MICROSTRUCTURAL EVOLUTION AND EPITAXIAL ALIGNMENT OF THIN-FILMS OF LITHIUM-NIOBATE DEPOSITED ONTO SAPPHIRE BY METALLOORGANIC DECOMPOSITION

LiNbO3 films were prepared by spin coating and thermal decomposition of a solution of metallo-organic precursors on single-crystal [0001] oriented Al2O3 substrates, followed by heat treatment in a quartz tube furnace at temperatures ranging from 500 to 1000 degrees C. X-ray diffraction and ion-channeling analyses reveal that the LiNbO3 grows epitaxially aligned with respect to the Al2O3 substrate. The degree of epitaxial alignment depends on the heat treatment temperature, with the best films obtained on heat treatment at 900 degrees C for 30 min to 1 h. The morphology of the films appears to depend on the kinetics of the decomposition process. Films pyrolyzed by slow heating from room temperature to about 500 degrees C, and subsequently heat treated at higher temperatures, tend to be non-uniform, breaking into a network of grains and partially uncovering the substrate. Interestingly, pole-figure analysis shows that all the grains share the same in-plane as well as out-of-plane epitaxial orientation. Films prepared by rapid thermal decomposition of the precursor solution at 500 degrees C. followed by heat treatment at 900 degrees C, are continuous, smooth, and epitaxially aligned.