Elastic wave device

Abstract

The present application provides an elastic wave device capable of improving heat dissipation with a hollow portion provided in a support substrate. The elastic wave device (1) of the present application includes a support substrate (2) having a hollow portion (10) and a support portion (12); a piezoelectric film (lithium niobate film (3)) provided on the support portion (12) and having a first main surface (3a) and a second main surface (3b); a functional electrode (4) provided on the first main surface (3a); and a heat dissipation film (5) provided on at least one of the first main surface (3a) and the second main surface (3b) of the piezoelectric film and containing a semiconductor or an insulator. The functional electrode (4) has at least one pair of a first electrode (6) and a second electrode (7). In a case where a thickness of the piezoelectric film is dx and a center-to-center distance between the adjacent first electrode (6) and the second electrode (7) is p, dx / p is 0.5 or less. The heat dissipation film (5) overlaps at least a part of the support portion (12) in a plan view. The heat dissipation film (5) has a higher thermal conductivity than the piezoelectric film, and a thickness of the heat dissipation film (5) is thinner than a thickness of the piezoelectric film.

Description

Technical Field

[0001] This invention relates to elastic wave devices. Background Technology

[0002] Conventional elastic wave devices utilizing plate waves propagating in a piezoelectric film containing LiNbO3 or LiTaO3 are known. For example, Patent Document 1 disclosed 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.

[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 the elastic wave device described in Patent Document 1, the heat dissipation is low in the portion of the piezoelectric substrate facing the void. Therefore, the overall heat dissipation of the elastic wave device is also low. Here, if electricity is applied to the IDT electrode, the portion where the IDT electrode is located heats up. In cases of low heat dissipation like the aforementioned elastic wave device, the elastic wave device may break due to the heat generated in the portion where the IDT electrode is located. Therefore, in elastic wave devices with low heat dissipation, it is difficult to improve electrical resistance.

[0008] The purpose of this invention is to provide an elastic wave device that can improve heat dissipation when the support substrate has a cavity.

[0009] Technical solutions for solving the problem

[0010] In a broad aspect of the elastic wave device of the present invention, the device comprises: a support substrate having a cavity and a support portion; a piezoelectric film disposed on the support portion such that it covers the cavity and has a first main surface and a second main surface facing each other; a functional electrode disposed on the first main surface of the piezoelectric film; and a heat dissipation film disposed on at least one of the first main surface and the second main surface of the piezoelectric film, comprising a semiconductor or an insulator, wherein the functional electrode has at least one pair of first electrodes and second electrodes facing each other, and when the thickness of the piezoelectric film is dx and the center-to-center distance between adjacent first electrodes and second electrodes is p, dx / p is 0.5 or less, and in plan view, the heat dissipation film overlaps at least a portion of the support portion, the thermal conductivity of the heat dissipation film is higher than that of the piezoelectric film, and the thickness of the heat dissipation film is thinner than that of the piezoelectric film.

[0011] In another broader aspect of the elastic wave device of the present invention, the device comprises: a support substrate having a cavity and a support portion; a piezoelectric film disposed on the support portion such that it covers the cavity and has a first main surface and a second main surface facing each other; a functional electrode disposed on the first main surface of the piezoelectric film; and a heat dissipation film disposed on at least one of the first main surface and the second main surface of the piezoelectric film, wherein the functional electrode has at least one pair of first electrodes and second electrodes facing each other, and when the thickness of the piezoelectric film is dx and the center-to-center distance between adjacent first electrodes and second electrodes is p, dx / p is 0.5 or less, and in plan view, the heat dissipation film overlaps at least a portion of the support portion, and the thickness of the heat dissipation film is thinner than the thickness of the piezoelectric film, wherein the heat dissipation film is a silicon film, a silicon nitride film, or a silicon carbide film.

[0012] Invention Effects

[0013] The elastic wave device according to the present invention can improve heat dissipation when the support substrate has a cavity. 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 graph showing the relationship between the thickness of the heat dissipation film and the thickness of the lithium niobate film, dh / dn, and the relative bandwidth.

[0017] Figure 4(a) is a schematic front sectional view illustrating the propagation of a Lamb wave by a piezoelectric film in a conventional elastic wave device, and Figure 4(b) is a schematic front sectional view illustrating the propagation of a bulk wave by a thickness shear mode by 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 the body wave in the thickness shear mode.

[0019] Figure 6 This is a graph showing the relationship between dn / p and the relative frequency band of the resonator when the center-to-center distance between adjacent first and second electrodes is set as p and the thickness of the piezoelectric film is set as dn.

