Piezoelectric device

Abstract

Provided is a piezoelectric device in which breakage of a piezoelectric layer can be suppressed.　The piezoelectric device comprises: a piezoelectric layer (20) that has a thickness in a first direction (Z) and that has an upper surface (20a) which is one surface in the first direction (Z) and a lower surface (20b) which is the other surface in the first direction (Z); a support member (11) that is provided on the lower surface side of the piezoelectric layer (20); and functional electrodes (31a, 32a) that are provided on at least one of the upper surface (20a) and the lower surface (20b) of the piezoelectric layer (20). The piezoelectric layer (20) or the support member (11) has a space (14) in a region overlapping at least a portion of the functional electrodes (31a, 32a). In plan view in the first direction (Z), in a case where the piezoelectric layer in a region overlapping the space section (14) and the functional electrodes (31a, 32a) is defined as a first section (21) and where the piezoelectric layer in a region overlapping the space (14) and not overlapping the functional electrodes (31a, 32a) is defined as a second section (22), the maximum thickness of the second section (22) is greater than the minimum thickness of the first section (21).

Description

Piezoelectric Devices

[0001] The present invention relates to a piezoelectric device.

[0002] Japanese Patent Application Laid-Open No. 2003-124999 discloses a thin film piezoelectric resonator device in which the thickness of a piezoelectric layer is made different at a position overlapping an opening in a support substrate.

[0003] JP 2023-62889 A

[0004] The piezoelectric layer of the thin film piezoelectric resonator device disclosed in Patent Document 1 may be damaged due to distortion occurring at the boundary between the area where the functional electrode is provided and the area where the functional electrode is not provided.

[0005] The present invention is intended to solve the above-mentioned problems, and has an object to provide a piezoelectric device that can suppress damage to the piezoelectric layer.

[0006] A piezoelectric device according to one aspect of the present invention comprises a piezoelectric layer having a thickness in a first direction and having an upper surface which is one surface in the first direction and a lower surface which is the other surface in the first direction; a support member provided on the lower surface side of the piezoelectric layer; and a functional electrode provided on at least one of the upper and lower surfaces of the piezoelectric layer, wherein the piezoelectric layer or the support member has a space in an area that overlaps with at least a portion of the functional electrode, and when viewed in a plane in the first direction, the piezoelectric layer in the area that overlaps with the space and the functional electrode is defined as a first part, and the piezoelectric layer in the area that overlaps with the space but does not overlap with the functional electrode is defined as a second part, the maximum thickness of the second part is greater than the minimum thickness of the first part.

[0007] According to the present invention, it is possible to provide a piezoelectric device that can suppress damage to the piezoelectric layer.

[0008] FIG. 1 is a schematic plan view showing an example of a piezoelectric device according to the first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1 . FIG. 3 is a diagram showing the thickness distribution of the piezoelectric layer according to the first embodiment. FIG. 4 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to the first embodiment. FIG. 5 is a plan view showing a piezoelectric device according to a first modified example of the first embodiment. FIG. 6 is a schematic cross-sectional view taken along line VI-VI in FIG. 5 . FIG. 7 is a diagram showing the thickness distribution of the piezoelectric layer according to the first modified example. FIG. 8 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to the first modified example. FIG. 9 is a schematic cross-sectional view showing a piezoelectric device according to a second embodiment. FIG. 10 is a diagram showing the thickness distribution of the piezoelectric layer according to the second embodiment. FIG. 11 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to the second embodiment. FIG. 12 is a schematic cross-sectional view showing a piezoelectric device according to a second modified example of the second embodiment. FIG. 13 is a diagram showing the thickness distribution of the piezoelectric layer according to the second modified example of the second embodiment. FIG. 14 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to the second modified example of the second embodiment. FIG. 15 is a schematic cross-sectional view showing a piezoelectric device according to a third modified example of the second embodiment. FIG. 16 is a schematic cross-sectional view showing a piezoelectric device according to a fourth modified example of the second embodiment. FIG. 17 is a schematic cross-sectional view showing a piezoelectric device according to the third embodiment. FIG. 18 is a diagram showing the thickness distribution of the piezoelectric layer according to the third embodiment. FIG. 19 is an explanatory diagram for describing a method for manufacturing a piezoelectric device according to the third embodiment. FIG. 20 is a diagram showing a step for thinning the piezoelectric layer according to the third embodiment. FIG. 21 is a diagram showing a step for thinning the piezoelectric layer according to the third embodiment. FIG. 22 is a schematic cross-sectional view showing a piezoelectric device according to a fifth modified example of the third embodiment. FIG. 23 is a diagram showing the thickness distribution of the piezoelectric layer according to the fifth modified example of the third embodiment. FIG. 24 is an explanatory diagram for describing a method for manufacturing a piezoelectric device according to the fifth modified example of the third embodiment. FIG. 25 is a diagram showing a step for thinning the piezoelectric layer according to the fifth modified example of the third embodiment. FIG. 26 is a schematic cross-sectional view showing a piezoelectric device according to the fourth embodiment. FIG. 27 is an explanatory diagram for describing a method for manufacturing a piezoelectric device according to the fourth embodiment.FIG. 28 is a schematic cross-sectional view showing a piezoelectric device according to a fifth embodiment. FIG. 29 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to the fifth embodiment. FIG. 30 is a schematic plan view showing a piezoelectric device according to a sixth embodiment. FIG. 31 is a schematic plan view showing a piezoelectric device according to a seventh embodiment. FIG. 32 is a schematic cross-sectional view showing a piezoelectric device according to an eighth embodiment. FIG. 33 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to the eighth embodiment. FIG. 34 is a schematic cross-sectional view showing a piezoelectric device according to a sixth modified example of the eighth embodiment. FIG. 35 is a schematic cross-sectional view showing a piezoelectric device according to a seventh modified example of the eighth embodiment.

[0009] 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.

[0010] First Embodiment FIG. 1 is a schematic plan view showing an example of a piezoelectric device according to a first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. A piezoelectric device 10 according to the first embodiment includes a support member 11, a piezoelectric layer 20, an upper electrode 31, and a lower electrode 32. The piezoelectric device 10 is a piezoelectric element that utilizes bulk waves, i.e., a BAW (Bulk Acoustic Wave) element. 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 Y direction is referred to as the Y direction.

[0011] The piezoelectric layer 20 is a flat layer having an upper surface 20a and a lower surface 20b opposite to the upper surface 20a. The upper surface 20a is a first main surface of the piezoelectric layer 20. The lower surface 20b is a second main surface of the piezoelectric layer 20. In the first embodiment, the piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ), lithium tantalate (LiTaO ３The substrate is made of a single crystal, such as quartz, that can excite bulk waves. The thickness of the piezoelectric layer 20 will be described in detail later.

[0012] As shown in FIG. 1 , the upper electrode 31 is provided on the upper surface 20 a of the piezoelectric layer 20. The upper electrode 31 is an example of a “functional electrode.” The upper electrode 31 has a circular main electrode portion 31 a and an extension portion 31 b extending in the X direction from the main electrode portion 31 a. The upper electrode 31 is made of a metal or alloy such as aluminum (Al), platinum (Pt), copper (Cu), tungsten (W), or molybdenum (Mo). The upper electrode 31 may also have an adhesion layer made of titanium (Ti), a nickel-chromium alloy (NiCr), or the like.

