Elastic wave device and method for manufacturing elastic wave device

Abstract

Deterioration of filter characteristics caused by residues of an inorganic film is suppressed. An elastic wave device is provided with a support substrate, an inorganic film provided on the support substrate, a piezoelectric layer provided on the inorganic film, and an electrode provided on the piezoelectric layer. A hollow portion is provided in a portion of the support substrate. The hollow portion overlaps at least a portion of the electrode in a thickness direction of the support substrate. An inner wall of the inorganic film is located farther from the hollow portion than a position in the inner wall of the support substrate closest to the piezoelectric layer side.

Description

Technical Field

[0001] This disclosure relates to an elastic wave device and a method for manufacturing an elastic wave device. Background Technology

[0002] Patent document 1 describes an elastic wave device.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-257019 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In Patent Document 1, when an inorganic insulating layer (hereinafter referred to as an inorganic film) is provided between the support substrate and the piezoelectric substrate, if there is residue of the inorganic film in the area overlapping with the void portion when viewed from above along the thickness direction, the filter characteristics may deteriorate. Therefore, it is desirable to suppress the deterioration of filter characteristics caused by residue of the inorganic film.

[0008] This disclosure is intended to solve the above-mentioned problems, and its purpose is to provide an elastic wave device and a method for manufacturing the elastic wave device to suppress the degradation of filter characteristics caused by inorganic membrane residues.

[0009] means for solving problems

[0010] The elastic wave device disclosed herein includes: a support substrate; an inorganic film disposed on the support substrate; a piezoelectric layer disposed on the inorganic film; and an electrode disposed on the piezoelectric layer. A cavity is provided in a portion of the support substrate, the cavity overlapping at least a portion of the electrode in the thickness direction of the support substrate. The inner wall of the inorganic film is located away from the cavity compared to the position closest to the piezoelectric layer in the inner wall of the support substrate forming the cavity.

[0011] The method for manufacturing the elastic wave device disclosed herein includes: a roughening step of a support substrate, wherein a first surface of a support substrate having a first surface and a second surface is roughened; an inorganic film forming step, wherein an inorganic film is formed on the first surface; a piezoelectric layer forming step, wherein a piezoelectric layer is formed on the inorganic film; a piezoelectric layer thinning step, wherein the piezoelectric layer is thinned; an electrode forming step, wherein an electrode is formed on the piezoelectric layer; a first etching step, wherein a void portion is formed on a portion of the support substrate; and a second etching step, wherein the inorganic film exposed in the void portion is etched.

[0012] Invention Effects

[0013] According to this disclosure, it is possible to suppress the degradation of filter characteristics caused by residues in inorganic films. Attached Figure Description

[0014] Figure 1A This is a perspective view showing the elastic wave device according to the first embodiment.

[0015] Figure 1B This is a top view showing the electrode structure of the first embodiment.

[0016] Figure 2 It is along Figure 1A A sectional view of the portion along line II-II.

[0017] Figure 3A This is a schematic cross-sectional view used to illustrate the Lamb wave propagating in the piezoelectric layer of the comparative example.

[0018] Figure 3B This is a schematic cross-sectional view used to illustrate the bulk wave propagating in the thickness shear primary mode of the piezoelectric layer in the first embodiment.

[0019] Figure 4 It is a schematic cross-sectional view used to illustrate the amplitude direction of the bulk wave in the thickness shear primary mode propagating in the piezoelectric layer of the first embodiment.

[0020] Figure 5 This is an explanatory diagram showing an example of the resonant characteristics of the elastic wave device according to the first embodiment.

[0021] Figure 6 This is an explanatory diagram showing the relationship between d / 2p and the fractional bandwidth of the resonator when the center-to-center distance or the average center-to-center distance of adjacent electrodes is set as p and the average thickness of the piezoelectric layer is set as d in the elastic wave device of the first embodiment.

[0022] Figure 7 This is a top view showing an example of an elastic wave device in the first embodiment having a pair of electrodes.

[0023] Figure 8 In the first embodiment, along Figure 1B A cross-sectional view of the IX-IX line section.

[0024] Figure 9 This is a top view showing an example of the elastic wave device according to the first embodiment.

[0025] Figure 10 This is a flowchart of the manufacturing method of the elastic wave device according to the first embodiment.

[0026] Figure 11 This is a top view showing an example of insufficient etching in the elastic wave device of the first embodiment.

[0027] Figure 12 This is an explanatory diagram showing the relationship between d / 2p, metallization ratio MR, and fractional bandwidth in the elastic wave device of the second embodiment.

[0028] Figure 13 This is an explanatory diagram showing the mapping of the fractional bandwidth relative to the Euler angles (0°, θ, ψ) of LiNbQ3 in the elastic wave device of the third embodiment, when d / p is infinitely close to 0. Detailed Implementation

[0029] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the present disclosure is not limited by these embodiments.

[0030] (First Implementation)

[0031] Figure 1A This is a perspective view showing the elastic wave device according to the first embodiment. Figure 1B This is a top view showing the electrode structure of the first embodiment.

[0032] The elastic wave device 1 of the first embodiment has a piezoelectric layer 2 comprising LiNbO3. The piezoelectric layer 2 may also comprise LiTaO3. In the first embodiment, the cutting angle of LiNbO3 and LiTaO3 is Z-cut. The cutting angle of LiNbO3 and LiTaO3 may also be rotational Y-cut or X-cut. Preferably, the propagation orientation is ±30° of Y propagation and X propagation.

