A surface acoustic wave (SAW) filter includes a bottom substrate, a piezoelectric layer disposed above the bottom substrate, the piezoelectric layer having a bottom surface facing the bottom substrate and a top surface opposite to the bottom surface, a lower cavity disposed below the piezoelectric layer, an interdigital transducer (IDT) disposed on the top surface of the piezoelectric layer, and a back electrode disposed on the bottom surface of the piezoelectric layer, and exposed in the lower cavity.

An acoustic wave device includes: a support substrate; a piezoelectric substrate bonded to the support substrate; a first acoustic wave element formed on the piezoelectric substrate; a frame formed on the support substrate to surround the first acoustic wave element; and a substrate formed on the frame so that a cavity to which the first acoustic wave element is exposed is formed above the piezoelectric substrate, wherein a difference in linear expansion coefficient between the support substrate and the substrate in a first direction in a surface direction of the piezoelectric substrate is less than a difference in linear expansion coefficient between the support substrate and the piezoelectric substrate in the first direction, and the piezoelectric substrate remains in a region where the first acoustic wave element is formed and is removed in a region where the frame is formed.

An elastic wave element having a piezoelectric substrate equipped with a first main surface, and an excitation electrode arranged on the first main surface and having multiple electrode fingers, wherein, in a cross-sectional view in the direction orthogonal to the first main surface, the width of the electrode fingers at a first height at a distance from the first main surface is greater than the width at a second height located closest to the first main surface.

Packaged integrated circuit devices include an oscillator circuit having a resonator (e.g., quartz crystal, MEMs, etc.) associated therewith, which is configured to generate a periodic reference signal. A built-in self-test (BIST) circuit is provided, which is selectively electrically coupled to first and second terminals of the resonator during an operation by the BIST circuit to test at least one performance characteristic of the resonator, such as at least one failure mode. These test operations may occur during a built-in self-test time interval when the oscillator circuit is at least partially disabled. In this manner, built-in self-test circuitry may be utilized to provide an efficient means of testing a resonating element/structure using circuitry that is integrated within an oscillator chip and within a wafer-level chip-scale package (WLCSP) containing the resonator.

A surface acoustic wave (SAW) device includes a first interdigital transducer (IDT) and a second IDT each including interdigital electrodes disposed on a first surface of a substrate of piezoelectric material. The SAW device includes a diamond bridge enclosing an air cavity over a wave propagation region on the first surface of the substrate. The diamond bridge has a reduced height and provides improved thermal conductivity to avoid a reduction in performance and/or life span caused by heat generated in the SAW device. A process of fabricating a SAW device includes forming the first IDT and the second IDT in a metal layer on a first surface of a substrate comprising a piezoelectric material, the first IDT and the second IDT disposed in a wave propagation region of the first surface of the substrate, and forming a diamond bridge disposed above the wave propagation region.

An acoustic wave device includes a support substrate, a piezoelectric film, a functional electrode, and a support. The support substrate includes a cavity. The piezoelectric film is provided on the support substrate to cover the cavity. The functional electrode is provided on the piezoelectric film to overlap the cavity when viewed in a plan view. The support is in the cavity of the support substrate to support the piezoelectric film. The functional electrode includes electrodes arranged in a direction crossing the thickness direction of the piezoelectric film. The electrodes include a first electrode and a second electrode. The first electrode and the second electrode oppose each other in a direction crossing the thickness direction of the piezoelectric film and are connected to different potentials. Adjacent ones of the electrodes overlap each other in a direction orthogonal to a longitudinal direction of the first electrode.

An elastic wave device includes a spacer layer on or above a support substrate and outside a piezoelectric film as seen in a plan view from a thickness direction of the support substrate. A cover layer is disposed on the spacer layer. A through electrode extends through the spacer layer and the cover layer and is electrically connected to the wiring electrode. The wiring electrode includes a first section overlapping the through electrode as seen in the plan view from the thickness direction, a second section overlapping the piezoelectric film as seen in the plan view from the thickness direction, and a step portion defining a step in the thickness direction between the first section and the second section. The spacer layer includes an end portion embedded in the cover layer.

An acoustic wave device includes a support substrate having a thickness in a first direction, a piezoelectric layer on the support substrate, an interdigital transducer electrode on the piezoelectric layer and including first and second electrode fingers, the first electrode fingers extending in a second direction crossing the first direction, the second electrode fingers extending in the second direction and facing the first electrode fingers in a third direction orthogonal or substantially orthogonal to the second direction, and a reinforcing film on the piezoelectric layer. The support substrate and the piezoelectric layer include a hollow therebetween at a position overlapping the interdigital transducer electrode in the first direction. At least one through hole penetrates the piezoelectric layer at a position not overlapping the interdigital transducer electrode in the first direction, and the through hole communicates with the hollow. The reinforcing film overlaps the hollow in the first direction.

A wafer has a layer containing silicon, a layer of polycrystalline diamond deposited on the silicon-containing layer, and a bow-compensation layer on the other side of the silicon-containing layer for reducing wafer-bow. A method of making a bonded structure includes an activation process for creating dangling bonds on the surface of one substrate, followed by contact-bonding the surface to a second substrate at low temperature. A bonded structure may include two substrates contact bonded to each other, one substrate including a layer containing silicon, a layer of polycrystalline diamond, a bow-compensation layer for reducing wafer-bow of the first substrate, and the other substrate including gallium nitride, silicon carbide, lithium niobate, lithium tantalate, gallium arsenide, indium phosphide, or another suitable material other than diamond.

An elastic wave device includes a piezoelectric film laminated on a first main surface of a support substrate including a recessed portion open to a first main surface. A cavity portion including the recessed portion is defined by the support substrate and the piezoelectric film. An electrode is on the piezoelectric film. The electrode includes first and second bus bars, a first electrode finger connected to the first bus bar, and a second electrode finger connected to the second bus bar. The first and second bus bars include corner portions inside the cavity portion when viewed in plan view. A curved portion as a pressure relaxation portion to relax pressure on the piezoelectric film at at least one of the corner portions of the first and second bus bars is provided between the corner portion and an outer edge of the cavity portion.