Improvement in the Bias Stability of Zinc-Tin Oxide Thin-Film Transistors by Hafnium Doping

The influence of hafnium (Hf) doping on negative-bias temperature instability in zinc-tin oxide thin-film transistors was studied. Hafnium-zinc-tin oxide TFTs exhibited a turn-on voltage (V (ON)) that shifted from 0 V to -1 V with negligible changes in the subthreshold swing and field-effect mobility after 3 h of total stresses. The enhanced improvement of the V (ON) shift (Delta V (ON)) was attributed to the reduction in the interface trap density, which may result from the suppression of oxygen-vacancy-related defects by the Hf ions.