Elastic wave device

Abstract

The invention provides an elastic wave device which can improve the power resistance of electrode fingers of an IDT electrode and reduce the resistance. This elastic wave device is provided with a piezoelectric substrate (2) and an IDT electrode (7) provided on the piezoelectric substrate (2). The IDT electrode (7) has an adhesion layer (12) provided on the piezoelectric substrate (2), a Cu-Al alloy layer (13) provided on the adhesion layer (12), and an Al electrode layer (14) provided on the Cu-Al alloy layer (13) and having a weight percentage concentration [wt%] of Al higher than 50 wt%. The Cu-Al alloy layer (13) and the Al electrode layer (14) are epitaxial layers. The thickness of the Cu-Al alloy layer (13) is 40% or less of the total thickness of the Cu-Al alloy layer (13) and the Al electrode layer (14).

Description

Technical Field

[0001] The present invention relates to elastic wave devices. Background Art

[0002] In the past, elastic wave devices have been widely used in filters for portable phones and the like. An example of an elastic wave device is disclosed in the following patent document 1. In the elastic wave device described in patent document 1, an IDT (Interdigital Transducer) electrode is provided on a piezoelectric substrate. The IDT electrode is composed of stacked metal films. Specifically, a Ti film, an AlCu film, and a Ti film are stacked in sequence. In addition, the AlCu film is set as an epitaxial film.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2015-088896 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] In recent years, there has been a demand for further improvement in the power handling performance of elastic wave devices. However, when an AlCu alloy in which Cu is added to an Al electrode is used as the material of the IDT electrode as in the elastic wave device described in Patent Document 1, the power handling performance is often insufficient. Furthermore, when a Ti film is provided on the AlCu film, the stress applied to the AlCu film increases, and the power handling performance may be deteriorated.

[0008] An object of the present invention is to provide an elastic wave device capable of improving the power handling capability of electrode fingers of an IDT electrode and reducing the electrical resistance.

[0009] Technical solutions to solve problems

[0010] The elastic wave device according to the present invention comprises a piezoelectric substrate and an IDT electrode arranged on the piezoelectric substrate, wherein the IDT electrode has a bonding layer arranged on the piezoelectric substrate, a Cu-Al alloy layer arranged on the bonding layer, and an Al electrode layer arranged on the Cu-Al alloy layer and having an Al weight percentage concentration [wt%] higher than 50wt%, wherein the Cu-Al alloy layer and the Al electrode layer are epitaxial layers, and the thickness of the Cu-Al alloy layer is less than 40% of the total thickness of the Cu-Al alloy layer and the Al electrode layer.

[0011] Effects of the Invention

[0012] According to the elastic wave device of the present invention, it is possible to improve the power handling capability of the electrode fingers of the IDT electrode and reduce the resistance. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0014] Figure 2 It is along Figure 1 Cross-sectional view of line II in FIG.

[0015] Figure 3 This is a front cross-sectional view showing an enlarged view of the vicinity of one electrode finger of the IDT electrode in the first embodiment of the present invention.

[0016] Figure 4 This is a diagram showing an example of the boundary between the Cu—Al alloy layer and the Al electrode layer of the electrode finger of the IDT electrode in the first embodiment of the present invention.

[0017] Figure 5 This is a front cross-sectional view showing, in an enlarged manner, the vicinity of one electrode finger of the IDT electrode in the second comparative example.

[0018] Figure 6 It is a diagram showing the relationship between the resistance of the electrode fingers of the IDT electrode and the failure power in the first embodiment of the present invention and the first to third comparative examples.

[0019] Figure 7 It is a front cross-sectional view of an elastic wave device according to a first modified example of the first embodiment of the present invention.

[0020] Figure 8 It is a front cross-sectional view of an elastic wave device according to a second modified example of the first embodiment of the present invention. DETAILED DESCRIPTION

[0021] Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings to clarify the present invention.

[0022] In addition, it should be noted that each embodiment described in this specification is an example, and some structures can be replaced or combined among different embodiments.

