piezoelectric device

Abstract

A piezoelectric device (100) includes a support substrate (110), an intermediate layer (140) disposed on a first region (RG1) of the support substrate (110), a piezoelectric layer (130) disposed on the intermediate layer (140), a functional element (120) formed on the piezoelectric layer (130), and an insulating layer (150). The insulating layer (150) is disposed on a second region (RG2) of the support substrate (110) adjacent to the first region (RG1). A surface roughness (R2) of the support substrate (110) in the second region (RG2) is greater than a surface roughness (R1) of the support substrate (110) in the first region (RG1).

Description

Technical Field

[0001] This disclosure relates to piezoelectric devices, and more specifically, to techniques for reducing stray high-order modes generated in piezoelectric devices. Background Technology

[0002] Piezoelectric devices in which functional elements are formed on piezoelectric thin films are known. For example, International Patent Publication No. 2015 / 098678 (Patent Document 1) discloses an elastic wave device in which comb-shaped IDT (Interdigital Transducer) electrodes are formed on a multilayer film, wherein the multilayer film is a piezoelectric thin film stacked on a laminate of low-velocity and high-velocity films.

[0003] In the elastic wave device disclosed in International Publication No. 2015 / 098678 (Patent Document 1), an insulating layer is formed in the area on the support substrate where the aforementioned multilayer film is not formed, and wiring electrodes for connecting IDT electrodes and external terminals are formed on the insulating layer.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: International Publication No. 2015 / 098678 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] In the piezoelectric device with multilayer films disclosed in International Patent Publication No. 2015 / 098678 (Patent Document 1), a resonant mode originating in the stacking direction of the multilayer film thickness is generated together with the signal of the main mode based on the resonant frequency of the IDT electrode. Due to this resonant mode, unwanted waves (spurious waves) with higher-order modes having frequencies higher than the resonant frequency of the IDT electrode may inevitably be generated. If such spurious waves are generated, they become noise superimposed on the high-frequency signal of the main mode propagated by the IDT electrode, and may become a major cause of performance degradation of the piezoelectric device.

[0009] Furthermore, the resulting stray high-order modes can sometimes leak into areas where the insulating layer has not formed a multilayer film. In this case, it may also affect the characteristics of piezoelectric devices adjacent to the insulating layer.

[0010] This disclosure was made to solve such a problem, with the aim of suppressing the characteristic degradation associated with higher-order mode straying generated in piezoelectric devices.

[0011] Technical solutions for solving the problem

[0012] The piezoelectric device disclosed herein includes: a support substrate; an intermediate layer, a first region disposed on the support substrate; a piezoelectric layer disposed on the intermediate layer; a functional element formed on the piezoelectric layer; and an insulating layer. The insulating layer is disposed on the support substrate in a second region adjacent to the first region. The surface roughness of the support substrate in the second region is greater than the surface roughness of the support substrate in the first region.

[0013] Invention Effects

[0014] According to the piezoelectric device based on this disclosure, the surface roughness of the second region forming the insulating layer in the support substrate is greater than the surface roughness of the first region forming the piezoelectric layer and the intermediate layer. Therefore, if the surface roughness increases, the thickness deviation of that region increases, and thus, compared to the case of low surface roughness, it becomes less likely to generate resonant modes corresponding to the generated stray emissions. Therefore, the stray emissions of higher-order leakage modes become easier to attenuate, thus suppressing the characteristic degradation associated with stray emissions. Attached Figure Description

[0015] Figure 1 This is a cross-sectional view of the piezoelectric device according to Embodiment 1.

[0016] Figure 2 yes Figure 1 A partial cross-sectional view of a piezoelectric device.

[0017] Figure 3 This is a partial cross-sectional view of the piezoelectric device involved in Embodiment 2.

[0018] Figure 4 This is a partial cross-sectional view of the piezoelectric device involved in Embodiment 3. Detailed Implementation

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Furthermore, identical or equivalent parts in the drawings are labeled with the same reference numerals, and their descriptions will not be repeated.

