Modeling And Simulation Of Carbon Nanotube Field Effect Transistors

Based on careful summation of basic characteristics of carbon nanotube (CNT) and basic theory of nanoscale transistor, this thesis is aim to model and simulate a novel type of field effect transistor which incorporates semiconducting carbon nanotube as the channel material, and to analysis the performance and physics behind it.This work is mainly focused on the study of MOSFET-like carbon nanotube array field effect transistors (CNTFET). We derived the existed analytical model of single-walled CNTFET, which includes the semiclassical current source, accurate channel capacitors, parasitic capacitors, doping resistances, and Schottky-barrier resistances. Based on this model, we further derived an analytical model for double-walled CNTFET. The main novelty of this model is a set of analytical non-equilibrium charge control equations, the solution of which are the self-consistent surface potentials of the inner wall and the outer wall. The charge densities and currents of both walls can then be determined. Various non-idealities are also taken into accout, including the screening effect of neighbouring double-walled CNTs, the parasitic capacitances, and the parasitic resistances.Using the single-walled and double-walled CNTFET models, we first analyze the intrinsic channel behaviors, we then examine the roles of doping, screening and parasitic effects, which will significantly influence the drive current and capacitance. Finally, numerical results are presented to show their performance parameters, such as delay, and cutoff frequency, with different array geometries, such as CNT diameters and inter-CNT distances. By comparision, we found that although the intrinsic part of double-walled CNTFET has no speed advantage over its single-walled counterpart, the overall performance of double-walled CNTFET can be better with low array densities and large diameters. Therefore, double-walled CNTs can be utillized as an alternative to single-walled CNTs in the furture design of carbon nanotube electronics.Since small-diameter multi-walled CNTs are semiconducting and can be used as channel material, we further extend the double-walled CNTFET model to multi-walled CNTFET.