Negative-bias illumination stress (NBIS) of amorphous InGaZnO (IGZO) transistors can cause a large negative shift (>7.1 V) in threshold voltage, something frequently attributed to the trapping of photoinduced hole carriers. This work demonstrates that the deterioration of threshold voltage by NBIS can be strongly suppressed by high-pressure annealing under 10 atm O2 ambient. This improvement occurred through a reduction in oxygen vacancy defects in the IGZO film, indicating that a photoinduced transition from VO to VO2+ was responsible for the NBIS-induced instability.

This study examined the effect of the thickness of interfacial indium-tin oxide (ITO) on the performance and bias reliability of zinc-tin oxide (ZTO) thin film transistors (TFTs). The 3.5-nm-thick ITO-inserted ZTO TFTs exhibited superior mobility (43.2 cm2/V s) to that of the ZTO only TFTs (31.6 cm2/V s). Furthermore, the threshold voltage shifts for the ZTO/ITO bi-layer device decreased from 1.43 and −0.88 V (ZTO only device) to 0.46 V and −0.41 V under positive and negative bias stress, respectively. This improvement can be attributed to a decrease in the interfacial trap density for the ITO-inserted ZTO device.

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