Elastic wave device

Abstract

The present application provides an elastic wave device which is not easily vulnerable in construction when a cavity is provided in a support substrate. The elastic wave device (1) of the present application includes a support substrate (2) having a cavity (10), a piezoelectric film (3) provided on the support substrate so as to cover the cavity, a functional electrode (4) provided on the piezoelectric film so as to overlap the cavity in plan view, and a support member (5) disposed in the cavity of the support substrate to support the piezoelectric film. The functional electrode has a plurality of electrodes arranged in a direction intersecting the thickness direction of the piezoelectric film. The plurality of electrodes include a first electrode (6) and a second electrode (7) which are opposed in the direction intersecting the thickness direction of the piezoelectric film and are connected to mutually different potentials. When viewed from a direction orthogonal to the direction in which the first electrode extends, the region in which adjacent electrodes overlap is a cross region (A). In plan view, the cross region overlaps the support member.

Description

[0001] This application is a divisional application of the invention patent application filed on March 15, 2021, with application number 202180002548.8 and invention title "Elastic Wave Device". Technical Field

[0002] This invention relates to elastic wave devices. Background Technology

[0003] Conventional elastic wave devices utilizing plate waves propagating in a piezoelectric film containing LiNbO3 or LiTaO3 are known. For example, Patent Document 1 discloses an elastic wave device utilizing a Lamb wave as a plate wave. Here, a piezoelectric substrate is provided on a support. A cavity is provided in the support, i.e., the support substrate. The piezoelectric substrate overlaps with the cavity. The piezoelectric substrate contains LiNbO3 or LiTaO3. An IDT electrode is provided on the upper surface of the piezoelectric substrate. A voltage is applied between multiple electrode fingers of the IDT electrode connected to one potential and multiple electrode fingers connected to another potential. This excites a Lamb wave. Reflectors are provided on both sides of the IDT electrode. Thus, an elastic wave resonator utilizing a plate wave is constructed.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-257019 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] When the size of the elastic wave device described in Patent Document 1 is increased, the size of the cavity in the support substrate also increases. Therefore, the elastic wave device often becomes structurally fragile.

[0009] The purpose of this invention is to provide an elastic wave device that is less prone to structural fragility when the support substrate has a cavity.

[0010] Technical solutions for solving the problem

[0011] The elastic wave device of the present invention comprises: a support substrate having a cavity; a piezoelectric film disposed on the support substrate such that it covers the cavity; a functional electrode disposed on the piezoelectric film such that it overlaps with the cavity when viewed from above; and a support member disposed on the cavity of the support substrate to support the piezoelectric film. The functional electrode has a plurality of electrodes arranged in a direction intersecting the thickness direction of the piezoelectric film. The plurality of electrodes includes a first electrode and a second electrode, which are opposed to each other in a direction intersecting the thickness direction of the piezoelectric film and connected to different potentials. When viewed from a direction orthogonal to the direction extending from the first electrode, the overlapping area of ​​adjacent electrodes is a cross region, which overlaps with the support member when viewed from above.

[0012] Invention Effects

[0013] According to the elastic wave device of the present invention, when the support substrate is provided with a cavity, structural fragility is not easily generated. Attached Figure Description

[0014] Figure 1 This is a front sectional view of the elastic wave device according to the first embodiment of the present invention.

[0015] Figure 2 This is a top view of the elastic wave device according to the first embodiment of the present invention.

[0016] Figure 3 This is a schematic perspective view showing a portion of the elastic wave device, used to illustrate the interior of the cavity in the support substrate of the first embodiment of the present invention and the structure on the piezoelectric film.

[0017] Figure 4 (a) is a schematic front sectional view illustrating the propagation of a Lamb wave in a piezoelectric film in a conventional elastic wave device. Figure 4 (b) is a schematic front sectional view illustrating a bulk wave in a thickness-shear primary mode propagating in a piezoelectric film in an elastic wave device according to an embodiment of the present invention.

[0018] Figure 5 This is a diagram showing the amplitude direction of a body wave in a first-order thickness shear mode.

[0019] Figure 6 This is a graph showing the relationship between d / p and the relative bandwidth of the resonator when the average distance between the centers of adjacent first and second electrodes is set as p, and the thickness of the piezoelectric film is set as d.

[0020] Figure 7This is a graph showing the impedance frequency characteristics of the elastic wave device according to the first embodiment and comparative example of the present invention.

[0021] Figure 8 This is a top view of an elastic wave device according to a first variation of the first embodiment of the present invention.

[0022] Figure 9 This is a top view of an elastic wave device according to a second variation of the first embodiment of the present invention.

[0023] Figure 10 This is a top view of the elastic wave device according to the third variation of the first embodiment of the present invention.

[0024] Figure 11 This is a top view of the elastic wave device according to the fourth variation of the first embodiment of the present invention.

[0025] Figure 12 This is a top view of the elastic wave device according to the fifth variation of the first embodiment of the present invention.

[0026] Figure 13 This is a front sectional view of the elastic wave device according to the sixth variation of the first embodiment of the present invention.

[0027] Figure 14 This is a front sectional view of the elastic wave device according to the seventh variation of the first embodiment of the present invention.

[0028] Figure 15 This is a top view of the elastic wave device according to the second embodiment of the present invention.

[0029] Figure 16 This is a schematic perspective view showing a portion of the elastic wave device, used to illustrate the interior of the cavity in the support substrate of the third embodiment of the present invention and the structure on the piezoelectric film.

[0030] Figure 17 This is a front sectional view of the elastic wave device according to the fourth embodiment of the present invention.

[0031] Figure 18 This is a front sectional view of the elastic wave device according to the fifth embodiment of the present invention.

[0032] Figure 19 This is a top view of the elastic wave device according to the fifth embodiment of the present invention.

[0033] Figure 20 (a) ~ Figure 20 (c) is a front sectional view illustrating an example of the method for forming the functional electrode and the support member in the fifth embodiment.

[0034] Figure 21 (a) ~ Figure 21 (c) is a front sectional view illustrating an example of the method for forming the support member in the fifth embodiment.

