Elastic wave device

Abstract

The present application improves the electric power resistance while suppressing the characteristic degradation. An elastic wave device (1) includes a piezoelectric substrate (2) and an electrode (60). The electrode (60) is formed on the piezoelectric substrate (2). The electrode (60) has a first layer (601) and a second layer (602). The first layer (601) contains Al and Cu. The second layer (602) is formed on the side opposite to the piezoelectric substrate (2) side of the first layer (601) and contains Al. The first layer (601) has at least a part of Al crystals (611) and CuAl2 grains (612) arranged in a direction orthogonal to a thickness direction (D1) of the piezoelectric substrate (2). In the electrode (60), the CuAl2 grains (612) do not reach a main surface (621) of the second layer (602) on the side opposite to the first layer (601) side.

Description

Technical Field

[0001] The present invention generally relates to elastic wave devices, and more specifically, to elastic wave devices having electrodes. Background Technology

[0002] Conventionally, as an elastic wave device, a surface acoustic wave element having a piezoelectric substrate and electrodes formed on the piezoelectric substrate is known (for example, see Patent Document 1).

[0003] In the surface acoustic wave element described in Patent Document 1, the electrode has a layer comprising aluminum and copper. In this layer, columnar grains comprising an aluminum-copper alloy are formed at the grain boundaries of the columnar grains comprising aluminum.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-13815 Summary of the Invention

[0007] The technical problem that the invention aims to solve

[0008] In the surface acoustic wave element described in Patent Document 1, when the copper concentration of the electrode is increased in order to further improve the electrical resistance, there is a problem that the resistance increases and the characteristics of the surface acoustic wave element tend to decrease.

[0009] The purpose of this invention is to provide an elastic wave device that can improve electrical resistance while suppressing the degradation of characteristics.

[0010] Solutions for solving technical problems

[0011] One aspect of the present invention relates to an elastic wave device comprising a piezoelectric substrate and electrodes. The electrodes are formed on the piezoelectric substrate. The electrodes have a first layer and a second layer. The first layer comprises Al and Cu. The second layer, formed on the side of the first layer opposite to the piezoelectric substrate side, comprises Al. The first layer has at least a portion of Al crystals and CuAl2 grains arranged in a direction orthogonal to the thickness direction of the piezoelectric substrate. In the electrodes, the CuAl2 grains do not reach the main surface of the second layer opposite to the side of the first layer.

[0012] One aspect of the present invention relates to an elastic wave device comprising a piezoelectric substrate and electrodes. The electrodes are formed on the piezoelectric substrate. The electrodes have a first layer and a second layer. The first layer comprises Al and Cu. The second layer, formed on the side of the first layer opposite to the piezoelectric substrate side, comprises Cu. The first layer has Al crystals and CuAl2 grains arranged in a direction orthogonal to the thickness direction of the piezoelectric substrate. In the electrodes, the CuAl2 grains do not reach the main surface of the second layer opposite to the side of the first layer.

[0013] Invention Effects

[0014] The elastic wave device described above by the present invention can improve electrical resistance while suppressing the decline in characteristics. Attached Figure Description

[0015] Figure 1 This is a top view of the elastic wave device according to Embodiment 1.

[0016] Figure 2 This is a cross-sectional view of the same elastic wave device.

[0017] Figure 3 This is a longitudinal sectional view of the electrodes of the same elastic wave device.

[0018] Figure 4 This is a cross-sectional view of the electrodes of the same elastic wave device.

[0019] Figure 5 This is a schematic diagram of an STEM (Scanning Transmission Electron Microscope) image of the same elastic wave device.

[0020] Figure 6 A~ Figure 6 F is a process cross-sectional view used to illustrate the manufacturing method of the elastic wave device described above.

[0021] Figure 7 This is an explanatory diagram illustrating the manufacturing method of the elastic wave device mentioned above.

[0022] Figure 8 This is a graph showing the relationship between Cu concentration, normalized resistivity, and electrical resistance of the same elastic wave device.

[0023] Figure 9 This is a longitudinal sectional view of the electrodes of the elastic wave device according to a variation of Embodiment 1.

[0024] Figure 10 This is a longitudinal sectional view of the elastic wave device according to Embodiment 2.

[0025] Figure 11 This is an explanatory diagram illustrating the manufacturing method of the elastic wave device mentioned above.

[0026] Figure 12 This is a cross-sectional view of the elastic wave device according to Embodiment 3.

[0027] Figure 13 This is a cross-sectional view of the elastic wave device according to Embodiment 4. Detailed Implementation

[0028] The following implementation methods, etc., refer to Figures 1-4 , Figure 6 A~ Figure 6 F, Figure 7 as well as Figures 9-13 These are all schematic diagrams, and the size and thickness ratios of the constituent elements in the diagrams may not necessarily reflect the actual size ratios.

[0029] (Implementation Method 1)

[0030] (1) Overall structure of elastic wave device

[0031] The following is for reference Figures 1-5 The elastic wave device 1 according to Embodiment 1 will be described.

[0032] The elastic wave device 1 includes a piezoelectric substrate 2 and an IDT (Interdigital Transducer) electrode 6. The IDT electrode 6 is formed on the piezoelectric substrate 2. The IDT electrode 6 has two electrodes 60.

[0033] In addition, the elastic wave device 1 also includes two reflectors 7. The two reflectors 7 are formed on the piezoelectric substrate 2. One of the two reflectors 7 is provided on one side and one side of the IDT electrode 6 in the direction along the propagation direction of the elastic wave.

[0034] In addition, the elastic wave device 1 also includes a wiring portion 8 connected to the IDT electrode 6. The wiring portion 8 is formed on the piezoelectric substrate 2.

[0035] Furthermore, the elastic wave device 1 also has a protective film 9 covering the IDT electrode 6, each reflector 7, and each wiring portion 8 on the piezoelectric substrate 2 (see reference). Figure 2 ).exist Figure 1 The protective film 9 is omitted from the illustration. Alternatively, the elastic wave device 1 may also have a structure without the protective film 9.

[0036] Although an IDT electrode 6 is formed on the piezoelectric substrate 2 in the elastic wave device 1, the number of IDT electrodes 6 is not limited to one, and there can be multiple IDT electrodes 6. That is, the elastic wave device 1 can also have multiple IDT electrodes 6. In this case, the elastic wave device 1 can, for example, be configured as a bandpass filter by electrically connecting multiple surface acoustic wave resonators, each containing multiple IDT electrodes 6.

[0037] (2) Components of an elastic wave device

[0038] (2.1) Piezoelectric substrate

[0039] In the elastic wave device 1 according to Embodiment 1, the piezoelectric substrate 2 is a piezoelectric substrate. The material of the piezoelectric substrate is, for example, lithium tantalate (LiTaO3). The piezoelectric substrate is formed, for example, from a Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal. The Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal is a LiTaO3 single crystal cut with a plane whose normal is an axis rotated Γ° from the Y-axis to the Z-axis with the X-axis as the central axis, with the three crystal axes of the LiTaO3 piezoelectric single crystal set as the X-axis, Y-axis, and Z-axis, and it is a single crystal in which surface acoustic waves propagate in the X-axis direction. If the cutting angle is set to Γ [°] and the Euler angle of the piezoelectric substrate is set to The cutting angle of the piezoelectric substrate is then Γ = θ + 90°. Here, Γ and Γ ± 180 × n are synonymous (crystallographically equivalent). Here, n is a natural number. The piezoelectric substrate is not limited to a Γ°Y-cut X-propagated LiTaO3 piezoelectric single crystal; for example, it can also be a Γ°Y-cut X-propagated LiTaO3 piezoelectric ceramic.

[0040] The piezoelectric substrate 2 has a first main surface 21 and a second main surface 22 facing each other. The first main surface 21 and the second main surface 22 are facing each other in the thickness direction D1 of the piezoelectric substrate 2. When viewed from the thickness direction D1 of the piezoelectric substrate 2, the piezoelectric substrate 2 is rectangular, but it is not limited to this, for example, it can also be square.

