Sound wave device

Abstract

A sound wave device comprises: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal surface; an upper electrode provided on the first principal surface of the piezoelectric layer; a lower electrode provided on the second principal surface of the piezoelectric layer; and a support element facing the second principal surface of the piezoelectric layer, wherein the piezoelectric layer has an opening extending through the piezoelectric layer in a thickness direction in a region that overlaps the lower electrode and does not overlap the upper electrode, and wherein the sound wave device further comprises an overlapping electrode provided on the lower electrode in a region that overlaps the opening and is formed from the same material as the upper electrode.

Description

TECHNICAL AREA

[0001] The present invention relates to sound wave devices. GENERAL STATE OF THE ART

[0002] Patent document 1 discloses a piezoelectric device having an upper and a lower electrode, which have a flat plate shape, on both sides of the piezoelectric layer. Citation list patent document

[0003] Patent document 1: US patent application publication no. 2012 / 0205754 BRIEF DESCRIPTION OF THE INVENTION Technical Problem

[0004] In the piezoelectric device disclosed in patent document 1, there is a possibility of damage to the electrodes and the piezoelectric layer if an unintentional potential difference occurs between the upper electrode and the lower electrode.

[0005] One object of the present invention is to provide a sound wave device in which damage to the electrodes is reduced. Solution to the problem

[0006] A sound wave device according to one aspect comprises: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal surface; an upper electrode provided on the first principal surface of the piezoelectric layer; a lower electrode provided on the second principal surface of the piezoelectric layer; and a support element facing the second principal surface of the piezoelectric layer, wherein the piezoelectric layer has an opening extending through the piezoelectric layer in a thickness direction in a region that overlaps the lower electrode and does not overlap the upper electrode, and wherein the sound wave device further comprises an overlapping electrode provided on the lower electrode in a region that overlaps the opening and is formed from the same material as the upper electrode. Advantageous effects of the invention

[0007] In the sound wave device of the present invention, damage to the electrodes can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a top view of a sound wave device according to a first embodiment. Fig. 2 is a cross-sectional view along line II-II' in Fig. 1. Fig. Figure 3 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the first embodiment. Fig. Figure 4 is a cross-sectional view of a sound wave device according to a first modification of the first embodiment. Fig. Figure 5 is a cross-sectional view of a sound wave device according to a second modification of the first embodiment. Fig. Figure 6 is a cross-sectional view of a sound wave device according to a third modification of the first embodiment. Fig. Figure 7 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the third modification of the first embodiment. Fig. Figure 8 is a cross-sectional view of a sound wave device according to a second embodiment. Fig. Figure 9 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the second embodiment. Fig. Figure 10 is a cross-sectional view of a sound wave device according to a fourth modification of the second embodiment. Fig. Figure 11 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the fourth modification of the second embodiment. Fig. Figure 12 is a cross-sectional view of a sound wave device according to a fifth modification of the second embodiment. Fig. Figure 13 is a top view of a sound wave device according to a third embodiment. Fig. 14 is a cross-sectional view along line XIV-XIV' in Fig. 13. Fig. Figure 15 is a cross-sectional view of a sound wave device according to a sixth modification of the third embodiment. Fig. Figure 16 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the sixth modification of the third embodiment. Fig. Figure 17 is a top view of a sound wave device according to a seventh modification of the third embodiment. Fig. Figure 18 is a cross-sectional view of a sound wave device according to a fourth embodiment. Fig. Figure 19 is a cross-sectional view of a sound wave device according to a fifth embodiment. Fig. Figure 20 is an explanatory diagram to illustrate a method for manufacturing the sound wave device according to the fifth embodiment. Fig. Figure 21 is a cross-sectional view of a sound wave device according to a sixth embodiment. Fig. Figure 22 is an explanatory diagram to illustrate a method for manufacturing a sound wave device according to an eighth modification of the first embodiment. DESCRIPTION OF EXECUTION FORMS

[0008] In the following, embodiments of the present disclosure are described in detail with reference to the drawings. These embodiments are not intended to limit the present disclosure. Each embodiment described in the present disclosure serves to illustrate an example. Therefore, for modifications and a second and subsequent embodiment in which features from different embodiments may be partially substituted or combined, the description of the features that are the same as those of a first embodiment is omitted, and only the differences are described. In particular, the same or similar functional advantages resulting from the same or similar features are not discussed in each embodiment. (First embodiment)

[0009] Fig. Figure 1 is a top view of a sound wave device according to the first embodiment. Fig. 2 is a cross-sectional view along line II-II' in Fig. 1. The resonator, which serves as the sound wave device 10 according to the first embodiment, is a resonator that uses volume acoustic waves, that is, a volume acoustic wave element (Bulk-Acoustic-Wave, BAW element).

[0010] As in Fig. 1 and Fig. As illustrated in Figure 2, the sound wave device 10 comprises a support element 13, a piezoelectric layer 20, an upper electrode 31, a lower electrode 32, and an overlapping electrode 33. As shown in Figure 2, the sound wave device 10 comprises a support element 13, a piezoelectric layer 20, an upper electrode 31, a lower electrode 32, and an overlapping electrode 33. Fig. As illustrated in Figure 2, the lower electrode 32, the piezoelectric layer 20 and the upper electrode 31 are laminated onto the support element 13 in this order.

[0011] In the following description, the thickness direction of the piezoelectric layer 20 is considered the Z-direction, a direction orthogonal to the Z-direction is considered the X-direction, and the direction orthogonal to both the Z-direction and the X-direction is considered the Y-direction. The X-direction and the Y-direction run parallel to a surface (a first principal surface 20a) of the piezoelectric layer 20. In the following description, top views show the arrangement when viewed in the direction (the Z-direction) perpendicular to the first principal surface 20a of the piezoelectric layer 20.

[0012] The support element 13 faces a second main surface 20b of the piezoelectric layer 20. The support element 13 comprises 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 formed of an insulating material such as silicon oxide. It should be noted that the support element 13 can have a configuration without an insulating layer 12, in which the piezoelectric layer 20 is provided on the support substrate 11.

[0013] The support element 13 (the insulating layer 12) has a cavity section 14 (a hollow section) on the surface facing the second main surface 20b of the piezoelectric layer 20. The cavity section 14 is positioned to overlap the excitation region of the resonator, which consists of the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32, which overlap each other in plan view. This arrangement allows volume sound waves to be reflected through the cavity section 14.

[0014] The piezoelectric layer 20 has a flat plate shape, comprising the first principal surface 20a and the second principal surface 20b, which is opposite the first principal surface 20a. The piezoelectric layer 20 is a substrate made of single-crystal lithium niobate (LiNbO3) or single-crystal lithium tantalate (LiTaO3). There are no specific limitations on the thickness of the piezoelectric layer 20; it is preferably 1 µm or less.

[0015] As in Fig. As illustrated in Figure 1, the piezoelectric layer 20 has etch windows 22 in a region that overlaps the cavity section 14. The etch windows 22 are openings for etching when the cavity section 14 of the insulating layer 12 is formed. More precisely, a sacrificial layer 50 (see Figure 1) is formed. Fig. 3) in the region where the cavity section 14 is to be formed. After the piezoelectric layer 20 and the support element 13 have been joined together, the sacrificial layer 50 is then removed through the etching windows 22, so that the cavity section 14 is formed.

[0016] The upper electrode 31 is provided on the first main surface 20a of the piezoelectric layer 20. As shown in Fig. As illustrated in Figure 1, the upper electrode 31 comprises a main electrode section 31a and an extension section 31b, which is coupled to the main electrode section 31a and extends in the X direction. The main electrode section 31a is provided in a region that overlaps the cavity section 14 of the insulating layer 12 and is approximately circular. The extension section 31b has a width greater than that of the main electrode section 31a and is approximately rectangular. The extension section 31b is electrically connected to an external terminal (an input terminal or an output terminal) or to ground.

[0017] The lower electrode 32 is provided on the second main surface 20b of the piezoelectric layer 20 in a region that at least partially overlaps the upper electrode 31. As shown in Fig. As illustrated in Figure 1, the lower electrode 32 comprises a main electrode section 32a and an extension section 32b coupled to the main electrode section 32a and extending in the X direction. The main electrode section 32a is provided in a region that overlaps the cavity section 14 of the insulating layer 12 and is approximately circular. In other words, the main electrode section 32a is provided in a region that overlaps the main electrode section 31a of the upper electrode 31. An adhesion layer, formed of Ti, NiCr, or the like, may be provided between the lower electrode 32 and the insulating layer 12.

[0018] The sound wave device 10 has a so-called membrane structure, in which the cavity section 14 (the hollow section) is provided on the side of the second main surface 20b of the piezoelectric layer 20. In a region overlapping the cavity section 14, the piezoelectric layer 20 is located between the main electrode section 31a of the upper electrode 31 and the main electrode section 32a of the lower electrode 32 in the Z-direction. This arrangement enables the propagation of volume sound waves between the main electrode section 31a of the upper electrode 31 and the main electrode section 32a of the lower electrode 32. In the following description, the region where the upper electrode 31 and the lower electrode 32 overlap in a top view is sometimes referred to as the excitation region of the resonator.

