Surface acoustic wave device, radio-frequency front-end module, and electronic device

Abstract

The present application relates to a surface acoustic wave device, a radio-frequency front-end module, and an electronic device. The surface acoustic wave device comprises a piezoelectric layer, and an interdigital electrode, which is provided on a first surface of the piezoelectric layer. The interdigital electrode comprises a plurality of electrode fingers. During the operation of the surface acoustic wave device, acoustic waves comprise surface acoustic waves and bulk acoustic waves, wherein the propagation direction of the surface acoustic waves is an X direction. A first characteristic thickness of the surface acoustic wave device is Ty, and the thickness of the piezoelectric layer is Dy, and the thickness of the piezoelectric layer and the first characteristic thickness meet the following conditions [equation I], wherein the piezoelectric layer comprises a piezoelectric crystal, and the value of the first characteristic thickness is determined on the basis of the centerline spacing between two adjacent electrode fingers, the bulk acoustic wave velocity of the piezoelectric crystal in the X direction, and an operating frequency. The thickness of the piezoelectric layer is defined by means of a first characteristic thickness, thereby preventing the acoustic functions of other structures from being affected by the excessive thickness of the piezoelectric layer, and thus improving the operation performance of the surface acoustic wave device.

Description

Surface acoustic wave devices, radio frequency front-end modules and electronic devices

[0001] This application claims priority to Chinese patent applications filed on October 29, 2024, with application number 202411514619.4 entitled "Surface Acoustic Wave Device, Radio Frequency Front-End Module and Electronic Equipment" and filed on October 28, 2024, with application number 202411513291.4 entitled "Surface Acoustic Wave Device, Radio Frequency Front-End Module and Electronic Equipment". Technical Field

[0002] This application relates to the field of radio frequency, and more particularly to a surface acoustic wave (SAW) device, a radio frequency front-end module including the SAW device, and an electronic device including the radio frequency front-end module. Background Technology

[0003] In the field of radio frequency, surface acoustic wave (SAW) devices typically consist of a piezoelectric substrate and interdigitated electrodes. The interdigitated electrodes on the piezoelectric substrate work in conjunction with the substrate to achieve the conversion between electrical signals and acoustic signals.

[0004] In existing technologies, different functional layers can be placed beneath the piezoelectric substrate to control the performance of interdigital electrodes, achieving characteristics such as high quality factor (Q value) and low temperature coefficient of frequency (TCF). However, the theoretical basis for setting functional layers in existing technologies is not yet perfect, resulting in low development efficiency. Inappropriate functional layer placement can make it difficult for the interdigital electrodes to achieve the intended effects.

[0005] Application content

[0006] In view of the shortcomings of the prior art, the purpose of this application is to provide a solution to improve the working performance of surface acoustic wave devices, specifically including the following technical solution:

[0007] In a first aspect, embodiments of this application provide a surface acoustic wave (SAW) device, including a piezoelectric layer and interdigitated electrodes disposed on a first surface of the piezoelectric layer, the interdigitated electrodes including a plurality of electrode fingers; the acoustic waves during operation of the SAW device include surface acoustic waves and volume waves, the surface waves propagating in the X direction; the first characteristic thickness of the SAW device is T. y The thickness of the piezoelectric layer is D y The thickness of the piezoelectric layer and the thickness of the first feature satisfy the following condition: The piezoelectric layer includes a piezoelectric crystal, and the first characteristic thickness is determined based on the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric crystal along the X-direction, and the operating frequency. Since the amplitude of the surface acoustic wave excited during operation of the surface acoustic wave device mainly acts on the first surface of the piezoelectric layer and a portion of the piezoelectric layer near one surface, the surface acoustic wave device of this application further utilizes the first characteristic thickness T... y The ratio range of the thickness of the piezoelectric layer to the piezoelectric layer limits the thickness of the piezoelectric layer, ensuring that the energy of the surface acoustic wave can be effectively transferred to the remaining structure of the interdigitated electrodes. This ensures the acoustic performance of the surface acoustic wave device and improves the operating performance of the surface acoustic wave device of this application.

[0008] In this embodiment, by setting the ratio of the piezoelectric layer thickness to the first feature thickness between 0.2 and 1.5, the piezoelectric layer thickness is avoided from being too thin due to an excessively small ratio, which would affect the stability of the surface acoustic wave device. Conversely, the piezoelectric layer thickness is avoided from being too thick due to an excessively large ratio, which would affect the acoustic performance of the remaining structures of the surface acoustic wave device. This improves the stability and performance of the surface acoustic wave device of this application.

[0009] In this embodiment, a temperature compensation layer is provided on the side of the piezoelectric layer away from the interdigitated electrodes to improve the temperature stability of the surface acoustic wave device of this application and avoid the performance of the surface acoustic wave device being affected by temperature changes.

[0010] In this embodiment, by limiting the ratio of the thickness of the first feature to the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer, the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer is limited, ensuring that the energy of the surface acoustic wave can be effectively transferred to the temperature compensation layer, thereby ensuring the temperature compensation function of the temperature compensation layer for the piezoelectric layer and realizing the acoustic effect of the temperature compensation layer on the surface acoustic wave device of this application.

[0011] In this embodiment, by further limiting the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer, the influence of the waveguide mode generated by the body wave on the frequency of the surface acoustic wave is avoided after the reflection of the two surfaces of the piezoelectric layer and the temperature compensation layer that are opposite to each other.

[0012] In this embodiment, by limiting the range of the ratio between the thickness of the temperature compensation layer and the thickness of the piezoelectric layer, a matching setting for the thicknesses of the temperature compensation layer and the piezoelectric layer is achieved. This improves the operating performance of the surface acoustic wave device of this application.

[0013] In this embodiment, a functional layer is provided on the side of the piezoelectric layer away from the interdigitated electrodes to reduce the loss of the surface acoustic wave (SAW) device of this application. The SAW device of this application also limits the thickness of the functional layer by the ratio range of the second feature thickness to the thickness of the functional layer, which is beneficial for reducing the leakage of high-frequency miscellaneous modes in the bulk wave. This improves the operating performance of the SAW device of this application.

[0014] In this embodiment, by setting the ratio of the functional layer thickness to the second feature thickness between 0.2 and 1.5, the excessively thin functional layer due to a ratio that is too small is avoided, which would affect the performance of the surface acoustic wave device. Conversely, an excessively large ratio would also prevent the functional layer from becoming too thick, which would affect the leakage of high-frequency miscellaneous modes in the bulk wave. This ensures the performance of the surface acoustic wave device of this application.

[0015] In this embodiment, a monocrystalline silicon layer is formed on the surface of the functional layer away from the piezoelectric layer, and the monocrystalline silicon layer is confined. <110> The spatial angle between the crystal orientation group and the propagation direction of the surface acoustic wave excited by multiple interdigitated electrodes on the first surface is conducive to the leakage of waveguide mode energy.

[0016] Secondly, embodiments of this application provide a surface acoustic wave device, including a functional layer and a piezoelectric layer stacked along its own thickness direction, and an interdigitated electrode disposed on a first surface of the piezoelectric layer away from the functional layer, the interdigitated electrode including a plurality of electrode fingers;

[0017] The acoustic waves produced when a surface acoustic wave device is in operation include surface acoustic waves and volume waves, with the surface waves propagating in the X direction.

[0018] The second characteristic thickness of the surface acoustic wave device is T d The thickness of the functional layer is D d The thickness of the functional layer and the thickness of the second feature satisfy the following condition:

[0019] The thickness of the second feature is determined based on the volume wave velocity and operating frequency of the material of the functional layer along the X direction.

[0020] This application's surface acoustic wave (SAW) device reduces losses by setting a functional layer on the side of the piezoelectric layer away from the interdigitated electrodes. Furthermore, the thickness of the functional layer is limited by the ratio range of the second feature thickness to the thickness of the functional layer, preventing excessive thickness of the functional layer from affecting the leakage of high-frequency miscellaneous modes in the bulk wave. This improves the operating performance of the SAW device.

[0021] Thirdly, embodiments of this application provide a radio frequency front-end module, including a surface acoustic wave device.

[0022] Fourthly, embodiments of this application provide an electronic device, including a radio frequency front-end module.

[0023] Understandably, the RF front-end module provided in the third aspect and the electronic device provided in the fourth aspect of this application, due to the use of the surface acoustic wave device provided in the first and second aspects of this application, also possess better operating performance. Attached Figure Description

[0024] Figure 1 is a schematic diagram of the structure of an electronic device provided in one embodiment of this application;

[0025] Figure 2 is a schematic diagram of the structure of the radio frequency front-end module provided in one embodiment of this application;

[0026] Figure 3 is a schematic diagram of the structure of the filter provided in one embodiment of this application;

[0027] Figure 4 is a schematic diagram of another structure of the filter provided in one embodiment of this application;

[0028] Figure 5 is a schematic diagram of the structure of a surface acoustic wave device provided in one embodiment of this application;

[0029] Figure 6 is a cross-sectional structural diagram of a surface acoustic wave device provided in one embodiment of this application;

[0030] Figure 7 is a cross-sectional enlarged schematic diagram of a surface acoustic wave device provided in one embodiment of this application;

[0031] Figure 8 is a comparison of the admittance curves of the surface acoustic wave device provided in one embodiment of this application;

[0032] Figure 9 is a partial cross-sectional structural diagram of a surface acoustic wave device provided in one embodiment of this application;

[0033] Figure 10 is a partial cross-sectional structural schematic diagram of a surface acoustic wave device provided in one embodiment of this application;

[0034] Figure 11 is a partial curve showing the relationship between the first reinforcement angle of the piezoelectric layer of the surface acoustic wave device provided in one embodiment of this application and the volume wave velocity;

[0035] Figure 12 is a schematic diagram of another structure of the surface acoustic wave device provided in one embodiment of this application;

[0036] Figure 13 is a schematic cross-sectional view of another surface acoustic wave device provided in one embodiment of this application;

[0037] Figure 14 is another enlarged cross-sectional view of the surface acoustic wave device provided in one embodiment of this application;

[0038] Figure 15 is a schematic diagram of the conductivity curve of a surface acoustic wave device provided in one embodiment of this application;

[0039] Figure 16 is another partial cross-sectional structural schematic diagram of the surface acoustic wave device provided in one embodiment of this application;

[0040] Figure 17 is a schematic diagram of the structure of the surface acoustic wave device proposed in the embodiment of this application;

[0041] Figure 18 is a schematic diagram of the bulk wave excitation of the surface acoustic wave device proposed in the embodiment of this application;

[0042] Figure 19 is a schematic diagram of the acoustic wave transmission into the sound velocity layer of the surface acoustic wave device proposed in the embodiment of this application.

[0043] Figure 20 is a schematic diagram of the deformation mode of the surface acoustic wave device proposed in the embodiment of this application;

[0044] Figure 21 is a graph showing the surface wave sound velocity as a function of the piezoelectric layer thickness in an embodiment of this application.

[0045] Figure 22 is a graph showing the change of surface wave velocity with the thickness of the sound velocity layer in an embodiment of this application. Detailed Implementation

[0046] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0047] The following descriptions of the embodiments are based on the accompanying illustrations and are used to illustrate specific embodiments in which this application can be implemented. The component designations used herein, such as "first," "second," etc., are merely for distinguishing the described objects and do not have any sequential or technical meaning. Unless otherwise specified, the terms "connection" and "linkage" used in this application include both direct and indirect connections (linkages). Directional terms used in this application, such as "up," "down," "front," "rear," "left," "right," "inner," "outer," "side," etc., are merely for reference to the accompanying drawings. Therefore, the use of directional terms is for better and clearer explanation and understanding of this application, and does not indicate or imply that the referred device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this application.

[0048] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising," "may include," "include," or "may include" used in this application indicate the presence of the corresponding disclosed function, operation, element, etc., and do not limit one or more other functions, operations, elements, etc. Moreover, the terms "comprising" or "include" indicate the presence of the corresponding features, numbers, steps, operations, elements, components, or combinations thereof disclosed in the specification, but do not exclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, and are intended to cover non-exclusive inclusion.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0050] Please refer to Figure 1, which shows a schematic diagram of the structure of an electronic device 400 provided in one embodiment of this application.

[0051] As shown in Figure 1, the electronic device 400 of this application includes a substrate 401 and a radio frequency front-end module 300, with the radio frequency front-end module 300 mounted on the substrate 401. The substrate 401 and the radio frequency front-end module 300 are electrically connected.

[0052] In one embodiment, the substrate 401 is a printed circuit board to control the operation of the radio frequency front-end module 300. The electronic device 400 of this application receives and / or transmits signals through the radio frequency front-end module 300. Exemplarily, the electronic device 400 includes at least one of a computer, mobile phone, tablet computer, smartwatch, and navigator, etc., and this application does not impose any particular limitation on it.

[0053] Please refer to Figure 2, which shows a schematic diagram of the structure of the radio frequency front-end module 300 provided in one embodiment of this application.

[0054] As shown in Figure 2, the RF front-end module 300 includes a signal terminal 301, a switch 302, an amplifier 303, and a filter 200. The signal terminal 301 is used to receive external signals or transmit RF signals. The switch 302 is communicatively connected between the signal terminal 301 and the filter 200 to control signal transmission between them. When the amplifier 303 is a low-noise amplifier, the filter 200 receives the external signal received by the signal terminal 301 when the switch 302 is closed and outputs a signal with a preset frequency. The amplifier 303 is electrically connected to the filter 200 to amplify the signal processed by the filter 200 and output it to subsequent structures. When the amplifier 303 is a power amplifier, the filter 200 receives the amplified RF signal from the amplifier 303 when the switch 302 is closed, filters the received RF signal, and then transmits the filtered RF signal to the signal terminal 301 through the switch 302. In one embodiment, the signal terminal 301 is an antenna.

[0055] In one embodiment, the number of filters 200 can be multiple, and all multiple filters 200 are communicatively connected to the signal terminal 301.

[0056] In one embodiment, the radio frequency front-end module 300 further includes a multiplexer, which includes a filter 200.

[0057] Please refer to Figure 3, which shows a schematic diagram of the structure of the filter 200 provided in one embodiment of this application.

[0058] As shown in Figure 3, the filter 200 of this application includes a signal input terminal 201, a signal output terminal 202, a ground port 203, a piezoelectric substrate 204, and a surface acoustic wave device 100. In this embodiment, the surface acoustic wave device 100 includes interdigitated electrodes 20. The interdigitated electrodes 20 are disposed on the piezoelectric substrate 204.

[0059] As shown in Figure 3, there are three interdigitated electrodes 20. One end of one interdigitated electrode 20 is connected to the signal input terminal 201, and the other end is connected to the ground port 203. The remaining two interdigitated electrodes 20 are arranged on both sides of the interdigitated electrode 20 connected to the signal input terminal 201. One end of the two interdigitated electrodes 20 is connected to the signal output terminal 202, and the other end of the two interdigitated electrodes 20 is connected to the ground port 203.

[0060] When a signal enters the surface acoustic wave device 100 from the signal input terminal 201, the interdigitated electrodes 20 inside the surface acoustic wave device 100 receive the electrical signal. The interdigitated electrodes 20 can internally realize the conversion between electroacoustic and acoustic-electric signals, and ultimately realize the processing of the electrical signal.

[0061] In one embodiment, the piezoelectric substrate 204 and the interdigital electrodes 20 disposed on the piezoelectric substrate 204 can constitute an interdigital transducer, meaning that the interdigital electrodes 20 must be fabricated on the piezoelectric substrate 204 to generate sound waves. In another embodiment, the interdigital transducer can also be the interdigital electrodes 20 formed on the piezoelectric substrate 204.

[0062] In one embodiment, the surface acoustic wave device 100 includes a resonator.

[0063] Please refer to Figure 4 for another structural schematic diagram of the filter 200 provided in one embodiment of this application.

[0064] As shown in Figure 4, one group of resonators is connected in series between the signal input terminal 201 and the signal output terminal 202, while one end of another group of resonators is connected to the ground port 203, and the other end is connected to the series circuit between the signal input terminal 201 and the signal output terminal 202. It can be understood that the series and parallel connection of multiple resonators enables the filter 200 of this application to filter signals of a preset frequency.

[0065] Please refer to Figure 5, which shows a schematic diagram of the structure of the surface acoustic wave device 100 provided in one embodiment of this application.

[0066] As shown in Figure 5, the surface acoustic wave device 100 of this application includes a piezoelectric layer 10 and interdigitated electrodes 20. Along the thickness direction of the piezoelectric layer 10, the interdigitated electrodes 20 are disposed on the first surface 11 of the piezoelectric layer 10. The interdigitated electrodes 20 include two parallel and spaced-apart busbars 21 and a plurality of parallel and spaced-apart electrode fingers 22.

[0067] In this configuration, one of the two busbars 21 is used to receive external signals, while the other busbar 21 is used to output signals. Multiple electrode fingers 22 are located between the two busbars 21. Some of the electrode fingers 22 are connected to one busbar 21, while other electrode fingers 22 are connected to the other busbar 21.

[0068] For ease of description, the busbar 21 used for receiving external signals is defined as the first busbar 21a, and the busbar 21 used for outputting signals is defined as the second busbar 21b. The electrode finger 22 connected to the first busbar 21a is defined as the first electrode finger 22a, and the electrode finger 22 connected to the second busbar 21b is defined as the second electrode finger 22b.

[0069] Specifically, both the first electrode finger 22a and the second electrode finger 22b extend along the first direction 001 towards opposite sides of the piezoelectric layer 10. Along the second direction 002, the first electrode finger 22a and the second electrode finger 22b are arranged alternately. Specifically, as shown in Figure 5, along the second direction 002, there is a second electrode finger 22b between any two adjacent first electrode fingers 22a, and a first electrode finger 22a between any two adjacent second electrode fingers 22b.

[0070] Both the first busbar 21a and the second busbar 21b extend along the second direction 002 to opposite sides of the piezoelectric layer 10, wherein the first direction 001 and the second direction 002 are perpendicular to each other. In practical applications, the surface acoustic wave device 100 of this application may have errors, and the angle between the first direction 001 and the second direction 002 may not be equal to 90°.

[0071] In this embodiment, due to the inverse piezoelectric effect of the piezoelectric layer 10, when an electrical signal is transmitted to each of the first electrode fingers 22a via the first busbar 21a, the electrical signal on each of the first electrode fingers 22a releases electrostatic force on the piezoelectric layer 10, causing deformation of the surface of the piezoelectric layer 10. Since the electrical signal is an alternating signal, it can be understood that the electrostatic force acting on the surface of the piezoelectric layer 10 by each of the first electrode fingers 22a exhibits periodic variation. Correspondingly, the amount of deformation of the surface of the piezoelectric layer 10 also varies with the periodic variation of the electrical signal, thereby generating outwardly released sound waves.

