Elastic wave device, filter, multiplexer, and method for manufacturing an elastic wave device

Abstract

The present invention provides an elastic wave device that can suppress spurious emissions and prevent a decrease in the bonding strength of the insulating layer. [Solution] The elastic wave device 100 comprises a substrate 10, a piezoelectric layer 14 provided on the substrate 10, a pair of comb-shaped electrodes 20 provided on the piezoelectric layer 14 and each having a plurality of electrode fingers 27, and an insulating layer 13 provided between the substrate 10 and the piezoelectric layer 14, having a plurality of modified regions 30 that overlap with an intersection region 25 where the plurality of electrode fingers 27 of the pair of comb-shaped electrodes 20 intersect in a plan view, and the plurality of modified regions 30 having a different crystalline state from the region 31 surrounding the plurality of modified regions 30.

Description

Technical Field

[0001] The present invention relates to an elastic wave device, a filter, a multiplexer, and a method for manufacturing an elastic wave device.

Background Art

[0002] In an elastic wave device, it is known to bond a piezoelectric substrate to a support substrate. It is known that spurious caused by bulk waves can be suppressed by making the thickness of the piezoelectric substrate bonded to the support substrate equal to or less than the wavelength of the elastic wave (for example, Patent Document 1). It is known that the influence of bulk waves can be suppressed by making the support substrate have a polycrystalline structure or a porous structure (for example, Patent Document 2). It is known that the influence of bulk waves can be suppressed by providing a modified region in the piezoelectric substrate (for example, Patent Document 3). In a configuration in which an insulating layer is provided between the substrate and the piezoelectric layer, it is known that spurious can be suppressed by scattering the energy of the elastic wave by providing a plurality of regions made of a material different from other regions in the insulating layer (for example, Patent Document 4).

Prior Art Documents

Patent Documents

[0003] [[ID=​​​​​​​​​​​​​​​​​​​​​​​​Patent Document 1 does not describe the case where an insulating layer is provided between the support substrate and the piezoelectric substrate. When the support substrate has a polycrystalline or porous structure, as in Patent Document 2, and when a modified region is provided in the piezoelectric substrate, as in Patent Document 3, the functions of the support substrate and the piezoelectric substrate may be impaired. When the insulating layer provided between the substrate and the piezoelectric layer has multiple regions made of different materials from other regions, as in Patent Document 4, the bonding strength of the insulating layer may decrease.

[0005] This invention has been made in view of the above problems, and aims to suppress spurious emissions and reduce the bonding strength of the insulating layer. [Means for solving the problem]

[0006] The present invention relates to an elastic wave device comprising: a substrate; a piezoelectric layer provided on the substrate; a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers; and an insulating layer provided between the substrate and the piezoelectric layer, having a plurality of modified regions that overlap with the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect in a plan view, wherein the plurality of modified regions have a different crystalline state from the region surrounding the plurality of modified regions.

[0007] In the above configuration, the insulating layer has a first layer provided between the substrate and the piezoelectric layer, and a second layer provided between the first layer and the piezoelectric layer, and the plurality of modified regions can be configured to be provided at the interface between the first layer and the second layer, extending across both the first layer and the second layer.

[0008] In the above configuration, the speed of sound of the bulk wave in the first layer can be set to be faster than the speed of sound of the bulk wave in the second layer.

[0009] In the above configuration, the piezoelectric layer may be a lithium tantalate layer or a lithium niobate layer, the first layer may be an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, an aluminum oxide nitride layer, a silicon carbide layer, or a silicon layer, and the second layer may be a silicon oxide layer.

[0010] In the above configuration, the distance between the surface of the piezoelectric layer on which the pair of comb-shaped electrodes are provided and the surface of the second layer opposite to the piezoelectric layer can be configured to be 4 times or less the average pitch of the plurality of electrode fingers.

[0011] In the above configuration, the crystalline state of the surrounding region can be single crystal or polycrystalline, while the crystalline state of the multiple modified regions can be amorphous.

[0012] The present invention is a filter that includes the elastic wave device described above.

[0013] The present invention is a multiplexer comprising the filter described above.

[0014] The present invention is a method for manufacturing an elastic wave device, comprising the steps of: forming an insulating layer on a substrate; forming a piezoelectric layer on the insulating layer; forming a pair of comb-shaped electrodes, each having a plurality of electrode fingers, on the piezoelectric layer; and, after forming the insulating layer on the substrate, irradiating the insulating layer with laser light to form a plurality of modified regions that overlap with the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect in a plan view, and which have a different crystalline state from the surrounding region.

