Effects of Al2O3 gate insulator on the instability of amorphous indium-gallium zinc oxide thin film transistors

This study analyzes bottom-gated amorphous indium-gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with different gate insulators of Si3N4 and Si3N4/Al2O3. The aim is to investigate the effect of Al2O3 on the instability of IGZO TFTs with respect to native point defects. Although the DC properties of Si3N4/Al2O3 devices are inferior to those of Si3N4 devices, the bias stress-induced hump is not observed in Si3N4/Al2O3 devices. From calculations of the oxygen exchange kinetics between the insulator and IGZO, it appears that more oxygen atoms diffuse from Al2O3 to the IGZO than from the Si3N4. This oxygen diffusion is confirmed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Auger electron spectroscopy depth-profiling analysis. In addition, more oxygen interstitials with fewer zinc interstitials are detected at the IGZO interface with Al2O3. From the results, it can be concluded that the distribution of native defects in Al2O3 devices reduces the instability of IGZO TFTs.