Quantifying Corrosion Growths on Perpendicular Magnetic Recording Media

High media roughness associated with perpendicular recording introduces the phenomenon of widely separated single needle-like corrosion growths after temperature-humidity stress. Previous generation longitudinal recording media demonstrated clusters of corrosion growths around a central media defect, which were detectable by reflected light. However, because of the isolated nature of this new type of corrosion, traditional ellipsometry is no longer effective. As a result, we have developed a method for quantifying scattered isolated corrosion growths on perpendicular recording media disk surfaces, using existing optical surface technology. Our method can detect corrosion densities down to 5000 corrosion sites/mm², given corrosion size at least 0.3 mum in length and 7 nm in height. The amount of corrosion reveals itself as an increase in laser light scatter across a disk surface referenced to its original prestress scatter. Scanning electron microscopy and atomic force microscopy analysis of the corrosion growths verified that the scatter measurements correlate to physical properties such as density and size of corrosion needles.