Elastic wave devices

Abstract

The present invention provides an elastic wave device that exhibits reduced generation of high-frequency spurious emissions, excellent temperature characteristics, and improved ratio of admittance at the resonant frequency to the anti-resonant frequency, as well as enhanced steepness of the frequency response. [Solution] The elastic wave device 100 comprises a first piezoelectric layer 1, a first insulating layer 3 formed on the first piezoelectric layer, a plurality of electrode fingers consisting of metal layers 5 formed on the first insulating layer, a second insulating layer 4 formed on the first insulating layer and provided between the metal layers, and a second piezoelectric layer 2 formed on the metal layers constituting the plurality of electrode fingers.

Description

Technical Field

[0001] The present invention relates to an elastic wave device.

Background Art

[0002] For example, as an elastic wave device used in a demultiplexer of a wireless communication device, a SAW (Surface acoustic wave) resonator having an IDT (Interdigital Transducer) electrode provided on the main surface of a piezoelectric substrate is known.

[0003] In Patent Document 1, an elastic wave device using a surface wave in which an IDT electrode is provided between a first piezoelectric substrate and a second piezoelectric substrate, and a gap or a dielectric is filled between electrode fingers of the comb teeth electrodes of the IDT electrode is disclosed. In Patent Document 1, since the comb teeth electrodes in the elastic wave device are sandwiched between the first piezoelectric substrate and the second piezoelectric substrate, the capacitance between the comb teeth electrodes increases compared to the case where the second piezoelectric substrate is not present, and thus miniaturization of the elastic wave device can be achieved.

[0004] In Patent Document 2, an elastic wave device in which an IDT electrode is provided between a first piezoelectric substrate and a second piezoelectric substrate and uses a thickness shear primary mode which is a bulk wave is disclosed. Since the elastic wave device of this Patent Document 2 uses the thickness shear primary mode, the first piezoelectric substrate and the second piezoelectric substrate are configured to be thin, for example, 400 [nm], and it is necessary that the side opposite to the IDT electrode is exposed in the space portion. According to the elastic wave device of this Patent Document 2, since the resonance frequency of the excited mode does not depend on the pitch of the IDT electrode, miniaturization of the elastic wave device can be achieved.

[0005] Conventionally, a SAW resonator as an elastic wave device in which a metal layer 5x constituting an IDT electrode is provided on a piezoelectric substrate 1x shown in FIG. 3 is known.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-191535 [Patent Document 2] International Publication No. 2023 / 090434 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, conventional elastic wave devices, as shown in Figure 3, Patent Document 1, and Patent Document 2, are used in filter circuits and therefore require a high Q factor, low generation of high-frequency spurious emissions, and superior temperature characteristics.

[0008] The present invention has been made in view of the above problems, and aims to provide an elastic wave device that generates fewer high-frequency spurious emissions, has excellent temperature characteristics, and can improve the ratio of admittance at the resonant frequency to the anti-resonant frequency and the steepness of the frequency characteristics. [Means for solving the problem]

[0009] One embodiment of the elastic wave device of the present invention comprises a first piezoelectric layer, a first insulating layer formed on the first piezoelectric layer, a plurality of electrode fingers consisting of metal layers formed on the first insulating layer, a second insulating layer formed on the first insulating layer and provided between the plurality of electrode fingers, and a second piezoelectric layer formed on the metal layers constituting the electrode fingers.

[0010] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention has a thickness of the first insulating layer such that the wavelength of the wave excited on the metal layer side surface of the second piezoelectric layer is λ or more and 0.1λ or less.

[0011] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention has a thickness of the second piezoelectric layer such that, when the wavelength of the wave excited on the main surface of the second piezoelectric layer on the electrode finger side is λ, the thickness is 0.1λ or more and 0.4λ or less.

[0012] In a specific embodiment of the above-described aspect of the elastic wave device of the present invention, the thickness of the second insulating layer is the same as the thickness of the metal layer constituting the electrode finger. Furthermore, for the same thickness, a difference of 10 nm is considered to be within the range of manufacturing tolerances, meaning the thickness is the same.

[0013] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention is characterized in that the second insulating layer is made of silicon oxide.

