High mobility ultra-thin crystalline indium oxide thin film transistor using atomic layer deposition

Stoichiometric crystalline binary metal oxide thin films can be used as channel materials for transparent thin film transistors. However, the nature of the process used to fabricate these films causes most binary metal oxide thin films to be highly conductive, making them unsuitable for channel materials. We overcame this hurdle by forming stoichiometric ultra-thin (5 nm) crystalline In2O3 films by using a thermal atomic layer deposition method. Specifically, (3-(dimethylamino)propyl)dimethylindium was used as a liquid precursor and ozone as an oxygen source to grow In2O3 thin films at a high growth rate of 0.06 nm/cycle. Adjustment of the deposition processing temperature followed by annealing in an oxygen atmosphere enabled us to fully crystallize the film into a cubic bixbyite structure with the retained stoichiometry. The transparent crystalline ultra-thin In2O3-based bottom-gate thin film transistors showed excellent and statistically uniform switching characteristics such as a high Ion/Ioff ratio exceeding 107, a high linear mobility of 41.8 cm2/V s, a small subthreshold swing of 100 mV/dec, and a low hysteresis of 0.05 V. Our approach offers a straightforward scheme, which is compatible with oxide electronics, for fabricating a transparent metal oxide device without resorting to complicated oxide compositional strategies.