Substrate, surface acoustic wave resonator, filter, radio-frequency module and electronic device

Abstract

A substrate, a surface acoustic wave resonator, a filter, a radio-frequency module and an electronic device, which relate to the technical field of surface acoustic waves. The substrate comprises: a piezoelectric layer, a reflective layer and a base that are sequentially stacked, wherein the piezoelectric layer comprises a piezoelectric material; and the reflective layer comprises support structures and reflective structures, each reflective structure is located between support structures, and the reflection coefficient of each reflective structure relative to the piezoelectric material is greater than a reflection coefficient threshold value. When the substrate is applied to a surface acoustic wave device, as the energy of a surface acoustic wave generated by the substrate propagates downwards in the direction of thickness of the substrate, the efficiency of the reflective structures in reflecting the energy of the surface acoustic wave is relatively high due to the fact that the reflection coefficient of each reflective structure relative to the piezoelectric material is greater than the reflection coefficient threshold value, such that the energy of the surface acoustic wave can be concentrated in a region above the reflective layer of the substrate; therefore, the energy of the surface acoustic wave is confined within a shallower thickness range, thereby effectively controlling the dissipation of the energy of the surface acoustic wave on the surface of the substrate.

Description

Substrates, surface acoustic wave resonators, filters, RF modules, and electronic devices

[0001] This application claims priority to Chinese Patent Application No. 202510183572.6, filed on February 19, 2025, entitled "An Acoustic Device, Radio Frequency Module and Communication Device", and Chinese Patent Application No. 202510407779.7, filed on March 31, 2025, entitled "Substrate, Surface Acoustic Wave Resonator, Filter, Radio Frequency Module and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of surface acoustic wave (SAW) technology, and more specifically, to a substrate, a SAW resonator, a filter, a radio frequency module, and an electronic device. Background Technology

[0003] Surface acoustic wave (SAW) resonators are acoustic devices that utilize the propagation characteristics of SAW waves on a substrate surface to achieve functions such as signal processing, filtering, and sensing. A SAW resonator consists of a substrate and an interdigital transducer (IDT). The IDT, deployed on one side of the substrate, converts the input electrical signal into an acoustic signal through the inverse piezoelectric effect. This acoustic signal propagates along the substrate surface and is then converted back into an electrical signal by the IDT deployed on the other side of the substrate.

[0004] To achieve a high quality factor for SAW resonators, a substrate structure is employed, consisting of a piezoelectric layer, a low-velocity layer, a high-velocity layer, and a substrate stacked sequentially from top to bottom. This structure aims to confine the energy of the SAW generated by the inverse piezoelectric effect of the IDT (Inverse Piezoelectric Transformer) within the thickness range above (including) the high-velocity layer of the substrate. However, this structure still cannot effectively control the energy dissipation of the SAW at the substrate surface. Summary of the Invention

[0005] This application provides a substrate, a surface acoustic wave resonator, a filter, a radio frequency module, and an electronic device that can effectively control the energy dissipation of SAW on the substrate surface.

[0006] In a first aspect, a substrate is provided, comprising: a piezoelectric layer, a reflective layer, and a substrate. The piezoelectric layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in the first direction. The piezoelectric layer comprises a piezoelectric material, and the reflective layer comprises a support structure and a reflective structure, the reflective structure and the support structure being arranged along a second direction perpendicular to the first direction, the reflective structure being located between the support structures, and the reflective structure having a reflectance coefficient relative to the piezoelectric material greater than a reflectance coefficient threshold.

[0007] In this embodiment, the reflection coefficient of the reflective structure relative to the piezoelectric material is greater than the reflection coefficient threshold. This is achieved by the acoustic impedance of the reflective structure and the acoustic impedance of the piezoelectric material. For example, when the acoustic impedance of the reflective structure is less than the acoustic impedance of the piezoelectric material, a suitable reflective structure and piezoelectric material can be selected to support the reflection coefficient of the reflective structure relative to the piezoelectric material being greater than the reflection coefficient threshold. Alternatively, when the acoustic impedance of the reflective structure is greater than the acoustic impedance of the piezoelectric material, a suitable reflective structure and piezoelectric material can be selected to support the reflection coefficient of the reflective structure relative to the piezoelectric material being greater than the reflection coefficient threshold.

[0008] Because the reflection coefficient of the reflective structure relative to the piezoelectric material is greater than the reflection coefficient threshold, the reflective structure has a high efficiency in reflecting the energy of surface acoustic waves. When the above-mentioned substrate is applied to a surface acoustic wave device, when the energy of the surface wave formed by the substrate propagates downward along the thickness direction of the substrate, the reflective structure has a high efficiency in reflecting the energy of the surface acoustic wave, and can concentrate the energy of the surface acoustic wave in the region above the reflective layer of the substrate, that is, the piezoelectric layer.

[0009] Compared to existing substrate structures, the surface acoustic wave energy formed by the above substrate propagates downward along the thickness direction of the substrate to a lesser depth than that formed by existing substrates. This allows the surface acoustic wave energy to be confined to a shallower thickness range, thereby effectively controlling the dissipation of surface acoustic wave energy on the substrate surface.

[0010] In some implementations of the first aspect, the reflecting structure includes a cavity structure. In the cavity structure, the acoustic impedance of air is 0.0004 MRayl. The acoustic impedance of air is less than that of the piezoelectric material (taking lithium tantalate (LiTaO3) as an example; the acoustic impedance of LiTaO3 is typically between 29.8 MRayl and 44.7 MRayl). Therefore, the difference between the acoustic impedance of air and the acoustic impedance of the piezoelectric material is greater than the acoustic impedance threshold. This increases the reflection coefficient of air relative to the piezoelectric material, thereby improving the efficiency of reflecting the energy of surface acoustic waves.

[0011] In some implementations of the first aspect, the reflective structure includes one or more of the following: organic materials, aerogels (such as silica aerogels, ultralight aerogels, etc.), or porous composite materials (such as polymer foams, metal foams, carbon fiber reinforced porous composite materials, etc.). Organic materials may also be replaced with organic polymer materials.

[0012] Because organic materials, aerogels, or porous composite materials have relatively low acoustic impedance—for example, natural rubber has an acoustic impedance of 1.6 MNayl—the acoustic impedance of organic materials, aerogels, or porous composite materials is lower than that of piezoelectric materials (taking LiTaO3 as an example). Therefore, the difference between the acoustic impedance of organic materials, aerogels, or porous composite materials and that of piezoelectric materials is greater than the acoustic impedance threshold. This can increase the reflection coefficient of organic materials, aerogels, or porous composite materials relative to piezoelectric materials, thereby improving the efficiency of reflecting the energy of surface acoustic waves.

[0013] In some implementations of the first aspect, the aforementioned reflection coefficient threshold is equal to 0.65. This can support enhanced reflection of surface acoustic wave energy by the reflective structure.

[0014] In a second aspect, a substrate is provided, comprising: a piezoelectric layer, a reflective layer, and a substrate. The piezoelectric layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in the same first direction. The piezoelectric layer comprises a piezoelectric material, and the reflective layer comprises a support structure and a reflective structure. The reflective structure and the support structure are arranged along a second direction perpendicular to the first direction. The reflective structure is located between the support structures and comprises a cavity structure. Alternatively, the reflective structure comprises one or more of an organic material, an aerogel, or a porous composite material.

