious response better while maintaining the original organic electrical coupling coefficient unchanged, and this structure is relatively simple to implement and will not cause an increase in manufacturing difficulty and cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a quasi-three-dimensional equivalent model diagram of the improved double-layer piezoelectric substrate SAW device under one periodic structure.

[0019] Figure 2 It is a front view of the improved double-layer piezoelectric substrate SAW device in the xz plane.

[0020] Figure 3 It is a side view of the improved double-layer piezoelectric substrate SAW device in the yz plane.

[0021] Figure 4 This is the admittance frequency response diagram of the traditional single-layer lithium niobate piezoelectric substrate SAW device.

[0022] Figure 5 This is a comparison chart of the admittance frequency response of c = 0.1*b and c = 0.2*b under the improved double-layer lithium niobate piezoelectric substrate SAW device.

[0023] Figure 6 This is a comparison chart of the admittance frequency response of c = 0.3*b and c = 0.4*b under the improved double-layer lithium niobate piezoelectric substrate SAW device.

[0024] Figure 7 This is the admittance frequency response diagram of the improved double-layer lithium niobate piezoelectric substrate SAW device with c=0.5*b.

[0025] Figure 8 This is a comparison chart of the admittance frequency response of c = 0.6*b and c = 0.7*b under the improved double-layer lithium niobate piezoelectric substrate SAW device.

[0026] Figure 9 This is a comparison chart of the admittance frequency response of c = 0.8*b and c = 0.9*b under the improved double-layer lithium niobate piezoelectric substrate SAW device.

[0027] Figure 10 This is a comparison chart of the admittance frequency response of a traditional single-layer lithium niobate piezoelectric substrate SAW device and an improved double-layer lithium niobate piezoelectric substrate SAW device under c=0.5*b.

[0028] Figure 11 This is the admittance frequency response diagram of the traditional single-layer lithium tantalate piezoelectric substrate SAW device.

[0029] Figure 12 This is a comparison chart of the admittance frequency response of c = 0.1*b and c = 0.2*b under the improved double-layer lithium tantalate piezoelectric substrate SAW device.

[0030] Figure 13 This is a comparison chart of the admittance frequency response of c = 0.3*b and c = 0.4*b under the improved double-layer lithium tantalate piezoelectric substrate SAW device.

[0031] Figure 14 This is the admittance frequency response diagram of the improved double-layer lithium tantalate piezoelectric substrate SAW device with c=0.5*b.

[0032] Figure 15 This is a comparison chart of the admittance frequency response of c = 0.6*b and c = 0.7*b under the improved double-layer lithium tantalate piezoelectric substrate SAW device.

[0033] Figure 16 This is a comparison chart of the admittance frequency response of c = 0.8*b and c = 0.9*b under the improved double-layer lithium tantalate piezoelectric substrate SAW device.

[0034] Figure 17 This is a comparison chart of the admittance frequency response of a traditional single-layer lithium tantalate piezoelectric substrate SAW device and an improved double-layer lithium tantalate piezoelectric substrate SAW device under c=0.5*b.

[0035] Figure Number:

[0036] 1. First piezoelectric substrate layer; 2. Second piezoelectric substrate layer; 3. IDT layer; 4. First electrode; 5. Second electrode; b. The sum of the heights of the first and second piezoelectric substrate layers; c. The height of the second piezoelectric substrate layer; d. The length of the first electrode; f. The distance between the first electrode and the left periodic boundary of the SAW device. DETAILED DESCRIPTION

[0037] The following is a detailed and clear description of the embodiments of the present invention in conjunction with the accompanying drawings and specific implementation methods of the present invention. The described embodiments are only part of the embodiments included in the present invention.