[0015] In the above configuration, the step of forming the insulating layer includes the step of forming a first layer on the substrate and the step of forming a second layer on the first layer, and the step of forming the plurality of modified regions can be configured to form the plurality of modified regions extending over both the first and second layers by irradiating the interface between the first and second layers with the laser light. [Effects of the Invention]

[0016] According to the present invention, spurious can be suppressed and a decrease in the bonding strength of the insulating layer can be suppressed.

Brief Description of the Drawings

[0017] [Figure 1] FIG. 1(a) and FIG. 1(b) are a plan view and a cross-sectional view of an elastic wave device according to Example 1. [Figure 2] FIGS. 2(a) to 2(d) are cross-sectional views showing a method for manufacturing an elastic wave device according to Example 1. [Figure 3] FIG. 3(a) and FIG. 3(b) are cross-sectional views of elastic wave devices according to Comparative Example 1 and Comparative Example 2. [Figure 4] FIG. 4 is a cross-sectional view showing the effect of the elastic wave device according to Example 1. [Figure 5] FIGS. 5(a) and 5(b) are cross-sectional views of elastic wave devices according to Modification Example 1 and Modification Example 2 of Example 1, and FIG. 5(c) is a plan view of an elastic wave device according to Modification Example 3 of Example 1. [Figure 6] FIG. 6 is a cross-sectional view of an elastic wave device according to Example 2. [Figure 7] FIGS. 7(a) and 7(b) are cross-sectional views of elastic wave devices according to Comparative Example 2 and Comparative Example 3. [Figure 8] FIG. 8 is a cross-sectional view showing the effect of the elastic wave device according to Example 2. [Figure 9] FIG. 9 is a cross-sectional view of an elastic wave device according to Modification Example 1 of Example 2. [Figure 10] FIG. 10(a) is a circuit diagram of a filter according to Example 3, and FIG. 10(b) is a circuit diagram of a duplexer according to Modification Example 1 of Example 3. <00​​​​​​​​​​​​Example 1 describes an example in which an elastic wave device has an elastic wave resonator. Figures 1(a) and 1(b) are a plan view and a cross-sectional view of the elastic wave device 100 according to Example 1. The arrangement direction of the multiple electrode fingers 27 is the X direction, the extension direction of the electrode fingers 27 is the Y direction, and the stacking direction of the substrate 10 and the piezoelectric layer 14 is the Z direction. The X, Y, and Z directions do not necessarily correspond to the X-axis and Y-axis directions of the crystal orientation of the piezoelectric layer 14. If the piezoelectric layer 14 is a piezoelectric layer with rotational Y-cut X propagation, the X direction is the X-axis direction of the crystal orientation.

[0020] As shown in Figures 1(a) and 1(b), a piezoelectric layer 14 is provided on a substrate 10. An insulating layer 13 is provided between the substrate 10 and the piezoelectric layer 14. The insulating layer 13 includes a first layer 11 provided between the substrate 10 and the piezoelectric layer 14, and a second layer 12 provided between the first layer 11 and the piezoelectric layer 14. The thickness of the first layer 11 is T1, the thickness of the second layer 12 is T2, and the thickness of the piezoelectric layer 14 is T4.

[0021] An elastic wave resonator 26 is provided on the piezoelectric layer 14. The elastic wave resonator 26 has an IDT (Interdigital Transducer) 22 and a reflector 24. The reflector 24 is provided on both sides of the IDT 22 in the X direction. The IDT 22 and the reflector 24 are formed by a metal film 16 on the piezoelectric layer 14.

[0022] The IDT22 comprises a pair of opposing comb-shaped electrodes 20. Each comb-shaped electrode 20 includes multiple electrode fingers 27 and a busbar 28 to which the multiple electrode fingers 27 are connected. The region where the electrode fingers 27 of the pair of comb-shaped electrodes 20 intersect is the intersection region 25. In at least a portion of the intersection region 25, the pair of comb-shaped electrodes 20 have alternating electrode fingers 27. The elastic wave that mainly excites the multiple electrode fingers 27 in the intersection region 25 propagates mainly in the X direction. The pitch of the electrode fingers 27 of one of the pair of comb-shaped electrodes 20 is approximately equal to the wavelength λ of the elastic wave. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 27. The average pitch D of the electrode fingers 27 can be calculated by dividing the width of the IDT22 in the X direction by the number of electrode fingers 27. The reflector 24 reflects the elastic wave (surface acoustic wave) excited by the electrode fingers 27 of the IDT22. As a result, the elastic waves are confined within the intersection region 25 of IDT22.

