The effect of slider roughness on asperity testing of thin-film media

Sliders used for glide (asperity) testing are typically composed of Al₂O₃-TiC composites, with average grain sizes from under 1 μm to 1.5 μm. The air bearing surfaces are polished to an average roughness of less than 25 nm. Atomic force micrographs measured on sliders of different grain sizes, but polished by the same manufacturer, showed a wide variety of surface morphology. However, all slider surfaces had asperities which were 25 nm or higher and on the order of the Al₂O₃-TiC grain size in diameter. These asperities will result in slider-disk spacing that is smaller than predicted from optical fly height measurement systems. consequently, avalanche curves measured using calibrated asperities show initial contact occurring a micro-inch or more above where optical fly height measurements had predicted. With slider-disk spacing, for asperity testing, falling below 50 nm, slider asperities represent a substantial portion of the slider-disk spacing and must therefore be factored into both testing and calibration