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.
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ItemPlanar nanoelectronic devices and biosensors using two-dimensional nanomaterials( 2015)Graphene, a monolayer of carbon atoms and the first two-dimensional (2D) material to be isolated, has sparked great excitement and vast opportunities in the global research community. Its isolation led to the discovery of a new family of materials that are completely 2D, each of which exhibits unique properties in its own right. Such a wide range of new nanomaterials in a completely unexplored 2D platform offers a potential treasure for the electronics industry, which is yet to be explored. However, after more than a decade of research, nanoelectronic devices based on 2D nanomaterials have not yet met the high expectations set for them by the electronics industry. This thesis hopes to drive these efforts forward by proposing a different approach for the conceptualization of nanoelectronic devices, in light of the new opportunities offered by 2D nanomaterials. The proposed approach is centred on exploiting the truly unique property of two-dimensionality, which defines and distinguishes this exciting family of 2D nanomaterials, for the realization of completely 2D planar nanoelectronic devices. Less reliance is made on individual properties that are unique to individual 2D nanomaterials, however, wherever possible; such properties are exploited in enhancing the performance of the proposed devices. The proposed approach is applied to the conceptualization of a number of planar nanoelectronic devices that have a potential in a range of direct as well as long term envisioned applications, complementing conventional electronics on the short term but also having the potential to revolutionize electronics on the long term. All of the proposed devices are planar, completely 2D and realizable within a single 2D monolayer, reducing the required number of processing steps and enabling extreme miniaturization and CMOS compatibility. For the first time, a 2D Graphene Self-Switching Diode (G-SSD) is proposed and investigated, showing promising potential as a nanoscale rectifier. By exploiting some of graphene’s unique properties, the G-SSD is transformed into different types of planar devices that can achieve rectification, Negative Differential Resistance (NDR) operation and tunable biosensing. The extension of the proposed approach to other types of 2D nanomaterials is also investigated, by exploring the implementation of SSDs using MoS2 and Silicene. Finally, new classes of graphene resonant tunneling diodes (RTDs), with completely 2D planar architectures, are proposed, showing unique transport properties and with promising performance, while requiring minimal process steps during fabrication.