Positive Bias Instability in ZnO TFTs with Al₂O₃ Gate Dielectric

Positive bias instability stress (PBI) was done on ZnO thin-film transistors (TFTs) with Al₂O₃ deposition at 100°C and 250°C. The threshold voltage (VT), transconductance (g ₘ), and subthreshold slope (SS) were monitored where the 100°C samples demonstrated a 'turn-around' phenomenon in the ΔVₜ compared to the 250°C samples. The 250°C samples show consistent ΔVₜ, suggesting a higher Al₂O₃ deposition temperature results in the absence of the defect responsible for the 'turn-around' effect. Both sets also demonstrate negligible degradation in Δgₘ and ASS -suggesting little to no influence on the Vₜ shift by interfacial state generation. © 2019 IEEE.