Acoustic wave device

Abstract

To provide an acoustic wave device having improved power resistance.SOLUTION: The acoustic wave device includes a piezoelectric substrate and an IDT electrode 4 formed on the piezoelectric substrate, the IDT electrode including a multilayer portion 60 in which first metal layers 20,31,32,33 made of a first metal and second metal layers 41,42,43 made of a second metal having a higher density and a lower electrical resistivity than the first metal are alternately provided, and a third metal layer 50 formed on the multilayer portion and made of a third metal having a lower density and a lower electrical resistivity than the first metal and the second metal. At least three first metal layers are provided, and at least two second metal layers are provided.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device in which an IDT electrode is provided on a piezoelectric layer. [Background technology]

[0002] For example, SAW (Surface Acoustic Wave) devices are used in the duplexers of mobile phones. A SAW resonator has an IDT (Interdigital Transducer) electrode formed of a metal film provided on the main surface of a piezoelectric substrate.

[0003] Patent Document 1 discloses an acoustic wave device (SAW resonator) including an IDT electrode having a first metal film, which is a titanium or titanium alloy film, provided on a piezoelectric substrate; a second metal film, which is an aluminum or aluminum alloy film, provided on the first metal film; and a barrier film, such as titanium nitride, provided between the first and second metal films to suppress interdiffusion of titanium and aluminum. According to the acoustic wave device of Patent Document 1, a titanium or titanium alloy film, which has high stress resistance, is provided between aluminum, which has low stress resistance, and the piezoelectric substrate on which surface acoustic waves are excited. This prevents stress caused by deformation of the piezoelectric substrate from being applied to the aluminum film. This improves the stress resistance of the entire metal film, thereby improving power durability. Furthermore, the barrier film prevents the formation of intermetallic compound or alloy regions due to interdiffusion between titanium and aluminum, thereby preventing deterioration of the electrode fingers in the IDT electrode. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-064367 Summary of the Invention [Problem to be solved by the invention]

[0005] Thus, the IDT electrodes of surface acoustic wave devices are required to have high power resistance.

[0006] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an acoustic wave device having excellent power durability. [Means for solving the problem]

[0007] One aspect of the acoustic wave device of the present invention is a device comprising: a piezoelectric substrate; an IDT electrode formed on the piezoelectric substrate, the IDT electrode has a laminated portion in which first metal layers made of a first metal and second metal layers made of a second metal having a density higher than that of the first metal and a lower electrical resistivity are alternately provided, and a third metal layer formed on the laminated portion and made of a third metal having a density lower than that of the first metal and the second metal and a lower electrical resistivity; The laminated section has an uppermost layer and a lowermost layer which are the first metal layers, and includes at least three first metal layers and at least two second metal layers. In this way, in the IDT electrode of the acoustic wave device, a laminated portion is provided in which first metal layers made of a first metal and second metal layers made of a second metal that has a higher density and lower electrical resistivity than the first metal are alternately arranged, and the laminated portion is configured to have at least three first metal layers and at least two second metal layers, thereby improving the power resistance of the IDT electrode and increasing the reliability of the acoustic wave device.

[0008] In a specific embodiment of the acoustic wave device of the present invention, the laminated portion includes at least four first metal layers and at least three second metal layers. In this way, by configuring the IDT electrode to have at least four first metal layers and at least three second metal layers, the power durability of the IDT electrode can be improved, thereby increasing the reliability of the acoustic wave device.

[0009] In a specific embodiment of the acoustic wave device of the present invention, the total thickness of the first metal layers in the IDT electrode is smaller than the total thickness of the second metal layers in the IDT electrode. In this way, by configuring the total thickness of the first metal layers in the IDT electrode to be thinner than the total thickness of the second metal layers and making the second metal layers, which have lower electrical resistivity, thicker than the first metal layers, the electrical resistance of the IDT electrode can be reduced, which prevents the IDT electrode from becoming too hot during operation due to the first metal layers, which have higher electrical resistance.This prevents the acoustic wave device from becoming too hot during operation, thereby improving the reliability of the acoustic wave device.

[0010] In a specific aspect of the acoustic wave device of the present invention, the weight ratio of the second metal in the IDT electrode is greater than the weight ratio of the third metal in the IDT electrode. In this way, by increasing the weight ratio of the second metal to the third metal in the IDT electrode, the specific gravity of the IDT electrode can be increased, slowing the sound velocity, which makes it possible to narrow the electrode finger pitch of the IDT electrode and miniaturize the acoustic wave device.

[0011] In a specific embodiment of the acoustic wave device of the present invention, the total thickness of the second metal layer in the IDT electrode is 50 nm or more and 350 nm or less.

[0012] In a specific embodiment of the acoustic wave device of the present invention, the thickness of each of the second metal layers in the IDT electrodes is 20 nm or more and 150 nm or less. By forming the second metal layer thin in this manner, the power durability of the acoustic wave device can be improved.