[0041] The material of the piezoelectric substrate is not limited to lithium tantalate (LiTaO3), and can also be, for example, lithium niobate (LiNbO3), zinc oxide (ZnO), aluminum nitride (AlN), or lead zirconate titanate (PZT). When the piezoelectric substrate is made of, for example, a Y-cut X-propagating LiNbO3 piezoelectric single crystal or piezoelectric ceramic, the elastic wave device 1 can utilize a Love wave as the elastic wave, thereby using a mode with SH wave as the main component as the master mode. Furthermore, the single crystal material and cutting angle of the piezoelectric substrate can be appropriately determined, for example, according to the required specifications of the filter (filter characteristics such as pass-through characteristics, attenuation characteristics, temperature characteristics, and bandwidth).

[0042] (2.2) IDT electrode

[0043] The IDT electrode 6 is formed on the piezoelectric substrate 2. More specifically, the IDT electrode 6 is formed on the first main surface 21 of the piezoelectric substrate 2.

[0044] As described above, the IDT electrode 6 has two electrodes 60. Each of the two electrodes 60 is conductive. The two electrodes 60 are separated from each other and electrically insulated from each other. Hereinafter, in the description distinguishing the two electrodes 60 from each other, one of the two electrodes 60 will be referred to as the first electrode 60A, and the other electrode 60 will be referred to as the second electrode 60B.

[0045] The first electrode 60A is comb-shaped when viewed from the thickness direction D1 of the piezoelectric substrate 2. The first electrode 60A has a first busbar 61 and a plurality of first electrode fingers 63. The first busbar 61 is a conductor portion for setting the plurality of first electrode fingers 63 to the same potential. The second electrode 60B is comb-shaped when viewed from the thickness direction D1 of the piezoelectric substrate 2. The second electrode 60B has a second busbar 62 and a plurality of second electrode fingers 64. The second busbar 62 is a conductor portion for setting the plurality of second electrode fingers 64 to the same potential (equipotential). In the IDT electrode 6, the first busbar 61 and the second busbar 62 are opposite each other.

[0046] Multiple first electrode fingers 63 are connected to the first busbar 61 and extend toward the second busbar 62. The multiple first electrode fingers 63 are integrally formed with the first busbar 61 and are separate from the second busbar 62.

[0047] Multiple second electrode fingers 64 are connected to the second busbar 62 and extend toward the first busbar 61. The multiple second electrode fingers 64 are integrally formed with the second busbar 62 and are separate from the first busbar 61.

[0048] IDT electrode 6 is, for example, a standard type of IDT electrode. The IDT electrode 6 will be described in more detail below.

[0049] The first busbar 61 and the second busbar 62 of the IDT electrode 6 are elongated strips with a second direction D2, orthogonal to the thickness direction D1 (first direction) of the piezoelectric substrate 2, as their long side direction. In other words, the first busbar 61 and the second busbar 62 of the IDT electrode 6 are elongated strips with the second direction D2, which is the direction of elastic wave propagation, as their long side direction. In the IDT electrode 6, the first busbar 61 and the second busbar 62 are opposite each other in a third direction D3, orthogonal to both the thickness direction D1 and the second direction D2 of the piezoelectric substrate 2. In other words, the first busbar 61 and the second busbar 62 are opposite each other in the third direction D3, which is the direction in which the first electrode finger 63 and the second electrode finger 64, described later, extend.

[0050] A plurality of first electrode fingers 63 are connected to a first busbar 61 and extend toward a second busbar 62. Here, the plurality of first electrode fingers 63 extend from the first busbar 61 along a third direction D3. The tips of the plurality of first electrode fingers 63 are separated from the second busbar 62. For example, the plurality of first electrode fingers 63 are of the same length and the same width as each other.

[0051] A plurality of second electrode fingers 64 are connected to a second busbar 62 and extend toward a first busbar 61. Here, the plurality of second electrode fingers 64 extend from the second busbar 62 along a third direction D3. The leading edge of each of the plurality of second electrode fingers 64 is separate from the first busbar 61. For example, the plurality of second electrode fingers 64 are of the same length and the same width. Figure 1 In the example, the lengths of the plurality of second electrode fingers 64 are the same as the lengths of the plurality of first electrode fingers 63. Furthermore, in... Figure 1 In the example, the width of the plurality of second electrode fingers 64 is the same as the width of the plurality of first electrode fingers 63.

[0052] In the IDT electrode 6, a plurality of first electrode fingers 63 and a plurality of second electrode fingers 64 are arranged alternately and spaced apart from each other in the second direction D2. Therefore, adjacent first electrode fingers 63 and second electrode fingers 64 are separated. A group of electrode fingers containing a plurality of first electrode fingers 63 and a plurality of second electrode fingers 64 can be a structure in which the plurality of first electrode fingers 63 and a plurality of second electrode fingers 64 are arranged spaced apart in the second direction D2, or it can be a structure in which the plurality of first electrode fingers 63 and a plurality of second electrode fingers 64 are not alternately spaced apart. For example, it is also possible to have a region where the first electrode fingers 63 and the second electrode fingers 64 are arranged spaced apart from each other and a region where two of the first electrode fingers 63 or the second electrode fingers 64 are arranged in the second direction D2.

[0053] The IDT electrode 6 has an intersection region defined by a plurality of first electrode fingers 63 and a plurality of second electrode fingers 64. The intersection region is the area between the envelope of the leading edge of the plurality of first electrode fingers 63 and the envelope of the leading edge of the plurality of second electrode fingers 64. The IDT electrode 6 excites an elastic wave in the piezoelectric substrate 2 in the intersection region.

[0054] IDT electrode 6 is a standard type of IDT electrode, but it is not limited to this. For example, it can also be an IDT electrode with apodization weight applied, or it can be a tilted IDT electrode. In an IDT electrode with apodization weight applied, the cross width increases as one end approaches the center from the direction of elastic wave propagation, and decreases as the other end approaches the center from the direction of elastic wave propagation.

[0055] like Figure 1As shown, the electrode finger spacing P1 of the IDT electrode 6 is defined by the distance between the center lines of two adjacent first electrode fingers 63 or the distance between the center lines of two adjacent second electrode fingers 64. The distance between the center lines of two adjacent second electrode fingers 64 is the same as the distance between the center lines of two adjacent first electrode fingers 63.

[0056] In the IDT electrode 6 of the elastic wave device 1 according to Embodiment 1, the number of logarithms of the first electrode finger 63 and the second electrode finger 64 is, for example, 100. That is, as an example, the IDT electrode 6 has 100 first electrode fingers 63 and 100 second electrode fingers 64.

[0057] The specific construction of each of the two electrodes 60 will be explained in the section “(3) Construction of the electrodes” below.

[0058] (2.3) Reflector

[0059] In the elastic wave device 1, two reflectors 7 are formed on the first main surface 21 of the piezoelectric substrate 2. Each of the two reflectors 7 is conductive. Each of the two reflectors 7 is, for example, a short-circuit grid. Each reflector 7 reflects elastic waves.

[0060] Each of the two reflectors 7 has a plurality of electrode fingers 71, one end of which is short-circuited to the other, and the other end of which is short-circuited to the other. For example, the number of electrode fingers in each of the two reflectors 7 is 20. In the elastic wave device 1 according to Embodiment 1, each reflector 7 is a short-circuit grid, but it is not limited to this; for example, it can also be an open-circuit grid, a positive and negative reflective grid, or a grid combining a short-circuit grid and an open-circuit grid, etc.

[0061] In the elastic wave device 1, if each reflector 7 and IDT electrode 6 are made of the same material and are set to the same thickness, each reflector 7 and IDT electrode 6 can be formed in the same process when manufacturing the elastic wave device 1. The manufacturing method of the elastic wave device 1 will be explained in the section "(4) Manufacturing method of elastic wave device" described later.

