Acoustic wave device, filter, and manufacturing method of acoustic wave device

Abstract

To provide an acoustic wave device capable of suppressing leakage of a bulk wave to the outside.SOLUTION: An acoustic wave device 100 includes: a support substrate 10 having a concave part 17; an insulating film 15 filling the concave part 17;, a piezoelectric layer 16 provided from above the insulating film 15 to above the support substrate 10; and a pair of comb-shaped electrodes 20 provided on the piezoelectric layer 16 so as to overlap the insulating film 15 when viewed from above the support substrate 10 and including a plurality of electrode fingers 18. A manufacturing method of the acoustic wave device 100 includes the steps of: forming the concave part 17 in the support substrate 10; filling the concave part 17 with the insulating film 15; directly bonding the piezoelectric layer 16 to the insulating film 15 and the support substrate 10; and forming the pair of comb-shaped electrodes 20 including the plurality of electrode fingers 18 on the piezoelectric layer 16 so as to overlap the insulating film 15 when viewed from above the support substrate 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device, a filter, and a method for manufacturing an acoustic wave device. [Background technology]

[0002] Surface acoustic wave resonators are known as acoustic wave devices used in communication devices such as smartphones. Bonding a piezoelectric substrate that forms a surface acoustic wave resonator to a support substrate is known. Providing a low acoustic velocity layer between the piezoelectric substrate and the support substrate, which has a lower acoustic velocity than the piezoelectric substrate, is known (e.g., Patent Document 1). Providing a sealing portion on the piezoelectric substrate or the support substrate that seals the surface acoustic wave resonator in a gap is known (e.g., Patent Documents 2 and 3). Providing a groove in the piezoelectric substrate to prevent bulk waves propagating through the piezoelectric substrate from leaking to the outside is known (e.g., Patent Document 4). Known configurations include providing a recess in the support substrate below the surface acoustic wave resonator and providing an acoustic reflection film in the recess (e.g., Patent Documents 5 and 6). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-201345 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-246112 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-236387 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-336503 [Patent Document 5] International Publication No. 2016 / 052129 [Patent Document 6] Japanese Patent Application Laid-Open No. 2013-223025 Summary of the Invention [Problem to be solved by the invention]

[0004] When a piezoelectric layer is provided on a substrate via an insulating film such as a temperature compensation film, bulk waves excited by electrode fingers on the piezoelectric layer may propagate through the insulating film and leak to the outside.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to suppress leakage of bulk waves to the outside. [Means for solving the problem]

[0006] The present invention is an acoustic wave device comprising a substrate having a recess, an insulating film filled in the recess, a piezoelectric layer provided on top of the insulating film and extending over the substrate, and a pair of comb-shaped electrodes provided on the piezoelectric layer and overlapping the insulating film when viewed from above the substrate, the comb-shaped electrodes having a plurality of electrode fingers.

[0007] In the above configuration, at least a portion of the side wall of the recess may be inclined in cross section.

[0008] In the above configuration, the thickness of the piezoelectric layer may be equal to or less than twice the average pitch of the plurality of electrode fingers.

[0009] In the above configuration, the insulating film can include a first film which is a silicon oxide film or a silicon oxide film doped with fluorine, phosphorus, or boron, and which is spaced from the inner surface of the recess and overlaps the pair of comb electrodes when viewed from above the substrate, and a second film which is an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film and which is provided between the inner surface of the recess and the first film, and which surrounds the first film.

[0010] In the above configuration, the inner surface of the recess may have projections and recesses.

[0011] In the above configuration, the substrate may have another recess adjacent to the recess, and may be provided with another insulating film filled in the other recess, and another pair of comb-shaped electrodes provided on the piezoelectric layer overlapping the other insulating film when viewed from above the substrate, and having another plurality of electrode fingers, and the plurality of electrode fingers and the other plurality of electrode fingers may be arranged in a direction in which the recess and the other recess are adjacent to each other.

[0012] In the above configuration, the piezoelectric layer may be divided between the recess and the other recess.

[0013] The above configuration may further comprise a lid provided over the pair of comb electrodes with a gap therebetween, made of the same material as the substrate, and sealing the pair of comb electrodes in the gap.

[0014] The present invention is a filter including the acoustic wave device described above.

[0015] The present invention provides a method for manufacturing an acoustic wave device, comprising the steps of forming a recess in a substrate, filling the recess with an insulating film, directly bonding a piezoelectric layer to the insulating film and the substrate, and forming a pair of comb-shaped electrodes having multiple electrode fingers on the piezoelectric layer so as to overlap the insulating film when viewed from above the substrate. [Effects of the Invention]

