Analytical current equation for short channel SOI multigate FETs including 3D effects

Current flow in short-channel multigate FETs is strongly influenced by 2D or even 3D effects. In subthreshold operation the channel current is located in the device center, whereas above threshold the channel moves to the silicon-to-oxide interface. This movement of the most leaky path can result in an abnormal behavior in the transconductance. In this paper an analytical current equation for lightly doped devices is proposed which takes into account these effects. The leakage current is calculated from a three-dimensional solution of the electrostatic potential at the barrier within the channel. For the current above threshold, which is located at the channel surface, a bulk MOS model is superposed. The final current equation takes into account short-channel effects as threshold voltage shift, drain-induced barrier lowering, subthreshold slope degradation and the movement of the most leaky path within the channel cross section. The model has been benchmarked by numerical results and is in good agreement down to a channel length of 30 nm.