Elastic wave devices, filters, and multiplexers

Abstract

This invention provides an elastic wave device capable of improving the power handling capacity of electrode fingers. [Solution] The elastic wave device 100 comprises a piezoelectric layer 15, a pair of comb-shaped electrodes 22 provided on the piezoelectric layer 15 and each having a plurality of electrode fingers 23 and a bus bar 24 connecting the plurality of electrode fingers 23, and an additional film 40 provided between the piezoelectric layer 15 and the plurality of electrode fingers 23 in a first region 50 that includes at least the range from the tips 27 of the plurality of electrode fingers 23 to twice the average pitch D of the plurality of electrode fingers 23, and not provided in a second region 52 between the first region 50 and the bus bar 24.

Description

[Technical Field]

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

[0002] In high-frequency communication systems, such as mobile phones, high-frequency filters are used to remove unwanted signals outside the frequency band used for communication. Surface acoustic wave (SAW) resonators are used as high-frequency filters. In a surface acoustic wave resonator, a pair of comb-shaped electrodes, each having multiple electrode fingers, are provided on a piezoelectric layer. Electrode fingers are known in which an aluminum layer or an aluminum alloy layer is provided on a titanium alloy layer or a titanium nitride layer (e.g., Patent Document 1). Furthermore, acoustic wave devices utilizing the piston mode are known to suppress spurious signals. A configuration is known in which a mass loading film is provided on the tip of the electrode finger to establish the piston mode (e.g., Patent Document 2). A configuration is also known in which a mass loading film is provided between the piezoelectric layer and the tip of the electrode finger (e.g., Patent Document 3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Special Publication No. 2005-518127 [Patent Document 2] Special Publication No. 2013-518455 [Patent Document 3] International Publication No. 2023 / 140354 [Overview of the initiative] [Problems that the invention aims to solve]

[0004] When a high-power signal is applied to a pair of comb-shaped electrodes, damage to the electrode fingers may occur.

[0005] This invention has been made in view of the above problems, and aims to improve the power resistance of electrode fingers. [Means for solving the problem]

[0006] The present invention is an elastic wave device comprising: a piezoelectric layer; a pair of comb-shaped electrodes provided on the piezoelectric layer, each having a plurality of electrode fingers and a busbar connecting the plurality of electrode fingers; and an additional film provided between the piezoelectric layer and the plurality of electrode fingers in a first region that includes at least a range from the tips of the plurality of electrode fingers to twice the average pitch of the plurality of electrode fingers, and not provided in a second region between the first region and the busbar.

[0007] In the above configuration, the plurality of electrode fingers may include an adhesion layer provided on the piezoelectric layer and a conductive layer provided on the adhesion layer and made of a metal having a lower electrical resistivity than the adhesion layer.

[0008] In the above configuration, the additional film and the adhesion layer can have a Young's modulus greater than that of the conductive layer.

[0009] In the above configuration, in the first region, the ratio of the total thickness of the additional film and the adhesion layer to the distance from the piezoelectric layer to the upper surface of the plurality of electrode fingers can be 25% or more.

[0010] In the above configuration, the additional film can be formed from a conductive material.

[0011] In the above configuration, the additional film can be formed from the same material as the adhesion layer.

[0012] In the above configuration, the conductive layer may be an aluminum layer or an aluminum alloy layer, and the adducting film and the adhesion layer may be a titanium layer, a titanium nitride layer, or a chromium layer.

[0013] In the above configuration, the first region may be configured to include a range from the tips of the plurality of electrode fingers to 4.8 times the average pitch.

[0014] The present invention provides a filter including the acoustic wave device described above.