[0016] According to the present invention, it is possible to suppress leakage of bulk waves to the outside. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Figure 2] 2(a) to 2(e) are cross-sectional views illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 3] FIG. 3 is a cross-sectional view of an acoustic wave device according to a comparative example. [Figure 4] FIG. 4A is a cross-sectional view illustrating a problem that occurs in the acoustic wave device according to the comparative example, and FIG. 4B is a cross-sectional view illustrating the effect of the acoustic wave device according to the first embodiment. [Figure 5] 5A to 5C are cross-sectional views of acoustic wave devices according to first to third modifications of the first embodiment. [Figure 6] 6A and 6B are cross-sectional views of acoustic wave devices according to fourth and fifth modifications of the first embodiment. [Figure 7] 7A and 7B are a plan view and a cross-sectional view of an acoustic wave device in accordance with a second embodiment. [Figure 8] 8A to 8C are cross-sectional views of acoustic wave devices according to first to third modifications of the second embodiment. [Figure 9] FIG. 9(a) is a circuit diagram of a filter according to the third embodiment, and FIG. 9(b) is a circuit diagram of a duplexer according to a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0019] In the first embodiment, an example in which an acoustic wave device has an acoustic wave resonator will be described. FIG. 1(a) is a plan view of an acoustic wave device 100 according to the first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). The arrangement direction of the electrode fingers 18 is defined as the X direction, the extension direction of the electrode fingers 18 as the Y direction, and the stacking direction of the support substrate 10 and the piezoelectric layer 16 as the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer 16. When the piezoelectric layer 16 is a rotated Y-cut X-propagation substrate, the X direction corresponds to the X-axis direction of the crystal orientation.

[0020] As shown in FIGS. 1(a) and 1(b), the support substrate 10 has a recess 17. At least a portion of the sidewall of the recess 17 is inclined in cross-sectional view. For example, the sidewall of the recess 17 has a curved shape in cross-sectional view. If the sidewall has a curved shape, the radius of curvature may be 90% to 110% or 95% to 105% of the depth of the recess 17. The bottom surface of the recess 17 is substantially flat. An insulating film 15 is filled in the recess 17. That is, the insulating film 15 contacts the inner surface of the recess 17, and the recess 17 is filled with the insulating film 15, with no voids formed. The insulating film 15 is filled so as to fit within the recess 17. That is, the insulating film 15 is provided only in the recess 17, and is not provided on the upper surface of the support substrate 10. The insulating film 15 includes a first film 11 and a second film 12. The upper surface of the insulating film 15 is substantially flush with the upper surface of the support substrate 10. A piezoelectric layer 16 is provided on the insulating film 15 and on the support substrate 10. The thickness of the first film 11 is T1, the thickness of the second film 12 is T2, and the thickness of the piezoelectric layer 16 is T6.

[0021] An acoustic wave resonator 26 is provided on the piezoelectric layer 16 above the insulating film 15. In a plan view seen from the Z direction, the entire acoustic wave resonator 26 overlaps the insulating film 15. The acoustic wave resonator 26 has an IDT (Interdigital Transducer) 22 and a reflector 24. The reflectors 24 are 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 21 on the piezoelectric layer 16.

[0022] The IDT 22 includes a pair of opposing comb electrodes 20. The comb electrodes 20 include a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. The region where the electrode fingers 18 of the pair of comb electrodes 20 intersect is an intersection region 25. The pair of comb electrodes 20 have the electrode fingers 18 arranged alternately in at least a portion of the intersection region 25. The acoustic waves excited primarily by the plurality of electrode fingers 18 in the intersection region 25 propagate primarily in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb electrodes 20 is approximately the wavelength λ of the acoustic waves. If the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, the pitch of the electrode fingers 18 of one of the comb electrodes 20 is twice the pitch D. The reflector 24 reflects the acoustic waves (surface acoustic waves) excited by the plurality of electrode fingers 18.

[0023] The piezoelectric layer 16 is, for example, a single-crystal lithium tantalate (LiTaO3) layer, a single-crystal lithium niobate (LiNbO3) layer, or a single-crystal quartz crystal layer. The piezoelectric layer 16 may be, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer. The thickness T6 of the piezoelectric layer 16 is preferably 1.0λ or less, more preferably 0.5λ or less, from the viewpoint of suppressing spurious and loss. Since an excessively thin piezoelectric layer 16 makes it difficult to excite acoustic waves, the thickness T6 is preferably 0.1λ or more. Here, λ is 2×D, where D is the average pitch of the IDT 22 in the X direction. The average pitch D can be calculated by dividing the width of the IDT 22 in the X direction by the number of electrode fingers 18.

[0024] The support substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel 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, the silicon substrate is a single-crystal or polycrystalline silicon substrate, the spinel substrate is a polycrystalline or amorphous MgAl2O4 substrate, and the silicon carbide substrate is a polycrystalline or single-crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than the linear expansion coefficient of the piezoelectric layer 16 in the X direction. This reduces the frequency temperature dependence of the acoustic wave resonator 26.

[0025] The first film 11 is, for example, a temperature compensation film, an insulating film having a temperature coefficient of elastic constant with a sign opposite to that of the piezoelectric layer 16. For example, the temperature coefficient of the elastic constant of the piezoelectric layer 16 is negative, and the temperature coefficient of the elastic constant of the first film 11 is positive. The first film 11 is, for example, a silicon oxide (SiO2) film that is undoped or contains an additive element such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. The first film 11 overlaps the acoustic wave resonator 26 in a plan view seen from the Z direction. For example, the first film 11 overlaps the entire acoustic wave resonator 26. This reduces the frequency temperature coefficient of the acoustic wave resonator 26. When the first film 11 is a silicon oxide film that is undoped or contains an additive element, the acoustic velocity of the bulk wave propagating through the first film 11 is slower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer 16.