[0015] In a cavity structure, the acoustic impedance of air is 0.0004 MRayl, which is lower than that of piezoelectric materials. Therefore, the difference between the acoustic impedance of air and the piezoelectric material is greater than the acoustic impedance threshold. This increases the reflection coefficient of air relative to the piezoelectric material, thereby improving the efficiency of reflecting surface acoustic wave energy. Similarly, organic materials, aerogels, or porous composite materials have lower acoustic impedances. For example, natural rubber has an acoustic impedance of 1.6 MRayl. Again, the difference between the acoustic impedance of organic materials, aerogels, or porous composite materials and that of piezoelectric materials is greater than the acoustic impedance threshold. This further increases the reflection coefficient of organic materials, aerogels, or porous composite materials relative to the piezoelectric material, thus improving the efficiency of reflecting surface acoustic wave energy.

[0016] In summary, when the aforementioned substrate is applied to a surface acoustic wave (SAW) device, the energy of the surface waves generated by this substrate propagates downwards along the thickness direction of the substrate. Due to the larger reflection coefficient of the reflective structure compared to the piezoelectric material, the reflective structure is highly efficient in reflecting the energy of the SAW, thus concentrating the energy of the SAW in the region above the reflective layer of the substrate, i.e., the piezoelectric layer. Compared to existing substrate structures, the depth to which the energy of the SAW generated by the aforementioned substrate propagates downwards along the thickness direction is less than that of the SAW generated by existing substrates. This confines the energy of the SAW to a shallower thickness range, thereby effectively controlling the dissipation of the SAW energy at the substrate surface.

[0017] In conjunction with either the first or second aspect, the substrate further includes a first bonding layer located between the piezoelectric layer and the reflective layer for connecting the piezoelectric layer and the reflective layer. By providing the first bonding layer, the bonding strength between the piezoelectric layer and the reflective layer can be enhanced.

[0018] In combination with either the first or second aspect, the first connecting layer and the support structure contain the same material. When the first connecting layer and the support structure contain the same material, this is advantageous for processing, as it eliminates the need to select other materials, and it can further enhance the bonding strength between the piezoelectric layer and the reflective layer.

[0019] In conjunction with either the first or second aspect, the substrate further includes a second bonding layer located between the reflective layer and the substrate for connecting the reflective layer and the substrate. By providing the second bonding layer, the bonding strength between the reflective layer and the substrate can be enhanced.

[0020] In combination with either the first or second aspect, the second connecting layer and the support structure contain the same material. When the second connecting layer and the support structure contain the same material, this is advantageous for processing, as it eliminates the need to select other materials, and it can further enhance the bonding strength between the substrate and the reflective layer.

[0021] Combining any of the first and second aspects, the thickness of the reflective layer ranges from 0.01P to 1P, where P is the period of the IDT. This range allows for the limitation of SAW energy within a certain thickness range without increasing the substrate thickness, while also enhancing the mechanical strength of the reflective layer.

[0022] Combining any one of the first and second aspects, the thickness of the piezoelectric layer ranges from 0.2P to 1P. This range improves the mechanical strength of the piezoelectric layer.

[0023] Combining any one of the first and second aspects, the thickness of the first bonding layer ranges from 0.01P to 0.2P. This range enhances the bonding strength between the piezoelectric layer and the reflective layer without increasing the substrate thickness.

[0024] Combining any one of the first and second aspects, the thickness of the second bonding layer ranges from 0.02P to 1P. This range enhances the bonding strength between the reflective layer and the substrate without increasing the substrate thickness.

[0025] Combining any of the first and second aspects, the piezoelectric layer material includes any one or more of lithium niobate, lithium tantalate, aluminum nitride, or zinc oxide. Because the above materials have good overall performance, such as Q-value and electromechanical coupling coefficient, this can enhance the performance of the device.

[0026] In combination with either the first or second aspect, the material of the supporting structure includes one or more of silicon oxide or fluorinated silicon oxide. Since the temperature coefficient of frequency (TCF) (TCF represents the relative change in the material's resonant frequency for every 1°C change in temperature) of both silicon oxide and fluorinated silicon oxide is positive, while the TCF of piezoelectric materials is generally negative, this allows for adjustment of the combined TCF of the piezoelectric layer and the reflective layer.

[0027] In combination with any of the first and second aspects, the substrate material includes any one or more of monocrystalline silicon, silicon carbide, diamond, polycrystalline silicon, porous silicon, sapphire, spinel, or yttrium aluminum garnet. Since these materials are relatively easy to obtain, this reduces the difficulty of obtaining the materials.

[0028] In combination with either the first or the second aspect, the material of the first connecting layer includes one or more of silicon oxide or fluorinated silicon oxide. Since the TCF of both silicon oxide and fluorinated silicon oxide is positive, while the TCF of piezoelectric materials is generally negative, this allows for adjustment of the combined TCF of the piezoelectric layer, the reflective layer, and the first connecting layer.

[0029] Combining any of the first and second aspects, the material of the second connecting layer includes one or more of silicon oxide or quartz. Since silicon oxide and quartz both have positive TCF values, while piezoelectric materials generally have negative TCF values, this allows for adjustment of the combined TCF of the piezoelectric layer, the reflective layer, and the second connecting layer.

[0030] Thirdly, a surface acoustic wave resonator is provided, which includes the aforementioned substrate and IDT.

[0031] In some implementations of the third aspect, the ratio of the area of ​​overlap between the projected area of ​​the reflective structure in the piezoelectric layer and the projected area of ​​the IDT region in the piezoelectric layer to the projected area of ​​the IDT region in the piezoelectric layer ranges from 15% to 85%.

[0032] When the ratio is greater than 85%, the bonding strength between the reflective layer and the piezoelectric layer will be weak; when the ratio is less than 15%, the reflective layer may not be able to reflect the energy of the SAW. By setting the ratio range mentioned above, this can both support the reflective layer to reflect the energy of the SAW and enhance the bonding strength between the reflective layer and the piezoelectric layer.

[0033] Fourthly, a filter is provided that includes the aforementioned surface acoustic wave resonator.

[0034] Fifthly, a radio frequency module is provided, which includes the filter described in the fourth aspect.

[0035] In a sixth aspect, an electronic device is provided, which includes the radio frequency module described in the fifth aspect.

[0036] For a description of the beneficial effects of aspects three through six, please refer to the description of the beneficial effects of aspect one. Attached Figure Description

[0037] Figure 1 is a schematic diagram of a substrate structure according to an embodiment of this application.

[0038] Figure 2 is a schematic diagram of another structure of the substrate according to an embodiment of this application.

[0039] Figure 3 is a schematic diagram of the relationship between the reflective structure and the support structure in an embodiment of this application.

[0040] Figure 4 is a schematic diagram of another structure of the substrate according to an embodiment of this application.

[0041] Figure 5 is a schematic diagram of another structure of the substrate according to an embodiment of this application.

[0042] Figure 6 is a schematic diagram of another structure of the substrate according to an embodiment of this application.

[0043] Figure 7 is a schematic diagram of a SAW resonator according to an embodiment of this application.

[0044] Figure 8 is a schematic diagram of another structure of the SAW resonator according to an embodiment of this application.

[0045] Figure 9 is a schematic diagram showing the relationship between the projected area of ​​the reflective structure in the piezoelectric layer and the projected area of ​​the IDT region in the piezoelectric layer.

[0046] Figure 10 is a schematic diagram showing the relationship between the position of the reflective structure in the piezoelectric layer and the position of the IDT region in the piezoelectric layer.

