Fractal Analysis of Hard Disk Surface Roughness and Correlation With Static and Low-Speed Friction

The purpose of this work was to use new scale-sensitive fractal parameters to characterize the surface topography of computer hard disks and to correlate the fractal parameters with measured start-up friction (or stiction) behavior of textured hard disks. The topographies of glass disks with three different surface textures and aluminum disks with two different textures were measured using an atomic force microscope. Two parameters derived from area-scale fractal analysis by the patchwork method were chosen to characterize the surface topography: smooth-rough crossover and area-scale fractal complexity. The two fractal parameters were found to be characteristic of the disks’ texture; disks which had been processed in the same batch had similar values of complexity and smooth-rough crossover, but those values differed for disks subjected to a different texturing process. Friction behavior of unlubricated glass disks and lubricated aluminum disks was determined at startup and during low speed drag testing. The results show a high correlation between the smooth-rough crossover parameter and start-up friction (stiction) for both lubricated and unlubricated disks. Additional tests showed that the area-scale fractal parameter is related to low speed sliding friction. The friction results for the unlubricated glass disks were dependent on humidity and roughness in a manner that is consistent with a meniscus model of stiction.