Transcript Integral Solutions Int’l

Challenges of cost effective screening of current and
future TMR/PMR design heads
Henry Patland
President & CEO
[email protected]
www.us-isi.com
Abstract
As 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
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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
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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
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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
Soft Kink at 160 Oe
Patent: US6943545
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
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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
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Both Pin-Holes and µSmearing occur during manufacturing of TMR
stacks with extremely thin insulation layer
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Both Pin-Holes and µSmearing disrupt the tunneling mechanism
and essentially create a short across the insulation layer
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When Pin-Holes are present, some of the Bias current flows through
the created shorts, and SNR is deteriorated
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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
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By raising the TMR sensor temperature either
through Bias Source or external means, and
measuring the Resistance change, both PinHole & µSmearing can be detected
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DeltaR/R, Transfer Curve, Hysteresis, and Slope
of Transfer Curve are also good indicators of
Pin-Hole or µSmearing presence
Problem: Lower Frequency Instability
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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
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This type of instability can cause high BER or
losing servo in the drive
QST Solution: Lower Frequency instability
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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
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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
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By testing heads at high magnetic fields and
various angles, weakly pinned head can be
screened out by QST
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Weakly pinned heads might require additional
re-initialization before final QST test
Problem: Stray Side Field sensitivity and
New Larger Shield Geometries
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Stray side field sensitivity can cause sensor
saturation and transition shifts as caused by
adjacent tracks
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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
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By testing QST with different magnetic field
orientation, stray side field sensitivity can be
simulated and sensitive heads can be screened
out
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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
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Vertical Pole heads have poor write gradient
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Write distortions when head is skewed with
respect to track direction
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Thin pole heads exhibit pole remnance problems
due to magnetic domains in the pole tips
(sometimes overwriting servo patterns)
QST Solutions: Writer Pole Design
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With current technology QST is not capable of
detecting this failure
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Currently through improved writer pole material
and geometry design, this issue is getting
resolved
ISI Quasi-Static Testing Portfolio
Available Electrical Test Technologies
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Dynamic Testing
Quasi-Static Testing
Dynamic Head Test Advantages
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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
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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
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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
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Cannot characterize writer
Cannot predict head/media interface problems
since there is no flying
No off-track analysis
Conventional Electrical Test Flow Model
100%
100%
100%
100%
Bar/Slider
Dynamic Head
Test
Head Stack
Actuator
Final HDD
Test/Burn-in
QST
QST
Conventional Electrical Test Cost Model
Annual
Slider
Volume
(M)
3,947
3,036
2,530
2,200
2,000
Total
Yield
70%
80%
85%
90%
Test
Type
QST Wafer
QST Bar
DET HGA
QST HSA
ReFinal
work
Avg
HDD Yield Cost Hds/HDD
98.00% $3.00
2.50
ASP
(K)
$750
$150
$250
$45
Annual
Cost
%
Number of
/w
Of
%
Testers 5 Yr Depr. Slider Sliders Cost per Of Total
Required
(M)
UPH Tested
slider Test Cost
221
$33
3000
100%
$0.017
5.56%
729
$22
700
100%
$0.011
3.66%
10,630
$532
40
100%
$0.266
89.06%
1,138
$10
325
100%
$0.005
1.72%
$0.30
HDD
Total
(M)
800
Note:
Assumes 17hr/day tester utilization
Assumes Rework Cost labor only
Total
Rework
Cost
(M)
$48
Proposed Electrical Test Flow Model
Sampling or
NO DET
Testing
100%
5%
100%
100%
Bar/Slider
Dynamic Head
Test
Head Stack
Actuator
Final HDD
Test/Burn-in
QST
QST
More Cost-Effective Test Cost Model
Annual
Slider
Volume
(M)
3,947
3,036
2,530
2,300
2,000
Total
Yield
70%
80%
90%
85%
Annual Cost
%
Number of
/w 5 Yr
Of
%
Test
ASP
Testers Depreciation Slider Sliders Cost per Of Total
Type
(K)
Required
(M)
UPH Tested
slider Test Cost
QST Wafer $750
221
$33
3000
100%
$0.017
35.93%
QST Bar $150
729
$22
700
100%
$0.011
23.69%
DET HGA $250
532
$27
40
5%
$0.013
28.79%
QST HSA $45
1,189
$11
325
100%
$0.005
11.60%
ReFinal
work
Avg
HDD Yield Cost Hds/HDD
95.00% $3.00
2.50
$0.05
HDD
Total
(M)
800
Note:
Assumes 17hr/day tester utilization
Assumes Rework Cost labor only
Total
Rework
Cost
(M)
$120
Conclusion
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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
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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