[0035] Figure 22 This is a front sectional view of an elastic wave device according to a variation of the fifth embodiment of the present invention.

[0036] Figure 23 This is a top view of the elastic wave device according to the sixth embodiment of the present invention.

[0037] Figure 24 This is a front sectional view of the elastic wave device according to the sixth embodiment of the present invention. Detailed Implementation

[0038] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0039] In addition, it should be noted that the embodiments described in this specification are illustrative and that partial substitutions or combinations of structures can be made between different embodiments.

[0040] Figure 1 This is a front sectional view of the elastic wave device according to the first embodiment of the present invention. Figure 2 This is a top view of the elastic wave device according to the first embodiment. Additionally, Figure 1 It is along Figure 2 A sectional view along line II. Figure 2 The supporting components, described later, are shown in the diagram with shading. Figure 2 The same applies to top views other than those above.

[0041] like Figure 1 As shown, the elastic wave device 1 includes a support substrate 2, a piezoelectric film 3, a functional electrode 4, and a support member 5. The piezoelectric film 3 is disposed on the support substrate 2. The functional electrode 4 is disposed on the piezoelectric film 3. The support member 5 supports the piezoelectric film 3.

[0042] The support substrate 2 has a cavity 10, a support portion 12, and a bottom 13. The support portion 12 has a frame-like shape. The support portion 12 is disposed on the bottom 13. The cavity 10 is a recess provided in the support substrate 2. More specifically, the cavity 10 is a recess surrounded by the support portion 12 and the bottom 13. The cavity 10 opens on the piezoelectric film 3 side. Furthermore, Figure 1 The dashed lines in the diagram schematically show the boundary between the bottom 13 of the support base plate 2 and the support portion 12, as well as the boundary between the support base plate 2 and the support member 5.

[0043] like Figure 2As shown, the support portion 12 includes a first inner surface 12A, a second inner surface 12B, a third inner surface 12C, and a fourth inner surface 12D. The first inner surface 12A and the third inner surface 12C are opposite to each other. The second inner surface 12B and the fourth inner surface 12D are opposite to each other. Both ends of the first inner surface 12A are connected to the second inner surface 12B and the fourth inner surface 12D. Similarly, both ends of the third inner surface 12C are connected to the second inner surface 12B and the fourth inner surface 12D.

[0044] The support substrate 2 is a silicon substrate. The orientation of the surface on the side of the piezoelectric film 3 of the support substrate 2 is preferably (100), (110), or (111). The resistivity of the support substrate 2 is preferably 4 kΩ or higher. However, the material of the support substrate 2 is not limited to the above-mentioned materials. For example, various ceramics such as alumina, lithium tantalate, lithium niobate, and quartz, alumina, magnesium oxide, sapphire, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, andalusite, block talc, and forsterite, as well as dielectrics such as diamond and glass, and semiconductors such as silicon and gallium nitride can be used.

[0045] A piezoelectric film 3 is provided on the support portion 12 of the support substrate 2, covering the void portion 10. The piezoelectric film 3 has a first main surface 3a and a second main surface 3b. The first main surface 3a and the second main surface 3b are opposite to each other. Of the first main surface 3a and the second main surface 3b, the second main surface 3b is the main surface on the support substrate 2 side. In this embodiment, the piezoelectric film 3 is a lithium niobate film. More specifically, the piezoelectric film 3 is a LiNbO3 film. In addition, the material of the piezoelectric film 3 is not limited to the above-mentioned materials; for example, lithium tantalate such as LiTaO3 can also be used. The thickness of the piezoelectric film 3 is preferably 40 nm or more and 1000 nm or less.

[0046] like Figure 2 As shown, a functional electrode 4 is provided on the first main surface 3a of the piezoelectric film 3. The functional electrode 4 has multiple electrodes. The multiple electrodes are arranged in a direction intersecting the thickness direction of the piezoelectric film 3. Each electrode has a rectangular shape. The multiple electrodes include multiple pairs of first electrodes 6 and second electrodes 7. In this embodiment, the first electrodes 6 and second electrodes 7 extend in parallel. Adjacent first electrodes 6 and second electrodes 7 are opposite each other in a direction orthogonal to the direction in which the first electrodes 6 extend. Hereinafter, the direction in which the first electrodes 6 extend is defined as the y-direction, and the direction orthogonal to the y-direction is defined as the x-direction. Both the x-direction and the y-direction are directions that intersect the thickness direction of the piezoelectric film 3. Therefore, adjacent first electrodes 6 and second electrodes 7 can also be said to be opposite each other in a direction intersecting the thickness direction of the piezoelectric film 3. Here, in this specification, the term "orthogonal" is not limited to the case of strict orthogonality, but also includes approximately orthogonality. Approximately orthogonal, in this specification, for example, refers to an angle within the range of 90° ± 10°.

[0047] The functional electrode 4 has a first busbar 8 and a second busbar 9. The first busbar 8 and the second busbar 9 are opposite to each other. One end of a plurality of first electrodes 6 is connected to the first busbar 8. One end of a plurality of second electrodes 7 is connected to the second busbar 9. The plurality of first electrodes 6 and the plurality of second electrodes 7 are interleaved with each other. The first electrodes 6 and the second electrodes 7 are connected to different potentials.

[0048] The functional electrode 4 comprises a suitable metal or alloy such as Al or an AlCu alloy. In the AlCu alloy, Cu is preferably 1% by weight or more and 10% by weight or less. The functional electrode 4 may also comprise a stacked metal film. In this case, for example, a close-bonding layer may be used. Examples of close-bonding layers include Ti layers and Cr layers.

[0049] like Figure 2 As shown, functional electrode 4 has a cross region A. Cross region A is the region that overlaps with adjacent electrodes when viewed from the x-direction. Cross region A is the region in the x-direction extending from one of the outermost electrodes of functional electrode 4 to the other of the outermost electrodes. In addition, cross region A includes the outermost end of the aforementioned outermost electrode in the x-direction.

