Metallization strategies for In2O3-based amorphous oxide semiconductor materials

Amorphous oxide semiconductors based on indium oxide [e. g., In-Zn-O (IZO) and In-Ga-Zn-O (IGZO)] are of interest for use in thin-film transistor (TFT) applications. We report that the stability of amorphous In-Zn-O (a-IZO) used in TFT applications depends, in part, on the metallization materials used to form the source and drain contacts. A thermodynamics-based approach to the selection of IZO metallization materials is presented along with a study of the microstructural stability of a-IZO metallized with Mo and Ti. In situ transmission electron microscopy (TEM), x-ray diffraction, and atomic force microscopy studies are presented that show that the crystallization temperature of a-IZO metallized with Ti is sharply reduced (to congruent to 200 degrees C), while a-IZO metallized with Mo remains amorphous. The effects of the unstable Ti/IZO interface are shown to include: vacancy injection, enhanced amorphous-to-crystal transformation kinetics, interfacial oxide formation, and the lateral growth on adjacent IZO of rutile TiO2 needles.