[0013] As a specific embodiment of the above-described aspect, the acoustic wave device of the present invention includes: The first metal is titanium, the second metal is platinum, and the third metal is aluminum or an alloy of aluminum and copper. [Effects of the Invention]

[0014] According to the acoustic wave device of the present invention, an IDT electrode of the acoustic wave device includes a laminated section including alternating first metal layers made of a first metal and second metal layers made of a second metal having a higher density and lower electrical resistivity than the first metal, and the laminated section includes at least three first metal layers and at least two second metal layers, thereby improving the power durability of the IDT electrode and increasing the reliability of the acoustic wave device. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view illustrating a first embodiment of an acoustic wave device according to the present invention. [Figure 2] 1 is a plan view illustrating an acoustic wave device according to a first embodiment of the present invention. [Figure 3] 2 is a cross-sectional view of the vicinity of an IDT electrode of the acoustic wave device according to the first embodiment. FIG. [Figure 4] FIG. 10 is a cross-sectional view of the vicinity of an IDT electrode in an acoustic wave device of a comparative example. [Figure 5] FIG. 10 is a graph showing output power versus input power of the acoustic wave device of Example 1 and the acoustic wave device of the comparative example. [Figure 6] FIG. 10 is a graph showing admittance |Y| versus frequency for the acoustic wave device of Example 1 and the acoustic wave device of the comparative example. [Figure 7] 10 is a graph showing the Q value versus frequency of the acoustic wave device of Example 1 and the acoustic wave device of the comparative example. FIG. [Figure 8] FIG. 10 is a cross-sectional view of the vicinity of an IDT electrode in an acoustic wave device according to a second embodiment of the present invention. [Figure 9] FIG. 10 is a cross-sectional view of the vicinity of an IDT electrode in an acoustic wave device according to a third embodiment of the present invention. [Figure 10]FIG. 10 is a cross-sectional view of the vicinity of an IDT electrode in an acoustic wave device according to a fourth embodiment of the present invention. [Figure 11] FIG. 10 is a cross-sectional view of the vicinity of an IDT electrode in an acoustic wave device according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] First Embodiment Fig. 1 is a cross-sectional view showing a first embodiment of an acoustic wave device according to the present invention. Fig. 2 is a plan view of the acoustic wave device. The acoustic wave device 1 according to the first embodiment is a SAW resonator, and includes a support substrate 2, a piezoelectric substrate 3, an IDT electrode 4 formed on the piezoelectric substrate 3, and an intermediate layer 6 provided between the support substrate 2 and the piezoelectric substrate 3.

[0017] The support substrate 2 is, for example, a spinel substrate, but may be made of other materials such as a sapphire substrate, silicon substrate, quartz substrate, crystal substrate, alumina substrate, or silicon carbide substrate as long as it can solve the problems of the present invention.

[0018] For example, 36° or 42° rotated Y-cut X-propagation lithium tantalate (LiTaO3) is used for the piezoelectric substrate 3. However, the piezoelectric substrate 3 is not limited to this material, and other materials such as lithium niobate (LiNbO3) can also be used.

[0019] The intermediate layer 6 is a layer provided for at least one of the purposes of increasing the bonding strength between the support substrate 2 and the piezoelectric substrate 3 and increasing the propagation speed of the elastic wave. When the intermediate layer 6 is provided for the purpose of increasing the bonding strength between the support substrate 2 and the piezoelectric substrate 3, silicon dioxide (SiO2) or the like is used for the intermediate layer 6. When the intermediate layer 6 is provided as a layer for increasing the speed of the elastic wave, for example, aluminum nitride (AlN) or boron aluminum nitride (B X Al 1-X In this embodiment, the intermediate layer 6 may be omitted. This also applies to other embodiments described later.

[0020] The pitch of the electrode fingers 7 constituting the IDT electrode 4 is set to be half the wavelength λ of the acoustic wave at the frequency at which the acoustic wave device 1 is desired to resonate.

[0021] 3 is a cross-sectional view showing the vicinity of the IDT electrode 4 provided on the piezoelectric substrate 3 in the first embodiment. The IDT electrode 4 includes a laminated portion 60 provided on the piezoelectric substrate 3, and an aluminum (Al) layer 50 as a third metal layer provided on the laminated portion 60.

[0022] The laminated section 60 includes a bottom titanium (Ti) layer 20 and titanium layers 31, 32, and 33 as first metal layers, and platinum layers 41, 42, and 43 as second metal layers, which are alternately formed. A more detailed description follows. A bottom titanium layer 20 is formed on a piezoelectric substrate 3 as a first metal layer made of titanium. A platinum layer 41 is formed on the bottom titanium layer 20 as a second metal layer made of platinum (Pt), which has a higher density and lower electrical resistivity than titanium. A titanium layer 31 is formed on the platinum layer 41 as a second metal layer. Similarly, a platinum layer 42, a titanium layer 32, a platinum layer 43, and a titanium layer 33 are formed on the titanium layer 31 in this order. The bottom titanium layer 20 may also be simply referred to as the titanium layer 20.

[0023] In this embodiment, the laminated section 60 has a titanium layer 33 as the top layer and a bottom titanium layer 20 as the bottom layer, and has a total of four titanium layers 20, 31, 32, and 33 as first metal layers, and a total of three platinum layers 41, 42, and 43 as second metal layers.