[0033] The thickness of the piezoelectric layer 2 is not particularly limited, but in order to effectively excite the thickness shearing primary mode, it is preferably 50 nm or more and 1000 nm or less.

[0034] The piezoelectric layer 2 has a first surface 2a and a second surface 2b opposite to each other in the Z direction. An electrode 3 and an electrode 4 are disposed on the first surface 2a.

[0035] Here, electrode 3 is an example of a "first electrode," and electrode 4 is an example of a "second electrode." Figure 1A and Figure 1B In this configuration, multiple electrodes 3 are connected to the first busbar electrode 5. Multiple electrodes 4 are connected to the second busbar electrode 6. The multiple electrodes 3 and multiple electrodes 4 are inserted alternately.

[0036] Electrodes 3 and 4 are rectangular in shape and have a length direction. Electrode 3 is positioned opposite to its adjacent electrode 4 in a direction orthogonal to this length direction. The length directions of electrodes 3 and 4, as well as the directions orthogonal to their length directions, intersect the thickness direction of the piezoelectric layer 2. Therefore, it can also be said that electrode 3 and its adjacent electrode 4 are opposite each other in a direction intersecting the thickness direction of the piezoelectric layer 2. In the following description, the thickness direction of the piezoelectric layer 2 is sometimes defined as the Z direction (or a first direction), the direction orthogonal to the length directions of electrodes 3 and 4 as the X direction (or a second direction), and the length directions of electrodes 3 and 4 as the Y direction (or a third direction).

[0037] Alternatively, the length directions of electrodes 3 and 4 can be replaced with... Figure 1A and Figure 1B The direction shown is orthogonal to the length directions of electrodes 3 and 4. That is, in Figure 1A and Figure 1B Alternatively, electrodes 3 and 4 can extend in the same direction as the first busbar electrode 5 and the second busbar electrode 6. In this case, the first busbar electrode 5 and the second busbar electrode 6 are in... Figure 1A and Figure 1B The middle extends along the direction of the electrodes 3 and 4. Moreover, in a direction orthogonal to the length direction of the electrodes 3 and 4, there are multiple pairs of structures in which an electrode 3 connected to one potential is adjacent to an electrode 4 connected to another potential.

[0038] Here, "adjacent to electrode 3" does not mean that electrode 3 and electrode 4 are configured in direct contact, but rather that electrode 3 and electrode 4 are configured with a gap between them. Furthermore, when electrode 3 and electrode 4 are adjacent, no other electrodes (including those connected to signal electrodes and ground electrodes) are placed between electrode 3 and electrode 4. This pairing does not need to be an integer; it can be 1.5 pairs, 2.5 pairs, etc.

[0039] The center-to-center distance, i.e., the spacing, between electrodes 3 and 4 is preferably in the range of 1 μm or more and 10 μm or less. Furthermore, the center-to-center distance between electrodes 3 and 4 is the distance obtained by connecting the center of the width dimension of electrode 3 in a direction orthogonal to the length direction of electrode 3 and the center of the width dimension of electrode 4 in a direction orthogonal to the length direction of electrode 4.

[0040] Furthermore, when at least one of the electrodes 3 and 4 has multiple electrodes (when the electrodes 3 and 4 are set as a pair of electrode groups, there are 1.5 or more pairs of electrode groups), the center-to-center distance of the electrodes 3 and 4 refers to the average value of the center-to-center distances of adjacent electrodes 3 and 4 in 1.5 or more pairs of electrodes 3 and 4.

[0041] Furthermore, the widths of electrodes 3 and 4, i.e., the dimensions of electrodes 3 and 4 in their opposing directions, are preferably in the range of 150 nm or more and 1000 nm or less. It should be noted that the center-to-center distance between electrodes 3 and 4 is the distance obtained by connecting the center of the dimension (width dimension) of electrode 3 in a direction orthogonal to the length direction of electrode 3 and the center of the dimension (width dimension) of electrode 4 in a direction orthogonal to the length direction of electrode 4.

[0042] Furthermore, in the first embodiment, a Z-cut piezoelectric layer is used, therefore, the direction orthogonal to the length direction of electrodes 3 and 4 becomes the direction orthogonal to the polarization direction of piezoelectric layer 2. This is not limited to cases where a piezoelectric material with a different cut angle is used as piezoelectric layer 2. Here, "orthogonal" is not limited to strictly orthogonal, but can also be approximately orthogonal (the angle between the direction orthogonal to the length direction of electrodes 3 and 4 and the polarization direction is, for example, 90° ± 10°).

[0043] On the second surface 2b of the piezoelectric layer 2, a support substrate 8 is stacked with an intermediate layer 7 in between. The intermediate layer 7 and the support substrate 8 have a frame-like shape, such as... Figure 2 As shown, it has openings 7a and 8a. As a result, a cavity (air gap) 9 is formed.

[0044] The void 9 is provided so as not to interfere with the vibration of the excitation region C of the piezoelectric layer 2. Therefore, the support substrate 8 is stacked on the second surface 2b with an intermediate layer 7 in a position that does not overlap with the portion where at least one pair of electrodes 3 and 4 are provided.

[0045] Intermediate layer 7 is an insulating layer formed of silicon oxide. Intermediate layer 7 is formed of an inorganic film. However, in addition to silicon oxide, intermediate layer 7 can also be formed of suitable inorganic insulating materials such as silicon oxynitride or bauxite.