[0015] The present invention provides a multiplexer including the filter described above. Effects of the Invention

[0016] According to the present invention, the power durability of electrode fingers can be improved. Brief Description of Drawings

[0017] [Figure 1] Fig. 1(a) is a plan view of the acoustic wave device according to Example 1, and Fig. 1(b) is a cross-sectional view taken along line A-A in Fig. 1(a). [Figure 2] Fig. 2(a) is a plan view showing wavenumbers in the X direction and the Y direction in Fig. 1(a), and Fig. 2(b) is a diagram showing ky / ω versus kx / ω. [Figure 3] Fig. 3(a) is a plan view of an acoustic wave device according to a comparative example, and Fig. 3(b) is a cross-sectional view taken along line A-A in Fig. 3(a). [Figure 4] Fig. 4 is a diagram showing the result of displacement relative to the position in the Y direction of an intersection region in the comparative example. [Figure 5] Fig. 5 is a perspective view of a model corresponding to the acoustic wave device according to the comparative example used in Simulation 2. [Figure 6] Fig. 6 is a diagram showing the strain generated in the conductive layer and the breakdown power when fracture occurs in the electrode finger, versus the ratio of the thickness of the adhesion layer to the conductive layer in the comparative example. [Figure 7] Fig. 7(a) is a circuit diagram of a filter according to Example 2, and Fig. 7(b) is a circuit diagram of a duplexer according to a modification of Example 2. Mode for Carrying Out the Invention

[0018] The embodiments of the present invention will be described below with reference to the drawings. [Examples]

[0019] Example 1 describes an example in which an elastic wave device has an elastic wave resonator. Figure 1(a) is a plan view of the elastic wave device 100 according to Example 1, and Figure 1(b) is a cross-sectional view AA of Figure 1(a). The arrangement direction of the multiple electrode fingers 23 is the X direction, the longitudinal direction of the electrode fingers 23 is the Y direction, and the stacking direction of the substrate 10 and the piezoelectric layer 15 is the Z direction. The X, Y, and Z directions do not necessarily correspond to the X-axis and Y-axis directions of the crystal orientation of the piezoelectric layer 15. If the piezoelectric layer 15 is a piezoelectric layer with rotational Y-cut X propagation, the X direction is the X-axis direction of the crystal orientation.

[0020] As shown in Figures 1(a) and 1(b), a piezoelectric layer 15 is provided on the substrate 10. An insulating layer 11 is provided between the substrate 10 and the piezoelectric layer 15. An insulating layer 12 is provided between the insulating layer 11 and the piezoelectric layer 15. An elastic wave resonator 20 is provided on the piezoelectric layer 15.

[0021] The elastic wave resonator 20 includes an IDT (Interdigital Transducer) 21 and a reflector 25. The reflector 25 is provided on both sides of the IDT 21 in the X direction. The IDT 21 comprises a pair of opposing comb-shaped electrodes 22. The comb-shaped electrodes 22 comprise a plurality of electrode fingers 23 and a busbar 24 to which the plurality of electrode fingers 23 are connected. The region where the electrode fingers 23 of the pair of comb-shaped electrodes 22 intersect is the intersection region 26. The length of the intersection region 26 in the Y direction is the aperture length. The anisotropy coefficient γ in the intersection region 26 is positive.

[0022] The pair of comb-shaped electrodes 22 have alternating electrode fingers 23, one at a time, in at least a portion of the intersection region 26. The elastic wave that primarily excites the multiple electrode fingers 23 in the intersection region 26 propagates mainly in the X direction. The pitch of the electrode fingers 23 of one of the pair of comb-shaped electrodes 22 is approximately equal to the wavelength λ of the elastic wave. The wavelength λ is approximately twice the average pitch D of the multiple electrode fingers 23. The average pitch D can be calculated by dividing the length of the IDT 21 in the X direction by the number of electrode fingers 23. The reflector 25 reflects the elastic wave (surface acoustic wave) excited by the electrode fingers 23 of the IDT 21. As a result, the elastic wave is confined within the intersection region 26 of the IDT 21.

