Kinetic stress testing and the influence of long-time anneals on the behavior of IZO thin film transistors

Stability testing of indium-zinc oxide under extreme conditions is necessary before the metal oxide can be deemed a reliable alternative to a-Si as channel layer in thin film transistors (TFTs). In this paper, we apply thermal stress under positive and negative gate bias stress creating practical application conditions. This stress scenario gives greater insight into thermally activated defects in the presence of an electrical field. Operational temperatures of 20 °C, 50 °C, and 80 °C are used, and a more rapid degradation of the devices is seen with increased temperatures. Kink and dip are observed due to the donor-like trapped charges increasing the subthreshold swing and acceptor-like trapped charges reducing the ON current, respectively. Post fabrication, long-time anneals for 12-, 24-, 36-, 48-, and 60-h at low temperatures (150 °C) are performed to alleviate defects. The 48-h annealed TFTs show remarkable stability under extreme temperatures and electric fields maintaining a high ON-OFF ratio (∼10⁸) after 10⁴ s. This is attributed to the reduced density of charges in acceptor-like trap states, modeled to reduce by 58% from a 12-h anneal and to insignificant extent over a 48-h anneal.