[0023] Figure 1 It is a plan view of the elastic wave device according to the first embodiment of the present invention. Figure 2 It is along Figure 1 Cross-sectional view of line II in FIG.

[0024] like Figure 1 as well as Figure 2As shown, the elastic wave device 1 has a piezoelectric substrate 2. The piezoelectric substrate 2 is a laminated substrate including a piezoelectric layer 6. In addition, the piezoelectric substrate 2 may be a substrate composed only of a piezoelectric material. That is, the piezoelectric substrate may be a substrate as long as it has piezoelectricity. An IDT electrode 7 is provided on the piezoelectric substrate 2. More specifically, an IDT electrode 7 is provided on the piezoelectric layer 6 in the piezoelectric substrate 2.

[0025] like Figure 1 As shown, the IDT electrode 7 has a first bus bar 16 and a second bus bar 17 and a plurality of first electrode fingers 18 and a plurality of second electrode fingers 19. The first bus bar 16 and the second bus bar 17 are opposite to each other. One end of the plurality of first electrode fingers 18 is respectively connected to the first bus bar 16. One end of the plurality of second electrode fingers 19 is respectively connected to the second bus bar 17. The plurality of first electrode fingers 18 and the plurality of second electrode fingers 19 are interlaced with each other. In the following, the first electrode fingers 18 and the second electrode fingers 19 are sometimes recorded only as electrode fingers.

[0026] By applying an AC voltage to the IDT electrode 7, elastic waves are excited. In addition, in the present embodiment, when the direction in which the plurality of electrode fingers extend is set as the electrode finger extension direction, the elastic wave propagation direction is orthogonal to the electrode finger extension direction. A pair of reflectors 8A and 8B are provided on the piezoelectric layer 6. The reflectors 8A and 8B are opposed to each other with the IDT electrode 7 sandwiched therebetween in a direction orthogonal to the electrode finger extension direction.

[0027] Figure 3 This is a front cross-sectional view showing an enlarged view of the vicinity of one electrode finger of the IDT electrode in the first embodiment.

[0028] The IDT electrode 7 has a plurality of electrode layers. Specifically, the IDT electrode 7 has a bonding layer 12, a Cu-Al alloy layer 13, an Al electrode layer 14, and a Ti layer 15. More specifically, a bonding layer 12 is provided on the piezoelectric substrate 2. A Cu-Al alloy layer 13 is provided on the bonding layer 12. An Al electrode layer 14 is provided on the Cu-Al alloy layer 13. A Ti layer 15 is provided on the Al electrode layer 14. However, the Ti layer 15 may not necessarily be provided on the Al electrode layer 14.

[0029] The adhesion layer 12, Cu-Al alloy layer 13, Al electrode layer 14 and Ti layer 15 in the IDT electrode 7 are electrode layers that have been epitaxially grown. In this specification, the so-called epitaxial layer refers to an electrode layer composed of an oriented film that has been epitaxially grown. Furthermore, in this specification, the so-called oriented film that has been epitaxially grown refers to a polycrystalline film with a twin crystal structure. Whether the electrode layer is an epitaxial layer can be confirmed by performing pole measurement using an X-ray diffraction method. When the electrode layer has a twin crystal structure, the diffraction pattern has multiple symmetry centers. In this case, the electrode layer is an epitaxial layer.

[0030] The lattice constant of the adhesion layer 12 is a size between the lattice constant of the Cu-Al alloy layer 13 and the lattice constant of the portion of the piezoelectric substrate 2 where the adhesion layer 12 is provided. In addition, in the present embodiment, the portion of the piezoelectric substrate 2 where the adhesion layer 12 is provided is the piezoelectric layer 6. Therefore, the lattice constant of the adhesion layer 12 is a size between the lattice constant of the Cu-Al alloy layer 13 and the lattice constant of the piezoelectric layer 6. Thus, the adhesion layer 12 can be set as an epitaxial layer, and the Cu-Al alloy layer 13 can be set as an epitaxial layer. In addition, in the case where the piezoelectric substrate 2 is a substrate composed only of piezoelectric material, the lattice constant of the adhesion layer 12 is a size between the lattice constant of the Cu-Al alloy layer 13 and the lattice constant of the piezoelectric substrate 2.