[0023] The piezoelectric layer 15 is, for example, a single-crystal lithium tantalate (LiTaO3) layer or a single-crystal lithium niobate (LiNbO3) layer, and is, for example, a rotating Y-cut X-propagating lithium tantalate layer or a rotating Y-cut X-propagating lithium niobate layer. The thickness of the piezoelectric layer 15 is preferably 1.0λ or less from the viewpoint of suppressing spurious emissions and losses, and preferably 0.2λ or more from the viewpoint of exciting elastic waves. The substrate 10 is, for example, a sapphire substrate, an alumina substrate, a silicon substrate, a spinel substrate, a quartz substrate, a silica substrate, or a silicon carbide substrate. The coefficient of linear expansion of the substrate 10 in the X direction is smaller than the coefficient of linear expansion of the piezoelectric layer 15 in the X direction. This makes it possible to reduce the frequency-temperature dependence of the elastic wave resonator 20.

[0024] The insulating layer 11 is, for example, polycrystalline or amorphous, and is an aluminum oxide layer, silicon nitride layer, aluminum nitride layer, silicon carbide layer, or polysilicon layer. The speed of sound of the bulk wave propagating through the insulating layer 11 is faster than the speed of sound of the bulk wave propagating through the insulating layer 12 and the piezoelectric layer 15. As a result, the energy of the main response elastic wave is confined in the piezoelectric layer 15 and the insulating layer 12. From the viewpoint of confining the elastic wave within the insulating layer 12 and the piezoelectric layer 15, the thickness of the insulating layer 11 is preferably 0.3λ or more. From the viewpoint of improving the characteristics, the thickness of the insulating layer 11 is preferably 10λ or less. The speed of sound of the bulk wave in each layer is the speed of sound of the transverse wave Vs, and if the shear modulus is G and the density is ρ, then Vs = (G / ρ) 1 / 2It is expressed as follows. The shear modulus G is expressed as G = E / 2(1+ν), where E is Young's modulus and ν is Poisson's ratio.

[0025] The insulating layer 12 is, for example, a temperature compensation film and has a temperature coefficient of elasticity with the opposite sign to the sign of the temperature coefficient of elasticity of the piezoelectric layer 15. For example, the temperature coefficient of elasticity of the piezoelectric layer 15 is negative, and the temperature coefficient of elasticity of the insulating layer 12 is positive. The insulating layer 12 is, for example, a silicon oxide (SiO2) layer with no additives or containing additive elements such as fluorine, phosphorus, or boron, and is, for example, polycrystalline or amorphous. This makes it possible to reduce the frequency temperature coefficient of the elastic wave resonator 20. For the insulating layer 12 to have a temperature compensation function, it is required that some of the energy of the elastic wave of the main response be present within the insulating layer 12. Since the range in which the energy of the surface acoustic wave is concentrated is typically in the range of 2.0λ from the upper surface of the piezoelectric layer 15, the distance from the lower surface of the insulating layer 12 to the upper surface of the piezoelectric layer 15 is preferably 2.0λ or less.

[0026] The IDT 21, such as the electrode finger 23, and the reflector 25 include an adhesion layer 30 provided on the piezoelectric layer 15, and a conductive layer 32 provided on the adhesion layer 30 and formed of a metal with lower electrical resistivity than the adhesion layer. The adhesion layer 30 has a higher Young's modulus than the conductive layer 32, for example. The adhesion layer 30 is formed of, for example, titanium, titanium nitride, or chromium. The conductive layer 32 is formed of, for example, aluminum or an aluminum alloy.

[0027] An additional film 40 is provided between the piezoelectric layer 15 and the electrode finger 23 in a first region 50 that includes at least the area from the tip 27 of the electrode finger 23 to 1.0λ. In a second region 52 between the first region 50 and the busbar 24, the additional film 40 is not provided between the piezoelectric layer 15 and the electrode finger 23. The additional film 40 has a Young's modulus greater than that of the conductive layer 32, for example. The additional film 40 is formed of a conductive material, for example, the same metal as the adhesion layer 30. If the additional film 40 is formed of the same metal as the adhesion layer 30, the conductive layer 32 will be formed of a metal with a lower electrical resistivity than the additional film 40. The additional film 40 is formed of, for example, titanium, titanium nitride, or chromium.