[0014] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention is characterized in that the first insulating layer is made of silicon oxide.

[0015] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention is characterized in that the electrode fingers are made of an alloy containing copper and aluminum.

[0016] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention is such that the first insulating layer and the second insulating layer are made of the same insulating material. Thus, if the first insulating layer and the second insulating layer are made of the same insulating material, it becomes possible to deposit the first insulating layer and the second insulating layer in a single process. This reduces the number of steps in manufacturing compared to when the materials of the first insulating layer and the second insulating layer are different, and thus lowers the manufacturing cost of elastic wave devices.

[0017] In a specific embodiment of the above-described aspect, the elastic wave device of the present invention is provided with a support substrate having a higher thermal conductivity than the first piezoelectric layer below the first piezoelectric layer. Thus, by providing a support substrate with high thermal conductivity under the first piezoelectric layer, the heat dissipation performance of the elastic wave device of the present invention can be enhanced, and an elastic wave device with high power resistance can be realized.

Effects of the Invention

[0018] According to the elastic wave device of the present invention, by adopting the above structure, an elastic wave device can be realized that has excellent temperature characteristics, few high-frequency spurious signals, and improved ratios of admittance at the resonance frequency and anti-resonance frequency serving as the criteria of the Q value and the steepness of the frequency characteristics.

Brief Description of the Drawings

[0019] [Figure 1] It is a cross-sectional view showing an elastic wave device according to the first embodiment of the present invention. [Figure 2] It is a plan view showing the elastic wave device according to the first embodiment of the present invention with the second piezoelectric layer omitted. [Figure 3] It is a cross-sectional view of an elastic wave device of a conventional example. [Figure 4] It is a graph showing the change in admittance with respect to frequency for Examples 2, 3, 5, 7 of an elastic wave device with the thickness of the second piezoelectric layer changed and the conventional example of the elastic wave device in FIG. 3. [Figure 5] It is a graph showing the change in admittance with respect to frequency for Examples 1 to 7 of an elastic wave device with the thickness of the second piezoelectric layer 2 changed and the conventional example of the elastic wave device. [Figure 6] It is a graph showing the change in admittance with respect to frequency for Examples 8 to 11 with the thickness of the first insulating layer changed. [Figure 7] It is a cross-sectional view showing the second embodiment of the present invention. [Figure 8] It is a cross-sectional view showing the third embodiment of the present invention. [Figure 9] FIGS. 9(a) to (d) are cross-sectional views showing a part of the manufacturing process of an elastic wave device. [Figure 10] It is a cross-sectional view showing a part of the manufacturing process of an elastic wave device. [Figure 11] Figure 11(a) is a cross-sectional view showing an elastic wave device with vias formed in the second piezoelectric layer. Figure 11(b) is a cross-sectional view showing an elastic wave device with pads provided. [Figure 12] This is a circuit diagram showing a ladder-type filter equipped with an elastic wave device according to one of the first to third embodiments. [Figure 13] This is a configuration diagram showing a duplexer equipped with a transmit filter and a receive filter, which include an elastic wave device according to one of the first to third embodiments. [Modes for carrying out the invention]

[0020] <First Embodiment> Figure 1 is a cross-sectional view showing a first embodiment of the elastic wave device of the present invention. Figure 2 is a plan view of the elastic wave device with the second piezoelectric layer 2 omitted. This elastic wave device 100 comprises a first piezoelectric layer 1, a first insulating layer 3, and a second insulating layer 4 provided between the metal layers 5.

[0021] As shown in Figure 2, the metal layer 5 constitutes the IDT electrode 6 and the reflector 8. The IDT electrode 6 is equipped with comb-shaped electrodes 61 and 62, and the comb-shaped electrodes 61 and 62 are equipped with electrode fingers 61a and 62a. As shown in Figure 2, a second insulating layer 4 is provided between the metal layers 5 (including between the electrode fingers 61a and 62a) and around them.

[0022] The first piezoelectric layer 1 is, for example, 42° rotated Y-cut X-propagating lithium tantalate (LiTaO3), but is not limited to this, and other materials such as lithium niobate (LiNbO3) can also be used. The thickness of the first piezoelectric layer 1 is, for example, 200 [μm].

