A ceramic substrate is formed of polycrystalline ceramic and has a supporting main surface. At the supporting main surface of the ceramic substrate, the mean of grain sizes of the polycrystalline ceramic is 15 μm or more and less than 40 μm and the standard deviation of the grain sizes is less than 1.5 times the mean.

A bonded body includes a supporting substrate, silicon oxide layer provided on the supporting substrate, and a piezoelectric material substrate provided on the silicon oxide layer and composed of a material selected from the group consisting of lithium niobate, lithium tantalate and lithium niobate-lithium tantalite. A nitrogen concentration at an interface between the piezoelectric material substrate and silicon oxide layer is higher than a nitrogen concentration at an interface between the silicon oxide layer and the supporting substrate.

A method for fabricating a surface acoustic wave (SAW) device includes the steps of forming a first dielectric layer on a substrate, forming a piezoelectric layer on the first dielectric layer, forming a second dielectric layer on the piezoelectric layer, performing a photo-etching process to remove the second dielectric layer for forming a recess in the second dielectric layer, forming a metal layer in the recess, and then performing a planarizing process to remove the metal layer for forming an electrode in the recess.

A fabrication method of a surface acoustic wave (SAW) filter includes obtaining a piezoelectric substrate, forming a first interdigital transducer (IDT) on a first portion of the piezoelectric substrate, forming a first pad metal layer on the first IDT, forming a first dielectric layer on the first portion of the piezoelectric substrate, covering the first IDT and the first pad metal layer, forming a trench in the first dielectric layer, forming a second dielectric layer on the first dielectric layer, forming a third dielectric layer on the second dielectric layer, removing a second portion of the piezoelectric substrate to obtain a piezoelectric layer, forming a second IDT on the piezoelectric layer, and etching and releasing a portion of the first dielectric layer surrounded by the trench to form a cavity.

A fabrication method of a surface acoustic wave (SAW) filter, includes: obtaining a piezoelectric substrate; forming a back electrode on a first portion of the piezoelectric substrate; forming a sacrificial layer on the first portion of the piezoelectric substrate, covering the back electrode; forming a first dielectric layer on the first portion of the piezoelectric substrate, covering the sacrificial layer; bonding a bottom substrate to the first dielectric layer; removing a second portion of the piezoelectric substrate to expose the first portion of the piezoelectric substrate, the first portion of the piezoelectric substrate constituting a piezoelectric layer; forming one or more release holes through the piezoelectric layer; forming an interdigital transducer (IDT) on the piezoelectric layer; and etching and releasing the sacrificial layer via the one or more release holes to form a lower cavity exposing the back electrode.

An acoustic wave device includes a piezoelectric body made of lithium niobate and disposed directly or indirectly on a supporting substrate, and IDT electrode disposed directly or indirectly on the piezoelectric body. When the wavelength of an acoustic wave that is determined by a pitch of electrode fingers of the IDT electrode is denoted by λ, the thickness of the piezoelectric body is equal to or less than about 1λ. The acoustic wave device uses the plate wave S0 mode propagating in the piezoelectric body. The Euler angles of the lithium niobate are (0°±10°, θ, 90°±10°), provided that θ is from about 0° to about 180° inclusive.

An acoustic wave device includes a support substrate, a silicon nitride film stacked on the support substrate, a silicon oxide film stacked on the silicon nitride film, a piezoelectric body stacked on the silicon oxide film and made of lithium tantalite, and an IDT electrode provided on one main surface of the piezoelectric body. For a wavelength normalized film thickness of the piezoelectric body, an Euler angle of the piezoelectric body, a wavelength normalized film thickness of the silicon nitride film, a wavelength normalized film thickness of the silicon oxide film, and a wavelength normalized film thickness of the IDT electrode, values are set so that at least one of a response intensity of a first higher order mode, corresponding to the response intensity of a second higher order mode, and of a response intensity of a third higher mode is greater than about −2.4.

A method of manufacturing a packaged surface acoustic wave filter chip is disclosed. The method can include providing a structure having first interdigital transducer electrodes formed with a first piezoelectric layer, second interdigital transducer electrodes formed with a second piezoelectric layer, and a substrate between the first and second piezoelectric layers. The method can include forming a plurality of through electrodes extending at least partially through a thickness of the structure such that a first set of through electrodes of the plurality of through electrodes are electrically connected to the first interdigital transducer electrodes and a second set of through electrodes of the plurality of through electrodes are electrically isolated from the first interdigital transducer electrodes.

An elastic wave device includes an IDT electrode on a second main surface of an element substrate that includes a piezoelectric layer, a support layer on the second main surface and surrounding the IDT electrode, a cover member on the support layer, and routing wiring lines extending from the second main surface of the element substrate onto side surfaces of the element substrate.

The multiplexer includes a plurality of IDT electrodes on a substrate, an insulating cover located on the substrate so as to configure one or more spaces above the plurality of IDT electrodes, an antenna terminal, transmission terminal, and reception terminal which are all located on the substrate and pass through the cover, and a reinforcing layer which is located on the cover and is made of metal. By the plurality of IDT electrodes, a transmission filter located in a signal path connecting the antenna terminal and the transmission terminal and a receiving filter located in a signal path connecting the antenna terminal and the reception terminal. The reinforcing layer includes a first area part facing the transmission filter and a second area part which faces the receiving filter and is separated from the first area part.