High order mode surface acoustic wave device

Abstract

A high-order mode elastic surface wave device has a piezoelectric substrate (11) and an interdigital electrode (12) and utilizes an elastic surface wave of a high-order mode, wherein the piezoelectric substrate (11) is composed of a LiTaO3 crystal or a LiNbO3 crystal, and the interdigital electrode (12) is embedded in the surface of the piezoelectric substrate (11) but can also be formed so as to protrude from the surface of the piezoelectric substrate (11). Further, a thin film (13) or a substrate can be laminated on the piezoelectric substrate (11), and a support substrate (14) and / or a multilayer film (15) can be provided so as to contact the surface of the piezoelectric substrate (11) opposite to the surface on which the interdigital electrode (12) is provided. The high-order mode elastic surface wave device can obtain good characteristics even in a high frequency band of 3.8 GHz or more and can maintain sufficient mechanical strength.

Description

TECHNICAL FIELD

[0001] The present application relates to a high-order mode surface acoustic wave (SAW) device which provides utilization of a high-order mode which is an overtone of a fundamental mode. BACKGROUND

[0002] In recent years, there are nearly 80 frequency bands from 700 MHz to 3 GHz, which are very congested, mainly in smartphones and the like. As a countermeasure, the 5th generation mobile communication system (5G) of the next generation wireless communication system plans to utilize a frequency band of 3.6 GHz to 4.9 GHz, and further, the next generation thereof also plans to use a frequency band of 6 GHz or more.

[0003] For these plans, an elastic surface wave device, which is a representative elastic wave device, cannot reduce the period (λ) of an interdigital transducer (IDT) due to limitations of power endurance and manufacturing technology, and has limitations to high frequency. Figure 1 In (a) and (b), as an example of an existing SAW device, a plan view and a cross-sectional view of a structure in which a 42° rotated Y plate of a LiTaO3 crystal is used for a piezoelectric substrate and an interdigital transducer 52 propagating in the X direction is formed of Al are shown. Figure 1 The cross-sectional view of (b) shows Figure 1 The cross-sectional view of (a) along the cutting line I-I in the plan view.

[0004] Figure 1 The frequency characteristics of the impedance when the period of the interdigital transducer 52 is 1.2 μm are shown in (c). The resonance frequency is about 3.2 GHz, the relative bandwidth is 3.8%, and the impedance ratio is 65 dB. In addition, although a small response is seen in a high-order mode such as 17.2 GHz, it is not a usable level. Even if the period of the interdigital transducer 52 is made finer to 1 μm, the resonance frequency is about 3.8 GHz, and thus, in the existing SAW device, the frequency band required after 5G (of course, including 5G) cannot be covered.

[0005] Here, in Patent Literature 1, an elastic surface wave device is disclosed that is made in such a manner that a base mode of a Love wave is excited by embedding an electrode of Pt, Cu, Mo, Ni, Ta, W, or the like, which is heavier than Al, with a metallization ratio of 0.45 or less, into a LiNbO3 substrate of Euler angles (0°, 80-130°, 0°), thereby obtaining a wide bandwidth. Further, in Non-Patent Literature 1, an elastic surface wave device is disclosed that is made in such a manner that a Cu electrode of 0.1 wavelength or less is embedded into a LiTaO3 substrate of a 42°-rotated Y plate, an Al electrode is formed thereon, and excitation is performed in a base mode, thereby obtaining a high Q value. On the other hand, a film bulk acoustic resonator (FBAR) using a piezoelectric thin film of AlN, ScAlN as a bulk elastic wave device of an elastic wave filter having a frequency band of 1.9 GHz has been studied (see, for example, Non-Patent Literature 2).

[0006] Prior Art Documents

[0007] Patent Literature

[0008] Patent Literature 1: International Publication No. 2014 / 054580

[0009] Non-Patent Literature

[0010] Non-Patent Literature 1: T. Kimura, M. Kadota, and Y. IDA, "High Q SAW resonator using upper-electrodes on Grooved-electrode in LiTaO3", Proc. IEEE Microwave Symp. (IMS), p. 1740, 2010.

[0011] Non-Patent Literature 2: Keiichi Umeda et al., "PIEZOELECTRIC PROPERTIES OF ScAlN THIN FILMS FOR PIRZO-MEMS DEVICES", MEMS 2013, Taipei, Taiwan January 20-24, 2013. SUMMARY

[0012] Problems to be Solved by the Invention

[0013] However, the technology described in Patent Literature 1 and Non-Patent Literature 1 has a small metal weight and a small metallization rate for the electrode, and cannot obtain sufficient performance in a high frequency band of 3.6 GHz or more sought for 5G. The bulk elastic wave device described in Non-Patent Literature 2 can only obtain an impedance ratio of 55 dB at 1.9 GHz because the piezoelectric thin film is a polycrystal thin film, and has a large attenuation in an ultrahigh frequency band, and it is difficult to achieve good characteristics. In addition, the frequency of the FBAR depends on the acoustic velocity of the thin film / (2 x thickness of the thin film), and in order to increase the frequency, the thickness of the thin film must be extremely thin. The existing FBAR has a piezoelectric thin film that is self-supported, and thus cannot maintain mechanical strength in an ultrahigh frequency band in which the piezoelectric thin film becomes extremely thin.

[0014] The present application aims at solving the above problems, and provides a high-order mode elastic surface wave device that can obtain good characteristics even in a high frequency band of 3.8 GHz or more and can maintain sufficient mechanical strength.

[0015] Means for solving the problems

[0016] In order to achieve the above object, the high-order mode elastic surface wave device according to the present application includes a piezoelectric substrate including a LiTaO3 crystal or a LiNbO3 crystal, an interdigital electrode embedded in a surface of the piezoelectric substrate, and an elastic surface wave of a high-order mode.

[0017] The high-order mode elastic surface wave device can excite a high-order mode (1st mode, 2nd mode, 3rd mode, etc.) of a SAW by embedding the interdigital electrode in the surface of the piezoelectric substrate, and can obtain a high-order mode having a large impedance ratio. The high-order mode elastic surface wave device can seek high frequency by utilizing the high-order mode thereof, and can obtain good characteristics even in a high frequency band of 3.8 GHz or more. In addition, by utilizing the high-order mode, it is not necessary to thin the piezoelectric substrate or reduce the period of the interdigital electrode even in a high frequency band of 3.8 GHz or more, and sufficient mechanical strength can be maintained. In addition, the piezoelectric substrate includes a piezoelectric thin film or a piezoelectric thin plate.

[0018] In the high-order mode elastic surface wave device, the interdigital electrode can be formed so as to protrude from the surface of the piezoelectric substrate. Even in this case, a high-order mode having a large impedance ratio can be obtained.

[0019] The high-order mode elastic surface wave device can have a thin film or a substrate provided in contact with the piezoelectric substrate. In addition, a support substrate and / or a multilayer film can be provided in contact with a surface opposite to the surface of the piezoelectric substrate in which the interdigital electrode is provided. When the support substrate is provided, the support substrate can be composed of a material other than metal. In addition, the support substrate can be composed of at least one of Si, quartz, sapphire, glass, quartz, germanium, and alumina. In addition, when the multilayer film is provided, the multilayer film can be composed of an acoustic multilayer film formed by laminating a plurality of layers having different acoustic impedances. In this case, a high-order mode having a large impedance ratio can be obtained.

[0020] Regarding the high-order mode elastic surface wave device, the metallization ratio of the interdigital electrode is preferably 0.45 or more and 0.9 or less, and more preferably 0.63 or more. In this case, a high-order mode having a larger impedance ratio can be obtained. In addition, the bandwidth can be widened.

