Acoustic wave device, filter, and multiplexer

Abstract

To provide an acoustic wave device capable of achieving both improvement in a temperature characteristic and miniaturization of the device.SOLUTION: An acoustic wave device 100 includes a piezoelectric layer 10, and a pair of comb-shaped electrodes 20 provided on the piezoelectric layer 10 and each having a plurality of electrode fingers 18, and the plurality of electrode fingers 18 include a first metal layer 31, and a second metal layer 32 provided between the piezoelectric layer 10 and the first metal layer 31 and having a first part 36 located at a center in a transverse direction of the plurality of electrode fingers 18 and a second portion 37 having a Young modulus and an acoustic impedance smaller than those of the first part 36 while sandwiching the first part 36 from the transverse direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to acoustic wave devices, filters, and multiplexers. [Background technology]

[0002] Acoustic wave devices are used in high-frequency communication systems, such as mobile phones. A known example of an acoustic wave device is one that includes a pair of interdigital electrodes each having a plurality of electrode fingers. To improve power durability, it is known to use electrode fingers that are stacked with a first metal film that is a titanium film or a titanium alloy film, a second metal film that is an aluminum film or an aluminum alloy film provided on the first metal film, and a barrier film provided between the first and second metal films (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-64367 Summary of the Invention [Problem to be solved by the invention]

[0004] BACKGROUND ART There is a demand for acoustic wave devices to have improved temperature characteristics such as temperature coefficient of frequency (TCF). In addition, as electronic devices become smaller, there is a demand for smaller acoustic wave devices.

[0005] The present invention has been made in view of the above-mentioned problems, and has as its object to achieve both improved temperature characteristics and miniaturization of the device. [Means for solving the problem]

[0006] The present invention is an acoustic wave device comprising a piezoelectric layer and a pair of comb electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers, the plurality of electrode fingers including a first metal layer and a second metal layer provided between the piezoelectric layer and the first metal layer, the second metal layer having a first portion located in the center in the short direction of the plurality of electrode fingers and a second portion sandwiching the first portion in the short direction and having a Young's modulus and acoustic impedance smaller than those of the first portion.

[0007] In the above configuration, the ratio of the thickness of the second metal layer to the thickness of the plurality of electrode fingers may be 10% or more.

[0008] In the above configuration, the thickness of the plurality of electrode fingers may be 0.14 times or more the average pitch of the plurality of electrode fingers of the pair of comb-shaped electrodes.

[0009] In the above configuration, the ratio of the total length in the short side direction of the second portions sandwiching the first portion to the length in the short side direction of the plurality of electrode fingers can be 20% or more and 60% or less.

[0010] In the above configuration, the ratio of the total length in the short-side direction of the second portions sandwiching the first portion to the length in the short-side direction of the plurality of electrode fingers can be 40% or more and 50% or less.

[0011] In the above configuration, the first portion may be mainly composed of titanium nitride, and the second portion may be mainly composed of titanium.

[0012] In the above configuration, the first metal layer may be composed mainly of aluminum.

[0013] The present invention is a filter including the acoustic wave device described above.

[0014] The present invention is a multiplexer including the filter described above. [Effects of the Invention]

[0015] According to the present invention, it is possible to achieve both improved temperature characteristics and miniaturization of the device. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1(a) is a plan view of an acoustic wave device in accordance with a first embodiment, and FIG. 1(b) is a cross-sectional view taken along line AA of FIG. 1(a). [Figure 2] 2(a) to 2(c) are cross-sectional views illustrating a method for manufacturing the acoustic wave device in accordance with the first embodiment. [Figure 3] 3(a) to 3(d) are cross-sectional views of electrode fingers in acoustic wave resonators of models A to D. FIG. [Figure 4] FIG. 4(a) is a diagram showing the simulation results of the TCFs of Models A to D, and FIG. 4(b) is a diagram showing the simulation results of the phase velocities. [Figure 5] FIG. 5(a) is a diagram showing the simulation results of the TCF when the width of the end portion of Model A is changed, and FIG. 5(b) is a diagram showing the simulation results of the phase velocity. [Figure 6] FIG. 6(a) is a diagram showing the simulation results of the improvement in TCF when the thickness of the metal layer in model A is changed, and FIG. 6(b) is a diagram showing the simulation results of the improvement in phase velocity. [Figure 7] FIG. 7 is a cross-sectional view of an electrode finger according to a modification of the first embodiment. [Figure 8] FIG. 8(a) is a circuit diagram of a filter according to the second embodiment, and FIG. 8(b) is a circuit diagram of a duplexer according to a modified example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [Example]

