Elastic wave device

Abstract

An elastic wave device is provided that can suppress the warping of a piezoelectric layer even when the coefficient of linear expansion of the piezoelectric layer is anisotropic. The elastic wave device (1) of the present invention includes a support substrate (2), a piezoelectric layer (4) disposed on the support substrate (2) and having opposing first and second main surfaces (4a, 4b), a first electrode (5) disposed on the first main surface (4a), and a second electrode (6) disposed on the second main surface (4b) and opposite to the first electrode (5). An energy sealing portion is provided between the support substrate (2) and the piezoelectric layer (4). The piezoelectric layer (4) has a first direction (W1) and a second direction (w2) orthogonal to the first direction (W1). In the piezoelectric layer (4), the coefficient of linear expansion of the piezoelectric layer (4) in the first direction (W1) is different from the coefficient of linear expansion of the piezoelectric layer (4) in the second direction (w2). At least one of the piezoelectric layer (4), the first electrode (5) and the second electrode (6) extends parallel to the first direction (W1).

Description

Technical Field

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

[0002] Previously, elastic wave devices have been widely used in filters for portable telephones, etc. An example of an elastic wave device is disclosed in Patent Document 1 below. In this elastic wave device, a piezoelectric film is provided on a substrate. An upper electrode is provided on one main surface of the piezoelectric film, and a lower electrode is provided on the other main surface. A gap is provided between the lower electrode and the substrate.

[0003] Prior art literature

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2005-347898 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] For example, in piezoelectric single crystals such as LiNbO3 and LiTaO3, the coefficient of linear expansion differs in-plane. In other words, piezoelectric materials such as LiNbO3 and LiTaO3 exhibit anisotropic coefficients of linear expansion. When such piezoelectric materials are used in the piezoelectric film described in Patent Document 1, warping sometimes occurs in the piezoelectric film due to deviations in the coefficient of linear expansion when temperature changes occur.

[0008] The purpose of this invention is to provide an elastic wave device that can suppress the warping of a piezoelectric layer even when the coefficient of linear expansion of the piezoelectric layer is anisotropic.

[0009] means for solving problems

[0010] The elastic wave device of the present invention comprises: a support substrate; a piezoelectric layer disposed on the support substrate and having a first main surface and a second main surface facing each other; a first electrode disposed on the first main surface of the piezoelectric layer; and a second electrode disposed on the second main surface of the piezoelectric layer and facing the first electrode. An energy sealing portion is disposed between the support substrate and the piezoelectric layer. The piezoelectric layer has a first direction and a second direction orthogonal to the first direction. The piezoelectric layer has an anisotropic coefficient of linear expansion. The coefficient of linear expansion of the piezoelectric layer in the first direction is different from the coefficient of linear expansion of the piezoelectric layer in the second direction. At least one of the piezoelectric layer, the first electrode, and the second electrode extends parallel to the first direction.

[0011] Invention Effects

[0012] According to the elastic wave device of the present invention, even when the linear expansion coefficient of the piezoelectric layer is anisotropic, the warping of the piezoelectric layer can be suppressed. Attached Figure Description

[0013] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention.

[0014] Figure 2 It is along Figure 1 A sectional view along line II in the diagram.

[0015] Figure 3 This is a top view of the elastic wave device of the comparative example.

[0016] Figure 4 This is a front sectional view of an elastic wave device of a first variation of the first embodiment of the present invention.

[0017] Figure 5 This figure shows the simulation results related to the warping of the piezoelectric layer caused by temperature changes when electrodes and dielectric films with small coefficients of linear expansion are formed.

[0018] Figure 6 This is a front cross-sectional view of the elastic wave device of the second variation of the first embodiment of the present invention.

[0019] Figure 7 This is a front cross-sectional view of the elastic wave device of the third variation of the first embodiment of the present invention.

[0020] Figure 8 This is a top view of the elastic wave device of the fourth variation of the first embodiment of the present invention.

[0021] Figure 9 This is a top view of the elastic wave device of the fifth variation of the first embodiment of the present invention.

[0022] Figure 10 This is a top view of the elastic wave device according to the second embodiment of the present invention.

[0023] Figure 11 This figure shows the simulation results related to the warping of the piezoelectric layer caused by temperature changes when electrodes and dielectric films with large coefficients of linear expansion are formed.

[0024] Figure 12 This is a front cross-sectional view of the elastic wave device according to the third embodiment of the present invention.

[0025] Figure 13 This is a front cross-sectional view of the elastic wave device according to the fourth embodiment of the present invention.

[0026] Figure 14This is a circuit diagram of the filter device according to the fifth embodiment of the present invention.

[0027] Figure 15 This is a schematic top view showing a portion of the filter device according to the fifth embodiment of the present invention.

[0028] Figure 16 This is a schematic top view showing a portion of a filter device according to a modified example of the fifth embodiment of the present invention.

[0029] Figure 17 This is a front sectional view showing an example of the configuration of the dielectric film in this invention.

[0030] Figure 18 This is a front sectional view showing an example of the configuration of the dielectric film in this invention.

[0031] Figure 19 This is a front sectional view showing an example of the configuration of the dielectric film in this invention. Detailed Implementation

[0032] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings, thereby making the present invention clear.

[0033] It should be noted that the embodiments described in this specification are illustrative embodiments, and it is indicated in advance that partial substitutions or combinations of structures can be made between different embodiments.

[0034] Figure 1 This is a top view of the elastic wave device according to the first embodiment of the present invention. Figure 2 It is along Figure 1 A sectional view along line II. Figure 1 and Figure 2 In this example, the wiring and other details are omitted. Figure 1 and Figure 2 The same applies to the other attached figures.

