Elastic wave device and method for manufacturing the same

Abstract

To provide an elastic wave device capable of improving power durability.SOLUTION: An elastic device includes: a piezoelectric layer 10; and an electrode finger 14 that is provided on the piezoelectric layer 10 and has a polycrystalline metal layer 19, the metal layer 19 containing crystal grains 50 whose maximum length H in a thickness direction (Z direction) of the metallic layer 19 is 70% or more of a thickness T2 of the metallic layer 19 in a cross-sectional view. Preferably, in the cross-sectional view, the crystal grains 50 extend from one side to the other side of the metal layer 19 facing each other in the thickness direction (Z direction) of the metal layer 19.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device and a method for manufacturing an acoustic wave device. [Background technology]

[0002] Acoustic wave devices are used in communication devices such as smartphones. It is known that a single-crystal metal film is used for the interdigital electrodes to improve power durability (for example, Patent Document 1). Also, a transfer method for transferring a metal film to an electronic component or the like is known (for example, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-92321 [Patent Document 2] Japanese Patent Application Publication No. 9-46024 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-129555 Summary of the Invention [Problem to be solved by the invention]

[0004] Although Patent Document 1 can improve power durability, the use of a single-crystal metal film formed from a single-crystal metal ingot for the electrode makes manufacturing difficult and increases costs, and therefore there is a need for other methods to improve power durability.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to improve power durability. [Means for solving the problem]

[0006] The present invention is an acoustic wave device comprising a piezoelectric layer and an electrode provided on the piezoelectric layer, the electrode having a polycrystalline metal layer, the metal layer containing crystal grains whose maximum length in the thickness direction of the metal layer is 70% or more of the thickness of the metal layer when viewed in cross section.

[0007] In the above configuration, the crystal grains may extend from one side to the other side of the metal layer that are opposed to each other in the thickness direction when viewed in the cross section.

[0008] In the above configuration, the electrode may be a comb-shaped electrode having a plurality of electrode fingers.

[0009] In the above configuration, when one of the plurality of electrode fingers is viewed in cross section in the longitudinal direction, the number of crystal grains located on a line parallel to the longitudinal direction within a range of 1.5 μm in the longitudinal direction can be 10 or less.

[0010] In the above configuration, the thickness of the metal layer may be 100 nm or more and 150 nm or less.

[0011] In the above structure, the metal layer may be an aluminum layer or an aluminum alloy layer.

[0012] The present invention is a method for manufacturing an acoustic wave device having an electrode with a polycrystalline metal layer, comprising the steps of: depositing a metal film on a substrate until a first region containing crystal grains whose maximum length in the thickness direction is 70% or more of the thickness of the metal layer is formed; bonding the metal film to a piezoelectric layer; removing the remaining second region of the metal film and the substrate so that the first region remains on the piezoelectric layer; and patterning the first region to form the electrode. [Effects of the Invention]

[0013] According to the present invention, it is possible to improve the power durability. [Brief explanation of the drawings]

[0014] [Figure 1] 1(a) is a plan view of an acoustic wave device according to a first embodiment, FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a), and FIG. 1(c) is a cross-sectional view of electrode fingers in the first embodiment. [Figure 2] FIG. 2(a) is a plan view of the electrode fingers in Example 1, and FIG. 2(b) and FIG. 2(c) are AA and BB cross-sectional views of FIG. 2(a). [Figure 3] 3A to 3D are cross-sectional views illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 4] FIG. 4(a) is a plan view of electrode fingers in a modified example of the first embodiment, and FIG. 4(b) and FIG. 4(c) are cross-sectional views taken along the lines AA and BB of FIG. 4(a). [Figure 5] FIG. 5 is a cross-sectional view of an electrode finger in a comparative example. [Figure 6] 6(a) and 6(b) are cross-sectional views illustrating a method for manufacturing an acoustic wave device according to a comparative example. [Figure 7] 7(a) is a cross-sectional view of an acoustic wave resonator in Example 2, FIG. 7(b) is a cross-sectional view of a sensor element according to Modification 1 of Example 2, and FIG. 7(c) is a cross-sectional view of a sensor element according to Modification 2 of Example 2. [Figure 8] FIG. 8(a) is a circuit diagram of a filter according to the third embodiment, and FIG. 8(b) is a circuit diagram of a duplexer according to a modified example of the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0016] 1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a), and FIG. 1(c) is a cross-sectional view of an electrode finger 14 in the first embodiment. The arrangement direction of the electrode fingers 14 is defined as the X direction, the extension direction of the electrode fingers 14 is defined as the Y direction, and the normal direction to the top surface of the piezoelectric layer 10 is defined as the Z direction. Note that the X direction, Y direction, and Z direction do not necessarily coincide with the crystal orientation of the piezoelectric layer 10.

