Elastic wave device

Abstract

[Problem] To provide an elastic wave device having a relatively wide band and high impedance ratio even in a frequency band of 3.5 GHz or more. [Solution] This elastic wave device comprises a piezoelectric thin plate 11 composed of one of LiNbO3 and LiTaO3, a plurality of electrode bodies 12 arranged side by side at intervals on one surface of the piezoelectric thin plate 11, and a floating electrode 13 provided on the other surface of the piezoelectric thin plate 11. In the piezoelectric thin plate 11, the Euler angles (φ, θ, ψ) when the arrangement direction of the electrode bodies is ψ is one of (90°±10°, 90°±10°, 6° to 56°) and (30°±10°, 90°±10°, 124° to 174°) or an Euler angle crystallographically equivalent to one of the above. The elastic wave device is configured to excite a basic mode or a higher-order mode of the thickness-shear vibration.

Description

Acoustic Wave Devices

[0001] The present invention relates to acoustic wave devices.

[0002] The fifth-generation mobile communication system (5G) is allocated a frequency band between 3.7 GHz and 4.5 GHz called Sub-6 to enable high-capacity, high-speed communication while eliminating radio wave saturation. This band includes three bands: n77, n78, and n79, all of which have large bandwidths.

[0003] Conventionally, filters that define the frequencies of each band have used surface acoustic wave (SAW) devices or bulk acoustic wave (BAW) devices. In SAW devices, where V is the sound velocity in the substrate and pitch is the period (pitch) of the interdigital transducer, the frequency f is determined by f = V / pitch. Therefore, due to the limitations of sound velocity and pitch, the high-frequency limit was 3.5 GHz.

[0004] BAW devices using piezoelectric thin films include FBARs (film bulk acoustic resonators), which require cavities above and below the piezoelectric thin film, and SMRs (solidly mounted resonators), which have an acoustic multilayer and a support substrate instead of a cavity on one side of the piezoelectric thin film. In BAW devices, where V is the sound velocity of the piezoelectric thin film including the electrodes and t is its film thickness, the frequency f is determined by f = V / (2t). Therefore, by making the piezoelectric thin film thinner, frequencies above 3.5 GHz can be supported. Piezoelectric thin films made of AlN or ScAlN are commonly used (see, for example, Non-Patent Documents 1 and 2). It is known that the piezoelectricity of these AlN-based piezoelectric thin films increases when the Sc concentration is increased to approximately 40%. Meanwhile, the bandwidth of an acoustic wave filter is roughly proportional to the piezoelectricity, so a piezoelectric material with high piezoelectricity is required to form a filter that can handle a wide bandwidth. Therefore, in order to support the wideband 5G band, it is sufficient to use ScAlN with a relatively high Sc concentration, but increasing the Sc concentration has the side effect of increasing loss.

[0005] LiNbO ３Lithium nitrate (LN) is a material with higher piezoelectricity than ScAlN. It has traditionally been used as a substrate for surface acoustic wave (SAW) devices, but by thinning it, it can also be used for BAW devices. For example, a BAW device using a 42° Y-cut LN thin plate with a thickness of 1 μm has been reported to have a resonant frequency of 2.12 GHz, an antiresonant frequency of 2.28 GHz, a bandwidth of 7.5%, and an impedance ratio of 64 dB (see, for example, Non-Patent Document 3).

[0006] In addition, a Z-cut LN thin plate is used, and its thickness is set to A, which is one of the plate waves. １ An acoustic wave device called "XBAR" has also been developed, which has a structure in which a thin interdigital transducer (IDT) is formed on one side of an LN thin plate, and the wavelength is significantly smaller than the wavelength of the modal Lamb wave and half the wavelength of the longitudinal wave in the plate thickness direction (see, for example, Non-Patent Documents 4 and 5, or Patent Document 1). It has been reported that this "XBAR" has a resonant frequency of 5 GHz, a bandwidth of 10.5%, and an impedance ratio of 64 dB when a 375 nm thick ZYLN thin plate is used.

[0007] Furthermore, an acoustic wave device called "YBAR" has been developed, which has a structure in which an interdigital transducer (IDT) is formed on one surface of an LN thin plate close to a Y-cut at Euler angles (0°, θ, 0°) around θ=90° and a common floating electrode is formed on the other surface of the LN thin plate (see, for example, Non-Patent Documents 6 and 7, or Patent Document 2). In this "YBAR," the piezoelectric stress constant e corresponding to the thickness-shear vibration of the bulk wave is particularly high when θ=81.5°. ３４ Simulations have shown that the bandwidth reaches 16%.

[0008] John D. Larson III et al., “Power Handling and Temperature Coefficient Studies in FBAR Duplexers for the 1900 MHz PCS Band”, Proc. IEEE Ultrason. Symp., 2000, p.869-874Keiichi Umeda et al., “PIEZOELECTRIC PROPERTIES OF ScAlN THIN FILMS FOR PIRZO-MEMS DEVICES”, Proc. MEMS (Taipei, Taiwan), 2013, p.20-24, Tomoyoshi Tai and 3 others, “Development of single crystal FBAR using LiNbO3, LiTaO3”, Proceeding of Symposium on Ultrasonic Electronics, 2007, Vol. 28, p.151-152 Victor Plessky, “XBAR”, Proc. IEEE International Ultrasonics Symposium 2022Soumya Yandrapalli et al., “Study of Thin Film LiNbO3 Laterally Excited Bulk Acoustic Resonators”, Journal of Microelectromechanical Systems, 31, 2 (2022) pp. 217-225V. P. Plessky et al., “Crystalline Y-cut Lithium Niobate Layers for the Bulk Acoustic Wave Resonator (YBAR)”, [online], 17 November 2020, IEEE, [Retrieved on July 31, 2020], Internet, DOI: 10.1109 / IUS46767.2020.9251647S. Yandrapalli et al., “Toward Band n78 Shear Bulk Acoustic Resonators Using Crystalline Y-Cut Lithium Niobate Films With Spurious Suppression”, [online], 15 June 2023, IEEE, [Retrieved July 31, 2023], Internet, DOI: 10.1109 / JMEMS.2023.3282024.

[0009] U.S. Patent No. 10,491,192 U.S. Patent Application Publication No. 2022 / 0407498

[0010] The acoustic wave devices described in Non-Patent Documents 6 and 7, or Patent Document 2, can realize a wide bandwidth and a high impedance ratio not only in the frequency band from several hundred MHz to 3.5 GHz, but also in high frequency bands above 3.5 GHz, by utilizing the high piezoelectricity and low loss of Y-cut LN. However, development of devices with an even wider bandwidth and higher impedance ratio is expected.

[0011] The present invention has been made in light of the above-mentioned problems, and has an object to provide an acoustic wave device that has a relatively wide bandwidth and a high impedance ratio even in a frequency band of 3.5 GHz or more.

[0012] In order to achieve the above object, an acoustic wave device according to the present invention is ３ and LiTaO ３ a plurality of electrodes arranged at intervals on one surface of the piezoelectric thin plate; and a floating electrode provided on the other surface of the piezoelectric thin plate, wherein the piezoelectric thin plate has Euler angles (φ, θ, ψ) of either (90°±10°, 90°±10°, 6° to 56°) and (30°±10°, 90°±10°, 124° to 174°) when the arrangement direction of the electrodes is ψ, or an Euler angle crystallographically equivalent to either of these, and is configured to excite a fundamental mode or a higher-order mode of thickness-shear vibration.

[0013] The acoustic wave device according to the present invention can excite the fundamental mode and higher modes of thickness-shear vibration, and therefore has a wider bandwidth and a higher impedance ratio than conventional devices, even in the frequency band of 3.5 GHz or higher. Furthermore, the acoustic wave device according to the present invention can reduce vibration components of higher modes other than thickness-shear vibration to zero or nearly zero, thereby suppressing spurious responses. Furthermore, the acoustic wave device according to the present invention can excite not only the first mode of thickness-shear vibration but also third and fifth modes at higher frequency bands, making it advantageous for use at higher frequencies.

[0014] In the acoustic wave device according to the present invention, in particular, in order to widen the band, the piezoelectric thin plate is made of LiNbO ３ and the Euler angles are either one of (90°±10°, 90°±10°, 41°±10°) and (30°±10°, 90°±10°, 139°±10°), or Euler angles crystallographically equivalent to either one of these.

[0015] In addition, in the acoustic wave device according to the present invention, in order to improve the temperature characteristics, the piezoelectric thin plate is made of LiTaO ３ and the Euler angles are either one of (90°±10°, 90°±10°, 43.5°±10°) and (30°±10°, 90°±10°, 136.5°±10°), or Euler angles crystallographically equivalent to either one of these.

[0016] In the acoustic wave device according to the present invention, the piezoelectric thin plate preferably has a thickness of 100 nm to 5 μm depending on the frequency to be used.

[0017] In the acoustic wave device according to the present invention, each electrode body may be configured to apply a voltage such that the phases of adjacent electrode bodies are opposite. Furthermore, each electrode body may be configured such that, among the arranged electrode bodies, a first electrode group is formed by electrically connecting a plurality of electrode bodies from one end to the electrode body, and a second electrode group is formed by electrically connecting the remaining plurality of electrode bodies from the other end, and a voltage is applied such that the voltage phases of the first electrode group and the second electrode group are opposite to each other. In these cases, each electrode can be taken out from only one surface of the piezoelectric thin plate, simplifying the device configuration. The length, width, or ratio (aspect ratio) of each electrode body is preferably designed to suppress spurious responses. Furthermore, the number of electrode bodies is preferably determined based on the characteristic impedance required for the device. The characteristic impedance is typically 50 Ω.

