Two-step Electrical Degradation Behavior in α-InGaZnO Thin-film Transistor Under Gate-bias Stress

Investigated transfer characteristics on threshold voltage instability behavior in amorphous indium-gallium-zinc oxide thin-film transistor (α-IGZO TFT). A two-step electrical degradation behavior of α-IGZO TFT was found under gate-bias stress. A usual small positive shift followed by a special negative shift of threshold voltage is characterized in the α-IGZO TFT device. We suggest that the positive shift of the threshold voltage is due to the charge trapping in the gate dielectric and/or at the channel/dielectric interface, while the negative shift of threshold voltage is assigned to electric field-induced extra electron carriers from H
₂
O molecules in the back channel protective layer. We conclude that the H
₂
O molecules and the quality of passivation layer affect the degradation behavior of α-IGZO TFT devices.