Surface acoustic wave device and radio frequency front-end module

Abstract

The application discloses a surface acoustic wave device and a radio frequency front-end module. The surface acoustic wave device comprises a piezoelectric layer, a sound velocity layer and an interdigital electrode, wherein the interdigital electrode comprises a plurality of electrode fingers. The piezoelectric layer has a first surface and a second surface arranged oppositely, the interdigital electrode is arranged on the first surface of the piezoelectric layer, and the sound velocity layer is arranged on the second surface of the piezoelectric layer. The sound wave of the surface acoustic wave device in operation comprises a surface acoustic wave and a bulk wave. The surface acoustic wave device has a first characteristic depth, and the thickness of the piezoelectric layer is less than the first characteristic depth. The first characteristic depth is related to the center line spacing of two adjacent electrode fingers of the interdigital electrode, the bulk wave sound velocity of the piezoelectric crystal along the x direction and the working frequency. By arranging the sound velocity layer directly below the piezoelectric layer and limiting the thickness of the piezoelectric layer to be less than the first characteristic depth, the thickness of the piezoelectric layer is reasonably thinned, the surface wave sound velocity is obviously improved or decreased, and the influence on other functional layers is avoided.

Description

Technical Field

[0001] This application relates to the field of radio frequency filtering technology, and in particular to a surface acoustic wave device and a radio frequency front-end module. Background Technology

[0002] The basic structure of surface acoustic wave (SAW) devices involves fabricating interdigitated electrodes on a piezoelectric substrate. They have advantages such as low electro-acoustic conversion loss, flexible design, and ease of mass production using semiconductor processes, and have been widely used in modern communication systems.

[0003] Different applications place different requirements on surface acoustic wave (SAW) devices. For example, in applications requiring high-frequency response, the velocity of sound needs to be increased to allow for larger fabrication linewidths and meet process requirements. Conversely, in applications requiring low-frequency response, the velocity of sound needs to be reduced to achieve miniaturization. However, current technologies offer limited options for increasing or decreasing the velocity of sound. Therefore, effectively increasing or decreasing the velocity of sound in SAW devices has become a pressing issue. Summary of the Invention

[0004] In view of this, this application proposes a surface acoustic wave device and a radio frequency front-end module.

[0005] The first aspect of this application discloses a surface acoustic wave (SAW) device, comprising 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 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 sound waves emitted by the SAW device during operation include SAW waves and volume waves, with the SAW waves propagating in the x-direction. The SAW device has a first characteristic depth, and the thickness of the piezoelectric layer is less than the first characteristic depth. The piezoelectric layer includes a piezoelectric crystal. The first characteristic depth is related to the midline distance between two adjacent electrode fingers, the volume wave velocity of the piezoelectric crystal in the x-direction, and the operating frequency.

[0006] A second aspect of this application provides a surface acoustic wave (SAW) device, comprising 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 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 sound waves emitted by the SAW device during operation include SAW waves and volume waves. The SAW device has a second characteristic depth, and the thickness of the sound velocity layer is less than the second characteristic depth. The second characteristic depth is related to the midline distance between two adjacent electrode fingers, the sound velocity of the sound velocity layer, and the operating frequency.

[0007] A third aspect of this application provides a surface acoustic wave device, comprising a piezoelectric substrate and interdigitated electrodes, wherein the interdigitated electrodes include a plurality of electrode fingers, and the piezoelectric substrate comprises:

[0008] 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;

[0009] 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;

[0010] A temperature compensation layer is disposed on the side of the sound velocity layer opposite to the piezoelectric layer;

[0011] A substrate is disposed on the side of the temperature compensation layer that is opposite to the sound velocity layer.

[0012] The fourth aspect of this application provides a radio frequency front-end module including the aforementioned surface acoustic wave device.

[0013] As can be seen from the above technical solution, the surface acoustic wave device proposed in this application, by directly setting a sound velocity layer below the piezoelectric layer and limiting the thickness of the piezoelectric layer to less than the first feature depth, reasonably reduces the thickness of the piezoelectric layer, so that the sound velocity can be significantly increased or decreased while avoiding affecting the function of other functional layers. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the structure of the surface acoustic wave device proposed in the embodiments of this application;

[0016] Figure 2 This is a schematic diagram of the bulk wave excitation of the surface acoustic wave device proposed in the embodiments of this application;

[0017] Figure 3 This is a schematic diagram of the acoustic wave transmission into the sound velocity layer of the surface acoustic wave device proposed in the embodiments of this application;

[0018] Figure 4 This is a schematic diagram of the modified structure of the surface acoustic wave device proposed in the embodiments of this application;

[0019] Figure 5 This is a graph showing the surface wave sound velocity as a function of the piezoelectric layer thickness in an embodiment of this application.

