UC San Diego

In this dissertation, non-GCA models are developed for both DG (Double-Gate) MOSFETs and ground-plane bulk MOSGETs. It is widely known that MOSFET velocity saturation region is beyond the framework of GCA first invoked by Shockley in 1952, the bedrock of virtually all MOSFET models. A few papers in the literature have dealt with the 2-D nature of the field pattern in the saturation region of bulk or DG. In general, such models are unable to generate Ids-Vds curves continuous from the triode region into the velocity saturation region.

A DG MOSFET model that goes beyond the gradual channel approximation is developed by incorporating the effect of lateral field gradient on carrier density. It is shown that while the oxide field crosses zero at the point of saturation and becomes negative beyond it, the channel is not pinched off of charge carriers. The model generates Ids-Vds characteristics continuous into the saturation region with finite output conductance consistent with TCAD. An explicit expression is derived for the output conductance in saturation in terms of basic device parameters.

The continuous model is later extending MOSFET I-V characteristics into the velocity saturation region with finite output conductance. Both the n = 1 and n = 2 models have been employed. It is shown that the standard relation of channel length modulation (CLM) for constant mobility must be modified for velocity saturation because the drain current is not simply inversely proportional to the channel length. Regional approximations are applied to derive explicit expressions for the output conductance in the velocity saturation region in terms of basic device parameters.

In the following section, a non-GCA (Gradual Channel Approximation) model continuous into the velocity saturation region is developed for ground-plane bulk MOSFETs. The Ids-Vds characteristics generated by both the n = 1 and the n = 2 models are consistent with 2-D simulations. By incorporating source and drain series resistance into the model, it is shown that the model can reproduce the Ids-Vds data of 20 nm bulk MOSFETs published in the literature.