Enhanced electrical properties and stability of solution processed IYZO thin film transistors by controlling 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 indium–gallium–zinc oxide (IGZO) TFTs with gallium (Ga) as a typical dopant. In particular, under a negative bias illumination stress (NBIS), among the various operating condition stability evaluations, the Δ threshold voltage (V_th) of the IGZO (Ga: 3%) TFT (−7.6 V) was 23% better than that of the IZO TFT (−9.8 V); however, ΔV_th of the IYZO (Yb: 3%) (−5.8 V) TFT was not only 41% 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 (V_O) donates electrons to the conduction band minimum, causing a large negative shift in V_th. Therefore, the improved stability of the IYZO TFT indicates that Yb doping effectively reduced the formation of defect state like deep level V_O, which was demonstrated by theoretical density functional calculations. In addition, the mobility of the IYZO TFT was 12.22 cm² V⁻¹ s⁻¹, which was 3% better than that of the IZO TFT (11.83 cm² V⁻¹ s⁻¹). Conversely, the mobility of the IGZO TFT was 10.34 cm² V⁻¹ s⁻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.