Influence of Thermal Postdeposition on Trap States in Sol-Gel Indium-Zinc Oxide TFTs

In solution-processed oxide thin-film transistors, postdeposition thermal processing significantly changes the film's transport properties and is essential for high-performance devices. The mobility, bias stability, and trapping-detrapping related hysteresis are improved with higher processing temperatures, which is generally attributed to decreased concentrations of localized states that act as electron traps. Fabricating and characterizing 29 devices, we provide further experimental evidence that postdeposition processing, indeed, leads to enhanced channel electron mobility in sol-gel indium-zinc oxide TFTs, and on the basis of a simple model, we extract physical parameters that yield a quantitative assessment of the changes in the densities and the properties of the localized trap states. The data are obtained for sol-gel indium-zinc oxide thin films and TFTs subjected to thermal postdeposition processing from 300 °C to 500 °C. The extracted parameters indicate that the trap state densities in the bulk semiconductor and at the interface decrease by factors of 5 and 3, respectively. Furthermore, the localized states become shallower, and the band mobility increases with higher processing temperatures.