The Future of Magnetic Data Storage Technology

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The Future of Magnetic Data Storage Technology

• Stanley Kon
• Prof. Roberto Horowitz
• CML Control Lab
• University of California at Berkeley

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Roadmap of HDD
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Scaling

• Why simple scaling never followed completely?
• Electronic capability
• Increasing disk RPM for high performance
• Inductive readback signal
• Thin-film heads limited by lithography
• Material properties are different
• Air bearing and lubrication
• Bit Length ? Mr t Hc-1
• Mr Magnetization Remanence
• t Physical thickness
• Hc Coercivity

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Superparamagnetism Limit

• Whats superparamagnetism?
• At about 40Gb/in2
• Ways to avoid superparamagnetic
• Aspect Ratio 20 1 ? 4 1
• Error-Correcting Codes
• Perpendicular Recording
• Antiferromagnetically-coupled (AFC) media
• Patterned Media

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Perpendicular Recording
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Patterned Media

• Potentially up to hundreds of Gb/in2
• One bit for each island
• Little Magnetic interaction
• Larger grains
• Lower Coercivity
• Time consuming
• Nanoimprint

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Antiferromagnetically-Coupled media

• Three-atom-thick layer of Ru sandwiched between
  two magnetic layers
• Expected to increase current areal density limits
  to surpass 100 gigabits/inch2

Magnetic thickness (Mr t)top - (Mr t)bottom
Magnetic thickness Mr t
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AFC ( cont. )
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Modern Read/Write Head
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MR Head

• NiFe ( Permalloy )
• 2 - 4 resistance change
• Horizontal Transverse bias

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MR Head ( cont. )
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Giant Magneto-Resistive Heads
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GMR ( cont. )

• Read areal densities beyond 15 Gb/in2
• At least twice to six times more sensitive than
  MR heads
• Efficiency strongly depends on conducting layer
  thickness and mechanical defects
• Symmetric or dual GMR offer possibility of
  achieving large GMR coefficients

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With Increasing Areal Density
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Some Other Problems

• Read / write heads
• Head to disk spacing
• Ultrathin dlc overcoats
• Switching-speed limitations in the head and
  medium

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