[0017] As shown in FIGS. 1(a) to 1(c), an acoustic wave element 24 is provided on a piezoelectric layer 10. The piezoelectric layer 10 is a single-crystal piezoelectric layer made of, for example, lithium tantalate, lithium niobate, or quartz. The piezoelectric layer 10 may be, for example, a single-crystal rotated Y-cut X-propagation lithium tantalate layer or a single-crystal rotated Y-cut X-propagation lithium niobate layer. In this case, the X direction corresponds to the X-axis direction in the crystal orientation of the piezoelectric layer 10. In Example 1, the piezoelectric layer 10 is a piezoelectric substrate having a sufficient thickness.

[0018] Acoustic wave element 24 has an IDT (Interdigital Transducer) 20 and a reflector 22 provided on piezoelectric layer 10. IDT 20 includes a pair of opposing comb electrodes 17. Comb electrode 17 includes a plurality of electrode fingers 14 and a bus bar 16 to which the plurality of electrode fingers 14 are connected. A region where electrode fingers 14 of a pair of comb electrodes 17 intersect is an intersection region 25. In at least a part of intersection region 25, electrode fingers 14 of pair of comb electrodes 17 are alternately arranged.

[0019] The reflectors 22 are provided on both sides of the IDT 20 in the X direction. The acoustic waves excited primarily by the electrode fingers 14 in the intersection region 25 propagate primarily in the X direction. The pitch (the center-to-center pitch of the electrode fingers 14) of the electrode fingers 14 of one of the pair of interdigital transducers 17 is approximately equal to the wavelength λ of the acoustic waves. If the pitch of the electrode fingers 14 is D, the pitch of the electrode fingers 14 of one interdigital transducer 17 is D, which is the pitch of two electrode fingers 14. The reflectors 22 reflect the acoustic waves (surface acoustic waves) excited by the electrode fingers 14. This confines the acoustic waves within the intersection region 25 of the IDT 20. An insulating film such as a silicon oxide film or a silicon nitride film may be provided to cover the electrode fingers 14. The insulating film may be thicker or thinner than the electrode fingers 14.

[0020] The electrode fingers 14 include an adhesion layer 18 and a metal layer 19. The adhesion layer 18 is a layer for adhesion between the piezoelectric layer 10 and the electrode fingers 14, and is, for example, a metal film containing titanium (Ti) as a main component. The thickness of the adhesion layer 18 is, for example, 5 nm to 30 nm. The metal layer 19 is provided on the adhesion layer 18 and is an aluminum (Al) / aluminum alloy film (for example, an AlCu alloy film). The metal layer 19 has a thickness T2 that is 55% or more of the thickness T1 of the electrode fingers 14. The thickness T2 may be 60% or more, 70% or more, or 80% or more of the thickness T1.

[0021] Fig. 2(a) is a plan view of electrode fingers 14 in Example 1, and Fig. 2(b) and Fig. 2(c) are cross-sectional views taken along lines AA and BB in Fig. 2(a). Fig. 2(a) to Fig. 2(c) schematically illustrate electrode fingers 14 when acoustic wave element 24 in Example 1 is used in a high-band filter having a passband of 2 GHz or more, for example.

