A resonant structure capable of suppressing spurious responses of multilayer SAW devices

Abstract

The present application provides a resonant structure that suppresses the spurious response of multilayer SAW devices. The multilayer SAW device combines the advantages of traditional SAW and BAW devices. It can flexibly change the material and thickness ratio between different layers to maintain a large bandwidth at high frequencies, thereby meeting the demand for filtering devices in the 5G era. However, when the multilayer SAW device is working, it is easy to produce spurious responses near its resonant frequency. These spurious responses will cause the deterioration of the device insertion loss and in-band ripple, and the reduction of the electromechanical coupling coefficient and quality factor. The present application performs partial through-hole processing on the temperature compensation layer in the multilayer SAW device, and finally selects the appropriate through-hole length under different through-hole methods by analyzing the change of its admittance frequency response and electromechanical coupling coefficient with the length of the through-hole. While having a good effect on suppressing the stray response of the traditional multilayer SAW device, the electromechanical coupling coefficient is also improved.

Description

Technical Field

[0001] The present invention relates to the technical field of surface acoustic wave devices, and more particularly to a resonant structure capable of suppressing stray responses of multi-layer SAW devices. Background Art

[0002] With the advent of the 5G era, the communications market has been presented with new opportunities and challenges. Taking the filtering devices in the RF front end as an example, the demand for high frequency and large bandwidth has been put forward. Therefore, multilayer surface acoustic wave (SAW) devices have come to the fore. Compared with traditional SAW devices and traditional bulk acoustic wave (BAW) devices, multilayer SAW devices have the advantages of traditional SAW and traditional BAW devices while avoiding the disadvantages of traditional SAW being limited by high frequency and traditional BAW being limited by large bandwidth. By flexibly changing the material and thickness ratio between different layers, multilayer SAW devices that still maintain a large electromechanical coupling coefficient at high frequencies can be obtained, thus well meeting the demand for filtering devices in the 5G era.

[0003] However, multilayer SAW devices are prone to generating spurious responses near their resonant frequencies during operation. These spurious responses can increase device insertion loss, degrade in-band ripple, and reduce electromechanical coupling coefficient and quality factor. The current standard approach to suppressing spurious responses in multilayer SAW devices is to employ apodization weighting with interdigital transducers (IDTs). However, the effectiveness of this approach is directly related to the apodization trajectory, and even when achieving good suppression, it can still lead to a reduction in quality factor and insertion loss. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned existing technical problems and proposes a resonant structure with the function of suppressing the stray response of a multilayer SAW device: on the basis of a traditional multilayer SAW device, its temperature compensation layer is partially processed into through-holes, and the through-holes include parallel through-holes and vertical through-holes. By changing the lengths of different through-holes and analyzing the changes in their admittance frequency response and electromechanical coupling coefficient with the through-hole length, the appropriate through-hole length under different through-hole methods is finally selected. While having a good effect on suppressing the stray response of the traditional multilayer SAW device, the electromechanical coupling coefficient is also improved.

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

[0006] A multilayer SAW device is designed, which includes a first base layer, a second base layer, a temperature compensation layer, a piezoelectric layer, and an IDT layer; the second base layer is located on the first base layer; the temperature compensation layer is located on the second base layer; the piezoelectric layer is located on the temperature compensation layer; the IDT layer is located on the piezoelectric layer; the temperature compensation layer includes a through hole; the IDT layer is composed of a first electrode and a second electrode; the multilayer SAW device is a periodic structure, and its period length in the x direction is λ, and its period length in the y direction is c.

[0007] Furthermore, the first base layer and the second base layer are substrate layers, and both are made of the same material, which can be Si. The first base layer is a perfect matching layer for absorbing excess anchor loss.

[0008] Furthermore, the material of the temperature compensation layer is SiO2.

[0009] Furthermore, the material of the piezoelectric layer may be lithium niobate or lithium tantalate.

[0010] Furthermore, the material of the IDT layer can be Al, and its height can be 0.18 um.

[0011] Furthermore, the first electrode and the second electrode have the same shape and are symmetrically positioned relative to a center line of the multilayer SAW device in the x-direction.

[0012] Furthermore, the through holes can be arranged in two ways: parallel to the first electrode and the second electrode, which are parallel through holes; or perpendicular to the first electrode and the second electrode, which are vertical through holes.

