Elastic wave device

Abstract

The present application provides an elastic wave device capable of more reliably suppressing diffusion of Cu constituting an IDT electrode to a piezoelectric substrate. The elastic wave device of the present application includes a piezoelectric substrate (2) and an IDT electrode (3) having a barrier layer (7) (outer layer) disposed on the piezoelectric substrate (2) and a first layer (5) (electrode layer) disposed on the barrier layer (7) and having Cu as a main component, and having a plurality of electrode fingers. The first layer (5) includes a first main surface (5a) on the piezoelectric substrate (2) side, a second main surface (5b) opposite the first main surface (5a), and a side surface (5c) connecting the first main surface (5a) and the second main surface (5b). The barrier layer (7) covers the first main surface (5a) and the side surface (5c) of the first layer (5). The thickness of the portion of the barrier layer (7) covering the first main surface (5a) of the first layer (5) is thinner than the thickness of the portion of the barrier layer (7) covering the side surface (5c) of the first layer (5).

Description

TECHNICAL FIELD

[0001] The present application relates to an elastic wave device. BACKGROUND

[0002] Conventionally, elastic wave devices have been widely used for filters of portable telephones and the like. One example of an elastic wave device is disclosed in Patent Literature 1 described below. In the elastic wave device, an IDT (Interdigital Transducer) electrode is provided on a piezoelectric substrate. The IDT electrode includes a Cu film. Further, a silicon oxide film is provided on the piezoelectric substrate so as to cover the IDT electrode. In order to prevent Cu in the Cu film from diffusing to the silicon oxide film, a protective film is provided on the piezoelectric substrate so as to cover the IDT electrode.

[0003] In the elastic wave device described in Patent Literature 2, the IDT electrode has a barrier layer provided on a piezoelectric substrate and a main electrode layer provided on the barrier layer. The barrier layer is provided in order to prevent metal of the main electrode layer from diffusing to the piezoelectric substrate.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2019-068309

[0007] Patent Literature 2: Japanese Patent Application Publication No. 2017-157944 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] If the protective film of Patent Literature 1 is assumed to be provided on the piezoelectric substrate so as to cover the IDT electrode of Patent Literature 2, it is also considered that diffusion of metal constituting the IDT electrode to the silicon oxide film and the piezoelectric substrate can be suppressed. However, the present inventors have found that metal can possibly diffuse to the piezoelectric substrate via a boundary between a side surface of the barrier layer and the protective film.

[0010] An object of the present application is to provide an elastic wave device capable of more reliably suppressing diffusion of Cu constituting an IDT electrode to a piezoelectric substrate.

[0011] TECHNICAL SOLUTION FOR SOLVING THE PROBLEM

[0012] The elastic wave device according to the present application includes: a piezoelectric substrate; and an IDT electrode having an outer layer and an electrode layer, and having a plurality of electrode fingers, the outer layer being provided on the piezoelectric substrate, the electrode layer being provided on the outer layer and having Cu as a main component, the electrode layer including: a first main surface on the piezoelectric substrate side; a second main surface opposite to the first main surface; and a side surface connecting the first main surface and the second main surface, the outer layer covering the first main surface and the side surface of the electrode layer, a thickness of a portion of the outer layer covering the first main surface of the electrode layer being thinner than a thickness of a portion of the outer layer covering the side surface of the electrode layer.

[0013] Effects of the Invention

[0014] According to the elastic wave device according to the present application, Cu constituting the IDT electrode can be more reliably suppressed from diffusing to the piezoelectric substrate. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a plan view of the elastic wave device according to the first embodiment of the present application.

[0016] Figure 2 is a cross-sectional view of the electrode finger along the line I-I in Figure 1 .

[0017] Figure 3 is a cross-sectional view of the electrode finger in the first comparative example.

[0018] Figure 4 is a cross-sectional view of the electrode finger in the second comparative example.

