Near Ideal Operation of Nanometer Gate Length Carbon Nanotube FETs

Performance of coaxially gated carbon nanotube FETs is investigated in their scaling limit with gate lengths down to 2 nm. Both single-walled carbon nanotube (SWCNT) and double-walled carbon nanotube (DWCNT) are used as the conducting channels. With SWCNT as the conducting channel, the device has nearly ideal subthreshold slope $\sim $ 63 mV/dec, high on/off ratio $\sim $ 10$^{6}$, and low intrinsic switching time $\sim $ 18 fs. While with DWCNT as the channel, the tube with larger diameter contributes more than 99{\%} to the total current, the subthreshold slope is more than 120 mV/dec, and the on/off current ratio is very low ($\sim $ 100) although the drive current is a few times larger. The leakage current is a combination of inter-band and intra-band tunneling. This current can be significantly reduced by changing the tube length as well as the tube diameter. The simulation model is based on the $\pi $-bond of CNT and self-consistent solution of non-equilibrium Green function (NEGF) equations and Poisson's equation. The NEGF equations are solved using recursive Green function algorithm.