An acoustic wave device includes a silicon substrate, a piezoelectric layer, and an IDT electrode. Each of the silicon substrate and the piezoelectric layer includes first and second opposed main surfaces. The IDT electrode is on the first main surface of the piezoelectric layer, and includes first and second electrode fingers. When a wavelength of an acoustic wave determined by an electrode finger pitch of the IDT electrode is denoted as λ, a distance between the first main surface of the silicon substrate and the second main surface of the piezoelectric layer in a thickness direction of the silicon substrate is less than about 0.84λ. The first main surface of the silicon substrate is rougher than the first main surface of the piezoelectric layer.

An acoustic wave device includes a piezoelectric substrate including a piezoelectric layer, an IDT electrode provided on the piezoelectric substrate and including electrode fingers, and a dielectric film between the piezoelectric substrate and the IDT electrode. A portion of the IDT electrode in which the electrode fingers overlap with each other when seen in a propagation direction of an acoustic wave is an intersecting range. The intersecting range includes a central range and a first range and a second range sandwiching the central range in an electrode finger extending direction. Permittivity and density of the dielectric film are lower than that of the piezoelectric layer. When seen in plan view, the dielectric film is provided at a portion overlapping with the central range, and not provided at a portion overlapping with one of the first range and the second range.

An acoustic wave resonator includes a piezoelectric body and electrode fingers. The electrode fingers are positioned on the piezoelectric body and arrayed in a propagation direction of acoustic waves. The electrode fingers include a first and second electrode finger groups. Electrode fingers are formed between adjacent two of the electrode fingers of the other electrode group. A duty ratio of the electrode fingers of the first and second electrode finger groups is gradually changed along one of opposite directions specifying the propagation direction by first and second change amounts, respectively which are different, and in the opposite direction. In a region in which the electrode fingers are positioned, a pitch between the electrode fingers is changed to cancel an effect of a difference in the duty ratio of the electrode fingers on a difference in resonance frequency.

An elastic wave device includes an elastic wave element chip, a bump electrically connected to the elastic wave element chip, a package substrate including an electrode bonded to the bump, the elastic wave element chip mounted on the package substrate with the bump, and a sealing resin portion covering the elastic wave element chip on the package substrate. A space surrounded by the elastic wave element chip, the package substrate, and the sealing resin portion is provided. The elastic wave element chip includes a substrate having piezoelectricity, an interdigital transducer electrode, and a pad electrode. A first main surface of the substrate having piezoelectricity includes a first region and a second region closer to a second main surface than the first region. The interdigital transducer electrode is disposed in the first region. The pad electrode is disposed in the second region and bonded to the bump.

An acoustic wave device is provided between a first terminal that is an antenna terminal and a second terminal that is different from the first terminal, and includes a plurality of acoustic wave resonators. The plurality of acoustic wave resonators include a plurality of series arm resonators and a plurality of parallel arm resonators. When the acoustic wave resonator electrically closest to the first terminal among the plurality of acoustic wave resonators is an antenna end resonator, the antenna end resonator is a SAW resonator or a BAW resonator. At least one acoustic wave resonator other than the antenna end resonator among the plurality of acoustic wave resonators is a first acoustic wave resonator.

An acoustic wave device includes a semiconductor substrate having a first main surface and a second main surface, a piezoelectric thin film provided directly on or indirectly above the first main surface of the semiconductor substrate, and an IDT electrode provided on the piezoelectric thin film. A semiconductor defining the semiconductor substrate is a high acoustic velocity material in which an acoustic velocity of a bulk wave propagating therethrough is higher than an acoustic velocity of an acoustic wave propagating through the piezoelectric thin film. The semiconductor substrate includes a first region including the first main surface and a second region which is a region other than the first region and includes the second main surface. An electric resistance of the first region is lower than an electric resistance of the second region.

An acoustic wave device includes a silicon support substrate, a silicon nitride film on the support substrate, a silicon oxide film on the silicon nitride film, a piezoelectric layer on the silicon oxide film and using Y-cut X-SAW propagation lithium tantalate, and an IDT electrode on the piezoelectric layer. A film thickness of the piezoelectric layer is equal to or less than about 1λ, Euler angles of the piezoelectric layer are (0±5°, θ, 0±5°) or (0±5°, θ, 180±5°), θ in the Euler angles of the piezoelectric layer is about 95.5°≤θ<117.5° or about −84.5°≤θ<−62.5°, and a relationship between θ in the Euler angles of the piezoelectric layer and a film thickness of the silicon nitride film is a combination shown in Table 1 or Table 2.

An acoustic wave device includes a piezoelectric film stacked directly on or indirectly above a support substrate; and an IDT electrode on the piezoelectric film and including an intersecting region in which first and second electrode fingers overlap with each other in an acoustic wave propagation direction, the intersecting region includes a central region in a direction in which the first and second electrode fingers extend and first and second edge regions on sides outside the central region, acoustic velocities in the first and second edge regions are lower than an acoustic velocity in the central region, a thickness Ht in the central region is different from thicknesses He in the first and second edge regions, and at least either of Ht and He is not more than about 1λ, where λ is a wavelength which is determined by an electrode finger pitch of the IDT electrode.

An acoustic wave device includes a support substrate including silicon, a piezoelectric layer in which a rotated Y-cut X-propagation lithium tantalate is included, and an IDT electrode. A film thickness of the piezoelectric layer is less than or equal to about 1λ. When α.sub.111 is an angle between a directional vector k.sub.111, and a direction of silicon and n is an arbitrary integer, the angle α.sub.111 is in a range of about 0°+120°×n≤α.sub.111≤45°+120°×n or in a range of about 75°+120°×n≤α.sub.111≤120°+120°×n when the IDT electrode is on a positive surface of the piezoelectric layer and the angle α.sub.111 is in a range of about 15°+120°×n≤α.sub.111≤105°+120°×n when the IDT electrode is on the negative surface of the piezoelectric layer.

A micro-acoustic device comprises a confinement structure (CS) adapted to block propagation of acoustic waves of an acoustic wave resonator (TEL, PL, BEL; ES) at an operation frequency of the device to confine the acoustic waves to the acoustic path or the acoustic volume. It is proposed to use a phononic crystal material for producing the confinement structure.