Fabrication and Characterisation of Epitaxial Graphene on SiC/Si for High-Frequency Applications

Katzmarek, David Alexander

Fabrication and Characterisation of Epitaxial Graphene on SiC/Si for High-Frequency Applications

Katzmarek, David Alexander

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Publication Type:: Thesis
Issue Date:: 2023

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Field	Value	Language
dc.contributor.author	Katzmarek, David Alexander
dc.date.accessioned	2024-04-11T03:50:16Z
dc.date.available	2024-04-11T03:50:16Z
dc.date.issued	2023
dc.identifier.uri	http://hdl.handle.net/10453/177724
dc.description	University of Technology Sydney. Faculty of Engineering and Information Technology.	en_US.UTF-8
dc.description.abstract	Graphene attracts considerable attention for electromagnetic (EM) applications due to its electrical and plasmonic properties and the possibility of dynamic tunability with direct current (DC) to light sources. In order to extract the electrical characteristics of graphene at high frequencies, a straightforward method to pattern graphene, preferably without the need for material etching, is necessary. Hence, this work introduces a methodology for directly synthesising planar micro and nanopatterned epitaxial graphene (EG) on SiC/Si wafers by pre-patterning a Ni/Cu metal catalyst alloy via lift-off processes. This method is compatible with electron-beam lithography (EBL) and ultraviolet (UV)-lithography, and features down to ~200 nm pitch can be realised. High-frequency characteristics of this graphene platform were evaluated using metal coplanar waveguides (CPWs) that employed patterned graphene as a shunt between the centre and ground planes. A strong frequency-dependent behaviour of the graphene’s sheet resistance was observed. This is attributed to the progressively smaller influence of small-scale defects, such as grain sizes, at higher frequencies. While graphene and other two-dimensional (2D) materials notoriously lead to high contact resistances, this study stresses the importance of obtaining a high-quality graphene-metal contact for high-frequency applications. In order to characterise the intrinsic electrical properties of large-area graphene without consideration of the electrical contacts, this work also devises a methodology that uses Ka-band rectangular waveguide adaptors. The high-frequency sheet impedance was extracted from S-parameter measurements using an ABCD-Matrix model. The results indicate a ~2-fold higher sheet resistance compared to DC measurements. However, the monotonic decrease for increasing frequencies is once again confirmed. Finally, THz EM antennas and metasurface absorbers based on the EG on SiC/Si platform were designed and numerically simulated. Results confirm the dynamic tunability of the resonance frequency by varying graphene's Fermi level and the potential for antenna miniaturisation. However, the simulations show that a trade-off must be made as graphene antennas tend to provide lower radiation efficiencies and gains compared to thicker metallic ones. At the same time, employing graphene in absorbing structures, such as SiC-based Salisbury screens and gratings, demonstrates significant absorptivity enhancement and enables the dynamic tuning of resonance and absorptivity. These examples give a perspective of how graphene could benefit future EM devices. However, note that for a truly predictive capability, more specific input data for the numerical model deriving from measured characteristics of EG on SiC/Si at THz frequencies (or any other type of considered graphene) will be necessary.	en_US.UTF-8
dc.format	Thesis (PhD)
dc.language.iso	en_US	en_US.UTF-8
dc.relation	https://opus.lib.uts.edu.au/bitstream/10453/177724/1/thesis.pdf
dc.rights	info:eu-repo/semantics/openAccess
dc.rights	The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
dc.rights	© 2023 David Alexander Katzmarek
dc.rights.uri	au.edu.uts.lib/nph
dc.title	Fabrication and Characterisation of Epitaxial Graphene on SiC/Si for High-Frequency Applications	en_US.UTF-8
dc.type	Thesis
utslib.copyright.status	open_access	*

Abstract:

Graphene attracts considerable attention for electromagnetic (EM) applications due to its electrical and plasmonic properties and the possibility of dynamic tunability with direct current (DC) to light sources. In order to extract the electrical characteristics of graphene at high frequencies, a straightforward method to pattern graphene, preferably without the need for material etching, is necessary. Hence, this work introduces a methodology for directly synthesising planar micro and nanopatterned epitaxial graphene (EG) on SiC/Si wafers by pre-patterning a Ni/Cu metal catalyst alloy via lift-off processes. This method is compatible with electron-beam lithography (EBL) and ultraviolet (UV)-lithography, and features down to ~200 nm pitch can be realised. High-frequency characteristics of this graphene platform were evaluated using metal coplanar waveguides (CPWs) that employed patterned graphene as a shunt between the centre and ground planes. A strong frequency-dependent behaviour of the graphene’s sheet resistance was observed. This is attributed to the progressively smaller influence of small-scale defects, such as grain sizes, at higher frequencies. While graphene and other two-dimensional (2D) materials notoriously lead to high contact resistances, this study stresses the importance of obtaining a high-quality graphene-metal contact for high-frequency applications. In order to characterise the intrinsic electrical properties of large-area graphene without consideration of the electrical contacts, this work also devises a methodology that uses Ka-band rectangular waveguide adaptors. The high-frequency sheet impedance was extracted from S-parameter measurements using an ABCD-Matrix model. The results indicate a ~2-fold higher sheet resistance compared to DC measurements. However, the monotonic decrease for increasing frequencies is once again confirmed. Finally, THz EM antennas and metasurface absorbers based on the EG on SiC/Si platform were designed and numerically simulated. Results confirm the dynamic tunability of the resonance frequency by varying graphene's Fermi level and the potential for antenna miniaturisation. However, the simulations show that a trade-off must be made as graphene antennas tend to provide lower radiation efficiencies and gains compared to thicker metallic ones. At the same time, employing graphene in absorbing structures, such as SiC-based Salisbury screens and gratings, demonstrates significant absorptivity enhancement and enables the dynamic tuning of resonance and absorptivity. These examples give a perspective of how graphene could benefit future EM devices. However, note that for a truly predictive capability, more specific input data for the numerical model deriving from measured characteristics of EG on SiC/Si at THz frequencies (or any other type of considered graphene) will be necessary.

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