Transparent conductive Nb-doped TiO2 films deposited by reactive dc sputtering using Ti–Nb alloy target, precisely controlled in the transition region using impedance feedback system

Abstract In this study, a stable reactive sputtering process using a Ti–Nb alloy target was achieved by applying a plasma impedance feedback system. High-quality transparent conductive Nb-doped TiO 2 (Nb:TiO 2 ) films were fabricated with high reproducibility. The films were deposited on unheated substrate and subsequently annealed at 873 K under vacuum conditions (below 6.0 × 10 −4 Pa) for 1 h. During reactive sputtering, the feedback system precisely controlled the oxidation of the target surface in the so-called transition region. The post-annealing process yielded polycrystalline Nb:TiO 2 films whose lattice defects decreased with increasing Nb concentration. An extremely low resistivity (7.2 × 10 −4 Ω cm) was achieved for Nb:TiO 2 film with 60–70% transmittance in the visible region. The reactive sputtering using Ti–Nb alloys is considered to be a strong candidate for industrial-scale thin-film deposition. Furthermore, it can also control the metal-oxygen stoichiometry of Nb:TiO 2 films precisely to achieve desirable properties for each industrial application.