[0072] The acoustic waves emitted by the surface acoustic wave device 100 during operation include surface acoustic waves and volume waves. Specifically, when the component of the acoustic wave vector along the thickness direction of the piezoelectric layer 10 is imaginary, this type of acoustic wave can only propagate along the planar direction of the first surface 11, and is therefore a surface acoustic wave. The propagation direction of the surface acoustic wave is defined as the X-direction. When the acoustic wave vector has a real component along the thickness direction of the piezoelectric layer 10, it is a volume wave.

[0073] Surface acoustic waves (SAWs) are used to realize the frequency selection and signal processing functions of the SAW device 100 of this application. During SAW propagation, the main propagation direction is the second direction 002, that is, the X direction is the second direction 002. However, in practice, due to edge effects and acoustic diffraction, the propagation direction of the SAW formed on the first surface 11 of the piezoelectric layer 10 may also be in other directions, corresponding to an angle between the X direction and the second direction 002. In one embodiment, SAWs propagating in other directions are absorbed by a sound-absorbing material (not shown in the figure).

[0074] In one embodiment, along the second direction 002, a reflective grating (not shown in the figure) is provided on both sides of the interdigital electrode 20. The reflective grating is used to confine the surface acoustic wave generated when the surface acoustic wave device 100 of this application is working within the interdigital electrode 20.

[0075] It is understood that this application can be applied to dual-mode surface acoustic wave (DMS) devices and filter devices formed by their interconnection through a certain topology, including interdigitated electrodes, and this application does not limit them.

[0076] Please refer to Figure 6, which shows a cross-sectional view of the surface acoustic wave device 100 provided in one embodiment of this application.

[0077] As shown in Figure 6, the surface acoustic wave device 100 of this application has other structures on the side of the piezoelectric layer 10 away from the interdigitated electrode 20. Exemplarily, the surface acoustic wave device 100 of this application has a temperature compensation layer 30 on the side of the piezoelectric layer 10 away from the interdigitated electrode 20. For ease of description, in the embodiments of this application and subsequent embodiments, the temperature compensation layer 30 is used to refer to the other structures of the surface acoustic wave device 100.

[0078] The material parameters of the piezoelectric layer 10 change with temperature, thus affecting the propagation characteristics of surface acoustic waves on the first surface 11. The temperature compensation layer 30 is made of a material with a smaller or opposite temperature coefficient to that of the piezoelectric layer 10. When the temperature changes, the temperature compensation layer 30 can compensate for the temperature effect of the piezoelectric layer 10. This reduces the impact of temperature changes on the propagation of surface acoustic waves.

[0079] For surface acoustic waves (SAWs), the amplitude of the SAW can cause deformation of a portion of the structure within the piezoelectric layer 10. When the energy of the SAW can be effectively transferred to the temperature compensation layer 30 of the SAW device 100, the amplitude of the SAW can also cause deformation of the temperature compensation layer 30. Correspondingly, the temperature compensation layer 30 can also act on the first surface 11 through the piezoelectric layer 10. The range within which the amplitude of the SAW causes deformation of a portion of the structure within the piezoelectric layer 10 is defined as the acoustic field range of the SAW or the disturbance range of the SAW.

[0080] That is, when the acoustic field range of the surface acoustic wave overlaps with the temperature compensation layer 30 of the surface acoustic wave device 100, the acoustic effect of the temperature compensation layer 30 can compensate for the influence of temperature changes on the first surface 11 of the piezoelectric layer 10. This improves the working performance of the surface acoustic wave device 100 of this application.

[0081] The amplitude of surface acoustic waves (SAWs) has a limited range of influence within the piezoelectric layer 10. In practical applications, the sound field of SAWs mainly acts on the first surface 11 of the piezoelectric layer 10, and a portion of the piezoelectric layer 10 near the first surface 11. Therefore, the SAW device 100 of this application needs to limit the thickness of the piezoelectric layer 10 to ensure that the temperature compensation layer 30 and the piezoelectric layer 10 can interact.

[0082] In the embodiments of this application, the surface acoustic wave device 100 of this application determines the size of the first characteristic thickness of the surface acoustic wave device 100 of this application, and defines the thickness of the piezoelectric layer 10 by the ratio range of the first characteristic thickness to the thickness of the piezoelectric layer 10.

[0083] Specifically, the first characteristic thickness of the surface acoustic wave device 100 is T. y The thickness of the piezoelectric layer 10 is D. y The thickness of the piezoelectric layer 10 and the thickness of the first feature satisfy the following condition: That is, the ratio between the thickness of the piezoelectric layer 10 and the thickness of the first feature is less than or equal to 1.5.

[0084] The piezoelectric layer 10 includes a piezoelectric crystal, and the first characteristic thickness is determined by the midline distance between two adjacent electrode fingers 22, the volume wave velocity of the piezoelectric crystal along the X direction, and the operating frequency. In this embodiment, the volume wave velocity of the piezoelectric crystal along the X direction is determined by the material of the piezoelectric layer 10. When the crystal material of the piezoelectric layer 10 is determined, the volume wave velocity of the piezoelectric crystal along the X direction is also determined.

[0085] It is worth noting that, in the embodiments of this application and subsequent embodiments, the two electrode fingers 22 of the interdigitated electrode 20 within one period length can refer to adjacent first electrode fingers 22a and second electrode fingers 22b, or to two adjacent first electrode fingers 22a or two adjacent second electrode fingers 22b. That is, the two electrode fingers 22 of the interdigitated electrode 20 within one period length can be two adjacent electrode fingers 22 with the same polarity, or two adjacent electrode fingers 22 with different polarities. For ease of description, in the embodiments of this application and subsequent embodiments, the two electrode fingers 22 of the interdigitated electrode 20 within one period length are used to represent two adjacent electrode fingers 22 with the same polarity.

[0086] Specifically, please refer to Figure 7, which shows an enlarged cross-sectional view of the surface acoustic wave device 100 provided in one embodiment of this application.

[0087] As shown in Figures 6 and 7, the midline distance between two adjacent finger 22 of the interdigitated electrode 20 is P, and the volume wave velocity of the piezoelectric crystal along the X direction is V. b1The operating frequency is f, and the bulk wavelength of the piezoelectric crystal along the X direction at the operating frequency is λ1. The first characteristic thickness satisfies the following equation:

[0088] Since, after the surface acoustic wave device 100 of this application is fabricated, the center-to-line distance P between two adjacent electrode fingers 22 of the interdigitated electrode 20, and the volume wave velocity V of the piezoelectric crystal along the X direction are... b1 And the operating frequency f are both measurable or determinable values. Therefore, the surface acoustic wave device 100 of this application can be based on the centerline spacing P and the volume wave velocity V. b1 The first feature thickness is obtained by using the operating frequency f.

[0089] Therefore, given a determined first characteristic thickness, the thickness of the piezoelectric layer 10 can be determined based on the relationship between the first characteristic thickness and the thickness of the piezoelectric layer 10. The surface acoustic wave (SAW) device 100 of this application limits the thickness of the piezoelectric layer 10 by using a range of ratios between the first characteristic thickness and the thickness of the piezoelectric layer 10, thus avoiding a situation where the energy of the SAW cannot be effectively transferred to the temperature compensation layer 30 of the SAW device 100 due to excessive thickness of the piezoelectric layer 10. This ensures the acoustic function of the temperature compensation layer 30 of the SAW device 100 and guarantees the operating performance of the SAW device 100 of this application.

[0090] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer 10 and the first characteristic thickness satisfy the following condition:

[0091] When the ratio of the thickness of the piezoelectric layer 10 to the thickness of the first feature is less than 0.2, the thickness of the piezoelectric layer 10 is too thin. On the one hand, an excessively thin piezoelectric layer 10 will reduce the acoustic-to-electric conversion efficiency of the surface acoustic wave device 100, thereby affecting the working performance of the surface acoustic wave device 100 of this application. On the other hand, an excessively thin piezoelectric layer 10 is more sensitive to temperature changes and has relatively poor mechanical strength. As a result, the stability and reliability of the surface acoustic wave device 100 of this application are relatively poor.

[0092] When the ratio of the thickness of the piezoelectric layer 10 to the thickness of the piezoelectric feature is greater than 1.5, the thickness of the piezoelectric layer 10 is too thick, which leads to an increase in the distance between the temperature compensation layer 30 of the surface acoustic wave device 100 and the first surface 11 along the third direction 003. This may cause the energy of the surface acoustic wave to be difficult to be effectively transferred to the temperature compensation layer 30 of the surface acoustic wave device 100, thereby affecting the acoustic function of the temperature compensation layer 30.

[0093] Here, the third direction 003 refers to the thickness direction of the piezoelectric layer 10. The third direction 003 is perpendicular to the first direction 001 and the second direction 002 respectively. In actual application, there may be errors. At least one of the angles between the third direction 003 and the first direction 001 and between the third direction 003 and the second direction 002 may not be equal to 90°.

[0094] Therefore, the surface acoustic wave device 100 of this application sets the ratio of the thickness of the piezoelectric layer 10 to the thickness of the first feature between 0.2 and 1.5. This avoids the piezoelectric layer 10 becoming too thin due to an excessively small ratio, which would affect the working performance and stability of the surface acoustic wave device 100. It also avoids the piezoelectric layer 10 becoming too thick due to an excessively large ratio, which would affect the acoustic function of the temperature compensation layer 30 of the surface acoustic wave device 100. This ensures the stability and working performance of the surface acoustic wave device 100 of this application.

[0095] Specifically, admittance can be used to describe the response process of components and signals. In the surface acoustic wave (SAW) device 100 of this application, admittance is used to measure the influence of clutter propagating on the surface of the piezoelectric layer 10 on the acoustic wave quality. Figure 8 shows a comparison of admittance curves obtained for the SAW device 100 of this application and a comparative example SAW device based on different SAW frequencies. The horizontal axis is in GHz, and the vertical axis is in dB.

[0096] For the comparative example, the surface acoustic wave (SAW) device includes a piezoelectric layer and interdigitated electrodes disposed on the surface of the piezoelectric layer. The centerline spacing P between two adjacent interdigitated electrodes is 1.0 μm, the duty cycle of the interdigitated electrodes is 0.4, the piezoelectric layer is 42°YX-LiTaO3, the interdigitated electrodes are made of aluminum, and the thickness of the interdigitated electrodes is 0.16 μm. Along the thickness direction of the piezoelectric layer, a temperature compensation layer is disposed on the side of the piezoelectric layer opposite to the interdigitated electrodes. Ideally, the thickness of the piezoelectric layer is considered infinite, and correspondingly, the temperature compensation layer can be considered to be infinitely far from the interdigitated electrodes. As shown in Figure 8, the admittance curve corresponding to the comparative example is represented by a solid line.

[0097] For the embodiments, there are four sets of embodiments. Each set of embodiments' surface acoustic wave device 100 includes a functional layer 40, a temperature compensation layer 30, a piezoelectric layer 10, and interdigitated electrodes 20 disposed on the first surface 11 of the piezoelectric layer 10, which are stacked sequentially. The centerline spacing P between two adjacent interdigitated electrodes 22 is 1.0 μm, the duty cycle of the interdigitated electrodes 20 is 0.4, the piezoelectric layer 10 is made of 42°YX-LiTaO3, the electrode fingers 22 are made of aluminum, and the thickness of the electrode fingers 22 is 0.16 μm.

[0098] The four sets of embodiments are Examples 1 through 4. Along the third direction 003, the thickness of the piezoelectric layer 10 in Example 1 is 0.2 μm. The thickness of the piezoelectric layer 10 in Example 2 is 0.6 μm. The thickness of the piezoelectric layer 10 in Example 3 is 1.0 μm. The thickness of the piezoelectric layer 10 in Example 4 is 1.4 μm. As shown in Figure 8, the admittance curves corresponding to Examples 1 through 4 are represented by different dashed lines.

[0099] Based on the material parameters of 42°YX-LiTaO3, the sound velocity of the bulk wave propagating along the second direction 002 in the piezoelectric layer 10 of Examples 1-4 and the comparative example piezoelectric layer can be calculated to be approximately 4230 m / s. The surface acoustic wave resonant frequency is 1.982 GHz, and the surface acoustic wave anti-resonant frequency is 2.058 GHz.

[0100] Regarding proportions, according to It can be concluded that when the surface acoustic wave frequency is the surface acoustic wave resonant frequency, the first characteristic thickness T is... y =0.91μm. When the surface acoustic wave frequency is the surface acoustic wave anti-resonance frequency, the first characteristic thickness T is... y = 1.4 μm. For ease of description, the first characteristic thickness T is used. y Let's take 0.91μm as an example for introduction.

[0101] As shown in Figure 8, for Examples 1-4, the thicker the piezoelectric layer 10, the closer the admittance curve of the examples is to the admittance curve of the comparative examples. In the comparative examples, because the thickness of the piezoelectric layer can be considered infinite, the corresponding surface acoustic wave disturbance region does not overlap with the temperature compensation layer disposed on the piezoelectric layer. That is, the temperature compensation layer in the comparative examples does not play an acoustic role.

[0102] On the other hand, because of the 1.5T y = 1.365 μm. It can be seen that the thickness of the piezoelectric layer 10 corresponding to Examples 1-3 is less than 1.5 T. y The thickness of the piezoelectric layer 10 in Example 4 is greater than 1.5T. y It is evident that the admittance curves of Examples 1-3 are poorly consistent with the admittance curves of the comparative examples, and correspondingly, the acoustic effect of the temperature compensation layer 30 in Examples 1-3 is more pronounced.

[0103] In other words, compared to the comparative example, the surface acoustic wave device 100 of this application, by limiting the thickness of the piezoelectric layer 10, enables the energy of the surface acoustic wave to be effectively transferred to the temperature compensation layer 30, thereby ensuring the acoustic function of the temperature compensation layer 30. This improves the working performance of the surface acoustic wave device 100 of this application.

[0104] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer 10 is less than the first characteristic thickness.

[0105] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer 10 and the first characteristic thickness satisfy the following condition:

[0106] In one embodiment, as shown in FIG6, the surface acoustic wave device 100 of this application further includes a temperature compensation layer 30, which is disposed along a third direction 003 on the side of the piezoelectric layer 10 away from the interdigitated electrode 20. In this embodiment, the temperature compensation layer 30 mainly improves the temperature stability of the surface acoustic wave device 100 by its own response to temperature changes, thereby demonstrating its acoustic function.

[0107] Specifically, during the use of the surface acoustic wave device 100 of this application, the acoustic properties of the piezoelectric layer 10 change with temperature variations. The temperature compensation layer 30 is made of a material with a temperature coefficient opposite to or smaller than that of the piezoelectric layer 10. In actual operation, the temperature compensation layer 30 can partially or completely offset the temperature effect of the piezoelectric layer 10.

[0108] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 is H, and the first feature thickness and the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 satisfy the following condition:

[0109] The value of the first characteristic thickness after the surface acoustic wave device 100 is fabricated can be calculated. It is understandable that the ratio of the first characteristic thickness to the sum of the thicknesses of the temperature compensation layer 30 and the piezoelectric layer 10 limits the sum of the thicknesses of the temperature compensation layer 30 and the piezoelectric layer 10, further ensuring that the energy of the surface acoustic wave can be effectively transferred to the temperature compensation layer 30. This ensures the temperature compensation function of the temperature compensation layer 30 on the piezoelectric layer 10, realizing the acoustic effect of the temperature compensation layer 30 on the surface acoustic wave device 100 of this application.

[0110] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the first characteristic thickness, the thickness of the temperature compensation layer 30, and the thickness of the piezoelectric layer 10 satisfies the following condition:

[0111] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 is less than the first characteristic thickness.

[0112] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the first characteristic thickness, the thickness of the temperature compensation layer 30, and the thickness of the piezoelectric layer 10 satisfies the following condition:

[0113] In one embodiment, when the angle between the propagation direction of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 and the first surface 11 is equal to the first reinforcement angle θ, the bulk wave in the piezoelectric layer 10 and the temperature compensation layer 30 is in a reinforced state. The propagation speed of the bulk wave excited by the two electrode fingers 22 of the interdigitated electrode 20 into the piezoelectric layer 10 and the temperature compensation layer 30 within one periodic segment length is V0, and the first angle satisfies the equation with respect to the propagation speed of the bulk wave in the piezoelectric layer 10 and the temperature compensation layer 30: The surface acoustic wave device 100 has a surface acoustic wave frequency of f, and the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 satisfies the following condition: Wherein, the surface acoustic wave frequency f is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency.

[0114] In the above description of the relationship satisfied by the sum of the thicknesses of the temperature compensation layer 30 and the piezoelectric layer 10, the refraction effect of the bulk wave at the interface between the piezoelectric layer 10 and the temperature compensation layer 30 is neglected for the sake of simplification. Correspondingly, the propagation speed of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 and the temperature compensation layer 30 is the propagation speed under the ideal condition of neglecting the difference in sound speed between the piezoelectric layer 10 and the temperature compensation layer 30.

[0115] In this embodiment, along the third direction 003, the temperature compensation layer 30 is disposed on the surface of the piezoelectric layer 10 facing away from the first surface 11, and the surface of the temperature compensation layer 30 facing away from the piezoelectric layer 10 is defined as the second surface 31. It is understood that when a volume wave propagates to the second surface 31, at least a portion of the volume wave will be reflected on the second surface 31. The reflected volume wave will also be reflected when it propagates to the first surface 11.

[0116] When the phases of the bulk wave after two reflections from the first surface 11 and the second surface 31 match, the bulk wave will form a waveguide mode within the piezoelectric layer 10 and the temperature compensation layer 30. The surface acoustic wave device 100 of this application further limits the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 by the above conditions, thereby reducing the influence of the waveguide mode frequency on the surface acoustic wave frequency. This ensures the operating performance of the surface acoustic wave device 100 of this application.

[0117] In one embodiment, the thickness of the temperature compensation layer 30 is D. w The thicknesses of the temperature compensation layer 30 and the piezoelectric layer 10 satisfy the following conditions: When the thickness of the piezoelectric layer 10 is determined, if the ratio of the thickness of the piezoelectric layer 10 to the thickness of the temperature compensation layer 30 is less than 0.5, then the thickness of the temperature compensation layer 30 is too thick. An excessively thick temperature compensation layer 30 will not significantly improve the frequency temperature coefficient of the device, but will cause deterioration in the device's operating frequency and noise characteristics, affecting the operating performance of the surface acoustic wave device 100 of this application.

[0118] When the thickness of the piezoelectric layer 10 is determined, if the ratio of the thickness of the piezoelectric layer 10 to the thickness of the temperature compensation layer 30 is greater than 2, then the thickness of the temperature compensation layer 30 is too thin, which may make it difficult for the temperature compensation layer 30 to achieve the predetermined temperature stability of the surface acoustic wave device 100.

[0119] Therefore, the surface acoustic wave device 100 of this application achieves a matching setting of the thicknesses of the temperature compensation layer 30 and the piezoelectric layer 10 by limiting the range of the ratio between the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10. This improves the operating performance and temperature stability of the surface acoustic wave device 100 of this application.