[0020] [Implementation Method 1]

[0021] Figure 1 This is a cross-sectional view of the piezoelectric device 100 according to Embodiment 1. Furthermore, Figure 2 yes Figure 1 An enlarged view of a portion of the cross-section of the piezoelectric device 100. (Refer to...) Figure 1 as well as Figure 2 The piezoelectric device 100 includes a support substrate 110, a functional element 120, a piezoelectric layer 130, an intermediate layer 140, an insulating layer 150, and a cover layer 175. Furthermore, in the following description, the positive direction of the Z-axis in each figure will sometimes be referred to as the upper surface side, and the negative direction as the lower surface side.

[0022] The support substrate 110 is formed, for example, from various ceramics such as lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, etc., dielectrics such as bauxite (Al2O3), magnesium oxide, silicon nitride (SiN), aluminum nitride (AlN), silicon carbide (SiC), zirconium oxide (ZrO2), cordierite, mullite, block talc, forsterite, etc., or semiconductors such as silicon (Si), sapphire, gallium nitride (GaN), etc., as well as resin substrates.

[0023] A laminate 105 comprising a piezoelectric layer 130 and an intermediate layer 140 is formed on a portion of the upper surface 111 of the support substrate 110, and a functional element 120 is formed on the upper surface 131 of the piezoelectric layer 130.

[0024] The piezoelectric layer 130 is formed, for example, from piezoelectric single crystal materials such as lithium tantalate, lithium niobate, zinc oxide (ZnO), aluminum nitride, or lead zirconate titanate (PZT), or their piezoelectric stacked materials.

[0025] Functional element 120 includes an elastic wave resonator comprising comb-shaped IDT electrodes. A surface acoustic wave (SAW) resonator is formed by piezoelectric layer 130 and functional element 120. Functional element 120 can be formed using a metallic material such as an elemental metal containing at least one of aluminum (Al), copper (Cu), silver (Ag), gold (Au), titanium (Ti), tungsten (W), platinum (Pt), chromium (Cr), nickel (Ni), and molybdenum (Mo), or an alloy thereof. Furthermore, functional element 120 may also have a structure in which multiple metal films comprising these metals or alloys are stacked.

[0026] The intermediate layer 140 includes a high-velocity acoustic layer 142 disposed on the upper surface 111 of the support substrate 110 and a low-velocity acoustic layer 141 disposed on the high-velocity acoustic layer 142. The high-velocity acoustic layer 142 is configured to propagate an elastic wave at a speed higher than that of the elastic wave propagating in the piezoelectric layer 130. As the high-velocity acoustic layer 142, for example, various ceramics such as DLC (diamond-like carbon) film, aluminum nitride, alumina, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, etc., alumina, zirconium oxide, cordierite, mullite, block talc, forsterite, etc., magnesium oxide diamond, or any material mainly composed of the above materials, or a mixture of the above materials as the main component.

[0027] The low-velocity layer 141 is configured to propagate elastic waves at a speed lower than that of the bulk waves propagating in the piezoelectric layer 130. The low-velocity layer 141 can be made of, for example, silicon oxide, glass, silicon oxynitride, tantalum oxide, silicon oxide compounds with added fluorine, carbon, or boron, or any material whose main components are the aforementioned materials. The sound velocity difference generated at the boundary between the low-velocity layer 141 and the high-velocity layer 142 causes the elastic waves excited from the functional element 120 to the piezoelectric layer 130 to be reflected, thereby effectively confining the energy of the elastic waves within the piezoelectric layer 130.

[0028] Furthermore, in the piezoelectric device 100 of Embodiment 1, an example was described where the intermediate layer 140 each includes a low-velocity layer 141 and a high-velocity layer 142. However, the intermediate layer 140 may also be a structure in which multiple low-velocity layers 141 and high-velocity layers 142 are alternately stacked. Additionally, an adhesive layer may be provided between the low-velocity layer 141 and the high-velocity layer 142. Furthermore, the intermediate layer 140 may also be composed solely of the low-velocity layer 141.