[0019] The extension section 32b of the lower electrode 32 has a greater width than that of the main electrode section 32a and is approximately rectangular. The extension section 32b extends in the X direction on the side opposite the extension section 31b of the upper electrode 31. In other words, the extension section 32b is provided in a region that does not overlap the extension section 31b of the upper electrode 31. The extension section 32b is electrically connected to an external terminal (an input terminal or an output terminal) or to ground.

[0020] The upper electrode 31 and the lower electrode 32 are formed from 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. The upper electrode 31 and the lower electrode 32 can be laminated films.

[0021] The piezoelectric layer 20 has an opening 21 that extends through it in the thickness direction. The opening 21 is located in a region that overlaps the extension section 32b of the lower electrode 32 but does not overlap the upper electrode 31. The extension section 32b of the lower electrode 32 has an area larger than the opening 21 and covers the lower portion of the opening 21.

[0022] The overlapping electrode 33 is provided on the extension section 32b of the lower electrode 32 in a region that overlaps the opening 21. The overlapping electrode 33 is in direct contact with the lower electrode 32. The overlapping electrode 33 is formed from the same material as the upper electrode 31. More precisely, the overlapping electrode 33 is formed from a metal such as Al, Pt, Cu, W, or Mo, or an alloy containing at least one of these materials. The overlapping electrode 33 is formed simultaneously in the same step as the upper electrode 31. The film formation step of the overlapping electrode 33 will be described later with reference to Fig. 3 described.

[0023] The area of ​​the overlapping electrode 33 is smaller than the area of ​​the opening 21. In other words, the overlapping electrode 33 is provided in a region that overlaps the opening 21 such that it overlaps part of the extension section 32b of the lower electrode 32. In the region that overlaps the opening 21, the extension section 32b of the lower electrode 32 comprises a section covered by the overlapping electrode 33 and a section not covered by the overlapping electrode 33. As shown in Fig. As illustrated in Figure 1, both the opening 21 and the overlapping electrode 33 are rectangular. The width W1 of the overlapping electrode 33 in the X-direction is smaller than the width W2 of the opening 21 in the X-direction. The width of the overlapping electrode 33 in the Y-direction is also smaller than the width of the opening 21 in the Y-direction.

[0024] As described above, the sound wave device 10 of the present embodiment comprises the opening 21 of the piezoelectric layer 20 and the overlapping electrode 33 in a region that overlaps the extension section 32b of the lower electrode 32. Thus, the lower electrode 32 and the overlapping electrode 33 are exposed through the opening 21 of the piezoelectric layer 20 on the upper surface (the side of the first main surface 20a) on which the lower electrode 32 is located.

[0025] In a manufacturing step of the detection device 1, a certain potential sometimes occurs in the upper electrode 31 when the side of the first main surface 20a of the piezoelectric layer 20 is exposed to a special atmosphere (for example, a plasma atmosphere). In the present embodiment, the overlapping electrode 33 and the lower electrode 32 are also exposed to the atmosphere on the side of the first main surface 20a of the piezoelectric layer 20 through the opening 21 of the piezoelectric layer 20. Thus, essentially the same potential is applied to the lower electrode 32 as to the upper electrode 31. Accordingly, the sound wave device 10 of the present embodiment prevents the occurrence of an unintended potential difference between the upper electrode 31 and the lower electrode 32.This results in less damage to the electrodes and the piezoelectric layer 20 caused by the potential difference between the upper electrode 31 and the lower electrode 32.

[0026] It should be noted that the in Fig. The shapes of the upper electrode 31 and the lower electrode 32 illustrated in the top view are merely examples and can be modified as needed. The shapes of the opening 21 of the piezoelectric layer 20 and the overlapping electrode 33 shown in the top view are also not limited to rectangular shapes and can be other shapes, such as circular and polygonal shapes.

[0027] Next, a method for manufacturing the sound wave device 10 of the present embodiment is described. Fig. Figure 3 is an explanatory diagram illustrating the method for manufacturing the sound wave device according to the first embodiment. As in Fig. As illustrated in Figure 3, the piezoelectric layer 20, which is a single-crystal substrate of LiNbO3, LiTaO3, or the like, is prepared, and then the lower electrode 32 is formed on the second main surface 20b of the piezoelectric layer 20 (step ST1). The lower electrode 32 is formed, for example, by a vapor deposition and removal process. More precisely, in step ST1, a resist structure is formed on the second main surface 20b of the piezoelectric layer 20 by photolithography. A metal film is deposited, and then the resist is removed, thus structuring the metal film to form the lower electrode 32. In step ST1, the lower electrode 32 is formed such that it comprises the main electrode section 32a and the extension section 32b (see Figure 3). Fig. 1) encompassed by structuring.

[0028] Next, the sacrificial layer 50 is formed on the second main surface 20b of the piezoelectric layer 20 (step ST2). The sacrificial layer 50 is provided in the region where the cavity section 14 of the support element 13 (the insulating layer 12) is to be formed. In other words, the sacrificial layer 50 is provided such that it covers the main electrode section 32a of the lower electrode 32. The sacrificial layer 50 is formed as a film by sputtering using a material such as zinc oxide (ZnO).

[0029] The insulating layer 12 is formed on the second main surface 20b of the piezoelectric layer 20 such that it covers the lower electrode 32 and the sacrificial layer 50 (step ST3). The insulating layer 12 is formed as a film by sputtering using a material such as silicon oxide. An adhesion layer made of Ti, NiCr, or the like can be provided between the layers of the lower electrode 32 and the insulating layer 12. The underside (the surface facing the piezoelectric layer 20) of the insulating layer 12 can be planarized by chemical-mechanical polishing (CMP) if required.

[0030] The support substrate 11, which has an intermediate layer 12a on one surface, is prepared, and then the intermediate layer 12a on the support substrate 11 is bonded to the insulating layer 12 formed on the second main surface 20b of the piezoelectric layer 20. In this step, the support substrate 11 and the combination of the insulating layer 12 and the piezoelectric layer 20 are bonded together (step ST4). More precisely, the intermediate layer 12a is formed from the same material as the insulating layer 12, for example, silicon oxide or the like. The support substrate 11 is bonded to the insulating layer 12 by direct bonding, plasma-activated bonding, atomic diffusion bonding, or the like. In this step, the intermediate layer 12a and the insulating layer 12 are integrated together.In the following description, the intermediate layer 12a and the insulating layer 12 are simply referred to as the insulating layer 12 when they do not need to be distinguished.

[0031] The first principal surface 20a of the piezoelectric layer 20 is ground and polished to reduce its thickness (step ST5). The first principal surface 20a of the piezoelectric layer 20 is polished, for example, by mechanical polishing or CMP. The thickness of the piezoelectric layer 20 is adjusted to approximately 1 µm or less. Step ST5 is not limited to polishing. For example, the thickness of the piezoelectric layer 20 can be reduced by creating a damage layer within the piezoelectric layer 20 through ion implantation and then removing a layer from the top of the created damage layer.

[0032] The opening 21 is formed in the piezoelectric layer 20 at a position that overlaps the lower electrode 32 but does not overlap the region where the upper electrode 31 is to be formed (step ST6). The opening 21 is formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0033] Next, a structure consisting of a resist 81 is formed on the first main surface 20a of the piezoelectric layer 20 by photolithography (step ST7). In this step, the resist 81 is not formed in the region where the upper electrode 31 is to be formed, nor in the region overlapping the opening 21, where the lower electrode 32 is to be formed. Then, a film of a metal layer 82 is formed over the entire surface (step ST8). In step ST8, the metal layer 82 is formed both on the resist 81 and in the regions where the resist 81 is not formed. Simultaneously with the metal film 82, which serves as the upper electrode 31, the metal film 82, which serves as the overlapping electrode 33, is formed on the lower electrode 32 in a region overlapping the opening 21.The resist 81 is then removed, and the metal film 82 in the sections that do not overlap the resist 81 serves as the upper electrode 31 and the overlapping electrode 33 (step ST9). As described above, in the present embodiment a deposition-lifting process is used to form the upper electrode 31 on the first main surface 20a of the piezoelectric layer 20 and the overlapping electrode 33 on the lower electrode 32 in a region that overlaps the opening 21.

[0034] In step ST9, the upper electrode 31 is structured to have the main electrode section 31a and the extension section 31b (see Fig. 1) The overlapping electrode 33 is formed simultaneously in the same step as the upper electrode 31. In this step, during the formation of the upper electrode 31, a portion of the lower electrode 32 is also exposed to the atmosphere on the side of the first main surface 20a of the piezoelectric layer 20 through the opening 21 of the piezoelectric layer 20. With this arrangement, even if a certain potential occurs in the upper electrode 31 during the film formation of the upper electrode 31, essentially the same potential also occurs in the lower electrode 32 as in the upper electrode 31, because the overlapping electrode 33 is formed on the lower electrode 32 through the opening 21 of the piezoelectric layer 20.Therefore, in the manufacturing process of the present embodiment it is possible to reduce the potential difference between the upper electrode 31 and the lower electrode 32, which occurs during the film formation of the upper electrode 31.

