A bulk acoustic wave (BAW) device includes a substrate, a reflector on the substrate, a piezoelectric layer on the reflector and including a first opening through which a portion of the reflector is exposed, an electrode layer on the portion of the reflector exposed through the first opening, a passivation layer on the piezoelectric layer and a portion of the electrode layer and including a second opening through which a portion of the electrode layer is exposed, an under-bump metallization layer on the portion of the electrode layer exposed through the second opening and extending over the second opening and the first opening on the passivation layer, and a copper pillar structure on the under-bump metallization layer such that the entirety of the under-bump metallization layer is covered by the copper pillar structure.

An acoustic wave device includes a piezoelectric layer, electrodes, a support substrate, a first cover section and a first support section. As viewed in a stacking direction of the support substrate and the piezoelectric layer, at least a portion of each of first and second functional electrodes overlaps a hollow portion. As viewed in the stacking direction, the first cover section overlaps the first and second functional electrodes and first and second wiring electrodes. As viewed in the stacking direction of the support substrate and the piezoelectric layer, at least a portion of a first relay electrode overlaps at least one of the first and second functional electrodes.

A resonator comprising a piezoelectric film which creates an acoustic path that is slightly longer in a central region of the resonator than at an edge of the resonator.

A bulk acoustic resonator operable in a bulk acoustic mode includes a resonator body mounted to a separate carrier that is not part of the resonator body. The resonator body includes a piezoelectric layer, a device layer, and a top conductive layer on the piezoelectric layer opposite the device layer. A surface of the device layer opposite the piezoelectric layer is for mounting the resonator body to the carrier.

A resonator is provided that suppresses vibration of a retainer caused by undesired vibration of a vibrating portion and also achieves size reduction. Specifically, the resonator includes a vibrating member that includes a semiconductor layer, a first piezoelectric film formed on the semiconductor layer, and a first upper electrode formed on the first piezoelectric film. Moreover, a retainer is provided to retain the vibrating member such that the vibrating portion can vibrate and one or more coupling members are provided to couple the vibrating member to the retainer. Finally, the resonator includes a vibration suppressing member that includes a second piezoelectric film formed on the retainer and a second upper electrode formed on the second piezoelectric film.

A bulk acoustic wave (BAW) device comprises a layer stack including first and second electrodes, a first piezoelectric layer between the electrodes, and a second piezoelectric layer between the first piezoelectric layer and the second electrode. A polarization of a crystal structure of the second piezoelectric layer is opposite to a polarization of a crystal structure of the first piezoelectric layer to achieve higher order resonant frequencies in the BAW device by means other than merely thinning layers in the layer stack. In some examples, the BAW device is a two-terminal device and does not include a metal layer configured to be a third electrode. In some examples, the BAW device includes at least one intermediate layer between the first and second piezoelectric layers, and a total combined thickness of the at least one intermediate layer is less than 4% of a total thickness of the layer stack.

A bulk-acoustic wave (BAW) resonator includes a central portion in which a first electrode, a piezoelectric layer, and a second electrode are sequentially stacked on a substrate, and an extension portion extending externally from the central portion, and an insertion layer and a loss prevention film are disposed in the extension portion between the substrate and the second electrode. The loss prevention film is formed to have a thickness of 50 ? to 500 ?. The insertion layer is stacked on the loss prevention film, and has a side surface opposing the central portion, the side surface is formed as a first inclined surface having a first inclination angle. The loss prevention film has a side surface opposing the central portion, the side surface is formed as a second inclined surface having a second inclination angle. The second inclination angle is formed to be greater than the first inclination angle.

A bulk acoustic wave resonant structure includes a substrate, and a reflection structure, a first electrode layer, a piezoelectric layer and a second electrode layer, which are sequentially stacked on the substrate, wherein ring-shaped grooves are provided in the piezoelectric layer; and the grooves are located in an active area and are close to an edge of the active area.

An acoustic wave device includes a substrate, a lower electrode provided on the substrate, a piezoelectric layer provided on the lower electrode, an upper electrode provided on the piezoelectric layer to form a resonance region facing the lower electrode, and a multilayered acoustic reflection film provided between the substrate and the lower electrode in the resonance region, the acoustic reflection film having low acoustic impedance films and high acoustic impedance films alternately laminated, and the acoustic reflection film satisfying 0<(G3G2)/G1<0.96 where G1 is a product of an average thickness in the resonance region and a density of a first film, G2 is a product of an average thickness and a density of the lower electrode in the resonance region, and the G3 is a product of an average thickness in the resonance region and a density of a second film.

Modern RF front end filters feature acoustic resonators in a film bulk acoustic resonator (FBAR) structure. An acoustic filter is a circuit that includes at least (and typically significantly more) two resonators. The acoustic resonator structure comprises a substrate including sidewalls and a vertical cavity between the sidewalls and two or more resonators deposited in the vertical cavity.