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Characterization of Perpendicular Write Heads using Inductance Measurements Alexander TaratorinPowerPoint Presentation

Characterization of Perpendicular Write Heads using Inductance Measurements Alexander Taratorin

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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

E-Mail: [email protected]

Web: www.us-isi.com

Need for Production Testing of Write Heads Inductance Measurements

- 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

Blazer-X6B Advanced Test Platform Inductance Measurements

Computer

QST-2002Low & High Freq QST Measurement

RIA-2008Relative Inductance Analyzer

QPS-1050QST & Transverse Magnet Power Supply

QMS-1050Longitudinal Magnet Power Supply

HGA Level System Arrangement Inductance Measurements

Computer

QST-2002Low & High Freq QST Measurement

RIA-2008Relative Inductance Analyzer

QPS-1050QST & Transverse Magnet Power Supply

QMS-1050Longitudinal Magnet Power Supply

Perpendicular Write Head Geometry, Inductance MeasurementsCross-section side view

Upper yoke

Coil

Return pole

Main pole

Trailing pole

Main pole Recession

Recording pole

Trailing shield

Write Head Defects & Inductance Measurements Inductance Measurements

Main Pole

Coil

flare

Recording

pole

LSATI – Inductance Saturation using DC write current Inductance Measurements

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

LSATF - Inductance Saturation in Magnetic Field Inductance Measurements

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

LSATF - Inductance Saturation in Magnetic Field Inductance Measurements

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

LSATF - Inductance Saturation in Magnetic Field Inductance Measurements

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

CYCET –Coil-Yoke Coupling Efficiency Test Inductance Measurements

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

Main Pole Inductance Measurements

flare

Recording

pole

YDT – Yoke Defect TestNormal 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

Tilted Magnetic Field Inductance Measurements

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

YAT - Yoke Anisotropy Test Inductance Measurements

Different Flare Designs

Narrow

Wide

Hext

Inductance Saturation in rotating magnetic field :

- Preferable saturation direction (apex/yoke anisotropy)

- Flare Geometry Detection

Patents Pending

YAT - Yoke Anisotropy Test Inductance Measurements

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

Yoke Hysteresis & Domains: YHDFT & YHDIT Inductance Measurements

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

Write Head Measurements Summary Inductance Measurements

- 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

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