Acoustic wave device, branching filter, communication apparatus and manufacturing method of acoustic wave device

Abstract

To provide an acoustic wave device having excellent frequency characteristics, a branching filter including the acoustic wave device, a communication apparatus including the acoustic wave device and a manufacturing method of the acoustic wave device.SOLUTION: An acoustic wave device comprises a piezoelectric substrate, a support substrate, and an acoustic multilayer film which is positioned between the piezoelectric substrate and the support substrate. In the acoustic multilayer film, a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers are alternately laminated. Acoustic impedance of the high acoustic impedance layer is higher than acoustic impedance of the low acoustic impedance layer. Arithmetic average roughness of an interface of the high acoustic impedance layer at the side of the support substrate is within a predetermined first range not including 0 nm.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an acoustic wave device that utilizes acoustic waves, a duplexer including the acoustic wave device, a communication device including the acoustic wave device, and a method for manufacturing the acoustic wave device. [Background technology]

[0002] Conventionally, acoustic wave devices have been widely used in electronic devices, etc. Patent Document 1 discloses an acoustic wave device including an acoustic reflection film composed of a plurality of acoustic impedance layers including a low acoustic impedance layer having a relatively low acoustic impedance and a high acoustic impedance layer having a relatively high acoustic impedance.

[0003] The acoustic wave device disclosed in Patent Document 1 has an acoustic reflection film that has a first acoustic impedance layer that is one of a plurality of acoustic impedance layers, and a second acoustic impedance layer that is one of the plurality of acoustic impedance layers and has an arithmetic mean roughness (Ra) different from that of the first acoustic impedance layer, and effectively suppresses unwanted waves. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6809595 Summary of the Invention [Problem to be solved by the invention]

[0005] It is desirable to provide an acoustic wave device, a duplexer, and a communication device that have excellent frequency characteristics. [Means for solving the problem]

[0006] An acoustic wave device according to one embodiment of the present disclosure has a piezoelectric substrate, a support substrate, and an acoustic multilayer film located between the piezoelectric substrate and the support substrate, the acoustic multilayer film being formed by alternatingly stacking a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers, the acoustic impedance of the high acoustic impedance layers being higher than the acoustic impedance of the low acoustic impedance layers, and the arithmetic mean roughness of the interface of the high acoustic impedance layer on the support substrate side being within a predetermined first range not including 0 nm.

[0007] A duplexer according to one embodiment of the present disclosure has an antenna terminal, a transmit filter that filters a signal output to the antenna terminal, and a receive filter that filters a signal input from the antenna terminal, and at least one of the transmit filter and the receive filter includes the above-mentioned elastic wave device.

[0008] A communication device according to an embodiment of the present disclosure includes an antenna, the above-mentioned duplexer having an antenna terminal connected to the antenna, and an IC connected to a transmit filter and a receive filter.

[0009] A manufacturing method of an elastic wave device according to an embodiment of the present disclosure includes a first step of providing an acoustic multilayer film on a first surface side of a piezoelectric substrate, and a second step of providing a support substrate on a surface of the acoustic multilayer film opposite the piezoelectric substrate, the first step including a third step of providing a low acoustic impedance layer, a fourth step of providing a high acoustic impedance layer having an acoustic impedance higher than that of the low acoustic impedance layer, and a fifth step of performing a smoothing process on a surface of the low acoustic impedance layer farther from the piezoelectric substrate or a surface of the high acoustic impedance layer close to the piezoelectric substrate, and the third step includes The fourth and fifth steps are repeated at least two times. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of an elastic wave device according to an embodiment of the present disclosure. [Diagram 2] FIG. 1 is a schematic plan view of an elastic wave device according to an embodiment of the present disclosure. [Diagram 3] 11 is a diagram comparing frequency characteristics of an elastic wave device according to an embodiment of the present disclosure with those of a comparative example. [Figure 4] 11 is a diagram comparing frequency characteristics of an elastic wave device according to an embodiment of the present disclosure with those of a comparative example. [Diagram 5] FIG. 1 is a schematic cross-sectional view of an elastic wave device according to an embodiment of the present disclosure. [Figure 6] 11 is a diagram comparing frequency characteristics of an elastic wave device according to an embodiment of the present disclosure with those of a comparative example. [Figure 7] FIG. 1 is a schematic cross-sectional view of an elastic wave device according to an embodiment of the present disclosure. [Figure 8] 11 is a diagram comparing frequency characteristics of an elastic wave device according to an embodiment of the present disclosure with those of a comparative example. [Figure 9] 13 is a schematic cross-sectional view of an elastic wave device according to a modified example of the present disclosure. [Figure 10] FIG. 1 is a diagram illustrating a duplexer as an example of a use of an elastic wave device according to an embodiment of the present disclosure. [Figure 11] 11 is a block diagram showing a configuration of a main part of a communication device as an example of using the duplexer of FIG. 10. [Figure 12] 1A to 1C are diagrams illustrating a method for manufacturing an acoustic wave device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the drawings used in the following description are schematic, and the dimensional ratios and the like in the drawings do not necessarily correspond to the actual ones.

[0012] For convenience, the drawings may be illustrated with an orthogonal coordinate system consisting of an X-axis, a Y-axis, and a Z-axis. In the elastic wave device according to the present disclosure, either direction may be considered to be upward or downward. However, for convenience, the terms upper surface and lower surface may be used with the Z-axis direction being the up-down direction. The X-axis is defined to be parallel to the propagation direction of elastic waves propagating along the upper surface of the piezoelectric substrate 2, which will be described later. The Y-axis is defined to be parallel to the upper surface of the piezoelectric substrate 2 and perpendicular to the X-axis. The Z-axis is defined to be perpendicular to the upper surface of the piezoelectric substrate 2.