[0120] In one embodiment, when the angle between the propagation direction of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 and the first surface 11 is equal to the first reinforcement angle θ, the bulk wave in the piezoelectric layer 10 is in a reinforced state; the wavelength λ of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 is... B1 The bulk wavelength is the wavelength of the piezoelectric layer 10 in the enhanced state.

[0121] When a bulk wave excited by the interdigitated electrode 20 propagates along the third direction 003 at a certain angle, the angle between the propagation direction of the bulk wave and the first surface 11 is the propagation angle. For any two different propagation angles, the intensity of the bulk wave corresponding to one propagation angle may be different from the intensity of the bulk wave corresponding to the other propagation angle. When the propagation angle is equal to the first reinforcement angle, the intensity of the bulk wave in the piezoelectric layer 10 is the greatest compared to the intensity of the bulk wave corresponding to other propagation angles.

[0122] In one embodiment, the midline distance between two adjacent electrode fingers is P, and the first reinforcement angle is θ, which satisfies the following equation: Among them, V B1 λ is the volume wave velocity within the piezoelectric layer 10, f is the operating frequency, and λ is the velocity of sound. B1 The first reinforcement angle θ is the bulk wave wavelength excited by the interdigitated electrode 20 in the piezoelectric layer 10, and the range of the first reinforcement angle θ satisfies: 0° < θ < 180°.

[0123] Based on the limitations of the above embodiments, please refer to FIG9, which is a partial cross-sectional structural schematic diagram of the surface acoustic wave device 100 provided in one embodiment of this application. In FIG9, the solid line with arrows below the interdigitated electrodes 20 represents the volume wave propagating in the piezoelectric layer 10 and the direction of propagation of the volume wave.

[0124] In this application, the surface acoustic wave (SAW) device 100 exhibits a surface acoustic wave intensity that gradually decreases with increasing depth along the third direction 003 as the surface acoustic wave propagates along the piezoelectric layer 10. The first characteristic thickness represents the decrease in SAW intensity to the point where the surface acoustic wave intensity attenuates to the first surface 11. The distance between the time and the first surface 11.

[0125] That is, the surface acoustic wave device 100 of this application obtains the surface acoustic wave intensity attenuated to the first surface 11 by acquiring the surface acoustic wave intensity attenuated to the first surface 11. The distance between the piezoelectric layer 10 and the first surface 11 is used to define the thickness of the piezoelectric layer 10 and to ensure that the characteristic depth of the surface acoustic wave can cover the temperature compensation layer or overlap with the temperature compensation layer 30 below the thickness of the piezoelectric layer 10.

[0126] Specifically, in the embodiments of this application, the acoustic wave vector generated by the surface acoustic wave device 100 during operation has a real component along the thickness direction of the piezoelectric layer 10, which is a volume wave. The enhancement condition for volume wave excitation refers to the phase matching of the volume waves excited by the electrode fingers 22 of the same polarity in a specific direction. As shown in Figure 9, the volume wave vector β excited by two adjacent first electrode fingers 22a of the interdigitated electrodes 20 into the piezoelectric layer 10 is... B1 The angle between the propagation direction and the first surface 11 is equal to the first reinforcing angle θ.

[0127] At this time, the wavelength λ of the bulk wave in the enhanced state within the piezoelectric layer 10 B1 The distance P between the central axes of two adjacent electrode fingers 22 and the first reinforcement angle θ satisfy the condition: 2Pcosθ=nλ B1 Where n is a positive integer.

[0128] In this embodiment, the case where n=1 is considered. That is, The propagation speed of the bulk wave in the enhanced state within the piezoelectric layer 10 is V. B1 The volume wave vector β in the piezoelectric layer 10 is in an enhanced state. B1 The operating frequency is f.

[0129] In this embodiment, the magnitude of the first strengthening angle is determined by the operating frequency f. When When, cosθ=1.

[0130] When f <f c1When cosθ > 1, the first reinforcement angle θ is a complex number, and correspondingly, the acoustic wave vector generated by the surface acoustic wave device 100 of this application does not have a real component along the thickness direction of the piezoelectric layer 10. That is, when the first reinforcement angle is complex, the acoustic wave vector component propagating in the piezoelectric layer 10 along the third direction θ03 away from the first surface 11 is imaginary, and the acoustic wave is an evanescent wave. Therefore, under ideal conditions, for the surface acoustic wave device 100 of this application, only the energy of the surface acoustic wave is concentrated on the surface of the device.

[0131] To facilitate the distinction between the sound wave state when the first reinforcement angle is a real number and the sound wave state when the first reinforcement angle is a complex number, β1 is used to represent the sound wave state when the first reinforcement angle is a complex number.

[0132] At this time, the intensity of the acoustic wave vector β1 rapidly attenuates along the third direction 003 in a direction away from the first surface 11. The surface acoustic wave device 100 of this application utilizes the attenuation characteristics of evanescent waves to characterize the distribution range of the surface acoustic waves. Specifically, the evanescent wave intensity attenuates to the evanescent wave intensity at the first surface 11... The distance between the time and the first surface 11 has a certain correspondence with the thickness of the piezoelectric layer 10 when the amplitude of the surface acoustic wave overlaps with the temperature compensation layer 30.

[0133] The wave vector component of the acoustic wave vector β1 on the third direction 003 is β 1z Since the first reinforcement angle is a complex number, the acoustic wave of the surface acoustic wave device 100 of this application only manifests as an acoustic wave along the X direction. At this time, the modulus of the acoustic wave vector β1 satisfies the equation: Where λ1 is the bulk wavelength of the piezoelectric crystal along the X direction at the operating frequency f.

[0134] The wave vector component β1 on the third direction 003 is β 1z Satisfying the equation:

[0135] In the above equation, the first enhancement angle θ is selected as the operating frequency f = f c1 At that time, the value of the first strengthening angle.

[0136] The intensity of the surface acoustic wave propagating along the third direction 003 in the piezoelectric layer 10 towards the direction away from the first surface 11 is denoted by u, wherein the intensity of the surface acoustic wave in the piezoelectric layer 10 satisfies the equation The body wave component of the acoustic wave vector β1 in the second direction 002 is β 1x z represents the distance between any point within the piezoelectric layer 10 and the first surface 11.

[0137] In this embodiment, the first characteristic thickness represents the surface acoustic wave intensity attenuated to the surface acoustic wave intensity at the first surface 11. The distance between the time and the first surface 11. That is,

[0138] Will Substituting into the equation for the acoustic wave intensity within the piezoelectric layer 10, the z-value in the above equation is obtained. The calculated z-value is the first characteristic thickness. Since V B1 The volume wave velocity within the piezoelectric layer 10 is given. When the first reinforcement angle is a complex number, the sound wave velocity of the surface acoustic wave device in this application depends only on the material of the piezoelectric layer 10. Therefore, the first characteristic thickness... Wherein, the volume wave velocity of the piezoelectric crystal along the X direction is V. b1 .

[0139] In this embodiment, after calculating the first characteristic thickness based on the above equation, the thickness of the piezoelectric layer 10 is determined by the range of the ratio between the thickness of the piezoelectric layer 10 and the first characteristic thickness. For a piezoelectric layer 10 with this thickness, the energy of the surface acoustic wave can act on the temperature compensation layer 30 through the piezoelectric layer 10. That is, the amplitude of the surface acoustic wave overlaps with that of the temperature compensation layer 30.

[0140] Please refer to Figure 10, which is a partial cross-sectional view of the surface acoustic wave device 100 provided in one embodiment of this application. In Figure 10, solid lines with arrows indicate the bulk waves propagating within the piezoelectric layer 10 and the temperature compensation layer 30, and the direction of bulk wave propagation.

[0141] As shown in Figure 10, the first reinforcement angle is a real number, the propagation speed of the bulk wave inside the piezoelectric layer 10 and the temperature compensation layer 30 is V0, the operating frequency of the interdigitated electrode 20 is f, and the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 is H.

[0142] It is worth noting that the propagation speed of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 and the temperature compensation layer 30 is the propagation speed under ideal conditions where the difference in sound speed between the piezoelectric layer 10 and the temperature compensation layer 30 is ignored. That is, the propagation speed V0 of the bulk wave in the piezoelectric layer 10 and the temperature compensation layer 30 is V0. B1 The values ​​are equal, but different superscripts are used in the embodiments of this application for easy distinction.

[0143] When the phase difference between the two reflections of the bulk wave on the first surface 11 and the second surface 31 is 2nπ, the bulk wave will form a waveguide mode within the piezoelectric layer 10 and the temperature compensation layer 30. Here, n is a positive integer.

[0144] The frequency of the waveguide mode is f g The frequency of the waveguide mode satisfies the equation:

[0145] Where 2n represents the ratio of the path length of the volume wave between the reflections on the first surface 11 and the second surface 31 to the wavelength of the volume wave. This represents the ratio of the phase introduced by the body wave when reflected from the first surface 11 and the second surface 31 to π.

[0146] In practical use of the surface acoustic wave (SAW) device 100 of this application, the waveguide mode may affect the ripple of the SAW filter passband. Typically, the waveguide mode frequency f is required to be... g The surface acoustic wave frequency f (e.g., the surface acoustic wave resonant frequency f) r It is η times the value of 1.07. Where η > 1.07 or η = 1.05. For ease of description, we will take η > 1.07 as an example.

[0147] That is, the sum H of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 satisfies the condition:

[0148] Based on the above conditions, it can be seen that in order to determine the maximum range of the sum H of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10, Correspondingly, The minimum value should be taken. That is, n = 1. The phase difference introduced by the body wave when reflected from the first surface 11 and the second surface 31 is 0, that is, Therefore, we obtain

[0149] The first reinforcement angle is defined to satisfy the equation with respect to the propagation velocity of the bulk wave within the piezoelectric layer 10 and the temperature compensation layer 30: Therefore, we obtain

[0150] In this embodiment, during the fabrication of the surface acoustic wave (SAW) device 100, the range of the sum of the thicknesses H of the temperature compensation layer 30 and the piezoelectric layer 10 can be calculated by obtaining the first reinforcement angle θ, the propagation velocity V0 of the bulk wave excited by the interdigitated electrode 20 into the piezoelectric layer 10 and the temperature compensation layer 30 when in the reinforcement state, and the SAW frequency f. This limits the range of the sum of the thicknesses H of the temperature compensation layer 30 and the piezoelectric layer 10, facilitating the selection of the thickness D of the piezoelectric layer 10. y and the thickness D of the temperature compensation layer w .

[0151] Wherein, for the first strengthening angle θ. Since the first strengthening angle is a real number, according to Using Christoph's formula, we can obtain a local curve showing the relationship between F(θ) and the first strengthening angle θ, as shown in Figure 11. The horizontal axis represents the first strengthening angle θ, in degrees. The vertical axis represents F(θ), in m / s.

[0152] Based on the equation relationship between G(θ) and F(θ), it can be known that, That is, when calculating G(θ), F(θ) and the first strengthening angle θ can be obtained through Figure 11 to calculate G(θ).

[0153] Therefore, in the process of fabricating the surface acoustic wave device 100 of this application, the distance P between the midlines of two adjacent electrode fingers 22 and the volume wave velocity V of the piezoelectric crystal along the X direction can be obtained. b1 The first characteristic thickness T is calculated based on the operating frequency f. y .

[0154] The first characteristic thickness T is calculated. y On this premise, it is necessary to further limit the selection range of the sum H of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10. Specifically, this can be achieved by obtaining the midline distance P between two adjacent electrode fingers 22 and the volume wave velocity V within the piezoelectric layer 10. B1 The first strengthening angle θ is calculated based on the operating frequency f.

[0155] On the other hand, the F(θ) value corresponding to the first strengthening angle θ can also be calculated by the operating frequency f and the distance P between the central axes of two adjacent electrode fingers 22, and the first strengthening angle θ can be obtained by relying on Figure 11 (as shown by the double-dotted line parallel to the horizontal axis in Figure 11).

[0156] In this embodiment, the body wave includes longitudinal waves and transverse waves, and the transverse waves include fast shear waves and slow shear waves. When obtaining the first reinforcement angle θ, different intersection points can be selected to choose different first reinforcement angles θ based on actual needs.

[0157] Based on the first reinforcement angle θ, another limited range of the sum H of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 is calculated by obtaining the propagation velocity V0 of the bulk wave in the piezoelectric layer 10 and the temperature compensation layer 30, as well as the surface acoustic wave frequency f (surface acoustic wave resonant frequency or surface acoustic wave anti-resonant frequency) selected in the embodiment of this application.

[0158] During the fabrication of the surface acoustic wave device 100 of this application, the first characteristic thickness T can be used. y The sum H of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 is limited, and... The range of the sum H of the thickness of the temperature compensation layer 30 and the piezoelectric layer 10 is defined, thereby limiting the range of the sum H of the thickness of the temperature compensation layer 30 and the piezoelectric layer 10. This facilitates the selection of the thickness D of the piezoelectric layer 10. y and the thickness D of the temperature compensation layer w .

[0159] In one embodiment, the surface acoustic wave device 100 further includes a functional layer 40, which is disposed on the side of the piezoelectric layer 10 away from the interdigitated electrode 20 along the thickness direction of the piezoelectric layer 10. Specifically, referring back to Figure 6, along the third direction 003, the functional layer 40 is disposed on the side of the temperature compensation layer 30 away from the piezoelectric layer 10 to block the leakage of bulk waves and reduce the loss of the surface acoustic wave device 100.

[0160] When the surface acoustic wave device 100 of this application is in operation, the bulk wave generated will be released to the piezoelectric layer 10 and then propagate through the temperature compensation layer 30 into the functional layer 40, and propagate in a direction away from the second surface 31.

[0161] The second characteristic thickness of the surface acoustic wave device 100 in this application is T. d The thickness of functional layer 40 is D. d The thickness of functional layer 40 and the thickness of the second feature satisfy the following condition: That is, the ratio between the thickness of the functional layer 40 and the thickness of the second feature is less than or equal to 1.5.

[0162] The thickness of the second feature is determined by the volume wave velocity and operating frequency of the material of the pressure functional layer 40 along the X direction.

[0163] Specifically, in one embodiment, the wavelength of a bulk wave in the enhanced state within the piezoelectric layer 10 refracted into the functional layer 40 is λ2, and the second characteristic thickness satisfies the equation:

[0164] Since, after the surface acoustic wave device 100 of this application is fabricated, the center-to-center distance between two adjacent electrode fingers 22 is P, and the volume wave velocity of the material of the functional layer 40 along the X direction is V. b2 The operating frequency is f, and both are measurable or calculable values. Therefore, the surface acoustic wave device 100 of this application can be based on the volume wave velocity V. b2 The wavelength λ2 corresponding to the bulk sound velocity of the material of functional layer 40 along the X direction at the operating frequency is calculated using the operating frequency f, and the second characteristic thickness is obtained based on the bulk wave wavelength λ2 and the centerline spacing P.

[0165] Therefore, given the second characteristic thickness, the thickness of the functional layer 40 can be determined based on the relationship between the second characteristic thickness and the thickness of the functional layer 40. The surface acoustic wave device 100 of this application limits the thickness of the functional layer 40 by defining the range of the ratio between the second characteristic thickness and the functional layer 40, allowing high-frequency bulk waves in the bulk wave to leak outwards, thereby reducing the quality factor (Q value) of high-frequency miscellaneous modes. This reduces the impact of high-frequency miscellaneous modes in practical applications and ensures the operating performance of the surface acoustic wave device 100 of this application.

[0166] In one embodiment, the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, and the thickness of the functional layer 40 and the thickness of the second feature satisfy the following condition: When the ratio of the thickness of the functional layer 40 to the thickness of the second feature is less than 0.2, the thickness of the functional layer 40 is too thin. An excessively thin functional layer 40 is more sensitive to temperature changes and has relatively poor mechanical strength. This results in relatively poor stability and reliability of the surface acoustic wave device 100 of this application.

[0167] When the ratio of the thickness of the functional layer 40 to the thickness of the second feature is greater than 1.5, the thickness of the functional layer 40 is too thick, and the blocking effect of the functional layer 40 on bulk wave leakage is enhanced, which may make it difficult for high-frequency noise modes in the bulk wave to leak out, thereby causing high-frequency noise modes to affect the working performance of the surface acoustic wave device 100 of this application.

[0168] Therefore, the surface acoustic wave (SAW) device 100 of this application sets the ratio of the thickness of the functional layer 40 to the thickness of the second feature between 0.2 and 1.5. This avoids the functional layer 40 becoming too thin due to an excessively small ratio, which would affect the working performance and stability of the SAW device 100. It also avoids the functional layer 40 becoming too thick due to an excessively large ratio, which would affect the leakage of high-frequency miscellaneous modes in the SAW device 100. This ensures the stability and working performance of the SAW device 100 of this application.

[0169] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer 40 is less than the second feature thickness.

[0170] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer 40 and the thickness of the second feature satisfy the following condition:

[0171] In one embodiment, as shown in FIG6, the surface acoustic wave device 100 of this application includes a single crystal silicon layer 50, which is disposed on the surface of the functional layer 40 away from the piezoelectric layer 10 along the third direction 003.

[0172] The bulk wave generated by the surface acoustic wave device 100 during operation, after being released to the piezoelectric layer 10, leaks sequentially through the temperature compensation layer 30 and the functional layer 40 to the monocrystalline silicon layer 50. In the embodiments of this application, the monocrystalline silicon layer 50... <110> The spatial angle between the crystal orientation and the propagation direction of the surface acoustic waves excited on the first surface 11 by the multiple electrode fingers 22 is less than or equal to 10°. That is, the single-crystal silicon layer 50... <110> The space angle between the crystal orientation group and the second orientation 002 is less than or equal to 10°.

[0173] Because the sound velocity of functional layer 40 is greater than that of monocrystalline silicon layer 50 along... <110> The speed of sound propagation in the direction of propagation. Understandably, functional layer 40 is a less dense medium than the monocrystalline silicon layer 50. When a bulk wave is incident at a certain angle to the interface between the monocrystalline silicon layer 50 and functional layer 40, the angle of refraction of the bulk wave refracted into the monocrystalline silicon layer 50 is smaller than the angle of incidence. Correspondingly, the angle between the propagation direction of the bulk wave refracted into the monocrystalline silicon layer 50 and the second direction 002 is greater than the angle between the propagation direction of the bulk wave incident into the monocrystalline silicon layer 50 and the second direction 002.

[0174] Furthermore, due to the 50% of the single-crystal silicon layer <110> Crystalline orientations exhibit lower sound wave propagation speeds and lower acoustic losses. Understandably, a 50-layer monocrystalline silicon crystal... <110> The space angle between the crystal orientation group and the second orientation 002 is less than or equal to 10°, which is conducive to the leakage of bulk waves through the functional layer 40 to the single crystal silicon layer 50.