[0035] Since the thickness of the piezoelectric layer 20 is reduced to 1 µm or less, damage to the electrodes (the upper electrode 31 and the lower electrode 32) can occur in this structure, as described above, if an unintended potential difference arises between the upper electrode 31 and the lower electrode 32. Because the potential difference between the upper electrode 31 and the lower electrode 32 can be reduced, damage to the electrodes can be minimized in the present embodiment, even with the thickness of the piezoelectric layer 20 reduced to 1 µm or less.

[0036] Next, the sacrificial layer 50 is removed, so that the cavity section 14 is formed in the insulating layer 12 (step ST10). This step forms the membrane structure of the piezoelectric layer 20. The sacrificial layer 50 is removed by wet etching. In this step, an etchant is introduced through the etch windows 22 to dissolve the sacrificial layer 50 (see Fig. 1).

[0037] The sound wave device 10 of the present embodiment is produced by the steps described above. It should be noted that the Fig. The 3 illustrated steps are merely a schematic representation and can be modified as appropriate. (First modification of the first embodiment)

[0038] Fig. Figure 4 is a cross-sectional view of a sound wave device according to the first modification of the first embodiment. As in Fig. As illustrated in Figure 4, the sound wave device 10A according to the first modification differs from the first embodiment described above in that the area of ​​the overlapping electrode 33 is larger than the area of ​​the opening 21 of the piezoelectric layer 20.

[0039] The overlapping electrode 33 is positioned on the extension section 32b of the lower electrode 32 in a region that overlaps the opening 21. The overlapping electrode 33 is positioned such that it extends along the inner wall of the opening 21 of the piezoelectric layer 20 and onto the first principal surface 20a of the piezoelectric layer 20. The outer edge 33e of the overlapping electrode 33 is located on the first principal surface 20a of the piezoelectric layer 20 and away from the upper electrode 31.

[0040] Since the overlapping electrode 33 in the first modification has a large area, it is possible to protect the inner wall of the opening 21 of the piezoelectric layer 20. The overlapping electrode 33 prevents separation between the piezoelectric layer 20 and the lower electrode 32 near the opening 21 of the piezoelectric layer 20.

[0041] It should be noted that the first modification can also be carried out using the same or similar steps as in the one mentioned above, in Fig. The 3 illustrated manufacturing processes can be formed. More precisely, in the evaporation-lifting process, steps ST7 to ST9 are used. Fig. 3. When the resist structure is formed by photolithography, the resist is not formed in the region overlapping the aperture 21, but rather near the aperture 21 on the first principal surface 20a of the piezoelectric layer 20. With this step, the metal film is formed in a region overlapping the aperture 21 of the piezoelectric layer 20 such that it extends onto the extension section 32b of the lower electrode 32, along the inner wall of the aperture 21 of the piezoelectric layer 20, and onto the first principal surface 20a of the piezoelectric layer 20. This results in the overlapping electrode 33 having an area larger than the area of ​​the aperture 21 of the piezoelectric layer 20. (Second modification of the first embodiment)

[0042] Fig. Figure 5 is a cross-sectional view of a sound wave device according to the second modification of the first embodiment. As in Fig. As illustrated in Figure 5, the sound wave device 10B according to the second modification differs from the first modification described above in that it has an intermediate insulating layer 34 covering the outer edge of the opening 21 of the piezoelectric layer 20.

[0043] The intermediate insulating layer 34 is provided between the inner wall of the opening 21 and the overlapping electrode 33, and between the first main surface 20a of the piezoelectric layer 20 and the overlapping electrode 33. The intermediate insulating layer 34 is also provided between the overlapping electrode 33 and the outer edge of the lower electrode 32 in the region that overlaps the opening 21 of the piezoelectric layer 20. In other words, the intermediate insulating layer 34 has an opening in a region that overlaps the opening 21 of the piezoelectric layer 20, and the lower electrode 32 and the overlapping electrode 33 are in direct contact with each other through the opening of the intermediate insulating layer 34.

[0044] Although the illustration of this state has been omitted, the intermediate insulating layer 34 is formed along the inner wall of the opening 21 in the top view. The intermediate insulating layer 34 can be formed continuously in a frame-like shape along the inner wall of the opening 21 or can be provided along a portion of the inner wall of the opening 21.

[0045] Since the intermediate insulating layer 34 is provided in the second modification between the outer edge 33e of the overlapping electrode 33 and the first main surface 20a of the piezoelectric layer 20, the distance between the outer edge 33e of the overlapping electrode 33 and the upper electrode 31 is longer than in a device without the intermediate insulating layer 34. This arrangement reduces stray capacitance formed between the upper electrode 31 and the overlapping electrode 33. More precisely, it reduces stray capacitance formed between the upper electrode 31 and the lower electrode 32, with the overlapping electrode 33 positioned between them. (Third modification of the first embodiment)

[0046] Fig. Figure 6 is a cross-sectional view of a sound wave device according to the third modification of the first embodiment. As in Fig. As illustrated in Figure 6, the sound wave device 10C according to the third modification differs from the first modification described above in that it has a conductive intermediate layer 39 between the lower electrode 32 and the overlapping electrode 33 in a region that overlaps the opening 21 of the piezoelectric layer 20.

[0047] The conductive intermediate layer 39 covers the entire region of the lower electrode 32 in the region overlapping the opening 21. The conductive intermediate layer 39 is also provided between the inner wall of the opening 21 and the overlapping electrode 33, and between the first main surface 20a of the piezoelectric layer 20 and the overlapping electrode 33.

[0048] The conductive intermediate layer 39 is formed from a material (a metal or an alloy) that differs from that of the upper electrode 31 and the overlapping electrode 33. In cases where the overlapping electrode 33 is laminated directly onto the lower electrode 32, the surface of the lower electrode 32 is alloyed, depending on the combination of materials of the lower electrode 32 and the upper electrode 31 and the overlapping electrode 33. In a third modification, the conductive intermediate layer 39 prevents alloying between the lower electrode 32 and the overlapping electrode 33. In other words, the conductive intermediate layer 39 acts as a barrier layer between the lower electrode 32 and the overlapping electrode 33.

[0049] Furthermore, the provision of the conductive intermediate layer 39 results in the total thickness of the lower electrode 32, the conductive intermediate layer 39, and the overlapping electrode 33 being greater than in a device without the conductive intermediate layer 39. This provision reduces the wiring resistance of the lower electrode 32.

[0050] Fig. Figure 7 is an explanatory diagram illustrating a method for manufacturing the sound wave device according to the third modification of the first embodiment. The method for manufacturing the sound wave device 10C according to the third modification differs from that in Fig. 3 illustrated manufacturing processes with regard to the process for forming the upper electrode 31 in steps ST7 to ST9. Steps ST1 to ST6 and ST10 in Fig. 3 are also the same or similar in the method for manufacturing the sound wave device 10C according to the third modification.

[0051] As in Fig. As illustrated in Figure 7, after the formation of the opening 21 of the piezoelectric layer 20 in step ST6, the conductive intermediate layer 39 is formed on the lower electrode 32 in a region that overlaps the opening 21 (step ST7A), before the upper electrode 31 and the overlapping electrode 33 are formed. The conductive intermediate layer 39 is formed, for example, by a vapor deposition and peeling process.

[0052] Next, the upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20, and the overlapping electrode 33 is formed on the conductive intermediate layer 39 in a region overlapping the opening 21 (step ST7B). The upper electrode 31 and the overlapping electrode 33 are formed, for example, by a deposition-lifting process in the same or a similar manner as in steps ST7 to ST9 described above (see Fig. 3) formed.

[0053] Even in such a setup, where alloying occurs when the overlapping electrode 33 is laminated directly onto the lower electrode 32, the overlapping electrode 33 is not in direct contact with the lower electrode 32 because, in the present modification, the conductive intermediate layer 39 is provided beforehand. This prevents alloying of the surface of the lower electrode 32, and the overlapping electrode 33 and the lower electrode 32 maintain favorable conductivity while the conductive intermediate layer 39 is positioned between them. The sound wave device 10C in the present modification reduces the potential difference between the upper electrode 31 and the lower electrode 32 that occurs during film formation of the upper electrode 31. (Second embodiment)

[0054] Fig. Figure 8 is a cross-sectional view of a sound wave device according to the second embodiment. As in Fig. As illustrated in Figure 8, the sound wave device 1D according to the second embodiment differs from the first modification of the first embodiment (see Figure 8). Fig. 4) by having front electrodes 35 and 36 and a rear electrode 37,

[0055] The front electrode 35 is laminated onto the extension section 31b of the upper electrode 31. The front electrode 36 is laminated onto the overlapping electrode 33. In the present embodiment, the overlapping electrode 33 is formed such that it has an area larger than the area of ​​the opening 21. The front electrode 36 is also formed such that it has an area larger than the area of ​​the opening 21. The front electrode 36 is formed on the overlapping electrode 33 in a region that overlaps the opening 21 and is furthermore formed on the overlapping electrode 33 such that it covers the inner wall of the opening 21 and a portion of the first main area 20a of the piezoelectric layer 20 near the opening 21.

[0056] The rear electrode 37 is laminated between the extension section 32b of the lower electrode 32 and the insulating layer 12. The front electrodes 35 and 36 and the rear electrode 37 are not provided on the main electrode section 31a of the upper electrode 31 and the main electrode section 32a of the lower electrode 32, which form the membrane structure.