[0046] The support substrate 8 is formed of Si. The orientation of the surface on the piezoelectric layer 2 side of Si can be (100), (110), or (111). Preferably, it is desirable to use Si with a high resistivity of 4kΩ or higher. However, the support substrate 8 can also be constructed using suitable insulating materials or semiconductor materials. For example, piezoelectric materials such as alumina, lithium tantalate, lithium niobate, and quartz, bauxite, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite, as well as various ceramics such as diamond, glass, and semiconductors such as gallium nitride can be used as materials for the support substrate 8.

[0047] The aforementioned electrodes 3, 4, first busbar electrode 5, and second busbar electrode 6 comprise suitable metals or alloys such as Al or AlCu alloys. In the first embodiment, electrodes 3, 4, first busbar electrode 5, and second busbar electrode 6 have a structure in which an Al film is laminated on a Ti film. It should be noted that a bonding layer other than a Ti film may also be used.

[0048] During driving, an alternating voltage is applied between multiple electrodes 3 and multiple electrodes 4. More specifically, an alternating voltage is applied between the first busbar electrode 5 and the second busbar electrode 6. As a result, the resonant characteristics of a bulk wave utilizing the thickness shear primary mode excited in the piezoelectric layer 2 can be obtained.

[0049] Furthermore, in the elastic wave device 1, when the thickness of the piezoelectric layer 2 is set to d and the center-to-center distance between any two adjacent pairs of electrodes 3 and 4 is set to p, d / p is 0.5 or less. Therefore, the bulk wave of the aforementioned thickness shear primary mode can be effectively excited, resulting in good resonance characteristics. More preferably, d / p is 0.24 or less, in which case even better resonance characteristics can be obtained.

[0050] It should be noted that, as in the first embodiment, when at least one of the electrodes 3 and 4 has multiple electrodes, that is, when the electrodes 3 and 4 are set as a pair of electrode groups and there are 1.5 or more pairs of electrodes 3 and 4, the center-to-center distance p of adjacent electrodes 3 and 4 becomes the average distance between the centers of each adjacent electrode 3 and 4.

[0051] In the elastic wave device 1 of the first embodiment, due to the above-described structure, even if the number of pairs of electrodes 3 and 4 is reduced to achieve miniaturization, it is difficult to cause a decrease in the Q value. This is because it is a resonator that does not require reflectors on both sides, resulting in low propagation loss. Furthermore, the absence of the aforementioned reflectors is due to the utilization of a thickness shear primary mode body wave.

[0052] Figure 3A This is a schematic cross-sectional view used to illustrate the Lamb wave propagating in the piezoelectric layer of the comparative example. Figure 3B This is a schematic cross-sectional view used to illustrate the bulk wave propagating in the thickness shear primary mode of the piezoelectric layer in the first embodiment. Figure 4 It is a schematic cross-sectional view used to illustrate the amplitude direction of the bulk wave in the thickness shear primary mode propagating in the piezoelectric layer of the first embodiment.

[0053] exist Figure 3A In this case, it is an elastic wave device as described in Patent Document 1, in which Lamb waves propagate in a piezoelectric layer. For example... Figure 3AAs shown, the wave propagates in the piezoelectric layer 201 as indicated by the arrow. Here, the piezoelectric layer 201 has a first surface 201a and a second surface 201b, and the thickness direction connecting the first surface 201a and the second surface 201b is the Z-direction. The X-direction is the direction in which the electrode fingers of the IDT electrodes are arranged. Figure 3A As shown, for a Lamb wave, the wave propagates along the X direction as illustrated. Since it is a plate wave, although the piezoelectric layer 201 vibrates as a whole, the wave propagates along the X direction, thus achieving resonant characteristics by placing reflectors on both sides. Therefore, wave propagation loss occurs, and the Q value decreases when miniaturization is achieved, i.e., when the number of electrode finger pairs is reduced.

[0054] In contrast, such as Figure 3B As shown, in the elastic wave device of the first embodiment, the vibration displacement is in the thickness shear direction. Therefore, the wave propagates approximately along the Z direction, which is the direction connecting the first surface 2a and the second surface 2b of the piezoelectric layer 2, and resonates. That is, the X-direction component of the wave is significantly smaller than the Z-direction component. Moreover, since the resonant characteristic is obtained through the propagation of the wave in this Z-direction, a reflector is not required. Therefore, no propagation loss occurs when propagating towards a reflector. Therefore, even if the number of electrode pairs, including electrodes 3 and 4, is reduced to achieve miniaturization, it is difficult to cause a decrease in the Q value.

[0055] It should be noted that, as Figure 4 As shown, the amplitude direction of the bulk wave in the thickness shear primary mode is in the excitation region C of the piezoelectric layer 2 (reference). Figure 1B The first region 451 contained in the excitation region C is opposite to the second region 452 contained in the excitation region C. Figure 4 The diagram schematically illustrates a body wave when a voltage is applied between electrodes 3 and 4, with electrode 4 having a higher potential than electrode 3. The first region 451 is the region between the virtual plane VP1 and the first surface 2a in the excitation region C. This virtual plane VP1 is orthogonal to the thickness direction of the piezoelectric layer 2 and divides the piezoelectric layer 2 into two parts. The second region 452 is the region between the virtual plane VP1 and the second surface 2b in the excitation region C.

