Acoustic wave devices

Abstract

An acoustic wave device (10) using a surface acoustic wave, comprising: a substrate (11) containing 70 mass% or more of silicon dioxide (SiO2); a piezoelectric thin film (12) formed of LiTaO3 crystal or LiNbO3 crystal disposed on the substrate (11); and an interdigital transducer electrode (13) arranged in contact with the piezoelectric thin film (12); wherein Euler angle of the substrate (11) and Euler angle of the piezoelectric thin film (12) are selected such that a phase velocity of the surface acoustic wave propagating along the substrate (11) is greater than a phase velocity of the surface acoustic wave propagating along the piezoelectric thin film (12).

Description

Technical area

[0001] The present invention relates to an acoustic wave device (also referred to as an acoustic wave device). Background of the invention

[0002] In recent years, mobile phones and smartphones have become popular, and as many as fifty bands have been combined at 2.4 GHz or lower, so that adjacent bands are very close to each other. Accordingly, there is a great need for filters and duplexers with steep frequency characteristics and better temperature characteristics so that the adjacent band does not interfere with each other. In addition, there is a need for resonators with larger impedance ratios and higher Qs (quality factors) to realize such filters and duplexers with steep frequency characteristics. Here, Q, a parameter that indicates the steepness of a filter, affects not only the steepness but also the insertion loss (also called insertion loss) of the filter. The higher the Q value becomes, the lower the insertion loss can be, and the battery consumption for mobile phones and smartphones can be reduced.Therefore, such filters must have better insertion loss, better temperature characteristics, and greater transconductance, and the resonators must have higher Qs and larger impedance ratios. It should be noted that the Q values ​​are proportional to the impedance ratios and inversely proportional to the bandwidths, so that in a case where the bandwidths are essentially equal, the Q and the impedance ratio are proportional.

[0003] The bandwidth of a surface acoustic wave (SAW) filter depends on the electromechanical coupling coefficient (coupling factor) of a piezoelectric substrate used in the SAW filter. Accordingly, a large number of piezoelectric substrates, each formed from an LT (LiTaO3 crystal) or an LN (LiNbO3 crystal) with a coupling factor required for the filter's bandwidth, have been conventionally used. However, these substrates can have thermal frequency coefficients (TCFs) ranging from -40 ppm / °C to -120 ppm / °C, which cannot be considered favorable. It should be noted that a theoretical formula for a thermal frequency coefficient (TCF) can be defined as follows: TCF=(V(35°C)V(15°C))20×(V(25°C))−α where α = a linear expansion coefficient and V(T) is an excitation phase velocity. Furthermore, an actual measurement may indicate TCF = (f(45°C) - f(25°C)) / (20 x f(25°C)), where f(T) is a measured frequency, and a resonant frequency and / or anti-resonant frequency may be measured for a resonator, while a center frequency may be measured for a filter. It should be noted that if a frequency is actually measured but not linearly varied, a maximum frequency variation within the measured temperature range can be divided by the measured temperature range to obtain a frequency variation per degree.

[0004] Therefore, in order to obtain a required coupling factor and a better TCF, the present inventors and the like have developed a surface acoustic filter fabricated by first combining an LT / LN substrate having a negative TCF with an SiO2 thin film having a positive TCF into a SiO2 thin film / high-density electrode / LT or LN substrate structure, and then removing protrusions on the SiO2 thin film derived from the electrode to planarize the surface (e.g., see Non-Patent Literature 1). This structure can achieve a TCF of -10 ppm / °C, which is relatively better, and further achieve characteristics such as an impedance ratio and a Q value equivalent to those of a single LT / LN substrate. The impedance ratio and the Q value of this resonator can be about 60 dB and 800 dB, respectively.

[0005] It should be noted that a quartz substrate has a better thermal frequency coefficient; however, its coupling factor, indicating a piezoelectric type, may be smaller and would not meet the bandwidth requirements of the filter required for a smartphone or mobile phone. Furthermore, after a filter with an AlN (aluminum nitride) film bulk acoustic wave, the Q value of the resonator can be 2000, which can provide a steeper filter characteristic than a SAW filter, while the thermal frequency coefficient can be as low as -30 ppm / °C, which may not be as favorable. BibliographyNon-patent literature

[0006] Non-Patent Literature 1: Michio Kadota, Takeshi Nakao, Kenji Nishiyama, Norio Taniguchi and Toshiyuki Fuyutsume, "Small Surface Acoustic Wave Duplexer Having Good Temperature Characteristics", Institute of Electronics, Information and Communication Engineers (IEICE), TRANSACTIONS A, 2013, Vol. J96-A, No. 6, pp. 301-3088

[0007] Document US 2012 0194032 A1 describes an acoustic wave device with a piezoelectric substrate.

[0008] Document JP 2004 282232 A describes an acoustic wave device with a piezoelectric thin film on a dielectric layer. Summary of the inventionTechnical problem

[0009] The acoustic wave filter described in Non-Patent Literature 1 can achieve a relatively better TCF; however, there were problems that the Q value and impedance ratio of its resonator are similar to those of a single LT or LN substrate, and the steepness of the frequency characteristic was far from sufficient because the SiO2 thin film is a polycrystalline film with a columnar structure.

[0010] The present invention has been made in view of such problems and has an object to provide an acoustic wave device which has a better TCF and can improve the Q and impedance ratio of its resonator. Solution to the problem

[0011] To achieve the above-described object, an acoustic wave device according to the present invention may be an acoustic wave device using a surface acoustic wave, the acoustic wave device including a substrate containing 70 mass % or more of silicon dioxide (SiO2), a piezoelectric thin film formed of LiTaO3 or LiNbO3 crystal and disposed on the substrate, and an interdigital transducer electrode disposed in contact with the piezoelectric thin film, in which the piezoelectric thin film may include a piezoelectric thin plate. The Euler angle of the substrate and the Euler angle of the piezoelectric thin film are selected such that a phase velocity of the surface acoustic wave propagating along the substrate is larger than a phase velocity of the surface acoustic wave propagating along the piezoelectric thin film.

[0012] In an acoustic wave device according to the present invention, the substrate may preferably have a shear wave phase velocity of a bulk or volume wave in the range of 3,400 m / s to 4,800 m / s, which is close to the shear wave velocity of LT or LN. Most of these substrates are isotropic and non-anisotropic in the x-, y-, and z-axes, while a quartz substrate, which is a piezoelectric single crystal, may be anisotropic and have a different property. For this reason, when using such a quartz substrate, it is contemplated to configure the quartz substrate so that the phase velocity of the surface acoustic wave propagating along the quartz substrate is greater than the phase velocity of the surface acoustic wave propagating along the piezoelectric thin film.Furthermore, the difference between the phase velocities may preferably be 300 m / s or more, and more preferably 600 m / s or more. Furthermore, in an acoustic wave device according to the present invention, the surface acoustic wave may preferably be a leaky surface acoustic wave (LSAW). Moreover, an SH (Shear Horizontal) component of the LSAW may preferably be 50% or more, and more preferably 65% ​​or more. Furthermore, the surface acoustic wave may be an S-wave having a phase velocity of 4,500 m / s or more. It should be noted that whether the surface acoustic wave used is a leaky surface acoustic wave or not can be theoretically determined by the Euler angles of the substrate.

[0013] A substrate containing 70 mass % or more of silicon dioxide (SiO2) can result in a positive TCF for a surface acoustic wave (SAW). Thus, in an acoustic wave device according to the present invention, disposing a piezoelectric thin film formed of LiTaO3 (LT) or LiNbO3 (LN) crystal with a negative TCF on a substrate with a positive TCF can enable a better TCF close to zero ppm / °C. Furthermore, configuring the piezoelectric thin film formed of LT or LN to have Euler angles for exciting a leaky surface acoustic wave (LSAW), while configuring the piezoelectric substrate to have Euler angles for a phase velocity similar to or greater than the phase velocity activated for LSAW of LT or LN, can enable the use of an LSAW mode with no leakage component in the piezoelectric thin film.Accordingly, for example, an impedance ratio 15 to 20 dB higher than the characteristics of a single LT or LN substrate can be achieved. Furthermore, this impedance ratio can be 6 to 10 times higher in Q for the same bandwidths, thus resulting in excellent transconductance and insertion loss characteristics. Furthermore, the coupling factor can be configured to be larger than that of the piezoelectric thin film itself, although the difference may be small.

[0014] The acoustic wave device according to the present invention may include a grounded shunt electrode and / or an insulating bonding film between the substrate and the piezoelectric thin film. In this case, the device may have a structure such as: an interdigital transducer electrode / piezoelectric thin film / substrate structure; an interdigital transducer electrode / piezoelectric thin film / bonding film / substrate structure; an interdigital transducer electrode / piezoelectric thin film / shunt electrode / substrate structure; an interdigital transducer electrode / piezoelectric thin film / shunt electrode / bonding film / substrate structure; or an interdigital transducer electrode / piezoelectric thin film / bonding film / shunt electrode / substrate structure.In this case, the device can achieve better TCF and higher Q and impedance ratios without losing its superior characteristics, even if it includes a shunt electrode or a bonding film. In particular, with a shunt electrode, the coupling factor can be increased and the propagation loss of the leakage surface acoustic wave can be reduced. Note that the bonding film preferably has no sound absorption and can be formed of a hard material. For example, the bonding film can be formed of a Si film or SiO2 film.

[0015] In the acoustic wave device according to the present invention, the interdigital transducer electrode may be configured to have at least a lower portion embedded in the piezoelectric thin film and / or to have at least an upper portion protruding from the piezoelectric thin film. In this case, the device can have better characteristics and achieve a higher impedance ratio even in each structure. Particularly, in a structure in which the entire portion or the lower portion of the interdigital transducer electrode is embedded in the piezoelectric thin film, the phase velocity can become faster and thus advantageous for higher frequencies. Note that in this case, an electrical shunt may exist between the piezoelectric thin film and the substrate.

[0016] In an acoustic wave device according to the present invention, the substrate may preferably contain 80 mass% or more of silicon dioxide (SiO2), and preferably 99 mass% or more and less than 100 mass%. The substrate may preferably be a quartz glass containing 100 mass% of SiO2, and more preferably formed from a quartz substrate that is a piezoelectric single crystal. Furthermore, the substrate may enable the propagating surface acoustic wave to have a phase velocity in the range of 3,400 m / s to 4,800 m / s. Furthermore, the substrate may be formed from an isotropic substrate other than a quartz substrate, and the piezoelectric thin film may have a thickness of 0.001 mm or more and less than 0.01 mm. Furthermore, the substrate may be formed of a quartz substrate and the propagating surface acoustic wave may have a phase velocity of 4,500 m / s or more, 4,800 m / s or more, or 5.000 m / s or more. Each of these configurations can exhibit excellent characteristics, resulting in a better TCF, higher Q, and better impedance ratio. It should be noted that since a quartz substrate has a positive TCF that is larger than that of an isotropic substrate, any thickness in the piezoelectric thin film can be accepted.

[0017] There is no dependence on the propagation direction of an acoustic wave in an isotropic substrate, except for a quartz substrate. In an anisotropic quartz substrate, the properties of the quartz substrate may vary depending on the orientation angle or propagation direction (Euler angle), and it is therefore important to select appropriate Euler angles. First, for an acoustic wave according to the present invention, it may be desirable to select Euler angles such that the power flow angle (PFA) can be zero. This is because if the Euler angles are significantly shifted from zero, an acoustic wave may propagate in a direction oblique to an interdigital transducer electrode.Example Euler angles that allow the PFA to be approximately zero can be (0°±5°, 0°-180°, 40°±12°), (10°±5°, 0°-180°, 42°±8°), (20°±5°, 0°-180°, 50°±8°), (0°±5°, 0°-180°, 0°±5°), (10°±5°, 0°-180°, 0°±5°), (20°±5°, 0°-180°, 0°±5°), (0°±5°, 0°-180°, 90°±5°), (10°±5°, 0°-180°, 90°±5°), (20°±5°, 0°-180°, 90°±5°) and equivalent orientation angles.

[0018] Furthermore, in an acoustic wave device according to the present invention, the substrate can have Euler angles such as (0°±5°, 0°-125°, 0°±5°), (0°±5°, 0°-36°, 90°±5°), (0°±5°, 172°-180°, 90°±5°), (0°±5°, 120°-140°, 30°-49°), (0°±5°, 25°-105°, 0°:t5°), (0°±5°, 0°-45°, 15°-35°), (0°±5°, 10°-20°, 60°-70°), (0°±5°, 90°-180°, 30°-45°), (0°±5°, 0°±5°, 85°-95°), (90°±5°, 90°±5°-31°), and (0°±5°, 90°±5°, -3°-3°). Furthermore, the substrate can have Euler angles such as (20°±5°, 120°±10°, 115°±10°), (0°±5°, 90°±5°, 0°±10°), (0°±5°, 90°±5°, 75°±10°), (0°±5°, 0°±5°, 0°±10°), and (0°±5°, 0°±5°, 60°±10°). These cases can lead to better TCF.

[0019] Furthermore, the following phase velocities, Euler angles, and film thicknesses may be preferred to obtain higher Q characteristics and impedance ratios. In an acoustic wave device according to the present invention, the substrate can propagate the acoustic wave at a phase velocity of 4,500 m / s or more and have Euler angles of (0°+5°, 70°-165°, 0°±5°) or (0°+5°, 95°-155°, 90°±5°). Preferably, the substrate may have the acoustic wave propagating at a phase velocity of 4,800 m / s or more and may have Euler angles of (0°±5°, 90°-150°, 0°±5°) or (0°±5°, 103°-140°, 90°±5°), and may further cause the acoustic wave to propagate at a phase velocity of 5,000 m / s or more and may have Euler angles of (0°±5°, 100°-140°, 0°±5°) or (0°±5°, 110°-135°, 90°±5°).

[0020] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-132°, 0°±5°), (0°±5°, 0°-18°, 0°±5°), (0°±5°, 42°-65°, 0°±5°) or (0°±5°, 126°-180°, 0°±5°), which can provide a positive TCF for a Rayleigh wave or LSAW, and the piezoelectric thin film may be formed of LiTaO2 crystal and may have Euler angles of (0°±5°, 82°-148°, 0°±5°). In this case, the substrate may preferably have Euler angles of (0°±5°, 0°-12°, 0°±5°), (0°±5°, 44°-63°, 0°±5°), or (0°±5°, 135°-180°, 0°±5°). Furthermore, the piezoelectric thin film may preferably have Euler angles of (0°+5°, 90°-140°, 0±5°). This combination can lead to a particularly good TCF.

[0021] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-42°, 90°±5°), (0°±5°, 170°-190°, 90°±5°), (0°±5°, 0°-45°, 90°±5°), or (0°±5°, 123°-180°, 90°±5°), which can provide a positive TCF for a Rayleigh or an LSAW, and the piezoelectric thin film may be formed of LiTaO3 crystal and have Euler angles of (0°±5°, 80°-148°, 0°±5°). In this case, the substrate may preferably have Euler angles of (0°±5°, 0°-34°, 90°±5°) or (0°±5°, 126°-180°, 90°±5°). Furthermore, the piezoelectric thin film may preferably have Euler angles of (0°±5°, 90°-140°, 0°, 0°±5°), more preferably (0°±5°, 95°-143°, 0°±5°), and further more preferably (0°±5°, 103°-125°, 0°±5°).

[0022] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles with a high phase velocity LSAW of (1°-39°, 100°-150°, 0°-20° or 70°-120° or 160°-180°), and the piezoelectric thin film may be formed of LiTaO3 crystal and have Euler angles of (0°±5°, 80°-148°, 0°±5°). In addition, the substrate can have Euler angles with a fast shear wave with high phase velocity of about 5,000 m / s (20°±5°, 120°±10°, 115°±10°), (0°±5°, 90°±5°, 0°±10°), (0°±5°, 90°, 75°±10°), (0°±5°, 0°, 0°±10°) or (0°±5°, 0°, 60°±10°).

[0023] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-23°, 0°±5°), (0°±5°, 32°-69°, 0°±5°), (0°±5°, 118°-180°, 0°±5°), (0°±5°, 0°-62°, 90°±5°), (0°±5°, 118°-180°, 90°±5°), (0°±5°, 0°-72°, 30°-60°) or (0°±5°, 117°-180°, 30°-60°), and the piezoelectric thin film may be formed of LiTaO3 crystal and have Euler angles of (0°±5°, 80°-148°, 0°±5°). In this case, the Euler angles of the substrate may preferably be (0°±5°, 0°-12°, 0°±5°), (0°±5°, 37°-66°, 0°±5°), (0°±5°, 132°-180°, 0°±5°), (0°±5°, 0°-50°, 90°±5°), (0°±5°, 126°-180°, 90°±5°), (0°±5°, 0°-17°, 30°-60°), (0°±5°, 35°-67°, 30°-60°), or (0°±5°, 123°-180°, 30°-60°).