[0057] The provision of the front electrode 35 reduces the wiring resistance of the main electrode section 31a of the upper electrode 31. The provision of the rear electrode 37 reduces the wiring resistance of the main electrode section 32a of the lower electrode 32. Furthermore, the provision of the front electrode 36 reduces the wiring resistance in the section where the extension section 32b of the lower electrode 32 and the overlapping electrode 33 are laminated.

[0058] Fig. Figure 9 is an explanatory diagram illustrating a method for manufacturing the sound wave device according to the second embodiment. In the description of the [description] in Fig. The description of the sections relating to the manufacturing process mentioned above is omitted in section 9, which illustrates the process. Fig. The three illustrated manufacturing processes overlap. As shown in Fig. As illustrated in Figure 9, the lower electrode 32 is first formed on the second main surface 20b of the piezoelectric layer 20 (step ST11).

[0059] Next, the sacrificial layer 50 and the back electrode 37 are formed on the second main surface 20b of the piezoelectric layer 20 (step ST12). The back electrode 37 is positioned to cover the extension section 32b of the lower electrode 32 in the region where the opening 21 of the piezoelectric layer 20 is to be formed. The back electrode 37 is formed, for example, by a deposition-deposition process similar to that used for the lower electrode 32. Then, the sacrificial layer 50 is positioned to cover the main electrode section 32a of the lower electrode 32. The sacrificial layer 50 is formed as a film by sputtering using a material such as zinc oxide (ZnO).

[0060] The insulating layer 12 is formed on the second main surface 20b of the piezoelectric layer 20 such that it covers the bottom electrode 32, the back electrode 37, and the sacrificial layer 50 (step ST13). The insulating layer 12 is formed as a film by sputtering using a material such as silicon oxide. An adhesion layer composed of Ti, NiCr, or the like can be provided between the layers of the bottom electrode 32 and the insulating layer 12, and between the layers of the back electrode 37 and the insulating layer 12. The underside (the surface facing the piezoelectric layer 20) of the insulating layer 12 can be planarized by CMP if required.

[0061] The support substrate 11, which has the intermediate layer 12a on one surface, is prepared, and then the intermediate layer 12a on the support substrate 11 is connected to the insulating layer 12 formed on the second main surface 20b of the piezoelectric layer 20. With this step, the support substrate 11 and the combination of the insulating layer 12 and the piezoelectric layer 20 are joined together (step ST14). As in step ST5 (see Fig. 3) The first main surface 20a of the piezoelectric layer 20 is ground and polished to reduce its thickness.

[0062] The opening 21 is formed in the piezoelectric layer 20 in a region that overlaps the lower electrode 32 and the rear electrode 37, but does not overlap the upper electrode 31 (step ST15). The opening 21 is formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0063] The upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20, and the overlapping electrode 33 is formed on the lower electrode 32 in a region that overlaps the opening 21 (step ST16). The upper electrode 31 and the overlapping electrode 33 are formed, for example, by a deposition-lifting process. In the present embodiment, the overlapping electrode 33 is formed such that it has an area larger than the area of ​​the opening 21 of the piezoelectric layer 20. Also in the present embodiment, the overlapping electrode 33 is formed simultaneously in the same step as the upper electrode 31. This arrangement makes it possible to reduce the potential difference between the upper electrode 31 and the lower electrode 32 that occurs during the film formation of the upper electrode 31.

[0064] Next, the front electrode 35 is formed on the extension section 31b of the upper electrode 31, and the front electrode 36 is formed on the overlapping electrode 33 (step ST17). The front electrodes 35 and 36 are formed, for example, by a deposition-lifting process.

[0065] In the present embodiment, the front electrode 36, which overlaps the overlapping electrode 33, is formed simultaneously in the same step as the front electrode 35, which overlaps the upper electrode 31. In this step, during the formation of the front electrode 35, the overlapping electrode 33 is also exposed to the atmosphere on the side of the first main surface 20a of the piezoelectric layer 20. That is, even if a certain potential occurs in the front electrode 35 and the upper electrode 31 during the film formation of the front electrode 35, essentially the same potential also occurs in the lower electrode 32 as in the upper electrode 31, because the front electrode 36 is formed on the overlapping electrode 33.Therefore, in the manufacturing process of the present embodiment it is possible to reduce the potential difference between the upper electrode 31 and the lower electrode 32, which occurs during the film formation of the front electrode 35.

[0066] Next, the sacrificial layer 50 is removed, so that the cavity section 14 is formed in the insulating layer 12 (step ST18). This step forms the membrane structure of the piezoelectric layer 20.

[0067] The sound wave device 10D of the second embodiment is manufactured by the steps described above. It should be noted that the in Fig. The 9 illustrated steps are merely a schematic representation and can be modified as appropriate. (Fourth modification of the second embodiment)

[0068] Fig. Figure 10 is a cross-sectional view of a sound wave device according to the fourth modification of the second embodiment. As in Fig. As illustrated in Figure 10, the sound wave device 10E according to the fourth modification differs from the sound wave device 10D of the second embodiment described above in that the areas of the overlapping electrode 33 and the front electrode 36 are smaller than the area of ​​the opening 21.

[0069] The overlapping electrode 33 and the front electrode 36 are positioned such that they overlap a portion of the extension section 32b of the lower electrode 32 in the region overlapping the opening 21. In other words, the extension section 32b of the lower electrode 32 in the region overlapping the opening 21 comprises a section covered by the overlapping electrode 33 and the front electrode 36, and a section not covered by the overlapping electrode 33 and the front electrode 36.

[0070] Since the areas occupied by the overlapping electrode 33 and the front electrode 36 are smaller in the fourth modification than in the second embodiment described above, the sound wave device 10E can be reduced in size. Furthermore, the distance between the combination of the upper electrode 31 and the front electrode 35 and the combination of the overlapping electrode 33 and the front electrode 36 is greater than in the second embodiment described above. This arrangement reduces stray capacitance that forms between the combination of the upper electrode 31 and the front electrode 35 and the combination of the overlapping electrode 33 and the front electrode 36.

[0071] Fig. Figure 11 is an explanatory diagram illustrating a method for manufacturing the sound wave device according to the fourth modification of the second embodiment. In the Fig. In the 11 illustrated methods for manufacturing the sound wave device 10E according to the fourth modification, steps ST21 to ST25 are the same as or similar to those above with reference to Fig. The 9 steps described in ST11 to ST15 are therefore omitted.

[0072] As in Fig. As illustrated in Figure 11, after forming the opening 21 in the piezoelectric layer 20, the upper electrode 31 is formed on the first main surface 20a of the piezoelectric layer 20, and the overlapping electrode 33 is formed on the lower electrode 32 in a region that overlaps the opening 21 (step ST26). The upper electrode 31 and the overlapping electrode 33 are formed, for example, by a deposition-deposition process. In the fourth modification, the overlapping electrode 33 is formed such that it has an area smaller than the area of ​​the opening 21 of the piezoelectric layer 20.

[0073] Next, the front electrode 35 is formed on the extension section 31b of the upper electrode 31, and the front electrode 36 is formed on the overlapping electrode 33 (step ST27). The front electrode 36 is formed such that its area is smaller than the area of ​​the opening 21 of the piezoelectric layer 20. The front electrodes 35 and 36 are formed, for example, by a deposition-deposition process.

[0074] Next, the sacrificial layer 50 is removed, so that the cavity section 14 is formed in the insulating layer 12 (step ST28). This step forms the membrane structure of the piezoelectric layer 20.

[0075] The sound wave device 10E of the fourth embodiment is manufactured by the steps described above. It should be noted that the in Fig. The 11 illustrated steps are merely a schematic representation and can be modified as appropriate. (Fifth modification of the second embodiment)

[0076] Fig. Figure 12 is a cross-sectional view of a sound wave device according to the fifth modification of the second embodiment. As in Fig. As illustrated in Figure 12, the sound wave device 10F according to the fifth modification differs from the sound wave device 10D according to the second embodiment described above in that it has the rear electrode 37 and does not have front electrodes 35 and 36.

[0077] In the fifth modification, the provision of the rear electrode 37 also reduces the wiring resistance of the lower electrode 32.

[0078] The layouts, surfaces, and other conditions of the front electrodes 35 and 36 and the rear electrode 37, illustrated in the second embodiment, the fourth modification, and the fifth modification, can be modified as needed to meet the requirements of the sound wave device 10F. The setup example is not limited to the fifth modification. A setup in which the front electrodes 35 and 36 are provided but no rear electrode 37 is provided is also possible.

[0079] The front electrodes 35 and 36 and the rear electrode 37, which are illustrated in the second embodiment, the fourth modification and the fifth modification, can be combined with the second or third modification of the first embodiment described above. (Third embodiment)

[0080] Fig. Figure 13 is a top view of a sound wave device according to the third embodiment. Fig. 14 is a cross-sectional view along line XIV-XIV' in Fig. 13. As in Fig. 13 and Fig. As illustrated in Figure 14, the sound wave device 10G according to the third embodiment differs from the first and second embodiments described above in that it has two resonators.

