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

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

Henry Patland President CEO hpatland_at_us-isi.com
www.us-isi.com
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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.

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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

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GMR/LMR Heads
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TMR/PMR
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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

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LMR Transition Field Component
Structure of media stray field and read-back
pulse for longitudinal recording
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PMR Transition Field Component
Media stray fields for perpendicular media with
soft under-layer
U-Shape bending caused by Perpendicular Stray
Field
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Low Frequency Cut-off in PMR
Read-back of low density perpendicular square
wave pattern with different LF cut-off
frequency Signal shape distortions
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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)

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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
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Field Induced Instability
Soft Kink at 160 Oe
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Field Induced Instability _at_ 150 Oe
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Field Induced Instability _at_160 Oe
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Field Induced Instability _at_ 170 Oe
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Spectral Maximum Amplitude Noise (SMAN) Test
Soft Kink at 160 Oe
Patent US6943545
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Spectrum Analysis
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Pin-Layer-Reversal due to ESD damage
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QST has good track record at conventional
testing. Can QST testing address TMR/PMR
Specific Problems?
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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

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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
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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

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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

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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

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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

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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

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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

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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

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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)

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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

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ISI Quasi-Static Testing Portfolio
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Available Electrical Test Technologies

• Dynamic Testing
• Quasi-Static Testing

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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

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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

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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

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QST Head Test Disadvantages

• Cannot characterize writer
• Cannot predict head/media interface problems
  since there is no flying
• No off-track analysis

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Conventional Electrical Test Flow Model
100 Bar/Slider QST
100 Dynamic Head Test
100 Head Stack Actuator QST
100 Final HDD Test/Burn-in
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Conventional Electrical Test Cost Model
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Proposed Electrical Test Flow Model
Sampling or NO DET Testing
100 Bar/Slider QST
5 Dynamic Head Test
100 Head Stack Actuator QST
100 Final HDD Test/Burn-in
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More Cost-Effective Test Cost Model
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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?

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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 Intl, Quasi 97,
  Blazer-X5B and QST-2002 Tester