[0019] Figure 5 is a cross-sectional view of the electrode finger in the modified example of the first embodiment of the present application.

[0020] Figure 6 is a cross-sectional view of the electrode finger in the second embodiment of the present application.

[0021] Figure 7 is a cross-sectional view of the electrode finger in the modified example of the second embodiment of the present application.

[0022] Figure 8 is a cross-sectional view of the electrode finger in the third embodiment of the present application.

[0023] Figure 9 is a front cross-sectional view of the elastic wave device according to the fourth embodiment of the present application.

[0024] Figure 10 is a front cross-sectional view of the elastic wave device according to the fifth embodiment of the present application.

[0025] Figure 11 is a front view cross-sectional view of an elastic wave device to which the sixth embodiment of the present application relates. DETAILED DESCRIPTION

[0026] Hereinafter, specific embodiments of the present application will be described with reference to the drawings, thereby making the present application clear.

[0027] Note that each of the embodiments described in the present specification is illustrative, and a part of the structure can be replaced or combined between different embodiments.

[0028] Figure 1 is a plan view of an elastic wave device to which the first embodiment of the present application relates.

[0029] The elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 of the present embodiment is a piezoelectric substrate including only a piezoelectric layer. The piezoelectric substrate 2 includes lithium niobate. In the present specification, the piezoelectric substrate 2 including lithium niobate also includes a case where the piezoelectric substrate 2 contains a trace amount of impurities. The same applies to the relationship between other structures and materials of the elastic wave device to which the present application relates. More specifically, the piezoelectric substrate 2 includes 128° rotated Y-cut X-propagation LiNbO3. However, the cut angle and the material of the piezoelectric substrate 2 are not limited to the above-described cut angle and material. As the material of the piezoelectric substrate 2, for example, lithium tantalate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate), or the like can be used. In addition, the piezoelectric substrate 2 can also be a laminated substrate including a piezoelectric layer.

[0030] The IDT electrode 3 has a first bus bar 18a, a second bus bar 18b, a plurality of first electrode fingers 19a, and a plurality of second electrode fingers 19b. The first bus bar 18a and the second bus bar 18b are opposed to each other. One ends of the plurality of first electrode fingers 19a are connected to the first bus bar 18a, respectively. One ends of the plurality of second electrode fingers 19b are connected to the second bus bar 18b, respectively. The plurality of first electrode fingers 19a and the plurality of second electrode fingers 19b are alternately and oppositely inserted to each other. In addition, a wavelength defined by an electrode finger pitch of the IDT electrode 3 is set to λ. The electrode finger pitch refers to a center distance between adjacent electrode fingers. In a case where the IDT electrode 3 has a portion where the above-described center distance is different, an average value of the above-described center distance can be used as the electrode finger pitch.

[0031] An elastic wave is excited by applying an alternating voltage to the IDT electrode 3. A pair of reflectors 9A and 9B are provided on both sides of the IDT electrode 3 in the direction of elastic wave propagation on the piezoelectric substrate 2. In this way, the elastic wave device 1 of the present embodiment is a surface acoustic wave resonator. However, the elastic wave device according to the present application can also be a boundary acoustic wave resonator. Furthermore, the elastic wave device according to the present application is not limited to a resonator, but can also be a filter device or a multiplexer having a resonator.

[0032] Figure 2 is a cross-sectional view of the electrode fingers along the line I-I in Figure 1

[0033] The IDT electrode 3 has a barrier layer 7, a first layer 5, and a second layer 6. The barrier layer 7 is an outer layer in the present application. More specifically, the barrier layer 7 is provided on the piezoelectric substrate 2. The first layer 5 is provided on the barrier layer 7. The second layer 6 is provided on the first layer 5.