[0035] like Figure 1 and Figure 2 As shown, the elastic wave device 1 includes a support substrate 2, a piezoelectric layer 4, a first electrode 5, and a second electrode 6. Figure 2 As shown, the support substrate 2 has a support portion 2a and a cavity portion 2b. The support substrate 2 supports the piezoelectric layer 4 in the support portion 2a. The support portion 2a has a frame-like shape. The cavity portion 2b is a recess provided in the support substrate 2. The cavity portion 2b is surrounded by the support portion 2a. It should be noted that the cavity portion 2b can also be a through hole provided in the support substrate 2.

[0036] Materials used as the support substrate 2 include, for example, piezoelectric materials such as alumina, lithium tantalate, lithium niobate, and quartz, bauxite, sapphire, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, magnesium olivine, diamond, glass, semiconductors such as silicon and gallium nitride, or resins.

[0037] The piezoelectric layer 4 has a first main surface 4a and a second main surface 4b. The first main surface 4a and the second main surface 4b are opposite to each other. The second main surface 4b is the main surface on the side supporting the substrate 2. The piezoelectric layer 4 has a first direction w1 and a second direction w2. The second direction w2 is orthogonal to the first direction w1. Here, the piezoelectric layer 4 has an anisotropic coefficient of linear expansion. In the piezoelectric layer 4, the coefficient of linear expansion in the first direction w1 is smaller than the coefficient of linear expansion in the second direction w2.

[0038] Specifically, the piezoelectric layer 4 in this embodiment is a lithium niobate layer. More specifically, the piezoelectric layer 4 includes Y-cut lithium niobate. It should be noted that in this specification, when the piezoelectric layer 4 is described as including lithium niobate, it also includes the case where the piezoelectric layer 4 contains trace amounts of impurities to a degree that does not affect the electrical characteristics of the elastic wave device 1. The first direction w1 corresponds to the Z direction in the crystal axis direction. The second direction w2 corresponds to the X direction in the crystal axis direction. It should be noted that in this embodiment, the first direction w1 is the direction with the smallest linear expansion coefficient in the piezoelectric layer 4. On the other hand, the second direction w2 is the direction with the largest linear expansion coefficient in the piezoelectric layer 4. However, the material and cutting direction of the piezoelectric layer 4 are not limited to the above. For example, lithium tantalate, quartz, or lanthanum gallium silicate can also be used as the material of the piezoelectric layer 4.

[0039] A first electrode 5 is disposed on the first main surface 4a of the piezoelectric layer 4. A second electrode 6 is disposed on the second main surface 4b. The first electrode 5 and the second electrode 6 are positioned opposite each other, sandwiching the piezoelectric layer 4. The portion of the first electrode 5, the second electrode 6, and the piezoelectric layer 4 that overlaps in a top view is the excitation section. In the excitation section, a bulk wave is excited. The elastic wave device 1 is a BAW (Bulk Acoustic Wave) element. It should be noted that, in this specification, "top view" refers to... Figure 2 The direction of observation from above, that is, the direction of observation from the first main surface 4a side of the piezoelectric layer 4.

[0040] In this embodiment, the first electrode 5 and the second electrode 6 are not opposite each other in the portion overlapping with the support portion 2a of the support substrate 2 when viewed from above. On the other hand, the first electrode 5 and the second electrode 6 are opposite each other in the portion overlapping with the cavity portion 2b when viewed from above. It should be noted that the first electrode 5 and the second electrode 6 may also be opposite each other in the portion overlapping with the support portion 2a of the support substrate 2 when viewed from above.

[0041] like Figure 1 As shown, the piezoelectric layer 4 and the first electrode 5 have a rectangular shape when viewed from above. The second electrode 6 also has a rectangular shape when viewed from above. It should be noted that the shapes of the piezoelectric layer 4, the first electrode 5, and the second electrode 6 when viewed from above are not limited to the above; for example, they can also be rhomboid or elliptical.

[0042] For the first electrode 5 and the second electrode 6, materials such as W, Mo, Cr, Ti, Pt, Pd, Ni, or Au can be used. It should be noted that the materials of the first electrode 5 and the second electrode 6 are not limited to those described above.

[0043] like Figure 2 As shown, the aforementioned void 2b is provided between a portion of the piezoelectric layer 4 and a portion of the support substrate 2. Within the void 2b, the excited elastic wave does not propagate along the support substrate 2. Therefore, the elastic wave can be effectively confined to the piezoelectric layer 4. Thus, in this embodiment, the void 2b is an energy-sealing portion.

[0044] like Figure 1 and Figure 2 As shown, this embodiment is characterized in that, in the piezoelectric layer 4, the coefficient of linear expansion in the first direction w1 is smaller than the coefficient of linear expansion in the second direction w2, and the piezoelectric layer 4, the first electrode 5, and the second electrode 6 extend parallel to the first direction w1. It should be noted that, in this specification, parallelism between one direction and another includes not only the case where the angle between the two directions is 0°, but also the case where the angle is within the range of 0° ± 15°. By having the above structure, the elastic wave device 1 can suppress the warping of the piezoelectric layer 4. This will be explained in detail below.

[0045] Figure 3 This is a top view of the elastic wave device of the comparative example.

[0046] The comparative example of the elastic wave device 101 differs from the first embodiment in that the directions in which the piezoelectric layer 104, the first electrode 5, and the second electrode 6 extend are not parallel to the first direction w1 and the second direction w2. The elastic wave device 101 expands or contracts due to temperature changes, such as during manufacturing processes or use. Here, the piezoelectric layer 104 has an anisotropic coefficient of linear expansion. Therefore, deviations occur during the expansion or contraction of the piezoelectric layer 104. Furthermore, the piezoelectric layer 104 is not constrained within the energy enclosure. Therefore, in the comparative example, it is difficult to suppress the warping of the piezoelectric layer 104.

