Light induced instabilities in amorphous indium–gallium–zinc–oxide thin-film transistors

The effect of exposure to ultraviolet radiation on the characteristics of amorphous indium–gallium–zinc–oxide thin-film transistors (TFTs) fabricated by sputtering is investigated. After illumination with 1.5 mW cm−2 of 365 nm radiation, in the absence of any bias stress, a persistent negative shift in the characteristics is observed in the dark. The magnitude of the shift increases with exposure time, saturating after about 10 min. Under these conditions the subthreshold exhibits a rigid shift of around 3.6 V and 7.5 V for TFTs with an active layer thickness of 20 nm and 50 nm, respectively. The shift in the dark increases (decreases) when a negative (positive) bias stress is applied under illumination. The instability behavior caused by exposure to light, in the absence of any bias stress, can be explained on the basis of ionization of neutral oxygen vacancies.