[0013] Note that the embodiments described in this specification are merely illustrative, and different embodiments and modifications may be partially substituted with each other. Also, different embodiments and modifications may be partially combined with each other.

[0014] Fig. 1 is a schematic cross-sectional view of an acoustic wave device 1 according to a preferred embodiment of the present disclosure. As shown in Fig. 1, the acoustic wave device 1 includes a piezoelectric substrate 2, an acoustic multilayer film 4, and a supporting substrate 3. An IDT (Interdigital Transducer) electrode 5 is located on the upper surface of the piezoelectric substrate 2.

[0015] The thickness of the support substrate 3 is not particularly limited, but is, for example, thicker than the thickness of the piezoelectric substrate 2 described below.

[0016] The material of the support substrate 3 is not particularly limited as long as it has a certain strength. For example, if the support substrate 3 is made of a material with a smaller linear expansion coefficient than the piezoelectric substrate 2, it is possible to reduce the deformation of the piezoelectric substrate 2 due to temperature changes, thereby reducing the change in characteristics due to temperature changes. In addition, the material of the support substrate 3 is preferably made of a material having a linear expansion coefficient smaller than that of the piezoelectric substrate 2, and the linear expansion coefficient is smaller than that of the piezoelectric substrate 2. When a material in which the shear wave acoustic velocity of the propagating elastic waves is greater than the shear wave acoustic velocity of the elastic waves propagating through piezoelectric substrate 2 is selected as the material for support substrate 3, the elastic waves can be confined within piezoelectric substrate 2, and elastic wave device 1 with excellent frequency characteristics can be provided.

[0017] Examples of materials for the support substrate 3 include sapphire (Al2O3) and silicon (Si). In one embodiment of the present disclosure, a case in which the support substrate 3 is made of Si will be described as an example.

[0018] The piezoelectric substrate 2 has an upper surface and a lower surface perpendicular to the Z axis, with the Z axis being the up-down direction. An acoustic multilayer film 4 (described later) and the support substrate 3 described above are located on the lower surface side of the piezoelectric substrate 2, and an IDT electrode 5 (described later) is located on the upper surface of the piezoelectric substrate 2.

[0019] As the material of the piezoelectric substrate 2, for example, a single crystal substrate having piezoelectricity containing lithium tantalate (LiTaO3) crystal, a single crystal substrate having piezoelectricity containing lithium niobate (LiNbO3) crystal, etc. can be used. In the embodiment of the present disclosure, specifically, the piezoelectric substrate 2 is made of LiTaO3.

[0020] In an embodiment of the present disclosure, the thickness of the piezoelectric substrate 2 is not particularly limited, but may be, for example, thinner than the thickness of the above-mentioned support substrate 3. Also, the thickness may be thicker than the low acoustic impedance layer 42 and the high acoustic impedance layer 41 of the acoustic multilayer film 4 described below. As an example, the thickness of the piezoelectric substrate 2 is 100 nm to 1000 nm.

[0021] The lower surface of the piezoelectric substrate 2 and the acoustic multilayer film 4 may be in direct contact with each other, or may be in indirect contact with each other, for example, via an intermediate layer (not shown).

[0022] Examples of such an intermediate layer include insulating materials such as silicon oxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), etc. Providing such an insulating intermediate layer can reduce the generation of unnecessary potential and unnecessary capacitance, thereby improving the electrical characteristics of acoustic wave device 1.

[0023] The acoustic multilayer film 4 is located between the piezoelectric substrate 2 and the support substrate 3. The acoustic multilayer film 4 is formed by alternately laminating low acoustic impedance layers 42 and high acoustic impedance layers 41. The acoustic impedance of the low acoustic impedance layer 42 is lower than the acoustic impedance of the piezoelectric substrate 2, and the acoustic impedance of the high acoustic impedance layer 41 is higher than the acoustic impedance of the low acoustic impedance layer 42.

[0024] An example of the material of the low acoustic impedance layer 42 is SiO2. When a plurality of low acoustic impedance layers 42 are provided, each low acoustic impedance layer 42 may be made of a different material. Specifically, in the embodiment of the present disclosure, the low acoustic impedance layer 42 is SiO2.

[0025] Examples of materials for the high acoustic impedance layer 41 include Si3N4, Al2O3, platinum (Pt), aluminum nitride (AlN), titanium oxide (TiO2), tantalum oxide (Ta2O5), hafnium oxide (HfO2), zirconium oxide (ZrO2), tungsten (W), LiTaO3, and LiNbO3. When a plurality of high acoustic impedance layers 41 are provided, each high acoustic impedance layer 41 may be made of a different material. The same high acoustic impedance layer 41 may contain a plurality of materials. Specifically, in the embodiment of the present disclosure, the high acoustic impedance layer 41 contains HfO2 and ZrO2.

[0026] The number of layers of the low acoustic impedance layers 42 and the high acoustic impedance layers 41 may be set appropriately. Specifically, in one embodiment of the present disclosure, there are four low acoustic impedance layers 42 and four high acoustic impedance layers 41 each.

[0027] When the acoustic multilayer film 4 has a plurality of high acoustic impedance layers 41, the layers are named, in order from the layer located closest to the piezoelectric substrate 2, as high acoustic impedance layers 41a, 41b, 41c, and 41d.

[0028] Furthermore, when the acoustic multilayer film 4 has a plurality of low acoustic impedance layers 42, the layers are designated, in order from the layer located closest to the piezoelectric substrate 2, as low acoustic impedance layers 42a, 42b, 42c, and 42d.

