Improved Field-Effect Mobility of In-Ga-Zn-O TFTs by Oxidized Metal Layer

The application of an aluminum (Al) capping layer on top of an In-Ga-Zn-O (IGZO) active layer is proposed to enhance the mobility of IGZO thin-film transistors (TFTs). The Al metal layer forms a very thin and dense oxide film on the surface that prevents further internal oxidation, and an additional AlOx interlayer between Al and IGZO is formed using oxygen in the IGZO back-channel region due to its strong oxidation power. The formation of an aluminum oxide interlayer induces an oxygen-deficient region in the active layer, inducing free carriers that enhance the field-effect mobility from 11.3 to 72.6 cm2/Vs. The device reliability under positive and negative bias stress in the dark is relatively unaffected by the presence of the Al capping layer; however, the stability under negative bias illumination stress is accelerated, likely originating from the ionization of oxygen vacant sites.