The electrical and optical properties of amorphous indium zinc tin oxide (a-IZTO) thin films were examined as a function of chemical composition. Effects of Sn/Zn composition ratio and In content on the electrical and optical properties of a-IZTO thin films are discussed. The electron mobility of thin film transistors with higher Sn/Zn composition ratio was dramatically improved due to a shorter zinc-zinc separation distance. The thin film transistor with the composition of In:Zn:Sn = 20:48:32 exhibits a high mobility of 30.6 cm(2) V-1 s(-1) and a high on-off current ratio of 10(9). (C) 2014 Elsevier B.V. All rights reserved.