[0018] In the acoustic wave device of the present invention, it is preferable that the floating electrode is provided on the other surface of the piezoelectric thin plate at a position corresponding to each electrode body provided on at least one surface of the piezoelectric thin plate, and it may be provided, for example, over the entire other surface of the piezoelectric thin plate.

[0019] Each electrode body and floating electrode is preferably made of one or more of Al, Cu, Mo, Au, Cr, Ti, W, and alloys thereof, and may be made of multiple layers of Al-Cr, Al-Ti, Ti-Al-Ti, etc. Each electrode body and floating electrode preferably has a thickness of, for example, 5 nm to 2 μm.

[0020] In the acoustic wave device according to the present invention, it is preferable that the surface of the floating electrode opposite the piezoelectric thin plate is in contact with a space. Also, the acoustic wave device according to the present invention may have an acoustic multilayer film provided on the surface of the floating electrode opposite the piezoelectric thin plate, and the surface of the floating electrode opposite the piezoelectric thin plate may be in contact with the acoustic multilayer film. When this acoustic multilayer film is provided, spurious responses can be suppressed compared to when a space is provided instead of the acoustic multilayer film. Note that the acoustic multilayer film is provided by alternately stacking low acoustic impedance layers with relatively low acoustic impedance and high acoustic impedance layers with high acoustic impedance, and the low acoustic impedance layers are made of, for example, SiO ２ or Al, and the high acoustic impedance layer is, for example, W, Pt, or HfO ２ The acoustic multilayer film may be formed by laminating four or more pairs of layers, each of which is made up of one low acoustic impedance layer and one high acoustic impedance layer, thereby achieving a particularly high impedance ratio.

[0021] In addition, when this acoustic multilayer film is used, the piezoelectric thin plate is made of LiNbO ３ The piezoelectric thin plate is preferably made of a single crystal of LiTaO, and the Euler angles are either (90°±10°, 90°±10°, 38°±10°) or (30°±10°, 90°±10°, 142°±10°), or an Euler angle crystallographically equivalent to either of these. In this case, the impedance ratio is particularly high. ３ It is preferable that the Euler angles are either one of (90°±10°, 90°±10°, 40°±10°) and (30°±10°, 90°±10°, 140°±10°), or Euler angles crystallographically equivalent to either one of these. In this case, spurious responses can be particularly suppressed.

[0022] In the acoustic wave device according to the present invention, the piezoelectric thin plate preferably has a groove or a through-hole extending to the other surface in a portion between adjacent electrode bodies on one surface. In this case, spurious responses can be more effectively suppressed and the impedance ratio of the excited vibration can be further increased. In particular, it is preferable that the piezoelectric thin plate has the through-hole, and the floating electrode has an electrode hole extending through its thickness so as to communicate with the through-hole. In this case, spurious responses can be more effectively suppressed and the impedance ratio of the excited vibration can be further increased.

[0023] The acoustic wave device according to the present invention is ２ , Si, SiC, HfO ２ , AlN, Si ３ N ４ , Al ２ O ３ Alternatively, a cover layer made of diamond may be provided to cover at least one of the surface of the floating electrode opposite the piezoelectric thin plate and the surface of each electrode body opposite the piezoelectric thin plate. In this case, the cover layer can protect the floating electrode and each electrode body, thereby maintaining the performance of the acoustic wave device. The cover layer can also provide temperature compensation and reduce energy loss.

[0024] Here, the Euler angles (φ, θ, ψ) are in a right-handed system and represent the cross section of the piezoelectric thin plate and the propagation direction of the elastic wave (generally, SAW). That is, with respect to the X, Y, and Z crystal axes of the LN, LT, etc. that make up the piezoelectric thin plate, the X axis is rotated counterclockwise by φ around the Z axis as the rotation axis to obtain the X' axis. Next, the Z axis is rotated counterclockwise by θ around the X' axis to obtain the Z' axis. In this case, the Z' axis is the normal, and the plane containing the X' axis is the cross section of the piezoelectric thin plate. The direction of the counterclockwise rotation of the X' axis by ψ around the Z' axis is the propagation direction of the elastic wave. The axis perpendicular to the X' and Z' axes, obtained by moving the Y axis through these rotations, is defined as the Y' axis.

[0025] By defining Euler angles in this way, for example, propagation in the X direction with a 40° rotated Y-plate is expressed as (0°, -50°, 0°) in Euler angles, and propagation in the X direction with a 40° rotated Y-plate is expressed as (0°, -50°, 90°) in Euler angles. Furthermore, the Z-cut, Y-cut, and X-cut are expressed as (0°, 0°, 0°), (0°, 90°, 0°), and (90°, 90°, 0°) in Euler angles, respectively.

[0026] When cutting out a piezoelectric thin plate at a desired Euler angle, an error of up to ±0.10° may occur in each component of the Euler angle.

[0027] The impedance ratio (Z-ratio) is the ratio of the resonant impedance Zr at the resonant frequency fr to the anti-resonant impedance Za at the anti-resonant frequency fa [20 × log (Za / Zr)]. The bandwidth (BW) of the acoustic wave device is (fa - fr) / fr.

[0028] According to the present invention, it is possible to provide an acoustic wave device that has a relatively wide bandwidth and a high impedance ratio even in a frequency band of 3.5 GHz or higher.

[0029] 1A and 1B are a plan view and an A-A' end view, respectively, of an acoustic wave device according to an embodiment of the present invention. (a) Plan view and (b) A-A' cross-sectional view showing a modification of the acoustic wave device according to an embodiment of the present invention, in which a plurality of electrode bodies form a pair of ladder-shaped electrodes. (c) Plan view showing the portion within the dashed line in (a), and (d) B-B' cross-sectional view. (e) Plan view showing a first modification of the portion within the dashed line in (a), and (f) C-C' cross-sectional view. (g) Plan view showing a second modification of the portion within the dashed line in (a), and (h) D-D' cross-sectional view. (a) Plan view and (b) A-A' cross-sectional view showing a modification of the acoustic wave device according to an embodiment of the present invention, in which an acoustic multilayer film is provided. (c) A partially enlarged cross-sectional view showing a modification in which a groove is formed in the acoustic multilayer film. ３ ) and the piezoelectric constants e when the Euler angles are (90°, 90°, ψ)１５ , e １６ , e ２４ , e ３４ (b) A graph showing the dependence of the piezoelectric stress constant e on the Euler angle ψ of a conventional resonator when the piezoelectric thin plate is LN and the Euler angles are (0°, θ, 0°). １５ , e １６ , e ２４ , e ３４ 10A is a graph showing the Euler angle θ dependence of the frequency characteristics of an acoustic wave device according to an embodiment of the present invention when the piezoelectric thin plate is LN and the Euler angles are (90°, 90°, 41°), and a graph showing the frequency characteristics of a conventional resonator when the piezoelectric thin plate is LN and the Euler angles are (0°, 81.5°, 0°). 10B is a graph showing the relationship between the impedance ratio (Impedance) and bandwidth (BW) and ψ when the Euler angles are (90°, 90°, ψ) for the acoustic wave device according to an embodiment of the present invention. 10C is a graph showing the relationship between the impedance ratio (Impedance) and bandwidth (BW) and ψ when the piezoelectric thin plate is LT and the Euler angles are (90°, 90°, ψ) for the acoustic wave device according to an embodiment of the present invention. 10B is a graph showing the relationship between the impedance ratio (Impedance) and bandwidth (BW) and ψ when the piezoelectric thin plate is LT and the Euler angles are (90°, 90°, ψ) for the acoustic wave device according to an embodiment of the present invention. 10C is a graph showing the relationship between the impedance ratio (Impedance) and bandwidth (BW) and ψ when the piezoelectric thin plate is LT and the Euler angles are (90°, 90°, ψ), and 10B is a graph showing the frequency characteristics when ψ is 0°, 35°, 45°, 90°, 150°. 10A and 10B are graphs showing the frequency characteristics of an acoustic wave device according to an embodiment of the present invention when the piezoelectric thin plate is LT and the Euler angles are (90°, 90°, 43.5°), and the frequency characteristics of a conventional resonator when the piezoelectric thin plate is LT and the Euler angles are (0°, 81.5°, 0°). 10B are graphs showing (a) the frequency characteristics and (b) the change in impedance ratio when the width of each electrode body is changed in the range of 10 μm to 50 μm when the piezoelectric thin plate is LT and the Euler angles are (90°, 90°, 40°) for an acoustic wave device according to an embodiment of the present invention. 10C are graphs showing the piezoelectric stress constant e of an acoustic wave device according to an embodiment of the present invention when the piezoelectric thin plate is LN and the Euler angles are (30°, 90°, ψ). １５ , e １６ , e ２４ , e ３４ (b) Graph showing the dependence of the piezoelectric stress constant e on the Euler angle ψ when the piezoelectric thin plate is LN and the Euler angles are (φ, 90°, 146.5°). １５ , e １６ , e ２４ , e３４10 is a graph showing the Euler angle φ dependence of the thickness shear vibration frequency characteristic of the third mode of thickness shear vibration when the piezoelectric thin plate of the acoustic wave device according to the embodiment of the present invention is made of LN, the Euler angles are (90°, 90°, 41°), and the thicknesses of the Al electrode bodies and floating electrodes are 200 nm and 150 nm, respectively. (b) is a graph showing the frequency characteristics of the fifth mode of thickness shear vibration when the thickness of the Al electrode bodies and floating electrodes is 100 nm. (c) is a graph showing the dependence of the resonance frequency, impedance ratio (Z-ratio), and bandwidth (BW) of the first, third, and fifth modes of thickness shear vibration on the thickness (IDT thickness) of the Al electrode bodies and floating electrodes of the acoustic wave device according to the embodiment of the present invention when the piezoelectric thin plate of the acoustic wave device is made of LN and the Euler angles are (90°, 90°, 41°). 12(c) and 12(d) are graphs showing frequency characteristics of an acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin plate is made of LN, and in which the piezoelectric thin plate has a groove and the floating electrode does not have an electrode hole. 1A and 1B are graphs showing the frequency characteristics and the relationship between the depth of the groove in the piezoelectric thin film and the impedance ratio of the acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin film is LT, and the piezoelectric thin film has (a) no groove in the piezoelectric thin film (Grooved depth = 0), (b) a groove depth of the piezoelectric thin film is 0.2 μm (Grooved depth = 0.2 μm), (c) a groove depth of 0.4 μm (Grooved depth = 0.4 μm), and the piezoelectric thin film has a through hole (Penetrated). 1A is a transverse end view of a modified acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin film is LT, and (d) a piezoelectric thin film has (a) a groove depth of 0.2 μm (Grooved depth = 0.2 μm), a groove depth of 0.4 μm (Grooved depth = 0.4 μm), and the piezoelectric thin film has a through hole (Penetrated). 1B is a graph showing the frequency characteristics and the relationship between the depth of the groove in the piezoelectric thin film and the impedance ratio of the acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin film has (a) a groove depth of 0.2 μm (Grooved depth = 0.2 μm), a groove depth of 0.4 μm (Grooved depth = 0.4 μm), and the piezoelectric thin film has a through hole (Penetrated). 1C is a cross-sectional view of a modified acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin film has (a) a groove depth of 0.2 μm (Grooved depth = 0.2 μm), a groove depth of 0.4 μm (Grooved depth = 0.4 μm), and the piezoelectric thin film has a through hole (Penetrated). 1D is a cross-sectional view of a modified acoustic wave device according to an embodiment of the present invention, in which the piezoelectric thin film has (a) a groove depth of 0.2 μ10 is a graph showing the relationship between the impedance ratio and the bandwidth and ψ when the Euler angles are (90°, 90°, ψ) for an acoustic wave device according to an embodiment of the present invention, the acoustic multilayer film is an LN piezoelectric thin plate, the Euler angles are (90°, 90°, ψ), and the low acoustic impedance layer is SiO2. ２ When the high acoustic impedance layer is made of W (SMR-SiO2 / W), the low acoustic impedance layer is made of SiO ２ The high acoustic impedance layer is made of HfO ２ 17A and 17B are graphs showing the frequency characteristics of a SMR-SiO2 / HfO2 composite and a comparative example without an acoustic multilayer (film type).

