Nano-asperity contact analysis and surface optimization for magnetic head slider/disk contact

Abstract

NiP coated AlMg (NiP) and glass-ceramic (GC) substrates for magnetic recording are measured by an atomic force microscope (AFM) using different scan sizes and sampling resolution. AFM measurements of the NiP and GC surfaces reveal finer and finer details as the sampling interval decreases and that the GC surface contains more high frequency details than the NiP surface. A three-dimensional numerical rough surface contact model (X. Tian and B. Bhushan, ASME J. Tribol., 118 (1996) 33–42) is used to perform contact analysis on the NiP and GC surfaces to study the effect of sampling resolution on contact pressure and contact area. The contact analysis shows that contact pressure increases and contact area decreases as the sampling interval decreases and asperity contact starts from plastic deformation, the scale of which depends on the different surface topographical structures. The analysis also shows that a high frequency structure will facilitate plastic deformation which is not desired for head/disk durability. The stiction in rough surface contact problem is also considered using a numerical stiction model (X. Tian and B. Bhushan, J. Phys. D: Appl. Phys., 29 (1996) 163–178). The stiction model is used to highlight how stiction can be assessed by the bearing ratio of a surface and how stiction is affected by the skewness of surface height distribution. Stiction analysis on two GC surfaces with different skewness shows that a surface with positive skewness has less stiction. A uniform patterned texture with an optimum number of identical asperities (such as produced by laser texturing) appears to be an ideal surface.