[0056] In the elastic wave device 1, at least one pair of electrodes, including electrode 3 and electrode 4, is provided. However, since the wave is not propagated along the X direction, the number of electrode pairs including electrode 3 and electrode 4 does not necessarily have to be multiple. That is, at least one pair of electrodes is sufficient.

[0057] For example, electrode 3 is an electrode connected to a signal potential, and electrode 4 is an electrode connected to a ground potential. However, it is also possible that electrode 3 is connected to a ground potential, and electrode 4 is connected to a signal potential. In the first embodiment, at least one pair of electrodes is either connected to a signal potential or connected to a ground potential as described above, and no floating electrode is provided.

[0058] Figure 5 This is an explanatory diagram illustrating an example of the resonant characteristics of the elastic wave device according to the first embodiment. It should be noted that... Figure 5 The design parameters of the elastic wave device 1 with the resonant characteristics shown are as follows.

[0059] Piezoelectric layer 2: LiNbO3 with Euler angles (0°, 0°, 90°)

[0060] Thickness of piezoelectric layer 2: 400nm.

[0061] Excitation region C (reference) Figure 1B Length: 40μm

[0062] The number of electrode pairs, including electrodes 3 and 4, is 21.

[0063] Center-to-center distance (split) between electrodes 3 and 4: 3 μm

[0064] Width of electrodes 3 and 4: 500 nm

[0065] d / p: 0.133

[0066] Intermediate layer 7: Silicon oxide film with a thickness of 1 μm.

[0067] Support substrate 8: Si.

[0068] It should be noted that the excitation region C (refer to...) Figure 1B The region C is the area where electrodes 3 and 4 overlap when viewed along the X direction, which is orthogonal to the length directions of electrodes 3 and 4. The length of the excitation region C is the dimension of the excitation region C along the length directions of electrodes 3 and 4.

[0069] In the first embodiment, the center-to-center distance between the electrode pairs, including electrodes 3 and 4, is equal in all pairs. That is, electrodes 3 and 4 are arranged at equal intervals.

[0070] Depend on Figure 5 It can be seen that, despite not having a reflector, a good resonant characteristic with a fractional bandwidth of 12.5% ​​was obtained.

[0071] However, when the thickness of the piezoelectric layer 2 is set to d and the center-to-center distance between the electrodes of electrode 3 and electrode 4 is set to p, in the first embodiment, d / p is 0.5 or less, more preferably 0.24 or less. (Refer to...) Figure 6 This needs to be explained.

[0072] With Get Figure 5 Similarly, multiple elastic wave devices are obtained by varying d / 2p, as shown in the example of the elastic wave device with resonant characteristics. Figure 6 This is an explanatory diagram showing the relationship between d / 2p and the fractional bandwidth of the resonator when the center-to-center distance or average center-to-center distance of adjacent electrodes is set as p and the average thickness of the piezoelectric layer is set as d in the elastic wave device of the first embodiment.

[0073] like Figure 6 As shown, when d / 2p exceeds 0.25, i.e., when d / p > 0.5, even with adjustments to d / p, the fractional bandwidth is less than 5%. Conversely, when d / 2p ≤ 0.25, i.e., d / p ≤ 0.5, varying d / p within this range allows for a fractional bandwidth exceeding 5%, enabling the construction of a resonator with a high coupling coefficient. Furthermore, when d / 2p is below 0.12, i.e., below 0.24, the fractional bandwidth can be increased to over 7%. Moreover, adjusting d / p within this range yields a resonator with an even wider fractional bandwidth, achieving a resonator with a higher coupling coefficient. Therefore, it can be concluded that by setting d / p to below 0.5, a resonator with a high coupling coefficient utilizing the aforementioned thickness shear primary mode of the bulk wave can be constructed.

[0074] It should be noted that at least one pair of electrodes can also be used, and the aforementioned p in the case of one pair of electrodes refers to the center-to-center distance between adjacent electrodes 3 and 4. Furthermore, in the case of 1.5 or more pairs of electrodes, the average distance between the centers of adjacent electrodes 3 and 4 can be set as p. Additionally, regarding the thickness d of the piezoelectric layer, if the piezoelectric layer 2 has a thickness deviation, the value averaging its thickness can be used.

[0075] Figure 7 This is a top view showing an example of an elastic wave device according to the first embodiment, in which a pair of electrodes are provided. In the elastic wave device 31, a pair of electrodes having electrodes 3 and 4 are provided on the first surface 2a of the piezoelectric layer 2. It should be noted that... Figure 7 K in the figure represents the cross width. As described above, in the elastic wave device of this disclosure, the number of electrode pairs can also be one. In this case, if the above d / p is 0.5 or less, it is also possible to effectively excite a bulk wave in the thickness shear primary mode.

[0076] As explained above, the elastic wave devices 1 and 31 utilize a thickness shear primary mode volume wave. Furthermore, in the elastic wave devices 1 and 31, a void 9 is provided to avoid interfering with the vibration of the excitation region C of the piezoelectric layer 2. Therefore, even with miniaturization of the elastic wave device, the Q value can be improved.

[0077] In the elastic wave devices 1 and 31, the support substrate 8 is formed of silicon. The support substrate 8 has a first surface and a second surface facing each other in the Z direction. The support substrate 8 is preferably stacked on the second surface 2b of the piezoelectric layer 2 at a position that does not overlap with the portion where at least a pair of electrodes 3 and 4 are provided, separated by an intermediate layer 7. Hereinafter, the first surface of the support substrate 8 will sometimes be described as the surface on the side of the second surface 2b of the piezoelectric layer 2, that is, the surface on the side where the intermediate layer 7 is stacked.

