Techniques for monolithic co-integration of polycrystalline thin-film bulk acoustic resonator devices and monocrystalline III-N semiconductor transistor devices

A method of fabricating an integrated circuit, the method comprising:

• forming a transistor device over a first portion of a substrate, the substrate comprising semiconductor material, and the transistor device comprising a monocrystalline III-N semiconductor layer;
• forming a resonator device over a second portion of the substrate, the resonator device comprising a polycrystalline piezoelectric III-N semiconductor layer;
• forming a cavity within the substrate, wherein the cavity extends under the resonator device;
• and
• performing at least one of
• prior to forming the cavity, forming a first layer comprising dielectric material over the substrate, laterally adjacent to the cavity;
• and/or
• after forming the cavity, forming a second layer comprising dielectric material over the polycrystalline piezoelectric III-N semiconductor layer and extending into the cavity.

An integrated circuit comprising:

• a substrate;
• a transistor device over a first portion of the substrate and comprising a monocrystalline layer including gallium and nitrogen;
• an acoustic resonator device over a second portion of the substrate, the acoustic resonator device comprising a polycrystalline layer including gallium and nitrogen;
• a third layer on the monocrystalline layer and comprising aluminum and nitrogen, wherein a two-dimensional electron gas (2DEG) is inducible in the monocrystalline layer;
• a gate dielectric layer over the third layer;
• and
• a gate electrode over the gate dielectric layer.