A method of producing a composite substrate includes: forming a first layer on a lower surface side of a piezoelectric substrate having an upper surface and a lower surface facing each other and having an electrode formed on the lower surface; performing flattening treatment to set a waviness of a surface of the first layer to more than 2 nm and 70 nm or less; and joining a support substrate to a first layer side of the piezoelectric substrate having the first layer formed thereon.

A method of producing a composite substrate includes: forming a first layer on a lower surface side of a piezoelectric substrate having an upper surface and a lower surface facing each other and having an electrode formed on the lower surface; performing flattening treatment to set a waviness of a surface of the first layer to more than 2 nm and 70 nm or less; and joining a support substrate to a first layer side of the piezoelectric substrate having the first layer formed thereon.

The present invention relates to a heterostructure, in particular, a piezoelectric structure, comprising a cover layer, in particular, a layer of piezoelectric material, the material of the cover layer having a first coefficient of thermal expansion, assembled to a support substrate, the support substrate having a second coefficient of thermal expansion substantially different from the first coefficient of thermal expansion, at an interface wherein the cover layer comprises at least a recess extending from the interface into the cover layer, and its method of fabrication.

The present invention relates to a heterostructure, in particular, a piezoelectric structure, comprising a cover layer, in particular, a layer of piezoelectric material, the material of the cover layer having a first coefficient of thermal expansion, assembled to a support substrate, the support substrate having a second coefficient of thermal expansion substantially different from the first coefficient of thermal expansion, at an interface wherein the cover layer comprises at least a recess extending from the interface into the cover layer, and its method of fabrication.

An IDT electrode of an elastic wave device includes a first electrode film made of Al or mainly containing Al, a second electrode film with a density larger than that of the first electrode film, an anti-diffusion film which is located between the first electrode film and the second electrode film and which significantly reduces or prevents interdiffusion between the first electrode film and the second electrode film, and a first Ti film located between the first electrode film and the anti-diffusion film, to diffuse a diffusion material into the first electrode film.

An IDT electrode of an elastic wave device includes a first electrode film made of Al or mainly containing Al, a second electrode film with a density larger than that of the first electrode film, an anti-diffusion film which is located between the first electrode film and the second electrode film and which significantly reduces or prevents interdiffusion between the first electrode film and the second electrode film, and a first Ti film located between the first electrode film and the anti-diffusion film, to diffuse a diffusion material into the first electrode film.

An acoustic wave device includes a piezoelectric substrate, a pair of interleaved interdigital transducer electrodes disposed on the piezoelectric substrate, and a dielectric film including silicon oxynitride covering the pair of interleaved interdigital transducer electrodes. The dielectric film exhibits a temperature coefficient of velocity of substantially zero throughout an operating temperature range of the acoustic wave device of between 55 C. and 125 C.

An acoustic wave device includes a piezoelectric substrate, a pair of interleaved interdigital transducer electrodes disposed on the piezoelectric substrate, and a dielectric film including silicon oxynitride covering the pair of interleaved interdigital transducer electrodes. The dielectric film exhibits a temperature coefficient of velocity of substantially zero throughout an operating temperature range of the acoustic wave device of between 55 C. and 125 C.

An elastic wave device including a sealing structure. Examples of the elastic wave device include a piezoelectric substrate, an IDT electrode provided on the substrate, a first wiring electrode provided on the substrate adjacent the IDT electrode, a second wiring electrode provided on the first wiring electrode, and a dielectric sealing structure that extends over and seals an excitation space above the IDT electrode in which the IDT electrode excites the elastic wave. The second wiring electrode includes a protrusion formed on its outer periphery and extending beyond the first wiring electrode into the excitation space. The first and/or second wiring electrodes are electrically connected to the IDT electrode. The dielectric sealing structure includes a sealing wall provided on the second wiring electrode, the sealing wall being spaced apart from the IDT electrode by the protrusion and having a side surface that defines a side edge of the excitation space.

An elastic wave device including a sealing structure. Examples of the elastic wave device include a piezoelectric substrate, an IDT electrode provided on the substrate, a first wiring electrode provided on the substrate adjacent the IDT electrode, a second wiring electrode provided on the first wiring electrode, and a dielectric sealing structure that extends over and seals an excitation space above the IDT electrode in which the IDT electrode excites the elastic wave. The second wiring electrode includes a protrusion formed on its outer periphery and extending beyond the first wiring electrode into the excitation space. The first and/or second wiring electrodes are electrically connected to the IDT electrode. The dielectric sealing structure includes a sealing wall provided on the second wiring electrode, the sealing wall being spaced apart from the IDT electrode by the protrusion and having a side surface that defines a side edge of the excitation space.