In one embodiment, a piezo-resistive resonator device includes one or more drive transistors with source and drain regions in a first well and a sense transistor with source and drain regions in a second well of opposite polarity than the first well. The gates of the drive and sense transistor are connected to a first direct current (DC) source. The drain region of the sense transistor is connected to a second DC source, and the source and drain regions of the drive transistor are connected to an alternating current (AC) source.

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.

Aspects of this disclosure relate to an acoustic wave device with a plurality of piezoelectric layers positioned laterally relative to each other between two electrodes. One of the piezoelectric layers has a different property than another of the piezoelectric layers. Examples of the different property include c-axis orientation, doping concentration, dopant material, and piezoelectric material. At least part of each of the piezoelectric layers can be in a main acoustically active region of the acoustic wave device.

Aspects and embodiments disclosed herein include a bulk acoustic wave (BAW) device comprising a first electrode, a second electrode, a stack of at least two first piezoelectric material layers of the same polarity type sandwiched between the first electrode and the second electrode, and a first interposer sandwiched between the at least two first piezoelectric material layers and including at least one intermediate electrode, the BAW device being configured to excite an even overtone mode as the main mode of operation.

A resonator including a vibration structure, a first electrode, and a second electrode is provided. The vibration structure includes a vibration region, a protrusion portion, an opening, and a frame portion. The vibration region has a first surface and a second surface opposite to the first surface. The protrusion portion surrounds the vibration region. The opening is disposed at a side of the vibration region and between the vibration region and the protrusion portion. The opening has a first side adjacent to the vibration region and a second side far away from the vibration region. The second side is opposite to the first side. A length of the first side is greater than a length of the second side. The frame portion surrounds the protrusion portion. The first electrode is disposed on the first surface. The second electrode is disposed on the second surface.

The present disclosure relates to a resonator structure including stacked resonators, which share a same reflector. The disclosed resonator structure includes a first resonator and a second resonator, which is vertically stacked with the first resonator and shares a common reflector with the first resonator. Herein, the first resonator is at least composed of a first top electrode, a first piezoelectric layer underneath the first top electrode, and the common reflector underneath the first piezoelectric layer. The second resonator is at least composed of the common reflector, a second piezoelectric layer underneath the common reflector, and a second bottom electrode underneath the second piezoelectric layer. The first resonator and the second resonator are acoustically isolated from each other.