Electrical instabilities of a-IGZO TFTs under different conditions of bias and illumination stress

Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) have been widely applied in display technologies. An important factor of these devices is the electrical stability to avoid misinterpretations of current or voltage values under different conditions such as: bias stress, recovery time, and illumination. This work presents the effects of ΔVT under positive bias stress, negative bias stress, positive bias illumination stress, negative bias illumination stress (PBS, NBS, PBIS, NBIS), stress recovery, cyclic bias stress, hysteresis, fixed bias, and aging effects. It was found that a full recovery was achieved only under illumination because of the de-trapping effect (PBS) and ionization of oxygen vacancies (NBS). Some tests showed a low ΔVT over time, however, some considerations must be taken to carry out this purpose. Finally, fixed polarization under illumination was shown to find a stable operating region over time showing negligible variations upon aging.