Abstract — A unified model is proposed to consistently explain
the degradation behaviors of a-IGZO TFTs under different light
illumination and gate bias stress conditions. In the proposed
model, photo-excited double ionized oxygen vacancies (Vo
2+) traps
and their transportation under the electric field are two key
factors that cause the threshold voltage (Vth) shift of TFTs.
Additional traps generated during the formation of Vo
2+ also
deteriorate the subthreshold characteristics.