Transcript Spintronics and Current Driven Domain Wall Motion

All About Hard
Drives
Lili Ji
2005. 4
EE 666 Advanced Semiconductor Devices
Outlines
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Hard Drive History
Hard Drive Structures
Hard Drive Disk Media
Hard Drive Writing Heads
Hard Drive Reading Heads
Hard Drive Limits
What’s next?
Summary
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Hard Drive History
 1956, IBM,
RAMAC
 5Mb Storage
 50 disks, 24
inch in diameter
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Hard Drive History
 First Modern Hard Disk Design (1973)
IBM's model 3340, nicknamed the "Winchester", is
introduced. With a capacity of 60 MB it introduces
several key technologies that lead to it being
considered by many the ancestor
 First 3.5" Form Factor Disk Drive (1983)
Rodime introduces the RO352, the first disk drive
to use the 3.5" form factor, which became one of the
most important industry standards
 First Drive to use Magnetoresistive Heads (1990):
IBM's model 681 (Redwing), an 857 MB drive.
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Hard Drive History
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Hard Drive Structures
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Hard Drive Disk Media
 The gap between the head and the disk surface is
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about 15 nm.
Surface roughness should be a few nanometers.
Traditionally it is Al-Mg substrate with Ni-P on
it. Now glass substrate is increasingly used.
Cr or Cr-V alloy are used as under layers to
control the crystallographic orientation of the
magnetic layer.
Co based alloy is used as the top magnetic
layer,10~30nm in thickness.
Limited by grain size, areal density <35 Gb/sq.inch
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Hard Drive Disk Media
Topography AFM picture
RMS is about 8-12Å
MFM image, dark and white
Represents the bit information
Sadamichi, Spin Dependent Transport in Magnetic Nanostructure
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Hard Drive Writing Head
---Longitudinal Writing Head
S. Khizroev and D. Litvinov, J.A.P Vol 95,Num 9, May 2004
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Hard Disk Writing Head
—Perpendicular Writing
S. Khizroev and D. Litvinov,
J.A.P Vol 95,Num 9, May 2004
The first one use
perpendicular is
Toshiba’s mini hard drive
MK8007GAH , which will be
used in IPod, 80GB 1.8in
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Hard Drive Reading Heads
---AMR Reading Heads
 Introduced by IBM in 1991.
 ∆R/R=2~5%,providing areal density 1~5Gb/sq.inch
 R=R0+ ∆Rcos2θ
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AMR Origin
 Spin-Orbit coupling leads to spin dependent
scattering of conduction electrons.(3d and 4s
electrons)
 3d orbitals will be affected by magnetization. They
will mix and reorient, and show a larger scattering
cross sections when electrons are moving parallel
to M. And more scattering, or resistance!
http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf
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Hard Drive Reading Heads
---GMR Reading Heads
 ∆R/R=10~50%, providing areal density
larger than 10Gb/sq.inch
http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf
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GMR Origin
 Spin-dependent transmission of carriers at
interface between non-magnetic layer and
magnetic layer.
http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf
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Hard Drive Bit Size
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Is there a limit?
----Yes…. Super Paramagnetic
 Transmission
Electron Micrograph
of a Co-Cr-Pr-B
magnetic media.
 Fine grain size is
around 85Å
 Capable of supporting
areal density
35Gb/sq.inch
Sadamichi, Spin Dependent Transport in Magnetic Nanostructure
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What’s the problem?
 Each bit usually contains hundreds of
grains. Magnetic recording relies on the
statistically averaging over those grains to
get a satisfactory signal to noise ratio .
 As bits size continue decrease, grain size
need to be reduced, too. This can be
achieved by under layer control.
 However, eventually, the grains will
become super paramagnetic.
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Super Paramagnetic
 Definition:
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Magnetic information of the grain undergoes
spontaneous switching by assistance of thermal
energies.
Ms ----Saturation magnetization
Ku ---- Uniaxial anisotropy
V --- Volume of the grain
KuV---Magnetic anisotropy energy of the grain
To save information more than 10 years,
KuV>40~50kT
As V decreasing, Ku need to be increased to
avoid super paramagnetic!
Hc ----Switching field, Hc=2Ku/0Ms, so a larger
field is needed to write information.
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Possible Solutions
 Engineering media with narrower grain size distribution,
so magnetic anisotropy Ku can be increased.
 Perpendicular writing will have larger writing field, and
supporting smaller bit size while at the same time allows
more amount of grains in each bit.
 Thermally assisted writing is to use laser to locally heat
the media, to lower the coercivity Hc in that spot.
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What’s next?
---Patterned Magnetic Media
 Bit size is
decided by
lithography.
 Information is
stored in a
single domain
magnet particle.
 A 50 nm-period
square dot
array gives 250
Gb /sq.inch
http://eltweb.mit.edu/3.063/lecturenotes/Lec.16.4.5.05.pdf
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What’s Next?
--BMR Reading Heads
 Ballistic Magnetoresistive can provide a
∆R/R of more than 300%.
Edward Price, CMRR& UCSD Physics.
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Summary
 Smaller Bit Size +More sensitive reading heads
Larger Hard Drive!
 Now let's have some fun!
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