Diffusion current effects in DMOS transistors

To show the effects of a non-constant impurity profile along the channel of a MOST, a simple numerical model has been developed. The analysis is applied to a DMOST intended for low voltage digital applications. The model accounts for the variation in flat band voltage, substrate potential, and surface mobility along the channel. Results show that diffusion current plays a significant role especially in the ´short channel´ mode of DMOST operation. This in part explains why unrealistic parameter values must often be assigned to existing DMOST models to obtain agreement with experimental results.