Efficient Transfer of Graphene –Physical and Electrical Performance Perspective
Graphene has become one of the most widely used atomic crystal structure materials since its first experimental proof by Geim-Novoselov in 2004 . This is
attributed to its reported incredible carrier mobility, mechanical strength and thermal conductivity   . These properties suggest interesting applications of Graphene ranging from electronics to energy storage and conversion . In 2008, Chen et al reported a 40,000 cm2V-1s-1 mobility for a Single Layer Graphene (SLG) on SiO2 compared to 285 cm2V-1s-1 for silicon channel devices . Chemical vapor deposition (CVD) is a common method for growing graphene on a metal surface as a catalyst for graphene nucleation. This adds a necessary transfer step to the target substrate ultimately desired for graphene devices fabrication. Interfacing with graphene is a critical challenge in preserving its promising high mobility. This initiated the motivation for studying the effect of intermediate interfaces imposed by transfer processes.
In this work, few layers graphene (FLG) was grown on copper foils inside a high temperature furnace. Then Raman spectroscopy was performed on grown graphene
sample to confirm few (in between 3-10) layers. Afterwards the sample was cut into three pieces and transferred to 300 nm SiO2 on Si substrates using three techniques, namely: (i) pickup transfer with top side of Graphene brought in contact with SiO2 , (ii) Ploy (methyl methacrylate) (PMMA) transfer with Graphene and a PMMA support layer on top scooped from bottom side , and (iii) a modified direct transfer which is
similar to PMMA transfer without the support layer . Comparisons were done using Raman spectroscopy to determine the relative defectivity, Scanning Electron Microscopy (SEM) to observe discontinuities and Atomic Force Microscopy (AFM) to measure surface roughness. Then we conclude with electrical data based on the contact resistivity measured for layers transferred using these different techniques. Contacts
were deposited using e-beam thermal evaporation and contact resistivity was calculated using Transmission Line Method (TLM) .
To date no comparative analysis for the aforementioned transfer methods has been done to determine which is the most efficient . Our contributions are: (i) determining the most efficient method, (ii) reporting a lift-off process for Graphene, (ii) and reporting lower specific contact resistivity for no-post transfer processing Graphene.
|Date of Award||Nov 2012|
- Computer, Electrical and Mathematical Science and Engineering
|Supervisor||Muhammad Mustafa Hussain (Supervisor)|