An acoustic wave device includes an IDT electrode on a piezoelectric substrate and reflector electrodes on both sides of the IDT electrode in an acoustic wave propagation direction and each including electrode fingers with gaps therebetween, and first dielectric films between the reflector electrodes and the piezoelectric substrate in regions where the electrode fingers and the gaps of the reflector electrodes are provided.

A single crystal piezoelectric layer includes a first recess in a first opposing surface opposing a first main surface of a base. The single crystal piezoelectric layer is bonded to the first main surface of the base at a portion of the first opposing surface other than the first recess. A lower electrode layer defining at least a portion of a pair of electrode layers and extending over a surface of the single crystal piezoelectric layer opposing the base is at least partially located in the first recess. A second opposing surface of the lower electrode layer opposing the first main surface of the base has surface roughness greater than the surface roughness of the first opposing surface of the single crystal piezoelectric layer.

An acoustic wave device includes an IDT electrode and reflector electrodes on or above a piezoelectric substrate. A region in which first and second electrode fingers of the IDT electrode overlap each other in an acoustic wave propagation direction defines an intersection region. The intersection region includes a center region and first and second edge regions on both sides of the center region. Dielectric films extend from the first and second edge regions to outer side regions in the acoustic wave propagation direction of the reflector electrodes via the reflector electrodes.

An acoustic wave device includes a piezoelectric substrate and an IDT electrode on the piezoelectric substrate and including electrode fingers. A portion where adjacent electrode fingers of the IDT electrode overlap each other in an acoustic wave propagation direction is an intersecting region. The intersecting region includes a central region located in a central portion in a direction in which the electrode fingers extend and first and second edge regions on both sides of the central region in the direction in which the electrode fingers extend. The acoustic wave device further includes dielectric films between the piezoelectric substrate and the electrode fingers in the first and second edge regions. The dielectric films include at least one of hafnium oxide, niobium oxide, tungsten oxide, or cerium oxide.

An acoustic wave device includes an intermediate layer and a piezoelectric film that are laminated in that order on the support substrate. An interdigital transducer (IDT) electrode is provided on the piezoelectric film. Cavities are provided at least one of a location between the support substrate and the intermediate layer and a location in the intermediate layer.

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 low velocity surface acoustic wave device, and a method of reducing the velocity of a surface acoustic wave generated by a surface acoustic wave device are described, the device including a piezoelectric layer, an interdigital transducer disposed on the piezoelectric substrate and configured to generate a surface acoustic wave in response to an electrical, and a temperature coefficient of frequency compensation layer disposed partially on the interdigital transducer and partially on the piezoelectric substrate, the temperature coefficient of frequency compensation layer having a low velocity layer disposed within it configured to reduce the velocity of a surface acoustic wave generated by the interdigital transducer, the method including disposing a wave velocity adjustment layer, the wave velocity adjustment layer being a low velocity layer, within a temperature compensation layer of the surface acoustic wave device.

A bulk-acoustic wave resonator may include: a substrate; a resonance portion; a first electrode disposed on the substrate; a piezoelectric layer disposed on the first electrode in the resonance portion; a second electrode disposed on the piezoelectric portion in the resonance portion; and a seed layer disposed in a lower portion of the first electrode. The seed layer may be formed of titanium (Ti) having a hexagonal close packed (HCP) structure, or an alloy of Ti having the HCP structure. The seed layer may have a thickness greater than or equal to 300 Å and less than or equal to 1000 Å, or may be thinner than the first electrode.

An acoustic resonator filter is provided. The acoustic resonator filter includes a rear filter electrically connected between a front port and a rear port, through which a radio frequency (RF) signal passes, the rear filter including at least one film bulk acoustic resonator (FBAR); and a front filter electrically connected between the front port and the rear filter and including at least one solidly mounted resonator (SMR).

An acoustic resonator filter is provided. The acoustic resonator filter includes a rear filter electrically connected between a front port and a rear port, through which a radio frequency (RF) signal passes, the rear filter including at least one film bulk acoustic resonator (FBAR); and a front filter electrically connected between the front port and the rear filter and including at least one solidly mounted resonator (SMR).