[0021] In addition, in order to obtain a high-order mode having a larger impedance ratio, the high-order mode elastic surface wave device can also have the following structure. That is, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Ti, Al, and Mg alloys. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth at which the wavelength / metalization ratio of the elastic surface wave is in the range of 0.075 to 0.3 (0.15 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth at which the wavelength / metalization ratio of the elastic surface wave is in the range of 0.115 to 0.3 (0.23 to 0.6 when the wavelength / metalization ratio is 0.5). Here, in the case where the cross section of the embedded electrode is not perpendicular to the surface of the substrate, the metalization ratio and the electrode width are set to the effective metalization ratio and the electrode width. The same applies below.

[0022] In addition, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Ag, Mo, Cu, and Ni. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth at which the wavelength / metalization ratio of the elastic surface wave is in the range of 0.08 to 0.3 (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth at which the wavelength / metalization ratio of the elastic surface wave is in the range of 0.09 to 0.3 (0.18 to 0.6 when the wavelength / metalization ratio is 0.5).

[0023] Further, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Pt, Au, W, Ta, and Hf. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth of 0.08 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth of 0.125 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.25 to 0.6 when the wavelength / metalization ratio is 0.5).

[0024] Further, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Pt, Au, W, Ta, and Hf. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth of 0.08 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth of 0.125 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.25 to 0.6 when the wavelength / metalization ratio is 0.5).

[0025] Further, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Pt, Au, W, Ta, and Hf. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth of 0.08 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth of 0.125 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.25 to 0.6 when the wavelength / metalization ratio is 0.5).

[0026] Further, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Pt, Au, W, Ta, and Hf. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth of 0.08 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth of 0.125 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.25 to 0.6 when the wavelength / metalization ratio is 0.5).

[0027] Further, the piezoelectric substrate can be composed of a LiTaO3 crystal, and the interdigital electrode can be composed of at least one of Pt, Au, W, Ta, and Hf. In this case, the interdigital electrode is preferably embedded from the surface of the piezoelectric substrate to a depth of 0.08 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.16 to 0.6 when the wavelength / metalization ratio is 0.5), and more preferably to a depth of 0.125 to 0.3 of the wavelength / metalization ratio of the surface acoustic wave (0.25 to 0.6 when the wavelength / metalization ratio is 0.5).

[0028] Further, the piezoelectric substrate is composed of a LiNbO3 crystal, preferably Euler angles are in the range of (0°±25°, 78°-153°, 0°±5°) or are crystallographically equivalent Euler angles thereof, further more preferably Euler angles are in the range of (0°±20°, 87°-143°, 0°±5°) or are crystallographically equivalent Euler angles thereof.

[0029] Here, Euler angles (φ, θ, ψ) are right-handed, and indicate a cut surface of the piezoelectric substrate and a propagation direction of the elastic surface wave. That is, for crystal axes X, Y, Z of a crystal constituting the piezoelectric substrate, LiTaO3 or LiNbO3, the Z axis is taken as a rotation axis and the X axis is rotated counterclockwise to obtain an X' axis. Next, the X' axis is taken as a rotation axis and the Z axis is θ-rotated counterclockwise to obtain a Z' axis. At this time, the Z' axis is taken as a normal line and a plane containing the X' axis is taken as a cut surface of the piezoelectric substrate. Further, the Z' axis is taken as a rotation axis and a direction in which the X' axis is ψ-rotated counterclockwise is taken as a propagation direction of the elastic surface wave. Further, an axis perpendicular to the X' axis and the Z' axis obtained by moving the Y axis by these rotations is taken as a Y' axis.

[0030] By defining the Euler angles in this way, for example, an X-direction propagation of a 40° rotated Y plate is expressed by Euler angles (0°, 130°, 0°), and a 90° X-direction propagation of a 40° rotated Y plate is expressed by Euler angles (0°, 130°, 90°). In addition, when a piezoelectric substrate is cut at desired Euler angles, there can be an error of about ±0.5° in each component of the Euler angles at the maximum. With respect to the shape of the interdigital electrode, there can be an error of about ±3° with respect to the propagation direction ψ. With respect to the characteristics of the elastic wave, in the Euler angles (φ, θ, ψ), there is almost no difference in characteristics with respect to φ and ψ due to a deviation of about ±5°.

[0031] At least one of a support substrate, a thin film, and a multilayer film can be further included, the support substrate, the thin film, and the multilayer film being disposed to contact a surface opposite to a surface in which the interdigital electrode is disposed in the piezoelectric substrate, a transverse wave sound velocity or an equivalent transverse wave sound velocity of the support substrate being in a range of 2000-3000 m / s or 6000-8000 m / s, and a thickness of the piezoelectric substrate can be in a range of 0.2 wavelengths to 20 wavelengths.

[0032] At least one of a support substrate, a thin film, and a multilayer film can be further included, the support substrate, the thin film, and the multilayer film being disposed to contact a surface opposite to a surface in which the interdigital electrode is disposed in the piezoelectric substrate, a transverse wave sound velocity or an equivalent transverse wave sound velocity of the support substrate being in a range of 3000-6000 m / s, and a thickness of the piezoelectric substrate can be in a range of 2 wavelengths to 20 wavelengths.

[0033] It may also include at least one of a support substrate, a thin film, and a multilayer film, wherein the support substrate, thin film, and multilayer film are configured to be in surface contact with the side opposite to the surface of the piezoelectric substrate on which interdigitated electrodes are disposed, and the linear expansion coefficient of the support substrate is 10.4 × 10⁻⁶. -6 Below / ℃, α is used as the coefficient of linear expansion, and the ratio TR of the thickness of the support substrate / piezoelectric substrate can be above the value of TR specified in the following formula (1).

[0034] TR = α × 0.55 × 10 6 +2.18 (1)

[0035] Invention Effects

[0036] According to the present invention, a high-order mode surface wave device can be provided, which exhibits good characteristics even in high-frequency bands above 3.8 GHz and maintains sufficient mechanical strength. Attached Figure Description

[0037] [ Figure 1 ], Figure 1 (a) A plan view showing an existing elastic surface wave device [Al interdigitated electrodes / LiTaO3 crystal propagating in the X direction with a 42° rotated Y plate]. Figure 1 (b) is a cross-sectional view. Figure 1 (c) To show Figure 1 (a) and Figure 1 (b) A graph showing the frequency characteristics of the impedance of the elastic surface wave device.

[0038] [ Figure 2 ], Figure 2 (a) is a high-order mode elastic surface wave device according to this embodiment. Figure 2 (b) For having Figure 2 (a) is a deformation example of the thin film. Figure 2 (c) is Figure 2 (a) is a variant of the interdigitated electrode protrusion. Figure 2 (d) is for having Figure 2 (a) A modified example of the support substrate. Figure 2 (e) is Figure 2 (d) is a deformed example of an interdigitated electrode protrusion. Figure 2 (f) is to show in Figure 2 (d) is a cross-sectional view of a deformed example in which a multilayer film exists between the piezoelectric substrate and the supporting substrate.

[0039] [ Figure 3 ],exist Figure 2 (a) to Figure 2 (f) shows a cross-sectional view of the side of the embedded electrode in the high-order mode surface wave device when it is not perpendicular to the substrate surface.

[0040] [ Figure 4 ] for the high-order mode elastic surface wave device shown in Figure 2 (a) [Al electrode / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 4 (a) is a graph showing the frequency characteristic of the impedance when the metallization ratio of the interdigital electrode is 0.5, Figure 4 (b) is a graph enlarged around the resonance frequency of the 1st mode of Figure 4 (a), Figure 4 (c) is a graph showing the displacement distribution in the resonance frequency of the 1st mode, Figure 4 (d) is a graph showing the frequency characteristic of the impedance of the 1st mode when the metallization ratio of the interdigital electrode is 0.7.

