Elastic wave device, and manufacturing method for elastic wave device

Abstract

Provided is an elastic wave device capable of suppressing a leakage wave transmitted to a protrusion part, and a method for manufacturing the elastic wave device. The elastic wave device comprises: a piezoelectric layer having a first main surface and a second main surface on the opposite side from the first main surface; an upper electrode provided on the first main surface of the piezoelectric layer; a lower electrode provided on the second main surface of the piezoelectric layer; and a support member facing the second main surface of the piezoelectric layer. The support member or the piezoelectric layer has a cavity part in a region overlapping at least a part of the upper electrode and the lower electrode. The support member has at least one protrusion part protruding from the bottom of the cavity part toward the piezoelectric layer.

Description

Acoustic wave device and method for manufacturing the same

[0001] The present disclosure relates to acoustic wave devices and methods for manufacturing acoustic wave devices.

[0002] Patent Document 1 describes a piezoelectric device in which flat upper and lower electrodes are provided on both sides of a piezoelectric layer.

[0003] JP 2009-124640 A

[0004] In the cavity of the piezoelectric device disclosed in Patent Document 1, protrusions (supports) that support the upper and lower electrodes are provided. With the technology disclosed in Patent Document 1, there is a possibility that leaky waves may be transmitted to the protrusions (supports).

[0005] An object of the present disclosure is to provide an acoustic wave device that can suppress leakage waves from propagating to a protrusion, and a method for manufacturing an acoustic wave device.

[0006] An elastic wave device according to one embodiment comprises a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, an upper electrode provided on the first main surface of the piezoelectric layer, a lower electrode provided on the second main surface of the piezoelectric layer, and a support member facing the second main surface of the piezoelectric layer, wherein the support member or the piezoelectric layer has a cavity portion in an area overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion protruding from the bottom of the cavity portion toward the piezoelectric layer, and the tip of the protrusion is not in contact with the piezoelectric layer or the lower electrode.

[0007] A method for manufacturing an elastic wave device according to one embodiment includes the steps of preparing a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, forming a lower electrode on the second main surface of the piezoelectric layer, preparing a support member having a cavity and a protrusion with a height equal to the depth of the cavity, bonding the piezoelectric layer to the support member, thinning the thickness of the piezoelectric layer bonded to the support member, forming an upper electrode on the first main surface of the piezoelectric layer, and melting the protrusion with laser light.

[0008] An elastic wave device according to one embodiment comprises a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, an upper electrode provided on the first main surface of the piezoelectric layer, a lower electrode provided on the second main surface of the piezoelectric layer, and a support member facing the second main surface of the piezoelectric layer, wherein the support member has a cavity portion in an area overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion protruding from a bottom of the cavity portion toward the piezoelectric layer, a first through hole formed in the upper electrode, and a second through hole formed in the piezoelectric layer, the tip of the protrusion abutting the piezoelectric layer or the lower electrode, and the first through hole, the second through hole, and the protrusion overlap when viewed from a direction perpendicular to the first main surface.

[0009] An elastic wave device according to one embodiment includes a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, an upper electrode provided on the first main surface of the piezoelectric layer, a lower electrode provided on the second main surface of the piezoelectric layer, and a support member facing the second main surface of the piezoelectric layer, wherein the support member or the piezoelectric layer has a cavity portion in an area overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion that protrudes from the bottom of the cavity portion toward the piezoelectric layer and abuts the upper electrode, and when viewed from a direction perpendicular to the first main surface, the protrusions are linear, lattice-shaped, or frame-shaped.

[0010] According to the elastic wave device and the method for manufacturing the elastic wave device disclosed herein, it is possible to suppress leaky waves from being transmitted to the support pillar.

[0011] FIG. 1 is a plan view illustrating an elastic wave device according to a first embodiment. FIG. 2 is a cross-sectional view taken along line II-II' of FIG. 1. FIG. 3 is a diagram illustrating a method for manufacturing an elastic wave device according to the first embodiment. FIG. 4A is a plan view illustrating an elastic wave device according to a first modification of the first embodiment. FIG. 4B is a cross-sectional view taken along line IVB-IVB' of FIG. 4A. FIG. 4C is a cross-sectional view taken along line IVC-IVC' of FIG. 4A. FIG. 4D is a cross-sectional view illustrating an elastic wave device according to a second modification of the first embodiment. FIG. 5 is a plan view illustrating an elastic wave device according to a second embodiment. FIG. 6 is a cross-sectional view taken along line VI-VI' of FIG. 5. FIG. 7 is a diagram illustrating a method for manufacturing an elastic wave device according to the second embodiment. FIG. 8 is a cross-sectional view illustrating an elastic wave device according to a first modification of the second embodiment. FIG. 9 is a plan view illustrating an elastic wave device according to a third embodiment. FIG. 10 is a cross-sectional view taken along line XX' of FIG. 9. FIG. 11 is a diagram illustrating a method for manufacturing an elastic wave device according to the third embodiment. FIG. 12 is a plan view illustrating an elastic wave device according to a fourth embodiment. FIG. 13 is a cross-sectional view taken along line XIII-XIII′ in FIG. 12 . FIG. 14 is a diagram illustrating a first manufacturing method of an elastic wave device according to embodiment 4. FIG. 15 is a diagram illustrating a second manufacturing method of an elastic wave device according to embodiment 4. FIG. 16 is a plan view illustrating an elastic wave device according to modification 1 of embodiment 4. FIG. 17 is a plan view illustrating an elastic wave device according to modification 2 of embodiment 4. FIG. 18 is a plan view illustrating an elastic wave device according to modification 3 of embodiment 4. FIG. 19 is a plan view illustrating an elastic wave device according to embodiment 5. FIG. 20 is a cross-sectional view taken along line XX-XX′ in FIG. 19 . FIG. 21 is a diagram illustrating a first manufacturing method of an elastic wave device according to embodiment 5. FIG. 22 is a diagram illustrating a second manufacturing method of an elastic wave device according to embodiment 5. FIG. 23 is a plan view illustrating an elastic wave device according to embodiment 6. FIG. 24 is a cross-sectional view taken along line XXIV-XXIV′ in FIG. 23 . FIG. 25 is a diagram illustrating a first manufacturing method of an elastic wave device according to embodiment 6. Fig. 26 is an explanatory diagram illustrating a second manufacturing method of an elastic wave device according to embodiment 6. Fig. 27 is a cross-sectional view illustrating an elastic wave device according to embodiment 7. Fig. 28 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to embodiment 7. Fig. 29 is a cross-sectional view illustrating an elastic wave device according to embodiment 8.FIG. 30 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to Embodiment 8. FIG. 31 is a plan view illustrating an elastic wave device according to Embodiment 9. FIG. 32 is a cross-sectional view taken along line XXXII-XXXII′ of FIG. 31. FIG. 33 is a plan view illustrating an elastic wave device according to Embodiment 10. FIG. 34 is a cross-sectional view taken along line XXXIV-XXXIV′ of FIG. 33. FIG. 35 is a cross-sectional view illustrating an elastic wave device according to Embodiment 11. FIG. 36 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to Embodiment 11. FIG. 37 is a cross-sectional view illustrating an elastic wave device according to Modification 1 of Embodiment 11. FIG. 38 is a cross-sectional view illustrating an elastic wave device according to Modification 2 of Embodiment 11. FIG. 39 is a cross-sectional view illustrating an elastic wave device according to Modification 3 of Embodiment 11. FIG. 40 is a cross-sectional view illustrating an elastic wave device according to Modification 4 of Embodiment 11. FIG. 41 is a cross-sectional view illustrating an elastic wave device according to Modification 5 of Embodiment 11.

[0012] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, the present disclosure is not limited to these embodiments. Note that each embodiment described in the present disclosure is an example, and in the second and subsequent embodiments, a description of modifications in which partial substitution or combination of configurations is possible between different embodiments, and of matters common to the first embodiment will be omitted, and only differences will be described. In particular, similar effects resulting from similar configurations will not be mentioned in each embodiment.

[0013] 1 is a plan view showing an elastic wave device according to embodiment 1. Fig. 2 is a cross-sectional view taken along line II-II' in Fig. 1. The resonators constituting an elastic wave device 1A according to embodiment 1 are resonators that utilize bulk waves, i.e., BAW (Bulk Acoustic Wave) elements.

[0014] 1 and 2, the elastic wave device 1A includes a support member 13, a piezoelectric layer 20, an upper electrode 31, and a lower electrode 32. As shown in Fig. 2, the lower electrode 32, the piezoelectric layer 20, and the upper electrode 31 are stacked in this order on the support member 13.

[0015] In the following description, the thickness direction of the piezoelectric layer 20 is referred to as the Z direction, the direction perpendicular to the Z direction is referred to as the X direction, and the direction perpendicular to the Z direction and the X direction is referred to as the Y direction. The X direction and the Y direction are each parallel to the surface (first main surface 20a) of the piezoelectric layer 20. In the following description, a plan view refers to the positional relationship when viewed from a direction perpendicular to the first main surface 20a of the piezoelectric layer 20 (Z direction).

[0016] The support member 13 is provided opposite to the second main surface 20b of the piezoelectric layer 20. The support member 13 of the first embodiment is a support substrate, and is made of silicon (Si), quartz crystal, or the like.

[0017] A cavity portion 14 (hollow portion) is formed on the surface of the support member 13 facing the second main surface 20b of the piezoelectric layer 20. A portion of the surface of the support member 13 facing the second main surface 20b of the piezoelectric layer 20 forms the bottom of the cavity portion 14. The cavity portion 14 is provided so as to overlap, in plan view, with the excitation region of a resonator formed by overlapping the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32. This allows bulk waves to be reflected by the cavity portion 14. The resonance formed by overlapping the upper electrode 31 and the lower electrode 32 is the functional electrode 30 of the first embodiment.

[0018] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of, for example, lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 1 μm or less.