[0023] Multiple modified regions 30 are provided in the insulating layer 13. The modified regions 30 are provided, for example, in the first layer 11. The modified regions 30 are provided, for example, in a grid pattern so as to overlap with the intersecting regions 25 in a plan view. The modified regions 30 are regions formed by irradiating the first layer 11 with laser light and are amorphous regions. That is, the modified regions 30 are regions formed from the same material as other regions of the first layer 11 but with a different crystalline state; in other words, they are regions formed from the same material as the surrounding regions 31 but with a different crystalline state. The multiple modified regions 30 are formed with approximately the same pitch (spacing) P1 in the X direction and approximately the same pitch (spacing) P2 in the Y direction, and are formed with approximately the same size L. The pitches P1 and P2 are, for example, 0.6λ to 3.0λ. The pitches P1 and P2 may be the same size or different. The size L is, for example, 0.9λ to 5.4λ.

[0024] The piezoelectric layer 14 is, for example, a single-crystal lithium tantalate (LiTaO3) layer or a single-crystal lithium niobate (LiNbO3) layer, and is, for example, a rotational Y-cut X-propagation lithium tantalate layer or a rotational Y-cut X-propagation lithium niobate layer.

[0025] The substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a silica substrate, or a silicon carbide substrate. The sapphire substrate is a single-crystal Al2O3 substrate, the alumina substrate is a polycrystalline or amorphous Al2O3 substrate, and the silicon substrate is a single-crystal or polycrystalline Si substrate. The spinel substrate is a polycrystalline or amorphous MgAl2O4 substrate, the quartz substrate is a single-crystal SiO2 substrate, the silica substrate is a polycrystalline or amorphous SiO2 substrate, and the silicon carbide substrate is a polycrystalline or single-crystal SiC substrate. The coefficient of linear expansion of the substrate 10 in the X direction is smaller than the coefficient of linear expansion of the piezoelectric layer 14 in the X direction. This makes it possible to reduce the frequency-temperature dependence of the elastic wave resonator.

[0026] The speed of sound of the bulk wave propagating through the first layer 11 is faster than the speed of sound of the bulk wave propagating through the second layer 12 and the piezoelectric layer 14. This confines the energy of the main response elastic wave within the piezoelectric layer 14 and the second layer 12. The speed of sound of the bulk wave propagating through the first layer 11 is preferably 1.1 times or more, and more preferably 1.2 times or more, than the speed of sound of the bulk wave propagating through the second layer 12. If the speed of sound of the bulk wave in the first layer 11 becomes too fast, the bulk wave is more likely to be reflected at the interface 15 between the first layer 11 and the second layer 12. Therefore, the speed of sound of the bulk wave propagating through the first layer 11 is preferably 2.0 times or less, and more preferably 1.5 times or less, than the speed of sound of the bulk wave propagating through the second layer 12. The speed of sound of the bulk wave propagating through the substrate 10 is faster than the speed of sound of the bulk wave propagating through the first layer 11, for example, 1.1 times or more. In Example 1, the first layer 11 is, for example, polycrystalline or single-crystal, and is an aluminum oxide layer, silicon nitride layer, aluminum nitride layer, aluminum oxide nitride layer, silicon carbide layer, or silicon layer. From the viewpoint of confining elastic waves within the second layer 12 and the piezoelectric layer 14, the thickness T1 of the first layer 11 is preferably 0.3λ or more, more preferably 1.0λ or more, and even more preferably 2.0λ or more. From the viewpoint of improving the characteristics, the thickness T1 is preferably 10λ or less. The speed of sound of the bulk wave in each layer is the speed of sound of the transverse wave V S And, if the shear modulus is G and the density is ρ, it can be expressed by equation 1.

number

number

[0027] The second layer 12 is, for example, a temperature compensation film, and has a temperature coefficient of elasticity with the opposite sign to the sign of the temperature coefficient of elasticity of the piezoelectric layer 14. For example, the temperature coefficient of elasticity of the piezoelectric layer 14 is negative, and the temperature coefficient of elasticity of the second layer 12 is positive. The second layer 12 is, for example, a silicon oxide (SiO2) layer that is additive-free or contains additive elements such as fluorine, and is, for example, polycrystalline or single-crystal. This makes it possible to reduce the frequency temperature coefficient of the elastic wave resonator. When the second layer 12 is a silicon oxide layer, the speed of sound of bulk waves propagating through the second layer 12 is slower than the speed of sound of bulk waves propagating through the piezoelectric layer 14.