[0041] [ Figure 5 ] for the high-order mode elastic surface wave device shown in Figure 2 (c) [Al electrode (metallization ratio 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate],

[0042] [ Figure 6 ] for the high-order mode elastic surface wave device shown in Figure 2 (d) [Al electrode (metallization ratio 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate / supporting substrate], Figure 6 (a) is a graph showing the frequency characteristic of the impedance when the supporting substrate is composed of a Si substrate, Figure 6 (b) is a graph showing the frequency characteristic of the impedance when the supporting substrate is composed of a crystal substrate.

[0043] [ Figure 7 ] for the high-order mode elastic surface wave device shown in Figure 2 (f) [Al electrode (metallization ratio 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate],

[0044] [ Figure 8 ] for the high-order mode elastic surface wave device shown in Figure 2 (a) [Al electrode (metallization ratio 0.5) / (0°, 116°, 0°) LiNbO3 crystal substrate], Figure 8 (a) is a graph showing the frequency characteristic of the impedance, Figure 8 (b) is a graph enlarged around the resonance frequency of the 1st mode of Figure 8 (a).

[0045] [ Figure 9 ] for the high-order mode elastic surface wave device shown inFigure 2 (a) a graph showing the frequency characteristics of the impedance of the high-order mode elastic surface wave device [Cu electrode (metallization rate 0.5) / (0°, 116°, 0°) LiNbO3 crystal substrate].

[0046] [ Figure 10 ] for Figure 2 (a) the high-order mode elastic surface wave device [interdigital electrode (metallization rate 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate] shown in Figure 10 (a) a graph showing the relationship between the thickness of each electrode and the relative bandwidth of the 1st mode, Figure 10 (b) a graph showing the relationship between the thickness of each electrode and the impedance ratio of the 1st mode.

[0047] [ Figure 11 ] for Figure 2 (a) the high-order mode elastic surface wave device [Al electrode (metallization rate 0.5) / (0°, θ, 0°) LiTaO3 crystal substrate] shown in Figure 11 (a) a graph showing the relationship between θ and the relative bandwidth of the 1st mode, Figure 11 (b) a graph showing the relationship between θ and the impedance ratio of the 1st mode.

[0048] [ Figure 12 ] for Figure 2 (a) the high-order mode elastic surface wave device [Al electrode (metallization rate 0.5) / (0°, θ, 0°) LiTaO3 crystal substrate] shown in Figure 12 (a) a graph showing the relationship between φ and the impedance ratio of the 1st mode in the (φ, 126.5°, 0°) LiTaO3 crystal substrate.

[0049] [ Figure 13 ] for Figure 2 (a) the high-order mode elastic surface wave device [interdigital electrode (metallization rate 0.5) / (0°, 116°, 0°) LiNbO3 crystal substrate] shown in Figure 13 (a) a graph showing the relationship between the thickness of each electrode and the relative bandwidth of the 1st mode, Figure 13 (b) a graph showing the relationship between the thickness of each electrode and the impedance ratio of the 1st mode.

[0050] [ Figure 14 ] for Figure 2 (a) the high-order mode elastic surface wave device [Al electrode (metallization rate 0.5) / (0°, θ, 0°) LiNbO3 crystal substrate] shown in Figure 14(a) a graph showing the relationship between θ and the relative bandwidth of the 1st mode, Figure 14 (b) a graph showing the relationship between θ and the impedance ratio of the 1st mode.

[0051] [ Figure 15 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode (metallization ratio: 0.5) / (φ, θ, 0°) LiNbO3 crystal substrate], Figure 2 (a) a graph showing the relationship between φ and the impedance ratio of the 1st mode in a (φ, 116°, 0°) LiNbO3 crystal substrate. Figure 15

[0052] [ Figure 16 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 2 (a) a graph showing the relationship between the metallization ratio of the Al electrode and the phase velocity of the 1st mode, Figure 16 (b) a graph showing the relationship between the metallization ratio of the Al electrode and the impedance ratio of the 1st mode. Figure 16

[0053] [ Figure 17 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode (metallization ratio: 0.85) / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 2 (a) a graph showing the frequency characteristics of the impedance of the high-order mode elastic surface wave device shown in (a) [Al electrode (metallization ratio: 0.85) / (0°, 126.5°, 0°) LiTaO3 crystal substrate].

[0054] [ Figure 18 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 17 (a) a graph showing the relationship between the thickness of the interdigital electrode and the phase velocity of the 0th to 3rd modes, Figure 18 (b) a graph showing the relationship between the thickness of the interdigital electrode and the impedance ratio of the 0th to 3rd modes. Figure 18

[0055] [ Figure 19 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 2 (a) a graph showing the dependence of the impedance ratio of the 1st mode on the thickness of the LiTaO3 crystal substrate when the supporting substrate is composed of c to sapphire, Si, quartz, Pyrex (registered trademark) glass, lead glass for the high-order mode elastic surface wave device shown in (d) [Cu electrode (metallization ratio: 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate / supporting substrate] having a groove depth of 0.2λ.

[0056] [ Figure 20 ] for the high-order mode elastic surface wave device shown in (a) [Al electrode / (0°, 126.5°, 0°) LiTaO3 crystal substrate], Figure 2 ​​​(d) A graph showing the thickness dependence of the impedance ratio of the 1st mode of the high-order mode elastic surface wave device [Cu electrode (metallization ratio: 0.5) of a groove depth of 0.23λ / (0°, 116°, 0°) LiNbO3 crystal substrate / supporting substrate] on the thickness of the LiNbO3 crystal substrate when the supporting substrate is formed of c-cut sapphire, Si, quartz, Pyrex glass, and lead glass.

[0057] [ Figure 21 ] for Figure 2 (d) A graph showing the thickness dependence of the frequency temperature coefficient of the high-order mode elastic surface wave device [Al electrode (metallization ratio: 0.5) of a groove depth of 0.3λ / (0°, 126.5°, 0°) LiTaO3 crystal substrate and (0°, 116°, 0°) LiNbO3 crystal substrate / supporting substrate] on the thickness of the LiTaO3 crystal substrate and the LiNbO3 crystal substrate with respect to the linear expansion coefficient of each supporting substrate. DETAILED DESCRIPTION

[0058] Hereinafter, an embodiment of the present application will be described with reference to the accompanying drawings. Figures 2 to 21 A high-order mode elastic surface wave device relating to the embodiment of the present application. As Figure 2 (a) shows, the high-order mode elastic surface wave device 10 utilizes an elastic surface wave (SAW) of a high-order mode, and has a piezoelectric substrate 11 and an interdigital transducer (IDT) 12.

[0059] The piezoelectric substrate 11 is composed of a LiTaO3 crystal or a LiNbO3 crystal. The interdigital transducer 12 is embedded in the surface of the piezoelectric substrate 11. In addition, the upper surface of the interdigital transducer 12 can be on the same plane as the surface of the piezoelectric substrate 11 or lower than the plane, or can protrude from the surface of the piezoelectric substrate 11. Hereinafter, the electrode thickness refers to the electrode thickness embedded in the groove.

[0060] As Figure 2 (b) shows, the high-order mode elastic surface wave device 10 can have a thin film 13 provided to cover the surface of the piezoelectric substrate 11 of the gap of the interdigital transducer 12. The thin film 13 is, for example, a SiO2 thin film. The upper surface of the interdigital transducer 12 is on the same plane as the surface of the thin film 13. In addition, as Figure 2 (a) shows, the interdigital transducer 12 of the high-order mode elastic surface wave device 10 can be the same as the surface of the piezoelectric substrate 11, or can be below the surface. As Figure 2 (c) shows, the interdigital transducer 12 can also be provided to protrude from the surface of the piezoelectric substrate 11.