[0033] Graphs showing the relationship between the thickness of each layer of the acoustic multilayer and (a) the impedance ratio and (b) the bandwidth for the SMR-SiO2 / W composite shown in FIG. 17A, (c) a graph showing an enlarged portion of (a), and (d) a graph showing an enlarged portion of (b). Graphs showing the relationship between the thickness of each layer of the acoustic multilayer and (a) the impedance ratio and (b) the bandwidth for the SMR-SiO2 / HfO2 composite shown in FIG. 17A, (c) a graph showing an enlarged portion of (a), and (d) a graph showing an enlarged portion of (b). Graphs showing the frequency characteristics (a) and the relationship between the number of pairs of low acoustic impedance layers and high acoustic impedance layers and the impedance ratio for the SMR-SiO2 / HfO2 composite shown in FIG. 17B are graphs showing the relationship between the number of pairs and the impedance ratio for the SMR-SiO2 / HfO2 composite shown in FIG. 17A, (b) and (c) are graphs showing the relationship between the number of pairs and the impedance ratio for the SMR-SiO2 / HfO2 composite shown in FIG. 17B. The acoustic wave device according to the embodiment of the present invention has an acoustic multilayer film, the piezoelectric thin plate is LT, the Euler angles are (90°, 90°, 40°), and the low acoustic impedance layer is SiO ２ When the high acoustic impedance layer is made of W (SMR-SiO2 / W), the low acoustic impedance layer is made of SiO ２ The high acoustic impedance layer is made of HfO ２21A and 21B are graphs showing the frequency characteristics of a piezoelectric thin plate made of SMR-SiO2 / HfO2, a comparative example in which the acoustic multilayer is not used and the piezoelectric thin plate has through holes (Penetrated), and a comparative example in which the piezoelectric thin plate has no grooves (No Groove). FIG. 22A is a graph showing the relationship between the thickness of each layer of the acoustic multilayer and (a) the impedance ratio and (b) the bandwidth for the SMR-SiO2 / W shown in FIG. 21A and 21B. FIG. 22B is a graph showing the relationship between the thickness of each layer of the acoustic multilayer and (a) the impedance ratio and (b) the bandwidth for the SMR-SiO2 / HfO2 shown in FIG. 21A and 21B. (a) to (d) are transverse cross-sectional views (upper) and plan views (lower) showing a method for manufacturing an enlarged macrodevice of an acoustic wave device according to an embodiment of the present invention. (a) are graphs showing the frequency characteristics of a macrodevice up to 50 Hz and simulation results for an acoustic wave device according to an embodiment of the present invention, and (b) are graphs showing the frequency characteristics of a macrodevice up to 200 Hz. 25( a) is a graph showing enlarged results of measurements and simulations of the first mode of thickness-shear vibration, the third mode of thickness-shear vibration, the fifth mode of thickness-shear vibration, and the seventh mode of thickness-shear vibration, as shown in FIG. 25( a). (a) to (e) are cross-sectional views showing an example of a manufacturing method of an acoustic wave device according to an embodiment of the present invention. (a) to (e) are cross-sectional views showing a manufacturing method different from that shown in FIG. 27 for an acoustic wave device according to an embodiment of the present invention.

[0030] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention will be described in detail below with reference to the accompanying drawings and examples. Figures 1 to 28 show an acoustic wave device according to an embodiment of the present invention. As shown in Figure 1, an acoustic wave device 10 includes a piezoelectric thin plate 11, a plurality of electrode bodies 12, a floating electrode 13, and a support substrate 14.

[0031] Since the acoustic wave device 10 according to the embodiment of the present invention is not a SAW device, the third Euler angle ψ of the Euler angles (φ, θ, ψ) does not represent the propagation direction of the SAW. However, since the multiple electrode bodies 12 are structurally similar to the IDTs of a SAW device, for convenience, ψ is defined in accordance with a SAW device. In other words, the direction in which the electrodes 12 are arranged is defined as ψ.

[0032] The piezoelectric thin plate 11 is made of LiNbO ３ or LiTaO ３ The piezoelectric thin plate 11 is made of a single crystal. The Euler angles of the piezoelectric thin plate 11 are either (90°±10°, 90°±10°, 6° to 56°) or (30°±10°, 90°±10°, 124° to 174°), or Euler angles crystallographically equivalent to either of these. The piezoelectric thin plate 11 has a thickness of, for example, 100 nm to 5 μm.

[0033] Note that the Euler angles (0°, θ, 0°) are equivalent to the Euler angles (0°, θ + 360°, 0°). On the other hand, the Euler angles (0°, θ + 180°, 0°) and (0°, θ, 0°) are not equivalent to each other in terms of Euler angles, since crystallographically, they are the difference between the + and - planes, i.e., the front and back of the substrate. However, acoustic wave devices exhibit the same frequency characteristics on both the front and back, so acoustically, the orientations of the front and back of the substrate are also considered to be equivalent planes.

[0034] The plurality of electrode bodies 12 are arranged on one surface of the piezoelectric thin plate 11 with a gap between adjacent electrode bodies 12. Each electrode body 12 is configured so that a voltage can be applied to it so that the voltage phases of adjacent electrode bodies 12 are opposite. In the specific example shown in FIG. 1 , each electrode body 12 is composed of electrode fingers 21a of a pair of interdigital transducer (IDT) electrodes 21. That is, the acoustic wave device 10 has a pair of IDT electrodes 21, and each IDT electrode 21 has a bus bar 21b extending in the direction in which the electrode bodies 12 are arranged and a plurality of electrode fingers 21a extending perpendicularly from the bus bar 21b. The electrode fingers 21a are arranged facing each other so as to interdigitate with a gap between them. Note that the width and spacing of the electrode fingers 21a do not need to be uniform.

[0035] The floating electrode 13 is an electrode that is not electrically connected and is provided on the other surface of the piezoelectric thin plate 11. The floating electrode 13 is provided on the other surface of the piezoelectric thin plate 11 at a position corresponding to each electrode body 12 provided on at least one surface of the piezoelectric thin plate 11. Each electrode body 12 and floating electrode 13 is made of, for example, one or more of Al, Cu, Mo, Au, Cr, Ti, W, and alloys thereof. Each electrode body 12 and floating electrode 13 may be made of multiple layers, for example, Al—Cr, Al—Ti, Ti—Al—Ti, etc. Each electrode body 12 and floating electrode 13 has a thickness of, for example, 5 nm to 2 μm.