[0020] Figure 7 This is a graph showing the relationship between thermal conductivity ratio and normalized temperature difference.

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

[0022] Figure 9 This is a front sectional view of the elastic wave device according to the second embodiment of the present invention.

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

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

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

[0026] Figure 13 This is a diagram showing the mapping of the relative frequency band to the Euler angles (0°, θ, ψ) of LiNbO3 when dn / p is infinitely close to 0. Detailed Implementation

[0027] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby clarifying the present invention.

[0028] 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.

[0029] 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 1It is along Figure 2 A sectional view along line II in the diagram.

[0030] like Figure 1 As shown, the elastic wave device 1 includes a support substrate 2, a lithium niobate film 3 as a piezoelectric film, a functional electrode 4, and a heat dissipation film 5. In the elastic wave device 1, the piezoelectric film of the present invention is a lithium niobate film 3, but the piezoelectric film can also be a lithium tantalate film. The lithium niobate film 3 is disposed on the support substrate 2. In addition, in this embodiment, a heat dissipation film 5 is disposed between the support substrate 2 and the lithium niobate film 3. The functional electrode 4 is disposed on the lithium niobate film 3.

[0031] 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 cavity 10 is a recess provided in the support substrate 2. The cavity 10 is surrounded by the support portion 12 and the bottom 13, and opens on the side of the lithium niobate film 3. Alternatively, the cavity 10 may be a through hole.

[0032] The support substrate 2 is a silicon substrate. The orientation of the surface on the side of the lithium niobate film 3 of the support substrate 2 is preferably (100), (111), or (110). The resistivity of the support substrate 2 is preferably 2 kΩ or higher. However, the material of the support substrate 2 is not limited to the above-mentioned materials. Regarding the material of the support substrate 2, a material with high thermal conductivity is preferred.

[0033] A lithium niobate film 3 is provided on the support portion 12 of the support substrate 2, covering the void portion 10. The lithium niobate 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 lithium niobate film 3 is a LiNbO3 film. The thickness of the lithium niobate film 3 is preferably 40 nm or more and 1000 nm or less.

[0034] A heat dissipation film 5 is provided on the second main surface 3b of the lithium niobate film 3. The heat dissipation film 5 is configured to cover the void portion 10 of the support substrate 2. Therefore, the heat dissipation film 5 is configured to span the support portion 12 of the support substrate 2. The thickness of the heat dissipation film 5 is thinner than that of the lithium niobate film 3. The thermal conductivity of the heat dissipation film 5 is higher than that of the lithium niobate film 3. The heat dissipation film 5 contains a semiconductor or an insulator. More specifically, as a material for the heat dissipation film 5, for example, silicon, aluminum nitride, silicon carbide, diamond, boron nitride, or nano-carbon can be used.

[0035] Furthermore, the heat dissipation film 5 only needs to overlap with at least a portion of the support portion 12 of the support substrate 2 when viewed from above. In this specification, "viewing from above" means from... Figure 1 The direction of observation from above.

[0036] like Figure 2As shown, a functional electrode 4 is provided on the first main surface 3a of the lithium niobate film 3. The functional electrode 4 has multiple electrodes. The multiple electrodes are arranged in a direction intersecting the thickness direction of the lithium niobate 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 intersecting the thickness direction of the lithium niobate film 3. Therefore, it can also be said that adjacent first electrodes 6 and second electrodes 7 are opposite each other in a direction intersecting the thickness direction of the lithium niobate film 3.

[0037] 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 and interlocked. The first electrodes 6 and the second electrodes 7 are connected to different potentials. In this embodiment, the functional electrode 4 is an IDT electrode. However, the functional electrode 4 is not limited to an IDT electrode. The functional electrode 4 only needs to have at least one pair of first electrodes 6 and second electrodes 7.

[0038] 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 20% 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 provided. Examples of close-bonding layers include Ti layers and Cr layers.

[0039] like Figure 2 As shown, the functional electrode 4 has an intersection region A. The intersection region A is the region where adjacent electrodes overlap when viewed from the x-direction. The intersection region A is the region from one of the outermost electrodes of the functional electrode 4 in the x-direction to the other of the outermost electrodes. Furthermore, the intersection region A includes the outermost end of the aforementioned outermost electrode in the x-direction. In top view, the entire intersection region A overlaps with the cavity 10.