[0031] In the present embodiment, the adhesion layer 12 is a Ti layer. However, the material of the adhesion layer 12 is not limited to Ti. As the material of the adhesion layer 12, for example, Cr or Ti, or an alloy with Cr or Ti as the main component can be used. In addition, in this specification, the so-called main component refers to a component that accounts for more than 50wt% of the entire component. The material of the above-mentioned main component can also exist in any state of single crystal, polycrystalline and amorphous or in a state where they are mixed.

[0032] In the Al electrode layer 14, the weight percentage concentration [wt%] of Al is higher than 50wt%, and it becomes an electrode layer with Al as the main body. In addition, in the Al electrode layer 14, Al is preferably 80wt% or more, more preferably 90wt% or more, and further preferably 95wt% or more. In the Al electrode layer 14, when the weight percentage concentration of Al is high, the resistance of the electrode fingers of the IDT electrode 7 can be appropriately reduced. In the Al electrode layer 14 of the present embodiment, 1wt% of Cu is added to Al. Therefore, the Al in the Al electrode layer 14 is 99wt%.

[0033] The present embodiment is characterized in that the Cu-Al alloy layer 13 and the Al electrode layer 14 are epitaxial layers, and the thickness of the Cu-Al alloy layer 13 is less than 40% of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14. As a result, the crystallinity of the Cu-Al alloy layer 13 and the Al electrode layer 14 can be effectively improved. As a result, the power resistance of the electrode fingers of the IDT electrode 7 can be improved and the resistance can be reduced. The details of this effect are described below together with the details of the structure of the present embodiment.

[0034] First, the details of the structure of this embodiment will be described. Figure 2 As shown, the piezoelectric substrate 2 includes a supporting substrate 3, a high-acoustic-velocity film 4 as a high-acoustic-velocity material layer, a low-acoustic-velocity film 5, and a piezoelectric layer 6. The high-acoustic-velocity film 4 is provided on the supporting substrate 3. The low-acoustic-velocity film 5 is provided on the high-acoustic-velocity film 4. The piezoelectric layer 6 is provided on the low-acoustic-velocity film 5.

[0035] The piezoelectric layer 6 in the elastic wave device 1 is made of lithium tantalate. In this specification, the term "a certain member is made of a certain material" includes the case where a trace amount of impurities is contained to such an extent that the electrical characteristics of the elastic wave device are not significantly deteriorated. However, the material of the piezoelectric layer 6 is not limited to the above, and for example, lithium niobate, zinc oxide, aluminum nitride, quartz, or PZT (lead zirconate titanate) can be used.

[0036] The low-acoustic-velocity film 5 is a film having a relatively low acoustic velocity. More specifically, the acoustic velocity of the body wave propagating in the low-acoustic-velocity film 5 is lower than the acoustic velocity of the body wave propagating in the piezoelectric layer 6. In the present embodiment, the low-acoustic-velocity film 5 is made of silicon oxide. However, the material of the low-acoustic-velocity film 5 is not limited to the above, and for example, dielectrics such as glass, silicon oxide, silicon oxynitride, lithium oxide, tantalum oxide, or compounds of silicon oxide to which fluorine, carbon, or boron is added, or materials having the above materials as main components can be used.

[0037] The high-acoustic-velocity material layer is a layer with a relatively high acoustic velocity. The acoustic velocity of the body wave propagating in the high-acoustic-velocity material layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer 6. In the present embodiment, the high-acoustic-velocity material layer is a high-acoustic-velocity film 4. The high-acoustic-velocity film 4 is made of silicon nitride. However, the material of the high-acoustic-velocity material layer is not limited to the above. For example, piezoelectrics such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, forsterite, spinel, ceramics such as sialon, dielectrics such as aluminum oxide, silicon oxynitride, DLC (diamond-like carbon), and diamond, or semiconductors such as silicon, or materials with the above materials as the main component can also be used. In addition, the above-mentioned spinel contains aluminum compounds containing one or more elements selected from Mg, Fe, Zn, Mn, etc. and oxygen. As examples of the above-mentioned spinel, MgAl 2 O 4、FeAl 2 O 4 、ZnAl 2 O 4 、MnAl 2 O 4 .