[0029] An insulating layer 150 is formed on the upper surface 111 of the support substrate 110 in the region where the laminate 105 is not formed. The insulating layer 150 is disposed on the support substrate 110 in contact with the side surface of the laminate 105 (the surface in the laminate 105 that connects the surface of the functional element 120 to the surface of the support substrate 110) and the upper surface 131 of the piezoelectric layer 130 (the surface in the piezoelectric layer 130 in which the functional element 120 is formed). The insulating layer 150 is formed, for example, from resins with epoxy, polyimide, acrylic, urethane, etc. as main components, silicone resin, and spin-coated glass (SOG).

[0030] The cover layer 175 is supported by the support layer 170 at a position spaced apart from the functional element 120. The cover layer 175 is formed, for example, from a resin whose main components are epoxy, polyimide, acrylic, urethane, etc.

[0031] A support layer 170 is disposed on the upper surface of the insulating layer 150 to surround the laminate 105. The support layer 170 is formed, for example, of a resin comprising organic materials such as polyimide, epoxy resin, cyclic olefin resin, benzocyclobutene, polybenzoxazole, phenolic resin, silicone, or acrylic resin. A hollow space 190 is formed between the laminate 105 and the cover layer 175 through the support layer 170 and the cover layer 175. Functional elements 120 are formed within this hollow space 190.

[0032] A columnar electrode 180 is formed through the support layer 170 and the cover layer 175. A first end 181 of the columnar electrode 180 on the cover layer 175 side is connected to a connection electrode 185 for connecting to an external device. A second end 182 of the columnar electrode 180 is electrically connected to a wiring electrode 160 formed on the upper surface of the insulating layer 150. The wiring electrode 160 extends from the upper surface of the insulating layer 150 to the upper surface of the piezoelectric layer 130 and is connected to a functional element 120 formed on the piezoelectric layer 130. The functional element 120 and the connection electrode 185 are electrically connected via the wiring electrode 160 and the columnar electrode 180. Furthermore, a wiring electrode 161 is formed on the upper surface 131 of the piezoelectric layer 130. The functional elements 120 are electrically connected to each other via the wiring electrode 161.

[0033] In the piezoelectric device 100 of Embodiment 1, the surface roughness of the first region RG1 forming the laminate 105 in the support substrate 110 is different from the surface roughness of the second region RG2 forming the insulating layer 150. Specifically, the surface roughness R2 of the second region RG2 is greater than the surface roughness R1 of the first region RG1 (R1 < R2).

[0034] In a structure like piezoelectric device 100, where an intermediate layer 140 is formed between the piezoelectric layer 130 and the support substrate 110, together with the elastic wave of the main mode propagating in the in-plane direction of the piezoelectric layer 130 based on the spacing of the IDT electrodes, a resonant mode propagating in the thickness direction (Z-axis direction) corresponding to the thickness of the intermediate layer 140 is formed. Due to the generation of this resonant mode in the thickness direction, spurious higher-order modes with frequencies higher than the resonant frequency of the main mode are inevitably generated. This spurious noise superimposed on the high-frequency signal of the main mode can potentially affect the characteristics of the piezoelectric device.

[0035] Furthermore, the resulting stray high-order modes sometimes leak from the laminate 105 to the insulating layer 150, which may affect the characteristics of other adjacent piezoelectric devices.

[0036] Regarding the resonant modes in the thickness direction mentioned above, the more fixed the thickness of the intermediate layer 140, the stronger the resonance, and consequently, the stronger the spurious emissions of higher-order modes. Therefore, by increasing the surface roughness of the support substrate 110 forming the first region RG1 of the intermediate layer 140, the thickness of the intermediate layer 140 becomes non-uniform, thereby reducing the intensity of the generated spurious emissions. However, if the surface roughness of the first region RG1 is too large, it may increase the influence on the main mode signal, thus degrading the characteristics. Therefore, the surface roughness of the first region RG1 is limited to a range that does not affect the main mode.

[0037] On the other hand, regarding the second region RG2 forming the insulating layer 150, it has little impact on the main mode. Therefore, it is preferable to minimize the impact on other adjacent piezoelectric devices by increasing the surface roughness as much as possible to reduce the intensity of stray leakage.