[0040] This embodiment is characterized by the following structure: 1) When the thickness of the piezoelectric film is set to dx and the center-to-center distance between adjacent first electrodes 6 and second electrodes 7 is set to p, dx / p is 0.5 or less. 2) In plan view, the heat dissipation film 5 overlaps with at least a portion of the support portion 12 of the support substrate 2. 3) The thermal conductivity of the heat dissipation film 5 is higher than that of the lithium niobate film 3, and the thickness of the heat dissipation film 5 is thinner than that of the lithium niobate film 3. Therefore, the heat dissipation performance of the elastic wave device 1 can be improved even when the support substrate 2 has a cavity portion 10. This will be explained below.

[0041] By utilizing bulk waves in a thickness shear mode, the elastic wave device 1 can be miniaturized. This miniaturization will be described later. However, miniaturizing the elastic wave device 1 results in a smaller surface area, thus reducing heat dissipation. Furthermore, if the support substrate 2 has a cavity 10, it becomes difficult to dissipate the heat generated in the area where the functional electrode 4 is located.

[0042] In contrast, in this embodiment, by providing a heat dissipation film 5, heat generated in the portion where the functional electrode 4 is provided can be conducted to the heat dissipation film 5. Furthermore, by overlapping at least a portion of the support portion 12 of the support substrate 2 in a top view, the distance between the heat dissipation film 5 and the support substrate 2 is small. Therefore, heat can be efficiently conducted from the heat dissipation film 5 to the support substrate 2. Thus, the heat dissipation performance of the elastic wave device 1 can be improved even when the support substrate 2 has a cavity portion 10. Furthermore, since the thickness of the heat dissipation film 5 is thinner than the thickness of the lithium niobate film 3, production efficiency can also be improved.

[0043] Furthermore, even in conventional plate-wave-based components, heat dissipation can be improved by increasing the size of the IDT electrode. However, increasing the size of the IDT electrode makes it easier for transitions to occur in the electrode fingers. Therefore, electrical withstand capability may deteriorate. In contrast, in this embodiment, heat dissipation can be improved without increasing the size of the functional electrode 4. Thus, heat dissipation can be improved without causing a deterioration in electrical withstand capability.

[0044] As in this embodiment, the heat dissipation film 5 is preferably disposed on the second main surface 3b of the lithium niobate film 3 and in contact with the support substrate 2. This allows for better heat conduction from the heat dissipation film 5 to the support substrate 2. More preferably, the heat dissipation film 5 is configured to extend across at least a portion of the support portion 12 of the support substrate 2. This further increases the heat dissipation path. More preferably, in plan view, the heat dissipation film 5 completely overlaps with the void portion 10. In this case, the heat dissipation film 5 extends across the entire support portion 12. Therefore, the heat dissipation path can be further increased.

[0045] Here, Table 1 shows the thermal conductivity of examples of materials that can be used in the heat dissipation film 5. Additionally, the thermal conductivity of LiNbO3 is 4.6 W / mK. The thermal conductivity of LiTaO3 is 4.2 W / mK.

[0046] [Table 1]

[0047] AIN 130～260 SiC 360 Si 140 diamond 2000 BN 550 Nano carbon ～2000

[0048] As can be seen, the thermal conductivity of all the materials shown in Table 1 is significantly higher than that of LiNbO3 and LiTaO3. The heat dissipation film 5 is preferably a silicon film, a silicon nitride film, or a silicon carbide film. More specifically, the heat dissipation film 5 is preferably a Si film, an AlN film, or a SiC film. In these cases, heat dissipation can be improved and costs can be reduced.

[0049] The thermal conductivity of the heat dissipation film 5 is preferably more than five times that of the lithium niobate film 3. This effectively improves heat dissipation. However, when the materials shown in Table 1 are used for the heat dissipation film 5, the thermal conductivity of the heat dissipation film 5 can be significantly increased, further enhancing heat dissipation. This is also true when the piezoelectric film is a lithium tantalate film.

[0050] Here, the thickness of the heat dissipation film 5 is set as dh, the thickness of the lithium niobate film 3 is set as dn, and the ratio of the thickness dh of the heat dissipation film 5 to the thickness dn of the lithium niobate film 3 is set as dh / dn. Figure 3 The diagram shows the relationship between dh / dn and relative bandwidth. A wider relative bandwidth indicates a higher coupling coefficient.

[0051] Figure 3 This is a graph showing the relationship between the thickness of the heat dissipation film and the thickness of the lithium niobate film, dh / dn, and the relative bandwidth.

