Comparison of Sub-Bandgap Impact Ionization in Deep-Sub-Micron Conventional and Lateral Asymmetrical Channel nMOSFETs

Abstract

(Vp) well below the bandgap voltage of silicon has received widespread attention [1,2,3]. Substrate currents (Isue) for drain voltages down to 0.6V [1] and floating body effects in SOI devices down to 0.8V [2] were reported. This would imply that the impact ionization induced operational and reliability issues in nMOSFETs will continue to deca-nano meter device generations. Based on Monte Carlo simulations it was suggested that various modes of elecffon-electron interactions resulting in the high energy tail (HET) of the electron energy distribution are responsible for some elecfrons to have more energy than that gained from the lateral electric field (E61) [3,4]. An anomalous increase of the gate voltage at which the Isus peaks (Vcp"ud which can not be explained by HET is presented. We have also compared the sub-bandgap impact ionization in CONventional (CON) and Lateral Asymmetrical Channel (LAC) nMOSFETs of channel length l00nm. An enhancement of the increase in V60..1 is found in the LAC devices. Based on the results presented we propose quantization of inversion layer as an additional energy gain mechanism for the electrons.