[0024] Furthermore, in an acoustic wave device according to the present invention, the piezoelectric thin film may be formed of LiTaO3 crystal and have Euler angles of (90°±5°, 90°±5°, 33°-55°) or (90°+5°, 90°±5°, 125°-155°). Furthermore, the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (90°±5°, 90°±5°, 38°-65°) or (90°±5°, 90°±5°, 118°-140°).

[0025] Furthermore, in an acoustic wave device according to the present invention, the piezoelectric thin film may be formed of LiTaO3 crystal and have a thickness between 0.001 and 2 times the wavelength of the acoustic wave. In this case, the thickness of the piezoelectric thin film may preferably be between 0.01 and 0.6 times the wavelength of the acoustic wave, more preferably between 0.02 and 0.6 times, even more preferably between 0.03 and 0.4 times, or even more preferably between 0.3 and 0.3 times.

[0026] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-132°, 0°±5°), (0°±5°, 0°-18°, 0°±5°), (0°±5°, 42°-65°, 0°±5°) or (0°±5°, 126°-180°, 0°±5°), which can provide a positive TCF for a Rayleigh wave or LSAW, and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (0°±5°, 75°-165°, 0°±5°), and may preferably have Euler angles of (0°±5°, 100°-160°, 0°±5°). In this case, the substrate may preferably have Euler angles of (0°±5°, 0°-12°, 0°±5°), (0°±5°, 44°-63°, 0°±5°) or (0°±5°, 135°-180°, 0°±5°).Furthermore, in this case, the piezoelectric thin film may preferably have a thickness between 0.001 times and 2 times the wavelength of the surface acoustic wave, preferably between 0.01 times and 0.6 times, more preferably between 0.012 times and 0.6 times, even more preferably between 0.02 times and 0.5 times, or even more preferably between 0.03 times and 0.33 times.

[0027] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-42°, 90°±5°), (0°±5°, 90°-155°, 90°±5°), (0°±5°, 0°-45°, 90°±5°), or (0°±5°, 123°-180°, 90°±5°), which can provide a positive TCF for a Rayleigh wave or an LSAW, and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (0°±5°, 70°-170°, 0°±5°). In this case, the substrate may preferably have Euler angles of (0°±5°, 0°-34°, 90°±5°) or (0°±5°, 126°-180°, 90°±5°). Furthermore, in this case, the piezoelectric thin film may preferably have a thickness between 0.001 and 2 times the wavelength of the surface acoustic wave, preferably between 0.01 and 0.5 times, more preferably between 0.02 and 0.33 times, even more preferably between 0.06 and 0.3 times.

[0028] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (1°-39°, 100°-150°, 0°-20° or 70°-120° or 160°-180°), and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (0°±5°, 95°-160°, 0°±5°). Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (1°-39°, 70°-150°, 0°-20° or 70°-120° or 160°-180°), and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (0°±5°, 25°-51°, 0°±5°).

[0029] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 90°-178°, 0°±5°) or (0°±5°, 80°-160°, 90°±5°), and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles for exciting a Rayleigh wave of (0°±5°, 35°-70°, 0°±5°), preferably (0°±5°, 45°-63°, 0°±5°), or more preferably (0°±5°, 48°-60°, 0°±5°). Furthermore, in this case, the substrate providing a positive TCF for an LSAW and a Rayleigh wave may preferably have Euler angles of (0°±5°, 90°-178°, 0°±5°) or (0°±5°, 125°-160°, 90°±5°).

[0030] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 0°-16°, 0°±5°), (0°±5°, 42°-64°, 0°±5°), (0°±5°, 138°-180°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 130°-180°, 90°±5°), (0°±5°, 0°-28°, 30°-60°), (0°±5°, 42°-70°, 30°-60°), or (0°±5°, 132°-180°, 30°-60°), and the piezoelectric thin film may be made of LiNbO3 crystal and have Euler angles of (0°±5°, 75°-165°, 0°±5°), or more preferably (0°±5°, 90°-160°, 0°±5°). In this case, the Euler angles of the substrate may more preferably be (0°±5°, 43°-61°, 0°±5°), (0°±5°, 147°-180°, 0°±5°), (0°±5°, 0°-15°, 90°±5°), (0°±5°, 134°-180°, 90°±5°), (0°±5°, 0°-23°, 30°-60°), (0°±5°, 43°-67°, 30°-60°), or (0°±5°, 137°-180°, 30°-60°).

[0031] Furthermore, in an acoustic wave device according to the present invention, the substrate may have Euler angles of (0°±5°, 32°-118°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 173°-180°, 90°±5°), or (0°±5°, 0°-142°, 30°-60°), and the piezoelectric thin film may be formed of LiNbO3 crystal and have Euler angles of (0°±5°, 35°-70°, 0°±5°) or preferably (0°±5°, 45°-63°, 0°±5°). In this case, the Euler angles of the substrate may preferably be (0°+5°, 40°-102°, 0°±5°), (0°±5°, 0°-17°, 90°±5°), (0°±5°, 175°-180°, 90°±5°) or (0°±5°, 13°-130°, 30°-60°).

[0032] Furthermore, in an acoustic wave device according to the present invention, a surface acoustic wave to be used may be either in a fundamental or 0-mode or in a higher-order mode. In a case where a higher-order mode is used, a piezoelectric thin film may preferably have a thickness between 0.35 times and 9.3 times the wavelength of a surface acoustic wave. Furthermore, in a case where a shunt electrode is provided between a substrate and a piezoelectric thin film, the piezoelectric thin film may have a thickness between 0.5 and 9 times the wavelength of a surface acoustic wave. In these cases, a higher impedance ratio can be achieved.

[0033] Here, the Euler angles (φ, θ, ψ) are in the right-hand system and represent a cross-sectional area of ​​the substrate or piezoelectric thin film and a propagation direction of the surface acoustic wave. In other words, for the crystal axes X, Y, and Z of the crystal or LT or LN constituting the substrate, an X' axis can be obtained by rotating the X axis counterclockwise around the Z axis as the rotation axis φ. Next, a Z' axis can be obtained by rotating the Z axis counterclockwise around the X' axis as the rotation angle θ. Then, the Z' axis is defined as a normal line, and a plane with the X' axis is defined as the cross-sectional area of ​​the substrate or piezoelectric thin film. Furthermore, a direction obtained by ψ-rotating the X'-axis counterclockwise around the Z'-axis as the rotation axis is defined as the propagation direction of a surface acoustic wave.Furthermore, these rotations result in the movement of the Y-axis and provide an axis defined as the Y'-axis perpendicular to the X'-axis and the Z'-axis.

[0034] According to these definitions of Euler angles, a propagation with 40° rotation-Y-plate-X direction can be expressed as an Euler angle of (0°, 130°, 0°) and a propagation with 40° rotation-Y-plate-90°-X direction can be expressed as an Euler angle of (0°, 130°, 90°), for example.

[0035] It should be noted that in an acoustic wave device according to the present invention, the substrate and the piezoelectric thin film may not only have the Euler angles described above, but also have crystallographically equivalent Euler angles. In this case, too, a better TCF and characteristics with higher Q and impedance ratio can be achieved. When the substrate or the piezoelectric thin film is cut out at desired Euler angles, an error of about ±0.5° at most can be included for each component of the Euler angles. The shape of an IDT may include an error of about ±3° for the propagation direction ψ. The properties of the acoustic wave substantially include no characteristic difference caused by a shift of about ±5° for the φ and ψ components of the Euler angles (φ, θ, ψ). Advantageous effects of the invention

[0036] According to the present invention, it may be possible to provide an acoustic wave device having a better TCF and allowing a resonator to have a Q and impedance ratio. Brief description of the drawings

[0037] Unless otherwise stated, an Al-IDT may refer to an interdigital transducer electrode that includes an aluminum electrode with a thickness of 0.08 wavelengths. The figures show the following: Fig. 1(a), Fig. 1(b) and Fig. 1(c) are perspective views illustrating a conventional acoustic wave device comprising an Al-IDT / piezoelectric substrate, an acoustic wave device according to an embodiment of the present invention, and an alternative example comprising a bonding film of the acoustic wave device of the present invention, respectively; Fig. 2(a) and Fig. Figure 2(b) are graphs illustrating the frequency characteristics of the impedance (Z) of an Al-IDT / (0°, 110°, 0°) LT substrate of a conventional acoustic wave resonator and an Al-IDT / (0°, 132°, 0°) LT substrate of a conventional acoustic wave resonator, respectively. In the graphs, the frequencies for the minimum Z and maximum Z are referred to as the resonance frequency (fr) and antiresonance (fa), respectively, and the corresponding Zs are referred to as Zr and Za, respectively. The bandwidth is expressed as (fa - fa) / fr, and the impedance ratio is expressed as 20 × Log (Za / Zr); Fig. 3(a) and Fig. 3(b) are graphs illustrating the frequency characteristics of the impedance (Z) of an acoustic wave resonator having a structure of an Al-IDT / (0°, 110°, 0°) LT thin film (thickness of 0.15 wavelengths) / (0°, 130°, 90°) quartz substrate and an acoustic wave resonator having a structure of an Al-IDT / (0°, 120°, 0°) LT thin film (thickness of 0.15 wavelengths) / (0°, 130°, 0°) quartz substrate; Fig. 4(a) and Fig. 4(b) are graphs illustrating the frequency characteristics of the impedance (Z) of an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (thickness 0.15 wavelength) / (0°, 130°, 30°) quartz substrate and an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (thickness 0.15 wavelength) / (0°, 130°, 60°) quartz substrate; Fig. Figure 5 is a diagram illustrating that the Rayleigh wave and LSAW phase velocities can depend on a propagation direction ψ on a (0°, 130°, ψ) quartz substrate; Fig. 6(a) and Fig. 6(b) are graphs illustrating the frequency characteristics of the impedance (Z) of an acoustic wave resonator having an Al-IDT / (0°, 132°, 0°) LT thin film / (110)Si substrate structure and an acoustic wave resonator having an Al-IDT / (0°, 132°, 0°) LT thin film / c-sapphire substrate structure; Fig. 7(a), Fig. 7(b) and Fig. 7(c) are diagrams illustrating that Rayleigh wave and LSAW phase velocities, Rayleigh wave and LSAW TCFs, and displacement ratios between an LSAW longitudinal wave displacement component U1, an SH component U2, and a shear vertical (SV) component U3, respectively, on a substrate surface can depend on θ for a (0°, θ, 0°) quartz substrate; Fig. 8(a), Fig. 8(b) and Fig. 8(c) are diagrams illustrating that Rayleigh wave and LSAW phase velocities, Rayleigh wave and LSAW TCFs, and displacement ratios between an LSAW longitudinal wave displacement component U1, SH component U2, and shear vertical (SV) component U3 on a substrate surface can depend on θ for a (0°, θ, 90°) quartz substrate; Fig. Figure 9 is a diagram illustrating that the phase velocities for different φs and θs can depend on ψ on a (φ, θ, ψ) quartz substrate; Fig. 10(a), Fig. 10(b) and Fig. 10(c) are diagrams illustrating that Rayleigh wave and LSAW phase velocities (the solid line (v f ) and the dashed line (v m) in the diagram correspond to the phase velocities in a case where the LT substrate surface is electrically open and where the LT substrate is short-circuited), Rayleigh wave and LSAW electromechanical conductances (coupling factors) or an LSAW TCF can depend on θ for a (0°, θ, 0°) LT substrate; Fig. 11(a) and Fig. 11(b) are diagrams illustrating that a bandwidth or an impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, θ, 0°) LT thin film (0.15 wavelength thickness) / (0°, 115°-145°, 0°) quartz substrate can depend on θ (θ in each diagram corresponds to θ of the quartz substrate); Fig. 12(a) and Fig. 12(b) are graphs illustrating that the impedance ratios when the Al thickness is 0.08 wavelength and when the Al thickness is 0.2 wavelength can be dependent on θ for an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength) / (0°, θ, 0°) quartz substrate (the solid line shows a characteristic with no ripple and the dashed line shows a characteristic with a ripple between the resonance and anti-resonance frequencies); Fig. 13(a) and Fig. 13(b) are diagrams illustrating that a bandwidth and an impedance ratio of an acoustic wave resonator with Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / (0°, 130°, 0°) quartz substrate can depend on the LT film thickness when the Al thickness is 0.08 wavelength and 0.2 wavelength; Fig. 14(a) and Fig. 14(b) are diagrams illustrating that a bandwidth or an impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, θ, 0°) LT thin film (0.15 wavelength thickness) / (0°, 100°-175°, 90°) quartz substrate can depend on θ (θ indicated in each diagram corresponds to θ of the quartz substrate); Fig. 15(a) and Fig. 15(b) are graphs illustrating that the impedance ratios of an acoustic wave resonator with a structure of Al-IDT / (0°, 110°, 0°) LT thin film / (0°, θ, 90°) quartz substrate when the LT thickness is 0.15 wavelengths and the Al thickness is 0.08 wavelengths ( Fig. 15(a)) and when the LT thickness is 0.15 wavelengths and the Al thickness is 0.1 wavelengths and the LT thickness is 1.25 wavelengths and 2 wavelengths and the Al thickness is 0.2 wavelengths ( Fig. 15(b)) can depend on θ (the solid line shows a property without ripple and the dashed line shows a property with a ripple between the resonance and antiresonance frequencies), and Fig. 15(c) is a diagram illustrating a frequency characteristic of the impedance (Z) when θ = 125.25° on the quartz substrate in Fig. 15(b); Fig. 16(a) and Fig. 16(b) are diagrams illustrating that a bandwidth and an impedance ratio of an acoustic wave resonator having an Al-IDT / (0°, 110°, 0°) LT thin film / (0°, 128°, 90°) quartz substrate structure may depend on the LT film thickness when the Al thickness is 0.08 wavelength and 0.2 wavelength; Fig. 17(a) is a diagram illustrating that a frequency characteristic of the impedance (Z) of an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / (0°, 45°, 0°) quartz substrate can depend on the LT layer thickness, and Fig. Figure 17(b) is a graph illustrating that impedance ratios when the Al thickness is 0.12 wavelength and 0.2 wavelength may depend on the LT layer thickness; Fig. 18 is a diagram illustrating that the impedance ratios of acoustic wave resonators with Al-IDT / (0°, 110°, 0°, 0°) LT thin film / (20°, 120°, 115°) quartz substrate and Al-IDT / (0°, 110°, 0°) LT thin film / (0°, 130°, 0°) quartz substrate structures can depend on the LT layer thickness; Fig. 19(a), Fig. 19(b) and Fig. 19(c) are diagrams illustrating that a (0°, θLT, 0°) LT thin film (0.15 wavelength thickness) / (0°, θ quartz, 0°) quartz substrate structure, a (0°, θ LT , 0°) LT thin film (0.15 wavelength thickness) / (0°, θ quartz , 90°) quartz substrate structure and a (0°, θLT, 0°) LT thin film (0.15 wavelength thickness) / (0°, θ quartz , 30°-60°) Quartz substrate - structure of θ quartz may depend on TCFs if θ LT = 80°, 125° and 148°; Fig. 20(a), Fig. 20(b) and Fig. 20(c) are diagrams illustrating that when the surface of the (0°, θ, 0°) LN substrate is electrically open (Vf) and short-circuited (Vm), Rayleigh wave and LSAW electromechanical coupling coefficients (coupling factors), and Rayleigh wave and LSAW TCFs, respectively, can depend on θ; Fig. 21 is a graph showing a frequency response of the impedance (Z) of an acoustic wave resonator having a structure of Al-IDT / (0°, 131°, 0°) LN thin film (0.15 wavelength thickness) / (0°, 115°, 90°) quartz substrate; Fig. Figure 22(a) is a graph illustrating that the wave impedance ratios of LSAW and Rayleigh of an acoustic wave resonator with a structure of Al-IDT / (0°, θ, 0°) LN thin film (0.15 wavelength thickness) / (0°, 130°, 0°) quartz substrate can depend on θ, and Fig. 22(b) is a diagram illustrating that an LSAW impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, 131°, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ, 0°) quartz substrate when the Al thickness is 0.08 wavelength and 0.2 wavelength can depend on θ, and that a Rayleigh wave impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, 55°, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ, 0°) quartz substrate can depend on θ when the Al thickness is 0.08 wavelength (the solid line shows a characteristic with no ripple and the dashed line shows a characteristic with a ripple between the resonance and the anti-resonance frequency); Fig. 23(a) and Fig. 23(b) are diagrams illustrating that a bandwidth and an impedance ratio of an acoustic wave resonator having an Al-IDT / (0°, 131°, 0°) LT thin film / (0°, 130°, 0°) quartz substrate structure can depend on the LT layer thickness when the Al thickness is 0.08 wavelength and 0.2 wavelength; Fig. Figure 24(a) is a diagram illustrating that the LSAW and Rayleigh wave impedance ratios of an acoustic wave resonator having a structure of Al-IDT / (0°, θ, 0°) LN thin film (0.15 wavelength thickness) / (0°, 130°, 90°) quartz substrate can depend on θ, and Fig. 24(b) is a graph illustrating that an LSAW impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, 131°, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ, 90°) quartz substrate can depend on θ when the Al thickness is 0.08 wavelength and 0.2 wavelength, and that a Rayleigh wave impedance ratio of an acoustic wave resonator having a structure of Al-IDT / (0°, 38°, 0°) LN thin film (0.15 wavelength) / (0°, θ, 90°) quartz substrate can depend on θ when the Al thickness is 0.08 wavelength (the solid line shows a characteristic with no ripple and the dashed line shows a characteristic with ripple between the resonance and anti-resonance frequency); Fig. 25(a) and Fig. 25(b) are diagrams illustrating that a bandwidth and an impedance ratio of an acoustic wave resonator having an Al-IDT / (0°, 131°, 0°) LT thin film / (0°, 115°, 90°) quartz substrate structure may depend on the LT film thickness when the Al thickness is 0.08 wavelength and 0.2 wavelength; Fig. 26(a), Fig. 26(b) and Fig. 26(c) are diagrams illustrating that a (0°, θLN, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ quartz , 0°) quartz substrate structure, a (0°, θLN, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ quartz , 90°) quartz substrate structure and a (0°, θLN, 0°) LN thin film (0.15 wavelength thickness) / (0°, θ quartz , 30°-60°) Quartz substrate structure each of θ quartz may depend on TCFs if θ LN = 38°, 85° and 154°; Fig. Figure 27 is a diagram illustrating that the impedance ratios of longitudinal leaky surface acoustic wave resonators with Al-IDT / (90°, 90°, ψ) LT thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate and Al-IDT / (90°, 90°, ψ) LN thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate structures can depend on ψ; Fig. 28 is a diagram showing a frequency characteristic of the impedance (Z) of an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / silica substrate; Fig. Figure 29 is a graph illustrating that the impedance ratios of acoustic wave resonators with Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / various substrates structures can depend on the LT layer thickness. Fig. 30 is a diagram illustrating that the impedance ratios of acoustic wave resonators with Al-IDT / (0°, 110°, 0°) LT thin film / SiO2 film / high phase velocity substrate and Al-IDT / (0°, 131°, 0°) LN thin film / SiO2 film / high phase velocity substrate structures can depend on the SiO2 layer thickness; Fig. 31(a) and Fig. 31(b) are diagrams illustrating that a bandwidth or an impedance ratio of acoustic wave resonators with structures of different IDTs / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrates may depend on the thickness of the interdigital transducer electrodes (electrode thickness) made of different materials; Fig. 32(a) and Fig. 32(b) are diagrams illustrating that a bandwidth or an impedance ratio of acoustic wave resonators with structures of different IDTs / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrates can depend on a metallization ratio of interdigital transducer electrodes made of different materials (metallization ratio = 2 × electrode width / wavelength); Fig. 33(a), Fig. 33(b), Fig. 33(c) and Fig. 33(d) are elevation views of acoustic wave devices having an IDT / piezoelectric thin film / substrate structure, an IDT / piezoelectric thin film / shunt electrodes / substrate structure, a piezoelectric thin film / IDT / substrate structure (an upper portion illustrates the IDT embedded in the substrate, and the lower portion illustrates the IDT embedded in the piezoelectric thin film), and a shunt electrodes / piezoelectric thin film / IDT / substrate structure (the upper portion illustrates the IDT embedded in the substrate, and the lower portion illustrates the IDT embedded in the piezoelectric thin film); Fig. 34(a) and Fig. 34(b) are diagrams illustrating that a bandwidth and an impedance ratio of an acoustic wave resonator including each in the Fig. 33(a) to 33(d) with a (0°, 110°, 0°) LT thin film and a (0°, 132.75°, 90°) quartz substrate may depend on the LT layer thickness; Fig. 35 is a diagram illustrating that the impedance ratios of acoustic wave resonators including a (0°, 110°, 0°) LT thin film and a (0°, 132.75°, 90°) quartz substrate and having a structure of Al-IDT fully or partially embedded in the LT thin film and a structure of Al-IDT not embedded in the LT thin film may depend on the LT layer thickness; Fig. 36(a), Fig. 36(b) and Fig. 36(c) are diagrams illustrating that a phase velocity, a bandwidth, and an impedance ratio, respectively, of an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / barrier film / (0°, 132.75°, 90°) quartz substrate can depend on the barrier film thickness; Fig. 37(a), Fig. 37(b), Fig. 37(c) and Fig. 37(d) are diagrams showing the impedance ratios of acoustic wave resonators with structures made of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / SiO2 / Si x N y / (0°, 132.75°, 90°) quartz substrate, Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / Si x N y / SiO2 / (0°, 132.75°, 90°) quartz substrate, Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / ZnO / SiO2 / (0°, 132.75°, 90°) quartz substrate and Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / Ta2O5 / SiO2 / (0°, 132.75°, 90°) quartz substrate may each depend on the SiO2 layer thickness; Fig. 38(a) and Fig. 38(b) are diagrams illustrating that the impedance ratios of acoustic wave resonators with structures made of Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / SiO2 / Si x N y / third layer of barrier film / (0°, 132.75°, 90°) quartz substrate and Al-IDT / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / Si x N y / SiO2 / third layer of the boundary film / (0°, 132.75°, 90°) quartz substrate, in which the third layer of the boundary film (third layer film) is made of different materials, may depend on the thickness of the third layer film; Fig. 39 is a graph showing a frequency response of the impedance (Z) of an acoustic wave resonator having a structure of Al-IDT / (0°, 110°, 0°) LN thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate; Fig. 40 is a diagram illustrating that the impedance ratios in higher-order modes of acoustic wave resonators with structures of different IDTs / (0°, 110°, 0°) LT thin film (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate can depend on the thickness of the interdigital transducer electrodes (electrode thickness) made of different materials; Fig. 41 is a diagram illustrating that the impedance ratios of acoustic wave resonators with Au-IDT / (0°, 110°, 0°, 0°) LT thin film / (0°, 132.75°, 90°) quartz substrate and Au-IDT / (0°, 110°, 0°) LT thin film / shunt electrode / (0°, 132.75°, 90°) quartz substrate structures can depend on the LT layer thickness; Fig. 42(a) and Fig. 42(b) are diagrams illustrating that the impedance ratios of acoustic wave resonators with Al-IDT / (0°, 110°, 0°) LT thin film / (0°, θ, 0°) quartz substrate and Al-IDT / (0°, 110°, 0°) LT thin film / (0°, θ, 90°) quartz substrate structures can each depend on θ in a higher mode (1st) for different LT layer thicknesses; and Fig. 43 illustrates side views showing a method of manufacturing an acoustic wave device according to an embodiment of the present invention. Description of the embodiments

