An acoustic wave filter includes series resonators and parallel resonators that have a piezoelectric film on an identical substrate and have a lower electrode and an upper electrode, wherein: one of the series resonators and the parallel resonators have a temperature compensation film on a face of the lower electrode or the upper electrode that is opposite to the piezoelectric film in a resonance region, the compensation film having an elastic constant of a temperature coefficient of which sign is opposite to a sign of a temperature coefficient of an elastic constant of the piezoelectric film; and the other have an added film on the same side as the temperature compensation film on the lower electrode side or the upper electrode side compared to the piezoelectric film in the resonance region in the one of the series resonators and the parallel resonators.

A method for producing a piezoelectric device includes a laminate formation step in which a laminate including a piezoelectric thin film, a support substrate, a metal layer, and a silicon oxide film respectively stacked on both of an upper surface and a lower surface of the metal layer interposed between the piezoelectric thin film and the support substrate is formed, a semi-conducting layer formation step in which a semi-conducting layer is formed by oxidizing the metal layer, and a functional electrode formation step in which a functional electrode that is electro-mechanically coupled to the piezoelectric thin film is formed on a first principal surface of the piezoelectric thin film. The semi-conducting layer is a layer composed of a mixture of a metal constituting the metal layer and an oxide thereof, or a layer composed of a semiconductor which is an oxide of a metal constituting the metal layer.

A crystal resonator includes a crystal element and excitation electrodes. The crystal element has a pair of principal surfaces parallel to an X-axis and a Z-axis. The X-axis is an axis of rotating an X-axis as a crystallographic axis of a crystal in a range of 15 degrees to 25 degrees around a Z-axis as a crystallographic axis of the crystal. The Z-axis is an axis of rotating the Z-axis in a range of 33 degrees to 35 degrees around the X-axis. The excitation electrodes are formed on the respective principal surfaces of the crystal element. Elliptical mesa portions or elliptical inverted mesa portions are formed on the respective principal surfaces. The mesa portions project from outer peripheries of the principal surfaces. The inverted mesa portions are depressed from the outer peripheries of the principal surfaces.

Provided is a composite substrate for surface acoustic wave device which does not cause peeling of an entire surface of a piezoelectric single crystal film even when heating the film to 400 C. or higher in a step after bonding. The composite substrate is formed by providing a piezoelectric single crystal substrate and a support substrate, forming a film made of an inorganic material on at least one of the piezoelectric single crystal substrate and the support substrate, and joining the piezoelectric single crystal substrate with the support substrate so as to sandwich the film made of the inorganic material.

An acoustic wave element which can be reduced in size and produced relatively easily, practically used without using harmful substances, and can suppress a surface acoustic wave propagation loss, which has an excellent temperature coefficient of frequency and a velocity dispersion characteristic, and with which an increase in the reflection coefficient of interdigital transducers can be suppressed, and a method for manufacturing the acoustic wave element are provided. The acoustic wave element includes a pair of electrodes provided on both surfaces of a piezoelectric substrate, and a dielectric film provided on a first surface of the piezoelectric substrate so as to cover the electrode. The acoustic wave element alternatively includes interdigital transducers provided on a first surface of the piezoelectric substrate, and a dielectric film provided on the interdigital transducers, a gap between the interdigital transducers, and/or a second surface of the piezoelectric substrate.

A surface elastic wave device comprises a stack including: a thin film made of a piezoelectric first material; a substrate made from a second material; and exciting means for generating at least one surface acoustic wave propagation mode in the piezoelectric film; wherein: the first material is a single-crystal material and the second material is a crystalline material, the thickness of the thin film of piezoelectric first material being smaller than or equal to 20 m, and the first material and the second material having viscoelastic coefficients lower than or equal to those of quartz for the propagation mode induced by the exciting means.

Surface acoustic wave (SAW) resonator, SAW filters, and methods of fabricating SAW filters. A first plurality of parallel conductors extending from a first bus bar are formed on a surface of a 128-degree Y-cut lithium niobate substrate. A second plurality of parallel conductors extending from a second bus bar are formed on the surface of the substrate, the second plurality of parallel conductors interleaved with the first plurality of parallel conductors. An SiO2 layer overlays the first and second pluralities of parallel conductors. The first and second pluralities of parallel conductors are substantially copper and have a thickness D.sub.CU defined by 0.12 PD.sub.CU0.24P, where P is a center-to-center spacing of adjacent parallel conductors. The SiO2 layer has a thickness D.sub.OX defined by 3.1D.sub.CUD.sub.OX4.5D.sub.CU.

A duplexer includes: a first filter connected between a common terminal and a first terminal and including first series and first parallel resonators; a second filter having a passband higher than that of the first filter, connected between the common terminal and a second terminal, and including second series and second parallel resonators; a first chip including the first series and second parallel resonators mounted thereon; a second chip including the first parallel and second series resonators mounted thereon, wherein when GA and HGB represent temperature coefficients of antiresonant frequencies of the first and second series resonators, and HGA and GB represent temperature coefficients of resonant frequencies of the first and second parallel resonators, a magnitude relationship among GA, GB, HGA, and HGB is none of a relationship in which GA (GB) differs from HGA (HGB), and GB (GA) and HGB (HGA) are located between GA (GB) and HGA (HGB).

A substrate for a surface acoustic wave device or bulk acoustic wave device, comprising a support substrate and an piezoelectric layer on the support substrate, wherein the support substrate comprises a semiconductor layer on a stiffening substrate having a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the material of the piezoelectric layer than that of silicon, the semiconductor layer being arranged between the piezoelectric layer and the stiffening substrate.

A method for forming an aluminum nitride layer (310, 320) comprises the provision of a substrate (100) and the forming of a patterned metal nitride layer (110). A bottom electrode metal layer (210) is formed on the exposed portions (101) of the substrate. An aluminum nitride layer portion (320) grown above the exposed portion (101) of the substrate (100) exhibits piezoelectric properties. An aluminum nitride layer portion (310) grown above the patterned metal nitride layer (110) exhibits no piezoelectric properties (310). Both aluminum nitride layer portions (320, 310) are grown simultaneously.