Use of Vacuum as a Gate Dielectric: The SiC VacFET

Abstract

We introduce the vacuum field-effect transistor (VacFET), the first SiC FET to use a vacuum-sealed cavity in place of the traditional, solid gate dielectric. This device architecture eliminates the need to thermally oxidize the SiC surface, a practice which has been widely reported to inhibit the performance and reliability of SiC MOSFETs. Using a combination of batch-compatible electronics and micromachining processing techniques, a polycrystalline SiC bridge is suspended above a 4H-SiC substrate, and the underlying cavity is sealed under vacuum. The fundamental studies made possible by such a device could shed much-needed light on the basic electronic properties of an inverted SiC surface. In this introductory report, we detail the analytical design and fabrication necessary to manufacture the VacFET, and we also demonstrate proof of the concept using turn-on and output characteristics of the first functional SiC device.