[0029] In the embodiment of the present disclosure, the low acoustic impedance layer 42a is located closer to the piezoelectric substrate 2 than the high acoustic impedance layer 41a.

[0030] In the embodiment of the present disclosure, the arithmetic mean roughness of the low acoustic impedance layer 42 at the interface on the supporting substrate side is defined as Ra2, and the arithmetic mean roughness of the high acoustic impedance layer 41 at the interface on the supporting substrate side is defined as Ra1.

[0031] In this specification, the arithmetic mean roughness of the interface of the low acoustic impedance layer 42 on the supporting substrate side may be simply referred to as the arithmetic mean roughness of the low acoustic impedance layer 42. Also, the arithmetic mean roughness of the interface of the high acoustic impedance layer 41 on the supporting substrate side may be simply referred to as the arithmetic mean roughness of the high acoustic impedance layer 41.

[0032] In this specification, the arithmetic mean roughness refers to the arithmetic mean roughness (Ra) defined in JIS B 0601:2013.

[0033] In order to distinguish between the arithmetic mean roughnesses of the low acoustic impedance layers 42, the arithmetic mean roughnesses of the low acoustic impedance layers 42a, 42b, 42c, and 42d are defined as Ra2a, Ra2b, Ra2c, and Ra2d, respectively. In order to distinguish between the arithmetic mean roughnesses of the high acoustic impedance layers 41, the arithmetic mean roughnesses of the high acoustic impedance layers 41a, 41b, 41c, and 41d are defined as Ra1a, Ra1b, Ra1c, and Ra1d, respectively.

[0034] In addition, in one embodiment of the present disclosure, the support substrate 3 may have a void on the upper surface. In this case, the piezoelectric substrate 2 covers the void of the support substrate 3 in a plan view, leaving a space inside the void. The size and depth of the void may be set appropriately.

[0035] Furthermore, a substrate (not shown) or the like may be provided on the upper surface side of the support substrate 3 having the void.

[0036] An IDT electrode 5 may be located on the upper surface of the piezoelectric substrate 2. The IDT electrode 5 is made of a conductive material. The IDT electrode 5 may be made of various conductive materials such as Al, Cu, Pt, Mo, Au, or alloys thereof, and may be made of a plurality of layers stacked together. When the IDT electrode 5 includes a laminate of a plurality of layers, a base layer (not shown) may be interposed at the interface between the layers.

[0037] 2 is a plan view of an elastic wave device 1 according to an embodiment of the present disclosure, as viewed from the Z-axis direction. The IDT electrode 5 constitutes a resonator having, for example, a pair of comb-shaped electrodes 51a and 51b. Hereinafter, the comb-shaped electrodes 51a and 51b may be collectively referred to as comb-shaped electrode 51.

[0038] Comb-shaped electrode 51 includes two bus bars 511 and a plurality of long electrode fingers 512 connected to either of bus bars 511. Electrode fingers 512a connected to one bus bar 511a and electrode fingers 512b connected to the other bus bar 511b are arranged alternately.

[0039] Furthermore, comb-shaped electrode 51 may include a plurality of dummy electrodes 513 that face the tips of electrode fingers 512 connected to one bus bar 511 and are connected to the other bus bar 511.

[0040] The lengths of the electrode fingers 512 are, for example, equal to each other. The IDT electrode 5 may be apodized, in which the length (or, from another point of view, the cross width) of the electrode fingers 512 varies depending on the position in the propagation direction. The length and thickness of the electrode fingers 512 may be appropriately set depending on the required electrical characteristics, etc.

[0041] The repetition interval between the electrode fingers 512a and 512b is defined as the electrode finger pitch p, and the width of the electrode fingers 512 is defined as the electrode finger width w. The electrode finger pitch p and electrode finger width w of the IDT electrode 5 may be designed appropriately according to the desired frequency characteristics. In FIG. 2, the electrode finger pitch p of the IDT electrode 5 is constant, but is not limited to this example. For example, the pitch p may be designed to gradually increase, or may be designed to have multiple types of pitches in stages.

[0042] When a high-frequency signal is applied to the IDT electrode 5, a SAW (Surface Acoustic Wave) is excited with a wavelength λ defined as twice the electrode finger pitch p of the IDT electrode 5. The resonant frequency fr of the acoustic wave device 1 is approximately equal to the frequency of the excited SAW. The anti-resonant frequency fa is determined by the resonant frequency fr and the capacitance ratio, which is determined mainly by the piezoelectric substrate 2 and is adjusted by the number, cross width, film thickness, etc. of the electrode fingers 512.

[0043] A pair of reflectors 52 may be located on both sides of the IDT electrode 5 in the propagation direction of the SAW. The reflector 52 includes a pair of reflector bus bars facing each other and a plurality of strip electrodes extending between the pair of reflector bus bars. The number of strip electrodes of the reflector 52 may be designed as appropriate.

[0044] 1, in one embodiment of the present disclosure, the arithmetic mean roughnesses Ra1a, Ra1b, Ra1c, and Ra1d of the high acoustic impedance layer 41 are predetermined first numerical values. Also, the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are predetermined second numerical values. In one embodiment of the present disclosure, the first numerical value is greater than the second numerical value.

[0045] The first numerical values ​​do not need to be exactly the same numerical value, and may include manufacturing error. For example, the manufacturing error in the first numerical values ​​refers to an error in a range equivalent to 30% of the average value of the first numerical values. Specifically, if the average value of the first numerical values ​​is the average first numerical value, the first numerical value may be in the range of 0.70 × average first numerical value to 1.30 × average first numerical value. In this way, the range that the first numerical value can take is called the first range.