[0050] Figure 3 This is a schematic perspective view showing a portion of the elastic wave device, used to illustrate the interior of the cavity in the support substrate of the first embodiment and the structure on the piezoelectric film. Figure 3 In the image, the outline of the cavity 10 is shown by dashed lines.

[0051] A support member 5 is disposed within the cavity 10 of the support substrate 2. In a top view, the support member 5 overlaps with the intersection region A. In this specification, "top view" refers to a view taken from... Figure 1 or Figure 3 Viewed from above. The support member 5 overlaps only with one of the second electrodes 7 when viewed from above. More specifically, the support member 5 overlaps only with the area in the piezoelectric film 3 where the second electrode 7 is located when viewed from above.

[0052] like Figure 2 As shown, the support member 5 traverses the cavity 10, dividing it. The support member 5 is connected to the support portion 12 of the support substrate 2. More specifically, the support member 5 is connected to the first inner surface 12A and the third inner surface 12C of the support substrate 2. In this way, the support member 5 is wall-shaped. However, the support member 5 may not be connected to the support portion 12.

[0053] The support member 5 of the elastic wave device 1 contains silicon. For example... Figure 1As shown, the support member 5 is integral with the support substrate 2. More specifically, the support member 5 protrudes from the bottom 13 of the support substrate 2 toward the piezoelectric film 3. The support member 5 is in direct contact with the piezoelectric film 3. Thus, the support member 5 supports the piezoelectric film 3.

[0054] The characteristic of this embodiment is that the support member 5 is disposed in the cavity 10 such that it overlaps with the intersection region A when viewed from above. Therefore, even when the support substrate 2 has the cavity 10, the piezoelectric film 3 can still be supported by the support member 5. Consequently, structural fragility of the elastic wave device 1 is less likely to occur.

[0055] However, in this embodiment, no reflector is provided on the piezoelectric film 3. The elastic wave device 1 does not have a reflector. Alternatively, if the elastic wave device 1 has a reflector, the number of electrode fingers of the reflector can be reduced. This is because the elastic wave device 1 utilizes a first-order thickness shear mode of volume wave. Hereinafter, details of the first-order thickness shear mode utilized by the elastic wave device 1 will be explained.

[0056] like Figure 2 As shown, multiple pairs of adjacent first electrodes 6 and second electrodes 7 are arranged in the x-direction. This number of pairs does not need to be an integer; it can be 1.5 pairs, 2.5 pairs, etc. Furthermore, the term "adjacent" in the functional electrodes 4 does not mean that the electrodes are configured to be in direct contact with each other, but rather that the electrodes are arranged with a gap between them. In addition, when the first electrode 6 and the second electrode 7 are adjacent, no other signal electrodes or ground electrodes are arranged between the first electrode 6 and the second electrode 7.

[0057] When driving the elastic wave device 1, an alternating voltage is applied between the plurality of first electrodes 6 and the plurality of second electrodes 7. More specifically, an alternating voltage is applied between the first busbar 8 and the second busbar 9. This allows for the resonant characteristics of a bulk wave utilizing a thickness shear first-order mode excited in the piezoelectric film 3. The region between the first electrodes 6 and the second electrodes 7 is thus the excitation region B. Although in Figure 2 In the example shown, an excitation region B is depicted, but the region between the plurality of first electrodes 6 and the plurality of second electrodes 7 is also an excitation region B. The excitation region B is contained within the intersection region A.

[0058] In the elastic wave device 1, when the thickness of the piezoelectric film 3 is set to d and the center-to-center distance between any two adjacent pairs of first electrodes 6 and second electrodes 7 is set to p, d / p is set to 0.5 or less. Therefore, the bulk wave of the aforementioned thickness shear first-order mode can be effectively excited, and good resonance characteristics can be obtained. Here, the center-to-center distance between the first electrode 6 and the second electrode 7 is the distance connecting the center of the first electrode 6 in the x-direction and the center of the second electrode 7 in the x-direction.

[0059] The elastic wave device 1 has the above-described structure and utilizes a first-order thickness shear mode. Therefore, even if the number of pairs of the first electrode 6 and the second electrode 7 is reduced, a decrease in the Q value is not easily observed.

[0060] In this embodiment, a Z-cut piezoelectric material is used for the piezoelectric film 3. Therefore, the x-direction is orthogonal to the polarization direction of the piezoelectric film 3. This is not a limitation if a piezoelectric material with other cut angles is used for the piezoelectric film 3.

[0061] Reference Figure 4 (a) and Figure 4 (b) explains the difference between the first-order thickness shear mode of the volume wave and the previously used Ram wave.

[0062] Figure 4 (a) is a schematic front sectional view illustrating a Lamb wave propagating in a piezoelectric film in an elastic wave device as described in Patent Document 1. Here, the wave propagates in the piezoelectric film 201 as indicated by the arrow. In the piezoelectric film 201, a first main surface 201a and a second main surface 201b are opposite each other, and the thickness direction connecting the first main surface 201a and the second main surface 201b is the z-direction. The x-direction is the direction in which the electrode fingers of the IDT electrodes are arranged. Figure 4 As shown in (a), the Ram wave propagates in the x-direction. Since the Ram wave is a plate wave, the piezoelectric film 201 vibrates as a whole, but the wave propagates in the x-direction. Therefore, resonant characteristics are obtained by placing reflectors on both sides of the IDT electrode in the x-direction.

[0063] In contrast, such as Figure 4 As shown in (b), in the elastic wave device of this embodiment, the vibration displacement is in the thickness shear direction. Therefore, the wave propagates and resonates approximately in the z-direction. Consequently, the x-direction component of the wave is significantly smaller than the z-direction component. Moreover, since the resonant characteristics can be obtained through the propagation of the wave in this z-direction, propagation loss is not easily generated even if the number of electrode fingers of the reflector is reduced. Furthermore, even if the number of electrode pairs including the first electrode 6 and the second electrode 7 is reduced for the purpose of miniaturization, the decrease in Q value is not easily generated.

