Synthesis, Processing, And Electrical Characterization of Graphene Synthesized by Chemical Vapor Deposition
Open Access
- Author:
- Howsare, Casey Alan
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 15, 2019
- Committee Members:
- Joshua Alexander Robinson, Thesis Advisor/Co-Advisor
Suzanne E Mohney, Committee Member
Mauricio Terrones, Committee Member
John C Mauro, Program Head/Chair - Keywords:
- graphene
chemical vapor deposition
ohmic contacts
electron transport
device fabrication - Abstract:
- Since its discovery in 2004, graphene has been the subject of an immense amount of research interest. Its two-dimensional structure gives rise to a multitude of unique electrical characteristics, which make it a candidate for use in many novel electronics applications. While initial graphene research was foundational in nature, more recent work has shifted to practical aspects of realizing functional graphene electronics. This has included an increased interest in scalable graphene synthesis techniques such as chemical vapor deposition (CVD), as well as the subsequent fabrication of graphene devices. This thesis establishes and investigates the procedures for fabricating graphene devices from beginning to end. It begins with a study of the graphene synthesis process by CVD on freestanding copper foils. It also evaluates the viability of synthesis on thin copper films on insulating substrates, for potential integration into scalable device manufacturing processes. Next, techniques for layer transfer of graphene films to arbitrary substrates are evaluated, including the processes for copper substrate removal and cleaning of the graphene film to produce high quality films free of mechanical defects or chemical modification by the layer transfer process. A full device fabrication flow is established for the transferred graphene films, including active device isolation, ohmic contact formation, gate dielectric deposition, and gate contact formation. Special attention is paid to optimization of the ohmic contact formation process, first by study of various pre-metallization plasma treatments, and subsequently by study of the effect of progressive contact anneals on observed contact resistance. This work demonstrates specific contact resitivities as low as 8x10-6 Ω-cm2, with discussion on a path towards meeting state of the art values. Finally, this work investigates the electrical transport behavior of CVD graphene when transferred to a variety of substrate materials. Temperature-dependent Hall mobility measurements are presented, along with transport modeling to assess the relative contributions of various scattering mechanisms. These measurements show that charged impurity scattering is the dominant mechanism across all substrates, with dielectric surface optical phonon scattering also serving as a minor contributor. Subsequent projections across a wide space of dielectric materials and graphene properties provide guidance on optimal selection of dielectrics based on the application.