[0046] Similarly, the second numerical value does not need to be exactly the same numerical value, and may include manufacturing error. For example, the manufacturing error in the second numerical value refers to an error in a range equivalent to 30% of the average value of the second numerical values. Specifically, if the average value of the second numerical values ​​is the average second numerical value, the second numerical value may be in the range of 0.70 × average second numerical value to 1.30 × average second numerical value. In this way, the range that the second numerical value can take is called the second range.

[0047] Fig. 3 is a diagram comparing simulation results of frequency characteristics for Example 1, Comparative Example 1, and Comparative Example 2 of elastic wave device 1 of the present disclosure. Fig. 3A shows frequency characteristics in the range of 4500 MHz to 8500 MHz, and Figs. 3B to 3F are each a partial enlarged view of Fig. 3A.

[0048] In Example 1, the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are 0 nm, and the arithmetic mean roughnesses Ra1a, Ra1b, Ra1c, and Ra1d of the high acoustic impedance layer 41 are 35 nm. In other words, the first numerical value is 35 nm, and the second numerical value is 0 nm. In Example 1, the first numerical value may be set to be larger than the second numerical value.

[0049] In Comparative Example 1, the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are 0 nm. Furthermore, with regard to the arithmetic mean roughnesses of the respective high acoustic impedance layers 41, the value of Ra1 increases as the high acoustic impedance layer 41 is closer to the support substrate 3. Specifically, in Comparative Example 1, Ra1a is 35 nm, Ra1b is 47 nm, Ra1c is 58 nm, and Ra1d is 70 nm.

[0050] In Comparative Example 1, the arithmetic mean roughnesses Ra1a, Ra1b, Ra1c, and Ra1d of the high acoustic impedance layer 41 are 0 nm, and the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are 35 nm.

[0051] 3B to 3F, it was found that the loss of the main resonance characteristic is improved and the intensity of the spurious signals located on the high frequency side of the main resonance is smaller in Example 1 than in Comparative Examples 1 and 2. For example, looking at the intensity of the spurious signals occurring around 7000-7250 MHz, it is found that Example 1 is smaller than Comparative Examples 1 and 2.

[0052] In this way, by adjusting the arithmetic mean roughness of high acoustic impedance layer 41 and the arithmetic mean roughness of low acoustic impedance layer 42 to predetermined values, scattering of the main resonance mode of the elastic wave can be reduced, and spurious modes, which are unwanted waves, can be effectively scattered while maintaining the characteristics. Therefore, when elastic wave device 1 is used as a filter, spurious waves located on the high frequency side of the pass band can be effectively reduced while maintaining the pass band characteristics of the filter, and an elastic wave device with excellent frequency characteristics can be provided.

[0053] In Example 1 and Comparative Examples 1-4, the arithmetic mean roughness of the high acoustic impedance layer 41 and the low acoustic impedance layer 42 are different, but the other conditions are the same.

[0054] The main resonance mode is the mode of the elastic wave to be used, and may be set appropriately. For example, in one embodiment of the present disclosure, the main resonance mode is the A1 mode of the Lamb wave.

[0055] Fig. 4 is a diagram comparing simulation results of frequency characteristics for Example 1, Comparative Example 3, and Comparative Example 4 of elastic wave device 1 of the present disclosure. Fig. 4A shows frequency characteristics in the range of 4500 MHz to 8500 MHz, and Figs. 4B to 4F are each a partial enlargement of Fig. 4A.

[0056] In Comparative Examples 3 and 4, the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are 0 nm, and the arithmetic mean roughnesses of the high acoustic impedance layer 41 are different for each. In other words, in Comparative Example 3, the closer the high acoustic impedance layer 41 is to the supporting substrate 3, the smaller the Ra1 value, and in Comparative Example 4, the closer the high acoustic impedance layer 41 is to the supporting substrate 3, the larger the Ra1 value.

[0057] As can be seen from the results in FIGS. 4B to 4C, Example 1 has a smaller loss in the main resonance characteristic than Comparative Example 3, and also has a smaller intensity of spurious emissions located on the high frequency side of the main resonance than Comparative Example 4.

[0058] In the first embodiment, the arithmetic mean roughness Ra1 of the high acoustic impedance layer 41 is 35 nm, but is not limited to this example. The arithmetic mean roughness Ra1 of the high acoustic impedance layer 41 may be set as appropriate. In other words, the first numerical value may be set as appropriate. For example, the first numerical value may be a predetermined numerical value in the range of 0.5 nm to 70 nm. More preferably, the first numerical value may be a predetermined numerical value in the range of 0.7 nm to 4.0 nm.

[0059] In the first embodiment, the arithmetic mean roughness Ra2 of the low acoustic impedance layer 42 is 0 nm, but is not limited to this example. The arithmetic mean roughness Ra2 of the low acoustic impedance layer 42 may be set as appropriate. In other words, the second numerical value may be set as appropriate. For example, the second numerical value may be a predetermined numerical value in the range of 0.01 nm to 1.0 nm. More preferably, the second numerical value may be a predetermined numerical value in the range of 0.2 nm to 0.5 nm.

[0060] As described above, in Example 1, the first numerical value is within a first range including a predetermined manufacturing error, and the second numerical value is within a second range including a predetermined manufacturing error, but is not limited to this example. For example, the first range and the second range may be a range wider than the range including the manufacturing error. As shown in FIG. 5, in Example 2 of the present disclosure, the arithmetic mean roughness of the high acoustic impedance layer 41 is appropriately set within a predetermined first range, and the arithmetic mean roughness of the low acoustic impedance layer 42 is appropriately set within a predetermined second range.

