An acoustic wave device includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate and includes a main electrode layer. In the IDT electrode, a central region, first and second low acoustic velocity regions and first and second high acoustic velocity regions are disposed in this order. A duty ratio in the first low acoustic velocity region of first electrode fingers and the second low acoustic velocity region of second electrode fingers is larger than a duty ratio in the central region. The main electrode layer includes any one of Au, Pt, Ta, Cu, Ni, and Mo as a main component.

An acoustic wave device includes a piezoelectric substrate including a piezoelectric layer made of lithium tantalate, an IDT electrode on the piezoelectric substrate, and a pair of reflectors on both sides of the IDT electrode on the piezoelectric substrate in an acoustic wave propagation direction. SH waves are used as a principal mode. The IDT electrode includes electrode fingers and the pair of reflectors each including electrode fingers. When a length along a direction orthogonal to a direction in which the electrode fingers extend is a width, each of the reflectors includes first and second electrode fingers having different widths. Four consecutive electrode fingers, which are any four of the electrode fingers of each of the reflectors, include both of the first and second electrode fingers and distances between centers of the four consecutive electrode fingers are equal or substantially equal.

An acoustic wave filter includes first and second series-arm resonators, each including an IDT electrode including electrode fingers and a busbar electrode connecting first ends of the electrode fingers to each other. A direction in which second ends of the electrode fingers are aligned with each other crosses a propagation direction of an acoustic wave. The electrode fingers of the IDT electrodes of the first and second series-arm resonators each include an electrode-finger central portion and a wide portion located at the second end and being wider than the electrode-finger central portion. The length of the wide portion of each of the electrode fingers in the first series-arm resonator is greater than the length of the wide portion of each of the electrode fingers in the second series-arm resonator.

An elastic wave filter device includes a ladder filter that includes series arm resonators and parallel arm resonators. In one series arm resonator in which the acoustic velocity in a first and second edge area is lower than in a central area, each first electrode finger includes a large-width portion having a width larger than in remaining portions in the second edge area, and each second electrode finger includes a large-width portion having a width larger than in remaining portions in the first edge area. In at least one of remaining series arm resonators and the parallel arm resonators, each first and second electrode finger includes a large-width portion having a width larger than in remaining portions in both of the first and second edge areas.

An acoustic wave device includes an IDT electrode on a piezoelectric body and the IDT electrode includes first and second busbars, and first and second electrode fingers. A first dielectric film extends from a region between tip end portions of the first electrode fingers and the piezoelectric body to a region between the second busbar and the piezoelectric body with a first gap in between. The second electrode fingers are in direct contact with the piezoelectric body at a center of an overlap width, and a permittivity of the first dielectric film is lower than a permittivity of the piezoelectric body.

An electroacoustic resonator (EAR) that allows RF filters in which transversal modes are suppressed in a wider frequency range and corresponding RF filters and methods are provided. The resonator has an electrode structure (BB,EF) on a piezoelectric material and a transversal acoustic wave guide. The wave guide has a central excitation area (CEA), trap stripes (TP) and barrier stripes (B). The difference in wave velocity (|VCEA−VB|) between the central excitation area and the barrier stripes determines the frequency range of suppressed transversal modes.

An acoustic wave device includes a piezoelectric substrate and an IDT electrode provided on the piezoelectric substrate. In the IDT electrode, a central region, first and second low acoustic velocity regions and first and second high acoustic velocity regions are disposed in this order. A duty ratio in the first low acoustic velocity region of first electrode fingers and the second low acoustic velocity region of second electrode fingers is larger than a duty ratio in the central region. When acoustic velocity of a transversal bulk wave propagating in metal that is a main component of a main electrode layer is defined as v (m/s), v≤3299 m/s, and when a wave length defined by an electrode finger pitch of the IDT electrode is defined as λ, and a film thickness of the main electrode layer normalized by the wave length λ is defined as T, then T≥0.00018e.sup.0.002V+0.014.

An acoustic wave device includes a piezoelectric substrate, an interdigital transducer electrode on the piezoelectric substrate, and two reflectors on both sides of the interdigital transducer electrode in an acoustic wave propagation direction. The reflectors include first and second busbars and first to third electrode fingers, respectively, and the first and second busbars are opposed to one another. The first busbars and the second busbars are connected by at least one third electrode finger. The reflectors each include a center area located centrally in a length direction and a first high-acoustic-velocity area that is located between the center area and the first busbars and has an acoustic velocity higher than the acoustic velocity of the center area, where the length direction is a direction in which the first to third electrode fingers extend.

Aspects of this disclosure relate to an acoustic wave resonator with hyperbolic mode suppression. The acoustic wave resonator can include a piezoelectric layer, an interdigital transducer electrode, a temperature compensation layer, and a mass loading strip. The mass loading strip can be a conductive strip. The mass loading strip can overlap edge portions of fingers of the interdigital transducer electrode. A layer of the mass loading strip can have a density that is at least as high as a density of a material of the interdigital transducer electrode. The material of the interdigital transducer can impact acoustic properties of the acoustic wave resonator.

An acoustic wave filter includes at least one serial arm resonance circuit on a path connecting input/output terminals, and at least one parallel arm resonance circuit between a node on the path and a ground, in which each of the at least one serial arm resonance circuit and the at least one parallel arm resonance circuit includes an acoustic wave resonator, a first parallel arm resonance circuit of the at least one parallel arm resonance circuit includes a bridging capacitor connected in parallel to the acoustic wave resonator, an anti-resonant frequency of the first parallel arm resonance circuit is positioned on a higher-frequency side than the pass band, and a resonant frequency of a first serial arm resonance circuit of the at least one serial arm resonance circuit is positioned on a lower-frequency side than the anti-resonant frequency of the first parallel arm resonance circuit.