[0028] For the second layer 12 to have a temperature compensation function, it is required that a certain amount of the energy of the main response elastic wave be present within the second layer 12. Although the range in which the energy of the surface acoustic wave is concentrated depends on the type of surface acoustic wave, typically the energy of the surface acoustic wave is concentrated in the range of 2.0λ from the upper surface of the piezoelectric layer 14, and particularly concentrated in the range of 1.0λ from the upper surface of the piezoelectric layer 14. Therefore, the distance from the lower surface of the second layer 12 to the upper surface of the piezoelectric layer 14 (thickness T2 + thickness T4) is preferably 2.0λ or less, and more preferably 1.0λ or less. In order for the energy of the surface acoustic wave to be present in the second layer 12, the thickness T4 of the piezoelectric layer 14 is preferably 1.0λ or less, and more preferably 0.6λ or less. If the piezoelectric layer 14 becomes too thin, it becomes difficult to excite the elastic wave, so the thickness T4 is preferably 0.1λ or more, and more preferably 0.2λ or more.

[0029] The metal film 16 is, for example, a film mainly composed of aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesion film such as a titanium (Ti) film, a chromium (Cr) film, or a titanium nitride (TiN) film may be provided between the electrode finger 27 and the piezoelectric layer 14. The adhesion film is thinner than the electrode finger 27. An insulating layer may be provided so as to cover the electrode finger 27. The insulating layer functions as a protective film or a temperature compensating film.

[0030] [Manufacturing method] Figures 2(a) to 2(d) are cross-sectional views showing a method for manufacturing an elastic wave device 100 according to Example 1. As shown in Figure 2(a), a first layer 11 is formed on a substrate 10. The first layer 11 is formed by depositing a film using, for example, sputtering, CVD (Chemical Vapor Deposition), or vacuum deposition. This allows for the formation of a polycrystalline first layer 11. Alternatively, the first layer 11 may be formed by bonding it to the substrate 10 using, for example, a surface activation method, and then achieving a desired thickness using CMP (Chemical Mechanical Polishing). In this case, a single-crystal first layer 11 can be formed.

[0031] As shown in Figure 2(b), a second layer 12 is formed on the first layer 11. The second layer 12 is formed by depositing a film using, for example, sputtering, CVD, or vacuum deposition. This allows for the formation of a polycrystalline second layer 12. Alternatively, the second layer 12 may be formed by bonding it to the first layer 11 using, for example, a surface activation method, and then using CMP to achieve the desired thickness. In this case, a single-crystal second layer 12 can be formed. An insulating layer 13 is formed by the first layer 11 and the second layer 12.

[0032] As shown in Figure 2(c), the piezoelectric layer 14 is bonded to the second layer 12, for example, using a surface activation method, and then the piezoelectric layer 14 is polished to the desired thickness, for example, using a CMP method. Next, a metal film 16 is deposited on the piezoelectric layer 14, and then the metal film 16 is patterned into the desired shape. This forms the IDT 22 and reflector 24 on the piezoelectric layer 14. The metal film 16 is deposited using, for example, sputtering, CVD, or vacuum deposition. The patterning of the metal film 16 is done using, for example, photolithography and etching.

[0033] As shown in Figure 2(d), laser light 50 is irradiated from the bottom surface (top surface in Figure 2(d)) of the substrate 10. The laser light 50 is irradiated so as to focus within the first layer 11, for example. Modified regions 30 are formed in the area where the laser light 50 is focused. The laser light 50 is, for example, pulsed light, and by irradiating the substrate 10 with the laser light 50 as indicated by arrow 52, ​​multiple modified regions 30 are formed within the first layer 11 at the same intervals and of the same size. The laser light 50 is, for example, the second harmonic of an Nd:YAG laser, and the wavelength of the laser light 50 is approximately 500 nm. The power of the laser light 50 is, for example, 0.01 W, and the scanning speed is, for example, 360 mm / second. As a result, the elastic wave device 100 according to Example 1 is formed.