[0038] The embodiments of the present invention are described below with reference to the drawings. Fig. 1 to 43 illustrate acoustic wave devices according to embodiments of the present invention. As shown in Fig. 1(b), an acoustic wave device 10 according to an embodiment of the present invention includes a substrate 11, a piezoelectric thin film 12 disposed on the substrate 11, and an interdigital transducer (IDT) electrode 13 disposed on the piezoelectric thin film 12.

[0039] The substrate 11 contains 70 mass% or more of SiO2. The substrate 11 is formed, for example, from quartz, Pyrex (registered trademark) glass, quartz glass, borosilicate glass, synthetic quartz, fused silica, or the like. The piezoelectric thin film 12 is formed from LiTaO3 (LT) crystal or LiNbO3 (LN) crystal. Furthermore, in the case of an acoustic wave resonator, reflectors 14 formed from a plurality of electrode fingers may be arranged to enclose or embed the interdigital transducer electrode 13.

[0040] The interdigital transducer (IDT) electrode 13 includes a pair of electrode fingers 21, each of which includes a bus bar and a plurality of electrode fingers 21 connected to the bus bar and extending perpendicular to the longitudinal direction of the bus bar. Each IDT 13 includes the plurality of electrode fingers 21 arranged to alternate with each other (interdigitate). Each IDT 13 has an approximately constant distance between the electrode fingers 21. In a case where the number of electrode fingers 21 is m, (m - 1) / 2 = N can be referred to as the pair number. If the length between (the center of) the adjacent electrode fingers 21 is defined as I, 2l = λ can be one period and corresponds to the wavelength of an acoustic wave excited by the acoustic wave device.

[0041] Each reflector 14 is arranged along the propagation direction of a surface acoustic wave and is spaced from the interdigital transducer electrode 13 to embed the interdigital transducer electrode 13 from both sides. Each reflector 14 includes a pair of bus bars and a plurality of electrode fingers bridged between and extending between the bus bars. Each reflector 14 has approximately the same spacing of the respective electrode fingers as each electrode finger spacing of the interdigital transducer electrode 13, and the spacing is kept constant.

[0042] It should be noted that Fig. 1(a) illustrates a conventional acoustic wave device 50 for comparison. As in Fig. As shown in Figure 1(a), the conventional acoustic waveguide 50 has a structure in which an interdigital transducer electrode (IDT) 52 is formed on a piezoelectric substrate 51 made of LT or LN. Furthermore, a pair of reflectors 53 are provided to embed the interdigital transducer electrode 52.

[0043] Note that Euler angles (φ, θ, ψ) can be represented simply as (φ, θ, ψ). Furthermore, the thickness of the piezoelectric thin film 12 or the interdigital transducer electrodes 13 and 52 can be represented as a magnification of the wavelength λ of an acoustic wave device to be used. Furthermore, unless otherwise stated, a quartz substrate 11 is used as the substrate 11. Furthermore, the Euler angles of the substrate 11 or the piezoelectric thin film 12 indicated below may be crystallographically equivalent Euler angles. [Specific examples of the properties of the respective LT, LN and quartz substrates]

[0044] The Fig. 2(a) and Fig. 2(b) illustrate the frequency characteristics of the impedance (Z) obtained from a SAW resonator designed based on the Fig. 1(a), in which an interdigital transducer electrode 52 made of Al with a thickness of 0.08 wavelength is formed on a piezoelectric substrate 51 having a (0°, 110°, 0°) LT substrate and a piezoelectric substrate 51 having a (0°, 132°, 0°) LT substrate.

[0045] As in Fig. As shown in Figure 2(a), when using the (0°, 110°, 0°) LT substrate, there are larger ripples between a resonant frequency fa and an anti-resonant frequency fa. The bandwidth BW between fr and fa (BW = (fa - fr) / fr) was 5.2%, and the ratio between resonant resistance and anti-resonant resistance (Z-ratio) was 53 dB. Furthermore, as shown in Fig. As shown in Figure 2(b), the ripples between fr and fa in the (0°, 132°, 0°) LT substrate were reduced. The BW was 3.8% and the impedance ratio was 63 dB.

[0046] The Fig. 3(a) and Fig. 3(b) illustrate the frequency characteristics of the impedance (Z) obtained by combining a piezoelectric LT thin film 12 with a quartz substrate 11 in the configuration shown in Fig. 1(b), in which an interdigital transducer electrode 13 made of Al having a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 130°, 90°) quartz substrate 11 structure and a (0°, 120°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 130°, 0°) quartz substrate 11 structure.

[0047] As in Fig. 3(a), there is no waviness, although the Euler angles of LT are identical to those of Fig. 2(a) at (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 130°, 90°) quartz substrate 11 are identical, so a significant improvement was achieved. In particular, the bandwidth (BW) is 6.1%, which is about 20% wider, and the impedance ratio is 77.5 dB, which is 24.5 dB larger. Such an increase in the impedance ratio corresponds to ten times or more Q. Furthermore, the BW, as shown in Fig. 3(b), 5.5% and the impedance ratio is 77.0 dB, where the BW has become wider and the impedance ratio has increased by 15 dB compared to those of Fig. 2(b) in the (0°, 120°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 130°, 0°) quartz substrate 11 structure has been significantly improved. These increases in the impedance ratio correspond to 10 times or higher Q. As a result, it has been found that the use of the quartz substrate 11 can provide extremely good transconductance and insertion loss characteristics compared to a single LT substrate alone. Furthermore, the coupling factor can be increased, although the difference may be small.

[0048] It should be noted that the (0°, 130°, 90°) quartz substrate 11 or the (0°, 130°, 0°) quartz substrate 11 can excite both an LSAW and a Rayleigh wave (see Fig. 5, Fig. 7 and Fig. 8); the properties of Fig. However, 3 were obtained using a LSAW. When using the Rayleigh wave, no or only a slight response was confirmed in the SAW.

[0049] The Fig. 4(a) and Fig. 4(b) illustrate the frequency characteristics of the impedance (Z) obtained by forming an interdigital transducer electrode 13 made of Al and having a thickness of 0.08 wavelength on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength) / (0°, 130°, 30°) quartz substrate 11 structure and a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength) / (0°, 130°, 60°) quartz substrate 11 structure. As in the Fig. 4(a) and Fig. 4(b), there are larger ripples within the bandwidth and no better characteristics can be achieved. However, when the ψ of quartz is 85°, 95°, -5° and 5°, similar characteristics to those shown in the Fig. 3(a) and Fig. 3(b). As described above, larger wavinesses can occur depending on the Al thickness and Euler angles, and therefore, how the Al thickness and Euler angles are chosen can be important.

[0050] Fig. Figure 5 illustrates that the Rayleigh wave and LSAW phase velocities can depend on a propagation direction ψ for a (0°, 130°, ψ) quartz substrate 11. As in Fig. 5, the LSAW phase velocities at the quartz substrate 11 at ψ = 0° and 90° are as high as about 5,000 m / s, while the LSAW phase velocities at ψ = 30° and 60° are as low as about 3,800 m / s. It should be noted that a power flow angle (PFA) = 0 can be achieved when the tangent δV / δψ of a phase velocity V to a propagation direction ψ is zero. The PFA = 0 at ψ = 0°, 35° and 90° by the Rayleigh wave of Fig. 5 and near ψ = 0°, 42° and 90° by an acoustic leakage surface wave.

[0051] As in the Fig. As shown in Figures 3 to 5, the LSAW phase velocity through the LT thin film 12 used is 4100 m / s, while using the (0°, 130°, 30°) and (0°, 130°, 60°) quartz substrates 11 with the LSAW phase velocity of only 3800 m / s, no better characteristic can be achieved at the Al thickness of 0.08 wavelength. In contrast, better characteristic can be achieved when using the (0°, 130°, 0°) and (0°, 130°, 90°) quartz substrates 11 with the LSAW phase velocity of up to 5000 m / s. Furthermore, as shown in Figures Fig. 2 and Fig. 3, the (0°, 110°, 0°) LT substrate, which can exhibit a larger leakage component, can provide a greater improvement in characteristics compared to the (0°, 132°, 0°) LT substrate. Therefore, as a measure for the characteristic improvement, it is assumed that a leakage component of the LSAW of the LT thin film 12 becomes zero by bonding the quartz substrate 11, which allows the LSAW to be larger than that of the LT thin film 12.

[0052] The Fig. 6(a) and Fig. Figure 6(b) illustrates the frequency characteristics of the impedance (Z) obtained in SAW resonators in which a (0°, 132°, 0°) LT thin film (0.15 wavelength thickness) is bonded to a (110) surface (001) directional propagation substrate Si and a c-sapphire substrate, each with a higher phase velocity, and then an interdigital transducer electrode made of Al with a thickness of 0.08 wavelength is formed thereon. As shown in Fig. 6(a), the BW was 4.4% and the impedance ratio was 69 dB when the Si substrate was used. As shown in Fig. As shown in Figure 6(b), the BW was 5.7% and the impedance ratio was 68 dB when the sapphire substrate was used.

[0053] The Fig. 6(a) and Fig. 6(b) indicate that the BW is wider and the impedance ratio is 5 to 6 dB better than the characteristics of the SAW resonator of a single LT substrate in Fig. 2(b); however, the provisions of Fig. 3 is far superior to the LT thin film 12 / quartz substrate 11 structure shown in FIG. Not only a Rayleigh wave but also an LSAW is excited with a piezoelectric substrate made of quartz, LT, LN, and the like, while only a Rayleigh wave of the SAW modes can be excited with the Si substrate or the sapphire substrate, which does not have piezoelectricity. Accordingly, it is assumed that, unlike the quartz substrate 11 used, which uses the same LSAW as the LT thin film 12, the Si substrate or the sapphire substrate has a higher shear wave velocity of a bulk wave than the LT thin film and uses a Rayleigh wave different from the LSAW of the LT thin film used.