[0047] Figure 11 is a schematic diagram comparing the performance of SAW resonator 1 and SAW resonator a according to an embodiment of this application.

[0048] Figure 12 is another performance comparison diagram of SAW resonator 1 and SAW resonator a according to an embodiment of this application.

[0049] Figure 13 is a schematic diagram comparing the performance of SAW resonator 2 and SAW resonator 1 according to an embodiment of this application.

[0050] Figure 14 is a schematic diagram comparing the performance of SAW resonator 3 and SAW resonator a1 according to an embodiment of this application.

[0051] Figure 15 is a schematic diagram comparing the performance of SAW resonator 4 and SAW resonator a1 according to an embodiment of this application.

[0052] Figure 16 is a schematic diagram comparing the performance of SAW resonator 5 and SAW resonator a1 according to an embodiment of this application.

[0053] Figure 17 is a schematic diagram comparing the performance of SAW resonator 6 and SAW resonator a2 according to an embodiment of this application.

[0054] Figure 18 is a schematic diagram of the structure of an electronic device according to an embodiment of this application. Detailed Implementation

[0055] To facilitate understanding of the embodiments of this application, the following points will be explained first.

[0056] 1. Unless otherwise stated, "multiple" means two or more. "At least one" means one or more.

[0057] 2. Unless otherwise specified or in case of logical conflict, the terms and / or descriptions in different embodiments of this application are consistent and can be referenced in each other. The technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

[0058] Third, the various numerical designations used in this application are for descriptive convenience only and do not limit the scope of protection of this application. For example, the terms "first (as in the first connecting layer below)", "second (as in the second connecting layer below)" and other various terminology in the specification, claims and drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0059] Furthermore, any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner for ease of understanding.

[0060] IV. The terms “comprising” and “having”, and their variations, are intended to cover non-exclusive inclusion. For example, a system, product, or device that includes a series of steps or units is not necessarily limited to those units listed, but may include other steps or units not listed or inherent to such product or device.

[0061] First, a brief introduction to the terminology used in the embodiments of this application will be given.

[0062] 1. Acoustic impedance Z

[0063] Acoustic impedance Z is a physical quantity used to describe the ability of a medium to impede the propagation of sound waves. Acoustic impedance Z can be defined as the product of the density ρ of the medium and the speed of sound v, i.e., Z = ρ·v. A description of acoustic impedance Z can be found in Table 1.

[0064] Table 1

[0065] As shown in Table 1, the acoustic impedance Z of different media is related to the density and sound velocity of the medium. Furthermore, the acoustic impedance Z of organic materials is generally between 1 MNayl and 3 MNayl, with the specific value depending on the composition of the organic material. Aerogels (such as silica aerogels and ultralight aerogels) also have relatively low acoustic impedance Z, as do porous composite materials (such as polymer foams, metal foams, and carbon fiber reinforced porous composite materials).

[0066] 2. Reflection coefficient

[0067] The reflection coefficient is a physical quantity used to describe the ability of a medium to reflect sound wave energy. When a sound wave propagates from one medium to another, if the acoustic impedance Z of the two media is different, the latter will reflect the energy of the sound wave. The larger the reflection coefficient, the stronger the ability of the medium to reflect sound wave energy; the smaller the reflection coefficient, the weaker the ability of the medium to reflect sound wave energy.

[0068] The reflection coefficient R can be defined as: Z1 and Z2 are the acoustic impedances Z of the two media, respectively.

[0069] According to the above definition, if one of the two media is fixed as LiTaO3 (the acoustic impedance Z of LiTaO3 is generally between 29.8 MNayl and 50 MNayl, and the specific value is related to the crystal orientation, doping and environmental conditions of LiTaO3), then the description of the reflection coefficient of different materials relative to LiTaO3 can be found in Table 2.

[0070] Table 2

[0071] As shown in Table 2, the reflectance of air relative to LiTaO3 and the reflectance of polyimide relative to LiTaO3 are both greater than the reflectance of materials other than air and polyimide relative to LiTaO3 in Table 1.

[0072] 3. IDT

[0073] The IDT is the core component of the SAW resonator, responsible for the conversion between electrical and acoustic signals. The IDT consists of two sets of interlaced metal electrodes (usually aluminum or gold), arranged periodically in a "cross-finger" shape.

[0074] The process parameters of an IDT include: period (pitch, P), finger width (W), spacing (d), and number of finger pairs (N). The period P of an IDT is defined as the distance between the centers of two adjacent electrodes (see the solid black line in Figure 8). The finger width W and the spacing d of the IDT are typically designed to be 1 / 4 of the acoustic wavelength (λ), i.e., W = d = λ / 4. P = 0.5λ. The more finger pairs an IDT has, the narrower its bandwidth and the higher its conversion efficiency.

[0075] As described in the background section, SAW resonators employ a substrate structure consisting of a piezoelectric layer, a low-velocity layer, a high-velocity layer, and a substrate stacked sequentially from top to bottom. This structure aims to confine the energy of the SAW formed by the inverse piezoelectric effect excited by the IDT within the thickness range above (including) the high-velocity layer of the substrate. A description of the aforementioned substrate structure can be found in Figure 1.

[0076] As shown in Figure 1, the substrate includes a piezoelectric layer, a low-velocity sound layer, a high-velocity sound layer, and a substrate. The high-velocity sound layer is stacked on the substrate, the low-velocity sound layer is stacked on top of the high-velocity sound layer, and the piezoelectric layer is stacked on top of the low-velocity sound layer. The high-velocity sound layer refers to a layer where the sound speed of surface waves propagating within the piezoelectric layer is higher than that of surface waves propagating within the piezoelectric layer. The low-velocity sound layer refers to a layer where the sound speed of surface waves propagating within the piezoelectric layer is lower than that of surface waves propagating within the piezoelectric layer.

[0077] When an IDT excites a piezoelectric layer to form a sound wave (SAW) through the inverse piezoelectric effect, some of the SAW's energy propagates downwards along the substrate's thickness. Because a low-velocity layer and a high-velocity layer are positioned beneath the piezoelectric layer, a waveguide effect forms between them, confining the acoustic energy primarily within the piezoelectric and low-velocity layers above the high-velocity layer. However, the portion of the acoustic energy outside the piezoelectric layer suffers energy conversion efficiency loss, and the quality factor of the low-velocity layer is typically lower than that of the piezoelectric layer. Therefore, the above structure cannot effectively control the energy dissipation of the SAW at the substrate surface; for example, the SAW's energy may leak into the low-velocity layer, or even into the deeper layers of the substrate. In view of this, this application provides a substrate capable of effectively controlling the energy dissipation of the SAW at the substrate surface. See Figure 2 for details.

[0078] As shown in Figure 2, the substrate includes a piezoelectric layer, a reflective layer, and a substrate. The piezoelectric layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in the same first direction. The piezoelectric layer includes a piezoelectric material, and the reflective layer includes a support structure and a reflective structure. The reflective structure and the support structure are arranged along a second direction, which is perpendicular to the first direction. The reflective structure is located between the support structures, and the reflective coefficient of the reflective structure relative to the piezoelectric material (the reflective structure can be in direct contact with the piezoelectric material or can be in contact with the piezoelectric material through other materials, such as the first connecting layer described below) is greater than a reflective coefficient threshold. The support structure supports the piezoelectric layer; in other words, the support structure acts as a pillar for the reflective layer, and the piezoelectric layer is located on this pillar. Furthermore, the aforementioned piezoelectric material can be used to form a SAW (Surface Mount Air) structure.