[0047] In contrast, Figure 2In the elastic wave device 1 shown, the piezoelectric layer 4, the first electrode 5, and the second electrode 6 extend parallel to the first direction w1. Therefore, the piezoelectric layer 4, the first electrode 5, and the second electrode 6 have a shape that is linearly symmetrical with respect to the axis extending along the first direction w1. Similarly, the piezoelectric layer 4, the first electrode 5, and the second electrode 6 also have a shape that is linearly symmetrical with respect to the axis extending along the second direction w2. Thus, even if the piezoelectric layer 4 has an anisotropic coefficient of linear expansion, deviations are unlikely to occur during the expansion or contraction of the piezoelectric layer 4. Therefore, warping of the piezoelectric layer 4 can be suppressed.

[0048] It should be noted that at least one of the piezoelectric layer 4, the first electrode 5, and the second electrode 6 may extend parallel to the first direction w1. However, it is preferable that the piezoelectric layer 4 extends parallel to the first direction w1. In this case, as described above, deviations can be effectively prevented from occurring during the expansion or contraction of the piezoelectric layer 4. On the other hand, even if the piezoelectric layer 4 does not extend parallel to the first direction w1, if the first electrode 5 or the second electrode 6 extends parallel to the first direction w1, the heat distribution of the piezoelectric layer 4 is easily made linearly symmetrical with respect to the axis extending along the first direction w1. Therefore, deviations are less likely to occur during the expansion or contraction of the piezoelectric layer 4. As in this embodiment, it is more preferable that the piezoelectric layer 4, the first electrode 5, and the second electrode 6 extend parallel to the first direction w1. As a result, deviations are even less likely to occur during the expansion or contraction of the piezoelectric layer 4.

[0049] In the elastic wave device 1, the piezoelectric layer 4, the first electrode 5, and the second electrode 6 are linearly symmetrical with respect to an axis extending along a first direction w1 and with respect to an axis extending along a second direction w2. This further reduces the likelihood of deviation during the expansion or contraction of the piezoelectric layer 4, and further suppresses warping of the piezoelectric layer 4. However, it is also possible for at least one of the piezoelectric layer 4, the first electrode 5, and the second electrode 6 to be linearly symmetrical with respect to an axis extending along the first direction w1 and with respect to an axis extending along the second direction w2.

[0050] Figure 4 This is a front cross-sectional view of the elastic wave device of the first variation of the first embodiment.

[0051] In this modified example, a dielectric film 8 is provided to cover the second electrode 6. Therefore, the second electrode 6 is difficult to damage. It should be noted that, as... Figure 17 As shown, the dielectric film 8 can also be configured to cover the first electrode 5 on the first main surface 4a of the piezoelectric layer 4. In this case, the first electrode 5 is difficult to damage. Alternatively, as... Figure 18 As shown, the dielectric film 8A can also be configured to cover the first electrode 5 on the first main surface 4a, and the dielectric film 8B can be configured to cover the second electrode 6 on the second main surface 4b. Figure 19 As shown, the dielectric film 8C can also be disposed on the second main surface 4b, covering both the second electrode 6 and the area outside the second electrode 6. In this case, for example, the dielectric film 8C can also cover the wiring electrode 9 connected to the second electrode 6. The dielectric film 8C can also have a frame-like shape, for example. It should be noted that the wiring electrode 9, etc., are located on... Figure 19 Other than those shown in the attached figures, they are omitted.

[0052] The arrangement of the first electrode 5 and the second electrode 6 is not limited to the arrangement in the first embodiment and this modified example. The first electrode 5 and the second electrode 6 can be placed opposite each other in the cavity 2b.

[0053] Even with the structure of this modified example, warping of the piezoelectric layer 4 can be suppressed in the same way as in the first embodiment. The coefficient of linear expansion of the dielectric film 8 is preferably less than the smaller of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer 4. Therefore, warping of the piezoelectric layer 4 can be effectively suppressed.

[0054] However, Figure 2 In the embodiment shown, the first electrode 5 and the second electrode 6 are directly disposed on the piezoelectric layer 4. The coefficient of linear expansion of the first electrode 5 and the second electrode 6 is less than the smaller of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 4. As described above, in the piezoelectric layer 4, the coefficient of linear expansion in the first direction w1 is less than the coefficient of linear expansion in the second direction w2. Furthermore, in the piezoelectric layer 4, the first electrode 5, and the second electrode 6, the dimension along the direction parallel to the first direction w1 is greater than the dimension along the direction parallel to the second direction w2. The same applies in the first modified example. It should be noted that it is also possible for at least one of the first electrode 5 and the second electrode 6 to have a coefficient of linear expansion less than the smaller of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 4, and this electrode is directly disposed on the piezoelectric layer 4.

[0055] In the first embodiment and its first modification, the warping of the piezoelectric layer 4 can be effectively suppressed by having the above-described structure. Details are shown below.

[0056] exist Figure 4In the layered structure shown, simulations were performed under elevated temperatures. The simulations were conducted with the support portion of the supporting substrate not bonded to the piezoelectric layer. The simulation conditions were as follows: 1) and 2). It should be noted that, in both 1) and 2), the coefficients of linear expansion of the first electrode, the second electrode, and the dielectric film are less than the smaller of the coefficients of linear expansion of the piezoelectric layer in the first direction w1 and the second direction w2. Furthermore, in the piezoelectric layer, the first electrode, and the second electrode, the dimension along the direction parallel to the first direction is larger than the dimension along the direction parallel to the second direction.

[0057] 1) Similar to the first embodiment, in the piezoelectric layer, the coefficient of linear expansion in the first direction is smaller than the coefficient of linear expansion in the second direction. 2) In the piezoelectric layer, the coefficient of linear expansion in the first direction is larger than the coefficient of linear expansion in the second direction. Simulations were performed for both 1) and 2) under conditions of heating from 25°C to 100°C.