[0024] On the uppermost titanium layer 33 of the laminated portion 60, an aluminum layer 50 is formed as a third metal layer made of aluminum, which is a third metal having a lower density and electrical resistivity than titanium and platinum.

[0025] The thickness of the piezoelectric substrate 3 is, for example, 1.0 μm. The thickness of the intermediate layer 6 is, for example, 2.5 μm. The thickness of the support substrate 2 is, for example, 400 μm.

[0026] The bottom titanium layer 20 functions as an adhesive layer between the piezoelectric substrate 3 and the platinum layer 41. The thickness of the bottom titanium layer 20 is, for example, 15 nm, but may be any thickness as long as it is 5 nm or more.

[0027] The titanium layers 31, 32, and 33 serve to separate the platinum layers 41, 42, and 43 and thin each of the platinum layers 41, 42, and 43. The titanium layers 31, 32, and 33 also serve as interdiffusion prevention layers between the platinum layers 43, 42, and 43 and the aluminum layer 50. The thickness of the titanium layers 31, 32, and 33 is, for example, 10 nm, but may be 5 nm or more.

[0028] Titanium layers 31, 32, and 33 enable platinum layers 41, 42, and 43 to be thinned while maintaining the total thickness of platinum layers 41, 42, and 43 in IDT electrode 4. That is, platinum in laminate section 60 is divided into thin platinum layers 41, 42, and 43 by titanium layers 31, 32, and 33. The total thickness of the platinum layers is, for example, 252 nm, but can be changed appropriately within the range of 50 nm to 350 nm.

[0029] The thickness of each of platinum layers 41, 42, and 43 is, for example, 84 nm, but can be changed appropriately within the range of 16 nm to 116 nm. It is preferable that platinum layers 41, 42, and 43 have the same thickness, but the total thickness of the IDT electrode 4 may be different.

[0030] The total thickness of all the metal layers of the IDT electrode 4 is preferably about h / λ=0.06 to 0.13, where λ is the wavelength of the resonant frequency and h is the total thickness of the IDT electrode. In this embodiment, the total thickness of all the metal layers of the IDT electrode 4 is, for example, 100 nm or more and 600 nm or less. These metal films are formed by vapor deposition, and the IDT electrode 4 is formed by a lift-off method.

[0031] The total thickness of the bottom titanium layer 20 and titanium layers 31, 32, and 33, which are the first metal layers in the IDT electrode 4, is thinner than the total thickness of the platinum layers 41, 42, and 43, which are the second metal layers in the IDT electrode. When the total thickness of the titanium layers is smaller than the total thickness of the platinum layers, the electrical resistivity of titanium is greater than that of platinum, and therefore, loss in the acoustic wave device 1 due to the electrical resistance of the IDT electrode 4 can be reduced. This thickness relationship also applies to other embodiments described below.

[0032] The weight ratio of platinum in the IDT electrode 4 is greater than the weight ratio of aluminum in the IDT electrode. More specifically, the ratio (platinum weight ratio) of the total weight of the platinum layers 41, 42, and 43, which are the second metal layers, to the weight of the IDT electrode 4 (the total weight of all platinum layers included in the IDT electrode 4) is greater than the weight ratio (aluminum weight ratio) of the aluminum layer 50, which is the third metal layer in the IDT electrode 4, to the weight of the IDT electrode 4. By increasing the total weight ratio of the platinum layers 41, 42, and 43 relative to the weight ratio of the aluminum layer 50 in the IDT electrode 4, the density of the electrode fingers 7 of the IDT electrode 4 can be increased, thereby slowing the acoustic velocity. Therefore, even if the pitch of the electrode fingers 7 is kept narrow without being widened, a low resonant frequency (preferably 600 MHz to 900 MHz, more preferably 617 MHz to 698 MHz, which is band 71) can be achieved by slowing the acoustic velocity, thereby enabling the acoustic wave device 1 to be miniaturized.

[0033] The density of each of these materials is 21.5 g / cm 3 ] and the density of aluminum is 2.7 [g / cm 3 ] and the density of titanium is 4.5 [g / cm 3From these densities, the weight ratio of the total weight of platinum layers 41, 42, and 43 (weight ratio) and the weight ratio of aluminum layer 50 (weight ratio) in IDT electrode 4 can be calculated from the thickness, cross-sectional area, or volume of these layers. The relationship between the weight ratio of platinum and aluminum is similar to that in other embodiments described later.

[0034] In this embodiment, the total thickness of platinum layers 41, 42, and 43 is set appropriately within the range of 50 nm to 350 nm, since they are provided to reduce the acoustic velocity compared to when the IDT electrode is formed using only aluminum layers, thereby contributing to the miniaturization of the IDT electrode. The resonant frequency of the acoustic wave device of this embodiment is set to be suitable for band 71, preferably 600 MHz to 900 MHz, more preferably 617 MHz to 698 MHz.