[0038] In the present embodiment, the support substrate 3 is made of silicon. However, the material of the support substrate 3 is not limited to the above, and for example, piezoelectric materials such as aluminum nitride, lithium tantalate, lithium niobate, and quartz, ceramics such as alumina, sapphire, magnesium oxide, silicon nitride, silicon carbide, zirconium oxide, cordierite, mullite, steatite, and forsterite, dielectrics such as diamond and glass, semiconductors such as silicon and gallium nitride, or resins, or materials mainly composed of the above materials can be used.

[0039] On the piezoelectric substrate 2 of the elastic wave device 1, a high acoustic velocity film 4 as a high acoustic velocity material layer, a low acoustic velocity film 5, and a piezoelectric layer 6 are sequentially stacked. Thus, the energy of the elastic wave can be effectively confined in the piezoelectric layer 6 side.

[0040] Moreover, as described above, in the IDT electrode 7, the thickness of the Cu-Al alloy layer 13 is less than 40% of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14. In this specification, the relationship of the thickness includes the following relationship. That is, the relationship includes the following situation: in a portion of the Cu-Al alloy layer 13 that is less than 20% of the bottom area of ​​the Cu-Al alloy layer 13 when viewed from above, the thickness of the Cu-Al alloy layer 13 exceeds 40% of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14. In addition, in this specification, the so-called top view refers to the view from the direction equivalent to Figure 2 Observe from the top of the middle. Figure 2 For example, of the support substrate 3 side and the piezoelectric layer 6 side, the piezoelectric layer 6 side is the upper side.

[0041] As an example, Figure 4 As shown in FIG. 1 , the boundary between the Cu-Al alloy layer 13 and the Al electrode layer 14 is not actually linear. This is because, during the manufacturing process, a heat load is applied to the IDT electrode 7, thereby promoting diffusion between Cu in the Cu-Al alloy layer 13 and Al in the Al electrode layer 14. Due to this diffusion, the thickness of a portion of the Cu-Al alloy layer 13 may become extremely thick relative to the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14.

[0042] exist Figure 4In the example shown, in the portion of the Cu-Al alloy layer 13 that is 80% of the bottom area of ​​the Cu-Al alloy layer 13, the thickness of the Cu-Al alloy layer 13 is 40% or less of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14. On the other hand, in the portion of the Cu-Al alloy layer 13 that is 20% of the bottom area of ​​the Cu-Al alloy layer 13, the thickness of the Cu-Al alloy layer 13 exceeds 40% of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14. In this case as well, the thickness of the Cu-Al alloy layer 13 is made 40% or less of the total thickness of the Cu-Al alloy layer 13 and the Al electrode layer 14.

[0043] In this embodiment, it is possible to improve the power resistance of the electrode fingers of the IDT electrode 7 and reduce the resistance. Hereinafter, the details of this effect will be described by comparing this embodiment with the first to third comparative examples.

[0044] The first comparative example is different from the first embodiment in that the thickness of the Cu-Al alloy layer exceeds 40% of the total thickness of the Cu-Al alloy layer and the Al electrode layer. The second comparative example is different from the first embodiment in the stacked structure of the IDT electrode. Specifically, Figure 5 As shown, in the second comparative example, the adhesion layer 12, the Cu-added Al layer 104, and the Ti layer 15 are stacked in this order. The third comparative example is different from the first embodiment in that all electrode layers in the IDT electrode are not epitaxial layers.

