Polarity dependent gate tunneling currents in dual-gate CMOSFET's

Polarity dependence of the gate tunneling current in dual-gate CMOSFET's is studied over a gate oxide range of 2-6 nm, It is shown that, when measured in accumulation, the I-g versus V-g characteristics for the p(+)/pMOSFET are essentially identical to those for the n(+)/nMOSFET; however, when measured in inversion, the p(+)/pMOSFET exhibits much lower gate current for the same \V-g\. This polarity dependence is explained by the difference in the supply of the tunneling electrons. The carrier transport processes in p(+)/pMOSFET biased in inversion are discussed in detail. Three tunneling processes are considered: 1) valence band hole tunneling from the Si substrate; 2) valence band electron tunneling from the p(+)-polysilicon gate; and 3) conduction band electron tunneling from the p(+)-polysilicon gate. The results indicate that all three contribute to the gate tunneling current in an inverted p(+)/pMOSFET, with one of them dominating in a certain voltage range.