Velocity-saturated characteristics of short-channel MOSFETs

A theory is developed for the I-V characteristics of metal oxide semiconductor field-effect transistors (MOSFETs) when the channel fields are sufficiently high to cause appreciable saturation of the carrier drift velocity. The full velocity-field curve for bulk silicon is used with the base value adjusted to account for surface scattering effects. Use of this form gave the best fit to experimental data. Using some simple expansions to reduce the rather complex integral produces a useful analytic result, which gives a continuous description from the square law results for long-channel devices throughout the whole range of velocity-saturated operation in short-channel devices. For the first time the electron temperature has been introduced as the parameter, which increases the channel charge at pinch-off, decreases the saturation voltage, and increases the channel field at the pinch-off point as the current (and hence bias voltages) is increased. The effects of series resistance and surface roughness scattering are incorporated into the analytic formulation. We compare the results with experimental submicron devices and find excellent agreement.