[0079] In this embodiment, the reflection coefficient of the reflective structure relative to the piezoelectric material is greater than the reflection coefficient threshold. This is achieved through the acoustic impedance of the reflective structure and the acoustic impedance of the piezoelectric material. For example, when the acoustic impedance of the reflective structure is less than that of the piezoelectric material, a suitable reflective structure and piezoelectric material can be selected to support a reflection coefficient of the reflective structure relative to the piezoelectric material that is greater than the reflection coefficient threshold. Alternatively, when the acoustic impedance of the reflective structure is greater than that of the piezoelectric material, a suitable reflective structure and piezoelectric material can be selected to support a reflection coefficient of the reflective structure relative to the piezoelectric material that is greater than the reflection coefficient threshold. A description of the reflection coefficient can be found in Table 2.

[0080] When the piezoelectric material is fixed, its acoustic impedance is also fixed. Therefore, the reflection structure can be selected based on the acoustic impedance of the piezoelectric material and the aforementioned reflection coefficient threshold. When the reflection coefficient of the reflection structure relative to the piezoelectric material is greater than the reflection coefficient threshold (the value is not limited and can be flexibly selected according to requirements), the reflection structure will have a higher efficiency in reflecting the energy of the surface acoustic wave, and can concentrate the energy of the surface acoustic wave in the region above the reflective layer of the substrate, i.e., the piezoelectric layer.

[0081] With the above structure, when the substrate is applied to a SAW device, the energy of the SAW wave formed on the substrate propagates downwards along the thickness direction of the substrate. Because the reflection coefficient of the reflective structure relative to the piezoelectric material is greater than the reflection coefficient threshold, the efficiency of reflecting the SAW energy is high, thus concentrating the SAW energy in the region above the reflective layer of the substrate. Compared to existing substrate structures (see Figure 1), the depth to which the energy of the surface acoustic wave formed by the above substrate (see Figure 2) propagates downwards along the thickness direction of the substrate is less than that of the surface acoustic wave formed by existing substrates. This confines the surface acoustic wave energy to a shallower thickness range, thereby effectively controlling the dissipation of surface acoustic wave energy on the substrate surface.

[0082] The relationship between the reflective structure and the supporting structure in the reflective layer is described below. See Figure 3, which is a top view. The relationship between the reflective structure and the supporting structure shown in Figure 3 is for illustrative purposes only and is not intended as a final limitation.

[0083] As shown in Figure 3(a), the reflection structure includes three reflection structures (represented by cross-textured boxes) and four support structures (represented by white boxes). The three reflection structures are surrounded by the four support structures, or in other words, the three reflection structures are positioned between the four support structures. The shape of the reflection structure is rectangular.

[0084] As shown in Figure 3(b), the reflective structure includes six reflective structures (represented by cross-textured boxes) and one support structure. The six reflective structures are surrounded by the support structure, or in other words, the reflective structures are set within the support structure. The reflective structures are circular in shape.

[0085] As shown in Figure 3(c), the reflective structure includes six reflective structures (represented by cross-textured boxes) and one support structure. The six reflective structures are surrounded by the support structure, or in other words, the reflective structures are set within the support structure. The reflective structures are square in shape.

[0086] As shown in Figure 3(d), the reflection structure consists of 12 reflection structures (represented by cross-textured boxes) and a support structure. The 12 reflection structures are surrounded by the support structure, or in other words, the reflection structures are set within the support structure. The reflection structures are rectangular in shape.

[0087] With the above structure, the support structure can support the piezoelectric layer, and the reflection structure can reflect the sound wave energy.

[0088] One possible implementation involves a cavity structure as the reflective structure. This cavity structure can be formed by supporting structures or other structures and is located between the supporting structures. See Figure 3 for a specific description of the reflective structure. For example, the reflective structure can be formed by supporting structures, and the cavity structure can be rectangular or circular in shape. In the cavity structure, the acoustic impedance of air is 0.0004 MRayl. The acoustic impedance of air is less than that of the piezoelectric material (taking lithium tantalate (LiTaO3) as an example; the acoustic impedance of LiTaO3 is generally between 29.8 MRayl and 44.7 MRayl). Therefore, the difference between the acoustic impedance of air and the acoustic impedance of the piezoelectric material is greater than the acoustic impedance threshold. This increases the reflection coefficient of air relative to the piezoelectric material, thereby improving the efficiency of reflecting the energy of surface acoustic waves (SAWs). For example, if the reflection coefficient of air relative to LiTaO3 is 1, air can reflect all the energy of the SAW.

[0089] One possible implementation is that the reflective structure includes one or more of organic materials, aerogels, or porous composite materials.

[0090] Organic materials can also be replaced with organic polymers. Because organic materials, aerogels, or porous composites have lower acoustic impedance—for example, natural rubber has an acoustic impedance of 1.6 MNayl—the acoustic impedance of organic materials, aerogels, or porous composites is lower than that of piezoelectric materials (taking lithium tantalate (LiTaO3) as an example, whose acoustic impedance is generally between 29.8 MNayl and 44.7 MNayl). Therefore, the difference between the acoustic impedance of organic materials, aerogels, or porous composites and that of piezoelectric materials is greater than the acoustic impedance threshold. This increases the reflection coefficient of organic materials, aerogels, or porous composites relative to piezoelectric materials, thereby improving the efficiency of reflecting surface acoustic wave energy.

[0091] As shown in Tables 1 and 2, when the organic material is Polyimide and the piezoelectric material is LiTaO3, the reflectance of the surface in contact between Polyimide and LiTaO3 is 0.93, indicating that Polyimide can reflect most of the energy of SAW.

[0092] One possible implementation is to set the reflection coefficient threshold to 0.65. This would allow the reflective structure to have a strong ability to reflect the energy of surface acoustic waves.

[0093] Taking a reflection coefficient threshold of 0.65 as an example, when the piezoelectric material is LiTaO3, the acoustic impedance of LiTaO3 is 31.5 MRayl. Therefore, the maximum acoustic impedance of the reflective structure is equal to 6.68 MRayl. Thus, a material with an acoustic impedance less than or equal to 6.68 MRayl can be selected to form the reflective structure.

[0094] One possible implementation is to set a reflection coefficient threshold of 0.7. This can further enhance the reflective structure's ability to reflect the energy of surface acoustic waves. Taking a reflection coefficient threshold of 0.7 as an example, when the piezoelectric material is LiTaO3, the acoustic impedance of LiTaO3 is 31.5 MRayl. Therefore, the maximum acoustic impedance of the reflective structure is equal to 5.56 MRayl. Thus, materials with an acoustic impedance less than or equal to 5.56 MRayl, such as polyvinyl chloride, can be selected to form the reflective structure.

[0095] One possible implementation is to set the reflection coefficient threshold to 0.8 or 0.9. This can further enhance the reflective structure's ability to reflect the energy of surface acoustic waves. Taking a reflection coefficient threshold of 0.9 as an example, when the piezoelectric material is LiTaO3, the acoustic impedance of LiTaO3 is 31.5 MRayl. Therefore, the maximum acoustic impedance of the reflective structure is 1.65 MRayl. Thus, materials with an acoustic impedance less than or equal to 1.65 MRayl can be selected to form the reflective structure, such as carbon fiber reinforced porous composite materials.