[0035] As described above, the thickness h of the entire metal layer of the IDT electrode 4 is preferably set to approximately h / λ=0.06 to 0.13. Therefore, the laminated portion 60 provided below the aluminum layer 50 is also constrained in thickness to be thinner than the thickness of the metal layer h. Within this thickness constraint, the laminated portion 60 is provided with four titanium layers 20, 31, 32, and 33 alternately arranged with three platinum layers 41, 42, and 43. Therefore, the platinum layers 41, 42, and 43 are separated from each other by the titanium layers 20, 31, 32, and 33, resulting in thin platinum layers. The power durability of the IDT electrode 4 is improved by the thin platinum layers 41, 42, and 43 separated from each other by the titanium layers 20, 31, 32, and 33. Therefore, the acoustic wave device 1 has excellent power durability.

[0036] <About the effects> In order to confirm the effect of the acoustic wave device according to the first embodiment of the present invention, an acoustic wave device (sample A) having the IDT electrode of Example 1 shown in FIG. 3 and a comparative example (sample B) having the IDT electrode shown in FIG. 4 were fabricated, and measurements were performed as shown in the diagrams in the following FIGS. 5, 6, and 7.

[0037] The acoustic wave device of Example 1 (sample A) having an IDT electrode 4 shown in FIG. 3 is similar to that described above.

[0038] In the acoustic wave device of the comparative example (sample B) shown in FIG. 4, the IDT electrode 4X includes, on the piezoelectric substrate 3, a bottom titanium layer 20X, a platinum layer 40X, a titanium layer 30X, and an aluminum layer 50X.

[0039] Generally, if the wavelength is λ, the electrode finger pitch P of the IDT electrode is 0.5λ, and (wavelength λ) = (sound velocity of material) / (resonant frequency). Given this, aluminum has a lower density than platinum. Therefore, if the IDT electrode is made solely of aluminum, the electrode finger pitch P must be large in low frequency bands (e.g., approximately 600 MHz to 900 MHz, more preferably, approximately 617 MHz to 698 MHz, known as Band 71), resulting in a larger IDT electrode. For this reason, the IDT electrode 4X includes a platinum layer 40X made of platinum, which has a higher density than aluminum. This platinum layer 40X increases the weight of the electrode fingers in the comparative example (Sample B), thereby reducing the sound velocity and enabling a more compact acoustic wave device 4X than an IDT electrode made solely of aluminum.

[0040] In the comparative example (sample B), the bottom titanium layer 20X is an adhesion layer, and the titanium layer 30X serves as a diffusion barrier between the platinum 40X and aluminum layer 50X.

[0041] The main differences between the comparative example and Example 1 are that the comparative example in Figure 4 has only one platinum layer 40X, whereas Example 1 in Figure 3 has three layers, platinum layers 41, 42, and 43, with titanium layers 31, 32, and 33 provided between them to form a three-part multilayer structure, and that the thickness of platinum layer 40X is the same as the total thickness of platinum layers 41, 42, and 43.

[0042] The conditions for fabricating the acoustic wave device (sample A) and the comparative example (sample B) are as follows. Common conditions for Example 1 (Sample A) and Comparative Example (Sample 2) Wavelength λ: 4.2μm Piezoelectric substrate 3: Material: 42° rotated Y-cut X-propagation lithium tantalate substrate Thickness: 1.0μm Middle tier 6: Material SiO2 Thickness: 2.5 μm Support substrate 2: Material: Spinel Thickness: 400μm IDT electrode finger: Pitch: 0.5λ Duty: 50% Number of electrode finger pairs: 110 Aperture length: 29λ Number of pairs per reflector: 10

[0043] The cross-sectional view of the IDT electrode of Example 1 (Sample A) is as shown in FIG. 3, and the film thickness is as follows.

[0044] Bottom titanium layer 20: 15nm Platinum layer 41: 84nm Titanium layer 31: 10nm Platinum layer 42: 84nm Titanium layer 32: 10nm Platinum layer 43: 84nm Titanium layer 33: 10nm Aluminum layer 50: 126nm

[0045] The cross-sectional view of the IDT electrode of the comparative example (sample B) is as shown in FIG. 4, and the film thickness is as follows. Bottom titanium layer 20X: 15nm Platinum layer 40X: 252nm Titanium layer 30X: 15nm Aluminum layer 50X: 126nm

[0046] In Figures 3 and 4, the inclination of the sides of the metal layer of the IDT electrode is omitted from the cross-sectional views and is shown as if the sides are standing upright at an angle of 90°. However, since the film is formed by vapor deposition and then by the lift-off method, the actual cross-section is inclined at an angle of about 75°, forming a trapezoid with a long base and a small top.

[0047] 5 is a graph showing output power versus input power for Example 1 (Sample A) and Comparative Example (Sample B). The solid line represents output power versus input power for the acoustic wave device of Example 1. The dashed line represents output power versus input power for the Comparative Example (Sample B).

[0048] The sudden drop in output power indicates that the IDT electrode could not withstand the input power and was destroyed. As shown in FIG. 5, in the comparative example (sample B), the output power increased up to an input power of about 29.4 dBm, but when the input power exceeded that, the IDT electrode was destroyed and the output power suddenly dropped. In contrast, in example 1 (sample A), the output power increased up to an input power of about 30.8 dBm, but when the input power exceeded that, the IDT electrode was destroyed and the output power suddenly dropped. The measurement results in FIG. 5 indicate that example 1 (sample A) was able to withstand a higher input power than the comparative example (sample B), and therefore had higher power durability.

