Indium-free transparent thin film transistors based on nanocrystalline ZnO

Wide bandgap semiconductors based on (Zn, In, Ga, Sn)-oxides are all good candidates for the channel material in transparent thin film transistors (TTFT) because of their simultaneous high electron mobility and optical transparency properties. The choice of contact layers are, however, more limited because not all metal oxides can be doped high enough to yield low resistivity layers. Historically, the most common contact layers are ternary compounds that include indium (e.g. indium-tin-oxide, indium-zinc-oxide etc). These indium-containing transparent conductive oxide (TCO) films find widespread applications in flat panel displays and touch-sensitive surfaces of many communication devices. Because of the rapidly expanding markets for such devices, and the limited availability of indium in the world markets, the increased demand-to-supply ratio has caused the cost of indium to increase very rapidly. There are concerns about the continuity of indium supply for future devices. 1