[0062] In the elastic wave device 1, each reflector 7 is a short-circuit grid, but it is not limited to this. For example, it can also be an open-circuit grid, a positive and negative reflective grid, etc.

[0063] (2.4) Wiring Section

[0064] In elastic wave device 1, such as Figure 1 As shown, the wiring portion 8 is formed on the first main surface 21 of the piezoelectric substrate 2. The wiring portion 8 is conductive.

[0065] The wiring section 8 includes a first wiring section 81 and a second wiring section 82. The first wiring section 81 is connected to the first busbar 61 of the IDT electrode 6, and the second wiring section 82 is connected to the second busbar 62 of the IDT electrode 6. The first wiring section 81 and the second wiring section 82 are separate from each other and electrically insulated from each other.

[0066] The first wiring portion 81 extends from the first busbar 61 to the side opposite to the plurality of first electrode fingers 63. The first wiring portion 81 may be formed to repeat a portion of the first busbar 61 in the thickness direction D1 of the piezoelectric substrate 2, or it may be integrally formed with the first busbar 61 using the same material and the same thickness as the first busbar 61. Furthermore, the first wiring portion 81 may also have a laminated structure of a first lower layer integrally formed with the first busbar 61 and a first upper layer formed on the first lower layer.

[0067] The second wiring portion 82 extends from the second busbar 62 to the side opposite to the plurality of second electrode fingers 64. The second wiring portion 82 may be formed to repeat a portion of the second busbar 62 in the thickness direction D1 of the piezoelectric substrate 2, or it may be integrally formed with the second busbar 62 using the same material and having the same thickness as the second busbar 62. Furthermore, the second wiring portion 82 may also have a stacked structure of a second lower layer integrally formed with the second busbar 62 and a second upper layer formed on the second lower layer.

[0068] The materials of the first upper layer of the first wiring section 81 and the second upper layer of the second wiring section 82 are, for example, Al (aluminum), Cu (copper), Pt (platinum), Au (gold), Ti (titanium), Cr (chromium), or alloys based on any of these metals. The materials of the first upper layer of the first wiring section 81 and the second upper layer of the second wiring section 82 may be, for example, NiCr.

[0069] The elastic wave device 1 may also include a first terminal and a second terminal. The first terminal is connected to the first busbar 61 via a first wiring portion 81, and the second terminal is connected to the second busbar 62 via a second wiring portion 82. Furthermore, the elastic wave device 1 may also include two third wiring portions, one of which is connected to each of the two reflectors 7. In this case, each of the two reflectors 7 may also be connected to a third terminal via at least the third wiring portion. In the elastic wave device 1, the plurality of external connection terminals including the first terminal, the second terminal, and the third terminal are electrodes for electrical connection to the circuit board, the mounting substrate (heat sink substrate), etc., for the package. Furthermore, the elastic wave device 1 may also include a plurality of dummy terminals that are not electrically connected to the IDT electrode 6. These dummy terminals are terminals used to improve the parallelism of the elastic wave device 1 relative to the circuit board, the mounting substrate, etc., and are different from terminals intended for electrical connection. In other words, a dummy terminal is a terminal used to suppress elastic wave device 1 which is mounted at an angle relative to the circuit board, mounting board, etc. It may not necessarily be required depending on the number and configuration of external connection terminals and the outer peripheral shape of elastic wave device 1.

[0070] The first terminal is integrally formed with the first wiring portion 81, for example, using the same material and having the same thickness as the first wiring portion 81. The second terminal is integrally formed with the second wiring portion 82, for example, using the same material and having the same thickness as the second wiring portion 82. The third terminal is integrally formed with the third wiring portion, for example, using the same material and having the same thickness as the third wiring portion 81. The third wiring portion is formed with the same material and having the same thickness as both the first wiring portion 81 and the second wiring portion 82.

[0071] (2.5) Protective film

[0072] The protective film 9 covers the IDT electrode 6, the first wiring portion 81, the second wiring portion 82, the third wiring portion, and each reflector 7 and a portion of the first main surface 21 of the piezoelectric substrate 2.

[0073] The protective film 9 is made of silicon oxide, but is not limited to it; for example, it can also be made of silicon nitride. The protective film 9 is not limited to a single-layer structure; for example, it can also be a multilayer structure with two or more layers.

[0074] In the elastic wave device 1 according to Embodiment 1, the thickness of the protective film 9 is thinner than the thickness of the IDT electrode 6, and the surface of the protective film 9 has an uneven shape along the shape of the substrate of the protective film 9. In the elastic wave device 1, the surface of the protective film 9 may also be planarized to become planar. Alternatively, in the elastic wave device 1, the thickness of the protective film 9 may be thicker than the thickness of the IDT electrode 6, and the surface of the protective film 9 may have an uneven shape along the shape of the substrate of the protective film 9.

[0075] (3) Electrode construction

[0076] like Figure 3 As shown in Figure 4, each of the two electrodes 60 has a first layer 601 and a second layer 602. The first layer 601 is formed on the side of the piezoelectric substrate 2 closer to the second layer 602, and contains Al (aluminum) and Cu (copper). The second layer 602 is formed on the side of the first layer 601 opposite to the side of the piezoelectric substrate 2, and contains Al. The second layer 602 has a main surface 621 opposite to the side of the first layer 601. Preferably, each of the two electrodes 60 also has a close-fitting layer 600 between the piezoelectric substrate 2 and the first layer 601. The material of the close-fitting layer 600 is, for example, Ti (titanium), but is not limited to this; for example, it can also be Cr or NiCr. In each of the two electrodes 60, the thicknesses of the close-fitting layer 600, the first layer 601, and the second layer 602 are 12 nm, 78 nm, and 78 nm, respectively. The thicknesses of the close-fitting layer 600, the first layer 601, and the second layer 602 are examples and are not limited to these values.

[0077] The first layer 601 has Al crystals 611 and CuAl2 grains 612 arranged in a direction orthogonal to the thickness direction D1 of the piezoelectric substrate 2. Here, the phrase "Al crystals 611 and CuAl2 grains 612 are arranged in a direction orthogonal to the thickness direction D1" includes at least one of the first and second cases. The first case refers to a situation where, when viewed from the third direction D3 along a cross section of the electrode 60 along the second direction D2, which is the aforementioned elastic wave propagation direction, at least a portion of the Al crystals 611 and at least one CuAl2 grain 612 in the first layer 601 are arranged not along the thickness direction D1 but along the second direction D2, which is orthogonal to the thickness direction D1. The second case refers to a situation where, when viewed from the second direction D2 along a cross section of the electrode 60 along the third direction D3, at least a portion of the Al crystal 611 and at least one CuAl2 grain 612 in the first layer 601 are arranged not along the thickness direction D1 but along the third direction D3, which is orthogonal to the thickness direction D1. In this case, at least a portion of the Al crystal 611 and the CuAl2 grain 612 do not necessarily have to be arranged in a straight line. Furthermore, the CuAl2 grain 612 is a metallic compound of Cu and Al, with a Cu concentration of approximately 54 ± 10 wt%. Viewed from the thickness direction D1 of the piezoelectric substrate 2, the Al crystal 611 has a portion sandwiched between two CuAl2 grains 612. The first layer 601 has CuAl2 grains 612 sandwiched between portions of the Al crystals 611. The first layer 601 may contain at least CuAl2 grains 612 as long as it is an aluminum-copper alloy, or it may contain CuAl grains in addition to CuAl2 grains 612. The Al crystal 611 can be an Al single crystal or an Al polycrystalline material containing multiple Al grains. Each of the multiple Al grains is columnar, extending along the thickness direction D1 of the piezoelectric substrate 2. The thickness direction D1 of the piezoelectric substrate 2 is approximately orthogonal to the first principal surface 21 of the piezoelectric substrate 2. Viewed from the thickness direction D1 of the piezoelectric substrate 2, the grain size of the CuAl2 grain 612 is smaller than the width of the electrode 60 in the second direction D2. The term "CuAl2 grain" as used in embodiments, etc., is not limited to a substance having a completely crystalline structure. "CuAl2 grain" is acceptable as long as the substance is not amorphous; in other words, even if there are few grains, it is acceptable as long as the orientation of the crystal can be confirmed.

