Positive bias stress reliability of InSnO TFTs: Analysis and Improvement strategies

• Systematic study of InSnO thin-film transistors with various channel thickness. • Illustration of the reliability dependent on the thickness and environment. • InGaZnO passivation remarkably improves reliability without negative effects. • The passivation method is compatible with the large-area manufacturing process. • Passivated devices realize excellent tradeoff between mobility and reliability. In this work, the electrical properties and positive bias stress (PBS) reliability of InSnO (ITO) thin-film transistors (TFTs) with various channel thicknesses (t ch = 4 nm, 5 nm, 6 nm) are systematically investigated. The positive threshold voltage variation (ΔV th ) occurs for the ITO TFT under PBS and the ΔV th diminishes with increasing t ch at the same stress time. The density of traps (N trap (E)) are calculated from high- and low-frequency capacitance measurements before and after PBS. The 6 nm-t ch TFT owns the lower N trap (E), due to the better quality of ITO film with fewer traps before PBS. During PBS, the absorbed ambient oxygen at the back channel captures electrons and contributes to the augment of N trap (E) due to the generation of acceptor-like defects (O and O - ). The reliability of the ITO TFTs can be significantly enhanced by incorporating a 40-nm a-IGZO passivation layer, which effectively isolates the back channel from the atmosphere. The a-IGZO passivation layer reduces the ΔV th of the ITO TFT by 80 %, without adversely affecting the electrical properties. This work elucidates the mechanisms underlying the PBS reliability of ITO TFTs for the first time and presents a strategy compatible with the large-area and low-temperature manufacturing process for improving the reliability of ITO TFTs.