[0064] In addition, such as Figure 5As shown, the amplitude direction of the bulk wave in the first-order mode of thickness shear becomes opposite in the first region 451 and the second region 452 included in the excitation region of the piezoelectric film 3. Figure 5 The diagram schematically illustrates a body wave when a voltage higher than that of the second electrode 7 is applied between the first electrode 6 and the second electrode 7. The first region 451 is the region within the excitation region between an imaginary plane VP1, orthogonal to the thickness direction of the piezoelectric film 3, and dividing the piezoelectric film 3 into two parts, and the first main surface 3a. The second region 452 is the region within the excitation region between the imaginary plane VP1 and the second main surface 3b.

[0065] As described above, the elastic wave device 1 includes multiple pairs of first electrodes 6 and second electrodes 7. The thickness shear first-order mode is not a mode that causes the wave to propagate in the x-direction, therefore, it is unnecessary to provide multiple pairs of electrodes including first electrodes 6 and second electrodes 7. That is, only at least one pair of first electrodes 6 and second electrodes 7 is required.

[0066] In the elastic wave device 1, the first electrode 6 is an electrode connected to the signal potential, and the second electrode 7 is an electrode connected to the ground potential. However, it is also possible that the first electrode 6 is connected to the ground potential, and the second electrode 7 is connected to the signal potential. In this embodiment, as described above, at least one pair of electrodes is either an electrode connected to the signal potential or an electrode connected to the ground potential, and no floating electrode is provided.

[0067] However, in this embodiment, d / p is 0.5 or less. Preferably, d / p is 0.24 or less. In this case, better resonance characteristics can be obtained. (Refer to...) Figure 6 This needs to be explained.

[0068] Multiple elastic wave devices were obtained by changing d / p. Figure 6 This is a graph showing the relationship between d / p and the relative bandwidth of the resonator as an elastic wave device.

[0069] according to Figure 6 It is clear that when d / p > 0.5, even adjusting d / p will result in a relative bandwidth of less than 5%. In contrast, when d / p ≤ 0.5, varying d / p within this range allows for a relative bandwidth of 5% or more. Therefore, a resonator with a high coupling coefficient can be constructed. Furthermore, when d / p is below 0.24, the relative bandwidth can be increased to 7% or more. Moreover, adjusting d / p within this range yields a resonator with an even wider relative bandwidth, enabling the realization of a resonator with a higher coupling coefficient. Additionally, for example, when the piezoelectric film 3 has a thickness deviation, an averaged value for that thickness can be used.

[0070] The center-to-center distance p between adjacent first electrode 6 and second electrode 7 is preferably 1 μm or more and 10 μm or less. When the dimensions of the multiple electrodes of the functional electrode 4 along the x-direction are set as widths, the widths of the first electrode 6 and the second electrode 7 are preferably 50 nm or more and 1000 nm or less, respectively.

[0071] Here, as Figure 1 As shown, in the first embodiment, the support member 5 overlaps only with the area where the second electrode 7 is provided when viewed from above. This ensures that the resonant characteristics are hardly degraded and suppresses the structural fragility of the elastic wave generating device 1. The details will be explained below by comparing the first embodiment and the comparative example. Furthermore, the comparative example differs from the first embodiment in that it does not have a support member.

[0072] Elastic wave devices according to the first embodiment and a comparative example were prepared, and their impedance-frequency characteristics were compared. The design parameters of the elastic wave device according to the first embodiment are as follows. Here, the dimension of the support member 5 along the x-direction is taken as the width of the support member 5. The design parameters of the comparative example are the same as those of the first embodiment, except for the support member 5.

[0073] Piezoelectric film 3: Material is LiNbO3, thickness is 400nm

[0074] The number of electrode pairs including electrode 6 (first electrode) and electrode 7 (second electrode) is 50.

[0075] Support substrate 2: Material is Si

[0076] Support component 5: Material is Si, width is 1.012μm

[0077] The center-to-center distance p between electrode 6 (first electrode) and electrode 7 (second electrode) is 3.75 μm.

[0078] Width of electrode 6 (first electrode) and electrode 7 (second electrode): 1.012 μm

[0079] d / p: 0.107

[0080] Figure 7 This is a graph showing the impedance frequency characteristics of the elastic wave device of the first embodiment and the comparative example.

[0081] like Figure 7As shown, the impedance-frequency characteristics of the first embodiment are almost identical to those of the comparative example. In the first embodiment, a thickness shear first-order mode is utilized. In this case, the displacement is large in the excitation region B of the piezoelectric film 3 located between the first electrode 6 and the second electrode 7. On the other hand, the displacement is small in the portion of the piezoelectric film 3 where the first electrode 6 and the second electrode 7 are disposed. The support member 5 of the elastic wave device 1 overlaps only with the region where the second electrode 7 is disposed when viewed from above. Therefore, the support member 5 only contacts the portion of the piezoelectric film 3 where the displacement is small, thus it is not easy to obstruct the displacement of the piezoelectric film 3. Therefore, the resonance characteristics can be made almost unaffected, and the structural fragility of the elastic wave generating device 1 can be suppressed. Similarly, when the support member 5 overlaps only with the region where the first electrode 6 is disposed when viewed from above, the resonance characteristics can also be made almost unaffected, and the structural fragility of the elastic wave generating device 1 can be suppressed.

[0082] The area where the support member 5 and the piezoelectric film 3 overlap in a top view is preferably smaller than the area where one electrode of the functional electrode 4 and the piezoelectric film 3 overlap in a top view. In this case, it is more reliable and less likely to hinder the displacement of the piezoelectric film 3. However, the support member 5 only needs to overlap with the intersection area A in a top view.

[0083] In the first embodiment, the dimension of the cavity 10 along the y-direction is the same as the dimension of the intersection region A along the y-direction. The support member 5 of the elastic wave device 1 overlaps only with the portion of the second electrode 7 located in the intersection region A when viewed from above. Furthermore, the arrangement of the cavity 10 is not limited to the above. It is sufficient that the entire intersection region A overlaps with the cavity 10 when viewed from above. The dimension of the cavity 10 along the y-direction only needs to be greater than or equal to the dimension of the intersection region A along the y-direction. Therefore, the displacement of the piezoelectric film 3 when a voltage is applied to the functional electrode 4 is not easily hindered.