[0026] In order for the first film 11 to have a temperature compensation function, it is necessary that the energy of the main response acoustic wave be present to a certain extent within the first film 11. The range in which the energy of the surface acoustic wave is concentrated depends on the type of surface acoustic wave, but it is typically concentrated within a range of 2.0λ from the upper surface of the piezoelectric layer 16, and particularly within a range of 1.0λ from the upper surface of the piezoelectric layer 16. Therefore, the distance from the lower surface of the first film 11 to the upper surface of the piezoelectric layer 16 (thickness T1+T6) is preferably 2.0λ or less, and more preferably 1.0λ or less.

[0027] The second film 12 is disposed within the recess 17 in contact with the bottom and sidewalls of the recess 17, surrounding the first film 11. In other words, the first film 11 is disposed so as to be embedded in the upper surface of the second film 12. The side surface of the first film 11 has, for example, a curved shape in cross section. At least a portion of the side surface of the first film 11 is not parallel to the side surface of the second film 12. The acoustic velocity of the bulk wave propagating through the second film 12 is faster than the acoustic velocity of the bulk wave propagating through the first film 11 and the piezoelectric layer 16. This confines the energy of the main response elastic wave within the piezoelectric layer 16 and the first film 11. The second film 12 is, for example, polycrystalline or amorphous, and is an insulating film such as an aluminum oxide film, a silicon nitride film, an aluminum nitride film, or a silicon carbide film. From the viewpoint of confining the main response elastic wave within the first film 11 and the piezoelectric layer 16, the thickness T2 of the second film 12 is preferably 1.0λ or more, more preferably 1.5λ or more. From the viewpoint of improving the characteristics, the thickness T2 is preferably 10.0λ or less. The acoustic velocity of the bulk wave in each film is the acoustic velocity V of the shear wave. S and is expressed by equation 1, where G is the modulus of rigidity and ρ is the density.

number

number

[0028] The metal film 21 is a film whose main component is, for example, aluminum (Al), copper (Cu), or molybdenum (Mo). An adhesive film such as a titanium (Ti) film, a chromium (Cr) film, or a titanium nitride (TiN) film may be provided between the electrode fingers 18 and the piezoelectric layer 16. The adhesive film is thinner than the electrode fingers 18. An insulating film may be provided to cover the electrode fingers 18. The insulating film may function as a protective film or a temperature compensation film.

[0029] The wavelength λ of the acoustic wave is, for example, 1 μm to 6 μm. When two electrode fingers 18 are considered as one pair, the number of pairs is, for example, 20 pairs to 300 pairs. The duty ratio of the IDT 22 is (thickness of the electrode finger 18) / (pitch of the electrode finger 18), and is, for example, 30% to 70%. The aperture length, which is the length in the Y direction of the intersection region 25 of the IDT 22, is, for example, 10λ to 50λ.

[0030] The width L1 of the overlap between the piezoelectric layer 16 and the support substrate 10 is preferably, for example, 0.5λ or more, and more preferably 1.0λ or more, from the viewpoint of preventing peeling of the piezoelectric layer 16. The distance L2 between the outer end of the reflector 24 and the outer end of the first film 11 may be 0.0λ or more. The distance L3 between the outer end of the IDT 22 and the outer end of the first film 11 is preferably, for example, 1.0λ or more, and more preferably 1.5λ or more, from the viewpoint of temperature compensation. The distance L4 between the outer end of the first film 11 and the outer end of the second film 12 is preferably, for example, 1.0λ or more, and more preferably 1.5λ or more, from the viewpoint of confining the main response acoustic wave within the first film 11 and the piezoelectric layer 16.

[0031] [Manufacturing method] 2(a) to 2(e) are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. As shown in FIG. 2(a), a recess 17 is formed on the upper surface of the support substrate 10. The recess 17 is formed using photolithography and etching. By adjusting the conditions for the photolithography and etching, the sidewall of the recess 17 can be made inclined or curved.

[0032] 2(b), the second film 12 and the first film 11 are formed in this order on the support substrate 10. The first film 11 and the second film 12 are formed by using, for example, a sputtering method or a CVD (Chemical Vapor Deposition) method.

[0033] 2(c), the first film 11 and the second film 12 are polished using, for example, chemical mechanical polishing (CMP) to expose the upper surface of the support substrate 10. As a result, the recess 17 is filled and an insulating film 15 including the first film 11 and the second film 12 is formed.