[0061] In addition, as Figure 2As shown in (d), the high-order mode surface acoustic wave device 10 has a support substrate 14. The piezoelectric substrate 11 is made of a thin plate with a small thickness. The support substrate 14 can be configured to make surface contact with the side opposite to the surface of the piezoelectric substrate 11 where the interdigitated electrodes 12 are disposed. The support substrate 14 is, for example, a semiconductor or insulating substrate such as a Si substrate, crystal substrate, sapphire substrate, glass substrate, quartz substrate, germanium substrate, or alumina substrate. In addition, except... Figure 2 In addition to the structure of (d), it can also be as follows: Figure 2 (b) In this manner, a thin film 13 is formed on the surface of the piezoelectric substrate 11. Furthermore, except... Figure 2 In addition to the structure of (d), there are also Figure 2 As shown in (e), the high-order mode elastic surface wave device 10 is as follows: Figure 2 (c) In this way, the interdigitated electrodes 12 can be configured to protrude from the surface of the piezoelectric substrate 11.

[0062] In addition, such as Figure 2 As shown in (f), except Figure 2 In addition to the structure shown in (d), the high-order mode surface wave device 10 may also have a multilayer film 15 disposed between the piezoelectric substrate 11 and the support substrate 14. The multilayer film 15 is an acoustic multilayer film formed by stacking, for example, multiple layers with different acoustic impedances. Furthermore, besides… Figure 2 Apart from the structure of (f), such as Figure 2 (b) In this way, a thin film 13 can also be formed on the surface of the piezoelectric substrate 11, such as Figure 2 (c) In this way, the interdigitated electrode 12 can protrude from the surface of the piezoelectric substrate 11.

[0063] The high-order mode surface wave device 10 can excite higher-order modes (first-order, second-order, third-order, etc.) of the SAW by embedding the interdigital electrodes 12 into the surface of the piezoelectric substrate 11, thus obtaining higher-order modes with a large impedance ratio. These higher-order modes are sometimes also referred to as harmonics that excite frequencies approximately 2, 3, or 4 times the harmonics. The high-order mode surface wave device 10 can achieve higher frequencies by utilizing its higher-order modes, obtaining good characteristics even in high-frequency bands above 3.8 GHz. Furthermore, by utilizing higher-order modes, even in high-frequency bands above 3.8 GHz, it is not necessary to make the piezoelectric substrate 11 ultrathin or reduce the period of the interdigital electrodes, thus maintaining sufficient mechanical strength.

[0064] The high-order mode surface acoustic wave device 10 can be manufactured, for example, in the following manner. First, electrode grooves for embedding interdigital electrodes 12 are formed on the surface of a piezoelectric substrate 11. That is, a resist layer or the like is applied to the portion of the surface of the piezoelectric substrate 11 where the electrode grooves are not to be formed, and the electrode grooves are formed on the surface of the piezoelectric substrate 11 by dry etching using ions such as Ar. Here, a material with a slower etching rate than that of the piezoelectric substrate 11 can be used instead of the resist layer or as a material other than the resist layer. In addition to dry etching, a wet etching method can also be used.

[0065] Next, electrode metal is deposited onto the entire surface of the piezoelectric substrate 11 to a thickness approximately equal to that required to fill the electrode groove. Then, the resist layer is removed by wet etching or cleaning. This forms the interdigitated electrode 12 embedded in the electrode groove. Furthermore, if the thickness of the interdigitated electrode 12 is not the desired thickness, the thickness can be adjusted by further etching or similar processes.

[0066] The following is about Figure 2 The impedance ratio or relative bandwidth of the various high-order mode elastic surface wave devices 10 with the shown structures were determined. (See also...) Figure 1 (c) The impedance ratio is given by the ratio of the resonant impedance Zr at the lowest resonant frequency fr to the anti-resonant impedance Za at the highest anti-resonant frequency fa, which is 20 × log (Za / Zr). The relative bandwidth is given by (fa - fr) / fr. See also... Figure 1 (a) The metallization rate of the interdigital electrode 52 is given by the ratio of the width F of the interdigital electrode 52 divided by half of the period (λ) of the interdigital electrode 52 (the sum of the width F of the interdigital electrode and the gap G between the interdigital electrodes) along the propagation direction of the elastic surface wave, i.e., by F / (F+G)=2×F / λ.

[0067] like Figure 3 As shown, there are cases where the interdigitated electrodes 12 are not perpendicular to the substrate surface but are embedded at an angle within the substrate. In this case, the metallization rate and electrode width are set as the effective metallization rate and electrode width. That is, when the angle γ formed by the side of the electrode groove and the surface of the piezoelectric substrate 11 is less than 90 degrees, if the width of the surface of each electrode is a, the width of the bottom is b, and the embedding depth is d, then the effective width c of the electrode is given by (a+b) / 2, and the metallization rate is given by (c / (c+e)). The embedding depth d remains unchanged.

[0068] Here, the period (λ) of the interdigital electrode 12 is made 1 μm, and the metallization ratio is made 0.5, i.e., the width of the electrode finger is made 0.25 μm, and the gap of the electrode finger is made 0.25 μm. Further, hereinafter, the Euler angles (φ, θ, ψ) are simply denoted by (φ, θ, ψ). Furthermore, the thickness of the piezoelectric substrate 11 or the interdigital electrode 12, etc. is expressed in terms of the multiple of the wavelength λ (the period of the interdigital electrode) of the elastic surface wave device used.

[0069] Figure 4 the high-order mode elastic surface wave device 10 having the structure shown in Figure 2 (a) is shown. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.36λ, which is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ. The frequency characteristics of the impedance when the metallization ratio of the interdigital electrode 12 is 0.5 are shown in Figure 4 (a) and Figure 4 (b), the displacement distribution in the resonance frequency of the 1st mode is shown in Figure 4 (c). Figure 4 (b) enlarges Figure 4 (a) near the resonance frequency of the 1st mode. Further, the frequency characteristics of the impedance when the metallization ratio of the interdigital electrode 12 is 0.7 are shown in Figure 4 (d).

[0070] As shown in Figure 4 (a), it is confirmed that by embedding the interdigital electrode 12 in the piezoelectric substrate 11, a 0th mode having a resonance frequency of 4.5 GHz, which is 1.36 times the resonance frequency of 3.3 GHz of the existing SAW device shown in Figure 1 , is obtained. Also, as shown in Figure 4 (a) and Figure 4 (b), it is confirmed that with respect to the 0th mode having a resonance frequency of 4.5 GHz, a 1st mode having a resonance frequency of about 2 times thereof, i.e., 9.6 GHz, is greatly excited. It is confirmed that the relative bandwidth of this 1st mode is 3%, and the impedance ratio is 67 dB, which is larger than that of the existing SAW device shown in Figure 1 . The resonance frequency of the 1st mode is about 2.9 times the resonance frequency of the existing SAW device.

[0071] Further, as shown in Figure 4 (c), it is understood that since the 1st mode having a resonance frequency of 9.5 GHz is composed of only an SH (horizontal shear) component, and the resonance frequency of the existing SAW device is also composed of an SH component, it is a high-order mode (1st mode) with respect to the base-order mode (0th mode). Further, Figure 4 (c), "L" indicates a longitudinal wave component, and "SV" indicates a vertical shear component. Further, as shown inFigure 4 (d) shows that by making the metallization ratio 0.7, the resonance frequency of the 1st order mode becomes 1.2 times, i.e. 11.2 GHz, the resonance frequency when the metallization ratio is 0.5, and the relative bandwidth becomes 3.4%, which is 13% wider, while the impedance ratio becomes 70 dB, which is 3 dB larger.

[0072] Figure 5 shows the frequency characteristics of the impedance of the high order mode elastic surface wave device 10 having Figure 2 (c) shows the structure. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.38λ, is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ, and protrudes 0.02λ from the surface of the piezoelectric substrate 11. The metallization ratio of the interdigital electrode 12 is 0.5.

