Alan M Spool oral presentation (OA3-Tue1-3-1)
Solving Problems With Rotating Disk Drive Devices Using TOF-SIMS
1 Western Digital Corporation, 1 Kirihara-cho, 252-0888 Fujisawa, Japan
2 Western Digital Corporation, 5601 Great Oaks Blvd, CA 95119 San Jose, United States
The modern disk drive is a remarkable technical feat in which a ceramic magnetic recording head glides near to but not quite touching the rapidly moving disk surface. At the magnetic element, the disk passes the head at a fraction of a nm distance. Contaminants of various types will disrupt the head disk interface, and therefore it is an industry wide objective to identify their sources and eliminate them. Because the distance between disk and head are so small, contaminants that are not batted away by the front of the head but that actually are ingested into the interface will leave only very thin traces of themselves. Surface sensitive analytical techniques in general, and TOF-SIMS in particular, are critically needed in the struggle to reduce failures due to contamination. For thin organic residues, TOF-SIMS is the only method that can identify the materials. The analysis is straightforward for polymers and discrete organic species whose spectra present unique peaks, if enough signal can be obtained from the contaminant. However some materials, such as polyolefin based polymers, do not present unique peaks in the mass spectrum, but instead must be identified by looking at the relative intensities of otherwise relatively commonly detected ions. These relative intensities vary somewhat not only due to the nature of the material, but also due to the heating that can occur in the head disk interface as the polymer is rubbed against the disk until the drive is stopped. Further, the contamination itself can be contaminated by adventitious hydrocarbon adsorbtion, especially after the head is removed from the drive for analysis. The distinction between polyethylene and polypropylene becomes particularly difficult. This paper shows how discriminate analysis was used to produce a method to confidently determine whether a smear of material on a magnetic recording head is polyethylene or polypropylene. The peak ratios used in the method turn out to involve peaks that are due to highly unsaturated ions, ions that might not appear at first to be the most obviously representative of these saturated polymers, peaks that would be found to be the least significant in a G-SIMS analysis, for example. In fact, the peak ratios utilized in this analysis are remarkably unaffected by primary beam energy or species, differences in sample mounting that inevitably leads to differences in the geometry of the sample relative to the spectrometer, and the method works equally well in varied TOF-SIMS instruments. Aside from their practical benefits, these results indicate that ion formation even of these highly altered ions is specific to the materials being analyzed.