Synthesis of Nb-doped TiO2 films on rigid and flexible substrates at low temperature

In this work, an attempt has been made to compare the physical properties of conductive films of Nb-doped TiO2 deposited on Kapton polyimide, glass and silicon substrates. Thin films were deposited by radio frequency sputtering at room temperature and subsequently characterized using X-ray diffraction, X-ray photoelectron spectroscopy, UV-VIS-NIR spectroscopy and Hall Effect measurement. Structurally, the films grown on the flexible substrate exhibit more strain and had inferior crystallinity (crystallite size ∼13.8 nm) compared to the films deposited on glass and silicon substrates (crystallite size ∼27 nm). The film on glass had a resistivity value around 1.67×10−3 Ω⋅cm while the resistivity of the films grown on polyimide was found about five-fold higher. Furthermore, the films deposited on glass substrate showed optical transparency of >80% in the visible range (400–750 nm). The inferior electrical transport properties of the films grown on polyimide were correlated with the poor crystallinity and cracks induced during the annealing process. Furthermore, various possible routes have been discussed to improve crystallinity and control cracks in the films.