[0073] As shown in Figure 5 (a), the resonance frequency of the 1st order mode is confirmed to be 9 GHz, the relative bandwidth is 2.8%, and the impedance ratio is 71 dB. Further, as shown in Figure 4 (b), the resonance frequency of the 1st order mode is confirmed to be 9 GHz, the relative bandwidth is 3.5%, and the impedance ratio is 68 dB. Figure 4 (a) and (b) are compared, the resonance frequency of the high order mode (1st order mode) is slightly higher. Further, while the impedance ratio becomes 50 dB, the relative bandwidth becomes 1%, which is narrower, and it can be said to be suitable for bandwidth narrowing. Further, it is confirmed that the spur produced by the excitation of the fundamental mode (0th order) is small.

[0074] Figure 6 shows the frequency characteristics of the impedance of the high order mode elastic surface wave device 10 having Figure 2 (d) shows the structure. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal having a thickness of 0.5λ. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.36λ, is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ. The metallization ratio of the interdigital electrode 12 is 0.5. The support substrate 14 is composed of Si or a crystal, and has a thickness of 350 μm, and is bonded to the piezoelectric substrate 11 by an adhesive or direct bonding. The frequency characteristics of the impedance when the support substrate 14 is composed of a Si substrate are shown in Figure 6 (a), and the frequency characteristics of the impedance when the support substrate 14 is composed of a crystal substrate are shown in Figure 6 (b).

[0075] As shown in Figure 6 (a), it is confirmed that in the case of having a Si support substrate, the resonance frequency of the 1st order mode is 9 GHz, the relative bandwidth is 2.8%, and the impedance ratio is 71 dB. Further, as shown in Figure 6 (b), it is confirmed that in the case of having a crystal substrate, the resonance frequency of the 1st order mode is 9 GHz, the relative bandwidth is 3.5%, and the impedance ratio is 68 dB. Figure 6 (a) and Figure 6 (b) are compared, the resonance frequency of the high order mode (1st order mode) is slightly higher. Further, while the impedance ratio becomes 50 dB, the relative bandwidth becomes 1%, which is narrower, and it can be said to be suitable for bandwidth narrowing. Further, it is confirmed that the spur produced by the excitation of the fundamental mode (0th order) is small. Figure 4(b) shows that the impedance ratio is increased by providing the support substrate 14. In addition, in order to obtain a larger impedance ratio, it is preferable that the piezoelectric substrate 11 is thinner than the support substrate 14, and more preferable that the piezoelectric substrate 11 is 20 wavelengths or less, and further preferable that the piezoelectric substrate 11 is 10 wavelengths or less.

[0076] Figure 7 shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 having Figure 2 (f) shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 having the structure shown in

[0077] Figure 7 It is confirmed that the resonance frequency of the 1st mode is 9.5 GHz, the relative bandwidth is 2.6%, and the impedance ratio is 69 dB. If the structure shown in Figure 7 is compared with Figure 6 (a), it is confirmed that the bandwidth is slightly narrower and the impedance ratio is slightly smaller by providing the multilayer film 15.

[0078] Figure 8 shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 having Figure 2 (a) shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 having Figure 8 (a) shows the frequency characteristics of the impedance, Figure 8 (b) shows an enlarged view of the vicinity of the resonance frequency of the 1st mode of Figure 8 (a). The piezoelectric substrate 11 is a (0°, 116°, 0°) LiNbO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.35λ, and is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.35λ. The metallization ratio of the interdigital electrode 12 is 0.5.

[0079] As shown in Figure 8 (a) and 8(b), it is confirmed that, as in the case of the LiTaO3 crystal (see Figure 4 ), the high-order mode (1st mode) of 10.4 GHz is also greatly excited in the case where the piezoelectric substrate 11 is a LiNbO3 crystal. It is confirmed that the relative bandwidth of this 1st mode is 6.4%, and the impedance ratio is 68 dB, which is the same as Figure 4Compared to the first-order mode of the LiTaO3 crystal shown in (b), the bandwidth is wider and the impedance ratio is larger.

[0080] Figure 9 Showing has Figure 2 (a) shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 with the structure shown. The piezoelectric substrate 11 is a (0°, 116°, 0°) LiNbO3 crystal. The interdigitated electrode 12 is composed of Cu electrodes with a thickness of 0.24λ, embedded from the surface of the piezoelectric substrate 11 to a depth of 0.24λ. The metallization of the interdigitated electrode 12 is 0.5.

[0081] like Figure 9 As shown, the situation with the Al electrode is confirmed (see...). Figure 8 Compared to (a), when the interdigital electrode 12 is a Cu electrode, although the resonant frequency of the first-order mode is slightly reduced to 9.5 GHz, even if it is formed thinner (shallower) than the Al electrode, an impedance ratio of 68 dB, which is the same as that of the Al electrode, can be obtained.

[0082] Figure 10 Showing has Figure 2 (a) shows the relationship between the thickness of the interdigitated electrodes 12 of the high-order mode surface acoustic wave device 10 and the relative bandwidth and impedance ratio of the first-order mode. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigitated electrodes 12 are composed of Al, Cu, or Au electrodes. The metallization of the interdigitated electrodes 12 is 0.5. The relationships between the thickness of each electrode and the relative bandwidth, and between the thickness of each electrode and the impedance ratio of the first-order mode, are shown when the thickness (depth) of each electrode is varied from 0.02λ to 0.6λ. Figure 10 (a) and Figure 10 (b)

[0083] like Figure 10 As shown in (a), it was confirmed that for the same thickness (depth), the Al electrode has the widest bandwidth, while the bandwidths of the Cu and Au electrodes decrease sequentially. Furthermore, it was also confirmed that the bandwidth of each electrode increases with increasing thickness (depth). Figure 10 As shown in (b), it was confirmed that the impedance ratio became 50 dB or more when the impedance was 0.15λ to 0.6λ with the Al electrode, and 0.16λ to 0.6λ with the Cu and Au electrodes. Furthermore, it was confirmed that the impedance ratio became 60 dB or more when the impedance was 0.23λ to 0.6λ with the Al electrode, 0.18λ to 0.6λ with the Cu electrode, and 0.25λ to 0.6λ with the Au electrode. Further confirmation showed that the impedance ratio became 65 dB or more when the impedance was 0.3λ to 0.6λ with the Al electrode, 0.29λ to 0.6λ with the Cu electrode, and 0.55λ to 0.6λ with the Au electrode.

[0084] In addition, the thickness of the electrode x the metallization ratio is a constant value, for example, for a metallization ratio of 0.5 and a thickness of the electrode of 0.15λ, in the case of a metallization ratio of 0.75, the thickness of the electrode becomes 0.5 x 0.15λ / 0.75 = 0.10λ. Therefore, for example, for a thickness of the Al electrode of 0.15λ for a metallization ratio of 0.5, in the case of a metallization ratio of 0.75, the thickness of the Al electrode can be 0.10λ or more.

[0085] In addition, it is considered that the above-described tendency is not limited to Figure 2 (a) shown in the drawing, even if Figure 2 (b) ~ Figure 2 (f) shown in the drawing, the relationship of the impedance ratio with respect to the thickness of each electrode is not changed. In addition, for the relationship of the impedance ratio with respect to the thickness of each electrode, the electrode material having a density of 1500 to 6000 kg / m 3 shows the same tendency as the Al electrode, the electrode material having a density of 6000 to 12000 kg / m 3 shows the same tendency as the Cu electrode, and the electrode material having a density of 12000 to 23000 kg / m 3 shows the same tendency as the Au electrode. In addition, in the case where the electrode material used is an alloy or is stacked by different metals, the tendency of the above-described relationship of the impedance ratio with respect to the thickness of the electrode is determined by the average density calculated from the thickness and the density of each material.

[0086] Figure 11 shows the relationship of the Euler angle of the piezoelectric substrate 11 of the high-order mode elastic surface wave device 10 having Figure 2 (a) shown in the drawing with the relative bandwidth and the impedance ratio of the 1st order mode. The piezoelectric substrate 11 is a (0°, θ, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.36λ and is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ. The metallization ratio of the interdigital electrode 12 is 0.5. The relationship of θ with the relative bandwidth and the relationship of θ with the impedance ratio when θ constituting the Euler angle is changed to 0° to 180° are shown in Figure 11 (a) and Figure 11 (b), respectively.