[0034] [Comparative Example] Figure 3(a) is a cross-sectional view of the elastic wave device 500 according to Comparative Example 1. As shown in Figure 3(a), in Comparative Example 1, a modified region is not formed in the first layer 11. The other configurations are the same as in Example 1, so their description is omitted. The electrode fingers 27 excite spurious response unwanted waves 54 in addition to the main response surface acoustic wave. The surface acoustic wave is, for example, SH (Shear Horizontal), and the unwanted wave 54 is, for example, a bulk wave. The unwanted wave 54 is reflected at the interface 15 between the first layer 11 and the second layer 12 and at the interface 17 between the substrate 10 and the first layer 11, resulting in a spurious response. In Comparative Example 1, the spurious response is large.

[0035] Figure 3(b) is a cross-sectional view of the elastic wave device 510 according to Comparative Example 2. As shown in Figure 3(b), in Comparative Example 2, an embedded layer 32 having an upper surface is provided on the first layer 11 at the interface 15 between the first layer 11 and the second layer 12. The embedded layer 32 is a layer made of a different material from the first layer 11. No modified region is formed in the first layer 11. The other configurations are the same as in Example 1, so their description is omitted. The unwanted waves 54 excited by the electrode fingers 27 are scattered in the embedded layer 32. As a result, the spurious response is suppressed compared to Comparative Example 1. However, in Comparative Example 2, the embedded layer 32 is embedded in a recess provided on the upper surface of the first layer 11, and then the second layer 12 is formed on the first layer 11. The upper surface of the first layer 11 may have irregularities formed by the embedded layer 32. As a result, voids may occur between the first layer 11 and the second layer 12, and the bonding strength between the first layer 11 and the second layer 12 may decrease.

[0036] [Effects of Example 1] Figure 4 is a cross-sectional view showing the effect of the elastic wave device 100 according to Example 1. As shown in Figure 4, in Example 1, a modified region 30 is provided within the first layer 11. Therefore, unwanted waves 54 are scattered in the modified region 30, and spurious responses can be suppressed. Furthermore, since the modified region 30 is formed by irradiating the first layer 11 with laser light 50 after forming the second layer 12 on the first layer 11, a decrease in bonding strength between the first layer 11 and the second layer 12 can be suppressed.

[0037] [Differentiation] Figure 5(a) is a cross-sectional view of the elastic wave device 110 according to Modification 1 of Example 1. As shown in Figure 5(a), in Modification 1 of Example 1, when a plurality of modified regions 30 arranged in the X and Y directions within the first layer 11 are considered as one modified region group 35, the plurality of modified region groups 35 are provided in the Z direction. The modified regions 30 included in each of the adjacent modified region groups 35 in the Z direction are formed with offsets in the X and Y directions. That is, in a cross-sectional view, the plurality of modified regions 30 are provided in a staggered pattern. The other configurations are the same as in Example 1, so their description is omitted.

[0038] Figure 5(b) is a cross-sectional view of an elastic wave device 120 according to a modified example 2 of Example 1. As shown in Figure 5(b), in modified example 2 of Example 1, the insulating layer 13 has a third layer 18 between the substrate 10 and the first layer 11. The bulk wave propagating through the third layer 18 is slower than the bulk wave propagating through the first layer 11. In modified example 2 of Example 1, the first layer 11 is, for example, polycrystalline or single-crystal, and is an aluminum oxide layer, aluminum oxide nitride layer, aluminum nitride layer, silicon layer, silicon nitride layer, silicon carbide layer, titanium nitride layer, or diamond-like carbon layer. The third layer 18 is, for example, polycrystalline or single-crystal, and is an aluminum oxide layer, silicon nitride layer, aluminum nitride layer, silicon layer, or silicon carbide layer. In addition to the first layer 11 having a modified region 30, the third layer 18 has a modified region 30a. The modified region 30a is a region in the third layer 18 that is formed from the same material as the surrounding region 31a, but with a different crystalline state. The other components are the same as in Example 1, so their description is omitted.

