Residue-free photolithographic patterning of graphene

Abstract

Photolithography of graphene using an organic photoresist (PR), whereby the graphene film is patterned into a desired geometry, is required for the fabrication of graphene-based sensors and electronic devices. However, because the PR hardens during the O2 plasma etching process, its complete removal is difficult. Herein, we present a new route to obtain residue-free patterned graphene by introducing a buffer layer between graphene and the PR. The modified photolithography process allows complete removal of the hardened PR and eliminates poly(methyl methacrylate) residues on the graphene surface during the wet transfer process. Density functional theory calculations revealed that the binding strength between the buffer layer and graphene is weaker than that between the PR and graphene. This led to a clean graphene surface without PR and other organic residues. The graphene films patterned using the modified photolithography process are of superior quality; they have the lowest surface roughness, natural hydrophobicity, and the highest transmittance of 94.1% at the wavelength of 550 nm. In addition, graphene-based field-effect transistors fabricated using the new process present the electron mobility of 800 cm2 V-1 s-1, and their charge neutrality point is located near zero bias, indicating that the unintended doping effect was effectively eliminated. This work demonstrates a new process that is compatible with silicon-based nanosystems and can be readily applied in the mass production of residue-free graphene electronics.