[0087] As shown in Figure 11 (a) and Figure 11 (b), it is confirmed that the relative bandwidth is 2.5% or more when θ = 112° to 168°, and the impedance ratio becomes 50 dB or more when θ = 112° to 140°. In addition, it is confirmed that the relative bandwidth is 2.6 to 2.7% when θ = 120° to 132°, and the impedance ratio becomes 60 dB or more. In addition, as shown in Figure 12As shown, it is confirmed that the impedance ratio becomes 50 dB or more at φ = -20° to 20°, and 60 dB or more at φ = -10° to 10°.

[0088] Figure 13 The high-order mode elastic surface wave device 10 having the structure shown in Figure 2 (a) was fabricated. The piezoelectric substrate 11 was (0°, 116°, 0°) LiNbO3 crystal. The interdigital electrode 12 was composed of an Al electrode, a Cu electrode, or an Au electrode. The metallization ratio of the interdigital electrode 12 was 0.5. The relationship between the thickness (depth) of each electrode and the relative bandwidth and the relationship between the thickness (depth) of each electrode and the impedance ratio were shown in Figure 13 (a) and Figure 13 (b).

[0089] As shown in Figure 13 (a), it was confirmed that the bandwidth of the Al electrode was the widest, and the bandwidths of the Cu electrode and the Au electrode were sequentially narrower when the thickness (depth) was the same or more than 0.1λ. In addition, it was also confirmed that the bandwidth of each electrode became wider as the thickness (depth) became larger when the thickness (depth) was less than 0.4λ. In addition, as shown in Figure 13 (b), it was confirmed that the impedance ratio became 50 dB or more when the thickness (depth) was 0.14λ to 0.6λ for the Al electrode, 0.13λ to 0.6λ for the Cu electrode, and 0.15λ to 0.6λ for the Au electrode. In addition, it was confirmed that the impedance ratio became 60 dB or more when the thickness (depth) was 0.21λ to 0.6λ for the Al electrode, 0.18λ to 0.6λ for the Cu electrode, and 0.23λ to 0.6λ for the Au electrode. In addition, as described above, the thickness of the electrode x the metallization ratio was constant.

[0090] In addition, it was considered that the relationship between the impedance ratio and the thickness of each electrode did not change not only for the structure shown in Figure 2 (a), but also for the structures shown in Figure 2 (b) to Figure 2 (f). In addition, regarding the relationship between the impedance ratio and the thickness of each electrode, the electrode material having a density of 1500 to 6000 kg / m 3 (such as Ti, Mg alloy) showed the same tendency as the Al electrode, the electrode material having a density of 6000 to 12000 kg / m 3 (such as Ag, Mo, Ni) showed the same tendency as the Cu electrode, and the electrode material having a density of 12000 to 23000 kg / m 3electrode materials (e.g. Pt, W, Ta, Hf) show the same tendency as the Au electrode. In addition, in the case where the electrode material used is an alloy or is stacked by different metals, the tendency of the above-described impedance ratio with respect to the thickness of the electrode is determined by the average density calculated from the thickness and the density of each material.

[0091] Figure 14 shows the relationship between the Euler angle of the piezoelectric substrate 11 of the high-order mode elastic surface wave device 10 of the structure shown in Figure 2 (a) and the relative bandwidth and the impedance ratio of the 1st mode. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.36λ and is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ. The relationship between the metallization ratio of the Al electrode and the phase velocity and the relationship between the metallization ratio and the impedance ratio when the metallization ratio is changed to 0.3 to 0.9 are shown in Figure 14 (a) and Figure 14 (b), respectively.

[0092] As shown in Figure 14 (a) and Figure 14 (b), it is confirmed that the relative bandwidth is 4.4 to 6.5% and the impedance ratio becomes 50 dB or more when θ = 78° to 153°. In addition, it is confirmed that the relative bandwidth becomes 5.2 to 6.5% and the impedance ratio becomes 60 dB or more when θ = 87° to 143°. Further, it is confirmed that the relative bandwidth becomes 5.7 to 6.5% and the impedance ratio becomes 65 dB or more when θ = 94° to 135°. In addition, as shown in Figure 15 , it is confirmed that the impedance ratio becomes 50 dB or more when φ = -25° to 25°, the impedance ratio becomes 60 dB or more when φ = -20° to 20°, and the impedance ratio becomes 70 dB or more when φ = -10° to 10°.

[0093] Figure 16 shows the relationship between the metallization ratio of the interdigital electrode 12 of the high-order mode elastic surface wave device 10 of the structure shown in Figure 2 (a) and the phase velocity and the impedance ratio of the 1st mode. The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.36λ and is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.36λ. The relationship between the metallization ratio of the Al electrode and the phase velocity and the relationship between the metallization ratio and the impedance ratio when the metallization ratio is changed to 0.3 to 0.9 are shown in Figure 16 (a) and Figure 16 (b), respectively.

[0094] As shown in Figure 16(a) shows, it is confirmed that the phase velocity is about 10,000 to 11,500 m / s, and it is generally the case that the larger the metallization ratio, the faster the phase velocity becomes. Further, as shown in Figure 16 (b) shows, it is confirmed that when the metallization ratio is 0.4 or more, the impedance ratio is 50 dB or more; when the metallization ratio is 4.5 or more, the impedance ratio is 60 dB or more; when the metallization ratio is 0.52 or more, the impedance ratio is 65 dB or more; and when the metallization ratio is 0.63 or more, the impedance ratio is 70 dB or more.

[0095] Figure 17 shows the frequency characteristics of the impedance of the high-order mode elastic surface wave device 10 having Figure 2 the structure shown in (a). The piezoelectric substrate 11 is a (0°, 126.5°, 0°) LiTaO3 crystal. The interdigital electrode 12 is composed of an Al electrode having a thickness of 0.2λ, and is embedded from the surface of the piezoelectric substrate 11 to a depth of 0.2λ. The metallization ratio of the interdigital electrode 12 is 0.85.

[0096] As shown in Figure 17 , it is confirmed that the 1st-order mode, the 2nd-order mode, and the 3rd-order mode, which are high-order modes of the 0th-order mode, are excited. As shown in Figure 4 , Figure 8 , it is considered that since the 2nd-order mode or the 3rd-order mode cannot be confirmed when the metallization ratio is 0.5, the 2nd-order mode or the 3rd-order mode is excited by increasing the metallization ratio.

[0097] The relationship between the thickness of the interdigital electrode 12 and the phase velocity of the 0th-order to 3rd-order modes, and the relationship between the thickness of the interdigital electrode 12 and the impedance ratio of the 0th-order to 3rd-order modes when the thickness of the interdigital electrode 12 of the same structure as that of Figure 17 is changed to 0.05λ to 0.55λ are shown in Figure 18 (a) and Figure 18 (b). As shown in Figure 18 (a), it is confirmed that, for example, when the thickness of the interdigital electrode 12 is 0.3λ, the 1st-order mode having a phase velocity about 2.7 times that of the 0th-order mode, the 2nd-order mode having a phase velocity about 4.7 times that of the 0th-order mode, and the 3rd-order mode having a phase velocity about 6.9 times that of the 0th-order mode, which are high-order modes, are excited. Further, as shown in Figure 18 (b), it is confirmed that the impedance ratio with respect to the 0th-order mode is 47 dB, the impedance ratio of the 1st-order mode is 57 dB, the impedance ratio of the 2nd-order mode is 40 dB, and the impedance ratio of the 3rd-order mode is 45 dB, which are levels that can be sufficiently used.

