Piezoelectric substrate, surface acoustic wave filter and forming method thereof

Abstract

The invention provides a piezoelectric substrate, a surface acoustic wave filter and a forming method of the surface acoustic wave filter. The piezoelectric substrate comprises a high-sound-velocity base; the low-sound-velocity layer is laminated on the high-sound-velocity substrate, and the sound velocity of the low-sound-velocity layer is lower than that of the high-sound-velocity substrate; the piezoelectric structures are embedded in the surface of the low-sound-velocity layer at intervals, and the piezoelectric structures are used for arranging a functional layer. The problems that a piezoelectric layer in a POI wafer cutting channel is prone to layering and stripping, cracks can extend to an effective chip area along an interface, and a device fails are solved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor fabrication technology, and more specifically, to a piezoelectric substrate, a surface acoustic wave filter, and a method for forming the same. Background Technology

[0002] With the increasing number of frequency bands supported by wireless communication devices, the frequency bands used by these devices are becoming increasingly dense. To improve communication quality and reduce interference between frequency bands, higher requirements are inevitably placed on the performance and size of surface acoustic wave (SAW) filters. Among them, POI-SAW (Piezoelectric on Insulator Surface Acoustic Wave) is a novel surface acoustic wave filter technology based on a piezoelectric thin film on an insulator (i.e., POI wafer substrate). This type of filter has advantages such as high quality factor, low insertion loss, and strong band suppression, making it a promising candidate for application.

[0003] POI wafer substrates typically consist of a high-resistivity silicon substrate layer, an oxide layer, and a piezoelectric layer. In the fabrication of SAW filters, the functional layer needs to be formed and packaged on the POI wafer substrate before the wafer is diced using a blade to form individual SAW filter chips. However, during wafer dicing, the piezoelectric layer within the dicing path is prone to delamination from the underlying oxide layer, and cracks can extend along the interface into the effective chip area, leading to device failure.

[0004] Existing technologies attempt to alleviate delamination by reducing blade speed, increasing water cooling, or applying a UV protective film, but these all lead to reduced production capacity or increased costs, failing to fundamentally eliminate the mechanical fragility of the piezoelectric layer within the cutting path. Summary of the Invention

[0005] The problem solved by this invention is that the piezoelectric layer in the cutting channel is prone to delamination during the cutting process, and cracks can extend along the interface to the effective chip area, leading to device failure.

[0006] To address the above problems, the present invention provides a piezoelectric substrate comprising: a high-velocity substrate; a low-velocity layer, wherein the low-velocity layer is stacked on the high-velocity substrate and the velocity of sound in the low-velocity layer is lower than that in the high-velocity substrate; and piezoelectric structures, wherein the piezoelectric structures are spacedly embedded on the surface of the low-velocity layer and the piezoelectric structures are used to form functional layers.

[0007] High-velocity substrates can confine surface acoustic waves (SAWs) within piezoelectric structures and low-velocity layers, preventing SAW leakage from the lower part of the high-velocity substrate. The low-velocity layer further encapsulates the SAW energy within the piezoelectric structure, reducing energy loss and improving the device's Q-value. Since the piezoelectric structures are intermittently embedded on the surface of the low-velocity layer, they exist only below the functional layers. After the functional layers are installed, the area between adjacent functional layers forms a dicing region, where the piezoelectric structure is completely removed. Thus, during blade cutting, the blade directly contacts the low-velocity layer between the piezoelectric structures. Since there are no brittle piezoelectric structures within the dicing region, the blade does not come into contact with the piezoelectric structures, preventing peeling or cracking. This fundamentally eliminates the risk of piezoelectric structure peeling, avoiding failures caused by peeling extending into the chip's interior. Stable bonding is maintained between the piezoelectric structure and the low-velocity layer, as well as between the piezoelectric structure and the functional layers, significantly improving the production yield after piezoelectric substrate cutting.

[0008] Furthermore, the piezoelectric structural material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate.

[0009] Furthermore, the high-speed acoustic substrate material is silicon, silicon carbide, gallium nitride, or diamond.

[0010] Furthermore, the low-velocity layer material is silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

[0011] When the low-velocity layer material is made of silicon dioxide or a material with silicon dioxide as the main component, the absolute value of the device's temperature coefficient of frequency (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded.

