Low-temperature fabrication of an HfO passivation layer for amorphous indium-gallium-zinc oxide thin film transistors using a solution process.

We report low-temperature solution processing of hafnium oxide (HfO) passivation layers for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). At 150 °C, the hafnium chloride (HfCl) precursor readily hydrolyzed in deionized (DI) water and transformed into an HfO film. The fabricated HfO passivation layer prevented any interaction between the back surface of an a-IGZO TFT and ambient gas. Moreover, diffused Hf in the back-channel layer of the a-IGZO TFT reduced the oxygen vacancy, which is the origin of the electrical instability in a-IGZO TFTs. Consequently, the a-IGZO TFT with the HfO passivation layer exhibited improved stability, showing a decrease in the threshold voltage shift from 4.83 to 1.68 V under a positive bias stress test conducted over 10,000 s.