AVS 47th International Symposium
    Magnetic Interfaces and Nanostructures Friday Sessions
       Session MI-FrM

Paper MI-FrM6
Measuring Drive and Media Performance using Quantitative Analysis of MFM Images

Friday, October 6, 2000, 10:00 am, Room 206

Session: Magnetic Recording: Media and Heads
Presenter: D.A. Chernoff, Advanced Surface Microscopy, Inc.
Authors: D.A. Chernoff, Advanced Surface Microscopy, Inc.
D.L. Burkhead, Advanced Surface Microscopy, Inc.
C.S. Cook, Advanced Surface Microscopy, Inc.
Correspondent: Click to Email
MFM imaging of magnetic hard disks provides a direct physical examination of magnetic marks that complements electrical measurements made on test stands. Valuable information can be obtained because the MFM is free of interference from cross-talk and other read head limitations. Such images have mostly been used for qualitative analyses, such as bit shape, erase band structure, and missing information (defects). However, quantitative analysis of track and bit position and of bit signal amplitude can provide important information to aid in the design and engineering of higher density drives. To assess the accuracy of disk drive servo tracking or of the disk servo writer, we captured several MFM images, each showing 10-15 tracks in the data or the servo mark areas of an ordinary disk. We have demonstrated that our proprietary method@footnote 1@ for calibration and measurement can measure track pitch with precision better than 0.3% (1 s.d.) on calibration specimens and on optical discs.@footnote 2@ For data tracks on a magnetic disk, track pitch variation (1 s.d.) was 3% of the mean track pitch. Drive system engineers can use this information to set target values and tolerances for track pitch. To assess media performance and noise, we captured images of a special test disk, written with constant frequency test patterns. Using similar tools, we analyzed the bit position and amplitude data. Bit position variation (1 s.d.) was 1.5% of the bit spacing and bit amplitude variation was 6.3% of mean amplitude. The variation in bit position (jitter) and in bit amplitude are fundamental sources of digital errors and can be a figure of merit for media response at a given spatial frequency. @FootnoteText@ @footnote 1@ MagneTrack and DiscTrack Plus Media Measurement Systems, www.asmicro.com. @footnote 2@ Automated, high precision measurement of critical dimensions using the Atomic Force Microscope, D. A. Chernoff and D. L. Burkhead, J. Vac. Sci. Technol. A 17, 1457 (1999).