[0038] The specific implementation scheme of the present invention to solve the above technical problems is as follows:

[0039] A structure that suppresses spurious responses of SAW devices, such as Figure 1-Figure 3 As shown, an improved double-layer piezoelectric substrate SAW device is designed, and the improved double-layer piezoelectric substrate SAW device includes a first piezoelectric substrate layer 1, a second piezoelectric substrate layer 2, and an IDT layer 3; the second piezoelectric substrate layer 2 is placed on the first piezoelectric substrate layer 1, and the IDT layer 3 is placed on the second piezoelectric substrate layer 2; the IDT layer 3 is composed of a first electrode 4 and a second electrode 5; and the first piezoelectric substrate layer 1, the second piezoelectric substrate layer 2, the first electrode 4 and the second electrode 5 are all periodic structures. In the following embodiments, the stretching length in the y direction is 0.5um, so it is necessary to set periodic boundary conditions on both sides of the yz plane and the xz plane respectively.

[0040] Furthermore, the first piezoelectric substrate layer 1 and the second piezoelectric substrate layer 2 are made of the same material, which may be lithium niobate or lithium tantalate.

[0041] Furthermore, the material of the IDT layer 3 includes Al, Cu or Au. Optionally, the thickness thereof is 0.01*λ, where λ is the period length of the SAW device. In the following embodiments, λ is 10 μm.

[0042] Furthermore, the first electrode 4 and the second electrode 5 have the same shape, and the distance between the first electrode 4 and the left periodic boundary of the SAW device is the same as the distance between the second electrode 5 and the right periodic boundary of the SAW device.

[0043] Furthermore, the length of the first electrode 4 is d, and the distance between the first electrode 4 and the left periodic boundary of the SAW device is f, wherein the value range of d is 0<d<0.5*λ, and f=λ / 4-d / 2.

[0044] Furthermore, the first electrode 4 is configured as a terminal 1V, and the second electrode 5 is configured as a ground terminal.

[0045] Furthermore, the first piezoelectric substrate layer 1 is an X-shaped cut material, and its rotation angle is expressed as (α, -90°, 90°) using Euler angles, where the value range of α is -180°≤α≤0°.

[0046] Furthermore, the second piezoelectric substrate layer 2 is also made of X-shaped cut material, and its rotation angle is (-α, 90°, 90°) expressed by Euler angles.

[0047] Furthermore, the sum of the heights of the first piezoelectric substrate layer 1 and the second piezoelectric substrate layer 2 is b. Optionally, b=0.1*λ.

[0048] Furthermore, the height of the second piezoelectric substrate layer 2 is c, and the height of the first piezoelectric substrate layer 1 is bc, wherein the value range of c is 0<c<b.

[0049] Example 1:

[0050] Figure 4 This is the admittance frequency response diagram of the traditional single-layer lithium niobate piezoelectric substrate SAW device. Figure 5-Figure 9 This is the admittance frequency response diagram of the improved double-layer lithium niobate piezoelectric substrate layer SAW device under different second substrate layer thicknesses, wherein the Euler angle of the piezoelectric substrate in the traditional single-layer lithium niobate SAW device is the same as the Euler angle of the first piezoelectric substrate layer 1 in the improved double-layer lithium niobate SAW device, the height of the piezoelectric substrate in the traditional single-layer lithium niobate SAW device is the same as the sum of the heights of the first piezoelectric substrate layer 1 and the second piezoelectric substrate layer 2, and all other settings are the same as those of the improved double-layer lithium niobate piezoelectric substrate layer SAW device, wherein the first piezoelectric substrate layer 1 in the improved double-layer lithium niobate SAW device is X-20° Y-cut lithium niobate, expressed in Euler angles as (-160°, -90°, 90°), that is, α = -160°.

[0051] Furthermore, if Figure 4 As shown in the figure, the conventional single-layer lithium niobate piezoelectric substrate layer has a spurious response caused by horizontal shear waves near the resonance frequency, and a spurious response caused by Rayleigh waves near the anti-resonance frequency.