[0038] Therefore, in the piezoelectric device of Embodiment 1, the surface roughness of the support substrate 110 is made greater than the surface roughness of the support substrate formed by conventional processes. Furthermore, the surface roughness R2 of the second region RG2 forming the insulating layer 150 is made greater than the surface roughness R1 of the first region RG1 forming the laminate 105 (R1 < R2). Specifically, if expressed in terms of arithmetic mean roughness Ra, the surface roughness R1 in the first region RG1 is set in the range of 0.1 nm < R1 < 0.3 nm, and the surface roughness R2 in the second region RG2 is set in the range of 0.1 nm < R2 < 100 nm (where R1 < R2).

[0039] In the manufacturing process, before forming the intermediate layer 140 on the support substrate 110, the surface of the support substrate 110 is processed using laser polishing or ion polishing. Next, the intermediate layer 140 and the piezoelectric layer 130 are formed integrally on the support substrate 110, and then the portion of the laminate 105 forming the insulating layer 150 is removed by laser polishing or etching. At this time, the portion of the laminate 105 in the second region RG2 is removed using conditions that result in a rougher surface roughness compared to the surface processing conditions performed before forming the laminate 105. By employing this process, the surface roughness R2 of the second region RG2 can be made greater than the surface roughness R1 of the first region RG1.

[0040] As described above, in piezoelectric devices, by making the surface roughness of the region of the support substrate forming the insulating layer greater than the surface roughness of the region of the support substrate forming the laminate, the effects of generated higher-order mode strays can be reduced.

[0041] Furthermore, by roughening the surface roughness of the support substrate, the contact area between the intermediate layer and the support substrate, as well as between the insulating layer and the support substrate, is increased, thereby increasing the bonding strength of the intermediate layer and the insulating layer and suppressing peeling from the support substrate.

[0042] [Implementation Method 2]

[0043] In Embodiment 1, the surface roughness of the second region RG2 forming the insulating layer was described as being approximately uniform. However, the intensity of leakage strays is stronger closer to the laminate and gradually decreases as it moves away from the laminate. Therefore, in Embodiment 2, a structure is described in which the surface roughness of the portion of the second region RG2 closer to the laminate is made greater than that of the portion relatively farther away from the laminate, thereby more effectively attenuating the leakage strays.

[0044] Figure 3 This is a partial cross-sectional view of the piezoelectric device 100A according to Embodiment 2. In the piezoelectric device 100A, the support substrate 110 of the piezoelectric device 100 of Embodiment 1 is replaced with the structure of the support substrate 110A. Therefore, in the following description, the description of elements that are the same as those of the piezoelectric device 100 will not be repeated.

[0045] Reference Figure 3 In the piezoelectric device 100A, in the support substrate 110A, the second region RG2 forming the insulating layer 150 is divided into a first portion RG2-1 and a second portion RG2-2. The first portion RG2-1 is the region in the support substrate 110A adjacent to the first region RG1 forming the laminate 105. The second portion RG2-2 is the region farther away from the first region RG1 than the first portion RG2-1.

[0046] Furthermore, the surface roughness R21 of the first part RG2-1 is made greater than the surface roughness R22 of the second part RG2-2. That is, the relationship between the surface roughness of the first region RG1 and the second region RG2-2 is R1 < R22 < R21.

[0047] By setting the surface roughness of the support substrate 110A as described above, leakage strays can be effectively reduced in the region near the laminate.

[0048] Furthermore, in the example above, the case where the surface roughness R22 of the second part RG2-2 of the second region RG2 is greater than the surface roughness R1 of the first region RG1 was explained. However, if leakage stray particles can be sufficiently reduced by the first part RG2-1 of the second region RG2, the surface roughness R22 of the second part RG2-2 may also be less than the surface roughness R1 of the first region RG1.

[0049] [Implementation Method 3]

[0050] In Embodiment 3, a structure for reducing stress at the boundary between the first region and the second region in the support substrate will be described.

