A surface acoustic wave device using a longitudinally polarized guided wave comprises a composite substrate comprising a piezoelectric layer formed over a base substrate, wherein the crystalline orientation of the piezoelectric layer with respect to the base substrate is such that, the phase velocity of the longitudinally polarized wave is below the critical phase velocity of the base substrate at which wave guiding within the piezoelectric layer vanishes. A method of fabrication of such surface acoustic wave device is also disclosed.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

In an acoustic wave device, an antenna end resonator that is electrically closest to a first terminal is a first acoustic wave resonator. In each of the first acoustic wave resonator and a second acoustic wave resonator, a thickness of a piezoelectric layer is about 3.5 or less when a wavelength of an acoustic wave is denoted as . The first acoustic wave resonator and the second acoustic wave resonator satisfy at least one of a first condition, a second condition, and a third condition. The first condition is a condition that the first acoustic wave resonator further includes a dielectric film provided between the piezoelectric layer and an interdigital transducer electrode, and the second acoustic wave resonator does not include the dielectric film.

A method for manufacturing an elastic wave device includes successively stacking conductive films on a piezoelectric substrate on which a pattern of a first resist has been formed, removing the first resist from the piezoelectric substrate on which the conductive films have been stacked; applying a second resist to the piezoelectric substrate from which the first resist has been removed and subjecting the second resist to exposure and development, thus forming a protective layer that protects a first region with the second resist, and etching the second conductive material in a state in which the first region is protected by the protective layer.

An acoustic wave device includes: a piezoelectric film made of an aluminum nitride film containing a divalent element and a tetravalent element, or a divalent element and a pentavalent element; and an electrode that excites an acoustic wave propagating through the piezoelectric film.

An elastic wave device includes a support substrate, a film stack including a piezoelectric thin film, and an IDT electrode. The film stack is partially absent in a region outside a region where the IDT electrode is located in plan view. The elastic wave device further includes a support layer located on the support substrate in at least a portion of a region where the film stack is partially absent and surrounds a region where the film stack is located in plan view and a cover member located on the support layer. The cover member defines a hollow space facing the IDT electrode together with the piezoelectric thin film and the support layer.

An elastic wave device includes a supporting substrate, a high-acoustic-velocity film stacked on the supporting substrate and in which an acoustic velocity of a bulk wave propagating therein is higher than an acoustic velocity of an elastic wave propagating in a piezoelectric film, a low-acoustic-velocity film stacked on the high-acoustic-velocity film and in which an acoustic velocity of a bulk wave propagating therein is lower than an acoustic velocity of a bulk wave propagating in the piezoelectric film, the piezoelectric film is stacked on the low-acoustic-velocity film, and an IDT electrode stacked on a surface of the piezoelectric film.

An elastic wave element having a piezoelectric substrate equipped with a first main surface, and an excitation electrode arranged on the first main surface and having multiple electrode fingers, wherein, in a cross-sectional view in the direction orthogonal to the first main surface, the width of the electrode fingers at a first height at a distance from the first main surface is greater than the width at a second height located closest to the first main surface.

An acoustic wave device includes a material layer which has Euler angles and an elastic constant at the Euler angles, a piezoelectric body which includes first and second principal surfaces opposing each other, is laminated directly or indirectly on the material layer so that the second principal surface is on the material layer side and has Euler angles, and whose elastic constant at the Euler angles, and an IDT electrode which is disposed on at least one of the first principal surface and the second principal surface of the piezoelectric body. At least one elastic constant among elastic constants C.sub.11 to C.sub.66 of the material layer not equal to 0 and at least one elastic constant among elastic constants C.sub.11 to C.sub.66 of the piezoelectric body not equal to 0 have opposite signs to each other.

A composite filter device includes bandpass filters whose respective one ends are electrically connected in common. A first bandpass filter of the bandpass filters includes a first filter, a switch, a second filter, and an impedance element that is electrically connected to the switch and having an impedance value larger than the input impedance value of the second filter. The switch is configured to be switched between a first state in which the first filter and the second filter are electrically connected and a second state in which the first filter and the impedance element are electrically connected.