[0034] As shown in FIG. 2(d), the piezoelectric layer 16 is bonded to the upper surface of the support substrate 10 and the upper surface of the insulating film 15. The piezoelectric layer 16 is bonded by direct bonding using, for example, surface activation. Specifically, the support substrate 10 and the piezoelectric layer 16, each provided with the insulating film 15, are cleaned using RCA cleaning. An ion beam, a neutron beam, or plasma of an inert gas such as argon (Ar) or oxygen is then irradiated onto the bonding surfaces of the support substrate 10 and the piezoelectric layer 16. As a result, an amorphous layer containing atoms of the irradiated material is formed on the bonding surfaces of the support substrate 10 and the piezoelectric layer 16. An amorphous layer containing atoms of the constituent components and the irradiated beam atoms is formed on the bonding surface of the support substrate 10, on which the insulating film 15 is provided. An amorphous layer containing atoms of the constituent components and the irradiated beam atoms is formed on the bonding surface of the piezoelectric layer 16. Thereafter, the amorphous layer formed on the support substrate 10 and the amorphous layer formed on the piezoelectric layer 16 are bonded together, thereby attaching the piezoelectric layer 16 to the upper surface of the support substrate 10 and the upper surface of the insulating film 15. Therefore, an amorphous layer exists between the support substrate 10 and the piezoelectric layer 16, and between the insulating film 15 and the support substrate 10.

[0035] 2(e), the upper surface of the piezoelectric layer 16 is polished by, for example, CMP to thin the piezoelectric layer 16. Thereafter, an acoustic wave resonator 26 is formed on the piezoelectric layer 16 using a metal film 21.

[0036] [Comparative Example] 3 is a cross-sectional view of an acoustic wave device 500 according to a comparative example. As shown in FIG. 3, in the comparative example, no recess is provided on the upper surface of the support substrate 10. The second film 12 is provided on the flat upper surface of the support substrate 10. The first film 11 is provided on the flat upper surface of the second film 12. The piezoelectric layer 16 is provided on the flat upper surface of the second film 12. The other configurations are the same as those in Example 1, so a description thereof will be omitted.

[0037] FIG. 4A is a cross-sectional view illustrating a problem that occurs in an acoustic wave device 500 according to a comparative example. As shown in FIG. 4A, the electrode fingers 18 excite bulk waves 50 in addition to the main response surface acoustic waves (e.g., SH (Shear Horizontal) waves). Like the surface acoustic waves, the bulk waves 50 also propagate primarily in the X direction. The range in which the bulk waves 50 exist is within a 10λ range from the upper surface of the piezoelectric layer 16. Therefore, the bulk waves 50 also exist within the insulating film 15, including the first film 11 and the second film 12. The bulk waves 50 propagate within the insulating film 15 and may leak to the outside. If the bulk waves 50 leak to the outside, they may adversely affect an external acoustic wave resonator or the like.

[0038] FIG. 4B is a cross-sectional view illustrating the effect of the acoustic wave device 100 according to the first embodiment. As shown in FIG. 4B, in the first embodiment, a recess 17 is formed on the upper surface of the support substrate 10, and the insulating film 15 is filled in the recess 17. Therefore, the bulk waves 50 excited by the electrode fingers 18 propagate through the insulating film 15 and are reflected at the interface between the insulating film 15 and the support substrate 10, which is the side wall of the recess 17. This prevents the bulk waves 50 from leaking to the outside. From the viewpoint of reflecting the bulk waves 50 at the interface between the insulating film 15 and the support substrate 10, the acoustic velocity of the bulk waves 50 in the support substrate 10 is preferably faster than the acoustic velocity of the bulk waves 50 in the second film 12, more preferably 1.1 times or more, and even more preferably 1.2 times or more.

[0039] [Variations] 5A is a cross-sectional view of an acoustic wave device 110 according to a first modification of the first embodiment. As shown in FIG. 5A, in the first modification of the first embodiment, the insulating film 15 is formed of a single material. For example, the insulating film 15 may be a silicon oxide film with no additives or containing additive elements, an aluminum oxide film, a silicon nitride film, an aluminum nitride film, a silicon carbide film, or other films. The other configurations are the same as those of the first embodiment, and therefore will not be described here.

[0040] Fig. 5(b) is a cross-sectional view of an acoustic wave device 120 according to Modification 2 of Example 1. As shown in Fig. 5(b), in Modification 2 of Example 1, the entire inner surface of the recess 17 has a curved shape. The other configurations are the same as those of Example 1, and therefore, description thereof will be omitted.

[0041] FIG. 5(c) is a cross-sectional view of an acoustic wave device 130 according to a third modification of the first embodiment. As shown in FIG. 5(c), in the third modification of the first embodiment, the recess 17 has an inner surface provided with irregularities 30. The irregularities 30 may be provided regularly or irregularly. The irregularities 30 are formed by, for example, blasting or etching. The other configurations are the same as those of the first embodiment, and therefore will not be described again.