[0054] Therefore, by using, as a base substrate, a substrate with a higher phase velocity close to the shear wave velocity of the bulk wave and mainly including an SH component as the shear wave phase velocity, and bonding the base substrate to the piezoelectric thin film 12 to be used made of LT, LN, and the like, better characteristics can be achieved. The larger the LSAW velocity difference between the piezoelectric thin film 12 and the substrate, the better. For example, the difference is preferably 300 m / s or greater, and more preferably 600 m / s or greater.

[0055] The Fig. 7(a) and Fig. 7(b) illustrate the θ-dependence of phase velocities and TCFs for Rayleigh wave and LSAW of a (0°, θ, 0°) quartz substrate 11. Furthermore, Fig. 7(c) the displacement ratios on the substrate surface between a displacement component U1, an SH component U2, and an SV component U3 of the longitudinal wave of the LSAW. As in Fig. 7(a), higher phase velocities of 4,500 m / s or more, 4,800 m / s or more, and 5,000 m / s or more can be achieved at θ = 70°-165°, θ = 90°-150°, and θ = 100°-140°, respectively. Furthermore, the TCFs, as shown in Fig. 7(b), positive at θ = 0°-132° for the Rayleigh wave and positive at θ = 0°-18°, 43°-66°, and 132°-180° for the LSAW. The quartz substrate 11 with Euler angles that allow the Rayleigh wave or LSAW to have positive TCFs is preferably combined with LT and LN with negative TCFs for the LSAW, so that better TCFs close to zero ppm / °C can be obtained. Preferably, better TCFs can be obtained in combination with the quartz substrate 11 with TCFs of +5 ppm / °C under θ = 0°-130° for Rayleigh wave or under θ = 0°-16°, 44°-65°, and 135°-180° for LSAW. Furthermore, as in Fig. 7(c), it is found that the SH component (U2 component) increases by about 50% or more at θ = 70°-165°, where the LSAW phase velocity is larger.

[0056] The Fig. 8(a) and Fig. 8(b) illustrate the dependence of phase velocities and TCFs for the Rayleigh wave and the LSAW of a (0°, θ, 90°) quartz substrate 11. Furthermore, Fig. 8(c) shows the displacement ratios on the substrate surface between a displacement component U1, a SH component U2, and an SV component U3 of the longitudinal wave from the LSAW. As in Fig. 8(a), higher phase velocities of 4,500 m / s or more, 4,800 m / s or more, and 5,000 m / s or more are achieved at θ = 90°-150°, θ = 103°-143°, and θ = 110°-135°, respectively. Furthermore, the TCFs, as shown in Fig. 8(b), positive at θ = 0°-42° and 170°-180° for the Rayleigh wave and positive at θ = 0°-41° and 123°-180° for the LSAW. The quartz substrate 11 with Euler angles that allow the Rayleigh wave or LSAW to have positive TCFs is preferably combined with LT and LN with negative TCFs for the LSAW, so that better TCFs close to zero ppm / °C can be obtained. Preferably, better TCFs can be obtained in combination with the quartz substrate 11 with TCFs of +5 ppm / °C at θ = 0°-39° and 172°-180° for the Rayleigh wave or at θ = 0°-39° and 126°-180° for the LSAW. Furthermore, as in Fig. 8(c), it is found that the SH component (U2 component) increases approximately by 65% ​​or more at θ = 85°-165°, where the LSAW phase velocity is larger.

[0057] Fig. Figure 9 illustrates the phase velocities of quartz substrates 11 with different Euler angles. According to the quartz substrates 11 with Euler angles as shown in Fig. As indicated in Figure 9, higher phase velocities such as 4,500 m / s or more can be achieved at ψ = 0°-20°, 70°-120°, and 160°-180°. Furthermore, although not illustrated, LSAWs with higher phase velocities can be obtained by Euler angles of (1°-39°, 100°-150°, 0°-20°), (1°-39°, 100°-150°, 70°-120°), and (1°-39°, 100°-150°, 160°-180°).

[0058] Acoustic wave devices may preferably use a substrate with a direction close to zero in a power flow angle (a propagation direction with zero on a tangent line in the LSAW propagation direction) to prevent oblique propagation of the LSAW. According to the quartz substrates 11 with Euler angles as shown in Fig. 9, directions close to zero in the power flow angle are at (0°±5°, θ, 35°±8°), (10°±5° , θ, 42°±8°), (20°±5°, θ, 50°±8°), (0°±5° , θ, 0°±5°), (10°±5°, θ, 0°±5°), (20°± 5°, θ, 0°±5°), (0°± 5°, θ, 90°±5°), (10°± 5°, θ, 90°±5°) and (20°± 5°, θ, 90°±5°) and the substrates having these Euler angles can be preferably used. [Specific examples of acoustic wave devices with an LT thin film / quartz substrate structure]

[0059] The Fig. 10(a) and Fig. 10(b) illustrates the θ-dependence of phase velocities and electromechanical coupling coefficients (coupling factors) for a Rayleigh wave and a LSAW of a (0°, θ, 0°) LT substrate, respectively. Furthermore, Fig. 10(c) shows the θ-dependence of TCFs for the (0°, θ, 0°) LT substrate. As in the Fig. 10(a) and Fig. As shown in Figure 10(b), an LSAW at θ = 120°–146° with a small leakage component and a coupling factor of 4% or more is generally used in an LT substrate. In this case, the phase velocity Vm (phase velocity when the substrate surface is electrically short-circuited) is in the range of 4,000 to 4,100 m / s. However, the bandwidth of the filter depends on the coupling factor of the substrate used, so the coupling factor must be selected to achieve the desired bandwidth.According to an acoustic wave device 10 of an embodiment of the present invention, the LT is used with a substrate arranged below the LT having a phase velocity similar to or higher than that of the LT, so that a leakage component can be reduced and thus better characteristics can be achieved by using θ = 65°-148° which allows a larger coupling factor and then using a quartz substrate 11 having a phase velocity of about 3,700 to 4,100 m / s or higher.

[0060] Furthermore, as in Fig. 10(c), each TCF for LSAW of the LT substrate is negative and lies between -30 and -70 ppm / °C. Although the TCFs for LSAW at θ = 120°-146° used by a single LT substrate are about -33 ppm / °C, the combination of the LT substrate with a quartz substrate 11 with a positive TCF for the Rayleigh wave or LSAW, i.e., a (0°, 0°-130°, 0°) substrate for Rayleigh waves and a (0°, 132°-180°, 0°) substrate for LSAW, as shown in Fig. 7, as well as (0°, 0°-39°, 90°) and (0°, 172°-180°) substrates for Rayleigh wave and (0°, 0°-41°, 90°) and (0°, 123°-180°, 90°) substrates for LSAW, as in Fig. 8, can lead to better TCFs such as 1 / 3 or less of the TCF of the single LT substrate.

[0061] The Fig. 11(a) and Fig. 11(b) illustrate the θ dependence at LT on resonator bandwidths and impedance ratios, respectively, obtained by an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, θ, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 115°-145°, 0°) quartz substrate 11 structure. It should be noted that θ shown in the graphs of Fig. 11(a) and Fig. 11(b), θ of the quartz substrate 11. As shown in Fig. 11(a), the bandwidth of 3.5% is achieved at θ = 82°-148° in LT. Furthermore, as shown in Fig. 11(b), impedance ratios of 70 dB or more, 73 dB or more, and 75 dB or more are obtained at θ = 85°-148° in LT, θ = 90°-140° in LT, and θ = 95°-135° in LT.

[0062] The Fig. 12(a) and Fig. 12(b) illustrate the θ dependence of impedance ratios obtained by acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, θ, 0°) quartz substrate 11 structure when the Al thickness is 0.08 wavelength ( Fig. 12(a)) and when the Al thickness is 0.2 wavelength ( Fig. 12(b)). In Fig. In Figure 12(a), a solid line indicates a characteristic without ripple, and dashed lines indicate characteristics with ripple within a bandwidth between fr and fa of the resonator. Better impedance ratios can be achieved at (0°, 115°-145°, 0°) in quartz, while ripple can be observed at other angles. Fig. However, in Figure 12(b), almost no ripple is observed and a larger impedance can be achieved at any orientation angle. Accordingly, the θ dependence of the impedance ratio can vary due to the Al electrode thickness. It should be noted that, although not illustrated, a characteristic close to that of the Al electrode thickness of 0.2 wavelength can be achieved by the Al electrode thickness of 0.08 wavelength or more. Considering the range that allows the LSAW of quartz to be positive, as in Fig. As shown in Figure 7(b), when the Al electrode has a thickness of 0.08 wavelength, the quartz substrate 11 can preferably be at (0°, 132°-145°, 0°), and more preferably at (0°, 135°-145°, 0°). In this case, combining the LT thin film 12 with a negative TCF with the quartz substrate 11 with a positive TCF can significantly improve the TCF of the acoustic wave device 10. In particular, when the quartz substrate 11 is at (0°, 135°-145°, 0°), a better TCF can be obtained.

[0063] Fig. 13(a) and Fig. 13(b) illustrate that the bandwidths and impedance ratios can depend on LT layer thicknesses, respectively, for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength is on a (0°, 110°, 0°) LT thin film 12 / (0°, 130°, 0°) quartz substrate 11 structure. As in Fig. 13(a), bandwidths of 3% or more are obtained for the LT film thickness from 0.02 wavelength to 2 wavelength. Furthermore, as shown in Fig. As shown in Figure 13(b), impedance ratios of 70 dB or more, 73 dB or more, and 75 dB are obtained when the Al thickness is 0.08 wavelengths at the LT film thicknesses of 0.01 to 0.6 wavelengths, 0.02 to 0.4 wavelengths, and 0.03 to 0.3 wavelengths, respectively. On the other hand, when the Al thickness is 0.2 wavelengths, impedance ratios of 70 dB, 73 dB or more, and 75 dB can be achieved at the LT film thicknesses of 2 wavelengths or less, 0.02 to 0.043 wavelengths, and 0.03 to 0.33 wavelengths, respectively. Note that the values ​​when the Al thickness is 0.1 to 0.3 wavelengths are approximately the same as those for the Al thickness of 2 wavelengths.

[0064] Fig. 14(a) and Fig. 14(b) illustrate that the bandwidths and impedance ratios of acoustic wave resonators can depend on θ at LT, for an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, θ, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 100°-175°, 90°) quartz substrate 11. It should be noted that θ shown in the diagrams of Fig. 14(a) and Fig. 14(b), θ of the quartz substrate 11. As shown in Fig. 14(a), a bandwidth of 3.5% is achieved at θ = 75°-155° in LT, except for the cases of θ = 165° and θ = 175° in the quartz substrate 11. Furthermore, as shown in Fig. 14(b) illustrates impedance ratios of 70 dB or more, 73 dB or more, 75 dB or more, and about 77 dB are obtained at θ = 80°-152° in LT, θ = 90°-140°, θ = 95°-135°, and θ = 103°-125° in LT.

[0065] Fig. Figure 15(a) illustrates that the impedance ratios of acoustic wave resonators can depend on θ on a quartz substrate 11, for an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 120°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, θ, 90°) quartz substrate 11 structure. In the figure, a solid line shows a characteristic with no ripple, and dashed lines show characteristics with a ripple within a bandwidth of the resonator. On the other hand, Fig. 15(b) shows a relationship between the impedance ratios and Euler angles when the LT thickness is 0.15 wavelength and the Al thickness is 0.1 wavelength, and the LT thickness is 1.25 wavelength and 2 wavelength, and the Al thickness is 0.2 wavelength.

[0066] In the Fig. 15(a) the Al thickness of 0.08 wavelength, a better impedance ratio is achieved at (0°, 100°-165°, 90°) quartz. With regard to Fig. 8(b), the Euler angles of the quartz substrate 11 that enable the quartz Rayleigh wave or LSAW to have a positive TCF are preferably (0°, 123°-165°, 90°±5°) near the Al thickness of 0.08 wavelength, more preferably the Euler angles (0°, 126°-165°, 90°±5°) of quartz that enable the TCF to be +5 ppm / °C or more, and far more preferably (0°, 127°-165°, 90°±5°) that enable the TCF to be +7 ppm / °C or more. In this case, combining the LT thin film 12 with a negative TCF with the quartz substrate 11 with a positive TCF can significantly improve the TCF of the acoustic wave device 10. In particular, when the quartz substrate 11 is at (0°, 127°-165°, 0°), a better TCF can be achieved.

[0067] Fig. Figure 15(c) illustrates the frequency characteristics of a (0°, 120°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 125.25°, 90°) quartz substrate 11 structure when the Al thickness is 0.1 wavelength. In this quartz orientation angle, a ripple occurs within the bandwidth at a certain Al thickness, so the impedance ratio of Fig. 15(b) is smaller than the other orientation angle. Because the combination with a (0°, 126°, 0°) LT thin film 12 can easily lead to larger waviness, it may be particularly desirable to avoid the combination of the (0°, 126°, 0°) LT thin film 12 with the (0°, 125.25°, 90°) quartz substrate 11.

[0068] Fig. 16(a) and Fig. 16(b) illustrate that the bandwidths and impedance ratios, respectively, can depend on LT layer thicknesses for acoustic wave devices 10 in which interdigital transducer electrodes 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength are arranged on a (0°, 110°, 0°) LT thin film 12 / (0°, 128°, 90°) quartz substrate 11 structure. As in Fig. 16(a), essentially the same properties as in Fig. 13(a) and a bandwidth of 3% or more can be achieved at an LT layer thickness of 0.04 wavelengths or more and 2 wavelengths or less. Furthermore, as shown in Fig. 16(b) illustrates essentially the same properties as in Fig. 13(b), and impedance ratios of 70 dB or more, 73 dB or more, and 75 dB or more can be obtained when the Al thickness is 0.08 wavelengths at the LT layer thicknesses of 0.01 to 0.6 wavelengths, 0.02 to 0.4 wavelengths, and 0.03 to 0.3 wavelengths, respectively. On the other hand, when the Al thickness is 2 wavelengths, impedance ratios of 70 dB, 73 dB or more, and 75 dB or more can be achieved at the LT layer thicknesses of 2 wavelengths or less, 0.02 to 0.043 wavelengths, and 0.03 to 0.33 wavelengths, respectively. It should be noted that the values ​​when the Al thickness is 0.1 wavelength or less are similar to those of 0.08 wavelength, and the values ​​when the Al thickness ranges from 0.1 to 0.3 wavelength are substantially the same as those of 0.2 wavelength Al thickness.

[0069] The Fig. 17(a) and Fig. 17(b) illustrate that the frequency characteristics of the impedance (Z) and the impedance ratios depend on the LT layer thicknesses when the LT thin film 12 has a thickness of 0.15 wavelength, by acoustic wave devices 10 in which interdigital transducer electrodes 13 made of Al with thicknesses of 0.12 wavelength and 0.2 wavelength are formed on a (0°, 110°, 0°) LT thin film 12 / (0°, 45°, 0°) quartz substrate 11 structure. Here, the (0°, 45°, 0°) quartz substrate 11 used has a positive Rayleigh wave TCF of 25 ppm / °C, a Rayleigh wave phase velocity of 3270 m / s, and an LSAW phase velocity of 3950 m / s. As shown in Fig. 17(a), the frequency is as low as 3GHz; however, a better impedance ratio of 75 dB is achieved. Furthermore, as shown in Fig. As shown in Figure 17(b), impedance ratios of 70 dB or more can be achieved at the LT layer thickness of 0.43 wavelength. As above, a slightly increased Al electrode thickness can also lead to improved properties for a substrate with a low LSAW phase velocity.

[0070] Fig. Figure 18 illustrates that impedance ratios may depend on LT layer thicknesses for acoustic wave devices 10 in which an Al interdigital transducer electrode 13 having a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 / (20°, 120°, 115°) quartz substrate 11 structure and a (0°, 110°, 0°) LT thin film 12 / (0°, 130°, 0°) quartz substrate 11 structure. Here, the (20°, 120°, 115°) quartz substrate 11 used has an orientation angle for exciting an S-wave (fast shear wave) with a high phase velocity around 5,000 m / s, and the (0°, 130°, 0°) quartz substrate 11 has an orientation angle for exciting an LSAW with a high phase velocity. As shown in Fig. 18, the (0°, 130°, 0°) quartz substrate 11 allows an impedance ratio of 70 dB or more only when the LT thickness is 0.8 wavelength or less, while the (20°, 120°, 115°) quartz substrate 11 with a high phase velocity S wave allows an impedance ratio of 72 dB even at the LT thickness of 10 wavelength, and, although not shown, an impedance ratio of 70 dB can be achieved even at the LT thickness of 20 wavelength. Such Euler angles of an S-wave with high phase velocity are, for example, (20°±5°, 120°±10°, 115°+ 10°), (0°±5°, 90°±5°, 0°±10°), (0°±5°, 90°, 75°±10°), (0°±5°, 0°, 0°±10°) or (0°±5°, 0°, 60°+ 10°).

