Polarity-dependent tunneling current and oxide breakdown in dual-gate CMOSFET's

The gate tunneling leakage current in dual-gate CMOSFET's exhibits strong polarity dependence when measured in inversion, although it exhibits practically no polarity dependence when measured in accumulation. Specifically, p(+)-gate pMOSFET shows substantially lower tunneling current than n(+)-gate nMOSFET when measured in inversion. This polarity dependence arises from the difference in the supply of tunneling electrons. The polarity dependent tunneling current has a significant impact on oxide reliability measurements. For example, it gives rise to a higher T-bd value for p(+)/pMOSFET as compared to that for n(+)/nMOSFET when both are biased to inversion, Rationales are given as to why T-bd is a better gauge than Q(bd) for reliability assessment, and why nMOSFET is more prone to oxide breakdown than pMOSFET under normal operating conditions.