[0049] The total thickness of platinum layers 41, 42, and 43 in Example 1 is 252 nm, which is the same as the thickness of platinum layer 40X in the Comparative Example. The three platinum layers 41, 42, and 43 in Example 1 are obtained by dividing the thickness of platinum layer 40X in the Comparative Example into three layers, each 84 nm thick. In other words, although the total thickness of the platinum layers in the IDT electrodes is the same in Example 1 and the Comparative Example, the multilayer structure of platinum layers 41, 42, and 43 with titanium layers 31, 32, and 33 sandwiched between them significantly improves power durability. This is likely due in part to the fact that thinner platinum layers 41, 42, and 43 result in smaller platinum particle sizes, improving the IDT electrode 4's ability to withstand stress caused by vibrations from piezoelectric substrate 3. This, in turn, results in improved power durability of IDT electrode 4.

[0050] FIG. 6(a) is a graph showing the change in admittance |Y| with respect to the change in frequency for Example 1 (Sample A) and Comparative Example (Sample B). FIG. 6(b) is a graph showing the change in admittance |Y|, which is an expanded view of the frequency range from approximately 620 MHz to approximately 760 MHz in FIG. 6(a). In FIG. 6(a), the admittance |Y| for Example 1 (Sample A) is shown by a solid line, and the admittance |Y| for Comparative Example (Sample B) is shown by a dashed line. In FIG. 6(b), the admittance |Y| for Example 1 (Sample A) and Comparative Example (Sample B) overlap, so only the solid line appears. As can be seen from FIGS. 6(a) and 6(b), Example 1 (Sample A) does not show an increase in unwanted spurious emissions compared to Comparative Example (Sample B).

[0051] Titanium has a higher electrical resistivity than platinum. Although the total thickness of the titanium layer in the IDT electrode in Example 1 (Sample A) is greater than that in the Comparative Example (Sample B), no significant change in admittance |Y| was observed in Figures 6(a) and 6(b).

[0052] FIG. 7 is a diagram showing the change in Q value with respect to the change in frequency for Example 1 (Sample A) and Comparative Example (Sample B). In FIG. 7, the change in Q value with respect to the frequency for Example 1 (Sample A) is shown by a solid line, and the change in Q value with respect to the frequency for Comparative Example (Sample B) is shown by a dashed line. As can be seen from FIG. 7, Example 1 (Sample A) did not have a worse Q value than Comparative Example (Sample B). Note that, for example, with respect to the portion enclosed by the dashed line and labeled "Qmax" in FIG. 7, Example 1 (Sample A) exhibited a higher Q value than Comparative Example (Sample B), so it cannot be said that Example 1 (Sample A) had a worse Q value than Comparative Example (Sample B).

[0053] As described above, the fabrication and measurement of Example 1 (Sample A) and Comparative Example (Sample B) demonstrated that the power durability of an acoustic wave device having an IDT electrode, as in Example 1, is improved. This makes it possible to realize a highly reliable acoustic wave device. Furthermore, there was no degradation in performance, as there was no degradation in the Q value, no adverse effects on the resonant frequency or anti-resonant frequency, and no increase in unnecessary spurious signals.

[0054] To explain how the configuration of Example 1 (Sample A) was modified from the configuration of Comparative Example (Sample B), the configuration of IDT electrode 4 in Example 1 (Sample A) corresponds to IDT electrode 4 in Comparative Example (Sample B) in which the portions corresponding to bottom titanium layer 20X, platinum layer 40X, and titanium layer 30X in IDT electrode 4X are replaced with laminated section 60. In laminated section 60, the platinum layer is divided into three layers, platinum layers 41, 42, and 43, and titanium layers (titanium layers 31, 32, and 33 and bottom titanium layer 20) are formed between the three layers and at the top and bottom, and the total thickness of platinum layers 41, 42, and 43 is set to the same thickness as platinum layer 40X (when there is only one platinum layer) in IDT electrode 4X of Comparative Example (Sample B). That is, the configuration of Example 1 (Sample A) and the comparative example (Sample B) have the same total thickness of the aluminum layer and platinum layer, but the platinum layer and titanium layer are multi-layered so that Example 1 (Sample A) has more layers than the comparative example (Sample B).

[0055] That is, the IDT electrode 4 of Example 1 (Sample A) and the IDT electrode 4X of Comparative Example (Sample B) have the same total thickness of the aluminum layers and platinum layers, and the IDT electrode 4 of Example 1 (Sample A) is multi-layered so that the number of platinum layers and titanium layers is greater than that of the IDT electrode 4X of Comparative Example (Sample B). By configuring Example 1 in this manner, an acoustic wave device can be realized that has the same resonant frequency and anti-resonant frequency as an acoustic wave device (Comparative Example) having a single platinum layer and that has higher power durability than an acoustic wave device (Comparative Example) having a single platinum layer.

[0056] <How to calculate weight ratio> As described above, in Example 1, the ratio of the total weight of platinum layers 41, 42, and 43, which are the second metal layers, to the weight of IDT electrode 4 (platinum weight ratio) is greater than the ratio of the weight of aluminum layer 50, which is the third metal layer, to the weight of IDT electrode 4 (aluminum weight ratio). This can be calculated from the cross-sectional area of ​​each layer in FIG. 3 and the densities of platinum, aluminum, and titanium described above. An example of calculating the weight ratio is shown below.

