Electronic transport properties of amorphous indium-gallium-zinc oxide semiconductor upon exposure to water

The effect of water exposure on amorphous indium-gallium-zinc oxide (a-IGZO) semiconductors was reported. It was found that water can diffuse in and out of the a-IGZO film, reversibly affecting the transistor properties. Two competing mechanisms depending on the thickness of the active channel were clarified. The electron donation effect caused by water adsorption dominated for the thicker a-IGZO films (>= 100 nm), which was manifested in the large negative shift (>14 V) of the threshold voltage. However, in the case of the thinner a-IGZO films (<= 70 nm), the dominance of the water-induced acceptorlike trap behavior was observed. The direct evidence for this behavior was that the subthreshold swing was greatly deteriorated from 0.18 V/decade (before water exposure) to 4.4 V/decade (after water exposure) for the thinnest a-IGZO films (30 nm). These results can be well explained by the screening effect of the intrinsic bulk traps of the a-IGZO semiconductor. (C) 2008 American Institute of Physics.