[0078] In each of the two electrodes 60, the CuAl2 grains 612 do not reach the main surface 621 of the second layer 602. This can be confirmed, for example, by observing the electrodes 60 of the sample of the elastic wave device 1 using a STEM (Scanning Transmission Electron Microscope).

[0079] In each of the two electrodes 60, from the viewpoint of improving the electrical resistance of the elastic wave device 1, it is preferable that the Cu concentration of the first layer 601 is 15 wt% or more. Furthermore, in each of the two electrodes 60, from the viewpoint of suppressing the degradation of the elastic wave device 1's characteristics due to the increase in the resistance of the electrodes 60, it is preferable that the Cu concentration of the first layer 601 is 30 wt% or less. The relationship between the Cu concentration of the first layer 601, resistivity, and electrical resistance will be explained in "(5) Operation and Characteristics of the Elastic Wave Device" described later. In each of the two electrodes 60, from the viewpoint of suppressing the degradation of characteristics due to stress migration, it is preferable that the Cu concentration of the second layer 602 is 0.1 wt% or more. However, in each of the two electrodes 60, it is also possible that the Cu concentration of the second layer 602 is 0 wt% and the Al concentration is 100 wt%. In each of the two electrodes 60, from the viewpoint of suppressing the degradation of the elastic wave device 1's characteristics due to the increase in the resistance of the electrodes 60, the Cu concentration of the second layer 602 is preferably 10 wt% or less.

[0080] In one embodiment of the elastic wave device 1, the Cu concentration of the first layer 601 is 20 wt%, and the Cu concentration of the second layer 602 is 1 wt%. Figure 5 This is a schematic diagram of a STEM image of the electrode 60 of an elastic wave device 1 according to one embodiment.

[0081] The Cu concentrations of the first layer 601 and the second layer 602 can be obtained, for example, by observing the electrode 60 of the sample of the elastic wave device 1 using STEM. The Cu concentration of the first layer 601 is the average value obtained by analyzing a first specific region of the first layer 601 in the STEM image using EDX (Energy Dispersive X-ray Spectroscopy). The Cu concentration of the second layer 602 is the average value obtained by analyzing a second specific region of the second layer 602 in the STEM image using EDX. The first specific region is the region between the lower surface 613 of the first layer 601 and the first reference plane RP1. The first reference plane RP1 is the surface above 10% of the combined thickness of the first layer 601 and the second layer 602, as observed from the lower surface 613 of the first layer 601. Figure 5 In the diagram, to the right of electrode 60, a scale is shown dividing the total thickness of the first layer 601 and the second layer 602 into 10 equal parts. The second specific region is the area between the main surface 621 of the second layer 602 and the second reference surface RP2. The second reference surface RP2 is the surface located below 10% of the total thickness of the first layer 601 and the second layer 602, as viewed from the main surface 621 of the second layer 602.

[0082] Furthermore, when the electrode 60 is observed in a cross-section orthogonal to the second direction D2 or the third direction D3, a portion is found where Al crystals 611 and CuAl2 grains 612 are arranged in a direction orthogonal to the thickness direction D1, thus confirming that the electrode 60 includes a first layer 601. Additionally, when the electrode 60 is observed in a cross-section orthogonal to the second direction D2 or the third direction D3, in the aforementioned second specific region, a portion is found where Al crystals 611 and CuAl2 grains 612 are not arranged in a direction orthogonal to the thickness direction D1, or where only Al crystals 611 are present in a direction orthogonal to the thickness direction D1, thus confirming that the electrode 60 includes a second layer 602.

[0083] (4) Manufacturing method of elastic wave device

[0084] The following is based on Figure 6 A~ Figure 6 The manufacturing method of the elastic wave device 1 will be described in section F.

[0085] In the manufacturing method of elastic wave device 1, steps 1 to 7 are performed.

[0086] In the first step, a piezoelectric substrate 2 having a first main surface 21 and a second main surface 22 facing each other is prepared (see reference). Figure 6 (A).

[0087] In the second process, such as Figure 6 As shown in B, a resist layer 11 is formed on the first main surface 21 of the piezoelectric substrate 2. Here, in the second process, the resist layer 11 is formed and patterned to expose the predetermined formation areas of each electrode 60 in the first main surface 21 of the piezoelectric substrate 2. Here, the resist layer 11 is patterned to expose not only the predetermined formation areas of each electrode 60 but also the predetermined formation areas of each reflector 7.

[0088] In the third process, such as Figure 6 As shown in Figure C, a laminated film is formed by vapor deposition of a bonding film 630, which forms the basis of the bonding layer 600; a first AlCu film 631, which forms the basis of the first layer 601; and a second AlCu film 632, which forms the basis of the second layer 602. The material of the bonding film 630 is, for example, Ti. The thickness of the bonding film 630 is, for example, 12 nm. The Cu concentration of the first AlCu film 631 is, for example, 15 wt% or more and 30 wt% or less. The thickness T1 of the first AlCu film 631 is... Figure 7 For example, 78 nm. The Cu concentration of the second AlCu film 632 is, for example, 0.5 wt% or more and 1 wt% or less. The thickness T2 of the second AlCu film 632 (refer to...) Figure 7For example, 78 nm. The thickness T1 of the first AlCu film 631 and the thickness T2 of the second AlCu film 632 are set such that the weight of the first layer 601 and the weight of the second layer 602 are approximately equal, but there is no particular limitation. The ratio of the thickness T1 of the first AlCu film 631 to the thickness T2 of the second AlCu film 632 can also be appropriately varied within a range where neither thickness T1 nor thickness T2 is 100% of T1+T2.

[0089] In step 4, the resist layer 11 and any unwanted film on it are removed by stripping, thereby patterning the laminated film (see reference). Figure 6 (D). Thus, in the fourth process, portions of the laminated film corresponding to each electrode 60 are left on the first main surface 21 of the piezoelectric substrate 2. Furthermore, in the fourth process, portions of the laminated film corresponding to each reflector 7 are also left. Here, the unused film is the portion of the laminated film formed on the resist layer 11 in the third process.

[0090] In the fifth step, heat treatment is performed to form the first layer 601 and the second layer 602 of each electrode 60 (see reference). Figure 6 (E). In summary, in the fifth step, each electrode 60, etc., is formed by performing the heat treatment described above. The heat treatment is performed, for example, in an N2 atmosphere. As for the conditions for heat treatment, for example, the heat treatment temperature is 270°C and the heat treatment time is 4 hours, but it is not limited to these values. The heat treatment temperature and heat treatment time can be set appropriately so that the first layer 601 containing Al crystals 611 and CuAl2 grains 612 can be formed by the heat treatment in the fifth step.

[0091] In step 6, the first wiring portion 81, the second wiring portion 82, the third wiring portion, the first terminal, the second terminal, and the third terminal are formed. The first wiring portion 81, the second wiring portion 82, the third wiring portion, the first terminal, the second terminal, and the third terminal are formed, for example, using thin film deposition technology, photolithography technology, and etching technology, but are not limited to these; they can also be formed using a stripping method. Furthermore, the first wiring portion 81, the second wiring portion 82, the third wiring portion, the first terminal, the second terminal, and the third terminal can also be formed in step 3. Alternatively, the lower layers of each of the first wiring portion 81, the second wiring portion 82, the third wiring portion, the first terminal, the second terminal, and the third terminal can be pre-formed in step 3, and the upper layers of each of the first wiring portion 81, the second wiring portion 82, the third wiring portion, the first terminal, the second terminal, and the third terminal can be formed in step 6.