[0019] The upper electrode 31 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in Fig. 1, a first wiring layer 33 extending in the X direction is connected to the upper electrode 31. The upper electrode 31 is provided in a region overlapping with the cavity portion 14 and is formed in a substantially rectangular shape. An adhesive layer made of titanium (Ti), nickel chromium (NiCr), or the like may be provided between the upper electrode 31 and the piezoelectric layer 20.

[0020] The reflective layer 39 covers the upper electrode 31. The reflective layer 39 is made of a metal having a metallic luster, such as aluminum (Al), silver (Ag), gold (Au), copper (Cu), or titanium (Ti), thereby preventing the upper electrode 31 and the lower electrode 32 from being damaged when irradiated with laser light.

[0021] The first wiring layer 33 is formed in a substantially rectangular shape with a width in the Y direction that is the same as or larger than that of the upper electrode 31. The first wiring layer 33 is a copper (Cu) or copper (Cu) alloy layer. The first wiring layer 33 is electrically connected to an external terminal or a ground wiring (having a constant potential).

[0022] The lower electrode 32 is provided on the second main surface 20b of the piezoelectric layer 20, in a region where at least a portion of the electrode overlaps with the upper electrode 31. As shown in FIG. 1 , a second wiring layer 34 extending in the Y direction is connected to the lower electrode 32. The lower electrode 32 is provided in a region that overlaps with the cavity portion 14, and is formed in a substantially rectangular shape. That is, the lower electrode 32 is provided in a region that overlaps with the upper electrode 31. An adhesion layer made of titanium (Ti), nickel chromium (NiCr), or the like may be provided between the lower electrode 32 and the piezoelectric layer 20.

[0023] The elastic wave device 1A has a so-called membrane structure in which a cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20, and an upper electrode 31 and a lower electrode 32 are arranged at positions overlapping the cavity 14 (hollow portion). In the region overlapping with the cavity 14, the piezoelectric layer 20 is arranged between the upper electrode 31 and the lower electrode 32 in the Z direction. This allows bulk waves to propagate between the upper electrode 31 and the lower electrode 32. In the following description, the region where the upper electrode 31 and the lower electrode 32 overlap in a planar view may be described as the excitation region of the resonator.

[0024] The second wiring layer 34 is formed in a generally rectangular shape with a width greater than that of the lower electrode 32. The second wiring layer 34 is a Cu or Cu alloy layer. The second wiring layer 34 extends in the Y direction, but may also extend in the X direction on the opposite side to the first wiring layer 33. In other words, the second wiring layer 34 is provided in a region that does not overlap with the first wiring layer 33. The second wiring layer 34 is electrically connected to an external terminal or a ground wiring (having a constant potential).

[0025] The upper electrode 31 and the lower electrode 32 are formed of a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or an alloy containing at least one of these materials. The upper electrode 31 and the lower electrode 32 may be a laminated film of at least two or more metal layers such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or the like.

[0026] The support member 13 is provided with four protrusions 92 that protrude from the bottom of the cavity portion 14 toward the piezoelectric layer 20. The protrusions 92 are formed in a rod shape from a metal such as aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), titanium (Ti), or tin (Sn), or an alloy containing at least one of these materials.

[0027] When viewed from the direction perpendicular to the first main surface 20a (Z direction), the protrusion 92 is provided in a region that does not overlap with the reflective layer 39. This suppresses damage to the functional electrode 30 that overlaps with the reflective layer 39 due to the influence of the laser light. Furthermore, even if the reflective layer 39 is irradiated with laser light, the laser light is reflected by the reflective layer 39, so that damage to the functional electrode 30 that overlaps with the reflective layer 39 is suppressed.

[0028] The tip of the protrusion 92 is the portion closest to the piezoelectric layer 20. As shown in FIG.

[0029] As will be described later, the tip of the protrusion 92 is irradiated with laser light, which causes crystallization. The metal of the protrusion 92 is in an amorphous state because it is formed by vapor deposition. Therefore, the surface of the tip of the protrusion 92 is more crystallized than the inside of the protrusion, and it can be said that the crystalline state of the surface of the protrusion 92 is different from that of the inside of the protrusion 92.

[0030] 1 is merely an example and may be modified as appropriate. The planar shapes of the upper electrode 31 and the lower electrode 32 are not limited to rectangular shapes, and may be circular, polygonal, or other shapes.

[0031] Next, a method for manufacturing the elastic wave device 1A according to the first embodiment will be described. FIG. 3 is a diagram illustrating a method for manufacturing the elastic wave device according to the first embodiment. As shown in FIG. 3, a LiNbO ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared (step ST1). Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST2). The lower electrode 32 is formed, for example, by a vapor deposition lift-off method. That is, in step ST2, a resist is patterned on the second main surface 20b of the piezoelectric body 21 by photolithography. After a metal film is vapor-deposited, the resist is removed, thereby forming the metal film as the lower electrode 32. Next, a metal film is similarly vapor-deposited so as to cover the lower electrode 32, and a second wiring layer 34 is patterned (step ST3).

[0032] On the other hand, a support substrate 11 is prepared (step ST11). A portion of the support substrate 11 is recessed by reactive ion etching to form a support member 13 having a cavity portion 14 (step ST12). Next, a protrusion 91 is formed on the bottom of the cavity portion 14 (step ST13). The protrusion 91 is formed by, for example, a vapor deposition lift-off method. The height of the protrusion 91 is the same as the depth of the cavity portion 14.

[0033] Next, the support member 13 and the piezoelectric layer 20 are bonded together (step ST14). More specifically, the support member 13 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like.

[0034] Next, the first main surface of the piezoelectric body 21 is polished by, for example, mechanical polishing or CMP (Chemical Mechanical Polishing), and the thickness of the piezoelectric body 21 bonded in step ST14 is reduced (step ST15). This results in a piezoelectric layer 20 having a thickness of 1 μm or less. If the piezoelectric body 21 is thin before bonding in step ST14, the piezoelectric body 21 may be damaged during bonding. Therefore, the thickness of the piezoelectric body 21 must be reduced after bonding in step ST14. In step ST15, the protrusions 91 act as supports between the support member 13 and the piezoelectric layer 20, thereby reducing the thickness of the piezoelectric body 21 without causing the piezoelectric layer 20 to stick to the bottom of the cavity portion 14 (sticking). Furthermore, the presence of multiple protrusions 91 suppresses unevenness in the thickness distribution of the piezoelectric layer due to polishing.

[0035] A reflective layer 39 is formed to cover the upper electrode 31 (step ST16). The reflective layer 39 is formed by sputtering.

[0036] Next, the protrusion 91 is irradiated with laser light, and a portion of it melts to form a protrusion 92 (step ST17). As a result, the tip of the protrusion 92 is not in contact with the piezoelectric layer 20 or the lower electrode 32. Because the protrusion 91 was in contact with the piezoelectric layer 20, if the membrane structure was excited in this state, there was a possibility that leaky waves would be transmitted to the protrusion 91. However, because the tip of the protrusion 92 is not in contact with the piezoelectric layer 20 or the lower electrode 32, the leaky waves transmitted to the protrusion 92 are suppressed even if the membrane structure is excited.

[0037] Next, the first wiring layer 33 is formed to cover at least a part of the upper electrode 31 and the reflective layer 39 (step ST18).

[0038] As described above, the thickness of the piezoelectric layer 20 is reduced to 1 μm or less, and variations in the thickness of the piezoelectric layer 20, which can cause unevenness in the in-plane thickness of the piezoelectric layer 20, can easily affect the excitation characteristics. In this embodiment, unevenness in the in-plane thickness of the piezoelectric layer 20 can be suppressed, thereby improving the quality of the elastic wave device 1A even when the thickness of the piezoelectric layer 20 is reduced to 1 μm or less.

[0039] The elastic wave device 1A of this preferred embodiment is manufactured through the above steps. Note that the steps shown in FIG. 3 are merely schematic and can be modified as appropriate.

[0040] 4A is a plan view showing an elastic wave device according to Modification 1 of Embodiment 1. FIG. 4B is a cross-sectional view taken along line IVB-IVB' of FIG. 4A. FIG. 4C is a cross-sectional view taken along line IVC-IVC' of FIG. 4A. As shown in FIGS. 4A, 4B, and 4C, an elastic wave device 1B according to Modification 1 differs from Embodiment 1 described above in the relative positional relationship between the first wiring layer 33 and the reflective layer 39.

[0041] 4A and 4B, in Modification 1 of Embodiment 1, when viewed from the Z direction, the position of the first wiring layer 33 does not overlap with the reflective layer 39. As shown in Figures 4A and 4C, when viewed from the Z direction, the second wiring layer 34 does not overlap with the reflective layer 39. Note that Modification 1 also achieves the same effects as Embodiment 1.

[0042] 4D is a cross-sectional view of an elastic wave device according to Modification 2 of Embodiment 1. As shown in FIG. 4D , elastic wave device 1C according to Modification 2 differs from that of Embodiment 1 described above in the relative positional relationship between upper electrode 31 and lower electrode 32.

[0043] In the second modification of the first embodiment, the position of the upper electrode 31 and the position of the lower electrode 32 are misaligned when viewed from the Z direction. When viewed from the Z direction, the lower electrode 32 is not covered by the upper electrode 31, and the reflective layer 39 overlaps the lower electrode 32. Because the reflective layer 39 is a conductor, an excitation region of a resonator is generated where the reflective layer 39 and the lower electrode 32 overlap.

[0044] In the second modification, the reflective layer 39 has a larger area than the upper electrode 31, so that the upper electrode 31 and the lower electrode 32 can be protected from the laser light.

[0045] In the second modification, at least a portion of the lower electrode 32 may overlap with the upper electrode 31 .