[0078] Figure 8 In the first embodiment, along Figure 1B A sectional view of the IX-IX line section. For ease of understanding, it is shown enlarged compared to the actual view. Figure 8 The inner wall of the opening 7a and the surface of the first surface of the supporting substrate 8 are shown. Figure 8 As shown, the support substrate 8 has a rough surface at least in the X direction regarding its first surface. Its surface roughness is more preferably coarser than that of the piezoelectric layer 2, and more preferably 0.5 nm or more and 10 nm or less (equivalent to 5 nm or more and 100 nm or less in terms of Ra) in terms of Ra. The Ra value of the surface of the first surface of the support substrate 8 is a value measured based on a STEM image obtained during observation using a STEM (Scanning Transmission Electron Microscope), at a magnification of, for example, 80,000x.

[0079] The opening 8a penetrates the support substrate 8. That is, as shown... Figure 8 As shown, the void 9 penetrates the support substrate 8. Compared to the position of the inner wall of the opening 8a, which is closest to the piezoelectric layer 2, the inner wall of the opening 7a is located away from the void 9. That is, at the position closest to the piezoelectric layer 2, for a plane 8aX parallel to the YZ plane that includes the inner wall of the opening 8a on the first surface of the support substrate 8, the inner wall of the opening 7a is located on the outside with respect to the void 9. According to this structure, a gap 10 is provided in communication with the void 9. The gap 10 is a space surrounded by the inner wall of the opening 7a, the second surface 2b of the piezoelectric layer 2, and the first surface of the support substrate 8. By forming the gap 10, residue of the inorganic film of the intermediate layer 7 is suppressed.

[0080] Figure 9This is a top view illustrating an example of the elastic wave device according to the first embodiment. In the first embodiment, the piezoelectric layer 2 comprises lithium niobate or lithium tantalate, and the intermediate layer 7 comprises silicon oxide, thus allowing light to pass through. Therefore, as... Figure 9 Thus, when viewed from above along the Z direction, a contrast difference is generated in the area where the intermediate layer 7 is separated from the support substrate 8 (the area of ​​the gap 10) and in the area where the intermediate layer 7 is bonded to the support substrate 8.

[0081] like Figure 9 As shown, the gap 10 has a recess 10a. The recess 10a is a gap created by the rough surface of the support substrate 8. When viewed from above along the Z direction, the recess 10a extends outward from the inner wall of the opening 8a, and its width tapers away from the inner wall of the opening 8a. To further reduce residue in the intermediate layer 7, it is preferable to have two or more recesses 10a along one side of the inner wall of the opening 8a. Here, the maximum length of the recess 10a is more than 1 μm and less than 50 μm. It should be noted that the length of the recess 10a refers to the length from the top end 10b of the recess 10a to the plane 8aX when viewed from above along the Z direction. Here, the top end 10b of the recess 10a refers to the apex of the acute angle formed by the tapering width of the recess 10a when viewed from above along the Z direction, or the termination point of the recess 10a.

[0082] As described above, the elastic wave device includes a support substrate 8, an intermediate layer 7 disposed on the support substrate 8, a piezoelectric layer 2 disposed on the intermediate layer 7, and electrodes 3 and 4 disposed on the piezoelectric layer 2. A cavity 9 is provided in a portion of the support substrate 8. The cavity 9 overlaps with at least a portion of the electrodes 3 and 4 in the Z direction. Compared with the position closest to the piezoelectric layer 2 in the inner wall of the support substrate 8 where the cavity 9 is formed, it is located away from the inner wall of the intermediate layer 7.

[0083] As in the first embodiment, the gap 10 of the intermediate layer 7, which is surrounded by the inner wall of the intermediate layer 7, the piezoelectric layer 2, and the support substrate 8, communicates with the cavity 9 of the support substrate 8.

[0084] As in the first embodiment, and when viewed from above along the Z direction, the gap 10 of the intermediate layer 7 has at least two or more recesses 10a.

[0085] As a result, the residue in the intermediate layer 7 in the area overlapping with the void portion 9 of the support substrate 8 when viewed from above along the Z direction is suppressed, thus suppressing the deterioration of filter characteristics caused by the residue in the intermediate layer 7.

[0086] As in the first embodiment, the maximum length of the recess 10a is 1 μm or more and 50 μm or less. This makes it easy to confirm that residue in the intermediate layer 7 in the area overlapping with the void 9 of the support substrate 8 when viewed from above in the Z direction is suppressed, thus suppressing the degradation of filter characteristics caused by residue in the intermediate layer 7.

[0087] In the elastic wave devices 1 and 31, the surface roughness of the surface of the support substrate 8 of the intermediate layer 7 of the elastic wave device is coarser than the surface roughness of the piezoelectric layer 2. As a result, stray emissions are suppressed, and thus, the degradation of filter characteristics can be suppressed.

[0088] As a preferred embodiment, the surface roughness of the surface of the support substrate 8 of the stacked intermediate layer 7 is 0.5 nm or more and 10 nm or less in terms of Ra. This suppresses stray emissions and thus can suppress the degradation of filter characteristics.

[0089] In the elastic wave devices 1 and 31, the intermediate layer 7 is formed of silicon oxide. As a result, the intermediate layer 7 is transparent, and visual inspection related to the residue of the intermediate layer 7 can be performed when viewed from above along the Z direction. Therefore, the degradation of filter characteristics caused by the residue of the intermediate layer 7 can be suppressed.

