The Effect of Oxygen Partial Pressure during Active Layer Deposition on Bias Stability of a-InGaZnO TFTs

The effect of oxygen partial pressure (P_O2) during the channel layer deposition on bias stability of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) is investigated. As P_O2 increases from 10% to 30%, it is found that the device shows enhanced bias stress stability with significantly reduced threshold voltage drift under positive gate bias stress. Based on the x-ray photoelectron spectroscopy measurement, the concentration of oxygen vacancies (O_V) within the a-IGZO layer is suppressed by increasing P_O2. Meanwhile, the low-frequency noise analysis indicates that the average trap density near the channel/dielectric interface continuously drops with increasing P_O2. Therefore, the improved interface quality with increasing P_O2 during the channel layer deposition can be attributed to the reduction of interface O_V-related defects, which agrees with the enhanced bias stress stability of the a-IGZO TFTs.