Improvement in the negative bias stability of zinc oxide thin-film transistors by hafnium doping

Thin-film transistors (TFTs) with hafnium-doped zinc oxide (HZO) channels were fabricated and the effects of Hf content on the performance of ZnO-based TFT were investigated. HZO TFTs exhibit improved electrical characteristics, with increased ION/IOFF and decreased subthreshold swing. We also investigated the influence of hafnium doping on the bias stability of ZnO TFTs. HZO TFTs exhibited turn-on voltage (VON) shifts of −1 V in negative stress bias, compared with −8 V for intrinsic ZnO TFTs. The improvement in the VON shift may be due to a reduction in the total trap density resulting from the suppression of the defect-related oxidation state of the Zn ions caused by the high binding energy of Hf ions.

► Hf-doped ZnO (HZO) semiconductors were studied for improving NBTI.
► The addition of Hf slightly increases both ION/OFF and SS values.
►  HZO-TFT devices was improved bias stability considerable compared to ZnO.