[0013] Furthermore, the parallel through holes are composed of a first through hole and a second through hole, and the first through hole and the second through hole have the same shape and are symmetrically positioned relative to a center line of the multilayer SAW device in the x direction.

[0014] Furthermore, the length of the first through hole is m, and the value range of m is 0.05*λ≤m≤0.45*λ.

[0015] Furthermore, the distance between the first through hole and the left periodic boundary of the multilayer SAW device on the yz plane is a, where a=λ / 4-m / 2, and λ is the period length of the multilayer SAW device in the x direction.

[0016] Furthermore, the vertical through hole is constituted by a third through hole alone, the third through hole is arranged centrally relative to the multilayer SAW device, and the length of the third through hole is b, wherein the value range of b is 0.1*c≤b≤0.9*c.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] Multilayer SAW devices combine the advantages of traditional SAW and traditional BAW devices, and avoid the disadvantages of traditional SAW being limited to high frequency and traditional BAW being limited to large bandwidth. By flexibly changing the material and thickness ratio between different layers, a SAW device that still maintains a large electromechanical coupling coefficient at high frequency can be obtained, thereby well meeting the demand for filtering devices in the 5G era. However, multilayer SAW devices are prone to generate spurious responses near the resonant frequency during operation. The spurious responses will cause an increase in device insertion loss, deterioration of in-band ripple, and a decrease in electromechanical coupling coefficient and quality factor, which will have an adverse effect on the performance of multilayer SAW devices. This application proposes a resonant structure that suppresses the spurious response of multilayer SAW devices: on the basis of a traditional multilayer SAW device, its temperature compensation layer is partially through-hole treated, and the through-hole has parallel through-holes and vertical through-holes. By analyzing the changes in admittance frequency response and electromechanical coupling coefficient with through-hole length, the appropriate through-hole length under different through-hole methods is finally selected. While having a good effect on suppressing the spurious response of traditional multilayer SAW devices, its electromechanical coupling coefficient is also improved, and it is simple and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a three-dimensional equivalent model diagram of a traditional multi-layer SAW device under a periodic structure.

[0020] Figure 2 This is the admittance frequency response diagram of a traditional multilayer SAW device.

[0021] Figure 3 This is a three-dimensional equivalent model diagram of a periodic structure of an improved multilayer SAW device under parallel through holes.

[0022] Figure 4 This is the xz plane elevation view of a periodic structure of the improved multilayer SAW device under parallel through holes.

[0023] Figure 5 This is the yz-plane side view of a periodic structure of the improved multilayer SAW device under parallel through holes.

[0024] Figure 6 This is a comparison chart of the admittance frequency response of the first through hole in the parallel through holes of the improved multi-layer SAW device with length m = 0.05*λ, 0.1*λ, 0.15*λ, 0.2*λ, and 0.25*λ.

[0025] Figure 7 This is a comparison diagram of the admittance frequency response of the first through hole with a length m = 0.3*λ, 0.35*λ, 0.4*λ, and 0.45*λ in the parallel through holes of the improved multi-layer SAW device.

[0026] Figure 8 Graph showing the variation of the electromechanical coupling coefficient with the length m of the first through hole in the parallel through holes under the improved multilayer SAW device.

[0027] Figure 9 This is a graph showing how the sound velocity at the resonant frequency, the antiresonant frequency, and the spurious response varies with the length m of the first through hole in the parallel through holes under the improved multilayer SAW device.

[0028] Figure 10 This is a comparison diagram of the admittance frequency response of the conventional multilayer SAW device and the improved multilayer SAW device with the length m = 0.45*λ of the first through hole in the parallel through holes.

[0029] Figure 11 This is a three-dimensional equivalent model diagram of a periodic structure of an improved multilayer SAW device under vertical through holes.

[0030] Figure 12 This is the yz-plane side view of a periodic structure of the improved multilayer SAW device under the vertical through hole.

[0031] Figure 13 This is a comparison chart of the admittance frequency response of the third through hole in the vertical through hole of the improved multi-layer SAW device with length b = 0.1*c, 0.2*c, 0.3*c, 0.4*c, and 0.5*c.

[0032] Figure 14 This is a comparison diagram of the admittance frequency response of the third through hole in the vertical through hole of the improved multi-layer SAW device with length b = 0.6*c, 0.7*c, 0.8*c, and 0.9*c.

[0033] Figure 15 FIG. 1 is a graph showing the variation of the electromechanical coupling coefficient with the length b of the third through hole in the vertical through hole under the improved multilayer SAW device.

