Suspended Graphene based Electronic Devices

  • Omar Mhaidi Dawood Dawood

Student thesis: Phd

Abstract

This work concerns the development of scalable graphene electronics. The work started with attempting to identify a fabrication procedure compatible with microelectronics fabrication standards, and eventually found out that the only realistic way to advance the field was to utilize graphene suspended over a cavity. This is because interaction with a substrate tends to limit the mobility of graphene. There are three major themes in this thesis. Firstly, chemical vapour deposition (CVD) graphene was repeatedly transferred onto a GaAs semi-insulating substrate to form multilayers. These manually stacked graphene layers resulted in appreciable local variations of optical properties due to the local differences of stacking orders. Notwithstanding that multilayer CVD graphene is a good candidate for various GaAs-based electrical applications, the lack of uniformity and a sizeable bandgap and strong interaction with the substrate, needed to be resolved for the project to advance. It was known that the applying a tensile and a compressive stress on a graphene sheet can greatly modify its electronic and optical properties. Changing the band structure of graphene is expected to lead opening of a sizable bandgap. The second theme of this thesis, was to try and identify a route to bandgap opening in a long wrinkle formation in CVD graphene by means of depositing two electrodes with a small gap of 1μm on top of graphene. The type and amount of generated strain along the wrinkle are identified using a combined Atomic Force Microscopy and polarized Raman spectroscopy. Through using atomistic modelling, a sizeable bandgap opening of up to 0.4 eV was revealed. While the result was promising, the major problem was the flat graphene, no wrinkle, leading us to think that the interaction with the substrate needed eliminating. This lead to the third theme of this thesis, and what gives the thesis its title. Suspended graphene based electronic devices. A large suspended graphene area of up to 160 μm2 has been fabricated as three-terminal devices. The suspended areas exhibit static wrinkles which simultaneously introduce both tensile and compressive strain on the graphene surface. In conclusion, the variations of the Fermi level in the suspended graphene areas can be modulated by applying a bias to the top contacts while fixing the back gate. The large area of suspended graphene, combined with the Complementary metal-oxide-semiconductor (CMOS) fabrication process, and the modulation of the Fermi level observed, are a substantial step forward in demonstrating the potential of suspended graphene on the path towards commercial graphene-based electronic devices and sensors.
Date of Award31 Dec 2018
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRobert Young (Supervisor) & Max Migliorato (Supervisor)

Keywords

  • Density Functional theory
  • Suspended Graphene
  • Raman spectroscopy

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