[0081] As in Fig. 13 and Fig. As illustrated in Figure 14, the sound wave device 10G according to the third embodiment comprises a support element 13, a piezoelectric layer 20, a first upper electrode 41, a second upper electrode 42, a lower electrode 43 and an overlapping electrode 44.

[0082] The support element 13 (an insulating layer 12) comprises a first cavity section 15 (a hollow section) and a second cavity section 16 (a hollow section) on the surface facing the second main surface 20b of the piezoelectric layer 20. The first cavity section 15 and the second cavity section 16 are spaced apart from each other in the X-direction. The first cavity section 15 overlaps the excitation region of the resonator, which is composed of the piezoelectric layer 20, the first upper electrode 41, and the lower electrode 43, which overlap each other. The second cavity section 16 overlaps the excitation region of the resonator, which is composed of the piezoelectric layer 20, the second upper electrode 42, and the lower electrode 43, which overlap each other.

[0083] As in Fig. As illustrated in Figure 13, the piezoelectric layer 20 has etch windows 24 in a region that overlaps the first cavity section 15. The piezoelectric layer 20 has etch windows 25 in a region that overlaps the second cavity section 16. Etch windows 24 and 25 are openings for etching when the first cavity section 15 and the second cavity section 16 of the insulating layer 12 are formed.

[0084] The first upper electrode 41 and the second upper electrode 42 are provided on the first main surface 20a of the piezoelectric layer 20. The first upper electrode 41 and the second upper electrode 42 are spaced apart from each other in the X-direction. As shown in Fig. As illustrated in Figure 13, the first upper electrode 41 comprises a first main electrode section 41a and a first extension section 41b, which is coupled to the first main electrode section 41a and extends in the X direction. The first main electrode section 41a is provided in a region that overlaps the first cavity section 15 of the insulating layer 12 and is approximately circular. The first extension section 41b has a width that is approximately equal to the diameter of the first main electrode section 41a.

[0085] The second upper electrode 42 comprises a second main electrode section 42a and a second extension section 42b, which is coupled to the second main electrode section 42a and extends in the X direction. The second main electrode section 42a is provided in a region that overlaps the second cavity section 16 of the insulating layer 12 and is approximately circular. The second extension section 42b has a width approximately equal to the diameter of the second main electrode section 42a and extends on the side opposite the first extension section 41b.

[0086] The first extension section 41b and the second extension section 42b are electrically coupled to external connections (input connections or output connections) or to an earth.

[0087] The lower electrode 43 is provided on the second main surface 20b of the piezoelectric layer 20 in a region where the lower electrode 43 at least partially overlaps both the first upper electrode 41 and the second upper electrode 42. The lower electrode 43 extends in the X direction and comprises a first main electrode section 43a located at one end in the X direction, a second main electrode section 43b located at the other end in the X direction, and a coupling section 43c that couples the first main electrode section 43a and the second main electrode section 43b.

[0088] The first main electrode section 43a is provided in a region that overlaps the first cavity section 15 of the insulating layer 12 and is approximately circular. In other words, the first main electrode section 43a is provided in a region that overlaps the first main electrode section 41a of the first upper electrode 41. The second main electrode section 43b is provided in a region that overlaps the second cavity section 16 of the insulating layer 12 and is approximately circular. In other words, the second main electrode section 43b is provided in a region that overlaps the second main electrode section 42a of the second upper electrode 42.

[0089] The sound wave device 10 has membrane structures on the side of the second main surface 20b of the piezoelectric layer 20 in the sections where the first cavity section 15 and the second cavity section 16 are provided, respectively. In a region overlapping the first cavity section 15, the piezoelectric layer 20 is located between the first main electrode section 41a of the first upper electrode 41 and the first main electrode section 43a of the lower electrode 43 in the Z-direction. This arrangement enables the propagation of volume sound waves between the first main electrode section 41a of the first upper electrode 41 and the first main electrode section 43a of the lower electrode 43.

[0090] In a region overlapping the second cavity section 16, the piezoelectric layer 20 is located between the second main electrode section 42a of the second upper electrode 42 and the second main electrode section 43b of the lower electrode 43 in the Z-direction. This arrangement enables the propagation of volume sound waves between the second main electrode section 42a of the second upper electrode 42 and the second main electrode section 43b of the lower electrode 43.

[0091] In the following description, the region where the first upper electrode 41 and the lower electrode 43 overlap in plan view, and the region where the second upper electrode 42 and the lower electrode 43 overlap in plan view, are sometimes referred to as the excitation regions of the resonators.

[0092] The coupling section 43c of the lower electrode 43 has a width approximately equal to the diameters of the first main electrode section 43a and the second main electrode section 43b, and extends in the X direction. In plan view, the coupling section 43c is positioned between the first upper electrode 41 and the second upper electrode 42. In other words, the coupling section 43c is provided in a region that does not overlap either the first upper electrode 41 or the second upper electrode 42.

[0093] The piezoelectric layer 20 has an opening 23 located in a region that overlaps the coupling section 43c of the lower electrode 43 but does not overlap the first upper electrode 41 and the second upper electrode 42. The coupling section 43c of the lower electrode 43 has an area larger than the opening 23 and covers the lower portion of the opening 23.

[0094] The overlapping electrode 44 is provided on the coupling section 43c of the lower electrode 43 in a region that overlaps the opening 23. The overlapping electrode 44 is in direct contact with the lower electrode 43. The overlapping electrode 44 is made of the same material as the first upper electrode 41 and the second upper electrode 42. More precisely, the overlapping electrode 44 is made of a metal such as Al, Pt, Cu, W, or Mo, or an alloy containing at least one of these materials.

[0095] The overlapping electrode 44 is formed such that it has an area larger than the area of ​​the opening 23. The overlapping electrode 44 is provided on the coupling section 43c of the lower electrode 43 in the region that overlaps the opening 23 of the piezoelectric layer 20, and extends along the inner wall of the opening 21 of the piezoelectric layer 20 and onto the first main surface 20a of the piezoelectric layer 20. The outer edge of the overlapping electrode 44 is provided on the first main surface 20a of the piezoelectric layer 20 and away from the first upper electrode 41 and the second upper electrode 42.

[0096] As described above, in the sound wave device 10G of the present embodiment, the opening 23 of the piezoelectric layer 20 and the overlapping electrode 44 are positioned in regions that overlap the coupling section 43c of the lower electrode 43. In this arrangement, when the first upper electrode 41 and the second upper electrode 42 are formed, the lower electrode 43 receives, via the overlapping electrode 44, essentially the same potential as the upper electrode 31. Thus, the sound wave device 10G of the present embodiment prevents the occurrence of an unintended potential difference between the first and second upper electrodes 41 and 42 and the lower electrode 43. This reduces damage to the electrodes and the piezoelectric layer 20 caused by the potential difference between the first and second upper electrodes 41 and 42 and the lower electrode 43.

[0097] In the Fig. In the example illustrated in Figure 14, the thickness of the piezoelectric layer 20 is constant across the two resonators. However, the present disclosure is not limited to this example, and the thickness of the piezoelectric layer 20 can differ between the excitation region where the first main electrode section 41a of the first upper electrode 41 overlaps the first main electrode section 43a of the lower electrode 43, and the excitation region where the second main electrode section 42a of the second upper electrode 42 overlaps the second main electrode section 43b of the lower electrode 43. In this case, the frequency characteristics for each of the two resonators can be conveniently adjusted. (Sixth modification of the third embodiment)

[0098] Fig. Figure 15 is a cross-sectional view of a sound wave device according to the sixth modification of the third embodiment. As in Fig. As illustrated in Figure 15, the sound wave device 10H according to the sixth embodiment differs from the third embodiment in that it has front electrodes 45, 46 and 47 and a rear electrode 48.

[0099] The front electrode 45 is laminated onto the first extension section 41b of the first upper electrode 41. The front electrode 46 is laminated onto the second extension section 42b of the second upper electrode 42. The front electrode 47 is laminated onto the overlapping electrode 44. In the present embodiment, the overlapping electrode 44 is formed such that it has an area larger than the area of ​​the opening 23. The front electrode 47 is formed such that it has an area larger than the area of ​​the opening 23. The front electrode 47 is formed on the overlapping electrode 44 in a region that overlaps the opening 23 and is also formed on the overlapping electrode 44 such that it covers the inner wall of the opening 23 and a part of the first main area 20a of the piezoelectric layer 20 near the opening 23.

[0100] The rear electrode 48 is laminated between the coupling section 43c of the lower electrode 43 and the insulating layer 12. The front electrodes 45, 46 and 47 and the rear electrode 48 are not provided on the first main electrode section 41a of the first upper electrode 41, the second main electrode section 42a of the second upper electrode 42, and the first and second main electrode sections 43a and 43b of the lower electrode 43, which form the membrane structures.

[0101] Since the present modification includes the front electrodes 45 and 46, the wiring resistances of the first upper electrode 41 and the second upper electrode 42 can be reduced. Furthermore, the provision of the rear electrode 48 reduces the wiring resistance of the lower electrode 43. In addition, the provision of the front electrode 47 reduces the wiring resistance of the section where the coupling section 43c of the lower electrode 43 and the overlapping electrode 44 are laminated.