[0013] As shown in FIG. 2 , the lower electrode 32 is provided on the lower surface 20 b of the piezoelectric layer 20. The lower electrode 32 is an example of a “functional electrode.” The lower electrode 32 has a circular main electrode portion 32 a and an extension portion 32 b extending in the X direction from the main electrode portion 32 a. The lower electrode 32 is made of a metal or alloy containing Al, Pt, Cu, W, Mo, or the like. The lower electrode 32 may also have an adhesion layer made of Ti, NiCr, or the like.

[0014] In the first embodiment, the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32 overlap each other in a planar view in the Z direction. In other words, the piezoelectric layer 20 is sandwiched between the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32. As a result, bulk waves are propagated in the region between the circular main electrode portion 31a of the upper electrode 31 and the circular main electrode portion 32a of the lower electrode 32. Note that the shapes of the upper electrode 31 and the lower electrode 32 are merely examples and are not limited thereto. In the following description, the region where the upper electrode 31 and the lower electrode 32 overlap each other in a planar view in the Z direction may be described as an excitation region.

[0015] The support member 11 is provided opposite the lower surface 20b of the piezoelectric layer 20. In the first embodiment, the support member 11 includes a support substrate 12. The support substrate 12 is a substrate made of silicon (Si), quartz crystal, or the like.

[0016] The support member 11 has a space 14. In the example of Fig. 2, the space 14 is the space inside a recess provided on the piezoelectric layer 20 side of the support substrate 12. The space 14 is provided so as to overlap with the excitation region when viewed in a plane in the Z direction. This allows bulk waves to be reflected by the space 14. In the first embodiment, the space 14 is a vacuum and is sealed.

[0017] In the following description, the boundary 14a between the region that overlaps with the space portion 14 and the region that does not overlap with the space portion 14 in plan view in the Z direction will be described as the boundary 14a of the space portion. In the example of Fig. 1, the region that overlaps with the space portion 14 in plan view in the Z direction is rectangular, but this is merely an example and may be another shape, such as a circle.

[0018] The thickness of the piezoelectric layer 20 will be described below. In the following description, the region of the piezoelectric layer 20 that overlaps the space 14 and the upper electrode 31 or the lower electrode 32 in a planar view in the Z direction is referred to as the first portion 21. The region of the piezoelectric layer 20 that overlaps the space 14 in a planar view in the Z direction but does not overlap either the upper electrode 31 or the lower electrode 32 is referred to as the second portion 22. The region of the piezoelectric layer 20 that does not overlap either the space 14 or the excitation region in a planar view in the Z direction is referred to as the third portion 23. In the following description, the term "thickness" refers to the length in the thickness direction, i.e., the Z direction. "Average thickness" refers to the average value of the thickness. "Maximum thickness" refers to the maximum thickness value. "Minimum thickness" refers to the minimum thickness value. The thickness of the piezoelectric layer 20 can be compared by observing the cross section of the piezoelectric device using a scanning electron microscope (SEM).

[0019] Fig. 3 is a diagram showing the thickness distribution of the piezoelectric layer according to the first embodiment. More specifically, Fig. 3 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to positions in the Y direction in the cross section according to Fig. 2. As shown in Fig. 3, the maximum thickness of the second portion 22 is greater than the minimum thickness of the first portion 21. In the first embodiment, the thickness of the second portion 22 of the piezoelectric layer 20 is greater than the thickness of the first portion 21. This can prevent the piezoelectric layer 20 from being distorted at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0020] As described above, the piezoelectric device according to the first embodiment includes a piezoelectric layer having a thickness in a first direction and having an upper surface that is one surface in the first direction and a lower surface that is the other surface in the first direction; a support member provided on the lower surface side of the piezoelectric layer; and a functional electrode provided on at least one of the upper and lower surfaces of the piezoelectric layer. The piezoelectric layer or the support member has a space in a region that overlaps with at least a portion of the functional electrode. When viewed in a plan view in the first direction, the region of the piezoelectric layer that overlaps with the space and the functional electrode is defined as a first portion, and the region of the piezoelectric layer that overlaps with the space but does not overlap with the functional electrode is defined as a second portion. The maximum thickness of the second portion is greater than the minimum thickness of the first portion. This prevents distortion of the piezoelectric layer at the boundary between the region that overlaps with the functional electrode and the region that does not overlap with the functional electrode, i.e., the boundary between the first portion and the second portion, in a plan view in the first direction, thereby preventing damage to the piezoelectric layer.

[0021] In a preferred embodiment, the maximum thickness of the second portion is greater than the average thickness of the functional electrode, which prevents the lower surface of the piezoelectric layer from coming into contact with the bottom surface of the cavity portion and deteriorating the characteristics of the piezoelectric device even if the piezoelectric layer is deformed during the manufacturing process of the piezoelectric device.

[0022] In a preferred embodiment, a support member is provided in the first direction of the space, whereby the piezoelectric layer is supported by the support member, thereby further preventing the piezoelectric layer from being damaged.

[0023] In a preferred embodiment, the functional electrode includes an upper electrode provided on the upper surface of the piezoelectric layer and a lower electrode provided on the lower surface of the piezoelectric layer, at least a portion of which faces the upper electrode. Even in this case, damage to the piezoelectric layer can be suppressed.

[0024] Next, a method for manufacturing the piezoelectric device according to this embodiment will be described. Figure 4 is an explanatory diagram showing the method for manufacturing the piezoelectric device according to the first embodiment.

[0025] 4, the thickness of the first portion 21 of the piezoelectric layer 20 is reduced (step ST1). In step ST1, for example, a resist mask is patterned on the lower surface 20b of the piezoelectric layer 20 by lithography, except for the first portion 21, and a part of the first portion 21 is removed by reactive ion etching (RIE) (step ST1). As a result, the thickness of the second portion 22 becomes greater than the thickness of the first portion 21, thereby suppressing damage to the piezoelectric layer 20.

[0026] Next, a lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST2). The lower electrode 32 is formed by, for example, a vapor deposition lift-off method. That is, in step ST2, a metal film is vapor-deposited on the resist formed in step ST1, and then the resist is removed, thereby forming the metal film as the lower electrode 32.

[0027] Next, a support substrate 12 having a space 14 formed on one surface is prepared, and the support substrate 12 is bonded to the lower surface 20b of the piezoelectric layer 20. This bonds the support substrate 12 to the piezoelectric layer 20 (step ST3). The support substrate 12 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. The space 14 is formed, for example, by patterning a resist mask on the area other than the first portion 21 by lithography, and then removing a portion of the support substrate 12 by RIE.

[0028] Next, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST4). The upper surface 20a of the piezoelectric layer 20 is polished, for example, by mechanical polishing or CMP (Chemical-Mechanical Polishing). The thickness of the piezoelectric layer 20 is formed to about 1 μm or less. In step ST3, the method is not limited to polishing. For example, the piezoelectric layer 20 may be thinned by forming a damaged layer inside the piezoelectric layer 20 by ion implantation and then peeling off a layer on top of the formed damaged layer.

