The effect of the channel deposition pressure on the device performance of amorphous indium-gallium-zinc oxide (a-IGZO) transistors was investigated in detail. The performance of the fabricated transistors improved monotonously with decreasing chamber pressure: at a pressure of 1 mTorr, the field-effect mobility (mu(FE)) and subthreshold gate swing (S) of the a-IGZO thin-film transistors were dramatically improved to 21.8 cm(2)/Vs and 0.17 V/decade, respectively, compared to those (11.4 cm(2)/Vs and 0.87 V/decade) of the reference transistors prepared at 5 mTorr. This enhancement in the subthreshold characteristics was attributed to the reduction of the bulk defects of the a-IGZO channel, which might result from the greater densification of the a-IGZO films at the lower deposition pressure. (c) 2008 The Electrochemical Society.