A reversed c-axis bulk acoustic resonator (RBAR) device includes a bottom electrode disposed over a substrate and at least a portion of a cavity formed in the substrate; a first piezoelectric layer disposed over the bottom electrode, the first piezoelectric layer having a first polarity; a middle electrode disposed over the first piezoelectric layer; a second piezoelectric layer disposed over the bottom electrode, the second piezoelectric layer having a second polarity that is substantially opposite to the first polarity of the first piezoelectric layer; and a top electrode disposed over the second piezoelectric layer. The RBAR device further includes at least one air-ring formed between the top electrode and the second piezoelectric layer, between the second piezoelectric layer and the middle electrode, between the middle electrode and the first piezoelectric layer, or between the first piezoelectric layer and the bottom electrode.

A duplexer includes a reception filter that is connected between a reception terminal and an antenna terminal and includes one or a plurality of series resonators that are acoustic wave resonators, and a transmission filter that is connected between a transmission terminal and the antenna terminal and includes one or a plurality of acoustic wave resonators, a resonance frequency of a first series resonator that is one of the one or the plurality of series resonators and is closest to the antenna terminal in the reception filter being higher than an upper limit frequency of a reception band of the reception filter.

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 radio frequency (RF) filtering circuit. The RF circuit includes a first acoustic resonator disposed over a substrate; a second acoustic resonator disposed over the first acoustic resonator; and a via structure disposed between the first acoustic resonator and the second acoustic resonator, in contact with the first acoustic resonator and the second acoustic resonator. The first acoustic resonator and the second acoustic resonator are conductively connected to each other through the via structure.

A stacked filter package is disclosed. The stacked filter package can include a first acoustic wave device having a first device type. The first acoustic wave device includes a first substrate having a first coefficient of thermal expansion. The stacked filter package can include a second acoustic wave device having a second device type different from the first device type. The second acoustic wave device includes a second substrate having a second coefficient of thermal expansion. The second coefficient of thermal expansion is at least double the first coefficient of thermal expansion. The stacked filter package can include a bonding structure between the first and second substrates. The bonding structure couples the first and second substrate.

An acoustic transformer in a transmitter chain is disclosed. In one aspect, a differential power amplifier may produce a differential signal that is provided to a first transformer. A differential output of this first transformer is provided to an acoustic transformer that provides a single-ended output signal for use by an acoustic filter. By making the second transformer an acoustic transformer, the second transformer may be integrated into the same circuitry that forms the acoustic filter, thereby simplifying the die. Further, the acoustic transformer may be tuned if ferroelectric resonators are used, which provides strong out-of-band signal cancelation.

The present disclosure relates to filter circuitry, which includes a first node and a second node, a series resonator coupled between the first node and the second node, and a compensation circuit coupled in parallel with the series resonator and located between the first node and the second node. Herein, the compensation circuit includes a tunable acoustic resonator with at least one transduction structure. The at least one transduction structure includes at least one ferroelectric material, and polarization of the at least one ferroelectric material varies with an electric field across the at least one ferroelectric material. Upon adjusting a direct current voltage applied to the tunable acoustic resonator, the compensation circuit is capable of providing a variable negative equivalent capacitance to at least partially cancel out an equivalent capacitance presented by the series resonator between the first node and the second node.

A bulk acoustic wave device includes a first resonator having a first pair of electrodes and a first piezoelectric layer. The first pair of electrodes has a first top electrode and a first bottom electrode. The first piezoelectric layer is positioned between the first top electrode and a first bottom electrode. The device includes a second resonator having a second pair of electrodes and a second piezoelectric layer. The second pair of electrodes has a second top electrode and a second bottom electrode. The second piezoelectric layer is positioned between the second top electrode and a second bottom electrode. The first and second piezoelectric layers are positioned between the first bottom electrode and the second top electrode.

A multilayer structure and a piezoelectric device using the same, which have satisfactory crystal orientation even in the submicron region of the thickness of a piezoelectric layer, are provided. The multilayer structure includes a first wurtzite thin film, a first hexagonal metal layer, a first electrode layer, a second hexagonal metal layer, and a second wurtzite thin film stacked in this order. The first electrode layer is formed of a metallic material having an acoustic impedance higher than that of the second wurtzite thin film.