Fabrication of radio-frequency (RF) devices involves providing a field-effect transistor (FET), forming one or more electrical connections to the FET, forming one or more dielectric layers over at least a portion of the electrical connections, and disposing an electrical element over the one or more dielectric layers, the electrical element being in electrical communication with the FET via the one or more electrical connections. RF device fabrication further involves covering at least a portion of the electrical element with a sacrificial material, applying an interface material over the one or more dielectric layers, the interface material at least partially covering the sacrificial material, and removing at least a portion of the sacrificial material to form a cavity at least partially covered by the interface layer.