[0046] Second Embodiment Fig. 5 is a plan view showing an elastic wave device according to a second embodiment. Fig. 6 is a cross-sectional view taken along line VI-VI' in Fig. 5. As shown in Figs. 5 and 6, an elastic wave device 1D according to the second embodiment is different from that of the first embodiment (see Figs. 1 and 2) in that a reflective layer 35 is provided.

[0047] The reflective layer 35 is a laminated film in which dielectric layers with different refractive indices are alternately stacked, and reflects laser light by thin film interference. The reflective layer 35 is stacked on the upper electrode 31.

[0048] Since the reflective layer 35 has lower conductivity than metal, it is necessary to directly stack the upper electrode 31 and the first wiring layer 33. For this reason, in the second embodiment, the upper electrode 31 extends in the X direction, as compared with the first embodiment, and the first wiring layer 33 is stacked on the upper electrode 31 in the portion exposed from the reflective layer 35.

[0049] 7 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to embodiment 2. In the manufacturing method of an elastic wave device 1D according to embodiment 2 illustrated in FIG. 7, steps ST1 to ST3 are similar to steps ST1 to ST3 described above with reference to FIG. 3, and therefore, repeated description will be omitted. Furthermore, steps ST21 to ST25 are similar to steps ST11 to ST15 described above with reference to FIG. 3, and therefore, repeated description will be omitted.

[0050] A reflective layer 35 is formed to cover the upper electrode 31 (step ST26). The reflective layer 35 is formed by sputtering TiO ２ , SiO ２ , MgF ２ , Ta ２ O ５ , LaF ３ , Al ２ O ３ , HfO ２Two types of dielectrics having different refractive indices are selected from the above dielectrics, and these two types of dielectrics are alternately laminated to form the dielectric film.

[0051] Next, the protrusion 91 is irradiated with a laser beam, and a portion of it melts to form a protrusion 92 (step ST27). As a result, the tip of the protrusion 92 is not in contact with the piezoelectric layer 20 or the lower electrode 32. Because the protrusion 91 was in contact with the piezoelectric layer 20, if the membrane structure was excited in this state, there was a possibility that a leaky wave would be transmitted to the protrusion 91. However, because the tip of the protrusion 92 is not in contact with the piezoelectric layer 20 or the lower electrode 32, the leaky wave transmitted to the protrusion 92 is suppressed even if the membrane structure is excited.

[0052] Next, the first wiring layer 33 is formed to cover at least a part of the upper electrode 31 exposed from the reflective layer 35 (step ST28).

[0053] As described above, the thickness of piezoelectric layer 20 is reduced to 1 μm or less, and variations in the thickness of piezoelectric layer 20, which can cause unevenness in the in-plane thickness of piezoelectric layer 20, can easily affect the excitation characteristics. In this embodiment, unevenness in the in-plane thickness of piezoelectric layer 20 can be suppressed, thereby improving the quality of elastic wave device 1D even when piezoelectric layer 20 is reduced to 1 μm or less.

[0054] The above steps complete the manufacture of the elastic wave device 1D of Preferred Embodiment 2. Note that the steps shown in Fig. 7 are merely schematic and can be modified as appropriate.

[0055] 8 is a cross-sectional view of an elastic wave device according to Modification 1 of Embodiment 2. As shown in Fig. 8, elastic wave device 1E according to Modification 1 differs from that of Embodiment 2 described above in the relative positional relationship between upper electrode 31 and lower electrode 32.

[0056] In the first modification of the second embodiment, the position of the upper electrode 31 and the position of the lower electrode 32 are misaligned when viewed from the Z direction. When viewed from the Z direction, a portion of the lower electrode 32 is not covered by the upper electrode 31, the reflective layer 35 overlaps the lower electrode 32, and another portion of the lower electrode 32 overlaps the upper electrode 31. Because the reflective layer 35 is not a conductor, the other portion where the upper electrode 31 and the lower electrode 32 overlap becomes the excitation region of the resonator.

[0057] 9 is a plan view of an elastic wave device according to a third embodiment. Fig. 10 is a cross-sectional view taken along the line XX' in Fig. 9. As shown in Figs. 9 and 10, an elastic wave device 1F according to the third embodiment differs from the first and second embodiments in that the protrusions 94 are made of the same material as the support member 13.

[0058] The support member 13 is provided with four protrusions 94 that protrude from the bottom of the cavity portion 14 toward the piezoelectric layer 20. The protrusions 94 are part of the support member 13 and are formed in a rod shape. The protrusions 94 are made of the same material as the support member 13.

[0059] As will be described later, the tip of the protrusion 94 is irradiated with laser light and is therefore melted. Therefore, the surface of the tip of the protrusion 94 has a smaller roughness than the surface of the bottom of the cavity 14. In other words, the protrusion 94 is a part of the support member 13, and has a different roughness from the bottom of the cavity 14.

[0060] In the third embodiment, the position of the upper electrode 31 and the position of the lower electrode 32 are misaligned when viewed from the Z direction. When viewed from the Z direction, the lower electrode 32 is not covered by the upper electrode 31, and the reflective layer 39 overlaps the lower electrode 32. Because the reflective layer 39 is a conductor, an excitation region of a resonator is generated where the reflective layer 39 and the lower electrode 32 overlap.

[0061] In the third embodiment, the reflective layer 39 has a larger area than the upper electrode 31, so that the upper electrode 31 and the lower electrode 32 can be protected from laser light.

[0062] Also in the third embodiment, at least a portion of the lower electrode 32 may overlap the upper electrode 31. Also in the third embodiment, the entire lower electrode 32 may overlap the upper electrode 31.

[0063] 11 is an explanatory diagram illustrating a manufacturing method of an elastic wave device according to embodiment 3. In the manufacturing method of an elastic wave device 1F according to embodiment 3 illustrated in FIG. 11, steps ST1 to ST3 are the same as steps ST1 to ST3 described above with reference to FIG. 3, and therefore repeated description will be omitted.

[0064] In the third embodiment, a support substrate 11 is prepared (step ST31). A portion of the support substrate 11 is recessed by reactive ion etching to form a support member 13 having a cavity 14, and a protrusion 93 is simultaneously formed on the bottom of the cavity 14 (step ST32). The height of the protrusion 93 is the same as the depth of the cavity 14.

[0065] Next, the support member 13 and the piezoelectric layer 20 are bonded together (step ST33). The support member 13 is bonded to the piezoelectric body 21 by direct bonding, plasma activation bonding, atomic diffusion bonding, or the like.

[0066] Next, the first main surface of the piezoelectric body 21 is polished by, for example, mechanical polishing or CMP (Chemical Mechanical Polishing), thereby thinning the thickness of the piezoelectric body 21 bonded in step ST33 (step ST34). This results in a piezoelectric layer 20 of 1 μm or less. If the piezoelectric body 21 is thin before bonding in step ST34, the piezoelectric body 21 may be damaged during bonding. Therefore, the thickness of the piezoelectric body 21 must be thinned after bonding in step ST34. In step ST35, the protrusions 93 act as supports between the support member 13 and the piezoelectric layer 20, thinning the piezoelectric body 21 without causing the piezoelectric layer 20 to stick to the bottom of the cavity portion 14 (sticking). Furthermore, the presence of multiple protrusions 93 suppresses unevenness in the thickness distribution of the piezoelectric layer due to polishing.

[0067] A reflective layer 39 is formed to cover the upper electrode 31 (step ST35). The reflective layer 39 is formed by sputtering.

[0068] Next, the protrusion 93 is irradiated with a laser beam, and a portion of it melts to form a protrusion 94 (step ST36). As a result, the tip of the protrusion 92 is not in contact with the piezoelectric layer 20 or the lower electrode 32. Because the protrusion 93 was in contact with the piezoelectric layer 20, if the membrane structure was excited in this state, there was a possibility that a leaky wave would be transmitted to the protrusion 93. However, because the tip of the protrusion 94 is not in contact with the piezoelectric layer 20 or the lower electrode 32, the leaky wave transmitted to the protrusion 94 is suppressed even if the membrane structure is excited.

[0069] Next, the first wiring layer 33 is formed to cover at least a part of the upper electrode 31 and the reflective layer 39 (step ST37).

[0070] As described above, the thickness of the piezoelectric layer 20 is reduced to 1 μm or less, and variations in the thickness of the piezoelectric layer 20, which can cause unevenness in the in-plane thickness of the piezoelectric layer 20, can easily affect the excitation characteristics. In this embodiment, unevenness in the in-plane thickness of the piezoelectric layer 20 can be suppressed, thereby improving the quality of the acoustic wave device 1F even when the thickness of the piezoelectric layer 20 is reduced to 1 μm or less.

[0071] The elastic wave device 1F of this preferred embodiment is manufactured through the above steps. Note that the steps shown in FIG. 11 are merely schematic and can be modified as appropriate.

[0072] Fourth Embodiment Fig. 12 is a plan view of an elastic wave device according to a fourth embodiment. Fig. 13 is a cross-sectional view taken along line XIII-XIII' in Fig. 12. As shown in Figs. 12 and 13, an elastic wave device 2A according to the fourth embodiment has a different configuration in that the tip of the protrusion 95 abuts against the lower electrode 32. That is, in the fourth embodiment, even when the tip of the protrusion 95 abuts against the lower electrode 32, leaky waves transmitted to the protrusion 95 are suppressed.

[0073] 12 and 13 , the support member 13 is provided opposite the second main surface 20b of the piezoelectric layer 20. The support member 13 includes a support substrate 11 and an insulating layer 12. The support substrate 11 is made of silicon (Si), quartz crystal, or the like. The insulating layer 12 is provided between the support substrate 11 and the piezoelectric layer 20. The insulating layer 12 is made of an insulating material such as silicon oxide.

[0074] A cavity 14 (hollow portion) is formed on the surface of the insulating layer 12 of the support member 13 that faces the second main surface 20b of the piezoelectric layer 20. The cavity 14 is provided so as to overlap, in plan view, with the excitation region of the resonator that is formed by overlapping the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32. This allows bulk waves to be reflected by the cavity 14.