[0018] FIG. 1(a) is a plan view of an acoustic wave device 100 according to a first embodiment, and FIG. 1(b) is a cross-sectional view taken along the line AA of FIG. 1(a). In FIG. 1(a), the boundary between a first portion 36 and a second portion 37 of a second metal layer 32 is indicated by a dashed line. The short-side direction of the electrode fingers 18 is defined as the X direction, the long-side direction of the electrode fingers 18 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. The X direction, Y direction, and Z direction do not necessarily correspond to the X axis direction of the crystal orientation of the piezoelectric layer 10. When the piezoelectric layer 10 is a rotated Y-cut X-propagation substrate, the X direction corresponds to the X axis direction of the crystal orientation.

[0019] As shown in FIGS. 1(a) and 1(b), an acoustic wave resonator 26 is provided on a piezoelectric layer 10. The piezoelectric layer 10 may be, for example, a single-crystal lithium tantalate layer, a single-crystal lithium niobate layer, or a single-crystal quartz crystal layer. The piezoelectric layer 10 may be, for example, a rotated Y-cut X-propagation lithium tantalate layer or a rotated Y-cut X-propagation lithium niobate layer, or may be, for example, a 30° to 50° rotated Y-cut X-propagation lithium tantalate layer. The acoustic wave resonator 26 includes an IDT (Interdigital Transducer) 22 and a reflector 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. The IDT 22 includes a pair of interdigital electrodes 20. The interdigital electrode 20 includes multiple electrode fingers 18 and a bus bar 19 to which the multiple electrode fingers 18 are connected. The region where the electrode fingers 18 of the pair of interdigital electrodes 20 intersect is an intersection region 25. The length of the intersection region 25 in the Y direction is the aperture length.

[0020] The pair of comb electrodes 20 face each other so that the electrode fingers 18 are alternately arranged in the X direction in at least a part of the intersection region 25. The main mode acoustic waves (surface acoustic waves) excited by the electrode fingers 18 in the intersection region 25 propagate mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb electrodes 20 is approximately equal to the wavelength λ of the surface acoustic waves. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 18. The reflector 24 reflects the surface acoustic waves excited by the electrode fingers 18 of the IDT 22. As a result, the surface acoustic waves are confined within the intersection region 25 of the IDT 22.

[0021] The IDTs 22, such as the electrode fingers 18, and the reflectors 24 are formed by a conductive film 15 provided on the piezoelectric layer 10. The conductive film 15 includes a first metal layer 31 provided on the piezoelectric layer 10 and a second metal layer 32 provided between the piezoelectric layer 10 and the first metal layer 31. The first metal layer 31 and the second metal layer 32 are in contact with each other, for example. The second metal layer 32 is in contact with the piezoelectric layer 10, for example. The thicknesses of the first metal layer 31 and the second metal layer 32 are T1 and T2, respectively. The length of the electrode fingers 18 in the X direction (also referred to as the width of the electrode fingers 18) is W1.