[0020] Figure 6 This is a graph showing the change in surface wave velocity with the thickness of the sound velocity layer according to an embodiment of this application.

[0021] Explanation of reference numerals in the attached figures:

[0022] 100. Surface acoustic wave device; 10. Piezoelectric substrate; 11. Piezoelectric layer; 111. First surface; 112. Second surface; 12. Sound velocity layer; 13. Substrate; 14. Temperature compensation layer; 20. Interdigitated electrode; 21. Electrode finger. Detailed Implementation

[0023] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] It should be understood that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture. If the specific posture changes, the directional indication will also change accordingly.

[0025] It should also be understood that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or may be connected to an intermediary element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element through an intermediary element.

[0026] The terminology used in this application specification is for the purpose of describing particular embodiments only and is not intended to limit the application. Descriptions using terms such as "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature.

[0027] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0028] Please see Figures 1 to 3This application provides a surface acoustic wave (SAW) device 100, which 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 emitted by the SAW device 100 during operation include SAW waves and volume waves. The SAW waves propagate in 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 in the x-direction, and the operating frequency.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In some embodiments, the first feature depth satisfies the following formula:

[0041] Formula 1:

[0042] Formula 2:

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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. B1The 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.

[0047] 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 .

[0048] 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°.

[0049] 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:

[0050] Formula 4:

[0051] 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 |

[0052] 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.

[0053] Among them, if β B1zIt 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.

[0054] 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.

[0055] 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.

[0056] 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:

[0057] Formula 5:

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Please see Figure 1 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] Please see Figure 5 , Figure 5 The above embodiment shows the curve of surface wave sound velocity varying with the piezoelectric layer thickness. Figure 5 As can be seen, 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 velocity requirements of the device, the thickness of the piezoelectric layer 11 is limited to less than the first feature depth ds, thereby meeting the higher velocity requirements of the device.

[0069] It should be noted that the surface acoustic wave device 100 in this embodiment may also include other functional layers, for example, please refer to Figure 3 and Figure 4 In some embodiments, the piezoelectric substrate 10 further includes a substrate 13 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 midline distance 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 also has 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 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.

[0070] 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.

[0071] In some embodiments, the second feature depth satisfies the following formula:

[0072] Formula Six:

[0073] Formula 7: |β b2 |=2π / λ b2 ;

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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:

[0080] Formula Nine:

[0081] 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.

[0082] 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.

[0083] 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:

[0084]

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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).

[0091] In another implementation, for TF-SAWs with piezoelectric layers of 30–50 YX-LiTaO3, -15–+15 YX-LiNbO3, or 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.

[0092] Please see Figure 6 , Figure 6 This is a graph showing the variation of surface wave sound velocity with sound velocity layer thickness in the above embodiments. Figure 6It can be seen that when the thickness of the sound velocity layer 12 exceeds the second feature depth of 0.45 μm, the rate of increase of the surface wave velocity slows down significantly, indicating that the sound field intensity has been greatly attenuated relative to the upper interface after the sound field reaches 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 feature depth dt.

[0093] 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.

[0094] Please see Figure 4 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 piezoelectric layer 11 has a thickness of 0.1P-1.2P, where P is the midline distance between two adjacent electrode fingers 21 of the interdigitated electrodes 20, and the temperature compensation layer 14 has a thickness of 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.

[0095] 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.

[0096] Specifically, the piezoelectric layer 11 can be made of a piezoelectric material with the following cut:

[0097] 30~50YX-LiTaO3, -15~+15YX-LiNbO3 and 120~140YX-LiNbO3.

[0098] 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.

[0099] 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.

[0100] In some embodiments, the temperature compensation layer 14 may be one or a combination of several materials such as silicon oxide, silicon nitride, and silicon oxynitride.

[0101] 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.

[0102] Please see Figures 1 to 3 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.

[0103] 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.

[0104] 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.

[0105] In some embodiments, the second feature depth satisfies the following formula:

[0106] Formula Six:

[0107] Formula 7: |β b2 |=2π / λ b2 ;

[0108] 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.

[0109] 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. 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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. B2Satisfy the following formula:

[0114] Formula Nine:

[0115] 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.

[0116] 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.

[0117] 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:

[0118]

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] Please see Figure 4 This application 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 opposite to the piezoelectric layer 11. The substrate 13 is disposed on the side of the temperature compensation layer 14 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] In some embodiments, the first feature depth satisfies the following formula:

[0133] Formula 1:

[0134] Formula 2:

[0135] 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.

[0136] 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.

[0137] 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.

[0138] In some embodiments, when the interdigitated electrode 20 indicates that the bulk wave in the piezoelectric layer 11 is in an enhanced state, 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; where cosθ = λ B1 / 2P=VB1 / 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.

[0139] 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 .

[0140] 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°.