[0045] A plurality of elastic wave devices having the structure of the first embodiment and a plurality of elastic wave devices of the first to third comparative examples were prepared, and a power withstand test was performed on each elastic wave device. In the power withstand test, a certain power was applied to the elastic wave device for a certain period of time, and the applied power was increased by +0.125 dBm without causing a failure. By repeating this operation, the failure power of the elastic wave device was obtained. A plurality of elastic wave devices were prepared in the first embodiment, the second comparative example, and the third comparative example. The resistance of the electrode fingers of the IDT electrode was made different between the plurality of elastic wave devices. In the first comparative example, the resistance of the electrode fingers was one type. Thus, the relationship between the resistance of the electrode fingers and the failure power was obtained in the first embodiment and the first to third comparative examples. In addition, in this specification, the sheet resistance [mΩ / □] is used as the resistance of the electrode fingers. The design parameters of the elastic wave device having the structure of the first embodiment are as follows.

[0046] Support substrate: Material: silicon, thickness: 125μm

[0047] High acoustic velocity membrane: material is SiN, thickness is 300nm

[0048] Low acoustic velocity membrane: material is SiO 2 , thickness is 300nm

[0049] Piezoelectric layer: Material: LiTaO 3 , thickness is 400nm

[0050] Layer structure of IDT electrode: Adhesion layer (Ti layer) / Cu-Al alloy layer / Al electrode layer / Ti layer from the piezoelectric layer side

[0051] Thickness of the adhesive layer (Ti layer): 12nm

[0052] Thickness of Cu-Al alloy layer: 20nm or 40nm

[0053] The atomic ratio of Cu and Al in Cu-Al alloy is: Cu:Al=1:1

[0054] Total thickness of Cu-Al alloy layer and Al electrode layer: 100 nm

[0055] Materials added to the Al electrode layer: Cu, with a weight percentage concentration of 1wt%

[0056] Thickness of Ti layer: 4nm

[0057] In the first comparative example, the thickness of the Cu-Al alloy layer in the IDT electrode is different from that in the first embodiment. More specifically, the thickness of the Cu-Al alloy layer in the first comparative example is 80 nm. In addition, the total thickness of the Cu-Al alloy layer and the Al electrode layer is 100 nm.

[0058] In the second comparative example, the layer structure of the IDT electrode and the thickness of each layer are different from those in the first embodiment. The design parameters related to the layer structure of the IDT electrode and the thickness of each layer in the second comparative example are as follows.

[0059] Layer structure of IDT electrode: Adhesion layer (Ti layer) / Cu-doped Al layer / Ti layer from the piezoelectric layer side

[0060] Thickness of the adhesive layer (Ti layer): 12nm

[0061] Thickness of Cu-added Al layer: 100nm

[0062] Cu weight percentage concentration in Cu-added Al layer: 10wt%, 20wt% or 30wt%

[0063] Thickness of Ti layer: 4nm

[0064] In the third comparative example, the range of the thickness of the Cu-Al alloy layer in the IDT electrode is different from that in the first embodiment. More specifically, the thickness of the Cu-Al alloy layer in the third comparative example is set to 20 nm, 40 nm, or 80 nm. In addition, the total thickness of the Cu-Al alloy layer and the Al electrode layer is 100 nm.

[0065] Figure 6 It is a diagram showing the relationship between the resistance of the electrode fingers of the IDT electrode and the failure power in the first embodiment and the first to third comparative examples. Figure 6 The numerical values ​​near the plot points showing the results of the first embodiment, the first comparative example, and the third comparative example in show the thickness of the Cu-Al alloy layer. In addition, the total thickness of the Cu-Al alloy layer and the Al electrode layer is set to 100 nm. Therefore, for example, when the thickness of the Cu-Al alloy layer is 40 nm, the thickness of the Cu-Al alloy layer is 40% of the total thickness of the Cu-Al alloy layer and the Al electrode layer. On the other hand, Figure 6 The numerical values ​​near the plot points showing the results of the second comparative example in show the weight percentage concentration of Cu in the Cu-added Al layer.

[0066] like Figure 6 As shown, it can be seen that in the first embodiment, the failure power is higher than that in the first to third comparative examples. Therefore, it can be seen that in the first embodiment, the power resistance can be improved. In addition, it can be seen that in the first embodiment, the resistance of the electrode fingers of the IDT electrode is as low as less than 650 mΩ / □.

