Effect of the Electrode Materials on the Drain-Bias Stress Instabilities of In–Ga–Zn–O Thin-Film Transistors

Abstract

The effects of electrode materials on the device stabilities of In–Ga–Zn–O (IGZO) thin-film transistors (TFTs) were investigated under gate- and/or drain-bias stress conditions. The fabricated IGZO TFTs with a top-gate bottom-contact structure exhibited very similar transfer characteristics between the devices using indium–tin oxide (ITO) and titanium electrodes. Typical values of the mobility and threshold voltage of each device were obtained as 13.4 cm² V^–1 s^–1 and 0.72 V (ITO device) and 13.8 cm² V^–1 s^–1 and 0.66 V (titanium device). Even though the stabilities examined under negative and positive gate-bias stresses showed no degradation for both devices, the instabilities caused by the drain-bias stress were significantly dependent on the types of electrode materials. The negative shifts of the threshold voltage for the ITO and titanium devices after the 10⁴-s-long drain-bias stress were estimated as 2.06 and 0.96 V, respectively. Superior characteristics of the device using titanium electrodes after a higher temperature annealing process were suggested to originate from the formation of a self-limiting barrier layer at interfaces by nanoscale observations using transmission electron microscopy.