[0052] like Figure 3 As shown, the smaller the ratio dh / dn becomes, the wider the relative bandwidth becomes. The ratio dh / dn is preferably 0.25 or less. That is, the thickness of the heat dissipation film 5 is preferably 25% or less of the lithium niobate film 3. More specifically, the thickness of the thickest part of the heat dissipation film 5 is preferably 25% or less of the lithium niobate film 3. This allows for a wider relative bandwidth and further improves the coupling coefficient. On the other hand, the thickness of the heat dissipation film 5 is preferably 5% or more of the lithium niobate film 3. In this case, heat dissipation performance can be appropriately improved. The thickness of the heat dissipation film 5 is more preferably 50% or more of the lithium niobate film 3. In this case, heat dissipation performance can be further improved. Furthermore, hereafter, the relative bandwidth will sometimes be referred to as the relative frequency band.

[0053] Furthermore, in this embodiment, no reflector is provided on the lithium niobate film 3. The elastic wave device 1 does not have a reflector. The reason why propagation loss can be suppressed even in this case is because the elastic wave device 1 utilizes a thickness shear mode volume wave. More specifically, the elastic wave device 1 utilizes a thickness shear first-order mode volume wave. Hereinafter, details of the thickness shear mode utilized by the elastic wave device 1 will be explained.

[0054] 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 arranged 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.

[0055] 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 mode excited in the lithium niobate film 3. The region between the first electrodes 6 and the second electrodes 7 is thus the excitation region B. Figure 2 In the example shown, an excitation region B is illustrated, but the region between the plurality of first electrodes 6 and the plurality of second electrodes 7 is also an excitation region B. Excitation region B is contained within the intersection region A.

[0056] The heat dissipation film 5 preferably overlaps with the intersection region A when viewed from above, and more preferably overlaps with the excitation region B. In the elastic wave device 1, heat is generated in the excitation region B within the intersection region A. Therefore, with the above structure, heat can be efficiently conducted from the heated portion to the heat dissipation film 5. Thus, heat dissipation performance can be further improved.

[0057] In the elastic wave device 1, as described above, dx / p is set to 0.5 or less. More specifically, when the thickness of the lithium niobate film 3 is set to dn and the center-to-center distance between any two adjacent first electrodes 6 and second electrodes 7 is set to p, dn / p is set to 0.5 or less. Therefore, the bulk wave of the aforementioned thickness shear 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.

[0058] The elastic wave device 1 has the above-described structure and utilizes a thickness shear mode. Therefore, even if the number of pairs of the first electrode 6 and the second electrode 7 is reduced, the Q value is not easily decreased.

[0059] In this embodiment, the lithium niobate film 3 is a Z-cut piezoelectric film. Therefore, the x-direction is orthogonal to the polarization direction of the lithium niobate film 3. This is not a limitation if the lithium niobate film 3 is a piezoelectric film with other cut angles.

[0060] The differences between the bulk wave of the thickness shear mode and the previously used Lamb wave will be explained with reference to Figures 4(a) and 4(b).

[0061] Figure 4(a) is a schematic front cross-sectional view illustrating the propagation of a Lamb wave in a piezoelectric film of 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 face 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. As shown in Figure 4(a), the Lamb wave propagates in the x-direction. Because the Lamb wave is a plate wave, although the piezoelectric film 201 vibrates as a whole, the wave propagates in the x-direction. Therefore, reflectors are arranged on both sides of the IDT electrodes in the x-direction to obtain resonant characteristics.

[0062] In contrast, as shown in Figure 4(b), in the elastic wave device of this embodiment, the vibration displacement is in the thickness shear direction. Therefore, the wave propagates and resonates essentially in the z-direction. Consequently, the x-direction component of the wave is significantly smaller than the z-direction component. Moreover, since the resonance characteristic is 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 in order to achieve miniaturization, a decrease in the Q value is not easily generated.

[0063] In addition, such as Figure 5 As shown, the amplitude direction of the bulk wave in the thickness shear mode becomes opposite in the first region 451 and the second region 452 included in the excitation region of the lithium niobate film 3. Figure 5 The diagram schematically illustrates a bulk 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 between the imaginary plane VP1 and the first main surface 3a in the excitation region. The imaginary plane VP1 is orthogonal to the thickness direction of the lithium niobate film 3 and divides the lithium niobate film 3 into two parts. The second region 452 is the region between the imaginary plane VP1 and the second main surface 3b in the excitation region.

[0064] As described above, the elastic wave device 1 includes multiple pairs of first electrodes 6 and second electrodes 7. Since the thickness shearing mode is not a mode that causes the wave to propagate in the x-direction, it is not necessary to provide multiple pairs of electrodes including the first electrodes 6 and second electrodes 7. That is, it is sufficient to provide at least one pair of first electrodes 6 and second electrodes 7.

[0065] 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.

[0066] Furthermore, in this embodiment, dn / p is 0.5 or less. Preferably, dn / p is 0.24 or less. In this case, better resonance characteristics can be obtained. (Refer to...) Figure 6 This needs to be explained.

