Carbon-Based Multiple-Gate Field-Effect Transistors

Abstract

The goal of this study is to establish the importance of multiple-gate architecture for the realization of one-dimensional Field-effect transistors having a steep sub-threshold swing and an appreciable on-state performance. The task for the thesis comprised of, first, the implementation of a self-made simulation tool for quantum simulations on carbon-based nanostructures exploiting the superlattice effect based on multiple-gate substrate; Second, the experimental work including clean room fabrication and device characterization for determining some of the design features of the proposed device. For the said purpose, an arrangement consisting of a large number of gates placed next to each other with an inter-gate distance of the order of few nanometers is studied. Due to the excellent gate control attained from the multiple-gate organization, the manipulation of the conduction and the valence band profile at the nanoscale is achieved. This work provides a simulation platform to study the effect of electrostatic doping on the potential profile in carbon-material nanostructures like graphene/carbon nanotube. In addition, an energy filter obtained from a gate-induced superlattice is simulated. The application of alternating gate voltages on the multiple gates resulted in a superlattice structure that is employed as an energy-filter for blocking hot-electrons to achieve a superior switching behaviour in the device. The associated parameters like- voltages on the multiple gates, thickness of the gates and the inert-gate dielectric thickness are further varied to enable fine tuning of the gate-induced superlattice and hence, optimization of the energy-filter. Lastly, experiments to determine important design parameters for the proposed device are performed. For the implementation of an adjustable superlattice energy filter, high alternating voltages are applied on the multiple-gates. Hence, the breakdown voltage of the inter-gate dielectric becomes critical. Therefore, a set of experiments are carried out to determine the strength of the dielectric with variable thickness.