Comprehensive Studies on the Carrier Transporting Property and Photo-Bias Instability of Sputtered Zinc Tin Oxide Thin Film Transistors

This study examined the effects of the chamber pressure, radio frequency power and oxygen flow ratio during channel deposition on the performance and photobias stability of zinc tin oxide (ZTO) thin film transistors (TFTs). The densification of the ZTO thin film allowed the improvement in the field-effect mobility and the suppression in the negative bias illumination stress (NBIS) instability of the resulting TFTs simultaneously, irrespective of the specific process condition. The porosity in the ZTO channel layer was shown to prevent the effective intercalation of the Sn 5s orbital and, thus, deteriorate the field-effect mobility. Furthermore, the increased effective surface area in the porous ZTO film adversely affected the NBIS stability of the resulting TFTs because the porosity-related surface states and oxygen vacancy defects provide the hole trapping centers and the delocalized electron free carrier, respectively. Therefore, the densification of ZTO channel layer is a key factor for the high mobility and good photobias stability of the TFTs. This concept can be applicable for any metal-oxide-TFTs.