Low Cost, Al2O3 and ZrAlOx Stack Passivation by Spray Pyrolysis for Highly Stable Amorphous InGaZnO Thin-Film Transistors

A stack passivation by spray pyrolysis is demonstrated for high performance and stable amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The device performances and stabilities of a-IGZO TFTs are compared with single zirconium-aluminium-oxide (ZAO), aluminium oxide (Al2O3), and stack ZAO/Al2O3 and Al2O3/ZAO passivation layers. The a-IGZO TFTs with Al2O3/ZAO stack exhibit high performance and excellent stabilities under electrical, thermal, and environmental tests with negligible threshold voltage shift. The origin of the device performances and improved stabilities are analyzed using X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy analyses. It is found that the Zr elements diffuse into the a-IGZO channel when ZAO is directly deposited on the a-IGZO, resulting in the deterioration of the device performance. It is also found that the Al2O3 single layer on top of the a-IGZO cannot protect the back-channel from moisture diffusion. But a thin Al2O3 layer on top of the TFTs can protect the diffusion of Zr elements from ZAO into the a-IGZO channel and enhances the performance and stabilities. Therefore, the low cost, Al2O3/ZAO stack by spray pyrolysis on the sputtered a-IGZO can be an excellent passivation for highly stable metal-oxide TFTs.