True Figure of Merit (FOM) of a Power Semiconductor Switch

Abstract

Wide Band Gap (WBG) semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are known to be superior materials for the fabrication of power electronics switching devices compared to the industry work-horse silicon. This advantage primarily stems from wider energy bandgap, higher electric field strength for avalanche breakdown, and improved thermal conductivity of SiC and GaN semiconductors compared to silicon. This paper reviews the various “Figures of Merit (FOM)” proposed in the literature for the WBG power semiconductors. Unipolar power transistors with MOS channel conduction as well as transistors that employ two-dimensional electron gas (2DEG) channels are considered. A true FOM for a power semiconductor switching device needs to take into account all electrical power losses and thermal limitations. A new Safe Operating Area (SOA) limit that relates material defect density (Dit) to the switching current density (Jon) for a specified maximum junction temperature limit (Tjmax) is proposed as the true FOM for a power semiconductor switching device.