[0034] The first layer 5 is an electrode layer in the present application. The first layer 5 has a first main surface 5a and a second main surface 5b and a side surface 5c. The first main surface 5a and the second main surface 5b are opposed to each other. The first main surface 5a is in contact with the barrier layer 7. The second main surface 5b is in contact with the second layer 6. The side surface 5c is connected to the first main surface 5a and the second main surface 5b. The first layer 5 has Cu as a main component. In the present specification, the term "main component" means a component having a content ratio of more than 50%. However, the first layer 5 is preferably composed of Cu.

[0035] The second layer 6 contains Ti. In addition, the material of the second layer 6 is not limited to the above-described material. Alternatively, the second layer 6 can be a laminate.

[0036] The barrier layer 7 is located between the piezoelectric substrate 2 and the first layer 5. Thus, the barrier layer 7 covers the first main surface 5a of the first layer 5. Furthermore, the barrier layer 7 also covers the side surface 5c of the first layer 5. In addition, the barrier layer 7 has a first portion 7a and a second portion 7c. The first portion 7a is a portion covering the first main surface 5a of the first layer 5. The second portion 7c is a portion covering the side surface 5c of the first layer 5. In the present embodiment, the thickness of the first portion 7a in the barrier layer 7 is thinner than the thickness of the second portion 7c in the barrier layer 7.

[0037] In the present embodiment, the barrier layer 7 contains an oxide of Mn. However, the barrier layer 7 can contain an oxide of a metal as long as it contains an oxide of a metal. The barrier layer 7 preferably contains an oxide of one metal selected from the group consisting of Mn, Al, Mg, and Sn.

[0038] ​A protective film 8 is formed on the piezoelectric substrate 2, covering the IDT electrode 3. The protective film 8 comprises silicon oxide. More specifically, the protective film 8 comprises SiO2. However, the protective film 8 is not limited to the above; for example, it may also comprise silicon oxynitride, etc.

[0039] The characteristic of this embodiment is that the barrier layer 7 covers the first main surface 5a and the side surface 5c of the first layer 5, and the thickness of the first portion 7a in the barrier layer 7 is thinner than the thickness of the second portion 7c. Therefore, while suppressing the decrease in the electromechanical coupling coefficient, the diffusion of Cu constituting the IDT electrode 3 to the piezoelectric substrate 2 can be more reliably suppressed. In addition, the diffusion of Cu to the protective film 8 can be effectively suppressed. The effects of this embodiment will be explained in more detail below.

[0040] An elastic wave filter device incorporating the elastic wave device 1 of the first embodiment was prepared. Furthermore, elastic wave filter devices incorporating the elastic wave device of the first comparative example and elastic wave filter devices incorporating the elastic wave device of the second comparative example were prepared. In addition, multiple such elastic wave filter devices were prepared. Figure 3 As shown, the elastic wave device of the first comparative example differs from that of the first embodiment in that the IDT electrode does not have a blocking layer, and a NiCr layer 107 is disposed between the piezoelectric substrate 2 and the first layer 5. Figure 4 As shown, the second comparative example differs from the first embodiment in that the IDT electrode does not have a barrier layer, and a NiCr layer 117 is disposed between the piezoelectric substrate 2 and the first layer 5. Furthermore, in the second comparative example, the width of the NiCr layer 117 is wider than the width of the first layer 5. This is the same structure described in Patent Document 2 (Japanese Patent Application Publication No. 2017-157944). Here, the width of the electrode finger is the dimension of the electrode finger along the direction of elastic wave propagation.

[0041] The design parameters of the elastic wave device in the first embodiment are as follows.

[0042] Material of piezoelectric substrate 2: 128° rotation Y-cut X-propagation LiNbO3

[0043] Layer 1, 5: Material is Cu, thickness is 300 nm

[0044] Layer 2, 6: Material is Ti, thickness is 8nm

[0045] Barrier layer 7: The material is an oxide of Mn, with the thickness of part 7a being 2 nm and the thickness of part 7c being 15 nm.