[0102] Fig. Figure 16 is an explanatory diagram illustrating a method for manufacturing the sound wave device according to the sixth modification of the third embodiment. In the description of the Fig. In section 16, which illustrates the manufacturing process, the description of sections that overlap with the manufacturing processes mentioned above is omitted. As in Fig. As illustrated in Figure 16, the lower electrode 43 is first formed on the second main surface 20b of the piezoelectric layer 20 (step ST31).

[0103] Next, the sacrificial layers 51 and 52 and the back electrode 48 are formed on the second main surface 20b of the piezoelectric layer 20 (step ST32). The back electrode 48 is positioned to cover the coupling section 43c of the lower electrode 43 in the region where the opening 23 of the piezoelectric layer 20 is to be formed. The back electrode 48 is formed, for example, by a deposition-deposition process similar to that used for the lower electrode 43. Then, the sacrificial layer 51 is positioned to cover the first main electrode section 43a of the lower electrode 43. The sacrificial layer 51 is formed in the region where the first cavity section 15 of the insulating layer 12 is to be formed. The sacrificial layer 52 is positioned to cover the second main electrode section 43b of the lower electrode 43.The sacrificial layer 52 is formed in the region where the second cavity section 16 of the insulating layer 12 is to be formed. The sacrificial layers 51 and 52 are formed as films by sputtering using a material such as zinc oxide (ZnO).

[0104] The insulating layer 12 is formed on the second main surface 20b of the piezoelectric layer 20 such that it covers the bottom electrode 43, the back electrode 48, and the sacrificial layers 51 and 52 (step ST33). The insulating layer 12 is formed as a film by sputtering using a material such as silicon oxide. An adhesion layer composed of Ti, NiCr, or the like can be provided between the layers of the bottom electrode 43 and the insulating layer 12, and between the layers of the back electrode 48 and the insulating layer 12. The underside (the surface facing the piezoelectric layer 20) of the insulating layer 12 can be planarized by CMP if required.

[0105] The support substrate 11, which has the intermediate layer 12a on one surface, is prepared, and the support substrate 11 and the combination of the insulating layer 12 and the piezoelectric layer 20 are attached to one another (step ST34). As in step ST5 (see Fig. 3) The first main surface 20a of the piezoelectric layer 20 is ground and polished to reduce its thickness.

[0106] The opening 23 is formed in the piezoelectric layer 20 in a region that overlaps the lower electrode 43 and the rear electrode 48 and does not overlap either the first upper electrode 41 or the second upper electrode 42 (step ST35). The opening 23 is formed by removing a portion of the piezoelectric layer 20 by reactive ion etching (RIE).

[0107] The first upper electrode 41 and the second upper electrode 42 are formed on the first main surface 20a of the piezoelectric layer 20, and the overlapping electrode 44 is formed on the lower electrode 43 in a region that overlaps the opening 23 (step ST36). The first upper electrode 41, the second upper electrode 42, and the overlapping electrode 44 are formed, for example, by a deposition-lifting process. In the present embodiment, the overlapping electrode 44 is formed such that it has an area larger than the area of ​​the opening 23 of the piezoelectric layer 20. The overlapping electrode 44 is formed simultaneously in the same step as the first upper electrode 41 and the second upper electrode 42.This reduces the potential difference between the first and second upper electrodes 41 and 42 and the lower electrode 43, which occurs during the film formation of the first upper electrode 41 and the second upper electrode 42.

[0108] Next, the front electrode 45 is formed on the first extension section 41b of the first upper electrode 41, and the front electrode 46 is formed on the second extension section 42b of the second upper electrode 42. Additionally, in the same step, the front electrode 47 is formed on the overlapping electrode 44 (step ST37). The front electrodes 45, 46, and 47 are formed, for example, by a deposition-lifting process.

[0109] In the present embodiment, the front electrode 47, which overlaps the overlapping electrode 44, is formed simultaneously in the same step as the front electrodes 45 and 46, which overlap the first upper electrode 41 and the second upper electrode 42. In this step, during the formation of the front electrodes 45 and 46, the overlapping electrode 44 is also exposed to the atmosphere on the side of the first main surface 20a of the piezoelectric layer 20. With this arrangement, even if a certain potential occurs in the first upper electrode 41 and the second upper electrode 42 during the film formation of the front electrodes 45 and 46, essentially the same potential also occurs in the lower electrode 43 as in the first upper electrode 41 and the second upper electrode 42, because the front electrode 47 is formed on the overlapping electrode 44.Therefore, in the manufacturing process of the present embodiment it is possible to reduce the potential difference between the first and the second upper electrode 41 and 42 and the lower electrode 32, which occurs during the film formation of the front electrodes 45 and 46.

[0110] Next, the sacrificial layers 51 and 52 are removed, so that the first cavity section 15 and the second cavity section 16 are formed in the insulating layer 12 (step ST38). This step forms the membrane structures of the piezoelectric layer 20.

[0111] The sound wave device 10H according to the sixth modification of the third embodiment is manufactured by the steps described above. It should be noted that the in Fig. The 16 illustrated steps are merely a schematic representation and can be modified as needed. Furthermore, the sound wave device 10G (see Fig. 14) according to the third embodiment described above, in similar steps to those described in Fig. Figure 16 illustrates how the sound wave device 10G can be formed according to the third embodiment in the process of forming the front electrodes 45, 46 and 47 and the rear electrode 48 from the following steps. Fig. 16 are omitted.

[0112] It should be noted that in the sound wave device 10H according to the sixth modification, either the front electrodes 45, 46 and 47 or the rear electrode 48 can be omitted. For example, a device is possible in which the front electrodes 45, 46 and 47 are provided and the rear electrode 48 is not provided. Alternatively, a device is also possible in which the front electrodes 45, 46 and 47 are not provided and the rear electrode 48 is provided. (Seventh modification of the third embodiment)

[0113] Fig. Figure 17 is a top view of a sound wave device according to the seventh modification of the third embodiment. As in Fig. As illustrated in Figure 17, the sound wave device 101 according to the seventh modification differs from the third embodiment and the sixth modification described above in that the lower electrode 43 comprises a routing electrode section 43d.

[0114] The routing electrode section 43d of the lower electrode 43 is coupled to the coupling section 43c, which is provided in a region between the first upper electrode 41 and the second upper electrode 42, and extends in the Y direction. The opening 23 and the overlapping electrode 44 are provided at a position that overlaps the routing electrode section 43d of the lower electrode 43. In the Fig. In the illustrated example 17, the position of the opening 23 and the overlapping electrode 44 is shifted in the Y direction from the first upper electrode 41 and the second upper electrode 42.

[0115] This arrangement in the seventh modification increases the degree of freedom of the positions, shapes, and the like of the opening 23 and the overlapping electrode 44. More precisely, even in the case where the distance between the first upper electrode 41 and the second upper electrode 42 is short, the planar surfaces of the opening 23 and the overlapping electrode 44 can be ensured. Thus, regardless of the positional relationship between the first upper electrode 41, the second upper electrode 42, and the lower electrode 43, the potential difference between the first and second upper electrodes 41 and 42 and the lower electrode 43 can be advantageously reduced.

[0116] It should be noted that the in Fig. Figure 17 illustrates the arrangement of the routing electrode section 43d, which is merely an example and can therefore be modified as needed. For example, the routing electrode section 43d is not limited to a straight shape and can also have a bent or curved section. It should be noted that the third embodiment and each one shown in Figure 17 is an example of the arrangement of the routing electrode section 43d. Fig. The modifications illustrated in Figures 13 to 17 are based on devices in which two resonators are provided on the support element 13, but are not limited to these devices. A device in which three or more resonators are formed on the support element 13 and are electrically coupled to each other is also possible. (Fourth embodiment)

[0117] Fig. Figure 18 is a cross-sectional view of a sound wave device according to the fourth embodiment. As in Fig. As illustrated in Figure 18, the sound wave device 10J according to the fourth embodiment differs from the first embodiment described above in that it has a multilayer sound film 17 instead of the cavity section 14. More precisely, the sound wave device 10 of the first embodiment includes the cavity section 14 in the support element 13 (the insulating layer 12) and has a so-called membrane structure in which the cavity section 14 (the hollow section) is provided on the side of the second main surface 20b of the piezoelectric layer 20. However, the present disclosure is not limited to this arrangement.

[0118] As in Fig. As illustrated in Figure 18, the acoustic multilayer film 17 is laminated onto the second main surface 20b of the piezoelectric layer 20. The acoustic multilayer film 17 has a lamination structure comprising low-acoustic impedance layers 17a, 17c, and 17e, which have a relatively low acoustic impedance, and high-acoustic impedance layers 17b and 17d, which have a relatively high acoustic impedance. The low-acoustic impedance layers 17a, 17c, and 17e are, for example, SiO₂ layers, and the high-acoustic impedance layers 17b and 17d are, for example, metal layers of tungsten, platinum, or the like, or dielectric layers made of ammonium chloride, silicon dioxide, or the like. The use of the acoustic multilayer film 17 makes it possible to confine volumetric sound waves to the area of ​​the piezoelectric layer 20 without the cavity section 14.