[0039] Figure 5(c) is a plan view of the elastic wave device 130 according to Modification 3 of Example 1. As shown in Figure 5(c), in Modification 3 of Example 1, the multiple modification regions 30 are arranged in a staggered pattern in a plan view. That is, if the modification regions 30 arranged in the X direction are considered as one group of modification regions 36, the modification regions 30 included in each adjacent group of modification regions 36 in the Y direction are formed with a shift in the X direction. The other configurations are the same as in Example 1, so their explanation is omitted.

[0040] In Example 1 and its modified form, the insulating layer 13 between the substrate 10 and the piezoelectric layer 14 is provided with multiple modified regions 30 that overlap the intersection region 25 in a plan view and have a different crystalline state from the surrounding region 31. As a result, unwanted waves 54 are scattered in the modified regions 30, thereby suppressing spurious responses. Furthermore, the modified regions 30, which have a different crystalline state from the surrounding region 31, are formed by irradiating the insulating layer 13 with laser light 50 after forming the insulating layer 13 on the substrate 10, as shown in Figure 2(d). Therefore, a decrease in the bonding strength of the insulating layer 13 can be suppressed.

[0041] Furthermore, in Example 1 and its modified form, the crystalline state of the surrounding region 31 is single crystal or polycrystalline, while the crystalline state of the multiple modified regions 30, 30a is amorphous. This allows the modified region 30 that scatters unwanted waves 54 to be formed by irradiation with laser light 50. [Examples]

[0042] Figure 6 is a cross-sectional view of the elastic wave device 200 according to Example 2. As shown in Figure 6, in Example 2, the modified region 30b is provided at the interface 15 between the first layer 11 and the second layer 12, extending across both the first layer 11 and the second layer 12. The modified region 30b is formed by irradiating the interface 15 between the first layer 11 and the second layer 12 with laser light. The portion of the modified region 30b located in the first layer 11 is formed of the same material as the surrounding region 31b in the first layer 11, but with a different crystalline state. The portion of the modified region 30b located in the second layer 12 is formed of the same material as the surrounding region 31c in the second layer 12, but with a different crystalline state. The other configurations are the same as in Example 1, so their description is omitted.

[0043] [Comparative Example] Figure 7(a) is a cross-sectional view of the elastic wave device 510 according to Comparative Example 2. As shown in Figure 7(a), in Comparative Example 2, as described above, an embedded layer 32 having an upper surface is provided on the first layer 11 at the interface 15 between the first layer 11 and the second layer 12. In this case, unwanted waves 54 that pass through the interface 15 are scattered in the embedded layer 32, but some of the unwanted waves 54 are reflected at the interface 15. Therefore, the suppression of spurious response is not sufficient.

[0044] Figure 7(b) is a cross-sectional view of the elastic wave device 520 according to Comparative Example 3. As shown in Figure 7(b), in Comparative Example 3, an embedded layer 34 having a lower surface is provided on the second layer 12 at the interface 15 between the first layer 11 and the second layer 12. The embedded layer 34 is a layer made of a different material from the second layer 12. The other configurations are the same as in Example 1, so their description is omitted. Unwanted waves 54 are scattered by the embedded layer 34 before being reflected at the interface 15. However, since the embedded layer 34 is provided on the second layer 12, it cannot scatter the unwanted waves 54 passing through the interface 15, and unwanted waves 54 are generated that are reflected at the interface 17. For this reason, the suppression of spurious response is not sufficient. In addition, in Comparative Example 3, after forming the embedded layer 34 on the first layer 11, the second layer 12 is formed on the first layer 11 so as to cover the embedded layer 34. As a result, voids may occur between the first layer 11 and the second layer 12, which may reduce the bonding strength between the first layer 11 and the second layer 12.

[0045] [Effects of Example 2] Figure 8 is a cross-sectional view showing the effect of the elastic wave device 200 according to Example 2. As shown in Figure 8, in Example 2, a modified region 30b is provided at the interface 15 between the first layer 11 and the second layer 12, extending across both the first layer 11 and the second layer 12. Therefore, unwanted waves 54 are scattered by the portion of the modified region 30b located within the second layer 12 before being reflected at the interface 15. Furthermore, since the modified region 30b is formed extending from the first layer 11 to the second layer 12, a large modified region 30b can be formed. Thus, unwanted waves 54 that have passed through the interface 15 are scattered by the portion of the modified region 30b located within the first layer 11. Therefore, spurious response can be suppressed. In addition, since the modified region 30b is formed by irradiating the interface 15 with laser light 50 after forming the second layer 12 on the first layer 11, a decrease in bonding strength between the first layer 11 and the second layer 12 can be suppressed.