[0175] In other words, the matching arrangement of the monocrystalline silicon layer 50 and the functional layer 40 can facilitate the leakage of high-frequency miscellaneous modes (including waveguide modes) in the bulk wave, thereby reducing the interference of high-frequency miscellaneous modes on the surface acoustic wave in practical applications and improving the working performance of the surface acoustic wave device 100 of this application.

[0176] In one embodiment, the monocrystalline silicon layer 50 <110> The crystal orientation is parallel to the propagation direction of the surface acoustic wave excited on the first surface 11 by the multiple electrode fingers 22.

[0177] Please refer to Figures 12 and 13, where Figure 12 is another structural schematic diagram of the surface acoustic wave device 100 provided in one embodiment of this application, and Figure 13 is another cross-sectional structural schematic diagram of the surface acoustic wave device 100 provided in one embodiment of this application.

[0178] As shown in Figures 12 and 13, the surface acoustic wave device 100 of this application includes a functional layer 40 and a piezoelectric layer 10 stacked along its own thickness direction, and at least one interdigitated electrode 20 disposed on a first surface 11 of the piezoelectric layer 10 away from the functional layer 40.

[0179] The interdigitated electrode 20 includes two parallel and spaced-apart busbars 21 and a plurality of parallel and spaced-apart electrode fingers 22. One of the two busbars 21 is used to receive external signals, and the other busbar 21 is used to output signals. The plurality of electrode fingers 22 are located between the two busbars 21. Some of the electrode fingers 22 are connected to one busbar 21, and other electrode fingers 22 are connected to the other busbar 21.

[0180] For ease of description, the busbar 21 used for receiving external signals is defined as the first busbar 21a, and the busbar 21 used for outputting signals is defined as the second busbar 21b. The electrode finger 22 connected to the first busbar 21a is defined as the first electrode finger 22a, and the electrode finger 22 connected to the second busbar 21b is defined as the second electrode finger 22b.

[0181] Specifically, both the first electrode finger 22a and the second electrode finger 22b extend along the first direction 001 towards opposite sides of the piezoelectric layer 10. Along the second direction 002, the first electrode finger 22a and the second electrode finger 22b are arranged alternately. Specifically, as shown in Figure 12, along the second direction 002, there is a second electrode finger 22b between any two adjacent first electrode fingers 22a, and a first electrode finger 22a between any two adjacent second electrode fingers 22b.

[0182] The first busbar 21a and the second busbar 21b both extend along the second direction 002 to opposite sides of the piezoelectric layer 10, wherein the first direction 001 and the second direction 002 are perpendicular to each other. In practical applications, the surface acoustic wave device 100 of this application may have errors, and the angle between the first direction 001 and the second direction 002 may not be equal to 90°.

[0183] In this embodiment, based on the inverse piezoelectric effect of the piezoelectric layer 10, an electrical signal can be sequentially applied to the piezoelectric layer 10 via the first busbar 21a and each of the first electrode fingers 22a, causing periodic deformation of the surface of the piezoelectric layer 10. This generates an outwardly released sound wave.

[0184] The acoustic waves emitted by the surface acoustic wave device 100 during operation include surface acoustic waves and volume waves. Specifically, when the component of the acoustic wave along the thickness direction of the piezoelectric layer 10 is imaginary, this type of acoustic wave can only propagate along the plane of the first surface 11, and is therefore a surface acoustic wave. The propagation direction of the surface acoustic wave is defined as the X-direction. When the acoustic wave vector has a real component along the thickness direction of the piezoelectric layer 10, it is a volume wave.

[0185] Surface acoustic waves (SAWs) are used to realize the frequency selection and signal processing functions of the SAW device 100 of this application. During SAW propagation, the main propagation direction is the second direction 002. That is, the X direction is the second direction 002. However, in practice, due to edge effects and acoustic diffraction, the propagation direction of the SAW formed on the first surface 11 of the piezoelectric layer 10 may also be in other directions, corresponding to an angle between the X direction and the second direction 002. In one embodiment, SAWs propagating in other directions are absorbed by a sound-absorbing material (not shown in the figure).

[0186] In this embodiment, the bulk wave generated when the surface acoustic wave device 100 is working will be released to the piezoelectric layer 10 and propagate into the functional layer 40. The bulk wave in the functional layer 40 will propagate in a direction away from the first surface 11.

[0187] The second characteristic thickness of the surface acoustic wave device 100 in this application is T. d The thickness of functional layer 40 is D. d The thickness of functional layer 40 and the thickness of the second feature satisfy the following condition: That is, the ratio between the thickness of the functional layer 40 and the thickness of the second feature is less than or equal to 1.5.

[0188] The thickness of the second feature is determined by the volume wave velocity and operating frequency of the material of the functional layer 40 along the X direction. In this embodiment, the volume wave velocity of the material of the functional layer 40 along the X direction is determined by the material of the functional layer 40; when the material of the functional layer 40 is determined, the volume wave velocity of the material of the functional layer 40 along the X direction is also determined.

[0189] Specifically, please refer to Figure 14 for another enlarged cross-sectional view of the surface acoustic wave device 100 provided in one embodiment of this application.

[0190] As shown in Figure 14, the midline spacing between two adjacent electrode fingers 22 is P, and the volume wave velocity of the material of the functional layer 40 along the X direction is V. b2 The operating frequency is f, and the second feature thickness satisfies the equation:

[0191] Therefore, the surface acoustic wave device 100 of this application can be based on the volume wave velocity V. b2 The wavelength λ2 corresponding to the bulk wave velocity of the material of functional layer 40 along the X direction at the operating frequency is calculated using the operating frequency f, and the second characteristic thickness is obtained based on the bulk wave wavelength λ2 and the midline spacing P.

[0192] Therefore, given the second characteristic thickness, the thickness of the functional layer 40 can be determined based on the relationship between the second characteristic thickness and the thickness of the functional layer 40. The surface acoustic wave device 100 of this application limits the thickness of the functional layer 40 by defining the range of the ratio between the second characteristic thickness and the functional layer 40, allowing high-frequency bulk waves in the bulk wave to leak outwards, thereby reducing the quality factor (Q value) of high-frequency miscellaneous modes. This reduces the impact of high-frequency miscellaneous modes in practical applications and ensures the operating performance of the surface acoustic wave device 100 of this application.

[0193] Specifically, admittance can be used to describe the response process of components and signals. In the surface acoustic wave (SAW) device 100 of this application, admittance is used to measure the influence of clutter propagating on the surface of the piezoelectric layer 10 on the acoustic wave quality. Figure 15 shows schematic diagrams of the conductance curves of the SAW device 100 of this application and the SAW device in the comparative example based on different SAW frequencies. The horizontal axis is in GHz, and the vertical axis is in dB.

[0194] For the comparative examples, there are two sets, and the surface acoustic wave devices in each set include a piezoelectric layer and interdigitated electrodes disposed on the surface of the piezoelectric layer. The centerline spacing P between two adjacent interdigitated electrodes is 1.0 μm, the duty cycle of the interdigitated electrodes is 0.4, the piezoelectric layer is 0.6 μm thick 42°YX-LiTaO3, the interdigitated electrodes are made of aluminum, and the thickness of the interdigitated electrodes is 0.16 μm.

[0195] The two comparative examples are Comparative Example 1 and Comparative Example 2. In Comparative Example 1, a single-crystal silicon layer is provided on the side of the piezoelectric layer away from the interdigitated electrodes along the thickness direction of the piezoelectric layer. The upper surface of the single-crystal silicon layer is (111), where the [1-10] crystal orientation is parallel to the second direction 002. In Comparative Example 2, a functional layer is provided on the side of the piezoelectric layer away from the interdigitated electrodes along the thickness direction of the piezoelectric layer. As shown in Figure 15, the conductivity curves corresponding to Comparative Example 1 and Comparative Example 2 are represented by solid lines of different linewidths.

[0196] For the embodiments, there are six sets of embodiments. The surface acoustic wave device 100 in each set of embodiments includes a single crystal silicon layer 50, a functional layer 40, a temperature compensation layer 30, a piezoelectric layer 10, and interdigitated electrodes 20 disposed on the first surface 11 of the piezoelectric layer 10, which are stacked sequentially. Among them, the midline spacing P between two adjacent electrode fingers 22 of the interdigitated electrodes 20 is 1.0 μm, the duty cycle of the interdigitated electrodes 20 is 0.4, the piezoelectric layer 10 is made of 0.6 μm 42°YX-LiTaO3, the electrode fingers 22 are made of aluminum, and the electrode fingers 22 have a thickness of 0.16 μm. The upper surface of the single crystal silicon layer 50 is (111), wherein the crystal orientation of [1-10] is parallel to the second direction 002.

[0197] The six sets of embodiments are Examples 5 through 10. Along the third direction 003, the thickness of the functional layer 40 in Example 5 is 0.6 μm. The thickness of the functional layer 40 in Example 6 is 1.0 μm. The thickness of the functional layer 40 in Example 7 is 1.4 μm. The thickness of the functional layer 40 in Example 8 is 1.8 μm. The thickness of the functional layer 40 in Example 9 is 2.2 μm. The thickness of the functional layer 40 in Example 10 is 2.6 μm. As shown in Figure 15, the conductivity curves corresponding to Examples 5 through 10 are represented by different line segments.

[0198] Based on the material parameters of 42°YX-LiTaO3, the transverse wave velocity within the functional layer 40 can be calculated to be approximately 5340 m / s for this embodiment. This is further supported by a local curve showing the relationship between the second reinforcement angle of the functional layer 40 of the surface acoustic wave device and the volume wave velocity. The second characteristic thickness T for a body wave with a frequency of 2.4 GHz was calculated. d =0.73μm.

[0199] Figure 15 shows the variation of harmonic conductance with the thickness of functional layer 40, where conductance is directly related to system losses. For Comparative Example 1, there is an inflection point in the harmonic conductance curve at 2.34 GHz, indicating that the bulk wave released from the interdigitated electrode 20 into the piezoelectric layer 10 leaks from 2.34 GHz into the monocrystalline silicon layer 50. For Comparative Example 2, however, this inflection point appears in the harmonic conductance curve at 2.67 GHz.

[0200] For surface acoustic wave (SAW) devices, leakage of high-frequency clutter in the bulk wave can reduce the Q value of high-frequency clutter modes and weaken their interference with the operation of the SAW device. Therefore, SAW devices typically require control of the leakage frequency to avoid excessively high leakage frequencies that would hinder the leakage of high-frequency clutter.

[0201] As shown in Figure 15, for Examples 5-10, the thinner the functional layer 40, the closer its conductivity curve is to that of Comparative Example 1. The thicker the functional layer 40, the closer its conductivity curve is to that of Comparative Example 2.

[0202] On the other hand, because of the 1.5T d =1.095μm. It can be seen that the thickness of the functional layer 40 corresponding to Examples 5 and 6 is less than 1.5T. d The thickness of the functional layer 40 corresponding to Examples 7-10 is greater than 1.5T. dIt is evident that the inflection points of Embodiments 5 and 6 are relatively close to the inflection point of Comparative Example 1. That is, the surface acoustic wave devices 100 corresponding to Embodiments 5 and 6 are better able to achieve leakage of high-frequency clutter in the volume wave.

[0203] In other words, compared to Comparative Examples 1 and 2, the surface acoustic wave device 100 of this application, by limiting the thickness of the functional layer 40, allows bulk waves to leak across the functional layer 40 to the single-crystal silicon layer 50, thereby reducing interference from high-frequency noise modes in practical applications. This improves the operating performance of the surface acoustic wave device 100 of this application.

[0204] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer 40 and the thickness of the second feature satisfy the following condition: The surface acoustic wave (SAW) device 100 of this application sets the ratio of the thickness of the functional layer 40 to the thickness of the second feature between 0.2 and 1.5. This avoids the functional layer 40 becoming too thin due to an excessively small ratio, which would affect the working performance and stability of the SAW device 100. It also avoids the functional layer 40 becoming too thick due to an excessively large ratio, which would affect the leakage of high-frequency miscellaneous modes in the SAW device 100. This ensures the stability and working performance of the SAW device 100 of this application.

[0205] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer 40 is less than the second feature thickness.

[0206] In one embodiment, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer 40 and the thickness of the second feature satisfy the following condition:

[0207] In one embodiment, the first characteristic thickness of the surface acoustic wave device 100 is T. y The thickness of the piezoelectric layer 10 is D. y The thickness of the piezoelectric layer 10 and the thickness of the first feature satisfy the following condition: The thickness of the first feature is determined based on the midline spacing between two adjacent electrode fingers 22 and the volume wave velocity and operating frequency of the piezoelectric layer 10 along the X direction.

[0208] In one embodiment, the thickness of the first feature satisfies the equation:

[0209] In one embodiment, referring back to FIG13, the surface acoustic wave device 100 of this application further includes a temperature compensation layer 30 and a single-crystal silicon layer 50. Along the third direction 003, the temperature compensation layer 30 is located between the piezoelectric layer 10 and the functional layer 40 to improve the temperature stability of the surface acoustic wave device 100 of this application. The single-crystal silicon layer 50 is disposed on the side of the functional layer 40 away from the temperature compensation layer 30 to facilitate the leakage of waveguide mode capability.

[0210] In one embodiment, when the angle between the propagation direction of the acoustic wave excited by the interdigital electrode 20 and the first surface 11 is equal to the second reinforcement angle γ, the bulk wave in the functional layer 40 is in a reinforced state; the bulk wave wavelength λ of the acoustic wave excited by the interdigital electrode 20 propagating into the functional layer is... B2 The bulk wavelength within functional layer 40 in the enhanced state.

[0211] When the interdigitated electrode 20 excites a bulk wave within the functional layer 40, which propagates at a certain angle along the third direction 003, the angle between the propagation direction of the bulk wave and the first surface 11 is the propagation angle. For any two different propagation angles, the intensity of the bulk wave corresponding to one propagation angle may differ from the intensity of the bulk wave corresponding to the other propagation angle. When the propagation angle is equal to the second reinforcement angle, the intensity of the bulk wave within the functional layer 40 is the greatest compared to the intensity of the bulk wave corresponding to other propagation angles.

[0212] In one embodiment, the midline distance between two adjacent electrode fingers is P, and the second reinforcement angle is γ, which satisfies the equation: Among them, V B2 λ is the volume wave velocity within the functional layer, f is the operating frequency, and λ is the velocity of sound. B2 The second reinforcement angle γ is the bulk wavelength of the acoustic wave excited by the interdigital electrode that propagates into the functional layer, and satisfies: 0° < γ < 180°.

[0213] Based on the limitations of the above embodiments, please refer to FIG16, which is a partial cross-sectional structural schematic diagram of the surface acoustic wave device 100 provided in one embodiment of this application. In FIG16, the solid lines with arrows below the interdigitated electrodes 20 indicate the bulk waves propagating in the piezoelectric layer 10, the temperature compensation layer 30, and the functional layer 40, and the propagation direction of the bulk waves.

[0214] For ease of description, the refraction effect of bulk waves at the interface between the piezoelectric layer 10 and the temperature compensation layer 30 is ignored. The surface where the temperature compensation layer 30 is attached to the functional layer 40 is defined as the second surface 31.

[0215] During the propagation of the bulk wave in the surface acoustic wave device 100 of this application within the functional layer 40, the intensity of the bulk wave gradually decreases as the propagation depth along the third direction 003 gradually increases. The second characteristic thickness represents the attenuation of the bulk wave intensity to the point where it decreases to the second surface 31. The distance between the volume wave intensity and the second surface 31. That is, the surface acoustic wave device 100 of this application obtains the volume wave intensity attenuated to the volume wave intensity at the second surface 31. The distance between the second surface 31 and the second surface 31 is used to define the thickness of the functional layer 40 and to ensure that the bulk wave can leak into the monocrystalline silicon layer 50 below the thickness of the functional layer 40.

[0216] Specifically, in the embodiments of this application, the acoustic wave vector generated by the surface acoustic wave device 100 during operation has a real component along the thickness direction of the functional layer 40, which is a volume wave. The enhancement condition for volume wave excitation refers to the phase matching of the volume waves excited by the electrode fingers 22 of the same polarity in a specific direction. As shown in Figure 16, the volume wave vector β excited by two adjacent first electrode fingers 22a of the interdigitated electrodes 20 into the piezoelectric layer 10 and entering the functional layer 40 via the temperature compensation layer 30 is... B2 The angle between the propagation direction and the second surface 31 is equal to the second reinforcing angle γ.

[0217] At this time, the wavelength λ of the volume wave in the enhanced state within functional layer 40 B2 The distance P between the central axes of two adjacent electrode fingers 22 and the second reinforcement angle γ satisfy the condition: 2Pcosγ=nλ B2 Where n is a positive integer.

[0218] In this embodiment, the case where n=1 is considered. That is, The propagation speed of the body wave in the enhanced state within functional layer 40 is V. B2 The volume wave vector β in the enhanced state within functional layer 40 B2 The operating frequency is f.

[0219] In this embodiment, the magnitude of the second strengthening angle is determined by the operating frequency f. When When cosγ = 1.

[0220] When f <f c2 When cosγ > 1, the second reinforcement angle γ is a complex number. Correspondingly, the bulk wave generated by the surface acoustic wave device 100 of this application will undergo total emission on the second surface 31 when it enters the functional layer 40 from the piezoelectric layer 10 and the temperature compensation layer 30.

[0221] That is, the wave vector component of the acoustic wave propagating along the third direction 003 away from the first surface 11 within the functional layer 40 is an imaginary number, and the acoustic wave at this time is an evanescent wave. Thus, under ideal conditions, for the surface acoustic wave device 100 of this application, only the acoustic wave propagating along the X direction on the second surface 31 acts on the functional layer 40.

[0222] To facilitate the distinction between the sound wave state when the refraction angle is a real number and the sound wave state when the refraction angle is a complex number, β2 is used to represent the sound wave state when the second reinforcement angle is a complex number.

[0223] At this time, the acoustic wave vector β2 rapidly attenuates along the third direction 003 in a direction away from the first surface 11. The surface acoustic wave device 100 of this application utilizes the attenuation characteristics of evanescent waves to characterize the leakage of high-frequency volume waves. Specifically, the evanescent wave intensity attenuates to the evanescent wave intensity at the second surface 31. The distance between the time and the second surface 31 has a certain correlation with the leakage of high-frequency body waves.

[0224] Define the body wave component of the acoustic wave vector β2 in the third direction 003 as β 2z Since the refraction angle is complex, the acoustic wave of the surface acoustic wave device 100 of this application manifests as an acoustic wave along the X direction. In this case, the modulus of the acoustic wave vector β2 satisfies the equation: Wherein, λ2 is the wavelength corresponding to the volume wave velocity of the material of functional layer 40 along the X direction at the operating frequency f.