[0029] Next, an upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST5). The upper electrode 31 is formed by, for example, a vapor deposition lift-off method, similar to the above-described lower electrode 32. That is, in step ST5, a resist pattern is formed on the upper surface 20a of the piezoelectric layer 20 by photolithography. The resist is then removed, and the metal film in the remaining portion is formed as the upper electrode 31.

[0030] The piezoelectric device 10 of this embodiment can be manufactured through the above steps. Note that the steps shown in Fig. 4 are merely schematic and can be modified as appropriate.

[0031] As described above, the method for manufacturing a piezoelectric device according to the first embodiment includes the steps of grinding a portion of a piezoelectric layer having a thickness in a first direction to thin it (step ST1), bonding a support member to the bottom surface of the piezoelectric layer, which is one surface in the first direction, (step ST3), and forming a functional electrode on at least one of the top and bottom surfaces of the piezoelectric layer, which is the other surface in the first direction, (steps ST2 and ST5). The piezoelectric layer or the support member has a space in a region overlapping at least a portion of the functional electrode. When viewed in a plan view in the first direction, the piezoelectric layer in the region overlapping the space and the functional electrode is defined as a first portion, and the piezoelectric layer in the region overlapping the space but not the functional electrode is defined as a second portion. The maximum thickness of the second portion is greater than the minimum thickness of the first portion. This prevents distortion of the piezoelectric layer at the boundary between the region overlapping the functional electrode and the region not overlapping the functional electrode in a plan view in the first direction, thereby preventing damage to the piezoelectric layer.

[0032] (First Modification of First Embodiment) Fig. 5 is a plan view showing a piezoelectric device according to a first modification of the first embodiment. Fig. 6 is a schematic cross-sectional view taken along line VI-VI in Fig. 5. As shown in Fig. 5, a piezoelectric device 10A according to the first modification differs from the piezoelectric device 10 in that a part of the second portion 22 of the piezoelectric layer 20 is thicker than the first portion.

[0033] Fig. 7 is a diagram showing the thickness distribution of the piezoelectric layer according to the first modified example. More specifically, Fig. 7 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to the position in the Y direction in the cross section according to Fig. 6. In the first modified example, the second portion 22 of the piezoelectric layer 20 has a convex portion 22a on the lower surface 20b. This makes a part of the second portion 22 thicker than the first portion 21. This makes it possible to prevent distortion of the piezoelectric layer 20 at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0034] 5, the shape of the protrusion 22a is annular in plan view in the Z direction, with the portion overlapping with the lower electrode 32 missing, and the inner side of the ring is in contact with the side of the lower electrode 32. Note that the position and shape of the protrusion 22a are merely an example and are not limited to this. Also, in the example of FIG. 6, the thickness of the second portion 22 in the protrusion 22a is equal to that of the third portion 23, and the thickness of the second portion 22 other than the protrusion 22a is equal to that of the first portion, but this is merely an example and is not limited to this.

[0035] Next, a method for manufacturing a piezoelectric device according to this modification will be described. Fig. 8 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to the first modification. In the description of the manufacturing method shown in Fig. 8, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0036] 8 , the thickness of the first portion 21 of the piezoelectric layer 20 and the thickness of a portion of the second portion 22 are reduced (step ST11). In step ST11, for example, a resist mask is patterned on the lower surface 20b of the piezoelectric layer 20 by lithography to form a resist mask pattern on the convex portion 22a and the third portion 23 of the second portion 22, and the portion of the second portion 22 other than the first portion 21 and the convex portion 22a is removed by RIE (step ST11). This allows the portion of the second portion 22 to be thicker than the first portion 21, thereby suppressing damage to the piezoelectric layer 20. The resist is removed after step ST11.

[0037] Thereafter, similar to steps ST2 to ST5 in FIG. 4, a lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST12), a support substrate 12 having a space 14 formed on one surface thereof is bonded and attached to the lower surface 20b of the piezoelectric layer 20 (step ST13), the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST14), and an upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST15).

[0038] The piezoelectric device 10A of this embodiment is manufactured through the above steps. Note that the steps shown in FIG. 8 are merely schematic and can be modified as appropriate.

[0039] 9 is a schematic cross-sectional view showing a piezoelectric device according to a second embodiment. As shown in FIG. 9, the piezoelectric device 10B according to the second embodiment differs from the first embodiment in that a space 24 is provided in the piezoelectric layer 20.

[0040] In the second embodiment, the piezoelectric layer 20 has a space 24. In the second embodiment, as shown in Fig. 2, the space 24 is a space inside a recess provided in the lower surface 20b of the piezoelectric layer 20. The space 24 is provided so as to overlap with the excitation region in a plan view in the Z direction. This allows the bulk wave to be reflected by the space 24.

[0041] Fig. 10 is a diagram showing the thickness distribution of the piezoelectric layer according to the second embodiment. More specifically, Fig. 10 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to the position in the Y direction in the cross section according to Fig. 9. In the second embodiment, the thickness of the second portion 22 of the piezoelectric layer 20 is greater than the thickness of the first portion 21. This makes it possible to prevent the piezoelectric layer 20 from being distorted at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0042] Next, a method for manufacturing a piezoelectric device according to this embodiment will be described. Fig. 11 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to a second embodiment. In the description of the manufacturing method shown in Fig. 11, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0043] 11 , the thicknesses of the first portion 21 and the second portion 22 of the piezoelectric layer 20 are reduced (step ST21). In step ST21, for example, a resist mask is patterned on the third portion 23 of the lower surface 20b of the piezoelectric layer 20 by lithography, and parts of the first portion 21 and the second portion 22 are removed by RIE (step ST21). This forms a space 24. The resist is removed after step ST21.

[0044] Next, the thickness of the first portion 21 of the piezoelectric layer 20 is further reduced (step ST22). In step ST22, for example, a resist mask is patterned on the lower surface 20b of the piezoelectric layer 20 by lithography to form a pattern on the second portion 22 and the third portion 23, and a part of the first portion 21 is removed by RIE (step ST22). As a result, the thickness of the second portion 22 becomes greater than the thickness of the first portion 21, thereby preventing damage to the piezoelectric layer 20.

[0045] Next, similarly to step ST2 in FIG. 4, the lower electrode 32 is formed on the lower surface 20b of the piezoelectric layer 20 (step ST23).

[0046] Next, the support substrate 12 is prepared, and the support substrate 12 is bonded to the lower surface 20b of the piezoelectric layer 20. This bonds the support substrate 12 to the piezoelectric layer 20 (step ST24). The support substrate 12 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like.

[0047] Then, similar to steps ST4 and ST5 in FIG. 4, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST25), and an upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST26).

[0048] The piezoelectric device 10B according to the second embodiment is manufactured through the above steps. Note that the steps shown in FIG. 11 are merely schematic and can be modified as appropriate.

[0049] 12 is a schematic cross-sectional view showing a piezoelectric device according to a second modification of the second embodiment. As shown in FIG. 12, the piezoelectric device 10C according to the second modification differs from the second embodiment in that a part of the second portion 22 of the piezoelectric layer 20 is thicker than the first portion.

