Coupled NEGF-PSO method for maximizing the current ratio of CNTFETs based on oxide thickness optimization

Abstract

Carbon nanotube field-effect transistors (CNTFETs) with optimized oxide thicknesses have been proposed. The optimum oxide thickness that provides the maximum current ratio (on/off ratio) has been calculated for each design. The effect of oxide thickness on the on/off ratio has been investigated by changing its value as the independent variable and calculating on state and off state currents. PSO algorithm has been used to find the exact optimum value of the oxide thickness with the objective of having a maximum current ratio that is one of the most important parameters in switching applications. The optimum insulator thickness is calculated for CNTFETs with different chiral vectors, insulator types, channel lengths and source/drain doping levels. For further study of the CNTFETs, performance parameters such as cutoff frequency and transconductance of the devices have also been calculated and studied. The results of the paper show that the CNTFET designers should select the oxide thickness very carefully not only based on reported values in other works. Each design requires its own optimum oxide thickness which provides the maximum on/off current ratio only for that design.