[0036] As an example, the piezoelectric thin plate 11 has rectangular through-holes 11a that penetrate through to the other surface in a portion of one surface between adjacent electrode bodies 12. The floating electrode 13 has electrode holes 13a that penetrate through the thickness of the plate to communicate with the through-holes 11a. In the specific example shown in Fig. 1 , the piezoelectric thin plate 11 does not have through-holes 11a in a portion corresponding to the portion between the tip of the electrode finger 21a corresponding to each electrode body 12 and the bus bar 21b of the opposing IDT-like electrode 21, and in a portion corresponding to the bus bar 21b of each IDT-like electrode 21, and is formed in a ladder shape in a plan view.

[0037] The piezoelectric thin plate 11 may be a flat plate (a thin plate of uniform thickness) that does not have through-holes 11a or electrode holes 13a as shown in Fig. 1. The piezoelectric thin plate 11 may also have grooves (portions that do not penetrate the flat piezoelectric thin plate 11 but are formed in a recessed shape to thin the piezoelectric thin plate 11) at positions that are not located on the electrode bodies 12 of the flat piezoelectric thin plate 11. The depth of the grooves may be approximately 50 to 95% of the thickness of the piezoelectric thin plate 11.

[0038] The support substrate 14 is provided on the other surface of the piezoelectric thin plate 11, outside the floating electrode 13, so as to be able to support the piezoelectric thin plate 11, with a space formed inside. As a result, the surface of the floating electrode 13 opposite the piezoelectric thin plate 11 is in contact with the space. The support substrate 14 is made of, for example, Si, quartz crystal, sapphire, diamond, etc.

[0039] Next, the operation of the acoustic wave device 10 will be described. Because the acoustic wave device 10 can excite the fundamental mode and higher modes of thickness-shear vibration, it has a wider bandwidth and a higher impedance ratio than conventional devices, even in the frequency band of 3.5 GHz or higher. Furthermore, the acoustic wave device 10 can reduce vibration components of higher modes other than thickness-shear vibration to zero or nearly zero, thereby suppressing spurious responses. Furthermore, the acoustic wave device 10 can excite not only the first mode of thickness-shear vibration but also third and fifth modes of vibration at higher frequency bands, making it advantageous for higher frequencies.

[0040] The floating electrode 13 may be provided on the entire other surface of the piezoelectric thin plate 11 except for the portion where the support substrate 14 is provided.

[0041] 2( a) and 2(b), the acoustic wave device 10 may include a ladder electrode 22a including multiple electrode bodies 12 from the electrode body 12 at one end of the array of electrode bodies 12, and a ladder electrode 22b including the remaining multiple electrode bodies 12 from the electrode body 12 at the other end of the array of electrode bodies 12. Each of the ladder electrodes 22a, 22b may be configured by electrically connecting both ends of the respective multiple electrode bodies 12, and may be configured so that voltages can be applied to the ladder electrodes 22a, 22b such that the voltage phases of the ladder electrodes 22a, 22b are opposite to each other. Note that one of the ladder electrodes 22a forms a first electrode group, and the other ladder electrode 22b forms a second electrode group.

[0042] Furthermore, when the piezoelectric thin plate 11 has a pair of ladder-shaped electrodes 22a, 22b, as shown in Figures 2(c) and (d), the piezoelectric thin plate 11 may have a groove between the ladder-shaped electrodes 22a, 22b. Alternatively, as shown in Figures 2(e) to (h), the piezoelectric thin plate 11 may have one or more through holes 11a between the ladder-shaped electrodes 22a, 22b, and the floating electrode 13 may have an electrode hole 13a communicating with the through hole 11a. In the example shown in Figures 2(e) and (f), multiple through holes 11a are provided along the electrode bodies 12 of the opposing ladder-shaped electrodes 22a, 22b. In the example shown in Figures 2(g) and (h), a pair of elongated through holes 11a is provided along the electrode bodies 12 of the opposing ladder-shaped electrodes 22a, 22b. In the example shown in Figure 2, each electrode body 12 is supported at both ends, making it easy to manufacture and providing high strength. Furthermore, the floating electrode 13 is easy to manufacture.

[0043] 3, the acoustic wave device 10 may also have an acoustic multilayer film 23 provided on the surface of the floating electrode 13 opposite to the piezoelectric thin plate 11. The acoustic multilayer film 23 is provided by alternately laminating low acoustic impedance layers 23a having a relatively low acoustic impedance and high acoustic impedance layers 23b having a high acoustic impedance. The low acoustic impedance layers 23a may be made of, for example, SiO ２ , Al, etc., and the high acoustic impedance layer 23b is made of, for example, W, Pt, HfO ２ The acoustic multilayer film 23 may be made up of one set of one laminated low acoustic impedance layer 23a and one laminated high acoustic impedance layer 23b, or may be made up of multiple sets. The acoustic multilayer film 23 may have either the low acoustic impedance layer 23a or the high acoustic impedance layer 23b arranged on the floating electrode 13 side. The acoustic multilayer film 23 may also have an adhesive layer 23c on the support substrate 14 side. The adhesive layer 23c may be made of, for example, SiO ２In the case shown in Figure 3, thickness-shear vibration can be effectively excited, just as in the case where the surface of the floating electrode 13 opposite the piezoelectric thin plate 11 is in contact with space. As shown in Figure 3(c), grooves of depth D may be formed in the acoustic multilayer film 23 when forming the through-holes 11a and the electrode holes 13a. Even in this case, the performance of the acoustic wave device 10 remains almost unchanged compared to when no grooves are formed.

[0044] [When the piezoelectric thin plate is LN and its Euler angles are (90°, 90°, ψ)] Using the acoustic wave device 10 shown in FIG. 1, the piezoelectric thin plate 11 is made of LN (LiNbO ３ ), the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, ψ), and each electrode body 12 and floating electrode 13 are made of Al with a thickness of 0.05 μm. １５ , e １６ , e ２４ , e ３４ The Euler angle ψ dependence of the was determined and is shown in FIG. 4(a). For comparison, a conventional acoustic wave device described in Patent Document 2 was used, and the piezoelectric thin plate 11 was made of LN (LiNbO ３ ) and the Euler angles of the piezoelectric thin plate 11 are (0°, θ, 0°), the piezoelectric stress constant e １５ , e １６ , e ２４ , e ３４ The Euler angle θ dependence of is calculated and shown in Figure 4(b). １５ is related to the parallel shear vibration in the sagittal plane due to the parallel electric field generated between the IDTs, and A １ This is important for devices (XBAR) that utilize modal Lamb waves, as described in Patent Document 1 and Non-Patent Documents 4 and 5. １６ is related to the electric field due to the parallel electric field generated between the IDTs and the shear vibration in the perpendicular direction, and is important for devices that utilize the SH (Shear Horizontal) mode of SAW or plate waves. ３４ is related to thickness-shear vibration due to an electric field in the thickness direction, and is important for the devices (YBAR) described in Non-Patent Documents 6 and 7 and Patent Document 2, and the device of the present invention.

[0045] As shown in FIG. 4A, in the acoustic wave device 10, e ３４ is about 3.7 C / m in the range of ψ=0° to 60°. ２ The maximum value is 4.38 C / m when ψ = 33.5°. ２ It was confirmed that e １５ , e ２４ It was confirmed that e is almost zero for any ψ. １６ It was confirmed that, for example, when ψ = 41°, it becomes zero. From this, it can be said that by setting the Euler angles of the piezoelectric thin plate 11 to (90°, 90°, 41°), vibration components other than the higher modes of thickness-shear vibration become zero, and spurious responses can be suppressed.

[0046] In contrast, as shown in FIG. 4(b), in the conventional acoustic wave device, the piezoelectric stress constants change variously with respect to θ, and e ３４ is a maximum value of 3.84 C / m when θ = 81.5° ２ This value was confirmed to be e shown in FIG. ３４ Maximum value of 4.38 C / m ２ When the Euler angles are (90°, 90°, 33.5°), the e ３４ It was confirmed that the value of was about 14% larger. This means that by using the LN cut angle of acoustic wave device 10, a wider bandwidth and a higher impedance ratio can be achieved than in the conventional acoustic wave device (YBAR).

[0047] 5(a) and 5(b) show the frequency characteristics of the acoustic wave device 10 when the piezoelectric thin plate 11 in Fig. 4(a) is LN and the Euler angles are (90°, 90°, 41°), and the impedance ratio and the relationship between the bandwidth and ψ when the Euler angles are (90°, 90°, ψ), respectively. For comparison, Fig. 5(a) also shows the frequency characteristics of a conventional acoustic wave device when the piezoelectric thin plate 11 in Fig. 4(b) is LN and the Euler angles are (0°, 81.5°, 0°).

[0048] As shown in Figure 5(a), when the Euler angles of the piezoelectric thin plate 11 were (0°, 81.5°, 0°), the conventional acoustic wave device had an fr of 3.244 GHz, an fa of 4.063 GHz, an impedance ratio (Impedance) of 84.4 dB, and a bandwidth (BW) of 25.3%. In contrast, when the Euler angles of the piezoelectric thin plate 11 were (90°, 90°, 41°), the acoustic wave device 10 had an fr of 3.203 GHz, an fa of 4.321 GHz, an impedance ratio of 89.2 dB, and a bandwidth of 32.1%, demonstrating a larger impedance ratio and wider bandwidth than the conventional acoustic wave device. Furthermore, while the conventional acoustic wave device exhibited several relatively large spurious responses near 3.7 GHz and in the 5-6 GHz range, the acoustic wave device 10 exhibited significantly smaller spurious responses.