[0067] In addition, the difference between the first comparative example and the first embodiment is that the ratio of the thickness of the Cu-Al alloy layer to the thickness of the Cu-Al alloy layer and the Al electrode layer exceeds 40%. In the first comparative example, the power resistance is greatly deteriorated compared with the first embodiment. It can be considered that this is because the crystal state of the Cu-Al alloy layer deteriorates when the thickness of the Cu-Al alloy layer is too thick. In contrast, in the first embodiment, the thickness of the Cu-Al alloy layer is less than 40% of the total thickness of the Cu-Al alloy layer and the Al electrode layer. Thus, the crystal state of the Cu-Al alloy layer can be made good, and the power resistance can be improved.

[0068] In the second comparative example, Figure 6As shown, when the amount of Cu added in the Cu-added Al layer is small, the resistance of the electrode fingers is low. However, in this case, the power resistance is low. On the other hand, when the amount of Cu added in the Cu-added Al layer is large, the power resistance becomes higher, but the resistance of the electrode fingers becomes higher. Moreover, when the weight percentage concentration of Cu in the Cu-added Al layer is 30wt%, the resistance of the electrode fingers becomes higher than when the concentration is 20wt%. However, the power resistance of both parties is at the same level. In contrast, in the first embodiment, a Cu-Al alloy layer and an Al electrode layer are stacked, and the ratio of the thickness of the Cu-Al alloy layer to the thickness of the Cu-Al alloy layer and the Al electrode layer is less than 40%. As a result, it is possible to take into account both improving the power resistance of the electrode fingers and reducing the resistance.

[0069] according to Figure 6 It is clear that in the first embodiment and the third comparative example, when the thickness of the Cu-Al alloy layer is the same, the resistance of the electrode fingers in the first embodiment is lower than the resistance of the electrode fingers in the third comparative example. Furthermore, the power resistance in the first embodiment is higher than the power resistance in the third comparative example. This is because, in the first embodiment, each electrode layer of the IDT electrode is an epitaxial layer. More specifically, in the first embodiment, the crystal state of the Cu-Al alloy layer and the Al electrode layer is good. Therefore, when a heat load is applied to the IDT electrode in the manufacturing process, the diffusion between the Cu of the Cu-Al alloy layer and the Al of the Al electrode layer can be suppressed. Thus, the resistance of the electrode fingers can be suppressed from becoming higher. In addition, because the crystallinity of the Cu-Al alloy layer and the Al electrode layer is good, when a voltage is applied, even if stress is applied to the electrode fingers, the electrode fingers are not easily damaged. Therefore, the power resistance can be improved.

[0070] like Figure 3 As shown, in the first embodiment, the Ti layer 15 is provided on the Al electrode layer 14. In addition, the Ti layer 15 may not necessarily be provided. However, it is preferred that the Ti layer 15 is provided on the Al electrode layer 14. More preferably, the Ti layer 15 is an epitaxial layer. Thus, the power resistance can be effectively improved.

[0071] In more detail, stress is applied to the electrode fingers due to the provision of the Ti layer 15. In contrast, in the laminate of the Cu-Al alloy layer 13 and the Al electrode layer 14 in the first embodiment, the strength against stress is high. Therefore, the influence of the above stress due to the provision of the Ti layer 15 is small. On the other hand, by providing the Ti layer 15, the effect of protecting the Al electrode layer 14 can be obtained. Therefore, the power resistance can be effectively improved.

[0072] On the other hand, Figure 5The Cu-added Al layer 104 of the second comparative example shown does not have high strength against stress. This is because the weight percentage concentration of Cu in the Cu-added Al layer 104 is not high enough. In a structure in which the Ti layer 15 is provided on the Cu-added Al layer 104, the influence of stress applied to the Cu-added Al layer 104 is large, and the power resistance is likely to be reduced. Therefore, the structure having the Ti layer 15 is preferred in the first embodiment of the present invention.

