Instead of the conventional furnace annealing process with a temperature higher than 300 degrees C, two low temperature annealing methods are successfully demonstrated to suppress the instability problem of amorphous indium gallium zinc oxide (IGZO) thin film transistors (TFTs). With adequate Nd:yttrium aluminum garnet laser (266 nm) annealing energy density or Xe excimer UV lamp (172 nm) irradiation time, the on voltage shift is greatly suppressed from over 10 to 0.1 V. The influence of laser energy density and UV lamp irradiation time on the performance of IGZO TFTs is also investigated and explained. The proposed methods are promising for the development of amorphous IGZO TFTs on flexible substrates.