Techniques for improving Bulk Acoustic Wave (BAW) resonator structures are disclosed, including filters, oscillators and systems that may include such devices. A first layer of piezoelectric material having a piezoelectrically excitable resonance mode may be provided. The first layer of piezoelectric material may have a thickness so that the bulk acoustic wave resonator has a resonant frequency. The first layer of piezoelectric material may include a first pair of sublayers of piezoelectric material, and a first layer of temperature compensating material. A substrate may be provided.

A BAW resonator comprises: a substrate comprising an acoustic reflector; a first electrode disposed over the acoustic reflector, and comprising a first electrode layer comprising a comparatively high acoustic impedance material, and a second electrode layer comprising a comparatively low acoustic impedance; a piezoelectric layer disposed over the second electrode layer; and a second electrode disposed over the piezoelectric layer, and comprising a third electrode layer comprising the low acoustic impedance, and a fourth electrode layer comprising the comparatively high acoustic impedance material and being disposed directly on the piezoelectric layer. A total thickness of an acoustic stack of the BAW resonator is approximately /2, where is a wavelength corresponding to a thickness extensional resonance frequency of the BAW resonator.

Techniques for improving Bulk Acoustic Wave (BAW) 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 patterned layer.

An acoustic wave device includes a support, a piezoelectric layer, and an IDT electrode. The IDT electrode includes first and second electrode fingers and first and second busbar electrodes. The first electrode finger extends in a second direction intersecting with a first direction. The second electrode finger extends in the second direction and faces a corresponding one of the first electrode finger in a third direction perpendicular to the second direction. A space in the support at least partially matches the IDT electrode from above in the first direction. The first or second electrode finger includes an underlying metal layer contacting the piezoelectric layer and a first metal layer on the underlying metal layer. The piezoelectric layer includes a diffusion layer where the piezoelectric layer contacts the underlying metal layer. The underlying metal layer and the diffusion layer include at least one of Ni, Cr, and Ti.

A method for manufacturing an acoustic device includes providing a substrate, providing a bottom electrode over the substrate, providing a sacrificial layer on the bottom electrode, patterning the bottom electrode and the sacrificial layer, polishing the sacrificial layer such that a portion of the sacrificial layer remains on the bottom electrode, and removing the remaining portion of the sacrificial layer via a cleaning process such that a surface roughness of the bottom electrode is maintained. By performing the polishing such that a portion of the sacrificial layer remains on the bottom electrode and subsequently removing that portion of the sacrificial layer via a cleaning process that maintains the surface roughness of the bottom electrode, the subsequent growth of a piezoelectric layer on the bottom electrode can be substantially improved.

A longitudinally coupled resonator acoustic wave filter includes a piezoelectric substrate, IDT electrodes on the piezoelectric substrate along an acoustic wave propagation direction, and a pair of reflectors on the piezoelectric substrate on both sides of the IDT electrodes in the acoustic wave propagation direction. Each of the reflectors includes first and second reflector busbars, and first reflective electrode fingers connected to at least one of the first reflector busbar and the second reflector busbar. The reflector includes a first portion in which lengths of the first reflective electrode fingers change in the acoustic wave propagation direction.

A method of forming a film bulk acoustic wave resonator comprises depositing a bottom electrode on an upper surface of a layer of dielectric material disposed over a cavity defined between the layer of dielectric material and a substrate, depositing a seed layer of piezoelectric material on an upper surface of the bottom electrode, etching one or more openings through the seed layer of piezoelectric material, etching of the one or more openings including over-etching of the seed layer in an amount sufficient to damage portions of the upper surface of the bottom electrode exposed by etching of the one or more openings, and depositing a bulk film of the piezoelectric material on an upper surface of the seed layer, on a portion of the upper surface of bottom electrode including the damaged portions, and on a portion of the upper surface of the dielectric layer.

A bulk acoustic wave resonator with better performance and better manufacturability is described. The bulk acoustic wave resonator includes a composite piezoelectric film. The composite piezoelectric film includes a first sublayer of a first piezoelectric material, a second sublayer of a second piezoelectric material, and a third sublayer of a third piezoelectric material that is disposed between the first sublayer and the second sublayer. The first piezoelectric material has a first lattice constant, the second piezoelectric material has a second lattice constant, and the third piezoelectric material has a third lattice constant that is distinct from the first lattice constant and from the second lattice constant. The composite piezoelectric film may include a sequence of alternating sublayers of two or more distinct piezoelectric materials, or a sequence of composition graded layers having gradually changing composition.

An acoustic wave element which can be reduced in size and produced relatively easily, practically used without using harmful substances, and can suppress a surface acoustic wave propagation loss, which has an excellent temperature coefficient of frequency and a velocity dispersion characteristic, and with which an increase in the reflection coefficient of interdigital transducers can be suppressed, and a method for manufacturing the acoustic wave element are provided. The acoustic wave element includes a pair of electrodes provided on both surfaces of a piezoelectric substrate, and a dielectric film provided on a first surface of the piezoelectric substrate so as to cover the electrode. The acoustic wave element alternatively includes interdigital transducers provided on a first surface of the piezoelectric substrate, and a dielectric film provided on the interdigital transducers, a gap between the interdigital transducers, and/or a second surface of the piezoelectric substrate.

Embodiments of the disclosure are directed to a Bulk Acoustic Wave (BAW) filter structure with internal electrostatic shielding. In exemplary aspects disclosed herein, a shielded BAW filter structure includes a substrate, a plurality of transducers over the substrate, and a planar electrostatic shield between the substrate and a top electrode of the plurality of transducers. Each of the plurality of transducers forms a portion of a BAW resonator and resides in a filter including a parasitic capacitance. The planar electrostatic shield is coupled to a ground node and interrupts an electrical field associated with the parasitic capacitance of the filter to reduce the parasitic capacitance. Accordingly, the shielded BAW filter structure reduces the influence of parasitic capacitance providing improved filtering performance compared to an unshielded BAW filter structure.