[0046] [Differentiation] Figure 9 is a cross-sectional view of an elastic wave device 210 according to Modification 1 of Example 2. As shown in Figure 9, in Modification 1 of Example 2, similar to Modification 2 of Example 1, the insulating layer 13 has a third layer 18 between the substrate 10 and the first layer 11. In addition to having multiple modified regions 30b at the interface 15 between the first layer 11 and the second layer 12, multiple modified regions 30c are provided at the interface 19 between the first layer 11 and the third layer 18, extending across both the first layer 11 and the third layer 18. The modified regions 30c are formed by irradiation with laser light, similar to the modified regions 30b. The portion of the modified region 30c located in the first layer 11 is formed of the same material as the region 31d surrounding the modified region 30c in the first layer 11, but with a different crystalline state. The portion of the modified region 30c located in the third layer 18 is formed of the same material as the region 31e surrounding the modified region 30c in the third layer 18, but with a different crystalline state. The other components are the same as in Example 1, so their description will be omitted.

[0047] According to Example 2 and its modified form, the insulating layer 13 has a first layer 11 and a second layer 12. The modified region 30b is provided at the interface 15 between the first layer 11 and the second layer 12, extending across both the first layer 11 and the second layer 12. As a result, as explained in Figure 8, the scattering of unwanted waves 54 by the modified region 30b is effectively performed, thereby suppressing spurious responses. Furthermore, since the modified region 30b is formed by irradiating the interface 15 between the first layer 11 and the second layer 12 with laser light 50 after forming the first layer 11 and the second layer 12 on the substrate 10, a decrease in the bonding strength between the first layer 11 and the second layer 12 can be suppressed.

[0048] Furthermore, in Example 2 and its modified form, the sound velocity of the bulk wave in the first layer 11 is faster than the sound velocity of the bulk wave in the second layer 12. In this case, unwanted waves 54 are reflected at the interface 15 between the first layer 11 and the second layer 12, making it easy for spurious responses to occur. Therefore, in this case, it is preferable to form a modified region 30b that extends across both the first layer 11 and the second layer 12 at the interface 15 between the first layer 11 and the second layer 12.

[0049] Furthermore, in Example 2 and its modified form, the piezoelectric layer 14 is a lithium tantalate layer or a lithium niobate layer. The first layer 11 is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, an aluminum oxide nitride layer, a silicon carbide layer, or a silicon layer. The second layer 12 is a silicon oxide layer. When the piezoelectric layer 14 is a lithium tantalate layer or a lithium niobate layer and the second layer 12 is a silicon oxide layer, the frequency temperature coefficient of the elastic wave resonator can be reduced. When the first layer 11 is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, an aluminum oxide nitride layer, a silicon carbide layer, or a silicon layer, the sound velocity of the bulk wave in the first layer 11 is faster than in the second layer 12, so the energy of the elastic wave of the main response can be confined within the piezoelectric layer 14 and the second layer 12. However, unwanted waves 54 are reflected at the interface 15 between the first layer 11 and the second layer 12, making it easier for spurious responses to occur. Therefore, in order to suppress spurious emissions, it is preferable to form a modified region 30b that extends across both the first layer 11 and the second layer 12 at the interface 15 between the first layer 11 and the second layer 12. However, in order to avoid impairing the temperature compensation function of the second layer 12, it is undesirable to form a large modified region in the second layer 12. From this point of view as well, it is preferable to form the modified region 30b across both the first layer 11 and the second layer 12.

[0050] Furthermore, in Example 2 and its modified form, the distance (thickness T2 + T4) between the surface of the piezoelectric layer 14 on which the elastic wave resonator 26 is provided and the surface of the second layer 12 opposite to the piezoelectric layer 14 is 2.0λ or less (4 times or less the average pitch D of the multiple electrode fingers 27). In this case, in order not to impair the temperature compensation function of the second layer 12, it is undesirable to provide a size-modified region in the second layer 12 or to form a large embedded layer 34 in the second layer 12 as in Comparative Example 3. Therefore, in order to suppress spurious response, it is preferable to form a modified region 30b that extends over both the first layer 11 and the second layer 12 at the interface 15 between the first layer 11 and the second layer 12.