[0012] The present invention provides a piezoelectric substrate, the piezoelectric substrate comprising: a substrate; a high-velocity layer, the high-velocity layer being stacked on the substrate; a low-velocity layer, the low-velocity layer being stacked on the high-velocity layer, the sound velocity of the low-velocity layer being lower than that of the high-velocity layer; and piezoelectric structures, the piezoelectric structures being intermittently embedded on the surface of the low-velocity layer, the piezoelectric structures being used to form functional layers.

[0013] The high-velocity layer confines surface acoustic waves (SAWs) within the piezoelectric structure and the low-velocity layer, preventing SAW leakage from the lower part of the high-velocity layer. The low-velocity layer further encloses the SAW energy within the piezoelectric structure, reducing energy loss and improving the device's Q value. Since the piezoelectric structures are intermittently embedded on the surface of the low-velocity layer, they exist only below the functional layers. After the functional layers are installed, the area between adjacent functional layers forms a dicing region, where the piezoelectric structures are completely removed. Thus, during blade cutting, the blade directly contacts the low-velocity layer between the piezoelectric structures. Since there are no brittle piezoelectric structures within the dicing region, the blade does not come into contact with the piezoelectric structures, preventing peeling or cracking. This fundamentally eliminates the risk of piezoelectric structure peeling, avoiding failures caused by peeling extending into the chip's interior. Stable bonding is maintained between the piezoelectric structure and the low-velocity layer, as well as between the piezoelectric structure and the functional layers, significantly improving the production yield after piezoelectric substrate cutting.

[0014] Furthermore, the piezoelectric structural material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate.

[0015] Furthermore, the high-speed acoustic layer material is silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, or polycrystalline silicon.

[0016] Furthermore, the low-velocity layer material is silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

[0017] When the low-velocity layer material is made of silicon dioxide or a material with silicon dioxide as the main component, the absolute value of the device's temperature coefficient of frequency (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded.

[0018] Furthermore, the substrate is silicon, silicon carbide, gallium nitride, or diamond.

[0019] The present invention provides a piezoelectric substrate, the piezoelectric substrate comprising: a substrate; a trap-rich layer stacked on the substrate; a low-velocity layer stacked on the trap-rich layer; and piezoelectric structures spaced apart on the surface of the low-velocity layer, the piezoelectric structures being used to form functional layers.

[0020] The presence of a certain number of grain boundary defects in the trap-rich layer enriches it with carrier traps. These carrier traps restrict carrier movement at the interface, suppressing parasitic conductivity and reducing RF losses. The low-velocity acoustic layer further confines surface acoustic wave energy within the piezoelectric structure, reducing energy loss and improving the device's Q-value. Since the piezoelectric structures are intermittently embedded on the surface of the low-velocity acoustic layer, they exist only below the functional layers. After the functional layers are installed, the area between adjacent functional layers forms a dicing region, where the piezoelectric structures are completely removed. During cutting, the blade directly contacts the low-velocity acoustic layer between the piezoelectric structures. Since there are no brittle piezoelectric structures within the dicing region, the blade does not contact the piezoelectric structures, preventing peeling or cracking. This fundamentally eliminates the risk of piezoelectric structure peeling, avoiding failures caused by peeling extending into the chip. Stable bonding is maintained between the piezoelectric structures and the low-velocity acoustic layer, as well as between the piezoelectric structures and the functional layers, significantly improving the production yield after piezoelectric substrate cutting.

[0021] Furthermore, the piezoelectric structural material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate.

[0022] Furthermore, the trap-rich layer material is polycrystalline silicon, doped silicon glass, or a polycrystalline silicon-based composite material.

[0023] Furthermore, the low-velocity layer material is silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

[0024] When the low-velocity layer material is made of silicon dioxide or a material with silicon dioxide as the main component, the absolute value of the device's temperature coefficient of frequency (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded.

[0025] Furthermore, the substrate is silicon, silicon carbide, gallium nitride, or diamond.

[0026] This invention provides a method for forming a piezoelectric substrate, used to form a piezoelectric substrate provided by any of the above-mentioned technical solutions. The method for forming the piezoelectric substrate includes the following steps: forming a first low-velocity layer on a substrate; forming a concave-convex structure on an initial piezoelectric substrate, and forming a second low-velocity layer on the side of the initial piezoelectric substrate adjacent to the concave-convex structure; bonding the first low-velocity layer and the second low-velocity layer; and processing the initial piezoelectric substrate to form the piezoelectric substrate.

