Carbon Nanotube Field-Effect Transistors (CNFETs): Structure, Fabrication, Modeling, and Performance

Abstract

The problems associated with attempting to scale down traditional metal oxide field-effect transistors (MOSFET) have led researchers to look into CNT-based field-effect transistors (CNFETs), as an alternative. Though the scaling of MOSFET has been the driving force toward the technological advancement, but due to continuous scaling, various secondary effects which include short channel effects, high leakage current, excessive process variation, and reliability issues degrade the device performance. On the other hand, CNFETs are not subjected to the scaling problems. The operation principle of the CNFET is similar to traditional MOSFET but the conduction phenomena are different. The traditional MOSFETs are based on the drift and diffusion phenomena in which channel length is very large as compared to mean free path of charge carriers whereas the CNFETs are based on ballistic transport conduction mechanism, in which channel length is very small as compared to mean free path of charge carriers. In CNFET, electrons are injected from source to drain and transported through the nanotubes without scattering. Due to ballistic transport the nanotubes act as a perfect conductor for electrons such that the full quantum information of these electrons (momentum, energy, spin) can be transferred without losses. The channel current in CNFETs depends on gate voltage, number of nanotubes in channel, dielectric material and its thickness, and diameter and chirality of carbon nanotubes. So in this chapter we shall discuss different device structures of CNFET, steps involved in the fabrication of CNFETs, advantages and limitations of various methods involved in the synthesis of CNTs, conduction models, and performance parameters.