Instability of p-channel poly-Si thin-film transistors under dynamic negative bias temperature stress

Degradation of p-channel poly-Si thin-film transistors (TFTs) under dynamic negative bias temperature (NBT) stress has been investigated. Two-stage degradation behavior is first observed. In the first stage, significant positive threshold voltage (V_th) shift occurs. The dynamic effect which is associated with pulse falling time (t_f) and amplitude may be responsible for the instability. Short t_f and high amplitude will introduce more significant dynamic effect. After a long time stress, “turnaround” behavior in the V_th is observed. Equivalent DC negative bias temperature instability is the dominate degradation mechanism.