Abnormal Two-Stage Degradation on P-Type Low-Temperature Polycrystalline-Silicon Thin-Film Transistor Under Hot Carrier Conditions

In this study, an abnormal two-stage degradation of low-temperature polycrystalline-silicon (LTPS) thin-film transistors (TFTs) on a polyimide flexible substrate after hot carrier stress was investigated. The degradation mechanism was divided into two stages. In the first stage, the increases in capacitance in the off region and transconductance are caused by impact ionization induced electron trapping into the gate insulator (GI) at the drain edge. Furthermore, the threshold voltage (Vth ) shift in the positive direction is caused by electrons flowing back to the source side and trapping into the buffer that induces source barrier lowing. The second stage of degradation, including a Vth shift in the negative direction and a decrease in the transconductance is caused by Joule heating induced negative bias temperature instability (NBTI). Furthermore, NBTI hardly occurs behind the pinch off in the channel and fixed oxide charge does not compensate the trapped electron at drain side which is induced in the first stage.

Automated summary

This study investigates the abnormal degradation of low-temperature polycrystalline-silicon thin-film transistors on a polyimide flexible substrate after hot carrier stress. The degradation mechanism is divided into two stages, with the first stage causing an increase in capacitance and transconductance, and a positive shift in threshold voltage. The second stage is characterized by a negative shift in threshold voltage and a decrease in transconductance, attributed to negative bias temperature instability induced by Joule heating.