Elastic wave device

Abstract

Provided is an elastic wave device that can achieve good characteristics in an ultrahigh frequency band of 6 GHz or more and that can ensure sufficient mechanical strength. The elastic wave device has a piezoelectric substrate (11), an electrode (12) disposed in contact with the piezoelectric substrate (11), and an acoustic multilayer film (13) disposed in contact with the piezoelectric substrate (11) and / or the electrode (12), and is configured to utilize a high-order mode in a resonance characteristic of a bulk wave. The acoustic multilayer film (13) has a low acoustic impedance film (13a) and a high acoustic impedance film (13b) alternately laminated.

Description

Technical Field

[0001] This invention relates to an elastic wave device. Background Technology

[0002] In recent years, the 700MHz to 3GHz frequency band, which is mainly used for smartphones and other devices, has nearly 80 bands and is very mixed. As a countermeasure, the 3.6GHz to 4.9GHz frequency band is planned to be used in the fifth generation mobile communication system (5G), and the frequency band above 6GHz is planned to be used in the subsequent sixth generation.

[0003] Previously, in the 700MHz to 3GHz frequency band, piezoelectric thin films were used to create surface wave (SAW) devices using LiTaO3 crystals (LT) and LiNbO3 crystals (LN), as well as bulk wave elastic wave (FBAR) devices (film bulk acoustic resonators). However, regarding the frequency f of SAW devices, if the sound velocity of the substrate is set to V and the period (spacing) of the curtain electrodes is set to pitch, the frequency f of the SAW device is determined by f = V / pitch. Therefore, based on the limits of sound velocity and spacing, 3.5GHz is the limit on the high-frequency side.

[0004] On the other hand, FBAR devices using piezoelectric thin films for bulk elastic waves include: cavity-type FBARs requiring cavities above and below the piezoelectric thin film; and acoustic multilayer film structure FBARs, wherein the cavity on one side of the piezoelectric thin film is replaced by an acoustic multilayer film and a holding substrate. Furthermore, cavity-type FBARs include: structures using piezoelectric thin films of AlN or ScAlN (for example, see Non-Patent Document 1 or 2); and structures using single-crystal thin plates of LN (for example, see Non-Patent Document 3). In the former cavity-type FBAR, since the AlN or ScAlN films are c-axis oriented, the vibration mode of the bulk wave used is only longitudinal vibration. For the sound velocity of this longitudinal wave, (c33...) D / density) 1 / 2 To represent (c33) D The elastic stiffness constant (which is the constant of elasticity) is, strictly speaking, reduced by the mass load of the electrode for the excitation frequency, but can be roughly expressed as the speed of sound / (2 × film thickness). Therefore, to achieve a high excitation frequency, the thickness of the piezoelectric film must be extremely thin. Furthermore, in cavity-type FBARs using a single-crystal thin substrate with LN, the excitation frequency is inversely proportional to the substrate thickness; therefore, to achieve a high excitation frequency, the thickness of the piezoelectric film must also be extremely thin. In the cavity-type FBARs described in Non-Patent Documents 1 to 3, when the thickness of the piezoelectric film is 0.9–2 μm, an excitation frequency of approximately 2 GHz and an impedance ratio of approximately 60 dB are obtained.

[0005] However, in these cavity-type FBARs, AlN and ScAlN are used as piezoelectric films. Since these are polycrystalline films, they result in significant attenuation at ultra-high frequencies, making it difficult to achieve good characteristics. For example, it has been confirmed that in cavity-type FBARs using AlN, an impedance ratio of 70 dB is obtained at 2 GHz, but at 5 GHz, the impedance ratio decreases to 50 dB (for example, see Non-Patent Literature 4 or 5).

[0006] Furthermore, as a multilayer acoustic diaphragm structure FBAR for use at high frequencies, a scheme has been proposed, which has a structure consisting of: a piezoelectric thin film made of ZnO (thickness t = wavelength / 2), a multilayer acoustic diaphragm with multiple acoustic diaphragms stacked on top of each other, and a holding substrate (for example, see Non-Patent Document 6). In this elastic wave device, in order to increase the excitation of the fundamental mode, the thickness of each acoustic diaphragm is set to half the thickness of the piezoelectric thin film (i.e., wavelength / 4). In this elastic wave device, the vibration mode of the bulk wave is also longitudinal vibration of the thickness, but at 3 GHz of the fundamental mode, only an impedance ratio of 21 dB can be obtained through actual measurement. The characteristics are worse than those of a cavity-type FBAR made of AlN film, so it has not yet been put into practical use.

[0007] Furthermore, as a structure that achieves a higher resonant frequency through a multilayer acoustic anodizing (FBAR) structure, a high-order mode thin-film resonator has been developed. This resonator comprises a piezoelectric thin film disposed between upper and lower electrodes. This piezoelectric thin film is stacked with: a first piezoelectric layer composed of either ZnO or AlN, and oriented in a direction approximately parallel to the surface of the piezoelectric thin film; and a second piezoelectric layer oriented in a direction 180° different from the first piezoelectric layer (see, for example, Patent Document 1). According to this resonator, the resonant frequency is twice that of existing structures with the same piezoelectric thin film thickness.

[0008] Existing technical documents

[0009] Non-patent literature

[0010] Non-patent document 1: John D.Larson III et al., "Power Handling and TemperatureCoefficient Studies in FBAR Duplexers for the 1900MHz PCS Band", Proc.IEEEUltrason.Symp., 2000, p.869-874

[0011] Non-patent literature 2: Keiichi Umeda et al., “PIEZOELECTRIC PROPERTIES OF ScAlNTHIN FILMS FOR PIRZO-MEMS DEVICES”, Proc. MEMS (Taipei, Taiwan, China), 2013, pp. 20-24.

[0012] Non-Patent Document 3: Tomoyoshi Tai, et al., “Development of Single-Crystal FBAR Using LiNbO3 and LiTaO3”, Proceeding of Symposium on Ultrasonic Electronics, 2007, Vol. 28, pp. 151-152

[0013] Non-patent literature 4: Tsuyoshi Yokoyama et al., “Highly Piezoelectric Co-Doped AlN Thin Films for Wideband FBAR Applications”, IEEE Trans. Ultrason. Ferroelectr. & Freq. Control, June 2015, Vol. 62, No. 6, pp. 1007-1015

[0014] Non-patent literature 5: T. Nishihara et al., “High Performance and Miniature ThinFilm Bulk Acoustic Wave Filters for 5GHz”, 2002 IEEE ULTRASONICS SYMPOSIUM, pp. 969-972

[0015] Non-Patent Literature 6: Hideaki Kobayashi et al., “Fabrication of Piezoelectric Thin Film Resonators with Acoustic Quarter-Wave Multilayers”, Japan, J. Appl. Phys., 2002, Vol. 40, pp. 3455-3457

[0016] Patent documents

[0017] Patent Document 1: Japanese Patent Application Publication No. 2007-36915 Summary of the Invention

[0018] (a) Technical problems to be solved

[0019] For the cavity-type FBAR described in Non-Patent Documents 1 and 2, and the acoustic multilayer FBAR described in Non-Patent Document 6, the following problems exist: the impedance ratio decreases to 50dB at 5GHz and 3GHz respectively, and a good impedance ratio cannot be obtained in the ultra-high frequency band above 6GHz. Furthermore, for the cavity-type FBAR described in Non-Patent Documents 1 to 3, the piezoelectric film is extremely thin (0.3–0.6μm) in the ultra-high frequency band above 6GHz, thus making it difficult to ensure mechanical strength. In particular, the cavity-type FBAR described in Non-Patent Document 3, because the piezoelectric film is an LN single-crystal thin plate, cannot ensure mechanical strength compared to polycrystalline films, thus hindering its practical application.

[0020] As a multilayer acoustic thin-film resonator (FBAR), compared to the cavity-type FBAR using the fundamental wave described in Non-Patent Documents 1 to 3, the piezoelectric film thickness is twice that of the high-order mode thin-film resonator described in Patent Document 1 at the same resonant frequency. However, the two piezoelectric layers constituting the piezoelectric film have the same thickness as existing piezoelectric films. Therefore, in the ultra-high frequency band above 6 GHz, the following problems exist: each piezoelectric layer is extremely thin, making it difficult to ensure their mechanical strength. In addition, even if the piezoelectric film is twice as thick in the ultra-high frequency band above 6 GHz, it is still very thin, so it is also difficult to ensure the mechanical strength of the piezoelectric film itself. Furthermore, even at a frequency of 560 MHz, only an impedance ratio of 12 dB can be obtained, and at 6 GHz, the impedance ratio is even smaller, thus making it difficult to put into practical use. Moreover, for the multilayer acoustic FBAR described in Non-Patent Document 6 and Patent Document 1, only a polycrystalline piezoelectric film is used, which cannot achieve good characteristics in the fundamental mode, and its frequency is below 3 GHz.

[0021] The present invention addresses the aforementioned problems and aims to provide an elastic wave device that exhibits good characteristics in the ultra-high frequency band above 6 GHz and ensures sufficient mechanical strength.

[0022] (II) Technical Solution

[0023] To achieve the above objectives, the elastic wave device of the present invention is characterized by having a piezoelectric substrate, an electrode disposed in contact with the piezoelectric substrate, and an acoustic multilayer film disposed in contact with the piezoelectric substrate and / or the electrode, and is configured to utilize a higher-order mode that is 3 or 5 times the fundamental mode of the resonant characteristics of the bulk wave, or a higher-order mode having a frequency of 3 times or more than 3 times the fundamental mode.

[0024] In the elastic wave device of the present invention, higher-order modes (harmonics) (1st, 2nd, ...) with frequencies higher than the fundamental mode (0th order) can be excited using an acoustic multilayer film. Furthermore, by setting the type of piezoelectric substrate and the thickness of each layer of the acoustic multilayer film, higher-order modes with a large impedance ratio can be obtained. The elastic wave device of the present invention can achieve excellent impedance ratio characteristics in the ultra-high frequency band above 6 GHz using this higher-order mode. In addition, by using the higher-order mode, it is not necessary to make the piezoelectric substrate extremely thin, and no cavities are required above or below the piezoelectric substrate; therefore, sufficient mechanical strength can be ensured even in the ultra-high frequency band above 6 GHz. Here, the impedance ratio is the ratio of the resonant impedance Zr at the resonant frequency to the anti-resonant impedance Za at the anti-resonant frequency (20 × log(Za / Zr)).

