An elastic wave device includes a support layer with a through-hole or a recess opened at an upper surface thereof, a piezoelectric thin film arranged on the support layer to extend above the recess or the through-hole of the support layer, and an IDT electrode defined on at least one of upper and lower surfaces of the piezoelectric thin film in a region of the piezoelectric thin film, the region extending above the recess, or the through-hole. A secondary mode of a plate wave, which contains a U1 component as a main component, is utilized. The piezoelectric thin film is made of LiTaO.sub.3, and Euler angles (φ, θ, ψ) of the LiTaO.sub.3 fall within specific ranges.

In an elastic wave device, an IDT electrode is disposed on a piezoelectric substrate and includes a close contact layer, which includes first and second main surfaces and side surfaces. The first main surface is in contact with the piezoelectric substrate, and at least two electrode layers are disposed on the close contact layer. The at least two electrode layers include a first electrode layer and a second electrode layer. The first electrode layer is made of a material that has a higher density than that of Al. The second electrode layer has a lower density than the first electrode layer. One of the at least two electrode layers has higher weather resistance than the close contact layer and covers the side surfaces of the close contact layer.

A composite substrate includes a single crystal support substrate containing first element as a main component; an oxide single crystal layer provided on the single crystal support substrate and containing a second element (excluding oxygen) as a main component; and an amorphous layer provided in between the single crystal support substrate and the oxide single crystal layer and containing a first element, a second element, and Ar, the amorphous layer having a first amorphous region in which proportion of the first element is higher than proportion of the second element, and a second amorphous region in which the proportion of the second element is higher than the proportion of the first element, concentration of Ar contained in the first amorphous region being higher than concentration of Ar contained in the second amorphous region and being 3 atom % or more.

A first filter of a multiplexer includes a ladder filter structure with a plurality of series resonators and a plurality of parallel resonators. Each resonator is an acoustic wave resonator that includes an InterDigital Transducer (IDT) electrode including a pair of comb-shaped electrodes. A total number of reflection electrode fingers of the reflectors of at least one of the series resonator that is closest to the common terminal among the series resonators and the parallel resonator that is closest to the common terminal is smaller than a total number of reflection electrode fingers of the reflectors of each of a remainder of the resonators.

An acoustic wave device that includes a spinel layer, a piezoelectric layer, a temperature compensating layer between the spinel layer and the piezoelectric layer and an interdigital transducer electrode on the piezoelectric layer is disclosed. The piezoelectric layer is disposed between the interdigital transducer electrode and the spinel layer. The acoustic wave device is configured to generate an acoustic wave having a wavelength of λ. The piezoelectric layer can have a thickness that is less than λ. In some embodiments, the spinel layer can be a polycrystalline spinel layer.

A temperature-controlled RF resonator. The resonator includes an insulating thermal enclosure within which are implemented: at least one resonant element configured to deliver an RF output signal when supplied with an RF input signal; at least one heating element configured to supply thermal energy within the thermal enclosure when the at least one heating element is powered by an LF electric power signal; and at least one temperature sensor configured to deliver an LF electric measurement signal as a function of the temperature inside the thermal enclosure. Such an RF resonator has at least one input/output port crossing the insulating thermal enclosure and propagating at least: one signal from among the RF signals; and another signal from among the LF electric signals.

An elastic wave device includes IDT electrodes on a first main surface of a piezoelectric substrate and a heat dissipating film on a second main surface and including a pair of opposing main surfaces and side surfaces connecting the pair of main surfaces. At least a portion of the side surfaces of the heat dissipating film is located in an inner side portion relative to the outer circumference of the second main surface of the piezoelectric substrate on an arbitrary cross section along a direction connecting the pair of main surfaces of the heat dissipating film.

An apparatus is disclosed for site-selective piezoelectric-layer trimming. The apparatus includes at least one surface-acoustic-wave filter with an electrode structure and a piezoelectric layer. The electrode structure has multiple gaps. The piezoelectric layer has a planar surface defined by a first (X) axis and a second (Y) axis that is perpendicular to the first (X) axis. The piezoelectric layer is configured to propagate an acoustic wave along the first (X) axis. The piezoelectric layer includes a first portion that supports the electrode structure and a second portion that is exposed by the multiple gaps of the electrode structure. The second portion has different heights across the second (Y) axis. The different heights are defined with respect to a third (Z) axis that is substantially normal to the planar surface.

A surface acoustic wave device includes a substrate, a first electrode and a second electrode formed on the substrate to extend along a first direction, wherein the first electrode and the second electrode are alternately disposed along the second direction, one end of the first electrode on one side of the first direction is aligned along the second direction, and one end of the second electrode on the other side of the first direction is aligned along the second direction, a temperature compensation film which covers the first electrode and the second electrode, a first additional film formed on the temperature compensation film to vertically overlap a partial region from the one end of the first electrode on the one side of the first direction, and a second additional film formed on the temperature compensation film to vertically overlap a partial region from the one end of the second electrode.

An acoustic wave device includes a support substrate, a piezoelectric layer provided over the support substrate, comb-shaped electrodes disposed on the piezoelectric layer, each of the comb-shaped electrodes including electrode fingers exciting an acoustic wave, a temperature compensation film interposed between the support substrate and the piezoelectric layer and having a temperature coefficient of an elastic constant opposite in sign to that of the piezoelectric layer, a boundary layer interposed between the support substrate and the temperature compensation film, an acoustic velocity of a bulk wave propagating through the boundary layer being higher than an acoustic velocity of a bulk wave propagating through the temperature compensation film and being lower than an acoustic velocity of a bulk wave propagating through the support substrate, and an intermediate layer interposed between the support substrate and the boundary layer and having a Q factor less than a Q factor of the boundary layer.