[0022] 2(a) to 2(c), metal layer 19 is a polycrystalline metal film having a plurality of crystal grains 50. Crystal grains 50 are spaced apart by grain boundaries 51. Metal layer 19 includes crystal grains 50 having a grain size of, for example, 150 nm or greater. When acoustic wave element 24 is used in a high-band filter (passband: 2 GHz or greater), metal layer 19 has a thickness T2 of, for example, 100 nm to 150 nm and a width W1 of, for example, 300 nm to 400 nm.

[0023] As shown in FIG. 2( b), the metal layer 19 includes crystal grains 50 extending across the entire metal layer 19 on a straight line 53 parallel to the thickness direction (Z direction) of the metal layer 19 when viewed in cross section. In other words, the metal layer 19 includes crystal grains 50 extending from the lower edge to the upper edge of the metal layer 19 in the Z direction when viewed in cross section. That is, the metal layer 19 includes crystal grains 50 whose maximum length H in the Z direction is equal to the thickness T2 of the metal layer 19 when viewed in cross section. Note that the metal layer 19 may include crystal grains 50 whose maximum length H in the Z direction is 70% or more of the thickness T2 of the metal layer 19 when viewed in cross section. Here, the maximum length H is the length in the Z direction between the portion of the crystal grain 50 located closest to the lower edge of the metal layer 19 and the portion located closest to the upper edge. As shown in FIG. 2(b), the metal layer 19 includes crystal grains 50 whose maximum length in the X direction (X direction) is 37.5% or more of the width W1 of the metal layer 19 when viewed in cross section in the width direction (X direction). Here, the maximum length in the X direction refers to the length in the X direction between the location of the crystal grain 50 closest to the right side of the metal layer 19 and the location of the crystal grain 50 closest to the left side. When the metal layer 19 is viewed in cross section in the X direction, for example, one or two grain boundaries 51 appear. As shown in FIG. 2(c), when the metal layer 19 is viewed in cross section in the Y direction, the number of crystal grains 50 located on a line 54 parallel to the Y direction within a range of a length L of 1.5 μm in the Y direction is 10 or less. The crystal grains 50 in the metal layer 19 can be observed and measured, for example, using a scanning electron microscope (SEM).

[0024] [Manufacturing method] 3(a) to 3(d) are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. In FIGS. 3(a) to 3(d), crystal grains 50 are illustrated as rectangular shapes for clarity. As shown in FIG. 3(a), a metal film 92 is formed on a substrate 90, such as a silicon substrate, by sputtering or vacuum deposition. By forming the metal film 92 by sputtering or vacuum deposition, the metal film 92 has a polycrystalline structure having crystal grains 50. It is known that the thicker the metal film 92, the larger the grain size of the crystal grains 50 in the region where the metal film 92 is formed later. This is thought to be because, as the formation of the metal film 92 progresses, the crystal grains 50 become larger due to the influence of the underlying layer. For example, when an AlCu alloy film is formed on a silicon substrate by sputtering, experiments have shown that the grain size of the crystal grains near the top surface of the AlCu alloy film is 50 nm to 100 nm when the film is formed to a thickness of 200 nm, but this becomes 150 nm to 300 nm when the film is formed to a thickness of 1000 nm. The metal film 92 is formed until a first region 94 is formed, which includes crystal grains 50 whose length in the thickness direction of the metal film 92 is 70% or more of the thickness of the metal layer 19. An adhesive film such as a titanium film may be formed between the substrate 90 and the metal film 92.

[0025] As shown in FIG. 3(b), a metal film 92 formed on a substrate 90 is bonded to a metal film 91 formed on the piezoelectric layer 10. The metal film 92 is bonded to the metal film 91 using a direct bonding method. For example, in a vacuum, the upper surface of the metal film 91 and the lower surface of the metal film 92 are irradiated with ions as an ion beam, a neutralized beam, or plasma. The ions are, for example, ions of an inert element (e.g., a rare gas element) such as argon (Ar) ions. This activates the upper surface of the metal film 91 and the lower surface of the metal film 92. Thereafter, while maintaining the vacuum, the upper surface of the metal film 91 and the lower surface of the metal film 92 are bonded together. As a result, the upper surface of the metal film 91 and the lower surface of the metal film 92, which have been activated, are directly bonded together.