[0075] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ The thickness of the piezoelectric layer 20 is not particularly limited, but is 1 μm or less.

[0076] 12, an etching window 25H is provided in the piezoelectric layer 20. The etching window 25H is an opening for etching when forming the cavity portion 14 of the insulating layer 12. That is, a sacrificial layer 25 (see FIG. 14) is formed in the region that will become the cavity portion 14, and after bonding the piezoelectric layer 20 and the support member 13, the sacrificial layer 25 is removed through the etching window 25H to form the cavity portion 14.

[0077] The upper electrode 31 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in Fig. 12, the upper electrode 31 is provided in a region overlapping with the cavity portion 14 of the insulating layer 12, and has a substantially circular outer shape, that is, an annular shape. The first wiring layer 33 is connected to the upper electrode 31 and is formed in a substantially rectangular shape.

[0078] The lower electrode 32 is provided on the second main surface 20b of the piezoelectric layer 20, in a region where at least a portion of the lower electrode 32 overlaps with the upper electrode 31. As shown in Fig. 13, the second wiring layer 34 extends in the X direction and is connected to the lower electrode 32. The lower electrode 32 is provided in a region that overlaps with the cavity portion 14 of the insulating layer 12, and is formed in a substantially circular shape. In other words, the lower electrode 32 is provided in a region that overlaps with the upper electrode 31.

[0079] The elastic wave device 2A has a so-called membrane structure in which a cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20. In the region overlapping with the cavity 14, the piezoelectric layer 20 is disposed between the upper electrode 31 and the lower electrode 32 of the lower electrode 32 in the Z direction. This allows bulk waves to propagate between the upper electrode 31 and the lower electrode 32 of the lower electrode 32.

[0080] The second wiring layer 34 extends in the X direction on the opposite side of the upper electrode 31 from the first wiring layer 33. In other words, the second wiring layer 34 is provided in a region that does not overlap with the first wiring layer 33 of the upper electrode 31.

[0081] 13 , the insulating layer 12 of the support member 13 is provided with one protrusion 95 that protrudes from the bottom of the cavity 14 toward the piezoelectric layer 20. The protrusion 95 has a substantially circular shape when viewed in the Z direction. The tip of the protrusion 95 abuts against the lower electrode 32.

[0082] A first through hole 31H penetrating in the Z direction is formed in the upper electrode 31. A second through hole 20H penetrating in the Z direction is formed in the piezoelectric layer 20. When viewed from the Z direction, the first through hole 31H, the second through hole 20H, and the protrusion 95 overlap. The diameter of the first through hole 31H is larger than the diameter of the protrusion 95, and the diameter of the protrusion 95 is larger than the diameter of the second through hole 20H.

[0083] Without the second through hole 20H, the diameter of the protrusion 95 needs to be increased to suppress the interference waves caused by the influence of the first through hole 31H. In contrast, in the elastic wave device 2A of Embodiment 4, the second through hole 20H suppresses the interference waves caused by the influence of the first through hole 31H, so the diameter of the protrusion 95 can be reduced.

[0084] Next, a method for manufacturing the elastic wave device 2A according to the fourth embodiment will be described. FIG. 14 is a diagram illustrating a first method for manufacturing the elastic wave device according to the fourth embodiment. As shown in FIG. 14 , a LiNbO ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared (step ST41).

[0085] Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST42). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method. That is, in step ST42, a resist is patterned on the second main surface 20b of the piezoelectric layer 20 by photolithography. After a metal film is vapor-deposited, the resist is removed, thereby forming the metal film as the lower electrode 32.

[0086] Next, an auxiliary electrode 38 is formed on the lower electrode 32 (step ST43). The auxiliary electrode 38 is made of a metal material that is a good conductor, and reduces the resistivity of the lower electrode 32. The auxiliary electrode 38 does not necessarily have to be formed.

[0087] Next, a sacrificial layer 25 is formed on the second main surface 20b side of the piezoelectric body 21 (step ST44). The sacrificial layer 25 is provided in a region of the support member 13 (insulating layer 12) where the cavity portion 14 is to be formed. In other words, the sacrificial layer 25 is provided so as to cover a portion of the lower electrode 32. The sacrificial layer 25 is formed by sputtering using a material such as zinc oxide (ZnO).

[0088] An insulating layer 12 is formed to cover the lower electrode 32 and the sacrificial layer 25 (step ST45). The insulating layer 12 is formed by sputtering using a material such as silicon oxide. An adhesion layer made of Ti, NiCr, or the like may be provided between the lower electrode 32 and the insulating layer 12.

[0089] The surface of the insulating layer 12 opposite to the piezoelectric body 21 is flattened by CMP (Chemical Mechanical Polishing) (step ST46).

[0090] Meanwhile, a support substrate 11 is prepared, and the support substrate 11 is bonded to the insulating layer 12 formed on the piezoelectric body 21. This bonds the support substrate 11 to the insulating layer 12 and the piezoelectric body 21 (step ST47). The support substrate 11 is bonded to the insulating layer 12 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like.

[0091] The first main surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST48). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0092] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20 (step ST49). The upper electrode 31 is formed in an annular shape, and the first through-holes 31H are formed by patterning.

[0093] A second through-hole 20H is formed in the piezoelectric layer at a position overlapping the first through-hole 31H. An opening 34H is also formed in the piezoelectric layer 20 at a position overlapping the lower electrode 32 but not overlapping the region where the upper electrode 31 is to be formed (step ST50). At this time, an etching window 25H (see FIG. 12) is also formed at the same time. The second through-hole 20H, the etching window 25H, and the opening 34H are formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0094] A first wiring layer 33 is formed at a position where it connects to the upper electrode 31, and a second wiring layer 34 is formed on the lower electrode 32 in a region overlapping with the opening 34H (step ST51). The first wiring layer 33 and the second wiring layer 34 are formed by, for example, a vapor deposition lift-off method, similar to the above-described lower electrode 32.

[0095] Next, the sacrificial layer 25 is removed (step ST52). The sacrificial layer 25 is removed by wet etching. In this case, an etchant that dissolves the sacrificial layer 25 is injected through an etching window 25H (see FIG. 12). Then, a cavity 14 is formed in the insulating layer 12 (step ST53). This forms a membrane structure of the piezoelectric layer 20. Through the above steps, the acoustic wave device 2A of this preferred embodiment is manufactured.

[0096] 15 is a diagram illustrating a second manufacturing method of the elastic wave device according to the fourth embodiment. As another manufacturing method, as shown in FIG. ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon nitride film, is prepared (step ST61). Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST62). An auxiliary electrode 38 is formed on the lower electrode 32 (step ST63).

[0097] An insulating layer 12A is formed to cover the piezoelectric body 21, the lower electrode 32, and the auxiliary electrode 38 (step ST64). The insulating layer 12A is formed by sputtering using a material such as silicon oxide. The surface of the insulating layer 12A opposite to the piezoelectric body 21 is planarized by CMP (chemical mechanical polishing) (step ST65).

[0098] Next, the insulating layer 12A is patterned by dry etching or wet etching to form the protrusion 95 and the cavity portion 14 (step ST66).

[0099] A support substrate 11 having an intermediate layer 12B formed on one surface thereof is prepared, and the intermediate layer 12B on the support substrate 11 is bonded to the insulating layer 12A. This bonds the support substrate 11 to the insulating layer 12 and the piezoelectric layer 20 (step ST67). More specifically, the intermediate layer 12B is formed of the same material as the insulating layer 12A, such as silicon oxide. The intermediate layer 12B of the support substrate 11 is bonded to the insulating layer 12A by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. This bonds the insulating layer 12A and the intermediate layer 12B together. In the following description, when it is not necessary to distinguish between the intermediate layer 12B and the insulating layer 12A, they will simply be referred to as the insulating layer 12.

[0100] The first main surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST68). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0101] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20 (step ST69). The upper electrode 31 is formed in an annular shape, and the first through-holes 31H are formed by patterning.

[0102] A second through-hole 20H is formed in the piezoelectric layer at a position overlapping the first through-hole 31H. An opening 34H is also formed in the piezoelectric layer 20 at a position overlapping the lower electrode 32 but not overlapping the region where the upper electrode 31 is to be formed (step ST70). At this time, it is not necessary to process an etching window 25H (see FIG. 12 ). The second through-hole 20H and the opening 34H are formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0103] A first wiring layer 33 is formed at a position where it connects to the upper electrode 31, and a second wiring layer 34 is formed on the lower electrode 32 in a region overlapping with the opening 34H (step ST71A). The first wiring layer 33 and the second wiring layer 34 are formed by, for example, a vapor deposition lift-off method, similar to the above-mentioned lower electrode 32. This forms a membrane structure of the piezoelectric layer 20.

[0104] 16 is a plan view of an elastic wave device according to Modification 1 of Embodiment 4. In an elastic wave device 2B according to Modification 1 of Embodiment 4, first through holes 31H and second through holes 20H have rectangular shapes when viewed in the Z direction.

[0105] 17 is a plan view of an elastic wave device according to Modification 2 of Embodiment 4. In an elastic wave device 2C according to Modification 2 of Embodiment 4, first through holes 31H and second through holes 20H are rectangular when viewed from the Z direction. The outer shape of upper electrode 31 is also rectangular when viewed from the Z direction. Although not shown, the outer shape of lower electrode 32 is also rectangular when viewed from the Z direction.

[0106] 18 is a plan view of an elastic wave device according to a third modification of the fourth embodiment. The outer shape of the upper electrode 31 is polygonal when viewed from the Z direction. Although not shown, the outer shape of the lower electrode 32 is also polygonal when viewed from the Z direction.

[0107] 19 is a plan view of an elastic wave device according to a fifth embodiment. Fig. 20 is a cross-sectional view taken along the line XX-XX' of Fig. 19. As shown in Fig. 19, an elastic wave device 2E according to the fifth embodiment differs from the fourth embodiment in that it has a third through hole 32H in the lower electrode 32.

