Reactively sputtered titania films as high temperature carbon monoxide sensors

Sputtered films of titania have been explored for sensing of carbon monoxide (CO) at 550 °C. Film thickness was varied from 24 to 1000 nm by varying the sputtering time. The films were amorphous as prepared and converted to rutile upon thermal treatment. Highest sensor sensitivity, as measured by the resistance change of the film upon exposure to CO was noted for the ∼240 nm film, and characterization focused on this film. Microstructure studies using electron microscopy show that the film was dense, with grain sizes of rutile of ∼20 nm. Atomic force microscopy showed considerable surface roughness. The ∼240 nm sputtered films exhibited higher sensitivity (factor of 3) as compared to optimized porous films made with commercially available anatase particles.