[0034] Figure 16 This is a graph showing how the sound velocity at the resonant frequency, the antiresonant frequency, and the spurious response of the improved multilayer SAW device changes with the length b of the third through hole in the vertical through hole.

[0035] Figure 17 This is a comparison diagram of the admittance frequency response of the traditional multilayer SAW device and the improved multilayer SAW device with the length b = 0.9*c of the third through hole in the vertical through hole.

[0036] Figure Number:

[0037] 1. First substrate layer; 2. Second substrate layer; 3. Temperature compensation layer; 4. Piezoelectric layer; 5. IDT layer; 6. First electrode; 7. Second electrode; 8. First through hole; 9. Second through hole; 10. Third through hole; a. The distance of the first through hole relative to the periodic boundary on the left side of the yz plane of the improved multilayer SAW device; b. The length of the third through hole; c. The period length of the multilayer SAW device in the y direction; m. The length of the first through hole; λ. The period length of the multilayer SAW device in the x direction. DETAILED DESCRIPTION

[0038] 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.

[0039] The specific implementation scheme of the present invention to solve the above technical problems is as follows:

[0040] A resonant structure that suppresses the spurious response of multilayer SAW devices, such as Figure 3-Figure 5 and Figure 11-12 As shown, an improved multilayer SAW device is designed, and the improved multilayer SAW device includes a first substrate layer 1, a second substrate layer 2, a temperature compensation layer 3, a piezoelectric layer 4, and an IDT layer 5; wherein the second substrate layer 2 is located on the first substrate layer 1; the temperature compensation layer 3 is located on the second substrate layer 2; the piezoelectric layer 4 is located on the temperature compensation layer 3; the IDT layer 5 is located on the piezoelectric layer 4; the temperature compensation layer 3 includes a through hole; the IDT layer 5 is composed of a first electrode 6 and a second electrode 7; the multilayer SAW device is a periodic structure, and its period length in the x direction is λ, and its period length in the y direction is c. In the following embodiment, λ = 2um, c = 0.5um.

[0041] Furthermore, the first base layer 1 and the second base layer 2 are substrate layers, and both are made of the same material, optionally Si. The first base layer 1 is a perfectly matched layer for absorbing excess anchor loss. In the following embodiment, the height of the first base layer 1 is set to 1 μm, and the height of the second base layer 2 is set to 2 μm.

[0042] Furthermore, the material of the temperature compensation layer 3 is SiO 2 . In the following embodiment, the height of the temperature compensation layer 3 is 0.1*λ.

[0043] Furthermore, the material of the piezoelectric layer 4 can be optionally lithium niobate or lithium tantalate. In the following embodiments, the material of the piezoelectric layer 4 is preferably 10° YX-cut lithium niobate, and the Euler angle under quasi-3D modeling is set to: (0°, 80°, 0°), where the height of the piezoelectric layer 4 is 0.8um.

[0044] Furthermore, the material of the IDT layer 5 may be Al. In the following embodiment, its height is 0.18 um.

[0045] Furthermore, the first electrode 6 and the second electrode 7 have the same shape and are symmetrically positioned relative to the center line of the multilayer SAW device in the x direction.

[0046] Furthermore, the first electrode 6 is configured as a terminal 1V, and the second electrode 7 is configured as a ground terminal.

[0047] Furthermore, the ratio of the metallization rate of the first electrode 6 to the second electrode 7 in one period in the x direction is 50%, and the distance between the first electrode 6 and the left periodic boundary of the yz plane of the improved multilayer SAW device is λ / 8.

[0048] Furthermore, the through holes can be arranged in two ways: parallel to the first electrode 6 and the second electrode 7, which are parallel through holes; or perpendicular to the first electrode 6 and the second electrode 7, which are vertical through holes.

[0049] Further, Figure 1 and Figure 2 The three-dimensional equivalent model diagram and admittance frequency response diagram of a conventional multilayer SAW device under a periodic structure are shown respectively. Among them, the conventional multilayer SAW device is the same as the improved multilayer SAW device except that the through hole is not provided. Figure 2 It can be seen that during the operation of traditional multilayer SAW devices, spurious responses appear near their resonant frequencies. The spurious responses at these locations will cause the multilayer SAW devices to have adverse effects such as increased insertion loss, deterioration of in-band ripple, and reduction of electromechanical coupling coefficient and quality factor.