[0067] By varying dn / p, multiple elastic wave devices were obtained. Figure 6 This is a diagram showing the relative frequency bands of the dn / p and elastic wave devices as resonators.

[0068] according to Figure 6 It is clear that if dn / p > 0.5, even with adjustments to dn / p, the relative bandwidth will be less than 5%. Conversely, when dn / p ≤ 0.5, varying dn / 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 dn / p is below 0.24, the relative bandwidth can be increased to 7% or more. In addition, adjusting dn / p within this range yields a resonator with an even wider relative bandwidth, enabling the realization of a resonator with a higher coupling coefficient. Furthermore, for example, when the lithium niobate film 3 has a thickness deviation, an averaged value for that thickness can be used. These relationships also apply when the piezoelectric film is a lithium tantalate film.

[0069] The center-to-center distance p between adjacent first electrodes 6 and second electrodes 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 150 nm or more and 1000 nm or less, respectively.

[0070] Here, the relationship between the thermal conductivity ratio and heat dissipation is shown as follows. Let w be the average width of the first and second electrodes, De be the duty cycle of the functional electrode, Ce be the thermal conductivity of the functional electrode, and de be the thickness of the functional electrode. Also, let De = w / p. Let Cn be the thermal conductivity of the lithium niobate film, dn be the thickness of the lithium niobate film, Ci be the thermal conductivity of the heat dissipation film, and di be the thickness of the heat dissipation film. Let R be the ratio of the thermal conductivity of the functional electrode to that of the lithium niobate film and the heat dissipation film, and let R = (Ce × de × De) / (Cn × dn ​​+ Ci × di). For example, when the thermal conductivity Ci of the heat dissipation film is high or the thickness of the heat dissipation film is thick, the thermal conductivity ratio R becomes smaller.

[0071] Furthermore, the normalized temperature difference is used as an indicator of heat dissipation. The normalized temperature difference is a normalized difference between the temperature of the elastic wave device when the elastic wave is not excited and the temperature when the elastic wave is excited. When the elastic wave is excited, heat is generated in the area where the functional electrodes are located, and the temperature of the elastic wave device increases. Therefore, the higher the heat dissipation performance of the elastic wave device, the better it can dissipate heat. Thus, the higher the heat dissipation performance, the smaller the temperature difference between the unexcited and excited temperatures. Therefore, the smaller the normalized temperature difference, the higher the heat dissipation performance of the elastic wave device.

[0072] Figure 7 This is a graph showing the relationship between thermal conductivity ratio and normalized temperature difference. Figure 7 The dashed lines E1 and E2 in the figure show the slope of the change in normalized temperature difference relative to the change in thermal conductivity ratio R.

[0073] like Figure 7 As shown, the smaller the thermal conductivity ratio R becomes, the smaller the normalized temperature difference becomes. Specifically, as the thermal conductivity ratio R is gradually decreased, the normalized temperature difference begins to decrease significantly from R = 8. When R ≤ 4, the normalized temperature difference can be reduced even further. Furthermore, the smaller the thermal conductivity ratio R becomes, the steeper the slope of the change in the normalized temperature difference relative to the change in the thermal conductivity ratio R becomes. Here, as shown by the intersection of dashed lines E1 and E2, R = 1 is the inflection point of the change in the normalized temperature difference. Therefore, when R ≤ 1, the normalized temperature difference can be reduced even further.

[0074] Preferably, R ≤ 8, more preferably R ≤ 4, and even more preferably R ≤ 1. This effectively reduces the normalized temperature difference and improves heat dissipation.

[0075] As described above, the heat dissipation film 5 only needs to overlap with at least a portion of the support portion 12 in the support substrate 2 when viewed from above. Hereinafter, a variation of the first embodiment is shown, differing only in the arrangement of the heat dissipation film from the first embodiment.

[0076] exist Figure 8 In the modified example shown, the heat dissipation film 5A overlaps with a portion of the support portion 12 in the support substrate 2 when viewed from above. More specifically, in Figure 8 In the cross-section shown, one portion of the opposing parts of the support portion 12 overlaps with the heat dissipation film 5A when viewed from above. The other portion of the opposing parts of the support portion 12 does not overlap with the heat dissipation film 5A when viewed from above. The portion of the support portion 12 that does not overlap with the heat dissipation film 5A is in direct contact with the lithium niobate film 3. Furthermore, the heat dissipation film 5A also overlaps with the intersection region A of the functional electrode 4 when viewed from above. In this modified example, similar to the first embodiment, heat dissipation can be improved.

