Growth of high quality polycrystalline InGaO thin films by spray pyrolysis for coplanar thin-film transistors on polyimide substrate

The current mobile devices are moving towards flexible electronics. Introducing crystalline oxide semiconductors on flexible substrates is important to satisfy the requirements of high-resolution displays on flexible substrates. This study investigates the low-cost, as-grown polycrystalline (Poly) InGaO thin film transistor by spray pyrolysis on polyimide (PI) substrate. Grazing Incidence X-ray Diffraction (GI-XRD) measurements demonstrate that In _0.8Ga _0.2O, In _0.7Ga _0.3O, and In _0.5Ga _0.5 O compositions exhibit crystallization on-set temperatures of ∼330, ∼350, and ∼415°C, respectively. Poly-In _0.7Ga _0.3 O thin film with lower oxygen-vacancy (∼15 %) and less than 5 % O-H group could be achieved at the substrate temperature of 370°C. The hysteresis-free device performance with an average saturation mobility of 43.73 cm ²V ⁻¹s ⁻¹ has been obtained using the poly-In _0.7Ga _0.3O with optimized N ₂ O plasma treatment on the poly-oxide thin film. The TFTs show remarkable stability under humid environments and various stress conditions such as positive bias temperature, negative bias temperature, and mechanical stresses. In addition, the 96-stage gate shift register made of poly-In _0.7Ga _0.3 O TFTs by spray pyrolysis exhibits the rising and falling times of less than 820 ns. Therefore, the poly-In _0.7Ga _0.3 O TFTs by spray pyrolysis could be used for high-resolution, cost-effective, flexible active-matrix light-emitting displays.