[0046] Protective film 8: Material is SiO2, thickness is 1110nm

[0047] Wavelength λ in IDT electrode 3: 4μm

[0048] The design parameters of the elastic wave devices of the first and second comparative examples are as follows.

[0049] Material of piezoelectric substrate: 128° rotated Y-cut X-propagation LiNbO3

[0050] Thickness of NiCr layer: 6 nm

[0051] First layer: Cu, 300 nm thick

[0052] Second layer: Ti, 8 nm thick

[0053] Wavelength λ in IDT electrode: 4 μm

[0054] A high-temperature load test was performed on the elastic wave filter device including the elastic wave device 1 of the first embodiment, the elastic wave filter device including the elastic wave device of the first comparative example, and the elastic wave filter device including the elastic wave device of the second comparative example. In this test, the temperature was set to 125°C, and a direct current voltage of 3 V was applied between the first bus bar and the second bus bar of the IDT electrode. In this state, the filter electrical characteristics were measured at given time intervals.

[0055] The results of the high-temperature load test were that, in the first comparative example, deterioration of the insertion loss was observed in all samples when measured after a test time of 200 hours. In the second comparative example, deterioration of the insertion loss was observed in some samples when measured after a test time of 200 hours. Even in the samples of the second comparative example other than these, deterioration of the insulation resistance value was confirmed. After observing the electrode fingers of the samples in which deterioration of the insulation resistance value was confirmed, diffusion between Cu in the first layer 5 and LiNbO3 in the piezoelectric substrate 2 was confirmed. That is, by the configuration of Patent Literature 2, diffusion between Cu and LiNbO3 can be suppressed to some extent, but a degree of strength that can satisfy market requirements was not obtained.

[0056] On the other hand, in the elastic wave filter device including the elastic wave device 1 of the first embodiment, no deterioration of the insertion loss and the insulation resistance value was observed for a test time of 1000 hours.

[0057] The first portion 7a in the barrier layer 7 mainly has a function of suppressing diffusion of Cu of the first layer 5 to the piezoelectric substrate 2, and in addition, functions also as a close contact layer between the first layer 5 and the piezoelectric substrate 2. The oxide of the metal constituting the barrier layer 7 is an insulator. By disposing the insulator between the electrode layer of the IDT electrode 3 and the piezoelectric substrate 2, the electromechanical coupling coefficient becomes small. In contrast, in the present embodiment, the portion of the barrier layer 7 between the first layer 5 and the piezoelectric substrate 2 is thin. Thus, the electromechanical coupling coefficient can be suppressed from becoming small.

[0058] Although the diffusion between the first layer 5 and the piezoelectric substrate 2 can be suppressed by the thin barrier layer 7, it is difficult to suppress the diffusion between the first layer 5 and the protective film 8. In contrast, in the present embodiment, in the barrier layer 7, the thickness of the second portion 7c is thicker than the thickness of the first portion 7a. Thus, the diffusion of Cu of the first layer 5 to the protective film 8 can be suppressed.

[0059] In addition, the IDT electrode 3 is generally configured to have a width in the planar direction that is wider than the thickness direction. Thus, in the barrier layer 7, by making the thickness of the first portion 7a thinner than the thickness of the second portion 7c, the decrease in the cross-sectional area of Cu having a small specific resistance can be reduced. Thus, the resistance of the electrode finger can be reduced.

[0060] As described above, in the barrier layer 7, it is preferable that the thickness of the first portion 7a be made thinner than the thickness of the second portion 7c. Thereby, an elastic wave device 1 having high reliability, small loss due to small resistance of the electrode finger, and a large electromechanical coupling coefficient can be obtained.

[0061] The thickness of the first portion 7a of the barrier layer 7 is preferably in a range of 0.5 nm or more and 10 nm or less. In a case where the thickness of the first portion 7a is thinner than 0.5 nm, it can become difficult to suppress the diffusion of Cu of the first layer 5 to the piezoelectric substrate 2 in the barrier layer 7. On the other hand, in a case where the thickness of the first portion 7a is thicker than 10 nm, it becomes difficult to suppress the electromechanical coupling coefficient from becoming small, and the insertion loss of the device can become large.

