Reliability enhancement in thin film transistors using Hf and Al co-incorporated ZnO active channels deposited by atomic-layer-deposition.

Oxide thin films transistors (TFTs) with Hf and Al co-incorporated ZnO active channels prepared by atomic-layer deposition are presented. The Al concentration was fixed at 2.6 at% and the Hf concentration was varied from 3.3 to 6.3 at%. The HfAlZnO (HAZO) TFTs exhibited positive shifts in turn on voltages toward 0 V with a slight decrease in carrier mobility with increases in the incorporated Hf content and the post-annealing temperature. It was suggested that the carrier concentration and defect densities within the HAZO channels were reduced by incorporating Hf and performing the thermal annealing process. The TFT with HAZO channels with Hf content of 6.3 at% exhibited a turn-on operation at around 0 V and a low SS value of 0.3 V dec without a marked decrease in carrier mobility. Furthermore, the device stabilities under bias, illumination, and temperature stresses could be greatly enhanced by reducing the formation of additional carriers and defects caused by weak Zn-O bonds due to the high binding energy of Hf with oxygen.