[0096] In summary, the larger the reflection coefficient threshold, the stronger the energy reflected by the reflective structure from the surface acoustic wave.

[0097] The above description uses a substrate including a piezoelectric layer, a reflective layer, and a substrate as an example. The following description, in conjunction with Figures 4 to 6, describes other structures of the substrate.

[0098] As shown in Figure 4, the substrate includes a piezoelectric layer, a first bonding layer, a reflective layer, and a substrate. The piezoelectric layer is disposed on the first bonding layer in a first direction, the first bonding layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in a first direction. Alternatively, the first bonding layer is disposed between the piezoelectric layer and the reflective layer to connect the piezoelectric layer and the reflective layer. By providing the first bonding layer, the bonding strength between the piezoelectric layer and the reflective layer can be enhanced.

[0099] Since piezoelectric materials and reflective layers have different TCFs, by adding a first connecting layer, the combination of the piezoelectric layer, the first connecting layer, and the reflective layer can achieve a combined TCF of 0, thereby improving the stability of the material's resonant frequency. Furthermore, since multilayer structures may contain some extraneous modes beyond the dominant mode, adding a first connecting layer can change the conditions for extraneous mode generation, thus achieving extraneous mode suppression.

[0100] One possible implementation is that the first connecting layer and the support structure contain the same material. When the first connecting layer and the support structure contain the same material, this is advantageous for processing, such as eliminating the need to select other materials, and can further enhance the bonding strength between the piezoelectric layer and the reflective layer.

[0101] One possible implementation is that the first connecting layer comprises one or more of silicon oxide or fluorinated silicon oxide. Since the TCF of silicon oxide and fluorinated silicon oxide are both positive, while the TCF of the piezoelectric material and the reflective structure are generally negative, this allows for adjustment of the combined TCF of the piezoelectric layer, the reflective layer, and the first connecting layer.

[0102] As shown in Figure 5, the substrate includes a piezoelectric layer, a reflective layer, a second bonding layer, and a substrate. The piezoelectric layer is disposed on the reflective layer in a first direction, the reflective layer is disposed on the second bonding layer in the first direction, and the second bonding layer is disposed on the substrate in the first direction. Alternatively, the second bonding layer is disposed between the reflective layer and the substrate to connect the reflective layer and the substrate. By providing the second bonding layer, the bonding strength between the reflective layer and the substrate can be enhanced.

[0103] By adding a second interconnect layer, the following functions can also be achieved: adjusting TCF or suppressing heterodynes. In some scenarios, such as those using SiO2 / Si structures, parasitic conductivity effects may exist, which can affect the Q value of the device. Using a second interconnect layer can improve the Q value of the device.

[0104] One possible implementation is that the second connecting layer and the support structure comprise the same material. When the second connecting layer and the support structure comprise the same material, this is advantageous for processing, as it eliminates the need to select other materials, and it can further enhance the bonding strength between the reflective layer and the substrate.

[0105] One possible implementation is that the material of the second interconnecting layer includes silicon oxide or quartz. Since the TCF of silicon oxide and silicon oxyfluoride are both positive, while the TCF of the piezoelectric material and the reflective structure are generally negative relative to the TCF of the substrate, this allows for adjustment of the combined TCF of the piezoelectric layer, the reflective layer, the second interconnecting layer, and the substrate.

[0106] Optionally, the first connecting layer and the second connecting layer comprise the same material. This means that the first connecting layer and the second connecting layer can comprise the same material under different processes. "Same material under different processes" refers to materials with the same composition but different properties due to different preparation processes. For example, SiO2 prepared using a thermal oxidation process and SiO2 prepared using a plasma-enhanced chemical vapor deposition (PECVD) process differ in material properties and temperature compensation characteristics.

[0107] As shown in Figure 6, the substrate includes a piezoelectric layer, a first bonding layer, a reflective layer, a second bonding layer, and a substrate. The piezoelectric layer is disposed on the first bonding layer in a first direction, the first bonding layer is disposed on the reflective layer in a first direction, the reflective layer is disposed on the second bonding layer in a first direction, and the second bonding layer is disposed on the substrate in a first direction. Alternatively, the first bonding layer is disposed between the piezoelectric layer and the reflective layer to connect them, and the second bonding layer is disposed between the reflective layer and the substrate to connect them. By providing the first and second bonding layers, the bonding strength between the piezoelectric layer and the reflective layer, as well as the bonding strength between the reflective layer and the substrate, can be enhanced.

[0108] Figures 5 and 6 are described using the example of a second connecting layer between the reflective layer and the substrate, but the scenario is not limited to a scenario where more connecting layers are provided between the second connecting layer and the substrate.

[0109] One possible implementation includes a substrate comprising a piezoelectric layer, a reflective layer, a second bonding layer, a third bonding layer, and a substrate. The piezoelectric layer is disposed above the reflective layer in a first direction, the reflective layer is disposed above the second bonding layer in the first direction, the second bonding layer is disposed above the third bonding layer in the first direction, and the third bonding layer is disposed above the substrate in the first direction. Alternatively, the third bonding layer is disposed between the second bonding layer and the substrate to connect them. By providing the third bonding layer, the bonding strength between the second bonding layer and the substrate can be enhanced. By providing the third bonding layer, this application can also achieve functions such as adjusting TCF or suppressing unwanted modes.

[0110] Optionally, the third and second connecting layers can be disposed as a single unit between the reflective layer and the substrate. This helps to reduce the difficulty of fabrication.

[0111] The following section describes the substrate's material and thickness.

[0112] One possible implementation is to use a reflective layer thickness ranging from 0.01P to 1P, where P is the period of the IDT, P = 0.5λ, and λ is the wavelength of the SAW. This range allows for limiting the SAW energy within a certain thickness range without increasing the substrate thickness, while also enhancing the mechanical strength of the reflective layer.

[0113] One possible implementation is to use a piezoelectric layer thickness ranging from 0.2P to 1P. This range can improve the mechanical strength of the piezoelectric layer.

[0114] One possible implementation is that the thickness of the first bonding layer ranges from 0.01P to 0.2P. This range enhances the bonding strength between the piezoelectric layer and the reflective layer without increasing the substrate thickness.

[0115] One possible implementation is that the thickness of the second bonding layer ranges from 0.02P to 1P. This range enhances the bonding strength between the reflective layer and the substrate without increasing the substrate thickness.

[0116] One possible implementation involves using a piezoelectric layer made of one or more of lithium niobate, lithium tantalate, aluminum nitride, or zinc oxide. These materials offer good overall performance, including high Q-values ​​and electromechanical coupling coefficients, which can enhance device performance.

[0117] One possible implementation involves using silicon oxide or fluorinated silicon oxide as the supporting structure. The silicon oxide can be fabricated using one of the following methods: thermal oxidation, physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD). Since both silicon oxide and fluorinated silicon oxide have positive TCF values, while piezoelectric materials typically have negative TCF values, this allows for adjustment of the combined TCF of the piezoelectric layer and the reflective layer.

[0118] One possible implementation involves using a substrate material that includes one or more of the following: monocrystalline silicon, silicon carbide, diamond, polycrystalline silicon, porous silicon, sapphire, spinel, or yttrium aluminum garnet (YAG). Since these materials are relatively easy to obtain, this reduces the difficulty of acquiring the materials.