[0050] Fig. 13 is a diagram showing the thickness distribution of the piezoelectric layer according to a second modification of the second embodiment. More specifically, Fig. 13 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to the position in the Y direction in the cross section according to Fig. 12. In the second modification, the second portion 22 of the piezoelectric layer 20 has a convex portion 22a on the lower surface 20b, so that the convex portion 22a of the second portion 22 is thicker than the first portion 21. This makes it possible to prevent the piezoelectric layer 20 from being distorted at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0051] The shape of the convex portion 22a when viewed in a plane in the Z direction is not particularly limited, and may be, for example, a ring shape lacking portions that overlap with the upper electrode 31 and the lower electrode 32, similar to the first modified example of the first embodiment. In the example of Fig. 12, the thickness of the second portion 22 in the convex portion 22a is equal to the third portion 23, and the thickness of the second portion 22 other than the convex portion 22a is equal to the first portion 21, but this is merely an example and is not limiting.

[0052] Next, a method for manufacturing a piezoelectric device according to this modification will be described. Fig. 14 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to the second modification of the second embodiment. In the description of the manufacturing method shown in Fig. 14, content that overlaps with the manufacturing method shown in Fig. 11 will be omitted.

[0053] 14 , the thicknesses of the first portion 21 and the second portion 22 of the piezoelectric layer 20 are reduced (step ST31). In step ST31, for example, a resist mask is patterned on the third portion 23 of the lower surface 20b of the piezoelectric layer 20 by lithography, and parts of the first portion 21 and the second portion 22 are removed by RIE (step ST31). This forms a space 24. The resist is removed after step ST31.

[0054] Next, the thickness of the first portion 21 of the piezoelectric layer 20 and the thickness of part of the second portion 22 are reduced (step ST32). In step ST32, for example, a resist mask is patterned on the lower surface 20b of the piezoelectric layer 20 by lithography to form a resist mask pattern on the convex portion 22a and the third portion 23 of the second portion 22, and part of the second portion 22 other than the first portion 21 and the convex portion 22a is removed by RIE (step ST32). This allows part of the second portion 22 to be formed thicker than the first portion 21, thereby suppressing damage to the piezoelectric layer 20. The resist is removed after step ST32.

[0055] Thereafter, similar to steps ST23 to ST26 in FIG. 11, a lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST33), the support substrate 12 and the lower surface 20b of the piezoelectric layer 20 are bonded together (step ST34), the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST35), and an upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST36).

[0056] The piezoelectric device 10C of this embodiment is manufactured through the above steps. Note that the steps shown in FIG. 14 are merely schematic and can be modified as appropriate.

[0057] 15 is a schematic cross-sectional view showing a piezoelectric device according to a third modification of the second embodiment. As shown in Fig. 15, the piezoelectric device 10D according to the third modification is different from the second embodiment in that the thickness of the second portion 22 of the piezoelectric layer 20 on the boundary 14a side is greater than the thickness of the first portion 21 side.

[0058] In the third modified example, the second portion 22 of the piezoelectric layer 20 has a convex lower surface 20b, so that the thickness on the third portion 23 side is greater than the thickness on the first portion 21 side. That is, in the third modified example, the average thickness of the second portion 22 at the boundary 14a between the region overlapping with the space 14 and the region not overlapping with the space 14 is greater than the average thickness of the second portion 22 at the boundary between the region overlapping with the functional electrode and the region not overlapping with the functional electrode. This makes it possible to suppress distortion of the piezoelectric layer 20 at the boundary 14a and the boundary between the first portion 21 and the second portion 22, thereby suppressing damage to the piezoelectric layer 20.

[0059] The piezoelectric device 10D according to the third modification can be manufactured by the same method as the piezoelectric device 10C according to the second embodiment.

[0060] 16 is a schematic cross-sectional view showing a piezoelectric device according to a fourth modification of the second embodiment. As shown in Fig. 16, the piezoelectric device 10E according to the fourth modification differs from the second embodiment in that the thickness of the second portion 22 of the piezoelectric layer 20 on the boundary 14a side is greater than the thickness of the first portion 21 side.

[0061] In the fourth modified example, the second portion 22 of the piezoelectric layer 20 has a concave lower surface 20b, so that the thickness on the third portion 23 side is greater than the thickness on the first portion 21 side. That is, in the third modified example, the average thickness of the second portion 22 at the boundary 14a between the region overlapping with the space 14 and the region not overlapping with the space 14 is greater than the average thickness of the second portion 22 at the boundary between the region overlapping with the functional electrode and the region not overlapping with the functional electrode. This makes it possible to suppress distortion of the piezoelectric layer 20 at the boundary 14a and the boundary between the first portion 21 and the second portion 22, thereby suppressing damage to the piezoelectric layer 20.

[0062] The piezoelectric device 10E according to the fourth modification can be manufactured by the same method as the piezoelectric device 10C according to the second embodiment.

[0063] 17 is a schematic cross-sectional view showing a piezoelectric device according to a third embodiment. As shown in FIG. 17, the piezoelectric device 10F according to the third embodiment differs from the first embodiment in that the thickness of the second portion 22 is greater than the thickness of the third portion 23.

[0064] Fig. 18 is a diagram showing the thickness distribution of the piezoelectric layer according to the third embodiment. More specifically, Fig. 18 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to positions in the Y direction in the cross section according to Fig. 17. In the third embodiment, the maximum thickness of the second portion 22 of the piezoelectric layer 20 is greater than the thicknesses of the first portion 21 and the third portion 23. This makes it possible to prevent the piezoelectric layer 20 from being distorted at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0065] Next, a method for manufacturing a piezoelectric device according to this embodiment will be described. Fig. 19 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to a third embodiment. In the description of the method for manufacturing a piezoelectric device according to the third embodiment, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0066] 4, a lower electrode 32 is formed on the lower surface 20b of the piezoelectric layer 20 (step ST41), and the support substrate 12 and the lower surface 20b of the piezoelectric layer 20 are bonded and attached (step ST42). In the third embodiment, steps ST41 and ST42 are performed without reducing the thickness of the first portion 21 of the piezoelectric layer 20. That is, up until step ST43, the first portion 21, the second portion 22, and the third portion 23 of the piezoelectric layer 20 have uniform thicknesses, and the lower surface 20b is a flat surface.

[0067] 4, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20. The upper surface 20a of the piezoelectric layer 20 is polished by mechanical polishing. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less (step ST43).

[0068] 20 and 21 are diagrams illustrating the piezoelectric layer thinning process according to the third embodiment. The polishing of the upper surface 20a of the piezoelectric layer 20 in step ST43 is performed by rotating a polishing disk G and moving it along the XY plane to scan the upper surface 20a of the piezoelectric layer 20. During this process, a pressure P is applied to the piezoelectric layer 20 in a direction from the upper surface to the lower surface due to the pressure difference between the inside and outside of the space 14 and the pressing of the polishing disk G. As shown in FIG. 20, if the piezoelectric layer 20 is sufficiently thick, the piezoelectric layer 20 is less likely to bend, so the displacement D due to the pressure P is small and the difference in displacement D across position is also small, resulting in uniform polishing of the piezoelectric layer 20. On the other hand, as shown in FIG. 21, as the piezoelectric layer 20 becomes thinner, the piezoelectric layer 20 becomes more likely to bend, resulting in locally large displacements D1 of the second portions 22 not fixed by the lower electrode 32. As a result, the second portions 22 protrude into the space 14, resulting in a reduced amount of polishing of the second portions 22. This makes the thickness of the second portion 22 of the piezoelectric layer 20 greater than the thicknesses of the first portion 21 and the third portion 23, thereby preventing damage to the piezoelectric layer 20.