[0022] The first metal layer 31 is, for example, a polycrystalline or amorphous aluminum (Al) layer or aluminum alloy layer. When the first metal layer 31 is an aluminum alloy layer, the first metal layer 31 may contain at least one element of copper (Cu), magnesium (Mg), scandium (Sc), zirconium (Zr), titanium (Ti), neodymium (Ne), and silicon (Si) in addition to aluminum. When the first metal layer 31 is an aluminum layer, the first metal layer 31 may contain intentional or unintentional impurities in addition to aluminum. When the first metal layer 31 is an aluminum alloy layer, the first metal layer 31 may contain intentional or unintentional impurities in addition to the metal elements constituting the aluminum and aluminum alloy. Thus, the first metal layer 31 is a metal layer containing aluminum as its main component. Note that the first metal layer 31 is not limited to a metal layer containing aluminum as its main component, and may be a metal layer containing copper or molybdenum as its main component, such as a copper layer, a copper alloy layer, a molybdenum layer, or a molybdenum alloy layer.

[0023] The second metal layer 32 has a second portion 37 that is provided along the contours of the IDT 22 and the reflector 24, and a first portion 36 that is located inward of the second portion 37. In the electrode finger 18, the first portion 36 is located at the center in the X direction, and the second portion 37 is located on both sides of the first portion 36 in the X direction. In the electrode finger 18, the second portions 37 that are located on both sides of the first portion 36 are referred to as second portion 37a and second portion 37b. The length of the first portion 36 in the X direction (also referred to as the width of the first portion 36) is W2, and the length of each of the second portions 37a and 37b in the X direction (also referred to as the width of the second portions 37a and 37b) is W3. The width W3 of each of the second portions 37a and 37b is, for example, the same. The term "same" means that a difference of the order of manufacturing error is allowed, for example, a ratio of the difference in width between second portion 37a and second portion 37b to the width of second portion 37a is allowed to be ±3% or less.

[0024] The first portion 36 is, for example, a conductive polycrystalline or amorphous titanium nitride (TiN) layer. The first portion 36 may contain intentional or unintentional impurities other than titanium (Ti) and nitrogen (N). Thus, the first portion 36 is primarily composed of titanium nitride. The second portion 37 is, for example, a polycrystalline or amorphous titanium (Ti) layer. The second portion 37 may contain intentional or unintentional impurities other than titanium. Thus, the second portion 37 is primarily composed of titanium. The second portion 37 has a smaller Young's modulus and acoustic impedance than the first portion 36.

[0025] Here, when a certain film contains a certain element as its main component, the concentration of the certain element is, for example, 80 atomic % or more, for example, 90 atomic % or more. For example, when the first metal layer 31 contains aluminum as its main component, the aluminum content in the first metal layer 31 is 80 atomic % or more, for example, 90 atomic % or more. When the second portion 37 of the second metal layer 32 contains titanium as its main component, the titanium content in the second portion 37 is 80 atomic % or more, for example, 90 atomic % or more. When two or more elements are contained as its main components, the total concentration of the two or more elements is 80 atomic % or more, for example, 90 atomic % or more. Each of the two or more elements is 10 atomic % or more or 20 atomic % or more. When the first portion 36 of the second metal layer 32 contains titanium nitride as its main component, the total concentration of the titanium content and the nitrogen content in the first portion 36 is 80 atomic % or more, for example, 90 atomic % or more. The titanium content and the nitrogen content are each 10 atomic % or more or 20 atomic % or more.

[0026] [Manufacturing method] 2(a) to 2(c) are cross-sectional views illustrating a manufacturing method of the acoustic wave device 100 according to the first embodiment. As shown in FIG. 2(a), a titanium film is formed on the piezoelectric layer 10 using a sputtering method, a CVD (Chemical Vapor Deposition) method, or a vacuum deposition method. The titanium film is then patterned using a photolithography method and an etching method. This forms the second portion 37 of the second metal layer 32. The second portion 37 may also be formed by a lift-off method.

[0027] 2(b), the first portion 36, which is a titanium nitride film, is formed by using, for example, a lift-off method, thereby forming the second metal layer 32 having the first portion 36 and the second portion 37.

