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In this paper, the behavior of the low-temperature polycrystalline-silicon (LTPS) thin film transistors (TFTs) during x-ray irradiation and gate bias voltage (V G ) simultaneously is analyzed. Both n-type and p-type LTPS TFTs show negative shifts of threshold voltage under same dose of x-ray irradiation, regardless of the V G polarity, while the field effect mobility of n-type LTPS TFT keeps fairly well. The degradation of subthreshold swing is attributed to the interface states, which can be repaired by 300 °C annealing. A model is proposed to explain the results for different V G , and verified by changing the thickness of the gate oxide. More irradiation-induced holes are trapped by the far defects owing to the electric field. This study can be helpful to develop more stable devices or circuits for the application of x-ray image sensors.

In this paper, the reaction rate of oxygen vacancy (V O ) by the derivatives of threshold voltage (Vth) in the amorphous indium-gallium-zinc oxide thin-film transistors under light pulses with altering duty ratios is investigated. More importantly, after collecting and analyzing a lot of experimental results, a comprehensive model named V O pool is proposed. The proposed model can more universally describe the characteristic of V O reacting to the light and its degradation behavior under various kinds of stress condition.INDEX TERMS Amorphous indium gallium zinc oxide (a-IGZO), thin-film transistors (TFTs), reaction rate, illumination effect, multiple-pulse illumination, response time, oxygen vacancy.