As disclosed herein, methods of forming piezoelectric layers having alternating polarizations and related bulk acoustic wave filter devices. Pursuant to these embodiments, a method of forming a piezoelectric resonator device can include forming a first material, including metal and nitrogen atoms, using a first process to provide a first piezoelectric layer having the metal and the nitrogen atoms arranged in a first polar orientation, to establish a first polarization for the first piezoelectric layer and forming a second material, including the metal and the nitrogen atoms on the first piezoelectric layer, using a second process to provide a second piezoelectric layer having the metal and the nitrogen atoms arranged in a second polar orientation, to establish a second polarization for the second piezoelectric layer that is opposite of the first polarization.

Method of forming a termination angle in a titanium tungsten layer include providing a titanium tungsten layer and applying a photo resist material to the titanium tungsten layer. The photo resist material is exposed under a defocus condition to generate a resist mask, wherein an edge of the exposed photo resist material corresponds to the sloped termination. The titanium tungsten layer is etched with an etching material, wherein the etching material at least partially etches the photo resist material exposed under the defocused condition, and wherein the etching results in the sloped termination in the titanium tungsten layer.

A bulk acoustic wave resonator and a preparation method thereof, the bulk acoustic wave resonator includes a first electrode and a second electrode, and a piezoelectric film between the first and second electrodes, the piezoelectric film includes n layers of polarized piezoelectric films, and the polarities of any two adjacent layers of the polarized piezoelectric films are opposite. The acoustic mirror is disposed between the substrate and the first electrode, by preparing the polarized piezoelectric films with opposite polarities in layers, polarity inversion is achieved. The bulk acoustic wave resonator of the present disclosure can reduce the requirements for the piezoelectric film materials and increase the resonant frequency under the condition of not reducing the total thickness of the piezoelectric film or introducing a transition electrode. The process is simplified, the acoustic wave loss is reduced, and the quality factor is improved.

An acoustic resonator is provided that includes a first piezoelectric layer of a material with a first crystallographic orientation and a second piezoelectric layer coupled to the first piezoelectric layer and comprising a material with a second crystallographic orientation, such that a piezoelectric tensor of the second piezoelectric layer is an opposite polarity to a piezoelectric tensor of the fist piezoelectric layer. Moreover, an interdigital transducer (IDT) including interleaved fingers is disposed on a surface of the first piezoelectric layer; and a first dielectric coating layer is disposed over the IDT and the first piezoelectric layer.

A method for fabricating a multi-layer resonator assembly includes sequentially fabricating a plurality of vertically-stacked resonator layers including, for each resonator layer of the plurality of resonator layers, depositing a dielectric layer, forming at least one film bulk acoustic resonator (FBAR) cavity in the deposited dielectric layer, filling each FBAR cavity of the at least one FBAR cavity with a sacrificial material block, and depositing a FBAR material stack over the at least one FBAR cavity. The deposited FBAR material stack is in contact with the sacrificial material block and the dielectric layer. The method further includes removing the sacrificial material block from the at least one FBAR cavity for each resonator layer of the plurality of resonator layers subsequent to sequentially fabricating the plurality of resonator layers.

A volume acoustic device. The volume acoustic device includes a first electrode and a second electrode and a piezoelectric element disposed between the first electrode and the second electrode. The piezoelectric element is configured such that a first electromagnetic signal fed into the first electrode is converted to an acoustic signal in the piezoelectric element, and the acoustic signal is converted back into a second electromagnetic signal in the second electrode. A dielectric layer surrounds the first electrode, the second electrode, and the piezoelectric element, and has a substantially planar surface. At least one separation trench at least partially surrounds the piezoelectric element is formed in the dielectric layer.

As disclosed herein, methods of forming a piezoelectric resonator device can include forming a first stack of piezoelectric layers having alternating opposing ferroelectric polarizations comprising the following operations: (a) depositing a first material, including metal and nitrogen atoms, on a surface to form a first piezoelectric layer having a first ferroelectric polarization, (b) forming a first layer including Al on the first piezoelectric layer, (c) depositing a second material including the metal and the nitrogen atoms on the first layer to form a second piezoelectric layer having the first ferroelectric polarization, (d) forming first poling electrodes electrically laterally spaced apart from one another on a surface of the second piezoelectric layer and (e) applying a voltage across the first poling electrodes to change the first ferroelectric polarization of the second piezoelectric layer to a second ferroelectric polarization that is opposite to the first ferroelectric polarization.

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 radio frequency filter comprising a plurality of series bulk acoustic wave resonators and a plurality of shunt bulk acoustic wave resonators, at least one of the plurality of shunt bulk acoustic wave resonators exhibiting a different electromechanical coupling coefficient than at least one of the plurality of series bulk acoustic wave resonators, at least one of the bulk acoustic wave resonators exhibiting a higher electromechanical coupling coefficient than another one of the bulk acoustic wave resonators having a thicker piezoelectric material layer stack than the another one of the bulk acoustic wave resonators.

A method for fabricating a multi-layer resonator assembly includes sequentially fabricating a plurality of vertically-stacked resonator layers including, for each resonator layer of the plurality of resonator layers, depositing a dielectric layer, forming at least one film bulk acoustic resonator (FBAR) cavity in the deposited dielectric layer, filling each FBAR cavity of the at least one FBAR cavity with a sacrificial material block, and depositing a FBAR material stack over the at least one FBAR cavity. The deposited FBAR material stack is in contact with the sacrificial material block and the dielectric layer. The method further includes removing the sacrificial material block from the at least one FBAR cavity for each resonator layer of the plurality of resonator layers subsequent to sequentially fabricating the plurality of resonator layers.