Two-component model for long-term prediction of threshold voltage shifts in SiC MOSFETs under negative bias stress

Abstract

The negative bias temperature instability in SiC MOSFETs was investigated. Considering the time, temperature, and bias dependences of the threshold-voltage (Vth) shift, we propose a two-component model for long-term prediction. On the basis of fitting results, we discuss the origins of these components. The first component, which dominates short-term instability, was found to show reverse temperature and weak bias dependences. Such trends are consistent with the carrier exchange of pre-existing slow oxide traps, which are O vacancies. After subtracting the first component, the second component was found to show power-law time dependence, similar to that observed in Si devices. The forward temperature and strong bias dependences of the second component indicate the activation of additional traps. The activation energy of 0.1 eV is consistent with that of a Si device using nitrided gate oxide. Therefore, the origin of the long-term Vth shift of SiC-MOSFETs was suggested to be a nitrogen-related site. Control of the amount of nitrogen is expected to be important for the long-term threshold stability of SiC-MOSFETs.