A manufacturing method of a composite substrate capable of suppressing damage due to heat treatment after bonding, and a composite substrate manufactured by the method are provided. The manufacturing method of a composite substrate according to the present invention is a manufacturing method of a composite substrate in which a piezoelectric wafer, which is a lithium tantalate wafer or lithium niobate wafer, and a support wafer are bonded together. This manufacturing method is characterized by a step of bonding a piezoelectric wafer and a support wafer, and a step of performing heat treatment of the wafer bonded in the step of bonding, with the non-bonded surface of the piezoelectric wafer being a mirror surface.

A low velocity surface acoustic wave device, and a method of reducing the velocity of a surface acoustic wave generated by a surface acoustic wave device are described, the device including a piezoelectric layer, an interdigital transducer disposed on the piezoelectric substrate and configured to generate a surface acoustic wave in response to an electrical, and a temperature coefficient of frequency compensation layer disposed partially on the interdigital transducer and partially on the piezoelectric substrate, the temperature coefficient of frequency compensation layer having a low velocity layer disposed within it configured to reduce the velocity of a surface acoustic wave generated by the interdigital transducer, the method including disposing a wave velocity adjustment layer, the wave velocity adjustment layer being a low velocity layer, within a temperature compensation layer of the surface acoustic wave device.

A SAW device includes a mounting substrate including a mounting surface, a SAW chip mounted on the mounting surface, a dummy chip mounted on the mounting surface, and a resin part covering the acoustic wave chip and the dummy chip. The dummy chip includes an insulating dummy substrate, and one or more dummy terminals which are located on a surface of the dummy substrate on the mounting surface side and are bonded to the mounting surface. The dummy chip configures an open end when electrically viewed from the mounting substrate side.

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.

A lithium tantalate single crystal substrate for a surface acoustic wave device that is a rotated Y-cut LiTaO3 substrate whose crystal orientation has a Y-cut angle of not smaller than 36° and not larger than 49° and which has such a Li concentration profile after diffusion of Li into the substrate from the surface thereof that the Li concentration at the surface of the substrate differs from that inside the substrate. A shear vertical type elastic wave whose main components are vibrations in the thickness direction and in the propagation direction and which is among those elastic waves which propagate in the X axis direction within the surface of this LiTaO3 substrate has an acoustic velocity of not lower than 3140 m/s and not higher than 3200 m/s.

A substrate for a surface acoustic wave device or bulk acoustic wave device, comprising a support substrate and an piezoelectric layer on the support substrate, wherein the support substrate comprises a semiconductor layer on a stiffening substrate having a coefficient of thermal expansion that is closer to the coefficient of thermal expansion of the material of the piezoelectric layer than that of silicon, the semiconductor layer being arranged between the piezoelectric layer and the stiffening substrate.

In an elastic wave filter apparatus, IDT electrodes and first and second electrode lands are provided on a first main surface of a piezoelectric substrate. The piezoelectric substrate, a supporting layer, and a covering member define a hollow portion. A signal terminal, a ground terminal, and a heat diffusion layer are provided on a second main surface of the piezoelectric substrate. The first and second electrode lands are electrically connected by first and second connection electrodes to the signal terminal and the ground terminal, respectively. The heat diffusion layer is provided at a position where the heat diffusion layer overlaps at least a portion of the IDT electrodes across the piezoelectric substrate.

An elastic wave device includes an LiNbO.sub.3 substrate, a first elastic wave resonator including a first IDT electrode and a first dielectric film, and a second elastic wave resonator including a second IDT electrode and a second dielectric film. A Rayleigh wave travels along at least one surface of the elastic wave device. A thickness of the first dielectric film differs from a thickness of the second dielectric film. A propagation direction of an elastic wave in the first elastic wave resonator coincides with a propagation direction of an elastic wave in the second elastic wave resonator. Euler angles of the LiNbO.sub.3 substrate fall within a range of (0°±5°, θ, 0°±10°).

A composite substrate includes: a piezoelectric layer; and a reflective layer arranged on a rear surface side of the piezoelectric layer, wherein the reflective layer includes a high-impedance layer and a low-impedance layer containing silicon oxide, and wherein a ratio of a region of first structures in the high-impedance layer is more than 70%.

Embodiments of the invention relate to a surface acoustic wave device including a piezoelectric substrate, an interdigital transducer electrode on the piezoelectric substrate and a first thermally conductive layer arranged over the piezoelectric substrate and interdigital transducer electrode. The first thermally conductive layer is spaced apart from the piezoelectric substrate and interdigital transducer electrode. The surface acoustic wave device also includes a second thermally conductive layer configured to dissipate heat generated by the surface acoustic wave device. The second thermally conductive layer is arranged on an opposing side of the piezoelectric substrate to the interdigital transducer electrode. Related wafer-level packages, radio frequency modules and wireless communication devices are also provided.