Reaction-mediated texturing of barium ferrite magnetic thin films on ZnO underlayer
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Stephen S. Rosenblum and Hidetaka Hayashi Applied Electronics Center, Kobe Steel USA Inc., Palo Alto, California 94304 (Received 28 December 1994; accepted 22 May 1995)
Using facing target sputtering, crystalline magnetoplumbite-type barium ferrite (BaFei2Oi9 or BaM) thin films have been prepared in situ at a substrate temperature of 640 °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 (—230 A) on Si substrates, BaM thin films show excellent c-axis out-of-plane texture with a 0.2° 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 °C, the ZnFe 2 O 4 layer becomes thicker at the expense of BaM and ZnO. The lattice parameters of both BaM and ZnO decreased as annealing time increased.
I. INTRODUCTION Barium ferrite (BaM) has a hexagonal magnetoplumbite-type structure with a = 5.88 A and c = 23.2 A. BaM thin films have been attracting a great deal of interest for their potential applications in magnetic, magneto-optic, and millimeter-wave circuit devices. Particularly in magnetic recording applications, previous research results have shown their great potential to support a high recording density for both longitudinal and perpendicular recording. 1 " 4 In addition, good chemical and thermal stability5 as well as good expected tribological performance3 make BaM a very competitive material for high density thin film recording applications. There have been some reports on the preparation of perpendicularly oriented BaM films on thermally oxidized Si substrates, using conventional or facing target sputtering.6 However, our research results indicate that as-deposited BaM thin films (
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