[0050] Example 1:

[0051] Furthermore, if Figure 3-Figure 5 As shown, in this embodiment, the through holes are parallel through holes.

[0052] Furthermore, the parallel through holes are composed of a first through hole 8 and a second through hole 9 , and the first through hole 8 and the second through hole 9 have the same shape and are symmetrically positioned relative to the center line of the multilayer SAW device in the x direction.

[0053] Furthermore, the length of the first through hole 8 is m, and the value range of m is 0.05*λ≤m≤0.45*λ. In this embodiment, m={0.05*λ, 0.1*λ, 0.15*λ, 0.2*λ, 0.25*λ, 0.3*λ, 0.35*λ, 0.4*λ, 0.45*λ}.

[0054] Furthermore, the distance between the first through hole 8 and the left periodic boundary of the multilayer SAW device on the yz plane is a, where a=λ / 4-m / 2.

[0055] Further, Figure 6 and Figure 7 The following is a comparison of the admittance frequency response of the parallel through holes in the improved multilayer SAW device under different lengths m of the first through holes 8. Figure 6 and Figure 7 It can be seen that: as the length m of the first through hole 8 increases, the resonant frequency, antiresonant frequency and resonant frequency of the improved multilayer SAW device all decrease. Among them, the resonant frequency and antiresonant frequency decrease less with the increase of the length m of the first through hole 8, and the rate of decrease is similar; while the spurious response is more sensitive to the change of the length m of the first through hole 8. As the length m of the first through hole 8 increases, the amplitude of the spurious response reduction rate is greatly improved compared with the amplitude of the reduction of the resonant frequency and antiresonant frequency, and it decreases at a certain rate. The reason is that when the length m of the first through hole 8 increases, the impedance ratio between each layer of the improved multilayer SAW device changes accordingly, and this impedance change has a greater impact on the spurious response, so that the spurious response gradually moves away from the main mode as the length m of the first through hole 8 increases, thereby achieving the purpose of suppressing the spurious response.

[0056] Further, Figure 8 : is a graph showing the variation of the electromechanical coupling coefficient with the length m of the first through hole 8 in the parallel through holes under the improved multilayer SAW device. Figure 8 It can be seen that the electromechanical coupling coefficient of the improved multilayer SAW device generally increases with the increase of the length m of the first through hole 8, and reaches a peak when the length m of the first through hole 8 is 0.3*λ.

[0057] Further, Figure 9 This is a graph showing how the sound velocity at the resonant frequency, the anti-resonant frequency, and the spurious response varies with the length m of the first through hole 8 in the parallel through holes under the improved multilayer SAW device. Figure 9 It can be seen that the sound speeds at the resonant frequency, antiresonant frequency and spurious response resonant frequency gradually decrease with the increase of the length m of the first through hole 8. Among them, the three are decreasing at a uniform speed, and the sound speed at the spurious response decreases faster than the sound speed at the resonant frequency and antiresonant frequency.

[0058] Further, Figure 10 The following is a comparison of the admittance frequency response of the first through hole 8 in the lower parallel through hole of the traditional multilayer SAW device and the improved multilayer SAW device when the length m is 0.45*λ. Figure 10It can be seen that the admittance frequency response of the improved multilayer SAW device under parallel through holes is smoother and more even than that of the traditional multilayer SAW device. While suppressing spurious responses well, its electromechanical coupling coefficient is also improved compared with that of the traditional multilayer SAW device.

[0059] Example 2:

[0060] Furthermore, if Figure 11 and Figure 12 As shown, in this embodiment, the through hole is a vertical through hole.

[0061] Furthermore, the vertical through hole is composed of a third through hole 10 alone, the third through hole 10 is arranged centrally relative to the multilayer SAW device, and the length of the third through hole 10 is b, where the value range of b is 0.1*c≤b≤0.9*c. In the following embodiment, b={0.1*c, 0.2*c, 0.3*c, 0.4*c, 0.5*c, 0.6*c, 0.7*c, 0.8*c, 0.9*c}.

[0062] Further, Figure 13 and Figure 14 The following is a comparison of the admittance frequency response of different lengths b of the third through hole 10 in the vertical through hole of the improved multilayer SAW device. Figure 13 and Figure 14 It can be seen that, similar to the pattern in Example 1, as the length b of the third through hole 10 increases, its resonant frequency, antiresonant frequency, and resonant frequency of the spurious response all show a decreasing trend. The rates of decrease of the resonant frequency and antiresonant frequency are substantially the same as those in Example 1. The rate of decrease of the resonant frequency of the spurious response is lower than that in Example 1, but still slightly faster than the rates of decrease of the resonant frequency and antiresonant frequency in this embodiment.