[0069] Then, similarly to step ST5 in FIG. 4, the upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST44).

[0070] The piezoelectric device 10F according to the third embodiment is manufactured through the above steps. Note that the steps shown in Figures 19 to 21 are merely schematic and can be modified as appropriate.

[0071] As described above, the method for manufacturing a piezoelectric device according to the third embodiment includes the steps of: joining a support member to a bottom surface of a piezoelectric layer having a thickness in a first direction, the bottom surface being one surface in the first direction; forming a functional electrode on the bottom surface; and grinding the top surface of the piezoelectric layer, the other surface in the first direction, to reduce the thickness of the piezoelectric layer (step ST43). The support member has a space in a region overlapping at least a portion of the functional electrode. When viewed from above in the first direction, the piezoelectric layer in the region overlapping the space and the functional electrode is defined as a first portion, and the piezoelectric layer in the region overlapping the space but not the functional electrode is defined as a second portion. Before the step of reducing the thickness of the piezoelectric layer (step ST43), the average thickness of the second portion is equal to the average thickness of the first portion. After the step of reducing the thickness of the piezoelectric layer (step ST43), the maximum thickness of the second portion is greater than the minimum thickness of the first portion. This can prevent the piezoelectric layer from being distorted at the boundary between the area that overlaps with the functional electrode and the area that does not overlap with the functional electrode when viewed in plan in the first direction, thereby preventing damage to the piezoelectric layer.

[0072] 22 is a schematic cross-sectional view showing a piezoelectric device according to a fifth modification of the third embodiment. As shown in FIG. 22, the piezoelectric device 10G according to the third embodiment differs from the third embodiment in that the thickness of the first portion 21 is not uniform.

[0073] FIG. 23 is a diagram showing the thickness distribution of the piezoelectric layer according to a fifth modification of the third embodiment. More specifically, FIG. 23 is a diagram showing the thickness distribution of the piezoelectric layer 20 corresponding to the position in the Y direction in the cross section according to FIG. 22. As shown in FIGS. 22 and 23, the thickness of the first portion 21 is smaller at both ends (ends) on the second portion 22 side and is larger inside (center) both ends on the second portion 22 side. In the fifth modification, the maximum thickness of the second portion 22 of the piezoelectric layer 20 is greater than the minimum thickness of the first portion 21 and the thickness of the third portion 23. This prevents distortion of the piezoelectric layer 20 at the boundary between the first portion 21 and the second portion 22, thereby preventing damage to the piezoelectric layer 20.

[0074] Next, a method for manufacturing a piezoelectric device according to this modification will be described. Fig. 24 is an explanatory diagram for explaining a method for manufacturing a piezoelectric device according to a fifth modification of the third embodiment. In the description of the method for manufacturing a piezoelectric device according to the fifth modification, content that overlaps with the manufacturing methods shown in Figs. 4 and 19 will be omitted.

[0075] As in steps ST2 and ST3 of FIG. 4, the lower electrode 32 is formed on the lower surface 20b of the piezoelectric layer 20 (step ST51), and the support substrate 12 and the lower surface 20b of the piezoelectric layer 20 are bonded and attached to each other (step ST52).

[0076] 4, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST53). The upper surface 20a of the piezoelectric layer 20 is polished by mechanical polishing. The thickness of the piezoelectric layer 20 is formed to be approximately 1 μm or less.

[0077] FIG. 25 illustrates a piezoelectric layer thinning process according to a fifth modification of the third embodiment. The polishing of the upper surface 20a of the piezoelectric layer 20 in step ST53 is performed by rotating the polishing disk G and moving it along the XY plane to scan the upper surface 20a of the piezoelectric layer 20. During this process, a pressure P is applied to the piezoelectric layer 20 in a direction from the upper surface to the lower surface due to the pressure difference between the inside and outside of the space 14 and the pressing of the polishing disk G. As shown in FIG. 25, as the piezoelectric layer 20 becomes thinner, it becomes more likely to bend. In the fifth modification, the lower electrode 32 is thin, and therefore only the end of the first portion 21 is not fixed. Therefore, the displacement D2 is locally large not only in the second portion 22 but also in the center of the first portion 21. As a result, the center of the first portion 21 and the second portion 22 protrude into the space 14, resulting in a reduced amount of polishing of the center of the first portion 21 and the second portion 22. Even in this case, the maximum thickness of the second portion 22 of the piezoelectric layer 20 is greater than the minimum thickness of the first portion 21 and the thickness of the third portion 23, so damage to the piezoelectric layer 20 can be suppressed.

[0078] Then, similarly to step ST5 in FIG. 4, the upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST54).

[0079] The piezoelectric device 10G according to the fifth modification is manufactured through the above steps. Note that the steps shown in Fig. 25 are merely schematic and can be modified as appropriate.

[0080] 26 is a schematic cross-sectional view showing a piezoelectric device according to a fourth embodiment. As shown in FIG. 26, a piezoelectric device 10H according to the fourth embodiment differs from the first embodiment in that the support member 11 has an intermediate layer 13.

[0081] The intermediate layer 13 is provided between the support substrate 12 and the piezoelectric layer 20. The intermediate layer 13 is made of an insulating material such as silicon oxide.

[0082] Next, a method for manufacturing a piezoelectric device according to this embodiment will be described. Fig. 27 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to a fourth embodiment. In the description of the method for manufacturing a piezoelectric device according to the fourth embodiment, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0083] 4, the thickness of the first portion 21 of the piezoelectric layer 20 is reduced (step ST61), and the lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST62).

[0084] Next, the intermediate layer 13 is formed on the lower surface 20b of the piezoelectric layer 20, covering the lower electrode 32 (step ST63). The intermediate layer 13 is formed by sputtering using a material such as silicon oxide. An adhesive layer made of Ti, NiCr, or the like may be provided between the lower electrode 32 and the intermediate layer 13. Furthermore, the lower surface of the intermediate layer 13 (the surface opposite the piezoelectric layer 20) may be planarized by CMP, if necessary.

[0085] Next, a support substrate 12 having a space 14 formed on one surface is prepared, and the support substrate 12 is bonded to an intermediate layer formed on the lower surface 20b of the piezoelectric layer 20. This bonds the support substrate 12 to the piezoelectric layer 20 (step ST64). The support substrate 12 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. The space 14 is formed, for example, by patterning a resist mask on the area other than the first portion 21 by lithography, and then removing a portion of the support substrate 12 by RIE.

[0086] 4, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST65).The upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST66).

[0087] The piezoelectric device 10H of this embodiment is manufactured through the above steps. Note that the steps shown in Fig. 27 are merely schematic and can be modified as appropriate.

[0088] 28 is a schematic cross-sectional view showing a piezoelectric device according to a fifth embodiment. As shown in FIG. 28, a piezoelectric device 10I according to the fifth embodiment differs from the first embodiment in that the support member 11 has an intermediate layer 13 and a space 14 is provided in the intermediate layer 13.

[0089] The intermediate layer 13 is provided between the support substrate 12 and the piezoelectric layer 20. The intermediate layer 13 is made of an insulating material such as silicon oxide. In the example of Fig. 28, the space 14 is the space inside a recess provided on the piezoelectric layer 20 side of the intermediate layer 13.