[0028] As shown in FIG. 2(c), an aluminum film or an aluminum alloy film covering the second metal layer 32 is formed on the piezoelectric layer 10 using a sputtering method, a CVD (Chemical Vapor Deposition) method, or a vacuum deposition method. The aluminum film or the aluminum alloy film is then patterned using a photolithography method and an etching method. As a result, a first metal layer 31 is formed on the second metal layer 32. The first metal layer 31 may be formed by a lift-off method. In this manner, the acoustic wave device according to Example 1 is formed.

[0029] [Simulation 1] Simulations were performed on the temperature coefficient of frequency (TCF) and phase velocity for acoustic wave resonators Models A to D. The TCF was calculated for the resonant frequency. The phase velocity was calculated by calculating phase velocity = resonant frequency × (pitch D of electrode fingers 18) × 2.

[0030] 3(a) to 3(d) are cross-sectional views of electrode fingers 18 in acoustic wave resonators of Models A to D. As shown in FIG. 3(a), Model A corresponds to Example 1, and the conductive film 15 forming the IDT 22 and reflector 24, such as the electrode finger 18, includes a metal layer 41 made of aluminum and a metal layer 42 disposed between the piezoelectric layer 10 and the metal layer 41. The metal layer 42 has a centrally located central portion 43 made of titanium nitride and end portions 44 made of titanium sandwiching the central portion 43. The thicknesses of the metal layer 41 and the metal layer 42 are defined as T11 and T12, respectively. The length of the central portion 43 of the electrode finger 18 in the X direction (also referred to as the width of the central portion 43) is defined as W11, and the length of the end portion 44 in the X direction (also referred to as the width of the end portion 44) is defined as W12.

[0031] 3(b), model B is a model corresponding to a comparative example, and the conductive film 15 includes a metal layer 41 made of aluminum and a metal layer 45 made of titanium provided between the piezoelectric layer 10 and the metal layer 41. The thicknesses of the metal layer 41 and the metal layer 45 are T11 and T15, respectively.

[0032] 3(c), model C is a model corresponding to a comparative example, and the conductive film 15 includes a metal layer 41 made of aluminum and a metal layer 46 made of titanium nitride provided between the piezoelectric layer 10 and the metal layer 41. The thicknesses of the metal layer 41 and the metal layer 46 are T11 and T16, respectively.

[0033] 3(d), model D is a comparative example, and the conductive film 15 includes a metal layer 41 made of aluminum and a metal layer 47 provided between the piezoelectric layer 10 and the metal layer 41. The metal layer 47 includes a portion 48 made of titanium and a portion 49 made of titanium nitride, which are provided side by side. The thicknesses of the metal layer 41 and the metal layer 47 are T11 and T17, respectively. In the electrode finger 18, the length in the X direction of the portion 48 (also referred to as the width of the portion 48) is W13, and the length in the X direction of the portion 49 (also referred to as the width of the portion 49) is W14.

[0034] The simulation conditions are as follows: Note that the physical properties of each film, such as Young's modulus, can be values ​​disclosed in various databases. Common conditions for Models A to D Wavelength of surface acoustic waves: 1500 nm Piezoelectric layer 10: 42° rotated Y-cut X-propagation lithium tantalate substrate Width of electrode finger 18 W1: 375 nm Metal layer 41: Aluminum layer with a thickness T11 of 90 nm Model A Conditions The central portion 43 of the metal layer 42: a titanium nitride film having a thickness T12 of 60 nm and a width W11 of 187.5 nm Edge portion 44 of metal layer 42: titanium film having a thickness T12 of 60 nm and a width W12 of 93.75 nm Model B Conditions Metal layer 45: Titanium layer with a thickness T15 of 60 nm Model C Conditions Metal layer 46: Titanium nitride layer with a thickness T16 of 60 nm Model D Conditions Part 48 of the metal layer 47: a titanium film having a thickness T17 of 60 nm and a width W13 of 187.5 nm Part 49 of the metal layer 47: a titanium nitride film having a thickness T17 of 60 nm and a width W14 of 187.5 nm