[0058] Figure 5 This figure shows the simulation results when an electrode and dielectric film with a small coefficient of linear expansion are formed. It should be noted that... Figure 5 The simulation results for the structure under condition 1) are shown. Figure 5 The dashed line in the image shows the state of the piezoelectric layer and the second electrode stack before the temperature change. It should be noted that... Figure 5 The results shown are for a second electrode that is disposed on the entire second main surface of the piezoelectric layer. Figure 5 The warping shown in the results refers to the distance between the line connecting the two ends of the piezoelectric layer and the center of the piezoelectric layer.

[0059] like Figure 5 As shown, in structure 1) above, the warping direction of the piezoelectric layer is the direction in which the first main surface side becomes convex. Although not shown, the warping direction is the same in structure 2). In structure 1), the warping is 34 nm. On the other hand, in structure 2), the warping is 54 nm. Thus, it can be seen that warping can be suppressed in structure 1).

[0060] In 1) and 2) above, the coefficient of linear expansion of the first electrode, the second electrode, and the dielectric film is less than the smaller of the coefficients of linear expansion in the first and second directions of the piezoelectric layer. In this case, the coefficient of linear expansion of the piezoelectric layer becomes dominant in preventing warpage of the stack of the piezoelectric layer, the first electrode, the second electrode, and the dielectric film. Here, in 1), the coefficient of linear expansion in the first direction of the piezoelectric layer is less than the coefficient of linear expansion in the second direction. Therefore, when the dimensions of the piezoelectric layer, the first electrode, the second electrode, and the dielectric film in the direction parallel to the first direction are larger than the dimensions in the direction parallel to the second direction, warpage can be reduced. Therefore, as described above, warpage can be suppressed in the structure of 1).

[0061] exist Figure 1 In the embodiment shown, the coefficients of linear expansion of the first electrode 5 and the second electrode 6 are less than the smaller of the coefficients of linear expansion of the piezoelectric layer 4 in the first direction w1 and the second direction w2. Furthermore, the dimensions of the piezoelectric layer 4, the first electrode 5, and the second electrode 6 along the direction parallel to the first direction w1 are larger than the dimensions along the direction parallel to the second direction w2. Therefore, warping can be suppressed in the same way as in case 1). It should be noted that in at least one of the piezoelectric layer 4, the first electrode 5, and the second electrode 6, the dimension along the direction parallel to the first direction w1 is sufficient to be larger than the dimension along the direction parallel to the second direction w2.

[0062] However, in this embodiment, the first electrode 5 and the second electrode 6 comprise a single-layer metal film. However, the first electrode 5 and the second electrode 6 may also comprise a stacked metal film. In this case, in this specification, when comparing the coefficients of linear expansion of the first electrode 5 and the second electrode 6 with the coefficient of linear expansion of the piezoelectric layer 4, the following criteria are used.

[0063] When the first electrode 5 has multiple layers, if the thickness of any layer is set as dn, the coefficient of linear expansion is set as αn, and the overall thickness of the first electrode 5 is set as N, then the reference coefficient of linear expansion of the first electrode 5 is set as the sum of αn × dn / N of all layers. It should be noted that n is any natural number (1, 2, 3, ...). In this specification, when the reference coefficient of linear expansion of the first electrode 5 is greater than the larger of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer 4, the coefficient of linear expansion of the first electrode 5 is greater than the larger coefficient of linear expansion of the piezoelectric layer 4. When the reference coefficient of linear expansion of the first electrode 5 is less than the smaller of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer 4, the coefficient of linear expansion of the first electrode 5 is less than the smaller coefficient of linear expansion of the piezoelectric layer 4.

[0064] The linear expansion coefficient of the second electrode 6 is compared with that of the piezoelectric layer 4. More specifically, when the second electrode 6 has multiple layers, if the thickness of any layer is set to dm, the linear expansion coefficient is set to αm, and the overall thickness of the second electrode 6 is set to M, the reference linear expansion coefficient of the second electrode 6 is set to the sum of αm × dm / M of all layers. It should be noted that m is any natural number (1, 2, 3, ...). In this specification, when the reference linear expansion coefficient of the second electrode 6 is greater than the larger of the linear expansion coefficients in the first direction w1 and the second direction w2 of the piezoelectric layer 4, the linear expansion coefficient of the second electrode 6 is greater than the larger linear expansion coefficient of the piezoelectric layer 4. When the reference linear expansion coefficient of the second electrode 6 is less than the smaller of the linear expansion coefficients in the first direction w1 and the second direction w2 of the piezoelectric layer 4, the linear expansion coefficient of the second electrode 6 is less than the smaller linear expansion coefficient of the piezoelectric layer 4.

[0065] The structure of this embodiment is equivalent to the structure having the following first to third features. First, the coefficient of linear expansion of the first electrode 5 and the second electrode 6 is less than the smaller of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 4. Second, in the piezoelectric layer 4, the coefficient of linear expansion in the second direction w2 is less than the coefficient of linear expansion in the first direction w1. Third, in at least one of the piezoelectric layer 4, the first electrode 5, and the second electrode 6, the dimension along the second direction w2 is greater than the dimension along the first direction w1.

[0066] In this embodiment, the first electrode and the second electrode are directly disposed on the piezoelectric layer 4. However, the first electrode or the second electrode may also be disposed indirectly on the piezoelectric layer 4. Hereinafter, a second and third modification of the first embodiment are shown, which differ from the first embodiment only in that an intermediate film is disposed therein. In the second and third modifications, warping of the piezoelectric layer 4 can also be suppressed in the same way as in the first embodiment.