[0023] The second piezoelectric layer 2 is, for example, 42° rotated Y-cut X-propagating lithium tantalate (LiTaO3), but is not limited to this, and other materials such as lithium niobate (LiNbO3) can also be used. The thickness of the first piezoelectric layer 1 is, for example, 1 [μm].

[0024] The first piezoelectric layer 1 and the second piezoelectric layer 2 are preferably made of the same material. Furthermore, if the first piezoelectric layer 1 and the second piezoelectric layer 2 are single-crystal piezoelectric layers such as lithium tantalate, they are preferably made of the same cut angle and propagation direction. Here, the same cut angle and propagation direction includes at least an angle difference of ±3°.

[0025] The material of the metal layer 5 constituting the electrode fingers 61a and 62a of the IDT electrode 6 is, for example, aluminum. Alternatively, it may be an aluminum-copper alloy containing, for example, 0.5 to 3 wt% copper. However, it is not limited to these, and may be formed from other metals or alloys thereof as appropriate, or multiple layers of these metals may be stacked.

[0026] The first insulating layer 3 is, for example, a silicon oxide layer, but it may also be an inorganic insulator such as a silicon nitride layer or an aluminum oxide layer, or an organic insulator such as a resin. Of these, the silicon oxide layer has the advantage of being able to strengthen the bond between the first piezoelectric layer 1 and other layers such as the second insulating layer 4. Furthermore, while the sound velocity of lithium tantalate (LiTaO3) used in the piezoelectric layer has a negative temperature characteristic, the sound velocity of silicon oxide has a positive temperature characteristic. For this reason, by forming the first insulating layer 3 as a silicon oxide layer, the frequency-temperature characteristics (TCF: Temperature Coefficient of Frequency) of the elastic wave device 100 are improved. This is shown in Table 3 below.

[0027] The second insulating layer 4 is, for example, a silicon oxide layer, but it may also be an inorganic insulator such as a silicon nitride layer or an aluminum oxide layer, or an organic insulator such as a resin. When the second insulating layer 4 is a silicon oxide layer, there is the advantage that the silicon oxide layer can strengthen the bond with other layers such as the first insulating layer 3 and the second piezoelectric layer 2. Furthermore, as mentioned above, the sound velocity of silicon oxide has a positive temperature characteristic, which improves the frequency-temperature characteristic (TCF) of the elastic wave device.

[0028] The first insulating layer 3 and the second insulating layer 4 are preferably made of the same insulating material. However, the invention is not limited to this, and other insulating materials as described above may be used in appropriate combinations.

[0029] It is preferable that the metal layer 5 and the second insulating layer 4 have the same thickness. By making the metal layer 5 and the second insulating layer 4 the same thickness, these layers can make gapless contact with the second piezoelectric layer 2 and the first insulating layer 3, making it easier to manufacture elastic wave devices with the characteristics desired by the designer.

[0030] By configuring the elastic wave device 100 in this way, surface waves, specifically SH waves, are excited on the surface 2c of the second piezoelectric layer 2 that is on the metal layer 5 side, causing the elastic wave device 100 to operate as a resonator. Furthermore, by configuring the elastic wave device 100, it is possible to realize an elastic wave device with excellent temperature characteristics, low high-frequency spurious emissions, and improved ratio of admittance at the resonant frequency to the anti-resonant frequency (which is an indicator of the Q value) and steepness of the frequency characteristics.

[0031] <About the simulation> To confirm the effectiveness of the first embodiment, admittance was simulated for Examples 1 to 7 of the first embodiment and the conventional example shown in Figure 3. The simulation conditions were as follows: Conventional example in Figure 3: Material of metal layer 5x: Aluminum Thickness of metal layer 5x: 0.1λ Wavelength λ: 4[μm] Pitch: 0.5λ Duty: 50% Piezoelectric layer material: Lithium tantalate (LiTaO3) with 42° rotation Y-cut X propagation Piezoelectric layer thickness: 200 [μm] Common conditions in Examples 1-7: Material of metal layer 5: Aluminum (Al) Thickness of metal layer 5: 0.2λ Wavelength λ: 4[μm] Pitch: 0.5λ Duty: 50% Material of the first insulating layer 3: Silicon oxide (SiO2) Thickness of the first insulating layer 3: 0.05λ Material of the second insulating layer 4: Silicon oxide (SiO2) Thickness of the second insulating layer 4: 0.2λ Material of the first piezoelectric layer 1: Lithium tantalate with 42° rotation Y-cut X propagation Thickness of the first piezoelectric layer 1: 200 [μm] Material of the second piezoelectric layer 2: Lithium tantalate with 42° rotational Y-cut X propagation