[0026] 3(c), the second region 96 of the metal film 92 other than the first region 94 and the substrate 90 are peeled off from the piezoelectric layer 10 so that the first region 94 of the metal film 92 remains on the piezoelectric layer 10. The second region 96 of the metal film 92 and the substrate 90 are peeled off using, for example, a grinding method and / or a CMP (Chemical Mechanical Polishing) method.

[0027] 3(d), the first region 94 of the metal film 92 and the metal film 91 are patterned using, for example, photolithography and etching to form a plurality of electrode fingers 14 each having an adhesion layer 18 and a metal layer 19. When the electrode finger 14 is viewed in cross section, the metal layer 19 includes crystal grains 50 extending from the lower edge to the upper edge of the metal layer 19 in the thickness direction of the metal layer 19.

[0028] [Variations] The modified example of the first embodiment is an example in which acoustic wave element 24 is used in a low-band filter. Fig. 4(a) is a plan view of electrode fingers 14 in the modified example of the first embodiment, and Fig. 4(b) and Fig. 4(c) are cross-sectional views taken along lines AA and BB of Fig. 4(a). The low-band filter has a passband of 500 MHz to 900 MHz, for example.

[0029] As shown in Figures 4(a) to 4(c), when acoustic wave element 24 is used in a low-band filter (passband: 500 MHz to 900 MHz), thickness T2 of metal layer 19 is, for example, 200 nm to 300 nm, and width W1 is, for example, 900 nm to 1100 nm.

[0030] As shown in FIG. 4( b), the metal layer 19 includes crystal grains 50 that, when viewed in cross section, occupy 70% or more of the thickness of the metal layer 19 on a line 53 parallel to the thickness direction (Z direction) of the metal layer 19. In other words, when viewed in cross section, the metal layer 19 includes crystal grains 50 whose maximum length H in the Z direction is 70% or more of the thickness T2 of the metal layer 19. As described above, the maximum length H is the length in the Z direction between the location of the crystal grain 50 closest to the bottom side of the metal layer 19 and the location of the top side. Also, as shown in FIG. 4( b), when viewed in cross section in the width direction (X direction), the metal layer 19 includes crystal grains 50 whose maximum length in the X direction is 15% or more of the width W1 of the metal layer 19. As described above, the maximum length in the X direction is the length in the X direction between the location of the crystal grain 50 closest to the right side of the metal layer 19 and the location of the left side. As shown in Figure 4(c), when the metal layer 19 is viewed cross-sectionally in the Y direction, the number of crystal grains 50 located on a straight line 54 parallel to the Y direction within a range of length L of 1.5 μm in the Y direction is 10 or less.

[0031] Acoustic wave element 24 in the modified example of the first embodiment is formed by a method similar to that shown in FIGS. 3(a) to 3(d) of the first embodiment.

[0032] [Comparative Example] 5 is a cross-sectional view of electrode finger 14 in a comparative example. In the comparative example, similar to Example 1, a case will be described in which acoustic wave element 24 is used in a high-band filter. As shown in FIG. 5, in the comparative example, the grain size of crystal grains 50a is about 40 nm. The other configurations are the same as in Example 1, and therefore will not be described again.

[0033] 6(a) and 6(b) are cross-sectional views illustrating a method for manufacturing an acoustic wave device according to a comparative example. In FIGS. 6(a) and 6(b), for clarity, the crystal grains 50a are illustrated as rectangular. As shown in FIG. 6(a), an adhesion layer 18 and a metal layer 19 are formed on a piezoelectric layer 10 using sputtering or vacuum deposition. By forming the metal layer 19 using sputtering or vacuum deposition, the metal layer 19 has crystal grains 50a. Because the metal layer 19 is thin, the grain size of the crystal grains 50a is small, approximately 40 nm. As shown in FIG. 6(b), the adhesion layer 18 and the metal layer 19 are patterned using photolithography and etching to form multiple electrode fingers 14 each having the adhesion layer 18 and the metal layer 19.

