Improvement of the electrical properties of amorphous indium-gallium-zinc oxide thin-film transistors by cross-linked CYTOP passivation

In this study, we investigated the effect of a cross-linked CYTOP passivation layer on the electrical properties of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). Cross-linked CYTOP passivation showed a deeper fluorine diffusion depth than CYTOP passivation owing to the chemical reaction between the cross-linking agent and IGZO layer. The cross-linking agent reduces the weakly bonded oxygen in the IGZO layer via a chemical reaction, enhancing fluorine diffusion into the IGZO layer. Therefore, the effect of fluorine on the IGZO layer was enhanced by using cross-linked CYTOP as a passivation layer. The diffused fluorine reduced the defect states by passivating the oxygen-related defects such as oxygen vacancies and weakly bonded oxygen and increased the carrier concentration by replacing metal–oxygen bonds with metal-fluorine bonds. IGZO TFTs with cross-linked CYTOP passivation exhibited a threshold voltage of −0.35 V, saturation mobility of 1.93 cm²/V∙s, and subthreshold swing of 0.53 V/dec. Using a cross-linked passivation layer also improved the reliability under positive gate bias stress. Consequently, a cross-linked CYTOP passivation layer can effectively improve the electrical properties of IGZO TFTs by incorporating fluorine atoms into the IGZO layer.