[0073] Back to Figure 3 In the present invention, the composition ratio of the alloy in the Cu-Al alloy layer 13 is not particularly limited. For example, the Cu-Al alloy layer 13 may also be composed of CuAl 2 However, in the Cu-Al alloy layer 13, it is preferred that the weight percentage concentration of the Cu-Al alloy having an atomic ratio of Cu to Al of 1:1 is 50 wt % or more. This can further improve the power resistance.

[0074] In addition, you can also Figure 2 The dielectric film is provided on the piezoelectric substrate 2 shown so as to cover the IDT electrode 7. In this case, the IDT electrode 7 is protected by the dielectric film and is not easily damaged. As a material of the dielectric film, for example, silicon oxide, silicon nitride, or silicon nitride oxide can be used.

[0075] In the first embodiment, the piezoelectric substrate 2 is a stacked substrate including a piezoelectric layer 6. In the piezoelectric substrate 2, the piezoelectric layer 6 is indirectly provided on the high acoustic velocity film 4 as a high acoustic velocity material layer via the low acoustic velocity film 5. However, the structure of the piezoelectric substrate 2 is not limited to the above. Hereinafter, a first variant and a second variant of the first embodiment are shown, in which only the structure of the piezoelectric substrate 2 is different from that of the first embodiment. In the first variant and the second variant, as in the first embodiment, the power resistance of the electrode fingers of the IDT electrode 7 can be improved and the resistance can be reduced. In addition, the energy of the elastic wave can be effectively confined on the side of the piezoelectric layer 6.

[0076] exist Figure 7 In the first modification shown, the high-acoustic-velocity material layer of the piezoelectric substrate 22A is a high-acoustic-velocity supporting substrate 24. A low-acoustic-velocity film 5 is provided on the high-acoustic-velocity supporting substrate 24. A piezoelectric body layer 6 is provided on the low-acoustic-velocity film 5.

[0077] exist Figure 8 In the second modification shown, the piezoelectric substrate 22B does not include the low acoustic velocity film 5. More specifically, the high acoustic velocity film 4 is provided on the support substrate 3. The piezoelectric layer 6 is directly provided on the high acoustic velocity film 4.

[0078] In addition, the stacked structure of the piezoelectric substrate may also be a structure other than the first variant and the second variant. For example, a piezoelectric layer may be directly provided on a high-acoustic-velocity support substrate as a high-acoustic-velocity material layer. In this case, as in the first embodiment, the resistance of the electrode fingers of the IDT electrode can be reduced, and the power resistance can be improved. In addition, the energy of the elastic wave can be effectively confined on the piezoelectric layer side.

[0079] Alternatively, as described above, the piezoelectric substrate may be a substrate made of only a piezoelectric material. In this case, as in the first embodiment, the resistance of the electrode fingers of the IDT electrode can be reduced and the power handling performance can be improved.

[0080] Examples of aspects of the elastic wave device according to the present invention are summarized below.

[0081] <1>

[0082] An elastic wave device comprises a piezoelectric substrate and an IDT electrode arranged on the piezoelectric substrate, wherein the IDT electrode comprises a bonding layer arranged on the piezoelectric substrate, a Cu-Al alloy layer arranged on the bonding layer, and an Al electrode layer arranged on the Cu-Al alloy layer and having a weight percentage concentration [wt%] of Al higher than 50wt%, wherein the Cu-Al alloy layer and the Al electrode layer are epitaxial layers, and the thickness of the Cu-Al alloy layer is less than 40% of the total thickness of the Cu-Al alloy layer and the Al electrode layer.

[0083] <2>

[0084] The elastic wave device according to <1>,

[0085] The IDT electrode has a Ti layer provided on the Al electrode layer.

[0086] <3>

[0087] The elastic wave device according to <2>, wherein:

[0088] The Ti layer is an epitaxial layer.

[0089] <4>

[0090] The elastic wave device according to any one of <1> to <3>,

[0091] In the Cu-Al alloy layer, a weight percent concentration [wt%] of a Cu-Al alloy having an atomic ratio of Cu to Al of 1:1 is 50wt% or more.