[0025] In the elastic wave device of the present invention, it is preferable that the electrode is composed of two or more electrodes. Furthermore, the electrode may cover an entire surface of the piezoelectric substrate or a portion of the piezoelectric substrate. Additionally, the planar shape of the electrode can be any shape such as circular, polygonal, or elliptical. Furthermore, the elastic wave device of the present invention can have a structure with electrodes on both sides of the piezoelectric substrate, or it can have a structure with two resonators connected in series, i.e., a common electrode between the piezoelectric substrate and the acoustic multilayer film, and two electrodes on the surface of the piezoelectric substrate opposite to the acoustic multilayer film. Alternatively, multiple electrodes may be provided on one or both sides of the piezoelectric substrate, and three or more resonators may be formed on the piezoelectric substrate. By connecting them in series and / or parallel, a ladder filter or a multimode filter can be formed. Furthermore, the piezoelectric substrate may also include a piezoelectric thin film or a piezoelectric plate.

[0026] In the elastic wave device of the present invention, it is preferable that the acoustic multilayer film alternately stacks low acoustic impedance films and high acoustic impedance films. Particularly preferably, in the acoustic multilayer film, low acoustic impedance films and high acoustic impedance films are alternately and continuously stacked, with 3 or more layers and 20 or fewer layers. Furthermore, in this case, it is preferable that the thickness of at least 3 of the low acoustic impedance films and high acoustic impedance films in the acoustic multilayer film is 0.016 to 0.11 wavelengths of the bulk wave, and preferably, the acoustic impedance film is formed in a layer close to the piezoelectric substrate. Alternatively, the acoustic multilayer film may have 1 or more layers of the low acoustic impedance film and 2 or more layers of the high acoustic impedance film, wherein the thickness of the 1 layer of the low acoustic impedance film, or the sum of the average thickness of any two low acoustic impedance films and the average thickness of any two high acoustic impedance films, is 0.07 to 0.15 wavelengths of the bulk wave. Thus, higher-order modes can be excited at a frequency approximately 3 times or more of the fundamental mode. Furthermore, the wavelength of the bulk wave is defined as 2 × (thickness of the piezoelectric substrate). It can also be defined as the effective thickness (t+mt) obtained by adding the thickness t of the piezoelectric substrate to the average thickness mt of the electrodes on both sides of the piezoelectric substrate.

[0027] In the elastic wave device of the present invention, preferably, the low acoustic impedance films and / or high acoustic impedance films of the acoustic multilayer film are, for example, composed of Mg alloy, SiO2, Al, Si, Ge, Ti, ZnO, Si x N y SiO x F y (Here, x and y are positive real numbers), and the film is composed of at least one of AlN, SiC, Al2O3, Ag, Hf, TiO2, Ni, Au, Ta, Mo, Pt, W, and Cu, or an oxide film, nitride film, carbide film, or iodide film containing at least one of them. The low acoustic impedance film can be composed of a material whose acoustic impedance is smaller than that of the adjacent high acoustic impedance film.

[0028] In the elastic wave device of the present invention, it is preferable that the piezoelectric substrate is composed of a single crystal of LiNbO3, LiTaO3, Li2B4O7, or lanthanum gallium silicate. In this case, it is easy to excite higher-order modes. Furthermore, for c-axis oriented piezoelectric polycrystalline films such as AlN and ScAlN used in FBAR, it is difficult to excite higher-order modes due to their small piezoelectric constants. In addition, for single-crystal piezoelectric substrates such as LiNbO3 (LN) and LiTaO3 (LT), the coupling coefficient is larger, which is different from that of polycrystalline films, allowing the use of arbitrary azimuth angles. Therefore, in addition to utilizing the thickness longitudinal vibration of the bulk wave, it is also possible to use the thickness shear vibration utilizing the transverse wave.

[0029] Regarding the elastic wave device of the present invention, in order to obtain a larger impedance ratio, when utilizing the thickness shear vibration of a piezoelectric substrate made of LiNbO3 crystal, it is preferable that the Euler angle of the piezoelectric substrate is any one of (0°±5°, 66.5°~82°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them. More preferably, the Euler angle is (0°±5°, 70°~81°, 0°~180°), or a crystallographically equivalent Euler angle. Even more preferably, the Euler angle is (0°±5°, 72°~78°, 0°~180°), or a crystallographically equivalent Euler angle.

[0030] Furthermore, in the case of utilizing the thickness longitudinal vibration of the piezoelectric substrate made of LiNbO3 crystal, in order to obtain a larger impedance ratio, it is preferable that the Euler angle of the piezoelectric substrate is (0°±5°, 119°~133°, 0°~180°) or a crystallographically equivalent Euler angle, and more preferably, the Euler angle is (0°±5°, 123°~129°, 0°~180°) or a crystallographically equivalent Euler angle.

[0031] Furthermore, in the case of utilizing the thickness shear vibration of a strip-type piezoelectric substrate made of LiNbO3 crystal, in order to obtain a larger impedance ratio, it is preferable that the Euler angle of the piezoelectric substrate is (0°±5°, -123° to -80°, 0° to 180°) or a crystallographically equivalent Euler angle, and more preferably, the Euler angle is (0°±5°, -112° to -90°, 0° to 180°) or a crystallographically equivalent Euler angle.

[0032] Regarding the elastic wave device of the present invention, in order to obtain a larger impedance ratio, when utilizing the thickness shear vibration of a piezoelectric substrate made of LiTaO3 crystal, it is preferable that the Euler angle of the piezoelectric substrate is any one of (0°±5°, 56°~96°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them. More preferably, the Euler angle is (0°±5°, 62°~93°, 0°~180°), or a crystallographically equivalent Euler angle.

[0033] Furthermore, in the case of utilizing the thickness longitudinal vibration of a piezoelectric substrate made of LiTaO3 crystal, in order to obtain a larger impedance ratio, it is preferable that the Euler angle of the piezoelectric substrate is (0°±5°, 112°~138°, 0°~180°) or the Euler angle that is crystallographically equivalent to it.

[0034] Furthermore, in the case of using the thickness shear vibration of a strip-type piezoelectric substrate made of LiTaO3 crystal, in order to obtain a larger impedance ratio, it is preferable that the Euler angle of the piezoelectric substrate is any one of (0°±5°, 63°~91°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them.

[0035] Regarding the elastic wave device of the present invention, it is preferable to have a holding substrate disposed on the side of the acoustic multilayer film opposite to the piezoelectric substrate, such that the acoustic multilayer film is sandwiched between the piezoelectric substrate and the piezoelectric substrate. The holding substrate can be made of any material as long as it can support the piezoelectric substrate, the electrodes, and the acoustic multilayer film, for example, it can be made of a Si substrate, a crystal substrate, a sapphire substrate, a glass substrate, a quartz substrate, a germanium substrate, an alumina substrate, etc.

[0036] Regarding the elastic wave device of the present invention, in order to obtain a larger impedance ratio, the piezoelectric substrate can be composed of two overlapping components. In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In the other piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ), and the Euler angles of the lower surface are (φ, θ, ψ). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ+180°) and the Euler angles of the lower surface are (φ, θ, ψ+180°). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ) and the Euler angles of the lower surface are (φ, θ+180°, ψ). In another piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ+180°) and the Euler angles of the lower surface are (φ, θ+180°, ψ+180°). The piezoelectric substrate is configured to generate a higher-order mode that is approximately three or five times the length of a wave that is longitudinally vibrating using the thickness of the piezoelectric substrate. In this case, preferably, each piezoelectric substrate is composed of LiNbO3 crystal or LiTaO3 crystal, wherein the LiNbO3 crystal has φ = -5° to 5°, θ = 119° to 133°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography, and the LiTaO3 crystal has φ = -5° to 5°, θ = 112° to 138°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography. Furthermore, when two piezoelectric substrates are overlapped, the wavelength of the bulk wave is 2 × (the total thickness of the two piezoelectric substrates).

[0037] Furthermore, regarding the elastic wave device of the present invention, in order to obtain a larger impedance ratio, the piezoelectric substrate can be composed of two overlapping components. In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In the other piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ), and the Euler angles of the lower surface are (φ, θ, ψ). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ+180°), and the Euler angles of the lower surface are (φ, θ, ψ+180°). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In another piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ+180°), and the Euler angles of the lower surface are (φ, θ+180°, ψ+180°). These are configured to generate a higher-order mode approximately three or five times the second-order mode of a wave generated by shear vibration based on the thickness of the piezoelectric substrate. In this case, the piezoelectric substrate may be a strip type.

[0038] Furthermore, in this case, when using thickness shear vibration, it is preferable that each piezoelectric substrate is composed of LiNbO3 crystal or LiTaO3 crystal, wherein the LiNbO3 crystal has φ = -5° to 5°, θ = 66.5° to 82°, ψ = 0° to 180°, or φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography, and the LiTaO3 crystal has φ = -5° to 5°, θ = 56° to 96°, ψ = 0° to 180°, or φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography. In addition, when it is a strip type, preferably, each piezoelectric substrate is made of LiNbO3 crystal or LiTaO3 crystal, wherein the LiNbO3 crystal has φ = -5° to 5°, θ = -123° to -80°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography, and the LiTaO3 crystal has φ = -5° to 5°, θ = 63° to 91°, ψ = 0° to 180°, or φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, or Euler angles equivalent to them in crystallography.

[0039] Furthermore, when these piezoelectric substrates are composed of two overlapping layers, it is preferable that one or more low acoustic impedance films and two or more high acoustic impedance films are alternately stacked in the acoustic multilayer film, and the thickness of the one low acoustic impedance film or the sum of the average thickness of each of any two low acoustic impedance films and the average thickness of each of any two high acoustic impedance films is 0.02 to 0.09 wavelength of the bulk wave.

[0040] Here, Euler angles (φ, θ, ψ) are right-handed and represent the cross-section of the piezoelectric substrate and the propagation direction of the elastic wave. Specifically, relative to the crystal axes X, Y, Z of the crystal, LT, or LN constituting the piezoelectric substrate, the Z-axis is used as the rotation axis, and the X-axis is rotated counterclockwise by φ to obtain the X' axis. Next, the X' axis is used as the rotation axis, and the Z-axis is rotated counterclockwise by θ to obtain the Z' axis. At this point, the Z' axis is taken as the normal, and the surface containing the X' axis is taken as the cross-section of the piezoelectric substrate. Furthermore, the propagation direction of the elastic wave is set to the direction in which the X' axis is rotated counterclockwise by ψ using the Z' axis as the rotation axis. Additionally, the axis perpendicular to both the X' and Z' axes, obtained by moving the Y-axis through these rotations, is taken as the Y' axis.