[0077] Figure 9 This is a front sectional view of the elastic wave device according to the second embodiment.

[0078] The difference between this embodiment and the first embodiment is that the heat dissipation film 25 is provided on the first main surface 3a of the lithium niobate film 3. Furthermore, the heat dissipation film 5 is not provided on the second main surface 3b. 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.

[0079] A heat dissipation film 25 is disposed on the first main surface 3a of the lithium niobate film 3, thereby covering the functional electrode 4. Furthermore, in this embodiment, the thickness of the heat dissipation film 25 is also thinner than the thickness of the lithium niobate film 3. Viewed from above, the heat dissipation film 25 overlaps with the support portion 12 of the support substrate 2.

[0080] The lithium niobate film 3 has low thermal conductivity. Therefore, it is difficult to improve the efficiency of heat transfer from the portion of the lithium niobate film 3 where the functional electrode 4 is provided to the portion in contact with the support portion 12. In contrast, in this embodiment, heat can be efficiently transferred via the heat dissipation film 25 to the portion overlapping the support portion 12 in top view. Therefore, heat dissipation can be improved.

[0081] When a heat dissipation film 25 is provided on the first main surface 3a of the lithium niobate film 3, it is preferable that the heat dissipation film 25 completely overlaps with the void portion 10 when viewed from above. This increases the heat dissipation path, thereby effectively improving heat dissipation.

[0082] Figure 10 This is a front sectional view of the elastic wave device according to the third embodiment.

[0083] The difference between this embodiment and the first embodiment is that a heat dissipation film 25 is provided on the first main surface 3a of the lithium niobate film 3, and a heat dissipation film 5 is provided on the second main surface 3b. Apart from the aspects described above, the elastic wave device of the third embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0084] In this embodiment, similar to the first and second embodiments, heat can be efficiently transferred to the support substrate 2 via the heat dissipation film 5 and the heat dissipation film 25. Therefore, heat dissipation can be improved.

[0085] Figure 11 This is a front sectional view of the elastic wave device according to the fourth embodiment.

[0086] This embodiment differs from the first embodiment in that the heat dissipation film 35 and the support substrate 32 are integrated, and in the shape of the cavity 30. Apart from the aspects described above, the elastic wave device 31 of the fourth embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0087] In the elastic wave device 31, the heat dissipation film 35 is made of the same material as the support substrate 32. The heat dissipation film 35 spans the support portion 12 of the support substrate 32. In this embodiment, the heat dissipation film 35 spans the entire support portion 12. The heat dissipation film 35 and the support portion 12 are flush with each other on the lithium niobate film 3 side. The heat dissipation film 35 and the support portion 12 are in contact with the second main surface 3b of the lithium niobate film 3.

[0088] The cavity 30 of the support substrate 32 is a recess provided in the support substrate 32. More specifically, the cavity 30 is a recess surrounded by the support portion 12 and the heat dissipation film 35. The support substrate 32 of this embodiment does not have a bottom 13 like that of the first embodiment. The cavity 30 is a recess that opens on the side opposite to the heat dissipation film 35.

[0089] In this embodiment, the heat dissipation film 35 and the support substrate 32 are integral. Therefore, heat can be efficiently dissipated to the outside of the elastic wave device 31 via the heat dissipation film 35 and the support substrate 32. This further improves heat dissipation performance.

[0090] The heat dissipation film 35 and the support substrate 32 can be obtained, for example, by etching the base material of the support substrate 32. For example, a mask can be provided on the portion of the base material other than the portion forming the heat dissipation film 35 using a resist film, and then etching can be performed. Alternatively, the etching rate of the portion of the base material forming the heat dissipation film 35 can be made different from the etching rate of other portions. To make the etching rates different, for example, the base material can be appropriately doped. Etching can also be performed thereafter.

[0091] Furthermore, if the base material is doped during the formation of the heat dissipation film 35, the compositions of the heat dissipation film 35 and the support portion 12 of the support substrate 32 will differ. However, in this case, the compositions of the heat dissipation film 35 and the support portion 12 are the same except for the doped components.

[0092] However, the heat dissipation film 35 does not necessarily have to extend across the support portion 12. The heat dissipation film 35 only needs to be integrally formed with at least a portion of the support portion 12. In this case, heat dissipation performance can be improved. However, it is preferable that the heat dissipation film 35 extends across at least a portion of the support portion 12, and more preferably across the entire support portion 12. This further improves heat dissipation performance.

[0093] Figure 12 This is a front sectional view of the elastic wave device according to the fifth embodiment.

[0094] In this embodiment, the structure of the heat dissipation film 45 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.