[0090] In the elastic wave devices 1 and 31, the void 9 of the support substrate 8 penetrates the support substrate 8. As a result, the residue of the intermediate layer 7 in the area overlapping with the void 9 of the support substrate 8 when viewed from above in the Z direction is suppressed, and thus the degradation of filter characteristics caused by the residue of the intermediate layer 7 can be suppressed.

[0091] Furthermore, in the elastic wave devices 1 and 31, the electrodes include a plurality of first electrodes 3, a first busbar electrode 5 connected to the plurality of first electrodes 3, a plurality of second electrodes 4, and a second busbar electrode 6 connected to the plurality of second electrodes 4. This allows for the provision of an elastic wave device with excellent resonance characteristics.

[0092] As a preferred embodiment, when the center-to-center distance between adjacent first electrodes 3 and second electrodes 4 in the plurality of first electrodes 3 and the plurality of second electrodes 4 is set to p, the thickness d of the piezoelectric layer 2 is 2p or less. This allows for miniaturization of the elastic wave device and improves the Q value.

[0093] Furthermore, in the elastic wave devices 1 and 31, the piezoelectric layer 2 includes lithium niobate or lithium tantalate. Thus, the piezoelectric layer 2 becomes transparent, allowing for visual inspection of any residues in the intermediate layer 7 when viewed from above along the Z-direction. Therefore, it is possible to suppress the degradation of filter characteristics caused by residues in the intermediate layer 7.

[0094] As a preferred embodiment, the device is configured to utilize plate waves. This provides an elastic wave device with excellent resonance characteristics.

[0095] As a preferred embodiment, the device is configured to utilize a thickness shear mode for volume waves. This provides an elastic wave device with a high coupling coefficient and excellent resonance characteristics.

[0096] As a preferred embodiment, the electrodes include at least one pair of electrodes facing each other, where d / p is 0.5 or less when the thickness of the piezoelectric layer 2 is set as d and the center-to-center distance between the first electrode 3 and the second electrode 4 is set as p. This allows for miniaturization of the elastic wave device and improves the Q value.

[0097] As a more preferred option, d / p is 0.24 or less. This allows for miniaturization of the elastic wave device and improves the Q value.

[0098] (Manufacturing method of elastic wave device)

[0099] Next, the manufacturing method of the elastic wave device 1 according to the first embodiment will be described. Figure 10 This is a flowchart of the manufacturing method of the elastic wave device according to the first embodiment.

[0100] For example, the first surface of the support substrate 8 is roughened by mechanical processing such as sandblasting (step S10). At this time, the first surface of the support substrate 8 is roughened at least in the X direction.

[0101] Next, silicon oxide of the intermediate layer 7 is formed on the first surface of the support substrate 8 by sputtering or the like (step S20). At this time, the side of the intermediate layer 7 on which the piezoelectric layer 2 is formed is planarized by grinding.

[0102] Next, a piezoelectric layer 2 is formed on the intermediate layer 7 (step S30). In the first embodiment, silicon oxide is deposited on the second surface 2b of the piezoelectric layer 2 by ALD (Atomic Layer Deposition), sputtering, etc., and then stacked by bonding with the intermediate layer 7. However, the stacking method is not limited to this. For example, the piezoelectric layer 2 can also be directly bonded to the intermediate layer 7.

[0103] Next, the first surface 2a of the piezoelectric layer 2 is thinned (step S40). At this time, the first surface 2a of the piezoelectric layer 2 is ground to the desired thickness by any method such as mechanical polishing or CMP.

[0104] Next, electrodes 3, 4, a first busbar electrode 5, and a second busbar electrode 6 are formed on the first surface 2a of the piezoelectric layer 2 (step S50). In the first embodiment, a metal film is formed by sputtering, vapor deposition, or the like, but the formation method can be arbitrary. Alternatively, a protective film such as silicon oxide can be formed on the electrodes by any method as needed.

[0105] Next, a portion of the support substrate 8 is etched (first etching) to form a void 9 (step S60). The first etching is, for example, dry etching or reactive ion etching. At this time, the void 9 is formed to penetrate the support substrate 8. In addition, the intermediate layer 7 acts as a barrier layer against etching, thus protecting the piezoelectric layer 2 from damage by etching.

[0106] Next, the intermediate layer 7 exposed in the void 9 is etched (second etching) (step S70). The second etching is, for example, wet etching. At this time, the void 9 penetrates the support substrate 8, so the etching solution in the intermediate layer 7 can easily penetrate, and the etching state can be stabilized. The void 9 is formed such that it is separated from the inner wall of the opening 7a relative to the position of the inner wall of the opening 8a. That is, a gap 10 is also formed along the inner wall of the opening 8a.

[0107] Next, an appearance inspection is performed to determine whether the gap 10 is formed in a sawtooth shape (step S80). In the first embodiment, the appearance inspection is performed based on the contrast difference generated by the range of the gap 10 and the range of the intermediate layer 7 bonded to the support substrate 8 when viewed from above.

[0108] like Figure 9 As shown, during visual inspection, the second etching ends when the gap 10 in the intermediate layer 7 is formed in a serrated shape along the inner wall of the opening 8a (step S80: Yes). Here, the serrated shape of the gap 10 means that when viewed from above, there are two or more recesses 10a formed in the gap 10 along the inner wall of the opening 7a.