[0092] In the 7th process, such as Figure 6As shown in F, a protective film 9 is formed covering the IDT electrode 6, the first wiring portion 81, the second wiring portion 82, the third wiring portion, and each reflector 7 on the first main surface 21 of the piezoelectric substrate 2, and a portion of the first main surface 21 of the piezoelectric substrate 2.

[0093] In the method for manufacturing the elastic wave device 1, when preparing the piezoelectric substrate 2 in the first step, a piezoelectric wafer capable of manufacturing multiple elastic wave devices 1 is prepared as the piezoelectric substrate 2. In the method for manufacturing the elastic wave device 1, after the seventh step, multiple elastic wave devices 1 (chips) are obtained by dicing the wafer containing multiple elastic wave devices 1. This method for manufacturing the elastic wave device 1 is an example and is not particularly limited. The fifth step can be performed after the fourth step, for example, after the sixth or seventh step. Furthermore, if the elastic wave device 1 has a resin portion as part of a package, the fifth step may also include a heat treatment to thermally cure the resin layer that forms the basis of the resin portion.

[0094] (5) Operation and characteristics of elastic wave devices

[0095] Figure 8 This diagram illustrates the relationship between Cu concentration, normalized resistivity of layer 601, and electrical withstand capability of elastic wave device 1 when the Cu concentration of the second layer 602 is set to 1 wt% and the Cu concentration of the first layer 601 is varied. Figure 8 In the diagram, the horizontal axis represents the Cu concentration of the first layer 601, the left vertical axis represents the normalized resistivity of the first layer 601, and the right vertical axis represents the electrical withstand capability of the elastic wave device 1. Here, the normalized resistivity is the resistivity of the first layer 601 with a Cu concentration of 1 wt% normalized to 1.0. Figure 8 In the diagram, solid circles represent normalized resistivity data, and hollow circles represent electrical resistance data.

[0096] according to Figure 8 From the viewpoint of further improving the electrical resistance of the elastic wave device 1, the Cu concentration of the first layer 601 is preferably 15 wt% or more. Furthermore, according to... Figure 8 From the viewpoint of suppressing the increase in resistance of electrode 60, the Cu concentration of the first layer 601 is preferably 30 wt% or less.

[0097] (6) Summary

[0098] The elastic wave device 1 according to Embodiment 1 includes a piezoelectric substrate 2 and an electrode 60. The electrode 60 is formed on the piezoelectric substrate 2. The electrode 60 has a first layer 601 and a second layer 602. The first layer 601 contains Al and Cu. The second layer 602 is formed on the side of the first layer 601 opposite to the piezoelectric substrate 2 side and contains Al. The first layer 601 has at least a portion of Al crystals 611 and CuAl2 grains 612 arranged in a direction orthogonal to the thickness direction D1 of the piezoelectric substrate 2. In the electrode 60, the CuAl2 grains 612 do not reach the main surface 621 of the second layer 602 opposite to the side of the first layer 601.

[0099] In the elastic wave device 1 according to Embodiment 1, the electrical resistance can be improved while suppressing the decline in characteristics.

[0100] In the elastic wave device 1 according to Embodiment 1, when an electric current is applied, the first layer 601, which is subjected to greater stress among the first layer 601 and the second layer 602, contains CuAl2 grains 612 with high tensile strength, thus improving the electric current resistance. Furthermore, in the elastic wave device 1 according to Embodiment 1, the CuAl2 grains 612 do not reach the main surface 621 of the second layer 602 opposite to the side of the first layer 601. Therefore, even when the Cu concentration of the CuAl2 grains increases and the electric current resistance of the electrode 60 is improved, the increase in resistance of the second layer 602 can be suppressed, and the degradation of the characteristics of the elastic wave device 1 can be suppressed.

[0101] (A variation of Implementation Method 1)

[0102] Reference Figure 9 The elastic wave device 1a according to the variation of Embodiment 1 will be described. Regarding the elastic wave device 1a according to the variation of Embodiment 1, the same reference numerals are used for the same constituent elements as those in the elastic wave device 1 according to Embodiment 1, and the description is omitted.

[0103] In the modified elastic wave device 1a, the difference from the elastic wave device 1 according to embodiment 1 is that each of the plurality of electrodes 60 further has an intermediate layer 603 located between the first layer 601 and the second layer 602. The intermediate layer 603 is located between the first layer 601 and the second layer 602 and functions as a barrier layer to suppress diffusion between the first layer 601 and the second layer 602.

[0104] The intermediate layer 603 is conductive. The material of the intermediate layer 603 is, for example, Ti, but is not limited to it; it can also be any of Cr, NiCr, Mo, or AlTi. The thickness of the intermediate layer 603 is, for example, 5 nm. From the viewpoint of suppressing the increase in resistance of the electrode 60, the thickness of the intermediate layer 603 is preferably 30 nm or less. Furthermore, from the viewpoint of thickness uniformity and reproducibility, the thickness of the intermediate layer 603 is preferably 4 nm or more.

[0105] The manufacturing method of the elastic wave device 1a in the modified example of Embodiment 1 is largely the same as that of the elastic wave device 1 in Embodiment 1, except that in the third step, a laminated film is formed by vapor deposition, which forms the base of the close-fitting layer 600, the first AlCu film which forms the base of the first layer 601, the barrier film which forms the base of the intermediate layer 603, and the second AlCu film which forms the base of the second layer 602. This prevents the CuAl2 grains 612 formed in the first layer 601 during the heat treatment in the fifth step from reaching the second layer 602. In other words, during the heat treatment in the fifth step, the precipitated CuAl2 grains are blocked in the intermediate layer 603, and the precipitation of CuAl2 grains 612 into the second layer 602 can be suppressed by the intermediate layer 603.

[0106] In the modified elastic wave device 1a, each of the plurality of electrodes 60 further has an intermediate layer 603 located between the first layer 601 and the second layer 602, thereby improving the electrical withstand capability. Furthermore, the intermediate layer 603 in the modified elastic wave device 1a allows for the suppression of size deviations in the CuAl2 grains 612 in the thickness direction D1 of the piezoelectric substrate 2, thus suppressing characteristic deviations.

[0107] (Implementation Method 2)

[0108] Reference Figure 10 The elastic wave device 1b according to Embodiment 2 will be described. Regarding the elastic wave device 1b according to Embodiment 2, the same reference numerals are used for the same constituent elements as those in the elastic wave device 1 according to Embodiment 1, and descriptions are omitted.

[0109] In the elastic wave device 1b according to Embodiment 2, the second layer 602 of the electrode 60 contains Cu. The Cu concentration of the second layer 602 is, for example, 100 wt%. The Al concentration of the second layer 602 is below the detection limit of EDX. The second layer 602 may also contain Al in addition to Cu. In this case, the Cu concentration is preferably 95 wt% or more.

[0110] The manufacturing method of the elastic wave device 1b according to Embodiment 2 is largely the same as the manufacturing method of the elastic wave device 1 according to Embodiment 1. The difference from the manufacturing method of the elastic wave device 1 according to Embodiment 1 is that, in the third step, a layer is formed on the first main surface 21 of the piezoelectric substrate 2 by vapor deposition. Figure 11 The laminated film shown is a composite film consisting of a bonding film 630 forming the base of the bonding layer 600, a first AlCu film 631 forming the base of the first layer 601, and a Cu film 633 forming the base of the second layer 602. The thicknesses of the bonding film 630, the first AlCu film 631, and the Cu film 633 are 12 nm, 78 nm, and 24 nm, respectively. The thickness T1 of the first AlCu film 631 and the thickness T3 of the Cu film 633 are set such that the weight of the first layer 601 and the weight of the second layer 602 are approximately equal, but this is not a limitation. The ratio of the thickness T1 of the first AlCu film 631 to the thickness T3 of the Cu film 633 can be appropriately varied within a range where neither thickness T1 nor thickness T3 is 100% of T1+T3. In the manufacturing method of the elastic wave device 1b according to Embodiment 2, except for the third step, it is the same as the manufacturing method of the elastic wave device 1 according to Embodiment 1.

