A film bulk acoustic wave resonator includes a piezoelectric film disposed over a cavity. The cavity is shaped as partial ellipse including first, second, and third vertices. The film bulk acoustic wave resonator further includes three release ports in positions that minimize etch time to remove all sacrificial material from within the cavity.

A method for forming cavity of bulk acoustic wave resonator comprising following steps of: forming a sacrificial epitaxial structure mesa on a compound semiconductor substrate; forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; polishing the insulating layer by a chemical-mechanical planarization process to form a polished surface; forming a bulk acoustic wave resonance structure on the polished surface, which comprises following steps of: forming a bottom electrode layer on the polished surface; forming a piezoelectric layer on the bottom electrode layer; and forming a top electrode layer on the piezoelectric layer, wherein the bulk acoustic wave resonance structure is located above the sacrificial epitaxial structure mesa; and etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located under the bulk acoustic wave resonance structure.

A filter includes a multilayer structure having films configured as bulk acoustic wave resonators; a wiring line connected to the bulk acoustic wave resonators; a cap coupled to the multilayer structure on a bonding line; and the filtering characteristics of the filter being configured through a mutual inductance between the wiring line and the bonding line.

An acoustic wave device includes: a substrate; a first piezoelectric thin film resonator including a first resonance region in which a first lower electrode and a first upper electrode sandwich a first piezoelectric film; a second piezoelectric thin film resonator including a second resonance region in which a second lower electrode and a second upper electrode sandwich a second piezoelectric film; and a wiring layer that is located from an upper surface of the first lower electrode in a first extraction region, in which the first lower electrode is extracted from the first resonance region, to an upper surface of the second upper electrode located in a second extraction region, in which the second upper electrode is extracted from the second resonance region, and has a film thickness on the first lower electrode greater than a film thickness of the second piezoelectric film.

A filter may include a plurality of bulk acoustic wave resonators including one or more series resonators and one or more shunt resonators formed by a first electrode, a piezoelectric layer, and a second electrode sequentially stacked on a substrate, a cap accommodating the plurality of bulk acoustic wave resonators therein, and one or more switches provided on the cap.

A filter may include one or more series unit, and a shunt unit disposed between the one or more series unit and ground. The one or more series unit includes a plurality of series resonators which are selectively operated, and each of the plurality of series resonators includes a film bulk acoustic resonator.

A bulk acoustic wave (BAW) resonator includes: a substrate; a first BAW resonator including a first air cavity disposed in the substrate, and further including a first electrode, a first piezoelectric layer, and a second electrode stacked on the first air cavity; a second BAW resonator including a second air cavity disposed in the substrate, and further including a first electrode, a second piezoelectric layer, and a second electrode stacked on the second air cavity, wherein the second BAW resonator is connected in parallel to the first BAW resonator and has polarities that are opposite of polarities of the first BAW resonator; and a compensation capacitor circuit connected between the first BAW resonator and the second BAW resonator.

The present invention provides tunable film bulk acoustic resonators (FBARs) with the resonant frequency of the acoustic wave to be excited and to be transmitted tuned by digital to analog converters which convert an input digital signal to an output DC voltage and provide DC bias voltages to the FBARs through integrated thin film biasing resistors. The polarity and the value of the output DC voltage are controlled by the input digital signal to achieve selection and tuning of the resonant frequency of the FBARs. A plurality of the tunable FBARs are connected to form microwave filters with tunable bandpass frequencies and oscillators with selectable resonating frequencies by varying the input digital signals applied to the digital to analog converters.

Bulk acoustic wave resonators of two or more different filters can be on a common die. The two filters can be included in a multiplexer, such as a duplexer, or implemented as standalone filters. With bulk acoustic wave resonators of two or more filters on the same die, the filters can be implemented in less physical space compared to implementing the same filters of different die. Related methods, radio frequency systems, radio frequency modules, and wireless communication devices are also disclosed.

A thin film bulk acoustic resonator and a method for manufacturing the same. The thin film bulk acoustic resonator comprises a bottom electrode layer, a piezoelectric layer, and a top electrode layer, which are disposed on a substrate in which an acoustic reflection structure is located, where a portion which is of the piezoelectric layer and corresponds to a boundary of the acoustic reflection structure is depolarized to form a depolarized portion. The method comprises providing a bottom electrode layer on a substrate to cover an acoustic reflection structure which is formed or to be formed on the substrate; providing a piezoelectric layer on the bottom electrode layer; depolarizing a portion, which is of the piezoelectric layer and corresponds to a boundary of the acoustic reflection structure, to form a depolarized portion; and providing a top electrode layer on the piezoelectric layer.