[0067] exist Figure 6 In the second modified example shown, an intermediate film 17 is provided between the piezoelectric layer 4 and the first electrode 5. The first electrode 5 is indirectly disposed on the piezoelectric layer 4 via the intermediate film 17. The coefficient of linear expansion of the intermediate film 17 is preferably less than the maximum coefficient of linear expansion of the piezoelectric layer 4. For such an intermediate film 17, for example, metals such as W, Mo, Pt or Ti, or dielectrics such as SiO2 or bauxite can be used.

[0068] When the intermediate film 17 is metallic, the warpage of the piezoelectric layer 4 can be reduced, and the resistance on the first electrode 5 side can also be reduced. When the intermediate film 17 includes SiO2, the warpage of the piezoelectric layer 4 can be reduced, the absolute value of the temperature coefficient of frequency (TCF) can be reduced, and the temperature characteristics of frequency can be improved.

[0069] On the other hand, the second electrode 6 is directly disposed on the piezoelectric layer 4. It should be noted that an intermediate film 17 can also be disposed between the piezoelectric layer 4 and the second electrode 6. In this case, the first electrode 5 can also be directly disposed on the piezoelectric layer 4.

[0070] exist Figure 7 In the third variation shown, a first intermediate film 17A is provided between the piezoelectric layer 4 and the first electrode 5. A second intermediate film 17B is provided between the piezoelectric layer 4 and the second electrode 6. The first electrode 5 is indirectly disposed on the piezoelectric layer 4 via the first intermediate film 17A. The second electrode 6 is indirectly disposed on the piezoelectric layer 4 via the second intermediate film 17B. The coefficients of linear expansion of the first intermediate film 17A and the second intermediate film 17B are less than the maximum coefficient of linear expansion of the piezoelectric layer 4. The same material as the intermediate film 17 in the second variation can be used for the first intermediate film 17A and the second intermediate film 17B. In this case, it is sufficient that the dimension of at least one of the piezoelectric layer 4, the first electrode 5, and the second electrode 6 along the direction parallel to the first direction w1 is larger than the dimension along the direction parallel to the second direction w2. However, in the piezoelectric layer 4, it is preferable that the dimension along the first direction w1 is larger than the dimension along the second direction w2.

[0071] In the first embodiment, the piezoelectric layer 4, the first electrode 5, and the second electrode 6 have a rectangular shape when viewed from above. Hereinafter, a fourth and fifth modification of the first embodiment are shown, where only the shapes of the piezoelectric layer, the first electrode, and the second electrode differ from those of the first embodiment when viewed from above. In the fourth and fifth modifications, warping of the piezoelectric layer can also be suppressed, similar to the first embodiment.

[0072] exist Figure 8 In the fourth variation shown, the piezoelectric layer 14A, the first electrode 15A, and the second electrode 16A have a rhomboid shape when viewed from above. The major axis (the longest line connecting opposite vertices or edges) of the piezoelectric layer 14A, the first electrode 15A, and the second electrode 16A extends parallel to the first direction w1. The minor axis (the shortest line connecting opposite vertices or edges) of the piezoelectric layer 14A, the first electrode 15A, and the second electrode 16A extends parallel to the second direction w2.

[0073] It should be noted that the shapes of the piezoelectric layer, the first electrode, and the second electrode, when viewed from above, can also be polygons other than quadrilaterals. In this case, the number of vertices is preferably even. This allows the aforementioned shapes to be linearly symmetrical with respect to both an axis extending parallel to the first direction w1 and an axis extending parallel to the second direction w2. It should also be noted that in the aforementioned shapes, the portions corresponding to the vertices of the polygons can also be R-shaped. Furthermore, in this specification, an R-shaped shape refers to a corner that is curved.

[0074] exist Figure 9 In the fifth modified example shown, the piezoelectric layer 14B, the first electrode 15B, and the second electrode 16B have an elliptical shape when viewed from above. The major axes of the piezoelectric layer 14B, the first electrode 15B, and the second electrode 16B extend parallel to the first direction w1. The minor axes of the piezoelectric layer 14B, the first electrode 15B, and the second electrode 16B extend parallel to the second direction w2.

[0075] Figure 10 This is a top view of the elastic wave device according to the second embodiment.

[0076] like Figure 10 As shown, the difference between this embodiment and the first embodiment is that, in the piezoelectric layer 24, the coefficient of linear expansion in the first direction w1 is greater than the coefficient of linear expansion in the second direction w2. Furthermore, the difference between this embodiment and the first embodiment is that the coefficients of linear expansion of the first electrode 25 and the second electrode 26 are greater than the larger of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer 24. Apart from the above points, the elastic wave device 21 of this embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0077] In this embodiment, the piezoelectric layer 24, the first electrode 25, and the second electrode 26 also have a shape that is linearly symmetrical with respect to an axis extending parallel to the first direction w1. Therefore, even if the piezoelectric layer 24 has an anisotropic coefficient of linear expansion, deviations are unlikely to occur during the expansion or contraction of the piezoelectric layer 24. Thus, warping of the piezoelectric layer 24 can be suppressed.

[0078] In this embodiment, the first electrode 25 and the second electrode 26 are directly disposed on the piezoelectric layer 24. As described above, the coefficient of linear expansion of the first electrode 25 and the second electrode 26 is greater than the larger of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 24. Furthermore, in the piezoelectric layer 24, the coefficient of linear expansion in the first direction w1 is greater than the coefficient of linear expansion in the second direction w2. In the piezoelectric layer 24, the first electrode 25, and the second electrode 26, the dimension along the direction parallel to the first direction w1 is greater than the dimension along the direction parallel to the second direction w2.

[0079] It should be noted that, alternatively, at least one of the first electrode 25 and the second electrode 26 may have a linear expansion coefficient greater than the larger of the linear expansion coefficients in the first direction w1 and the second direction w2 of the piezoelectric layer 24, and the electrode may be directly disposed on the piezoelectric layer 24.

