REACTION-MEDIATED TEXTURING OF BARIUM FERRITE MAGNETIC THIN-FILMS ON ZNO UNDERLAYER

Using facing target sputtering, crystalline magnetoplumbite-type barium ferrite (BaFe12O19 or BaM) thin films have been prepared in situ at a substrate temperature of 640 degrees C without postdeposition annealing. Using our facing target sputtering system, BaM thin films grow randomly if they are directly deposited onto Si or thermally oxidized Si substrates. However, deposited onto a sputtered ZnO layer (similar to 230 Angstrom) on Si substrates, BaM thin films show excellent c-axis out-of-plane texture with a 0.2 degrees c-axis dispersion angle, as indicated by x-ray diffraction (XRD). Cross-section transmission electron microscopy (XTEM) reveals that the textured films epitaxially grow on a transition layer, which is formed between BaM and ZnO. No direct epitaxial relation between BaM and ZnO was observed. This transition layer is identified by TEM and XRD as ZnFe2O4, which, from a structure point of view, reduces the lattice mismatch between BaM and ZnO, and also enhances the c-axis out-of-plane epitaxial growth. ZnFe2O4 is a reaction product of BaM and ZnO, as indicated by both TEM and XRD. After ex situ annealing the film in air at 800 degrees C, the ZnFe2O4 layer becomes thicker at the expense of BaM and ZnO. The lattice parameters of both BaM and ZnO decreased as annealing time increased.