[0108] 19 and 20 , a third through hole 32H is formed in the lower electrode 32, and the protrusion 95 penetrates the third through hole 32H, with the tip of the lower electrode 32 abutting the piezoelectric layer 20. The tip of the protrusion 95 is larger than the second through hole 20H and blocks the second through hole 20H. When viewed from the Z direction, the first through hole 31H, the second through hole 20H, the third through hole 32H, and the protrusion 95 overlap. The diameter of the first through hole 31H is larger than the diameter of the protrusion 95, which is larger than the diameter of the second through hole 20H. The diameter of the first through hole 31H is larger than the diameter of the third through hole 32H, which is larger than the diameter of the second through hole 20H.

[0109] Without the second through hole 20H, the diameter of the protrusion 95 needs to be increased to suppress the interference waves caused by the influence of the first through hole 31H. In contrast, in the elastic wave device 2E of Embodiment 5, the second through hole 20H suppresses the interference waves caused by the influence of the first through hole 31H, so the diameter of the protrusion 95 can be reduced.

[0110] Next, a method for manufacturing the elastic wave device 2E according to Embodiment 5 will be described. FIG. 21 is a diagram illustrating a first method for manufacturing the elastic wave device according to Embodiment 5. As shown in FIG. 21 , a LiNbO ３ , LiTaO ３ A piezoelectric body 21, which is a single-crystal substrate such as a silicon dioxide film, is prepared (step ST71). Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST72). The lower electrode 32 is formed, for example, by a vapor deposition lift-off method. That is, in step ST72, a resist pattern is formed on the second main surface 20b of the piezoelectric layer 20 by photolithography. After a metal film is vapor-deposited, the resist is removed, thereby forming the metal film as the lower electrode 32. As a result, the lower electrode 32 is formed in an annular shape and has a third through-hole 32H. An auxiliary electrode 38 is formed on the lower electrode 32 (step ST73). The auxiliary electrode 38 is made of a metal material that is a good conductor and reduces the resistivity of the lower electrode 32. The auxiliary electrode 38 is not necessarily formed.

[0111] Next, a sacrificial layer 25 is formed on the second main surface 20b side of the piezoelectric body 21 (step ST74). The sacrificial layer 25 is provided in a region of the support member 13 (insulating layer 12) where the cavity portion 14 is to be formed. In other words, the sacrificial layer 25 is provided so as to cover a portion of the lower electrode 32. The sacrificial layer 25 is formed by sputtering using a material such as zinc oxide (ZnO).

[0112] An insulating layer 12 is formed to cover the lower electrode 32 and the sacrificial layer 25 (step ST75). The insulating layer 12 is formed by sputtering using a material such as silicon oxide. An adhesion layer of Ti, NiCr, or the like may be provided between the lower electrode 32 and the insulating layer 12. The surface of the insulating layer 12 opposite to the piezoelectric body 21 is planarized by CMP (chemical mechanical polishing) (step ST76).

[0113] Meanwhile, a support substrate 11 is prepared, and the support substrate 11 is bonded to the insulating layer 12 formed on the piezoelectric body 21. This bonds the support substrate 11 to the insulating layer 12 and the piezoelectric body 21 (step ST77). The support substrate 11 is bonded to the insulating layer 12 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like.

[0114] The first main surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST78). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0115] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20 (step ST79). The upper electrode 31 is formed in an annular shape, and the first through-holes 31H are formed by patterning.

[0116] A second through-hole 20H is formed in the piezoelectric layer at a position overlapping the first through-hole 31H. An opening 34H is also formed in the piezoelectric layer 20 at a position overlapping the lower electrode 32 but not overlapping the region where the upper electrode 31 is to be formed (step ST80). At this time, an etching window 25H (see FIG. 12) is also formed at the same time. The second through-hole 20H, the etching window 25H, and the opening 34H are formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0117] A first wiring layer 33 is formed at a position connected to the upper electrode 31, and a second wiring layer 34 is formed on the lower electrode 32 in a region overlapping with the opening 34H (step ST81). The first wiring layer 33 and the second wiring layer 34 are formed by, for example, a vapor deposition lift-off method, similar to the above-described lower electrode 32.

[0118] Next, the sacrificial layer 25 is removed (step ST82). The sacrificial layer 25 is removed by wet etching. In this case, an etchant that dissolves the sacrificial layer 25 is injected through an etching window 25H (see FIG. 12). Then, a cavity 14 is formed in the insulating layer 12 (step ST83). This forms a membrane structure of the piezoelectric layer 20. Through the above steps, the acoustic wave device 2E of this preferred embodiment is manufactured.

[0119] 22 is a diagram illustrating a second manufacturing method of the elastic wave device according to Embodiment 5. As another manufacturing method, as shown in FIG. ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon nitride film, is prepared (step ST91). Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST92). An auxiliary electrode 38 is formed on the lower electrode 32 (step ST93).

[0120] An insulating layer 12A is formed to cover the piezoelectric body 21, the lower electrode 32, and the auxiliary electrode 38 (step ST94). The insulating layer 12A is formed by sputtering using a material such as silicon oxide. The surface of the insulating layer 12A opposite to the piezoelectric body 21 is planarized by CMP (chemical mechanical polishing) (step ST95).

[0121] Next, the insulating layer 12A is patterned by dry etching or wet etching to form the protrusion 95 and the cavity 14 (step ST96).

[0122] A support substrate 11 having an intermediate layer 12B formed on one surface is prepared, and the intermediate layer 12B on the support substrate 11 is bonded to the insulating layer 12A. This bonds the support substrate 11 to the insulating layer 12 and the piezoelectric layer 20 (step ST97). More specifically, the intermediate layer 12B is formed of the same material as the insulating layer 12A, such as silicon oxide. The intermediate layer 12B of the support substrate 11 is bonded to the insulating layer 12A by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. This bonds the insulating layer 12A and the intermediate layer 12B together. In the following description, when it is not necessary to distinguish between the intermediate layer 12B and the insulating layer 12A, they will simply be referred to as the insulating layer 12.

[0123] The first main surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST98). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0124] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20 (step ST99). The upper electrode 31 is formed in an annular shape, and the first through-holes 31H are formed by patterning.

[0125] A second through-hole 20H is formed in the piezoelectric layer at a position overlapping the first through-hole 31H. An opening 34H is also formed in the piezoelectric layer 20 at a position overlapping the lower electrode 32 but not overlapping the region where the upper electrode 31 is to be formed (step ST100). At this time, it is not necessary to process an etching window 25H (see FIG. 12 ). The second through-hole 20H and the opening 34H are formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0126] A first wiring layer 33 is formed at a position connected to the upper electrode 31, and a second wiring layer 34 is formed on the lower electrode 32 in a region overlapping with the opening 34H (step ST101). The first wiring layer 33 and the second wiring layer 34 are formed by, for example, a vapor deposition lift-off method, similar to the lower electrode 32 described above. The elastic wave device 2E of this preferred embodiment is manufactured through the above steps.

[0127] Sixth Embodiment Fig. 23 is a plan view showing an elastic wave device according to a sixth embodiment. Fig. 24 is a cross-sectional view taken along line XXIV-XXIV' in Fig. 23. As shown in Figs. 23 and 24, an elastic wave device 3A according to the sixth embodiment differs from that according to the first embodiment in the shape of a protrusion 96 when viewed in the Z direction.

[0128] The support member 13 is provided opposite to the second main surface 20b of the piezoelectric layer 20. The support member 13 of the first embodiment is a support substrate, and is made of silicon (Si), quartz crystal, or the like.

[0129] A cavity portion 14 (hollow portion) is formed on the surface of the support member 13 facing the second main surface 20b of the piezoelectric layer 20. A portion of the surface of the support member 13 facing the second main surface 20b of the piezoelectric layer 20 forms the bottom of the cavity portion 14. The cavity portion 14 is provided so as to overlap, in plan view, with the excitation region of a resonator formed by overlapping the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32. This allows bulk waves to be reflected by the cavity portion 14. The resonance formed by overlapping the upper electrode 31 and the lower electrode 32 is the functional electrode 30 of the first embodiment.

[0130] The piezoelectric layer 20 is in the form of a flat plate having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of, for example, lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO ３ The thickness of the piezoelectric layer 20 is not particularly limited, but is preferably 1 μm or less.

[0131] The upper electrode 31 is provided on the first major surface 20a of the piezoelectric layer 20. The lower electrode 32 is provided on the second major surface 20b of the piezoelectric layer 20, in a region at least partially overlapping with the upper electrode 31. The upper electrode 31 and the lower electrode 32 are formed of a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or an alloy containing at least one of these materials. The upper electrode 31 and the lower electrode 32 may be a stacked film of at least two or more metal layers such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), molybdenum (Mo), or the like.

[0132] The elastic wave device 3A has a so-called membrane structure in which a cavity 14 (hollow portion) is provided on the second main surface 20b side of the piezoelectric layer 20, and an upper electrode 31 and a lower electrode 32 are arranged at positions overlapping the cavity 14 (hollow portion). In the region overlapping with the cavity 14, the piezoelectric layer 20 is arranged between the upper electrode 31 and the lower electrode 32 in the Z direction. This allows bulk waves to propagate between the upper electrode 31 and the lower electrode 32.

[0133] 23, the protrusions 96 are lattice-shaped and are formed of an insulating material such as silicon oxide, a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), or molybdenum (Mo), or an alloy containing at least one of these materials.

[0134] The protrusions 96 are in contact with both the bottom surface (support member 13) of the cavity 14 and the lower electrode 32. The lattice-shaped protrusions 96 also enable excitation of a membrane structure. Furthermore, the thickness of the piezoelectric layer 20 is thinned to 1 μm or less, and if the thickness of the piezoelectric layer 20 varies and the in-plane thickness of the piezoelectric layer 20 becomes non-uniform, this can easily affect the excitation characteristics. In this embodiment, the in-plane thickness of the piezoelectric layer 20 can be suppressed, thereby improving the quality of the acoustic wave device 3A even when the piezoelectric layer 20 is thinned to 1 μm or less.

