Effects of defect creation on bidirectional behavior with hump characteristics of InGaZnO TFTs under bias and thermal stress

We investigated the hump characteristics of amorphous indium–gallium–zinc oxide thin-film transistors. The device showed a field effect mobility of 24.3 cm 2 V −1 s −1 , a threshold voltage ( V th ) of 4.8 V, and a subthreshold swing of 120 mV/dec. Under positive gate bias stress, V th showed bidirectional shift with a hump. V th was positively and negatively shifted in the above-threshold and subthreshold regions, respectively. At high temperatures, V th was more positively shifted without bidirectional shift. Under simultaneous drain bias stress ( V DS,stress ), the hump was maintained. However, the bidirectional shift was not observed with an increasing V DS,stress . The hump and positive shift are related to the defect creation of the shallow donor-like and deep-level acceptor-like states, respectively. We performed a two-dimensional device simulation to further investigate this phenomenon. By varying the peak values of the Gaussian shallow donor-like and deep acceptor-like states, we qualitatively confirmed the relationship between the two states and transfer curve changes.