Solution-Processed Oxide TFT Based on Bilayer Channels With Graded Oxygen Vacancy

In this study, thin film transistors (TFTs) based on metal oxide with a regulated channel prepared by solution process were fabricated. The front channel was composed of indium zinc oxide (IZO) thin film, while the back channels were composed of hafnium (Hf) doped IZO (HIZO) thin film with various doping concentrations. It is confirmed that the oxygen ions in IZO can be adsorbed by Hf in HIZO layer and the concentration of oxygen vacancies in the front and back channel can be regulated after the subsequent annealing process, which forms a vertically graded oxygen-vacancy in the IZO/HIZO film. The field effect mobility and the device stability have been improved, and the TFT based on IZO/HIZO with Hf doping concentration of 15% exhibits the highest performance including on/off current ratio of ${2}.{3}\times {10} ^{{8}}$ , mobility of 7.08 cm2/Vs and excellent positive bias temperature stress (PBTS) and negative bias illumination stress (NBIS) stability. Additionally, the transparent IZO/HIZO TFT based on ZrO2 dielectric was demonstrated on ITO glass and a field-effect mobility of 20.64 cm2/Vs is obtained. This work provides an effective way for low-cost and high-performance transparent TFT.