Here, we report scaling effects on the electrical properties of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs). The a-IGZO TFTs had same channel width/length ratio (W/L = 20), but different channel lengths (L = 20, 10, 5, and 2.5 mu m). To examine the scaling-down behaviors, short-channel effects and contact resistance of the TFTs were investigated. As the channel length decreased, apparent shift of threshold voltage (V-th) and degradation of subthreshold swing (S-SUB) were shown. In addition, it is also found that the field-effect mobility (mu(FE)) was degraded as the channel length was decreased which was originated from contact resistance. Due to this contact resistance effect, drain current (I-DS) was decreased for short-channel devices. (C) 2011 Elsevier B.V. All rights reserved.