[0032] [Table 1]

[0033] Figure 4 is a graph showing the change in admittance Y[S] with respect to frequency [MHz] for Examples 2, 3, 5, and 7, and the conventional example, in which the thickness of the second piezoelectric layer 2 was changed for each example. Figure 5 is a graph showing the change in admittance Y[S] with respect to frequency [MHz] for Examples 1 to 7 and the conventional example. Note that the graph in Figure 4 has a wider frequency range on the horizontal axis than the graph in Figure 5, so the number of examples has been reduced in the display.

[0034] In the conventional example of elastic wave device 100x, as shown in Figure 3, a metal layer 5x constituting an IDT electrode is provided on a piezoelectric substrate 1x.

[0035] In the legend on the right side of Figure 4, the thickness of the second piezoelectric layer 2 in Examples 1 to 7 is indicated as a multiple of the wavelength λ. Conventional examples are indicated as LT Bulk.

[0036] In Figures 4 and 5, the admittance of the conventional example is shown by a solid line, and Examples 1 to 7 are shown by dashed or dotted lines. In Figure 4, the admittances of Examples 2, 3, 5, and 7 and the conventional example are shown.

[0037] As shown in Figure 4, the admittance at the resonant frequency Fr of Examples 1 to 7 is significantly higher than the admittance at the resonant frequency Frx of the Comparative Example. Furthermore, as shown in Figure 5, the admittance at the anti-resonant frequency Fa of Examples 1 to 7 is almost the same as or lower than the admittance at the anti-resonant frequency Fax of the Comparative Example. Examples 1 to 7 can be said to have a higher ratio and steeper steepness of admittance at the resonant frequency to the anti-resonant frequency compared to the conventional example. In other words, favorable results were obtained in Examples 1 to 7 when the thickness of the second piezoelectric layer 2 was in the range of 0.1λ to 0.4λ.

[0038] Regarding the admittance in Figure 5, Example 4, in which the thickness of the second piezoelectric layer 2 is 0.25λ, is the most preferred. This is because the ratio of admittance at the resonant frequency Fr(0.25λ) to the anti-resonant frequency Fa(0.25λ) in Example 4 shown in Figure 5 is larger than that of the other examples.

[0039] The high ratio and steepness of admittance at the resonant frequency to the anti-resonant frequency suggest a high Q factor, indicating that Examples 1-7 are superior to conventional examples as resonators.

[0040] As shown in Figures 4 and 5, the admittances of Examples 1 to 7 show almost no high-frequency spurious emissions. Therefore, it was found that the elastic wave devices of Examples 1 to 7 are elastic wave devices in which high-frequency spurious emissions are suppressed.

[0041] Note that K^2 in Table 1 represents the electromechanical coupling coefficient K. 2 This means the electromechanical coupling coefficient K of Examples 1-7. 2 This is the conventional electromechanical coupling coefficient K 2 Although smaller, it is considered a sufficiently good value for use.

[0042] In Figure 6, the admittance was simulated for Examples 8 to 11 of the first embodiment shown in Figure 1, by varying the thickness of the first insulating layer 3. The simulation conditions were as follows: Common conditions in Examples 8-11: Material of metal layer 5: Aluminum (Al) Thickness of metal layer 5: 0.2λ Wavelength λ: 4[μm] Pitch: 0.5λ Duty: 50% Material of the first insulating layer 3: Silicon oxide (SiO2) Material of the second insulating layer 4: Silicon oxide (SiO2) Thickness of the second insulating layer 4: 0.2λ Material of the first piezoelectric layer 1: Lithium tantalate with 42° rotation Y-cut X propagation Thickness of the first piezoelectric layer 1: 200 [μm] Material of the second piezoelectric layer 2: Lithium tantalate with 42° rotational Y-cut X propagation Thickness of the second piezoelectric layer: 0.25λ