[0028] In the first region 50, let T1 be the distance from the piezoelectric layer 15 to the upper surface of the electrode finger 23, T2 be the thickness of the conductive layer 32, and T3 be the total thickness of the adductive film 40 and the adhesion layer 30. The ratio of T3 to T1 (T3 / T1) is 40% or more. In other words, the ratio of T3 to T2 (T3 / T2) is 60% or more.

[0029] [Manufacturing method] A method for manufacturing the elastic wave device 100 according to Example 1 will now be described. First, an insulating layer 11 and an insulating layer 12 are formed on the substrate 10 in that order. The insulating layers 11 and 12 are formed using, for example, sputtering, CVD (Chemical Vapor Deposition), or vacuum deposition. Next, a piezoelectric layer 15 is bonded to the insulating layer 12 using, for example, a surface activation method. After that, the piezoelectric layer 15 is polished to a desired thickness using, for example, CMP (Chemical Mechanical Polishing). Next, a film of the material for the additional film 40 is formed on the piezoelectric layer 15 using, for example, sputtering, CVD, or vacuum deposition, and then the additional film 40 is formed by patterning the film using photolithography and etching. Next, the IDT 21 and the reflector 25 are formed using, for example, a lift-off method. As a result, the elastic wave device 100 according to Example 1 is formed.

[0030] [Regarding the anisotropy coefficient] Figure 2(a) is a plan view of the wavenumbers in the X and Y directions in Figure 1(a), and Figure 2(b) is k x k for / ω y This is a diagram showing / ω. In Figure 2(b), k x / ω corresponds to the inverse velocity of the X-direction component, k y / ω corresponds to the inverse velocity of the Y-direction component. As shown in Figure 2(a), the wavenumber of the elastic wave in the X-direction is k x k is the wave number of the elastic wave in the Y direction. y Let's assume that the wave number k0 of an elastic wave rotated from the X direction by an angle θ in the Y direction can be approximated as a parabola with respect to the angle θ. Then, using the anisotropy coefficient γ, the wave number k0 can be expressed as k x2 +γ·k y 2 =k0 2 is represented by.

[0031] As shown in FIG. 2(b), when the anisotropy coefficient γ in the intersecting region 26 is positive, the inverse velocity surface 60 is convex when viewed from the origin. Therefore, when the anisotropy coefficient γ>0, it is also referred to as a convex type. When the anisotropy coefficient γ is positive, transverse mode spurious is likely to occur. Accordingly, large displacement is likely to occur at the tip portions of the electrode fingers 23.

[0032] [Comparative Example] FIG. 3(a) is a plan view of an acoustic wave device 500 according to a comparative example, and FIG. 3(b) is a cross-sectional view taken along line A-A in FIG. 3(a). As shown in FIG. 3(a) and FIG. 3(b), in the comparative example, the additional film 40 is not provided between the piezoelectric layer 15 and the electrode fingers 23. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

[0033] [Simulation 1] A model having the same configuration as that of the acoustic wave device according to the comparative example was created, and a simulation was performed on displacement that occurs when a voltage is applied between a pair of comb-shaped electrodes 22. The simulation conditions are as follows. Wavelength λ of acoustic wave: 2.2 μm Substrate 10: sapphire substrate Insulating layer 11: aluminum oxide (Al₂O₃) layer with a thickness of 6000 nm Insulating layer 12: silicon oxide (SiO₂) layer with a thickness of 500 nm Piezoelectric layer 15: 48° rotated Y-cut X-propagation lithium tantalate layer with a thickness of 700 nm Adhesion layer 30: titanium layer with a thickness of 50 nm Conductive layer 32: aluminum layer with a thickness of 110 nm Aperture length: 20λ Voltage applied between the pair of comb-shaped electrodes 22: 1 V

