Challenges of cost effective screening of current and future TMR/PMR design heads

Henry Patland

President & CEO

hpatland@us-isi.com

www.us-isi.com

AbstractAs the industry makes the transition to PMR technology, with expected 100% transition by 2010, there are many challenges that head designers need to overcome to make this transition successful.

In addition to dealing with completely new head, media and channel designs, head manufacturers have to quickly anticipate the type of failures they will see from new head designs in volume production environments and be ready to cost effectively screen out those failures.

This presentation will concentrate on the challenges of testing these new head technologies, the type of solutions that are currently available and future requirements. Also a cost effective test strategy will be presented for discussion.

Outline GMR/LMR head technology overview TMR/PMR head technology overview Conventional quasi-static testing (QST) Specific problems for PMR/TMR heads Can QST testing address these specific problems for

TMR/PMR heads? Dynamic testing an alternative or complement to QST

testing Advantages/disadvantages of dynamic vs. QST testing Proposed cost efficient model for electrical head test Conclusion

GMR/LMR Heads

TMR/PMR

LMR vs. PMR Recording

LMR head sees zero field between transition and either a positive or negative field during transition

PMR head sees either positive or negative field between transitions and zero field during transition

LMR Transition Field Component

Structure of media stray field and read-back pulse for longitudinal recording

PMR Transition Field Component

Media stray fields for perpendicular media with soft under-layer

U-Shape bending caused by Perpendicular Stray Field

Low Frequency Cut-off in PMR

Read-back of low density perpendicular square wave pattern with different LF cut-off frequency: Signal shape distortions

Conventional QST Testing of both GMR/LMR and TMR/PMR Heads

High/Low resistance Low amplitude High asymmetry Barkh jump, hysteresis Low SNR Instability ESD damage (pin-layer-reversal)

QST Transfer Curve

Resistance

Amplitude

Asymmetry

Barkh Jump

Hysteresis

Bias Point

Delta R/R

Bias Angle

Slope

Max Slope

Parametrics extracted from QST Transfer Curve

Field Induced Instability

Soft Kink at 160 Oe

Field Induced Instability @ 150 Oe

Field Induced Instability @160 Oe

Field Induced Instability @ 170 Oe

Spectral Maximum Amplitude Noise (SMAN) Test

Patent: US6943545

Soft Kink at 160 Oe

Spectrum Analysis

Pin-Layer-Reversal due to ESD damage

QST has good track record at conventional testing.

Can QST testing address TMR/PMR Specific Problems?

PMR/TMR Specific Problems and Using QST Test Strategy

Pin-holes and µSmearing on insulating spacer Instability with lower cut off frequency Weak pin-layer Stray side field sensitivity and larger shield

geometries Writer pole problems

Problem: Pin-Hole & µSmearing Issues Both Pin-Holes and µSmearing occur during manufacturing of TMR

stacks with extremely thin insulation layer

Both Pin-Holes and µSmearing disrupt the tunneling mechanism and essentially create a short across the insulation layer

When Pin-Holes are present, some of the Bias current flows through the created shorts, and SNR is deteriorated

Additionally these shorts cause higher operating temperature of the TMR sensor which in turn causes reliability issues

Pin-Holes or µSmearing

QST Solution: Pin-Hole & µSmearing Issues By raising the TMR sensor temperature either

through Bias Source or external means, and measuring the Resistance change, both Pin-Hole & µSmearing can be detected

DeltaR/R, Transfer Curve, Hysteresis, and Slope of Transfer Curve are also good indicators of Pin-Hole or µSmearing presence

Problem: Lower Frequency Instability

Since PMR heads see more low frequency component and are exposed to multiple state magnetic fields between transitions, the probability of magnetic field induced instability is increased

This type of instability can cause high BER or losing servo in the drive

QST Solution: Lower Frequency instability

By lowering the cut-off freq to 100Khz from typical 3-5Mhz and using industry standard Spectral Maximum Amplitude Noise (SMAN) tests these unstable heads can be effectively screened out

Problem: Weakly Pinned Heads

If pinned layer is weak, the magnetization angle between pinned layer and free layer is compromised causing degraded DeltaR/R, SNR degradation and sensor instability

QST Solution: Weakly Pinned Heads

By testing heads at high magnetic fields and various angles, weakly pinned head can be screened out by QST

Weakly pinned heads might require additional re-initialization before final QST test

Problem: Stray Side Field sensitivity and New Larger Shield Geometries

Stray side field sensitivity can cause sensor saturation and transition shifts as caused by adjacent tracks

Larger shields absorb much of external magnetic field to shield the sensor and can also become magnetized causing sensor instability

QST Solution: Stray Side Field sensitivity and New Larger Shield Geometries

By testing QST with different magnetic field orientation, stray side field sensitivity can be simulated and sensitive heads can be screened out

By applying larger magnetic fields (typ: TMR/PMR – 500 to 600 Oe) the larger shields can be saturated to conventionally exercise the sensor