[0119] It should be noted that there are no special restrictions on the number of laminated layers, such as the low-acoustic impedance layers 17a, 17c and 17e and the high-acoustic impedance layers 17b and 17d, in the acoustic multilayer film 17. Only at least one of the high-acoustic impedance layers 17b and 17d must be located further away from the piezoelectric layer 20 than the low-acoustic impedance layers 17a, 17c and 17e.

[0120] The low-acoustic impedance layers 17a, 17c, and 17e and the high-acoustic impedance layers 17b and 17d mentioned above can be formed from suitable materials, provided the aforementioned acoustic impedance relationship is satisfied. Examples of materials for the low-acoustic impedance layers 17a, 17c, and 17e include silicon oxide and silicon oxynitride. Examples of materials for the high-acoustic impedance layers 17b and 17d include aluminum oxide, silicon nitride, and metals.

[0121] The sound multilayer film 17 illustrated in the fourth embodiment can be combined with any embodiment and modification described above. (Fifth embodiment)

[0122] Fig. Figure 19 is a cross-sectional view of a sound wave device according to the fifth embodiment. As in Fig. As illustrated in Figure 19, the sound wave device 10K according to the fifth embodiment differs from the embodiments and modifications described above in that it comprises a cover section 70 and a connecting element 71.

[0123] The cover section 70 faces the first main surface 20a of the piezoelectric layer 20. The connecting element 71 is positioned between the cover section 70 and the insulating layer 12 of the support element 13. More precisely, the piezoelectric layer 20 is not present on the outer edge of the support element 13. That is, the side surface 20c of the piezoelectric layer 20 on the outer edge is positioned on the inside of the side surface of the insulating layer 12 (closer to the cavity section 14 than the insulating layer itself). On the outer edge of the insulating layer 12, the connecting element 71 and the insulating layer 12 are in direct contact and connected to each other. The side surface 20c of the piezoelectric layer 20 on the outer edge is located away from the side surface of the support element 13.

[0124] The connecting element 71 is made of the same material as the insulating layer 12, for example, an insulating material such as silicon dioxide (SiO2). This arrangement ensures better adhesion between the insulating layer 12 and the connecting element 71, thereby improving the sealing properties compared to cases where the material of the connecting element 71 differs from that of the insulating layer 12 (for example, a metal material or the like).

[0125] The cover section 70 has a recessed section 70a on the surface facing the first main surface 20a of the piezoelectric layer 20. The recessed section 70a is formed such that its outer edge is thinner than the central section of the cover section 70. The connecting element 71 is connected to the recessed section 70a of the cover section 70. This arrangement increases the contact area between the connecting element 71 and the cover section 70 compared to cases where the recessed section 70a is not provided, thereby improving the connection strength.

[0126] Fig. Figure 20 is an explanatory diagram illustrating a method for manufacturing the sound wave device according to the fifth embodiment. Fig. For better understanding of the drawing, the illustration of the upper electrode 31, the lower electrode 32, the overlapping electrode 33 and the opening 21 has been omitted.

[0127] As in Fig. As illustrated in Figure 20, a multilayer body is formed (step ST41) comprising the support substrate 11, the insulating layer 12, and the piezoelectric layer 20, and exhibiting the membrane structure. The device illustrated in step ST41, comprising the support substrate 11, the insulating layer 12, and the piezoelectric layer 20, can employ any of the embodiments and modifications described above.

[0128] Next, a portion of the piezoelectric layer 20 on the outer edge is removed (step ST42). This portion of the piezoelectric layer 20 on the outer edge is removed, for example, by RIE. This step exposes the insulating layer 12 in the region on the outer surface of the side 20c of the piezoelectric layer 20.

[0129] The connecting element 71 is formed on the insulating layer 12 on the outer edge side of the insulating layer 12 (step ST43). Since the connecting element 71 is formed from the same insulating material as the insulating layer 12, the adhesion between the connecting element 71 and the insulating layer 12 is excellent, and the sealing property is advantageous.

[0130] In one step of forming the lid section 70, the lid section 70, which has a flat plate shape, is prepared (step ST44). The lid section 70 is formed, for example, from the same material as the support substrate 11, such as silicon (Si) or quartz crystal.

[0131] The recessed section 70a is formed on the outer edge of a surface of the cover section 70 (step ST45). The recessed section 70a is provided in a region where the cover section 70 and the connecting element 71 are to be joined. The cover section 70 is formed, for example, by dry etching, such as RIE.

[0132] Next, the connecting element 71 and the recessed section 70a of the cover section 70 are connected together (step ST46). This step connects the multilayer body, which has the membrane structure (the support substrate 11, the insulating layer 12 and the piezoelectric layer 20), and the cover section 70 with the connecting element 71 positioned between them.

[0133] An insulating film, made of the same insulating material as the connecting element 71 (for example, SiO2), can be formed on the surface of the cover section 70 that faces the first main surface 20a of the piezoelectric layer 20 and the recessed section 70a. In this case, the connecting element 71 is coupled to the insulating film provided on the cover section 70, thereby improving the sealing property between the cover section 70 and the connecting element 71. (Sixth embodiment)

[0134] Fig. Figure 21 is a cross-sectional view of a sound wave device according to the sixth embodiment. As in Fig. As illustrated in Figure 21, the sound wave device 10L according to the seventh embodiment differs from the embodiments and modifications described above in that the insulating layer 12A of the support element 13A is a porous film having a large number of pores 18. It should be noted that the pores 18 in Fig. Figure 21 is greatly enlarged for better understanding of the drawing.

[0135] The insulating layer 12A is formed from one of several types of oxide materials, such as yttrium oxide (Y₂O₃) and aluminum oxide (Al₂O₃). The porous film can be formed, for example, by a thermal spraying process, a plating process, or a process in which a mixed material consisting of an oxide material (to be retained as a porous film) and an organic material is deposited as a film by sputtering and then heated at a high temperature to remove the organic material, leaving only the oxide material.

[0136] Since the insulating layer 12A in the present embodiment is a porous film, thermal stresses between the support substrate 11 and the membrane structure of the piezoelectric layer 20 are relieved, thereby reducing warping and deformation of the membrane structure of the piezoelectric layer 20. This stabilizes the piezoelectric properties of the sound wave device 10L and ensures advantageous device characteristics. Because the insulating layer 12A is made of an inorganic material, irreversible positional deviations between the piezoelectric layer 20 and the support substrate 11 due to thermal stresses can also be reduced.

[0137] Furthermore, the support substrate 11 is made of silicon (Si) and possesses semiconducting properties. Therefore, parasitic capacitance is formed between the support substrate 11 and the upper and lower electrodes 31 and 32, and between the support substrate 11 and the routing wiring. Since the insulating layer 12A in the present embodiment is a porous film, the effective dielectric constant is reduced, and the parasitic capacitance can be reduced without increasing the thickness of the insulating layer 12A.

[0138] In the present embodiment, a silicon nitride (SiN) layer can be provided between the insulating layer 12A, which is a porous film, and the piezoelectric layer 20. This reduces the penetration of moisture through the insulating layer 12A, which is a porous film.

[0139] In this embodiment, the insulating layer 12A can be formed from a material in which -O-Si-O-Si-...-Si-O-Si-O frameworks are formed and a resin is arranged between the frameworks instead of the porous film.

[0140] Since a resin is arranged between the -O-Si-O-Si-...-Si-O-Si-O-- frameworks, thermal stresses caused by the difference in linear expansion coefficients between the support substrate 11 and the piezoelectric layer 20 are relieved in this insulating layer 12A, thereby reducing warping and deformation of the membrane structure of the piezoelectric layer 20. This arrangement stabilizes the piezoelectric properties of the sound wave device 10L and ensures advantageous device characteristics. Furthermore, the -O-Si-O-Si-...-Si-O-Si-O frameworks hold the support substrate 11 and the piezoelectric layer 20 firmly in place, thus reducing irreversible positional deviations between the piezoelectric layer 20 and the support substrate 11 caused by thermal stresses.

[0141] The insulating layer 12A illustrated in the present embodiment can be combined with any embodiment and modification described above. (Eighth modification of the first embodiment)

[0142] Fig. Figure 22 is an explanatory diagram illustrating a method for manufacturing a sound wave device according to the eighth modification of the first embodiment. The method for manufacturing the sound wave device according to the eighth modification differs from the first embodiment described above (see Figure 22). Fig. 3) by forming the upper electrode 31 and the overlapping electrode 33 in steps ST7 to ST9 using a dry process. It should be noted that in the eighth modification, step ST51 is replaced by step ST6 in Fig. 3 corresponds. Furthermore, the eighth modification includes, although this is in Fig. 22 is not illustrated, the same or similar steps as steps ST1 to ST5 and ST10 in Fig. 3.

[0143] As in Fig. As illustrated in Figure 22, as in the aforementioned step ST6, after the step (step ST51) in which the opening 21 is formed in the piezoelectric layer 20, a film of a metal layer 83 is formed over the entire surface of the piezoelectric layer 20 (step ST52). The metal layer 83 is positioned to extend over the first main surface 20a of the piezoelectric layer 20 and the lower electrode 32 in the region overlapping the opening 21. Also in the eighth modification, simultaneously with the formation of the metal layer 83 as the upper electrode 31, the metal film 83, serving as the overlapping electrode 33, is formed as a film on the lower electrode 32 in the region overlapping the opening 21.