[0080] However, even with the linear expansion coefficient and dimensional relationship of this embodiment, the same laminated structure as the first variation of the first embodiment can be used. In this case, warping of the piezoelectric layer 24 can also be suppressed.

[0081] In Figure 4 Simulations were performed under elevated temperatures in the same stacked structure. The simulations were conducted with the support portion of the supporting substrate and the piezoelectric layer not bonded. The simulation conditions were as described in 3) and 4) below. It should be noted that, in both 3) and 4), the linear expansion coefficient of the second electrode is greater than the larger of the linear expansion coefficients of the piezoelectric layer in the first and second directions. On the other hand, the linear expansion coefficients of the first electrode and the dielectric film are less than the smaller of the linear expansion coefficients of the piezoelectric layer in the first and second directions. In the piezoelectric layer, the first electrode, and the second electrode, the dimension along the direction parallel to the first direction is greater than the dimension along the direction parallel to the second direction.

[0082] 3) Similarly to this embodiment, in the piezoelectric layer, the coefficient of linear expansion in the first direction is greater than the coefficient of linear expansion in the second direction. 4) In the piezoelectric layer, the coefficient of linear expansion in the first direction is less than the coefficient of linear expansion in the second direction. Figure 11 The simulation results for case 3) are shown in the figure. Simulations were performed for both 3) and 4) under the condition of heating from 25°C to 100°C.

[0083] Figure 11 This figure shows the simulation results when an electrode and dielectric film with a large coefficient of linear expansion are formed. It should be noted that... Figure 11 The simulation results for the structure under condition 3) are shown. Figure 11 The single-dotted line in the figure shows the state of the piezoelectric layer and the stack of the second electrode before the temperature change. Figure 11 The warping shown in the results refers to the distance between the line connecting the two ends of the piezoelectric layer and the center of the piezoelectric layer.

[0084] like Figure 11 As shown, in structure 3) above, the warping direction of the piezoelectric layer is the direction in which the second main surface side becomes convex. Although not shown, the warping direction is the same in structure 4). In structure 3), the warping is 19 nm. On the other hand, in structure 4), the warping is 73 nm. Thus, it can be seen that warping can be suppressed in structure 3).

[0085] In 3) and 4) above, the coefficient of linear expansion of the second electrode is greater than the maximum coefficient of linear expansion of the piezoelectric layer. In this case, the warping of the second electrode cannot be ignored in relation to the warping of the stack of the piezoelectric layer, the first electrode, the second electrode, and the dielectric film. Here, in 4), the coefficient of linear expansion in the piezoelectric layer in the first direction is smaller than the coefficient of linear expansion in the second direction. Therefore, the difference in the coefficient of linear expansion between the second electrode and the piezoelectric layer is larger in the direction parallel to the first direction. Furthermore, the dimensions of the piezoelectric layer and the second electrode along the direction parallel to the first direction are larger than the dimensions along the second direction. Therefore, the effect of warping of the second electrode becomes greater. As a result, in the structure of 4), it is difficult to suppress the warping of the stack of the piezoelectric layer, the first electrode, the second electrode, and the dielectric film.

[0086] In contrast, in 3), the coefficient of linear expansion in the piezoelectric layer in the first direction is greater than the coefficient of linear expansion in the second direction. Therefore, the difference in the coefficient of linear expansion between the second electrode and the piezoelectric layer is smaller in the direction parallel to the first direction. Furthermore, the dimensions of the piezoelectric layer and the second electrode along the direction parallel to the first direction are larger than their dimensions along the second direction. Therefore, the warpage of the second electrode can be effectively counteracted by utilizing the warpage of the piezoelectric layer. Thus, as described above, warpage can be suppressed in the structure of 3).

[0087] In this embodiment, the coefficient of linear expansion of the first electrode 25 and the second electrode 26 is greater than the larger of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 24. Furthermore, the dimension of the piezoelectric layer 24, the first electrode 25, and the second electrode 26 along the direction parallel to the first direction w1 is greater than the dimension along the direction parallel to the second direction w2. Therefore, warping can be suppressed in the same way as in case 3). It should be noted that, in at least one of the piezoelectric layer 24, the first electrode 25, and the second electrode 26, the dimension along the direction parallel to the first direction w1 is sufficient to be greater than the dimension along the direction parallel to the second direction w2. Additionally, when the piezoelectric layer 24 is lithium niobate or lithium tantalate, Al, Ag, Mg, or Sn are preferably used as the first electrode 25 and the second electrode 26, whose coefficient of linear expansion is greater than the largest coefficient of linear expansion of the piezoelectric layer 24.

[0088] The structure of this embodiment is equivalent to the structure having the following first to third features. First, the coefficient of linear expansion of the first electrode 25 and the second electrode 26 is greater than the larger of the coefficient of linear expansion in the first direction w1 and the coefficient of linear expansion in the second direction w2 of the piezoelectric layer 24. Second, in the piezoelectric layer 24, the coefficient of linear expansion in the second direction w2 is greater than the coefficient of linear expansion in the first direction w1. Third, in at least one of the piezoelectric layer 24, the first electrode 25, and the second electrode 26, the dimension along the second direction w2 is greater than the dimension along the first direction w1.

[0089] Similarly to the second variation of the first embodiment, an interlayer film may be provided between at least one of the first electrode 25 and the second electrode 26 and the piezoelectric layer 24. The coefficient of linear expansion of the interlayer film is preferably greater than the maximum coefficient of linear expansion of the piezoelectric layer 24. For such an interlayer film, metals such as Al, Ag, Mg, or Sn, or resins, can be used, for example.