[0135] Next, a manufacturing method of elastic wave device 3A according to Embodiment 6 will be described. Fig. 25 is an explanatory diagram illustrating a first manufacturing method of the elastic wave device according to Embodiment 6. As shown in Fig. 25 , a support substrate that will become support member 13 is prepared. A portion of the support substrate is recessed by reactive ion etching to form support member 13 having cavity portion 14 (step ST111).

[0136] Next, LiNbO ３ , LiTaO ３A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared, and a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST112). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method. That is, in step ST112, a resist pattern is formed on the second main surface 20b of the piezoelectric body 21 by photolithography. After a metal film is vapor-deposited, the resist is removed, thereby forming the metal film as the lower electrode 32.

[0137] Next, a protrusion 96 is formed on the lower electrode 32 (step ST113). The protrusion 96 is formed by, for example, a vapor deposition lift-off method. The total height of the protrusion 96 plus the height of the lower electrode 32 is the same as the depth of the cavity 14.

[0138] Next, the support member 13 and the piezoelectric layer 20 are bonded together (step ST114). More specifically, the support member 13 is bonded to the piezoelectric layer 20 by direct bonding, plasma activation bonding, atomic diffusion bonding, or the like.

[0139] Next, the first main surface of the piezoelectric body 21 is polished by, for example, mechanical polishing or CMP (Chemical Mechanical Polishing), and the thickness of the piezoelectric body 21 bonded in step ST114 is reduced (step ST115). This results in a piezoelectric layer 20 having a thickness of 1 μm or less. If the piezoelectric body 21 is thin before bonding in step ST114, the piezoelectric body 21 may be damaged during bonding. Therefore, the thickness of the piezoelectric body 21 must be reduced after bonding in step ST114. In step ST115, the protrusions 96 act as supports between the support member 13 and the piezoelectric layer 20, preventing the piezoelectric layer 20 from adhering to the bottom of the cavity 14 (sticking). Furthermore, the presence of the lattice-shaped protrusions 96 suppresses unevenness in the thickness distribution of the piezoelectric layer due to polishing.

[0140] Next, upper electrode 31 is formed to cover at least a portion of piezoelectric layer 20 (step ST116). Through the above steps, elastic wave device 3A of Preferred Embodiment 6 is manufactured.

[0141] 26 is an explanatory diagram illustrating a second manufacturing method for an elastic wave device according to Embodiment 6. In this manufacturing method, as shown in FIG. 26 , a support substrate that serves as a support member is prepared (step ST121). ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared, and a lower electrode 32 and an insulating layer 12 are formed on the second main surface 20b of the piezoelectric body 21 (step ST122). The insulating layer 12 is patterned by dry etching or wet etching, so that the insulating layer 12 surrounds the lower electrode 32. The insulating layer 12 is formed by sputtering using a material such as silicon oxide. The surface of the insulating layer 12 opposite the piezoelectric body 21 may be planarized by chemical mechanical polishing (CMP).

[0142] Next, a protrusion 96 is formed on the lower electrode 32 (step ST123). The protrusion 96 is formed by, for example, a vapor deposition lift-off method. The total height of the lower electrode 32 plus the height of the protrusion 96 is the same as the height of the insulating layer 12.

[0143] Next, the support substrate 11 is bonded to the insulating layer 12. As a result, the support substrate 11 and the insulating layer 12 are attached to each other (step ST124).

[0144] The first main surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST125). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0145] Upper electrode 31 is formed on first main surface 20a of piezoelectric layer 20 (step ST126). Through the above steps, elastic wave device 3A of Preferred Embodiment 6 is manufactured.

[0146] Seventh Embodiment Fig. 27 is a plan view showing an elastic wave device according to a seventh embodiment. As shown in Fig. 27, an elastic wave device 3B according to the seventh embodiment differs from that according to the sixth embodiment in the shape of the piezoelectric layer 20. The planar shape of the seventh embodiment is the same as that shown in Fig. 23. The same components as those according to the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0147] Next, a method for manufacturing the elastic wave device 3B according to the first embodiment will be described. FIG. 28 is a diagram illustrating a method for manufacturing the elastic wave device according to the seventh embodiment. As shown in FIG. 28, a LiNbO ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared. A portion of the piezoelectric body 21 is recessed by reactive ion etching, thereby forming the piezoelectric body 21 having the cavity portion 14 (step ST131).

[0148] Next, the lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST132). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method.

[0149] Next, a protrusion 96 is formed on the lower electrode 32 (step ST133). The protrusion 96 is formed by, for example, a vapor deposition lift-off method. The total height of the protrusion 96 plus the height of the lower electrode 32 is the same as the depth of the cavity 14.

[0150] Next, a support substrate that will become the support member 13 is prepared, and the support member 13 and the piezoelectric body 21 are bonded together (step ST134). More specifically, the support member 13 is bonded to the piezoelectric body 21 by direct bonding, plasma activation bonding, atomic diffusion bonding, or the like.

[0151] Next, the first main surface of the piezoelectric body 21 is polished by, for example, mechanical polishing or CMP (Chemical Mechanical Polishing), and the thickness of the piezoelectric body 21 bonded in step ST134 is reduced (step ST135). This results in a piezoelectric layer 20 having a thickness of 1 μm or less. If the piezoelectric body 21 is thin before bonding in step ST134, the piezoelectric body 21 may be damaged during bonding. Therefore, the thickness of the piezoelectric body 21 must be reduced after bonding in step ST134. In step ST135, the protrusions 96 act as supports between the support member 13 and the piezoelectric layer 20, thereby thinning the piezoelectric body 21 without causing the piezoelectric layer 20 to stick to the bottom of the cavity portion 14 (sticking). Furthermore, the presence of the lattice-shaped protrusions 96 suppresses unevenness in the thickness distribution of the piezoelectric layer 20 due to polishing.

[0152] Next, upper electrode 31 is formed to cover at least a portion of piezoelectric layer 20 (step ST136). Through the above steps, acoustic wave device 3B of Preferred Embodiment 7 is manufactured.

[0153] 29 is a cross-sectional view of an elastic wave device according to embodiment 8. As shown in Fig. 29, an elastic wave device 3C according to embodiment 8 differs from embodiment 6 in the configuration of support member 13. The planar shape of embodiment 8 is the same as that shown in Fig. 23. The same components as embodiment 6 are denoted by the same reference numerals, and description thereof will be omitted.

[0154] As shown in Figure 29, the support member 13 is provided opposite the second main surface 20b of the piezoelectric layer 20. The support member 13 includes a support substrate 11 and an insulating layer 12. The support substrate 11 is made of silicon (Si), quartz crystal, or the like. The insulating layer 12 is provided between the support substrate 11 and the piezoelectric layer 20. The insulating layer 12 is made of an insulating material such as silicon oxide. An etching window 25H is provided in the piezoelectric layer 20. The etching window 25H is an opening for etching when forming the cavity portion 14 of the insulating layer 12.

[0155] Next, a method for manufacturing an elastic wave device 3C according to Embodiment 8 will be described. FIG. 30 is a diagram illustrating a method for manufacturing an elastic wave device according to Embodiment 8. As shown in FIG. 30 , a LiNbO ３ , LiTaO ３ A piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared, and a rectangular lower electrode 32 is formed on a second main surface 21b of the piezoelectric body 21 (step ST141). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method. Next, a protrusion 96 is formed on the lower electrode 32 (step ST142). The protrusion 96 is formed by, for example, a vapor deposition lift-off method.

[0156] Next, a sacrificial layer 25 is formed on the second main surface 21b side of the piezoelectric body 21 (step ST143). The sacrificial layer 25 is provided in a region of the support member 13 (insulating layer 12) where the cavity portion 14 is to be formed. In other words, the sacrificial layer 25 is provided so as to cover the lower electrode 32. The sacrificial layer 25 is formed by sputtering using a material such as zinc oxide (ZnO).

[0157] Next, the insulating layer 12 is formed to cover the sacrificial layer 25 (step ST144). The insulating layer 12 is formed by sputtering using a material such as silicon oxide.

[0158] The surface of the insulating layer 12 opposite to the piezoelectric body 21 is flattened by CMP (Chemical Mechanical Polishing).

[0159] Meanwhile, a support substrate 11 is prepared, and the support substrate 11 is bonded to the insulating layer 12 formed on the piezoelectric body 21. This bonds the support substrate 11 to the insulating layer 12 and the piezoelectric body 21 (step ST145). The support substrate 11 is bonded to the insulating layer 12 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like.

[0160] The first main surface 21a of the piezoelectric body 21 is ground and polished to form the piezoelectric layer 20, which is then thinned (step ST146). The first main surface 20a of the piezoelectric layer 20 is polished by, for example, mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0161] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20 (step ST147). The upper electrode 31 is formed in a rectangular shape.

[0162] An etching window 25H is formed in the piezoelectric layer 20. The etching window 25H is formed by removing a portion of the piezoelectric layer 20 using reactive ion etching (RIE). The sacrificial layer 25 is then removed. The sacrificial layer 25 is removed by wet etching. In this case, an etchant that dissolves the sacrificial layer 25 is injected through the etching window 25H. A cavity 14 is then formed in the insulating layer 12 (step ST148). This forms a membrane structure in the piezoelectric layer 20. The elastic wave device 3C of Embodiment 8 is manufactured through the above steps.

[0163] Ninth Embodiment Fig. 31 is a plan view showing an elastic wave device according to a ninth embodiment. Fig. 32 is a cross-sectional view taken along the line XXXII-XXXII' of Fig. 31. As shown in Figs. 31 and 32, an elastic wave device 3D according to the ninth embodiment differs from that according to the sixth embodiment in the configuration of a protrusion 96A. The same components as those according to the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted. The elastic wave device 3D according to the ninth embodiment can be manufactured using the same process as that according to the sixth embodiment.