[0062] The thickness of the second portion 7c of the barrier layer 7 is preferably in a range of 10 nm or more and 20 nm or less. In a case where the thickness of the second portion 7c is thinner than 10 nm, the barrier property can become insufficient, and it can become difficult to suppress the diffusion of Cu. On the other hand, in a case where the thickness of the second portion 7c is thicker than 20 nm, the proportion of the barrier layer 7 with respect to the cross-sectional area of the electrode finger increases, and the proportion of the first layer 5 decreases, and thus the resistance of the electrode finger increases.

[0063] As in this embodiment, the second layer 6 is preferably provided on the first layer 5. In this case, the periphery of the first layer 5 is covered with the barrier layer 7 and the second layer 6. Thereby, the diffusion of Cu in the first layer 5 into the protective film 8 can be effectively suppressed. In addition to this, the oxidation of Cu in the first layer 5 can also be suppressed.

[0064] Here, one example of a method of manufacturing the elastic wave device 1 in the first embodiment will be described. First, the electrode pattern for the first layer 5 and the second layer 6 are formed on the piezoelectric substrate 2, for example, by a lift-off method or the like. The electrode pattern for the first layer 5 is formed of a metal in which 0.1 to 20 atomic % of Mn is added to Cu. In addition, the electrode pattern for the first layer 5 and the second layer 6 can also be patterned by etching each metal layer.

[0065] Next, heat treatment is performed at 200 to 400°C for about one hour. At this time, the Mn in the electrode pattern combines with oxygen in the atmosphere to form an oxide film on the side surface of the electrode pattern. Further, the Mn combines with oxygen in the piezoelectric substrate 2 to form an oxide film on the bottom surface of the electrode pattern. On the other hand, the upper surface of the electrode pattern is covered with the second layer 6. Thus, the oxidation of the Mn does not progress. In addition, the bottom surface is the surface on the lower side in the Figure 2 . The upper surface is the surface on the upper side in the Figure 2 . With the oxidation of the Mn, the Mn in the electrode pattern further moves to the bottom surface and the side surface of the electrode pattern. As a result, the oxidation of the Mn progresses. Thereby, the first layer 5 as a Cu layer is formed of the electrode pattern including a mixture of Cu and Mn. Further, the barrier layer 7 including an oxide of Mn is formed on the first main surface 5a and the side surface 5c of the first layer 5. The electrode finger region is not formed in the portion between the electrode fingers on the piezoelectric substrate 2 and the like, and the barrier layer 7 is not directly formed. In addition, the reflectors 9A and 9B are also formed at the same time as the IDT electrodes 3. Then, the protective film 8 is formed on the piezoelectric substrate 2 by a sputtering method or the like so as to cover the IDT electrodes 3.

[0066] Before the above heat treatment is performed, that is, in a state in which a small amount of Mn is mixed in the Cu layer as the electrode pattern, the resistivity of the Cu layer is also high and does not have the barrier property against the diffusion of Cu. With the heat treatment, the Mn moves to the outside and forms an oxide film, whereby the barrier property is obtained, the Mn concentration of the Cu portion in the center portion decreases and becomes close to pure Cu, and thus the resistivity decreases, and the effects of the present application can be obtained.

[0067] The first layer 5 can also have Mn remaining as long as Cu is the main component. The concentration of the Mn in the first layer 5 is preferably 0.02 atomic % or less. In this case, the increase in the resistivity with respect to pure Cu can be made small. However, as described above, the first layer 5 preferably includes Cu that does not contain impurities. In this case, the resistivity can be further reduced.

