A lithium tantalate single crystal substrate for a surface acoustic wave device that is a rotated Y-cut LiTaO3 substrate whose crystal orientation has a Y-cut angle of not smaller than 36° and not larger than 49° and which has such a Li concentration profile after diffusion of Li into the substrate from the surface thereof that the Li concentration at the surface of the substrate differs from that inside the substrate. A shear vertical type elastic wave whose main components are vibrations in the thickness direction and in the propagation direction and which is among those elastic waves which propagate in the X axis direction within the surface of this LiTaO3 substrate has an acoustic velocity of not lower than 3140 m/s and not higher than 3200 m/s.

An AT-cut crystal resonator plate (2) includes a first main surface (2a) on which a first excitation electrode (211) is formed and a second main surface (2b) on which a second excitation electrode (212) is formed. The AT-cut crystal resonator plate (2) further includes: a substantially rectangular-shaped vibrating part (21) that is piezoelectrically vibrated when a voltage is applied to the first excitation electrode (211) and the second excitation electrode (212); a holding part (22) protruding from a corner part (21a) of the vibrating part (21) in a Z′ axis direction of the AT-cut crystal; and an external frame part (23) configured to surround an external circumference of the vibrating part (21) and to hold the holding part (22).

A substrate for a surface acoustic wave device or bulk acoustic wave device, comprising a support substrate and an piezoelectric layer on the support substrate, wherein the support substrate comprises a semiconductor layer on a stiffening substrate having a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the material of the piezoelectric layer than that of silicon, the semiconductor layer being arranged between the piezoelectric layer and the stiffening substrate.

In an elastic wave filter apparatus, IDT electrodes and first and second electrode lands are provided on a first main surface of a piezoelectric substrate. The piezoelectric substrate, a supporting layer, and a covering member define a hollow portion. A signal terminal, a ground terminal, and a heat diffusion layer are provided on a second main surface of the piezoelectric substrate. The first and second electrode lands are electrically connected by first and second connection electrodes to the signal terminal and the ground terminal, respectively. The heat diffusion layer is provided at a position where the heat diffusion layer overlaps at least a portion of the IDT electrodes across the piezoelectric substrate.

An acoustic resonator includes a wafer and a first phononic crystal disposed on the wafer to define an acoustic waveguide so as to propagate an acoustic wave along a propagation direction. The first phononic crystal includes a first two-dimensional (2D) array of metal stripes having a first period on the propagation direction. The apparatus also includes a second phononic crystal and a third phononic crystal disposed on two sides of the first phononic crystal and having a different period from the first period. The second phononic crystal and the wafer define a first reflector to reflect the acoustic wave. The third phononic crystal and the wafer define a second reflector to reflect the acoustic wave.

An RF filter system includes a plurality of bulk acoustic wave resonators arranged in a circuit having serial and parallel shunt configurations of resonators. Each resonator having a reflector, a support member including a surface, a first electrode including tungsten, overlying the reflector, a piezoelectric film including crystalline aluminum scandium nitride overlapping the first electrode, a second electrode including tungsten overlapping the piezoelectric film and the first electrode, and a passivation layer including silicon nitride overlying the second electrode. Portions of the support member surface of at least one resonator define a cavity region having a portion of the first electrode of the at least one resonator is located within the cavity region. The pass band circuit response has a bandwidth corresponding to a thickness of at least one of the first electrode, piezoelectric film, second electrode, and passivation layer. The system can include single crystal or polycrystalline BAW resonators.

An elastic wave device includes a support substrate made of silicon, a piezoelectric film disposed directly or indirectly on the support substrate, and an interdigital transducer electrode disposed on one surface of the piezoelectric film. A higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to an acoustic velocity V.sub.si=(V.sub.1).sup.1/2 of propagation through silicon or higher than the acoustic velocity V.sub.si, where V.sub.si is specified by V.sub.1 among solutions V.sub.1, V.sub.2, and V.sub.3 with respect to x derived from Ax.sup.3+Bx.sup.2+Cx+D=0.

A surface acoustic wave device includes a piezoelectric substrate, an interdigital transducer (IDT) electrode on the substrate, a cover over the substrate and IDT electrode, and hollow spaces between the IDT electrode and the cover. The hollow spaces are defined by partition supports between the substrate and the cover. The partition supports include a first and second partition supports extending in a first direction without contacting each other. The first and second partition supports each include first and second ends along the first direction. The first and second direction perpendicular to the first direction. The first end of the first partition support is closer to an outer periphery of the substrate than is the second end, and the first end of the second partition support is farther away from the outer periphery than is the second end.

An elastic wave device includes an LiNbO.sub.3 substrate, a first elastic wave resonator including a first IDT electrode and a first dielectric film, and a second elastic wave resonator including a second IDT electrode and a second dielectric film. A Rayleigh wave travels along at least one surface of the elastic wave device. A thickness of the first dielectric film differs from a thickness of the second dielectric film. A propagation direction of an elastic wave in the first elastic wave resonator coincides with a propagation direction of an elastic wave in the second elastic wave resonator. Euler angles of the LiNbO.sub.3 substrate fall within a range of (0°±5°, θ, 0°±10°).

A high-frequency apparatus includes a resin substrate, a first device including a substrate and provided on the resin substrate, and a second device provided adjacent to the first device on the resin substrate. Each of the first device and the second device includes an acoustic wave device. The second device includes a piezoelectric substrate and a functional element provided on the piezoelectric substrate. The substrate of the first device includes Si or a laminated material including Si. The piezoelectric substrate of the second device includes LiTaO.sub.3, LiNbO.sub.3, or a laminated material including LiTaO.sub.3 or LiNbO.sub.3. The resin substrate includes glass.