[0049] 5(b), it was confirmed that the impedance ratio of the acoustic wave device 10 when the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, ψ) is 89 dB or more when ψ is 28° to 44°, 88 dB or more when ψ is 18° to 50°, approximately 86 dB or more when ψ is 6° to 56°, and approximately 84 dB or more when ψ is 0° to 60°. It was also confirmed that when ψ is 2° to 58°, the impedance ratio is greater than the impedance ratio of 84.4 dB of the conventional acoustic wave device shown in FIG.

[0050] 5(b), it was confirmed that the bandwidth of the acoustic wave device 10 when the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, ψ) is 32.5% or more when ψ is 16° to 40°, approximately 32% or more when ψ is 4° to 54°, and approximately 31.5% or more when ψ is 0° to 60°. It was also confirmed that the bandwidth is wider than the 25.3% bandwidth of the conventional acoustic wave device shown in FIG. 5(a) at least when ψ is 0° to 66°.

[0051] [When the piezoelectric thin plate is LT and its Euler angles are (90°, 90°, ψ)] FIG. 4A shows the case where the piezoelectric thin plate 11 is LN, but when the piezoelectric thin plate 11 is LT (LiTaO ３), almost the same results were obtained, and when the Euler angles of the piezoelectric thin plate 11 were (90°, 90°, 31.5°), e ３４ It was confirmed that, at (90°, 90°, 43.5°), vibration components other than the higher modes of thickness-shear vibration become zero, and spurious responses can be suppressed.

[0052] The piezoelectric thin plate 11 is made of LT (LiTaO ３ 6( a ) and 6 ( b ) show graphs illustrating the relationship between the impedance ratio and the bandwidth and ψ when the piezoelectric thin plate 11 is used with the acoustic wave device 10 shown in FIG. 1 , the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, ψ), the electrode bodies 12 and floating electrode 13 are made of Al with a thickness of 0.05 μm, the width of each electrode body 12 is 40 μm, and there are no through-holes 11 a or electrode holes 13 a. The frequency characteristics of the acoustic wave device 10 when ψ is 0°, 35°, 45°, 90°, and 150° are also shown in FIG. 7 . For comparison, FIG. 7 also shows the frequency characteristics of a conventional acoustic wave device when the piezoelectric thin plate 11 is LT and the Euler angles are (0°, 81.5°, 0°).

[0053] As shown in FIG. 6(a), even if ψ is changed, there is almost no effect on the impedance ratio and the bandwidth. However, as shown in FIG. 6(b), it was confirmed that when ψ is between 30° and 50°, the spurious response is very small.

[0054] 7, when the Euler angles of the piezoelectric thin plate 11 are (0°, 81.5°, 0°), the conventional acoustic wave device has an fr of 3.403 GHz, an fa of 3.692 GHz, an impedance ratio of 77.5 dB, and a bandwidth of 8.5%. In contrast, when the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 43.5°), the acoustic wave device 10 has an fr of 3.540 GHz, an fa of 3.916 GHz, an impedance ratio of 81.6 dB, and a bandwidth of 10.6%, demonstrating a larger impedance ratio and a wider bandwidth than the conventional acoustic wave device. Furthermore, while the conventional acoustic wave device exhibits several relatively large spurious responses in the 4-7 GHz range, the acoustic wave device 10 exhibits significantly smaller spurious responses.

[0055] 8(a) and 8(b) show the frequency characteristics and the change in the impedance ratio of the acoustic wave device 10 when the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 40°) and the width of each electrode 12 is changed in the range of 10 μm to 50 μm. As shown in FIGS. 8(a) and 8(b), the impedance ratio and the bandwidth are hardly affected by the change in the width of each electrode 12. However, as shown in FIG. 8(b), when the width of each electrode 12 is 20 μm, the spurious response is smaller than when it is 10 μm. When the width of each electrode 12 is 30 μm or more, the spurious response is further reduced and is barely noticeable.

[0056] [When the piezoelectric thin plate is made of LN and its Euler angles are (30°, 90°, ψ)] Using the acoustic wave device 10 shown in FIG. 1, the piezoelectric thin plate 11 is made of LN with a thickness of 0.5 μm, and each electrode body 12 and floating electrode 13 is made of Al with a thickness of 0.05 μm. When the Euler angles of the piezoelectric thin plate 11 are set to (30°, 90°, ψ), which is different from the Euler angles in FIG. 4( a), the piezoelectric stress constant e １５ , e １６ , e ２４ , e ３４ The Euler angle ψ dependence of was calculated and is shown in FIG. 9(a).

[0057] As shown in FIG. 9A, in the acoustic wave device 10, e３４ is in the range of ψ=124° to 174°, and the absolute value is about 3.7 C / m ２ The maximum absolute value is 4.38 C / m when ψ = 146.5°. ２ It was confirmed that e １５ , e ２４ It was confirmed that e is almost zero for any ψ. １６ It was confirmed that, for example, when ψ = 139°, it becomes zero. From this, it can be said that by setting the Euler angles of the piezoelectric thin plate 11 to (30°, 90°, 139°), vibration components other than the higher modes of thickness-shear vibration become zero, and spurious responses can be suppressed.

[0058] In the acoustic wave device 10 when the piezoelectric thin plate 11 is LN, the Euler angle ψ is ３４ The absolute value of the piezoelectric stress constant e is set to 146.5° when it shows the maximum value, and when φ is changed, that is, when the Euler angles are (φ, 90°, 146.5°), １５ , e １６ , e ２４ , e ３４ The Euler angle φ dependence of is calculated and shown in FIG. 9(b).

[0059] As shown in FIG. 9B, in the acoustic wave device 10, e ３４ When φ=30°, 150°, and 270°, the maximum absolute value is 4.38 C / m ２ It was confirmed that e １５ , e １６ , e ２４ is e ３４ When the absolute value is the maximum value, the absolute value is about 0 to 1 C / m ２ From this, it can be said that when φ=30°, 150°, and 270°, vibration components other than the higher modes of thickness-shear vibration become very small, and spurious responses can be suppressed.

[0060] [When the piezoelectric thin plate is LT and its Euler angles are (30°, 90°, ψ)] Although FIG. 9A shows the case where the piezoelectric thin plate 11 is LN, almost the same results are obtained when the piezoelectric thin plate 11 is LT. When the Euler angles of the piezoelectric thin plate 11 are (30°, 90°, 148.5°), e ３４ It was confirmed that the absolute value of shows the maximum value, and when it is (30°, 90°, 136.5°), the vibration components other than the higher modes of thickness-shear vibration become zero, and the spurious response can be suppressed.

[0061] Furthermore, although Figures 6(a) and (b) show the case where a piezoelectric thin plate 11 with Euler angles of (90°, 90°, ψ) is used, it was also confirmed that when a piezoelectric thin plate 11 with Euler angles of (30°, 90°, ψ) is used, even if ψ is changed, there is almost no effect on the impedance ratio and bandwidth, but when ψ is between 130° and 150°, the spurious response is very small.

[0062] [Higher-order modes: when the piezoelectric thin plate is LN] Figures 10(a) and (b) show the frequency characteristics of the third and fifth modes of thickness-shear vibration, respectively, when the acoustic wave device 10 shown in Figure 1 is used, the piezoelectric thin plate 11 is LN with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 41°), and each electrode body 12 and floating electrode 13 is made of Al.

[0063] As shown in Figure 10(a), the third-order mode of thickness-shear vibration was confirmed to have an impedance ratio of 77.7 dB and a bandwidth of 6.3% when the thickness of each electrode body 12 and floating electrode 13 was 200 nm, and an impedance ratio of 74.1 dB and a bandwidth of 2.9% when the thickness of each electrode body 12 and floating electrode 13 was 150 nm. These results confirmed that the device had a relatively good impedance ratio and bandwidth in the frequency band of 5 GHz or higher. It was also confirmed that spurious responses were suppressed.

[0064] As shown in Figure 10(b), the fifth mode of thickness-shear vibration was confirmed to have an impedance ratio of 50.6 dB and a bandwidth of 1.7% when the thickness of each electrode body 12 and floating electrode 13 was 100 nm. These results confirmed that the device had a relatively good impedance ratio and bandwidth in the frequency band of 14 GHz and above. It was also confirmed that spurious responses were suppressed. Furthermore, the results of Figure 10 indicate that a good impedance ratio and bandwidth can be obtained by adjusting the thickness of each electrode body 12 and floating electrode 13.

[0065] 11(a) to 11(c) show the dependence of the resonance frequency, impedance ratio (Z-ratio), and bandwidth (BW) of the first, third, and fifth modes of thickness-shear vibration on the thickness (IDT thickness) of each electrode 12 and floating electrode 13, respectively, when the acoustic wave device 10 shown in Fig. 1 is used, the piezoelectric thin plate 11 is made of LN with a thickness of 0.5 µm, the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 41°), and the electrodes 12 and floating electrode 13 are made of Al. The width of each electrode is 10 µm.

[0066] As shown in Figure 11, by adjusting the thickness of each electrode body 12 and floating electrode 13, it is possible to adjust the resonant frequency, impedance ratio, and bandwidth of each higher mode vibration, and it is possible to obtain a good impedance ratio and bandwidth.

