A piezoelectric device includes a support substrate, an intermediate layer on the support substrate in a first region, a piezoelectric layer on the intermediate layer, a functional element on the piezoelectric layer, and an insulating layer. The insulating layer is located on the support substrate in a second region adjacent to the first region. A surface roughness of the support substrate in the second region is greater than a surface roughness of the support substrate in the first region.

An acoustic wave device includes a support substrate, a piezoelectric body layer, an interdigital transducer electrode, and an external connection electrode. The piezoelectric body layer is on the support substrate. The interdigital transducer electrode is on the piezoelectric body layer. The external connection electrode is electrically connected to the interdigital transducer electrode. The external connection electrode does not overlap the piezoelectric body layer in a plan view from a thickness direction of the support substrate. The support substrate includes a hollow portion. The hollow portion is at least on an end portion of the support substrate in a plan view from the thickness direction.

An acoustic wave device includes a piezoelectric substrate, functional elements, an outer peripheral support layer, a cover portion, and a protective layer covering the cover portion. A hollow space is defined by the piezoelectric substrate, the outer peripheral support layer, and the cover portion, and the functional elements are disposed in the hollow space. The acoustic wave device further includes an under bump metal layer, a wiring pattern, and a through-electrode that connects these elements. In the protective layer, a through-hole to be filled with a conductor to electrically connect a solder ball and the under bump metal layer is provided. The outer peripheral support layer includes a protruding portion protruding to the hollow space. When the acoustic wave device is seen in plan view, at least a portion of the through-hole overlaps the hollow space, and an end portion of the protruding portion overlaps an inner region of the through-hole.

A multi-level stacked AW filter package including a first acoustic wave (AW) filter stacked on a second AW filter employs semiconductor fabrication methods and structures, including a metallization layer comprising interconnects to couple a contact surface to the second AW filter. Each AW filter includes an AW filter circuit on a semiconductor substrate. A second substrate disposed on a frame on the substrate protects the AW filter circuit. In a multi-level AW filter package, the second substrate of the first AW filter comprises a glass substrate with a similar expansion rate as the semiconductor substrate. The interconnects coupling the second AW filter to the contact surface are disposed on insulators on the side wall surfaces of the semiconductor substrates of the first AW filter for isolation. In a stacked AW filter package comprising a single AW filter, the interconnects couple the contact surface to the AW filter.

A through-hole that extends from an upper surface of a cover opposite a support to a lower surface of the support facing a substrate is provided in the support and the cover. The through-hole overlaps a portion of a wiring line in a plan view. An acoustic wave device further includes an electrode film that is electrically connected to the wiring line in the through-hole, and a protective layer that includes an insulating material and that covers a portion of the electrode film. The protective layer is connected to the cover and the support in the through-hole. Differences in thermal expansion coefficients between the protective layer and the cover and between the protective layer and the support are smaller than a difference in thermal expansion coefficients between the protective layer and the electrode film.

A surface acoustic wave (SAW) filter includes a filter wafer including: a first substrate; and an interdigital transducer (IDT) disposed on the first substrate, the IDT including a first input and output end, a second input and output end, and an interdigital portion. The SAW filter also includes a dielectric layer disposed on the filter wafer, covering the first input and output end and the second input and output end of the IDT and exposing the interdigital portion; a passivation layer disposed on the dielectric layer; a bonding layer disposed on the passivation layer; a second substrate bonded to the filter wafer via the bonding layer; and a cavity enclosed by the second substrate and the bonding layer.

A fabrication method of a surface acoustic wave (SAW) filter includes obtaining a filter wafer, which includes: obtaining a first substrate; and forming an interdigital transducer (IDT) on the first substrate, the IDT including a first input and output end, a second input and output end, and an interdigital portion. The method further includes: forming a dielectric layer on the filter wafer, the dielectric layer covering the first input and output end and the second input and output end of the IDT, and exposing the interdigital portion; forming a passivation layer on the dielectric layer; forming a bonding layer on the passivation layer; and bonding a second substrate to the filter wafer via the bonding layer, wherein a cavity is enclosed by the second substrate and the bonding layer.

A surface acoustic wave device includes a piezoelectric substrate, an interdigital transducer electrode that is disposed on a main surface of the piezoelectric substrate, a plurality of partition-support layers each of which is arranged in a region of the main surface surrounded by an outer periphery of the main surface, and a cover layer that is disposed above the plurality of partition-support layers and that covers the interdigital transducer electrode. The plurality of partition-support layers include a first partition-support layer and a second partition-support layer that are adjacent to each other, and a portion of the first partition-support layer and a portion of the second partition-support layer do not overlap each other when viewed from a second direction perpendicular or substantially perpendicular to a first direction in which the plurality of partition-support layers extend.

An acoustic wave device includes a substrate, a functional element provided on the substrate, a cover layer provided on or above the substrate to cover the functional element, and a protection layer that covers the cover layer. The cover layer includes a curved portion that is curved to protrude outward. A hollow space is defined between the curved portion and the substrate, and the functional element is provided in the hollow space. The acoustic wave device also includes a conductive portion that is provided between the curved portion and the protection layer and extends along a surface of the curved portion.

An acoustic wave device includes a piezoelectric substrate made of LiNbO.sub.3 or LiTaO.sub.3 and including first and second main surfaces that face each other, a functional electrode provided on the first main surface of the piezoelectric substrate to excite acoustic waves, and a Li.sub.2CO.sub.3 layer provided on the second main surface of the piezoelectric substrate.