All Inkjet-Printed High On/Off Ratio Two-Dimensional Materials Field Effect Transistor
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This thesis introduces the development of a novel ink, design, fabrication, and characterization of an all inkjet printed high current on/off ratio field effect transistor (FET). The inks were obtained through the liquid phase exfoliation of nitrogen-doped graphene (NDG), and molybdenum disulfide (MoS2) nanosheets into appropriate solvents. A stable and efficient method of inkjet printing is developed for NDG nanosheets. The concentration of nanosheets and the presence of MoS2 were determined from UV-Vis spectra of the inks. The morphology of percolation clusters using NDG was studied using the thickness profile and scanning electron microscopy (SEM) images. The solvent-induced defects in NDG nanosheets were characterized by Raman spectroscopy. There were little or no solvent-induced defects in the nanosheets recovered by curing after printing. Barium titanate (BaTiO3) was prepared and used as a high k (~20.5) dielectric for the printed transistors. The NDG transistors were designed, fabricated, and characterized on the glass substrate. Due to the low on/off ratio of NDG transistors, NDG thin films were electrochemically doped with MoS2 by multiple printing passes. The incorporation of semiconducting MoS2 into NDG was confirmed by energy dispersive spectroscopy (EDS) for further analysis. A transistor with high current on/off ratio was obtained by NDG-MoS2 heterostructures channel. To our best knowledge, this is the highest on/off ratio for a fully inkjet printed transistor based on 2D materials.