[0090] Similarly to the third variation of the first embodiment, a first intermediate film can be provided between the piezoelectric layer 24 and the first electrode 25, and a second intermediate film can be provided between the piezoelectric layer 24 and the second electrode 26. The coefficients of linear expansion of the first and second intermediate films are greater than the maximum coefficient of linear expansion of the piezoelectric layer 24. In this case, at least one of the piezoelectric layer 24, the first electrode 25, and the second electrode 26 may have a dimension along the direction parallel to the first direction w1 that is also greater than a dimension along the direction parallel to the second direction w2. However, in the piezoelectric layer 24, it is preferable that the dimension along the first direction w1 is greater than the dimension along the second direction w2.

[0091] In the embodiments shown above, the energy sealing portion is provided in the cavity 2b of the support substrate 2. However, the energy sealing portion is not limited to this. Hereinafter, embodiments with energy sealing portions different from the first embodiment are shown. It should be noted that, in the following embodiments, similar to the first embodiment, in the piezoelectric layer, the coefficient of linear expansion in the first direction is smaller than the coefficient of linear expansion in the second direction, and the coefficients of linear expansion of the first electrode and the second electrode are smaller than the smaller of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer. However, similar to the second embodiment, in the piezoelectric layer, the coefficient of linear expansion in the first direction is larger than the coefficient of linear expansion in the second direction, and the coefficients of linear expansion of the first electrode and the second electrode are larger than the coefficient of linear expansion in the first direction of the piezoelectric layer.

[0092] Figure 12 This is a front cross-sectional view of the elastic wave device according to the third embodiment.

[0093] In this embodiment, the piezoelectric layer 34 has a bent portion 34c and a bent portion 34d. Thus, a cavity 30 is provided between the support substrate 32 and the piezoelectric layer 34. This cavity 30 serves as an energy sealing portion in this embodiment. On the other hand, the support substrate 32 does not have a recess or a through hole. At the portion overlapping the cavity 30 when viewed from above, the first electrode 35 and the second electrode 36 are positioned opposite each other. In this embodiment, warping of the piezoelectric layer 34 can be suppressed in the same manner as in the first embodiment.

[0094] Figure 13 This is a front cross-sectional view of the elastic wave device according to the fourth embodiment.

[0095] In this embodiment, an acoustic reflection film 43 is provided between the support substrate 32 and the piezoelectric layer 4. This acoustic reflection film 43 serves as an energy sealing portion in this embodiment. The support substrate 32 does not have a recess or a through hole. It should be noted that a recess may also be provided in the support substrate 32. The acoustic reflection film 43 may also be provided within the recess of the support substrate 32.

[0096] The acoustic reflective membrane 43 is a stack of multiple acoustic impedance layers. More specifically, the acoustic reflective membrane 43 has multiple low acoustic impedance layers and multiple high acoustic impedance layers. The low acoustic impedance layers are layers with relatively low acoustic impedance. The multiple low acoustic impedance layers of the acoustic reflective membrane 43 are low acoustic impedance layer 49a and low acoustic impedance layer 49b. On the other hand, the high acoustic impedance layers are layers with relatively high acoustic impedance. The multiple high acoustic impedance layers of the acoustic reflective membrane 43 are high acoustic impedance layer 48a and high acoustic impedance layer 48b. The low acoustic impedance layers and high acoustic impedance layers are stacked alternately. It should be noted that the low acoustic impedance layer 49a is the layer in the acoustic reflective membrane 43 located closest to the piezoelectric layer 4.

[0097] The acoustic reflector 43 has two low acoustic impedance layers and two high acoustic impedance layers. However, the acoustic reflector 43 may have at least one low acoustic impedance layer and at least one high acoustic impedance layer.

[0098] Materials for the low acoustic impedance layer, such as silicon oxide or aluminum, can be used. Materials for the high acoustic impedance layer, such as metals like platinum or tungsten, or dielectrics like aluminum nitride or silicon nitride, can be used. In this embodiment, warping of the piezoelectric layer 4 can be suppressed in the same way as in the first embodiment.

[0099] Figure 14 This is a circuit diagram of the filter device according to the fifth embodiment.

[0100] The filter device 50 is a trapezoidal filter including the elastic wave device of the present invention. The filter device 50 has multiple series-arm resonators and multiple parallel-arm resonators. More specifically, series-arm resonators S1, S2, S3, and S4 are connected in series. A parallel-arm resonator P1 is connected between the connection point between series-arm resonators S1 and S2 and the ground potential. A parallel-arm resonator P2 is connected between the connection point between series-arm resonators S2 and S3 and the ground potential. A parallel-arm resonator P3 is connected between the connection point between series-arm resonators S3 and S4 and the ground potential.

[0101] In this embodiment, all the series arm resonators and parallel arm resonators are elastic wave devices of the present invention. However, at least one series arm resonator or at least one parallel arm resonator in the filter device 50 may be the elastic wave device of the present invention.

[0102] Figure 15 This is a schematic top view showing a portion of the filter device according to the fifth embodiment.

[0103] The filter device 50 comprises multiple series-arm resonators and multiple parallel-arm resonators that share the same piezoelectric layer 4 as in the first embodiment. In the piezoelectric layer 4, the coefficient of linear expansion in the first direction w1 is less than the coefficient of linear expansion in the second direction w2. In this embodiment, all series-arm resonators and all parallel-arm resonators have the same first electrode 5 and second electrode 6 as in the first embodiment. The coefficient of linear expansion of the first electrode 5 and the second electrode 6 is less than the smaller of the coefficients of linear expansion in the first direction w1 and the second direction w2 of the piezoelectric layer 4. The dimensions of the first electrode 5 and the second electrode 6 of all series-arm resonators and all parallel-arm resonators along the first direction w1 are greater than their dimensions along the second direction w2. Therefore, warping of the piezoelectric layer 4 can be suppressed in all series-arm resonators and all parallel-arm resonators.