[0041] By defining Euler angles in this way, for example, propagation in the X direction with a 40° rotating Y-plate is represented by (0°, -50°, 0°), and propagation in the X direction with a 40° rotating Y-plate at 90° is represented by (0°, -50°, 90°). Furthermore, when cutting a piezoelectric substrate with the desired Euler angles, an error of up to ±0.5° may occur relative to each component of the Euler angle. Regarding the characteristics of elastic waves, in the (φ, θ, ψ) Euler angles, there is essentially no characteristic difference caused by a deviation of ±5° for φ and ψ. Additionally, for Euler angles (0°, θ, 0°), (0°, θ+360°, 0°) are equivalent planes. On the other hand, while (0°, θ+180°, 0°) are not equivalent to (0°, θ, 0°), they represent the front and back sides of the substrate. However, when the piezoelectric substrate is used as a single board, the front and back sides exhibit the same characteristics in the elastic wave device. Therefore, the orientation of the front and back sides of the substrate is also regarded as equivalent surfaces.

[0042] (III) Beneficial Effects

[0043] According to the present invention, an elastic wave device can be provided that exhibits good characteristics in the ultra-high frequency band above 6 GHz and can ensure sufficient mechanical strength. Attached Figure Description

[0044] exist Figure 1In the diagram, (a) is a perspective view of an elastic wave device according to an embodiment of the present invention, (b) is a side view of (a), (c) is a perspective view of a modified example of the elastic wave device of (a) with two upper electrodes, (d) is a side view of (c), (e) is a perspective view of a modified example of the elastic wave device of (a) with three upper electrodes, (f) is a side view of (e), and (g) is an equivalent circuit of (e).

[0045] exist Figure 2 In the diagram, (a) is a perspective view showing a modified example of the elastic wave device according to an embodiment of the present invention, which has a long strip-shaped structure; (b) is a side view of (a); (c) is a perspective view showing a modified example of the elastic wave device of (a) with two upper electrodes; (d) is a side view of (c); (e) is a perspective view showing a modified example of the elastic wave device of (a) with a long slot-shaped cut; (f) is a side view of (e); (g) is a perspective view showing a modified example of the elastic wave device of (a) with three upper electrodes; (h) is a side view of (g); and (i) is an equivalent circuit of (g).

[0046] Figure 3 It means Figure 1 The curves shown in (a) and (b) are the frequency characteristics of thickness shear vibration of the elastic wave device with the piezoelectric substrate set as (0°, 75°, ψ)LN substrate and the average thickness of each layer of the acoustic multilayer film set as (a) 0.25 wavelength and (b) 0.05 wavelength of the excited bulk wave.

[0047] Figure 4 It means Figure 1 The graphs (a) and (b) show the correlation between the bandwidth and impedance ratio of the higher-order modes of thickness shear vibration of the elastic wave device when the piezoelectric substrate is set to (0°, θ, ψ)LN substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength.

[0048] exist Figure 5 In the middle, Figure 1 The elastic wave device shown in (a) and (b) has a piezoelectric substrate set as (0°, 75°, ψ)LN substrate. (a) is a graph showing the relationship between the thickness of the low acoustic impedance film and the impedance ratio of the higher-order mode of thickness shear vibration when the thickness of the high acoustic impedance film is set to 0.0625 wavelength. (b) is a graph showing the relationship between the thickness of the high acoustic impedance film and the impedance ratio of the higher-order mode of thickness shear vibration when the thickness of the low acoustic impedance film is set to 0.0625 wavelength. (c) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order mode of thickness shear vibration.

[0049] Figure 6 It means Figure 1 The graphs shown in (a) and (b) depict the relationship between the number of layers of the acoustic multilayer film and the impedance ratio of the higher-order modes of the thickness shear vibration when the piezoelectric substrate is set to (0°, 75°, ψ)LN substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength.

[0050] Figure 7 It means Figure 1 The graphs shown in (a) and (b) depict the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to (90°, 90°, ψ)LN substrate for the elastic wave device.

[0051] exist Figure 8 In China, regarding Figure 1 The elastic wave devices shown in (a) and (b) are shown in graphs. (a) is a graph showing the frequency characteristics of longitudinal vibration of the thickness when the piezoelectric substrate is set to (0°, 126°, ψ)LN substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. (b) is a graph showing the θ correlation between the impedance ratio of the higher-order mode of longitudinal vibration of the thickness when the piezoelectric substrate is set to (0°, θ, ψ)LN substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. (c) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order mode of longitudinal vibration of the thickness when the piezoelectric substrate is set to (0°, 126°, ψ)LN substrate.

[0052] exist Figure 9 In China, regarding Figure 2 The strip-type elastic wave device shown in (a) and (b) is a graph showing the θ correlation between the impedance ratio of the higher-order mode of thickness shear vibration when the piezoelectric substrate is set to (0°, θ, 18°) LN substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. The graph shown in (b) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order mode of thickness shear vibration when the piezoelectric substrate is set to (0°, -100°, 18°) LN substrate.

[0053] exist Figure 10 In China, regarding Figure 1The elastic wave devices shown in (a) and (b) are shown in graphs. (a) is a graph showing the θ-correlation between the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to a (0°, θ, ψ)LT substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. (b) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to a (0°, 74°, ψ)LT substrate. (c) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to a (90°, 90°, ψ)LT substrate.

[0054] exist Figure 11 In China, regarding Figure 1 The elastic wave devices shown in (a) and (b) are shown in the figure. (a) is a graph showing the θ correlation between the impedance ratio of the higher-order mode of the longitudinal vibration of the thickness when the piezoelectric substrate is set to (0°, θ, ψ)LT substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. (b) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order mode of the longitudinal vibration of the thickness when the piezoelectric substrate is set to (0°, 130°, ψ)LT substrate.

[0055] exist Figure 12 In China, regarding Figure 2 The strip-type elastic wave device shown in (a) and (b) is a graph showing the θ correlation between the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to (0°, θ, ψ)LT substrate and the average thickness of each layer of the acoustic multilayer film is set to 0.05 wavelength. (b) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to (0°, 74°, 175°)LT substrate. (c) is a graph showing the relationship between the average thickness of each layer of the acoustic multilayer film and the impedance ratio of the higher-order modes of thickness shear vibration when the piezoelectric substrate is set to (90°, 90°, 37°)LT substrate.

[0056] Figure 13 It means Figure 1 The graphs shown in (a) and (b) depict the relationship between the average thickness of any two low acoustic impedance films and the sum of the average thicknesses of two high acoustic impedance films of the elastic wave device when the piezoelectric substrate is set to (90°, 90°, ψ)LN substrate, and the impedance ratio of the higher-order mode of thickness shear vibration.

[0057] Figure 14 This is a side view showing a modified example of an elastic wave device according to an embodiment of the present invention, wherein the piezoelectric substrate is composed of two layers.

[0058] Figure 15 It means Figure 14The graph shown is a curve of the frequency characteristics of the longitudinal vibration of the thickness of the elastic wave device when the piezoelectric substrate is set to (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ)LN substrate (0°, 126°, ψ).

[0059] Figure 16 (a) means Figure 1 The graphs (a) and (b) show the frequency characteristics of the elastic wave device near the higher-order mode, approximately three times the fundamental mode of the longitudinal vibration, when the piezoelectric substrate is set to an LN substrate (0°, 126°, 0°). (b) is a graph showing the frequency characteristics of the elastic wave device near the higher-order mode, approximately three times the fundamental mode of the longitudinal vibration. Figure 15 The graph shows the frequency characteristics of the second-order mode (9.8 GHz) of the longitudinal vibration of the thickness near the approximately third-order mode of the second-order wave.

[0060] Figure 17 It means Figure 14 The elastic wave device shown is configured with the piezoelectric substrate set to (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ)LN substrate (0°, 126°, ψ), and with the piezoelectric substrate set to (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ+180°)LN substrate (0°, 126°, ψ+180°), and... Figure 1 The graphs (a) and (b) show the relationship between the thickness of the low acoustic impedance film and the impedance ratio of the higher-order mode of the longitudinal vibration of the film when the piezoelectric substrate is set to (0°, 126°, ψ)LN substrate, and the relationship between the average thickness of the low acoustic impedance film and the average thickness of the high acoustic impedance film and the impedance ratio of the higher-order mode of the longitudinal vibration of the film.

[0061] Figure 18 It means Figure 14 The elastic wave device shown has its piezoelectric substrate set as (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 254°, 0°)LN substrate (0°, 74°, 0°), (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 254°, 180°)LN substrate (0°, 74°, 180°), (0°, 74°, 0°)LN substrate (0°, 254°). When LN substrate (0°, 254°, 180°) / (0°, 74°, 180°), LN substrate (0°, 74°, 0°) / (0°, 254°, 0°) / (0°, 254°, 90°) / LN substrate (0°, 74°, 90°), and LN substrate (0°, 74°, 0°) / (0°, 74°, 90°) / LN substrate (0°, 25 ...74°, 0°) / (0°, 74°, 90°), and LN substrate (0°, 254°, 90°), and LN substrate (0°, 74°, 0°) / (0°, 74°, 90°), and L Figure 1 The graphs shown in (a) and (b) depict the relationship between the sum of the average thickness with low acoustic impedance and the average thickness with high acoustic impedance of the elastic wave device when the piezoelectric substrate is set to (0°, 74°, 0°) LN substrate and the impedance ratio of the higher-order mode of thickness shear vibration. Detailed Implementation

[0062] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0063] Figures 1 to 18 This refers to an elastic wave device according to an embodiment of the present invention.

[0064] like Figure 1 and Figure 2 As shown, the elastic wave device 10 is constructed by utilizing the higher-order modes in the resonance characteristics of body waves, and includes a piezoelectric substrate 11, an electrode 12, an acoustic multilayer film 13, and a holding substrate 14.

[0065] The piezoelectric substrate 11 is made of a single crystal of LiNbO3, LiTaO3, Li2B4O7, or lanthanum gallium silicate. The electrode 12 consists of two or more electrodes, each formed into a thin plate shape. Each electrode 12 is attached to one or more surfaces of the piezoelectric substrate 11. Each electrode 12 can be arranged to cover either the entire surface of the piezoelectric substrate 11 or only a portion of its surface. Furthermore, the planar shape of each electrode 12 can be any shape, or it can be... Figure 1 (a) shows a circle, or it can be like... Figure 1 (c) and (e) are shown as rectangular shapes.

