Performance of 2 nm gate length carbon nanotube field-effect transistors with source/drain underlaps

The performance of coaxially gated, zero-Schottky-barrier, carbon nanotube field-effect transistors is investigated for gate lengths down to 2 nm with source and drain underlaps. Such devices can have nearly ideal subthreshold slopes of similar to 63 mV/dec and maximum on/off current ratios of 2.2x10(6) assuming 0.0-0.4 volt swing. The leakage mechanism is a combination of both intra-band and inter-band tunneling. For a 30 nm long carbon nanotube (CNT) with a 2 nm gate, C-g=3.13 aF, the intrinsic switching time, tau(s)=CgVDD/I-ON, is 370 fs, and the intrinsic cut-off frequency defined by f(T)=g(m)/(2 pi C-g) is 1.6 THz. The ambipolar leakage current is suppressed by Coulomb blockade. Calculations are performed using a pi-bond model and a self-consistent solution of the nonequilibrium Green function equations and Poisson's equation. (C) 2005 American Institute of Physics.