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

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

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

QST-2002Low & High Freq QST Measurement

QPS-1050QST & Transverse Magnet Power Supply

QMS-1050Longitudinal Magnet Power Supply

RIA-2008Relative Inductance Analyzer

Computer

HGA Level System Arrangement

QST-2002Low & High Freq QST Measurement

QPS-1050QST & Transverse Magnet Power Supply

QMS-1050Longitudinal Magnet Power Supply

RIA-2008Relative Inductance Analyzer

Computer

Perpendicular Write Head Geometry, Cross-section side view

Return pole

Trailing pole

Upper yoke

Main pole

Trailing shield

Recording pole

Coil

Main pole Recession

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

Recordingpole

Main Pole

Coil

LSATI – Inductance Saturation using DC write current

-60 -40 -20 0 20 40 600.5

1

1.5

2

Current, mA

Rel

ativ

e In

duct

ance

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

-60 -40 -20 0 20 40 600.6

0.8

1

1.2

1.4

1.6

1.8

2

Current, mA

Rela

tive I

nducta

nce

More efficient head

Less efficient head

Domainproblem

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 materialVariation 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

0 500 1000 1500 2000 25000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Field, OeR

elat

ive

Indu

ctan

ce

Flare Saturation

Main poleSaturation(head to headpermeabilityvariation)

Yoke defect

LSATF - Inductance Saturation in Magnetic Field

0 500 1000 1500 2000 25000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Field, Oe

Rel

ativ

e In

duct

ance

Yoke Defects and asymmetry can be detected using LSATF test

Different head designs

Longer yokeHigher inductance

Shorter yoke,Lower inductance

-2500 -2000 -1500 -1000 -500 0 500 1000 1500 2000 25000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Field, Oe

Rela

tive I

nducta

nce

Head Defect (Asymmetry)

StrongSaturationAsymmetry

Normalhead

Patents Pending

LSATF - Inductance Saturation in Magnetic Field

0 500 1000 1500 2000 25000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Field, Oe

Rel

ativ

e In

duct

ance

Combine Magnetic Field & Write CurrentShift of saturation kinks correlates with head efficiency and recording performance

Current opposite to field

Current & Field Same direction

Current = 0

Patents Pending

0 5 10 15 20 25 30 35 40 450.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Write Current, mA

Rela

tive I

nducta

nce

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

Compare inductance saturation in perpendicular/cross-track magnetic field

Differences in saturation – signature of defects

Hext

YDT – Yoke Defect Test

flare

Recordingpole

Main Pole

Hext

0 500 1000 1500 2000 25000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Field, Oe

Rel

ativ

e In

duct

ance

0 200 400 600 800 1000 1200 1400 1600 1800 20000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Field, Oe

Rel

ativ

e In

duct

ance

Normal head

Yoke defect signature

Cross-track

Cross-track

perpendicular

perpendicular

Hext0.8 1 1.2 1.4 1.6 1.8 2

x 108

-1

-0.5

0

0.5

1

1.5

x 10-10

Frequency, MHz

Indu

ctan

ce,

nH

800 Oe Long field, 300 Oe perp field

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

-80 -60 -40 -20 0 20 40 60 800.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Field Angle, degreesN

orm

aliz

ed R

ela

tive I

nducta

nce

YAT - Yoke Anisotropy Test

Hext

Inductance Saturation in rotating magnetic field :- Preferable saturation direction (apex/yoke anisotropy) - Flare Geometry Detection

Different Flare DesignsNarrow

Wide

Patents Pending

-80 -60 -40 -20 0 20 40 60 800.65

0.7

0.75

0.8

0.85

0.9

0.95

1

Field Angle, degrees

Norm

aliz

ed R

ela

tive I

nducta

nce

YAT - Yoke Anisotropy Test

-40 -30 -20 -10 0 10 20 30 400.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.05

1.1

Field Angle, degrees

Norm

aliz

ed R

ela

tive I

nducta

nce

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

0 10 20 30 40 50 60 70 80 90 1001.595

1.6

1.605

Trial #

Rela

tive I

nducta

nce

0 10 20 30 40 50 60 70 80 90 100-5

0

5x 10

-3

Trial #

Delta I

nducta

nce

Hext1

Hext2Head 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

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