[0095] The heat dissipation film 45 has a first portion 45a and a second portion 45b. The first portion 45a is the portion that overlaps with the first electrode 6 or the second electrode 7 when viewed from above. The second portion 45b is the portion that overlaps with the portion between the first electrode 6 and the second electrode 7 when viewed from above. Furthermore, the second portion 45b does not overlap with the first electrode 6 or the second electrode 7 when viewed from above. The thickness of the second portion 45b is greater than the thickness of the first portion 45a. Additionally, it is sufficient that at least a portion of the second portion 45b is thicker than the first portion 45a.

[0096] In the case of conventional plate waves or the like, which are used as elastic waves, the portion of the electrode fingers where the IDT electrode is provided heats up. On the other hand, in the case of bulk waves using a thickness shear mode as in this embodiment, the portion between the first electrode 6 and the second electrode 7 in the lithium niobate film 3 heats up. The second portion 45b of the heat dissipation film 45 comes into contact with this heated portion. The second portion 45b is thick, so heat can be efficiently conducted from the heated portion to the support substrate 2. In addition, because the first portion 45a and the second portion 45b form an uneven surface, the surface area of ​​the heat dissipation film 45 can be increased. Therefore, heat dissipation performance can be further improved.

[0097] Here, the center in the x-direction between the center of the first electrode 6 and the center of the second electrode 7 is defined as the electrode finger center portion O. Preferably, the thickness of the portion of the second part 45b that overlaps with the electrode finger center portion O when viewed from above is thicker than the thickness of the first part 45a. The portion of the lithium niobate film 3 located at the electrode finger center portion O generates heat particularly. By making the aforementioned portion of the heat dissipation film 45 thicker, heat dissipation can be improved more effectively.

[0098] The preferred Euler angles of the lithium niobate film 3 are shown below. Examples.

[0099] Figure 13 This is a diagram showing the mapping of the relative frequency band to the Euler angles (0°, θ, ψ) of LiNbO3 when dn / p is infinitely close to 0. Figure 13 The portion shown by the shading is the region where a relative frequency band of more than 5% can be obtained. If the range of this region is approximated, it becomes the range represented by the following equations (1), (2) and (3).

[0100] (0°±10°, 0°~20°, any ψ) …Equation (1)

[0101] (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)

[0102] (0°±10°,[180°-30°(1-(ψ-90) 2 / 8100) 1 / 2 [~180°, any ψ) …Equation (3)

[0103] Therefore, within the Euler angle range of equations (1), (2), or (3) above, the relative bandwidth can be sufficiently broadened, which is preferable. The same relationship applies to lithium tantalate films.

[0104] In addition, it is known that Figure 3 The same relationship applies when the piezoelectric film is a lithium tantalate film. Therefore, the thickness of the heat dissipation film is preferably 25% or less of that of the lithium tantalate film. This allows for a wider relative bandwidth and a higher coupling coefficient. On the other hand, the thickness of the heat dissipation film is preferably 5% or more of that of the lithium tantalate film, more preferably 50% or more. In this case, heat dissipation performance is further improved.

[0105] Furthermore, it can be known that Figure 7 The same relationship applies when the piezoelectric film is a lithium tantalate film. When the piezoelectric film is a lithium tantalate or lithium niobate film, the thermal conductivity of the piezoelectric film is set as Cx, and the thickness of the piezoelectric film is set as dx. The ratio of the thermal conductivity of the functional electrode to that of the piezoelectric film and the heat dissipation film is set as R, and is defined as R = (Ce × de × De) / (Cx × dx + Ci × di). Similarly, it is preferable that R ≤ 8, more preferably R ≤ 4, and even more preferably R ≤ 1. This effectively reduces the normalized temperature difference and effectively improves heat dissipation.

[0106] Explanation of reference numerals in the attached figures

[0107] 1: Elastic wave device;

[0108] 2: Support base plate;

[0109] 3: Lithium niobate membrane;

[0110] 3a, 3b: First main face, second main face;

[0111] 4: Functional electrodes;

[0112] 5, 5A: Heat dissipation film;

[0113] 6, 7: Electrode 1 and Electrode 2;

[0114] 8, 9: Busbar 1 and Busbar 2;

[0115] 10: Hollow section;

[0116] 12: Support section;

[0117] 13: Bottom;

[0118] 25: Heat dissipation film;

[0119] 30: Hollow section;

[0120] 31: Elastic wave device;

[0121] 32: Support base plate;

[0122] 35: Heat dissipation film;

[0123] 45: Heat dissipation film;

[0124] 45a, 45b: Part 1, Part 2;

[0125] 201: Piezoelectric film;

[0126] 201a, 201b: 1st main surface, 2nd main surface;

[0127] 451, 452: Region 1 and Region 2;

[0128] VP1: Imaginary plane.