[0104] It should be noted that the structures of the first and second electrodes can differ in all series-arm resonators and all parallel-arm resonators. For example, in Figure 16 In the variation of the fifth embodiment shown, the structures of the first and second electrodes differ in the series-arm resonator and the parallel-arm resonator. More specifically, all the series-arm resonators have the same first electrode 5 and second electrode 6 as in the first embodiment. On the other hand, all the parallel-arm resonators, namely parallel-arm resonators P51, P52, and P53, have the same first electrode 25 and second electrode 26 as in the second embodiment.

[0105] The first electrode 5 and the second electrode 6 in each series-arm resonator are configured in the same manner as in the first and fifth embodiments. On the other hand, the first electrode 25 and the second electrode 26 in each parallel-arm resonator have a structure equivalent to that in the second embodiment. More specifically, the linear expansion coefficient of the first electrode 25 and the second electrode 26 in each parallel-arm resonator is greater than the larger of the linear expansion coefficients in the first direction w1 and the second direction w2 of the piezoelectric layer 4. In the piezoelectric layer 4, the linear expansion coefficient in the second direction w2 is greater than the linear expansion coefficient in the first direction w1. The dimensions of the first electrode 25 and the second electrode 26 along the second direction w2 of each parallel-arm resonator are greater than their dimensions along the first direction w1. In this modified example, warping of the piezoelectric layer 4 can also be suppressed in all series-arm resonators and all parallel-arm resonators.

[0106] Explanation of reference numerals in the attached figures

[0107] 1...elastic wave device;

[0108] 2...support base plate;

[0109] 2a... Support portion;

[0110] 2b...cavity section;

[0111] 4...piezoelectric layer;

[0112] 4a, 4b... First main face, second main face;

[0113] 5, 6... First electrode, second electrode;

[0114] 8, 8A, 8B... dielectric films;

[0115] 9... Wiring electrodes;

[0116] 14A, 14B... piezoelectric layers;

[0117] 15A, 15B... First electrode;

[0118] 16A, 16B... Second electrode;

[0119] 17...intermediate membrane;

[0120] 17A, 17B... First intermediate membrane, second intermediate membrane;

[0121] 21...elastic wave device;

[0122] 24...piezoelectric layer;

[0123] 25, 26... First electrode, second electrode;

[0124] 30...cavity section;

[0125] 32...support base plate;

[0126] 34...piezoelectric layer;

[0127] 34c, 34d...bends;

[0128] 35, 36... First electrode, second electrode;

[0129] 43...acoustic reflective membrane;

[0130] 48a, 48b... high acoustic impedance layers;

[0131] 49a, 49b... Low acoustic impedance layers;

[0132] 50... filter device;

[0133] 101...elastic wave device;

[0134] 104... piezoelectric layer;

[0135] P1~P3, P51~P53... parallel arm resonators;

[0136] S1~S4... Series arm resonators.

Claims

1. An elastic wave device, comprising: support base plate; A piezoelectric layer is disposed on a support substrate and has a first main surface and a second main surface opposite to each other. A first electrode is disposed on the first main surface of the piezoelectric layer; as well as The second electrode is disposed on the second main surface of the piezoelectric layer, opposite to the first electrode. An energy sealing portion is provided between the support substrate and the piezoelectric layer. The piezoelectric layer has a first direction and a second direction orthogonal to the first direction. The linear expansion coefficient of the piezoelectric layer is anisotropic; the linear expansion coefficient of the piezoelectric layer in the first direction is different from that in the second direction. At least one of the piezoelectric layer, the first electrode, and the second electrode extends parallel to the first direction.

2. The elastic wave device according to claim 1, wherein, The coefficient of linear expansion of at least one of the first and second electrodes is less than the smaller of the coefficients of linear expansion in the first and second directions of the piezoelectric layer, and the electrode is directly disposed on the piezoelectric layer. The coefficient of linear expansion of the piezoelectric layer in the first direction is smaller than the coefficient of linear expansion of the piezoelectric layer in the second direction. In at least one of the piezoelectric layer, the first electrode, and the second electrode, the dimension along the direction parallel to the first direction is greater than the dimension along the direction parallel to the second direction.

3. The elastic wave device according to claim 1, wherein, At least one of the first and second electrodes has a coefficient of linear expansion greater than the larger of the coefficients of linear expansion in the first and second directions of the piezoelectric layer, and this electrode is directly disposed on the piezoelectric layer. The coefficient of linear expansion of the piezoelectric layer in the first direction is greater than the coefficient of linear expansion of the piezoelectric layer in the second direction. In at least one of the piezoelectric layer, the first electrode, and the second electrode, the dimension along the direction parallel to the first direction is greater than the dimension along the direction parallel to the second direction.

4. The elastic wave device according to any one of claims 1 to 3, wherein, The first electrode, the second electrode, the piezoelectric layer, and the energy sealing portion overlap when viewed from above.

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

6. The elastic wave device according to any one of claims 1 to 3, wherein, The energy sealing portion is a void disposed between the support substrate and the piezoelectric layer.

7. The elastic wave device according to any one of claims 1 to 3, wherein, The energy-sealing portion is an acoustic reflection film disposed between the supporting substrate and the piezoelectric layer. The acoustic reflective film has a high acoustic impedance layer with relatively high acoustic impedance and a low acoustic impedance layer with relatively low acoustic impedance. The high acoustic impedance layer and the low acoustic impedance layer are stacked alternately.

8. The elastic wave device according to any one of claims 1 to 3, wherein, The elastic wave device further includes an intermediate film, which is disposed between at least one of the first electrode and the second electrode and the piezoelectric layer.

9. A filter device comprising the elastic wave device of any one of claims 1 to 8 as at least one series arm resonator or at least one parallel arm resonator.

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