Polarity-dependent tunneling current and oxide breakdown indual-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⁺-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. Rationaless 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