[0034] Figure 4 shows the displacement results with respect to the Y-direction position of the intersection region 26 in the comparative example. The horizontal axis shows the Y-direction position of the intersection region 26, and the vertical axis shows the displacement that occurred in the intersection region 26. Position P on the horizontal axis is one end of the intersection region 26 in the Y-direction, and position Q is the other end of the intersection region 26 in the Y-direction. As shown in Figure 4, the displacement that occurred in the edge region 28 located at the Y-direction edge of the intersection region 26 was greater than the displacement that occurred in the central region 29 located inside the edge region 28. Let L1 be the distance from position P to the position of displacement equal to the maximum displacement in the central region 29. Similarly, let L2 be the distance from position Q to the position of displacement equal to the maximum displacement in the central region 29. Both distances L1 and L2 were approximately 2.4λ.

[0035] The simulation results in Figure 4 show that the displacement is larger in the range of 2.4λ from the Y-direction end of the intersection region 26. In particular, the displacement is larger in the range of 2.0λ from the Y-direction end of the intersection region 26, even larger in the range of 1.5λ, and even larger in the range of 1.0λ.

[0036] [Simulation 2] Figure 5 is a perspective view of a model corresponding to the elastic wave device in the comparative example used in Simulation 2. As shown in Figure 5, the model used in Simulation 2 has an insulating layer 11, an insulating layer 12, and a piezoelectric layer 15 on a substrate 10 in that order. An infinitely long electrode finger 23 is provided on the piezoelectric layer 15. The electrode finger 23 has a laminated structure of an adhesion layer 30 and a conductive layer 32. A simulation was performed to see how the strain generated in the conductive layer 32 changes according to the thickness ratio of the adhesion layer 30 and the conductive layer 32 when a voltage of 1V is applied between adjacent electrode fingers 23. The simulation conditions are as follows. Wavelength of elastic wave λ: 1.5 μm Substrate 10: Sapphire substrate Insulating layer 11: Aluminum oxide (Al2O3) layer with a thickness of 6000 nm. Insulating layer 12: Silicon oxide (SiO2) layer with a thickness of 300 nm. Piezoelectric layer 15: 450 nm thick, 42° rotated Y-cut X-propagating lithium tantalate layer Adhesion layer 30: Titanium layer Conductive layer 32: Aluminum layer Total thickness of adhesion layer 30 and conductive layer 32: 150 nm

[0037] Furthermore, multiple elastic wave devices 500 relating to the comparative example were fabricated by changing the ratio of the thickness of the adhesion layer 30 to the conductive layer 32, and the power at which fracture occurred in the electrode fingers 23 when a signal was applied to a pair of comb-shaped electrodes 22 was determined.

[0038] Figure 6 shows the results of the strain generated in the conductive layer 32 and the breakdown power when the electrode finger 23 broke, in relation to the ratio of the thickness of the adhesion layer 30 to the thickness of the conductive layer 32 in the comparative example. The horizontal axis shows the ratio of the thickness of the adhesion layer 30 to the thickness of the conductive layer 32 (adhesion layer 30 / conductive layer 32), the left vertical axis shows the strain generated in the conductive layer 32 in the simulation, and the right vertical axis shows the breakdown power when the electrode finger 23 broke in the experiment.