[0035] 4(a) shows the simulation results of the TCF of Models A to D, and FIG. 4(b) shows the simulation results of the phase velocity. As shown in FIGS. 4(a) and 4(b), Model C has a smaller absolute value of the TCF, improved temperature characteristics, and a faster phase velocity than Model B. When the phase velocity is faster, the pitch D of the electrode fingers 18 must be increased to obtain the same resonant frequency, which results in an increase in the size of the device.

[0036] The reason why Model C has an improved TCF compared to Model B is not clear, but it may be thought that the following applies: Model B has a metal layer 45 made of titanium between the piezoelectric layer 10 and the metal layer 41, while Model C has a metal layer 46 made of titanium nitride. The Young's modulus of titanium nitride is greater than that of titanium. The Young's moduli of aluminum constituting metal layer 41, titanium constituting metal layer 45, and titanium nitride constituting metal layer 46 change with temperature. However, because titanium nitride has a greater Young's modulus than titanium, it is less likely to deform with temperature changes than titanium. In other words, the metal layer 46 of Model C is less likely to deform with temperature changes than the metal layer 45 of Model B. For this reason, it is thought that Model C has an improved TCF compared to Model B.

[0037] The reason why the phase velocity of Model C is faster than that of Model B can be considered as follows. S is expressed by Equation 1, where G is the modulus of rigidity and ρ is the density.

number

number

[0038] The density of titanium nitride is greater than that of titanium, but the Young's modulus of titanium nitride is greater than that of titanium, so the sound velocity V of titanium nitride is lower than that of titanium. S Therefore, the metal layer 46 made of titanium nitride of Model C has a higher sound velocity V of the shear wave than the metal layer 45 made of titanium of Model B. S Therefore, it is thought that the phase velocity of Model C is faster than that of Model B.

[0039] Model A exhibited an improved TCF compared to Model B, with almost no change in phase velocity. The reason for this result is unclear, but the following is a possible explanation: Model A exhibited an improved TCF compared to Model B because central portion 43 of metal layer 42 in Model A was made of titanium nitride, whereas metal layer 45 in Model B was entirely made of titanium. Furthermore, acoustic waves are thought to be reflected at the end surfaces of electrode fingers 18 in the X direction. In this case, if the acoustic impedance of the end portions of electrode fingers 18 in the X direction is small, acoustic waves are thought to be less likely to be reflected. Suppressing the reflection of acoustic waves at the end surfaces of electrode fingers 18 is thought to slow the phase velocity. The acoustic impedance of titanium is smaller than that of titanium nitride. In Model A, end portions 44 of metal layer 42 were made of titanium, so acoustic waves were thought to be less likely to be reflected at the end surfaces of electrode fingers 18, similar to Model B, in which metal layer 45 was entirely made of titanium. For this reason, Model A exhibited a slower phase velocity than Model B.

[0040] In Model D, the TCF was comparable to that of Model A, but the phase velocity was faster than that of Model A and Model B. This shows that simply arranging the titanium portion 48 and the titanium nitride portion 49 side by side (providing the titanium portion 48 only on one side of the titanium nitride portion 49 in the X direction) has little effect in suppressing the reflection of acoustic waves at the end faces of the electrode fingers 18, and is unable to prevent the phase velocity from increasing. In other words, to improve both the TCF and the phase velocity, it is necessary to use a configuration like Model A, in which end portions 44 made of titanium are provided on either side of the central portion 43 made of titanium nitride.