[0042] FIG. 6(a) is a cross-sectional view of an acoustic wave device 140 according to a fourth modification of the first embodiment. As shown in FIG. 6(a), in the fourth modification of the first embodiment, the insulating film 15 includes a third film 13 between the first film 11 and the second film 12. The acoustic velocity of the bulk wave propagating through the third film 13 is faster than that of the bulk wave propagating through the second film 12. This facilitates confinement of the energy of the acoustic wave of the main response within the first film 11 and the piezoelectric layer 16. This further reduces the amount of acoustic wave leakage to the outside. The third film 13 is, for example, polycrystalline or amorphous, and may be an aluminum nitride film, a silicon nitride film, a silicon carbide film, or a diamond-like carbon (DLC) film. From the viewpoint of confining the acoustic wave of the main response within the first film 11 and the piezoelectric layer 16, the thickness T3 of the third film 13 is preferably 0.3λ or more, more preferably 0.5λ or more. The thickness T3 of the third film 13 is, for example, 5λ or less. The other configurations are the same as those in the first embodiment, so the description will be omitted.

[0043] FIG. 6B is a cross-sectional view of an acoustic wave device 150 according to a fifth modification of the first embodiment. As shown in FIG. 6B, in the fifth modification of the first embodiment, the insulating film 15 includes a third film 13 between the first film 11 and the second film 12, and a fourth film 14 between the second film 12 and the inner surface of the recess 17. The fourth film 14 is a film having voids such as holes, e.g., a porous film. This allows the fourth film 14 to have a low Q value of mechanical vibration. The fourth film 14 can attenuate bulk waves that cause spurious responses and can prevent bulk waves reflected by the inner surface of the recess 17 from reaching the acoustic wave resonator 26. The fourth film 14 may be made of the same material as or different from the second film 12. The fourth film 14 is, for example, an inorganic insulating film such as an aluminum oxide film, a silicon nitride film, an aluminum nitride film, an aluminum nitride oxide film, or a silicon carbide film, or an organic insulating film such as a resin. The acoustic velocity of the bulk waves in the fourth film 14 may be faster or slower than the acoustic velocity of the bulk waves in the second film 12. The thickness T4 of the fourth film 14 is preferably, for example, 0.3λ or more, and more preferably 0.5λ or more. The thickness T4 of the fourth film 14 is, for example, 5λ or less. The other configurations are the same as in Example 1, so a description thereof will be omitted.

[0044] According to the first embodiment and its modification, the recess 17 formed in the support substrate 10 is filled with the insulating film 15. The piezoelectric layer 16 is disposed on the insulating film 15 and over the support substrate 10, and the acoustic wave resonator 26 is disposed on the piezoelectric layer 16, overlapping the insulating film 15 when viewed from above the support substrate 10 (viewed from the Z direction). As a result, as shown in FIG. 4(b), bulk waves 50 excited by the electrode fingers 18 and propagating through the insulating film 15 are reflected by the sidewalls of the recess 17, thereby preventing the bulk waves 50 from leaking to the outside. This prevents adverse effects on other acoustic wave resonators, etc. Furthermore, when preventing bulk wave leakage by providing a groove as described in the above-mentioned Patent Document 4 (JP 2004-336503 A), the groove is provided deep from the upper surface of the piezoelectric layer 16 to the lower surface of the insulating film 15 in the comparative example of FIG. 3. This results in a decrease in the flexural strength of the acoustic wave device. On the other hand, in Example 1, since the insulating film 15 fills the recessed portion 17, it is possible to suppress a decrease in the bending strength of the acoustic wave device.

[0045] Furthermore, by providing the insulating film 15 in the recess 17, heat generated in the acoustic wave resonator 26 is more easily transferred to the support substrate 10 than when the insulating film 15 is provided on the support substrate 10, improving heat dissipation and enabling the acoustic wave device to have a lower profile. Furthermore, since the area where the insulating film 15 is formed is smaller, the support substrate 10 is dominant in thermal contraction and thermal expansion due to changes in ambient temperature, suppressing warpage and improving reliability. Furthermore, since the piezoelectric layer 16 is provided on the insulating film 15 and over the support substrate 10 to cover the insulating film 15, gas that has entered the insulating film 15 during the process is less likely to be released by the piezoelectric layer 16, thereby suppressing deterioration of the characteristics of the acoustic wave resonator 26 due to this gas.

[0046] Furthermore, in Example 1 and its modified example, at least a portion of the sidewall of recess 17 is inclined in cross section. This makes it easier for bulk waves 50 reflected by the sidewall of recess 17 to be scattered, thereby preventing bulk waves 50 from reaching acoustic wave resonator 26. This makes it possible to suppress spurious responses in acoustic wave resonator 26. From the viewpoint of scattering of bulk waves 50, it is preferable that the sidewall of recess 17 be curved in cross section. Furthermore, the curvature also prevents stress concentration at the corners of the bottom surface of recess 17.

[0047] In addition, in Example 1 and its modifications, the thickness T6 of the piezoelectric layer 16 is equal to or less than λ (equal to or less than twice the average pitch D of the plurality of electrode fingers 18). In this case, since the bulk wave 50 easily propagates through the insulating film 15, it is desirable to fill the recesses 17 with the insulating film 15.

