Investigation of Degradation Behavior during Illuminated Negative Bias Temperature Stress in P-channel Low-Temperature Polycrystalline Silicon Thin-Film Transistors

In this letter, a study of physical mechanisms is introduced to describe an abnormal phenomenon in transfer characteristics while p-type low-temperature polycrystalline silicon thin-film transistors (LTPS TFTs) were subjected to a negative bias temperature stress (NBTS) in an illuminated environment. In general, under NBTS, the transfer characteristics exhibits a negative shift of threshold voltage and a degradation of subthreshold swing. Here, however, experimental results reveal that the degree of degradation is different after NBTS is applied to poly-silicon TFTs in a darkened and in an ultraviolet condition. This variation is mainly a result of the light-generated electrons recombining with the inversed holes, and leading to a lower degree of degradation. Moreover, we found that the influence of the UV light is an edge effect at different channel lengths. This letter investigates the illumination effect in LTPS TFTs during NBTS, and the phenomenon is clarified by electrical measurements and by trap state extraction.