[0063] Further, Figure 15 : is a graph showing the variation of the electromechanical coupling coefficient with the length b of the third through hole 10 in the vertical through hole under the improved multilayer SAW device. Figure 15 It can be seen that the electromechanical coupling coefficient of the improved multilayer SAW device generally increases with the increase of the length b of the third through hole 10 , and reaches a peak when the length b of the third through hole 10 is 0.9*c.

[0064] Further, Figure 16 : This is a graph showing the change in the sound velocity at the resonant frequency, the anti-resonant frequency and the spurious response under the improved multilayer SAW device as a function of the length b of the third through hole 10 in the vertical through hole. Figure 16It can be seen that the sound velocities at the resonant frequency, antiresonant frequency and spurious response resonant frequency gradually decrease with the increase of the length b of the third through hole 10, wherein the three are all decreasing at a uniform speed, and the sound velocity at the spurious response decreases faster than the sound velocity at the resonant frequency and the antiresonant frequency, but the sound velocity decrease rate at the spurious response is still lower than that at the stray response in Example 1.

[0065] Further, Figure 17 The following is a comparison of the admittance frequency response of the third through hole 10 in the vertical through hole of the traditional multilayer SAW device and the improved multilayer SAW device with a length b = 0.9*c. Figure 17 It can be seen that the admittance frequency response of the improved multilayer SAW device under the vertical through hole is smoother and more even than that of the traditional multilayer SAW device. While suppressing the spurious response well, its electromechanical coupling coefficient is also improved compared with the traditional multilayer SAW device.

[0066] Furthermore, based on the above two embodiments, whether it is a parallel through hole or a vertical through hole, as the length of the through hole increases, its spurious response is gradually moving away from the main mode, and the spurious response of the traditional multi-layer SAW device can be well suppressed. While the suppression effect is good, its electromechanical coupling coefficient is improved.

[0067] 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 resonant structure capable of suppressing spurious responses of a multilayer SAW device, characterized in that: A multilayer device is designed, wherein the multilayer SAW device comprises a first substrate layer, a second substrate layer, a temperature compensation layer, a piezoelectric layer, and an IDT layer; the second substrate layer is located on the first substrate layer; the temperature compensation layer is located on the second substrate layer; the piezoelectric layer is located on the temperature compensation layer; the IDT layer is located on the piezoelectric layer; the temperature compensation layer comprises a through hole; the IDT layer comprises a first electrode and a second electrode; the multilayer SAW device is a periodic structure, wherein the period length in the x direction is λ and the period length in the y direction is c; the through hole comprises In summary: parallel through holes or vertical through holes; the parallel through holes are composed of a first through hole and a second through hole, the two are symmetrically placed relative to the midline position of the multilayer SAW device in the x direction, and the length m of the first through hole satisfies: 0.05*λ≤m≤0.45*λ, and its position satisfies: a=λ / 4-m / 2, a is the distance between the first through hole and the periodic boundary on the left side of the yz plane of the multilayer SAW device; the vertical through hole is composed of a third through hole alone, its length b satisfies: 0.1*c≤b≤0.9*c, and is arranged centrally relative to the multilayer SAW device.

2. The resonant structure for suppressing spurious responses of a multilayer SAW device according to claim 1, characterized in that: The first base layer and the second base layer are substrate layers, and are made of the same material, optionally Si, wherein the first base layer is a perfect matching layer.

3. The resonant structure for suppressing spurious responses of a multilayer SAW device according to claim 1, characterized in that: The material of the temperature compensation layer is SiO2.

4. The resonant structure for suppressing spurious responses of a multilayer SAW device according to claim 1, characterized in that: The material of the piezoelectric layer may be lithium niobate or lithium tantalate.

5. The resonant structure for suppressing spurious responses of a multilayer SAW device according to claim 1, characterized in that: The material of the IDT layer may be Al.

6. The resonant structure for suppressing spurious responses of a multilayer SAW device according to claim 1, characterized in that: The first electrode and the second electrode have the same shape and are symmetrically positioned relative to a center line of the multilayer SAW device in the x direction.

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