Factors affecting surface roughness and coercivity of Ni80Fe20 thin films

Abstract

This article reports the effects of dc sputter power, film thickness and rf substrate bias on surface roughness and magnetic properties of Ni80Fe20 thin films sputtered on Si (100) substrates for their application in magnetic tunneling junctions. The surface roughness of Ni80Fe20 thin films varied from 0.197 nm to 0.376 nm when dc sputter power was changed from 50 to 250 W. The optimum value was achieved with 200 W dc sputter power. Film thickness dependence study shows that the surface roughness of Ni80Fe20 thin films changes from 0.164 nm to 0.264 nm, with a minimum at film thickness of 8 nm. The small magnitude of change was attributed to a 20 W rf substrate bias that was applied during the thickness studies. We varied the substrate rf bias from 0–20 W, with fixed 200 W dc power and 8 nm film thickness. A dramatic change of surface roughness of Ni80Fe20 film from 0.984 nm (without rf bias) to 0.197 nm (with 20 W rf bias) on Si was achieved. The coercivity of the Ni80Fe20 thin films changes in a similar way as surface roughness. We conclude that the surface roughness of Ni80Fe20 thin films can be well controlled by applying a rf substrate bias during the deposition.