[0057] [Table 1]

[0058] [Table 2]

[0059] Table 1 shows the film thicknesses of Example 1, and Table 2 shows a list of values ​​used in an example where the weight ratios were calculated from the film thicknesses and material densities. For example, assuming the ratio of the cross-sectional areas of the above layers based on the thicknesses of the layers in Table 1, and assuming [cross-sectional area of ​​IDT electrode : total cross-sectional area of ​​platinum layers : total cross-sectional area of ​​aluminum layers : total cross-sectional area of ​​titanium layers] = [100 : 60 : 30 : 10] as shown in Table 2, and multiplying this by the density to calculate the weight ratios, the approximate weight ratio is [weight ratio of IDT electrode : weight ratio of platinum layers : weight ratio of aluminum layers : weight ratio of titanium layers] = [100.0 : 91.1 : 5.7 : 3.2]. Therefore, in this calculation example, the weight ratio of the sum of the weights of the platinum layers 41, 42, and 43, which are the second metal layers, to the weight of the IDT electrode 4 is greater than the weight ratio of the aluminum layer 50, which is the third metal layer, to the weight of the IDT electrode 4. Note that this calculation example is simplified for illustrative purposes. In the case of Example 1, this calculation example is sufficient to determine whether the weight ratio of platinum is greater than the weight ratio of aluminum. However, for a more precise calculation, if necessary, the cross-sectional area of ​​the IDT electrode may be measured or calculated according to its shape before calculating the weight ratio.

[0060] Second Embodiment 8 is a cross-sectional view showing the vicinity of an IDT electrode in a second embodiment of the acoustic wave device. In this second embodiment, an IDT electrode 4a is provided on a piezoelectric substrate 3. The IDT electrode 4a includes a laminated portion 60b and an aluminum layer 50 as a third metal layer provided thereon.

[0061] In the laminated portion 60a of the IDT electrode 4a, five titanium layers, namely, the bottom titanium layer 20a and titanium layers 31a, 32a, 33a, and 34a, are provided as first metal layers, and four platinum layers 41a, 42a, 43a, and 44a are provided as second metal layers.

[0062] 1 are the same as those in the first embodiment, and therefore will not be illustrated or described again. Other parts having the same names and functions as those in the first embodiment will be assigned the same reference numerals and will not be described again.

[0063] To make the resonant frequency and antiresonant frequency of the acoustic wave device of the second embodiment closer to those of the first embodiment, the total thickness of the platinum layers 41a, 42a, 43a, and 44a in the IDT electrode 4a can be 252 nm. Each of these platinum layers can have a thickness of 63 nm. To maintain the characteristics of the acoustic wave device, such as the resonant frequency, similar to those of the first embodiment, the thickness of the aluminum layer 50 can be 126 nm, the same as that of the first embodiment. The bottom titanium layer 20a is, for example, 15 nm, and the titanium layers 31a, 32a, 33a, and 34a are, for example, 10 nm.

[0064] In cases other than those described above, the resonant frequency of the acoustic wave device of this embodiment is preferably set to be suitable for band 71, which is between 600 MHz and 900 MHz, and more preferably between 617 MHz and 698 MHz.

[0065] When used in the above frequency bands, the overall thickness of the metal layers of the IDT electrode may be varied as appropriate between 100 nm and 600 nm. The total thickness of the platinum layers 41a, 42a, 43a, and 44a in the IDT electrode 4a may be varied between 50 nm and 350 nm. The thickness of the aluminum layer 50 may be varied as long as it is 50 nm or greater. Furthermore, the thickness of the titanium layers 20a, 31a, 32a, 33a, and 34a may be varied as appropriate between 5 nm and greater, more preferably between 10 nm and greater. However, because titanium has a higher electrical resistivity than platinum and aluminum, the total thickness of the titanium layers 20a, 31a, 32a, 33a, and 34a in the IDT electrode 4a is preferably thinner than the total thickness of the aluminum layer 50 and the platinum layers 41a, 42a, 43a, and 44a to reduce losses due to the electrical resistance of the IDT electrode 4a. Although the platinum layers 41a, 42a, 43a, and 44a have the same thickness, they do not necessarily have to have the same thickness.

[0066] In this way, by providing the laminated portion 60a in which five titanium layers and four platinum layers are alternately stacked, the thickness of each of the platinum layers 41a, 42a, 43a, and 44a can be made thinner than in the acoustic wave device having a single platinum layer such as the comparative example described above, thereby further improving the power resistance.

[0067] <Third embodiment> 9 is a cross-sectional view showing the vicinity of an IDT electrode in a third embodiment of the acoustic wave device. In this third embodiment, an IDT electrode 4b is provided on a piezoelectric substrate 3. The IDT electrode 4b is made of a laminated portion 60b and an aluminum layer 50 as a third metal layer provided thereon.

[0068] In the laminated portion 60b of the IDT electrode 4b, six titanium layers are provided as first metal layers: bottom titanium layer 20b and titanium layers 31b, 32b, 33b, 34b, and 35b, and five platinum layers 41b, 42b, 43b, 44b, and 45b are provided as second metal layers.