[0092] <5>

[0093] The elastic wave device according to any one of <1> to <4>,

[0094] The piezoelectric substrate includes a high-acoustic-velocity material layer and a piezoelectric layer disposed on the high-acoustic-velocity material layer. The IDT electrode is disposed on the piezoelectric layer. The acoustic velocity of the bulk wave propagating in the high-acoustic-velocity material layer is higher than the acoustic velocity of the elastic wave propagating in the piezoelectric layer.

[0095] <6>

[0096] The elastic wave device according to <5>, wherein:

[0097] A low-acoustic-velocity film is provided between the high-acoustic-velocity material layer and the piezoelectric layer, and an acoustic velocity of a bulk wave propagating through the low-acoustic-velocity film is lower than an acoustic velocity of a bulk wave propagating through the piezoelectric layer.

[0098] <7>

[0099] The elastic wave device according to <5> or <6>, wherein:

[0100] The high acoustic velocity material layer is a high acoustic velocity supporting substrate.

[0101] <8>

[0102] The elastic wave device according to <5> or <6>, wherein:

[0103] The piezoelectric substrate has a supporting substrate, and the high-acoustic-velocity material layer is a high-acoustic-velocity film provided on the supporting substrate.

[0104] Description of Reference Numerals

[0105] 1: Elastic wave device;

[0106] 2: Piezoelectric substrate;

[0107] 3: Support base plate;

[0108] 4: High sound velocity membrane;

[0109] 5: Low sound velocity membrane;

[0110] 6: piezoelectric layer;

[0111] 7: IDT electrode;

[0112] 8A, 8B: reflectors;

[0113] 12: Adhesion layer;

[0114] 13: Cu-Al alloy layer;

[0115] 14: Al electrode layer;

[0116] 15: Ti layer;

[0117] 16, 17: Bus bar 1, bus bar 2;

[0118] 18, 19: first electrode finger, second electrode finger;

[0119] 22A, 22B: piezoelectric substrate;

[0120] 24: high acoustic velocity support substrate;

[0121] 104: Cu added Al layer.

Claims

1. An elastic wave device comprising: a piezoelectric substrate; and IDT electrodes are provided on the piezoelectric substrate. The IDT electrode comprises: a bonding layer disposed on the piezoelectric substrate; a Cu-Al alloy layer disposed on the bonding layer; and an Al electrode layer disposed on the Cu-Al alloy layer, wherein the weight percentage concentration of Al is higher than 50wt%, wherein: The unit of weight percentage concentration is wt%, The Cu-Al alloy layer and the Al electrode layer are epitaxial layers, The thickness of the Cu—Al alloy layer is less than or equal to 40% of the total thickness of the Cu—Al alloy layer and the Al electrode layer.

2. The elastic wave device according to claim 1, wherein: The IDT electrode has a Ti layer provided on the Al electrode layer.

3. The elastic wave device according to claim 2, wherein: The Ti layer is an epitaxial layer.

4. The elastic wave device according to any one of claims 1 to 3, wherein: In the Cu-Al alloy layer, the weight percentage concentration of the Cu-Al alloy having an atomic ratio of Cu to Al of 1:1 is greater than 50 wt %, wherein the unit of the weight percentage concentration is wt %.

5. The elastic wave device according to any one of claims 1 to 4, wherein: The piezoelectric substrate comprises a high-acoustic-velocity material layer and a piezoelectric layer provided on the high-acoustic-velocity material layer. The IDT electrode is provided on the piezoelectric layer. The acoustic velocity of the bulk wave propagating through the high-acoustic-velocity material layer is higher than the acoustic velocity of the elastic wave propagating through the piezoelectric layer.

6. The elastic wave device according to claim 5, wherein: A low acoustic velocity film is provided between the high acoustic velocity material layer and the piezoelectric layer. The acoustic velocity of the bulk wave propagating through the low-acoustic-velocity film is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer.

7. The elastic wave device according to claim 5 or 6, wherein: The high acoustic velocity material layer is a high acoustic velocity supporting substrate.

8. The elastic wave device according to claim 5 or 6, wherein: The piezoelectric substrate has a supporting substrate. The high acoustic velocity material layer is a high acoustic velocity film disposed on the supporting substrate.

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