An RF integrated circuit device can includes a substrate and a High Electron Mobility Transistor (HEMT) device on the substrate including a ScAlN layer configured to provide a buffer layer of the HEMT device to confine formation of a 2DEG channel region of the HEMT device. An RF piezoelectric resonator device can be on the substrate including the ScAlN layer sandwiched between a top electrode and a bottom electrode of the RF piezoelectric resonator device to provide a piezoelectric resonator for the RF piezoelectric resonator device.

A bulk-acoustic wave resonator includes a substrate; a lower electrode formed on the substrate, and at least a portion of the lower electrode is formed on a cavity; a piezoelectric layer formed on the lower electrode; an upper electrode formed on the piezoelectric layer; a membrane layer formed below the lower electrode and forming the cavity together with the substrate; and a protruding portion formed on the membrane layer and further formed in the cavity in a direction that extends away from the membrane layer.

A piezoelectric vibrating piece includes a piezoelectric substrate and excitation electrodes. The excitation electrode includes a main thickness portion and an inclined portion, the main thickness portion has a constant thickness, the inclined portion is formed on a peripheral area of the main thickness portion, the inclined portion gradually decrease in thickness from a part contacting the main thickness portion toward an outermost periphery of the excitation electrode. The inclined portion has a width as an inclination width in a length of 0.84 times or more and 1.37 times or less of a first flexural wavelength and 2.29 times or more and 3.71 times or less of a second flexural wavelength, the first flexural wavelength is a wavelength of a flexure vibration at a fundamental wave of the thickness-shear vibration, the second flexural wavelength is a wavelength of a flexure vibration at a third harmonic of the thickness-shear vibration.

The oscillating element includes a crystal blank, a pair of excitation electrodes, and a pair of pad portions. The crystal blank includes a pair of major surfaces, at least partially configured by crystal planes, and side surfaces which connect outer edges of the pair of major surfaces. Further, it includes a mesa portion and an outer peripheral portion which surrounds the mesa portion and has a thickness between the pair of major surfaces thinner than that of the mesa portion. The excitation electrodes are individually located on the pair of major surfaces. The pair of pad portions are located on one of the pairs of major surfaces and are electrically connected with the excitation electrodes. At least a portion of an edge part which is in contact with a crystal plane includes a projecting portion, which does not exceed the height of the mesa portion from the outer peripheral portion.

The vibration substrate having a main surface extending parallel to a first direction and a second direction that are orthogonal to each other, and that includes a main body region having a vibrating portion at least in a part thereof and at least one holding region arranged side by side with the main body region along the first direction. The at least one holding region including a holding portion and a beam portion connecting the holding portion and the main body region. The beam portion includes a first arm portion extending from the holding portion along the first direction, a second arm portion extending along the second direction from an end portion of the first arm portion on a side thereof opposite to the holding portion, and a connection portion connecting the second arm portion and the main body region.

A crystal unit includes an AT-cut crystal element that has a planar shape in a rectangular shape and a part as a thick portion. The crystal element includes a first end portion, a first depressed portion, the thick portion, a second depressed portion, and a second end portion in an order from a side of one short side in viewing a cross section taken along a longitudinal direction near a center of the short side. The first depressed portion is a depressed portion disposed from the thick portion toward the first end portion side, depressed with a predetermined angle a and subsequently bulged, and connected to the first end portion. The second depressed portion is a depressed portion disposed from the thick portion toward the second end portion side, depressed with a predetermined angle b and subsequently bulged, and connected to the second end portion.

A piezoelectric vibrating piece includes a piezoelectric substrate, a first excitation electrode, and a second excitation electrode. The piezoelectric substrate is formed into a flat plate shape and vibrates in a thickness-shear vibration mode. The first excitation electrode is formed on one principal surface of the piezoelectric substrate. The second excitation electrode is formed on another principal surface of the piezoelectric substrate. The first excitation electrode is formed to entirely have an identical thickness. The second excitation electrode has a main thickness portion and an inclined portion. The main thickness portion has a constant thickness. The inclined portion is formed in a peripheral area of the main thickness portion and gradually decreases in thickness from a portion in contact with the main thickness portion to an outermost periphery of the second excitation electrode. The main thickness portion has a thickness larger than the thickness of the first excitation electrode.

A crystal blank includes a pair of tableland-shaped first mesa parts projecting from a flat plate and a pair of tableland-shaped second mesa parts projecting from the pair of first mesa parts. The flat plate's length in a long direction is less than 1000 m. The first mesa part is on an inner side of the flat plate's major surface. The second mesa part is on the first mesa part's inner side of an upper surface's outer edge at two ends of the long direction and has a width equivalent to the first mesa part's upper surface at two sides of a short direction. An excitation electrode reaches the second mesa part's outer edge of the upper surface, is located on the inner side of the first mesa part, and on the second mesa part's inner side of the upper surface's outer edge at two sides of the short direction.

A piezoelectric device includes a piezoelectric vibrating piece, a container, and a lid. The piezoelectric vibrating piece is bevel processed and has a bevel surface at one end of the piezoelectric vibrating piece. Thea container holds the piezoelectric vibrating piece with the bevel surface at the one end of the piezoelectric vibrating piece. The container has a connection pad at a holding region of the container and a pillow portion at a region corresponding to the other end of the piezoelectric vibrating piece. The lid member seals the container. The connection pad is buried in the container at the holding region in a state of a flat surface with a surface of the container and in a state where the surface of the connection pad is exposed. The piezoelectric vibrating piece is spanned between the surface of the connection pad and a top surface of the pillow portion.

A method and structure for a transfer process for an acoustic resonator device. In an example, a bulk acoustic wave resonator (BAWR) with an air reflection cavity is formed. A piezoelectric thin film is grown on a crystalline substrate. One or more patterned electrodes are deposited on the surface of the piezoelectric film. An etched sacrificial layer is deposited over the one or more electrodes and a planarized support layer is deposited over the sacrificial layer. The support layer is etched to form one or more cavities overlying the electrodes to expose the sacrificial layer. The sacrificial layer is etched to release the cavities around the electrodes. Then, a cap layer is fusion bonded to the support layer to enclose the electrodes in the support layer cavities.