[0051] Figure 4This is a partial cross-sectional view of the piezoelectric device 100B according to Embodiment 3. In the piezoelectric device 100B, the support substrate 110 of the piezoelectric device 100 of Embodiment 1 is replaced with the structure of the support substrate 110B. Therefore, in the following description, the description of elements that are the same as those of the piezoelectric device 100 will not be repeated.

[0052] Reference Figure 4 In the support substrate 110B of the piezoelectric device 100B, the thickness (dimension in the Z-axis direction) of the portion forming the second region RG2 of the insulating layer 150 is thinner than the thickness of the portion forming the first region RG1 of the laminate 105. In other words, the upper surface of the portion of the second region RG2 is located in the negative Z-axis direction than the upper surface of the first region RG1. Furthermore, an inclined region RG3, whose thickness continuously varies, is formed between the first region RG1 and the second region RG2. That is, the second region RG2 is adjacent to the first region RG1 across the inclined region RG3. In addition, the inclined region RG3 can be a shape with a straight cross-section or a shape with an arc cross-section.

[0053] like Figure 4 As shown, when the side of the laminate is formed perpendicular to the support substrate, stress tends to concentrate at the boundary between the laminate and the support substrate, which may lead to the laminate or insulating layer peeling off from the support substrate or cracks forming on the support substrate.

[0054] Like the piezoelectric device 100B in Embodiment 3, by providing an inclined region RG3 between the first region RG1 and the second region RG2 of the support substrate 110B, stress concentration at the boundary between the laminate 105 and the support substrate 110B can be alleviated. This suppresses the peeling of the laminate 105 and the insulating layer 150 from the support substrate 110B, as well as damage to the support substrate 110B.

[0055] It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of this disclosure is not shown by the description of the above embodiments, but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0056] Explanation of reference numerals in the attached figures

[0057] 100, 100A, 100B: Piezoelectric devices; 105: Laminated structure; 110, 110A, 110B: Support substrate; 120: Functional element; 130: Piezoelectric layer; 140: Intermediate layer; 141: Low-velocity layer; 142: High-velocity layer; 150: Insulating layer; 160, 161: Wiring electrodes; 170: Support layer; 175: Cover layer; 180: Columnar electrode; 181: First end; 182: Second end; 185: Connecting electrode; 190: Hollow space.

Claims

1. A piezoelectric device comprising: a support substrate; an intermediate layer provided on a first region of the support substrate; a piezoelectric layer provided on the intermediate layer; a functional element formed on the piezoelectric layer; and an insulating layer provided on the support substrate in a second region adjacent to the first region, wherein a surface roughness of the support substrate in the second region is greater than a surface roughness of the support substrate in the first region.

2. The piezoelectric device according to claim 1, wherein the second region includes a first portion adjacent to the first region and a second portion farther from the first region than the first portion, and wherein a surface roughness of the support substrate in the first portion is greater than a surface roughness of the support substrate in the second portion.

3. The piezoelectric device according to claim 1 or 2, wherein a thickness of the support substrate in the second region is thinner than a thickness of the support substrate in the first region, and wherein the support substrate has a sloped region between the first region and the second region.

4. The piezoelectric device according to claim 1 or 2, wherein the intermediate layer includes: a high acoustic velocity layer provided on the support substrate to propagate an elastic wave at a high velocity compared to a velocity of an elastic wave propagated in the piezoelectric layer; and a low acoustic velocity layer provided between the high acoustic velocity layer and the piezoelectric layer to propagate an elastic wave at a low velocity compared to the velocity of the elastic wave propagated in the piezoelectric layer.

5. The piezoelectric device according to claim 3, wherein the intermediate layer includes: a high acoustic velocity layer provided on the support substrate to propagate an elastic wave at a high velocity compared to a velocity of an elastic wave propagated in the piezoelectric layer; and a low acoustic velocity layer provided between the high acoustic velocity layer and the piezoelectric layer to propagate an elastic wave at a low velocity compared to the velocity of the elastic wave propagated in the piezoelectric layer. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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