[0119] One possible implementation is that the material of the first interconnect layer includes one or more of silicon oxide or fluorinated silicon oxide. Since the TCF of silicon oxide and fluorinated silicon oxide are both positive, while the TCF of piezoelectric materials is generally negative, this allows for adjustment of the combined TCF of the piezoelectric layer, the reflective layer, and the first interconnect layer.

[0120] One possible implementation is that the material of the second connecting layer includes one or more of silicon oxide or quartz. Since silicon oxide and quartz both have positive TCF values, while piezoelectric materials generally have negative TCF values, this allows for adjustment of the combined TCF of the piezoelectric layer, reflective layer, and second connecting layer.

[0121] Figures 2 to 6 illustrate examples where the difference between the acoustic impedance of the reflective structure and the acoustic impedance of the piezoelectric material is greater than the acoustic impedance threshold. However, the description is not limited to the structural level of the reflective layer. For example, the substrate may include a piezoelectric layer, a reflective layer, and a substrate; the piezoelectric layer may include a piezoelectric material; the reflective layer may include a support structure and a reflective structure; the reflective structure may include a cavity structure; or the reflective structure may include one or more of organic materials, aerogels, or porous composite materials. Specific structural relationships can be found in Figure 2.

[0122] Based on the aforementioned substrate, this application provides a SAW resonator, as shown in Figure 7. As shown in Figure 7, the SAW resonator includes the aforementioned substrate and an IDT. The IDT is disposed on the piezoelectric layer of the aforementioned substrate.

[0123] Optionally, the SAW resonator also includes a reflective grid. See Figure 8 for details. As shown in Figure 8, the SAW resonator includes an IDT and a reflective grid, with the reflective grid located on both sides of the IDT for reflecting the SAW signal.

[0124] One possible implementation is that the ratio between the area of ​​the reflection structure projected onto the piezoelectric layer and the area of ​​the IDT region (including the IDT's fingers and the area between the fingers) projected onto the piezoelectric layer is in the range of 15% to 85%.

[0125] When the ratio is greater than 85%, the bonding strength between the reflective layer and the piezoelectric layer will be weak; when the ratio is less than 15%, the reflective layer may not be able to reflect the energy of the SAW. By setting the ratio range mentioned above, this can both support the reflective layer to reflect the energy of the SAW and enhance the bonding strength between the reflective layer and the piezoelectric layer.

[0126] The following section, in conjunction with Figure 9, further describes the relationship between the projected area of ​​the reflective structure in the piezoelectric layer and the projected area of ​​the IDT region in the piezoelectric layer.

[0127] As shown in Figure 9(a), the IDT in the SAW resonator includes 3 fingers, and the reflective layer of the substrate includes 6 reflective structures. The reflective structures are rectangular in shape. The width of the projection of a column of reflective structures onto the piezoelectric layer is greater than the width of the projection of a finger onto the piezoelectric layer. Therefore, there is an overlapping area between the projected area of ​​the IDT region onto the piezoelectric layer and the projected area of ​​the reflective structures onto the piezoelectric layer.

[0128] As shown in Figure 9(b), the IDT in the SAW resonator includes 3 fingers, and the reflective layer of the substrate includes 6 reflective structures. The reflective structures are circular in shape. The width of the projection of a row of reflective structures onto the piezoelectric layer is greater than the width of the projection of a finger onto the piezoelectric layer. Therefore, there is an overlapping area between the projected area of ​​the IDT region onto the piezoelectric layer and the projected area of ​​the reflective structures onto the piezoelectric layer.

[0129] As shown in Figure 9(c), the IDT in the SAW resonator includes 3 fingers, and the reflective layer of the substrate includes 6 reflective structures. The reflective structures are square in shape. The width of the projection of a row of reflective structures onto the piezoelectric layer is greater than the width of the projection of a finger onto the piezoelectric layer. Therefore, there is an overlapping area between the projected area of ​​the IDT region onto the piezoelectric layer and the projected area of ​​the reflective structures onto the piezoelectric layer.

[0130] As shown in Figure 9(d), the IDT in the SAW resonator includes 3 fingers, and the reflective layer of the substrate includes 12 reflective structures (6 columns in total). The reflective structures are square in shape. The total width of the projection of two columns of reflective structures onto the piezoelectric layer is greater than the width of the projection of one finger onto the piezoelectric layer. That is, the width of the projection of one finger onto the piezoelectric layer spans the width of the projection of two columns of reflective structures onto the piezoelectric layer. Therefore, there is an overlapping area between the projection area of ​​the IDT region onto the piezoelectric layer and the projection area of ​​the reflective structures onto the piezoelectric layer.

[0131] Figure 9 illustrates an example where the IDT region is not offset from the center of the piezoelectric layer, but it does not limit the scenario to one where the IDT region is offset from the center of the piezoelectric layer. See Figure 10 for details. All figures in Figure 10 are top views.

[0132] As shown in Figure 10(a), there is an offset between the position of the IDT region and the center position of the piezoelectric layer.

[0133] As shown in Figure 10(b), there is an offset between the position of the IDT region and the center position of the piezoelectric layer.

[0134] As shown in Figure 10(c), the IDT region has no offset between the location of the piezoelectric layer and the center location of the reflective structure.

[0135] The performance of the SAW resonator is described below with reference to specific parameters.

[0136] Example 1:

[0137] The SAW resonator 1 includes an IDT, a piezoelectric layer, a first connecting layer, a reflective layer, a second connecting layer, a third connecting layer, and a substrate. The IDT is made of metallic Al with a thickness of 0.05λ and a metallization ratio (metallization ratio refers to the percentage of metallic iron in the direct reduction iron product relative to the total iron content) of 0.4. The piezoelectric material is 60°YX LiTaO3 with a thickness of 0.3λ. The supporting structure is made of SiO2, and the reflective structure is a cavity structure. The supporting structure occupies 25% of the plane of the reflective layer, and the reflective layer has a thickness of 0.1λ. The relationship between the reflective structure and the supporting structure can be seen in Figure 3(a). The substrate is made of monocrystalline silicon with a crystal orientation of (110) (or (111) and a similar crystal orientation). The first connecting layer is made of SiO2 and its fabrication process differs from that of the supporting structure. The first connecting layer has a thickness of 0.1λ. The second connecting layer is made of SiO2 and its fabrication process is the same as that of the supporting structure. The second connecting layer has a thickness of 0.3λ. The third connecting layer is made of polycrystalline silicon and has a thickness of 0.2λ.

[0138] To demonstrate the performance of SAW resonator 1, this application designs SAW resonator a (a device based on the substrate structure shown in Figure 1). The materials, orientations, and thicknesses of the piezoelectric layer, substrate, and IDT of SAW resonator a are the same as those of the piezoelectric layer, substrate, and IDT of SAW resonator 1. The materials and fabrication processes of the low-velocity layer of SAW resonator a are the same as those of the second connection layer of SAW resonator 1. The thickness of the low-velocity layer in SAW resonator a is the same as the total thickness of the first connection layer, reflective layer, and second connection layer in SAW resonator 1. The materials and thicknesses of the high-velocity layer of SAW device a are the same as those of the third connection layer of SAW resonator 1. See Figures 11 and 12 for details.

[0139] As shown in Figure 11(a), curve 1 represents the displacement amplitude in the X direction, curve 2 represents the displacement amplitude in the Z direction, and curve 3 represents the displacement amplitude in the Y direction. The dominant mode of SAW resonator a is the shear-horizontal (SH) mode, with the main displacement direction being the Y direction. By setting a low-velocity layer and a high-velocity layer between the piezoelectric layer and the substrate, when the SAW propagation depth reaches the high-velocity layer, the SAW energy decays rapidly, and the displacement amplitude in the Y direction becomes zero. Through the above structure, SAW resonator a mainly confines the SAW energy to the region above the high-velocity layer of the substrate.