[0071] The Fig. 19(a) to 19(c) illustrate the θ quarz -dependence of TCFs defined by a (0°, θ LT , 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, θ quartz , 0°) quartz substrate 11 structure, a (0°, θ LT, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, θ quartz , 90°) quartz substrate 11 structure or a (0°, θ LT , 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, θ quartz , 30°-60°) quartz substrate 11 structure can be obtained. The expression “30-60°” of the quartz substrate 11 in Fig. 19(c) refers to one propagation direction. The propagation direction at PFA = 0 can vary gradually, but each propagation direction at PFA = 0 lies in the range between 30° and 60°. Illustrated Euler angles for the LT thin film 12 between the optimal orientation angles (0°, 80°-148°, 0°) are (0°, 125°, 0°), which have a substantially maximum absolute value of the Fig. 10(c), and (0°, 80°, 0°) and (0°, 148°, 0°) which indicate the minimum value. As shown in the Fig. 19(a) to 19(c), orientation angles that can realize a practical range between -20 ppm / °C and +20 ppm / °C at one half of the TCFs of the LT thin film 12 are (0°+5°, 0°-23°, 0°±5°), (0°+5°, 32°-69°, 0°±5°), (0°±5°, 118°-180°, 0°±5°), (0°±5°, 0°-62°, 90°±5°), (0°±5°, 118°-180°, 90°±5°), (0°±5°, 0°-72°, 30°-60°) and (0°±5°, 117°-180°, 30°-60°). Orientation angles of the quartz substrate 11 that can realize a better range between -10 ppm / °C and +10 ppm / °C are (0°±5°, 0°-12°, 0°±5°), (0°±5° , 37°-66°, 0°±5°), (0°±5°, 132°-180°, 0°±5°), (0°±5°, 0°-50°, 90°±5°), (0°±5°, 126°-180°, 90°±5°), (0°±5° , 0°-17°, 30°-60°), (0°±5°, 35°-67°, 30°-60°) and (0°±5°, 123°-180°, 30°-60°). [Specific examples of acoustic wave devices with an LN thin film / quartz substrate structure]

[0072] The Fig. 20(a) and Fig. Figure 20(b) illustrates the θ-dependence of phase velocities and electromechanical coupling coefficients for a Rayleigh wave and a LSAW of a (0°, θ, 0°) LN substrate. Fig. 20(c) shows the θ-dependence of TCFs for a Rayleigh wave and a LSAW of a (0°, θ, 0°) LN substrate. As in the Fig. 20(a) and Fig. As shown in Figure 20(b), LN substrates generally use an LSAW at θ = 131°–154°, which allows for a smaller leakage component and a larger coupling factor, an LSAW near θ = 90°, which allows for a larger coupling factor, or a Love wave with no leakage component through an electrode, which allows for slow phase velocities on a substrate surface. The phase velocity Vm of the LSAW in use is between 4,150 and 4,450 m / s.

[0073] Furthermore, as in Fig. As shown in Figure 20(c), each TCF of the LSAW of the LN substrate is negative, and TCFs of the LSAW at θ = 131°-154° or near θ = 90° as used in a single LN substrate are as bad as a range between -73 and -93 ppm / °C.

[0074] Fig. Figure 21 illustrates the frequency characteristics of the impedance (Z) obtained by an acoustic wave resonator in which a (0°, 131°, 0°) LN thin film 12 (0.15 wavelength thickness) with an LSAW phase velocity of 4,250 m / s is combined with a (0°, 115°, 90°) quartz substrate 11 with an LSAW phase velocity of 5,040 m / s (see Fig. 8(a)), and then an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on the LN thin film 12. As shown in Fig. As shown in Figure 21, the impedance ratio is 79.3 dB, which is 19 dB higher than the conventional SAW characteristic of a single LN substrate. As described above, better characteristics similar to the case of LT can also be achieved with LN. In other words, better characteristics can be achieved by using an LN thin film 12 with a larger coupling factor and then using a quartz substrate 11 with a phase velocity around the LSAW or higher.

[0075] Fig. Figure 22(a) illustrates that the impedance ratios of acoustic wave resonators obtained for an LSAW and a Rayleigh wave can depend on θ at LN, for acoustic wave devices 10 in which interdigital transducer electrodes made of Al with a thickness of 0.08 wavelength and 0.2 wavelength are formed on a (0°, θ, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, 130°, 0°) quartz substrate 11 structure. In Fig. Figure 22(a) shows the impedance ratios of the resonators with the Al thickness of 0.08 wavelength and 0.2 wavelength for the LSAW case. Solid lines extending around the center and above the impedance ratio of 70 dB indicate better ripple-free characteristics, while dashed lines located on both sides and below 70 dB indicate ripple characteristics. Larger impedance ratios are obtained when the Al thickness is 0.8 wavelength and θ = 100°–160° for LN, and when the Al thickness is 0.2 wavelength and θ = 70°–165° for LN. The Al thickness in the range of 0.06 to 0.09 wavelengths can exhibit the same impedance ratios as that of the Al thickness of 0.08 wavelengths. The Al thickness in the range of 0.09 to 0.22 wavelengths can have the same impedance ratios as that of the Al thickness of 0.2 wavelengths.On the other hand, in the Rayleigh wave, impedance ratios of the resonators with the Al thickness of 0.08 wavelength are given, and larger impedance ratios can be achieved, for example, as 70 dB or more at θ = 35°-70° for LN and 75 dB or more at θ = 45°-63°.

[0076] Fig. 22(b) illustrates the θ dependence for the quartz substrate 11 of: impedance ratios of acoustic wave resonators obtained for LSAW by acoustic wave devices 10 in which interdigital transducer electrodes 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength are formed on a (0°, 131°, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ, 0°) quartz substrate 11 structure; and impedance ratios of acoustic wave resonators obtained for a Rayleigh wave by an acoustic wave device 10 in which an interdigital transducer electrode made of Al with a thickness of 0.08 wavelength is formed on a (0°, 55°, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ, 0°) quartz substrate 11 structure.In the figure, what indicates the impedance ratios separated on both sides below 75 dB is a characteristic that includes ripples within the bandwidth, while what indicates the values ​​above the 75 dB impedance ratio is a better characteristic without ripples. As shown in . Fig. As shown in Figure 22(b), the (0°, 131°, 0°) LN thin film 12 can lead to larger impedance ratios at θ = 120°-145° for quartz even at the Al thickness of 0.08 wavelength, while at the Al thickness of 0.2 wavelength, larger impedance ratios can be achieved at all orientation angles. Note that the Al thickness in the range of 0.06 to 0.09 wavelengths can exhibit the same impedance ratios as the Al thickness of 0.08 wavelengths. The Al thickness in the range of 0.09 to 0.22 wavelengths can exhibit the same impedance ratios as the Al thickness of 0.2 wavelengths. When the Al thickness is 0.08 wavelength, the Euler angles that allow the TCF of LSAW to be positive for the quartz substrate 11 can be calculated from Fig. 7(b) as (0°, 132°-180°, 0°±5°), and the Euler angles for the TCF of +5 ppm / °C can be determined as (0°, 135°-180°, 0°±5°). In this case, the combination of the LT thin film 12 with a negative TCF with the quartz substrate 11 with a positive TCF can significantly improve the TCF of the acoustic wave device 10. Considering the TCFs and the impedance ratios from the results of Fig. 7(b) and Fig. 22(b), the Euler angles of the quartz substrate 11 may preferably be (0°, 132°-145°, 0°±5°), and more preferably (0°, 135°-145°, 0°±5°). On the other hand, the (0°, 55°, 0°) LN thin film 12 may be Fig. 22(b), result in an impedance ratio of 70 dB at the Euler angles of the quartz substrate 11 of (0°, 90°-178°, 0°±5°), as indicated by the solid line. Furthermore, the dashed line portion indicates the presence of a ripple and, quite characteristically, indicates the impedance ratio of 70 dB or less. At the orientation angles of this quartz substrate 11, either an LSAW or Rayleigh wave indicates a positive TCF.

[0077] Fig. 23(a) and Fig. 23(b) illustrate that the bandwidths and impedance ratios of an acoustic wave resonator can depend on LN layer thicknesses, respectively, for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength is deposited on a (0°, 131°, 0°) LN thin film 12 / (0°, 130°, 0°) quartz substrate 11 structure. As in Fig. As shown in Figure 23(a), a bandwidth of 7% or more is obtained for the LN film thickness from 0.03 wavelength to 2 wavelength. Furthermore, as shown in Fig. As shown in Figure 23(b), impedance ratios of 70 dB or more, 73 dB or more, and 75 dB can be obtained when the Al thickness is 0.08 wavelengths at the LN film thicknesses of 0.012 to 0.6 wavelengths, 0.02 to 0.5 wavelengths, and 0.03 to 0.33 wavelengths. When the Al thickness is 0.2 wavelengths, impedance ratios of 70 dB or more, 73 dB or more, and 75 dB or more can be achieved at an LN film thickness of 0.012 to 2 wavelengths, 0.02 to 0.7 wavelengths, and 0.03 to 0.4 wavelengths.

[0078] Fig. Figure 24(a) illustrates that the impedance ratios of acoustic wave resonators obtained for an LSAW and a Rayleigh wave can depend on θ at LN, for acoustic wave devices 10 in which interdigital transducer electrodes made of Al with a thickness of 0.08 wavelength and 0.2 wavelength are formed on a (0°, θ, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, 130°, 90°) quartz substrate 11 structure. In Fig. Figure 24(a) shows the impedance ratios of the resonators with Al thicknesses of 0.08 wavelength and 0.2 wavelength for the LSAW case. Solid lines in the center and above the 70 dB impedance ratio indicate ripple-free characteristics within the bandwidth, while dashed lines on both sides and below 70 dB indicate ripple characteristics. Larger impedance ratios can be achieved when the Al thickness is 0.8 wavelength and θ = 95°–155° for LN, and when the Al thickness is 0.2 wavelength and θ = 95°–155° for LN. Note that the Al thickness in the range of 0.06 to 0.09 wavelengths can exhibit the same impedance ratios as the Al thickness of 0.08 wavelength. The Al thickness in the range of 0.09 to 0.22 wavelengths can have the same impedance ratios as that of the Al thickness of 0.2 wavelengths.On the other hand, in the Rayleigh wave, impedance ratios of the resonators with the Al thickness of 0.08 wavelength are given, and larger impedance ratios can be achieved, for example, as 70 dB or more at θ = 25°-51° for LN and 75 dB or more under θ = 29°-47°.

[0079] Fig. 24(b) illustrates the θ dependence for quartz substrate 11 of: impedance ratios of acoustic wave resonators obtained for LSAW by acoustic wave devices 10 in which interdigital transducer electrodes 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength were formed on a (0°, 131°, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ, 90°) quartz substrate 11; and impedance ratios of acoustic wave resonators obtained for a Rayleigh wave by an acoustic wave device 10 in which an interdigital transducer electrode made of Al with a thickness of 0.08 wavelength is formed on a (0°, 38°, 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ, 90°) quartz substrate 11. As in Fig. As shown in Figure 24(b), for LSAW, solid lines in the center and above the impedance ratio of 70 dB indicate features with no ripple within the bandwidth, while dashed lines on either side and below 70 dB indicate features with ripple. Larger impedance ratios can be achieved when the Al thickness is 0.8 wavelength and θ = 90°-155° for quartz, and when the Al thickness is 0.2 wavelength and all orientation angles are constant. Note that the Al thickness in the range of 0.06 to 0.09 wavelengths can exhibit the same impedance ratios as the Al thickness of 0.08 wavelength. The Al thickness in the range of 0.09 to 0.22 wavelengths can exhibit the same impedance ratios as those of the Al thickness of 0.2 wavelengths. On the other hand, the Euler angles that allow the TCF of LSAW to be positive for the quartz substrate 11 can be calculated from Fig. 8(b) as (0°, 123°-180°, 90°±5°), and the Euler angles for the TCF of +5 ppm / °C can be found as (0°, 126°-180°, 90°±5°). In this case, the combination of the LT thin film 12 with a negative TCF with the quartz substrate 11 with a positive TCF can significantly improve the TCF of the acoustic wave device 10. Considering the TCFs and the impedance ratios from the results of Fig. 8(b) and Fig. 24(b), the Euler angles of the quartz substrate 11 may preferably be (0°, 123°-155°, 90°±5°) and preferably (0°, 126°-155°, 90°±5°). It is far more preferable that the TCF of the LSAW for quartz be +7 ppm / °C or more. On the other hand, in the case of the Rayleigh wave, impedance ratios of 70 dB and 75 dB can be achieved at Euler angles of (0°, 80°-160°, 90°±5°) and (0°, 115°-145°, 90°±5°), respectively. Considering the orientation angles that allow the LSAW or Rayleigh wave to display a positive TCF, the Euler angles of the quartz substrate 11 may be desirable (0°, 125°-160°, 90°±5°).

[0080] Fig. 25(a) and Fig. 25(b) illustrate that the bandwidths and impedance ratios of the acoustic wave resonator can each depend on LN film thicknesses, for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al with thicknesses of 0.08 wavelength and 0.2 wavelength is present on a (0°, 131°, 0°) LN thin film 12 / (0°, 115°, 90°) quartz substrate 11. As in Fig. 25(a), a bandwidth of 5% or more is obtained for the LN film thickness from 0.012 wavelength to 2 wavelength. Furthermore, as shown in Fig. 25(b), impedance ratios of 70 dB or more, 73 dB or more, and 75 dB can be obtained when the Al thickness is 0.08 wavelengths at the LN layer thicknesses of 0.01 to 0.5 wavelengths, 0.02 to 0.33 wavelengths, and 0.06 to 0.3 wavelengths, respectively. On the other hand, when the Al thickness is 0.2 wavelengths, impedance ratios of 70 dB or more, 73 dB or more, and 75 dB or more can be obtained at the LN layer thickness of 0.01 to 2 wavelengths, 0.02 to 0.43 wavelengths, and 0.06 to 0.36 wavelengths.

[0081] The Fig. 26(a) to 26(c) illustrate the θ quartz Dependence on TCFs determined by a (0°, θ LN , 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ quartz , 90°) quartz substrate 11 structure, a (0°, θ LN , 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ quartz , 90°) quartz substrate 11 structure and a (0°, θ LN , 0°) LN thin film 12 (0.15 wavelength thickness) / (0°, θ quartz, 30°-60°) quartz substrate 11 structure can be obtained. The expression “30-60°” of the quartz substrate 11 in Fig. 26(c) refers to one propagation direction. The propagation direction at PFA = 0 can vary gradually, but each propagation direction at PFA = 0 is in the range between 30° and 60°. Illustrated Euler angles for the LN thin film 12 between the optimal orientation angles (0° + 5°, 75-165°, 0° ± 5°) are (0°, 154°, 0°), which are the minimum of the absolute values ​​of the Fig. 20(c), (0°, 85°, 0°) indicating the maximum value, and (0°, 38°, 0°) indicating an optimal alignment of the Rayleigh wave. As shown in the Fig. 26(a) to 26(c), are orientation angles that can realize a practical range between -20 ppm / °C and +20 ppm / °C, (0°+5°, 0°-16°, 0°±5°), (0°±5° , 42°-64°, 0°±5°), (0°±5°, 138°-180°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 130°-180°, 90°±5°), (0°±5°, 0°-28°, 30°-60°), (0°±5°, 42°-70°, 30°-60°), (0°±5°, 132°-180°, 30°-60°) for LSAW. For Rayleigh waves, the orientation angles are (0°±5°, 32°-118°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 173°-180°, 90°±5°) and (0°±5°, 0°-142°, 30-60°). Orientation angles of the quartz substrate 11 that can realize a better range between -10 ppm / °C and +10 ppm / °C are (0°+ 5°, 43°-61°, 0°±5°), (0°±5°, 147°-180°, 0°±5°), (0°±5° , 0°-15°, 90°±5°), (0°±5°, 134°-180°, 90°±5°), (0°±5° , 0°-23°, 30°-60°), (0°±5°, 43°-67°, 30°-60°) and (0°±5°, 137°-180°, 30°-60°) for LSAW. For Rayleigh waves the orientation angles are (0°±5°, 40°-102°, 0°±5°), (0°±5°, 0°-17°, 90°±5°), (0°±5°, 175°-180°, 90°±5°), (0°±5°, 13°-130°, 30-60°).

