In this work, we report on high-performance coplanar self-aligned (SA) amorphous-Indium-Tin-Zinc-Oxide (a-ITZO) thin-film transistors (TFTs) on flexible polyimide substrate. The a-ITZO films are first optimized with respect to the oxygen ratio, thickness and final anneal conditions with common-gate TFTs structure on Si/SiO 2 substrate. Optimized TFTs show mobility (μ lin) between 20.0-25.0 cm 2 /(V.s). Material characterization revealed some degree of order compared to a truly amorphous film like a-IGZO but no grain boundaries or crystalline domains were observed. The a-ITZO films were integrated in coplanar SA TFT architecture on polyimide using hydrogen rich plasma (SiH 4 based chemistry) as dopant for the source/drain (S/D) regions resulting in field-effect mobility (μ FE) of 27.0 cm 2 / (V.s), sub-threshold slope (SS −1) of 0.40 V/decade and I ON /I OFF ratio of >10 8. The threshold voltage shifts of the TFTs under both positive and negative gate bias stress of 1MV/cm for 10 4 seconds were less than 1.5 V. We have also investigated the applicability of the SA a-ITZO TFTs in logic circuitry such as 19-stage ring-oscillators (ROs).