[0140] As shown in Figure 11(b), curve 1 represents the displacement amplitude in the X direction, curve 2 represents the displacement amplitude in the Z direction, and curve 3 represents the displacement amplitude in the Y direction. The dominant mode of SAW resonator 1 is the SH mode, and the main displacement direction is the Y direction. By setting a reflective layer, a first connecting layer, a second connecting layer, and a third connecting layer between the piezoelectric layer and the substrate, when the SAW propagation depth reaches the reflective layer, the SAW energy will rapidly decay, and the displacement amplitude in the Y direction will be greater. That is, SAW resonator 1 mainly confines the SAW energy to the region above the reflective layer.

[0141] As shown in Figure 12, curve 1 represents the admittance curve of SAW resonator 1, and curve 2 represents the admittance curve of SAW resonator a. Comparing curves 1 and 2, it can be seen that SAW resonator 1 has the following advantages compared to SAW resonator a:

[0142] 1. Q-value improvement, i.e., Q-value = Y in curve 1. max -Y min = (-91.48dB) - (-162.12dB) = 70.64dB (Y represents the vertical axis), which is greater than the Q value in curve 2 = Y. max -Y min =(-92.75dB)-(-161.16dB)=68.41dB;

[0143] 2. The electromechanical coupling coefficient increases; the calculation method is as follows: The resonant frequency f of SAW resonator 1 r =1848MHz, the anti-resonant frequency f of SAW resonator 1 a =1944MHz, the frequency interval of SAW resonator 1 is: f r -f a =96MHz, the resonant frequency f of SAW resonator a r =1884MHz, the anti-resonance frequency f of SAW resonator a a =1972MHz, the frequency interval of SAW resonator a is: f r -f a =88MHz. Since the frequency interval of SAW resonator 1 is greater than that of SAW resonator a, the electromechanical coupling coefficient of SAW resonator 1 is greater than that of SAW resonator a. This indicates that SAW resonator 1 improves the utilization rate of sound wave energy in the sound-to-electric conversion.

[0144] 3. The resonant frequency decreases, which means the speed of sound decreases. This is beneficial for the miniaturization of SAW resonators (at the same frequency, the lower the speed of sound, the shorter the wavelength, the smaller the period P of the IDT, and the smaller the size of the SAW resonator).

[0145] In summary, SAW resonator 1 achieves lower insertion loss (the higher the Q value, the lower the insertion loss), greater bandwidth (the higher the electromechanical coupling coefficient, the greater the bandwidth), and smaller size compared to SAW1 resonator a.

[0146] Example 2:

[0147] SAW resonator 2 includes: IDT, piezoelectric layer, first interconnect layer, reflective layer, second interconnect layer, third interconnect layer, and substrate. The thickness of the first interconnect layer in SAW resonator 2 is 0.15λ and the thickness of the second interconnect layer is 0.25λ. The other parameters are the same as those in SAW resonator 1, and will not be described again.

[0148] A comparison of the performance of SAW resonator 1 and SAW resonator 2 can be seen in Figure 13. As shown in Figure 13, curve 1 represents the admittance curve of SAW resonator 1, and curve 2 represents the admittance curve of SAW resonator 2. Comparing curves 1 and 2, it can be seen that as the thickness of the first connecting layer increases and the position of the reflective layer decreases, the concentration depth of the acoustic wave energy increases. That is, adjusting the thickness of the first connecting layer can change the confinement depth of the acoustic wave energy, which has the effect of adjusting the electromechanical coupling coefficient, adjusting the TCF, and suppressing miscellaneous modes.

[0149] Example 3:

[0150] SAW resonator 3 includes: IDT, piezoelectric layer, first interconnect layer, reflective layer, second interconnect layer, third interconnect layer, and substrate. The piezoelectric layer in SAW resonator 3 is made of 20-45° YX lithium niobate LiNbO3, and the other parameters are the same as those of SAW resonator 1.

[0151] To demonstrate the performance of SAW resonator 3, this application designs SAW resonator a1. SAW device a1 adopts the same structure as SAW resonator a, but its materials and thickness are the same as those of SAW resonator 3. The performance comparison between SAW resonator 3 and SAW resonator a1 can be seen in Figure 14.

[0152] As shown in Figure 14, curve 1 represents the admittance curve of SAW resonator 3, and curve 2 represents the admittance curve of SAW resonator a1. Comparing curves 1 and 2, it can be seen that compared to SAW device a1, SAW resonator 3 can achieve a higher Q value (the Y value of SAW resonator 3 is higher than that of SAW device a1). max With Y min The difference between them is greater than the Y of SAW resonator a1. max With Y minThe larger electromechanical coupling coefficient (e.g., the frequency interval between the resonant frequency and anti-resonant frequency of SAW resonator 3 is greater than that between the resonant frequency and anti-resonant frequency of SAW resonator a1) and the lower sound velocity (e.g., the resonant frequency of SAW resonator 3 is less than that of SAW resonator a1) can also significantly reduce the Rayleigh spurious mode frequencies located on the low-frequency side of the main mode (e.g., the Rayleigh spurious mode frequency in curve 1 is 1300MHz (estimated value), and the Rayleigh spurious mode frequency in curve 2 is 1600MHz (estimated value)), widening the frequency interval between them and the main mode (the frequency of the main mode in curve 1 is 1750MHz (estimated value), and the frequency of the main mode in curve 2 is 1850MHz (estimated value)). This allows the spurious modes to be removed from the passband of the wide-bandwidth filter, further improving the insertion loss performance. Meanwhile, the SAW resonator 3 suppresses high-order clutter modes located on the high-frequency side of the main mode (such as the high-order clutter mode frequency of 2750MHz (estimated value) in curve 1), which can simultaneously improve the out-of-band suppression index of the filter on the high-frequency side.

[0153] Example 4:

[0154] SAW resonator 4 includes: IDT, piezoelectric layer, first connection layer, reflective layer, second connection layer, third connection layer, and substrate. The relationship between the reflective structure and the support structure in SAW resonator 4 can be seen in Figure 3(b), and the remaining parameters are the same as those in SAW resonator 3.

[0155] A comparison of the performance of SAW resonator 4 and SAW resonator a1 can be seen in Figure 15. As shown in Figure 15, curve 1 represents the admittance curve of SAW resonator 4, and curve 2 represents the admittance curve of SAW resonator a1. SAW resonator 4 also has similar benefits to SAW resonator 3, including improved Q value, increased electromechanical coupling coefficient, reduced sound velocity (e.g., the resonant frequency of curve 1 is lower than the resonant frequency of curve 2), and further away from Rayleigh spurious modes (e.g., the frequency interval between the Rayleigh spurious mode frequency near the dominant mode in curve 1 and the dominant mode frequency is greater than the frequency interval between the Rayleigh spurious mode frequency near the dominant mode and the dominant mode frequency in curve 2).

[0156] Example 5:

[0157] SAW resonator 5 includes: IDT, piezoelectric layer, first connecting layer, reflective layer, second connecting layer, third connecting layer, and substrate. The relationship between the reflective structure and the support structure in SAW resonator 5 can be seen in Figure 3(d), and the remaining parameters are the same as those of SAW resonator 4.

