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Characterization of Perpendicular Write Heads using Inductance Measurements Alexander Taratorin 3000 Olcott St. Santa Clara, CA 95054 Tel: 408 653-0300.

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Presentation on theme: "Characterization of Perpendicular Write Heads using Inductance Measurements Alexander Taratorin 3000 Olcott St. Santa Clara, CA 95054 Tel: 408 653-0300."— Presentation transcript:

1 Characterization of Perpendicular Write Heads using Inductance Measurements Alexander Taratorin 3000 Olcott St. Santa Clara, CA Tel: Web:

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 QST-2002 Low & High Freq QST Measurement QPS-1050 QST & Transverse Magnet Power Supply QMS-1050 Longitudinal Magnet Power Supply RIA-2008 Relative Inductance Analyzer Computer

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

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

6 Write Head Defects & Inductance Measurements Manufacturing problems Relative Inductance Measurement Yoke defects, magnetic properties variation + Coil Defects/ Coil-Yoke coupling + Flare Geometry, anisotropy + Recording Pole geometry and magnetics Small effect +/- flare Recording pole Main Pole Coil

7 LSATI – Inductance Saturation using DC write current 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 More efficient head Less efficient head Domain problem

8 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) H LSATF - Inductance Saturation in Magnetic Field Patents Pending Flare Saturation Main pole Saturation (head to head permeability variation) Yoke defect

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

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

11 Hext coil 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) Efficient head Less efficient heads CYCET –Coil-Yoke Coupling Efficiency Test Patents Pending

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

13 H ext Good sliders Bad sliders (pole corrosion) 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) Tilted Magnetic Field Patents Pending Heads with pole corrosion problem

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

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

16 H ext1 H ext2 Head with hystersis 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 Domain-free yoke Yoke Hysteresis & Domains: YHDFT & YHDIT Patents Pending

17 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 Write Head Measurements Summary


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