Characterization of density-of-states and parasitic resistance in a-InGaZnO thin-film transistors after negative bias stress

Instability mechanism of amorphous InGaZnO thin-film transistors under negative bias stress (NBS) was investigated. After strong NBS stress, we observed a negligible change in the subthreshold swing which is strongly dependent on the subgap density-of-states (DOS). On the other hand, there was substantial increase in the drain current at above-threshold operation. Therefore, the dominant mechanism of the NBS-induced instability is investigated not to be a change in the subgap DOS but a change in the parasitic resistance caused by the reduced Schottky barrier of the metal contacts. This was verified by the extracted source/drain resistance and Technology Computer-Aided Design simulation.