[0084] In the first embodiment, the first busbar 8 and the second busbar 9 extend parallel to the direction opposite to the first electrode 6 and the second electrode 7. However, the shape of the functional electrode 4 is not limited to this. For example, the first busbar 8 and the second busbar 9 may also extend perpendicular to the direction opposite to the first electrode 6 and the second electrode 7. In this case, the shape of the first electrode 6 and the second electrode 7 may also be, for example, L-shaped.

[0085] Hereinafter, various modifications of the first embodiment are shown. In each modification, as in the first embodiment, structural fragility of the elastic wave device is not easily generated.

[0086] exist Figures 8-10 The diagram shows the first to third modifications. In the first to third modifications, only the shape of the supporting member differs from that of the first embodiment. Figure 8In the first modified example shown, the width of the support member 25A is narrower than the width of the second electrode 7.

[0087] exist Figure 9 In the second modified example shown, the support member 25B is prismatic. The support member 25B is not connected to the support portion 12 of the support substrate 2. The width of the support member 25B is wider than the width of the second electrode 7. The overlapping area of ​​the support member 25B and the piezoelectric film 3 in top view is smaller than the overlapping area of ​​one electrode of the functional electrode 4 and the piezoelectric film 3 in top view. The support member 25B overlaps with the second electrode 7 and the excitation region B in top view. Furthermore, the support member 25B overlaps with the portion of the excitation region B near the second electrode 7 in the x-direction of the central C.

[0088] exist Figure 10 In the third modified example shown, the support member 25C is cylindrical. The support member 25C is not connected to the support portion 12 of the support base plate 2.

[0089] In the first embodiment, a single support member 5 is provided. Alternatively, multiple support members may be provided. This example is illustrated by the following fourth and fifth modifications of the first embodiment.

[0090] exist Figure 11 In the fourth modified example shown, a plurality of support members 25D are disposed in the cavity portion 10 of the support substrate 2. Each support member 25D is prismatic. The plurality of support members 25D overlap with the same second electrode 7 when viewed from above. The plurality of support members 25D overlap only with the area in the piezoelectric film 3 in which the second electrode 7 is disposed.

[0091] exist Figure 12 In the fifth modified example shown, a plurality of support members 25E are disposed in the cavity portion 10 of the support substrate 2. Each support member 25E is wall-shaped. The plurality of support members 25E overlap with different second electrodes 7 when viewed from above. The plurality of support members 25E overlap only with the area in the piezoelectric film 3 where the second electrode 7 is disposed. In this modified example, the plurality of support members 25E are respectively connected to the first inner surface 12A and the third inner surface 12C of the support substrate 2. However, it is also possible that at least one support member 25E is not connected to the first inner surface 12A or the third inner surface 12C.

[0092] In this modified example, the plurality of support members 25E overlap with all of the second electrode 7 when viewed from above. Alternatively, for example, one support member 25E may overlap with the first electrode 6 and another support member 25E may overlap with the second electrode 7 when viewed from above. The arrangement of the plurality of support members 25E is not limited to the above arrangement. The plurality of support members 25E need only overlap with the intersection region A when viewed from above.

[0093] Figure 13 This is a front sectional view of the elastic wave device according to the sixth variation of the first embodiment.

[0094] In this modified example, an insulating film 26 is provided on the surface of the support member 5 on the side of the piezoelectric film 3. The support member 5 is in indirect contact with the piezoelectric film 3 via the insulating film 26. Alternatively, the support member 5 may not be in direct contact with the piezoelectric film 3. An insulating film 27 is provided on the support portion 12 in the support substrate 2. The support substrate 2 is indirect contact with the piezoelectric film 3 via the insulating film 27. Alternatively, the support substrate 2 may not be in direct contact with the piezoelectric film 3. The insulating films 26 and 27 are silicon oxide films. However, the materials of the insulating films 26 and 27 are not limited to those described above; for example, suitable insulating materials such as silicon nitride, silicon oxynitride, or bauxite can be used.

[0095] Alternatively, one of the support member 5 and the support substrate 2 may be directly connected to the piezoelectric film 3. Or, the insulating film 26 and the insulating film 27 may be formed as an integral insulating film.

[0096] Figure 14 This is a front sectional view of the elastic wave device according to the seventh variation of the first embodiment.

[0097] In this modified example, the support member 25F is configured as a separate member from the support substrate 2. The support member 25F contains a suitable metal. Alternatively, the support member 25F may also contain a suitable semiconductor or insulator. Similar to the sixth modified example, an insulating film 27 is provided between the support portion 12 in the support substrate 2 and the piezoelectric film 3. However, the support substrate 2 and the piezoelectric film 3 may also be in direct contact.

[0098] The thermal conductivity of the support member 25F is preferably higher than that of the piezoelectric film 3. Therefore, heat generated when an elastic wave is excited can easily be conducted from the piezoelectric film 3 to the support member 25F. The heat conducted from the piezoelectric film 3 to the support member 25F is further dissipated towards the support substrate 2. Thus, heat dissipation can be improved. As in this modified example, it is preferable that the support member 25F comprises metal. In this case, the thermal conductivity of the support member 25F can be appropriately increased, and heat dissipation can be improved more reliably.

[0099] like Figure 14 As shown, the support member 25F is in direct contact with the piezoelectric film 3. This effectively improves heat dissipation. Alternatively, similar to the sixth modification, an insulating film 26 can be provided between the support member 25F and the piezoelectric film 3.

[0100] Figure 15 This is a top view of the elastic wave device according to the second embodiment.

