Influence of annealing on atomic layer deposited Cr2O3-TiO2 thin films

Thin films in the Cr-Ti-O system were atomic layer deposited from CrO2Cl2, TiCl4, and CH3OH on Si(1 0 0), fused SiO2, and a-Al2O3(0 1 2) substrates at 420 oC. The proportion between Ti and Cr resulted from the ratio of the CrO2Cl2/CH3OH and TiCl4/CH3OH pulsing. The films were grown up to the thickness of about 70 nm. Annealing of the films was performed in O2 at 1000 oC. A notable dependence of their microstructure, conductance, and conductometric response to CO, H2, and CH4 in dry air on the substrates, Ti content, and annealing has been demonstrated. The films were polycrystalline on Si and SiO2, and epitaxial on a-Al2O3. At temperatures above 400 oC, the films had a conductance, advantageous from the point of view of semiconductor gas sensors. In response to a 30-ppm CO exposure at 450 oC, an annealed film on the a-Al2O3(0 1 2) substrate, distinguished by a relatively high Ti/Cr atomic ratio, showed a 16-% conductance decrease in 20 s, with a 120-s recovery.