Effects of lithium doping and ultraviolet photo-patterning on electrical properties of InGaZnO thin film transistors

Alkali metals, such as Li and Na, have been added in solution-processed oxide thin-film transistors (TFTs) because they improved electrical characteristics of the oxide TFTs. In previous research, however, fine-patterning of the alkali metal-doped oxide layers was not performed due to potential performance degradation during photolithography process. In this work, we demonstrate ultraviolet (UV) photo-patterned solution-processed indium gallium zinc oxide (IGZO) TFTs containing various amount of lithium (Li). For patterning of active layer, we applied deep UV (184 nm, 10% and 254 nm, 90%) photo-patterning process. We also investigated the chemical composition and bonding structures of the Li doped IGZO (Li-IGZO) films. It was found that appropriate Li doping on IGZO films can reduce oxygen vacancies and improved the coordination of the metal-oxygen bonding. In addition, Li-IGZO TFTs showed improved mobility and bias stability compared to un-doped counterparts. We believe that this simple patterning process and Li doping can be applied to other types of the high-performance solution-processed oxide TFTs.