[0111] The elastic wave device 1b according to Embodiment 2 includes a piezoelectric substrate 2 and an electrode 60. The electrode 60 is formed on the piezoelectric substrate 2. The electrode 60 has a first layer 601 and a second layer 602. The first layer 601 is formed on the piezoelectric substrate 2 side and contains Al and Cu. The second layer 602 is formed on the side of the first layer 601 opposite to the piezoelectric substrate 2 side and contains Cu. The first layer 601 has Al crystals 611 and CuAl2 grains 612 arranged in a direction orthogonal to the thickness direction D1 of the piezoelectric substrate 2. In the electrode 60, the CuAl2 grains 612 do not reach the main surface 621 of the second layer 602 opposite to the side of the first layer 601.

[0112] In the elastic wave device 1b according to Embodiment 2, the electrical resistance can be improved while suppressing the decline in characteristics.

[0113] (Implementation Method 3)

[0114] The following is for reference Figure 12 The elastic wave device 1c according to Embodiment 3 will be described.

[0115] The elastic wave device 1c according to Embodiment 3 differs from the elastic wave device 1 according to Embodiment 1 in that it has a piezoelectric substrate 2c instead of the piezoelectric substrate 2 of the elastic wave device 1 according to Embodiment 1. Regarding the elastic wave device 1c according to Embodiment 3, the same reference numerals are used for the same constituent elements as those in the elastic wave device 1 according to Embodiment 1, and descriptions are omitted.

[0116] The piezoelectric substrate 2c of the elastic wave device 1c is not a piezoelectric substrate like the piezoelectric substrate 2 of the elastic wave device 1 according to Embodiment 1, but a laminated substrate. Specifically, the piezoelectric substrate 2c is a laminated substrate including a support substrate 20, a low-velocity film 4, and a piezoelectric layer 5.

[0117] A low-velocity sound film 4 is disposed on the support substrate 20. Here, "disposed on the support substrate 20" includes both cases where it is directly disposed on the support substrate 20 and cases where it is indirectly disposed on the support substrate 20. A piezoelectric layer 5 is disposed on the low-velocity sound film 4. Here, "disposed on the low-velocity sound film 4" includes both cases where it is directly disposed on the low-velocity sound film 4 and cases where it is indirectly disposed on the low-velocity sound film 4. Each electrode 60 of the IDT electrode 6 is formed on the piezoelectric layer 5.

[0118] The piezoelectric substrate 2c will be described in more detail below.

[0119] The support substrate 20 has a first main surface 201 and a second main surface 202 facing each other. The first main surface 201 and the second main surface 202 are facing each other in the thickness direction D1 of the piezoelectric substrate 2c. Although the support substrate 20 is rectangular when viewed from the thickness direction D1 of the piezoelectric substrate 2c, it is not limited to this and may be square for example.

[0120] In the support substrate 20, the sound speed of the bulk wave propagating in the support substrate 20 is higher than that of the elastic wave propagating in the piezoelectric layer 5. Here, the bulk wave propagating in the support substrate 20 is the bulk wave with the lowest sound speed among the multiple bulk waves propagating in the support substrate 20.

[0121] The support substrate 20 is, for example, a silicon substrate. The thickness of the support substrate 20 is preferably 10λ (λ: the wavelength of the elastic wave determined by the electrode finger spacing P1) or more and 180 μm or less; for example, it is 120 μm. When the support substrate 20 is a silicon substrate, the orientation of the first main surface 201 of the support substrate 20 is, for example, the (100) surface, but it is not limited to this; for example, it could also be the (110) surface, the (111) surface, etc. The propagation direction of the elastic wave can be set without being limited by the orientation of the first main surface 201 of the support substrate 20.

[0122] The support substrate 20 is not limited to a silicon substrate. The support substrate 20 may contain at least one material selected from the group consisting of silicon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, sapphire, lithium tantalate, lithium niobate, quartz, bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, and diamond.

[0123] The piezoelectric layer 5 has a first main surface 51 and a second main surface 52 that are opposite each other. The first main surface 51 and the second main surface 52 are opposite each other in the thickness direction D1 of the piezoelectric substrate 2c.

[0124] The piezoelectric layer 5 is formed, for example, from a Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal. The Γ°Y-cut X-propagating LiTaO3 piezoelectric single crystal is formed by cutting a LiTaO3 single crystal with a plane whose normal is an axis rotated Γ° from the Y-axis to the Z-axis, with the three crystal axes of the LiTaO3 piezoelectric single crystal set as the X-axis, Y-axis, and Z-axis. Furthermore, it is a single crystal in which surface acoustic waves propagate in the X-axis direction. If the cutting angle is set to Γ [°] and the Euler angle of the piezoelectric layer 5 is set to... The cutting angle of piezoelectric layer 5 is then Γ = θ + 90°. Here, Γ and Γ ± 180 × n are synonymous (equivalent in crystallography). Here, n is a natural number. Piezoelectric layer 5 is not limited to a Γ°Y-cut X-propagated LiTaO3 piezoelectric single crystal; for example, it can also be a Γ°Y-cut X-propagated LiTaO3 piezoelectric ceramic.

[0125] For example, in the electrode finger spacing P1 of the IDT electrode 6 (refer to...) Figure 1 When the wavelength of the elastic wave, determined by the piezoelectric layer 5, is set to λ, the thickness of the piezoelectric layer 5 is 3.5λ or less. When the thickness of the piezoelectric layer 5 is 3.5λ or less, the Q value becomes higher. Furthermore, by setting the thickness of the piezoelectric layer 5 to 2.5λ or less, the TCF (Temperature Coefficient of Frequency) can be reduced. Moreover, by setting the thickness of the piezoelectric layer 5 to 1.5λ or less, the adjustment of the sound velocity of the elastic wave becomes easier. However, the thickness of the piezoelectric layer 5 is not limited to 3.5λ or less; it can also be greater than 3.5λ.

[0126] However, when the thickness of the piezoelectric layer 5 is 3.5λ or less, although the Q value increases as described above, higher-order modes are generated. In the elastic wave device 1c, the aforementioned low-velocity film 4 is provided, so that even when the thickness of the piezoelectric layer 5 is 3.5λ or less, higher-order modes are reduced.

[0127] In the elastic wave device 1c, the modes of the elastic wave propagating in the piezoelectric layer 5 include longitudinal waves, SH waves, SV waves, or a combination of these. In the elastic wave device 1c, the mode dominated by SH waves is used as the dominant mode. Higher-order modes refer to stray modes generated at higher frequencies than the dominant mode of the elastic wave propagating in the piezoelectric layer 5. Whether the mode of the elastic wave propagating in the piezoelectric layer 5 is "the mode dominated by SH waves" can be confirmed, for example, by using parameters of the piezoelectric layer 5 (material, Euler angles, and thickness, etc.), parameters of the IDT electrode 6 (material, thickness, and electrode finger spacing, etc.), and parameters of the low-velocity membrane 4 (material, thickness, etc.), analyzing the displacement distribution and strain using the finite element method. The Euler angles of the piezoelectric layer 5 can be obtained through analysis.