[0101] The difference between this embodiment and the first embodiment is that the dimension of the cavity 10 along the y-direction is larger than the dimension of the intersection region A along the y-direction, and the arrangement of the support member 35 is also different. Apart from the aspects described above, the elastic wave device of this embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0102] The dimension of the cavity 10 along the y-direction is larger than the dimension of the functional electrode 4 along the y-direction. In top view, the support portion 12 of the support substrate 2 surrounds the functional electrode 4. Therefore, in top view, the entire functional electrode 4 overlaps with the cavity 10.

[0103] The support member 35 is connected to the first inner surface 12A and the third inner surface 12C of the support substrate 2. Therefore, the support member 35 overlaps with the first busbar 8 and the second busbar 9 when viewed from above. Furthermore, the support member 35 overlaps with the outer portion of the piezoelectric film 3 in the y-direction relative to the portion where the functional electrode 4 is provided when viewed from above.

[0104] In this embodiment, similar to the first embodiment, structural fragility of the elastic wave device is not easily generated. Furthermore, even if the dimension of the cavity 10 along the y-direction is larger than the dimension of the intersection region A along the y-direction, the arrangement of the support member 35 is not limited to the above. For example, the arrangement of the support member 35 may be the same as in the first embodiment or its various modifications.

[0105] Figure 16 This is a schematic perspective view showing a portion of the elastic wave device, used to illustrate the interior of the cavity in the support substrate of the third embodiment and the structure on the piezoelectric film.

[0106] In this embodiment, the arrangement of the plurality of electrodes in the functional electrode 44, as well as the positional relationship between the functional electrode 44 and the support member 5, differs from that in the first embodiment. Apart from the aspects described above, the elastic wave device of this embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0107] The functional electrode 44 has portions of the first electrodes 6 adjacent to each other. The portion of the piezoelectric film 3 between the portions of the adjacent first electrodes 6 is the non-excitation region D. In this embodiment, the center-to-center distance between adjacent first electrodes 6 is 2p. In the non-excitation region D, the first-order thickness shear mode of the bulk wave is not excited. The non-excitation region D is included in the intersection region A.

[0108] Furthermore, the center-to-center distance between adjacent first electrodes 6 is preferably within the range of 2p ± 0.5p. If it is within this range, there will be almost no degradation of the resonance characteristics.

[0109] The support member 5 overlaps with the non-excitation region D when viewed from above. In the non-excitation region D, the displacement of the piezoelectric film 3 is small. Therefore, in this embodiment, even when the piezoelectric film 3 is supported by the support member 5, the displacement of the piezoelectric film 3 is not easily impeded. Thus, the resonance characteristics are almost not degraded, and the structural fragility of the elastic wave generating device is suppressed.

[0110] picture Figure 16 As shown in this embodiment, the support member 5 preferably overlaps with the center of the non-excitation region D between two adjacent first electrodes 6 when viewed from above. The center of the non-excitation region D in the x-direction is far from the excitation region B, thus the displacement of the piezoelectric film 3 is smaller. Therefore, even when the piezoelectric film 3 is supported by the support member 5, it is less likely to impede the displacement of the piezoelectric film 3.

[0111] In this embodiment and the first embodiment, a first-order thickness shear mode is utilized. Therefore, although the elastic wave device of this embodiment has an unexcited region D, the resonance characteristics remain almost unchanged in both embodiments.

[0112] Figure 17 This is a front sectional view of the elastic wave device according to the fourth embodiment.

[0113] The difference between this embodiment and the third embodiment is that the functional electrode 44 is disposed on the second main surface 3b of the piezoelectric film 3, and the support portion 12 of the support substrate 2 surrounds the functional electrode 44 in a top view. Apart from the above aspects, the elastic wave device of this embodiment has the same structure as the elastic wave device of the third embodiment.

[0114] The support member 5 is disposed between adjacent first electrodes 6. The support member 5 overlaps with the non-excitation region D in the intersection region A when viewed from above. Therefore, similar to the third embodiment, the resonant characteristics are almost not degraded, and the structural fragility of the elastic wave generating device is suppressed.

[0115] Figure 18 This is a front sectional view of the elastic wave device according to the fifth embodiment. Figure 19 This is a top view of the elastic wave device according to the fifth embodiment.

[0116] like Figure 18 as well as Figure 19 As shown, the difference between this embodiment and the fourth embodiment is that the support member 55 is made of the same type of material as the second electrode 7 and is connected to the same potential as the second electrode 7. Apart from the aspects described above, the elastic wave device of this embodiment has the same structure as the elastic wave device of the fourth embodiment.

[0117] like Figure 19As shown, the support member 55 is connected to the second busbar 9. The support member 55 is in direct contact with the piezoelectric film 3. Thus, the support member 55, like the second electrode 7, contributes to the excitation of the first-order thickness shear mode of the bulk wave. More specifically, by applying an alternating voltage between the adjacent first electrode 6 and the support member 55, the first-order thickness shear mode of the bulk wave can be excited. Therefore, in this embodiment, the region between one of the adjacent first electrodes 6 and the support member 55 is the excitation region B. Similarly, the region between the other of the adjacent first electrodes 6 and the support member 55 is also the excitation region B. As described above, each electrode of the functional electrode 44 may also comprise a laminated metal film. In this case, the support member 55 may also comprise a laminated metal film.

[0118] In the portion of the piezoelectric film 3 that is in contact with the support member 55, bulk waves of the first-order thickness shear mode are essentially not excited. Therefore, it is less likely to impede the displacement of the piezoelectric film 3. In this embodiment, the resonant characteristics are less likely to deteriorate, and the structural fragility of the elastic wave generating device can be suppressed. Furthermore, the support member 55 may also contain the same type of material as the first electrode 6 and be connected to the same potential as the first electrode 6. In this case, the support member 55 may also be connected to the first busbar 8. Additionally, in this embodiment, the first electrode 6 and the second electrode 7 contain the same type of material.

[0119] When manufacturing the elastic wave device of this embodiment, for example, the piezoelectric film 3 and the support substrate 2 may be bonded after the functional electrode 44 and the support member 55 are formed on the piezoelectric film 3. The functional electrode 44 and the support member 55 can be formed, for example, by a peeling method. Hereinafter, an example of a method for forming the support member 55 and the functional electrode 44 will be described.

