Friction Force Measurements and Modeling in Hard Disk Drives

Friction in a head disk interface (HDI) is investigated considering the surface energy of the lubricant and the type of carbon overcoat (COC). Perfluoropolyether Z-Tetraol lubricant with A20H additive is applied on two types of COC (type-A and type-B) with lubricant thicknesses in the range of 11-19 A. The polar and dispersive components of the surface energy are measured from contact angle experiments. For each case, friction is measured using actual hard disk drives, and they are compared with the measured surface energy values of the disk samples. As the lubricant thickness increases, both the surface energy and friction decrease. Comparing friction and surface energy values for the two types of COC disks, type-A disks are found to exhibit lower surface energy and higher friction at all lubricant thicknesses. This is attributed to the effects of surface roughness, surface energy of the COC film, and lubricant interactions.