[0068] As a metal element which takes the same action as Mn and forms a stable oxide film, for example, there are Al, Mg, Sn, and the like. However, among the above-mentioned metal elements, the metal element which most reduces the resistance of the electrode finger when added to Cu in order to form the barrier layer 7 is Mn. On the other hand, when Ag is added in addition to the above-mentioned metal, the power resistance of the IDT electrode 3 can be improved.

[0069] In addition, in the case where the protective film 8 is an oxide such as SiO2, the above-mentioned heat treatment can be performed after the electrode pattern is formed, instead of after the protective film 8 is formed. In this case, Mn does not form an oxide film by combining with oxygen in the atmosphere, but by combining with oxygen in the protective film 8.

[0070] However, it is not necessary to form the protective film 8. In the case where the protective film 8 is not formed, the above-mentioned heat treatment can be performed after the electrode pattern is formed. Figure 5 In the modification of the first embodiment shown in FIG. 6, the protective film 8 is not formed on the piezoelectric substrate 2. In this case, as with the first embodiment, diffusion between Cu of the first layer 5 and the piezoelectric substrate 2 can be more reliably suppressed.

[0071] Figure 6 is a lateral cross-sectional view of an electrode finger in the second embodiment.

[0072] The present embodiment differs from the first embodiment in that, in the IDT electrode 23, the barrier layer 27 covers the first main surface 5a, the second main surface 5b, and the side surface 5c of the first layer 5, and the second layer 6 is not provided. Except for the above-mentioned aspect, the elastic wave device of the present embodiment has the same structure as the elastic wave device 1 of the first embodiment.

[0073] By the barrier layer 27 covering the side surface 5c and the second main surface 5b of the first layer 5, diffusion of Cu of the first layer 5 to the protective film 8 can be suppressed. Further, by the barrier layer 27 covering the first main surface 5a of the first layer 5, as with the first embodiment, diffusion between Cu of the first layer 5 and the piezoelectric substrate 2 can be more reliably suppressed.

[0074] When forming the IDT electrode 23 of this embodiment, for example, the second layer 6 is not provided, and a heat treatment is performed in the same manner as when forming the IDT electrode 3 of the first embodiment. At this time, Mn in the electrode pattern of the first layer 5 combines with oxygen in the atmosphere on the side surface and the top surface of the electrode pattern to form an oxide film. Furthermore, on the bottom surface of the electrode pattern, it combines with oxygen in the piezoelectric substrate 2 to form an oxide film. With the oxidation of Mn, Mn in the electrode pattern further moves to the bottom surface, side surface and top surface of the electrode pattern. Thus, the oxidation of Mn proceeds. As a result, the first layer 5, which is a Cu layer, is formed from the electrode pattern containing a mixture of Cu and Mn. Furthermore, a barrier layer 27 containing an oxide of Mn is formed on the first main surface 5a, the side surface 5c and the second main surface 5b of the first layer 5.

[0075] like Figure 6 As shown, the barrier layer 27 has a first connecting portion 27d and a second connecting portion 27e. More specifically, the first connecting portion 27d is the portion of the barrier layer 27 that connects the portion disposed on the side surface 5c of the first layer 5 and the portion disposed on the first main surface 5a. The second connecting portion 27e is the portion of the barrier layer 27 that connects the portion disposed on the side surface 5c of the first layer 5 and the portion disposed on the second main surface 5b. In this embodiment, the shapes of the first connecting portion 27d and the second connecting portion 27e in the cross-section of the IDT electrode 23 are those of connecting straight lines. The first connecting portion 27d and the second connecting portion 27e are configured as corners. Furthermore, the first connecting portion 27d is configured as a corner at both the boundary between the barrier layer 27 and the protective film 8, and at both the boundary between the barrier layer 27 and the first layer 5. Similarly, the second connecting portion 27e is configured as a corner at the boundaries of the aforementioned two boundaries.