[0051] In addition, in Example 2 and its modified form, the modified regions 30b and / or 30c may be arranged in a grid pattern in cross-sectional view, as in Modified Form 1 of Example 1, or in a grid pattern in plan view, as in Modified Form 3 of Example 1. [Examples]

[0052] Figure 10(a) is a circuit diagram of the filter 300 according to Embodiment 3. As shown in Figure 10(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. At least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3 can be an elastic wave device from Embodiments 1 and 2 and their modified versions. The number of resonators in the ladder-type filter can be set as appropriate. The filter may also be a multi-mode filter.

[0053] Figure 10(b) is a circuit diagram of a duplexer 310 according to Modification 1 of Example 3. As shown in Figure 10(b), a transmit filter 60 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 62 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 60 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 62 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 60 and the receive filter 62 can be the filter of Example 2. Although a duplexer has been described as an example of a multiplexer, a triplexer or quadplexer may also be used.

[0054] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of Symbols]

[0055] 10...Substrate, 11...First layer, 12...Second layer, 13...Insulating layer, 14...Piezoelectric layer, 15...Interface, 16...Metal film, 17...Interface, 19...Interface, 20...Comb-shaped electrode, 22...IDT, 24...Reflector, 25...Crossing region, 26...Elastic wave resonator, 27...Electrode fingers, 28...Busbar, 30, 30a, 30b, 30c...Modification region, 31, 31a, 31b, 3 1c, 31d, 31e... Surrounding region, 32... Embedding layer, 34... Embedding layer, 35... Modified region group, 36... Modified region group, 50... Laser light, 54... Unwanted waves, 60... Transmitting filter, 62... Receiving filter, 100, 110, 120, 130, 200, 210, 500, 510, 520... Elastic wave device, 300... Filter, 310... Duplexer

Claims

1. circuit board and A piezoelectric layer provided on the substrate, A pair of comb-shaped electrodes, each having multiple electrode fingers, are provided on the piezoelectric layer, An elastic wave device comprising: an insulating layer provided between the substrate and the piezoelectric layer, having a plurality of modified regions that overlap with the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect in a plan view, wherein the plurality of modified regions have a different crystalline state from the region surrounding the plurality of modified regions.

2. The insulating layer comprises a first layer provided between the substrate and the piezoelectric layer, and a second layer provided between the first layer and the piezoelectric layer. The elastic wave device according to claim 1, wherein the plurality of modified regions are provided at the interface between the first layer and the second layer, extending across both the first and second layers.

3. The elastic wave device according to claim 2, wherein the speed of sound of the bulk wave in the first layer is faster than the speed of sound of the bulk wave in the second layer.

4. The piezoelectric layer is a lithium tantalate layer or a lithium niobate layer. The first layer is an aluminum oxide layer, a silicon nitride layer, an aluminum nitride layer, an aluminum oxide nitride layer, a silicon carbide layer, or a silicon layer. The elastic wave device according to claim 2 or 3, wherein the second layer is a silicon oxide layer.

5. The elastic wave device according to claim 4, wherein the distance between the surface of the piezoelectric layer on which the pair of comb-shaped electrodes are provided and the surface of the second layer opposite to the piezoelectric layer is four times or less the average pitch of the plurality of electrode fingers.

6. The elastic wave device according to claim 1 or 2, wherein the crystalline state of the surrounding region is single crystal or polycrystalline, and the crystalline state of the plurality of modified regions is amorphous.

7. A filter comprising the elastic wave device according to claim 1 or 2.

8. A multiplexer comprising the filter described in claim 7.

9. A process of forming an insulating layer on a substrate, A step of forming a piezoelectric layer on the insulating layer, A step of forming a pair of comb-shaped electrodes, each having a plurality of electrode fingers, on the piezoelectric layer, A method for manufacturing an elastic wave device, comprising the steps of forming the insulating layer on the substrate, and then irradiating the insulating layer with laser light to form a plurality of modified regions that overlap with the intersection region where the plurality of electrode fingers of the pair of comb-shaped electrodes intersect in a plan view, and which have a different crystalline state from the surrounding region.

10. The step of forming the insulating layer includes the steps of forming a first layer on the substrate and forming a second layer on the first layer. The method for manufacturing an elastic wave device according to claim 9, wherein the step of forming the plurality of modified regions is to irradiate the interface between the first layer and the second layer with the laser light to form the plurality of modified regions extending over both the first layer and the second layer.

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