An IDT electrode includes first and second busbar electrodes opposed to each other, first and second electrode fingers extending respectively from the first and second busbar electrodes on a piezoelectric substrate. The first busbar electrode and a tip end of the second electrode finger are opposed to each other with a gap therebetween, and bottom surfaces of the first and second busbar electrodes are opposed to each other with a first gap therebetween. The first and second busbar electrodes respectively include portions opposed to each other with a second gap shorter than the first gap therebetween on the top surface side. In a first area located between a first side surface and a second side surface, a second area located between the piezoelectric substrate and the first busbar electrode or the second electrode finger includes a hollow portion.

An acoustic wave filter includes: a piezoelectric substrate; series resonators connected in series and located on the piezoelectric substrate, each of the series resonators including first electrode fingers that are arranged with a first duty ratio and excite an acoustic wave; parallel resonators connected in parallel and located on the piezoelectric substrate, each of the parallel resonators including second electrode fingers that are arranged with a second duty ratio and excite an acoustic wave, the second duty ratio in at least one parallel resonator being less than the first duty ratio in at least one series resonator; and a dielectric film that has a temperature coefficient of elastic modulus that is opposite in sign to that of the piezoelectric substrate, is located on the piezoelectric substrate so as to cover the first and second electrode fingers, has a film thickness greater than those of the first and second electrode fingers.

A coupled cavity filter structure that uses a surface acoustic wave, in particular, a guided surface acoustic wave, comprises an acoustic wave propagating substrate, at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes, at least one reflecting structure comprising at least one or more metallic strips, positioned at a distance and in between the input and output transducer structures, in the direction of propagation of an acoustic wave. The acoustic wave propagating substrate is a composite substrate comprising a base substrate and a piezoelectric layer. In additional embodiments, a coupled cavity filter structure comprises a groove. In additional embodiments, a SAW ladder filter device comprises at least two coupled cavity filter structures as described herein, wherein the at least two coupled cavity filter structures are positioned on a single line.

An acoustic wave device includes a silicon oxide film, a lithium tantalate film, an IDT electrode, and a protection film that are laminated on a support substrate made of silicon. A wavelength normalized film thickness of a lithium tantalate film is denoted by T.sub.LT, an Euler angle is θ.sub.LT, a wavelength normalized film thickness of the silicon oxide film is T.sub.S, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness is T.sub.E, a wavelength normalized film thickness of a protection film is T.sub.P, a propagation direction in the support substrate is ψ.sub.Si, and a wavelength normalized film thickness of the support substrate is T.sub.Si. Values of T.sub.LT, θ.sub.LT, T.sub.S, T.sub.E, T.sub.P, and ψ.sub.Si are set such that I.sub.h corresponding to an intensity of a response of a spurious response represented by Formula (1) is greater than about −2.4 in a spurious response.

A coupled cavity filter structure that uses a surface acoustic wave, in particular, a guided surface acoustic wave, comprises an acoustic wave propagating substrate, at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes, at least one reflecting structure comprising at least one or more metallic strips positioned at a distance and in between the input and output transducer structures, in the direction of propagation of an acoustic wave. The acoustic wave propagating substrate is a composite substrate comprising a base substrate and a piezoelectric layer. In additional embodiments, a coupled cavity filter structure comprises a groove. In additional embodiments, a SAW ladder filter device comprises at least two coupled cavity filter structures as described herein, wherein the at least two coupled cavity filter structures are positioned on a single line.

In a resonator, two interdigital transducers (W1,W2) are electrically series-connected and arranged next to each other in the longitudinal direction within an acoustic track delimited by reflectors. Between the two interdigital transducers, a transition area (UEB) is formed in that the finger period p, which is defined as the distance between the finger centers of adjacent transducer fingers, is higher in comparison to the remaining interdigital transducer.

An acoustic wave device includes a silicon oxide film, a lithium tantalate film, an IDT electrode, and a protection film that are laminated on a support substrate made of silicon. A wavelength normalized film thickness of a lithium tantalate film is denoted by T.sub.LT, an Euler angle is .sub.LT, a wavelength normalized film thickness of the silicon oxide film is T.sub.S, a wavelength normalized film thickness of the IDT electrode in terms of aluminum thickness is T.sub.E, a wavelength normalized film thickness of a protection film is T.sub.P, a propagation direction in the support substrate is .sub.Si, and a wavelength normalized film thickness of the support substrate is T.sub.Si. Values of T.sub.LT, .sub.LT, T.sub.S, T.sub.E, T.sub.P, and .sub.Si are set such that I.sub.h corresponding to an intensity of a response of a spurious response represented by Formula (1) is greater than about 2.4 in a spurious response.

A coupled cavity filter structure that uses a surface acoustic wave, in particular, a guided surface acoustic wave, comprises an acoustic wave propagating substrate, at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes, at least one reflecting structure comprising at least one or more metallic strips positioned at a distance and in between the input and output transducer structures, in the direction of propagation of an acoustic wave. The acoustic wave propagating substrate is a composite substrate comprising a base substrate and a piezoelectric layer. In additional embodiments, a coupled cavity filter structure comprises a groove. In additional embodiments, a SAW ladder filter device comprises at least two coupled cavity filter structures as described herein, wherein the at least two coupled cavity filter structures are positioned on a single line.

An acoustic wave filter includes: a piezoelectric substrate; series resonators connected in series and located on the piezoelectric substrate, each of the series resonators including first electrode fingers that are arranged with a first duty ratio and excite an acoustic wave; parallel resonators connected in parallel and located on the piezoelectric substrate, each of the parallel resonators including second electrode fingers that are arranged with a second duty ratio and excite an acoustic wave, the second duty ratio in at least one parallel resonator being less than the first duty ratio in at least one series resonator; and a dielectric film that has a temperature coefficient of elastic modulus that is opposite in sign to that of the piezoelectric substrate, is located on the piezoelectric substrate so as to cover the first and second electrode fingers, has a film thickness greater than those of the first and second electrode fingers.

A coupled cavity filter structure that uses a surface acoustic wave, in particular, a guided surface acoustic wave, comprises an acoustic wave propagating substrate, at least one input transducer structure and one output transducer structure, provided over the substrate, each comprising inter-digitated comb electrodes, at least one reflecting structure comprising at least one or more metallic strips positioned at a distance and in between the input and output transducer structures, in the direction of propagation of an acoustic wave. The acoustic wave propagating substrate is a composite substrate comprising a base substrate and a piezoelectric layer. In additional embodiments, a coupled cavity filter structure comprises a groove. In additional embodiments, a SAW ladder filter device comprises at least two coupled cavity filter structures as described herein, wherein the at least two coupled cavity filter structures are positioned on a single line.