[0052] Furthermore, if Figure 5-Figure 9As shown in the figure: in the improved double-layer lithium niobate piezoelectric substrate layer SAW device, as the height c of the second piezoelectric substrate layer 2 increases, its spurious response first decreases and then increases. More specifically, when the height c of the second piezoelectric substrate layer 2 is in the range of 0.1*b≤c≤0.5*b, its spurious response gradually decreases; when the height c of the second piezoelectric substrate layer 2 is in the range of 0.5*b<c≤0.9*b, its spurious response gradually increases again, and when the height c of the second piezoelectric substrate layer 2 is 0.5*b, that is, when the height of the second piezoelectric substrate layer 2 is 1:1 with the height of the first piezoelectric substrate layer 1, its spurious response is well suppressed. The reason is that the spurious response appearing near the frequency below the resonant frequency is the spurious mode caused by the horizontal shear wave, and the spurious response appearing near the frequency above the anti-resonant frequency is the spurious mode caused by the Rayleigh wave; and the electromechanical coupling coefficient of each wave is directly related to the coupling matrix of the material. For example: in the present embodiment, the main mode is the longitudinal leakage wave, and its electromechanical coupling coefficient is directly related to e11 in the coupling matrix, the electromechanical coupling coefficient of the horizontal shear wave is directly related to e16 in the coupling matrix, and the electromechanical coupling coefficient of the Rayleigh wave is directly related to e34 in the coupling matrix, where the coupling matrix is a matrix of 3 rows and 6 columns, and e11, e16 and e34 represent the element values of the first row and first column, the element values of the first row and sixth column, and the element values of the third row and fourth column in the coupling matrix, respectively. The coupling matrix of the second piezoelectric substrate layer 2 with the Euler angle of (-α, 90°, 90°) keeps the e11 in the coupling matrix of the first piezoelectric substrate layer 1 unchanged, and changes the e34 and e16 in the coupling matrix of the first piezoelectric substrate layer 1 to values of equal magnitude and opposite signs. Therefore, when the height c of the second piezoelectric substrate layer 2 continues to increase, the electromechanical coupling coefficient of the longitudinal leakage wave affected by e11 remains basically unchanged, and the e34 and e16 in the coupling matrix of the first piezoelectric substrate layer 1, which are equal in magnitude and opposite in sign, remain unchanged. e16 will continuously correct the horizontal shear wave and Rayleigh wave when 0.1*b≤c≤0.5*b, resulting in a continuously decreasing spurious response. In particular, when the height ratio of the second piezoelectric substrate layer 2 to the first piezoelectric substrate layer 1 is 1:1, e34 and e16 in the two layers are in the most balanced state, and the spurious suppression effect is the best; when 0.5*b<c≤0.9*b, e34 and e16 in the second piezoelectric substrate layer 2 dominate, causing the spurious response to increase again.

[0053] Furthermore, Figure 10 This is a comparison chart of the admittance frequency response of the traditional single-layer lithium niobate piezoelectric substrate SAW device and the improved double-layer lithium niobate piezoelectric substrate SAW device under c=0.5*b. It can be found that the admittance frequency response of the improved double-layer lithium niobate piezoelectric substrate SAW device is smoother and smoother. When the height of the second piezoelectric substrate layer is c=0.5*b, the spurious responses caused by horizontal shear waves and Rayleigh waves are well suppressed, and its electromechanical coupling coefficient remains unchanged.

[0054] Example 2:

[0055] Figure 11 This is the admittance frequency response diagram of the traditional single-layer lithium tantalate piezoelectric substrate SAW device. Figure 12-16 This is the admittance frequency response diagram of the improved double-layer lithium tantalate piezoelectric substrate layer SAW device under different thicknesses of the second substrate layer 2, wherein the Euler angle of the piezoelectric substrate in the traditional single-layer lithium tantalate SAW device is the same as the Euler angle of the first piezoelectric substrate layer 1 in the improved double-layer lithium tantalate SAW device, the height of the piezoelectric substrate in the traditional single-layer lithium tantalate SAW device is the same as the sum of the heights of the first piezoelectric substrate layer 1 and the second piezoelectric substrate layer 2, and all other settings are the same as the settings of the improved double-layer lithium tantalate piezoelectric substrate layer SAW device. The piezoelectric substrate material of the improved double-layer piezoelectric substrate layer SAW device in Example 2 is lithium tantalate, and the material of the first piezoelectric substrate layer 1 is X-31° Y-cut lithium tantalate, expressed in Euler angles as (-149°, -90°, 90°), that is, α = -149°.