[0048] 1(a) and 1(b), the insulating film 15 includes a first film 11 and a second film 12. The first film 11 is a silicon oxide film or a silicon oxide film doped with fluorine, phosphorus, or boron, and is spaced from the inner surface of the recess 17 and overlaps the acoustic wave resonator 26 when viewed from above (Z direction) of the support substrate 10. This reduces the frequency temperature coefficient of the acoustic wave resonator 26. The second film 12 is an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film, and is provided between the inner surface of the recess 17 and the first film 11, surrounding the first film 11. This allows the energy of the acoustic wave of the main response to be trapped within the piezoelectric layer 16 and the first film 11. Furthermore, since the insulating film 15 includes the first film 11 and the second film 12, the bulk waves 50 are reflected at two locations: the boundary between the first film 11 and the second film 12, and the boundary between the second film 12 and the support substrate 10. This further reduces leakage of the bulk waves 50 to the outside. From the viewpoint of reducing leakage of the bulk waves 50 to the outside, it is preferable that at least a part of the side surface of the first film 11 is not parallel to the side surface of the second film 12.

[0049] In Example 1, the piezoelectric layer 16 is directly bonded to the insulating film 15 and the support substrate 10. This improves the temperature compensation effect of the first film 11. In the case of direct bonding, the bonding strength between the first film 11, which is a silicon oxide film with no additives or containing additive elements, and the piezoelectric layer 16 is small, but the bonding strength between the piezoelectric layer 16 and the support substrate 10 is large. Therefore, by directly bonding the piezoelectric layer 16 to both the insulating film 15 and the support substrate 10, peeling of the piezoelectric layer 16 is suppressed.

[0050] 5(b), in the second modification of the first embodiment, the entire inner surface of the recess 17 has a curved shape in cross section. This makes it easier for the reflection of the bulk wave 50 to be scattered over the entire inner surface of the recess 17, and thus makes it possible to prevent the bulk wave 50 from reaching the acoustic wave resonator 26.

[0051] In addition, in Modification 3 of Example 1, as shown in Fig. 5(c), the inner surface of recess 17 has asperities 30. This makes it easier for the reflected bulk waves 50 to be scattered by the inner surface of recess 17, thereby preventing the bulk waves 50 from reaching elastic wave resonator 26. From the viewpoint of scattering the bulk waves 50, the height of asperities 30 is preferably 0.2λ or more, more preferably 0.3λ or more, and even more preferably 0.5λ or more. The width of the recesses and protrusions of asperities 30 is preferably 2λ or less, more preferably 1.5λ or less, and even more preferably 1λ or less. [Example]

[0052] In the second embodiment, an example in which the acoustic wave device is a ladder-type filter will be described. FIGS. 7(a) and 7(b) are a plan view and a cross-sectional view of an acoustic wave device 200 according to the second embodiment. FIG. 7(a) shows a perspective view of a lid 62, and FIG. 7(b) shows a schematic cross-section of FIG. 7(a). As shown in FIGS. 7(a) and 7(b), the second embodiment includes series resonators S1 and S2 and a parallel resonator P1. A plurality of terminals 40 are provided on the lower surface of a support substrate 10. The plurality of terminals 40 include an input terminal Tin, an output terminal Tout, and a ground terminal Gnd. A via wiring 42 penetrating the support substrate 10 is provided. A wiring 44 is provided on the support substrate 10. The series resonators S1 and S2 are connected in series between the input terminal Tin and the output terminal Tout via the wiring 44 and the via wiring 42. One end of the parallel resonator P1 is connected between the series resonators S1 and S2 by a wiring 44, and the other end is connected to the ground terminal Gnd through the wiring 44 and a via wiring 42. The terminal 40, the via wiring 42, and the wiring 44 are metal layers containing, for example, titanium, copper, aluminum, platinum, nickel, and / or gold.

[0053] The support substrate 10 has a plurality of recesses 17a to 17c. The recess 17a is filled with an insulating film 15a including a first film 11 and a second film 12. Similarly, the recess 17b is filled with an insulating film 15b including the first film 11 and the second film 12, and the recess 17c is filled with an insulating film 15c including the first film 11 and the second film 12. A piezoelectric layer 16 is provided from above the insulating films 15a to 15c to above the support substrate 10. The recesses 17a and 17b are adjacent to each other in the Y direction, and the recesses 17a and 17c are adjacent to each other in the X direction. The distance L5 between the recesses 17a and 17c is, for example, 1.0λ or more, and may be 1.5λ or more. The distance between the recesses 17a and 17b is also 1.0λ or more, and may be 1.5λ or more. The piezoelectric layer 16 is divided by a dividing groove 46a between the recessed portion 17a and the recessed portion 17b, and is divided by a dividing groove 46b between the recessed portion 17a and the recessed portion 17c.

[0054] A series resonator S1 made up of an acoustic wave resonator 26 is provided on the piezoelectric layer 16 above the insulating film 15a. A series resonator S2 made up of an acoustic wave resonator 26 is provided on the piezoelectric layer 16 above the insulating film 15b. A parallel resonator P1 made up of an acoustic wave resonator 26 is provided on the piezoelectric layer 16 above the insulating film 15c. The series resonator S1 and the parallel resonator P1 are aligned in the X direction, which is the arrangement direction of the electrode fingers 18 (see FIG. 1(a)).

