Device with electrical component formed over a cavity and method therefor

A method, comprising:

• providing a silicon-on-insulator (SOI) substrate including a layer of gallium nitride on a first surface of the SOI substrate;
• forming a device over the first surface of the substrate;
• forming a first conductive feature over the first surface of the substrate and electrically coupling the first conductive feature to the device;
• and
• forming a first cavity in a second surface of the SOI substrate directly below the first conductive feature, wherein the first cavity includes first upper cavity surface defined by a surface of a layer of silicon dioxide in the SOI substrate.

A device, comprising:

• a semiconductor substrate including a first region of silicon, a second region of silicon, a layer of silicon dioxide disposed between the first region and the second region of the substrate, and a layer of gallium nitride on a first surface of the substrate;
• a transistor formed over the first surface of the substrate, the transistor including a control electrode, a first current-conducting electrode, and a second current-conducting electrode over the first substrate surface;
• a first conductive feature formed over the first surface of the substrate, wherein the first conductive feature is electrically coupled to one of the control electrode, the first current-conducting electrode, or the second current-conducting electrode;
• a second conductive feature formed over a second surface of the substrate, wherein the second conductive region covers only a portion of the second substrate surface to define a first conductor-less region;
• and
• a first cavity formed within the first conductor-less region that includes a first upper cavity surface defined by a surface of the layer of silicon dioxide, wherein the first upper cavity surface is directly below the first conductive feature.