Control of Film Morphology via Coating Thickness in Thin-Channel, Blade-Coated In2O3 Transistors
Ahmad R. Kirmani, Huilang Chen, Christopher M. Stafford, Emily G. Bittle, Lee J. Richter
Overcoming present limitations on charge transport in scalable and solution-deposited metal- oxide (MO) thin films can potentially enable low-cost, flexible and transparent large-area electronics. In this study, we explore the role of coating thickness in determining nanoscale morphology in blade-coated indium oxide (In2O3) thin-film transistors (TFTs). TFTs were fabricated with total channel thickness ranging from 2 nm to 16 nm via varied multistep processes. Transport in channels fabricated from sequential, thin ( 4 nm) coatings is found to significantly exceed that from thicker coatings. We find a marked change in the In2O3 crystal texture with coating thickness. Thin coatings produce highly smooth films with strong c-axis texture while thicker coatings are rougher and exhibit little texture. In addition to the clear benefits in transport due to the smooth, aligned films, we find that deposition of sequential thin layers leads to the highest mobility, with either In2O3 or ZnO as the overcoat. This suggests defects at the air interface of the initial thin films limit performance. Optimizing both coating thickness and number of coatings, we demonstrate blade-coated 8 nm thick channel In2O3 TFTs with an impressive saturation electron mobility (sat) of (36.1 ± 6.8) cm2V-1s-1.