[0082] Fig. 27 illustrates that the impedance ratios may depend on ψ at LT, for acoustic wave devices 10 of longitudinal-wavelength leaky surface acoustic wave resonators in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (90°, 90°, ψ) LT thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11 structure and a (90°, 90°, ψ) LN thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11. As in Fig. As shown in Figure 27, impedance ratios of 70 dB or more can be achieved for the LT thin film 12 under ψ=33°-55° and 125°-155° and for the LN thin film 12 under ψ=38°-65° and 118°-140°. [Discussion about substrates other than quartz substrate]

[0083] Materials other than quartz to be used for the substrate 11 are explained below. Fig. Figure 28 illustrates the frequency characteristics of the impedance (Z) for an acoustic wave device 10 in which a fused quartz substrate is used as the substrate 11, and an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelengths is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / fused quartz substrate structure. Table 7 also shows constants of various materials used for a thin film of the substrate 11, such as fused quartz. As listed in Table 7, the fused quartz used contains 100 wt% SiO2 and has a shear wave phase velocity of a bulk wave of about 3,757 m / s. As shown in Fig. As shown in Figure 28, a better impedance ratio of 76 dB can be achieved in a fused quartz substrate. As shown in Table 7, the constants of a SiO2 film are the same as those of fused quartz. A film containing SiO is an example of a film made of SiOF, SiON, or the like, and indicates a film containing a compound of the formula SiO. x Z y where Z is a component other than SiO, x / (x+y) is 30% or more. This film can have the same properties as the SiO2 film. Table 7: Material Dichte (kg / m3) C33E (Pa) Longitudinal wave phase velocity (m / s) Acoustic impedance C44E (Pa) Shear wave phase velocity (m / s) Acoustic impedance Linear expansion coefficient ( / °C) SiO2 component TeO2 5990 1.058E+11 4202.71 2.517E+07 2.650E+10 2103.34 1.260E+07 0 Ta2O5 8015 2.148E+11 5176.85 4.149E+07 5.690E+10 2664.43 2.136E+07 0 TaN 14300 4.570E+11 5653.14 8.084E+07 1.056E+11 2717.46 3.886E+07 0 ZnO 5665 2.096E+11 6082.69 3.446E+07 4.230E+10 2732.56 1.548E+07 0 Silicate glass 2400 7.100E+10 5439.06 1.305E+07 2.500E+10 3227.49 7.746E+06 60% Pyrex 2230 7.270E+10 5709.72 1.273E+07 2.72E+10 3494.39 7.792E+06 81% Borosilicate glass 2365 7.470E+10 5620.11 1.329E+07 2.930E+10 3519.80 8.324E+06 82% LN 4640 2.424E+11 7227.82 3.354E+07 5.94E+10 3577.95 1.660E+07 1.54E-05 0 LT 7454 2.80E+11 6126.74 4.567E+07 9.68E+10 3603.65 2.686E+07 1.61E-05 0 Synthetic quartz 2200 7.820E+10 5962.00 1.312E+07 2.900E+10 3630.68 7.987E+06 4.70E-07 99% fused quartz 2210 7.850E+10 5959.90 1.317E+07 3.120E+10 3757.35 8.304E+06 5.90E-07 100% SiO2 film (same as those of fused quartz Film predominantly made of SiO 2000-2200 7.2-7.9E+10 5500-6000 1.26-1.32E+07 2.6-3.2E+10 3490-3760 7.7-8.4E+07 >30% Quartz glass 2200 7.860E+10 5977.23 1.315E+07 3.130E+10 3771-91 8.298E+06 4.70E-07 98% quartz 2650 1.07E+11 6360.25 1.685E+07 5.79E+10 4675.91 1,239E+07 1.04E-05 100% polycrystalline Si 2331 1.865E+11 8944.75 2.085E+07 6.650E+10 5341.21 1.245E+07 0 TiO2 4249 4.790E+11 10617.55 4.511E+07 1.232E+11 5384.71 2.288E+07 6.90E-06 0 Single crystal Si 2331 1.657E+11 8431.21 1.965E+07 7.960E+10 5843.67 1.362E+07 3.35E-06 0 Yes x N y 3200 3.710E+11 10767.43 3.446E+07 1.130E+11 5942.43 1.902E+07 0 AlN 3260 3.950E+11 11007.53 3.588E+07 1.180E+11 6016.34 1.961E+07 0 sapphire 3986 4.980E+11 11177.53 4.455E+07 1.470E+11 6072.81 2.421E+07 7.10E-06 0 Al2O3 (aluminum oxide) 3800 4.170E+11 10475.54 3.981E+07 1.460E+11 6198.47 2.355E+07 0 SiC 3200 4.580E+11 11963.49 3.828E+07 1.85E+11 7603.45 2.433E+07 0

[0084] Fig.29 illustrates that the impedance ratios can depend on LT layer thicknesses for acoustic wave devices 10 in which Pyrex glass, borosilicate glass, synthetic quartz, fused quartz, and quartz glass are used as substrate 11 and an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°, 0°) LT thin film 12 (0.15 wavelength thickness) / each substrate 11. As in Fig.As shown in Figure 29, a better impedance ratio of 70 dB or more can be achieved in fused glass, synthetic quartz, and quartz glass substrates with higher SiO2 content when the LT layer thickness is 0.52 wavelengths or less, as well as in Pyrex glass and borosilicate glass substrates with SiO2 content of about 70 to 80 mass% when the LT layer thickness is 0.34 wavelengths or less. It is confirmed that similar characteristics can be achieved even when using an LN thin film instead of the LT thin film.

[0085] Fig.Figure 30 illustrates that the impedance ratios for LSAW may depend on the SiO2 layer thickness for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 / SiO2 film / high-phase velocity substrate and a (0°, 131°, 0°) LN thin film 12 / SiO2 film / high-phase velocity substrate. Simply forming an LT or LN thin film on a high-speed substrate made of sapphire, alumina (Al2O3), or the like, as listed in Table 7, with a shear wave velocity of 5,900 m / s or more, may result in a poor impedance ratio such as 70 dB or less, which is similar to the impedance ratio shown in Table 7. Fig.6(b). However, further forming a SiO2 film with a wavelength of 0.15 at a boundary or junction between the high-speed substrate and the thin film can lead to larger impedance ratios of 73 dB for the LT thin film and 78 dB for the LN thin film. Furthermore, larger impedance ratios of 75 dB for the LT thin film and 79 dB for the LN thin film can be achieved when the thickness of the SiO2 layer is 0.3 wavelength or more. An excessively thick SiO2 layer is not preferable because a substrate on which a thicker SiO2 film is present may be warped. Accordingly, it is desirable that the thickness of the SiO2 film be 1 wavelength or less, and preferably 0.5 wavelength or less. [Discussion on interdigital transducer electrodes]

[0086] Optimal thicknesses and metallization ratios of an interdigital transducer electrode 13 are explained below. Fig. 31(a) and Fig. 31(b) illustrate that the bandwidths and impedance ratios of acoustic wave resonators can depend on the thickness of the interdigital transducer electrode 13, for acoustic wave devices 10 in which interdigital transducer electrodes 13 made of different materials are formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11 structure. Interdigital transducer electrodes 13 made of Al, Cu, Mo, and Pt are used. Furthermore, the metallization ratio of the interdigital transducer electrodes 13 is set to 0.5.

[0087] As in Fig.As shown in Figure 31(a), with an electrode thickness of 0.005 to 0.2 wavelengths, a bandwidth of 4% or more can be achieved even if the interdigital transducer electrode 13 is made of one of the materials. Furthermore, as shown in Fig. 31(b), impedance ratios of 70 dB or more at the electrode thickness of 0.005-0.32 wavelength and 75 dB or more at 0.005-0.25 wavelength can be obtained when the interdigital transducer electrode 13 is made of Al with a density of 2.699 kg / m 3 Furthermore, impedance ratios of 70 dB or more at the electrode thickness of 0.005-0.20 wavelength, 73 dB or more at 0.005-0.19 wavelength, and 75 dB or more at 0.005-0.18 wavelength can be obtained when the interdigital transducer electrode 13 is made of Cu with a density of 8,930 kg / m3.

[0088] Even further, impedance ratios of 70 dB or more at the electrode thickness of 0.005-0.28 wavelength, 73 dB or more at 0.005-0.27 wavelength and 75 dB or more at 0.005-0.20 wavelength can be obtained when the interdigital transducer electrode 13 is made of Mo with a density of 10,219 kg / m 3 Further, impedance ratios of 70 dB or more at the electrode thickness of 0.005-0.20 wavelength, 73 dB or more at 0.005-0.13 wavelength, and 75 dB or more at 0.005-0.11 wavelength can be obtained when the interdigital transducer electrode 13 is made of Pt with a density of 21,400 kg / m 3 consists.

[0089] As mentioned above, the optimal thickness may vary depending on the electrode type, and the lower the density, the wider the optimal thickness range to ensure greater impedance ratios. This means that the optimal thickness range may depend on the electrode density. Table 8 shows the relationships between the optimal thickness range and the electrode density. In Table 8, "A" indicates the conditions for achieving impedance ratios of 70 dB or more, "B" indicates the conditions for achieving impedance ratios of 73 dB or more, and "A" indicates the conditions for achieving impedance ratios of 75 dB or more. When using an alloy or multilayer electrode film, an average density is derived from the electrode thickness and the theoretical electrode density, and an optimal electrode thickness based on the average density can then be derived from Table 8.It should be noted that the relationships listed in Table 8 can be applied when the piezoelectric thin film 12 is made of LN. Table 8 Electrode thickness [wavelength (λ)] Density range (kg / m3) A B C 2000-5000 0,005-0,32 0,005-0,28 0,005-0,25 5001-9500 0,005-0.20 0,005-0,19 0,005-0,18 9501-15000 0,005-0,28 0,005-0,27 0,005-0,20 15001-220000 0,005-0,20 0,005-0,13 0,005-0,11

[0090] Fig. 32(a) and Fig. 32(b) illustrate that the bandwidths and impedance ratios of acoustic wave resonators can depend on the metallization ratios of the electrodes, for acoustic wave devices 10 in which interdigital transducer electrodes 13 are formed from corresponding materials on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11 structure. For the respective interdigital transducer electrodes 13, the Fig.31(b). In other words, the electrode thicknesses are set to 0.08 wavelength when the interdigital transducer electrode 13 is made of Al, 0.045 wavelength for Cu, 0.05 wavelength for Mo, and 0.03 wavelength for Pt.

[0091] As in Fig. 32(a), the widest bandwidth is achieved when the metallization degree is slightly below 0.5, even if the interdigital transducer electrode 13 is made of one of the materials. In addition, as shown in Fig.As shown in Figure 32(b), a metallization ratio that allows the metallization ratio to be higher, that is, the optimal metallization ratio, may vary depending on the electrode type. Table 9 shows relationships between the optimal metallization ratio and electrode density. In Table 9, "A" indicates the conditions for achieving higher impedance ratios (approximately 75.5 dB or higher), "B" indicates the conditions for achieving much higher impedance ratios (approximately 76.5 dB or higher), and "C" indicates the conditions for achieving the highest impedance ratios (approximately 77.5 dB or higher). When an alloy or multilayer metallization ratio film is used, an average density is derived from the electrode thickness and the theoretical electrode density, and then an optimal metallization ratio can be derived from Table 9 based on the average density.It is confirmed that the relationships shown in Table 9 can be applied when the piezoelectric thin film 12 is made of LN. Table 9 Electrode metallization ratio Density range (kg / m3) A B C 2000-5000 0,15-0,63 0,27-0,58 0,32-0,48 5001-9500 0,15-0,63 0,24-0,53 0,3-0,48 9501-15000 0,15-0,71 0,20-0,6 0,32-0,48 15001-220000 0,15-0,65 0,21-0,54 0,27-0,48 [Alternative examples of the arrangement of quartz substrate, piezoelectric thin film, interdigital transducer electrode, and shunt electrode]

[0092] Although Fig. 1(b) illustrates the acoustic wave device 10 of a structure with an IDT (interdigital transducer electrode) 13 / piezoelectric thin film 12 / quartz substrate 11 structure, other structures than in the Fig. 33(a) to 33(d), which include a shunt electrode 32. It should be noted that the Fig. 33(a) to 33(d) illustrate examples in which the piezoelectric thin film 12 is made of LiTaO3 crystal (LT) and the substrate 11 is made of quartz. Fig.33(a) illustrates a structure comprising an IDT 13 / piezoelectric thin film 12 (LT) / substrate 11 and the same structure as that of Fig. 1(b). Fig. Figure 33(b) illustrates an IDT 13 / piezoelectric thin film 12 (LT) / shunt electrode 32 / substrate 11 structure. Fig. 33(c) illustrates piezoelectric thin film 12 (LT) / IDT 13 / substrate 11 structures in which the IDT 13 is embedded in the substrate 11 (upper portion) and in the piezoelectric thin film 12 (lower portion). Fig. 33(d) illustrates piezoelectric thin film 12 (LT) / IDT 13 / substrate 11 structures in which the IDT 13 is embedded in the substrate 11 (upper portion) and in the piezoelectric thin film 12 (lower portion).

[0093] The Fig. 34(a) and Fig.34(b) illustrate that the bandwidths and impedance ratios of acoustic wave resonators each provided by acoustic wave devices 10 having structures of four types as shown in the Fig. 33(a) to 33(d) may depend on LT layer thicknesses. Here, the piezoelectric thin film 12 is a (0°, 110°, 0°) LT thin film, the quartz substrate 11 is a (0°, 132.75°, 90°) quartz substrate, and the IDT 13 is an Al electrode with a thickness of 0.08 wavelength. Note that the shunt electrode 31 is provided as thin electrode pads to cover the entire surface of the quartz substrate 11 and the piezoelectric thin film 12, and all the electrode pads are electrically short-circuited. Furthermore, the shunt electrode 31 may be a floating electrode that has no connection with the IDT 13.

[0094] As in Fig. 34(a), the widest bandwidth is achieved by the IDT / LT / quartz structure of Fig. 33(a), regardless of the LT layer thickness. In addition, as in Fig. 34(b) illustrates larger impedance ratios through the IDT / LT / quartz structure of Fig. 33(a) and the IDT / LT / shunt electrode / quartz structure of Fig. 33(b). It should be noted that, although the required bandwidth varies depending on the application, a larger impedance ratio would be better, since such an impedance ratio can largely affect the mechanical Q value. Accordingly, it is assumed that even the Fig. 33(b) can lead to an effect similar to that which would be obtained under the same structural conditions as in Fig. 33(a) is achieved.

[0095] Furthermore, the acoustic wave device 10, as in Fig.35, either the structure in which the IDT 13 is completely embedded in the piezoelectric thin film 12, or the structure in which the lower portion is embedded in the piezoelectric thin film 12 and the upper portion protrudes from the piezoelectric thin film 12. Fig. 35 illustrates that the impedance ratios created by the two structures mentioned above and the structure of Fig. 33(a) may depend on the layer thicknesses of the piezoelectric thin film 12. Here, the piezoelectric thin film 12 is a (0°, 110°, 0°) LT thin film, the quartz substrate 11 is a (0°, 132.75°, 90°) quartz substrate, and the IDT 13 is an Al electrode with a thickness of 0.08 wavelength. As shown in Fig. 35, the impedance ratios in each of the structures are obtained at an LT film thickness of 0.5 wavelengths or less. Furthermore, as shown in Fig.35, the structure in which the IDT 13 is embedded in the piezoelectric thin film 12 allows a higher phase velocity and is considered advantageous for higher frequencies compared to the structure without embedding. [Alternative examples with border films]

[0096] As in Fig. 1(c), the acoustic wave device 10 may include an insulating barrier film (also referred to as a junction film) 32 between the quartz substrate 11 and the piezoelectric thin film 12. The barrier film 32 may preferably be made of a hard material with lower sound absorption, such as tantalum pentoxide (Ta2O5), zinc oxide (ZnO), silicon dioxide (SiO2), polycrystalline Si, silicon nitride (Si x N y , where x and y are integers) and the like.

[0097] The Fig.36(a) to 36(c) illustrate that the phase velocities, bandwidths, and impedance ratios can depend on the layer thicknesses of the barrier film 32 for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength) / barrier film 32 / (0°, 132.75°, 90°) quartz substrate 11. Tantalum pentoxide (Ta2O5), zinc oxide (ZnO), silicon dioxide (SiO2), polycrystalline Si, and silicon nitride (Si x N y , where x and y are integers). Table 7 shows the material constants of the boundary films 32 used. It should be noted that Table 7 also contains material constants that are not discussed here but can be used for the boundary films 32.

