Analytical I-V relationship incorporating field-dependent mobility for a symmetrical DG MOSFET with an undoped body

A simple expression explicitly relating the surface potential to the surface electric field of a symmetrical double-gate (DG) MOS capacitor is proposed. The expression does not contain the floating-body potential as an implicit variable. It is used to derive, assuming the validity of the gradual-channel approximation, an analytical model expression for the current-voltage relationship of a DG MOS field-effect transistor. The effects of mobility degradation at high vertical electric field and velocity saturation at high lateral electric field are incorporated. The model expression is continuously valid from the subthreshold to the quasi-linear regimes of operation and up to a well-defined drain saturation voltage. Beyond this saturation voltage, the gradual-channel approximation breaks down within a region near the drain end of the channel. The electric-field distribution within this region is estimated by solving a two-dimensional Poisson's equation. Further implications of the model are derived by simplifying the expression in different regimes of operation using various approximations.