Claims

1. An elastic wave device, comprising: A support substrate having a cavity and a support portion; A piezoelectric film is disposed on the support portion such that it covers the cavity portion and has a first main surface and a second main surface that are opposite to each other; A functional electrode is disposed on the first main surface of the piezoelectric film; as well as A heat dissipation film, disposed on at least one of the first main surface and the second main surface of the piezoelectric film, comprises a semiconductor or an insulator. The functional electrode has at least one pair of first electrodes and second electrodes that are opposite each other. When the thickness of the piezoelectric film is set as dx and the center-to-center distance between adjacent first and second electrodes is set as p, dx / p is 0.5 or less. Viewed from above, the heat dissipation film overlaps with at least a portion of the support portion. The thermal conductivity of the heat dissipation film is higher than that of the piezoelectric film, and the thickness of the heat dissipation film is thinner than that of the piezoelectric film. The piezoelectric film is a lithium niobate film or a lithium tantalate film. Let the average width of the first electrode and the second electrode be w, the duty cycle of the functional electrode be De, the thermal conductivity of the functional electrode be Ce, the thickness of the functional electrode be de, the thermal conductivity of the piezoelectric film be Cx, the thermal conductivity of the heat dissipation film be Ci, the thickness of the heat dissipation film be di, and the thermal conductivity ratio be R. Let De = w / p, and let R = (Ce × de × De) / (Cx × dx + Ci × di). In this case, R ≤ 8.

2. An elastic wave device, comprising: A support substrate having a cavity and a support portion; A piezoelectric film is disposed on the support portion such that it covers the cavity portion and has a first main surface and a second main surface that are opposite to each other; A functional electrode is disposed on the first main surface of the piezoelectric film; as well as A heat dissipation film is disposed on at least one of the first main surface and the second main surface of the piezoelectric film. The functional electrode has at least one pair of first electrodes and second electrodes that are opposite each other. When the thickness of the piezoelectric film is set as dx and the center-to-center distance between adjacent first and second electrodes is set as p, dx / p is 0.5 or less. Viewed from above, the heat dissipation film overlaps with at least a portion of the support portion. The thickness of the heat dissipation film is thinner than the thickness of the piezoelectric film. The heat dissipation film is a silicon film, an aluminum nitride film, or a silicon carbide film. The piezoelectric film is a lithium niobate film or a lithium tantalate film. Let the average width of the first electrode and the second electrode be w, the duty cycle of the functional electrode be De, the thermal conductivity of the functional electrode be Ce, the thickness of the functional electrode be de, the thermal conductivity of the piezoelectric film be Cx, the thermal conductivity of the heat dissipation film be Ci, the thickness of the heat dissipation film be di, and the thermal conductivity ratio be R. Let De = w / p, and let R = (Ce × de × De) / (Cx × dx + Ci × di). In this case, R ≤ 8.

3. The elastic wave device according to claim 1 or 2, wherein, The heat dissipation film is disposed on the second main surface of the piezoelectric film and is in contact with the support portion of the support substrate.

4. The elastic wave device according to claim 3, wherein, The heat dissipation film and the supporting substrate are integrated into one unit.

5. The elastic wave device according to claim 1 or 2, wherein, Viewed from above, the heat dissipation film completely overlaps with the cavity.

6. The elastic wave device according to claim 1 or 2, wherein, The heat dissipation film has the following characteristics: Part 1, when viewed from above, overlaps with either the first electrode or the second electrode; and Part 2 overlaps with the portion between the first electrode and the second electrode when viewed from above. At least a portion of the second part is thicker than the first part.

7. The elastic wave device according to claim 1 or 2, wherein, The thermal conductivity of the heat dissipation film is more than 5 times that of the piezoelectric film.

8. The elastic wave device according to claim 1 or 2, wherein, The thickness of the heat dissipation film is less than 25% of the thickness of the piezoelectric film.

9. The elastic wave device according to claim 1 or 2, wherein, R≤4。 10. The elastic wave device according to claim 9, wherein, R≤1。 11. The elastic wave device according to claim 1 or 2, wherein, The Euler angles (φ, θ, ψ) of the lithium niobate film or the lithium tantalate film, which are the piezoelectric film, are within the range of the following equations (1), (2), or (3). (0°±10°, 0°~20°, any 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 ~180°) …Equation (2) (0°±10°, [180°-30° (1-(ψ-90) 2 / 8100) 1 / 2 ~180°, any ψ) …Formula (3).

Images