High-frequency and switching performance investigations of novel lightly doped drain and source hetero-material-gate CNTFET

The effects of lightly doped drain and source (LDDS) and hetero-material-gate (HMG) structure on the static characteristics and switching speed performance for a carbon nanotube field effect transistor (CNTFET) have been theoretically investigated by a quantum kinetic model. This model is based on two-dimensional non-equilibrium Green׳s functions (NEGF) solved self-consistently with Poisson׳s equation. A comparison study of electrical characteristics in conventional single-material-gate CNTFET (C-CNTFET), LDDS-CNTFET, HMG-CNTFET and LDDS-HMG-CNTFET structures has been performed. Simulations show that, compared with the other structures, LDDS-HMG-CNTFET significantly decreases leakage current, subthreshold swing, and increases on/off current ratio. In addition, effects of the gate electrode work function of the LDDS-HMG-CNTFET have been studied theoretically. The results indicate that the electron transport efficiency, and the cutoff frequency of the device, can be optimized by reasonably selecting the gate electrode work function. This work illustrates that the proposed LDDS-HMG-CNTFET might be useful for low-power high-speed CNTFET digital design.