[0055] The piezoelectric layer 16 is not provided in the peripheral region of the support substrate 10. In a plan view from the Z direction, a frame 60 is provided on the support substrate 10 so as to surround the piezoelectric layer 16. The frame 60 is a metal layer containing, for example, copper, nickel, kovar, gold, aluminum, and / or tungsten. A lid 62 is provided on the frame 60 so as to form a gap 64 between the frame 60 and the support substrate 10. The lid 62 is bonded to the frame 60 with a bonding material. The series resonators S1 and S2 and the parallel resonator P1 are sealed within the gap 64 by the frame 60 and the lid 62. The lid 62 includes a metal layer made of, for example, kovar, 42 alloy, an iron alloy such as stainless steel, an aluminum alloy such as duralumin, nickel, copper, or nickel silver. Furthermore, it is preferable to use sapphire for the lid 62. Using the same material for the support substrate 10 and the lid 62 allows the acoustic wave device 200 to have a more stable structure. The remaining configuration is the same as in Example 1, and therefore a description thereof will be omitted.

[0056] [Variations] 8(a) is a cross-sectional view of an acoustic wave device 210 according to a first modification of the second embodiment. As shown in FIG. 8(a), in the first modification of the second embodiment, the insulating film 15c below the parallel resonator P1 does not include the first film 11 and is made up of only the second film 12. The other configurations are the same as those of the second embodiment, and therefore, description thereof will be omitted.

[0057] 8(b) is a cross-sectional view of an acoustic wave device 220 according to Modification 2 of Example 2. As shown in FIG. 8(b), in Modification 2 of Example 2, the recess 17a and the recess 17c have different depths. Although the recess 17b is not shown, the depth of the recess 17b may be different from that of both the recesses 17a and 17c, or may be the same as that of one of the recesses 17a and 17c. The other configurations are the same as those of Example 2, and therefore a description thereof will be omitted.

[0058] 8(c) is a cross-sectional view of an acoustic wave device 230 according to a third modification of the second embodiment. As shown in FIG. 8(c), in the third modification of the second embodiment, a portion of the piezoelectric layer 16 on which the parallel resonator P1 is provided is embedded in the recess 17c. The other configurations are the same as those in the second embodiment, and therefore, description thereof will be omitted.

[0059] According to the second embodiment and its modification, a series resonator S1 (a pair of comb-shaped electrodes) is provided on the piezoelectric layer 16, overlapping the insulating film 15a filling the recess 17a when viewed from above (Z direction) of the support substrate 10. A parallel resonator P1 (another pair of comb-shaped electrodes) is provided on the piezoelectric layer 16, overlapping the insulating film 15c (another insulating film) filling the recess 17c (another recess) when viewed from above (Z direction) of the support substrate 10. The recess 17a and the recess 17c are adjacent to each other in the X direction. The electrode fingers 18 (see FIG. 1(a)) of each of the series resonator S1 and the parallel resonator P1 are arranged in the X direction, where the recess 17a and the recess 17c are adjacent to each other. Bulk waves excited by both the series resonator S1 and the parallel resonator P1 propagate in the X direction within the insulating films 15a and 15c. However, since the insulating films 15a and 15c are provided in the recesses 17a and 17c, leakage of the bulk waves to the other resonator is suppressed. This prevents the series resonator S1 and the parallel resonator P1 from suffering from deterioration in characteristics such as spurious responses.

[0060] In the second embodiment and its modified example, the piezoelectric layer 16 is divided by the dividing groove 46b between the recess 17a and the recess 17c. This prevents surface acoustic waves and bulk waves propagating in the X direction within the piezoelectric layer 16 from leaking to the other resonator. This further prevents degradation of characteristics, such as spurious responses, in the series resonator S1 and the parallel resonator P1. While the piezoelectric layer 16 is preferably completely divided in the Y direction between the recess 17a and the recess 17c, it may be divided by more than half or by more than three-quarters. Because the recess 17a and the recess 17b are adjacent to each other in the Y direction, the piezoelectric layer 16 may or may not be divided between the recess 17a and the recess 17b. The recess 17a and the recess 17b may be integrated into a single recess.

[0061] 8(a), the insulating films 15a and 15b below the series resonators S1 and S2 include the first film 11 that functions as a temperature compensation film, but the insulating film 15c below the parallel resonator P1 does not include the first film 11. Since the frequency temperature coefficients of the resonant frequency and the anti-resonant frequency differ in an acoustic wave resonator, the frequency temperature characteristics of the ladder-type filter can be improved according to the first modified example of the second embodiment.

[0062] 8(b), in the second modification of the second embodiment, the recesses 17a and 17c have different depths, and the insulating films 15a and 15c have different thicknesses, which causes the frequencies of the spurious responses caused by bulk waves to differ for each resonator, thereby reducing the spurious responses of the ladder filter.