[0061] Fig. 6 is a diagram comparing simulation results of frequency characteristics for Example 2, Comparative Example 1, and Comparative Example 2 in elastic wave device 1. Fig. 6A shows frequency characteristics in the range of 4500 MHz to 8500 MHz, and Figs. 6B to 6F are each a partial enlargement of Fig. 6A.

[0062] In Example 2, the arithmetic mean roughness of the high acoustic impedance layer 41 is Ra1a 35 nm, Ra1b 30 nm, Ra1c 35 nm, and Ra1d 30 nm, and the first range is 30 nm to 35 nm. In Example 2, the arithmetic mean roughness of the low acoustic impedance layer 42 is Ra2a 0 nm, Ra2b 5 nm, Ra2c 0 nm, and Ra2d 5 nm, and the second range is 0 nm to 5 nm.

[0063] In Example 2, the first range is a range that does not include 0 nm, and the lower limit of the first range is set to be greater than the upper limit of the second range.

[0064] 6A to 6F, it was found that the loss of the main resonance characteristic is improved and the intensity of the spurious signals located on the high frequency side of the main resonance is smaller in Example 2 than in Comparative Examples 1 and 2. For example, looking at the intensity of the spurious signals occurring around 7000-7250 MHz, it is found that Example 2 is smaller than Comparative Examples 1 and 2.

[0065] By configuring the acoustic wave device 1 in the manner as in the second embodiment, the acoustic wave device It is possible to reduce the influence of spurious modes, which are unwanted waves, while maintaining the characteristics of the main resonance mode of the unwanted waves.

[0066] In Example 2, the first range of the arithmetic mean roughness of the high acoustic impedance layer 41 is 30 nm to 35 nm, but is not limited to this example. The first range of the high acoustic impedance layer 41 may be set appropriately. For example, the first range may be a predetermined range of 0.5 nm to 70 nm. More preferably, the first range may be 0.7 nm to 4.0 nm.

[0067] In the second embodiment, the second range of the arithmetic mean roughness of the low acoustic impedance layer 42 is 0 nm to 5 nm, but is not limited to this example. The second range of the low acoustic impedance layer 42 may be set appropriately. For example, the second range may be a predetermined range of 0.01 nm to 1.0 nm. More preferably, the second range may be 0.2 nm to 0.5 nm.

[0068] In Example 2, the arithmetic mean roughness Ra1 of the high acoustic impedance layer 41 and the arithmetic mean roughness Ra2 of the low acoustic impedance layer are within a predetermined range, but are not limited to this example. For example, as shown in Fig. 7, in Example 3 of the present disclosure, the arithmetic mean roughness of each layer of the acoustic multilayer film 4 may be larger as the layer becomes closer to the support substrate 3. Specifically, in Example 3, the arithmetic mean roughness of the high acoustic impedance layer 41 on the support substrate 3 side is larger than the arithmetic mean roughness of the high acoustic impedance layer 41 on the piezoelectric substrate 2 side, and the arithmetic mean roughness of the low acoustic impedance layer 42 on the support substrate 3 side is larger than the arithmetic mean roughness of the low acoustic impedance layer 42 on the piezoelectric substrate 2 side.

[0069] Fig. 8 is a diagram comparing simulation results of frequency characteristics for elastic wave device 1 in Example 3, Comparative Example 5, and Comparative Example 6. Fig. 8A shows frequency characteristics in the range of 4500 MHz to 8500 MHz, and Figs. 8B to 8F are each a partial enlargement of Fig. 8A.

[0070] In Example 3, the arithmetic mean roughness of the high acoustic impedance layer 41 is Ra1a 14 nm, Ra1b 21 nm, Ra1c 28 nm, and Ra1d 35 nm. Also, in Example 3, the arithmetic mean roughness of the low acoustic impedance layer 42 is Ra2a 10 nm, Ra2b 17 nm, Ra2c 24 nm, and Ra2d 31 nm.

[0071] In Comparative Example 5, the arithmetic mean roughness of the high acoustic impedance layer 41 was Ra1a 31 nm, Ra1b 24 nm, Ra1c 17 nm, and Ra1d 10 nm. In Example 3, the arithmetic mean roughness of the low acoustic impedance layer 42 was Ra2a 35 nm, Ra2b 28 nm, Ra2c 21 nm, and Ra2d 14 nm.

[0072] In Comparative Example 6, the arithmetic mean roughnesses Ra1a, Ra1b, Ra1c, and Ra1d of the high acoustic impedance layer 41 are all 0 nm. In Example 3, the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layer 42 are all 0 nm.

[0073] As can be seen from the results of Figures 8A to 8F, in Example 3, the intensity of the spurious emissions located on the high frequency side of the main resonance was smaller than in Comparative Example 6, and the loss of the main resonance characteristics was improved compared to Comparative Example 4.

[0074] By configuring the elastic wave device 1 in this manner as in the third embodiment, the influence of spurious modes, which are unwanted waves, can be reduced while maintaining the characteristics of the main resonance mode of the elastic waves.

[0075] The arithmetic mean roughness of the high acoustic impedance layer 41 and the arithmetic mean roughness of the low acoustic impedance layer 42 in Example 3 are not limited to the above examples. When the arithmetic mean roughness of each layer of the acoustic multilayer film 4 increases as the layer becomes closer to the support substrate 3, the arithmetic mean roughness of each layer may be appropriately set.