[0144] Next, a structure consisting of a resist 84 is formed on the metal layer 83 by photolithography (step ST53). In this step, the resist 84 is formed in the region where the upper electrode 31 is to be formed and in the region where the lower electrode 32 is to be formed, in a region that overlaps the opening 21.

[0145] Next, the sections of the metal layer 83 not covered by the resist 84 are removed by dry etching (step ST54). Then, the resist 84 is removed, and the metal film 83 in the sections overlapping the resist 81 forms the upper electrode 31 and the overlapping electrode 33 (step ST55). As described above, the present embodiment uses the dry process to form the upper electrode 31 on the first main surface 20a of the piezoelectric layer 20 and the overlapping electrode 33 on the lower electrode 32 in a region overlapping the opening 21.

[0146] It should be noted that the embodiments described above serve to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without altering its essence, and the present invention also includes their equivalents.

[0147] The present disclosure may contain the following features. (1) Sound wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal 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 element facing the second main surface of the piezoelectric layer, wherein the piezoelectric layer has an opening that extends through the piezoelectric layer in a thickness direction in a region that overlaps the lower electrode and does not overlap the upper electrode, and wherein the sound wave device further comprises an overlapping electrode which is provided on the lower electrode in a region that overlaps the opening and is formed from the same material as the upper electrode. (2) Sound wave device according to (1), wherein the area of ​​the overlapping electrode is smaller than the area of ​​the opening. (3) Sound wave device according to (1) or (2), wherein the upper electrode has a first upper electrode and a second upper electrode, which is spaced apart from the first upper electrode, the lower electrode is provided such that it extends over a region overlapping the first upper electrode, a region overlapping the second upper electrode, and a region between the first upper electrode and the second upper electrode, the lower electrode further comprises a routing electrode section that is coupled to a region between the first upper electrode and the second upper electrode, and the opening and the overlapping electrode are provided in a position that overlaps the routing electrode section of the lower electrode. (4) Sound wave device according to one of (1) to (3), wherein the piezoelectric layer contains single-crystal lithium niobate or single-crystal lithium tantalate, and the thickness of the piezoelectric layer is 1 µm or less. (5) Sound wave device according to one of (1) to (4), which further comprises: a conductive intermediate layer provided between the lower electrode and the overlapping electrode in a region that overlaps the opening. (6) Sound wave device according to (1) or (2), wherein the upper electrode has a first upper electrode and a second upper electrode, which is spaced apart from the first upper electrode, the lower electrode is provided such that it extends over a region overlapping the first upper electrode, a region overlapping the second upper electrode, and a region between the first upper electrode and the second upper electrode, and the opening and the overlapping electrode are provided in a region that overlaps the lower electrode and is located between the first upper electrode and the second upper electrode. (7) Sound wave device according to (1), wherein the area of ​​the overlapping electrode is larger than the area of ​​the opening, and the overlapping electrode is provided on the lower electrode in a region that overlaps the opening and extends along an inner wall of the opening and onto the first main surface of the piezoelectric layer. (8) Sound wave device according to (7), which further comprises: an intermediate insulating layer covering an outer edge of the opening, wherein the intermediate insulating layer is provided between the inner wall of the opening and the overlapping electrode and between the first main surface of the piezoelectric layer and the overlapping electrode. (9) Sound wave device according to one of (1) to (8), which further comprises: Front electrodes that overlap the overlapping electrode or part of the upper electrode. (10) Sound wave device according to one of (1) to (9), which further comprises: a rear electrode that is provided between the lower electrode and the support element in a region that overlaps the opening. (11) Sound wave device according to one of (1) to (10), which further comprises: a hollow section provided on a surface of the support element facing the second main surface of the piezoelectric layer in a region where the upper electrode and the lower electrode face each other. (12) Sound wave device according to one of (1) to (10), which further comprises: a sound reflection film comprising a high-sound impedance layer, which has a relatively high sound impedance, and a low-sound impedance layer, which has a relatively low sound impedance, wherein The sound reflection film is provided on a surface of the support element facing the second main surface of the piezoelectric layer in a region where the upper electrode and the lower electrode face each other. Furthermore, the present disclosure may also include the following features. (13) Sound wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal 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; a supporting substrate facing the second main surface of the piezoelectric layer; an insulating layer provided between the support substrate and the second main surface of the piezoelectric layer; a lid section facing the first main surface of the piezoelectric layer; and a connecting element provided between the insulating layer and the cover section, wherein the insulating layer is in direct contact with the connecting element on an outer edge side of the insulating layer, and a recessed section is formed on an outer edge side of the cover section, and the recessed section of the cover section is in direct contact with the connecting element. (14) Sound wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal 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; a supporting substrate facing the second main surface of the piezoelectric layer; and an insulating layer provided between the support substrate and the second main surface of the piezoelectric layer, wherein The insulating layer is a porous film. (15) Sound wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal 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; a supporting substrate facing the second main surface of the piezoelectric layer; and an insulating layer provided between the support substrate and the second main surface of the piezoelectric layer, wherein the insulating layer has -O-Si-O-Si-...-Si-O-Si-O-frameworks and a resin is arranged between the frameworks. REFERENCE MARK LIST 10, 10A, 10B, 10C, 100, 10E, 10F, 10G, 10H, 10I, 10J, 10K, 10L Sound wave device 11 Support substrate 12, 12A Insulating layer 13, 13A Support element 14 Cavity section 15 first cavity section 16 second cavity section 17 Sound multilayer film 20 piezoelectric layer 20a first main area 20b second main area 21, 23 Opening 31 upper electrode 32, 43 lower electrode 33, 44 overlapping electrode 34 Intermediate insulating layer 35, 36, 45, 46, 47 front electrode 37, 48 rear electrode 39 conductive intermediate layer 41 first upper electrode 42 second upper electrode 43d Routing electrode section 50, 51, 52 Victim class 53 contact bumps 54 Coupling pad 56 Capacity element 57 Shielding electrode 70 Cover section

Claims

[1] Sound wave device comprising: a piezoelectric layer having a first principal surface and a second principal surface opposite the first principal 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 element facing the second main surface of the piezoelectric layer, wherein the piezoelectric layer has an opening that extends through the piezoelectric layer in a thickness direction in a region that overlaps the lower electrode and does not overlap the upper electrode, and wherein the sound wave device further comprises an overlapping electrode which is provided on the lower electrode in a region which overlaps the opening and is formed from the same material as the upper electrode. [2] Sound wave device according to claim 1, wherein the area of ​​the overlapping electrode is smaller than the area of ​​the opening. [3] Sound wave device according to claim 1 or 2, wherein the upper electrode has a first upper electrode and a second upper electrode, which is spaced apart from the first upper electrode, the lower electrode is provided such that it extends over a region overlapping the first upper electrode, a region overlapping the second upper electrode, and a region between the first upper electrode and the second upper electrode, the lower electrode further comprises a routing electrode section that is coupled to a region between the first upper electrode and the second upper electrode, and the opening and the overlapping electrode are provided in a position that overlaps the routing electrode section of the lower electrode. [4] Sound wave device according to one of claims 1 to 3, wherein the piezoelectric layer contains single-crystal lithium niobate or single-crystal lithium tantalate, and the thickness of the piezoelectric layer is 1 µm or less. [5] Sound wave device according to any one of claims 1 to 4, further comprising: a conductive intermediate layer provided between the lower electrode and the overlapping electrode in a region that overlaps the opening. [6] Sound wave device according to claim 1 or 2, wherein the upper electrode has a first upper electrode and a second upper electrode, which is spaced apart from the first upper electrode, the lower electrode is provided such that it extends over a region overlapping the first upper electrode, a region overlapping the second upper electrode, and a region between the first upper electrode and the second upper electrode, and the opening and the overlapping electrode are provided in a region that overlaps the lower electrode and is located between the first upper electrode and the second upper electrode. [7] Sound wave device according to claim 1, wherein the area of ​​the overlapping electrode is larger than the area of ​​the opening, and the overlapping electrode is provided on the lower electrode in a region that overlaps the opening and extends along an inner wall of the opening and onto the first main surface of the piezoelectric layer. [8] Sound wave device according to claim 7, further comprising: an intermediate insulating layer covering an outer edge of the opening, wherein the intermediate insulating layer is provided between the inner wall of the opening and the overlapping electrode and between the first main surface of the piezoelectric layer and the overlapping electrode. [9] Sound wave device according to any one of claims 1 to 8, further comprising: Front electrodes that overlap the overlapping electrode or part of the upper electrode. [10] Sound wave device according to any one of claims 1 to 9, further comprising: a rear electrode that is provided between the lower electrode and the support element in a region that overlaps the opening. [11] Sound wave device according to any one of claims 1 to 10, further comprising: a hollow section provided on a surface of the support element facing the second main surface of the piezoelectric layer in a region where the upper electrode and the lower electrode face each other. [12] Sound wave device according to any one of claims 1 to 10, further comprising: a sound reflection film comprising a high-sound impedance layer, which has a relatively high sound impedance, and a low-sound impedance layer, which has a relatively low sound impedance, wherein The sound reflection film is provided on a surface of the support element facing the second main surface of the piezoelectric layer in a region where the upper electrode and the lower electrode face each other.

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