A filter includes: one or more series resonators that are connected in series between an input terminal and an output terminal; one or more parallel resonators that are connected in parallel between the input terminal and the output terminal; and a laterally coupled resonator that is connected in parallel with at least one of the one or more series resonators.

A multiplexer device includes at least one acoustic band pass filter connected to a common port, and a hybrid LC/acoustic filter connected to the common port in parallel with the at least one acoustic band pass filter. Each acoustic band pass filter has a corresponding passband and includes multiple acoustic resonators. The hybrid LC/acoustic filter includes at least one acoustic resonator, and has at least one capacitor replaced by a corresponding at least one acoustic resonator, respectively. Each of the at least one acoustic resonator included in the hybrid LC/acoustic filter provides a stopband response when operating in a corresponding acoustic frequency range, and acts as a capacitor when operating in a corresponding non-acoustic frequency range.

The invention combines two filter technologies on a single device using the same substrate there for. On this substrate a filter circuit is arranged that has a ladder-type or a lattice arrangement of series and parallel impedance elements to provide a hybrid filter having for example a band pass function. The impedance elements are chosen from BAW resonators and LC elements.

A film bulk acoustic wave resonator (FBAR) includes a piezoelectric film disposed in a central region defining a main active domain in which a main acoustic wave is generated during operation and in recessed frame regions disposed laterally on opposite sides of the central region, and an electrode disposed on an upper surface of the piezoelectric film, the electrode having a lesser thickness in the recessed frame regions than the thickness of the electrode in the central region to increase a quality factor of the FBAR.

Acoustic filters devices and methods of making the same. A filter device includes two or more series resonators acoustically coupled along a shared acoustic track, and two or more shunt resonators electrically coupled to the two or more series resonators.

A duplexer includes: a transmit filter connected between a transmit terminal and an antenna terminal and including series resonators and parallel resonators connected in a ladder form; and a receive filter connected between a receive terminal and the antenna terminal, wherein at least one of resonators, which are resonators other than a first series resonator and a first parallel resonator located at a first stage as viewed from a side of the transmit terminal and a second series resonator and a second parallel resonator located at a first stage as viewed from a side of the antenna terminal and have electrostatic capacitances less than an electrostatic capacitance of at least one of the first series resonator, the first parallel resonator, the second series resonator, and the second parallel resonator in the series resonators and the parallel resonators, is divided in series.

An acoustic wave resonator includes: a piezoelectric substrate; an IDT located on the piezoelectric substrate and including comb-shaped electrodes facing each other, each of the comb-shaped electrodes including: electrode fingers exciting an acoustic wave; and a bus bar to which the electrode fingers are connected; a dielectric film located on the piezoelectric substrate in an overlap region, where the electrode fingers of one of the comb-shaped electrodes and the electrode fingers of the other overlap, so as to cover the electrode fingers; and an additional film located on the dielectric film in the overlap region and having a density greater than that of the dielectric film, and of which a film thickness in edge regions corresponding to both edges of the overlap region in an extension direction of the electrode fingers is greater than a film thickness in a central region sandwiched between the edge regions in the overlap region.

A filter includes: an input terminal; an output terminal; and a ladder circuit that includes one or more series acoustic wave resonators connected in series between the input terminal and the output terminal and one or more parallel acoustic wave resonators connected in parallel between the input terminal and the output terminal, and in which characteristic impedance of at least one point in a pathway between the input terminal and the output terminal in a passband is greater than at least one of input impedance of the input terminal and output impedance of the output terminal in the passband.

A bulk acoustic resonator includes: a substrate including an upper surface on which a substrate protection layer is disposed; and a membrane layer forming a cavity together with the substrate, wherein a thickness deviation of either one or both of the substrate protection layer and the membrane layer is 170 Å or less.

A variable filter circuit includes: a series arm connected in series between a signal input terminal and a signal output terminal; a parallel arm connected between the series arm and a ground terminal that has a resonator; and a variable reactance portion in the parallel arm, and the resonator of a parallel arm at an initial stage connected to the signal input terminal that has a resonant frequency fr and an anti-resonant frequency fa that satisfy 100×(fn−fr)/(fa−fr)≦23.9(%) for communication bands for each of which a stop band is set so as to be close to a high-frequency side of a pass band, among the plurality of communication bands, where a resonant frequency is fr, an anti-resonant frequency is fa, and a cutoff frequency at a high-frequency side of a pass band of each communication band is fn.