Problem: Writer Pole Design

Vertical Pole heads have poor write gradient

Write distortions when head is skewed with respect to track direction

Thin pole heads exhibit pole remnance problems due to magnetic domains in the pole tips (sometimes overwriting servo patterns)

QST Solutions: Writer Pole Design

With current technology QST is not capable of detecting this failure

Currently through improved writer pole material and geometry design, this issue is getting resolved

ISI Quasi-Static Testing Portfolio

Available Electrical Test Technologies

Dynamic Testing Quasi-Static Testing

Dynamic Head Test Advantages

Tests both writer and reader Resembles closely final head/media

arrangement Extensive tests such as MRR, Amp, Asym,

NLTS, SNR, OW, PW50, MRW, MWW, ATE, BER

Dynamic Head Test Disadvantages

High capital cost ($$$) Low UPH (typical 30-40) Media quality/flying height variation Difficult to separate writer vs. reader failures Can only be done at HGA level, high scrap cost High operating cost Larger and higher class cleanroom required Higher ESD danger due to more handling Poor correlation to final HDD yield

QST Head Test Advantages Low capital cost ($) High UPH (typical 1000) Can be done at row level (early test equals lower

scrap cost) Very detailed and effective reader testing with

and without various stresses Good correlation to final reader related HDD

Yield Low ESD risk due to automation Low operating cost Less clean room space and lower class

cleanroom required

QST Head Test Disadvantages

Cannot characterize writer Cannot predict head/media interface problems

since there is no flying No off-track analysis

Conventional Electrical Test Flow Model

100%

Bar/Slider

QST

100%

Dynamic Head Test

100%

Head Stack Actuator

QST

100%

Final HDD Test/Burn-in

Conventional Electrical Test Cost Model

Annual Slider

Volume(M) Yield

Test Type

ASP(K)

Number of Testers

Required

Annual Cost /w

5 Yr Depr.(M)

Slider UPH

%Of

Sliders Tested

Cost per slider

%Of Total

Test Cost3,947 70% QST Wafer $750 221 $33 3000 100% $0.017 5.56%3,036 80% QST Bar $150 729 $22 700 100% $0.011 3.66%2,530 85% DET HGA $250 10,630 $532 40 100% $0.266 89.06%2,200 90% QST HSA $45 1,138 $10 325 100% $0.005 1.72%2,000Total $0.30

Final HDD Yield

Re-work Cost

AvgHds/HDD

HDD Total(M)

Total Rework

Cost(M)

98.00% $3.00 2.50 800 $48

Note:Assumes 17hr/day tester utilizationAssumes Rework Cost labor only

Proposed Electrical Test Flow Model

100%

Bar/Slider

QST

5%

Dynamic Head Test

100%

Head Stack Actuator

QST

100%

Final HDD Test/Burn-in

Sampling or NO DET Testing

More Cost-Effective Test Cost Model

Annual Slider

Volume(M) Yield

Test Type

ASP(K)

Number of Testers

Required

Annual Cost /w 5 Yr

Depreciation(M)

Slider UPH

%Of

Sliders Tested

Cost per slider

%Of Total

Test Cost3,947 70% QST Wafer $750 221 $33 3000 100% $0.017 35.93%3,036 80% QST Bar $150 729 $22 700 100% $0.011 23.69%2,530 90% DET HGA $250 532 $27 40 5% $0.013 28.79%2,300 85% QST HSA $45 1,189 $11 325 100% $0.005 11.60%2,000Total $0.05

Final HDD Yield

Re-work Cost

AvgHds/HDD

HDD Total(M)

Total Rework

Cost(M)

95.00% $3.00 2.50 800 $120

Note:Assumes 17hr/day tester utilizationAssumes Rework Cost labor only

Conclusion Even though the final HDD yield is lowered in

the Proposed Test Model the total cost of annual DET cost and rework cost combined is: $147M vs. $580M in the Conventional Test Model

Quasi-Static Test is the cost effective test solutions for current and future TMR/PMR design heads

Can 100% DET testing be cost-effective?

References Alexander Taratorin, “Magnetic Recording Systems and

Measurements”, San Jose Research Center, HGST Bryan Oliver, Qing He, Xuefei Tang, and J. Nowaka), “Dielectric

breakdown in magnetic tunnel junctions having an ultrathin barrier”, JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 7

Sangmun Oh1, K. Nishioka2, H. Umezaki3, H. Tanaka1, T. Seki1, S. Sasaki1, T. Ohtsu2, K. Kataoka2, and K. Furusawa1 “The Behavior of Pinned Layers Using a High-Field Transfer Curve”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 10, OCTOBER 2005

H. Patland, W. Ogle, “High Frequency Instabilities in GMR Heads Due to Metal-To-Metal Contact ESD Transients”, EOS/ESD Symposium 2002

Integral Solutions Int’l, “Quasi 97”, “Blazer-X5B” and “QST-2002” Tester