Threshold voltage in short-channel MOS devices

The threshold voltage in short-channel MOS transistors was investigated by use of a two-dimensional numerical solution of Poisson's equation and experimental measurements on devices of 5.15-, 3.15-, and 2.15-µm channel length. The assumption of constant equipotential surface in the oxide implicit in the charge-sharing technique is not valid in devices of shorter Channel lengths and at larger operating voltages. The numerical determination of the threshold voltage from the two-dimensional analysis agrees with experimental results. Unlike previous work, the charge-sharing model was investigated from an electric-field point of view. The inadequacies of the charge-sharing model are elucidated qualitatively and quantitatively.