1 / 17

Characterization of Perpendicular Write Heads using Inductance Measurements

A new diagnostic tool for high-resolution, fast inductance measurement of write heads, allowing for the detection of head defects, yoke properties, and pole corrosion.

forster
Download Presentation

Characterization of Perpendicular Write Heads using Inductance Measurements

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Characterization of Perpendicular Write Heads using Inductance Measurements Alexander Taratorin 3000 Olcott St. Santa Clara, CA 95054 Tel: 408 653-0300 E-Mail: sales@us-isi.com Web: www.us-isi.com

  2. Need for Production Testing of Write Heads • Significant variations of write head performance during dynamic testing • Early production screening for wafer, bar or slider levels is currently not available New diagnostic tool: High resolution, fast relative inductance measurement • Changes of relative inductance in external magnetic field and with DC write current • Arbitrary Magnetic Field Orientation

  3. Blazer-X6B Advanced Test Platform Computer QST-2002Low & High Freq QST Measurement RIA-2008Relative Inductance Analyzer QPS-1050QST & Transverse Magnet Power Supply QMS-1050Longitudinal Magnet Power Supply

  4. HGA Level System Arrangement Computer QST-2002Low & High Freq QST Measurement RIA-2008Relative Inductance Analyzer QPS-1050QST & Transverse Magnet Power Supply QMS-1050Longitudinal Magnet Power Supply

  5. Perpendicular Write Head Geometry, Cross-section side view Upper yoke Coil Return pole Main pole Trailing pole Main pole Recession Recording pole Trailing shield

  6. Write Head Defects & Inductance Measurements Main Pole Coil flare Recording pole

  7. LSATI – Inductance Saturation using DC write current Less efficient head More efficient head Flux closure in Air: Mainly through the trailing shield ISAT - Inductance saturation vs. write current L(I) – combined influence of yoke properties, domains, head efficiency and trailing shield spacing Domain problem

  8. LSATF - Inductance Saturation in Magnetic Field Flare Saturation Main pole Saturation (head to head permeability variation) Yoke defect H • Inductance saturation in perpendicular field depends on: • Yoke properties (anisotropy, defects and domains) • Recording pole/main pole throat height and recession • Changes of L(H) slope dependence used for diagnostics • - Critical Field (main pole saturation) varies for different yoke length and material • Variation of critical field for the same head type correlates with head efficiency (saturation, OW, magnetic track width) Patents Pending

  9. LSATF - Inductance Saturation in Magnetic Field Head Defect (Asymmetry) Different head designs Normal head Strong Saturation Asymmetry Longer yoke Higher inductance Shorter yoke, Lower inductance Yoke Defects and asymmetry can be detected using LSATF test Patents Pending

  10. LSATF - Inductance Saturation in Magnetic Field Current = 0 Current opposite to field Current & Field Same direction Combine Magnetic Field & Write Current Shift of saturation kinks correlates with head efficiency and recording performance Patents Pending

  11. CYCET –Coil-Yoke Coupling Efficiency Test Efficient head coil Less efficient heads Hext • Flux generated by write current is opposite to Hext in the main pole – decreasing main pole saturation • Slope dL(I)/dI determines coil to yoke coupling – amount of flux, generated in the main pole per 1 ma of write current • CYCET correlates with head efficiency/overwrite (if pole definition is nominal) Patents Pending

  12. Main Pole flare Recording pole YDT – Yoke Defect Test Normal head Cross-track Hext perpendicular Hext Yoke defect signature Cross-track Compare inductance saturation in perpendicular/cross-track magnetic field Differences in saturation – signature of defects perpendicular

  13. Tilted Magnetic Field Heads with pole corrosion problem Bad sliders (pole corrosion) Good sliders Hext • Inductance dependence on arbitrary field angle relative to the ABS surface • Developed a set of measurements for: • - Detection of absent write pole (pole corrosion problem) • Yoke anisotropy characterization (preferable saturation direction) Patents Pending

  14. YAT - Yoke Anisotropy Test Different Flare Designs Narrow Wide Hext Inductance Saturation in rotating magnetic field : - Preferable saturation direction (apex/yoke anisotropy) - Flare Geometry Detection Patents Pending

  15. YAT - Yoke Anisotropy Test Flare shape variations Changes of yoke anisotropy anisotropic Angle 2 Angle 1 isotropic Detection of yoke/apex anisotropy (results in asymmetrical writing) Flare shape variation for production control Patents Pending

  16. Yoke Hysteresis & Domains: YHDFT & YHDIT Head with hystersis Hext2 Domain-free yoke Hext1 • Yoke domains cause variability of head switching and distort recorded transitions • Domains result in changes of inductance after external Field and current excitation • Detectable using developed inductance measurement in cycles of external field and write current Patents Pending

  17. Write Head Measurements Summary • Inductance saturation vs write current and external field • Coil to yoke coupling • Yoke anisotropy • Determination of yoke defects • Selecting hysteretic/domain write heads • Flare Geometry • Pole absence due to corrosion

More Related