[0066] In addition, such as Figure 1 (a), (b) Figure 2 As shown in (a), (b), (e), and (f), electrode 12 consists of a pair of electrodes, which can be respectively disposed on one surface and the other surface of piezoelectric substrate 11. Additionally, as... Figure 1 (c), (d) Figure 2 As shown in (c) and (d), the electrode 12 consists of three electrodes, forming a structure in which two resonators are connected in series. One electrode 12 is arranged to cover one surface of the piezoelectric substrate 11 as a common electrode, and the remaining two electrodes 12 are arranged side by side on the other surface of the piezoelectric substrate 11. Additionally, as... Figure 1 (e), (f) Figure 2As shown in (g) and (h), electrode 12 consists of four electrodes connected in series or parallel using three resonators. One electrode 12 is arranged to cover one surface of the piezoelectric substrate 11 as a common electrode, and the remaining three electrodes 12 are arranged side by side on the other surface of the piezoelectric substrate 11. Furthermore, the number of these electrodes 12 can be greater.

[0067] like Figure 1 and Figure 2 As shown, the acoustic multilayer film 13 is adhered to the side of the electrode 12 disposed on one surface of the piezoelectric substrate 11, opposite to the piezoelectric substrate 11. Regarding the acoustic multilayer film 13, low acoustic impedance films 13a and high acoustic impedance films 13b are alternately stacked from the side of the piezoelectric substrate 11 toward the opposite side. Furthermore, it is preferable that the low acoustic impedance films 13a and high acoustic impedance films 13b of the acoustic multilayer film 13 are alternately and continuously stacked in 3 or more layers and 20 or fewer layers. Figure 1 and Figure 2 In a specific example shown, the layer closest to the piezoelectric substrate 11 is a low acoustic impedance film 13a, which is stacked alternately and continuously with a high acoustic impedance film 13b for six layers.

[0068] Each low acoustic impedance membrane 13a and each high acoustic impedance membrane 13b, even when using either longitudinal or transverse bulk waves, is composed of a membrane containing at least one of the materials shown in Table 1 or Table 2, or an oxide, nitride, carbide, or iodide membrane containing at least one of these membranes. Furthermore, in Table 1, Zl is the acoustic impedance of the longitudinal bulk wave, and c33 is the elastic stiffness constant; in Table 2, Zs is the acoustic impedance of the transverse bulk wave, and c44 is the elastic stiffness constant. Additionally, Si in Tables 1 and 2... x N y x and y are positive real numbers.

[0069] [Table 1]

[0070] Material Density (kg·m3) C33 VI (m / s) ZI(Ns / m3) Mg alloy 1800 7.222E+10 6334 1.140E+07 SiO2 2210 7.850E+10 5960 1.317E+07 Al 2699 1.113E+11 6422 1.733E+07 Si 2329 2.365E+11 10077 2.347E+07 Ge 5323 1.26E+11 4866 2.590E+07 Ti 4510 1.661E+11 6069 2.737E+07 ZnO 5665 2.096E+11 6083 3.446E+07 <![CDATA[Si x N y ]]> 3200 3.710E+11 10767 3.446E+07 AIN 3260 3.950E+11 11008 3.588E+07 SiC 3200 4.580E+11 11963 3.828E+07 Al2O3 3800 4.170E+11 10476 3.981E+07 Ag 10500 1.527E+11 3814 4.004E+07 Hf 13310 1.380E+11 3219 4.285E+07 Cu 8930 2.106E+11 4856 4.337E+07 TiO2 4249 4.700E+11 10517 4.469E+07 Ni 8845 3.115E+11 5934 5.249E+07 Au 19300 2.202E+11 3378 6.519E+07 Ta 16678 2.668E+11 4000 6.671E+07 Mo 10219 4.696E+11 6779 6.927E+07 Pt 21400 3.356E+11 3960 8.474E+07 W 19265 5.214E+11 5202 1.002E+08

[0071] [Table 2]

[0072] Material Density (kg·m3) C44 V(m / s) Zs(Ns / m3) Mg alloy 1800 1.667E+10 3043 5.478E+06 SiO2 2210 3.120E+10 3757 8.304E+06 Al 2699 2.610E+10 3110 8.393E+06 Si 2329 7.227E+10 5570 1.297E+07 Ti 4510 4.380E+10 3116 1.405E+07 Ge 5323 4.09E+10 2771 1.475E+07 ZnO 5665 4.230E+10 2733 1.548E+07 Ag 10500 3.290E+10 1770 1.859E+07 <![CDATA[Si x N y ]]> 3200 1.130E+11 5942 1.902E+07 Hf 13310 2.847E+10 1462 1.947E+07 AlN 3260 1.180E+11 6016 1.961E+07 Cu 8930 5.140E+10 2399 2.142E+07 TiO2 4249 1.232E+11 5385 2.288E+07 SiC 3200 1.650E+11 7181 2.298E+07 Al2O3 3800 1.460E+11 6198 2.355E+07 Au 19300 2.990E+10 1245 2.402E+07 Ni 8845 9.290E+10 3241 2.867E+07 Mo 10219 1.068E+11 3233 3.304E+07 Pt 21400 5.968E+10 1670 3.574E+07 Ta 16678 8.249E+10 2224 3.709E+07 W 19265 1.604E+11 2885 5.559E+07

[0073] Each low acoustic impedance diaphragm 13a is made of a material with an acoustic impedance lower than that of the adjacent high acoustic impedance diaphragm 13b. Each low acoustic impedance diaphragm 13a can be made of the same material or different materials. Similarly, each high acoustic impedance diaphragm 13b can also be made of the same material or different materials. Figure 1 and Figure 2 In a specific example shown, each low acoustic impedance membrane 13a is composed of an A1 membrane, and each high acoustic impedance membrane 13b is composed of a W membrane.

[0074] The retaining substrate 14 is attached to the side of the acoustic multilayer film 13 opposite to the piezoelectric substrate 11, such that it sandwiches the acoustic multilayer film 13 between the piezoelectric substrate 11 and the piezoelectric substrate 11. The retaining substrate 14 is arranged to support the piezoelectric substrate 11, the electrode 12, and the acoustic multilayer film 13. Figure 1 and Figure 2 In one specific example shown, the substrate 14 is made of a Si substrate. In addition, it can also be made of a crystal substrate, a sapphire substrate, a glass substrate, a quartz substrate, a germanium substrate, an alumina substrate, etc.

[0075] like Figure 1 As shown in (a) and (b), the elastic wave device 10 can be a structure in which the electrode 12 is composed of a pair of electrodes. Additionally, as... Figure 1 As shown in (c) and (d), a structure can also be formed in which two electrodes (upper electrodes) 12 are provided on the other surface of the piezoelectric substrate 11, that is, on the side opposite to the acoustic multilayer film 13, and one electrode (lower electrode) 12 is provided on one surface of the piezoelectric substrate 11, with the two resonators connected in series. In this case, by making the upper electrode 12 the input and output electrodes and the lower electrode 12 the ground common electrode, a multimode filter can be constructed.

[0076] In addition, such as Figure 2 As shown, the elastic wave device 10 can be formed into an elongated strip-shaped structure. In this structure, the side surfaces of a pair of long sides of the electrode 12, which is disposed on the other surface of the piezoelectric substrate 11, i.e., the surface opposite to the acoustic multilayer film 13, are aligned with the side surfaces of the piezoelectric substrate 11. In this case, as... Figure 2 As shown in (a) and (b), electrode 12 can be a structure consisting of a pair of electrodes. Additionally, as... Figure 2 As shown in (c) and (d), a structure can also be formed in which two resonators are connected in series, with two electrodes (upper electrodes) 12 disposed on another surface of the piezoelectric substrate 11 and one electrode (lower electrode) 12 disposed on one surface of the piezoelectric substrate 11. In this case, by making the upper electrode 12 the input / output electrode and the lower electrode 12 the ground common electrode, a multimode filter can be constructed. Furthermore, as... Figure 2 As shown in (e) and (f), an elongated groove (rectangular) cutout 15 can also be made by leaving one end and the other end in such a way that the width between the two sides of the piezoelectric substrate 11 and the acoustic multilayer film 13 narrows, thus forming a strip-shaped structure.

[0077] In addition, such as Figure 1 (e), (f) Figure 2As shown in (g) and (h), the elastic wave device 10 can be configured with three upper electrodes 12 and one lower electrode, with those electrodes 12 connected together. In this case, by using the three upper electrodes 12 as the input electrode, output electrode, and common ground electrode of the filter, respectively, and the lower electrode 12 as the common electrode connecting the three resonators, it is possible to construct... Figure 1 (g) and Figure 2 The equivalent circuit of (i) shows a T-type ladder filter. Furthermore, the upper electrode 12 and the lower electrode 12 can be four or more, and two or more, respectively. In this case, a ladder filter with more stages can be constructed. Moreover, Figure 1 The elastic wave device 10 shown can utilize the thickness shear vibration of the piezoelectric substrate 11 or the thickness longitudinal vibration of the piezoelectric substrate 11. Furthermore, Figure 2 The elastic wave device 10 shown can utilize the thickness shear vibration of the piezoelectric substrate 11.

[0078] Next, the function will be explained.

[0079] The elastic wave device 10 utilizes an acoustic multilayer film 13 to excite higher-order modes (first-order, second-order, ...) with frequencies higher than the fundamental mode (0th order). Furthermore, by setting the type of piezoelectric substrate 11 and the thickness of each layer of the acoustic multilayer film 13, higher-order modes with a large impedance ratio can be obtained. Using this higher-order mode, the elastic wave device 10 achieves excellent impedance characteristics in ultra-high frequency bands above 6 GHz. Moreover, by using higher-order modes, it is not necessary to make the piezoelectric substrate 11 extremely thin, and no cavities are required above or below the piezoelectric substrate 11, thus ensuring sufficient mechanical strength even in ultra-high frequency bands above 6 GHz.

[0080] In addition, Figure 1 (a) and Figure 2 In (a), the M-axis represents the Y-axis when it is within the piezoelectric substrate (±90°, ±90°, ψ), and the X-axis when it is at Euler angles other than those angles. Additionally, as... Figure 1 (a) and Figure 2 As shown in (a), ψ is the angle from the M-axis in the counterclockwise direction to the direction N perpendicular to the plane in contact with the rotating M-axis.

