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

Abstract

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 ∼63mV∕dec and maximum on∕off current ratios of 2.2×106 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, Cg=3.13aF, the intrinsic switching time, τs=CgVDD∕ION, is 370 fs, and the intrinsic cut-off frequency defined by fT=gm∕(2πCg) is 1.6 THz. The ambipolar leakage current is suppressed by Coulomb blockade. Calculations are performed using a π-bond model and a self-consistent solution of the nonequilibrium Green function equations and Poisson’s equation.