Transcript All About Hard Drives Lili Ji 2005. 4 EE 666 Advanced Semiconductor Devices Outlines         Hard Drive History Hard Drive Structures Hard Drive Disk Media Hard Drive Writing Heads Hard.

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
EE666 Advanced Semiconductor Devices
Hard Drive History
 1956, IBM,
RAMAC
 5Mb Storage
 50 disks, 24
inch in diameter
EE666 Advanced Semiconductor Devices
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.
EE666 Advanced Semiconductor Devices
Hard Drive History
EE666 Advanced Semiconductor Devices
Hard Drive Structures
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
Hard Drive Writing Head
---Longitudinal Writing Head
S. Khizroev and D. Litvinov, J.A.P Vol 95,Num 9, May 2004
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
Hard Drive Bit Size
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
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.
EE666 Advanced Semiconductor Devices
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.
EE666 Advanced Semiconductor Devices
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.
EE666 Advanced Semiconductor Devices
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
EE666 Advanced Semiconductor Devices
What’s Next?
--BMR Reading Heads
 Ballistic Magnetoresistive can provide a
∆R/R of more than 300%.
Edward Price, CMRR& UCSD Physics.
EE666 Advanced Semiconductor Devices
Summary
 Smaller Bit Size +More sensitive reading heads
Larger Hard Drive!
 Now let's have some fun!
EE666 Advanced Semiconductor Devices