A resonant circuit includes: a capacitor of which a capacitance is variable; and an acoustic wave resonator to which the capacitor is connected in series and/or in parallel, a capacitance of the acoustic wave resonator being to be changed so that a change in input impedance and/or output impedance is reduced when the capacitance of the capacitor is changed.

An acoustic wave filter includes series resonators and parallel resonators that have a piezoelectric film on an identical substrate and have a lower electrode and an upper electrode, wherein: one of the series resonators and the parallel resonators have a temperature compensation film on a face of the lower electrode or the upper electrode that is opposite to the piezoelectric film in a resonance region, the compensation film having an elastic constant of a temperature coefficient of which sign is opposite to a sign of a temperature coefficient of an elastic constant of the piezoelectric film; and the other have an added film on the same side as the temperature compensation film on the lower electrode side or the upper electrode side compared to the piezoelectric film in the resonance region in the one of the series resonators and the parallel resonators.

The present invention relates to a filter chip (1), comprising an interconnection of at least one first and one second resonator (2, 3) operating with bulk acoustic waves, wherein the first resonator (2) operating with bulk acoustic waves comprises a first piezoelectric layer (4) that is structured in such a way that the first resonator (2) has a lower resonant frequency than the second resonator (3).

A piezoelectric thin film resonator includes: a piezoelectric film located on a substrate, and formed of stacked lower and upper piezoelectric films; lower and upper electrodes facing each other across at least a part of the piezoelectric film; and an insertion film inserted between the lower and upper piezoelectric films, wherein an air gap including a resonance region where the lower and upper electrodes face each other across the piezoelectric film and being larger than the resonance region is located under the lower electrode, and a multilayered film formed of the lower piezoelectric film, the insertion film, and the upper piezoelectric film is located in at least a part of a region located further out than an outer outline of the resonance region, further in than an outer outline of the air gap, and surrounding the resonance region, and is not located in a center region of the resonance region.

A piezoelectric thin film resonator includes: a substrate; a lower electrode and an upper electrode located on the substrate; a piezoelectric film, at least a part of the piezoelectric film being sandwiched between the upper electrode and the lower electrode, the piezoelectric film including a discontinuous portion in which the piezoelectric film discontinues in at least a part of a region surrounding a center region that includes a center of a resonance region where the upper electrode and the lower electrode face each other across the at least a part of the piezoelectric film.

A method of fabricating a rare-earth element doped piezoelectric material having a first component, a second component and the rare-earth element. The method includes: providing a substrate; initially flowing hydrogen over the substrate; after the initially flowing of the hydrogen over the substrate, flowing the first component to form the rare-earth element doped piezoelectric material over a surface of a target, the target comprising the rare-earth metal in a certain atomic percentage; and sputtering the rare-earth element doped piezoelectric material from the target on the substrate.

An acoustic wave filter with different bulk acoustic wave devices is disclosed. The filter includes a first bulk acoustic wave resonator and a second bulk acoustic wave resonator. The first bulk acoustic wave resonator includes a first raised frame structure. The first raised frame structure is a multi-layer raised frame structure. The second bulk acoustic wave resonator includes a second raised frame structure. The first raised frame structure has at least one more raised frame layer than the second raised frame structure.

Aspects of this disclosure relate to an acoustic wave filter configured to filter a radio frequency signal and a loop circuit coupled to the acoustic wave filter. The loop circuit is configured to generate an anti-phase signal to a target signal at a particular frequency. The loop circuit includes a Lamb wave element. Related radio frequency modules and wireless communication devices are disclosed.

An acoustic resonator device includes a bottom electrode disposed on a substrate over an air cavity, a first piezoelectric material layer disposed on the bottom electrode, an electrically-isolated layer of high-acoustic-impedance material disposed on the first piezoelectric material layer, a second piezoelectric material layer disposed on the electrically-isolated layer of high-acoustic impedance material, and a top electrode disposed on the second piezoelectric material layer, where an overlap among the top electrode, the first piezoelectric material layer, the electrically-isolated layer of high-acoustic-impedance material, the second piezoelectric material layer, and the bottom electrode over the air cavity defines a main membrane region.

A ladder type acoustic wave filter is disclosed. The acoustic wave filter can include a plurality of parallel arm resonators and a plurality of series arm resonators, in which an electromechanical coupling coefficient of a parallel arm resonator closest to an input node of the acoustic wave filter among the plurality of parallel arm resonators can be smaller than an electromechanical coupling coefficient of a series arm resonator closest to the input node among the plurality of series arm resonators.