P-11: DC/AC Electrical Instability of R.F. Sputter Amorphous In-Ga-Zn-O TFTs

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