Suitability of sol-gel derived amorphous and crystalline compositions of In-Ga-Zn oxide for thin film transistors

The present work focusses on thin film transistor (TFT) devices with polycrystalline and amorphous Indium-Gallium-Zinc-Oxide (IGZO) thin films fabricated using solution processing. Since it is easier to vary composition through solution processing, we have investigated suitability of various chemical compositions for TFT applications. We have found that a common composition In:Ga:Zn::1:1:1 used in sputtering leads to a crystalline film through solution processing route; the sputtered film is amorphous. Thus, we have systematically varied the composition to obtain amorphous phase with composition 3:1:5. Further, we report that both Zn/Ga and In/Ga ratio should be high in order to obtain amorphous films, but still some Ga must remain present to obtain acceptable resistivity. Thin film transistors fabricated using these compositions shows n-channel enhancement mode operation. The saturation mobility is found to be highest (0.39 cm²/V-s) for the amorphous composition with on-off ratio of the order of ~10³.