Enhancement in Performance and Reliability of Fully Transparent a-IGZO Top-Gate Thin-Film Transistors by a Two-Step Annealing Treatment

A two-step annealing treatment was applied on a fully transparent amorphous InGaZnO4 (a-IGZO) top-gate thin-film transistor (TG-TFT) to improve the device performance. The electrical properties and stabilities of a-IGZO TG TFTs were significantly improved as the first-annealing temperature increased from 150 °C to 350 °C with a 300 °C second-annealing treatment. The a-IGZO TG-TFT with the 300 °C first-annealing treatment demonstrated the overall best performance, which has a mobility of 13.05 cm²/(V·s), a threshold voltage (<i>V</i>_th) of 0.33 V, a subthreshold swing of 130 mV/dec, and a <i>I</i>_on/<i>I</i>_off of 1.73 × 10⁸. The <i>V</i>_th deviation (Δ<i>V</i>_th) was -0.032 V and -0.044 V, respectively, after a 7200 s positive and negative bias stress under the gate bias voltage <i>V</i>_G = ±3 V and <i>V</i>_D = 0.1 V. The Photoluminescence spectra results revealed that the distribution and the density of defects in a-IGZO films were changed after the first-annealing treatment, whereas the X-ray photoelectron spectroscopy results displayed that contents of the oxygen vacancy and Ga-O bond varied in annealed a-IGZO films. In addition, a-IGZO TG-TFTs had achieved a transmittance of over 90%. Research on the effects of the first-annealing treatment will contribute to the fabrication of highly stable top-gate TFTs in the fields of transparent flexible electronics.