A multiplexer (1) includes a plurality of filters connected to a common terminal (110). The multiplexer (1) includes: a low-frequency filter (11L) that is formed of at least one surface acoustic wave resonator arranged between the common terminal (110) and the input/output terminal (120) and has a first pass band; a high-frequency filter (12H) that is connected between the common terminal (110) and the input/output terminal (130) and has a second pass band located at a higher frequency than the first pass band; and a capacitor (C.sub.B1) that is serially arranged in a connection path between the common terminal (110) and the low-frequency filter (11L). The Q value of the capacitor (C.sub.B1) in the second pass band is higher than the Q value in the second pass band of a capacitance obtained by treating the at least one surface acoustic wave resonator of the low-frequency filter (11L) as a capacitance.

An acoustic wave device includes: a piezoelectric substrate: a pair of comb-shaped electrodes located on the piezoelectric substrate, each of the comb-shaped electrodes including a plurality of electrode fingers; a support substrate having protruding portions and/or recessed portions in a region overlapping with the pair of comb-shaped electrodes in plan view, the protruding portions and/or recessed portions being regularly arranged; and an insulating layer directly or indirectly bonded between the piezoelectric substrate and the support substrate, a boundary face between the insulating layer and the support substrate being provided along the protruding portions and/or the recessed portions.

A SAW transducer and a SAW resonator are proposed composed of consecutively arranged unit cells of length L. Slight geometry or material variations such as variations of the metallization ration or the unit cell length L affecting the pitch) between these unit cells result in improved spurious mode suppression while the main mode performance is unaffected.

A bonded body includes a supporting substrate, piezoelectric material substrate and a multilayer film, between the supporting substrate and piezoelectric material substrate. The multilayer film includes a lamination structure having a first layer, second layer, third layer and fourth layer in the order. The first layer and third layer are composed of silicon oxides, and the second layer and fourth layer are composed of metal oxides. The refractive index of the second layer is higher than the refractive index of the first layer and refractive index of the third layer. The refractive index of the second layer is different from the refractive index of the fourth layer.

In an acoustic wave device, a piezoelectric layer is provided directly or indirectly on a support substrate, an IDT electrode is provided on the piezoelectric layer, an overlap region includes a middle region and first and second edge regions, and first and second conductive layers are provided on a second main surface of the piezoelectric layer to overlap at least some portions of the first and second edge regions in plan view and at least some portions of first and second busbars in plan view.

An acoustic wave device includes a high acoustic velocity structure, a low acoustic velocity layer on the high acoustic velocity structure, a piezoelectric layer directly or indirectly on the low acoustic velocity layer, and an electrode on the piezoelectric layer. The low acoustic velocity layer is made of a dielectric material having a lower Young's modulus than silicon oxide, or includes the dielectric material as a main component.

An acoustic wave element includes an IDT electrode including electrode fingers, a first substrate on an upper surface of which the IDT electrode is located, which has a thickness of less than 2 times a repetition interval of the electrode fingers and is configured by a piezoelectric crystal, a second substrate bonded to a lower surface of the first substrate, and configured by an Si single crystal having a plane orientation of a (100) plane or (110) plane or a plane equal to them, in which substrate a crystal axis of the Si single crystal parallel to a substrate surface of Si single crystal is inclined at any angle of 25° to 65°, 115° to 155°, 205° to 245°, and 295° to 345° relative to a direction of propagation of an acoustic wave when viewed from the upper surface of the superposed first substrate.

An acoustic wave resonator includes a support substrate, a piezoelectric layer that is disposed on the support substrate and is a rotated Y-cut X-propagation lithium tantalate of which a cut angle is within a range of greater than 50° and less than 150°, and a pair of comb-shaped electrodes disposed on the piezoelectric layer, each of the comb-shaped electrodes including a plurality of electrode fingers, an average pitch of the electrode fingers of one of the comb-shaped electrodes being equal to or greater than ½ of a thickness of the piezoelectric layer.

An acoustic wave device that includes a spinel layer, a 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 than is less than A. In some embodiments, the acoustic wave device can include a temperature compensating layer that is disposed between the piezoelectric layer and the spinel layer.

An acoustic wave device includes a support substrate, a quartz-crystal layer provided directly or indirectly on the support substrate, a piezoelectric layer on the quartz-crystal layer, and an IDT electrode on the piezoelectric layer. When λ represents a wavelength defined by an electrode finger pitch of the IDT electrode, a thickness of the quartz-crystal layer is about 0.2λ or more and about 0.4λ or less, and the piezoelectric layer has a thickness smaller than the thickness of the quartz-crystal layer.