[0109] Figure 11 This is a top view illustrating an example of insufficient etching in the elastic wave device of the first embodiment. (Example) Figure 11 As shown, during visual inspection, if the gap 10 of the intermediate layer 7 is not formed in a serrated shape along the inner wall of the opening 7a (step S80: No), that is, if the recess 10a is not formed along the inner wall of the opening 8a, a second etching is performed. Thus, the intermediate layer 7 is sufficiently removed by etching, thereby suppressing the degradation of filter characteristics caused by residues in the intermediate layer 7.

[0110] Through the above processes, the elastic wave device 1 of the first embodiment can be manufactured. It should be noted that the above-described manufacturing method of the elastic wave device 1 is only one example and can be appropriately modified. For example, the process of forming electrodes 3 and 4 (step S50) can also be performed after the process of forming the cavity 9 (step S60).

[0111] As described above, the manufacturing method of the elastic wave device includes: a roughening process of roughening the first surface of a support substrate 8 having a first surface and a second surface; an inorganic film forming process of forming an intermediate layer 7 on the first surface; a piezoelectric layer forming process of forming a piezoelectric layer 2 on the intermediate layer 7; a piezoelectric layer thinning process of thinning the piezoelectric layer 2; an electrode forming process of forming electrodes 3 and 4 on the piezoelectric layer 2; a first etching process of forming a cavity 9 in a portion of the support substrate 8; and a second etching process of etching the intermediate layer 7 exposed in the cavity 9.

[0112] Therefore, etching can be prevented from ending with residue remaining in the intermediate layer 7, thus suppressing the degradation of filter characteristics caused by residue in the intermediate layer 7.

[0113] As in the first embodiment, the surface roughness of the first surface of the support substrate 8 is 0.5 nm or more and 10 nm or less in terms of Ra. As a result, stray emissions are suppressed, and thus, the degradation of filter characteristics can be suppressed.

[0114] As in the first embodiment, in the second etching process, a gap 10 is formed in the intermediate layer 7, which is surrounded by the inner wall of the intermediate layer 7, the piezoelectric layer 2, and the support substrate 8. The second etching process ends when the gap 10 in the intermediate layer 7 is formed in a serrated shape along the inner wall of the support substrate 8 when viewed from above in the Z direction. As a result, etching can be completed without any residue in the intermediate layer 7, and thus, the degradation of filter characteristics caused by residue in the intermediate layer 7 can be suppressed.

[0115] (Second Implementation)

[0116] Figure 12 This is an explanatory diagram illustrating the relationship between d / 2p, metallization ratio MR, and fractional bandwidth in the elastic wave device of the second embodiment. In the second embodiment, the same reference numerals are used for structures identical to those in the first embodiment, and descriptions are omitted. In the elastic wave device 1 of the second embodiment, various elastic wave devices 1 with different d / 2p and MR were configured, and the fractional bandwidth was measured. Figure 12 The area indicated by the shaded line to the right of the dashed line D is the region with a fractional bandwidth of 17% or less. The boundary between the shaded region and the unshaded region is represented by MR = 3.5(d / 2p) + 0.075, that is, MR = 1.75(d / p) + 0.075. Therefore, it is preferable that MR ≤ 1.75(d / p) + 0.075. In this case, it is easier to make the fractional bandwidth less than 17%. More preferably, Figure 12 The region to the right of MR = 3.5(d / 2p) + 0.05 is shown by the single-dotted line D1. That is, if MR ≤ 1.75(d / p) + 0.05, the fractional bandwidth can be reliably made to be below 17%.

[0117] (Third Implementation)

[0118] Figure 13 This is an explanatory diagram showing the mapping of the fractional bandwidth relative to the Euler angles (0°, θ, ψ) of LiNbO3 in the elastic wave device of the third embodiment, where d / p is infinitely close to 0. In the third embodiment, the same labels are used for the same structures as in the first embodiment, and the description is omitted. Figure 13 The area shown by the shading is the region that receives at least 5% of the fractional bandwidth. If the range of the region is approximated, it becomes the range represented by the following equations (1), (2) and (3).

[0119] (0°±10°, 0°~20°, any ψ)...Equation (1)

[0120] (0°±10°, 20°~80°, 0°~60°(1-(θ-50) 2 / 900) 1 / 2 () or (0°±10°, 20°~80°, [180°-60°(1-(θ-50))) 2 / 900) 1 / 2 [~180°)...Equation (2)

[0121] (0°±10°,[180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 [~180°, any ψ)...Equation (3)

[0122] Therefore, within the range of Euler angles in equations (1), (2), or (3) above, it is preferable to be able to sufficiently expand the fractional bandwidth.

[0123] It should be noted that the above-described embodiments are intended to facilitate understanding of this disclosure, and are not intended to limit the interpretation of this disclosure. This disclosure can be modified / improved without departing from its spirit, and equivalents are also included in this disclosure.

