Thermal Degradation of Tantalum-Nickel Thin Film Couples
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ABSTRACT Multilayered metal films including such couples as Ta-Permalloy (Ni80Fe 2 o) play a key role in magnetic recording sensors, where it is important to preserve the integrity of the thin permalloy layer under thermal conditions during processing and subsequent service. Earlier work' has indicated a fast grain boundary diffusion of Ta in Ni films at temperatures as low as 2500C. In this paper, we report measurements of the kinetics of this diffusion, in the temperature range 300-4000C. For this work, layered Ni/Ta systems were prepared under controlled conditions, annealed in a helium-flow furnace, and characterized by RBS, AES, XRD and SEM. The possible consequences of diffusion on magnetic performance are also discussed.
INTRODUCTION Due to small dimensions required for high density magnetic recording devices and the use of multilayered structures in magneto resistive (MR) heads it is important to understand low temperature diffusion and layer interaction effects. Grain boundary diffusion and grain boundary assisted diffusion may play an important role in layer interactions which, associated with interface roughening, may have important consequences to the magneto-electrical performance, if heating occurs during device fabrication or in normal service. For example, Huang et al reported that magnetic spin valve structures heated to 240-3600C display of interlayer boundaries, increased interface roughening which they attributed to intermixing 2 which was also associated with a decrease of magnetoresistivity . In MR heads, Ta is used both as a protective cap and as diffusion barrier for the Permalloy 3 (Ni8oFe 2 O)layers. At 8000C the bulk solubility of Ta in Ni is about 2.6 at%, while the solubility the solubilities are probably much temperatures, At lower at%.
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