[0069] 1 are the same as those in the first embodiment, and therefore will not be illustrated or described again. Other parts having the same names and functions as those in the first embodiment will be assigned the same reference numerals and will not be described again.

[0070] To make the resonant frequency and antiresonant frequency of the acoustic wave device of the third embodiment closer to those of the first embodiment, the total thickness of platinum layers 41b, 42b, 43b, 44b, and 45b in IDT electrode 4b can be 252 nm. Each of these platinum layers can have a thickness of approximately 50.4 nm. To maintain the characteristics of the acoustic wave device, such as the resonant frequency, similar to those of the first embodiment, the thickness of aluminum layer 50 can be 126 nm, the same as that of the first embodiment. The thickness of bottom titanium layer 20b is, for example, 15 nm, and the thickness of titanium layers 31b, 32b, 33b, 34b, and 35b is, for example, 10 nm.

[0071] In cases other than those described above, the resonant frequency of the acoustic wave device of this embodiment is preferably set to be suitable for band 71, which is between 600 MHz and 900 MHz, and more preferably between 617 MHz and 698 MHz.

[0072] When used in the above frequency bands, the overall thickness of the metal layers of the IDT electrode may be varied as appropriate between 100 nm and 600 nm. The total thickness of the platinum layers 41b, 42b, 43b, 44b, and 45b may be varied between 50 nm and 350 nm. The thickness of the aluminum layer 50 may be varied as appropriate between 50 nm and 50 nm. Furthermore, the thickness of the titanium layers 20b, 31b, 32b, 33b, 34b, and 35b may be varied as appropriate between 5 nm and 10 nm or more. However, because titanium has a higher electrical resistivity than platinum and aluminum, the total thickness of the titanium layers 20b, 31b, 32b, 33b, 34b, and 35b in the IDT electrode 4b is preferably thinner than the total thickness of the aluminum layer 50 and the platinum layers 41b, 42b, 43b, 44b, and 45b in the IDT electrode 4b to reduce losses due to the electrical resistance of the IDT electrode 4b. Although the platinum layers 41b, 42b, 43b, 44b, and 45b have the same thickness, they do not necessarily have to have the same thickness.

[0073] In this way, by providing stacked section 60b in which six titanium layers and five platinum layers are alternately stacked, the thickness of each of platinum layers 41b, 42b, 43b, 44b, and 45b can be made thinner than in an acoustic wave device with a single platinum layer such as the comparative example described above, thereby further improving power resistance.

[0074] <Fourth embodiment> 10 is a cross-sectional view showing the vicinity of an IDT electrode in a fourth embodiment of the acoustic wave device. In this fourth embodiment, an IDT electrode 4c is provided on a piezoelectric substrate 3. The IDT electrode 4c is made of a laminated portion 60c and an aluminum layer 50 provided thereon as a third metal layer.

[0075] In the laminated portion 60c of the IDT electrode 4c, three titanium layers, namely, the bottom titanium layer 20c and titanium layers 31c and 32c, are provided as first metal layers, and two platinum layers, namely, platinum layers 41c and 42c, are provided as second metal layers.

[0076] 1 are the same as those in the first embodiment, and therefore will not be illustrated or described again. Other parts having the same names and functions as those in the first embodiment will be assigned the same reference numerals and will not be described again.

[0077] To make the resonant frequency and antiresonant frequency of the acoustic wave device of the third embodiment closer to those of the first embodiment, the total thickness of the platinum layers 41c and 42c in the IDT electrode 4c can be 252 nm. The thickness of each of these platinum layers can be 126 nm. To maintain the characteristics of the acoustic wave device of the first embodiment, such as the resonant frequency, the thickness of the aluminum layer 50 can be 126 nm, the same as that of the first embodiment. The thickness of the bottom titanium layer 20c is, for example, 15 nm, and the thickness of the titanium layers 31c and 32c is, for example, 10 nm.

[0078] In cases other than those described above, the resonant frequency of the acoustic wave device of this embodiment is preferably set to be suitable for band 71, which is between 600 MHz and 900 MHz, and more preferably between 617 MHz and 698 MHz.

[0079] When used in the above frequency bands, the thickness of the entire metal layer of the IDT electrode 4c may be varied as appropriate between 100 nm and 600 nm. The total thickness of the platinum layers 41c and 42c in the IDT electrode 4c may be varied between 50 nm and 350 nm. The thickness of the aluminum layer 50 may be varied as appropriate between 50 nm and 50 nm. Furthermore, the thickness of the titanium layers 20c, 31c, and 32c may be varied as appropriate between 5 nm and 10 nm or more. However, because titanium has a higher electrical resistivity than platinum and aluminum, it is preferable that the total thickness of the titanium layers 20c, 31c, and 32c be thinner than the total thickness of the aluminum layer 50 and the platinum layers 41c and 42c to reduce losses due to the electrical resistance of the IDT electrode 4c. While the platinum layers 41c and 42c are assumed to have the same thickness, they do not necessarily have to be the same thickness.

