Improvement of photo-induced negative bias stability of oxide thin film transistors by reducing the density of sub-gap states related to oxygen vacancies

Abstract

The optical absorption in the sub-gap region of amorphous indium zinc oxide films and the photo-induced negative bias stability of the resulting thin film transistors were studied. As the indium ratio increases, optical absorption via sub-gap states increases, and the threshold voltage degradation under negative bias temperature stress (NBTS) with light illumination becomes more severe. By applying high pressure anneal treatments in oxygen ambient, the density of sub-gap states is reduced by an order of magnitude compared to air-annealed devices. Consequently, significant improvements are observed in the threshold voltage shifts and the stretched exponential parameters under NBTS with light illumination.