[0098] Table 1 shows Figure 2 the density, the longitudinal wave speed, and the transverse wave speed of the support substrate for the high-order mode elastic surface wave device [slot electrode / LiTaO3 crystal or LiNbO3 crystal substrate / support substrate] shown in (d). The longitudinal wave speed is calculated from (c33 The square root of the density is used to represent the transverse wave sound velocity, which is given by ((c)). 44 The square root of the density is represented here. ij It is the elastic stiffness constant. Based on the transverse wave sound velocity, it is divided into five groups: A, B, C, D, and E.

[0099] Table 1

[0100]

[0101]

[0102] Figure 19 Show Figure 2 (d) shows the dependence of the impedance ratio of a high-order mode surface acoustic wave device [Cu electrode with a trench depth of 0.2λ (metallization of 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate / support substrate] on the thickness of the LiTaO3 crystal substrate, where the support substrate is composed of c-axis sapphire, Si, crystal, Pyrex glass, or lead glass. In the figure, hollow symbols indicate the characteristics of the frequency response without in-band ripple, and black symbols indicate the characteristics with in-band ripple. Although the impedance ratio of any support substrate above 20 wavelengths of LiTaO3 crystal thickness is consistent with the impedance ratio of 62 dB when there is only a LiTaO3 crystal substrate and no support substrate, the impedance ratio in LiTaO3 crystal thickness below 20 wavelengths is larger compared to this.

[0103] In Table 1, the transverse wave velocity of Group A is 2000–3000 m / s, much slower than the 3604 m / s transverse wave velocity of LiTaO3 crystal shown in Table 1. When using lead glass with a transverse wave velocity of 2414 m / s (as shown in Group A), there is no in-band ripple when the LiTaO3 crystal thickness is 0.2λ or greater and less than 20λ, resulting in an impedance ratio of 62 dB. Below 10 wavelengths, an impedance ratio of 63 dB or greater is obtained. In Table 1, the transverse wave velocity of Group E is 6001–8000 m / s, much faster than that of LiTaO3 crystal. When using sapphire with a sound velocity of 6073 m / s (as shown in Group E), there is no in-band ripple when the LiTaO3 crystal thickness is 0.2λ or greater and less than 20λ, resulting in an impedance ratio of 62 dB or greater. When the LiTaO3 crystal thickness is 0.2λ or greater and less than 10λ, an impedance ratio of 63 dB or greater is obtained.

[0104] However, in Table 1 where the shear wave velocity of the LiTaO3 crystal is similar to the shear wave velocity of the B group Pyrex glass, the shear wave velocity of the C group quartz is 4220 to 5000 m / s, and the shear wave velocity of the D group Si substrate is 4220 to 5000 m / s, when the thickness of the LiTaO3 crystal is 0.2λ or more and less than 2λ, the ripple occurs in the band, when the thickness of the LiTaO3 crystal is from 2λ to less than 20λ, the impedance ratio of 62 dB or more is obtained, and when the thickness of the LiTaO3 crystal is from 2λ to 10λ, the impedance ratio of 64.5 dB or more is obtained.

[0105] Figure 20 Fig. 8 shows Figure 2 (d) Dependence of the impedance ratio of the high-order mode elastic surface wave device [Cu electrode (metallization ratio 0.5) / (0°, 112°, 0°) LiNbO3 crystal substrate / supporting substrate with a groove depth of 0.23λ] on the thickness of the LiTaO3 crystal substrate, where the supporting substrate is composed of sapphire, Si, quartz, Pyrex glass, and lead glass in the c direction. In the figure, the blank mark shows the characteristic of the frequency characteristic without the in-band ripple, and the black mark shows the characteristic with the in-band ripple. Although the impedance ratio of any supporting substrate is consistent with the impedance ratio of 68 dB when the thickness of the LiNbO3 crystal is 20 wavelengths or more and when there is only the LiNbO3 crystal substrate without the supporting substrate, the impedance ratio in the thickness of the LiNbO3 crystal of less than 20 wavelengths is larger than that.

[0106] In Table 1 where the thickness of the LiTaO3 crystal is 0.2λ or more and less than 20λ, there is no in-band ripple, and the impedance ratio of 68 to 80 dB or more is obtained, and when the thickness of the LiTaO3 crystal is 10 wavelengths or less, the impedance ratio of 71.5 dB or more is obtained, in the case of the A group of the lead glass with a shear wave velocity of 2414 m / s, which is much slower than the shear wave velocity of 3604 m / s of the LiTaO3 crystal shown in Table 1. In the case of the C group of the quartz with a shear wave velocity of 6073 m / s, which is much faster than the LiTaO3 crystal, there is no in-band ripple, and when the thickness of the LiTaO3 crystal is 0.2λ or more and less than 20λ, there is no in-band ripple, and the impedance ratio of 68 to 71 dB is obtained, and when the thickness of the LiTaO3 crystal is 10 wavelengths or less, the impedance ratio of 70 dB or more is obtained.

[0107] However, in the case of the supporting substrate of Pyrex, quartz, Si, whose shear wave velocity is 3000 to 6000 m / s, which is close to the shear wave velocity of the LiTaO3 crystal, of Group B, Group C, and Group D of Table 1, the in-band ripple occurs when the thickness of the LiTaO3 crystal is 0.2λ or more and less than 2λ, the impedance ratio of 68 to 77 dB is obtained when the thickness of the LiTaO3 crystal is from 2λ to less than 20λ, and the impedance ratio of 71.5 to 77 dB is obtained when the thickness of the LiTaO3 crystal is from 2λ to less than 10λ.

[0108] In addition, in the case where a thin film such as a SiO2 film, a SiO film, a SiOF film, or the like is present between the piezoelectric substrate of the LiTaO3 crystal or the LiNbO3 crystal and the supporting substrate, the average shear wave velocity of the film and the underlying supporting substrate is considered. Even in the case where the piezoelectric substrate and the supporting substrate are separated by a SiO2 film, a SiO compound film, or an acoustic multilayer film, the average value of the acoustic velocity apparent in the range of 2 wavelengths or less is determined depending on which group of the acoustic velocity of Group A, Group B, Group C of Table 1 the piezoelectric substrate belongs to, to determine the optimum film thickness of the piezoelectric substrate. In this case, the weight of the first layer material in contact with the piezoelectric substrate is 70%, and the other layers are all 30%. For example, in the case where the thickness of the SiO2 film (shear wave velocity 3572 m / s) of the first layer is 0.5 wavelengths, and the thickness of the sapphire (shear wave velocity 6073 m / s) supporting substrate is 1.5 wavelengths, it becomes (3572 x 0.5 x 0.7 + 6073 x 1.5 x 0.3) = 3983 m / s, and the LiTaO3 crystal substrate and the LiNbO3 crystal substrate of the optimum substrate thickness can be used in Group E.

[0109] Table 2 shows the linear expansion coefficients of the LiTaO3 crystal and the LiNbO3 crystal and the linear expansion coefficients of representative substrates smaller than the LiTaO3 crystal or the LiNbO3 crystal. Table 2 shows Figure 2 (d) the linear expansion coefficients of various supporting substrates used in the high-order mode elastic surface wave device [slot electrode / piezoelectric substrate / supporting substrate] structure shown.

[0110] Table 2

[0111]

[0112]

[0113] Figure 21 shows Figure 2(d) Dependence of the frequency temperature coefficient of the high-order mode elastic surface wave device [Al electrode with a groove depth of 0.3λ (metallization ratio 0.5) / (0°, 126.5°, 0°) LiTaO3 crystal substrate / supporting substrate] and Al electrode with a groove depth of 0.3λ (metallization ratio 0.5) / (0°, 112°, 0°) LiNbO3 crystal substrate / supporting substrate] on the linear expansion coefficient of each supporting substrate and the LiTaO3 crystal / supporting substrate and the LiNbO3 crystal / supporting substrate. The frequency temperature coefficient of the vertical axis is represented by the frequency change rate per 1°C when using the LiTaO3 crystal or the LiNbO3 crystal / supporting substrate, i.e., (maximum frequency change amount between -20 and 80°C / maximum change amount of temperature (in this case, 80) when the temperature is 100 to 20°C), and the left and right vertical axes are the frequency temperature coefficients when using the LiTaO3 crystal substrate and the LiNbO3 crystal substrate, respectively. The horizontal axis is represented by the ratio of the supporting substrate to the piezoelectric substrate, i.e., (thickness of the supporting substrate / thickness of the LiTaO3 crystal substrate or the LiNbO3 crystal substrate).