[0027] Furthermore, the step of forming a concave-convex structure on the initial piezoelectric substrate and forming a second low-velocity layer on the side of the initial piezoelectric substrate adjacent to the concave-convex structure specifically includes the following steps: providing an initial piezoelectric substrate; etching the initial piezoelectric substrate to form the concave-convex structure; and depositing the second low-velocity layer on the side of the initial piezoelectric substrate adjacent to the concave-convex structure.

[0028] By first patterning the initial piezoelectric substrate and then depositing the second low-velocity layer, it is ensured that the second low-velocity layer can perfectly fill the gaps between the initial piezoelectric substrates and cover the initial piezoelectric substrates to form a planarized surface, thus guaranteeing high-quality wafer bonding in the future.

[0029] Furthermore, the process of processing the initial piezoelectric substrate to form the piezoelectric substrate specifically includes the following steps: grinding the initial piezoelectric substrate on the side away from the uneven structure to expose the second low-velocity layer in order to form the piezoelectric substrate.

[0030] Since the final grinding endpoint when grinding the initial piezoelectric substrate is the second low-velocity layer, on the one hand, by precisely controlling the grinding endpoint, the piezoelectric material in the cutting area can be completely removed after the second low-velocity layer is exposed, thus completely avoiding the risk of piezoelectric substrate peeling or cracking; on the other hand, the piezoelectric substrate with the functional area has sufficient thickness to facilitate the fabrication of the functional layer on top, such as interdigital transducers, to achieve stable bidirectional conversion between electrical signals and surface acoustic waves.

[0031] Furthermore, the first and second low-velocity layers are made of the same material. The low-velocity layers are fabricated by directly bonding the first and second low-velocity layers, which uses the same material. This reduces the complexity of the process and ensures the bonding strength of the piezoelectric substrate.

[0032] Furthermore, the substrate is a high-velocity material, the velocity of which is higher than that of the first low-velocity layer and the second low-velocity layer; or, before forming the first velocity layer on the substrate, the substrate further includes forming a high-velocity layer, the velocity of which is higher than that of the first low-velocity layer and a majority of the second low-velocity layers; or, before forming the first velocity layer on the substrate, the substrate further includes forming a trap-rich layer.

[0033] The present invention also provides a method for forming a surface acoustic wave filter, the method comprising the following steps: preparing a piezoelectric substrate according to the piezoelectric substrate forming method provided by any of the above technical solutions; and preparing a functional layer on the piezoelectric substrate.

[0034] The present invention also provides a surface acoustic wave filter, the surface acoustic wave filter comprising a functional layer and a piezoelectric substrate provided by any of the above technical solutions, the functional layer being disposed on the piezoelectric substrate, the functional layer comprising an interdigital transducer.

[0035] In summary, the above-mentioned technical solutions of this application can have one or more of the following advantages or beneficial effects: i) The piezoelectric structure exists only below the functional layer. When the blade cuts the POI wafer, it directly contacts the low-velocity layer between the piezoelectric structures. There are no brittle piezoelectric structures in the cutting path, so the piezoelectric structure will not peel off or crack, avoiding failure caused by peeling and extending into the chip; ii) The low-velocity layer is prepared by directly bonding the first low-velocity layer and the second low-velocity layer of the same material, which reduces the process difficulty and ensures the bonding strength of the piezoelectric substrate; iii) Grinding the initial piezoelectric substrate to expose the second low-velocity layer can ensure that the piezoelectric material in the cutting path area is completely removed, completely avoiding the risk of piezoelectric structure peeling off or cracking, and retaining sufficient thickness of the piezoelectric structure in the functional area. Attached Figure Description

[0036] Figure 1 A flowchart illustrating a method for forming a piezoelectric substrate according to an embodiment of the present invention; Figure 2 This is one of the schematic diagrams showing the formation of the initial piezoelectric substrate in step S2; Figure 3 This is the second schematic diagram of the formation of the initial piezoelectric substrate in step S2; Figure 4 This is a schematic diagram of the formation of the second low-velocity layer in step S2; Figure 5 This is a schematic diagram of the substrate formation in step S1; Figure 6 This is a schematic diagram of the formation of the hypersonic layer in step S1; Figure 7 This is a schematic diagram of the formation of the first low-velocity layer in step S1; Figure 8 This is a schematic diagram of the bonding of the first low-sound layer and the second low-sound layer in step S3. Figure 9 This is a schematic diagram of the structure of a piezoelectric substrate provided in an embodiment of the present invention; Figure 10 A schematic diagram illustrating the formation of a hypersonic substrate; Figure 11 This is a schematic diagram of another piezoelectric substrate provided in an embodiment of the present invention; Figure 12 A schematic diagram illustrating the formation of the trap-rich layer and the substrate; Figure 13 This is a schematic diagram of another piezoelectric substrate provided in an embodiment of the present invention; Figure 14 This is a schematic diagram of the structure of a surface acoustic wave filter provided in an embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures: 100 - Piezoelectric substrate; 110 - Substrate; 110a - High-velocity substrate; 120 - High-velocity layer; 130 - Low-velocity layer; 131 - First low-velocity layer; 132 - Second low-velocity layer; 140 - Initial piezoelectric substrate; 141 - Piezoelectric structure; 150 - Trap-rich layer; 200 - Surface acoustic wave filter; 210 - Functional layer. Detailed Implementation

