Non-destructive defect detection scheme using Kerr-channel optical surface analyzer

Abstract

Magnetic defects on the surface of magnetic disks, unlike normal topological defects, are difficult to detect because they are solely due to magnetic signal loss as seen by the MR element and often do not have any obvious topological features. Defects without any topological features usually render conventional defect finding techniques such as visual inspection, optical microscopy, and SEM useless. In the past, the painstaking way of locating the defect was to index the drive with a strobe light and followed with ferrofluid decoration of the surface to determine the location of the defect. The disadvantage is that the magnetic particles in the decoration technique can often confound the origin of the defect. Furthermore, the old technique does not have high enough resolution to locate defect with a size on the order of a micrometer. In this work, we describe how a magnetic marking technique (MMT) is utilized to circumscribe the magnetic defects. The markers are written in such a way that both the defect and the magnetic markers are easily detected using a Kerr-channel optical surface analyzer and magnetic force microscope. Typically, the accuracy of locating the defect using the MMT is within a track-pitch radially and within one data sector circumferentially. The new scheme provides at least one order of magnitude improvement in detection resolution over the old technique.