[0124] Explanation of reference numerals in the attached figures

[0125] 1.31 Elastic wave device;

[0126] 2. Piezoelectric layer;

[0127] 2a First page;

[0128] 2b Second page;

[0129] 3. Electrode (first electrode);

[0130] 4. Electrode (second electrode);

[0131] 5. First busbar electrode;

[0132] 6. Second busbar electrode;

[0133] 7. Intermediate layer;

[0134] 7a Opening;

[0135] 8 support base plate;

[0136] 8a Opening;

[0137] 8aX plane;

[0138] 9. Cavity section;

[0139] 10. Gaps;

[0140] 10a concavity;

[0141] 10b Top;

[0142] 201 Piezoelectric layer;

[0143] 201a, Page 1;

[0144] 201b, second page;

[0145] 451 First Region;

[0146] 452 Second Zone;

[0147] C. Incentive region;

[0148] VP1 Virtual plane;

[0149] d Thickness;

[0150] p is the distance between centers.

Claims

1. An elastic wave device comprising: a support substrate; an inorganic film provided on the support substrate; a piezoelectric layer provided on the inorganic film; and an electrode provided on the piezoelectric layer, a hollow portion is provided in a portion of the support substrate, the hollow portion overlaps at least a portion of the electrode in a thickness direction of the support substrate, an inner wall of the inorganic film is located farther from the hollow portion than a position of an inner wall of the support substrate closest to a side of the piezoelectric layer, and a gap of the inorganic film surrounded by the inner wall of the inorganic film, the piezoelectric layer, and the support substrate communicates with the hollow portion of the support substrate.

2. The elastic wave device according to claim 1, wherein the inorganic film has at least two or more recesses in a direction intersecting the thickness direction.

3. The elastic wave device according to claim 2, wherein a maximum length of the recesses in the direction intersecting the thickness direction is 1 μm or more and 50 μm or less.

4. The elastic wave device according to any one of claims 1 to 3, wherein a surface roughness of a face of the support substrate on which the inorganic film is laminated is coarser than a surface roughness of the piezoelectric layer.

5. The elastic wave device according to claim 3, wherein a surface roughness of a face of the support substrate on which the inorganic film is laminated is 0.5 nm or more and 10 nm or less in terms of Ra.

6. The elastic wave device according to any one of claims 1 to 3, wherein the inorganic film is formed of silicon oxide.

7. The elastic wave device according to any one of claims 1 to 3, wherein the hollow portion of the support substrate penetrates through the support substrate.

8. The elastic wave device according to any one of claims 1 to 3, wherein the electrode has a plurality of first electrodes, a first bus bar electrode to which the plurality of first electrodes are connected, a plurality of second electrodes, and a second bus bar electrode to which the plurality of second electrodes are connected.

9. The elastic wave device according to claim 8, wherein a thickness of the piezoelectric layer is 2p or less in a case where a center-to-center distance between adjacent first and second electrodes of the plurality of first and second electrodes is p.

10. The elastic wave device according to any one of claims 1 to 3, wherein the piezoelectric layer includes lithium niobate or lithium tantalate.

11. The elastic wave device according to claim 10, wherein the elastic wave device is configured to be capable of utilizing a plate wave.

12. The elastic wave device according to claim 10, wherein the elastic wave device is configured to be capable of utilizing a bulk wave of a thickness shear mode.

13. The elastic wave device according to any one of claims 1 to 3, wherein the electrode includes at least one pair of electrodes facing each other, a thickness of the piezoelectric layer is d, and a center-to-center distance of adjacent electrodes is p, and d / p ≤ 0.

5.

14. The elastic wave device according to claim 13, wherein the d / p is 0.24 or less.

15. The elastic wave device according to claim 8, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The metallization ratio MR satisfies MR ≤ 1.75 (d / p) + 0.075, The metallization ratio MR is a ratio of areas of the first electrode and the second electrode within an excitation region, relative to the excitation region, The excitation region is a region in which the first electrode and the second electrode coincide when viewed in a direction in which the first electrode and the second electrode oppose each other.

16. The elastic wave device according to claim 15, wherein One second electrode is provided between adjacent first electrodes.

17. The elastic wave device according to any one of claims 1 to 3, wherein Euler angles (φ, θ, ψ) of lithium niobate or lithium tantalate constituting the piezoelectric layer are within a range of formula (1), formula (2), or formula (3) below, (0° ± 10°, 0° to 20°, arbitrary ψ) … formula (1) (0°±10°, 20°~80°, 0°~60° (1-(θ-50) 2 / 900) 1 / 2 ) or (0°±10°, 20°~80°, [180°-60° (1-(θ-50)]) 2 / 900) 1 / 2 [180°] …Equation (2) (0° ± 10°, [180° - 30° (1 - (ψ - 90) 2 / 8100) 1 / 2 ] ~ 180°, any ψ)... (3) 18. A manufacturing method of an elastic wave device, comprising: a roughening process of roughening a first surface of a support substrate having the first surface and a second surface; an inorganic film forming process of forming an inorganic film on the first surface; a piezoelectric layer forming process of forming a piezoelectric layer on the inorganic film; a piezoelectric layer thinning process of thinning the piezoelectric layer; an electrode forming process of forming an electrode on the piezoelectric layer; a first etching process of forming a hollow portion in a part of the support substrate; and a second etching process of etching the inorganic film exposed in the hollow portion.

19. The manufacturing method of an elastic wave device according to claim 18, wherein a surface roughness of the first surface is 0.5 nm or more and 10 nm or less in terms of Ra.

20. The manufacturing method of an elastic wave device according to claim 18 or 19, wherein in the second etching process, a void of the inorganic film surrounded by an inner wall of the inorganic film, the piezoelectric layer, and the support substrate is formed, in a direction intersecting a thickness direction of the support substrate, the second etching process is ended in a state in which the void of the inorganic film is formed in a zigzag shape. ​

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