Structure of hydrogen gas sensing TiO2 thin films prepared by sol-gel method and their comparison with magnetron sputtered films

TiO2 thin films with a thickness of about 150 nm were deposited by spin coating method on sapphire substrate from a sol-gel system. The hydrogen sensing properties of TiO2 films annealed at various temperatures were studied and correlated with their structure, optical and electrical properties. The annealing temperatures in the range of 600 - 800 degrees C lead to anatase films with a roughness in the range of 0.6 - 0.9 nm. Their sensitivity towards hydrogen is low. The thin films annealed at temperatures in the range 900 - 1000 degrees C consist of rutile phase and their roughness increased to 11.7 - 13.5 nm. They showed good hydrogen sensitivity with optimal operating temperature 200 - 250 degrees C. The structure and sensing properties of the prepared films are compared with those synthesized with magnetron sputtering. The maximum of sensitivity was measured on the thin films with diameter of the grains about 100 nm in both cases, i.e. on thin films prepared by sol-gel method as well as on thin films prepared by magnetron sputtering. The maximum sensitivity correlates with the diameter of the grains and don't depend on the allotropy of the titanium dioxide - anatase or rutile.