[0081] (Thickness shear vibration of LN substrate)

[0082] about Figure 1The elastic wave device 10 shown in (a) and (b) uses an LN substrate piezoelectric substrate 11 to determine the frequency characteristics of thickness shear vibration and the impedance ratio of higher-order modes. The electrode 12 (hereinafter referred to as the "upper electrode") disposed on the other surface of the piezoelectric substrate 11, i.e., the side opposite to the acoustic multilayer film 13, is set as an Al electrode (thickness 50 nm). The piezoelectric substrate 11 is set as an LN substrate (thickness 1 μm) with Euler angles of (0°, 75°, ψ). The electrode 12 between the piezoelectric substrate 11 and the acoustic multilayer film 13 (hereinafter referred to as the "lower electrode") is set as an Al electrode (thickness 50 nm). Furthermore, the acoustic multilayer film 13 is configured with six alternating layers of a low acoustic impedance Al film 13a and a high acoustic impedance W film 13b, and the holding substrate 14 is set as a Si substrate. Furthermore, although the thicknesses of the Al electrode of the lower electrode and the Al film of the first layer of low acoustic impedance film 13a are distinguished, if the two are made of the same material, the combined film thickness can be used as the thickness of the low acoustic impedance film 13a.

[0083] Furthermore, to suppress the frequency drop caused by mass loading, the upper electrode of electrode 12 is a low-density Al electrode that is as thin as 50 nm. Additionally, Euler angles (φ, θ, ψ) will be used only in the following description.

[0084] exist Figure 3 (a) shows the frequency characteristics when the average thickness of each layer of the acoustic multilayer 13 is 0.25 wavelengths of the excited bulk wave (half the thickness of the piezoelectric substrate 11). Figure 3 As shown in (a), it was confirmed that the fundamental resonant frequency (fundamental mode) of the thickness shear vibration at 1.9 GHz was strongly excited and an impedance ratio of 73 dB was obtained. In addition, it was also confirmed that the impedance ratio of the higher-order mode at 6.9 GHz, which is about 3.6 times that of the fundamental mode, was about 40 dB.

[0085] Next, in Figure 3 (b) shows that the average thickness of each layer of the acoustic multilayer 13 is made into Figure 3 The frequency response at 1 / 5 of (a), i.e., 0.05 wavelength. For example... Figure 3 As shown in (b), the resonant characteristics at the higher-order mode frequency of 6.9 GHz were confirmed to be strongly excited, resulting in an impedance ratio of 72 dB. This is consistent with... Figure 3 The impedance ratio of the fundamental mode in (a) is 73 dB, which is the same. In addition, it was confirmed that the excitation in the fundamental mode 1-2 GHz band was divided into three, and the impedance ratio of each was suppressed to below 17 dB, so that it had little effect as a parasitic effect.

[0086] Next, in Figure 4Figures (a) and (b) show the θ-relatedness of the bandwidth and impedance ratio of the higher-order mode at approximately 7 GHz when the piezoelectric substrate 11 is set as a (0°, θ, ψ) LN substrate and the average thickness of each layer of the acoustic multilayer film 13 is set to 0.05 wavelengths. Furthermore, under thickness vibration, the shape of the electrode 12 on the horizontal plane perpendicular to the thickness is substantially symmetrical with respect to the x and y directions, therefore ψ = 0° to 180° (and so on hereinafter). Figure 4 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB at θ = 66.5° to 82°, greater than 60 dB at θ = 70° to 81°, and greater than 70 dB at θ = 72° to 78°.

[0087] Next, according to Figure 4 The results in (b) show the relationship between the thickness of the low acoustic impedance film 13a and the impedance ratio of the higher-order mode at approximately 7 GHz when the piezoelectric substrate 11 is set as a (0°, 75°, ψ) LN substrate and the thickness of the high acoustic impedance film 13b is set to 0.0625 wavelengths. Figure 5 As shown in (a). Figure 5 As shown in (a), it was confirmed that the impedance ratio was greater than 50 dB when the thickness of the low acoustic impedance film 13a was 0.016 wavelength to 0.11 wavelength, greater than 60 dB when the thickness was 0.026 wavelength to 0.10 wavelength, and greater than 70 dB when the thickness was 0.0375 wavelength to 0.09 wavelength.

[0088] Next, the relationship between the thickness of the high acoustic impedance film 13b and the impedance ratio of the higher-order mode at approximately 7 GHz was determined when the piezoelectric substrate 11 was set as a (0°, 75°, ψ) LN substrate and the thickness of the low acoustic impedance film 13a was set to 0.0625 wavelengths. Figure 5 As shown in (b). Figure 5 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB when the thickness of the high acoustic impedance film 13b was 0.016 wavelength to 0.107 wavelength, greater than 60 dB when the thickness was 0.025 wavelength to 0.10 wavelength, and greater than 70 dB when the thickness was 0.038 wavelength to 0.08 wavelength.

[0089] Next, the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 7 GHz was determined when the piezoelectric substrate 11 was set as a (0°, 75°, ψ) LN substrate. Figure 5 As shown in (c). Figure 5As shown in (c), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.023 wavelength to 0.097 wavelength, greater than 60 dB when the average thickness of each layer was 0.032 wavelength to 0.087 wavelength, and greater than 70 dB when the average thickness of each layer was 0.043 wavelength to 0.07 wavelength.

[0090] Next, the relationship between the number of layers of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 7 GHz was determined when the piezoelectric substrate 11 was set as a (0°, 75°, ψ) LN substrate and the average thickness of each layer of the acoustic multilayer film 13 was set to 0.05 wavelengths. Figure 6 As shown in the image. Figure 6 As shown, the impedance ratio was confirmed to be above 60 dB when the acoustic multilayer film 13 has 3 or more layers, and above 70 dB when it has 4 to 20 layers. In addition, if the acoustic multilayer film 13 has more than 20 layers, large warping, cracks, etc. may occur on the piezoelectric substrate 11, which may cause manufacturing problems. Therefore, it is preferable to have 20 layers or less.

[0091] according to Figure 6 As a result, for example, when the thicknesses of the first to fourth layers of the acoustic multilayer film 13 are 0.05 wavelengths and the fifth and sixth layers are 2 wavelengths, the average thickness of the six layers of the acoustic multilayer film 13 is 0.7 wavelengths. However, in reality, since the thicknesses of the first to fourth layers each satisfy the condition of 0.05 wavelengths, high impedance can be achieved. Therefore, the average thickness of each layer of the acoustic multilayer film 13 can be calculated using the average thickness from the side of the piezoelectric substrate 11 to the third or fourth layer, or the average thickness of any three or four consecutive layers in the acoustic multilayer film 13. Furthermore, when a very thin multilayer film electrode 12 is used as an electrode 12 near the first layer, it may function as an electrode 12 but not as an acoustic multilayer film 13. In addition, the electrode 12, which can serve as both an electrode 12 and an acoustic impedance film, like the Al electrode, can also be included as a layer of the acoustic multilayer film 13.

[0092] Next, the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 7 GHz was determined when the piezoelectric substrate 11 was set as a (90°, 90°, ψ) LN substrate. Figure 7 As shown in the image. Figure 7 As shown, the impedance ratio was confirmed to be above 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.02 wavelength to 0.095 wavelength, above 60 dB when the average thickness of each layer was 0.03 wavelength to 0.088 wavelength, and above 70 dB when the average thickness of each layer was 0.05 wavelength to 0.07 wavelength.

[0093] (Longitudinal vibration of LN substrate thickness)

[0094] about Figure 1 The elastic wave device 10 shown in (a) and (b) uses an LN substrate piezoelectric substrate 11 to determine the frequency characteristics of longitudinal vibration and the impedance ratio of higher-order modes. The upper electrode is set to an Al electrode (thickness 50 nm), the piezoelectric substrate 11 is set to an (0°, 126°, ψ) LN substrate (thickness 1 μm), and the lower electrode is set to an Al electrode (thickness 50 nm). In addition, the acoustic multilayer film 13 is set to a structure in which six layers of low acoustic impedance film 13a of Al film and high acoustic impedance film 13b of W film are stacked alternately, and the holding substrate 14 is set to a Si substrate.

[0095] exist Figure 8 (a) shows the frequency characteristics when the average thickness of each layer of the acoustic multilayer 13 is set to 0.05 wavelengths. Figure 8 As shown in (a), the higher-order modes of longitudinal vibration of the thickness were confirmed. Figure 3 The resonant characteristics of the higher-order mode of thickness shear vibration (b) at approximately 1.6 times the frequency of 11 GHz were strongly excited, resulting in an impedance ratio of 63 dB. The difference in the frequency of the higher-order mode is caused by the difference between the sound velocity of the transverse wave and the sound velocity of the longitudinal wave in the body wave. Based on these results, it can be seen that although the impedance ratio is lower when using the higher-order mode of thickness longitudinal vibration, higher frequency devices can be realized.

[0096] Next, in Figure 8 (b) shows the θ correlation of the impedance ratio of the higher-order mode at approximately 11 GHz when the piezoelectric substrate 11 is set as a (0°, θ, ψ) LN substrate and the average thickness of each layer of the acoustic multilayer film 13 is set to 0.05 wavelengths. Figure 8 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB at θ = 119° to 133° and greater than 60 dB at θ = 123° to 129°.

[0097] Next, according to Figure 8 The results of (b) show the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 11 GHz when the piezoelectric substrate 11 is set as a (0°, 126°, ψ) LN substrate, and in Figure 8 As shown in (c). Figure 8 As shown in (c), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.032 wavelength to 0.08 wavelength, and greater than 60 dB when the average thickness of each layer was 0.043 wavelength to 0.07 wavelength.

[0098] (Thickness shear vibration of strip-type LN substrate)

[0099] about Figure 2The strip-type elastic wave device 10 shown in (a) and (b) uses an LN substrate piezoelectric substrate 11 to determine the impedance ratio of higher-order modes of thickness shear vibration. The upper electrode is set to an Al electrode (thickness 50 nm), the piezoelectric substrate 11 is set to an (0°, θ, 18°) LN substrate (thickness 1 μm), and the lower electrode is set to an Al electrode (thickness 50 nm). In addition, the acoustic multilayer film 13 is set to a structure in which six layers of low acoustic impedance film 13a of Al film and high acoustic impedance film 13b of W film are stacked alternately, and the holding substrate 14 is set to a Si substrate.

[0100] exist Figure 9 Figure (a) shows the θ correlation of the impedance ratio of higher-order modes when the average thickness of each layer of the acoustic multilayer 13 is set to 0.05 wavelengths. Figure 9 As shown in (a), it was confirmed that the impedance ratio is greater than 50 dB at θ = -123° to -80° and greater than 60 dB at θ = -112° to -90°. Furthermore, ψ is represented by 18°. Although the optimal value of ψ varies slightly due to factors such as the structure of the upper electrode 12, the difference in impedance ratio converges to within 2 dB in the range of ψ = 0° to 180°.