[0090] A through-hole 25 is provided in the piezoelectric layer 20. The through-hole 25 passes through the piezoelectric layer 20 in the Z direction and communicates with the space 14.

[0091] Next, a method for manufacturing a piezoelectric device according to this embodiment will be described. Fig. 29 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to a fifth embodiment. In the description of the method for manufacturing a piezoelectric device according to the fifth embodiment, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0092] 4, the thickness of the first portion 21 of the piezoelectric layer 20 is reduced (step ST71), and the lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST72).

[0093] Next, a sacrificial layer 13S is formed on the lower surface 20b of the piezoelectric layer 20 (step ST73). The sacrificial layer 13S is provided in a region where the space 14 of the support member 11 (intermediate layer 13) is to be formed. In other words, the sacrificial layer 13S is provided so as to cover the main electrode portion 32a of the lower electrode 32. The sacrificial layer 13S is formed by sputtering using a material such as zinc oxide (ZnO).

[0094] Next, the intermediate layer 13 is formed on the lower surface 20b of the piezoelectric layer 20, covering the lower electrode 32 and the sacrificial layer 13S (step ST74). The intermediate layer 13 is formed by sputtering using a material such as silicon oxide. An adhesive layer made of Ti, NiCr, or the like may be provided between the lower electrode 32 and the intermediate layer 13. Furthermore, the lower surface of the intermediate layer 13 (the surface opposite the piezoelectric layer 20) may be planarized by CMP, if necessary.

[0095] Next, a support substrate 12 having a space 14 formed on one surface is prepared, and the support substrate 12 is bonded to an intermediate layer formed on the lower surface 20b of the piezoelectric layer 20. This bonds the support substrate 12 to the piezoelectric layer 20 (step ST75). The support substrate 12 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. The space 14 is formed, for example, by patterning a resist mask on the area other than the first portion 21 by lithography, and then removing a portion of the support substrate 12 by RIE.

[0096] 4, the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST76).The upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST77).

[0097] Next, through holes 25 are formed in the piezoelectric layer 20 (step ST78). The through holes 25 are provided at positions overlapping the sacrificial layer 13S in plan view in the Z direction. The through holes 25 are provided by a method such as RIE.

[0098] Next, the sacrificial layer 13S is removed to form the space 14 in the intermediate layer 13 (step ST79). The sacrificial layer 13S is removed by wet etching. In this case, an etchant that dissolves the sacrificial layer 13S is injected through the through-holes 25.

[0099] The piezoelectric device 10I of this embodiment is manufactured through the above steps. Note that the steps shown in Fig. 29 are merely schematic and can be modified as appropriate.

[0100] 30 is a schematic plan view showing a piezoelectric device according to a sixth embodiment. As shown in Fig. 30, a piezoelectric device 10J according to the sixth embodiment differs from the first embodiment in that the main electrode portions 31 a, 32 a are rectangular.

[0101] 30 , the upper electrode 31A has a rectangular main electrode portion 31a and an extension portion 31b extending from the main electrode portion 31a in the X direction. The lower electrode 32A has a rectangular main electrode portion 32a and an extension portion 32b extending from the main electrode portion 32a in the X direction. The rectangular main electrode portion 31a of the upper electrode 31A and the rectangular main electrode portion 32a of the lower electrode 32A overlap each other. Here, a rectangle refers to a shape having two sets of parallel sides (sides 33b, 33c) extending in a direction intersecting the Z direction, and includes a shape with rounded corners 33a as shown in FIG. 30 .

[0102] In the sixth embodiment, the second portion 22 of the piezoelectric layer 20 has a protrusion 22a on the lower surface 20b at a position adjacent to a corner 33a of the rectangle. Here, the corner 33a of the rectangle refers to the point on the outline of the rectangle that is closest to the intersection of the rectangular sides 33b, 33c extending in intersecting directions or their extensions (the dashed dotted lines in FIG. 30 ). This makes the second portion 22 at the position adjacent to the corner 33a of the rectangle thicker than the first portion 21. This prevents distortion of the piezoelectric layer 20 at the position adjacent to the corner 33a of the rectangle, thereby preventing damage to the piezoelectric layer 20.

[0103] The piezoelectric device 10J according to the sixth embodiment can be manufactured using the same manufacturing process as the manufacturing method shown in FIG. 4 described above.

[0104] The functional electrodes (upper electrode 31A and lower electrode 32A) and piezoelectric layer according to the sixth embodiment can be combined with the above-described embodiments and modifications.

[0105] As described above, in the piezoelectric device according to the sixth embodiment, when viewed in a plan view in the Z direction, the shape of the region where the upper electrode and the lower electrode overlap is a rectangle having two sets of sides extending in two directions intersecting the first direction when viewed in a plan view in the first direction. When viewed in a plan view in the first direction, the maximum thickness of the second portion at positions adjacent to the corners of the rectangle is greater than the minimum thickness of the first portion. This makes it possible to suppress distortion of the piezoelectric layer 20 at positions adjacent to the corners of the rectangle, where distortion is particularly likely to occur, thereby further suppressing damage to the piezoelectric layer.

[0106] Seventh Embodiment Fig. 31 is a schematic plan view showing a piezoelectric device according to a seventh embodiment. As shown in Fig. 31, a piezoelectric device 10K according to the fifth embodiment differs from the first embodiment in that the functional electrodes are comb-teeth electrodes.

[0107] 31 , the first electrode 31B has electrode fingers 31Ba, a bus bar 31Bb to which the X-direction ends of the electrode fingers 31Ba are connected and which extends in the Y-direction, and an extension portion 31Bc extending in the X-direction from the bus bar 31Bb. The second electrode 32B has electrode fingers 32Ba, a bus bar 32Bb to which the Y-direction ends of the electrode fingers 32Ba are connected and which extends in the Y-direction, and an extension portion 32Bc extending in the X-direction from the bus bar 32Bb. Here, the first electrode 31B and the second electrode 32B are examples of "functional electrodes."

[0108] The electrode finger 31Ba and the electrode finger 32Ba are rectangular and have a length direction. In a direction perpendicular to the length direction, the electrode finger 31Ba faces the electrode finger 32Ba adjacent to the electrode finger 31Ba. The length direction of the electrode fingers 31Ba and 32Ba and the direction perpendicular to the length direction of the electrode fingers 31Ba and 32Ba are directions that intersect with the thickness direction of the piezoelectric layer 20. Therefore, it can be said that the electrode finger 31Ba faces the electrode finger 32Ba adjacent to the electrode finger 31Ba in a direction that intersects with the thickness direction of the piezoelectric layer 20.

[0109] Here, "electrode finger 31Ba and electrode finger 32Ba are adjacent" does not mean that electrode finger 31Ba and electrode finger 32Ba are arranged in direct contact with each other, but means that electrode finger 31Ba and electrode finger 32Ba are arranged with a gap therebetween. Furthermore, when electrode finger 31Ba and electrode finger 32Ba are adjacent to each other, no electrodes connected to hot electrodes or ground electrodes, including other electrode fingers 31Ba and 32Ba, are arranged between electrode finger 31Ba and electrode finger 32Ba. The number of pairs does not need to be an integer number, and may be 1.5 pairs, 2.5 pairs, or the like.

