Thin-film transistors (TFTs) with indium based metal oxide, aluminum indium oxide, channel layers were fabricated via a simple and low-cost solution process. The process temperature was reduced to 250 degrees C, an applicable temperature to plastic substrates, by applying post-annealing. Post-annealing under various atmospheric conditions effectively converts the remaining In(OH) species to a metal oxide at low temperature. It was revealed that humid O-2 post-annealing mostly facilitated the conversion of In(OH) species to a metal oxide. The optimized low temperature (i.e., 250 degrees C) solution processed AIO TFT exhibits a channel mobility of 2.37 cm(2)/V.s, a sub-threshold slope of 0.6 V/decade, and an on-to-off current ratio greater than 10(6). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3589252] All rights reserved.