Sputter deposition of anatase titanum dioxide transparent conducting films

We report recent progress on sputter-deposition of Ti_0.94Nb _0.06O₂ polycrystalline (poly-TNO) thin films as ITO-alternative transparent conductor. In order to achieve low resistivity (ρ) in TNO, it is necessary to introduce oxygen deficiencies into anatase phase. However, growth of poly-TNO films on glass under relatively reducing atmosphere tends to stabilize the rutile phase with higher resistivity. We overcame this difficulty by developing a bi-layer technique using a TNO seed-layer, which prevents the formation of the rutile phase even under reducing deposition conditions. As a result, we succeeded in directly fabricating poly-TNO films with ρ of ∼1 × 10^-3 Ω cm and visible transmittance of 60-80%, although we still need to further improve these properties towards practical applications. By comparing carrier transport properties between poly-TNO films obtained by different synthesis routes, we discuss on material parameters that govern resistivity of poly-TNO films.