This study reports the performance and stability of hafnium-indium zinc oxide (HflnZnO) thin film transistors (TFTs) with thermally grown SiO(2). The HflnZnO channel layer was deposited at room temperature by a co-sputtering system. We examined the effects of hafnium addition on the X-ray photoelectron spectroscopy properties and on the electrical characteristics of the TFTs varying the concentration of the added hafnium. We found that the transistor on-off currents were greatly influenced by the composition of hafnium addition, which suppressed the formation of oxygen vacancies. The field-effect mobility of optimized HflnZnO TFT was 1.34 cm(2) V(-1) s(-1), along with an on-off current ratio of 10(8) and a threshold voltage of 4.54 V. We also investigated the effects of bias stress on HflnZnO TFTs with passivated and non-passivated layers. The threshold voltage change in the passivated device after positive gate bias stress was lower than that in the non-passivated device. This result indicates that HflnZnO TFTs are sensitive to the ambient conditions of the back surface. (C) 2011 Elsevier B.V. All rights reserved.