We report on the fabrication and performance of amorphous oxide thin film transistors with indium zinc oxide (In(2)O(3):ZnO = 1:1 mol%) and various ratios of hafnium-doped indium zinc oxide (IZO:HfO(2) = 2:0, 0.3, 0.7, and 1.1 mol%) deposited at the same deposition conditions for semiconductor channel layer. The carrier concentration (N(cp)) of the HIZO films was further decreased from 7.08 x 10(17) to 5.0 x 10(16) cm(-3). This indicates that Hf metal cations effectively suppress carrier generation due to the high electron negativity (1.3) of Hf. In addition, we compared bias instability of both devices after bias temperature stress (US) test under on-current state at V(DS) of 10 V and I(DS) of 3 mu A at 60 degrees C for 420 min. It was found that the Hf metal cations could be effectively incorporated in the IZO thin films as a suppressor against both the oxygen deficiencies and the carrier generation in the ZnO-based system. (C) 2011 Elsevier B.V. All rights reserved.