Role of Rare Earth Ions in Anodic Gate Dielectrics for Indium-Zinc-Oxide Thin-Film Transistors

Al-alloys and their anodic oxides were used as the gate and the gate dielectric, respectively, for the indium-zinc-oxide (IZO) thin-film transistors (TFTs). The influence of the Al-alloys on the performances of the IZO-TFTs was investigated. It was found that the hillock formation could be completely suppressed by doping neodymium (Nd) or cerium (Ce) into Al. However, the mobility of the IZO-TFT with Al-Ce gate was only 2 × 10 −4 cm 2 V −1 s −1 , about five orders lower than that of the IZO-TFT with Al-Nd gate (11.6 cm 2 V −1 s −1 ). Further analysis showed that Ce 3+ and Ce 4+ ions were existence in the oxide film obtained by anodizing Al-Ce alloy, and they would diffuse into IZO film. The Ce 4+ ion could act as an electron trap due to its strong oxidizability, so the IZO-TFTs with Al-Ce gate would experience seriously degradation. In the case of the oxide film obtain by anodizing Al-Nd alloy, only Nd 3+ were found, which was stable and would not produce electron traps. Moreover, the existence of Nd would suppress undesirable free electron formation in the channel, resulting in low off-current, low subthreshold swing, little hysteresis, and high electrical stability under gate bias stress.