[0039] As shown in Figure 6, the greater the ratio of the thickness of the adhesion layer 30 to the thickness of the conductive layer 32, the smaller the strain generated in the conductive layer 32 and the greater the breakdown power that causes the electrode finger 23 to break. In other words, the greater the ratio of the thickness of the adhesion layer 30 to the thickness of the electrode finger 23, the smaller the strain generated in the conductive layer 32 and the greater the breakdown power that causes the electrode finger 23 to break. The reason why the strain generated in the conductive layer 32 decreased as the ratio of the thickness of the adhesion layer 30 increased is not clear, but the following reasons can be considered. When a voltage is applied to the electrode finger 23 and the piezoelectric layer 15 is distorted, it is thought that the thicker the adhesion layer 30 provided between the conductive layer 32 and the piezoelectric layer 15, the less likely the strain in the piezoelectric layer 15 is to be transmitted to the conductive layer 32. For this reason, it is thought that the strain generated in the conductive layer 32 decreased. In addition, the adhesion layer 30 is a titanium layer, and its Young's modulus is greater than that of the aluminum layer which is the conductive layer 32. Therefore, even if the piezoelectric layer 15 is distorted, the deformation of the adhesion layer 30 is suppressed, which also contributes to the reduced strain on the conductive layer 32. Furthermore, since the deformation of the adhesion layer 30 is suppressed, its displacement is also considered to be small.

[0040] As the ratio of the thickness of the adhesion layer 30 increases, the strain generated in the conductive layer 32 decreases, which is thought to increase the breakdown power that causes the electrode finger 23 to break. From the viewpoint of reducing the strain generated in the conductive layer 32, a ratio of the thickness of the adhesion layer 30 to the thickness of the conductive layer 32 of 0.3 or more is preferable. In other words, a ratio of the thickness of the adhesion layer 30 to the total thickness of the adhesion layer 30 and the conductive layer 32 (distance from the piezoelectric layer 15 to the upper surface of the electrode finger 23) of 25% or more is preferable. In addition, a breakdown power of 34.5 dBm or more is sometimes required. In this case, a ratio of the thickness of the adhesion layer 30 to the thickness of the conductive layer 32 of 0.6 or more is preferable. That is, a ratio of the thickness of the adhesion layer 30 to the total thickness of the adhesion layer 30 and the conductive layer 32 (distance from the piezoelectric layer 15 to the upper surface of the electrode finger 23) of 40% or more is preferable.

[0041] The strain generated in the conductive layer 32 can be reduced by increasing the proportion of the thickness of the adhesion layer 30 and by using a material with a high Young's modulus for the adhesion layer 30. However, increasing the proportion of the thickness of the adhesion layer 30 reduces the thickness of the conductive layer 32, which increases the electrical resistance of the electrode fingers 23. A higher electrical resistance of the electrode fingers 23 leads to increased losses.

[0042] As shown in Figure 4, the displacement occurring in the range of 1.0λ from the Y-direction end of the intersection region 26 is large, suggesting that fracture is likely to occur at the tip of the electrode finger 23. Therefore, increasing the thickness of the adhesion layer 30 at the tip of the electrode finger 23 would make it more difficult for strain in the piezoelectric layer 15 to be transmitted to the conductive layer 32, thereby suppressing fracture of the electrode finger 23. Furthermore, increasing the thickness of the adhesion layer 30 only at the tip of the electrode finger 23 would suppress an increase in the electrical resistance of the electrode finger 23. Considering these points, it is thought that not only by increasing the thickness of the adhesion layer 30 at the tip of the electrode finger 23, but also by providing an additional film between the tip of the electrode finger 23 and the piezoelectric layer 15, fracture of the electrode finger 23 and an increase in the electrical resistance of the electrode finger 23 can be suppressed.

[0043] In Example 1, as shown in Figures 1(a) and 1(b), an additional film 40 is provided between the piezoelectric layer 15 and the electrode finger 23 in a first region 50 that includes at least the area from the tip 27 of the electrode finger 23 to 1.0λ (twice the average pitch D). In the second region 52 between the first region 50 and the busbar 24, the additional film 40 is not provided between the piezoelectric layer 15 and the electrode finger 23. This reduces the strain that occurs at the tip of the electrode finger 23. Therefore, even when a high-power signal is applied to the pair of comb-shaped electrodes 22, the displacement that occurs at the tip of the electrode finger 23 can be suppressed, thus preventing damage to the electrode finger 23. Consequently, the power withstand capability of the electrode finger 23 can be improved.