[0076] As an example, the arithmetic mean roughness of the acoustic impedance layer 41 may be Ra1a 1.4 nm, Ra1b 2.1 nm, Ra1c 2.8 nm, and Ra1d 3.5 nm, and the arithmetic mean roughness of the low acoustic impedance layer 42 may be Ra2a 1.0 nm, Ra2b 1.7 nm, Ra2c 2.4 nm, and Ra2d 3.1 nm.

[0077] 9A and 9B show modified examples of the first to third embodiments of the present disclosure. Fig. 9A shows a modified example of the first embodiment, Fig. 9B shows a modified example of the second embodiment, and Fig. 9C shows a modified example of the third embodiment.

[0078] 9, in a modification of the present disclosure, a bonding layer 43 may be located between the acoustic multilayer film 4 and the support substrate 3. The thickness and material of the bonding layer 43 are appropriately set. For example, the bonding layer 43 may contain the same material as the low acoustic impedance layer 42, or the same material as the high acoustic impedance layer 41.

[0079] The arithmetic mean roughness Ra3 of the interface between the bonding layer 43 and the support substrate 3 may be set appropriately, for example, to 0 nm. When the bonding layer 43 has such a configuration, the bonding strength of the interface between the bonding layer 43 and the support substrate 3 is improved, and the bonding strength between the acoustic multilayer film 4 and the support substrate 3 can be improved.

[0080] When the bonding layer 43 is made of the same material as the low acoustic impedance layer 42, the arithmetic mean roughness Ra3 of the adhesive layer 43 at the bonding interface with the support substrate 3 may be a different value from the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the other low acoustic impedance layers 42. In other words, the arithmetic mean roughness Ra3 of the bonding layer 43 may be a different value from the predetermined second value satisfied by the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the low acoustic impedance layers 42. Furthermore, Ra3 may be a value that is not included in the predetermined second range satisfied by the arithmetic mean roughnesses Ra2a, Ra2b, Ra2c, and Ra2d of the other low acoustic impedance layers 42.

[0081] Although the configuration of the SAW resonator has been described in Examples 1-3, the present invention is not limited to this example. For example, the acoustic wave device 1 may be a BAW resonator. When the acoustic wave device 1 is a BAW resonator, the acoustic wave device 1 has an upper electrode on the upper surface side of the piezoelectric substrate 2 and a lower electrode on the lower surface side, instead of the IDT electrode 5. The acoustic multilayer film 4 is located on the lower surface side of the lower electrode.

[0082] (Example of use of acoustic wave device 1: splitter) 10 is a circuit diagram showing a schematic configuration of a duplexer 101 as an example of the use of the acoustic wave device 1. As can be seen from the reference numerals in the upper left corner of the figure, in this figure, comb-shaped electrode 51 is shown diagrammatically in a two-pronged fork shape, and reflector 52 is represented by a single line bent at both ends.

[0083] The splitter 101 has, for example, a transmit filter 105 that filters a transmit signal from a transmit terminal 103 and outputs the signal to an antenna terminal 102, and a receive filter 106 that filters a receive signal from the antenna terminal 102 and outputs the signal to a pair of receive terminals 104.

[0084] For example, the elastic wave device 1 according to an embodiment of the present disclosure may be used as at least one of the transmission filter 105 and the reception filter 106. It may be used for both the receiving filter 105 and the receiving filter 106 .

[0085] The transmit filter 105 may be configured, for example, as a ladder filter configured by connecting a plurality of resonators in a ladder shape. That is, the transmit filter 105 may have a plurality of resonators (or one) connected in series between the transmit terminal 103 and the antenna terminal 102, and a plurality of resonators (or one) connecting the series line (series arm) to a reference potential (parallel arm).

[0086] The receiving filter 106 may be configured to include, for example, a resonator and a multimode filter (including a double-mode filter) 107. The multimode filter 11 has a plurality of IDT electrodes 5 (three in the illustrated example) arranged in the propagation direction of the acoustic waves, and a pair of reflectors 52 arranged on both sides thereof.

[0087] 10 is merely one example of the configuration of the duplexer 101, and is not limited to this example. For example, in the duplexer 101, the receiving filter 106 may be configured by a ladder filter like the transmitting filter 105.

[0088] 10, both the transmit filter 105 and the receive filter 106 are acoustic wave filters including acoustic wave resonators, but this is not limiting. For example, one of the transmit filter 105 and the receive filter 106 may be an LC filter including one or more inductors and one or more capacitors.

[0089] Although the description has been given of a case in which the duplexer 101 includes the transmission filter 105 and the reception filter 106, the present invention is not limited to this. For example, the duplexer 101 may be a diplexer or a multiplexer including three or more filters.

[0090] (Example of use of splitter 101: communication equipment) 11 is a block diagram showing a main part of a communication device 111 as an example of using the duplexer 101. The communication device 111 performs wireless communication using radio waves, and includes the duplexer 101.

[0091] In the communication device 111, a transmission information signal TIS including information to be transmitted is modulated and frequency-raised (converted to a high-frequency signal of a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 113 to become a transmission signal TS. Unnecessary components outside the transmission passband are removed from the transmission signal TS by a bandpass filter 115a, amplified by an amplifier 114a, and input to a splitter 101 (transmission terminal 103). The splitter 101 (transmission filter 105) then removes unnecessary components outside the transmission passband from the input transmission signal TS, and outputs the removed transmission signal TS from an antenna terminal 102 to an antenna 112. The antenna 112 converts the input electrical signal (transmission signal TS) into a wireless signal (radio wave) and transmits it.