[0076] However, the shapes of the first connecting portion 27d and the second connecting portion 27e are not limited to the shapes described above. Figure 7 In the modified example of the second embodiment shown, the first connecting portion 27x and the second connecting portion 27y of the barrier layer 27A have curved shapes. More specifically, the second connecting portion 27y has a curved shape at both the boundary between the barrier layer 27A and the protective film 8, and at the boundary between the barrier layer 27A and the first layer 5. The first connecting portion 27x is configured as a corner at the boundary between the barrier layer 27A and the protective film 8. On the other hand, the first connecting portion 27x has a curved shape at the boundary between the barrier layer 27A and the first layer 5.

[0077] Figure 8 This is a cross-sectional view of the electrode finger in the third embodiment.

[0078] The present embodiment differs from the first embodiment in that a dielectric film 33 is provided between the piezoelectric substrate 2 and the IDT electrode 3. The elastic wave device of the present embodiment has the same structure as the elastic wave device 1 of the first embodiment except for the above aspect.

[0079] By providing the dielectric film 33, it is possible to adjust the electromechanical coupling coefficient to an appropriate value, and to effectively suppress diffusion between the Cu of the first layer 5 and the piezoelectric substrate 2. The thickness of the dielectric film 33 is preferably 1% or less of the wavelength λ. Thereby, it is possible to suppress the electromechanical coupling coefficient from becoming too small. Thus, the insertion loss is less likely to become large.

[0080] Figure 9 is a front sectional view of the elastic wave device according to the fourth embodiment.

[0081] The present embodiment differs from the first embodiment in that the piezoelectric substrate 42 is a laminated substrate of a support substrate 43 and a piezoelectric layer 44. The piezoelectric layer 44 is provided on the support substrate 43. The IDT electrode 3 is provided on the piezoelectric layer 44. The elastic wave device of the present embodiment has the same structure as the elastic wave device 1 of the first embodiment except for the above aspect.

[0082] The piezoelectric layer 44 contains lithium niobate. However, the material of the piezoelectric layer 44 is not limited to the above material, and for example, lithium tantalate, zinc oxide, aluminum nitride, quartz, PZT, or the like can also be used.

[0083] The support substrate 43 contains silicon. However, the material of the support substrate 43 is not limited to the above material, and for example, various ceramics such as alumina, lithium tantalate, lithium niobate, quartz, piezoelectrics, alumina, sapphire, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, bulk talc, forsterite, dielectrics such as diamond, glass, semiconductors such as gallium nitride, or resins, or the like can also be used.

[0084] In the present embodiment, the IDT electrode 3 is also configured as in the first embodiment. Thus, it is possible to more reliably suppress diffusion of Cu constituting the IDT electrode 3 to the piezoelectric substrate 42 and the protective film 8. The thickness of the piezoelectric layer 44 is preferably 1λ or less. In this case, it is possible to improve the excitation efficiency of the elastic wave.

[0085] Figure 10 is a front sectional view of the elastic wave device according to the fifth embodiment.

[0086] The present embodiment differs from the fourth embodiment in that the support substrate 53 has a hollow portion 53a and a support portion 53b. The elastic wave device of the fifth embodiment has the same structure as the elastic wave device of the fourth embodiment except for the above aspect.

[0087] The hollow portion 53a supporting the substrate 53 is surrounded by the support portion 53b and is open on the piezoelectric layer 44 side. The substrate 53 supports the piezoelectric layer 44 at the support portion 53b. In this case, the excitation efficiency of the elastic wave can be effectively improved.

[0088] In the present embodiment, the IDT electrode 3 is configured similarly to the fourth embodiment. Thus, the diffusion of Cu constituting the IDT electrode 3 to the piezoelectric substrate 52 and the protective film 8 can be more reliably suppressed.

[0089] Figure 11 is a front sectional view of an elastic wave device according to the sixth embodiment.