[0038] The purpose of this invention is to provide a piezoelectric substrate that prevents the piezoelectric structure on the POI wafer from peeling off or cracking, thus avoiding the effect of peeling extending into the chip and causing chip failure.

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0040] See Figure 11 The present invention provides a piezoelectric substrate 100, comprising: a high-velocity substrate 110a; a low-velocity layer 130, which is stacked on the high-velocity substrate 110a and has a sound velocity lower than that of the high-velocity substrate 110a; and piezoelectric structures 141, which are spaced and embedded on the surface of the low-velocity layer 130 and are used to provide a functional layer 210.

[0041] The high-velocity substrate 110a can confine surface acoustic waves (SAWs) within the piezoelectric structure 141 and the low-velocity layer 130, preventing SAW leakage from the lower part of the high-velocity substrate 110a. The low-velocity layer 130 further confines the SAW energy within the piezoelectric structure 141, reducing energy loss and improving the Q value of the device. Since the piezoelectric structures 141 are spaced apart and embedded on the surface of the low-velocity layer 130, the piezoelectric structures 141 can exist only below the functional layer 210. After the functional layer 210 is set, the area between adjacent functional layers 210 is a cut-out region, and the piezoelectric structures 141 in the cut-out region are completely removed. In this way, when the blade cuts, it directly contacts the low-velocity layer 130 between the piezoelectric structures 141. There are no brittle piezoelectric structures 141 in the cutting path, the blade will not come into contact with the piezoelectric structures 141, and the piezoelectric structures 141 will not peel off or crack. This fundamentally eliminates the risk of the piezoelectric structures 141 peeling off, avoiding chip failure caused by peeling extending into the chip. The piezoelectric structures 141 and the low-velocity layer 130, as well as the piezoelectric structures 141 and the functional layer 210, can maintain a stable bonding state. Therefore, the production yield after cutting the piezoelectric substrate 100 is greatly improved.

[0042] In one specific embodiment, the surface of the piezoelectric structure 141 is flush with the surface of the low-velocity layer 130 around the piezoelectric structure 141, which facilitates the formation of a functional layer 210 on the piezoelectric structure 141 with a projected area greater than or equal to that of the piezoelectric structure 141. That is, after the functional layer 210 completely covers the piezoelectric structure 141, some of its edges can be located on the low-velocity layer 130 to achieve stable support.

[0043] In one specific embodiment, the piezoelectric structure 141 is made of lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate. Because lithium niobate and lithium tantalate have higher electromechanical coupling coefficients, the piezoelectric structure 141 using lithium niobate can more efficiently convert electrical energy into acoustic energy; while the piezoelectric structure 141 using lithium tantalate has better temperature compensation, and the low-velocity layer 130 has better temperature stability.

[0044] In one specific embodiment, the hypersonic substrate 110a is made of silicon, silicon carbide, gallium nitride, or diamond. Using silicon as the hypersonic substrate 110a provides a high sound velocity, allowing it to form an effective acoustic reflection layer with silicon dioxide. This confines sound wave energy within the piezoelectric structure 141, reducing sound wave leakage and thus contributing to an improved quality factor (Q) of the filter. Furthermore, silicon as the hypersonic substrate 110a is relatively inexpensive and has good mechanical properties. Silicon carbide and gallium nitride, as hypersonic substrates 110a, possess extremely high thermal conductivity and excellent high-temperature resistance, making them suitable for high-power radio frequency devices and effectively solving heat dissipation problems. Diamond, on the other hand, has even higher thermal conductivity.

[0045] In one specific embodiment, the low-velocity layer 130 is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material, wherein the silicon dioxide-based composite material is a material whose main component is silicon dioxide. When the low-velocity layer 130 is made of silicon dioxide or a material whose main component is silicon dioxide, the absolute value of the device's temperature coefficient of frequency (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded.

