Adhesion of chromium metallization on alumina surfaces prepared by sol-gel techniques

The adhesion of a sputter-deposited Cr metallization layer to alumina films prepared by a solution-gelation method has been investigated using a pull test. Alumina films with a range of thicknesses (1 to 6 Μm) were prepared by dipping commercially available polycrystalline alumina substrates into hydrolysed aluminium butoxide sols and fired for 1 h at 500, 900, or 1200 ‡C. Monolithic, crack-free films resulted both from pure alumina and Ti-doped alumina sols. The adhesion strength was dependent on the thickness of the alumina films, as well as on the temperature of the heat treatment. Failure occurred in part between the alumina film and the substrate and in part between the alumina film and the chromium layer. For alumina films fired at 500 ‡C, the adhesion strengths of 1 Μm thick films were greater than those measured for 3 and 6 Μm thick films because of the formation of greater mechanical bonds between alumina films and the substrate. The adhesion strength of the chromium layers was greatly improved by firing at 1200 ‡C. This increase in adhesion strength was attributed to an increase in the surface roughness of these specimens, which occurred due to crystallization of the sol layer. The adhesion strengths of films doped with Ti was not significantly different from those of the undoped films.