[0120] Figure 20 (a) ~ Figure 20 (c) is a front sectional view illustrating an example of the method for forming the functional electrode and the support member in the fifth embodiment. Figure 21 (a) ~ Figure 21 (c) is a front sectional view illustrating an example of the method for forming the support member in the fifth embodiment.

[0121] like Figure 20 As shown in (a), a resist pattern 53A is formed on the piezoelectric film 3. The resist pattern 53A has an opening shaped like a functional electrode 44 and a support member 55. When forming the resist pattern 53A, for example, a resist layer is formed by printing. Then, for example, patterning can be performed by exposure and development.

[0122] Next, as Figure 20As shown in (b), a metal layer 54A for forming the functional electrode 44 and the support member 55 is formed on the piezoelectric film 3 and the resist pattern 53A. The metal layer 54A can be a single-layer metal film or a multilayer metal film. The metal layer 54A can be formed, for example, by sputtering or vacuum evaporation. Next, the resist pattern 53A is removed, for example, by etching. Thus, as... Figure 20 As shown in (c), functional electrode 44 is obtained.

[0123] Next, as Figure 21 As shown in (a), a resist pattern 53B is formed on the piezoelectric film 3, covering the functional electrode 44. The resist pattern 53B has an opening in the shape of a support member 55. The resist pattern 53B can be formed in the same manner as the resist pattern 53A described above.

[0124] Next, as Figure 21 As shown in (b), a metal layer 54B for supporting member 55 is formed on metal layer 54A and resist pattern 53B. Figure 21 The dashed lines in (b) schematically show the boundaries of metal layers 54A and 54B. Metal layers 54A and 54B can be single-layer metal films or multilayer metal films, respectively. Next, the resist pattern 53B is peeled off. Thus, as... Figure 21 As shown in (c), the support member 55 is obtained.

[0125] Figure 22 This is a front sectional view of an elastic wave device according to a variation of the fifth embodiment.

[0126] In this modified example, multiple support members 65A and support members 65B are provided. Figure 22 The diagram shows two support members 65A and two support members 65B. However, the number of support members 65A and 65B is not limited to those shown above.

[0127] Support member 65A is made of the same type of material as the first electrode 6 and is connected to the same potential as the first electrode 6. Support member 65A is connected to the first busbar 8. On the other hand, support member 65B is made of the same type of material as the second electrode 7 and is connected to the same potential as the second electrode 7. Support member 65B is connected to the second busbar 9. In this modified example, structural fragility of the elastic wave device is also less likely to occur.

[0128] Similar to the case where an AC voltage is applied between adjacent first electrodes 6 and second electrodes 7, an AC voltage can be applied between adjacent support members 65A and second electrodes 7 to excite a first-order thickness shear mode volume wave. An AC voltage can also be applied between adjacent first electrodes 6 and support members 65B to excite a first-order thickness shear mode volume wave. Furthermore, an AC voltage can also be applied between adjacent support members 65A and support members 65B to excite a first-order thickness shear mode volume wave. In this way, multiple support members 65A and support members 65B may contribute to the excitation of the first-order thickness shear mode volume wave.

[0129] Figure 23 This is a top view of the elastic wave device according to the sixth embodiment. Figure 24 This is a front sectional view of the elastic wave device according to the sixth embodiment.

[0130] Figure 23 as well as Figure 24 The elastic wave device 71 shown utilizes plate waves. In this embodiment, the piezoelectric film 3 is an aluminum nitride film. More specifically, the piezoelectric film 3 is an AlN film. Furthermore, the material of the piezoelectric film 3 is not limited to the above; for example, it could be lithium tantalate or lithium niobate, etc.

[0131] The functional electrode in the elastic wave device 71 is an IDT electrode 74. The IDT electrode 74 has a first busbar 78, a second busbar 79, a plurality of first electrode fingers 76, and a plurality of second electrode fingers 77. The plurality of first electrode fingers 76 are the plurality of first electrodes in this invention. The plurality of second electrode fingers 77 are the plurality of second electrodes in this invention. One end of each of the plurality of first electrode fingers 76 is connected to the first busbar 78. One end of each of the plurality of second electrode fingers 77 is connected to the second busbar 79. The plurality of first electrode fingers 76 and the plurality of second electrode fingers 77 intersect and interlock with each other. Therefore, adjacent first electrode fingers 76 and second electrode fingers 77 are opposite each other in the x-direction. The IDT electrode 74, like the functional electrode 4 in the first embodiment, has a cross region A. In this embodiment, the cross region A itself is the excitation region.

[0132] A pair of reflectors 72A and 72B are disposed on both sides of the IDT electrode 74 in the x-direction on the piezoelectric film 3. In the elastic wave device 71, in top view, the support portion 12 of the support substrate 2 surrounds the IDT electrode 74 and the pair of reflectors 72A and 72B. Therefore, in top view, the entire IDT electrode 74 and the pair of reflectors 72A and 72B overlap with the cavity portion 10.

[0133] The support member 5 overlaps with the second electrode finger 77 when viewed from above. However, the support member 5 only needs to overlap with the intersection area A when viewed from above. In this embodiment, it is also less likely to cause structural fragility in the elastic wave device 71.