[0044] From the viewpoint of suppressing displacement occurring in the electrode finger 23, the first region 50 on which the additional film 40 is provided preferably includes a range from the tip 27 of the electrode finger 23 to 1.5λ (3 times the average pitch D), more preferably includes a range up to 2.0λ (4 times the average pitch D), and even more preferably includes a range up to 2.4λ (4.8 times the average pitch D). If the area on which the additional film 40 is provided becomes too large, it is thought that the adverse effects on the electrode finger 23 will increase. Therefore, the first region 50 preferably includes a range from the tip 27 of the electrode finger 23 to 4.0λ (8 times the average pitch D), more preferably up to 3.5λ (7 times the average pitch D), and even more preferably up to 3.0λ (6 times the average pitch D).

[0045] Furthermore, in Example 1, as shown in Figure 1(b), the electrode finger 23 includes an adhesion layer 30 provided on the piezoelectric layer 15 and a conductive layer 32 provided on the adhesion layer 30 and made of a metal with a lower electrical resistivity than the adhesion layer 30. In this case, by providing an additional film 40 between the piezoelectric layer 15 and the electrode finger 23 in the first region 50, it is possible to suppress the occurrence of damage to the electrode finger 23 without increasing the thickness of the adhesion layer 30. Thus, it is possible to suppress the damage to the electrode finger 23 and also suppress an increase in the electrical resistance of the electrode finger 23.

[0046] Furthermore, in Example 1, the added film 40 and the adhesion layer 30 have a higher Young's modulus than the conductive layer 32. As a result, even if the piezoelectric layer 15 is distorted, the added film 40 and the adhesion layer 30 are less likely to deform, thus reducing the strain transmitted to the conductive layer 32. Therefore, damage to the electrode fingers 23 can be suppressed.

[0047] Furthermore, in Example 1, in the first region 50, the ratio of the total thickness T3 of the additional film 40 and the adhesion layer 30 to the distance T1 from the piezoelectric layer 15 to the upper surface of the electrode finger 23 is 25% or more. In other words, the ratio of the total thickness T3 of the additional film 40 and the adhesion layer 30 to the thickness T2 of the conductive layer 32 is 30% or more. As a result, as shown in Figure 6, the strain generated in the conductive layer 32 can be reduced, and thus the failure of the electrode finger 23 can be suppressed.

[0048] From the viewpoint of suppressing the destruction of the electrode finger 23, the ratio of thickness T3 to distance T1 is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more. If the added film 40 becomes too thick, there is a risk of cracks or breakage in the electrode finger 23 at the location of the added film 40, so the ratio of thickness T3 to distance T1 is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less.

[0049] Furthermore, in Example 1, the additional film 40 is formed of a conductive material. This makes it possible to reduce the electrical resistance at the tip of the electrode finger 23 compared to the case where the additional film 40 is formed of an insulating material.

[0050] Furthermore, in Example 1, the additional film 40 is formed from the same material as the adhesion layer 30. This suppresses film peeling at the tip of the electrode finger 23.

[0051] In Example 1, the conductive layer 32 is an aluminum layer or an aluminum alloy layer. The addition film 40 and the adhesion layer 30 are a titanium layer, a titanium nitride layer, or a chromium layer. In this case, since the addition film 40 and the adhesion layer 30 have a higher Young's modulus than the conductive layer 32, the transmission of strain from the piezoelectric layer 15 to the conductive layer 32 can be suppressed, and the occurrence of fracture in the electrode finger 23 can be suppressed. Furthermore, the occurrence of film peeling in the electrode finger 23 can also be suppressed. The titanium nitride layer is, for example, a TiN layer or a TiAlN layer. [Examples]

[0052] Figure 7(a) is a circuit diagram of the filter 200 according to Embodiment 2. As shown in Figure 7(a), one or more series resonators S1 to S4 are connected in series between the input terminal Tin and the 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. At least one of the series resonators S1 to S4 and the parallel resonators P1 to P3 can be the elastic wave device of Embodiment 1. The number of series and parallel resonators can be set as appropriate. A ladder filter is shown as an example of the filter, but a multimode filter may also be used.

