Polarity-dependent tunneling current and oxide breakdown in dual-gate CMOSFETs

The gate tunneling leakage current in dual-gate CMOSFETs exhibits strong polarity dependence when measured in inversion, although it exhibits practically no polarity dependence when measured in accumulation. Specifically, p/sup +/-gate pMOSFET shows substantially lower tunneling current than n/sup +/-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/sub bd/ value for p/sup +//pMOSFET as compared to that for n/sup +//nMOSFET when both are biased to inversion. Rationaless are given as to why T/sub bd/ is a better gauge than Q/sub bd/ for reliability assessment, and why nMOSFET is more prone to oxide breakdown than pMOSFET under normal operating conditions.