Negative bias instability in 4H-SiC MOSFETS: Evidence for structural changes in the SiC

The negative bias temperature instability (NBTI) has been investigated for quite some time in Si based MOSFETs. In these MOSFETs, the response has been interpreted in several ways, primarily in terms of the reaction diffusion model and newer model based on the occupation of a near interface oxide hole trap triggering the generation of silicon dielectric interface traps. SiC based MOSFETs have enormous promise for high power and high temperature applications. Consequently, device performance at elevated temperatures of these devices is a topic of great current interest. We have begun a magnetic resonance based study of NBTI in 4H-SiC devices and find, among other things, that elevated temperature and negative gate bias generates structural changes (associated with electrically active defects) within the SiC. These observations strongly suggest that SiC NBTI is significantly different and likely more complex than the NBTI processes taking place in silicon based devices. However, other observations suggest that one aspect of NBTI, the occupation of near-interfacial oxide hole traps called E´ centers, takes place in both systems.