[0225] The component β of the acoustic wave vector β2 in the third direction 003 2z Satisfying the equation:

[0226] In the above equation, the second enhancement angle γ is selected as the operating frequency f = f c2 At that time, the value of the second strengthening angle.

[0227] The intensity of the sound wave within functional layer 40 is ν, and the volume wave component of the sound wave β2 in the second direction 002 is β. 2x Let z represent the distance between the volume wave at any point within the functional layer 40 and the second surface 31. The volume wave intensity within the functional layer 40 satisfies the equation:

[0228] In this embodiment, the second characteristic thickness represents the volume wave intensity attenuated to the volume wave intensity at the second surface 31. The distance between the time and the second surface 31. That is,

[0229] Will Substituting into the equation for the acoustic wave intensity within functional layer 40, the z-value in the above equation is obtained. The calculated z-value is the second characteristic thickness. Since V B2 The volume wave velocity within the functional layer 40 is given. When the second reinforcement angle is complex, the sound wave velocity of the surface acoustic wave device in this application depends only on the material of the functional layer 40. The second characteristic thickness...

[0230] In this embodiment, after calculating the second characteristic thickness based on the above equation, the thickness of the functional layer 40 is determined by the range of the ratio between the thickness of the functional layer 40 and the second characteristic thickness. For the functional layer 40 with this thickness, high-frequency noise modes in the bulk wave can leak into the single-crystal silicon layer 50.

[0231] Therefore, in the process of fabricating the surface acoustic wave device 100 of this application, on the one hand, the midline distance P between two adjacent electrode fingers 22 and the volume wave velocity V along the X direction in the functional layer 40 can be obtained. b2 Based on the operating frequency f, the second strengthening angle γ is calculated.

[0232] On the other hand, the F(γ) value corresponding to the second reinforcement angle γ can be calculated by obtaining the frequency of the bulk wave in the functional layer 40 and the distance P between the midlines of two adjacent electrode fingers 22, and the second reinforcement angle γ can be obtained by relying on the example similar to that shown in Figure 11 corresponding to the functional layer 40.

[0233] Based on the second reinforcement angle γ, the propagation velocity V of the bulk wave along the X direction of the material in the functional layer 40 is obtained. b2 The second characteristic thickness T is calculated using the surface acoustic wave frequency f (surface acoustic wave resonant frequency or surface acoustic wave anti-resonant frequency) selected in the embodiments of this application. d Thus, the thickness D of functional layer 40 is obtained. d The scope is limited.

[0234] In one embodiment, the thickness of the piezoelectric layer 10 and the thickness of the first feature satisfy the following condition: At this time, the thickness of the piezoelectric layer 10 can satisfy the condition: 0.4P≤D y ≤0.8P.

[0235] In one embodiment, the first feature thickness is satisfied when the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 meets the following condition: At that time, the thickness of the temperature compensation layer 30 can satisfy the condition: 0.4P≤D w ≤0.8P.

[0236] In one embodiment, the first feature thickness is satisfied when the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 meets the following condition: At that time, the sum of the thickness of the temperature compensation layer 30 and the thickness of the piezoelectric layer 10 can satisfy the condition: H < 1.4P.

[0237] In one embodiment, the thickness of the functional layer 40 and the thickness of the second feature satisfy the following condition: At that time, the thickness of functional layer 40 can satisfy the condition: 0.2P≤D d ≤0.6P.

[0238] In one embodiment, the material of the functional layer 40 is anisotropic or isotropic.

[0239] In one embodiment, the functional layer 40 is a sound velocity layer or a polysilicon layer.

[0240] In one embodiment, the material of the piezoelectric layer 10 is anisotropic.

[0241] Please refer to Figures 17 to 19. This application embodiment proposes a surface acoustic wave (SAW) device 100. The SAW device 100 includes a piezoelectric substrate 10 and interdigitated electrodes 20. The interdigitated electrodes 20 include multiple electrode fingers 21. The piezoelectric substrate 10 includes a piezoelectric layer 11 and a sound velocity layer 12. The piezoelectric layer 11 has a first surface 111 and a second surface 112 disposed opposite to each other. The interdigitated electrodes 20 are disposed on the first surface 111 of the piezoelectric layer 11, and the sound velocity layer 12 is disposed on the second surface 112 of the piezoelectric layer 11. The sound waves of the SAW device 100 during operation include SAW waves and volume waves. The direction of SAW wave propagation is the x-direction. The SAW device 100 has a first characteristic depth. The thickness of the piezoelectric layer 11 is less than the first characteristic depth. The material of the piezoelectric layer 11 is a piezoelectric crystal. The first characteristic depth is related to the midline distance between two adjacent electrode fingers 21, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency.

[0242] In one specific embodiment, the piezoelectric substrate 10 and the interdigitated electrodes 20 disposed on the piezoelectric layer 11 can constitute an interdigitated transducer, meaning that the interdigitated electrodes 20 must be fabricated on the piezoelectric layer 11 to generate sound waves. In another specific embodiment, the interdigitated transducer can also be an interdigitated electrode formed on the piezoelectric substrate 10.

[0243] For example, the sound velocity layer 12 can be made of a high sound velocity material or a low sound velocity material to increase or decrease the sound velocity of the device.

[0244] Piezoelectric crystals are the materials used for the piezoelectric layer. Piezoelectric crystals can be single-crystal LiTaO3, LiNbO3, etc., in various cuts. A piezoelectric crystal is a non-centrosymmetric crystal that deforms under mechanical force, causing relative displacement of charged particles, resulting in positive and negative bound charges on the crystal surface. This property is called piezoelectricity.

[0245] The surface acoustic wave device 100 proposed in this application includes a piezoelectric layer 11, a sound velocity layer 12, and interdigitated electrodes 20. By directly setting the sound velocity layer 12 below the piezoelectric layer 11 and limiting the thickness of the piezoelectric layer 11 to less than the first feature depth, the thickness of the piezoelectric layer 11 is reasonably reduced, so that the sound velocity can be significantly increased or decreased while avoiding affecting the function of other functional layers.

[0246] It should be noted that the surface acoustic wave device 100 provided in this application can be applied to ordinary surface acoustic wave resonators, TC-SAW (TemPerature comPensated SAW) resonators, piezoelectric thin film resonators and other resonators; it can also be a dual-mode or multi-mode surface acoustic wave filter (DMS), or a filter composed of multiple resonators and / or DMS, etc., which are not limited here.

[0247] In some embodiments, the surface acoustic wave (SAW) device 100 includes two busbars disposed opposite each other on a piezoelectric substrate 10 along a second direction (y-direction) and interdigitated electrodes 20 respectively connected to the two busbars. Each interdigitated electrode 20 includes multiple electrode fingers 21. The electrode fingers 21 connected to the two busbars are sequentially staggered in a first direction (x-direction), and there is a gap between each electrode finger 21 connected to one busbar and the other busbar. The first direction is perpendicular to the second direction, and the first direction is the propagation direction of the SAW. Specifically, the interdigitated electrodes 20 cooperate with the piezoelectric substrate 10 to excite acoustic signals, thereby achieving mutual conversion between electrical signals and acoustic signals. The busbars are used to connect the interdigitated electrodes 20 and transmit electrical signals. For example, when multiple interdigitated electrodes 20 are provided in the resonator, different interdigitated electrodes 20 can be electrically connected through busbars and wiring.

[0248] In some embodiments, the busbar is primarily composed of aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, or tungsten. Exemplarily, the busbar material can be one or more of the following metallic materials: aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, or tungsten. It is understood that the busbar of this application can also be made of other metallic materials, including single metals, alloys, and structures formed by stacking multiple metals. No limitation is made here, as long as the desired performance is achieved.

[0249] In some embodiments, the interdigital electrode 20 and the busbar may be made of the same or different metal materials. Exemplarily, the material of the interdigital electrode 20 may be one or more of the following metal materials: aluminum, molybdenum, copper, gold, platinum, silver, nickel, chromium, or tungsten. It is understood that the interdigital electrode 20 of this application may also be made of other metal materials, which may be a single metal, an alloy, or a structure formed by stacking multiple metals. No limitation is made here, as long as the required performance can be achieved.

[0250] In some embodiments, the thickness of the interdigitated electrode 20 is the same as the thickness of the busbar. Exemplarily, the interdigitated electrode 20 and the busbar can be integrally formed, i.e., formed in the same process.

[0251] The acoustic waves emitted during operation of the surface acoustic wave (SAW) device 100 of this application include SAW waves and volume waves. The SAW waves propagate along the planar direction of the first surface 111, with the direction of SAW propagation defined as the x-direction. The volume waves propagate into the piezoelectric layer 11 at a certain tilt angle θ (a first reinforcement angle). A key feature of the SAW device of this application is that it has a first characteristic depth. The thickness of the piezoelectric layer 11 is less than the first characteristic depth. The first characteristic depth is related to the centerline distance between two adjacent electrode fingers 21, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency.

[0252] In some embodiments, the first feature depth is positively correlated with the centerline spacing between two adjacent electrode fingers 21, negatively correlated with the volume wave velocity of the piezoelectric crystal along the x-direction, and positively correlated with the operating frequency. Therefore, the first feature depth can be calculated based on the centerline spacing between two adjacent electrode fingers 21, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency, thereby limiting the thickness of the piezoelectric layer 11 to a suitable range so that the device performance meets the requirements.

[0253] In some embodiments, the first feature depth satisfies the following formula:

[0254] Formula 1:

[0255] Formula 2:

[0256] P is the midline distance between two adjacent electrode fingers, ds is the first characteristic depth, and β b1 Let β be the wave vector corresponding to the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency. b1 The modulus is 2π / λ b1 , λ b1 =V b1 / f,V b1 Let λ be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the operating frequency, and λ be the velocity of the piezoelectric crystal. b1 Let λ be the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency.

[0257] Based on the above formula, the first feature depth can be calculated, thereby limiting the thickness of the piezoelectric layer 11 to a suitable range so that the performance of the device can meet the requirements.

[0258] Understandably, the midline spacing P between two adjacent electrode fingers 21 can be set according to the requirements of different devices. For example, P can be limited to 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm or 3μm, etc.

[0259] In some embodiments, when the interdigitated electrode 20 indicates that the bulk wave in the piezoelectric layer 11 is in an enhanced state when the angle between the propagation direction of the volume wave excited into the piezoelectric layer 11 and the first surface 111 is equal to the first reinforcement angle θ; wherein, Formula 3: cosθ=λ B1 / 2P=V B1 / 2Pf, 0°<θ<180°, where V B1 The velocity of the bulk wave within the piezoelectric layer 11 in its enhanced state is given by f, where f is the operating frequency and λ is the velocity of the bulk wave. B1 The wavelength of the bulk wave excited by the interdigitated electrodes 20 within the piezoelectric layer 11 is given. It should be noted that the angle between the propagation direction of the bulk wave within the piezoelectric layer 11 and the first surface 111 is equal to the first reinforcement angle θ. The centerline spacing P between two adjacent electrode fingers 21 can be defined according to the requirements of different devices.

[0260] In some embodiments, according to λ B1＝ V B1 / f,V B1 Let f be the volume wave velocity within the piezoelectric layer 11 in its reinforced state, and f be the operating frequency. The volume wave wavelength λ can be calculated when the angle between the propagation direction of the volume wave and the first surface 111 is equal to the first reinforcement angle θ. B1 .

[0261] In some embodiments, the volume wave wavelength λ is equal to the angle between the propagation direction of the volume wave and the first surface 111 when the angle is equal to the first reinforcement angle θ. B1 This refers to the bulk wave wavelength within the piezoelectric layer 11 in its enhanced state. Specifically, the enhanced condition for bulk wave excitation is that the bulk waves excited by the interdigitated electrodes 20 of the same polarity are phase-matched in a specific direction, i.e., 2Pcosθ=nλ. B1 Where n is a positive integer. As an example, in practical applications, if we only consider the case of n=1, we can derive Formula 3: cosθ=λ B1 / 2P=V B1 / 2Pf, 0°<θ<180°.

[0262] In some embodiments, due to the wave vector β of the sound wave B1 It is a vector, and its magnitude is taken when calculating the depth of the first feature:

[0263] Formula 4:

[0264] Where, β B1zV is the z-component of the acoustic wave vector of piezoelectric layer 11 (the z-direction is perpendicular to both the first and second directions mentioned above). b1 Let λ be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the current operating frequency, and λ be the velocity of the piezoelectric crystal along the x-direction. B1 =V B1 / f. Therefore, according to Formula 4 above, the z-component |β| of the wave vector of the surface acoustic wave excited by the interdigital electrode 20 can be calculated. B1z |

[0265] Among them, if β B1z Since it is a real number, the sound wave is a traveling wave within the piezoelectric layer 11, which is a volume wave.

[0266] Among them, if β B1z It is an imaginary number. At this point, the sound wave is no longer a body wave, the wave vector is β1, and the z-component is β. 1z , β b1 It is the volume wave vector along the x-direction of the piezoelectric layer 11 at the operating frequency f.

[0267] The sound wave propagating towards the depth of the piezoelectric layer 11 is an evanescent wave. At this point, the sound wave propagating along the surface is called a surface acoustic wave.

[0268] As an example, in practical applications, the current operating frequency is 2 GHz, and the wavelength of the sound wave is relatively short (in surface acoustic wave devices, the operating frequency is inversely proportional to the wavelength; as the operating frequency increases, the wavelength becomes shorter). Since surface acoustic waves mainly propagate on the surface, and their energy decays rapidly as they penetrate deeper into the piezoelectric layer 11, the sound wave at this frequency is an evanescent wave in the direction of depth of the piezoelectric layer 11.

[0269] When the sound wave propagating towards the depth of the piezoelectric layer 11 is an evanescent wave, the sound wave propagating towards the depth of the piezoelectric layer 11 (-z direction) can be described by the following formula:

[0270] Formula 5:

[0271] Where u is the amplitude of the sound wave, β b1 It is the volume wave vector of piezoelectric layer 11 along the x-direction, β 1x It is the x-component of the piezoelectric layer acoustic wave vector, β 1z This is the z-component of the acoustic wave vector of the piezoelectric layer. As the acoustic wave propagates towards depth, its intensity gradually decreases. The depth at which the volumetric acoustic wave attenuates to 1 / e at the surface is denoted as the first characteristic depth ds, where e is a mathematical constant, approximately equal to 2.718. Therefore, the first characteristic depth ds can be easily calculated by substituting Formula 5 into Formula 1.

[0272] In some embodiments, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer 11 is 0.1 to 0.9 times the first characteristic depth. Since the intensity of the first sound field decays exponentially from the surface to the depth direction, limiting the thickness of the piezoelectric layer 11 to the range of 0.1 to 0.9 times the first characteristic depth can meet the sound velocity requirements of the device. Exemplarily, the thickness of the piezoelectric layer 11 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 times the first characteristic depth.

[0273] In some embodiments, to better meet the sound velocity requirements of the device, the thickness of the piezoelectric layer 11 can be further defined as 0.1 to 0.5 times the first characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency. For example, the thickness of the piezoelectric layer 11 can be 0.1, 0.2, 0.3, 0.4, or 0.5 times the first characteristic depth.

[0274] Referring to Figure 17, in some embodiments, when the piezoelectric substrate 10 includes only the piezoelectric layer 11 and the high-velocity layer, the thickness of the high-velocity layer can be 100 μm-800 μm to ensure the mechanical strength and other properties of the device. For example, the thickness of the high-velocity layer can be 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, or 800 μm, etc.

[0275] In some embodiments, the sound velocity layer 12 is a high-velocity sound layer. Therefore, to meet the high-frequency requirements of the device, the sound velocity layer 12 can be configured as a high-velocity sound layer to satisfy the high-velocity sound requirements of the device and increase the operating frequency of the device.

[0276] In some embodiments, when the sound velocity layer 12 is a hypersonic layer, the sound velocity layer 12 is primarily composed of silicon nitride, aluminum oxide, silicon carbide, silicon, aluminum nitride, or diamond. Exemplarily, the material of the sound velocity layer 12 can be one or more combinations of materials such as silicon nitride, aluminum oxide, silicon carbide, silicon, aluminum nitride, and diamond. It is understood that the sound velocity layer 12 of this application can also employ other hypersonic materials; this is not limited here, as long as the desired performance is achieved.

[0277] In some embodiments, when the sound velocity layer 12 is a low sound velocity layer, the sound velocity layer 12 is mainly composed of tantalum pentoxide or indium phosphide. Exemplarily, the material of the sound velocity layer 12 can be one or more of materials such as tantalum pentoxide and indium phosphide. It is understood that the sound velocity layer 12 of this application can also use other low sound velocity materials, which are not limited here, as long as the required performance can be achieved.

[0278] In some embodiments, the piezoelectric layer 11 is primarily composed of lithium niobate or lithium tantalate. This results in the piezoelectric layer 11 exhibiting a good piezoelectric effect, capable of converting mechanical stress into an electrical signal or vice versa. Exemplarily, the material of the piezoelectric layer 11 can be one or more combinations of materials such as lithium niobate and lithium tantalate. It is understood that the piezoelectric layer 11 of this application can also employ other piezoelectric materials; this is not limited here, as long as the desired performance is achieved.

[0279] In some embodiments, the duty cycle of the interdigital electrode is DF, where DF is 0.3-0.7. Therefore, limiting the duty cycle of the interdigital electrode within the above range can improve the stability and reliability of the device and extend its service life. For example, the duty cycle DF of the interdigital electrode can be 0.3, 0.4, 0.5, 0.6, or 0.7, etc.

[0280] In one embodiment, the surface acoustic wave device 100, from top to bottom, consists of interdigitated electrodes, a piezoelectric layer 11 (42YX-LiTaO3), and a high-velocity acoustic layer (Si3N4), with P = 1 μm, λ = 2P, and DF = 0.4. The bulk wave velocity V of the piezoelectric layer 11 along the first direction is... b1 Including the first transverse wave sound velocity V S1 The second transverse wave sound velocity V S2 and longitudinal wave speed V L ; where λ b1 =V b1 / f, where f is the operating frequency of the surface acoustic wave device 100; the first transverse wave velocity V S1 Approximately 3340 m / s, the speed of sound of the second transverse wave V S2 Approximately 4200 m / s, longitudinal wave speed V L The velocity is 5592 m / s, and the first direction is the propagation direction of the surface acoustic wave. Since the dominant mode of the piezoelectric layer 11 mainly relies on V... S2 Calculations show that when P is 1 μm and f is 2 GHz, the first feature depth ds is 1.16 μm. Specifically, the piezoelectric layer 11 can be lithium tantalate, and the piezoelectric layer 11 has a 42YX-LiTaO3 cut. The sound velocity layer 12 can be a high-velocity layer, and the high-velocity layer is made of silicon nitride (Si3N4). Therefore, the bulk wave velocity V of the piezoelectric layer 11 along the first direction can be determined by the specific material of the piezoelectric layer 11. b1 Then, based on the determined center-to-center distance P between two adjacent electrode fingers 21 and the current operating frequency f, the first feature depth ds is calculated, thereby limiting the thickness of the piezoelectric layer 11 to a suitable range so that the performance of the device can meet the requirements.

