Annealing-Temperature-Dependent Electrical and Optical Performance of Solution-Processed Amorphous IGZO TFTs

Solution-processed amorphous InGaZnO (IGZO) thin-film transistors (TFTs) were investigated across a higher-Ga composition regime to examine the relationship between annealing-induced structural changes, film properties, and TFT performance. IGZO precursor solutions were prepared using a sol–gel process, and the films were annealed at 300, 350, and 400 °C. After determining a suitable annealing condition, the effect of the In:Ga:Zn ratio was examined using three compositions: 3:3:3, 3:4:3, and 3:5:3. The films and TFTs were characterised using structural, surface, optical, and electrical measurements. The results show that higher annealing temperatures promote structural changes and the onset of crystallisation, while annealing at 300 °C provides a suitable condition for maintaining the amorphous structure and high optical transparency of the IGZO layer. Changing the metal composition also affects the electrical behaviour of the devices: increasing the Ga content reduces the off-state current, but excessive Ga content leads to a reduction in carrier mobility. The device with an In:Ga:Zn ratio of 3:4:3 exhibited the best overall performance, with an on/off current ratio of 1.31 × 107, a subthreshold swing of 0.31 V/dec, a threshold voltage of −0.56 V, an off-state current of 2.25 × 10−13 A, and a field-effect mobility of 20.32 cm2 V−1 s−1. The corresponding IGZO film showed an average optical transmittance above 90%. The combination of high transparency, low off-state current, and good switching characteristics makes the optimised IGZO TFTs promising for sensor applications, transparent electronics, and emerging artificial intelligence related electronic systems.