Enhanced Electrical Properties and Stability of Solution Processed IYZO Thin Film Transistor by Controlling of Deep Level Oxygen Vacancies

Abstract

In this study, ytterbium (Yb) was introduced as a dopant to improve the stability of indium-zinc oxide (IZO) thin film transistors (TFTs). The stability and electrical performance of indium-ytterbium-zinc oxide (IYZO) TFTs were compared with those of an indium-gallium-zinc oxide (IGZO) TFTs with Gallium (Ga) as a typical dopant. In particular, under a negative bias illumination stress (NBIS) among the stability evaluations of the various operating conditions the Δ threshold voltage (Vth) of the IGZO (Ga: 3%) TFT (-6.4V) was 24% better than that of the IZO TFT (-8.4 V); however, Δ Vth of the IYZO (Yb: 3%) (-5.2 V) TFT was not only 49% better than that of the IZO TFT, but also 19% better than that of the IGZO TFT. Under NBIS conditions, the deep level oxygen vacancy (Vo) donates electrons to the conduction band minimum, causing a large negative shift in Vth. Therefore, the improved stability of IYZO TFT indicates that Yb doping effectively reduced formation of defect state like deep level Vo, which was demonstrated by theoretical density functional calculations. In addition, the mobility of the IYZO TFT was 11.86 cm2V-1s-1, which was 2% better than that of the IZO TFT (11.63 cm2V-1s-1). Conversely, the mobility of the IGZO TFT was 10.13 cm2V-1s-1, demonstrating a 13% decrease compared to the IZO TFT. Notably, Ga doping improved the stability but degraded the electrical performance, whereas Yb doping improved the stability and electrical properties.