Graphene Device Fabrication and Applications in Communication Systems

Abstract

High carrier mobility, saturation velocity and thermal conductivity make graphene a promising material for high-frequency, analog and communication applications. The ambipolar properties of graphene provide opportunities for increased functionality in unconventional circuit architectures. In this dissertation, I describe the fabrication process of graphene devices, including the optical and Raman spectroscopic characterization and electron-beam lithography. The different electrical characteristics of the single-layer and bilayer graphene field-effect devices reflect differences in the electron band structures of the two systems. The fabricated graphene transistors have been used to design and experimentally demonstrate electronic circuits with communication functionalities such as phase-shift keying, frequency-shift keying and phase detection. Compared with conventional semiconductor electronic designs based on multiple unipolar transistors, the demonstrated graphene amplifiers and phase detectors have advantage of a simplified structure. An important issue for high-frequency and analog applications is the low-frequency noise, which up-converts and contributes to the phase noise of the systems. It was found that the low-frequency noise in graphene devices is dominated by 1/f noise in the frequency range from 1 Hz to 100 kHz (f is the frequency). The device exposure to different gases results in appearance of characteristic peaks in the noise spectral density. The latter can be utilized for selective gas sensing with graphene. The metal-graphene contact contributions to the 1/f noise can be strongly reduced via the use of the graded thickness graphene channels in the device structure. I have also investigated a possibility of tuning graphene properties via controllable exposure to the low-energy electron-beam irradiation. It was found that the charge neutrality point and resistivity can be tuned over a wide range of values. The obtained results are important for the proposed applications of graphene in analog electronics, communications and sensors.