[0043] [Table 2]

[0044] As shown in Table 2, the thickness of the first insulating layer 3, which is a silicon oxide layer, was varied. In Table 2, K^2 represents the electromechanical coupling coefficient K. 2 This means the electromechanical coupling coefficient K of Examples 8-10. 2 The electromechanical coupling coefficient K in the conventional example shown in Table 1. 2 It is smaller than that, but is considered a perfectly usable value.

[0045] The admittance simulation in Figure 6 shows that spurious emissions can occur in the region indicated as P, around a frequency of 1040-1050 MHz. In Example 10, where the thickness of the first insulating layer 3 is 0.10λ, these spurious emissions are noticeable, and in Example 11, where the thickness of the first insulating layer 3 is 0.20λ, these spurious emissions are large. Therefore, it can be seen that the larger the thickness of the first insulating layer 3, the larger the spurious emissions become. Thus, a thickness of 0.1λ or less for the first insulating layer 3 is preferable. Furthermore, in Example 8, where the thickness of the first insulating layer 3 is 0.01λ, no spurious emissions were observed, which is a favorable result. Therefore, a thickness of 0.01λ or more and 0.10λ or less for the first insulating layer 3 is preferable because spurious emissions are not large.

[0046] As shown in Table 3, simulations were performed on the temperature characteristic TCF. The simulation conditions are as follows: Material of metal layer 5: Aluminum (Al) Thickness of metal layer 5: 0.2λ Wavelength λ: 4[μm] Pitch: 0.5λ Duty: 50% Material of the first insulating layer 3: Silicon oxide (SiO2) Material of the second insulating layer 4: Silicon oxide (SiO2) Thickness of the second insulating layer 4: 0.2λ Material of the first piezoelectric layer 1: Lithium tantalate with 42° rotation Y-cut X propagation Thickness of the first piezoelectric layer 1: 200 [μm] Material of the second piezoelectric layer 2: Lithium tantalate with 42° rotational Y-cut X propagation Thickness of the second piezoelectric layer: 0.25λ Calculation conditions: The TCF was calculated based on the admittance at the resonant frequency Fr and anti-resonant frequency Fa, with the low-temperature state set to 25°C and the high-temperature state to 125°C.

[0047] [Table 3]

[0048] As shown in Table 3, when the thickness of the first insulating layer 3, which is a silicon oxide layer, was changed, it was found that increasing the thickness of the silicon oxide layer reduced the absolute value of the TCF. Therefore, it was found that the temperature characteristics improved as the thickness of the first insulating layer 3, which is a silicon oxide layer, increased. Generally, the temperature characteristics of a SAW resonator with the configuration shown in Figure 3 have a TCF at the resonant frequency Fr that is at least around -20.0 [ppm / K], and a TCF at the anti-resonant frequency Fa that is at least around -30.0 [ppm / K]. Therefore, it was found that the temperature characteristics in Examples 8 and 9 are significantly superior.

[0049] <Second Embodiment> Figure 7 is a cross-sectional view showing a second embodiment of the elastic wave device of the present invention. As shown in Figure 7, the elastic wave device 200 includes a support substrate 9 below the first piezoelectric layer 1. In the second embodiment, components with the same role and name as those in the first embodiment shown in Figure 1 are given the same reference numerals and their descriptions are omitted.

[0050] For example, sapphire is used for the support substrate 9. However, other materials such as silicon, alumina, spinel, quartz, or glass may be used for the support substrate 9, as long as the material has a higher thermal conductivity than the first piezoelectric layer.

[0051] <Third Embodiment> Figure 8 is a cross-sectional view showing a third embodiment of the present invention. As in the third embodiment, vias 2a may be provided on the second piezoelectric layer 2 on the metal layer 5, a metal via wiring 21 may be provided in the via 2a, and a metal pad 20 may be provided that is electrically connected to the via wiring 21.