[0053] Figure 7(b) is a circuit diagram of a duplexer 210 according to a modified example of Embodiment 2. As shown in Figure 7(b), a transmit filter 70 is connected between the common terminal Ant and the transmit terminal Tx. A receive filter 72 is connected between the common terminal Ant and the receive terminal Rx. The transmit filter 70 allows the transmit band signal from the high-frequency signal input from the transmit terminal Tx to pass to the common terminal Ant as the transmit signal, and suppresses signals of other frequencies. The receive filter 72 allows the receive band signal from the high-frequency signal input from the common terminal Ant to pass to the receive terminal Rx as the receive signal, and suppresses signals of other frequencies. At least one of the transmit filter 70 and the receive filter 72 can be the filter of Embodiment 2. A duplexer is shown as an example of a multiplexer, but a triplexer or quadplexer may also be used.

[0054] Although embodiments of the present invention have been described in detail above, the present invention is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as described in the claims. [Explanation of symbols]

[0055] 10...Substrate, 11...Insulating layer, 12...Insulating layer, 15...Piezoelectric layer, 20...Elastic wave resonator, 21...IDT, 22...Comb-type electrode, 23...Electrode fingers, 24...Busbar, 25...Reflector, 26...Crossing region, 27...Tip, 28...Edge region, 29...Central region, 30...Adhesion layer, 32...Conductive layer, 40...Additional film, 50...First region, 52...Second region, 60...Inverse velocity surface, 70...Transmitting filter, 72...Receiving filter, 100, 500...Elastic wave device, 200...Filter, 210...Duplexer

Claims

1. Piezoelectric layer and A pair of comb-shaped electrodes are provided on the piezoelectric layer, each having a plurality of electrode fingers and a busbar connecting the plurality of electrode fingers, An elastic wave device comprising: an additional film provided between the piezoelectric layer and the plurality of electrode fingers in a first region that includes at least a range from the tips of the plurality of electrode fingers to twice the average pitch of the plurality of electrode fingers, and not provided in a second region between the first region and the busbar.

2. The elastic wave device according to claim 1, wherein the plurality of electrode fingers include an adhesion layer provided on the piezoelectric layer and a conductive layer provided on the adhesion layer and formed of a metal having a lower electrical resistivity than the adhesion layer.

3. The elastic wave device according to claim 2, wherein the added film and the adhesion layer have a Young's modulus greater than that of the conductive layer.

4. The elastic wave device according to claim 2 or 3, wherein in the first region, the ratio of the total thickness of the additional film and the adhesion layer to the distance from the piezoelectric layer to the upper surface of the plurality of electrode fingers is 25% or more.

5. The elastic wave device according to any one of claims 1 to 3, wherein the additional film is formed of a conductive material.

6. The elastic wave device according to claim 2 or 3, wherein the additional film is formed from the same material as the adhesion layer.

7. The conductive layer is an aluminum layer or an aluminum alloy layer. The elastic wave device according to claim 2 or 3, wherein the adducting film and the adhesion layer are a titanium layer, a titanium nitride layer, or a chromium layer.

8. The elastic wave device according to any one of claims 1 to 3, wherein the first region includes a range from the tips of the plurality of electrode fingers to 4.8 times the average pitch.

9. A filter comprising an elastic wave device according to any one of claims 1 to 3.

10. A multiplexer comprising the filter described in claim 9.

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