Glass-substrate-based high-performance ZnO-TFT by using a Ta2O5 insulator modified by thin SiO2 films

Thin SiO2 films were used to modify the Ta2O5 insulator (STS) in the ZnO-TFTs fabricated at room temperature by RF magnetron sputtering. The performance of the device was obviously improved after adding thin SiO2 layers, such as: enhancement of on/off ratio by one order of magnitude, reduction of the subthreshold swing from 0.32 to 0.28 V/dec, increase of the field effect mobility (from 46.2 to 52.4 cm(2)/V s), as well as reduction of the hysteresis in I-DS versus V-GS curves and capacitance voltage characteristics. The capacitance voltage and C-2 versus voltage characteristics were investigated, from which the trapped charge density at or near the interface between insulator and ZnO layer as well as the carriers concentration of the ZnO film are calculated. The performance enhancements are attributed to the reduce of leakage current, smoother surface morphology, and suppress of charge trapping by using SiO2 films to modify the high-kappa Ta2O5 dielectric. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim