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

摘要

We investigated the hump characteristics of amorphous indium-gallium-zinc oxide thin-film transistors. The device showed a field effect mobility of 24.3cm~2V~(-1)s~(-1), a threshold voltage (V_(th)) of 4.8V, and a subthreshold swing of 120mV/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.