DC/AC Electrical Instability of RF Sputter Amorphous In-Ga-Zn-O TFTs

The paper presents the study of electrical instability of RF sputter amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor (TFT) induced by negative steady-state (or D.C.) bias-temperature-stress (BTS). Similarly to positive BTS results [8], the stress time evolution of the threshold voltage shift (Delta V-th) induced by negative BTS under different stress voltages and temperatures can all be described by the stretched-exponential model. For the first time, we also present the results for Delta V-th under pulse (or A.C.) BTS. The Delta V-th for positive A. C. BTS is found to have a pulse period dependence while a huge reduction of AV,h is found for all negative A.C. BTS results. This might suggest the lime for holes to accumulate near the a-IGZO/SiO2 interface is much longer than the time for electrons. The effect of bi-polar stressing is also discussed.