As-Grown Crystalline InGaZnO by Spray Pyrolysis on a Flexible Substrate for a Thin-Film Transistor with Excellent Stability

The development of low-cost, high-mobility oxide thin-film transistors (TFTs) with excellent stability is of increasing interest. The coplanar oxide TFTs can be used for high-speed, large-area, and high-resolution displays. Here, we report highly oriented, as-grown crystalline InGaZnO (c-IGZO) with very low oxygen vacancy defects using spray pyrolysis at the substrate temperature of 425 °C. The c-IGZO exhibits a highly oriented, c -axis aligned crystal perpendicular to the substrate with a high mass density of 6.73 g cm –3 without any disordered incubation layer. Its resistivity can be decreased to 0.42 mΩ cm by NF 3 plasma doping, which is essential to achieving high-performance coplanar TFT. We have demonstrated the application of this material to high-performance flexible TFTs. The self-aligned, coplanar c-IGZO TFTs on the polyimide substrate exhibit an average field-effect mobility of 39.60 cm 2 V –1 s –1, threshold voltage of −1.00 V, subthreshold swing of 0.21 V dec –1, and on/off current ratio over 10 8 . The ring oscillator and gate driver made of the c-IGZO TFTs exhibit a propagation delay of 8.77 ns/stage and rising/falling times of 648/564 ns, respectively. Therefore, the as-grown c-IGZO by spray pyrolysis has the potential to be utilized as a new oxide semiconductor for the production of low-cost, flexible TFT electronics.