Preparation Of Graphene By CVD And Its Application In Organic Thin-Film Transistors

Graphene, a two-dimensional (2D) form of carbon atoms with the hexagonal lattice structure, has attracted much attention due to its fascinating electrical and mechanical properties. In particular, its high carrier mobility, appropriate work function, good optical transparency and high chemical stability make it have a wide application prospect in the fields of display devices, electronic devices, optoelectronic devices. Recently, considerable research efforts focused on synthesizing high-quality and large-area graphene.In this paper, we grew large area and uniform single-layer graphene on copper foil in a chemical vapour deposition system, and then transfer them to SiO2/Si and PET substrate. We fabricated graphene films with different surface characteristics prepared by layer-by-layer method, and investigated the performance of OTFTs based on graphene electrodes. The main conclusions are as follows:(1) The growth parameters of monolayer graphene are optimized and High-quality graphene are obtained. The result shows that, after mechanical polishing and annealing the surface of copper foil becomes clean, and the grain is also larger. This result is helpful to prepare high quality graphene. The concentration of hydrocarbon determines the number of graphene layers. Hydrogen played an important role in the growth process as it can etch the graphene in a particular way and assists the decompose of the hydrocarbon. Based on this, the exists of hydrogen can help to control the quality of graphene. Large-area high-quality and single-layer graphene was synthesized according to the analysis and experiment above.(2) We treated the SiO2/Si substrate and preprocess the PMMA coated sample before substrate etching in graphene transfer experiment. As to our experiments, the UV-treated substrate can transfer complete graphene films, which ascribed to the high adhesion between the UV-treated substrate and the graphene. The cleanness of the transferred graphene was significantly improved when through an oxygen plasma process for the backside. Lithography was used to pattern the graphene electrodes.(3) We have successfully fabricated high-performance pentacene TFTs with graphene source/drain electrodes by transferring and patterning CVD-grown monolayer graphene films. The highest mobility of the monolayer graphene OTFTs can reach 0.56 cm2V-1s-1, which is much higher than mobilities of TFTs based on Au electrodes. Monolayer graphene, with a high transparency and good conductivity, provides an alternative electrode material for use in field of microelectronics.(4) The effects of semiconductor/electrode interface on the performance of pentacene thin film transistors using graphene as electrodes are investigated. The morphology and properties of graphene electrodes were varied by controlling the number of graphene layers through a layer-by-layer (LBL) stacking method. It was discovered that increasing the stacking layers of graphene films resulted in an increased surface roughness and accompanied by a decrease in sheet resistance as well as an increase in work function. Although an increase in stacking layers provide better conductivity and energy level match between electrode and pentacene semiconductor, the spontaneous increase surface roughness disorder the growth of pentacene crystals adjacent to the electrodes and breaks the connectivity of a single-phase domain in the active film. As a result, the field-effect performance is substantially decreased by increasing the surface roughness. The roughness factor becomes predominant in graphene devices. Hence, obtaining a smooth graphene film is critical to future research.