[0067] 12(a) to 12(c), in an acoustic wave device 10, the piezoelectric thin plate 11 does not have a through-hole 11a, but has a rectangular groove 31 between adjacent electrode bodies 12 on one surface, and the floating electrode 13 does not have to have an electrode hole 13a. In this case, the groove has a depth that does not penetrate to the other surface of the piezoelectric thin plate 11. Alternatively, as shown in FIG. 12(d), in an acoustic wave device 10, the piezoelectric thin plate 11 has a through-hole 11a, and the floating electrode 13 does not have to have an electrode hole 13a.

[0068] [When the Piezoelectric Thin Plate is LN] Figure 13 shows the frequency characteristics of the acoustic wave device 10 shown in Figure 1, which has through holes 11a and electrode holes 13a (hereinafter also referred to as the "through-type"); the acoustic wave device 10 shown in Figure 12(c), which has grooves 31 half the thickness of the piezoelectric thin plate 11 (hereinafter also referred to as the "grooved type"); and the acoustic wave device 10 shown in Figure 12(d), which has through holes 11a but no electrode holes 13a (hereinafter also referred to as the "piezoelectric thin plate-only through-type"). In each acoustic wave device 10, the piezoelectric thin plate 11 is made of LN with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 41°), and the electrodes 12 and floating electrodes 13 are made of Al with a thickness of 0.05 μm. The frequency characteristics of the through-type device in Figure 13 are the same as those of the acoustic wave device 10 shown in Figure 5(a).

[0069] 13, all acoustic wave devices 10 have relatively good impedance ratios and bandwidths in the frequency band of 3.5 GHz or higher, but the grooved type has slightly lower impedance ratios and bandwidths than the thin piezoelectric plate-only through-type and through-type devices. This is thought to be because when the thin piezoelectric plate 11 has grooves 31, part of the energy of the excited waves is dissipated along the thin piezoelectric plate 11, whereas when the thin piezoelectric plate 11 has through-holes 11a, the thin piezoelectric plate 11 is divided by the through-holes 11a, which can almost completely prevent the energy of the excited waves from being dissipated.

[0070] 13, it was confirmed that the grooved type and the type with only a through-hole piezoelectric plate generated larger spurious responses than the through-hole type. This is thought to be because, when the piezoelectric plate 11 has the groove 31 or when the floating electrode 13 does not have the electrode hole 13a, the spurious responses are caused by the electric field in the in-plane direction of the piezoelectric plate 11, whereas when the through-hole 11a and the electrode hole 13a are present, the piezoelectric plate 11 is divided by the through-hole 11a and the electrode hole 13a, so that the spurious responses caused by the electric field in the in-plane direction can be effectively suppressed.

[0071] Even if the piezoelectric thin plate 11 has a groove 31 or the floating electrode 13 does not have an electrode hole 13a, spurious responses can be suppressed by adjusting the length and width dimensions, thickness and shape of each electrode body 12, the spacing between each electrode body 12, the width and depth of the groove 31, etc.

[0072] [When the piezoelectric thin plate is LT] Figures 14(a) and 14(b) show the frequency characteristics and the relationship between the groove depth of the piezoelectric thin plate 11 and the impedance ratio for acoustic wave devices 10 in which the piezoelectric thin plate 11 is made of LT with a thickness of 0.5 μm, with no grooves 31 in the piezoelectric thin film 11 between each electrode body 12 (hereinafter also referred to as "Grooved depth = 0"), one in which the grooves 31 in the piezoelectric thin film 11 between each electrode body 12 are 0.2 μm deep (hereinafter also referred to as "Grooved depth = 0.2 μm"), one in which the grooves 31 in the piezoelectric thin film 11 between each electrode body 12 are 0.4 μm deep (hereinafter also referred to as "Grooved depth = 0.4 μm"), and one in which the grooves 31 between each electrode body 12 have through holes 11 a penetrating the piezoelectric thin plate 11 (hereinafter also referred to as "Penetrated"). Here, the Euler angles of the piezoelectric thin plate 11 were (90°, 90°, 40°), each electrode body 12 and floating electrode 13 were made of Al with a thickness of 0.05 μm, and each electrode body 12 had a width of 40 μm.

[0073] 14(a) and 14(b), all of the acoustic wave devices 10 have relatively excellent impedance ratios and bandwidths. However, it was confirmed that the acoustic wave device with a grooved depth of 0.2 μm had a smaller impedance ratio than the other devices. It was also confirmed that the penetrating device had the largest impedance ratio, at 82 dB. It was also confirmed that the bandwidths were almost the same regardless of whether or not the grooves 31 were present.

[0074] Furthermore, as shown in FIG. 14( a ), it was confirmed that larger spurious responses were generated in the grooved depths of 0, 0.2 μm, and 0.4 μm than in the penetrated case.

[0075] 15(a), the acoustic wave device 10 may have a cover layer 32 provided to cover the surface of the floating electrode 13 opposite to the piezoelectric thin plate 11. Also, as shown in Fig. 15(b), the acoustic wave device 10 may have a cover layer 32 provided to cover the surface of the floating electrode 13 opposite to the piezoelectric thin plate 11 and the surface of each electrode body 12 opposite to the piezoelectric thin plate 11. The cover layer 32 may be made of any material as long as it has a good temperature coefficient of frequency (TCF), good heat dissipation, or good energy trapping performance, and may be made of, for example, SiO ２ , Si, SiC, HfO ２ , AlN, Si ３ N ４ , Al ２ O ３ Alternatively, it is preferably made of diamond.

[0076] In this case, the cover layer 32 can protect the floating electrode 13 and each electrode body 12, thereby maintaining the performance of the acoustic wave device 10. The cover layer 32 can also perform temperature compensation and reduce energy loss. For example, as shown in FIG. 15, the cover layer 32 can be made of SiO ２ In this case, good frequency-temperature characteristics can be realized, and temperature compensation is possible. Furthermore, by adjusting the thickness of the cover layer 32, the floating electrode 13, and each electrode body 12, it is possible to effectively excite a higher-order mode of thickness-shear vibration.

[0077] [Acoustic Wave Device with Acoustic Multilayer Film: When the Piezoelectric Thin Plate is LN] Using the acoustic wave device 10 having the acoustic multilayer film 23 shown in FIGS. 3( a) and 3(b), the piezoelectric thin plate 11 was made of LN with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 were (90°, 90°, ψ), the electrode bodies 12 and the floating electrode 13 were made of Al with a thickness of 0.05 μm, and the low acoustic impedance layer 23 a was made of SiO ２ FIG. 16 is a graph showing the relationship between the impedance ratio and the band and ψ when the high acoustic impedance layer 23b is made of W and the number of pairs of the low acoustic impedance layer 23a and the high acoustic impedance layer 23b is three.

[0078] As shown in Figure 16, it was confirmed that the impedance ratio of the acoustic wave device 10 when the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, ψ) is maximum when ψ is approximately 38°, 89 dB or more when ψ is 36° to 40°, approximately 88 dB or more when ψ is 34° to 42°, approximately 86 dB or more when ψ is 32° to 46°, and approximately 84 dB or more when ψ is 28° to 50°.

[0079] Furthermore, as shown in Figure 16, it was confirmed that when the Euler angles of the piezoelectric thin plate 11 of the acoustic wave device 10 are (90°, 90°, ψ), the bandwidth does not change significantly within the range of ψ from 20° to 60°, and is approximately 22% to 25%.

[0080] It has also been confirmed that when the Euler angles of the piezoelectric thin plate 11 of the acoustic wave device 10 are (30°, 90°, ψ), the impedance ratio is maximized when ψ is approximately 142°, and the bandwidth does not change significantly when ψ is in the range of 120° to 160°.

[0081] The low acoustic impedance layer 23a of the acoustic multilayer film 23 is made of SiO ２ The acoustic wave device 10 in which the high acoustic impedance layer 23a is made of SiO2 / W (hereinafter also referred to as "SMR-SiO2 / W"), and the low acoustic impedance layer 23a is made of SiO2 / W. ２ The high acoustic impedance layer 23b is made of HfO ２ FIG. 17 shows the frequency characteristics of the acoustic wave device 10 (hereinafter also referred to as "SMR-SiO2 / HfO2") when made of SMR-SiO2 / HfO2. Here, the piezoelectric thin plate 11 is made of LN with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 41°), each electrode body 12 is made of Al with a thickness of 0.1 μm, the width of each electrode body 12 is 1.5 μm, the floating electrode 13 is made of Al with a thickness of 0.05 μm, and the number of pairs of low acoustic impedance layer 23a and high acoustic impedance layer 23b is three. In addition, the SiO ２ The thickness of the W layer was set to 0.21 μm, and the thickness of the SiO layer of SMR-SiO2 / HfO2 was set to 0.21 μm. ２ The layer thickness is 0.23 μm, HfO ２The thickness of the layers was set to 0.25 μm. For comparison, the frequency characteristics without the acoustic multilayer film 23 (the structure shown in FIG. 1; hereinafter, also referred to as "Film type") are also shown in the figure.

[0082] As shown in Figure 17, the SMR-SiO2 / W acoustic wave device 10 had an impedance ratio of 86 dB and a bandwidth of 22.3%, while the SMR-SiO2 / HfO2 acoustic wave device 10 had an impedance ratio of 84 dB and a bandwidth of 21.4%. The comparative film-type acoustic wave device 10 also had an impedance ratio of 90 dB and a bandwidth of 31.3%. Thus, the presence of the acoustic multilayer film 23 resulted in a slightly lower impedance ratio and a slightly narrower bandwidth than the presence of a space instead of the acoustic multilayer film 23, but it can be said to have relatively high performance. It was also confirmed that the presence of the acoustic multilayer film 23 resulted in a smaller spurious response than the presence of a space instead of the acoustic multilayer film 23.