[0092] Furthermore, in the communication device 111, a radio signal (radio wave) received by the antenna 112 is converted by the antenna 112 into an electric signal (received signal RS) and input to the duplexer 101 (antenna terminal 102). The duplexer 101 (receiving filter 106) removes unnecessary components outside the receiving passband from the inputted received signal RS and outputs the signal from the receiving terminal 104 to the amplifier 114b. The outputted received signal RS is amplified by the amplifier 114b, and the unnecessary components outside the receiving passband are removed by the bandpass filter 115b. The received signal RS is then frequency-downgraded and demodulated by the RF-IC 113 to become a received information signal RIS.

[0093] The transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, such as analog voice signals or digitized voice signals. The passband of the wireless signal may be set appropriately, and in this embodiment, a relatively high-frequency passband (for example, 5 GHz or higher) is also possible. The modulation method may be any of phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more of these.

[0094] Although the circuit system shown in Fig. 11 is a direct conversion system, other suitable systems may be used, for example, a double superheterodyne system. Fig. 11 shows only the essential parts in a schematic manner, and low-pass filters or isolators may be added at suitable positions, and the positions of amplifiers and the like may be changed.

[0095] (Manufacturing Method of Acoustic Wave Device 1) Next, a manufacturing method of the acoustic wave device 1 according to the present disclosure will be described with reference to FIG.

[0096] One manufacturing method of the present disclosure for an elastic wave device 1 includes a first step of providing an acoustic multilayer film 4 on one of the two main surfaces of a prepared first substrate, and a second step of providing a second substrate, containing a material different from the material of the first substrate, on the surface of the acoustic multilayer film opposite the first substrate.

[0097] The first step will be described in detail. First, a first substrate containing an arbitrary material is prepared. For example, the first substrate may be a piezoelectric substrate 2 having piezoelectricity, or a support substrate 3. FIG. 12A shows an example in which a piezoelectric substrate 2 is prepared as the first substrate. Then, a first acoustic impedance layer is formed on one of the two main surfaces of the first substrate. In addition, the thickness of the first acoustic impedance layer can be 100 nm to 300 nm, for example. FIG. 12B shows an example in which a low acoustic impedance layer 42a is formed as the first acoustic impedance layer. In this way, the step of forming the first acoustic impedance layer is set as the third step.

[0098] Of the two principal surfaces of the first acoustic impedance layer, the principal surface closer to the first substrate is referred to as principal surface A, and the principal surface farther from the first substrate is referred to as principal surface B. Since the interface of principal surface B of the first acoustic impedance layer becomes rough due to deposition conditions, etc., the arithmetic mean roughness of principal surface B is relatively larger than that of principal surface A.

[0099] Next, as shown in FIG. 12C, the main surface B of the first acoustic impedance layer is smoothed. The method of smoothing is not particularly limited. For example, the method of smoothing can be an etching method using an ion beam or plasma. For example, the smoothing can be performed by an etching method using an ion beam, so that the arithmetic mean roughness of the main surface B of the first acoustic impedance layer can be set to 0.01 nm to 1.0 nm. The step of smoothing the main surface of the first acoustic impedance layer that is farther from the first substrate in this manner is called the fifth step. Note that the third step of forming the first acoustic impedance layer and the fifth step of smoothing the main surface B of the first acoustic impedance layer may be performed in order or simultaneously.

[0100] Next, a second acoustic impedance layer is formed on the main surface B of the first acoustic impedance layer. The acoustic impedance of the second acoustic impedance layer is different from that of the first acoustic impedance layer. The thickness of the second acoustic impedance layer can be 100 nm to 300 nm, for example. FIG. 12D shows an example in which a high acoustic impedance layer 41a is formed as the second acoustic impedance layer. The process of forming the second acoustic impedance layer in this manner is referred to as a fourth process.

[0101] The two principal surfaces of the second acoustic impedance layer are the principal surface closer to the first substrate as principal surface C, and the principal surface farther away as principal surface D. At this time, the principal surface B of the first acoustic impedance layer and the principal surface C of the second acoustic impedance layer are joined together. The arithmetic mean roughness of the principal surface D is larger than that of the principal surface C. In order to increase the arithmetic mean roughness of the principal surface D, the principal surface D may be roughened by an etching method using an ion beam or plasma, or the arithmetic mean roughness of the principal surface D may be increased by the film formation conditions of the second acoustic impedance layer. In addition, when the second acoustic impedance layer contains a plurality of types of oxides, the high acoustic impedance layer 41a may be a composite oxide, thereby increasing the arithmetic mean roughness of the principal surface D.

[0102] Specifically, in one manufacturing method disclosed herein, no roughening treatment is performed on principal surface D, and the arithmetic mean roughness of principal surface D is adjusted according to the deposition conditions of the second acoustic impedance layer. For example, if the arithmetic mean roughness of principal surface B of the first acoustic impedance layer is approximately 0.01 nm to 1.0 nm, and the second acoustic impedance layer is deposited under conditions approximately equivalent to the deposition conditions of the first acoustic impedance layer, then principal surface D will have an arithmetic mean roughness of approximately 0.5 nm to 4.0 nm.

[0103] Next, the third, fourth, and fifth steps are repeated. In the third step, a first acoustic impedance layer is formed again on the principal surface D of the second acoustic impedance layer. For example, as shown in Fig. 12D, a low acoustic impedance layer 42b, which is a first acoustic impedance layer, is formed again on the principal surface D of the high acoustic impedance layer 41a, which is the second acoustic impedance layer. Of the two principal surfaces of the first acoustic impedance layer thus formed, the principal surface closer to the first substrate is designated as principal surface E, and the principal surface farther from the first substrate is designated as principal surface F.