[0041] From the above considerations, it is believed that the effect of improving TCF can be achieved not only when the central portion 43 of the metal layer 42 of Model A is made of titanium nitride and the end portions 44 are made of titanium, but also when the central portion 43 has a larger Young's modulus than the end portions 44. It is believed that the effect of suppressing an increase in phase velocity can be achieved when the end portions 44 have a smaller acoustic impedance than the central portion 43. In other words, it is believed that the effect of suppressing an increase in phase velocity and improving TCF can be achieved when the end portions 44 have a smaller Young's modulus and acoustic impedance than the central portion 43. Since acoustic impedance is calculated from the product of density and sound velocity, based on the above equations 1 and 2, it can be calculated from the square root of the product of density, Young's modulus, and a constant. Therefore, it can also be said that the effect of suppressing an increase in phase velocity and improving TCF can be achieved when the end portions 44 have a smaller Young's modulus and density than the central portion 43.

[0042] [Simulation 2] Simulations were performed on the TCF and phase velocity when the width W12 of the end portion 44 was changed for Model A. The simulation conditions were the same as in Simulation 1, except that the width W12 was changed.

[0043] Fig. 5(a) shows the simulation results of the TCF when the width W12 of the end portion 44 in Model A is changed, and Fig. 5(b) shows the simulation results of the phase velocity. The horizontal axes of Fig. 5(a) and Fig. 5(b) represent the ratio of the total width (W12 × 2) of the end portion 44 to the width W1 of the electrode finger 18. The vertical axis of Fig. 5(a) represents the TCF of the resonant frequency. The vertical axis of Fig. 5(b) represents the phase velocity.

[0044] As shown in Figure 5(a), as the width ratio of the end portion 44 decreased, the absolute value of the TCF decreased. When the width ratio of the end portion 44 was 10%, the absolute value of the TCF was smallest. As shown in Figure 5(b), when the width ratio of the end portion 44 was in the range of 50% to 100%, the phase velocity hardly changed. When the width ratio of the end portion 44 was in the range of 20% to 50%, the phase velocity gradually increased as the width ratio of the end portion 44 decreased. When the width ratio of the end portion 44 was 20% or less, the phase velocity suddenly increased as the width ratio of the end portion 44 decreased.

[0045] From the viewpoint of improving the TCF, the width ratio of the end portion 44 is preferably 60% or less, more preferably 50% or less, and even more preferably 40% or less. From the viewpoint of suppressing an increase in the phase velocity, the width ratio of the end portion 44 is preferably 20% or more, more preferably 30% or more, and even more preferably 40% or more.

[0046] [Simulation 3] Simulations were performed on the improvement in TCF and the improvement in phase velocity when the thickness T12 of the metal layer 42 in Model A was changed. The improvement in TCF was determined by subtracting the TCF at the resonance frequency of Model B from the TCF at the resonance frequency of Model A when the thicknesses T12 and T15 of the metal layer 42 in Model A and the metal layer 45 in Model B were the same. The improvement in phase velocity was determined by subtracting the phase velocity of Model A from the phase velocity of Model C when the thicknesses T12 and T16 of the metal layer 42 in Model A and the metal layer 46 in Model C were the same. The simulation conditions were the same as in Simulation 1, except that the thicknesses T12, T15, and T16 were changed.

[0047] 6(a) shows the simulation results of the improvement in TCF when the thickness T12 of the metal layer 42 in Model A is changed, and FIG. 6(b) shows the simulation results of the improvement in phase velocity. The horizontal axis in FIG. 6(a) and FIG. 6(b) represents the thickness of the electrode finger 18. The vertical axis represents the ratio of the thickness T12 of the metal layer 42 to the thickness of the electrode finger 18.

[0048] As shown in Figures 6(a) and 6(b), it was confirmed that the effect of improving the TCF and phase velocity increases as the thickness of the electrode fingers 18 increases and the proportion of the thickness T12 of the metal layer 42 increases.It was confirmed that the TCF and phase velocity are improved when the thickness of the electrode fingers 18 is 0.07λ or more and the proportion of the thickness T12 of the metal layer 42 is 10% or more.