[0083] In order to determine the optimal layer thicknesses of the low acoustic impedance layer 23a and the high acoustic impedance layer 23b in the structure of the acoustic wave device 10 shown in Figure 17, the thickness of each layer was changed and the impedance ratio and bandwidth were determined. The relationship between the thickness of each layer, the impedance ratio, and the bandwidth of the SMR-SiO2 / W acoustic wave device 10 is shown in Figure 18. Furthermore, the relationship between the thickness of each layer, the impedance ratio, and the bandwidth of the SMR-SiO2 / HfO2 acoustic wave device 10 is shown in Figure 19.

[0084] When the thicknesses of the low acoustic impedance layer 23a and the high acoustic impedance layer 23b are within the elliptical ranges shown in FIGS. 18(a) and 19(a), the impedance ratio is large. When the thicknesses are within the elliptical ranges shown in FIGS. 18(c) and 19(c), the impedance ratio is large. ２ When the thickness of the W layer is 0.17 to 0.26 μm and the thickness of the SiO layer is 0.1 to 0.29 μm, ２ Layer thickness: 0.21-0.27 μm, HfO ２It was confirmed that the impedance ratio was even larger when the layer thickness was 0.1 to 0.3 μm. In addition, within these ranges, it was confirmed that the bandwidth was also relatively wide, as shown in Figures 18(b) and 18(d) and Figures 19(b) and 19(d).

[0085] The low acoustic impedance layer 23a is made of SiO ２ The high acoustic impedance layer 23b is made of HfO ２ Using an acoustic wave device 10 (SMR-SiO2 / HfO2) made of a material, frequency characteristics were obtained by varying the number of pairs of low acoustic impedance layers 23a and high acoustic impedance layers 23b from 1 pair to 5 pairs. The obtained frequency characteristics and the relationship between the number of pairs and the impedance ratio are shown in Figures 20(a) and (b), respectively. Here, the piezoelectric thin plate 11 was made of LN with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 were (90°, 90°, 40°), each electrode body 12 was made of Al with a thickness of 0.1 μm, each electrode body 12 had a width of 1.5 μm, and the floating electrode 13 was made of Al with a thickness of 0.05 μm. The SiO2 / HfO2 acoustic multilayer film 23 ２ The layer thickness is 0.23 μm, HfO ２ The layer thickness was 0.25 μm.

[0086] 20(a) and 20(b), it was confirmed that the impedance ratio increases as the number of pairs of low acoustic impedance layers 23a and high acoustic impedance layers 23b increases, and becomes 90 dB or more when the number of pairs is 4 or more. Furthermore, as shown in FIG. 20(a), it was confirmed that the bandwidth hardly changes even when the number of pairs is changed.

[0087] [Acoustic Wave Device Having Acoustic Multilayer Film: When the Piezoelectric Thin Plate is LT] The acoustic wave device 10 having the acoustic multilayer film 23 shown in FIGS. 3(a) and 3(b) was used, and the low acoustic impedance layer 23a of the acoustic multilayer film 23 was made of SiO ２ The acoustic wave device 10 in which the high acoustic impedance layer 23a is made of SiO2 / W (hereinafter also referred to as "SMR-SiO2 / W"), and the low acoustic impedance layer 23a is made of SiO2 / W. ２ The high acoustic impedance layer 23b is made of HfO ２The frequency characteristics of the acoustic wave device 10 (hereinafter also referred to as "SMR-SiO2 / HfO2") when made of SMR-SiO2 / HfO2 are shown in Figure 21. Here, the piezoelectric thin plate 11 is LT with a thickness of 0.5 μm, the Euler angles of the piezoelectric thin plate 11 are (90°, 90°, 40°), each electrode body 12 is made of Al with a thickness of 0.1 μm, the width of each electrode body 12 is 1 μm, the floating electrode 13 is made of Al with a thickness of 0.05 μm, and the number of pairs of low acoustic impedance layer 23a and high acoustic impedance layer 23b is three. In addition, the SiO2 of SMR-SiO2 / W ２ The thickness of the W layer was set to 0.23 μm, the thickness of the SiO layer was set to 0.22 μm, and the thickness of the SiO layer of the SMR-SiO2 / HfO2 ２ The layer thickness is 0.23 μm, HfO ２ The thickness of the layer was set to 0.22 μm. For comparison, the figure also shows the frequency characteristics of a device without the acoustic multilayer film 23 and with through holes 11 a where grooves 31 between each electrode body 12 penetrate the thin piezoelectric plate 11 (hereinafter also referred to as "Penetrated"), and a device without grooves 31 in the thin piezoelectric plate 11 between each electrode body 12 (hereinafter also referred to as "No groove"). Note that the device with the acoustic multilayer film 23 does not have grooves in the thin piezoelectric plate 11 between each electrode body 12.

[0088] As shown in Figure 21, the SMR-SiO2 / W acoustic wave device 10 had an impedance ratio of 80 dB and a bandwidth of 8.4%, while the SMR-SiO2 / HfO2 acoustic wave device 10 had an impedance ratio of 79 dB and a bandwidth of 8.3%. Furthermore, the comparative example, the penetrated acoustic wave device 10, had an impedance ratio of 82 dB and a bandwidth of 10.6%, while the no-groove acoustic wave device 10 had an impedance ratio of 77 dB and a bandwidth of 10.6%. Thus, while the acoustic multilayer film 23 provided a slightly narrower bandwidth than the case where a space was used instead of the acoustic multilayer film 23, the impedance ratio was nearly the same, indicating relatively high performance. It was also confirmed that the spurious response was smaller when the acoustic multilayer film 23 was used than when a space was used instead of the acoustic multilayer film 23.

[0089] In order to determine the optimal layer thicknesses of the low acoustic impedance layer 23a and the high acoustic impedance layer 23b in the structure of the acoustic wave device 10 shown in Figure 21, the thickness of each layer was changed and the impedance ratio and bandwidth were determined. The relationship between the thickness of each layer, the impedance ratio, and the bandwidth of the SMR-SiO2 / W acoustic wave device 10 is shown in Figure 22. Furthermore, the relationship between the thickness of each layer, the impedance ratio, and the bandwidth of the SMR-SiO2 / HfO2 acoustic wave device 10 is shown in Figure 23.

[0090] When the thickness of each of the low acoustic impedance layer 23a and the high acoustic impedance layer 23b is within the elliptical ranges of FIGS. 22(a) and 23(a) (in FIG. 22(a), SiO ２ When the thickness of the W layer is 0.1 to 0.3 μm, the thickness of the SiO ２ Layer thickness: 0.22-0.29 μm, HfO ２ It was confirmed that the impedance ratio was large when the layer thickness was 0.11 to 0.3 μm. In addition, it was confirmed that within these ranges, the bandwidth was also relatively wide, as shown in Figures 22(b) and 23(b).

[0091] [Example Using Macro Device] To confirm the validity of the results of each of the above examples, an acoustic wave device (hereinafter also referred to as a "macro device") was fabricated by enlarging the size of the acoustic wave device 10, and its frequency characteristics were measured. The macro device 40 was fabricated as follows. As shown in FIG. 24( a), an LN substrate with a thickness of 350 μm, a diameter of 100 mm, and Euler angles of (90°, 90°, 40°) was first prepared as the piezoelectric plate 41, and cut into a 20 mm × 45 mm rectangle. Next, as shown in FIG. 24( b), a Cu film was formed on one surface of the piezoelectric plate 41 to a thickness of 1 μm as the electrode 42. After the Cu electrode 42 was formed, eight grooves 43 were machined at predetermined intervals from the Cu electrode 42 to the piezoelectric plate 41 using a dicing blade along the width direction of the piezoelectric plate 41, as shown in FIG. 24( c). The groove 43 was 0.2 mm wide and 270 μm deep, and the Cu electrode 42 was divided into nine electrodes 4.8 mm wide and 20 mm long. Furthermore, as shown in FIG. 24( d ), a Cu film was formed to a thickness of 1 μm on the entire other surface of the piezoelectric plate 41 as a floating electrode 44.

[0092] The manufactured microdevice 40 has a piezoelectric body 41 that is approximately 1,000 times thicker than the piezoelectric thin plate 11 of the acoustic wave device 10, resulting in an excitation vibration frequency that is approximately 1,000 times lower. In other words, the frequency in the acoustic wave device 10 is on the order of GHz, whereas in the macrodevice 40 it is on the order of MHz. However, the thickness of the electrode 42 should also be scaled to match the piezoelectric plate 41. In this case, for example, each electrode body 12 that is 50 nm thick in the acoustic wave device 10 would be 50 μm thick in the macrodevice 40, making film formation difficult. For this reason, the thickness of the Cu electrode 42 in the macrodevice 40 is 1 μm. Taking density into consideration, a Cu electrode 42 with a thickness of 1 μm is equivalent to an Al electrode with a thickness of 3.3 μm.