[0141] 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:

[0142] Formula 4:

[0143] 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 |

[0144] Among them, if β b1zSince it is a real number, the sound wave is a traveling wave within the piezoelectric layer 11, which is a volume wave.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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:

[0149] Formula 5:

[0150] 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.

[0151] 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.

[0152] 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.

[0153] In some embodiments, the second feature depth satisfies the following formula:

[0154] Formula Six:

[0155] Formula 7: |β b2 |=2π / λ b2 ;

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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:

[0162] Formula Nine:

[0163] 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.

[0164] 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.

[0165] 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:

[0166]

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] This application also proposes a radio frequency front-end module, characterized in that it includes the aforementioned surface acoustic wave device 100. The surface acoustic wave device 100 may be a resonator.

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples.

[0178] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A surface acoustic wave device, characterized by, The surface acoustic wave device comprises a piezoelectric layer, a sound velocity layer and an interdigital electrode, the interdigital electrode comprises a plurality of electrode fingers, the piezoelectric layer has a first surface and a second surface arranged oppositely, the interdigital electrode is arranged on the first surface of the piezoelectric layer, and the sound velocity layer is arranged on the second surface of the piezoelectric layer. The acoustic wave of the surface acoustic wave device in operation comprises a surface acoustic wave and a bulk wave, and the surface acoustic wave propagates in an 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 comprises a piezoelectric crystal. The first characteristic depth satisfies the following formula: When the frequency of the surface acoustic wave excited by the interdigital electrode is a surface acoustic wave resonance frequency or a surface acoustic wave anti-resonance frequency, the thickness of the piezoelectric layer is 0.1-0.9 times the first characteristic depth. ； wherein P is the midline distance between two adjacent electrode fingers, ds is the first characteristic depth, β b1 is the wave vector corresponding to the bulk wave wavelength of the piezoelectric crystal along the x direction at the operating frequency, β b1 has a modulus of 2π / λ b1 , , V b1 is the bulk wave sound velocity of the piezoelectric crystal along the x direction, f is the operating frequency, λ b1 is the bulk wave wavelength of the piezoelectric crystal along the x direction at the operating frequency.

2. The SAW device of claim 1, wherein, An included angle between a propagation direction of a bulk wave excited by the interdigital electrode in the piezoelectric layer and the first surface is equal to a first strengthening angle θ when it is indicated that the bulk wave in the piezoelectric layer is in a strengthening state; wherein cosθ = λ B1 / 2P = V B1 / 2P f , 0° < θ < 180°, wherein P is a center line distance between adjacent two electrode fingers, V B1 is a bulk wave sound speed in the piezoelectric layer in the strengthening state, f is an operating frequency, and λ B1 is a bulk wave wavelength excited by the interdigital electrode in the piezoelectric layer.

3. The SAW device of claim 2, wherein, The z component of the wave vector of the surface acoustic wave excited by the interdigital electrode is β 1z ; wherein , β b1 is a bulk wave vector in the x direction of the piezoelectric layer at the operating frequency f .

4. The SAW device of claim 1, wherein, When the frequency of the surface acoustic wave excited by the interdigital electrode is a surface acoustic wave resonance frequency or a surface acoustic wave anti-resonance frequency, the thickness of the piezoelectric layer is 0.1-0.5 times the first characteristic depth.

5. The SAW device of claim 1, wherein, The sound velocity layer is a high sound velocity layer.

6. The SAW device of claim 1, wherein, The surface acoustic wave device further comprises:

7. The SAW device of claim 1, wherein, a substrate arranged on a 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. The second characteristic depth satisfies the following formula: The z component of the wave vector entering the sound velocity layer is an evanescent wave, wherein the z component is an imaginary number, and the amplitude of the evanescent wave rapidly attenuates with the increase of the depth of the sound velocity layer. ； wherein P is the centerline distance between two adjacent electrode fingers, dt is the second feature depth, β b2 is the wave vector corresponding to the bulk wave wavelength of the acoustic velocity layer material along the x direction at the operating frequency, β b2 has a modulus of 2π / λ b2 , , V b2 is the bulk wave velocity of the acoustic velocity layer material along the x direction, f is the operating frequency, λ b2 is the bulk wave wavelength of the acoustic velocity layer material along the x direction at the operating frequency.

8. The SAW device of claim 7, wherein, An angle between a propagation direction of a bulk wave excited and propagated by the interdigital electrode in the piezoelectric layer into the acoustic velocity layer and the second surface is equal to γ, where cos γ = λ B2 / 2P = V B2 / 2P f , 0° < θ < 180°; wherein P is a centerline distance between two adjacent electrode fingers, V B2 is a bulk wave acoustic velocity in the acoustic velocity layer, f is an operating frequency, and λ B2 is a bulk wave wavelength of the interdigital electrode excited and propagated in the piezoelectric layer into the acoustic velocity layer.

