CS1: A two-dimensional finite element charge-sheet model of a short-channel MOS transistor

A two dimensional charge sheet model for short channel MOS transistors was developed. The unique feature of the model is that the effect of channel inversion layer charge is included as a nonlinear integral boundary condition on the two dimensional electrostatic fluid in the transistor. The average inversion layer charge density and source drain current are obtained directly from the model rather than from the electron density or electron quasi-Fermi level. The model retains all of the physical detail of more complex two dimensional models such as sensitivity to source drain profile shape, channel profile, and oxide field shape. This allows the model to represent the changes in drain current associated with short channel effects while still allowing simple comparison with long channel models. For long channel transistors, the results of this model are identical to Brevs' long channel charge sheet model. The accuracy of this model is verified by modelling a sequence of transistors with channel lengths between 4.6 and 1.1 micron. In short channel transistors, effects previously attributed to high field mobility are explained by simple two dimensional electrostatics. The simulations produced using this model were compared to experimental measurements on an array of n-channel MOSPETs; the model is in good agreement for transistors with channel lengths as short as 1.1 micron. In this verification process, the model represented accurately the onset of subthreshold current, channel length induced threshold voltage offset, and drain field induced output conductance changes.