[0110] In the seventh embodiment, the second portion 22 of the piezoelectric layer 20 has a protrusion 22a on the lower surface 20b at a position adjacent to the inner corner of the bus bars 31Bb, 32Bb in the Y direction. This makes the second portion 22 at the position adjacent to the inner corner of the bus bars in the Y direction thicker than the first portion 21. This makes it possible to prevent distortion of the piezoelectric layer 20 at the position adjacent to the inner corner of the bus bars in the Y direction, thereby preventing damage to the piezoelectric layer 20.

[0111] The piezoelectric device 10K according to the seventh embodiment can be manufactured using the same manufacturing process as the manufacturing method shown in FIG.

[0112] The functional electrode and the piezoelectric layer according to the seventh embodiment can be combined with each of the above-described embodiments and modifications.

[0113] As described above, in the piezoelectric device according to the seventh embodiment, the functional electrode includes an IDT electrode including a plurality of electrode fingers arranged in a predetermined direction. Even in this case, damage to the piezoelectric layer 20 can be suppressed.

[0114] Eighth Embodiment Fig. 32 is a schematic cross-sectional view showing a piezoelectric device according to an eighth embodiment. As shown in Fig. 32, a piezoelectric device 10L according to the eighth embodiment differs from the first embodiment in that the space 14 is filled with an inert gas.

[0115] In the eighth embodiment, the support member 11 further includes an intermediate layer 13. The intermediate layer 13 is provided between the support substrate 12 and the piezoelectric layer 20, and covers the piezoelectric layer 20 side of the support substrate 12 and the lower surface 20b side of the piezoelectric layer 20. The intermediate layer 13 is formed of an insulating material such as silicon oxide. In the example of FIG. 28 , the space 14 is a sealed space surrounded by the intermediate layer 13. An inert gas such as argon is sealed in the space 14. This prevents the piezoelectric layer 20 from being depressed by atmospheric pressure and coming into contact with the bottom surface of the space 14, even when the piezoelectric device 10L reaches a high temperature.

[0116] The piezoelectric device 10L further includes a package 40. The package 40 is provided on the upper surface 20a of the piezoelectric layer 20 so as to cover the upper electrode 31A. The package 40 is bonded to the upper surface 20a of the third portion 23 of the piezoelectric layer 20. In the example of FIG. 32 , the package 40 includes a package substrate 42 and an adhesive portion 43. The package substrate 42 is a substrate having a thickness in the Z direction. The material of the package substrate 42 is, for example, silicon. The adhesive portion 43 is a member provided on the piezoelectric layer 20 side of the package substrate 42. The adhesive portion 43 has a frame shape when viewed in a plan view in the Z direction. The material of the adhesive portion 43 is, for example, metal. The package 40 may be made of a metal, a resin material, or the like. The adhesive portion 43 may be resin. The adhesive portion 43 is not limited to a single layer and may be a metal laminate or a metal-resin laminate.

[0117] Inside the package 40, there is a space 41 surrounded by the upper surface 20a of the piezoelectric layer 20 and the package 40. The space 41 is sealed. The pressure in the space 41 is the same as the pressure in the space portion 14.

[0118] When the pressure in the space 14 is lower than atmospheric pressure, a film stress is generated in the piezoelectric layer 20 in the portions (first portion 21 and second portion 22) that overlap with the space 14 in plan view in the Z direction, causing the piezoelectric layer 20 to warp toward the support member 11 in the Z direction. Alternatively, when the pressure in the space 14 is higher than atmospheric pressure, a film stress is generated in the piezoelectric layer 20 in the portions (first portion 21 and second portion 22) that overlap with the space 14 in plan view in the Z direction, causing the piezoelectric layer 20 to warp toward the opposite side of the support member 11 in the Z direction. Here, atmospheric pressure refers to standard atmospheric pressure, i.e., 1.01325×10 ６ This means that, in the manufacturing process of the piezoelectric device 10L, it is possible to further prevent the piezoelectric layer 20 from being damaged due to the pressure difference between the pressure in the space 14 and atmospheric pressure.

[0119] Next, a method for manufacturing a piezoelectric device according to this embodiment will be described. Fig. 33 is an explanatory diagram showing a method for manufacturing a piezoelectric device according to an eighth embodiment. In the description of the method for manufacturing a piezoelectric device according to the eighth embodiment, content that overlaps with the manufacturing method shown in Fig. 4 will be omitted.

[0120] 4, the thickness of the first portion 21 of the piezoelectric layer 20 is reduced (step ST81), and the lower electrode 32 is formed on the lower surface 20b of the first portion 21 of the piezoelectric layer 20 (step ST82).

[0121] Next, the intermediate layer 13 is formed on the lower surface 20b of the piezoelectric layer 20, covering the lower electrode 32 (step ST83). The intermediate layer 13 is formed by sputtering using a material such as silicon oxide. An adhesive layer made of Ti, NiCr, or the like may be provided between the lower electrode 32 and the intermediate layer 13. Furthermore, the lower surface of the intermediate layer 13 (the surface opposite the piezoelectric layer 20) may be planarized by CMP, if necessary.

[0122] Next, a support substrate 12 having a space 14 and an insulating film formed on one surface is prepared, and the insulating film of the support substrate 12 is bonded to the intermediate layer 13 formed on the lower surface 20b of the piezoelectric layer 20. This bonds the support substrate 12 and the piezoelectric layer 20 together (step ST84). The support substrate 12 is bonded to the piezoelectric layer 20 by direct bonding, plasma activated bonding, atomic diffusion bonding, or the like. Step ST84 is performed in an inert gas atmosphere, thereby sealing the inert gas in the space 14.

[0123] Then, similar to steps ST4 and ST5 of FIG. 4 , the upper surface 20a of the piezoelectric layer 20 is ground and polished to thin the piezoelectric layer 20 (step ST85). An upper electrode 31 is formed on the upper surface 20a of the piezoelectric layer 20 (step ST86). In the eighth embodiment, the thickness of the second portion 22 is greater than the thickness of the first portion, thereby suppressing displacement of the second portion, which is not fixed by the functional electrode, and thus suppressing displacement of the piezoelectric layer 20. Here, after step ST86, the displacement rate of the piezoelectric layer 20 is preferably between −5% and 5%. Here, the displacement rate of the piezoelectric layer 20 is the ratio calculated by {(average height of the space 14 in the region overlapping with the first portion 21) - (average height of the space 14 at the boundary 14a)} / (average height of the space 14 at the boundary 14a). Here, the height of the space 14 refers to the length of the space 14 in the Z direction, i.e., the distance in the Z direction between the surfaces exposed in the space 14.

[0124] Next, a package 40 is formed on the piezoelectric layer 20 (step ST87). The package 40 is bonded to the upper surface 20a of the third portion of the piezoelectric layer 20 by metal bonding, direct bonding, or the like. In the example of FIG. 33 , the package 40 is formed by the following method. First, a portion of one side of the adhesive portion 43 in the Z direction is formed on the upper surface 20a of the third portion of the piezoelectric layer 20. Next, a portion of the other side of the adhesive portion 43 in the Z direction is formed on the surface of the package substrate 42 facing the piezoelectric layer 20. Then, the portions of the adhesive portions 43 are bonded together. This completes the formation of the package 40 on the piezoelectric layer 20.

