In recent years, amorphous indium-gallium-zinc-oxide (α-IGZO) thin-film transistors (TFTs) with much better performance compared with the low-temperature polysilicon (LTPS) counterpart have been demonstrated [1-2], nevertheless, continuous efforts are still urged to further polish its electrical properties for display application. To strengthen field effect and reduce gate leakage current, many research works have been focused on the feasibility of other alternative high-κ dielectric for α-IGZO TFTs . In the present work, the use of co-sputtered zirconium silicon oxide (ZrSiOx) gate dielectrics to improve both mobility and subthreshold swing (SS) of α-IGZO TFT is proposed and demonstrated. The ZrSiOx dielectric is expected to have a good compromise between the field effect (κ-value) and gate leakage current, because silicon dioxide (SiO2) is with the widest bandgap and zirconium dioxide (ZrO2) could have a much better interface with α-IGZO in comparison with hafnium dioxide (HfO2) . The suitable RF power ratio for the co-sputtering of ZrO2 and SiO2 targets at room temperature to maximize the role of ZrSiOx dielectrics is investigated. Immunity of poly-structure formation of the ZrSiOx dielectrics with RF power ratio (ZrO2:SiO2) > 2 found in experiments is examined. In addition, effect of post annealing after dielectric deposition (PA) on device performance are also studied.