[0101] Next, according to Figure 9 The results of (a) show the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of higher-order modes when the piezoelectric substrate 11 is set as an LN substrate at (0°, -100°, 18°), and in Figure 9 As shown in (b). Figure 9 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.02 wavelength to 0.1 wavelength, and greater than 60 dB when the average thickness of each layer was 0.02 wavelength to 0.088 wavelength.

[0102] (Thickness shear vibration of LT substrate)

[0103] about Figure 1 The elastic wave device 10 shown in (a) and (b) uses an LT substrate piezoelectric substrate 11 to determine the impedance ratio of higher-order modes of thickness shear vibration. The upper electrode is set to an Al electrode (thickness 50 nm), the piezoelectric substrate 11 is set to an LT substrate (thickness 1 μm) at (0°, θ, ψ), and the lower electrode is set to an Al electrode (thickness 50 nm). In addition, the acoustic multilayer film 13 is set to a structure in which six layers of low acoustic impedance Al film 13a and high acoustic impedance W film 13b are alternately stacked, and the holding substrate 14 is set to a Si substrate.

[0104] When using an LT substrate, the higher-order mode frequency of thickness shear vibration is lower because the transverse wave velocity is slower than that of an LN substrate. The higher-order mode frequency is approximately 6.1 GHz when using an LT near the optimal azimuth angle. Figure 10 Figure (a) shows the θ correlation of the impedance ratio of the approximately 6.1 GHz higher-order mode when the average thickness of each layer of the acoustic multilayer 13 is set to 0.05 wavelengths. Figure 10 As shown in (a), it was confirmed that the impedance ratio was greater than 50 dB at θ = 56° to 96° and greater than 60 dB at θ = 62° to 93°.

[0105] Next, according to Figure 10 The results of (a) show the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 6.1 GHz when the piezoelectric substrate 11 is set as a (0°, 74°, ψ)LT substrate, and in Figure 10 As shown in (b). Figure 10 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.02 wavelength to 0.083 wavelength, and greater than 60 dB when the average thickness of each layer was 0.033 wavelength to 0.075 wavelength.

[0106] Next, the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 6.1 GHz was determined when the piezoelectric substrate 11 was set as a (90°, 90°, ψ)LT substrate. Figure 10 As shown in (c). Figure 10 As shown in (c), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.023 to 0.088 wavelengths, and greater than 60 dB when the average thickness of each layer was 0.036 to 0.07 wavelengths.

[0107] (Thickness longitudinal vibration of LT substrate)

[0108] about Figure 1 The elastic wave device 10 shown in (a) and (b) uses an LT substrate piezoelectric substrate 11 to determine the impedance ratio of higher-order modes of longitudinal vibration. The upper electrode is set to an Al electrode (thickness 50 nm), the piezoelectric substrate 11 is set to an (0°, θ, ψ) LT substrate (thickness 1 μm), and the lower electrode is set to an Al electrode (thickness 50 nm). In addition, the acoustic multilayer film 13 is set to a structure in which six layers of low acoustic impedance Al film 13a and high acoustic impedance W film 13b are alternately stacked, and the holding substrate 14 is set to a Si substrate.

[0109] In this case, because the longitudinal wave velocity is slower when using an LT substrate than an LN substrate, the higher-order mode frequencies of the longitudinal vibrations are lower. The higher-order mode frequencies are approximately 10 GHz when using an LT substrate near the optimal azimuth angle. Figure 11 (a) shows the θ correlation of the impedance ratio of the approximately 10 GHz high-order mode when the average thickness of each layer of the acoustic multilayer 13 is set to 0.05 wavelengths. Figure 11 As shown in (a), the impedance ratio was confirmed to be above 50 dB at θ = 112° to 138°.

[0110] Next, according to Figure 11 The results of (a) show the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 10 GHz when the piezoelectric substrate 11 is set as a (0°, 130°, ψ)LT substrate, and in Figure 11 As shown in (b). Figure 11 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.037 to 0.07 wavelengths.

[0111] (Thickness shear vibration of strip-type LT substrate)

[0112] about Figure 2 The strip-type elastic wave device 10 shown in (a) and (b) uses an LT substrate piezoelectric substrate 11 to determine the impedance ratio of higher-order modes of thickness shear vibration. The upper electrode is set to an Al electrode (thickness 50 nm), the piezoelectric substrate 11 is set to an (0°, θ, ψ) LT substrate (thickness 1 μm), and the lower electrode is set to an Al electrode (thickness 50 nm). In addition, the acoustic multilayer film 13 is set to a structure in which six layers of low acoustic impedance Al film 13a and high acoustic impedance W film 13b are alternately stacked, and the holding substrate 14 is set to a Si substrate.

[0113] In this case, the frequency of the higher-order mode is approximately 6 GHz. Figure 12 (a) shows the θ correlation of the impedance ratio of the approximately 6 GHz high-order mode when the average thickness of each layer of the acoustic multilayer 13 is set to 0.05 wavelengths. Figure 12 As shown in (a), it was confirmed that the impedance ratio was greater than 50 dB at θ = 63° to 91° and greater than 55 dB at θ = 68° to 86°.

[0114] Next, according to Figure 12 The results of (a) show the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 6 GHz when the piezoelectric substrate 11 is set as an LT substrate (0°, 74°, 175°). Figure 12 As shown in (b). Figure 12 As shown in (b), it was confirmed that the impedance ratio was greater than 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.02 to 0.08 wavelengths, and greater than 55 dB when the average thickness of each layer was 0.03 to 0.07 wavelengths. Furthermore, ψ was represented by 175°. Although the optimal value of ψ varied slightly due to factors such as the structure of the upper electrode 12, the difference in impedance ratio converged to within 2 dB in the range of ψ = 0° to 180°.

[0115] Next, the relationship between the average thickness of each layer of the acoustic multilayer film 13 and the impedance ratio of the higher-order mode at approximately 6 GHz was determined when the piezoelectric substrate 11 was set as a (90°, 90°, 37°) LT substrate. Figure 12 As shown in (c). Figure 12 As shown in (c), the impedance ratio was confirmed to be above 50 dB when the average thickness of each layer of the acoustic multilayer film 13 was 0.031 to 0.077 wavelengths, and above 60 dB when the average thickness of each layer was 0.040 to 0.055 wavelengths. Furthermore, ψ was represented by 37°. Although the optimal value of ψ varied slightly due to factors such as the structure of the upper electrode 12, the difference in impedance ratio converged to within 2 dB in the range of ψ = 0° to 180°.

[0116] In addition, Figure 5 , Figures 7-12 The diagram illustrates the relationship between the impedance ratio of higher-order (harmonic) modes and the average thickness of each layer of the acoustic multilayer film. Even when the average thicknesses of the low-acoustic impedance film and the high-acoustic impedance film differ, a larger impedance ratio can still be obtained. For example, when the piezoelectric substrate 11 is set as a (90°, 90°, ψ) LN substrate and the acoustic multilayer film 13 is set as a structure in which four layers of low-acoustic impedance SiO2 film 13a and high-acoustic impedance Ta film 13b are alternately stacked, the relationship between the average thickness of two low-acoustic impedance film 13a and the average thickness of two high-acoustic impedance film 13b and the impedance ratio is determined. Figure 13 As shown in the image.

[0117] like Figure 13 As shown, the impedance ratio was confirmed to be above 60 dB at wavelengths of 0.07–0.15, above 65 dB at wavelengths of 0.083–0.142, and above 70 dB at wavelengths of 0.1–0.13. This relationship can also be demonstrated in… Figure 5 , Figures 7-12 The LN and LT shown are applicable to azimuth angles, thickness slip, and thickness longitudinal vibration. A larger impedance ratio is obtained at wavelengths of 0.07 to 0.15, an even larger impedance ratio is obtained at wavelengths of 0.083 to 0.142, and an even larger impedance ratio is obtained at wavelengths of 0.1 to 0.13.

[0118] (Higher-order modes when two piezoelectric substrates are overlapped)

[0119] about Figure 1 The elastic wave device 10 shown in (a) and (b) has a piezoelectric substrate 11 that is a single plate, but the piezoelectric substrate 11 can also be as shown in (a) and (b). Figure 14 As shown, it is formed by bonding two piezoelectric substrates 11a and 11b. As... Figure 14 The structure shown, for example, is such that the piezoelectric substrate 11 is composed of piezoelectric substrate 11a, which is composed of (0°, 126°, ψ)LN substrates (1 μm thick), and piezoelectric substrate 11b, which is composed of (0°, 306°, ψ)LN substrates (1 μm thick). Al electrodes (100 nm thick) are provided as electrodes 12 at the top and bottom of the piezoelectric substrate 11, respectively. As an acoustic multilayer film 13, five layers of low acoustic impedance SiO2 film 13a (100 nm thick) and high acoustic impedance Ta film 13b (100 nm thick) are alternately formed below the lower electrode. A Si substrate is bonded to the bottommost Ta film as a holding substrate 14. The frequency characteristics of the longitudinal vibration of the thickness at this time are... Figure 15 As shown in the image.

[0120] Furthermore, the structure of the two piezoelectric substrates 11a and 11b joined together by the piezoelectric substrate 11 is a combination of (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ)LN substrate (0°, 126°, ψ). Here, when the +Z direction is set as the + plane, (0°, -90° to 90°, ψ) is the + plane of the LN substrate, and (0°, 90° to 270°, ψ) is the - plane, thus equivalent to a -LN+ / +LN- joint. The + plane and the - plane are respectively the period of θ every 360°. This structure is different from the structure in Patent Document 1, which overlaps a ZnO film with

[0001] orientation (equivalent to (0°, 0°, ψ)) and a ZnO film with [000-1] orientation (equivalent to (0°, 180°, ψ)), in terms of substrate material and azimuth angle. Furthermore, polycrystalline thin films such as ZnO and AlN films are isotropic in the X and Y directions. Specifically, ψ = ∞. The

[0001] -oriented film corresponds to (0°, 0°, ∞), and the [000-1]-oriented film corresponds to (0°, 180°, ∞). The value of ψ is undetermined, and there are no + or - symbols in the X and Y directions. Thus, polycrystalline thin films are significantly different from single-crystal thin plates. Similarly, in the case of films oriented with the c-axis parallel to the plane, the

[1000] -oriented film corresponds to (∞, -90°, 0°), and the [-1000]-oriented film corresponds to (∞, 90°, 0°). The value of φ is undetermined, and there are no + or - symbols in the X and Y directions. Therefore, even in this orientation, they are significantly different from single-crystal thin plates.

