Particularities of the Short-Circuit Operation and Failure Modes of SiC-MOSFETs
Christian Unger, Martin Pfost
Abstract
During short-circuit operation, silicon carbide MOSFETs exhibit several peculiarities compared to conventional silicon MOSFETs. These comprise the influence of the <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</b> -state gate–source voltage on the short-circuit (SC) current, the emergence of high gate leakage currents, and finally special failure types, such as the gate breakdown and the delayed thermal runaway. We investigate all those particularities but pay special attention to the impact and composition of the drain leakage current and the breakdown of the gate insulation. We use special measurement techniques to determine the threshold voltage and transfer characteristics at temperatures close to those during an SC event. Under these conditions, the threshold voltage can become negative. Thus, in addition to thermally generated carriers and the parasitic BJT, the channel can also contribute to the drain leakage current. To investigate the gate failure, we apply repetitive stress in different operating points. The results comply with Weibull and Coffin–Manson models, which indicates that the underlying defect mechanism is of thermomechanical nature.