[0056] Furthermore, if Figure 12-16 As shown in the figure, in the improved double-layer lithium tantalate piezoelectric substrate layer SAW device, as the height c of the second piezoelectric substrate layer 2 increases, its spurious response shows the same rule as in Example 1: when the height c of the second piezoelectric substrate layer 2 is in the range of 0.1*b≤c≤0.5*b, its spurious response gradually decreases; when the height c of the second piezoelectric substrate layer 2 is in the range of 0.5*b<c≤0.9*b, its spurious response gradually increases, and when the height c of the second piezoelectric substrate layer 2 is 0.5*b, that is, when the height c of the first piezoelectric substrate layer 1 is 1:1, its spurious response is well suppressed.

[0057] Furthermore, Figure 17 This is a comparison chart of the admittance frequency response of the traditional single-layer lithium tantalate piezoelectric substrate SAW device and the improved double-layer lithium tantalate piezoelectric substrate SAW device under c=0.5*b. It can be found that the admittance frequency response of the improved double-layer lithium niobate piezoelectric substrate SAW device is smoother and smoother. When the height of the second piezoelectric substrate layer 2 is c=0.5*b, the spurious responses caused by horizontal shear waves and Rayleigh waves are well suppressed, and its electromechanical coupling coefficient remains unchanged.

[0058] Furthermore, in combination with the above two embodiments, the present invention provides a structure for suppressing the spurious response of the SAW device. By changing the original single-layer piezoelectric substrate layer SAW device into a double-layer piezoelectric substrate layer SAW device, the Euler angle of the second piezoelectric substrate layer 2 is changed accordingly according to the Euler angle of the original single-layer SAW device, and the admittance frequency response of the second substrate layer 2 at different thicknesses is analyzed, and finally the appropriate height of the second piezoelectric substrate layer 2 is selected, which can better suppress the stray response while keeping the original organic electrical coupling coefficient unchanged.

[0059] The embodiments described above should be understood as specific descriptions of the present invention and are not intended to limit the specific scope of protection of the present invention. After reading the contents of the present invention, it will be apparent to those skilled in the art that various changes and modifications may be made to the present invention. Any changes, modifications, substitutions, combinations, simplifications, improvements, etc. made within the spirit and principles of the present invention shall be deemed to be equivalent replacement methods and shall be included in the scope of protection of the present invention.

Claims

1. A structure for suppressing spurious responses of a SAW device, characterized in that: A SAW device is designed, which includes a first piezoelectric substrate layer, a second piezoelectric substrate layer, and an IDT layer; the rotation angle of the first piezoelectric substrate layer material expressed by Euler angles is (α, -90°, 90°), and the value range of α is -180°≤α≤0°; the second piezoelectric substrate layer is placed on the first piezoelectric substrate layer, and the rotation angle of the second piezoelectric substrate layer material expressed by Euler angles is (-α, 90°, 90°); the IDT layer is placed on the second piezoelectric substrate layer; the IDT layer is composed of a first electrode and a second electrode; the sum of the heights of the first piezoelectric substrate layer and the second piezoelectric substrate layer is b, and the height of the second piezoelectric substrate layer is c, wherein the value range of c is 0<c<b.

2. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: The first piezoelectric substrate layer and the second piezoelectric substrate layer are made of the same material, which can be lithium niobate or lithium tantalate.

3. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: The first piezoelectric substrate layer and the second piezoelectric substrate layer are both made of X-shaped cut materials.

4. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: b=0.1*λ, where λ is the period length of the SAW device.

5. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: c and b satisfy: c=0.5b; the height of the first piezoelectric substrate layer is bc.

6. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: The materials of the first electrode and the second electrode may be Al, Cu or Au.

7. The structure for suppressing spurious response of a SAW device according to claim 1, characterized in that: The first electrode and the second electrode have the same shape, and a distance between the first electrode and the left periodic boundary of the SAW device is the same as a distance between the second electrode and the right periodic boundary of the SAW device.

8. The structure for suppressing spurious response of a SAW device according to claim 4, characterized in that: The length of the first electrode is d, and the distance between the first electrode and the left periodic boundary of the SAW device is f, wherein the value range of d is 0<d<0.5*λ, and f=λ / 4-d / 2.

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