[0121] like Figure 15As shown, a second harmonic mode was confirmed at 3.3 GHz, and a higher-order mode of three times that of the second harmonic mode was confirmed at 9.8 GHz. Thus, it was confirmed that in the elastic wave device 10 with two piezoelectric substrates 11a and 11b overlapping with different axial methods, a harmonic response (higher-order mode) of approximately three times that of the second harmonic mode was excited. Furthermore, although in Figure 15 It is not recorded in the literature, but it has been confirmed that it stimulated about 5 times the harmonic response.

[0122] Performed Figure 1 The characteristics of the structure shown in (a) are similar to Figure 14 A comparison of the characteristics of the structures shown. As Figure 1 The structure shown in (a) is as follows: the piezoelectric substrate 11 is composed of (0°, 126°, ψ)LN substrate (thickness 2μm). Al electrodes (thickness 100nm) are provided as electrodes 12 at the top and bottom of the piezoelectric substrate 11. As an acoustic multilayer film 13, a low acoustic impedance film 13a (thickness 100nm) of SiO2 film and a high acoustic impedance film 13b (thickness 100nm) of Ta film are alternately formed into 6 layers at the bottom of the lower electrode. A Si substrate is bonded on the Ta film as a holding substrate 14. Figure 14 The structure shown is set as described above.

[0123] In respectively Figure 16 (a) and (b) show Figure 1 The structure shown in (a) has approximately three times the harmonics (higher-order modes) of the fundamental mode, and Figure 14 The frequency characteristics of the structure shown are approximately three times the harmonic (higher-order mode) of the second harmonic. For example... Figure 16 As shown in (a), it was confirmed that when the piezoelectric substrate 11 is a single layer, an impedance ratio of 63 dB was obtained at 4.8 GHz. In contrast, as Figure 16 As shown in (b), when the piezoelectric substrate 11 is composed of two layers, a larger impedance ratio of 75 dB is obtained at 9.8 GHz. Furthermore, it was also confirmed that compared to... Figure 1 In the structure shown in (a), as Figure 16 As shown in (a), there are fluctuations within the frequency band, in Figure 14 In the structure shown, such as Figure 16 As shown in (b), there is no pulsation within the frequency band. Thus, as the piezoelectric substrate 11, it can be said that by overlapping the two piezoelectric substrates 11a, 11b+ surfaces with each other or one surface with each other, a significant advantage is obtained. In addition, a 6-layer acoustic multilayer film 13 was studied, but the same characteristics were observed as long as there are 3 layers or more.

[0124] Next, the following three structures were studied.

[0125] Structure A: In Figure 14In the structure shown, the piezoelectric substrate 11 is a (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ)LN substrate (0°, 126°, ψ), and the total thickness of the two layers is 2μm.

[0126] Structure B: In Figure 14 In the structure shown, the piezoelectric substrate 11 is a (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 306°, ψ+180°)LN substrate (0°, 126°, ψ+180°), and the total thickness of the two layers is 2μm.

[0127] C structure (comparative example): In Figure 1 In the structure shown in (a), the piezoelectric substrate 11 is a (0°, 126°, ψ)LN substrate (thickness 2μm).

[0128] Regarding the three cases of structures A through C, Figure 17 Figure (a) shows the relationship between the thickness and impedance ratio of the low acoustic impedance SiO2 film 13a when the thickness of the high acoustic impedance Ta film 13b is 0.04 wavelengths (twice the thickness of the piezoelectric substrate 11, i.e., 4 μm). Furthermore, regarding these three cases, in... Figure 17 (b) shows the relationship between the sum of the average thickness of the low acoustic impedance membrane 13a and the average thickness of the high acoustic impedance membrane 13b and the impedance ratio.

[0129] like Figure 17 As shown in (a), it was confirmed that in the case of structure A, the impedance ratio is 60 dB or more when the thickness of the low acoustic impedance film 13a is 0.005 to 0.05 wavelengths, 65 dB or more when the thickness is 0.0068 to 0.041 wavelengths, and 70 dB or more when the thickness is 0.009 to 0.035 wavelengths. Furthermore, although not shown, when the thickness of the low acoustic impedance film 13a is set to 0.04 wavelengths and the thickness of the high acoustic impedance film 13b is varied, the impedance ratio is also confirmed to be 60 dB or more when the thickness of the high acoustic impedance film 13b is 0.005 to 0.05 wavelengths, 65 dB or more when the thickness is 0.0068 to 0.041 wavelengths, and 70 dB or more when the thickness is 0.009 to 0.035 wavelengths.

[0130] Furthermore, in the case of structure B, it was confirmed that the impedance ratio was greater than 60 dB when the thickness of the low acoustic impedance film 13a was 0.008 to 0.04 wavelengths. Similarly, although not shown, when the thickness of the low acoustic impedance film 13a was set to 0.04 wavelengths and the thickness of the high acoustic impedance film 13b was varied, it was also confirmed that the impedance ratio was greater than 60 dB when the thickness of the high acoustic impedance film 13b was 0.008 to 0.04 wavelengths. Furthermore, it was confirmed that structure A had an impedance ratio approximately 12 dB higher than structure C, and structure B had an impedance ratio similar to that of structure C.

[0131] In addition, such as Figure 17 As shown in (b), it was confirmed that in the case of structure A, the impedance ratio is greater than 60 dB at wavelengths where the sum of the average thicknesses of the low acoustic impedance film 13a and the high acoustic impedance film 13b is 0.02 to 0.09 wavelengths, greater than 65 dB at wavelengths of 0.028 to 0.085 wavelengths, and greater than 70 dB at wavelengths of 0.04 to 0.08 wavelengths. Furthermore, in the case of structure B, it was confirmed that the impedance ratio is greater than 60 dB at wavelengths where the sum is 0.034 to 0.082 wavelengths. It was also confirmed that structure A has an impedance ratio approximately 14 dB higher than structure C, while structure B has an impedance ratio similar to that of structure C. Moreover, the optimal thicknesses of the low acoustic impedance film 13a and the high acoustic impedance film 13b in structures A and B are also consistent with combinations other than SiO2 and Ta films. Furthermore, although not shown in the figure, it is confirmed that the structure with (0°, 126°, ψ)LN substrate (0°, 306°, ψ) / (0°, 126°, ψ+180°)LN substrate (0°, 306°, ψ+180°) and a total thickness of 2μm for both layers also exhibits the same characteristics as structure B.

[0132] in addition, Figures 15-17The results shown are also applicable to 2-harmonic waves of longitudinal vibrations of other thicknesses on LN and LT substrates. Specifically, they apply to the cases of (φ, θ, ψ)(LN substrate or LT substrate)(φ, θ+180°, ψ) / (φ, θ+180°, ψ)(LN substrate or LT substrate)(φ, θ, ψ), (φ, θ, ψ)(LN substrate or LT substrate)(φ, θ+180°, ψ) / (φ, θ+180°, ψ+180°)(LN substrate or LT substrate)(φ, θ, ψ+180°), and (φ, θ, ψ)(LN substrate or LT substrate)(φ, θ+180°). In the case of (φ, θ, ψ+180°) / (φ, θ, ψ+180°) (LN substrate or LT substrate) (φ, θ+180°, ψ+180°), when using an LN substrate, it is applicable to the case of φ=-5°~5°, θ=119°~133°, ψ=0°~180° and the Euler angles that are crystallographically equivalent to them. When using an LT substrate, it is applicable to the case of φ=-5°~5°, θ=112°~138°, ψ=0°~180° and the Euler angles that are crystallographically equivalent to them.

[0133] Next, the thickness shear vibration 2x wave of the piezoelectric substrate 11, which is composed of two overlapping (0°, 74°, 0°) LN substrates, was studied. The piezoelectric substrate 11 studied has the following six structures.

[0134] D-structure: (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 254°, 0°)LN substrate (0°, 74°, 0°)

[0135] E-structure: (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 254°, 180°)LN substrate (0°, 74°, 180°)

[0136] F-structure: (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 74°, 180°)LN substrate (0°, 254°, 180°)

[0137] G structure: (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 254°, 90°)LN substrate (0°, 74°, 90°)

[0138] H-structure: (0°, 74°, 0°)LN substrate (0°, 254°, 0°) / (0°, 74°, 90°)LN substrate (0°, 254°, 90°)

[0139] I-structure (comparative example): (0°, 74°, 0°) LN substrate (thickness 2μm)

[0140] All five structures from D to H involve overlapping two 1μm thick LN substrates. Furthermore, in each structure, the upper and lower electrodes 12 of the piezoelectric substrate 11 are set as 100nm thick Al electrodes, the acoustic multilayer film 13 is configured as a structure in which six layers of low acoustic impedance SiO2 film 13a and high acoustic impedance Ta film 13b are alternately stacked, and the holding substrate 14 is set as a Si substrate. Regarding the six cases of D to I structures, in... Figure 18 The figure shows the relationship between the sum of the average thickness of the low acoustic impedance membrane 13a and the average thickness of the high acoustic impedance membrane 13b and the impedance ratio.

[0141] like Figure 18 As shown, it was confirmed that in the case of structure D, the impedance ratio is greater than 60 dB when the sum of the average thickness of the low acoustic impedance film 13a and the average thickness of the high acoustic impedance film 13b is 0.045–0.073 wavelengths, greater than 65 dB when the sum is 0.0456–0.072 wavelengths, greater than 70 dB when the sum is 0.046–0.069 wavelengths, and greater than 75 dB when the sum is 0.049–0.063 wavelengths. Furthermore, in the case of structure E, it was confirmed that the impedance ratio is greater than 55 dB when the sum is 0.047–0.065 wavelengths, and greater than 60 dB when the sum is 0.05–0.062 wavelengths. Furthermore, it was confirmed that in the F-structure case, the impedance ratio reached over 60 dB in wavelengths of 0.046–0.06, over 65 dB in wavelengths of 0.047–0.058, and over 70 dB in wavelengths of 0.049–0.0563. Additionally, it was confirmed that in the G and H structures, the impedance ratio was below 50 dB, and good characteristics could not be obtained. Furthermore, the acoustic multilayer film 13 was studied with 6 layers, but the same characteristics were observed with 3 or more layers.

