An acoustic wave device includes a piezoelectric layer, an IDT electrode, a high-acoustic-velocity support substrate, and a low-acoustic-velocity film. The high-acoustic-velocity support substrate is located on an opposite side of the piezoelectric layer from the IDT electrode in the thickness direction of the piezoelectric layer. The low-acoustic-velocity film is disposed between the high-acoustic-velocity support substrate and the piezoelectric layer in the thickness direction. The high-acoustic-velocity support substrate includes a base region and a surface region disposed nearer to the low-acoustic-velocity film than the base region in the thickness direction and whose crystal quality is worse than that of the base region. The surface region includes first and second layers disposed nearer to the base region than the first layer in the thickness direction and whose crystal quality is better than that of the first layer.

An acoustic wave device includes a scandium-containing aluminum nitride film (ScAlN film), and an electrode on the ScAlN film. The ScAlN film includes at least one portion where a crystal orientation toward 90 from a crystal c-axis direction is rotated about 305 or rotated about 155, the crystal c-axis direction being a film thickness direction of the ScAlN film or substantially a film thickness direction of the ScAlN film.

A hybrid structure for a surface acoustic wave device comprises a useful layer of piezoelectric material having a free first surface and a second surface disposed on a support substrate that has a lower coefficient of thermal expansion than that of the useful layer. The hybrid structure further comprises a trapping layer disposed between the useful layer and the support substrate, and at least one functional interface of predetermined roughness between the useful layer and the trapping layer.

An elastic wave device includes a support substrate made of silicon, a piezoelectric film disposed directly or indirectly on the support substrate, and an interdigital transducer electrode disposed on one surface of the piezoelectric film. A higher-order mode acoustic velocity of propagation through the piezoelectric film is equal or substantially equal to an acoustic velocity V.sub.si=(V.sub.1).sup.1/2 of propagation through silicon or higher than the acoustic velocity V.sub.si, where V.sub.si is specified by V.sub.1 among solutions V.sub.1, V.sub.2, and V.sub.3 with respect to x derived from Ax.sup.3+Bx.sup.2+Cx+D=0.

An elastic wave device includes a SiN.sub.x layer stacked directly or indirectly on a supporting substrate made of a semiconductor material, a piezoelectric film stacked on directly or indirectly the SiN.sub.x layer, and an interdigital transducer electrode stacked directly or indirectly on at least one main surface of the piezoelectric film. In the SiN.sub.x layer, x is about 1.34 or more and about 1.66 or less.

A method for fabricating a semiconductor die involves providing a semiconductor substrate, forming a plurality of active devices and a plurality of passive devices over the semiconductor substrate, forming one or more electrical connections to the plurality of active devices and the plurality of passive devices, forming one or more dielectric layers over at least a portion of the electrical connections, applying an interface material over at least a portion of the one or more dielectric layers, removing portions of the interface material to form a plurality of trenches, and covering at least a portion of the interface material and the plurality of trenches with a substrate layer to form a plurality of radio-frequency isolation cavities.

A method for fabricating a radio-frequency device involves providing a semiconductor wafer including a transistor device, applying a form of sacrificial material on the semiconductor wafer, applying an interface material over the form of sacrificial material, and removing at least a portion of the form of sacrificial material to form a cavity at least partially covered by the interface material.

A method of constructing a layer transferred radio frequency (RF) filter-on-insulator wafer includes exposing a front-side of a bulk RF wafer to a laser light source to form a modified layer at a predetermined depth along a horizontal length of the bulk RF wafer. The method also includes bonding the front-side of the bulk RF wafer to a front-side of a semiconductor handle wafer through an insulator layer. The method further includes forming an RF filter layer from the bulk RF wafer. The method also includes selectively etching away the modified layer from the RF filter layer to the predetermined depth to complete the layer transferred RF filter-on-insulator wafer.

A supporting substrate for a composite substrate comprises a ceramic and has a polished surface for use in bonding. An orientation degree of the ceramic forming the supporting substrate at the polished surface is 50% or higher, and an aspect ratio of each crystal grain included in the supporting substrate is 5.0 or less.

An encapsulated integrated circuit is provided that includes an integrated circuit (IC) die. An encapsulation material encapsulates the IC die. A phononic bandgap structure is included within the encapsulation material that is configured to have a phononic bandgap with a frequency range approximately equal to a range of frequencies of thermal phonons produced by the IC die when the IC die is operating.