[0093] The frequency characteristics of thickness-shear vibration were measured using the macrodevice 40 shown in FIG. 24(d). In the measurement, voltages were applied to two of the nine electrodes 42 from one end so that the voltage phases were opposite to each other. Measurement results up to 50 Hz are shown in FIG. 25(a), and measurement results up to 200 Hz are shown in FIG. 25(b). Simulation results are also shown in FIG. 25(a). As shown in FIG. 25(a), it was confirmed that the measurement results and simulation results were in good agreement with respect to the frequency and bandwidth of thickness-shear vibration. Furthermore, as shown in FIG. 25(b), it was confirmed that higher modes of thickness-shear vibration were excited up to at least the high-frequency region of 200 Hz.

[0094] FIG. 26(a) shows enlarged views of the measurement and simulation results for the first-order thickness-shear vibration mode, among the results shown in FIG. 25(a). Also, FIGS. 26(b) to 26(d) show enlarged views of the measurement results for the third-order, fifth-order, and seventh-order thickness-shear vibration modes, respectively. As shown in FIG. 26(a), the first-order thickness-shear vibration mode had a bandwidth of 30.2% and an impedance ratio of 78.6 dB, demonstrating a particularly wide bandwidth. As shown in FIGS. 26(b) to 26(d), the third-order, fifth-order, and seventh-order thickness-shear vibration modes also demonstrated relatively wide bandwidths. While many spurious responses were observed in the measurement results, it is believed that these can be suppressed by optimizing the length and width and thickness of each electrode 42, optimizing the width and depth of the groove 43, or by completely penetrating the groove 43.

[0095] [Method of Manufacturing Acoustic Wave Device - Part 1] The acoustic wave device 10 according to the embodiment of the present invention can be manufactured, for example, by the method shown in FIG. 27 . Specifically, first, as shown in FIG. 27( a), a piezoelectric substrate 51 and a supporting substrate 52 are bonded (wafer bonding). This bonding can be achieved, for example, by direct bonding. After bonding, as shown in FIG. 27( b), the piezoelectric substrate 51 is polished to a thickness predetermined depending on the frequency of the excited wave and the material of the piezoelectric substrate 51, thereby forming the piezoelectric thin plate 11. Smart Cut technology may be used before polishing to thin the piezoelectric substrate 51. For example, when using LN to excite a 5 GHz wave, the thickness is reduced to approximately 400 nm. Mechanical polishing, chemical mechanical polishing, or other polishing methods can be used for polishing.

[0096] After forming the piezoelectric thin plate 11, as shown in FIG. 27( c), through-holes 11 a are formed in the piezoelectric thin plate 11 by etching. For example, ion milling can be used for etching. The etching pattern can be formed by the steps of photoresist coating, lithography, and development. After forming the through-holes 11 a, as shown in FIG. 27( d), each electrode body 12 is formed on the piezoelectric thin plate 11 by electron beam (EB) evaporation or sputtering. The electrode pattern can be formed by the steps of photoresist coating, lithography, and development.

[0097] After forming each electrode body 12, as shown in FIG. 27( e), the support substrate 52 is etched from the side opposite the electrode bodies 12 by deep reactive ion etching (DRIE) to form the support substrate 14. Furthermore, a floating electrode 13 is formed on the surface of the piezoelectric thin plate 11 opposite the electrode bodies 12 by electron beam evaporation or sputtering. This completes the manufacture of the acoustic wave device 10 shown in FIG. 1 .

[0098] 15(a), after forming the support substrate 14 and the floating electrode 13 in FIG. 27(e), the cover layer 32 is formed on the surface of the floating electrode 13 by electron beam evaporation or sputtering. This allows the acoustic wave device 10 shown in FIG. 15(a) to be manufactured.

[0099] [Method for Manufacturing Acoustic Wave Device - Part 2] In addition to the method shown in FIG. 27 , the acoustic wave device 10 according to the embodiment of the present invention can also be manufactured by, for example, the method shown in FIG. 28 . That is, first, as shown in FIG. 28( a), a thin film 53 of electrode material is sandwiched between a piezoelectric substrate 51 and a supporting substrate 52, and the piezoelectric substrate 51 and the supporting substrate 52 are atomic diffusion bonded together. After bonding, as shown in FIG. 28( b), the piezoelectric substrate 51 is polished to a thickness predetermined depending on the frequency of the excited wave and the material of the piezoelectric substrate 51, thereby forming the piezoelectric thin plate 11. Smart Cut technology may be used before polishing to thin the piezoelectric substrate 51. For example, when using LN to excite a 5 GHz wave, the thickness is reduced to approximately 400 nm. Mechanical polishing, chemical mechanical polishing, or the like may be used for polishing.

[0100] After forming the piezoelectric thin plate 11, as shown in FIG. 28(c), through-holes 11a and electrode holes 13a are formed in the piezoelectric thin plate 11 and the thin film 53 of electrode material by etching. Ion milling, for example, can be used for etching. The etching pattern can be formed by the steps of photoresist coating, lithography, and development. Next, as shown in FIG. 28(d), each electrode body 12 is formed on the piezoelectric thin plate 11 by electron beam (EB) evaporation or sputtering. The electrode pattern can be formed by the steps of photoresist coating, lithography, and development.

[0101] After forming each electrode body 12, as shown in Fig. 28(e), the support substrate 52 is etched with xenon difluoride (XeF) through the through-holes 11a and the electrode holes 13a to form a cavity below the thin film of electrode material 53. This makes the thin film of electrode material 53 into a floating electrode 13, and also forms the support substrate 14. This completes the manufacture of the acoustic wave device 10 shown in Fig. 1.

[0102] 15(a), before bonding the piezoelectric substrate 51 and the supporting substrate 52 shown in Fig. 28(a), a thin film of the material for the cover layer 32 is formed and sandwiched between the piezoelectric substrate 51 and the supporting substrate 52 together with a thin film 53 of the electrode material. This allows the acoustic wave device 10 shown in Fig. 15(a) to be manufactured.

[0103] REFERENCE SIGNS LIST 10 Acoustic wave device 11 Piezoelectric thin plate 11a Through hole 12 Electrode body 13 Floating electrode 13a Electrode hole 14 Support substrate 21 IDT-shaped electrode 21a Electrode finger (electrode body) 21b Bus bar 22a, 22b Ladder-shaped electrode 23 Acoustic multilayer film 23a Low acoustic impedance layer 23b High acoustic impedance layer 23c Adhesive layer 31 Groove 32 Cover layer 40 Macrodevice 41 Piezoelectric plate 42 (Cu) electrode 43 Groove 44 Floating electrode 51 Piezoelectric substrate 52 Support substrate 53 Thin film of electrode material

Claims

1. LiNbO ３ and LiTaO ３ an Euler angle (φ, θ, ψ) of the piezoelectric thin plate, when the arrangement direction of the electrode bodies is ψ, is either one of (90°±10°, 90°±10°, 6° to 56°) and (30°±10°, 90°±10°, 124° to 174°), or an Euler angle that is crystallographically equivalent to either one of these, and the elastic wave device is configured to excite a fundamental mode or a higher mode of thickness-shear vibration.

2. The acoustic wave device according to claim 1, wherein each electrode body is configured so that a voltage can be applied thereto so that the phases of adjacent electrode bodies are opposite to each other.

3. The elastic wave device of claim 1, characterized in that each electrode body is configured such that, of the lined-up electrode bodies, a plurality of electrode bodies are electrically connected from one end to form a first electrode group, and the remaining plurality of electrode bodies are electrically connected from the other end to form a second electrode group, and a voltage is applied so that the voltage phases of the first electrode group and the second electrode group are opposite to each other.

4. The acoustic wave device according to claim 1, wherein the surface of said floating electrode opposite said piezoelectric thin plate is in contact with a space.

5. The acoustic wave device according to claim 1, further comprising an acoustic multilayer film provided on the surface of said floating electrode opposite said piezoelectric thin plate.

6. The acoustic multilayer film is formed by alternately laminating low acoustic impedance layers having a relatively low acoustic impedance and high acoustic impedance layers having a high acoustic impedance, and the low acoustic impedance layers are made of SiO ２ or Al, and the high acoustic impedance layer is W, Pt or HfO ２ The acoustic wave device according to claim 5 , comprising:

7. The acoustic wave device according to claim 6, wherein the acoustic multilayer film is formed by laminating four or more pairs of one low acoustic impedance layer and one high acoustic impedance layer.

8. The acoustic wave device according to claim 1, wherein the piezoelectric thin plate has a groove or a through hole extending through to the other surface between adjacent electrodes on the one surface.

9. The acoustic wave device according to claim 5, wherein the piezoelectric thin plate has the through hole, and the floating electrode has an electrode hole extending through the thickness thereof so as to communicate with the through hole.

10. The piezoelectric thin plate is LiNbO ３ 10. The elastic wave device according to claim 1, characterized in that it is made of a single crystal of 0.1 mm×0.1 mm and has Euler angles of either (90°±10°, 90°±10°, 41°±10°) and (30°±10°, 90°±10°, 139°±10°), or Euler angles crystallographically equivalent to either one of these.

11. The piezoelectric thin plate is LiTaO ３ 10. The elastic wave device according to claim 1, characterized in that it is made of a single crystal of 0.1 mm×0.1 mm and has Euler angles of either (90°±10°, 90°±10°, 43.5°±10°) or (30°±10°, 90°±10°, 136.5°±10°), or an Euler angle crystallographically equivalent to either one of these.

12. SiO ２ , Si, SiC, HfO ２ , AlN, Si ３ N ４ , Al ２ O ３ or diamond, and provided to cover at least one of the surface of the floating electrode opposite the piezoelectric thin plate and the surface of each electrode body opposite the piezoelectric thin plate.

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