[0125] The piezoelectric device 10L of this embodiment is manufactured through the above steps. Note that the steps shown in Fig. 33 are merely schematic and can be modified as appropriate.

[0126] 34 is a schematic cross-sectional view showing a piezoelectric device according to a sixth modification of the eighth embodiment. As shown in Fig. 34, the piezoelectric device 10M according to the sixth modification differs from the eighth embodiment in that the piezoelectric layer 20 is warped toward the support member 11 in the Z direction.

[0127] In the sixth modification, the second portion 22 of the piezoelectric layer 20 is warped toward the support member 11 in the Z direction. In the sixth modification, the thickness of the second portion 22 is greater than the thickness of the first portion 21, which suppresses displacement of the second portion 22, which is the portion not fixed by the functional electrode, and thereby suppresses displacement of the piezoelectric layer 20. In the sixth modification, the displacement rate of the piezoelectric layer 20 is greater than 0% and not more than 5%. In this case, damage to the piezoelectric layer due to temperature changes can be suppressed during the manufacturing process of the piezoelectric device 10M.

[0128] The piezoelectric device 10M according to the sixth modification can be manufactured by the same method as the piezoelectric device 10L according to the eighth embodiment.

[0129] 35 is a schematic cross-sectional view showing a piezoelectric device according to a seventh modification of the eighth embodiment. As shown in Fig. 35, the piezoelectric device 10N according to the seventh modification differs from the eighth embodiment in that the piezoelectric layer 20 is warped in the Z direction away from the support member 11.

[0130] In the seventh modification, the second portion 22 of the piezoelectric layer 20 is warped in the Z direction away from the support member 11. In the seventh modification, the thickness of the second portion 22 is greater than the thickness of the first portion 21, which suppresses displacement of the second portion 22, which is not fixed by the functional electrode, and thus suppresses displacement of the piezoelectric layer 20. In the seventh modification, the displacement rate of the piezoelectric layer 20 is greater than or equal to -5% and less than 0%. In this case, damage to the piezoelectric layer due to temperature changes can be suppressed during the manufacturing process of the piezoelectric device 10N.

[0131] The piezoelectric device 10N according to the seventh modification can be manufactured by the same method as the piezoelectric device 10L according to the eighth embodiment.

[0132] The above-described embodiment is intended to facilitate understanding of the present invention, and is not intended to limit the present invention. The present invention may be modified or improved without departing from the spirit and scope of the present invention, and equivalents thereof are also included in the present invention.

[0133] The present disclosure may also have the following configurations.

[0134] (1) A piezoelectric device comprising: a piezoelectric layer having a thickness in a first direction, an upper surface that is one surface in the first direction, and a lower surface that is the other surface in the first direction, a support member provided on the lower surface side of the piezoelectric layer, and a functional electrode provided on at least one of the upper and lower surfaces of the piezoelectric layer, wherein the piezoelectric layer or the support member has a space in a region overlapping with at least a part of the functional electrode, and when, in a planar view in the first direction, the piezoelectric layer in a region overlapping with the space and the functional electrode is defined as a first portion, and the piezoelectric layer in a region overlapping with the space but not overlapping with the functional electrode is defined as a second portion, a maximum thickness of the second portion is greater than a minimum thickness of the first portion. (2) The piezoelectric device according to (1), wherein, in a planar view in the first direction, an average thickness of the second portion at a boundary between the region overlapping with the space and the region not overlapping with the space is greater than an average thickness of the second portion at a boundary between the region overlapping with the functional electrode and the region not overlapping with the functional electrode. (3) The piezoelectric device according to (1) or (2), wherein the maximum thickness of the second portion is greater than the average thickness of the functional electrode. (4) The piezoelectric device according to any one of (1) to (3), wherein the support member is present in the first direction of the space. (5) The piezoelectric device according to any one of (1) to (4), wherein the functional electrode includes: an upper electrode provided on an upper surface of the piezoelectric layer; and a lower electrode provided on a lower surface of the piezoelectric layer, at least a portion of which faces the upper electrode. (6) The piezoelectric device according to (5), wherein, in a planar view in the Z direction, the shape of an area where the upper electrode and the lower electrode overlap is a rectangle having two sets of sides extending in two directions intersecting the first direction, when viewed in a planar view in the first direction, and wherein, in a planar view in the first direction, the maximum thickness of the second portion at positions adjacent to corners of the rectangle is greater than the minimum thickness of the first portion. (7) The piezoelectric device according to any one of (1) to (4), wherein the functional electrode includes an IDT electrode including a plurality of electrode fingers arranged in a predetermined direction.

[0135] 10, 10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J, 10K, 10L, 10M, 10N Piezoelectric device 11 Support member 12 Support substrate 13 Intermediate layer 14 Space portion 20 Piezoelectric layer 20a Upper surface 20b Lower surface 21 First portion 22 Second portion 23 Third portion 24 Space portion 25 Through hole 31, 31A Upper electrode 32, 32A Lower electrode 31B First electrode 32B Second electrode 33a Corner 33b, 33c Side 40 Package

Claims

1. A piezoelectric device comprising: a piezoelectric layer having a thickness in a first direction, the piezoelectric layer having an upper surface which is one surface in the first direction, and a lower surface which is the other surface in the first direction; a support member provided on the lower surface side of the piezoelectric layer; and a functional electrode provided on at least one of the upper and lower surfaces of the piezoelectric layer, wherein the piezoelectric layer or the support member has a space in a region overlapping at least a portion of the functional electrode, and when, when viewed in a plane in the first direction, the piezoelectric layer in the region overlapping the space and the functional electrode is defined as a first part, and the piezoelectric layer in the region overlapping the space and not overlapping the functional electrode is defined as a second part, the maximum thickness of the second part is greater than the minimum thickness of the first part.

2. A piezoelectric device as described in claim 1, wherein, when viewed in a plane in the first direction, the average thickness of the second portion at the boundary between the area overlapping with the space portion and the area not overlapping with the space portion is greater than the average thickness of the second portion at the boundary between the area overlapping with the functional electrode and the area not overlapping with the functional electrode.

3. The piezoelectric device according to claim 1 or 2, wherein the maximum thickness of the second portion is greater than the average thickness of the functional electrode.

4. A piezoelectric device according to any one of claims 1 to 3, wherein the support member is located in the first direction of the space.

5. A piezoelectric device as claimed in any one of claims 1 to 4, wherein the functional electrode includes: an upper electrode provided on an upper surface of the piezoelectric layer; and a lower electrode provided on a lower surface of the piezoelectric layer, at least a portion of which faces the upper electrode.

6. The piezoelectric device described in claim 5, wherein, when viewed in a plane in the Z direction, a shape of a region overlapping the upper electrode and the lower electrode is a rectangle having two sets of sides extending in two directions intersecting the first direction when viewed in a plane in the first direction, and wherein, when viewed in a plane in the first direction, a maximum thickness of the second portion at a position adjacent to a corner of the rectangle is greater than a minimum thickness of the first portion.

7. The piezoelectric device according to claim 1, wherein the functional electrode includes an IDT electrode including a plurality of electrode fingers arranged in a predetermined direction.

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