[0046] See Figure 9 The present invention provides a piezoelectric substrate 100, comprising: a substrate 110; a high-velocity layer 120 stacked on the substrate 110; a low-velocity layer 130 stacked on the high-velocity layer 120, wherein the velocity of sound in the low-velocity layer 130 is lower than that in the high-velocity layer 120; and piezoelectric structures 141 spacedly embedded on the surface of the low-velocity layer 130, wherein the piezoelectric structures 141 are used to provide a functional layer 210.

[0047] The high-velocity layer 120 confines surface acoustic waves (SAWs) within the piezoelectric structure 141 and the low-velocity layer 130, preventing SAW leakage from the lower part of the high-velocity layer 120. The low-velocity layer 130 further confines the SAW energy within the piezoelectric structure 141, reducing energy loss and improving the Q value of the device. Since the piezoelectric structures 141 are spaced apart and embedded on the surface of the low-velocity layer 130, the piezoelectric structures 141 can exist only below the functional layer 210. After the functional layer 210 is installed, the area between adjacent functional layers 210 is a cut-out region, and the piezoelectric structures 141 in the cut-out region are completely removed. In this way, when the blade cuts, it directly contacts the low-velocity layer 130 between the piezoelectric structures 141. There are no brittle piezoelectric structures 141 in the cutting path, the blade will not come into contact with the piezoelectric structures 141, and the piezoelectric structures 141 will not peel off or crack. This fundamentally eliminates the risk of the piezoelectric structures 141 peeling off, avoiding chip failure caused by peeling extending into the chip. The piezoelectric structures 141 and the low-velocity layer 130, as well as the piezoelectric structures 141 and the functional layer 210, can maintain a stable bonding state. Therefore, the production yield after cutting the piezoelectric substrate 100 is greatly improved.

[0048] In one specific embodiment, the piezoelectric structure 141 is made of lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate. Because lithium niobate and lithium tantalate have higher electromechanical coupling coefficients, the piezoelectric structure 141 using lithium niobate can more efficiently convert electrical energy into acoustic energy; while the piezoelectric structure 141 using lithium tantalate has better temperature compensation, and the low-velocity layer 130 has better temperature stability.

[0049] In one specific embodiment, the hypersonic layer 120 is made of silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, or polycrystalline silicon.

[0050] In one specific embodiment, the low-velocity layer 130 is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material, wherein the silicon dioxide-based composite material is a material whose main component is silicon dioxide.

[0051] When the low-velocity layer 130 is made of silicon dioxide or a material with silicon dioxide as the main component, the absolute value of the device's frequency temperature coefficient (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded. Using a polycrystalline silicon layer as the high-velocity layer 120, compared to silicon dioxide, provides a higher sound velocity and can form an effective acoustic reflection layer with silicon dioxide, confining sound wave energy to the vicinity of the piezoelectric structure 141, reducing sound wave leakage, and thus helping to improve the filter's quality factor (Q value). Furthermore, polycrystalline silicon is easier to process.

[0052] In one specific embodiment, the substrate 110 is silicon, silicon carbide, gallium nitride, or diamond. Using silicon as the substrate 110 results in relatively low cost and good mechanical properties, while silicon carbide and gallium nitride as the substrate 110 have extremely high thermal conductivity and excellent high-temperature resistance, making them suitable for high-power radio frequency devices and effectively solving heat dissipation problems; diamond has even higher thermal conductivity.

[0053] See Figure 13 The present invention provides a piezoelectric substrate 100, which includes: a substrate 110; a trap-rich layer 150 stacked on the substrate 110; a low-velocity layer 130 stacked on the trap-rich layer 150; and piezoelectric structures 141 spaced apart on the surface of the low-velocity layer 130, the piezoelectric structures 141 being used to provide a functional layer 210.