[0080] In this way, by providing laminate section 60c in which three titanium layers and two platinum layers are alternately stacked, the thickness of each of platinum layers 41c and 42c can be made thinner than in the acoustic wave device having a single platinum layer as in the comparative example described above, thereby further improving power resistance.

[0081] Fifth Embodiment 11 is a cross-sectional view showing the vicinity of an IDT electrode in a fifth embodiment of the acoustic wave device. In this fifth embodiment, an IDT electrode 4d is provided on a piezoelectric substrate 3. The IDT electrode 4d includes a laminated portion 60 and an aluminum layer 50 as a third metal layer provided thereon. A top titanium layer 70 is formed on the aluminum layer 50.

[0082] The laminated portion 60 of the IDT electrode 4 is the same as that in the first embodiment.

[0083] 1 are the same as those in the first embodiment, and therefore will not be illustrated or described again. Other parts having the same names and functions as those in the first embodiment will be assigned the same reference numerals and will not be described again.

[0084] By providing the top titanium layer 70 on the aluminum layer 50 serving as the third metal layer of the IDT electrode 4d in this manner, deterioration of the upper surface of the aluminum layer 50 during operation of the acoustic wave device can be suppressed, thereby improving the reliability of the acoustic wave device.

[0085] The top titanium layer 70 is, for example, 10 nm thick, but may be 5 nm or thicker.

[0086] In the fifth embodiment, the top titanium layer 70 is formed on the IDT electrode of the first embodiment. However, as in the other embodiments, the top titanium layer 70 may be formed on an IDT electrode having three or five or more first metal layers and two or four or more second metal layers. The total thickness of the metal layers of the IDT electrode is determined by the relationship between the support substrate 2, the piezoelectric substrate 3, the intermediate layer 6, and the wavelength λ of the resonant wave. Therefore, when the top titanium layer 70 is formed, the thickness of the platinum layers 41, 42, and 43, the titanium layers 20, 31, 32, and 33, and the aluminum layer 50 may be appropriately changed from the thicknesses of the first embodiment after calculating the total thickness of the metal layers of the IDT electrode taking into account the thickness of the top titanium layer 70.

[0087] The first to fifth embodiments have been described above. In these embodiments, an acoustic wave device having a stacked portion in which the second metal layer is five layers and the first metal layer is multi-layered up to six layers has been described. However, the number of second metal layers and first metal layers may be even greater.

[0088] In these embodiments, aluminum is used as the material for the third metal layer, but an alloy of aluminum and copper (Al-Cu alloy) may also be used. Also, in the present embodiment, the IDT electrode manufacturing method involves depositing the metal layer by vapor deposition and then using a lift-off method, but the IDT electrode may also be formed by depositing the metal film by sputtering and then etching it.

[0089] The film thickness is within the error range of -1 nm to +1 nm.

[0090] Furthermore, the drawings used in the above explanation are schematic, and the dimensions and ratios on the drawings do not necessarily correspond to those of the actual product.

[0091] The present invention has been described above, but when specifically implementing the present invention as an acoustic wave device, it is not limited to the above-described embodiments, and various modifications and additions are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0092] 1. Acoustic wave devices 2 Support substrate 3 Piezoelectric substrate 4 IDT electrode 6. Middle class 7 electrode fingers 20, 20a, 20b, 20c Bottom titanium layer (first metal layer) 31, 32, 33, 31a, 32a, 33a, 34a, 31b, 32b, 33b, 34b, 35b, 31c, 32c Titanium layer (first metal layer) 41,42,43,41a,42a,43a,44a,41b,42b,43b,44b,45b,41c,42c Platinum layer (second metal layer) 50 Aluminum layer (third metal layer) 60, 60a, 60b, 60c Laminated section 70 top titanium layer

Claims

1. a piezoelectric substrate; an IDT electrode formed on the piezoelectric substrate, the IDT electrode has a laminated section in which first metal layers made of a first metal and second metal layers made of a second metal having a density higher than that of the first metal and a lower electrical resistivity are alternately provided, and a third metal layer formed on the laminated section and made of a third metal having a density lower than that of the first metal and the second metal and a lower electrical resistivity; The laminated portion has an uppermost layer and a lowermost layer which are the first metal layers, and includes at least three layers of the first metal layers and at least two layers of the second metal layers. Acoustic wave devices.

2. The laminated portion includes at least four first metal layers and at least three second metal layers. The acoustic wave device according to claim 1 .

3. The total thickness of the first metal layers in the IDT electrode is smaller than the total thickness of the second metal layers in the IDT electrode.

3. The acoustic wave device according to claim 1 or 2.

4. The weight ratio of the second metal in the IDT electrode is greater than the weight ratio of the third metal in the IDT electrode. The acoustic wave device according to claim 1 or 2.

5. The total thickness of the second metal layer in the IDT electrode is 50 nm or more and 350 nm or less. The acoustic wave device according to claim 1 or 2.

6. The thickness of each of the second metal layers in the IDT electrodes is 20 nm or more and 150 nm or less. The acoustic wave device according to claim 5 .

7. The first metal is titanium, the second metal is platinum, and the third metal is aluminum or an alloy of aluminum and copper. The acoustic wave device according to claim 1 or 2.

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