[0164] 31 and 32, the two protrusions 96A are linear and are formed of an insulating material such as silicon oxide, a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), or molybdenum (Mo), or an alloy containing at least one of these materials.

[0165] The protrusion 96A contacts both the bottom surface (support member 13) of the cavity 14 and the lower electrode 32. The two protrusions 96A are linear and arranged parallel to the edge of the lower electrode 32, enabling excitation of a membrane structure. Furthermore, the thickness of the piezoelectric layer 20 is reduced to 1 μm or less. Variations in the thickness of the piezoelectric layer 20, resulting in unevenness in the in-plane thickness of the piezoelectric layer 20, can easily affect the excitation characteristics. In this embodiment, unevenness in the in-plane thickness of the piezoelectric layer 20 can be suppressed, thereby improving the quality of the acoustic wave device 3D even when the piezoelectric layer 20 is thinned to 1 μm or less.

[0166] Tenth Embodiment Fig. 33 is a plan view showing an elastic wave device according to a tenth embodiment. Fig. 34 is a cross-sectional view taken along line XXXIV-XXXIV' in Fig. 33. As shown in Figs. 33 and 34, an elastic wave device 3E according to the tenth embodiment differs from that according to the sixth embodiment in the configuration of a protrusion 96B. The same components as those according to the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted. The elastic wave device 3E according to the tenth embodiment can be manufactured using the same process as that according to the sixth embodiment.

[0167] 33 and 34, the protrusion 96B is frame-shaped and is made of an insulating material such as silicon oxide, a metal such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), or molybdenum (Mo), or an alloy containing at least one of these materials.

[0168] The protrusion 96B contacts both the bottom surface (support member 13) of the cavity portion 14 and the lower electrode 32. The frame-shaped protrusion 96B creates a cavity within the area surrounded by the protrusion 96B, enabling excitation of a membrane structure. Furthermore, the thickness of the piezoelectric layer 20 is reduced to 1 μm or less. Variations in the thickness of the piezoelectric layer 20, resulting in unevenness in the in-plane thickness of the piezoelectric layer 20, can easily affect the excitation characteristics. In this embodiment, unevenness in the in-plane thickness of the piezoelectric layer 20 can be suppressed, thereby improving the quality of the acoustic wave device 3E even when the piezoelectric layer 20 is thinned to 1 μm or less.

[0169] 35 is a cross-sectional view of an elastic wave device according to an eleventh embodiment. As shown in FIG. 35 , an elastic wave device 4A according to the eleventh embodiment differs from that according to the first embodiment in the shape of a protrusion 97. Unlike the first embodiment, the protrusion 97 is not melted by laser light. The same components as those according to any of the first to tenth embodiments are denoted by the same reference numerals, and description thereof will be omitted.

[0170] The support member 13 is provided with three protrusions 97 that protrude from the bottom of the cavity portion 14 toward the piezoelectric layer 20. The number of protrusions 97 is an example and is not limited to three. The protrusions 97 are formed in a rod shape from a metal such as aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), titanium (Ti), or tin (Sn), or an alloy containing at least one of these materials. The protrusions 97 are electrically conductive.

[0171] The tip of the protrusion 97 is the portion closest to the piezoelectric layer 20. As shown in Fig. 35, the tip of the protrusion 97 is not in contact with the piezoelectric layer 20 and the lower electrode 32. The protrusion 97 is not in contact with the piezoelectric layer 20 and the lower electrode 32 when the acoustic wave device 4A is excited, and is set to a height that allows it to come into contact with the piezoelectric layer 20 and the lower electrode 32 only when the piezoelectric layer 20 is deformed during the manufacturing process. Because the tip of the protrusion 97 is not in contact with the piezoelectric layer 20 and the lower electrode 32, leaky waves transmitted to the protrusion 97 are suppressed even when the membrane structure is excited.

[0172] The multiple protrusions 97 are electrically connected to each other via the conductive layer 97a. A wiring 37 (ground wiring) to which a constant potential is applied is routed on the back surface of the support member 13. A through-wire 97T penetrating the support member 13 electrically connects the conductive layer 97a to the wiring 37. When the piezoelectric body 21 or the piezoelectric layer 20 is heated during the manufacturing process, polarization may occur due to the pyroelectric effect. When heated during the manufacturing process, if any of the multiple protrusions 97 is in contact with the piezoelectric layer 20, the piezoelectric layer 20 is connected to the wiring 37 (ground wiring) to which a constant potential is applied via the protrusion 97, the conductive layer 97a, and the through-wire 97T. As a result, unintended polarization of the piezoelectric layer 20 is suppressed, improving the quality of the piezoelectric layer 20.

[0173] Next, a method for manufacturing the elastic wave device 4A according to Embodiment 11 will be described. FIG. 36 is a diagram illustrating a method for manufacturing the elastic wave device according to Embodiment 11. As shown in FIG. 36 , a LiNbO ３ , LiTaO ３ First, a piezoelectric body 21, which is a single crystal substrate such as a silicon dioxide film, is prepared (step ST151). Next, a lower electrode 32 is formed on the second main surface 20b of the piezoelectric body 21 (step ST152). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method.

[0174] Meanwhile, a support member 13 is prepared. A portion of the support member 13 is recessed by reactive ion etching to form the support member 13 having a cavity portion 14 (step ST161). Next, a protrusion 97 is formed on the bottom of the cavity portion 14 (step ST162). The protrusion 97 is formed by, for example, a vapor deposition lift-off method. The height of the protrusion 97 is smaller than the depth of the cavity portion 14.

[0175] Next, a conductive layer 97a is formed on the bottom surface of the cavity portion 14, and the plurality of protrusions 97 are electrically connected to one another (step ST163).

[0176] Next, the support member 13 and the piezoelectric layer 20 are bonded together (step ST164). More specifically, the support member 13 is bonded to the piezoelectric layer 20 by direct bonding, plasma activation bonding, atomic diffusion bonding, or the like.

[0177] Next, the first main surface of the piezoelectric body 21 is polished by, for example, mechanical polishing or CMP (Chemical Mechanical Polishing), and the thickness of the piezoelectric body 21 bonded in step ST164 is reduced (step ST165). This results in a piezoelectric layer 20 having a thickness of 1 μm or less. If the piezoelectric body 21 is thin before bonding in step ST164, the piezoelectric body 21 may be damaged during bonding. Therefore, the thickness of the piezoelectric body 21 must be reduced after bonding in step ST164. In step ST165, the protrusions 97 act as supports between the support member 13 and the piezoelectric layer 20, thereby thinning the piezoelectric body 21 without causing the piezoelectric layer 20 to stick to the bottom of the cavity portion 14 (sticking). Furthermore, the presence of multiple protrusions 97 reduces unevenness in the thickness distribution of the piezoelectric layer due to polishing.

[0178] Next, a hole is formed in a part of the back surface of the support member 13 by reactive ion etching to form a through hole 13H that extends from the back surface to the conductive layer 97a (step ST166). Next, the through hole 13H is filled with a conductive metal by a plating process or the like to form a through wiring 97T (step ST167).

[0179] Next, wiring 37 is formed on the rear surface of support member 13, and wiring 37 is electrically connected to through wiring 97T. Upper electrode 31 is formed to cover at least a portion of piezoelectric layer 20 (step ST168).

[0180] The elastic wave device 4A of this preferred embodiment is manufactured through the above steps. Note that the steps shown in FIG. 36 are merely schematic and can be modified as appropriate.

[0181] 37 is a cross-sectional view of an elastic wave device according to Modification 1 of Embodiment 11. Elastic wave device 4B of Modification 1 of Embodiment 11 differs in that protrusion 97 is composed of an inner layer 97A and an outer layer 97B formed around inner layer 97A.

[0182] In the first modification of the eleventh embodiment, similarly to the third embodiment, a portion of the support substrate is recessed by reactive ion etching to form the support member 13 having the cavity portion 14, and an inner layer 97A is simultaneously formed on the bottom of the cavity portion 14. The inner layer 97A is a part of the protruding portion 97, and protrudes from the bottom of the cavity portion 14 toward the piezoelectric layer 20.

[0183] The outer layer 97B is a conductive metal film made of aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), titanium (Ti), tin (Sn), or the like, and is attached around the inner layer 97A.

[0184] The outer layers 97B are electrically connected to one another by conductive layers 97a. Wiring 37 to which a constant potential is applied is routed on the back surface of the support member 13. Through wiring 97T that penetrates the inside of the support member 13 electrically connects the conductive layers 97a and the wiring 37.

[0185] 38 is a cross-sectional view of an elastic wave device according to Modification 2 of Embodiment 11. Elastic wave device 4C according to Modification 2 of Embodiment 11 differs in that protrusion 97 is composed of inner layer 97C and outer layer 97D formed around inner layer 97C.

[0186] In the second modification of the eleventh embodiment, the support member 13 is provided with three inner layers 97C that protrude from the bottom of the cavity portion 14 toward the piezoelectric layer 20. The number of inner layers 97C is an example and is not limited to three. The inner layers 97C are formed in a rod shape from a metal such as aluminum (Al), silver (Ag), copper (Cu), platinum (Pt), titanium (Ti), or tin (Sn), or an alloy containing at least one of these materials. The inner layers 97C are electrically conductive.

[0187] The outer layer 97D is a film with higher abrasion resistance than the inner layer 97C, and is attached around the inner layer 97C. The outer layer 97D is made of, for example, diamond-like carbon. As a result, although the outer layer 97D comes into contact with the piezoelectric layer 20 and the lower electrode 32 only when the piezoelectric layer 20 is deformed during the manufacturing process, the outer layer 97D is less likely to be damaged due to its high abrasion resistance.