[0052] The conductors constituting the pad 20 and via wiring 21 are formed from suitable metals such as aluminum, gold, copper, silver, titanium, chromium, or nickel, or alloys containing these metals.

[0053] By providing the pad 20 that connects to the metal layer 5 on the second piezoelectric layer 2 side in this manner, the via 2a only needs to be formed by etching the second piezoelectric layer 2. Therefore, in order to provide the pad 20 on the underside of the first piezoelectric layer 1, the number of manufacturing steps can be reduced compared to etching both the first piezoelectric layer 1 and the first insulating layer 3 so that the via 2a (opening for providing a conductor) reaches the metal layer 5 from below. As a result, an elastic wave device 300 with low manufacturing costs can be realized.

[0054] <About the manufacturing method> Figures 9(a) to 9(d) are cross-sectional views showing part of the manufacturing process of the elastic wave device 100. In the first embodiment, the manufacturing method for an example of an elastic wave device 100 in which the first insulating layer 3 and the second insulating layer 4 are made of silicon oxide will be described.

[0055] As shown in Figure 9(a), a metal layer 5 is formed on the second piezoelectric layer 2. The metal layer 5 is formed by depositing a metal film on the second piezoelectric layer 2 using vacuum deposition, ion-assisted deposition, or sputtering, and then forming a pattern using photolithography and etching.

[0056] Next, as shown in Figure 9(b), an insulating layer (silicon oxide (SiO2) layer) 3a is formed to cover the second piezoelectric layer 2 and the metal layer 5. As described above, for the formation of the silicon oxide film, for example, CVD or sputtering methods are used. In this embodiment, the insulating layer 3a corresponds to the first insulating layer 3 and the second insulating layer 4 in Figure 1 showing the first embodiment, and since these are formed from the same material, the first insulating layer 3 and the second insulating layer 4 are formed simultaneously as the insulating layer 3a.

[0057] Next, as shown in Figure 9(c), the upper part 3b of the silicon oxide, which is the insulating layer 3a, is smoothed by polishing, for example, by the CMP method. This forms the insulating layer 3a.

[0058] Next, as shown in Figure 9(d), the first piezoelectric layer 1 is bonded to the insulating layer 3a (first insulating layer 3). The bonding is performed by directly joining the insulating layer 3a and the first piezoelectric layer 1 after the bonding surface has been activated.

[0059] Next, as shown in Figure 10, the surface 2b of the second piezoelectric layer 2 is thinned by CMP or grinding. These steps are used to manufacture the elastic wave device of the embodiment. Note that the elastic wave device in Figure 9 is shown upside down compared to Figure 9(d).

[0060] As described above, in this embodiment, the first insulating layer 3 and the second insulating layer 4 in Figure 1 are made of the same insulating material, silicon oxide (silicon oxide layer 3a). Therefore, since the first insulating layer 3 and the second insulating layer 4 can be deposited simultaneously as silicon oxide layer 3a, the manufacturing process can be reduced compared to the case where the first insulating layer 3 and the second insulating layer 4 are made of different insulating materials.

[0061] In the first embodiment of Figure 1, both the first insulating layer 3 and the second insulating layer 4 are silicon oxide, but if the first insulating layer 3 and the second insulating layer 4 are made of different insulating materials, a metal layer 5 may be formed on the second piezoelectric layer 2, then the second insulating layer 4 (e.g., an aluminum oxide layer) may be deposited to cover the metal layer 5, and then the second insulating layer 4 may be polished by CMP to approximately the same thickness as the metal layer 5, and then the first insulating layer 3 (e.g., silicon oxide) may be deposited to cover the second insulating layer 4 and the metal layer 5.

[0062] Next, as shown in Figure 11(a), the second piezoelectric layer 2, made of lithium tantalate, is etched to form vias 2a. For this etching, dry etching using a mixed gas of carbon tetrafluoride (CF4), argon (Ar), and hydrogen (H2) can be used.

[0063] As shown in Figure 11(b), via wiring 21 is provided on via 2a. Via wiring 21 is formed to be in contact with the metal layer 5. Via wiring 21 is formed integrally with pad 20. As a result, pad 20 is formed on the surface on the second piezoelectric layer 2 side.

