A bulk acoustic wave (BAW) device comprises a piezoelectric layer disposed between a first electrode layer and a sandwich electrode. The sandwich electrode includes a first layer of a first material having a first acoustic impedance and a second layer of a second material having a second acoustic impedance that is less than the first acoustic impedance of the first layer. The second layer of the sandwich electrode having the lower acoustic impedance is disposed between the first layer and the piezoelectric layer. The sandwich electrode combined with the piezoelectric layer and first electrode can cause the BAW device to resonate at a frequency whose wavelength corresponds to an acoustic cavity length of the BAW device, depending on an acoustic mirror included on one side of the BAW device. In one example, the acoustic cavity length is about 1.5 times of the resonant frequency wavelength.

An acoustic resonator device with low thermal impedance has a substrate and a single-crystal piezoelectric plate having a back surface attached to a top surface of the substrate via a bonding oxide (BOX) layer. An interdigital transducer (IDT) formed on the front surface of the plate has interleaved fingers disposed on the diaphragm. The piezoelectric plate and the BOX layer are removed from a least a portion of the surface area of the device to provide lower thermal resistance between the conductor pattern and the substrate.

Techniques for improving Bulk Acoustic Wave (BAW) mass loading of resonator structures are disclosed, including filters, oscillators and systems that may include such devices. First and second layers of piezoelectric material may be acoustically coupled with one another to have a piezoelectrically excitable resonance mode. The first layer of piezoelectric material may have a first piezoelectric axis orientation, and the second layer of piezoelectric material may have a second piezoelectric axis orientation that substantially opposes the first piezoelectric axis orientation of the first layer of piezoelectric material. An acoustic reflector electrode may include a first pair of top metal electrode layers electrically and acoustically coupled with the first and second layer of piezoelectric material to excite the piezoelectrically excitable resonance mode at a resonant frequency of the BAW resonator. The acoustic reflector may include a mass load layer to facilitate a preselected frequency compensation in the resonant frequency.

A frequency-tunable film bulk acoustic resonator and a preparation method therefor are provided. The resonator includes a substrate, an air gap, a sandwiched structure formed by electrodes and piezoelectric layers, and an electrode lead-out layer, wherein the substrate is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers, and a connection face of the substrate and the sandwiched structure formed by the electrodes and the piezoelectric layers is recessed towards inside of the substrate to form the air gap; and the electrode lead-out layer is connected to the sandwiched structure formed by the electrodes and the piezoelectric layers. The sandwiched structure formed by the electrodes and the piezoelectric layers includes a bottom electrode, piezoelectric layers, intermediate electrodes, and a top electrode, wherein the electrodes and the piezoelectric layers are alternately arranged to form the sandwiched structure.

A method of forming a piezoelectric thin film can include depositing a material on a first surface of a Si substrate to provide a stress neutral template layer. A piezoelectric thin film including a Group III element and nitrogen can be sputtered onto the stress neutral template layer and a second surface of the Si substrate that is opposite the first surface can be processed to remove that Si substrate and the stress neutral template layer to provide a remaining portion of the piezoelectric thin film. A piezoelectric resonator can be formed on the remaining portion of the piezoelectric thin film.

A piezoelectric bulk wave device includes a support including a support substrate, a piezoelectric layer on the support and including first and second principal surfaces, an IDT electrode on the first principal surface and including a pair of comb-shaped electrodes each including electrode fingers and a busbar connecting the electrode fingers, and a frequency adjustment film on the second principal surface and overlapping at least a portion of the IDT electrode. The support includes a hollow portion overlapping at least a portion of the IDT electrode. d/p is less than or equal to about 0.5. Via holes are provided to the piezoelectric layer and the frequency adjustment film. Wiring electrodes are provided in the via holes and on the frequency adjustment film and electrically connected to the busbars of the comb-shaped electrodes.

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.

An acoustic wave element includes: a substrate; a bonding structure on the substrate; a support layer on the bonding structure; a first electrode including a lower surface on the support layer; a cavity positioned between the support layer and the first electrode and exposing a lower surface of the first electrode; a piezoelectric layer on the first electrode; and a second electrode on the piezoelectric layer, wherein at least one of the first electrode and the second electrode includes a first layer and a second layer that the first layer has a first acoustic impedance and a first electrical impedance, the second layer has a second acoustic impedance and a second electrical impedance, wherein the first acoustic impedance is higher than the second acoustic impedance, and the second electrical impedance is lower than the first electrical impedance.

A bulk-acoustic wave (BAW) resonator includes a central portion in which a first electrode, a piezoelectric layer, and a second electrode are sequentially stacked on a substrate, and an extension portion extending externally from the central portion, and an insertion layer and a loss prevention film are disposed in the extension portion between the substrate and the second electrode. The loss prevention film is formed to have a thickness of 50 ? to 500 ?. The insertion layer is stacked on the loss prevention film, and has a side surface opposing the central portion, the side surface is formed as a first inclined surface having a first inclination angle. The loss prevention film has a side surface opposing the central portion, the side surface is formed as a second inclined surface having a second inclination angle. The second inclination angle is formed to be greater than the first inclination angle.

The present disclosure provides a film bulk acoustic resonator and its fabrication method. The film bulk acoustic resonator includes a first substrate, a support layer bonded on the first substrate, a first cavity formed in the support layer, a piezoelectric stacked layer on the support layer, a first trench and a second trench which are formed in the piezoelectric stacked layer, a dielectric layer over the piezoelectric stacked layer, a second cavity formed in the dielectric layer, and a second substrate covering the second cavity, where the first trench is connected to the first cavity, and the second trench is connected to the second cavity.