[0054] The trap-rich layer 150 contains a certain number of grain boundary defects, making it rich in carrier traps. These carrier traps restrict carrier movement at the interface, suppressing parasitic conductivity and reducing RF loss. The low-velocity layer 130 further confines surface acoustic wave energy within the piezoelectric structure 141, reducing energy loss and improving the device's Q value. Since the piezoelectric structures 141 are intermittently embedded on the surface of the low-velocity layer 130, they exist only below the functional layer 210. After the functional layer 210 is established, the area between adjacent functional layers 210 forms a cut-out region, where the piezoelectric structures 141 are completely removed. In this way, when the blade cuts, it directly contacts the low-velocity layer 130 between the piezoelectric structures 141. There are no brittle piezoelectric structures 141 in the cutting path, the blade will not come into contact with the piezoelectric structures 141, and the piezoelectric structures 141 will not peel off or crack. This fundamentally eliminates the risk of the piezoelectric structures 141 peeling off and avoids failure caused by peeling extending into the chip. The piezoelectric structures 141 and the low-velocity layer 130, as well as the piezoelectric structures 141 and the functional layer 210, can maintain a stable bonding state. Therefore, the production yield after cutting the piezoelectric substrate 100 is greatly improved.

[0055] In one specific embodiment, the piezoelectric structure 141 is made of lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic, or lithium tantalate. Because lithium niobate and lithium tantalate have higher electromechanical coupling coefficients, the piezoelectric structure 141 using lithium niobate can more efficiently convert electrical energy into acoustic energy; while the piezoelectric structure 141 using lithium tantalate has better temperature compensation, and the low-velocity layer 130 has better temperature stability.

[0056] In one specific embodiment, the trap-rich layer 150 is made of polycrystalline silicon, doped silicon glass, or a polycrystalline silicon-based composite material.

[0057] In one specific embodiment, the low-velocity layer 130 is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material, wherein the silicon dioxide-based composite material is a material whose main component is silicon dioxide. When the low-velocity layer 130 is made of silicon dioxide or a material whose main component is silicon dioxide, the absolute value of the device's temperature coefficient of frequency (TCF) can be reduced, the device's electromechanical coupling coefficient can be increased, and the relative bandwidth can be expanded.

[0058] In one specific embodiment, the substrate 110 is silicon, silicon carbide, gallium nitride, or diamond. Using silicon as the substrate 110 results in relatively low cost and good mechanical properties, while silicon carbide and gallium nitride as the substrate 110 have extremely high thermal conductivity and excellent high-temperature resistance, making them suitable for high-power radio frequency devices and effectively solving heat dissipation problems; diamond has even higher thermal conductivity.

[0059] See Figures 1-14 The present invention provides a method for forming a piezoelectric substrate 100, for forming the piezoelectric substrate 100 provided by any of the above-described technical solutions. The method for forming the piezoelectric substrate 100 includes the following steps: Step S1: Form a first low-velocity layer 131 on the substrate 110; Step S2: Form a concave-convex structure on the initial piezoelectric substrate 140, and form a second low-velocity layer 132 on the side of the initial piezoelectric substrate 140 adjacent to the concave-convex structure; Step S3: Bond the first low-velocity layer 131 to the second low-velocity layer 132; Step S4: Process the initial piezoelectric substrate 140 to form the piezoelectric substrate 100.

[0060] See Figures 2-4 In one specific embodiment, a bump structure is formed on the initial piezoelectric substrate 140, and a second low-velocity layer 132 is formed on the side of the initial piezoelectric substrate 140 adjacent to the bump structure, specifically including the following steps: Provide an initial piezoelectric substrate 140; The initial piezoelectric substrate 140 is etched to form an uneven structure; A second low-velocity layer 132 is deposited on the side of the initial piezoelectric substrate 140 adjacent to the concave-convex structure.

[0061] Because the order of first patterning the initial piezoelectric substrate 140 and then depositing the second low-velocity layer 132 ensures that the second low-velocity layer 132 can perfectly fill the gaps between the initial piezoelectric substrates 140 and cover the initial piezoelectric substrates 140 to form a planarized surface, it provides a guarantee for subsequent high-quality wafer bonding.

[0062] The initial piezoelectric substrate 140 can be achieved by chemical vapor deposition.

[0063] See Figures 8-9 In one specific embodiment, the initial piezoelectric substrate 140 is processed to form the piezoelectric substrate 100, specifically including the following steps: grinding the initial piezoelectric substrate 140 on the side away from the uneven structure to expose the second low-velocity layer 132 to form the piezoelectric substrate 100.

[0064] Since the final grinding endpoint of the initial piezoelectric substrate 140 is the second low-velocity acoustic layer 132, on the one hand, by precisely controlling the grinding endpoint, the exposure of the second low-velocity acoustic layer 132 ensures that the piezoelectric material in the cutting area is completely removed, thus completely avoiding the risk of peeling or cracking of the piezoelectric substrate 100; on the other hand, the piezoelectric substrate 100 retains sufficient thickness to facilitate the fabrication of the functional layer 210 above it, such as an interdigital transducer, to achieve stable bidirectional conversion between electrical signals and surface acoustic waves. Specifically, the piezoelectric structure 1411 can convert electrical signals into surface acoustic waves; and through the piezoelectric effect, it can convert reflected sound waves back into electrical signals.

