Investigation of phases and chemical states of tin titanate films grown by atomic layer deposition

Although perovskite tin titanate (SnTiO₃, STO) has been predicted to have ferroelectricity with a large spontaneous polarization, the implementation of metastable perovskite STO remains a great challenge. In this study, the atomic layer deposition of STO films was attempted using bis(1-dimethylamino-2-methyl-2-propoxy)tin(II) as the Sn source, titanium-tetrakis-isopropoxide as the Ti source, and water as the oxygen source. It was found that during the process, adsorption of both the precursors was enhanced on the heterogeneous reaction surface because of the correlation growth behavior. STO films remained amorphous below 250 °C. Furthermore, although the film was crystallized at 270 °C, the perovskite phase was not identified. Despite the use of the Sn precursor with Sn²⁺, Sn ions in all the films transformed into Sn⁴⁺. Although the postdeposition annealing process in a forming gas atmosphere was conducted for the perovskite conversion, the STO film transformed into Ti₅Sn₃, an intermetallic compound, at 500 °C.