A novel field-effect transistor architecture is introduced that uses a micromachined, sealed vacuum cavity as the gate dielectric and 4H-SiC as the semiconductor material. The device is called a vacuum field-effect transistor, or VacFET. First and foremost, the SiC VacFET has been developed as a technology platform for the fundamental characterization of SiC inversion layer properties in a way that is not confounded by interface states, traps, fixed charge, mobile ions, or other defects whose origin and influence have been the subject of much debate in the SiC MOSFET community for decades. The SiC VacFET has tremendous potential in other application spaces as well, such as integrated pressure sensing-electronics, ultra-radiation-resistant device technology, and more.
This work takes us from conception to characterization. Following a thorough design stage consisting of first-principles analysis, simulation of mechanical and electronic performance, and development and optimization of a process flow, the SiC VacFET has been fabricated and successfully demonstrated on the very first run. The device exhibits the two marks of a field-effect transistor: non-negligible drain current and conductivity modulation, both due to voltage applied at the gate. Turn-on behavior, threshold voltage and its deviation from ideal, output characteristics, effective inversion layer mobility, and threshold voltage instability have been measured in the dark and under ultraviolet illumination. These performance parameters of the SiC VacFET have also been compared to SiC MOSFETs fabricated on the same wafer, and important observations have already been made regarding fixed positive charge and interface traps in the SiO2-SiC system.