[0065] In one specific embodiment, the first low-velocity layer 131 and the second low-velocity layer 132 are made of the same material. The low-velocity layer 130 is prepared by directly bonding the first low-velocity layer 131 and the second low-velocity layer 132, which are made of the same material. This reduces the difficulty of the process and ensures the bonding strength of the piezoelectric substrate 100.

[0066] For example, the first low-velocity layer 131 and the second low-velocity layer 132 are silicon dioxide layers. Bonding the first low-velocity layer 131 and the second low-velocity layer 132 specifically includes: chemically cleaning the first low-velocity layer 131 and the second low-velocity layer 132, activating the silicon dioxide surface, performing bonding, and finally high-temperature annealing to strengthen the bonding state.

[0067] In one specific embodiment, prior to step S3, the method for forming the piezoelectric substrate 100 further includes the following steps: The first low-velocity layer 131 is ground or polished; and / or the second low-velocity layer 132 is ground or polished.

[0068] It should be noted that an extremely flat bonding surface can achieve ultra-high bonding strength, improve bonding yield and bonding strength, and prevent delamination during subsequent grinding.

[0069] Because the initial piezoelectric substrate 140 has raised piezoelectric structures 141, the deposited second low-velocity layer 132 may be uneven. Preferably, the deposited second low-velocity layer 132 is chemically mechanically polished to smooth out all raised portions of the surface, forming a globally flat and smooth surface.

[0070] See Figures 10-11Optionally, the substrate 110 is a hypersonic material, the speed of sound of which is higher than that of the first low-sonic layer 131 and the second low-sonic layer 132. For example, the substrate 110 is a hypersonic substrate 110a made of silicon, silicon carbide, gallium nitride, or diamond.

[0071] See Figures 5-9 Optionally, before forming the first sound velocity layer on the substrate 110, the method further includes forming a high-velocity layer 120 on the substrate 110, the high-velocity layer 120 having a sound velocity higher than that of the first low-velocity layer 131 and a plurality of the second low-velocity layers 132. For example, the high-velocity layer 120 is made of silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, or polycrystalline silicon.

[0072] See Figures 12-13 Optionally, before forming the first sound velocity layer on the substrate 110, the method further includes forming a trap-rich layer 150 on the substrate 110. For example, the trap-rich layer 150 is made of polycrystalline silicon, doped silicon glass, or a polycrystalline silicon-based composite material.

[0073] The present invention also provides a method for forming a surface acoustic wave filter 200, the method comprising the following steps: preparing a piezoelectric substrate 100 according to the method for forming a piezoelectric substrate 100 provided by any of the above technical solutions; and preparing a functional layer 210 on the piezoelectric substrate 100.

[0074] Preferably, the functional layer 210 is prepared on the piezoelectric substrate 100 by processes such as deposition and etching. The functional layer 210 is, for example, an interdigital transducer.

[0075] See Figure 14 The present invention also provides a surface acoustic wave filter 200, which includes a functional layer 210 and a piezoelectric substrate 100 provided by any of the above technical solutions. The functional layer 210 is disposed on the piezoelectric substrate 100 and includes an interdigital transducer.

[0076] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A piezoelectric substrate, characterized in that, The piezoelectric substrate includes: High-speed substrate (110a); A low-velocity layer (130) is stacked on the high-velocity substrate (110a), wherein the velocity of sound in the low-velocity layer (130) is lower than that in the high-velocity substrate (110a). A piezoelectric structure (141) is intermittently embedded on the surface of the low-velocity layer (130), the piezoelectric structure (141) being used to provide a functional layer.

2. The piezoelectric substrate according to claim 1, characterized in that, The piezoelectric structure (141) material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic or lithium tantalate.

3. The piezoelectric substrate according to claim 1, characterized in that, The high-speed acoustic substrate (110a) is made of silicon, silicon carbide, gallium nitride, or diamond.

4. The piezoelectric substrate according to claim 1, characterized in that, The low-velocity layer (130) is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

5. A piezoelectric substrate, characterized in that, The piezoelectric substrate includes: Base (110); A high-speed acoustic layer (120) is stacked on the substrate (110). A low-velocity layer (130) is stacked on top of the high-velocity layer (120), wherein the velocity of sound in the low-velocity layer (130) is lower than that in the high-velocity layer (120). A piezoelectric structure (141) is intermittently embedded on the surface of the low-velocity layer (130), the piezoelectric structure (141) being used to provide a functional layer.