[0034] The bonding strength between the crystal grains 50, 50a at the grain boundary 51 between the crystal grains 50, 50a is weak. Therefore, when a high-power radio-frequency signal is applied between the pair of interdigital electrodes 17, a phenomenon in which metal atoms diffuse along the grain boundary 51 may occur. In this case, if the grain size is small like the crystal grain 50a in the comparative example, there are many grain boundaries such as the grain boundary 51 between the crystal grains 50a, and metal atoms are more likely to diffuse along the grain boundary 51. Such stress migration may cause hillocks and / or voids in the electrode finger 14, which may result in deformation and / or melting of the electrode finger 14.

[0035] On the other hand, according to Example 1 and its modifications, as shown in FIGS. 2(b) and 4(b), the polycrystalline metal layer 19 includes crystal grains 50 whose maximum length H in the thickness direction (Z direction) of the metal layer 19 is 70% or more of the thickness T2 of the metal layer 19 when viewed in cross section. This reduces the number of grain boundaries 51 between the crystal grains 50. Therefore, even when a high-power radio-frequency signal is applied between the pair of comb electrodes 17, metal atoms are less likely to diffuse along the grain boundaries 51, and the generation of hillocks and voids in the electrode fingers 14 is suppressed. This improves power durability. Furthermore, the large crystal grains 50 reduce the electrical resistance of the electrode fingers 14. Therefore, even when a high-power radio-frequency signal is applied between the pair of comb electrodes 17, heat generation in the electrode fingers 14 is suppressed, thereby improving power durability.

[0036] From the viewpoint of improving the power durability, the maximum length H is preferably 80% or more of the thickness of the metal layer 19, more preferably 85% or more, and even more preferably 90% or more.

[0037] According to the manufacturing method of Example 1 and its modified example, as shown in FIG. 3( a), a metal film 92 is formed on a substrate 90 until a first region 94 is formed, the first region 94 including crystal grains 50 whose maximum length in the thickness direction is 70% or more of the thickness of the metal layer 19. As shown in FIG. 3( b), the metal film 92 is bonded to the piezoelectric layer 10. As shown in FIG. 3( c), the remaining second region 96 of the metal film 92 and the substrate 90 are removed so that the first region 94 of the metal film 92 remains on the piezoelectric layer 10. As shown in FIG. 3( d), the first region 94 of the metal film 92 is patterned to form electrode fingers 14 having a metal layer 19. This increases the size of the crystal grains 50 in the metal layer 19, thereby suppressing the occurrence of hillocks and voids in the electrode fingers 14 and improving power durability. Furthermore, the large crystal grains 50 reduce the electrical resistance of the electrode fingers 14, thereby also improving power durability.

[0038] 2(c) and 4(c), when the electrode finger 14 is viewed in cross section in the longitudinal direction (Y direction), the number of crystal grains 50 located on a line 54 parallel to the Y direction within a range of 1.5 μm in the Y direction (within the range of length L) is 10 or less. By having crystal grains 50 of such a size, it is possible to suppress the occurrence of hillocks and voids in the electrode finger 14, and improve the power durability.

[0039] 2(b), in the first embodiment, the metal layer 19 includes, when viewed in cross section, crystal grains 50 that extend from one side to the other side of the metal layer 19 that are opposed to each other in the thickness direction (Z direction) of the metal layer 19. This can further improve the power durability.

[0040] In Example 1, the thickness T2 of the metal layer 19 is 100 nm or more and 150 nm or less. As the frequency increases, the thickness T1 and width W1 of the electrode fingers 14 become smaller, and the thickness T2 of the metal layer 19 may become 100 nm or more and 150 nm or less. In this case, when a high-power high-frequency signal is applied between a pair of comb-shaped electrodes 17, deformation and / or melting of the electrode fingers 14 is likely to occur. Therefore, in order to improve the power durability of the electrode fingers 14 in such a case, it is preferable that the metal layer 19 includes crystal grains 50 whose maximum length H in the thickness direction (Z direction) of the metal layer 19 is 70% or more of the thickness T2 of the metal layer 19 when viewed in cross section.