[0188] The multiple inner layers 97C are electrically connected to one another by conductive layers 97a. Wiring 37 to which a constant potential is applied is routed on the back surface of the support member 13. Through wiring 97T that penetrates the inside of the support member 13 electrically connects the conductive layers 97a and the wiring 37.

[0189] 39 is a cross-sectional view of an elastic wave device according to Modification 3 of Embodiment 11. As shown in Fig. 39 , an elastic wave device 4D according to Modification 3 of Embodiment 11 differs from that of Embodiment 11 in the shape of piezoelectric layer 20. The same components as those of Embodiment 11 are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0190] In the third modification of the eleventh embodiment, the cavity 14 is formed by a recess provided inside the piezoelectric layer 20 .

[0191] 40 is a cross-sectional view of an elastic wave device according to a fourth modification of the 11th embodiment. As shown in Fig. 40, an elastic wave device 4E according to the fourth modification of the 11th embodiment differs from the 11th embodiment in the structure of the support member 13. The same components as those in the 11th embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0192] In the fourth modification of the eleventh embodiment, the support member 13 includes a support substrate 11 and an insulating layer 12. A cavity portion 14 is formed inside the insulating layer 12.

[0193] 41 is a cross-sectional view of an elastic wave device according to a fifth modification of the 11th embodiment. As shown in Fig. 41 , an elastic wave device 4F according to the fifth modification of the 11th embodiment differs from the 11th embodiment in the structure of the support member 13 and the wiring 37 (ground wiring) to which a constant potential is applied. The same components as those of the 11th embodiment are denoted by the same reference numerals, and descriptions thereof will be omitted.

[0194] In the fifth modification of the eleventh embodiment, the support member 13 includes a support substrate 11 and an insulating layer 12. A cavity 14 is formed inside the insulating layer 12 and the support substrate 11. The wiring 37 is routed on the first main surface 20a of the piezoelectric layer 20, and the conductive layer 97a and the wiring 37 are connected by a connection wiring 97b. The functional electrodes of the elastic wave device 4F in the fifth modification of the eleventh embodiment are IDT (interdigital transducer) electrodes.

[0195] The insulating layer 12A shown in this embodiment can be combined with each of the above-described embodiments and modifications.

[0196] The above-described embodiments are intended to facilitate understanding of the present disclosure and are not intended to limit the present disclosure. The present disclosure may be modified or improved without departing from the spirit thereof, and equivalents thereof are also included in the present disclosure.

[0197] The present disclosure may also have the following configurations.

[0198] (1) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an upper electrode provided on the first main surface of the piezoelectric layer; a lower electrode provided on the second main surface of the piezoelectric layer; and a support member facing the second main surface of the piezoelectric layer, wherein the support member or the piezoelectric layer has a cavity in a region overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion protruding from a bottom of the cavity toward the piezoelectric layer, and a tip of the protrusion is not in contact with the piezoelectric layer or the lower electrode. (2) The elastic wave device according to (1), further comprising a reflective layer covering at least the upper electrode and having a higher reflectivity for laser light than the piezoelectric layer. (3) The elastic wave device according to (2), wherein the reflective layer has a metallic luster. (4) The elastic wave device according to (2), wherein the reflective layer reflects the laser light by thin film interference and is a laminated film formed by alternately stacking dielectrics having different refractive indices. (5) The elastic wave device according to any one of (2) to (4), wherein the protrusion is provided in a region that does not overlap the reflective layer when viewed in a direction perpendicular to the first main surface. (6) The elastic wave device according to (2) or (3), wherein the upper electrode and the lower electrode are misaligned when viewed in a direction perpendicular to the first main surface, the reflective layer overlaps the lower electrode, and the reflective layer is a conductor. (7) The elastic wave device according to any one of (1) to (6), wherein the surface of the protrusion has a different crystal state from the interior of the protrusion. (8) The elastic wave device according to any one of (1) to (6), wherein the protrusion is made of the same material as the support member, is part of the support member, and has a different roughness from the bottom of the cavity. (9) The elastic wave device according to any one of (1) to (6), wherein the protrusion is conductive, and is connected to wiring to which a constant potential is applied.(10) A method for manufacturing an elastic wave device, comprising: preparing a piezoelectric layer having a first main surface and a second main surface opposite to the first main surface, and forming a lower electrode on the second main surface of the piezoelectric layer; preparing a support member having a cavity and a protrusion with a height equal to a depth of the cavity; bonding the piezoelectric layer to the support member; thinning the thickness of the piezoelectric layer bonded to the support member; forming an upper electrode on the first main surface of the piezoelectric layer; and melting the protrusion with laser light. (11) The method for manufacturing an elastic wave device according to (10), further comprising forming a reflective layer that covers at least the upper electrode before the step of melting the protrusion with laser light. (12) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an upper electrode provided on the first main surface of the piezoelectric layer; a lower electrode provided on the second main surface of the piezoelectric layer; and a support member facing the second main surface of the piezoelectric layer, wherein the support member has a cavity portion in an area overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion protruding from a bottom of the cavity portion toward the piezoelectric layer, a first through hole formed in the upper electrode, and a second through hole formed in the piezoelectric layer, and a tip of the protrusion abuts against the piezoelectric layer or the lower electrode, and the first through hole, the second through hole, and the protrusion overlap when viewed in a direction perpendicular to the first main surface. (13) The elastic wave device according to (12), wherein a tip of the protrusion abuts the lower electrode, the first through hole is larger than the second through hole when viewed from a direction perpendicular to the first main surface, the lower electrode is between the protrusion and the second through hole and closes the second through hole. (14) The elastic wave device according to (12), wherein a third through hole is formed in the lower electrode, the first through hole is larger than the second through hole when viewed from a direction perpendicular to the first main surface, the tip of the protrusion is larger than the second through hole and closes the second through hole, and the tip of the protrusion passes through the third through hole and abuts the piezoelectric layer.(15) An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an upper electrode provided on the first main surface of the piezoelectric layer; a lower electrode provided on the second main surface of the piezoelectric layer; and a support member facing the second main surface of the piezoelectric layer, wherein the support member or the piezoelectric layer has a cavity portion in a region overlapping with at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion that protrudes from a bottom of the cavity portion toward the piezoelectric layer and abuts the upper electrode, and when viewed in a direction perpendicular to the first main surface, a plurality of the protrusions are linear, lattice-shaped, or frame-shaped.

[0199] REFERENCE SIGNS 1A, 1B, 1C, 1D, 1E, 1F, 2A, 2B, 2E, 3A, 3B, 3C, 3D, 3E, 4A, 4B, 4C, 4D, 4E, 4F Acoustic wave device 11 Support substrate 12, 12A Insulating layer 12B Intermediate layer 13 Support member 13H Through hole 14 Cavity portion 20 Piezoelectric layer 20H Second through hole 20a First main surface 20b Second main surface 21 Piezoelectric body 21a First main surface 21b Second main surface 25 Sacrificial layer 25H Etching window 30 Functional electrode 31 Upper electrode 31H First through hole 32 Lower electrode 32H Third through hole 33 First wiring layer 34 Second wiring layer 35 Reflecting layer 36 IDT electrode 37 Wiring 38 Auxiliary electrode 39 Reflective layer 91, 92, 93, 94, 95, 96, 96A, 96B, 97 Projection 97A, 97C Inner layer 97B, 97D Outer layer 97T Through wiring 97a Conductive layer 97b Connection wiring

Claims

1. An elastic wave device comprising: a piezoelectric layer having a first main surface and a second main surface opposite the first main surface; an upper electrode provided on the first main surface of the piezoelectric layer; a lower electrode provided on the second main surface of the piezoelectric layer; and a support member facing the second main surface of the piezoelectric layer, wherein the support member or the piezoelectric layer has a cavity portion in an area overlapping at least a portion of the upper electrode and the lower electrode, and the support member has at least one protrusion protruding from a bottom of the cavity portion toward the piezoelectric layer, and a tip of the protrusion is not in contact with the piezoelectric layer or the lower electrode.

2. The acoustic wave device according to claim 1, further comprising a reflective layer covering at least the upper electrode and having a higher reflectivity for laser light than the piezoelectric layer.

3. The acoustic wave device according to claim 2, wherein the reflective layer has a metallic luster.

4. The acoustic wave device according to claim 2, wherein the reflective layer reflects the laser light by thin film interference and is a laminated film in which dielectric layers having different refractive indices are alternately laminated.

5. The elastic wave device according to claim 2, wherein the protrusion is provided in a region that does not overlap the reflective layer when viewed in a direction perpendicular to the first main surface.

6. The elastic wave device according to claim 2 or 3, wherein the position of the upper electrode and the position of the lower electrode are misaligned when viewed in a direction perpendicular to the first main surface, the reflective layer overlaps the lower electrode, and the reflective layer is a conductor.

7. The elastic wave device according to claim 1, wherein a surface of the protrusion has a different crystal state from an inside of the protrusion.

8. The elastic wave device according to claim 1, wherein the protrusion is made of the same material as the support member, the protrusion is part of the support member, and has a roughness different from that of a bottom of the cavity.

9. The elastic wave device according to claim 1, wherein the protrusion is conductive, and the protrusion is connected to a wiring to which a constant potential is applied.

10. A method for manufacturing an elastic wave device, comprising the steps of: preparing a piezoelectric layer having a first main surface and a second main surface opposite the first main surface, and forming a lower electrode on the second main surface of the piezoelectric layer; preparing a support member having a cavity and a protrusion with the same height as the depth of the cavity; bonding the piezoelectric layer to the support member; thinning the thickness of the piezoelectric layer bonded to the support member; forming an upper electrode on the first main surface of the piezoelectric layer; and melting the protrusion with laser light.

11. The method for manufacturing an acoustic wave device according to claim 10, further comprising the step of forming a reflective layer that covers at least the upper electrode before the step of melting the protruding portion with laser light.

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