[0049] From the viewpoint of improving the TCF and phase velocity, the ratio of the thickness T12 of the metal layer 42 is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more.

[0050] According to the first embodiment, as shown in FIG. 1(b), the electrode finger 18 includes a first metal layer 31 and a second metal layer 32 disposed between the piezoelectric layer 10 and the first metal layer 31. The second metal layer 32 includes a first portion 36 located at the center in the X direction and second portions 37 that sandwich the first portion 36 in the X direction and have a smaller Young's modulus and acoustic impedance than the first portion 36. This makes it possible to suppress an increase in phase velocity and improve the TCF, as in model A in FIGS. 4(a) and 4(b). In other words, it is possible to achieve both improved temperature characteristics and a smaller device size.

[0051] In Example 1, the ratio of the thickness T2 of the second metal layer 32 to the thickness of the electrode fingers 18 (the thickness T1 of the first metal layer 31 plus the thickness T2 of the second metal layer 32) is 10% or more. This makes it possible to suppress an increase in phase velocity and improve the TCF, as shown in FIGS. 6(a) and 6(b). From the viewpoint of improving the TCF and phase velocity, the ratio of the thickness T2 of the second metal layer 32 to the thickness of the electrode fingers 18 is preferably 15% or more, more preferably 20% or more, and even more preferably 25% or more. Because the first metal layer 31 is a low-resistance layer through which current mainly flows, the ratio of the thickness T2 of the second metal layer 32 to the thickness of the electrode fingers 18 is preferably 40% or less, more preferably 35% or less, and even more preferably 30% or less.

[0052] In Example 1, the thickness of the electrode fingers 18 is 0.14 times (i.e., 0.07λ) or more the average pitch D of the electrode fingers 18 of a pair of comb electrodes 20. This makes it possible to suppress an increase in phase velocity and improve the TCF, as shown in FIGS. 6(a) and 6(b). From the viewpoint of improving the TCF and phase velocity, the thickness of the electrode fingers 18 is preferably 0.16 times or more the average pitch D, more preferably 0.18 times or more, and even more preferably 0.20 times or more. The average pitch D of the electrode fingers 18 can be calculated by dividing the length of the IDT 22 in the X direction by the number of electrode fingers 18.

[0053] In Example 1, the ratio of the total length (W3×2) in the X direction of the second portions 37 to the length W1 in the X direction of the electrode fingers 18 is 20% or more and 60% or less. This makes it possible to suppress an increase in phase velocity and improve the TCF, as shown in Figures 5(a) and 5(b). From the viewpoint of improving the TCF and phase velocity, the ratio of the total length (W3×2) in the X direction of the second portions 37 to the length W1 in the X direction of the electrode fingers 18 is preferably 30% or more and 60% or less, more preferably 40% or more and 60% or less, and even more preferably 40% or more and 50% or less.

[0054] In Example 1, the first portion 36 of the second metal layer 32 is mainly composed of titanium nitride, and the second portion 37 is mainly composed of titanium, which makes it possible to suppress an increase in phase velocity and improve the TCF.

[0055] [Variations] FIG. 7 is a cross-sectional view of an electrode finger 18 in a modification of the first embodiment. As shown in FIG. 7, a third metal layer 33 may be provided between the first metal layer 31 and the second metal layer 32. The third metal layer 33 may be a titanium nitride layer made of the same material as the first portion 36 of the second metal layer 32, a titanium layer made of the same material as the second portion 37 of the second metal layer 32, or another metal material. The thickness T3 of the third metal layer 33 is, for example, 10% or less of the thickness of the second metal layer 32, and may be 5% or less. The other configurations are the same as those of the first embodiment, and therefore description thereof will be omitted.

