Comparative study of electrical instabilities in top-gate InGaZnO thin film transistors with $Al2O3$ and $Al2O3/SiNx$ gate dielectrics

A comparative study was made of the performance and electrical instabilities in amorphous indium-gallium-zinc oxide $(a-IGZO)$ thin film transistors with $Al2O3$ and $Al2O3/SiNx$ gate dielectrics. Steeper subthreshold slope is observed in $Al2O3$ devices, which shows that the density of trap states at the interface of $a-IGZO/Al2O3$ is lower than that of $a-IGZO/SiNx$⁠. Under high bias-stresses, a larger degradation is observed in $Al2O3/SiNx$ devices. The device degradation for both devices are mainly attributed to the charge trapping phenomenon, but the different time dependence of threshold voltage shift shows that trapped electrons are more easily redistributed inside the $Al2O3$ dielectrics.