Suppression in the Negative Bias Illumination Instability of ZnSnO Thin-Film Transistors Using Hafnium Doping by Dual-Target Magnetron Cosputtering System

In this paper, the highly improved negative bias illumination stress (NBIS) stability of zinc-tin-oxide (ZTO) thin-film transistors (TFTs) is achieved by Hf doping, using dual-target magnetron cosputtering system. Compared with a large negative threshold voltage shift (Delta V-T) of 9 V in pristine ZTO TFT, the Hf-doped ZTO TFTs shows superior stability and device D only shows 1.9 V negative Delta V-T under the same NBIS. The enhancement in NBIS stability of Hf-doped ZTO TFTs is attributed to a lower oxygen vacancy concentrations and a fewer interface trap states suppressed by Hf ion. The decrease of oxygen vacancy concentrations and interface trap states are confirmed by X-ray photoelectron spectroscopy measurement and capacitance voltage (C-V) measurement, respectively. It is consistent with trap density extracted from temperature-dependent field-effect measurements, which verifies further the factor of the improvement of in NBIS stability of Hf-doped ZTO TFTs.