[0128] The material of the piezoelectric layer 5 is not limited to lithium tantalate (LiTaO3), and can also be, for example, lithium niobate (LiNbO3), zinc oxide (ZnO), aluminum nitride (AlN), or lead zirconate titanate (PZT). When the piezoelectric layer 5 is, for example, composed of a Y-cut X-propagating LiNbO3 piezoelectric single crystal or piezoelectric ceramic, the elastic wave device 1c can utilize a Love wave as the elastic wave, thereby using a mode dominated by SH waves as the primary mode. Furthermore, the single crystal material and cutting angle of the piezoelectric layer 5 can be appropriately determined, for example, according to the required specifications of the filter (filter characteristics such as pass-through characteristics, attenuation characteristics, temperature characteristics, and bandwidth).

[0129] The low-velocity membrane 4 is a membrane in which the velocity of the bulk wave propagating in the low-velocity membrane 4 is lower than the velocity of the bulk wave propagating in the piezoelectric layer 5.

[0130] In the elastic wave device 1c according to Embodiment 3, a low-velocity sound membrane 4 is disposed between the support substrate 20 and the piezoelectric layer 5. By disposing of the low-velocity sound membrane 4 between the support substrate 20 and the piezoelectric layer 5, the velocity of sound of the elastic wave is reduced. Elastic waves inherently possess the property of concentrating energy in a low-velocity medium. Therefore, the energy of the elastic wave can be effectively contained within the piezoelectric layer 5 and within the IDT electrode 6 that excites the elastic wave. As a result, compared to the case where the low-velocity sound membrane 4 is not disposed, losses can be reduced and the Q value can be increased.

[0131] The material of the low-velocity membrane 4 is, for example, silicon oxide. However, the material of the low-velocity membrane 4 is not limited to silicon oxide. The material of the low-velocity membrane 4 can also be, for example, silicon oxide, glass, silicon oxynitride, tantalum oxide, silicon oxide compounds with added fluorine, carbon, or boron, or materials with the above-mentioned materials as the main components.

[0132] When the low-velocity membrane 4 is made of silicon oxide, the temperature characteristics can be improved. Lithium tantalate has a negative temperature constant, while silicon oxide has a positive temperature constant. Therefore, in the elastic wave device 1c, the absolute value of TCF can be reduced.

[0133] If the wavelength of the elastic wave, determined by the electrode finger spacing P1, is set to λ, then the thickness of the low-velocity film 4 is preferably 2.0λ or less. The thickness of the low-velocity film 4 is, for example, 670 nm. By setting the thickness of the low-velocity film 4 to 2.0λ or less, the film stress can be reduced. As a result, during the manufacture of the elastic wave device 1c, the warpage of the silicon wafer that forms the basis of the support substrate 20 can be reduced, yield can be improved, and characteristics can be stabilized.

[0134] Furthermore, in the elastic wave device 1c, the piezoelectric substrate 2c may, for example, include a bonding layer between the low-velocity film 4 and the piezoelectric layer 5. This improves the adhesion between the low-velocity film 4 and the piezoelectric layer 5. The bonding layer may include, for example, a resin (epoxy resin, polyimide resin, etc.) or a metal. Furthermore, in the elastic wave device 1c, the piezoelectric substrate 2c is not limited to a bonding layer; a dielectric film may also be provided between the low-velocity film 4 and the piezoelectric layer 5, on the piezoelectric layer 5, or below the low-velocity film 4.

[0135] (Implementation Method 4)

[0136] Reference Figure 13 The elastic wave device 1d according to Embodiment 4 will be described. Regarding the elastic wave device 1d according to Embodiment 4, the same reference numerals are used for the same constituent elements as those in the elastic wave device 1c according to Embodiment 3, and the description is omitted.

[0137] The difference between the elastic wave device 1d according to Embodiment 4 and the elastic wave device 1c according to Embodiment 3 is that the piezoelectric substrate 2d is provided instead of the piezoelectric substrate 2c of the elastic wave device 1c according to Embodiment 3.

[0138] The difference between piezoelectric substrate 2d and piezoelectric substrate 2c is that it also has a high-velocity film 3.

[0139] The hypersonic membrane 3 is not positioned between the support substrate 20 and the low-velocity membrane 4. Here, the hypersonic membrane 3 is disposed on the support substrate 20. The term "disposed on the support substrate 20" includes both cases where it is directly disposed on the support substrate 20 and cases where it is indirectly disposed on the support substrate 20. The low-velocity membrane 4 is disposed on the hypersonic membrane 3. The term "disposed on the hypersonic membrane 3" includes both cases where it is directly disposed on the hypersonic membrane 3 and cases where it is indirectly disposed on the hypersonic membrane 3.

[0140] The hypersonic membrane 3 is a membrane in which the speed of sound of the bulk wave propagating in the hypersonic membrane 3 is higher than the speed of sound of the elastic wave propagating in the piezoelectric layer 5. The thickness of the hypersonic membrane 3 is, for example, 200 nm, 300 nm, or 400 nm.

[0141] The hypersonic membrane 3 functions to suppress energy leakage of the primary mode elastic wave into structures lower than the hypersonic membrane 3. In the elastic wave device 1d, when the thickness of the hypersonic membrane 3 is sufficiently thick, the energy of the primary mode elastic wave is distributed throughout the piezoelectric layer 5 and the low-velocity membrane 4, and also in a portion on the low-velocity membrane 4 side of the hypersonic membrane 3, but not on the support substrate 20. The mechanism by which the hypersonic membrane 3 blocks the elastic wave is the same as that of surface waves of the Love wave type, which are non-leaking SH waves, as described, for example, in the literature "Introduction to Simulation Technology of Surface Acoustic Wave Devices," Kenya Hashimoto, Realize Corporation, pp. 26-28. This mechanism differs from the mechanism by which a Bragg reflector composed of a multilayer acoustic membrane blocks the elastic wave.

[0142] The material of the hypersonic membrane 3 may be at least one material selected from the group consisting of diamond-like carbon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, piezoelectric material (lithium tantalate, lithium niobate, or quartz), bauxite, zirconium oxide, cordierite, mullite, block talc, forsterite, magnesium oxide, and diamond. The material of the hypersonic membrane 3 may also be a material whose main component is any of the above-mentioned materials, or a material whose main component is a mixture containing any of the above-mentioned materials.

[0143] Regarding the thickness of the hypersonic membrane 3, in order for the hypersonic membrane 3 to have the function of confining elastic waves within the piezoelectric layer 5 and the low-velocity membrane 4, the thicker the hypersonic membrane 3, the better. The piezoelectric substrate 2d can also serve as other membranes besides the hypersonic membrane 3, the low-velocity membrane 4, and the piezoelectric layer 5, and may have a bonding layer, a dielectric film, etc.

[0144] The above-described embodiments 1 to 4 are merely one of many embodiments of the present invention. Various modifications can be made to embodiments 1 to 4, etc., depending on design and other factors, as long as the objectives of the present invention are achieved.

[0145] For example, although the electrode 60 of the elastic wave device 1c in Embodiment 3 and the electrode 60 of the elastic wave device 1d in Embodiment 4 are the same as the electrode 60 of the elastic wave device 1 in Embodiment 1, they are not limited to this. They may also be the electrode 60 of the elastic wave device 1a in Modification 1 of Embodiment 1 or the electrode 60 of the elastic wave device 1b in Embodiment 2.

[0146] Furthermore, although the laminated film that forms the basis of the electrode 60 is formed by vapor deposition and stripping in the manufacturing method of the elastic wave device 1, it is not limited to this. For example, it can also be formed by vapor deposition, sputtering, photolithography, and etching.

[0147] Furthermore, elastic wave devices 1, 1a, and 1b can be trapezoidal filters having multiple IDT electrodes 6 on the piezoelectric substrate 2, or they can be longitudinally coupled resonator type filters. Similarly, elastic wave devices 1c and 1d can be trapezoidal filters having multiple IDT electrodes 6 on the piezoelectric substrates 2c and 2d, or they can be longitudinally coupled resonator type filters.

[0148] Furthermore, in the elastic wave device 1c according to Embodiment 3 or the elastic wave device 1d according to Embodiment 4, the piezoelectric layer 5 may be directly disposed on the support substrate 20.

