Instability Behavior of Oxide-based Top-gate TFTs under Electrical and Optical Stress Test

We report instability behavior of oxide-based top-gate thin-film transistors under electrical and optical stresses. For electrical stress, transfer curve shifts to the right and left for positive and negative gate stress voltages, respectively, while sub-threshold slope (SS) barely changed for both cases. Although this behavior is consistent with the previously reported oxide-based TFT instability behavior explained by charge trapping mechanism, threshold voltage shift seemed to have power-law-time dependency unlike the previous results. We also tested optical stress behavior of the oxide-based TFTs with a blue power-LED. Under prolonged exposure of 3.5mW/cm2 blue light, both transfer curves under dark and illumination conditions shift to the left, but with significant change in sub-threshold slope for illumination condition. After the electrical and optical stress tests, stress effect was relaxed without any annealing process.