The drain velocity overshoot in an 80 nm metal-oxide-semiconductor field-effect transistor

摘要

The current at the onset of saturation in a metal-oxide-semiconductor field-effect transistor (MOSFET) is shown to be limited by the drain velocity that increases toward its saturation value with the increase in the drain voltage. The saturation of velocity crops up as randomly oriented velocity vectors in equilibrium realign themselves to become unidirectional in the presence of an extremely high electric field. The intrinsic velocity, the ultimate saturation velocity, is the function of carrier concentration and temperature, consistent with the predictions of the ballistic transport. The presence of a quantum emission either by emission of a phonon or photon lowers the saturation velocity below its intrinsic value. Channel conduction beyond the quasisaturation point enhances due to the drain velocity overshoot as a result of enhanced drain electric field as drain voltage is increased. The excellent agreement with experimental data on an 80 nm channel, without using any artificial parameters, confirms the value of ballistic transport in a high electric field.