[0098] As in the Fig.36(a) to 36(c) illustrates when the boundary film 32 is made of Ta2O5 or ZnO, in which a bulk shear wave phase velocity [(C 44 E / Density) 1 / 2 ] is much slower than the phase velocity of quartz, the phase velocity of SAW decreases drastically, the bandwidth narrows drastically, and the impedance ratio decreases drastically with increasing film thickness of the barrier film 32. Furthermore, if the barrier film 32 is made of Si x N ywhere the shear wave phase velocity is faster, the phase velocity of SAW increases, the bandwidth decreases slightly, and the impedance ratio decreases slightly as the film thickness of the barrier film 32 increases. Furthermore, when the barrier film 32 is made of polycrystalline Si or SiO2, where the shear wave phase velocity is close to the phase velocity of quartz, the phase velocity of SAW varies slightly and the bandwidth decreases slightly with increasing thickness of the barrier film 32, while the impedance ratio is not considered to vary greatly until the barrier film 32 reaches a thickness of three wavelengths. In particular, when formed of SiO2 with a positive TCF, the barrier film 32 is effective for improving the TCF. The TCF is improved by +5 ppm / °C for the SiO2 film with a wavelength of 0.1 or more, and by +10 ppm / °C for the SiO2 film with a wavelength of 0.2 or more.Furthermore, the same TCF can be achieved even if the orientation angle θ of quartz is shifted by about ±10°. Furthermore, as shown in . Fig. 36(c), no deterioration of the impedance ratio when the SiO2 film is below 1.2 wavelength. Furthermore, as shown in Fig. 36(b), the bandwidth does not decrease, and thus the bandwidth of 94% can be ensured even at 0.5 wavelengths when the SiO2 film is below 0.3 wavelengths. Furthermore, the same properties as SiO2 can also be achieved by a SiO x Z y film formed mainly of SiO, as mentioned above.

[0099] Table 7 and Fig.36 show that the relationship between the boundary film 32 and its optimal thickness depends on the phase velocity of the bulk shear waves. According to the characteristics of the acoustic wave device 10 using the boundary film 32, a larger impedance ratio can be achieved substantially independent of the phase velocity of the bulk shear waves when the boundary film 32 has a thickness of 0.34 wavelength or less, as shown in Fig. 36(c). However, when the thickness is larger than the above value, the optimal thickness of the boundary film 32 largely depends on the phase velocity of the bulk shear waves of the boundary film 32. Furthermore, a larger impedance ratio can be achieved when the thickness of the boundary film 32 is 0.13 wavelength or less, and a much larger impedance ratio can be achieved when the thickness of the boundary film 32 is 0.04 wavelength or less.

[0100] Table 10 shows relationships between the shear wave phase velocity of the barrier film 32 and the optimal film thickness of the barrier film 32. In Table 10, "A" indicates the conditions for achieving higher impedance ratios (approximately 70 dB or higher), "B" indicates the conditions for achieving much higher impedance ratios (approximately 73 dB or higher), and "C" indicates the conditions for achieving the highest impedance ratios (approximately 75 dB or higher). It is confirmed that the relationships listed in Table 10 can be applied when the piezoelectric thin film 12 is made of LN. Table 10 Gravity wave phase velocity Thickness T (wavelength) A B C Vs (m / s) 1500 <= Vs1 <= 2200 0 < T <= 0,5 0 < T <= 0,22 0 < T <= 0,12 2200 < Vs2 <= 3400 0 < T <= 0,67 0 < T <= 0,54 0 < T <= 0,23 3400 < Vs3 <= 5900 0 < T <= 3 0 < T <= 3 0 < T <= 3 5900 < Vs4 <= 13000 0 < T <= 0,6 0 < T <= 0,22 0 < T <= 0,12 [Alternative examples with multiple border films]

[0101] The case where the boundary layer 32 has two layers will be explained below. For an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength) / first layer of the boundary film 32 / second layer of the boundary film 32 / (0°, 132.75°, 90°) quartz substrate 11, it is evaluated how the resonator impedance ratio may depend on the film thicknesses of the first and second layers of the boundary film 32. Next, materials of four types with different shear wave phase velocities listed in Table 10 are classified as Vs1, Vs2, Vs3, and Vs4, respectively, and the evaluation is performed on two of them, which are differently combined as the first and second layers of the boundary film 32. Also cases where Vs1 is Ta2O5, Vs2 is ZnO, Vs3 is SiO2 and Vs4 is Si x N y are being investigated.

[0102] Among the study results, the Fig.Figures 37(a) to 37(d) show the results of the layer thickness dependence of the Vs3(SiO2) film, where the first and second layers are assumed to be Vs3 and Vs4 films, Vs4 and Vs3 films, Vs2 and Vs3 films, Vs2 and Vs3 films, and Vs1 and Vs3 films. Each of the numerical values ​​shown in each figure indicates a film thickness (wavelength) of the layers of the barrier film 32 other than Vs3. Table 11 also shows relationships between the combination of the first and second layers of the barrier film 32 and an optimal total film thickness derived from these investigation results. In Table 11, “A” indicates the conditions for achieving higher impedance ratios (approximately 70 dB or higher), “B” indicates the conditions for achieving much higher impedance ratios (approximately 73 dB or higher), and “C” indicates the conditions for achieving the highest impedance ratios (approximately 75 dB or higher).To obtain better impedance ratios, the first layer of the barrier foil 32 must satisfy the conditions listed in Table 10 and the total film thickness of the first and second layers must satisfy the conditions listed in Table 11. It should be noted that, as shown in the . Fig. 37(a) to 37(d), impedance ratios of 75 dB or more can be achieved when the SiO2 film is 1.5 wavelengths or less by appropriately selecting the type and thickness of the first layer when the second layer is the SiO2 film. Table 11 Cases of two layers Combination of first and second layer Total film thickness T [wavelength] A B C Vs1 Vs2 0 < T <= 1,17 0 < T <= 0,76 0 < T <= 0,35 Vs1 Vs3 0 < T <= 3,5 0 < T <= 3,22 0 < T <= 3,12 Vs1 Vs4 0 < T <= 1.1 0 < T <= 0,44 0 < T <= 0,24 Vs2 Vs3 0 < T <= 3,67 0 < T <= 3,54 0 < T <= 3,23 Vs2 Vs4 0 < T <= 1,27 0 < T <= 0,76 0 < T <= 0,35 Vs3 Vs4 0 < T <= 3,6 0 < T <= 3,22 0 < T <= 3,12

[0103] Next, the case where the barrier film 32 has three layers will be explained. For an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.08 wavelength is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength) / first layer of the barrier film 32 / second layer of the barrier film 32 / third layer of the barrier film 32 / (0°, 132.75°, 90°) quartz substrate 11, it will be evaluated how the resonator impedance ratio may depend on the film thickness of the third layer of the barrier film 32. Subsequently, materials of four types with different shear wave phase velocities listed in Table 10 are classified as Vs1, Vs2, Vs3, and Vs4, respectively, and the evaluation is made on three of them, which are differently combined as the first, second, and third layers of the boundary film 32. Also, cases where Vs1 is Ta2O5, Vs2 is ZnO, Vs3 is SiO2, and Vs4 is Si x N yare being investigated.

[0104] Among the study results, Fig. 38(a) shows the results where the first layer of the barrier film 32 is Vs3 (0.1 wavelength thickness), the second layer is Vs4 (0.1 wavelength thickness), and the third layer is Vs1, Vs2, Vs3, or Vs4. As in Fig. 38(a), impedance ratios of 70 dB or more can be achieved when the third layer is a Vs1 (Ta2O5) film or a Vs2 (ZnO) film and has a thickness of 1 wavelength or less, and impedance ratios of about 75 dB can be achieved when the third layer is a Vs3 (SiO2) film or a Vs4 (Si x N y ) film and has a thickness of 5 wavelengths or less.

[0105] Among the study results, Fig.38(b) also shows the results where the first layer of the barrier film 32 is Vs4 (0.01 wavelength thickness), the second layer is Vs3 (0.1 wavelength thickness), and the third layer is Vs1, Vs2, Vs3, or Vs4. As in Fig. As shown in Figure 38(b), impedance ratios of 70 dB or more can be achieved when the third layer is a Vs1 (Ta2O5) film or a Vs2 (ZnO) film and has a thickness of 1 wavelength or less, and impedance ratios of about 73 dB can be achieved when the third layer is a Vs3 (SiO2) film or a Vs4 (Si x N y ) film and has a thickness of 5 wavelengths or less.

[0106] Table 12 also shows relationships between the combination of the first to third layers of the barrier film 32 and an optimal total film thickness derived from these test results. In Table 12, "A" indicates the conditions for achieving higher impedance ratios (approximately 70 dB or higher), and "B" indicates the conditions for achieving significantly higher impedance ratios (approximately 73 dB or higher). To obtain better impedance ratios, the first layer of the barrier film 32 must meet the conditions listed in Table 10, and the total film thickness of the first to third layers must meet the conditions listed in Table 12. It should be noted that even if the barrier film 32 includes four or more layers, the first layer must meet the conditions listed in Table 10.

[0107] It should be noted that the material constants for deriving phase velocity and the like are based on publicly published constants. Furthermore, for mixed films where the thin film has two or more layers, the arithmetic mean of the respective layers can be used.

[0108] It should be noted that, as in the Fig. 38(a) and Fig. 38(b), impedance ratios of 75 dB or more can be achieved when the SiO2 film is 1.5 wavelengths or less by appropriately selecting the type and thickness of the layer other than the SiO2 film when the first or second layer is the SiO2 film. Table 12 Cases of three layers Combination of first, second and third layer Total film thickness of the first, second and third layers T [wavelength] A B Vs1 Vs2 Vs1 0 < T <= 1,67 0 < T <= 0,98 Vs1 Vs2 Vs3 0 < T < = 4,17 0 < T <= 3,76 Vs1 Vs2 Vs4 0 < T <= 1,77 0 < T <= 0,98 Vs1 Vs3 Vs1 0 < T <= 4,00 0 < T <= 3,44 Vs1 Vs3 Vs4 0 < T < = 4,17 0 < T <= 3,44 Vs1 Vs4 Vs1 0 < T <= 1,6 0 < T <= 0,66 Vs2 Vs1 Vs2 0 < T <= 1,84 0 < T <= 1,3 Vs2 Vs3 Vs2 0 < T <= 4,34 0 < T <= 4,08 Vs2 Vs3 Vs4 0 < T <= 4,27 0 < T <= 3,76 Vs3 Vs1 Vs3 0 < T <= 6,5 0 < T <= 6,22 Vs3 Vs2 Vs3 0 < T <= 6,67 0 < T <= 6,54 Vs3 Vs4 Vs3 0 < T <= 6,6 0 < T <= 6,22 Vs4 Vs1 Vs4 0 < T <= 1,70 0 < T <= 0,66 Vs4 Vs2 Vs4 0 < T <= 1,87 0 < T <= 0,98 Vs4 Vs3 Vs4 0 < T <= 4,20 0 < T <= 3,44 [Discussion of cases where higher-order modes of surface waves are used]

[0109] The case where higher order modes of surface acoustic waves are used is explained below. Fig. Figure 39 illustrates the frequency characteristics of the impedance (Z) for an acoustic wave device 10 in which an interdigital transducer electrode 13 made of Al with a thickness of 0.6 wavelengths is formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11 structure. As shown in Fig. 39, it is confirmed that a fundamental mode (the 0th) exists at 1.25 GHz and its higher mode (the 1st) is present at 3.6 GHz.

[0110] Fig.Figure 40 illustrates the relationships between the impedance ratios and the electrode thicknesses of acoustic wave devices 10 in higher-order modes for interdigital transducer electrodes 13 made of different materials. In this case, the acoustic wave devices 10 use interdigital transducer electrodes 13 of various types with a thickness of 0.6 wavelengths, which are formed on a (0°, 110°, 0°) LT thin film 12 (0.15 wavelength thickness) / (0°, 132.75°, 90°) quartz substrate 11 structure. As shown in Fig.As shown in Figure 40, the optimal thickness can vary depending on the electrode type. The lower the electrode density, the wider the optimal thickness ranges to allow for larger impedance ratios, and the larger the optimal thickness. Table 13 shows relationships between the optimal thickness range and the electrode density. Table 13 refers to the case where the metallization ratio of the interdigital transducer electrode 13 is 0.5. Table 13 Density range (kg / m3) Relevant electrode example Suitable electrode thickness [wavelength] 2000-5000 Al, Ti 0,17-0,8 5001-9500 Cu, Ni 0,08-0,44 9501-15000 Mon, Ag 0,08-0,43 15000-220000 Au, Pt 0,06-0,4

[0111] When an alloy or multilayer electrode film is used as the interdigital transducer electrode 13, an average density is derived from the electrode thickness and the theoretical electrode density, and then an optimal electrode thickness based on the average density can be derived from Table 13. For example, if the metallization degree is 0.25, the electrode thickness to be considered can be twice that in Table 13, because Table 13 refers to the case where the metallization degree is 0.5, and the electrode thickness can be calculated as 0.5 / 0.25 = 2.

[0112] The thickness of the piezoelectric thin film 12 is discussed for the case where a higher order mode of the surface acoustic wave is used. Fig.41 illustrates that the impedance ratios depend on the film thicknesses of the piezoelectric thin film 12 for acoustic wave devices 10 having an IDT 13 / piezoelectric thin film 12 / quartz substrate 11 structure as shown in Fig. 33(a), and an IDT 13 / piezoelectric thin film 12 / shunt electrode 31 / quartz substrate 11 structure. Here, the piezoelectric thin film 12 is a (0°, 110°, 0°) LT thin film, the quartz substrate 11 is a (0°, 132.75°, 90°) quartz substrate, and the IDT 13 is a Au electrode with a thickness of 0.2 wavelength. As shown in Fig. 41, impedance ratios of 70 dB or more can be achieved at the LT layer thickness of 0.35-9.3 wavelength when the structure of Fig. 33(a) without shunt electrode 31 and at the LT film thickness of 0.5-9 wavelength, when the structure of Fig.33(b) with the shunt electrode 31. It is confirmed that similar characteristics are achieved even when an LN thin film is used instead of the LT thin film.

[0113] The Fig. 42(a) and Fig. 42(b) illustrate that the impedance ratios of acoustic wave resonators in a higher-order (1st-order) mode can depend on θ on the quartz substrate 11 for acoustic wave devices 10 in which an interdigital transducer electrode 13 made of Au is formed on a (0°, 110°, 0°) LT thin film 12 / (0°, θ, 0°) quartz substrate 11 ( Fig. 42(a)) or a (0°, 110°, 0°) LT thin film 12 / (0°, θ, 90°) quartz 11 ( Fig. 42(b)). Here, the LT thickness is set to four types, i.e., 0.5 wavelength (λ), 1λ, 2λ, and 4λ. Furthermore, the thickness of the interdigital transducer electrode 13 is set to 0.2λ.

[0114] As in the Fig. 42(a) and Fig.As shown in Figure 42(b), impedance ratios of approximately 70 dB or more can be achieved over almost all angles of θ when the LT film thickness is 0.5-4λ. This is presumably because the Au thickness of the interdigital transducer electrode 13 is similar to 0.2λ in the fundamental mode and relatively thick, even though the LT layer thickness is thicker. [Methods for manufacturing acoustic wave devices according to embodiments of the present invention]

[0115] As in Fig. 43, the acoustic wave device 10 can be manufactured as follows. First, a piezoelectric substrate 12a having LT or LN is prepared (see Fig. 43(a)), and the piezoelectric substrate 12a is bonded to a quartz substrate 11 (see left section of Fig.43(b)). Alternatively, when a shunt electrode 31 or a barrier film 32 is formed between the piezoelectric substrate 12a and the quartz substrate 11, the shunt electrode 31 or the barrier film 32 is bonded to the quartz substrate 11 and then the piezoelectric substrate 12a is bonded thereto (see the right portion of Fig. 43(b)). Respective substrates and layers can be bonded using adhesives, while these can be bonded by a method of activating a bonding surface with plasma or the like, which is referred to as a direct bonding method.

