A Unified Degradation Model of a-InGaZnO TFTs Under Negative Gate Bias With or Without an Illumination

Degradation behaviors of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) under negative bias stress (NBS) and negative bias illumination stress (NBIS) are investigated systematically. In some cases, a two-stage degradation behavior of a-IGZO TFTs is observed under both NBS and NBIS, which begins with a small positive shift of threshold voltage (V
_th
), and is followed by a large negative V
_th
shift. There is an intrinsic correlation between the degradations of NBS and NBIS. Quantitatively, both stress gate biases (V
_G
) and temperature dependencies of ΔV
_th
of the two degradations are found to be the same and the recovery processes are also very similar. A unified model of NBS and NBIS is proposed to consistently explain the degradation behaviors of a-IGZO TFTs and their correlation.