Apparatus and associated methods relate to forming an epitaxial layer of aluminum on an aluminum-nitride compound. The aluminum is epitaxially grown on the crystalline aluminum-nitride compound by maintaining temperature of a crystalline aluminum-nitride compound below a cluster-favoring temperature threshold within a vacuum chamber. Then, the crystalline aluminum-nitride compound is exposed to atoms of elemental aluminum for a predetermined time duration. The aluminum is epitaxially grown in this fashion for a predetermined time duration so as to produce a layer of epitaxial aluminum of a predetermined thickness. Such epitaxially-grown mono-crystalline aluminum has a lower resistivity than poly-crystalline aluminum.

A bulk acoustic resonator device and filter device including the same is provided. The resonator includes a substrate; a piezoelectric layer attached to the substrate; and an interdigital transducer having interleaved fingers on the piezoelectric layer. The interleaved fingers include a first layer proximate the piezoelectric layer, a second layer over the first layer, and a third layer over the second layer such that the second layer is between the first and third layers. Adjacent layers of the first, second and third layers are comprised of different metals. Moreover, a primary shear acoustic mode is excited in the piezoelectric layer and is a bulk shear mode where acoustic energy propagates in a direction predominantly orthogonal to the surface of the piezoelectric layer and predominantly orthogonal to a direction of an electric field created by the interleaved fingers of the IDT that is predominantly lateral in the piezoelectric layer.

Radio frequency filters are disclosed. A bandpass filter is discloses that includes one first bulk acoustic resonator on a first chip including a first piezoelectric layer having an LN-equivalent thickness less than or equal to 535 nm; a second bulk acoustic resonator on a second chip including a second piezoelectric layer having a thickness greater than the LN-equivalent thickness of the piezoelectric layer on the first chip; and a circuit card coupled to the first chip and the second chip and that electrically connects the first chip to the second chip.

A filter device is provided that includes a substrate comprising a base and an intermediate layer; a piezoelectric layer coupled to the substrate; a first interdigital transducer (IDT) of a first bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a first cavity the first bulk acoustic resonator device; a second IDT of a second bulk acoustic resonator device on the piezoelectric layer and having interleaved fingers over a second cavity of the second bulk acoustic resonator device; a first dielectric layer having a first thickness disposed on the piezoelectric layer and between the interleaved fingers of the first IDT; and a second dielectric layer having a second thickness disposed on the piezoelectric layer and between the interleaved fingers of the second IDT. Moreover, the first thickness is greater than the second thickness.

Radio frequency filters. A radio frequency filter includes a substrate attached to a piezoelectric plate, portions of the piezoelectric plate forming a plurality of diaphragms spanning respective cavities in the substrate. A conductor pattern formed on the piezoelectric plate includes a plurality of interdigital transducers (IDTs) of a respective plurality of resonators, interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms. The conductor pattern connects the plurality of resonators in a matrix filter circuit including a first sub-filter and a second sub-filter, each sub-filter comprising two or more resonators from the plurality of resonators.

A bulk acoustic wave resonator, a method for manufacturing the same and an electronic device are provided, and belong to the field of communication technology. The bulk acoustic wave resonator includes: a base substrate, a first electrode, a piezoelectric layer, and a second electrode. The bulk acoustic wave resonator further includes: a first bias resistance layer on a side of the first electrode close to the base substrate, and a first electric isolation layer between the first bias resistance layer and the first electrode; the first bias resistance layer is made of a material with a high resistivity; and/or a second bias resistance layer on a side of the second electrode away from the base substrate, and a second electric isolation layer between the second bias resistance layer and the second electrode; and the second bias resistance layer is made of a material with a high resistivity.

Described is a technology that facilitates fabrication of an acoustic wave resonator. For instance, an acoustic wave resonator can comprise a silicon layer comprising a base surface, a multi-layer film disposed at the silicon layer opposite the base surface and comprising a metal electrode and a piezoelectric material, and a cavity within the silicon layer, wherein the cavity is sealed, at a location opposite the base surface, by a silicon membrane. The silicon layer and the silicon membrane can be provided as a unitary silicon element. In another instance, a batch of the acoustic wave resonators can be fabricated using a common silicon-on-insulator wafer platform.

A bulk acoustic wave (BAW) resonator includes a piezoelectric layer oriented so that an N-polar surface forms a frontside surface that faces away from the substrate while a metal-polar surface forms the backside surface and faces toward the substrate. A process for the manufacture of a bulk acoustic wave (BAW) resonator includes orienting a piezoelectric layer on a substrate so that an N-polar surface forms a frontside surface that faces away from the substrate while a metal-polar surface forms the backside surface and faces toward the substrate; etching a via though the backside of the substrate to the metal-polar surface of the piezoelectric layer; and removing etch residue from a sidewall of the resonator cavity.

Acoustic resonator devices is provided that includes a piezoelectric layer having a first surface and a second surface; and a first electrode and a second electrode on the first surface of the piezoelectric layer. At least one of the first electrode and second electrode has a side that extends at an angle relative to the first surface of the piezoelectric layer. Moreover, the angle is greater than or equal to 70 degrees and less than 90 degrees. Furthermore, a thickness of the piezoelectric layer is less than a distance between a center of the first electrode and a center of the second electrode.

A filter device is provided that includes a substrate and a piezoelectric plate attached to the substrate. A conductor pattern is formed at a first surface of the piezoelectric plate and includes interdigital transducers of series and shunt resonators that each have interleaved fingers at respective diaphragms of the plate suspended. A first dielectric coating layer is formed over the interleaved fingers of the IDTs and on the first surface of the piezoelectric plate; and a second dielectric coating layer is formed on the second surface of the piezoelectric plate that is opposite the first surface. The second dielectric coating layer of the shunt resonator has a greater thickness than a thickness of the at least one second dielectric coating layer of the series resonator.