High performance and transparent amorphous indium gallium zinc oxide thin-film transistors (a-IGZO TFT) have been successfully fabricated on the colorless polyimide plastic substrate using a high quality HfO2 dielectric film formed by the low temperature atomic layer deposition process as the gate insulator. Besides, the effects of source/drain material, ITO film and Mo metal, are also studied and compared in this work. With the optimized process condition, the devices with ITO source/drain exhibit a high ION/IOFF current ratio of ∼4.25 × 1011, a lower sub-threshold swing value of 0.087 V/decade, a desirable positive threshold voltage value of 0.1379 V and an acceptable field effect mobility of 19.69 cm2/Vs. while it also shows excellent reliability characteristic and low hysteresis. These results may appear highly promising potentials for the next generation fully transparent flexible display application.