Analytical Modeling of Wrap-Gate Carbon Nanotube FET With Parasitic Capacitances and Density of States

A computationally efficient analytical model to accurately predict the electrical characteristics of wrap-gate carbon nanotube FETs (CNTFETs) is proposed and described in this paper. A wrap-gate structure offers an ideal geometry with minimum body thickness and maximum control over the channel as well as improved device scalability. The parasitic effects present in a real device are incorporated into an ideal wrap-gate device model, and the Poisson-Schrödinger equations are solved self-consistently to obtain the potential and carrier density at the top of the barrier. Exact analytical expressions, such as CNTFET density-of-states are used for approximately evaluating the integral expressions. Finally, the drain current is obtained for near-ballistic transport in the device. The electrical characteristics from our model are validated with recently reported experimental results from the literature, demonstrating good accuracy when the device is on. The subthreshold characteristics are underestimated and offer scope for improvement. Various performance metrics, including threshold voltage and subthreshold swing, and on-current are within 2-11% error. The proposed model can thus be used to study the performance of wrap-gate CNTFETs under various parametric conditions, and extended to circuit simulation models, such as SPICE.