Electrical and Electronic Engineering - Theses
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ItemGraphene nanoelectronics( 2016)Graphene is a two-dimensional material consists of tightly packed carbon atoms in a hexagonal lattice with surprising electrical properties. Patterning graphene into nanostructures to achieve desirable electronic properties is an active research area. The aim of the thesis is to explore diverse graphene nanostructures for electronic and biological applications. Novel graphene structures have been proposed including graphene nanoribbons, break junctions and nanopores and investigated for circuit interconnects, negative differential resistance devices and biosensors. Interconnects and nanoscale transmission lines are critical components in the design of nanoelectronic systems. In this thesis, high frequency characteristics of chemical vapour deposition graphene nanoribbon (GNR) interconnects and radio frequency propagation in GNRs embedded in a coplanar waveguide structure up to 20 GHz have been studied. An equivalent transmission line model is proposed to model the GNRs at high frequencies. The solid agreement between the model and the measured data suggests that it can be used in the design of nanoscale circuits in which GNRs are utilized as the interconnect elements. The study provides insight into microwave behavior of GNRs for developing high speed graphene devices. Graphene-based negative differential resistance (NDR) devices hold great potential for enabling the implementation of several elements required in electronic circuits and systems. However, previously proposed devices manifest several drawbacks due to their complex structures and the multiple steps required in the fabrication processes. This research presents a novel structure based on GNR junctions for NDR devices, which can be fabricated using standard lithography techniques. Theoretical simulation shows that GNR junctions with a nano gap in the transport direction of the ribbons can manifest a pronounced NDR phenomenon. The predicted NDR effect is then confirmed through the experimental investigation on the current-voltage characteristics of the fabricated devices. A natural extension of GNR systems is to incorporate graphene nanopores (GNPs). GNPs are promising building blocks for electronic circuitry and bio applications. A large numbers of studies on the fabrication of GNPs have been reported, in which GNPs were realized from GNRs by drilling a tiny hole in the middle of GNRs. However, methods to design GNPs that achive desirable conduction performance and sensing characteristics have not been well understood. Therefore, this dissertation investigated the quantum transport properties of GNPs created by drilling pores in armchair and zigzag GNRs. The study reveals that the quantum transmission spectra of GNPs are highly tunable and GNPs with specific transport properties able to be produced by properly designing pore shapes. This thesis shows that the biological sensing capabilities of GNPs are transmission dependent and can vary dramatically with pore geometry. Finally, it is shown that GNPs with suitable edge passivation can potentially be used as NDR devices. The insight presented in this thesis serves as a guideline for developing several graphenebased devices to obtain required performance characteristics for various applications.