[0158] A comparison of the performance of SAW resonator 5 and SAW resonator a1 can be seen in Figure 16. As shown in Figure 16, curve 1 represents the admittance curve of SAW resonator 5, and curve 2 represents the admittance curve of SAW device a1. SAW resonator 5 also has similar benefits to SAW resonator 3, including improved Q value, increased electromechanical coupling coefficient, reduced sound velocity (e.g., the resonant frequency of curve 1 is lower than the resonant frequency of curve 2), and further away from Rayleigh spurious modes (e.g., the frequency interval between the Rayleigh spurious mode frequency near the dominant mode in curve 1 and the dominant mode frequency is greater than the frequency interval between the Rayleigh spurious mode frequency near the dominant mode and the dominant mode frequency in curve 2).

[0159] Example 6:

[0160] The SAW resonator 6 includes an IDT, a piezoelectric layer, a first interconnect layer, a reflective layer, a second interconnect layer, a third interconnect layer, and a substrate. The piezoelectric material is 20°X cut LiNbO3 with a thickness of 0.1λ; the support structure is made of SiO2; the reflective structure includes a cavity structure, with SiO2 accounting for 40% of the planar area in the reflective layer; the reflective layer has a thickness of 0.01λ. The substrate is made of silicon carbide; the first interconnect layer is made of silicon oxyfluoride with a thickness of 0.002λ; the second interconnect layer is made of SiO2, fabricated using the same process as the support structure, with a thickness of 0.02λ; the IDT is made of metallic Al with a thickness of 0.03λ and a metallization ratio of 0.4.

[0161] To demonstrate the performance of SAW resonator 6, this application designs SAW resonator a2. The materials, tangents, and thicknesses of the piezoelectric layer, substrate, and IDT of SAW resonator a2 are the same as those of the piezoelectric layer, substrate, and IDT of SAW resonator 6. The materials and thicknesses of the high-velocity layer of SAW resonator a2 are the same as those of the third connecting layer of SAW resonator 1. The materials and fabrication processes of the low-velocity layer of SAW resonator a2 are the same as those of the second connecting layer of SAW resonator 1. The thickness of the low-velocity layer of SAW resonator a2 is the same as the total thickness of the first connecting layer, reflective layer, and second connecting layer of SAW resonator 1. See Figure 17.

[0162] As shown in Figure 17, curve 1 represents the admittance curve of SAW resonator 6, and curve 2 represents the admittance curve of SAW resonator a2. Comparing curves 1 and 2, it can be seen that SAW resonator 6 can achieve an increase in Q value and an increase in electromechanical coupling coefficient. Meanwhile, the frequency interval between the miscellaneous mode frequency (6400MHz (estimated value)) and the main mode frequency (4800MHz (estimated value)) on the high-frequency side of the main mode in curve 1 is greater than 1000MHz, which can reduce the deterioration of out-of-band rejection caused by miscellaneous modes.

[0163] Example 6 uses a longitudinal leaky surface acoustic wave (LLSAW) resonator as an example. LLSAW resonators utilize the longitudinal modes of surface acoustic waves, which possess higher sound velocities, thus enabling higher resonant frequencies. They are typically used in acoustic filters above 3 GHz. A significant advantage of LLSAW resonators is that their substrate structure and fabrication processes are compatible with conventional SAW resonator production lines, making them simpler and less expensive than other high-frequency resonators.

[0164] Based on the aforementioned SAW resonator, this application also provides a filter that includes the aforementioned SAW resonator.

[0165] Based on the aforementioned filter, this application also provides a radio frequency module that includes the aforementioned filter.

[0166] This application also provides an electronic device that includes the radio frequency module described above, as shown in Figure 18.

[0167] As shown in Figure 18, the exemplary electronic device includes a radio frequency (RF) module, an antenna, a transceiver, and a modulator. The RF module includes a SAW duplexer / filter, a power amplifier (PA), and switches, etc. The SAW duplexer / filter includes a SAW resonator.

[0168] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0169] In the embodiments provided in this application, it should be understood that the disclosed systems and devices can be implemented in other ways. For example, the electronic device embodiments described above are merely illustrative. For instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed.

[0170] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included 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 substrate, characterized in that, include: The piezoelectric layer, the reflective layer, and the substrate are provided, wherein the piezoelectric layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in the first direction; The piezoelectric layer includes a piezoelectric material, and the reflective layer includes a support structure and a reflective structure. The reflective structure and the support structure are arranged along a second direction, which is perpendicular to the first direction. The reflective structure is located between the support structures, and the reflective coefficient of the reflective structure relative to the piezoelectric material is greater than a reflective coefficient threshold.

2. The substrate according to claim 1, characterized in that, The reflective structure includes a cavity structure.

3. The substrate according to claim 1, characterized in that, The reflective structure includes one or more of organic materials, aerogels, or porous composite materials.

4. The substrate according to any one of claims 1 to 3, characterized in that, The substrate further includes a first connection layer, which is located between the piezoelectric layer and the reflective layer and is used to connect the piezoelectric layer and the reflective layer.

5. The substrate according to claim 4, characterized in that, The first connecting layer and the supporting structure contain the same material.

6. The substrate according to any one of claims 1 to 5, characterized in that, The substrate further includes a second connecting layer, which is located between the reflective layer and the substrate and is used to connect the reflective layer and the substrate.

7. The substrate according to claim 6, characterized in that, The second connecting layer and the supporting structure contain the same material.

8. The substrate according to any one of claims 1 to 7, characterized in that, The reflection coefficient threshold is equal to 0.

65.

9. A substrate, characterized in that, include: The piezoelectric layer, the reflective layer, and the substrate are provided, wherein the piezoelectric layer is disposed on the reflective layer in a first direction, and the reflective layer is disposed on the substrate in the first direction; The piezoelectric layer includes a piezoelectric material, the reflective layer includes a support structure and a reflective structure, the reflective structure and the support structure are arranged along a second direction, the second direction is perpendicular to the first direction, the reflective structure is located between the support structures, the reflective structure includes a cavity structure, or the reflective structure includes one or more of organic materials, aerogels or porous composite materials.

10. The substrate according to claim 9, characterized in that, The substrate further includes a first connection layer, which is located between the piezoelectric layer and the reflective layer and is used to connect the piezoelectric layer and the reflective layer.

11. The substrate according to claim 10, characterized in that, The first connecting layer and the supporting structure are made of the same material.

12. The substrate according to any one of claims 9 to 11, characterized in that, The substrate further includes a second connecting layer, which is located between the reflective layer and the substrate and is used to connect the reflective layer and the substrate.

13. The substrate according to claim 12, characterized in that, The second connecting layer and the supporting structure are made of the same material.

14. A surface acoustic wave resonator, characterized in that, It includes an interdigital transducer and a substrate according to any one of claims 1 to 13.

15. The surface acoustic wave resonator according to claim 14, characterized in that, The ratio of the area of ​​overlap between the projected area of ​​the reflective structure on the piezoelectric layer and the projected area of ​​the interdigitated transducer region on the piezoelectric layer to the projected area of ​​the interdigitated transducer region on the piezoelectric layer is in the range of 15% to 85%.

16. A filter, characterized in that, Includes the surface acoustic wave resonator as described in claim 14 or 15.

17. A radio frequency module, characterized in that, Includes the filter as described in claim 16.

18. An electronic device, characterized in that, The electronic device includes the radio frequency module of claim 17.

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