[0281] Please refer to Figure 21, which is a graph showing the change of surface wave velocity with the thickness of the piezoelectric layer in the above embodiment. As can be seen from Figure 21, the surface wave velocity of the surface acoustic wave device 100 in this embodiment is significantly greater than that of the existing standard device. In addition, the surface wave velocity gradually decreases as the thickness of the piezoelectric layer 11 increases. Therefore, in order to better meet the sound velocity requirements of the device, the thickness of the piezoelectric layer 11 is limited to be less than the first feature depth ds, thereby meeting the higher sound velocity requirements of the device.

[0282] It should be noted that the surface acoustic wave device 100 in this embodiment may also include other functional layers. For example, referring to Figures 19 and 20, in some embodiments, the piezoelectric substrate 10 further includes a substrate 13, which is disposed on the side of the sound velocity layer 12 opposite to the piezoelectric layer 11. The surface acoustic wave device includes a second characteristic depth, and the thickness of the sound velocity layer 12 is less than the second characteristic depth. The second characteristic depth is related to the centerline spacing between two adjacent electrode fingers 21, the sound velocity of the sound velocity layer 12 (the sound velocity of the sound velocity layer 12 is related to the material of the sound velocity layer 12), and the operating frequency. Therefore, when the piezoelectric substrate 10 is also provided with other functional layers, the distribution of the sound field in the sound velocity layer 12 needs to be further considered. By limiting the thickness of the sound velocity layer 12 to be less than the second characteristic depth, the sound velocity of the device can meet higher requirements while avoiding affecting the performance of other functional layers.

[0283] In some embodiments, the second feature depth is positively correlated with the centerline spacing between two adjacent electrode fingers 21, negatively correlated with the sound velocity of the sound velocity layer 12, and positively correlated with the operating frequency. Therefore, the second feature depth can be calculated based on the centerline spacing between two adjacent electrode fingers 21, the sound velocity of the sound velocity layer 12 (which is related to the material of the sound velocity layer 12), and the operating frequency, thereby limiting the thickness of the sound velocity layer 12 to a suitable range so that the device performance meets requirements.

[0284] In some embodiments, the second feature depth satisfies the following formula:

[0285] Formula Six:

[0286] Formula 7: |β b2 |=2π / λ b2 ;

[0287] Where P is the midline distance between two adjacent electrode fingers 21, dt is the second feature depth, and β b2 Let β be the wave vector corresponding to the bulk wave wavelength of the material of the sound velocity layer 12 along the x-direction at the operating frequency. b2 The modulus is 2π / λ b2， λ b2 =V b2 / f,Vb2 Let f be the volume wave velocity of the material in sound layer 12 along the x-direction, f be the operating frequency, and λ be the velocity of sound. b2 Let be the bulk wavelength of the sound velocity layer 12 material along the x-direction at the operating frequency. Based on the above formula, the second characteristic depth can be calculated, thereby limiting the thickness of the sound velocity layer 12 to a suitable range so that the device performance meets the requirements.

[0288] In some embodiments, the angle between the propagation direction of the bulk wave excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12 and the second surface 112 is equal to γ; where cosγ = λ B2 / 2P=V B2 / 2Pf(0°<θ<180°;λ B2 V is the volume wave wavelength excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12. B2 Let f be the volume wave velocity within the sound velocity layer 12, and f be the operating frequency. It should be noted that the sound velocity layer 12 can be an isotropic or anisotropic material, and the sound velocity can be determined.

[0289] In some embodiments, the z-component of the wave vector entering the sound velocity layer 12 is an evanescent wave, wherein the z-component is an imaginary number, and the amplitude of the evanescent wave decays rapidly with the increase of the depth of the sound velocity layer 12.

[0290] In some embodiments, the enhancement condition for body wave excitation is that the body waves excited by the interdigitated electrodes 20 of the same polarity are phase-matched in a specific direction, i.e., 2Pcosθ=nλ. B2 Where n is a positive integer. As an example, in practical applications, if we only consider the case of n=1, we can derive Formula 8: cosγ=λ B2 / 2P.

[0291] Through theoretical deduction, the formula for the z-component of the wave vector in the sound velocity layer 12 has the same form as Formula 4.

[0292] In some embodiments, due to the wave vector β of the sound wave B2 It is a vector, and its magnitude β is taken when calculating the second feature depth dt. B2 Satisfy the following formula:

[0293] Formula Nine:

[0294] Where, β B2z V is the z-component of the acoustic wave vector of sound velocity layer 12. B2 Let λ be the volume wave velocity within sound velocity layer 12, f be the current operating frequency of the surface acoustic wave device, and λ be the velocity of the sound waves within the sound velocity layer 12. B2 =V B2 / f. Therefore, the z-component of the acoustic wave vector of the sound velocity layer 12 can be calculated according to Formula 9 above.

[0295] Among them, if β B2Z Since it is a real number, the sound wave is a traveling wave within the sound speed layer 12, which is a body wave.

[0296] Among them, if At this time β B2 =β b2 , β 2z Let be an imaginary number, representing the z-component of the sound wave vector of sound velocity layer 12. The intensity of the sound wave entering sound velocity layer 12 gradually decreases with increasing depth of sound velocity layer 12, thus its characteristic depth dt is calculated as follows:

[0297] In some embodiments, the thickness of the sound velocity layer 12 is 0.1P-0.6P, where P is the center-to-line distance between two adjacent electrode fingers 21. When the thickness of the sound velocity layer 12 is too thick, the waveguide mode cannot leak into the depth direction of the substrate 13, thus affecting device performance. When the thickness of the sound velocity layer 12 is too thin, its effect on increasing or decreasing the sound velocity is weak, making it difficult to meet the required sound velocity. Therefore, the thickness of the sound velocity layer 12 can be calculated based on the second characteristic depth dt and limited to the above range, which can meet the sound velocity requirements without affecting device performance.

[0298] For example, when the sound velocity layer 12 is made of silicon nitride or aluminum oxide, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.6P. When the sound velocity layer 12 is made of silicon carbide or aluminum nitride, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.5P. When the sound velocity layer 12 is made of diamond, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.4P.

[0299] For example, when P is 1 μm, the thickness of the sound velocity layer 12 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm or 0.6 μm, etc.

[0300] In some embodiments, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the sound velocity layer 12 is 0.1 to 0.9 times the second characteristic depth. To ensure that other functions below the sound velocity layer 12 provide acoustic support, the thickness of the sound velocity layer 12 should preferably not exceed the second characteristic depth. Since the sound field intensity of the sound wave decays exponentially from the surface to the depth direction, limiting the thickness of the sound velocity layer 12 to the range of 0.1 to 0.9 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency can meet the sound velocity requirements of the device. Exemplarily, the thickness of the sound velocity layer 12 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 times the second characteristic depth.

[0301] In some embodiments, to better meet the sound velocity requirements of the device, the thickness of the sound velocity layer 12 may be further defined as 0.1 to 0.5 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency. For example, the thickness of the sound velocity layer 12 may be 0.1, 0.2, 0.3, 0.4, or 0.5 times the second characteristic depth.

[0302] In one embodiment, the surface acoustic wave device 100, from top to bottom, comprises interdigitated electrodes, a piezoelectric layer 1 (42YX-LiTaO3), a high-velocity acoustic layer (Si3N4), a temperature compensation layer (TC), and a substrate (Poly-Si), with P = 1 μm, λ = 2P, DF = 0.4, a LiTaO3 thickness of 0.6 μm, a variable thickness for the high-velocity acoustic layer Si3N4, a TC layer thickness of 1 μm, and a volume wave velocity of the sound velocity layer 12 along a first direction including the transverse wave velocity VS. B2 and longitudinal wave speed VL B2 Transverse wave speed of sound VS B2 The longitudinal wave velocity is 5725.6 m / s, and the longitudinal wave velocity VL B2 The velocity is 9669.1 m / s, and the first direction is the propagation direction of the surface acoustic wave. Since the dominant mode of the sound velocity layer 12 mainly relies on VS B2 Calculations show that when P is 1 μm and f is 2 GHz, the second feature depth dt is 0.45 μm. Specifically, the piezoelectric layer 11 can be lithium tantalate, and the piezoelectric layer 11 has a 42YX-LiTaO3 cut. The acoustic velocity layer 12 can be a high-velocity acoustic layer, and the material of the high-velocity acoustic layer is silicon nitride Si3N4. The substrate 13 can be polycrystalline silicon (Poly-Si).

[0303] In another implementation, for TF-SAWs with piezoelectric layers of 30–50 YX-LiTaO3, -15–+15 YX-LiNbO3, and 120–140 YX-LiNbO3, the thickness of the piezoelectric layer is limited to 0.05·2P–0.6·2P. Below the piezoelectric layer is a high-velocity layer; the thickness of Si3N4 ranges from 0.05·2P to 0.3·2P; the thickness of Al2O3 ranges from 0.05·2P to 0.3·2P; the thickness of SiC ranges from 0.05·2P to 0.25·2P; the thickness of AlN ranges from 0.05·2P to 0.25·2P; the thickness of Diamond ranges from 0.05·2P to 0.2·2P; and a dielectric layer can be applied to the surface of the TFSAW.

[0304] Please refer to Figure 22, which is a graph showing the surface wave velocity as a function of the sound velocity layer thickness in the above embodiment. As can be seen from Figure 22, when the thickness of the sound velocity layer 12 exceeds the second characteristic depth of 0.45 μm, the rate of increase in surface wave velocity slows significantly, indicating that the sound field intensity has been significantly attenuated relative to the upper interface after reaching the lower interface of the sound velocity layer 12. Therefore, in order to meet the sound velocity requirements while avoiding affecting the performance of other functional layers, the thickness of the sound velocity layer 12 is limited to less than the second characteristic depth dt.

[0305] Of course, in other embodiments, the substrate 13 may also be made of other silicon materials with high resistivity, or it may be an insulating substrate 13 such as sapphire or spinel.

[0306] Referring to Figure 20, in some embodiments, the piezoelectric substrate 10 further includes a temperature compensation layer 14 disposed between the substrate 13 and the acoustic velocity layer 12. The thickness of the piezoelectric layer 11 is 0.1P-1.2P, where P is the midline distance between two adjacent electrode fingers 21 of the interdigitated electrodes 20, and the thickness of the temperature compensation layer 14 is 0μm-1μm. The function of the temperature compensation layer 14 is to compensate for the impact of temperature changes on the performance of the piezoelectric substrate 10 through its specific temperature characteristics, which helps maintain the stability and reliability of the device under different temperature conditions.

[0307] If the piezoelectric layer 11 is too thick, it will affect the function of other functional layers. If the piezoelectric layer 11 is too thin, it will affect the device performance. By calculating the thickness of the piezoelectric layer 11 through the first feature depth and limiting the thickness of the piezoelectric layer 11 within the above range, the sound velocity requirements of the device can be met while avoiding affecting the device performance.

[0308] Specifically, the piezoelectric layer 11 can be made of a piezoelectric material with the following cut:

[0309] 30~50YX-LiTaO3, -15~+15YX-LiNbO3 and 120~140YX-LiNbO3.

[0310] For example, when P is 1 μm, the thickness of the piezoelectric layer 11 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm or 1.2 μm, etc.

[0311] For example, the thickness of the temperature compensation layer 14 can be 0 μm (i.e., without a temperature compensation layer 14), 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm, etc.

[0312] In some embodiments, the temperature compensation layer 14 may be one or a combination of materials such as silicon oxide, silicon nitride, and silicon oxynitride.

[0313] In some embodiments, the thickness of the substrate 13 is 100μm-800μm. A suitable thickness can be selected within this range according to the application requirements of the device to ensure its mechanical strength and other properties. For example, the thickness of the substrate 13 can be 100μm, 200μm, 300μm, 400μm, 500μm, 600μm, 700μm, or 800μm, etc.

[0314] Referring to Figures 17 to 19, this application also proposes a surface acoustic wave (SAW) device 100, including a piezoelectric layer 11, a sound velocity layer 12, and interdigitated electrodes 20. The piezoelectric layer 11 has a first surface 111 and a second surface 112 disposed opposite to each other. The interdigitated electrodes 20 are disposed on the first surface 111 of the piezoelectric layer 11, and the sound velocity layer 12 is disposed on the second surface 112 of the piezoelectric layer 11. The sound waves emitted by the SAW device 100 during operation include surface waves and volume waves. The SAW device 100 has a first characteristic depth including a second characteristic depth, and the thickness of the sound velocity layer 12 is less than the second characteristic depth. The second characteristic depth is related to the centerline spacing between two adjacent interdigitated electrodes 21, the sound velocity of the sound velocity layer 12, and the operating frequency. Thus, by limiting the thickness of the sound velocity layer 12 to be less than the second characteristic depth, the sound velocity of the device can meet higher requirements while avoiding affecting the performance of other functional layers.

[0315] For example, the sound velocity layer 12 can be made of a high sound velocity material or a low sound velocity material to increase or decrease the sound velocity of the device.

[0316] The surface acoustic wave (SAW) device 100 proposed in this application has a sound velocity layer 12 directly disposed below the piezoelectric layer 11. By limiting the thickness of the sound velocity layer 12 to be less than the second characteristic depth, the sound velocity of the device can meet higher requirements while avoiding affecting the performance of other functional layers. In some embodiments, the second characteristic depth is positively correlated with the centerline spacing between two adjacent electrode fingers 21, negatively correlated with the sound velocity of the sound velocity layer 12, and positively correlated with the operating frequency. Therefore, the second characteristic depth can be calculated based on the centerline spacing between two adjacent electrode fingers 21 of the interdigitated electrodes 20, the sound velocity of the sound velocity layer 12, and the operating frequency, thereby limiting the thickness of the sound velocity layer 12 to a suitable range so that the performance of the device can meet the requirements.

[0317] In some embodiments, the second feature depth satisfies the following formula:

[0318] Formula Six:

[0319] Formula 7: |β b2 |=2π / λ b2 ;

[0320] Where P is the midline distance between two adjacent electrode fingers 21, dt is the second feature depth, and β b2 Let β be the wave vector corresponding to the bulk wave wavelength of the material of the sound velocity layer 12 along the x-direction at the operating frequency. b2 The modulus is 2π / λ b2， λ b2 =V b2 / f, V b2 is the volume wave velocity of the material in sound velocity layer 12 along the x-direction, f is the operating frequency, and λ is the velocity of sound. b2 Let be the bulk wavelength of the sound velocity layer 12 material along the x-direction at the operating frequency. Based on the above formula, the second characteristic depth can be calculated, thereby limiting the thickness of the sound velocity layer 12 to a suitable range so that the device performance meets the requirements.

[0321] In some embodiments, the angle between the propagation direction of the surface acoustic wave excited and propagating into the sound velocity layer 12 by the interdigitated electrode 20 and the second surface 112 is equal to the second angle γ; wherein, formula eight: cosγ=λ B2 / 2P=V B2 / 2Pf(0°<θ<180°). λ B2 V is the volume wave wavelength excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12. B2 Let f be the volume wave velocity within the sound velocity layer 12, and f be the operating frequency. Therefore, according to Formula 8 above, the volume wave wavelength λ excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12 can be calculated. B2It should be noted that the sound velocity layer 12 can be an isotropic or anisotropic material, and the sound velocity can be determined.

[0322] In some embodiments, the z-component of the wave vector entering the sound velocity layer 12 is an evanescent wave, wherein the z-component is an imaginary number, and the amplitude of the evanescent wave decays rapidly with the increase of the depth of the sound velocity layer 12.

[0323] In some embodiments, the enhancement condition for body wave excitation is that the body waves excited by the interdigitated electrodes 20 of the same polarity are phase-matched in a specific direction, i.e., 2Pcosθ=nλ. B2 Where n is a positive integer. As an example, in practical applications, if we only consider the case of n=1, we can derive Formula 8: cosγ=λ B2 / 2P.

[0324] Through theoretical deduction, the formula for the z-component of the wave vector in the sound velocity layer 12 has the same form as Formula 4.

[0325] In some embodiments, due to the wave vector β of the sound wave B2 It is a vector, and its magnitude β is taken when calculating the second feature depth dt. B2 Satisfy the following formula:

[0326] Formula Nine:

[0327] Where, β B2z V is the z-component of the acoustic wave vector of sound velocity layer 12. B2 Let λ be the volume wave velocity of sound layer 12, f be the current operating frequency of the surface acoustic wave device, and λ be the velocity of sound in the sound layer 12. B2 =V B2 / f. Therefore, the z-component of the acoustic wave vector of the sound velocity layer 12 can be calculated according to Formula 9 above.

[0328] Among them, if β B2Z Since it is a real number, the sound wave is a traveling wave within the sound speed layer 12, which is a body wave.

[0329] Among them, if At this time β B2 =β b2 , β 2z Let be an imaginary number, representing the z-component of the sound wave vector of sound velocity layer 23. The intensity of the sound wave entering sound velocity layer 12 gradually decreases with increasing depth, thus its characteristic depth dt is calculated as follows:

[0330] In some embodiments, the thickness of the sound velocity layer 12 is 0.1P-0.6P, where P is the center-to-line distance between two adjacent electrode fingers 21. When the thickness of the sound velocity layer 12 is too thick, the waveguide mode cannot leak into the depth direction of the substrate 13, thus affecting device performance. When the thickness of the sound velocity layer 12 is too thin, its effect on increasing or decreasing the sound velocity is weak, making it difficult to meet the required sound velocity. Therefore, the thickness of the sound velocity layer 12 can be calculated based on the second characteristic depth dt and limited to the above range, which can meet the sound velocity requirements without affecting device performance.

[0331] For example, when the sound velocity layer 12 is made of silicon nitride or aluminum oxide, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.6P. When the sound velocity layer 12 is made of silicon carbide or aluminum nitride, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.5P. When the sound velocity layer 12 is made of diamond, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.4P.

[0332] For example, when P is 1 μm, the thickness of the sound velocity layer 12 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm or 0.6 μm, etc.

[0333] In some embodiments, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the sound velocity layer 12 is 0.1 to 0.9 times the second characteristic depth. To ensure that other functions below the sound velocity layer 12 provide acoustic support, the thickness of the sound velocity layer 12 should preferably not exceed the second characteristic depth. Since the sound field intensity of bulk waves decays exponentially from the surface to the depth direction, limiting the thickness of the sound velocity layer 12 to the range of 0.1 to 0.9 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency satisfies the sound velocity requirements of the device. Exemplarily, the thickness of the sound velocity layer 12 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 times the second characteristic depth.