[0063] In Example 2 and its modifications, the insulating films 15a to 15c may be films formed from a single material, as in Modification 1 of Example 1 (FIG. 5(a)). The entire inner surfaces of the recesses 17a to 17c may be curved, as in Modification 2 of Example 1 (FIG. 5(b)). As in Modification 3 of Example 1 (FIG. 5(c)), unevenness 30 may be formed on the inner surfaces of the recesses 17a to 17c. As in Modification 4 of Example 1 (FIG. 6(a)), a third film 13 may be provided between the first film 11 and the second film 12. As in Modification 5 of Example 1 (FIG. 6(b)), a fourth film 14 may be provided between the inner surfaces of the recesses 17a to 17c and the second film 12.

[0064] In Example 2 and its modified examples, at least a portion of the sidewall of each of the recesses 17a to 17c is inclined in cross section, for example, the sidewall is curved in cross section, but this is not limiting. At least a portion of the sidewall of either the recess 17a or the recess 17c may be inclined in cross section, for example, the sidewall may be curved in cross section.

[0065] In the second embodiment and its modified examples, a resin sealing portion may be provided on the support substrate 10 instead of the frame body 60 and the lid 62, thereby sealing the series resonators S1 and S2 and the parallel resonator P1 in the cavity 64. Alternatively, the frame body 60 and the lid 62 may not be provided, the support substrate 10 may be flip-chip mounted on a package substrate, and a resin sealing portion may be provided on the package substrate surrounding the support substrate 10, thereby sealing the series resonators S1 and S2 and the parallel resonator P1 in the cavity 64. [Example]

[0066] FIG. 9(a) is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 9(a), one or more series resonators S11 to S14 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P11 to P13 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave device according to the first embodiment and its modifications can be used for at least one of the one or more series resonators S11 to S14 and the one or more parallel resonators P11 to P13. The number of resonators in the ladder filter can be set as appropriate. The filter may be a multimode filter.

[0067] FIG. 9(b) is a circuit diagram of a duplexer 310 according to a modified example of the third embodiment. As shown in FIG. 9(b), a transmit filter 70 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 70 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 72 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of the second or third embodiment. Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0068] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0069] 10...support substrate, 11...first film, 12...second film, 13...third film, 14...fourth film, 15, 15a, 15b, 15c...insulating film, 16...piezoelectric layer, 17, 17a, 17b, 17c...recess, 18...electrode finger, 19...bus bar, 20...comb-shaped electrode, 21...metal film, 22...IDT, 24...reflector, 25...intersection region, 26...acoustic wave resonator, 30...concave and concave, 4 0...terminal, 42...via wiring, 44...wiring, 46a, 46b...dividing groove, 50...bulk wave, 60...frame, 62...lid, 64...gap, 70...transmitting filter, 72...receiving filter, 100, 110, 120, 130, 140, 150, 200, 210, 220, 230, 500...acoustic wave device, 300...filter, 310...duplexer

Claims

1. a substrate having a recess; an insulating film filled in the recess; a piezoelectric layer provided on the insulating film and on the substrate; an acoustic wave device comprising: a pair of comb-shaped electrodes provided on the piezoelectric layer so as to overlap the insulating film when viewed from above the substrate, the comb-shaped electrodes having a plurality of electrode fingers;

2. The acoustic wave device according to claim 1 , wherein at least a portion of a sidewall of the recess is inclined in cross section.

3. 3. The acoustic wave device according to claim 1, wherein the thickness of the piezoelectric layer is equal to or less than twice the average pitch of the plurality of electrode fingers.

4. 3. The acoustic wave device according to claim 1, wherein the insulating film includes: a first film which is a silicon oxide film or a silicon oxide film doped with fluorine, phosphorus, or boron, and which is spaced from the inner surface of the recess and overlaps the pair of comb electrodes when viewed from above the substrate; and a second film which is an aluminum oxide film, a silicon film, an aluminum nitride film, a silicon nitride film, or a silicon carbide film and is provided between the inner surface of the recess and the first film, surrounding the first film.

5. The acoustic wave device according to claim 1 , wherein the inner surface of the recess has projections and recesses.

6. the substrate has another recess adjacent to the recess, Another insulating film filled in the other recess; another pair of comb-shaped electrodes provided on the piezoelectric layer so as to overlap the another insulating film when viewed from above the substrate, the comb-shaped electrodes including another plurality of electrode fingers; The acoustic wave device according to claim 1 , wherein the plurality of electrode fingers and the other plurality of electrode fingers are arranged in a direction in which the recess and the other recess are adjacent to each other.

7. The acoustic wave device according to claim 6 , wherein the piezoelectric layer is divided between the recess and the other recess.

8. 3. The acoustic wave device according to claim 1, further comprising a lid provided over the pair of interdigital transducers with a gap interposed therebetween, the lid being made of the same material as the substrate and sealing the pair of interdigital transducers in the gap.

9. A filter comprising the acoustic wave device according to claim 1 or 2.

10. forming a recess in a substrate; filling the recess with an insulating film; directly bonding a piezoelectric layer to the insulating film and the substrate; and forming a pair of comb-shaped electrodes having a plurality of electrode fingers on the piezoelectric layer so as to overlap the insulating film when viewed from above the substrate.

Images