[0116] After the bonding process, the piezoelectric substrate 12a is polished into a thin film (piezoelectric thin film 12) (see Fig.43(c)). An electrode film made of Al or the like is formed on the surface of the piezoelectric thin film 12, and a resist (photoresist) is applied thereon. Subsequently, the resist is removed by a patterning (exposure and development) and etching process, so that an interdigital transducer electrode 13 and reflectors 14 are formed (see Fig. 43(d)). Thereafter, unnecessary parts are removed and the acoustic wave device 10 is manufactured (see Fig. 43(e)). It should be noted that, although the

[0117] Fig. 43(c) to 43(e) illustrate the processes associated with the left-hand section of Fig. 43(b), the acoustic wave device 10 can be manufactured with the shunt electrode 31 or the barrier film 32 between the quartz substrate 11 and the piezoelectric thin film 12. List of reference symbols 10 acoustic wave device 11 Substrate (quartz substrate) 12 piezoelectric thin film (LT thin film or LN thin film) 12a piezoelectric substrate 13 interdigital transducer electrode (IDT) 21 electrode fingers 14 Reflector 31 Shunt electrode 32 Border Film 50 conventional acoustic wave device 51 piezoelectric substrate 52 interdigital transducer electrodes (IDT) 53 Reflector

Claims

[1] Acoustic wave device (10) using a surface acoustic wave, comprising: a substrate (11) containing 70 mass% or more of silicon dioxide (SiO2); a piezoelectric thin film (12) formed of LiTaO3 crystal or LiNbO3 crystal disposed on the substrate (11); and an interdigital transducer electrode (13) arranged in contact with the piezoelectric thin film (12); wherein Euler angle of the substrate (11) and Euler angle of the piezoelectric thin film (12) are selected such that a phase velocity of the surface acoustic wave propagating along the substrate (11) is greater than a phase velocity of the surface acoustic wave propagating along the piezoelectric thin film (12). [2] The acoustic wave device (10) according to claim 1, further comprising a shunt electrode (31) and / or an insulating barrier film (32) between the substrate (11) and the piezoelectric thin film (12). [3] The acoustic wave device (10) according to any one of claims 1 to 2, wherein the interdigital transducer electrode (13) is arranged such that at least a lower portion is embedded in the piezoelectric thin film (12) and / or at least an upper portion protrudes from the piezoelectric thin film (12). [4] The acoustic wave device (10) according to any one of claims 1 to 3, wherein the substrate (11) includes a quartz substrate (11). [5] Acoustic wave device (10) according to one of claims 1 to 4, wherein the substrate (11) has a shear wave phase velocity of a bulk wave of 3,400 to 4,800 m / s. [6] The acoustic wave device (10) according to any one of claims 1 to 3 and 5, wherein the substrate (11) includes an isotropic substrate and the piezoelectric thin film (12) has a thickness of 0.001 mm or more and less than 0.01 mm. [7] The acoustic wave device (10) according to any one of claims 1 to 6, wherein the substrate (11) includes a quartz substrate (11) and a phase velocity of the propagating surface acoustic wave is 4,500 m / s or more. [8] The acoustic wave device (10) according to any one of claims 1 to 6, wherein the substrate (11) includes a quartz substrate (11) and a phase velocity of the propagating surface acoustic wave is 4,800 m / s or more. [9] The acoustic wave device (10) according to any one of claims 1 to 6, wherein the substrate (11) includes a quartz substrate (11) and a phase velocity of the propagating surface acoustic wave is 5,000 m / s or more. [10] The acoustic wave device (10) according to any one of claims 1 to 9, wherein the substrate (11) includes a quartz substrate (11), and the surface acoustic wave to be propagated is a leaky acoustic wave mainly including an SH component or an S wave having a phase velocity of 4,500 m / s or more. [11] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) propagates the surface acoustic wave at 4,500 m / s or more and has Euler angles of (0°±5°, 70°-165°, 0°±5°), (0°±5°, 95°-155°, 90°±5°) or crystallographically equivalent Euler angles thereof. [12] Acoustic wave device (10) according to one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-125°, 0°±5°), (0°±5°, 0°-36°, 90°±5°), (0°±5°, 172°-180°, 90°±5°), (0°±5°, 120°-140°, 30°-49°), (0°±5°, 25°-105°, 0°±5°), (0°±5°, 0°-45°, 15°-35°), (0°±5°, 10°-20°, 60°-70°), (0°±5°, 90°-180°, 30°-45°), (0°±5°, 0°±5°, 85°-95°), (90°±5°, 90°:t5°, 25°-31°), (0°±5°, 90°:t5°, -3° to 3°) or crystallographically equivalent Euler angles thereof. [13] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (20°±5°, 120°±10°, 115°±10°), (0°±5°, 90°:t5°, 0°±10°), (0°±5°, 90°:t5°, 75°±10°), (0°±5°, 0°±5°, 0°±5°, 0°±10°), (0°±5°, 0°±5°, 60°±10°) or crystallographically equivalent Euler angles thereof. [14] The acoustic wave device (10) according to any one of claims 1 to 13, wherein the piezoelectric thin film (12) includes LiTaO3 crystal and has Euler angles of (90°±5°, 90°±5°, 33°-55°), (90°±5°, 90°±5°, 125°-155°) or crystallographically equivalent Euler angles thereof. [15] The acoustic wave device (10) according to any one of claims 1 to 13, wherein the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (90°±5°, 90°±5°, 38°-65°), (90°±5°, 90°±5°, 118°-140°) or crystallographically equivalent Euler angles thereof. [16] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-132°, 0°±5°), (0°±5°, 0°-18°, 0°±5°), (0°±5°, 42°-65°, 0°±5°), (0°±5°, 126°-180°, 0°±5°), or crystallographically equivalent Euler angles thereof, the piezoelectric thin film (12) includes LiTaO3 crystal and has Euler angles of (0°±5°, 82°-148°, 0°±5°) or crystallographically equivalent Euler angles thereof. [17] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-42°, 90°±5°), (0°±5°, 170°-190°, 90°±5°), (0°±5°, 0°-45°, 90°±5°), (0°±5°, 123°-180°, 90°±5°) or crystallographically equivalent Euler angles thereof, the piezoelectric thin film (12) includes LiTaO3 crystal and has Euler angles of (0°±5°, 80°-148°, 0°±5°) or crystallographically equivalent Euler angles thereof. [18] The acoustic wave device (10) according to claim 17, wherein the substrate (11) has Euler angles of (0°±5°, 126°-180°, 90°±5°) or crystallographically equivalent Euler angles thereof. [19] The acoustic wave device (10) according to claim 17 or 18, wherein the piezoelectric thin film (12) has Euler angles of (0°±5°, 103°-125°, 0°±5°) or crystallographically equivalent Euler angles thereof. [20] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (1°-39°, 100°-150°, 0°-20° or 70°-120° or 160°-180°) or crystallographically equivalent Euler angles thereof, and the piezoelectric thin film (12) includes LiTaO3 crystal and has Euler angles of (0°±5°, 80°-148°, 0°±5°) or crystallographically equivalent Euler angles thereof. [21] Acoustic wave device (10) according to one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°+5°, 0°-23°, 0°±5°), (0°±5°; 32°-69°, 0°±5°), (0°±5°, 118°-180°, 0°±5°), (0°±5°, 0°-62°, 90°±5°), (0°±5°, 118°-180°, 90°±5°), (0°±5°, 0°-72°, 30°-60°), (0°±5°, 117°-180°, 30°-60°) or crystallographically equivalent Euler angles thereof and the piezoelectric thin film (12) contains LiTaO3 crystal and has Euler angles of (0°±5°, 80°-148°, 0°±5°) or crystallographically equivalent Euler angles thereof. [22] The acoustic wave device (10) according to any one of claims 16 to 21, wherein the piezoelectric thin film (12) has a thickness of 0.001 times to 2 times a wavelength of the surface acoustic wave. [23] The acoustic wave device (10) according to any one of claims 16 to 21, wherein the piezoelectric thin film (12) has a thickness of 0.01 times to 0.6 times a wavelength of the surface acoustic wave. [24] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-132°, 0°±5°), (0°±5°, 0°-18°, 0°±5°), (0°±5°, 42°-65°, 0°±5°), (0°±5°, 126°-180°, 0°±5°), or crystallographically equivalent Euler angles thereof, and the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (0°±5°, 75°-165°, 0°±5°) or crystallographically equivalent Euler angles thereof. [25] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-42°, 90°±5°), (0°±5°, 90°-155°, 90°±5°), (0°±5°, 0°-45°, 90°±5°), (0°±5°, 123°-180°, 90°±5°), or crystallographically equivalent Euler angles thereof, wherein the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (0°±5°, 70°-170°, 0°±5°) or crystallographically equivalent Euler angles thereof. [26] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (1°-39°, 100°-150°, 0°-20° or 70°-120° or 160°-180°) or crystallographically equivalent Euler angles thereof, and the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (0°±5°, 95°-160°, 0°±5°) or crystallographically equivalent Euler angles thereof. [27] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 90°-178°, 0°±5°), (0°±5°, 80°-160°, 90°±5°) or crystallographically equivalent Euler angles thereof, and the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (0°+5°, 35°-70°, 0°±5°) or crystallographically equivalent Euler angles thereof. [28] Acoustic wave device (10) according to one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 0°-16°, 0°±5°), (0°±5°, 42°-64°; 0°±5°), (0°±5°, 138°-180°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 130°-180°, 90°±5°), (0°±5°, 0°-28°, 30°-60°), (0°±5°, 42°-70°, 30°-60°), (0°±5°, 132°-180°, 30°-60°) or crystallographically equivalent Euler angles thereof and the piezoelectric thin film (12) comprises LiNbO3 crystal and has Euler angles of (0°±5°, 75°-165°, 0°±5°) or crystallographically equivalent Euler angles thereof. [29] The acoustic wave device (10) according to any one of claims 1 to 10, wherein the substrate (11) has Euler angles of (0°±5°, 32°-118°, 0°±5°), (0°±5°, 0°-30°, 90°±5°), (0°±5°, 173°-180°, 90°±5°), (0°±5°, 0°-142°, 30°-60°), or crystallographically equivalent Euler angles thereof, and the piezoelectric thin film (12) includes LiNbO3 crystal and has Euler angles of (0°±5°, 35°-70°, 0°±5°) or crystallographically equivalent Euler angles thereof. [30] The acoustic wave device (10) according to any one of claims 24, 26, 27, 28 and 29, wherein the piezoelectric thin film (12) has a thickness of 0.001 times to 2 times a wavelength of the surface acoustic wave. [31] The acoustic wave device (10) according to any one of claims 24, 26, 27, 28 and 29, wherein the piezoelectric thin film (12) has a thickness of 0.012 times to 0.6 times a wavelength of the surface acoustic wave. [32] The acoustic wave device (10) according to any one of claims 25, 26, 27, 28 and 29, wherein the piezoelectric thin film (12) has a thickness of 0.01 times to 0.5 times a wavelength of the surface acoustic wave. [33] The acoustic wave device (10) according to any one of claims 1 to 32, further comprising a Si-containing film disposed between the substrate (11) and the piezoelectric thin film (12), wherein the Si-containing film contains 30% or more of SiO2 or SiO, the substrate (11) has a shear wave phase velocity of a bulk wave of 5900 m / s or more, and the Si-containing film has a thickness of 0.15 times to 1 time of a wavelength of the surface waves. [34] The acoustic wave device (10) according to any one of claims 1 to 32, further comprising a Si-containing film disposed between the substrate (11) and the piezoelectric thin film (12), wherein the Si-containing film contains 30% or more of SiO2 or SiO, the substrate (11) has a shear wave phase velocity of a bulk acoustic wave of 5,900 m / s or more, and the Si-containing film has a thickness of 0.3 times to 0.5 times a wavelength of the surface acoustic wave. [35] Acoustic wave device (10) according to one of claims 1 to 34, wherein the interdigital transducer electrode (13) has a thickness specified in Table 1 depending on its density. Table 1 Density range (kg / m3) Electrode thickness [wavelength (λ)] 2000-5000 0,005-0,32 5001-9500 0,005-0,20 9501-15000 0,005-0,28 15001-220000 0,005-0,20 [36] An acoustic wave device (10) according to any one of claims 1 to 35, wherein the interdigital transducer electrode (13) has a metallization ratio as shown in Table 2 depending on its density. Table 2 Density range (kg / m3) Electrode metallization ratio 2000-5000 0,15-0,63 5001-9500 0,15-0,63 9501-15000 0,15-0,71 15001-220000 0,15-0,65 [37] The acoustic wave device (10) according to any one of claims 1 to 36, further comprising an insulating barrier film (32) disposed between the substrate (11) and the piezoelectric thin film (12) and having a thickness corresponding to 0.34 times a wavelength or more. [38] The acoustic wave device (10) according to any one of claims 1 to 36, further comprising an insulating barrier film (32) disposed between the substrate (11) and the piezoelectric thin film (12) and having one or more layers, with a layer closest to the piezoelectric thin film (12) having a thickness shown in Table 3 depending on its bulk shear wave phase velocity. Table 3 Gravity wave phase velocity Vs (m / s) Thickness T [wavelength] 1500 <= Vs1 <= 2200 0 < T <= 0,5 2200 < Vs2 <= 3400 0 < T <= 0,67 3400 < Vs3 <= 5900 0 < T <= 3 5900 < Vs4 <= 13000 0 < T <= 0,6 [39] The acoustic wave device (10) according to claim 38, wherein the boundary film (32) has two layers, with a layer closer to the piezoelectric thin film (12) and a thickness given in Table 3 depending on the bulk shear wave phase velocity of each layer, with a total film thickness of the respective layers having a thickness given in Table 4. Table 4 Combination of first and second layer Total film thickness T [wavelength] Vs1 Vs2 0 < T <= 1,17 Vs1 Vs3 0 < T <= 3,5 Vs1 Vs4 0 < T <= 1,1 Vs2 Vs3 0 < T <= 3,67 Vs2 Vs4 0 < T <= 1,27 Vs3 Vs4 0 < T <= 3,6 [40] The acoustic wave device (10) according to claim 38, wherein the boundary film (32) has three layers, with a layer closest to the piezoelectric thin film (12) having a thickness given in Table 3 depending on the bulk shear wave phase velocity of each layer, with a total film thickness of the respective layers having a thickness given in Table 5. Table 5 Combination of first, second and third layer Total film thickness T [wavelength] Vs1 Vs2 Vs1 0 < T <= 1,67 Vs1 Vs2 Vs3 0 < T <= 4,17 Vs1 Vs2 Vs4 0 < T <= 1,77 Vs1 Vs3 Vs1 0 < T <= 4,00 Vs1 Vs3 Vs4 0 < T <= 4,17 Vs1 Vs4 Vs1 0 < T <= 1,6 Vs2 Vs1 Vs2 0 < T <= 1,84 Vs2 Vs3 Vs2 0 < T <= 4,34 Vs2 Vs3 Vs4 0 < T <= 4,27 Vs3 Vs1 Vs3 0 < T <= 6,5 Vs3 Vs2 Vs2 0 < T <= 6,67 Vs3 Vs4 Vs3 0 < T <= 6,6 Vs4 Vs1 Vs4 0 < T <= 1,70 Vs4 Vs2 Vs4 0 < T <= 1,87 Vs4 Vs3 Vs4 0 < T <= 4,20 [41] The acoustic wave device (10) according to any one of claims 37 to 39, wherein a layer of the barrier film (32) closest or second closest to the piezoelectric thin film (12) includes 30% or more of SiO2 or SiO and has a thickness of 0.001 times to 1.2 times a wavelength of the surface acoustic wave. [42] The acoustic wave device (10) according to any one of claims 37 to 39, wherein a layer of the barrier film (32) closest or second closest to the piezoelectric thin film (12) includes 30% or more of SiO2 or SiO and has a thickness of 0.001 times to 0.3 times a wavelength of the surface acoustic wave. [43] The acoustic wave device (10) of claim 38, wherein the boundary film (32) includes four layers, a layer closest to the piezoelectric thin film (12) having a thickness given in Table 3 depending on a bulk shear wave phase velocity. [44] An acoustic wave device (10) according to any one of claims 1 to 43, wherein the surface acoustic wave has a higher order mode and the interdigital transducer electrode (13) has a thickness as shown in Table 6 depending on its density. Table 6 Density range (kg / m3) Electrode thickness [wavelength] 2000-5000 0,17-0,8 5001-9500 0,08-0,44 9501-15000 0,08-0,43 15000-220000 0,06-0,4 [45] The acoustic wave device (10) according to any one of claims 1 to 44, wherein the surface acoustic wave has a higher order mode and the piezoelectric thin film (12) has a thickness of 0.35 times to 9.3 times a wavelength of the surface acoustic wave. [46] The acoustic wave device (10) according to any one of claims 1 to 45, wherein the surface acoustic wave is a leakage surface acoustic wave. [47] The acoustic wave device (10) according to any one of claims 1 to 15, wherein the surface acoustic wave is a leakage surface acoustic wave of a longitudinal wave type. [48] ​​The acoustic wave device (10) according to any one of claims 1 to 14 and 24 to 45, wherein the piezoelectric thin film (12) includes LiNbO3 crystal and the surface acoustic wave is a Rayleigh wave.

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