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

Abstract 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.