Depth-Profiling Study on Amorphous Indium–Gallium–Zinc Oxide Thin-Film Transistors by X-ray Photoelectron Spectroscopy

We performed an X-ray photoelectron spectroscopy (XPS) depth-profiling study on the materials used in amorphous indium–gallium–zinc oxide thin-film transistors (a-IGZO TFTs) with Ti and Mo source/drain (S/D) electrodes. The XPS results suggested that there are some differences between the interface regions of Ti/a-IGZO and Mo/a-IGZO for different chemical states of the materials. The chemical states of the back-channel surfaces were also found to be different between the TFTs with Ti and Mo S/D electrodes. In addition, we fabricated indium–gallium–zinc–titanium oxide composite thin films by deposition using multitarget co-sputtering. The electronic structure of these films observed by XPS is similar to that of the Ti/a-IGZO interface region. The fabricated films were found to have a very low resistivity, much lower than that of an a-IGZO film using typical TFT fabrication processes.