6. The piezoelectric substrate according to claim 5, characterized in that, The piezoelectric structure (141) material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic or lithium tantalate.

7. The piezoelectric substrate according to claim 5, characterized in that, The high-speed acoustic layer (120) is made of silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, or polycrystalline silicon.

8. The piezoelectric substrate according to claim 5, characterized in that, The low-velocity layer (130) is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

9. The piezoelectric substrate according to claim 5, characterized in that, The substrate (110) is silicon, silicon carbide, gallium nitride, or diamond.

10. A piezoelectric substrate, characterized in that, The piezoelectric substrate includes: Base (110); A trap-rich layer (150) is stacked on the substrate (110). Low-velocity layer (130), which is stacked on the trap-rich layer (150); A piezoelectric structure (141) is intermittently embedded on the surface of the low-velocity layer (130), the piezoelectric structure (141) being used to provide a functional layer.

11. The piezoelectric substrate according to claim 10, characterized in that, The piezoelectric structure (141) material includes: lithium niobate, zinc oxide, aluminum nitride, lead zirconate titanate ceramic or lithium tantalate.

12. The piezoelectric substrate according to claim 10, characterized in that, The trap-rich layer (150) is made of polycrystalline silicon, doped silicon glass, or polycrystalline silicon-based composite material.

13. The piezoelectric substrate according to claim 10, characterized in that, The low-velocity layer (130) is made of silicon dioxide, silicon oxynitride, tantalum oxide, or a silicon dioxide-based composite material.

14. The piezoelectric substrate according to claim 10, characterized in that, The substrate (110) is silicon, silicon carbide, gallium nitride, or diamond.

15. A method for forming a piezoelectric substrate, for forming a piezoelectric substrate as described in any one of claims 1-14, characterized in that, The method for forming the piezoelectric substrate includes the following steps: A first low-sound-velocity layer is formed on the substrate; A bumpy structure is formed on an initial piezoelectric substrate, and a second low-velocity layer is formed on the side of the initial piezoelectric substrate adjacent to the bumpy structure. The first low-velocity layer is bonded to the second low-velocity layer; The initial piezoelectric substrate is processed to form the piezoelectric substrate.

16. The method for forming a piezoelectric substrate according to claim 15, characterized in that, The process of forming an uneven structure on an initial piezoelectric substrate and forming a second low-velocity layer on the side of the initial piezoelectric substrate adjacent to the uneven structure specifically includes the following steps: Provide the initial piezoelectric substrate; The initial piezoelectric substrate is etched to form the uneven structure; The second low-velocity layer is deposited on the side of the initial piezoelectric substrate adjacent to the uneven structure.

17. The method for forming a piezoelectric substrate according to claim 16, characterized in that, The process of processing the initial piezoelectric substrate to form the piezoelectric substrate specifically includes the following steps: The initial piezoelectric substrate is ground on the side away from the uneven structure to expose the second low-velocity layer, thereby forming the piezoelectric substrate.

18. The method for forming a piezoelectric substrate according to claim 15, characterized in that, The first low-sound-velocity layer and the second low-sound-velocity layer are made of the same material.

19. The method for forming a piezoelectric substrate according to claim 15, characterized in that, The substrate is a high-velocity material, and the velocity of sound in the high-velocity material is higher than that in the first low-velocity layer and the second low-velocity layer. Alternatively, before forming the first sound velocity layer on the substrate, the method further includes forming a high sound velocity layer on the substrate, the high sound velocity layer having a higher sound velocity than the first low sound velocity layer and a majority of the second low sound velocity layers. Alternatively, before forming the first sound velocity layer on the substrate, the method further includes forming a trap-rich layer on the substrate.

20. A method for forming a surface acoustic wave filter, characterized in that, The method for forming the surface acoustic wave filter includes the following steps: The piezoelectric substrate is prepared according to the method for forming a piezoelectric substrate according to any one of claims 15-19; A functional layer is fabricated on the piezoelectric substrate.

21. A surface acoustic wave filter, characterized in that, The surface acoustic wave filter includes a functional layer (210) and a piezoelectric substrate as described in any one of claims 1-14, wherein the functional layer (210) is disposed on the piezoelectric substrate and the functional layer includes an interdigital transducer.

Images