[0041] In Example 1 and its modified examples, the metal layer 19 is an aluminum layer or an aluminum alloy layer. In this case, the metal layer 19 can be easily formed to have crystal grains 50 with a grain size of 150 nm or more. Therefore, the maximum length H of the crystal grains 50 in the thickness direction (Z direction) of the metal layer 19 can be set to 70% or more of the thickness T2 of the metal layer 19.

[0042] In Example 1 and its modifications, the adhesion layer 18 is a metal film mainly composed of titanium, but it may be a metal film mainly composed of titanium nitride (TiN), chromium (Cr), or nickel (Ni). The metal layer 19 is an aluminum layer or an aluminum alloy layer, but it may be a metal film mainly composed of aluminum (Al), molybdenum (Mo), tungsten (W), ruthenium (Ru), rhodium (Rh), platinum (Pt), or copper (Cu), or an alloy film containing these metals.

[0043] Although Example 1 and its modified examples have been described with reference to a case where the piezoelectric layer 10 is a piezoelectric substrate, the present invention is not limited to this case, and the piezoelectric layer 10 may be provided on a support substrate. Alternatively, one or more insulating layers, such as a silicon oxide film, a silicon film, an aluminum oxide film, an aluminum nitride film, an aluminum oxynitride film, a silicon nitride film, and / or a silicon carbide film, may be provided between the support substrate and the piezoelectric layer 10. The upper surface of the support substrate may be smooth or rough. [Example]

[0044] FIG. 7A is a cross-sectional view of acoustic wave element 24a according to Example 2. As shown in FIG. 7A, piezoelectric layer 10a is provided on support substrate 60. Lower electrode 61 and upper electrode 63 are provided on either side of piezoelectric layer 10a. Lower electrode 61 includes metal layer 11 and metal layer 19a. Upper electrode 63 includes metal layer 19b and metal layer 13. A gap 64 is formed between lower electrode 61 and support substrate 60. A resonance region 65 is a region where lower electrode 61 and upper electrode 63 face each other, sandwiching at least a portion of piezoelectric layer 10a. In resonance region 65, lower electrode 61 and upper electrode 63 excite an acoustic wave in piezoelectric layer 10a. Like metal layer 19, metal layer 19a is a polycrystalline metal layer occupying 55% or more of the thickness of lower electrode 61. Metal layer 19a includes crystal grains 50 whose maximum length in the thickness direction of metal layer 19a is 70% or more of the thickness of metal layer 19a when viewed in cross section. The same applies to the metal layer 19b. The piezoelectric layer 10a is, for example, an aluminum nitride layer, a zinc oxide layer, a single-crystal lithium tantalate layer, or a single-crystal lithium niobate layer. An acoustic reflection film that reflects elastic waves may be provided instead of the voids 64. In this way, the elastic wave element is not limited to a surface acoustic wave resonator, but may also be a piezoelectric thin film resonator.

[0045] FIG. 7(b) is a cross-sectional view of a sensor device 200 according to a first modification of the second embodiment. As shown in FIG. 7(b), two IDTs 20a and 20b are provided on a piezoelectric layer 10. A sensitive film 74 is provided on the piezoelectric layer 10 between the IDTs 20a and 20b. When a high-frequency signal is applied to the IDT 20a, an elastic wave is excited in the piezoelectric layer 10. The elastic wave propagates through the piezoelectric layer 10 below the sensitive film 74 and is converted into a high-frequency signal by the IDT 20b. When a substance in the gas is adsorbed by the sensitive film 74, the speed of the elastic wave propagating through the piezoelectric layer 10 below the sensitive film 74 decreases. By measuring the phase difference between the high-frequency signal applied to the IDT 20a and the high-frequency signal output by the IDT 20b, the substance in the gas can be detected.