[0142] In addition, such as Figure 18 As shown, it was confirmed that the impedance ratios of structures D and F are approximately 15 dB and 8 dB higher, respectively, compared to structure I. It was also confirmed that structure E achieves an impedance ratio similar to that of structure I. Furthermore, it was confirmed that the thickness of each film in the acoustic multilayer film 13 using structures D to F, when normalized to the wavelength (wavelength being twice the thickness of the piezoelectric substrate 11), is half that of structure I.

[0143] in addition, Figure 18 The results shown can also be applied to thickness shear vibration of LN and LT substrates, strip-type thickness shear vibration, and... Figure 1 , Figure 2The structure is as follows: In structure D, it is (φ, θ, ψ) (LN substrate or LT substrate) (φ, θ+180°, ψ) / (φ, θ+180°, ψ) (LN or LT) (φ, θ, ψ); in structure E, it is (φ, θ, ψ) (LN substrate or LT substrate) (φ, θ+180°, ψ) / (φ, θ+180°, ψ+180°) (LN substrate or LT substrate) (φ, θ, ψ+180°); and in structure F, it is (φ, θ, ψ) (LN substrate or LT substrate) (φ, θ+180°, ψ) / (φ, θ, ψ+180°) (LN substrate or LT substrate) (φ, θ+180°, ψ+180°). Each of these structures is applicable to the following situations. For LN substrates, the cases are φ = -5° to 5°, θ = 66.5° to 82°, ψ = 0° to 180°, and φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, as well as their crystallographically equivalent Euler angles. For LT substrates, the cases are φ = -5° to 5°, θ = 56° to 96°, ψ = 0° to 180°, and φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, as well as their crystallographically equivalent Euler angles. In the case of strip-type thickness shear vibration, for LN substrate, the values ​​are φ = -5° to 5°, θ = -123° to -80°, ψ = 0° to 180°, and the crystallographically equivalent Euler angles. For LT substrate, the values ​​are φ = -5° to 5°, θ = 63° to 91°, ψ = 0° to 180°, and φ = 85° to 95°, θ = 85° to 95°, ψ = 0° to 180°, and the crystallographically equivalent Euler angles.

[0144] Explanation of reference numerals in the attached figures

[0145] 10-Elastic wave device; 11-Piezoelectric substrate; 12-Electrode; 13-Acoustic multilayer film; 13a-Low acoustic impedance film; 13b-High acoustic impedance film; 14-Retaining substrate; 15-Notch.

Claims

1. An elastic wave device, characterized in that, have: Piezoelectric substrate; Electrodes, which are disposed in contact with the piezoelectric substrate; and An acoustic multilayer film is disposed in contact with the piezoelectric substrate and / or the electrode. Furthermore, it is configured to utilize a higher-order mode that is 3 or 5 times the fundamental mode of the body wave, or a higher-order mode with a frequency more than 3 times that of the fundamental mode, and the fundamental mode of the body wave is parasitic.

2. The elastic wave device according to claim 1, characterized in that, The acoustic multilayer film alternately consists of low acoustic impedance films and high acoustic impedance films.

3. The elastic wave device according to claim 1, characterized in that, In the aforementioned acoustic multilayer film, low acoustic impedance films and high acoustic impedance films alternate continuously, stacked in more than 3 layers and less than 20 layers.

4. The elastic wave device according to claim 2 or 3, characterized in that, In the acoustic multilayer film, among the low acoustic impedance films and the high acoustic impedance films, the thickness of at least three layers is 0.016 to 0.11 wavelengths of the bulk wave.

5. The elastic wave device according to claim 2 or 3, characterized in that, The acoustic multilayer film has one or more layers of the low acoustic impedance film and two or more layers of the high acoustic impedance film. The thickness of the one layer of the low acoustic impedance film or the sum of the average thickness of any two layers of the low acoustic impedance film and the average thickness of any two layers of the high acoustic impedance film is 0.07 to 0.15 wavelength of the bulk wave.

6. The elastic wave device according to claim 2 or 3, characterized in that, The low acoustic impedance films and / or high acoustic impedance films of the aforementioned acoustic multilayer film are composed of Mg alloy, SiO2, Al, Si, Ge, Ti, ZnO, and Si. x N y SiO x F y It consists of a film of at least one of AlN, SiC, Al2O3, Ag, Hf, TiO2, Ni, Au, Ta, Mo, Pt, W, and Cu, or an oxide film, nitride film, carbide film, or iodide film containing at least one of them, wherein x and y are positive real numbers.

7. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is composed of a single crystal of LiNbO3, LiTaO3, Li2B4O7, or lanthanum gallium silicate.

8. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is made of LiNbO3 crystal, and the Euler angle is any one of (0°±5°, 66.5°~82°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them. It is configured to utilize the thickness shear vibration of the piezoelectric substrate.

9. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is made of LiNbO3 crystal, and the Euler angles are (0°±5°, 119°~133°, 0°~180°), or their crystallographic equivalents. It is configured to utilize the longitudinal vibration of the thickness of the piezoelectric substrate.

10. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is composed of LiNbO3 crystals and is of strip type, with Euler angles of (0°±5°, -123°~-80°, 0°~180°) or crystallographically equivalent Euler angles. It is configured to utilize the thickness shear vibration of the piezoelectric substrate.

11. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is made of LiTaO3 crystal, and the Euler angle is any one of (0°±5°, 56°~96°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them. It is configured to utilize the thickness shear vibration of the piezoelectric substrate.

12. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is made of LiTaO3 crystal, and the Euler angles are (0°±5°, 112°~138°, 0°~180°), or their crystallographic equivalents. It is configured to utilize the longitudinal vibration of the thickness of the piezoelectric substrate.

13. The elastic wave device according to any one of claims 1 to 3, characterized in that, The piezoelectric substrate is made of LiTaO3 crystal and is of strip type. The Euler angle is any one of (0°±5°, 63°~91°, 0°~180°) and (90°±5°, 90°±5°, 0°~180°), or a crystallographically equivalent Euler angle to any one of them. It is configured to utilize the thickness shear vibration of the piezoelectric substrate.

14. The elastic wave device according to any one of claims 1 to 3, characterized in that, It has a holding substrate disposed on the side of the acoustic multilayer film opposite to the piezoelectric substrate in such a way that it clamps the acoustic multilayer film between itself and the piezoelectric substrate.

15. An elastic wave device, characterized in that, have: Piezoelectric substrate; Electrodes, which are disposed in contact with the piezoelectric substrate; and An acoustic multilayer film is disposed in contact with the piezoelectric substrate and / or the electrode. Furthermore, it is configured as a higher-order mode that utilizes the resonance characteristics of the bulk wave, which is 3 or 5 times the frequency of the fundamental mode, or a higher-order mode with a frequency more than 3 times that of the fundamental mode. The piezoelectric substrate is composed of two overlapping layers. In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In the other piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ), and the Euler angles of the lower surface are (φ, θ, ψ). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ), and in the other… In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ+180°) and the Euler angles of the lower surface are (φ, θ, ψ+180°). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ) and the Euler angles of the lower surface are (φ, θ+180°, ψ). In another piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ+180°) and the Euler angles of the lower surface are (φ, θ+180°, ψ+180°). It is configured as a higher-order mode that is about 3 times or about 5 times the length of the longitudinal vibration of the thickness of the piezoelectric substrate.

16. The elastic wave device according to claim 15, characterized in that, Each piezoelectric substrate is composed of LiNbO3 crystal or LiTaO3 crystal. The LiNbO3 crystal has φ=-5°~5°, θ=119°~133°, ψ=0°~180°, or Euler angles equivalent to them in crystallography. The LiTaO3 crystal has φ=-5°~5°, θ=112°~138°, ψ=0°~180°, or Euler angles equivalent to them in crystallography.

17. An elastic wave device, characterized in that, have: Piezoelectric substrate; Electrodes, which are disposed in contact with the piezoelectric substrate; and An acoustic multilayer film is disposed in contact with the piezoelectric substrate and / or the electrode. Furthermore, it is configured as a higher-order mode that utilizes the resonance characteristics of the bulk wave, which is 3 or 5 times the frequency of the fundamental mode, or a higher-order mode with a frequency more than 3 times that of the fundamental mode. The piezoelectric substrate is composed of two overlapping layers. In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ). In the other piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ), and the Euler angles of the lower surface are (φ, θ, ψ). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ), and the Euler angles of the lower surface are (φ, θ+180°, ψ), and in the other… In one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ+180°, ψ+180°) and the Euler angles of the lower surface are (φ, θ, ψ+180°). Alternatively, in one piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ) and the Euler angles of the lower surface are (φ, θ+180°, ψ). In another piezoelectric substrate, the Euler angles of the upper surface are (φ, θ, ψ+180°) and the Euler angles of the lower surface are (φ, θ+180°, ψ+180°). It is configured as a higher-order mode that is about 3 times or about 5 times the second-order wave generated by the thickness shear vibration of the piezoelectric substrate.

18. The elastic wave device according to claim 17, characterized in that, Each piezoelectric substrate is composed of LiNbO3 crystal or LiTaO3 crystal. The LiNbO3 crystal has φ=-5°~5°, θ=66.5°~82°, ψ=0°~180°, or φ=85°~95°, θ=85°~95°, ψ=0°~180°, or Euler angles equivalent to them in crystallography. The LiTaO3 crystal has φ=-5°~5°, θ=56°~96°, ψ=0°~180°, or φ=85°~95°, θ=85°~95°, ψ=0°~180°, or Euler angles equivalent to them in crystallography.

19. The elastic wave device according to claim 17, characterized in that, The piezoelectric substrate is strip-shaped.

20. The elastic wave device according to claim 19, characterized in that, Each piezoelectric substrate is composed of LiNbO3 crystal or LiTaO3 crystal. The LiNbO3 crystal has φ=-5°~5°, θ=-123°~-80°, ψ=0°~180°, or Euler angles equivalent to them in crystallography. The LiTaO3 crystal has φ=-5°~5°, θ=63°~91°, ψ=0°~180°, or φ=85°~95°, θ=85°~95°, ψ=0°~180°, or Euler angles equivalent to them in crystallography.

21. The elastic wave device according to any one of claims 15 to 20, characterized in that, In the acoustic multilayer film, one or more low acoustic impedance films and two or more high acoustic impedance films are alternately stacked. The thickness of the one low acoustic impedance film or the sum of the average thickness of any two low acoustic impedance films and the average thickness of any two high acoustic impedance films is 0.02 to 0.09 wavelength of the bulk wave.

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