[0104] Next, as a fifth step, as shown in FIG. 12E, the main surface F of the first acoustic impedance layer is again subjected to a smoothing process, and as a fourth step, a second acoustic impedance layer is again formed on the main surface F of the first acoustic impedance layer.

[0105] Next, a second substrate made of any material is provided on the acoustic multilayer film 4 obtained by repeating the third, fourth, and fifth steps. This step is called the second step. For example, FIG. 12F shows a case where the second substrate is the support substrate 3, but this is not limited to this example. For example, when the first substrate is the support substrate 3, the second substrate may be the piezoelectric substrate 2.

[0106] In addition, in Fig. 12F, the third step, the fourth step, and the fifth step are repeated three times, but this is not limited to this example. For example, the third step, the fourth step, and the fifth step can be repeated any number of times, at least one or more.

[0107] Furthermore, a step of forming a bonding layer 43 on the acoustic multilayer film 4 may be included before the second step.

[0108] Also, the method may include a step of polishing one of the two main surfaces of the first substrate opposite to the main surface on which the acoustic multilayer film 4 is located. When the first substrate is a piezoelectric substrate 2, the thickness of the piezoelectric substrate 2 can be appropriately designed by polishing, and the frequency characteristics can be adjusted. For example, the first substrate may be polished until the thickness is 100 nm to 1000 nm. There is no particular limitation on the method of polishing.

[0109] 12, an example has been described in which the first substrate, the second substrate, the first acoustic impedance layer, and the second acoustic impedance layer are the piezoelectric substrate 2, the support substrate 3, the low acoustic impedance layer 42, and the high acoustic impedance layer 41, respectively, but the present invention is not limited to this example. For example, the first substrate, the second substrate, the first acoustic impedance layer, and the second acoustic impedance layer may be They may be the support substrate 3, the piezoelectric substrate 2, the high acoustic impedance layer 41, and the low acoustic impedance layer 42, respectively. [Explanation of symbols]

[0110] 1: Elastic wave device 2: Piezoelectric substrate 3: Support substrate 4: Acoustic multilayer film layer 41: High acoustic impedance layer 42: Low acoustic impedance layer 43: Bonding layer 5:IDT electrode 51: Comb-shaped electrode 511: Busbar 512: Electrode finger 513: Dummy electrode finger 52:Reflector 101: Duplexer 102: Antenna terminal 103: Transmission terminal 104: Receiving terminal 105: Transmission filter 106: Receive filter 111: Communication equipment 112: Antenna 113: RF-IC 114: Amplifier

Claims

1. A piezoelectric substrate; A support substrate; an acoustic multilayer film disposed between the piezoelectric substrate and the support substrate; The acoustic multilayer film is formed by alternately stacking a plurality of low acoustic impedance layers and a plurality of high acoustic impedance layers, the acoustic impedance of the high acoustic impedance layer is higher than the acoustic impedance of the low acoustic impedance layer; The arithmetic mean roughness of the interface of the high acoustic impedance layer on the supporting substrate side is within a predetermined first range not including 0 nm. Elastic wave device.

2. The arithmetic mean roughness of the interface of the low acoustic impedance layer on the supporting substrate side is within a predetermined second range. The acoustic wave device according to claim 1 .

3. The lower limit of the first range is greater than the upper limit of the second range. The acoustic wave device according to claim 2 .

4. The range width of the first range is greater than the range width of the second range. The acoustic wave device according to claim 2 .

5. The first range is 0.5 nm to 70 nm. The acoustic wave device according to claim 1 .

6. The second range is 0.01 nm to 1.0 nm. The acoustic wave device according to claim 2 .

7. When the average of the arithmetic mean roughness of the interface of the high acoustic impedance layer on the supporting substrate side is defined as an average first numerical value, The first range is a range from 0.70 x the average first numerical value to 1.30 x the average first numerical value; The acoustic wave device according to claim 1 .

8. The average of the arithmetic mean roughness of the interface of the low acoustic impedance layer on the supporting substrate side is defined as an average second numerical value, The second range is a range of 0.70 x the average second numerical value to 1.30 x the average second numerical value; The acoustic wave device according to claim 2 .

9. a bonding layer between the acoustic multilayer and the support substrate, the bonding layer containing the same material as the low acoustic impedance layer; The acoustic wave device according to claim 1 .

10. An antenna terminal; a transmission filter that filters a signal output to the antenna terminal; a receiving filter that filters a signal input from the antenna terminal, A duplexer, wherein at least one of the transmission filter and the reception filter includes the acoustic wave device according to claim 1 .

11. The antenna, The duplexer according to claim 10, wherein the antenna terminal is connected to the antenna; and an IC connected to the transmit filter and the receive filter.

12. a first step of providing an acoustic multilayer film on a first surface side of a piezoelectric substrate; a second step of providing a support substrate on a surface of the acoustic multilayer film opposite to the piezoelectric substrate, The first step comprises: a third step of providing a low acoustic impedance layer; a fourth step of providing a high acoustic impedance layer having an acoustic impedance higher than that of the low acoustic impedance layer; and a fifth step of smoothing a surface of the low acoustic impedance layer that is farther from the piezoelectric substrate or a surface of the high acoustic impedance layer that is closer to the piezoelectric substrate, The third step, the fourth step, and the fifth step are repeated at least twice. A method for manufacturing an acoustic wave device.

13. a surface of the high acoustic impedance layer that is farther from the piezoelectric substrate or a surface of the low acoustic impedance layer that is closer to the piezoelectric substrate is not roughened; A method for manufacturing the acoustic wave device according to claim 12.

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