Effect of Wavelength and Intensity of Light on a-InGaZnO TFTs under Negative Bias Illumination Stress

We investigated degradation mechanism of a-IGZO TFTs under NBIS with different wavelengths λ and intensities I L of light. Negative gate bias was applied for 4000 s while drain and source were grounded, and illuminations with λ = 450, 530, or 700 nm were applied. Illumination with photon energy exceeding ∼2.3 eV (530 nm) induced noticeable change in threshold voltage shift Δ V th , which can be interpreted in terms of ionization of oxygen vacancies V O . In addition, I L of blue illumination (450 nm) was varied from 6 to 200 lux and saturation in Δ V th was observed after exceeding a certain I L . We suggest that the saturation occurs because V O -ionization rate is saturated by outward relaxation of metal atoms in the a-IGZO film.