Exploiting negative quantum capacitance of carbon nanotube FETs for low power applications

As conventional silicon-based CMOS technology is approaching its fundamental physical limits due to aggressive scaling, carbon nanotubes (CNTs) have been explored as promising candidates for both on-chip switching device and interconnect in post-Si nanoelectronics due to their superior current carrying and heat transfer capabilities. This paper investigates the prospect of bulk-modulated CNT field-effect transistors (CNTFETs) for low-power high-speed applications. It has been seen from atomistic density-functional theory (DFT) calculations that a negative quantum capacitance regime is achieved due to the one-dimensional (1D) screening of gate field in nanoscale CNTFETs. This unconventional negative quantum capacitance can be exploited to obtain a step-up voltage transformation at the gate of CNTFETs and, subsequently, sub-60mv/decade subthreshold swing. It is shown that a boosting efficiency greater than 2.2 is obtained at the gate of the CNTFETs.