[0114] Although the frequency temperature coefficients are -45 ppm / °C and -100 ppm / °C, respectively, only when the Al groove electrode is provided in the supporting substrate, in the case of using the supporting substrate with a linear expansion coefficient of 0.5 x 10 -6 / °C, when the thickness ratio of the piezoelectric substrate / supporting substrate is 2.5 or more, a frequency temperature coefficient better than -25 ppm / °C is obtained in the LiTaO3 crystal, and a frequency temperature coefficient better than -35 ppm / °C is obtained in the LiNbO3 crystal. In the case of using the supporting substrate with a linear expansion coefficient of 3.35 x 10 -6 / °C, when the thickness ratio of the piezoelectric substrate / supporting substrate is 4 or more. In the case of using the supporting substrate with a linear expansion coefficient of 8.4 x 10 -6 / °C, when the thickness ratio of the piezoelectric substrate / supporting substrate is 6.7 or more. In the case of using the supporting substrate with a linear expansion coefficient of 10.4 x 10 -6 / °C, when the thickness ratio of the piezoelectric substrate / supporting substrate is 8 or more, a frequency temperature coefficient better than -25 ppm / °C is obtained in the LiTaO3 crystal, and a frequency temperature coefficient better than -35 ppm / °C is obtained in the LiNbO3 crystal. The relationship between the linear expansion coefficient α and the thickness ratio TR of the piezoelectric substrate / supporting substrate is represented by the following equation (2).

[0115] TR = α x 0.55 x 10 6 + 2.18 (2)

[0116] Therefore, a piezoelectric substrate and a support substrate can be used, which have a thickness ratio greater than TR obtained by formula (2). Even in the case where a SiO2 film, a SiO compound film, or an acoustic multilayer film is interposed between the piezoelectric substrate and the support substrate, TR can be calculated from the average of the linear expansion coefficients with respect to the thickness and the total thickness. It is preferable to use a support substrate having a linear expansion coefficient less than the linear expansion coefficients of the LiTaO3 crystal or the LiNbO3 crystal shown in Table 2 and 10.4 x 10 -6 / °C or less, and a linear expansion coefficient less than that is more preferable.

[0117] Reference Signs

[0118] 10 High-order mode elastic surface wave device

[0119] 11 Piezoelectric substrate

[0120] 12 Interdigital transducer (IDT)

[0121] 13 Thin film

[0122] 14 Support substrate

[0123] 15 Multilayer film

Claims

1. A high-order mode surface wave device, which utilizes a high-order mode surface wave, the high-order mode surface wave device comprising: A piezoelectric substrate comprising LiTaO3 crystals or LiNbO3 crystals; Interdigitated electrodes embedded in the surface of the piezoelectric substrate; and A support substrate is provided, wherein the support is configured to be in surface contact with the surface of the piezoelectric substrate on the opposite side from the surface where the interdigitated electrodes are disposed. The transverse wave velocity or equivalent transverse wave velocity of the support substrate is in the range of 2000–3000 m / s or 6000–8000 m / s, and the thickness of the piezoelectric substrate is in the range of 0.2 wavelengths to 20 wavelengths. Alternatively, the transverse wave velocity or equivalent transverse wave velocity of the support substrate is in the range of 3000–6000 m / s, and the thickness of the piezoelectric substrate is in the range of 2 wavelengths to 20 wavelengths.

2. The high-order mode elastic surface wave device according to claim 1, wherein the interdigitated electrodes are formed in a manner that is not coplanar with the surface of the piezoelectric substrate.

3. The high-order mode elastic surface wave device according to claim 1 further comprises a thin film configured to contact the piezoelectric substrate.

4. The high-order mode elastic surface wave device according to claim 1 further comprises a multilayer film, the multilayer film being disposed on the surface of the piezoelectric substrate opposite to the surface on which the interdigitated electrodes are disposed.

5. The high-order mode elastic surface wave device according to claim 4, wherein the supporting substrate comprises a material other than metal.

6. The high-order mode elastic surface wave device according to claim 5, wherein the supporting substrate comprises at least one of Si, crystal, sapphire, glass, quartz, germanium and alumina.

7. The high-order mode elastic surface wave device according to claim 4, wherein the multilayer film comprises an acoustic multilayer film having multiple layers with different acoustic impedances stacked on top of each other.

8. The high-order mode elastic surface wave device according to claim 1, wherein the metallization of the interdigitated electrodes is 0.45 or higher.

9. The high-order mode elastic surface wave device according to claim 8, wherein the metallization of the interdigitated electrodes is 0.63 or higher.

10. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal, the interdigitated electrode comprises at least one of a Ti, Al, and Mg alloy, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.15 to 0.6 wavelengths.

11. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal, the interdigitated electrode comprises at least one selected from Ag, Mo, Cu, Ni, Pt, Au, W, Ta and Hf, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth in the range of 0.16 to 0.6 wavelengths of the surface wave.

12. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal, the interdigitated electrode comprises at least one of a Ti, Al, and Mg alloy, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.23 to 0.6 wavelengths.

13. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal, the interdigitated electrode comprises at least one of Ag, Mo, Cu and Ni, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.18 to 0.6 wavelengths.

14. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal, the interdigitated electrode comprises at least one of Pt, Au, W, Ta and Hf, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.25 to 0.6 wavelengths.

15. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of a Ti, Al, and Mg alloy, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.14 to 0.6 wavelengths.

16. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of Ag, Mo, Cu and Ni, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.13 to 0.6 wavelengths.

17. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of Pt, Au, W, Ta and Hf, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate into the surface wave at a depth in the range of 0.15 to 0.6 wavelengths.

18. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of a Ti, Al, and Mg alloy, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.21 to 0.6 wavelengths.

19. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of Ag, Mo, Cu and Ni, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.18 to 0.6 wavelengths.

20. The high-order mode surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal, the interdigitated electrode comprises at least one of Pt, Au, W, Ta and Hf, the interdigitated electrode has a metallization of 0.5, and is embedded from the surface of the piezoelectric substrate to a depth of the surface wave in the range of 0.23 to 0.6 wavelengths.

21. The high-order mode elastic surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal and the Euler angle is in the range of (0°±20°, 112°~140°, 0°±5°) or is a crystallographically equivalent Euler angle.

22. The high-order mode elastic surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiTaO3 crystal and the Euler angle is in the range of (0°±10°, 120°~132°, 0°±5°) or is a crystallographically equivalent Euler angle.

23. The high-order mode elastic surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal and the Euler angle is in the range of (0°±25°, 78°~153°, 0°±5°) or is a crystallographically equivalent Euler angle.

24. The high-order mode elastic surface wave device according to any one of claims 1 to 8, wherein the piezoelectric substrate comprises a LiNbO3 crystal and the Euler angle is in the range of (0°±20°, 87°~143°, 0°±5°) or is a crystallographically equivalent Euler angle.

25. The high-order mode elastic surface wave device according to claim 1 or 2, wherein the linear expansion coefficient of the supporting substrate is 10.4 × 10⁻⁶. -6 Below / ℃, α is set as the coefficient of linear expansion, and the ratio of the thickness of the supporting substrate / piezoelectric substrate is above the value of TR specified by the following formula (1). TR=α×0.55×10 6 +2.18 (1)。

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