An acoustic wave device includes a piezoelectric substrate and an IDT electrode. The IDT electrode includes a center area and first and second edge areas. Areas including the first and second edge areas and overlapping the areas in an acoustic-wave propagation direction include first and second expansion edge areas. First and second acoustic-velocity adjusters are provided in the first and second expansion edge areas. The first and second acoustic-velocity adjusters respectively includes first and second end portions and third and fourth end portions. The first to fourth end portions are located at outer sides of the first and second edge areas. End portions in at least one of two pairs including a pair of first and third end portions and a pair of second and fourth end portions do not overlap each other in a direction in which electrode fingers extend.

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.

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.

Disclosed is a device that includes a crystalline substrate and a patterned aluminum-based material layer disposed onto the crystalline substrate. The patterned aluminum-based material layer has a titanium-alloyed surface. A titanium-based material layer is disposed over select portions of the titanium-alloyed surface. In an exemplary embodiment, the patterned aluminum-based material layer forms a pair of interdigitated transducers to provide a surface wave acoustic (SAW) device. The SAW device of the present disclosure is usable to realize SAW-based filters for wireless communication equipment.

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.

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.

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°).

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 radio-frequency module includes a module substrate, an inductor, and an acoustic wave filter. The inductor overlaps at least a portion of the acoustic wave filter when seen in a plan view from the normal direction of the module substrate. The inductor includes first and second coils connected in series. Each of the first and second coils is a spiral or helical coil that is wound with more than one turn. At least a portion of the first coil overlaps the second coil when seen in a plan view from the normal direction of the module substrate. A direction of a magnetic field generated by the first coil is opposite to a direction of a magnetic field generated by the second coil.

An acoustic wave resonator includes: a piezoelectric substrate; and an interdigital transducer (IDT) located on the piezoelectric substrate, the IDT including a pair of comb-shaped electrodes having a plurality of electrode fingers and a bus bar to which the plurality of electrode fingers are coupled, the IDT having: a first region in which a pitch of electrode fingers is substantially constant; a second region in which a pitch of electrode fingers decreases at closer distances to an outer side; and a third region in which a pitch of electrode fingers increases at closer distances to an outer side, the second region being located outside the first region in an arrangement direction of the plurality of electrode fingers, and the third region being located outside the second region in the arrangement direction.