[0334] In some embodiments, to better meet the sound velocity requirements of the device, the thickness of the sound velocity layer 12 may be further defined as 0.1 to 0.5 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency. For example, the thickness of the sound velocity layer 12 may be 0.1, 0.2, 0.3, 0.4, or 0.5 times the second characteristic depth.

[0335] Referring to Figure 20, this application embodiment also proposes a surface acoustic wave (SAW) device 100, including a piezoelectric substrate 10 and interdigitated electrodes 20. The interdigitated electrodes 20 include multiple electrode fingers 21. The piezoelectric substrate 10 includes a piezoelectric layer 11, a sound velocity layer 12, a temperature compensation layer 14, and a substrate 13. The piezoelectric layer 11 has a first surface 111 and a second surface 112 disposed opposite to each other. The interdigitated electrodes 20 are disposed on the first surface 111 of the piezoelectric layer 11. The sound velocity layer 12 is disposed on the second surface 112 and is used to increase or decrease the sound velocity of the SAW device 100. The temperature compensation layer 14 is disposed on the side of the sound velocity layer 12 that is opposite to the piezoelectric layer 11. The substrate 13 is disposed on the side of the temperature compensation layer 14 that is opposite to the sound velocity layer 12. Thus, by inserting a sound velocity layer 12 between the piezoelectric layer 11 and the temperature compensation layer 14, the sound velocity of the device can be increased or decreased. At the same time, the temperature compensation layer 14 is placed in the middle of the overall structure of the piezoelectric substrate 10, so that the temperature compensation efficiency can reach a high value.

[0336] If the sound velocity layer 12 is disposed between the temperature compensation layer 14 and the substrate 13, the temperature compensation layer 14 needs a certain thickness to ensure the temperature compensation effect, resulting in a large gap between the sound velocity layer 12 and the piezoelectric layer 11, which leads to limited increase or decrease in sound velocity. Therefore, the surface acoustic wave device 100 of this application disposed the sound velocity layer 12 between the piezoelectric layer 11 and the temperature compensation layer 14, which can simultaneously meet the sound velocity requirements and good frequency temperature coefficient characteristics.

[0337] Specifically, the temperature coefficient of frequency (TCF) of a piezoelectric resonator is determined by the thickness of each layer and their relative positions and effects within the resonant cavity. Generally, to obtain a lower TCF, a thicker layer of silicon dioxide needs to be deposited above the piezoelectric resonator to compensate for the drift of the resonant frequency with temperature. Therefore, this embodiment achieves the same temperature compensation effect by fabricating a thinner temperature compensation layer 14 (e.g., silicon dioxide), which significantly improves the efficiency of temperature compensation.

[0338] In some embodiments, the sound velocity layer 12 is a high-velocity sound layer. Therefore, in order to meet the high-frequency requirements of the device, the sound velocity layer 12 can be configured as a high-velocity sound layer to satisfy the high-velocity sound requirements of the device.

[0339] In some embodiments, when the piezoelectric substrate 10 includes a piezoelectric layer 11, a sound velocity layer 12, a temperature compensation layer 14, and a substrate 13, and the sound velocity layer 12 is a high sound velocity layer, the sound velocity layer 12 is mainly composed of silicon. Therefore, by utilizing the high sound velocity characteristics of silicon, acoustic filters with specific frequency responses can be designed.

[0340] In some embodiments, when the sound velocity layer 12 is a low sound velocity layer, the sound velocity layer 12 is mainly composed of tantalum pentoxide or indium phosphide. Exemplarily, the material of the sound velocity layer 12 can be one or more of materials such as tantalum pentoxide and indium phosphide. It is understood that the sound velocity layer 12 of this application can also use other low sound velocity materials, which are not limited here, as long as the required performance can be achieved.

[0341] In some embodiments, the acoustic waves emitted by the surface acoustic wave device 100 during operation include surface acoustic waves and volume waves. The surface acoustic waves propagate along the planar direction of the first surface 111, i.e., the x-direction; the volume waves propagate into the piezoelectric layer 11 along its thickness direction. The surface acoustic wave device 100 of this application has a first characteristic depth, the thickness of the piezoelectric layer 11 is less than the first characteristic depth, and the material of the piezoelectric layer 11 is a piezoelectric crystal. The first characteristic depth is related to the centerline distance between two adjacent electrode fingers 21 of the interdigitated electrodes 20, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency. Furthermore, the surface acoustic wave device 100 of this application also has a second characteristic depth, the thickness of the sound velocity layer 12 is less than the second characteristic depth; the second characteristic depth is related to the centerline distance between two adjacent electrode fingers 21, the sound velocity of the sound velocity layer 12, and the operating frequency, and the wavelength of the acoustic waves is related to the operating frequency and the sound velocity of the sound velocity layer 12. Therefore, in order to modify the acoustic performance of the surface acoustic wave device 100, a sound velocity layer 12 is directly set below the piezoelectric layer 11, and the thickness of the piezoelectric layer 11 is limited to less than the first feature depth. The thickness of the piezoelectric layer 11 is reasonably reduced, and the thickness of the sound velocity layer 12 is limited to less than the second feature depth. This allows the sound velocity of the device to meet higher requirements while avoiding affecting the performance of other functional layers.

[0342] In some embodiments, the first characteristic depth is positively correlated with the centerline spacing between two adjacent electrode fingers 21, negatively correlated with the bulk wave velocity of the piezoelectric crystal along the x-direction, and positively correlated with the operating frequency; the second characteristic depth is positively correlated with the centerline spacing between two adjacent electrode fingers 21, negatively correlated with the sound velocity layer 12, and positively correlated with the operating frequency. Therefore, the first characteristic depth can be calculated based on the centerline spacing between two adjacent electrode fingers 21, the bulk wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency, thereby limiting the thickness of the piezoelectric layer 11 to a suitable range. Simultaneously, the second characteristic depth can be calculated based on the centerline spacing between two adjacent electrode fingers 21 of the interdigitated electrode 20, the sound velocity of the sound velocity layer 12, and the operating frequency, thereby limiting the thickness of the sound velocity layer 12 to a suitable range, ensuring that the device performance meets requirements.

[0343] In some embodiments, the first feature depth satisfies the following formula:

[0344] Formula 1:

[0345] Formula 2:

[0346] P is the midline distance between two adjacent electrode fingers, ds is the first characteristic depth, and β b1 Let β be the wave vector corresponding to the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency. b1 The modulus is 2π / λ b1 , λ b1 =V b1 / f,V b1 Let λ be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the operating frequency, and λ be the velocity of the piezoelectric crystal. b1 Let λ be the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency.

[0347] Based on the above formula, the first feature depth can be calculated, thereby limiting the thickness of the piezoelectric layer 11 to a suitable range so that the performance of the device can meet the requirements.

[0348] Understandably, the midline spacing P between two adjacent electrode fingers 21 can be set according to the requirements of different devices. For example, P can be limited to 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 2μm or 3μm, etc.

[0349] In some embodiments, when the interdigitated electrode 20 indicates that the bulk wave in the piezoelectric layer 11 is in an enhanced state when the angle between the propagation direction of the volume wave excited into the piezoelectric layer 11 and the first surface 111 is equal to the first enhancement angle θ; wherein, cosθ=λ B1 / 2P=V B1 / 2Pf(0°<θ<180°), where V B1 The velocity of the bulk wave within the piezoelectric layer 11 in its enhanced state is given by f, where f is the operating frequency and λ is the velocity of the bulk wave. B1 The wavelength of the bulk wave excited by the interdigitated electrodes 20 within the piezoelectric layer 11 is given. It should be noted that the angle between the propagation direction of the bulk wave within the piezoelectric layer 11 and the first surface 111 is equal to the first reinforcement angle θ. The centerline spacing P between two adjacent electrode fingers 21 can be defined according to the requirements of different devices.

[0350] In some embodiments, according to λ B1＝ V B1 / f,V B1 Let f be the volume wave velocity within the piezoelectric layer 11 in its reinforced state, and f be the operating frequency. The volume wave wavelength λ can be calculated when the angle between the propagation direction of the volume wave and the first surface 111 is equal to the first reinforcement angle θ. B1 .

[0351] In some embodiments, the volume wave wavelength λ is equal to the angle between the propagation direction of the volume wave and the first surface 111 when the angle is equal to the first reinforcement angle θ.B1 This refers to the bulk wave wavelength within the piezoelectric layer 11 in its enhanced state. Specifically, the enhanced condition for bulk wave excitation is that the bulk waves excited by the interdigitated electrodes 20 of the same polarity are phase-matched in a specific direction, i.e., 2Pcosθ=nλ. B2 Where n is a positive integer. As an example, in practical applications, if we only consider the case of n=1, we can derive Formula 3: cosθ=λ B1 / 2P=V B1 / 2Pf, 0°<θ<180°.

[0352] In some embodiments, due to the wave vector β of the sound wave B1 It is a vector, and its magnitude is taken when calculating the depth of the first feature:

[0353] Formula 4:

[0354] Where, β B1z V is the z-component of the acoustic wave vector of piezoelectric layer 11 (the z-direction is perpendicular to both the first and second directions mentioned above). b1 Let λ be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the current operating frequency, and λ be the velocity of the piezoelectric crystal along the x-direction. B1 =V B1 / f. Therefore, according to Formula 4 above, the z-component |β| of the wave vector of the surface acoustic wave excited by the interdigital electrode 20 can be calculated. b1z |

[0355] Among them, if β b1z Since it is a real number, the sound wave is a traveling wave within the piezoelectric layer 11, which is a volume wave.

[0356] Among them, if β B1z It is an imaginary number. At this point, the sound wave is no longer a body wave, the wave vector is β1, and the z-component is β. 1z . β b1 It is the volume wave vector along the x-direction of the piezoelectric layer 11 at the operating frequency f.

[0357] At this point, the sound wave propagating towards the depth of the piezoelectric layer 11 is an evanescent wave, and the sound wave propagating along the surface is a surface acoustic wave.

[0358] As an example, in practical applications, the current operating frequency is 2 GHz, and the wavelength of the sound wave is relatively short (in surface acoustic wave devices, the operating frequency is inversely proportional to the wavelength; as the operating frequency increases, the wavelength becomes shorter). Since surface acoustic waves mainly propagate on the surface, and their energy decays rapidly as they penetrate deeper into the piezoelectric layer 11, the sound wave at this frequency is an evanescent wave in the direction of depth of the piezoelectric layer 11.

[0359] When the sound wave propagating towards the depth of the piezoelectric layer 11 is an evanescent wave, the sound wave propagating towards the depth of the piezoelectric layer 11 (-z direction) can be described by the following formula:

[0360] Formula 5:

[0361] Where u is the amplitude of the sound wave, β b1 It is the volume wave vector of piezoelectric layer 11 along the x-direction, β 1x It is the x-component of the piezoelectric layer acoustic wave vector, β 1z This is the z-component of the acoustic wave vector of the piezoelectric layer. As the acoustic wave propagates towards depth, its intensity gradually decreases. The depth at which the volumetric acoustic wave attenuates to 1 / e at the surface is denoted as the first characteristic depth ds, where e is a mathematical constant, approximately equal to 2.718. Therefore, the first characteristic depth ds can be easily calculated by substituting Formula 5 into Formula 1.

[0362] In some embodiments, when the frequency of the surface acoustic wave excited by the interdigitated electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer 11 is 0.1 to 0.9 times the first characteristic depth. Since the intensity of the first sound field decays exponentially from the surface to the depth direction, limiting the thickness of the piezoelectric layer 11 to the range of 0.1 to 0.9 times the first characteristic depth can meet the sound velocity requirements of the device. Exemplarily, the thickness of the piezoelectric layer 11 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 times the first characteristic depth.

[0363] In some embodiments, to better meet the sound velocity requirements of the device, the thickness of the piezoelectric layer 11 can be further defined as 0.1 to 0.5 times the first characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency. For example, the thickness of the piezoelectric layer 11 can be 0.1, 0.2, 0.3, 0.4, or 0.5 times the first characteristic depth.

[0364] In some embodiments, the second feature depth satisfies the following formula:

[0365] Formula Six:

[0366] Formula 7: |β b2 |=2π / λ b2 ;

[0367] Where P is the midline distance between two adjacent electrode fingers 21, dt is the second feature depth, and β b2 Let β be the wave vector corresponding to the bulk wave wavelength of the material of the sound velocity layer 12 along the x-direction at the operating frequency.b2 The modulus is 2π / λ b2 , λ b2 =V b2 / f,V b2 Let f be the volume wave velocity of the material in sound layer 12 along the x-direction, f be the operating frequency, and λ be the velocity of sound. b2 Let be the bulk wavelength of the sound velocity layer 12 material along the x-direction at the operating frequency. Based on the above formula, the second characteristic depth can be calculated, thereby limiting the thickness of the sound velocity layer 12 to a suitable range so that the device performance meets the requirements.

[0368] In some embodiments, the angle between the propagation direction of the bulk wave excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12 and the second surface 112 is equal to γ; where cosγ = λ B2 / 2P=V B2 / 2Pf(0°<θ<180°). λ B2 V is the volume wave wavelength excited by the interdigitated electrode 20 within the piezoelectric layer 11 and propagating into the sound velocity layer 12. B2 Let f be the volume wave velocity within sound velocity layer 12, and f be the operating frequency. Therefore, the volume wave wavelength λ can be calculated using the above formula. B2 It should be noted that the sound velocity layer 12 can be an isotropic or anisotropic material, and the sound velocity can be determined.

[0369] In some embodiments, the z-component of the wave vector entering the sound velocity layer 12 is an evanescent wave, wherein the z-component is an imaginary number, and the amplitude of the evanescent wave decays rapidly with the increase of the depth of the sound velocity layer 12.

[0370] In some embodiments, the enhancement condition for body wave excitation is that the body waves excited by the interdigitated electrodes 20 of the same polarity are phase-matched in a specific direction, i.e., 2Pcosθ=nλ. B2 Where n is a positive integer. As an example, in practical applications, if we only consider the case of n=1, we can derive Formula 8: cosγ=λ B2 / 2P.

[0371] Through theoretical deduction, the formula for the z-component of the wave vector in the sound velocity layer 12 has the same form as Formula 4.

[0372] In some embodiments, due to the wave vector β of the sound wave B2 It is a vector, and its magnitude β is taken when calculating the second feature depth dt. B2 Satisfy the following formula:

[0373] Formula Nine:

[0374] Where, β B2z V is the z-component of the acoustic wave vector of sound velocity layer 12.B2 Let λ be the volume wave velocity within sound velocity layer 12, f be the current operating frequency of the surface acoustic wave device, and λ be the velocity of the sound waves within the sound velocity layer 12. B2 =V B2 / f. Therefore, the z-component of the acoustic wave vector of the sound velocity layer 12 can be calculated according to Formula 9 above.

[0375] Among them, if β b2Z Since it is a real number, the sound wave is a traveling wave within the sound speed layer 12, which is a body wave.

[0376] Among them, if At this time β B2 =β b2 , β 2z Let be an imaginary number, representing the z-component of the sound wave vector of sound velocity layer 12. The intensity of the sound wave entering sound velocity layer 12 gradually decreases with increasing depth of sound velocity layer 12, thus its characteristic depth dt is calculated as follows:

[0377] In some embodiments, the thickness of the sound velocity layer 12 is 0.1P-0.6P, where P is the center-to-line distance between two adjacent electrode fingers 21. When the thickness of the sound velocity layer 12 is too thick, the waveguide mode cannot leak into the depth direction of the substrate 13, thus affecting device performance. When the thickness of the sound velocity layer 12 is too thin, its effect on increasing or decreasing the sound velocity is weak, making it difficult to meet the required sound velocity. Therefore, the thickness of the sound velocity layer 12 can be calculated based on the second characteristic depth dt and limited to the above range, which can meet the sound velocity requirements without affecting device performance.

[0378] For example, when the sound velocity layer 12 is made of silicon nitride or aluminum oxide, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.6P. When the sound velocity layer 12 is made of silicon carbide or aluminum nitride, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.5P. When the sound velocity layer 12 is made of diamond, the thickness of the sound velocity layer 12 ranges from 0.1P to 0.4P.

[0379] For example, when P is 1 μm, the thickness of the sound velocity layer 12 can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm or 0.6 μm, etc.

[0380] In some embodiments, when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the sound velocity layer 12 is 0.1 to 0.9 times the second characteristic depth. To ensure that other functions below the sound velocity layer 12 provide acoustic support, the thickness of the sound velocity layer 12 should preferably not exceed the second characteristic depth. Since the sound field intensity of the sound wave decays exponentially from the surface to the depth direction, limiting the thickness of the sound velocity layer 12 to the range of 0.1 to 0.9 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency can meet the sound velocity requirements of the device. Exemplarily, the thickness of the sound velocity layer 12 can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 times the second characteristic depth.

[0381] In some embodiments, to better meet the sound velocity requirements of the device, the thickness of the sound velocity layer 12 may be further defined as 0.1 to 0.5 times the second characteristic depth when the frequency of the surface acoustic wave excited by the interdigital electrode 20 is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency. For example, the thickness of the sound velocity layer 12 may be 0.1, 0.2, 0.3, 0.4, or 0.5 times the second characteristic depth.

[0382] This application also proposes a radio frequency front-end module, which includes the aforementioned surface acoustic wave device 100. The surface acoustic wave device 100 may be a resonator.

[0383] In some implementations, the radio frequency front-end module can be applied to electronic devices, which may include, but are not limited to, LED panels, tablet computers, laptops, computers, navigators, mobile phones, and electronic watches, etc., and this application does not impose any limitations on them.

[0384] In some implementations, the RF front-end module may include multiple filters, which can be two, three, or more. The filters may include multiple resonators, which can be arranged as needed. The multiple resonators can be two, three, four, or more.

[0385] In some implementations, the RF front-end module may also include a low-noise amplifier, an RF switch, and a power amplifier, etc. The specific connection methods can be referred to the prior art, and will not be described in detail here.

[0386] Furthermore, since the RF front-end module includes filters, and filters include resonators, the RF front-end module has all the beneficial effects of filters and resonators, which will not be elaborated here.

[0387] It should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0388] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0389] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Those skilled in the art will understand that implementing all or part of the processes of the above embodiments, and making equivalent changes according to the claims of this application, still falls within the scope of this application.

Claims

1. A surface acoustic wave device, wherein, It includes a piezoelectric layer and interdigitated electrodes disposed on a first surface of the piezoelectric layer, wherein the interdigitated electrodes include a plurality of electrode fingers; The acoustic waves emitted by the surface acoustic wave device during operation include surface acoustic waves and volume waves, and the surface acoustic waves propagate in the X direction. The first characteristic thickness of the surface acoustic wave device is T. y The thickness of the piezoelectric layer is D. y The thickness of the piezoelectric layer satisfies the condition that the thickness of the first feature is: The piezoelectric layer includes a piezoelectric crystal, and the thickness of the first feature is determined based on the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric crystal along the X direction, and the operating frequency.