[0064] Thus, by providing the pad 20 on the upper surface of the second piezoelectric layer 2 (the surface opposite to the metal layer 5 of the second piezoelectric layer 2 in Figure 11(b)), only the second piezoelectric layer 2 needs to be etched to provide the via 2a. On the other hand, if the pad 20 is provided on the lower side of the first piezoelectric layer 1 (the side opposite to the metal layer 5 of the first piezoelectric layer 1 in Figure 11(b)), multiple layers of the first piezoelectric layer 1 and the first insulating layer 3 must be etched. For this reason, by providing the pad 20 on the upper surface of the second piezoelectric layer 2, the pad 20 connected to the metal layer 5 can be formed with fewer steps than if the pad were provided on the lower side of the first piezoelectric layer 1.

[0065] <About filter circuits> The elastic wave device according to the above embodiment can be configured as a ladder-type filter 400 as shown in Figure 12, with respect to the resonator. This ladder-type filter comprises series resonators S1, S2, S3 connected between terminal 401 and terminal 402, and parallel resonators P1, P2 provided between the series resonators S1, S2, S3 and ground. At least one of these series resonators S1, S2, S3 and parallel resonators P1, P2 can be fitted with the elastic wave device 100, elastic wave device 200, or elastic wave device 300 according to the above embodiment.

[0066] The filter circuit equipped with the elastic wave device according to the above embodiment can be configured as a duplexer 500 comprising a transmit filter 501 and a receive filter 502, as shown in Figure 13.

[0067] In the embodiments described above, examples were shown in which elastic wave device 100, elastic wave device 200, or elastic wave device 300 is used in the duplexer 500, but it is also applicable to other multiplexers, for example. Furthermore, in the embodiments described above, an example was shown that included a ladder-type filter 400, but it is also applicable to other filters.

[0068] Please note that the diagrams used in the above explanation are schematic, and the dimensions and proportions shown in the drawings may not necessarily match those of the actual product.

[0069] The present invention has been described above, but in the specific implementation of the present invention as an elastic wave device, various modifications and additions are possible, not limited to the embodiments described above, as long as they do not depart from the spirit of the invention. [Explanation of symbols]

[0070] 1. First piezoelectric layer 2. Second piezoelectric layer 2a via 3. First insulating layer 3a Insulating layer (silicon oxide layer) 4. Second insulating layer 5 metal layer 6 IDT electrode 9. Support substrate 20 electrode pads 21 via wiring 30 space 31 areas 100, 200, 300 elastic wave devices 500 Duplexa 501 Transmit Filter 502 Incoming Filter S1,S2,S3 series resonator P1,P2 parallel resonator

Claims

1. First piezoelectric layer and A first insulating layer formed on the first piezoelectric layer, A plurality of electrode fingers, each consisting of a metal layer formed on the first insulating layer, A second insulating layer is formed on the first insulating layer and provided between the plurality of electrode fingers, The electrode finger comprises a second piezoelectric layer formed on the metal layer constituting the electrode finger. Elastic wave device.

2. The thickness of the first insulating layer is 0.01λ or more and 0.1λ or less, where λ is the wavelength of the wave excited on the metal layer side surface of the second piezoelectric layer. The elastic wave device according to claim 1.

3. The thickness of the second piezoelectric layer is 0.1λ or more and 0.4λ or less, where λ is the wavelength of the wave that excites the main surface of the second piezoelectric layer on the electrode finger side. The elastic wave device according to claim 1.

4. The thickness of the second insulating layer is the same as the thickness of the metal layer that constitutes the electrode finger. The elastic wave device according to claim 1.

5. The second insulating layer is made of silicon oxide. The elastic wave device according to claim 1.

6. The first insulating layer is made of silicon oxide. The elastic wave device according to claim 1.

7. The electrode fingers are made of an alloy containing copper and aluminum. The elastic wave device according to claim 1.

8. The first insulating layer and the second insulating layer are made of the same insulating material. The elastic wave device according to claim 1.

9. A support substrate with a higher thermal conductivity than the first piezoelectric layer is provided below the first piezoelectric layer. The elastic wave device according to claim 1.

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