Deposition of Nb-doped TiO2 films on large area by co-sputtering with precise process control

A co-sputtering approach based on bipolar pulsed reactive magnetron sputtering of different metallic targets was used to deposit niobium-doped titania (TiO2:Nb) layers in the thickness range between 50 and 250 nm. The composition of the grown films was varied by changing the pulse ratio and the reactive working point of the process control. For the latter, a spectrometer-based plasma emission control with fast feedback onto the reactive gas flow was utilized. It allowed for a stable and reproducible adjustment of the film composition up to some tenths of a percent. Energy-dispersive X-ray spectroscopy (EDX) disclosed a clear correlation between process settings and film composition and could be used as calibration procedure. After a thermal annealing step at 450°C, the optical and electrical properties of the films in the optimum range of composition were found to be comparable to those of established TCOs. Moreover, the studied process allows large-area coating at higher deposition rates than sputtering of planar oxide targets