2. The surface acoustic wave device according to claim 1, wherein, First feature thickness: Wherein, the midline distance between two adjacent electrode fingers is P, and the volume wave velocity of the piezoelectric crystal along the X direction is V. b1 The operating frequency is f, and the bulk wavelength of the piezoelectric crystal along the X direction at the operating frequency is λ1.

3. The surface acoustic wave device according to claim 2, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer and the first characteristic thickness satisfy the following condition:

4. The surface acoustic wave device according to claim 2, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer is less than the first characteristic thickness.

5. The surface acoustic wave device according to claim 2, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer and the first characteristic thickness satisfy the following condition:

6. The surface acoustic wave device according to claim 2, wherein, The surface acoustic wave device further includes a temperature compensation layer, which is disposed on the side of the piezoelectric layer away from the interdigitated electrodes along the thickness direction of the piezoelectric layer.

7. The surface acoustic wave device according to claim 6, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer is H, and the first characteristic thickness and the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer satisfy the following condition:

8. The surface acoustic wave device according to claim 7, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the sum of the first characteristic thickness, the thickness of the temperature compensation layer, and the thickness of the piezoelectric layer satisfies the following condition:

9. The surface acoustic wave device according to claim 6, wherein, When the angle between the propagation direction of the bulk wave excited by the interdigitated electrode into the piezoelectric layer and the first surface is equal to the first reinforcement angle θ, the bulk wave in the piezoelectric layer and the temperature compensation layer is in a reinforced state; the propagation speed of the bulk wave excited by the interdigitated electrode into the piezoelectric layer and the temperature compensation layer is V0, and the first reinforcement angle and the propagation speed of the bulk wave in the piezoelectric layer and the temperature compensation layer satisfy the following equation: The surface acoustic wave frequency of the surface acoustic wave device is f, and the sum of the thickness of the temperature compensation layer and the thickness of the piezoelectric layer satisfies the following condition: Wherein, the surface acoustic wave frequency f is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency.

10. The surface acoustic wave device according to claim 9, wherein, The thickness of the temperature compensation layer is D. w The thicknesses of the temperature compensation layer and the piezoelectric layer satisfy the following conditions:

11. The surface acoustic wave device according to any one of claims 1-10, wherein, When the propagation direction of the bulk wave excited by the interdigitated electrode into the piezoelectric layer makes an angle equal to the first reinforcement angle θ with the first surface, the bulk wave in the piezoelectric layer is in a reinforced state; the wavelength λ of the bulk wave excited by the interdigitated electrode into the piezoelectric layer is... B1 The bulk wavelength is the wavelength of the piezoelectric layer in the enhanced state.

12. The surface acoustic wave device according to claim 11, wherein, The midline distance between two adjacent electrode fingers is P, and the first reinforcement angle is θ. The first reinforcement angle satisfies the following equation: Among them, V B1 λ is the volume wave velocity within the piezoelectric layer, f is the operating frequency, and λ is the velocity of sound. B1 The first reinforcement angle θ is the bulk wave wavelength excited by the interdigitated electrode within the piezoelectric layer, and the range of the first reinforcement angle θ satisfies: 0° < θ < 180°.

13. The surface acoustic wave device according to any one of claims 1-10, wherein, The surface acoustic wave device includes a functional layer, which is disposed on the side of the piezoelectric layer away from the interdigitated electrodes along the thickness direction of the piezoelectric layer. The second characteristic thickness of the surface acoustic wave device is T. d The thickness of the functional layer is D. d The thickness of the functional layer and the thickness of the second feature satisfy the following condition: The thickness of the second feature is determined based on the volume wave velocity and operating frequency of the material of the functional layer along the X direction.

14. The surface acoustic wave device according to claim 13, wherein, The second characteristic thickness satisfies the following equation: Wherein, the midline distance between two adjacent electrode fingers is P, and the volume wave velocity of the functional layer material along the X direction is V. b2 The operating frequency is f, and λ2 is the wavelength corresponding to the volume wave velocity of the material of the functional layer along the X direction at the operating frequency.

15. The surface acoustic wave device according to claim 14, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer and the second feature thickness satisfy the following condition:

16. The surface acoustic wave device according to claim 14, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer is less than the second characteristic thickness.

17. The surface acoustic wave device according to claim 14, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer and the second feature thickness satisfy the following condition:

18. The surface acoustic wave device according to claim 13, wherein, The surface acoustic wave device includes a monocrystalline silicon layer. Along the thickness direction of the piezoelectric layer, the monocrystalline silicon layer is disposed on the surface of the functional layer opposite to the piezoelectric layer. <110> The spatial angle between the crystal orientation group and the propagation direction of the surface acoustic wave excited by the plurality of interdigitated electrodes on the first surface is less than or equal to 10°.

19. The surface acoustic wave device according to claim 18, wherein, The single-crystal silicon layer <110> The crystal orientation is parallel to the propagation direction of the surface acoustic waves excited by the plurality of interdigitated electrodes on the first surface.

20. The surface acoustic wave device according to claim 13, wherein, The material of the functional layer is either anisotropic or isotropic.

21. The surface acoustic wave device according to claim 13, wherein, The functional layer is a sound velocity layer or a polycrystalline silicon layer.

22. The surface acoustic wave device according to any one of claims 1-10, wherein, The material of the piezoelectric layer is anisotropic.

23. A surface acoustic wave device, wherein, It includes a functional layer and a piezoelectric layer stacked along its own thickness direction, and an interdigitated electrode disposed on a first surface of the piezoelectric layer away from the functional layer, wherein the interdigitated electrode includes a plurality of electrode fingers; The acoustic waves emitted by the surface acoustic wave device during operation include surface acoustic waves and volume waves, with the surface waves propagating in the X direction. The second characteristic thickness of the surface acoustic wave device is T. d The thickness of the functional layer is D. d The thickness of the functional layer and the thickness of the second feature satisfy the following condition: The thickness of the second feature is determined based on the volume wave velocity and operating frequency of the material of the functional layer along the X direction.

24. The surface acoustic wave device according to claim 23, wherein, The second characteristic thickness satisfies the following equation: Wherein, the midline distance between two adjacent electrode fingers is P, and the bulk acoustic velocity of the material of the functional layer along the X direction is V. b2 The operating frequency is f, and λ2 is the wavelength corresponding to the volume wave velocity of the material of the functional layer along the X direction at the operating frequency.

25. The surface acoustic wave device according to claim 23, wherein, When the angle between the propagation direction of the acoustic wave excited by the interdigitated electrode and the first surface is equal to the second reinforcement angle γ, the volume wave in the functional layer is in a reinforced state; the wavelength λ of the volume wave of the acoustic wave excited by the interdigitated electrode propagating into the functional layer is... B2 The bulk wavelength is the wavelength of the functional layer in the enhanced state.

26. The surface acoustic wave device according to claim 25, wherein, The midline distance between two adjacent electrode fingers is P, and the second reinforcement angle is γ, which satisfies the following equation: Among them, V B2 Let f be the volume wave velocity within the functional layer, f be the operating frequency, and λ be the velocity of sound. B2 The second reinforcement angle γ is the bulk wavelength of the acoustic wave excited by the interdigital electrode that propagates into the functional layer, and satisfies: 0° < γ < 180°.

27. The surface acoustic wave device according to claim 23, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer and the second feature thickness satisfy the following condition:

28. The surface acoustic wave device according to claim 23, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer is less than the second characteristic thickness.

29. The surface acoustic wave device according to claim 23, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is greater than or equal to the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the functional layer and the second feature thickness satisfy the following condition:

30. The surface acoustic wave device according to any one of claims 23-29, wherein, The first characteristic thickness of the surface acoustic wave device is T. y The thickness of the piezoelectric layer is D. y The thickness of the piezoelectric layer satisfies the condition that the thickness of the first feature is: The thickness of the first feature is determined based on the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric layer along the X direction, and the operating frequency.

31. The surface acoustic wave device according to claim 30, wherein, The thickness of the first feature satisfies the equation:

32. The surface acoustic wave device according to claim 31, wherein, The thickness of the piezoelectric layer satisfies the condition: 0.4P≤D y ≤0.8P.

33. The surface acoustic wave device according to claim 31, wherein, The thickness of the functional layer satisfies the condition: 0.2P≤D d ≤0.6P.

34. The surface acoustic wave device according to any one of claims 23-29, wherein, The material of the piezoelectric layer is anisotropic.

35. A surface acoustic wave device, wherein, include: The piezoelectric layer, the sound velocity layer, and the interdigitated electrode, wherein the interdigitated electrode includes a plurality of electrode fingers, the piezoelectric layer has a first surface and a second surface disposed opposite to each other, the interdigitated electrode is disposed on the first surface of the piezoelectric layer, and the sound velocity layer is disposed on the second surface of the piezoelectric layer; The acoustic waves emitted by the surface acoustic wave device during operation include surface acoustic waves and volume waves, with the surface acoustic waves propagating in the x-direction. The surface acoustic wave device has a first characteristic depth, the thickness of the piezoelectric layer is less than the first characteristic depth, and the piezoelectric layer includes a piezoelectric crystal; The first feature depth is related to the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency.

36. The surface acoustic wave device as claimed in claim 1, wherein, The first feature depth is positively correlated with the midline distance between two adjacent electrode fingers, the first feature depth is negatively correlated with the volume wave velocity of the piezoelectric crystal along the x-direction, and the first feature depth is positively correlated with the operating frequency.

37. The surface acoustic wave device as claimed in claim 1, wherein, The first feature depth satisfies the following formula: Where P is the midline distance between two adjacent electrode fingers, ds is the first feature depth, and β b1 β is the wave vector corresponding to the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency. b1 The modulus is 2π / λ b1 , λ b1 =V b1 / f,V b1 Let f be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the operating frequency, and λ be the velocity of sound. b1 The bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency is given.

38. The surface acoustic wave device as claimed in claim 1, wherein, When the propagation direction of the bulk wave excited by the interdigitated electrode within the piezoelectric layer makes an angle equal to the first reinforcement angle θ with respect to the first surface, it indicates that the bulk wave within the piezoelectric layer is in a reinforced state; where cosθ = λ B1 / 2P=V B1 / 2Pf, 0°<θ<180°, where P is the midline distance between two adjacent electrode fingers, and V B1 Let f be the volume wave velocity within the piezoelectric layer in its enhanced state, f be the operating frequency, and λ be the velocity of sound. B1 The bulk wavelength is the wavelength excited by the interdigitated electrodes within the piezoelectric layer.

39. The surface acoustic wave device as described in claim 38, wherein, The z-component of the wave vector of the surface acoustic wave excited by the interdigitated electrode is β. 1z ; Where, |β 1z |=|β b1 |sinθ,β b1 It is the volume wave vector along the x-direction of the piezoelectric layer at the operating frequency f.

40. The surface acoustic wave device as claimed in claim 1, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer is 0.1 to 0.9 times the first feature depth.

41. The surface acoustic wave device as claimed in claim 1, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the piezoelectric layer is 0.1 to 0.5 times the first characteristic depth.

42. The surface acoustic wave device as claimed in claim 1, wherein, The sound speed layer is a hypersonic layer.

43. The surface acoustic wave device as claimed in claim 1, wherein, The surface acoustic wave device further includes: A substrate is disposed on the side of the sound velocity layer opposite to the piezoelectric layer; The surface acoustic wave device has a second characteristic depth, and the thickness of the sound velocity layer is less than the second characteristic depth.

44. The surface acoustic wave device as claimed in claim 43, wherein, The second feature depth is positively correlated with the midline distance between two adjacent electrode fingers, negatively correlated with the sound velocity of the sound velocity layer, and positively correlated with the operating frequency.

45. The surface acoustic wave device as claimed in claim 43, wherein, The second feature depth satisfies the following formula: Where P is the midline distance between two adjacent electrode fingers, dt is the second feature depth, and β b2 β is the wave vector corresponding to the bulk wave wavelength of the sound velocity layer material along the x-direction at the operating frequency. b2 The modulus is 2π / λ b2 , λ b2 =V b2 / f,V b2 Let f be the volume wave velocity of the sound velocity layer material along the x-direction, f be the operating frequency, and λ be the velocity of sound. b2 The bulk wavelength of the sound velocity layer material along the x-direction at the operating frequency is given.

46. ​​The surface acoustic wave device as claimed in claim 44, wherein, The angle between the propagation direction of the volume wave excited and propagating into the sound velocity layer by the interdigitated electrode within the piezoelectric layer and the second surface is equal to γ, where cosγ = λ. B2 / 2P=V B2 / 2Pf, 0°<θ<180°; where P is the midline distance between two adjacent electrode fingers, V B2 Let f be the volume wave velocity within the sound velocity layer, f be the operating frequency, and λ be the velocity of the sound wave. B2 The interdigitated electrode is the volume wave wavelength that is excited within the piezoelectric layer and propagates into the sound velocity layer.

47. The surface acoustic wave device as claimed in claim 45, wherein, The z-component of the wave vector entering the sound velocity layer is an evanescent wave, where the z-component is an imaginary number, and the amplitude of the evanescent wave decreases rapidly with the increase of the depth of the sound velocity layer.

48. The surface acoustic wave device as claimed in claim 42, wherein, The thickness of the sound velocity layer is [0.1P-0.6P], where P is the distance between the centerlines of two adjacent electrode fingers.

49. The surface acoustic wave device as described in claim 43, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the sound velocity layer is 0.1 to 0.9 times the second characteristic depth.

50. The surface acoustic wave device as claimed in claim 43, wherein, When the frequency of the surface acoustic wave excited by the interdigitated electrode is the surface acoustic wave resonant frequency or the surface acoustic wave anti-resonant frequency, the thickness of the sound velocity layer is 0.1 to 0.5 times the second characteristic depth.

51. The surface acoustic wave device as described in claim 43, wherein, The surface acoustic wave device further includes a temperature compensation layer, which is disposed between the substrate and the sound velocity layer; The thickness of the piezoelectric layer is [0.1P-1.2P], where P is the midline distance between two adjacent electrode fingers, and the thickness of the temperature compensation layer is [0μm-1μm].

52. The surface acoustic wave device as described in claim 43, wherein, The thickness of the substrate is [100μm-800μm].

53. A surface acoustic wave device, wherein, It includes a piezoelectric layer, a sound velocity layer, and interdigitated electrodes. The interdigitated electrodes include multiple electrode fingers. The piezoelectric layer has a first surface and a second surface that are disposed opposite to each other. The interdigitated electrodes are disposed on the first surface of the piezoelectric layer, and the sound velocity layer is disposed on the second surface of the piezoelectric layer. The acoustic waves emitted by the surface acoustic wave device during operation include surface acoustic waves and volume waves. The surface acoustic wave device has a second characteristic depth, and the thickness of the sound velocity layer is less than the second characteristic depth; The second feature depth is related to the midline distance between two adjacent electrode fingers, the sound velocity of the sound velocity layer, and the operating frequency.

54. The surface acoustic wave device as described in claim 53, wherein, The second feature depth satisfies the following formula: Where P is the midline distance between two adjacent electrode fingers, dt is the second feature depth, and β b2 For the sound velocity layer material at the operating frequency along x The wave vector corresponding to the wavelength of the body wave in the direction ， β b2 The modulus is 2π / λ b2 , λ b2 =V b2 / f,V b2 Let f be the volume wave velocity of the sound velocity layer material along the x-direction, f be the operating frequency, and λ be the velocity of sound. b2 The bulk wavelength of the sound velocity layer material along the x-direction at the operating frequency is given.

55. A surface acoustic wave device, wherein, The piezoelectric substrate includes an interdigitated electrode, wherein the interdigitated electrode includes a plurality of electrode fingers, and the piezoelectric substrate includes: A piezoelectric layer having a first surface and a second surface disposed opposite to each other, wherein the interdigitated electrode is disposed on the first surface of the piezoelectric layer; A sound velocity layer is disposed on the second surface, the sound velocity layer being used to increase or decrease the sound velocity of the surface acoustic wave device; A temperature compensation layer is disposed on the side of the sound velocity layer opposite to the piezoelectric layer; A substrate is disposed on the side of the temperature compensation layer that is opposite to the sound velocity layer.

56. The surface acoustic wave device as described in claim 55, wherein, The sound velocity layer is mainly composed of silicon; or, the sound velocity layer is mainly composed of tantalum pentoxide or indium phosphide.

57. The surface acoustic wave device as described in claim 55, wherein, The sound speed layer is a hypersonic layer.

58. The surface acoustic wave device as described in claim 55, wherein, The acoustic waves emitted by the surface acoustic wave device during operation include surface acoustic waves and volume waves, with the surface acoustic waves propagating in the x-direction. The surface acoustic wave device has a first characteristic depth and a second characteristic depth, and the thickness of the piezoelectric layer is less than the first characteristic depth; the thickness of the sound velocity layer is less than the second characteristic depth, and the piezoelectric layer includes a piezoelectric crystal. The first feature depth is related to the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric crystal along the x-direction, and the operating frequency. The second feature depth is related to the midline distance between two adjacent electrode fingers, the sound velocity of the sound velocity layer, and the operating frequency.

59. The surface acoustic wave device as described in claim 58, wherein, The first feature depth is positively correlated with the midline distance between two adjacent electrode fingers, the first feature depth is negatively correlated with the volume wave velocity of the piezoelectric crystal along the x-direction, and the first feature depth is positively correlated with the operating frequency. The second feature depth is positively correlated with the midline distance between two adjacent electrode fingers, negatively correlated with the sound velocity of the sound velocity layer, and positively correlated with the operating frequency.

60. The surface acoustic wave device as claimed in claim 59, wherein, The first feature depth satisfies the following formula: Where P is the midline distance between two adjacent electrode fingers, ds is the first feature depth, and β b1 β is the wave vector corresponding to the bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency. b1 The modulus is 2π / λ b1 , λ b1 =V b1 / f,V b1 Let f be the volume wave velocity of the piezoelectric crystal along the x-direction, f be the operating frequency, and λ be the velocity of sound. b1 The bulk wavelength of the piezoelectric crystal along the x-direction at the operating frequency is given.

61. The surface acoustic wave device as described in claim 59, wherein, The second feature depth satisfies the following formula: Where P is the midline distance between two adjacent electrode fingers, dt is the second feature depth, and β b2 Let βb2 be the wave vector corresponding to the bulk wave wavelength of the sound velocity layer material along the x-direction at the operating frequency, and let λ be the modulus of βb2. b2 =V b2 / f,V b2 Let f be the volume wave velocity of the sound velocity layer material along the x-direction, f be the operating frequency, and λ be the velocity of sound. b2 The bulk wavelength of the sound velocity layer material along the x-direction at the operating frequency is given.

62. A radio frequency front-end module, wherein, Includes the surface acoustic wave device as described in any one of claims 1-61.

63. An electronic device, wherein, Includes the radio frequency front-end module as described in claim 35.

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