9. The SAW device of claim 8, wherein, The thickness of the sound velocity layer is [0.1P-0.6P], and P is the center line spacing between adjacent two electrode fingers.

10. The SAW device of claim 6, wherein, When the frequency of the surface acoustic wave excited by the interdigital electrode is a surface acoustic wave resonance frequency or a surface acoustic wave anti-resonance frequency, the thickness of the sound velocity layer is 0.1-0.9 times the second characteristic depth.

11. The SAW device of claim 7, wherein, When the frequency of the surface acoustic wave excited by the interdigital electrode is a surface acoustic wave resonance frequency or a surface acoustic wave anti-resonance frequency, the thickness of the sound velocity layer is 0.1-0.5 times the second characteristic depth.

12. The SAW device of claim 7, wherein, The surface acoustic wave device further comprises a temperature compensation layer arranged between the substrate and the sound velocity layer.

13. The SAW device of claim 7, wherein, The thickness of the piezoelectric layer is [0.1P-1.2P], P is the center line spacing between adjacent two electrode fingers, and the thickness of the temperature compensation layer is [0-1 μm]. The thickness of the substrate is [100-800 μm].

14. The SAW device of claim 7, wherein, The surface acoustic wave device comprises a piezoelectric layer, a sound velocity layer and an interdigital electrode, the interdigital electrode comprises a plurality of electrode fingers, the piezoelectric layer has a first surface and a second surface arranged oppositely, the interdigital electrode is arranged on the first surface of the piezoelectric layer, and the sound velocity layer is arranged on the second surface of the piezoelectric layer.

15. A surface acoustic wave device, characterized by, The acoustic wave of the surface acoustic wave device in operation comprises a surface acoustic wave and a bulk wave. 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 characteristic depth satisfies the following formula: The surface acoustic wave device comprises a piezoelectric substrate and an interdigital electrode, the interdigital electrode comprises a plurality of electrode fingers, and the piezoelectric substrate comprises: ； wherein P is the centerline distance between two adjacent electrode fingers, dt is the second feature depth, β b2 is the wave vector corresponding to the bulk wave wavelength of the acoustic velocity layer material along the x direction at the operating frequency, β b2 has a modulus of 2π / λ b2 , , V b2 is the bulk wave velocity of the acoustic velocity layer material along the x direction, f is the operating frequency, λ b2 is the bulk wave wavelength of the acoustic velocity layer material along the x direction at the operating frequency.

16. A surface acoustic wave device, characterized by, a piezoelectric layer having a first surface and a second surface arranged oppositely, and the interdigital electrode is arranged on the first surface of the piezoelectric layer. ​ a sound velocity layer disposed on the second surface, the sound velocity layer configured to increase or decrease a sound velocity of the surface acoustic wave device; a temperature compensation layer disposed on a surface of the sound velocity layer opposite to the piezoelectric layer; a substrate disposed on a surface of the temperature compensation layer opposite to the sound velocity layer; the sound wave of the surface acoustic wave device in operation includes a surface acoustic wave and a bulk wave, the surface acoustic wave propagating in an x direction; the surface acoustic wave device has a first characteristic depth and a second characteristic depth, a thickness of the piezoelectric layer being less than the first characteristic depth, a thickness of the sound velocity layer being less than the second characteristic depth, and the piezoelectric layer including a piezoelectric crystal; wherein the first characteristic depth satisfies the following formula: ； the second characteristic depth satisfies the following formula: ； wherein P is the centerline distance between two adjacent electrode fingers, ds is the first characteristic depth, β b1 is the wave vector corresponding to the bulk wave wavelength of the piezoelectric crystal along the x direction at the operating frequency, β b1 has a modulus of 2π / λ b1 , , V b1 is the bulk wave sound velocity of the piezoelectric crystal along the x direction, λ f is the operating frequency, λ b1 is the bulk wave wavelength of the piezoelectric crystal along the x direction at the operating frequency; dt is the second characteristic depth, β b2 is the wave vector corresponding to the bulk wave wavelength of the sound velocity layer material along the x direction at the operating frequency, β b2 has a modulus of 2π / λ b2 , , V b2 is the bulk wave sound velocity of the sound velocity layer material along the x direction, λ b2 is the bulk wave wavelength of the sound velocity layer material along the x direction at the operating frequency.

17. The SAW device of claim 16, wherein, the sound velocity layer has silicon as a main component; or the sound velocity layer has tantalum pentoxide or indium phosphide as a main component.

18. The SAW device of claim 16, wherein, the sound velocity layer is a high sound velocity layer.

19. A radio frequency front end module, comprising: a surface acoustic wave device as claimed in any one of claims 1 to 18.

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