Molybdenum Disulphide (MoS2) Nanosheet Inks Evaluated for Printed Electronics and Application to Thin-Film Transistors
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Inkjet printing is a versatile deposition technique that has been used for the fabrication of electronic circuits, from simple conductive tracks to complete 3D logic circuits. The emergence of solution-processable 2D layered materials pushes the performance boundaries of printed devices. The use of 2D functional materials combined with the growing knowledge in the field of inkjet printing processing has great potential for competing with traditional fabrication methods in terms of performance and cost. Molybdenum disulphide (MoS2) is the most researched 2D semiconductor owing to its tunable bandgap, high mobility and photo-responsivity and mechanical flexibility. Solution-processable MoS2 is needed for large-scale device fabrication. Unlike large MoS2 sheets, nano-scale sheets can be easily stabilized in suspension and used in various deposition methods. However, nanosheet MoS2 suspensions were used so far to fabricate two-terminal devices, with limited or no results for thin-film transistors. In this research, a significant first step was taken in studying the behaviour of MoS2 nanosheet suspensions through the introduction of ethyl cellulose as a stabilizing agent and the modification of substrate temperature and surface energy via hydrophobic coatings of the target substrates for improved printability and film formation. For the first time, it was shown that the ring-stain effect can be directly exploited for the fabrication of circular devices using inkjet printing. Minimal suspension concentration of 3.7 mg/L was evaluated for the first time by a continuum percolation simulation using real particle size distribution. Stability of MoS2 nanosheets under thermal treatment was studied for the first time and a decomposition temperature of 200°C in air and 300°C is inert atmosphere was determined. It was shown that thick films exhibit bulk conductivity but no field-effect was observed. In conclusion, the minimal concentration evaluation and the results of the thermal stability study imposed limitations on process development, which were addressed during device fabrication. Top-contact device architecture was shown to be superior to bottom-contact device architecture. The absence of an observable field-effect was attributed to poor inter-sheet charge transport.
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Leon Mintz (2017). Molybdenum Disulphide (MoS2) Nanosheet Inks Evaluated for Printed Electronics and Application to Thin-Film Transistors. UWSpace. http://hdl.handle.net/10012/12026