[0134] Explanation of reference numerals in the attached figures

[0135] 1: Elastic wave device;

[0136] 2: Support base plate;

[0137] 3: Piezoelectric film;

[0138] 3a: First main face;

[0139] 3b: Second main face;

[0140] 4: Functional electrodes;

[0141] 5: Supporting components;

[0142] 6, 7: Electrode 1 and Electrode 2;

[0143] 8, 9: Busbar 1 and Busbar 2;

[0144] 10: Hollow section;

[0145] 12: Support section;

[0146] 12A~12D: 1st inner surface to 4th inner surface;

[0147] 13: Bottom;

[0148] 25A~25F: Supporting components;

[0149] 26, 27: Insulating film;

[0150] 35: Supporting components;

[0151] 44: Functional electrode;

[0152] 53A, 53B: Resist pattern;

[0153] 54A, 54B: Metal layers;

[0154] 55: Supporting components;

[0155] 65A, 65B: Supporting components;

[0156] 71: Elastic wave device;

[0157] 72A, 72B: Reflectors;

[0158] 74: IDT electrode;

[0159] 76, 77: First electrode finger, second electrode finger;

[0160] 78, 79: Busbar 1 and Busbar 2;

[0161] 201: Piezoelectric film;

[0162] 201a, 201b: 1st main surface, 2nd main surface;

[0163] 451, 452: Region 1 and Region 2;

[0164] VP1: Imaginary plane.

Claims

1. An elastic wave device, comprising: The supporting substrate has a hollow portion; A piezoelectric film is disposed on the support substrate to cover the void portion; A functional electrode is disposed on the piezoelectric film such that it overlaps with the cavity when viewed from above; as well as At least one support member is disposed in the cavity of the support substrate to support the piezoelectric film; wherein The functional electrode has a plurality of electrodes arranged in a direction intersecting the thickness direction of the piezoelectric film; The plurality of electrodes includes a first electrode and a second electrode, which are opposed to each other in a direction intersecting the thickness direction of the piezoelectric film and connected to different potentials. From a top view, the at least one support member overlaps with an intersection region, in which adjacent electrodes of the plurality of electrodes overlap each other in a direction orthogonal or substantially orthogonal to the direction in which the first electrode extends; From a top view, the at least one support member overlaps with a portion of the plurality of electrodes, the number of overlapping electrodes being less than the total number of the plurality of electrodes, and the number being an integer greater than or equal to 1; as well as From a top view, the at least one support member is completely covered by the piezoelectric film.

2. The elastic wave device according to claim 1, wherein, The metallization ratio MR satisfies MR ≤ 1.75(d / p) + 0.075, where MR is the ratio of B) to A), and: A) is the excitation region where the first electrode and the second electrode overlap when viewed along a direction in which the first electrode and the second electrode are opposite to each other; and B) is the total area of ​​the first electrode and the second electrode located within the excitation region.

3. The elastic wave device according to claim 2, wherein, From a top view, the at least one support member overlaps only with a region that is part of the piezoelectric film and contains one of the electrodes.

4. The elastic wave device according to claim 1, wherein, The first electrode comprises a plurality of first electrodes, and the second electrode comprises a plurality of second electrodes; The functional electrode comprises multiple pairs of electrodes, and each pair of electrodes comprises the plurality of first electrodes and the plurality of second electrodes; In a portion of the functional electrodes, two adjacent electrodes among the plurality of electrodes are the plurality of first electrodes; The center-to-center distance between two adjacent first electrodes is approximately 2p, with an allowable error range of approximately ±0.5p, where p represents the center-to-center distance between one of the plurality of adjacent first electrodes and one of the plurality of second electrodes; as well as From a top view, the at least one support member overlaps with the area between the two adjacent first electrodes.

5. The elastic wave device according to claim 3, wherein... The piezoelectric film includes a first main surface and a second main surface that are opposite to each other; The second main surface is closer to the supporting substrate than the first main surface; The functional electrode is disposed on the second main surface of the piezoelectric film; The material of the at least one support member is of the same type as the material of the second electrode; as well as The at least one support member and the second electrode are connected to the same potential.

6. The elastic wave device according to claim 2, wherein, The at least one support member comprises a plurality of support members; From a top view, the plurality of support members overlap with the plurality of electrodes; as well as From a top view, each of the plurality of support members overlaps only with the corresponding electrode of the plurality of electrodes.

7. The elastic wave device according to claim 1, wherein, The piezoelectric film is made of lithium niobate or lithium tantalate; and d / p is less than or equal to about 0.5, where d represents the thickness of the piezoelectric film and p represents the center-to-center distance between the first electrode and the second electrode, which are adjacent to each other.

8. The elastic wave device according to claim 7, wherein, The d / p ratio is approximately 0.24 or less.

9. The elastic wave device according to claim 1, wherein, The piezoelectric film is made of lithium niobate, lithium tantalate, or aluminum nitride. The first electrode comprises a plurality of first electrodes, and the second electrode comprises a plurality of second electrodes; and The functional electrode is an interdigital transducer (IDT) electrode comprising multiple pairs of electrodes, each pair of which includes one of the plurality of first electrodes and one of the plurality of second electrodes.

10. The elastic wave device according to claim 9, wherein, The at least one support member is made of metal.

11. The elastic wave device according to claim 1, wherein, The piezoelectric film is made of lithium niobate or lithium tantalate; and The elastic wave device uses body waves in a thickness shear mode.

12. The elastic wave device according to claim 1, wherein, The piezoelectric film is made of lithium niobate or lithium tantalate; and The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate fall within the range of any one of the following equations 1), 2), and 3): (0°+10°, 0°~20°, ψ) Equation 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 Equation 2) (0° ± 10°, [180° - 30°(1 - (ψ - 90) 2 / 8100) 1 / 2 )] ~ 180°, ψ) Formula 3).

13. The elastic wave device according to claim 1, wherein, The piezoelectric film is made of lithium niobate or lithium tantalate; and The Euler angles (φ, θ, ψ) of the lithium niobate or lithium tantalate are located within the intersection region.

14. The elastic wave device according to claim 1, wherein, From a top view, the at least one support member overlaps with only one of the plurality of electrodes.

15. The elastic wave device according to claim 1, wherein, The at least one support member has a higher thermal conductivity than the piezoelectric film.

16. The elastic wave device according to claim 4, wherein, From a top view, the at least one support member overlaps with the middle portion of the region between the two adjacent first electrodes.

17. The elastic wave device according to claim 1, wherein, The piezoelectric film includes a first main surface and a second main surface that are opposite to each other; The second main surface is closer to the supporting substrate than the first main surface; and The functional electrode is disposed on the first main surface of the piezoelectric film.

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