[0149] (Way)

[0150] The following methods are disclosed in this specification.

[0151] The elastic wave device (1; 1a; 1c; 1d) according to the first embodiment includes a piezoelectric substrate (2; 2c; 2d) and an electrode (60). The electrode (60) is formed on the piezoelectric substrate (2; 2c; 2d). The electrode (60) has a first layer (601) and a second layer (602). The first layer (601) contains Al and Cu. The second layer (602) is formed on the side of the first layer (601) opposite to the piezoelectric substrate (2; 2c; 2d) side and contains Al. The first layer (601) has at least a portion of Al crystals (611) and CuAl2 grains (612) arranged in a direction orthogonal to the thickness direction (D1) of the piezoelectric substrate (2; 2c; 2d). In the electrode (60), the CuAl2 grains (612) do not reach the main surface (621) of the second layer (602) opposite to the side of the first layer (601).

[0152] In the elastic wave device (1; 1a; 1c; 1d) according to the first method, it is possible to improve the electrical resistance while suppressing the decline in characteristics.

[0153] In the elastic wave device (1; 1a; 1c; 1d) involved in the second method, based on the first method, the Cu concentration of the first layer (601) is higher than the Cu concentration of the second layer (602).

[0154] The elastic wave device (1; 1a; 1c; 1d) involved in the second method becomes easier to improve electrical resistance.

[0155] In the elastic wave device (1; 1a; 1c; 1d) involved in the third method, based on the second method, the Cu concentration of the first layer (601) is 15 wt% or more.

[0156] In the elastic wave device (1; 1a; 1c; 1d) involved in the third method, it is easy to improve the electrical resistance.

[0157] In the elastic wave device (1; 1a; 1c; 1d) involved in the fourth method, based on the third method, the Cu concentration of the first layer (601) is less than 30 wt%.

[0158] In the elastic wave device (1; 1a; 1c; 1d) involved in the fourth method, it is possible to suppress the resistance of the electrode (60) from becoming too large.

[0159] In the elastic wave device (1; 1a; 1c; 1d) involved in the fifth method, based on any of the methods 1 to 4, the Cu concentration of the second layer (602) is less than 10 wt%.

[0160] In the elastic wave device (1; 1a; 1c; 1d) involved in the fifth method, it is possible to suppress the resistance of the electrode (60) from becoming too large.

[0161] The elastic wave device (1b) according to the sixth embodiment includes a piezoelectric substrate (2; 2c; 2d) and an electrode (60). The electrode (60) is formed on the piezoelectric substrate (2; 2c; 2d). The electrode (60) has a first layer (601) and a second layer (602). The first layer (601) contains Al and Cu. The second layer (602) is formed on the side of the first layer (601) opposite to the piezoelectric substrate (2; 2c; 2d) side and contains Cu. The first layer (601) has Al crystals (611) and CuAl2 grains (612) arranged in a direction orthogonal to the thickness direction (D1) of the piezoelectric substrate (2; 2c; 2d). In the electrode (60), the CuAl2 grains (612) do not reach the main surface (621) of the second layer (602) opposite to the side of the first layer (601).

[0162] In the elastic wave device (1b) involved in the sixth method, it is possible to improve the electrical resistance while suppressing the decline in characteristics.

[0163] In the elastic wave device (1; 1a; 1b; 1c; 1d) according to the seventh embodiment, based on any of the embodiments 1 to 6, the electrode (60) further comprises an intermediate layer (603). The intermediate layer (603) is located between the first layer (601) and the second layer (602). The material of the intermediate layer (603) comprises one selected from the group consisting of Ti, Cr, NiCr, Mo, and AlTi.

[0164] The elastic wave device (1; 1a; 1b; 1c; 1d) involved in the seventh method can suppress the diffusion between the first layer (601) and the second layer (602) and can improve the electrical resistance.

[0165] Explanation of reference numerals in the attached figures

[0166] 1, 1a, 1b, 1c, 1d: Elastic wave devices;

[0167] 2, 2c, 2d: Piezoelectric substrate;

[0168] 21: 1st main side;

[0169] 22: The second main surface;

[0170] 20: Support base plate;

[0171] 201: 1st main surface;

[0172] 202: 2nd main surface;

[0173] 3: High-speed acoustic membrane;

[0174] 4: Low-velocity membrane;

[0175] 5: Piezoelectric layer;

[0176] 51: 1st main surface;

[0177] 52: 2nd main surface;

[0178] 6: IDT electrode;

[0179] 60: Electrode;

[0180] 60A: Electrode 1;

[0181] 60B: Second electrode;

[0182] 61: First busbar;

[0183] 62: Second busbar;

[0184] 63: The first electrode refers to;

[0185] 64: The second electrode indicates;

[0186] 600: Close-fitting layer;

[0187] 601: First floor;

[0188] 611: Al crystal;

[0189] 612: CuAl2 grains;

[0190] 602: Second floor;

[0191] 621: Main side;

[0192] 603: Intermediate layer;

[0193] 630: Adhesive film;

[0194] 631: First AlCu film;

[0195] 632: Second AlCu film;

[0196] 633: Cu film;

[0197] 7: Reflector;

[0198] 71: Electrode finger;

[0199] 8: Wiring Department;

[0200] 81: First wiring section;

[0201] 82: Second wiring section;

[0202] 9: Protective film;

[0203] 11: Resist layer;

[0204] D1: Thickness direction (first direction);

[0205] D2: Second direction;

[0206] D3: The third direction.

Claims

1. An elastic wave device, comprising: piezoelectric substrates; and Electrodes are formed on the piezoelectric substrate. The electrode has: The first layer contains Al and Cu; and The second layer, formed on the side of the first layer opposite to the piezoelectric substrate side, contains Al. The first layer has at least a portion of Al crystals and CuAl2 grains arranged in a direction orthogonal to the thickness direction of the piezoelectric substrate. In the electrode, the CuAl2 grains do not reach the main surface of the second layer opposite to the side of the first layer. On the main surface of the second layer, opposite to the side of the first layer, the CuAl2 grains are not exposed.

2. The elastic wave device according to claim 1, wherein, The Cu concentration in the first layer is higher than that in the second layer.

3. The elastic wave device according to claim 2, wherein, The Cu concentration in the first layer is above 15 wt%.

4. The elastic wave device according to claim 3, wherein, The Cu concentration in the first layer is below 30 wt%.

5. The elastic wave device according to any one of claims 1 to 4, wherein, The Cu concentration in the second layer is below 10 wt%.

6. The elastic wave device according to any one of claims 1 to 4, wherein, The electrode also has an intermediate layer located between the first layer and the second layer. The material of the intermediate layer comprises one selected from the group consisting of Ti, Cr, NiCr, Mo, and AlTi.

7. The elastic wave device according to claim 5, wherein, The electrode also has an intermediate layer located between the first layer and the second layer. The material of the intermediate layer comprises one selected from the group consisting of Ti, Cr, NiCr, Mo, and AlTi.

8. An elastic wave device, comprising: piezoelectric substrates; and Electrodes are formed on the piezoelectric substrate. The electrode has: The first layer contains Al and Cu; and The second layer, formed on the side of the first layer opposite to the piezoelectric substrate side, contains Cu. The first layer has Al crystals and CuAl2 grains arranged in a direction orthogonal to the thickness direction of the piezoelectric substrate. In the electrode, the CuAl2 grains do not reach the main surface of the second layer opposite to the side of the first layer. On the main surface of the second layer, opposite to the side of the first layer, the CuAl2 grains are not exposed.

9. The elastic wave device according to claim 8, wherein, The electrode also has an intermediate layer located between the first layer and the second layer. The material of the intermediate layer comprises one selected from the group consisting of Ti, Cr, NiCr, Mo, and AlTi.

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