[0056] When the first metal layer 31 is primarily composed of aluminum and the second portion 37 of the second metal layer 32 is primarily composed of titanium, if the first metal layer 31 and the second portion 37 are in contact as in Example 1, diffusion may occur between the aluminum and titanium. In this modification, a third metal layer 33 is provided between the first metal layer 31 and the second metal layer 32, so that the first metal layer 31 and the second portion 37 are not in contact. If the third metal layer 33 is, for example, a titanium nitride layer, which is the same material as the first portion 36, diffusion between the first metal layer 31 and the second portion 37 can be suppressed.

[0057] In the first embodiment and its modified examples, the piezoelectric layer 10 is a piezoelectric substrate, but the present invention is not limited to this, and the piezoelectric layer 10 may be provided on a support substrate. In this case, the thickness of the piezoelectric layer 10 may be 1.0λ or less, or 0.5λ or less. 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 a smooth surface or a rough surface. In addition, although the present invention is not limited to this, the acoustic wave device may be a sensor or the like. [Example]

[0058] FIG. 8(a) is a circuit diagram of a filter 200 according to a second 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 and its modifications can be used for at least one of the series resonators S1 to S4 and the parallel resonators P1 to P3. The numbers of the series resonators and the parallel resonators can be set as appropriate. Although a ladder-type filter is shown as an example of the filter, the filter may also be a multi-mode filter.

[0059] FIG. 8(b) is a circuit diagram of a duplexer 210 according to a modified example of the second embodiment. As shown in FIG. 8(b), a transmit filter 60 is connected between a common terminal Ant and a transmit terminal Tx. A receive filter 62 is connected between the common terminal Ant and a receive terminal Rx. The transmit filter 60 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 62 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 60 and the receive filter 62 can be the filter of the second embodiment. Although a duplexer has been shown as an example of a multiplexer, a triplexer or a quadplexer may also be used.

[0060] 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]

[0061] 10...piezoelectric layer, 15...conductive film, 18...electrode finger, 19...bus bar, 20...comb-shaped electrode, 22...IDT, 24...reflector, 25...intersection region, 26...acoustic wave resonator, 31...first metal layer, 32...second metal layer, 36...first portion, 37, 37a, 37b...second portion, 41...metal layer, 42...metal layer, 43...central portion, 44...end portion, 45...metal layer, 46...metal layer, 47...metal layer, 48...portion, 49...portion, 60...transmitting filter, 62...receiving filter, 100...acoustic wave device, 200...filter, 210...duplexer

Claims

1. a piezoelectric layer; an elastic wave device comprising: a pair of comb electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers, the plurality of electrode fingers including a first metal layer; and a second metal layer provided between the piezoelectric layer and the first metal layer, the second metal layer having a first portion located in the center in the short direction of the plurality of electrode fingers and a second portion sandwiching the first portion in the short direction and having a Young's modulus and acoustic impedance smaller than those of the first portion.

2. The acoustic wave device according to claim 1 , wherein a ratio of a thickness of the second metal layer to a thickness of the plurality of electrode fingers is 10% or more.

3. The acoustic wave device according to claim 2 , wherein the thickness of the plurality of electrode fingers is equal to or greater than 0.14 times the average pitch of the plurality of electrode fingers of the pair of interdigital transducers.

4. 3. The acoustic wave device according to claim 1, wherein a ratio of the total length in the short direction of the second portions sandwiching the first portion to the length in the short direction of the plurality of electrode fingers is 20% or more and 60% or less.

5. 3. The acoustic wave device according to claim 1, wherein a ratio of the total length in the short direction of the second portions sandwiching the first portion to the length in the short direction of the plurality of electrode fingers is 40% or more and 50% or less.

6. the first portion is primarily composed of titanium nitride; The acoustic wave device according to claim 1 , wherein the second portion is mainly composed of titanium.

7. The acoustic wave device according to claim 6 , wherein the first metal layer is primarily made of aluminum.

8. A filter comprising the acoustic wave device according to claim 1 or 2.

9. A multiplexer including the filter of claim 8.

Images