Atomic-Layer-Deposition of Indium Oxide Nano-films for Thin-Film Transistors

Atomic-layer-deposition (ALD) of In2O3 nano-films has been investigated using cyclopentadienyl indium (InCp) and hydrogen peroxide (H2O2) as precursors. The In2O3 films can be deposited preferentially at relatively low temperatures of 160-200 degrees C, exhibiting a stable growth rate of 1.4-1.5 A/cycle. The surface roughness of the deposited film increases gradually with deposition temperature, which is attributed to the enhanced crystallization of the film at a higher deposition temperature. As the deposition temperature increases from 150 to 200 degrees C, the optical band gap (Eg) of the deposited film rises from 3.42 to 3.75 eV. In addition, with the increase of deposition temperature, the atomic ratio of In to O in the as-deposited film gradually shifts towards that in the stoichiometric In2O3, and the carbon content also reduces by degrees. For 200 degrees C deposition temperature, the deposited film exhibits an In: O ratio of 1: 1.36 and no carbon incorporation. Further, high-performance In2O3 thin-film transistors with an Al2O3 gate dielectric were achieved by post-annealing in air at 300 degrees C for appropriate time, demonstrating a field-effect mobility of 7.8 cm(2)/V.s, a subthreshold swing of 0.32 V/dec, and an on/off current ratio of 107. This was ascribed to passivation of oxygen vacancies in the device channel.