Mechanism of device instability for unhydrogenated polysilicon TFTs under off-state stress

摘要

The effects of off state stress (V_gs = 0 V, V_ds = 0 to -20 V) on unhydrogenated p-channel polysilicon thin--film transistors (TFTs) were studied. It was observed that the post-stressed subthreshold swing is first improved due to the annealing effect from the interaction of tunnelling electrons and captured holes. As the stress time increases or as the stress bias increases, the generation of traps caused by tunnelling electrons will cancel out the annealing effect and then degrade the subthreshold swing. In addition, the trapping of tunnelling electrons in the gate oxide causes a shift of threshold voltage. However, improving the quality of the gate oxide interface by oxidation of the channel polysilicon on submicrometre bottom-gate TFFs can reduce the impact of the off state stress.