A surface acoustic wave resonator comprises a multi-layer piezoelectric substrate including a carrier substrate, a layer of a first dielectric material disposed on the carrier substrate, and a layer of piezoelectric material disposed on the layer of the first dielectric material, interdigital transducer electrodes disposed on the layer of piezoelectric material and including interleaved electrode fingers, and a layer of a second dielectric material disposed on a central interleaved region of the interleaved electrode fingers, gap regions of the interdigital transducer electrodes being either free of the layer of the second dielectric material or having a thinner layer of the second dielectric material than the central interleaved region to reduce spurious signals in an admittance curve of the surface acoustic wave resonator.

A surface acoustic wave (SAW) filter includes a bottom substrate, a piezoelectric layer disposed above the bottom substrate, the piezoelectric layer having a bottom surface facing the bottom substrate and a top surface opposite to the bottom surface, a cavity disposed below the piezoelectric layer, an interdigital transducer (IDT) disposed on the top surface of the piezoelectric layer, and a back electrode disposed on the bottom surface of the piezoelectric layer. At least a portion of the back electrode is exposed in the cavity.

A multiplexer includes a first transmission filter connected to a common terminal, a reception filter, a second transmission filter, and a multilayer substrate. The first transmission filter includes a first parallel-arm resonator connected to a first parallel-arm terminal and a second parallel-arm resonator connected to a second parallel-arm terminal. The second transmission filter includes a third parallel-arm resonator connected to a third parallel-arm terminal and a fourth parallel-arm resonator connected to a fourth parallel-arm terminal. The first to fourth parallel-arm resonators are surface-mounted on a main surface of the multilayer substrate. The second and third parallel-arm terminals are grounded on any dielectric layer from the main surface to an n-th dielectric layer of the multilayer substrate and the first and fourth parallel-arm terminals are isolated from each other on the dielectric layers from the main surface to the n-th dielectric layer.

An acoustic wave device includes a substrate, a multilayer film on the substrate, an LT layer configured by a single crystal of LiTaO.sub.3 on the multilayer film, and an IDT electrode on the LT layer. The thickness of the LT layer is 0.3λ or less where λ is two times a pitch p of electrode fingers in the IDT electrode. Euler angles of the LT layer are (0°±20°, −5° to 65°, 0°±10°), (−120°±20°, −5° to 65°, 0°±10°), or (120°±20°, −5° to 65°, 0°±10°). The multilayer film configured by alternately stacking at least one first layer and at least one second layer. The first layer is comprised of SiO.sub.2. The second layer is comprised of any one of Ta.sub.2O.sub.5, HfO.sub.2, ZrO.sub.2, TiO.sub.2, and MgO.

An elastic wave device includes a piezoelectric film, a high acoustic velocity member, a low acoustic velocity film located between the piezoelectric film and the high acoustic velocity member and through which an elastic wave propagates at a lower acoustic velocity than an elastic wave that propagates through the piezoelectric film, and an interdigital transducer electrode including electrode fingers separated from each other and disposed side by side in a first direction. At least one of the electrode fingers includes a first metal layer including first and second main body portions. A recessed portion is located in a central region in the first direction of the electrode finger and is recessed in the thickness direction of the piezoelectric film. A protrusion portion protrudes from at least a portion of the first main body portion in the first direction.

Provided is an acoustic wave device that uses a plate wave. The acoustic wave device includes a piezoelectric film and a first resonator and a second resonator each including an IDT electrode located on an upper surface of the piezoelectric film. The thickness of the piezoelectric film is smaller than twice the period of the electrode fingers of the IDT electrodes. The duty of the electrode fingers of the first resonator and the duty of the electrode fingers of the second resonator are different from each other.

RF filtering circuitry comprises a first node, a second node, and a series signal path between the first node and the second node. A number of acoustic resonators are coupled to one or more of the first node and the second node via the series signal path. A first one of the acoustic resonators is associated with a first quality factor and a first electromechanical coupling coefficient. A second one of the acoustic resonators is associated with a second quality factor and a second electromechanical coupling coefficient. The first quality factor is different from the second quality factor and the first electromechanical coupling coefficient is different from the second electromechanical coupling coefficient.

An acoustic wave device includes an interdigital transducer electrode connected to first and second terminals, and a reflector connected to the second terminal. In a group of electrode fingers of the interdigital transducer electrode, the electrode fingers at one end and another end in a second direction are respectively first and second end electrode fingers, the first end electrode finger includes a wide portion at a distal end portion. The first end electrode finger is located between the reflector and the second end electrode finger in the second direction. An inner busbar portion of one of first and second busbars not connected to the first end electrode finger, is located on an inner side in the second direction relative to the wide portion of the first end electrode finger so as not to overlap the wide portion of the first end electrode finger in a first direction.

A piezoelectric film laminated body includes a metal film, an amorphous film, and a scandium aluminum nitride film. The amorphous film has an insulation property and is disposed on the metal film. The scandium aluminum nitride film is disposed on the amorphous film and is in contact with a surface of the amorphous film.

A surface acoustic wave device includes a piezoelectric substrate formed from a Ca.sub.3Ta(Ga.sub.1-xAl.sub.x).sub.3Si.sub.2O.sub.14 single crystal, and an interdigital electrode formed on the surface of the piezoelectric substrate and formed from Al. The interdigital electrode is configured to generate a Love-wave-type SH wave on the surface of the piezoelectric substrate. A normalized film thickness obtained by dividing the film thickness of the interdigital electrode by the wavelength of the Love-wave-type SH wave is 0.16 or less.