[0090] The present embodiment differs from the fifth embodiment in that the elastic wave device 61 utilizes a bulk wave of a thickness shear first mode. More specifically, in the present embodiment, in a case where the thickness of the piezoelectric layer 44 is set to d and the electrode finger pitch of the IDT electrode 3 is set to p, d / p is 0.5 or less. By being configured in such a manner, a bulk wave of a thickness shear first mode can be utilized as a main mode. In addition, the elastic wave device 61 does not have a reflector. Except for the above aspect, the elastic wave device 61 of the present embodiment has the same configuration as the elastic wave device of the fifth embodiment.

[0091] In a case where a bulk wave of a thickness shear first mode is utilized, even if the number of electrode fingers in the reflector is reduced, the propagation loss is small. Thus, the miniaturization of the elastic wave device 61 can be effectively promoted. Furthermore, because the IDT electrode 3 is configured similarly to the fifth embodiment, the diffusion of Cu constituting the IDT electrode 3 to the piezoelectric substrate 52 and the protective film 8 can be more reliably suppressed.

[0092] Explanation of Reference Numerals

[0093] 1: elastic wave device;

[0094] 2: piezoelectric substrate;

[0095] 3: IDT electrode;

[0096] 5: first layer;

[0097] 5a, 5b: first main surface, second main surface;

[0098] 5c: side surface;

[0099] 6: second layer;

[0100] 7: barrier layer;

[0101] 7a, 7c: first portion, second portion;

[0102] 8: protective film;

[0103] 9A, 9B: reflector

[0104] 18a, 18b: first bus bar, second bus bar

[0105] 19a, 19b: first electrode finger, second electrode finger

[0106] 23: IDT electrode

[0107] 27, 27A: barrier layer

[0108] 27d, 27e: first connecting portion, second connecting portion

[0109] 27x, 27y: first connecting portion, second connecting portion

[0110] 33: dielectric film

[0111] 42: piezoelectric substrate

[0112] 43: support substrate

[0113] 44: piezoelectric layer

[0114] 52: piezoelectric substrate

[0115] 53: support substrate

[0116] 53a: hollow portion

[0117] 53b: support portion

[0118] 61: elastic wave device

[0119] 107, 117: NiCr layer

Claims

1. An elastic wave device comprising: a piezoelectric substrate; and an IDT electrode having an outer layer and an electrode layer, and having a plurality of electrode fingers, the outer layer being provided on the piezoelectric substrate, the electrode layer being provided on the outer layer and having Cu as a main component, the electrode layer including: a first main surface on the piezoelectric substrate side; a second main surface opposite to the first main surface; and a side surface connecting the first main surface and the second main surface, the outer layer covering the first main surface and the side surface of the electrode layer, a thickness of a portion of the outer layer covering the first main surface of the electrode layer is thinner than a thickness of a portion of the outer layer covering the side surface of the electrode layer, and the outer layer includes an oxide of a metal.

2. The elastic wave device according to claim 1, further comprising: a protective film provided on the piezoelectric substrate so as to cover the IDT electrode.

3. The elastic wave device according to claim 1 or 2, wherein: the electrode layer is a first layer of the IDT electrode, and the IDT electrode further has a second layer provided on the second main surface of the first layer.

4. The elastic wave device according to claim 1 or 2, wherein: the outer layer covers the first main surface, the side surface, and the second main surface of the electrode layer.

5. The elastic wave device according to claim 1, wherein: the outer layer includes an oxide of a metal selected from a group including Mn, Al, Mg, and Sn.

6. The elastic wave device according to claim 5, wherein: the outer layer includes an oxide of Mn.

7. The elastic wave device according to claim 1 or 2, wherein: the piezoelectric substrate has a support substrate and a piezoelectric layer provided on the support substrate.

8. The elastic wave device according to claim 1 or 2, further comprising: a dielectric film provided between the piezoelectric substrate and the IDT electrode, and a thickness of the dielectric film is 1% or less of a wavelength defined by an electrode finger pitch of the IDT electrode when the wavelength is set to λ. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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