[0046] 7(c) is a cross-sectional view of sensor device 210 according to a second modification of the second embodiment. As shown in FIG. 7(c), a protective film 76 is provided on electrode fingers 14 of acoustic wave element 24. A sensitive film 74 is provided on protective film 76. When a substance in the gas is adsorbed by sensitive film 74, the resonant frequency of acoustic wave element 24 decreases. By measuring the resonant frequency of acoustic wave element 24, the substance in the gas can be detected.

[0047] As in the first and second modifications of the second embodiment, the IDTs 20a and 20b or the acoustic wave element 24 may be used in a sensor device. [Example]

[0048] FIG. 8(a) is a circuit diagram of a filter 300 according to a third embodiment. As shown in FIG. 8(a), one or more series resonators S1 to S4 are connected in series between an input terminal Tin and an output terminal Tout. One or more parallel resonators P1 to P3 are connected in parallel between the input terminal Tin and the output terminal Tout. The acoustic wave device according to the first embodiment, its modification, and the second embodiment can be used for at least one of the one or more series resonators S1 to S4 and the one or more parallel resonators P1 to P3. The number of resonators in the ladder filter can be set as appropriate. The filter may be a multimode filter.

[0049] FIG. 8(b) is a circuit diagram of a duplexer 310 according to a modified example of the third embodiment. As shown in FIG. 8(b), a transmit filter 80 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 82 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 80 passes, to the common terminal Ant, signals in the transmit band among the high-frequency signals input from the transmit terminal Tx as transmit signals, and suppresses signals of other frequencies. The receive filter 82 passes, to the receive terminal Rx, signals in the receive band among the high-frequency signals input from the common terminal Ant as receive signals, and suppresses signals of other frequencies. At least one of the transmit filter 80 and the receive filter 82 can be the filter of the third embodiment. Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0050] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0051] 10, 10a...piezoelectric layer, 11...metal layer, 13...metal layer, 14...electrode finger, 16...bus bar, 17...comb-shaped electrode, 18...adhesion layer, 19, 19a, 19b...metal layer, 20, 20a, 20b...IDT, 22...reflector, 24, 24a...acoustic wave element, 25...intersection region, 50, 50a...crystal grain, 51...grain boundary, 60...support substrate, 61...lower electrode, 63...upper electrode, 64...gap, 65...resonance region, 74...sensitive film, 76...protection film, 80...transmitting filter, 82...receiving filter, 90...substrate, 91...metal film, 92...metal film, 94...first region, 96...second region, 100...acoustic wave device, 200, 210...sensor device, 300...filter, 310...duplexer

Claims

1. a piezoelectric layer; an electrode provided on the piezoelectric layer, having a polycrystalline metal layer, the metal layer including crystal grains whose maximum length in the thickness direction of the metal layer is 70% or more of the thickness of the metal layer when viewed in cross section;

2. The acoustic wave device according to claim 1 , wherein the crystal grains extend from one side to the other side of the metal layer that are opposed to each other in the thickness direction when viewed in the cross section.

3. The acoustic wave device according to claim 1 , wherein the electrode is a comb-shaped electrode having a plurality of electrode fingers.

4. 4. The acoustic wave device according to claim 3, wherein when one of the plurality of electrode fingers is viewed in cross section in the longitudinal direction, the number of crystal grains located on a line parallel to the longitudinal direction within a range of 1.5 μm in the longitudinal direction is 10 or less.

5. 3. The acoustic wave device according to claim 1, wherein the metal layer has a thickness of 100 nm or more and 150 nm or less.

6. 3. The acoustic wave device according to claim 1, wherein the metal layer is an aluminum layer or an aluminum alloy layer.

7. 1. A method for manufacturing an acoustic wave device having an electrode with a polycrystalline metal layer, comprising: forming a metal film on a substrate until a first region including crystal grains whose maximum length in the thickness direction is 70% or more of the thickness of the metal layer is formed; bonding the metal film to a piezoelectric layer; removing a remaining second region of the metal film and the substrate so that the first region remains on the piezoelectric layer; and patterning the first region to form the electrode.

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