Effects of the Al ₂ O ₃ interlayer in ZnO thin-film transistors fabricated via atomic layer deposition

In this paper, electrical analysis was carried out on ZnO thin-film transistors (TFTs) to investigate the effects of the Al2O3 interlayer between the ZnO active-layer and the SiO2 gate insulator. The Al2O3 interlayer was deposited via atomic layer deposition. From the electrical analysis, it was found that the Al2O3 interlayer improves the electrical properties, such as the subthreshold slope and on/off-current ratio. The stability degradation under positive bias stress, however, is severe in TFTs with an Al2O3 interlayer. According to the crystallographic view, the crystal structures in a ZnO film on Al2O3 are prone to align in the (002) direction compared with ZnO on SiO2, and can attract more oxygen ions because of the Zn polar, which degrades the stability of devices.