EE 666 Advanced Semiconductor EE 666 Advanced Semiconductor DevicesDevices

All About Hard DrivesAll About Hard Drives Lili JiLili Ji

2005. 42005. 4

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OutlinesOutlines

Hard Drive HistoryHard Drive History Hard Drive StructuresHard Drive Structures Hard Drive Disk MediaHard Drive Disk Media Hard Drive Writing HeadsHard Drive Writing Heads Hard Drive Reading HeadsHard Drive Reading Heads Hard Drive LimitsHard Drive Limits What’s next?What’s next? SummarySummary

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Hard Drive HistoryHard Drive History

1956, 1956, IBM, IBM, RAMACRAMAC

5Mb Storage5Mb Storage 50 disks, 24 50 disks, 24

inch in diameterinch in diameter

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Hard Drive HistoryHard 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 HistoryHard Drive History

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Hard Drive StructuresHard Drive Structures

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Hard Drive Disk MediaHard Drive Disk Media The gap between the head and the disk surface is The gap between the head and the disk surface is

about 15 nm.about 15 nm. Surface roughness should be a few nanometers.Surface roughness should be a few nanometers. Traditionally it is Al-Mg substrate with Ni-P on it. Now Traditionally it is Al-Mg substrate with Ni-P on it. Now

glass substrate is increasingly used. glass substrate is increasingly used. Cr or Cr-V alloy are used as under layers to control the Cr or Cr-V alloy are used as under layers to control the

crystallographic orientation of the magnetic layer.crystallographic orientation of the magnetic layer. Co based alloy is used as the top magnetic Co based alloy is used as the top magnetic

layer,10~30nm in thickness.layer,10~30nm in thickness. Limited by grain size, areal density <35 Gb/sq.inch Limited by grain size, areal density <35 Gb/sq.inch

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Hard Drive Disk MediaHard 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 HeadHard Drive Writing Head------Longitudinal Writing HeadLongitudinal 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

The first one use perpendicular is Toshiba’s mini hard drive MK8007GAH , which will be used in IPod, 80GB 1.8in S. Khizroev and D. Litvinov, J.A.P

Vol 95,Num 9, May 2004

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Hard Drive Reading HeadsHard Drive Reading Heads---AMR Reading Heads---AMR Reading Heads

Introduced by IBM in 1991.Introduced by IBM in 1991. ∆∆R/R=2~5%,providing areal density 1~5Gb/sq.inchR/R=2~5%,providing areal density 1~5Gb/sq.inch

R=R0+ ∆Rcos∆Rcos22θθ

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AMR OriginAMR Origin Spin-Orbit coupling leads to spin dependent Spin-Orbit coupling leads to spin dependent

scattering of conduction electrons.(3d and 4s scattering of conduction electrons.(3d and 4s electrons)electrons)

3d orbitals will be affected by magnetization. They 3d orbitals will be affected by magnetization. They will mix and reorient, and show a larger scattering will mix and reorient, and show a larger scattering cross sections when electrons are moving parallel cross sections when electrons are moving parallel to M. And more scattering, or resistance!to M. And more scattering, or resistance!

http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf

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Hard Drive Reading HeadsHard Drive Reading Heads---GMR Reading Heads---GMR Reading Heads

∆∆R/R=10~50%, providing areal density R/R=10~50%, providing areal density larger than 10Gb/sq.inchlarger than 10Gb/sq.inch

http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf

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GMR OriginGMR Origin Spin-dependent transmission of carriers at Spin-dependent transmission of carriers at

interface between non-magnetic layer and interface between non-magnetic layer and magnetic layer.magnetic layer.

http://www.owlnet.rice.edu/~phys533/notes/week14_lectures.pdf

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Hard Drive Bit SizeHard Drive Bit Size

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Is there a limit?Is there a limit?----Yes…. Super Paramagnetic----Yes…. Super Paramagnetic

Transmission Transmission Electron Micrograph Electron Micrograph of a Co-Cr-Pr-B of a Co-Cr-Pr-B magnetic media.magnetic media.

Fine grain size is Fine grain size is around 85around 85ÅÅ

Capable of supporting Capable of supporting areal density areal density 35Gb/sq.inch35Gb/sq.inch

Sadamichi, Spin Dependent Transport in Magnetic Nanostructure

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What’s the problem?What’s the problem?

Each bit usually contains hundreds of Each bit usually contains hundreds of grains. Magnetic recording relies on the grains. Magnetic recording relies on the statistically averaging over those grains to statistically averaging over those grains to get a satisfactory signal to noise ratio .get a satisfactory signal to noise ratio .

As bits size continue decrease, grain size As bits size continue decrease, grain size need to be reduced, too. This can be need to be reduced, too. This can be achieved by under layer control.achieved by under layer control.

However, eventually, the grains will However, eventually, the grains will become super paramagnetic.become super paramagnetic.

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Super ParamagneticSuper Paramagnetic Definition:Definition: Magnetic information of the grain undergoes Magnetic information of the grain undergoes

spontaneous switching by assistance of thermal spontaneous switching by assistance of thermal energies.energies.

Ms ----Saturation magnetizationMs ----Saturation magnetization Ku ---- Uniaxial anisotropyKu ---- Uniaxial anisotropy V --- Volume of the grainV --- Volume of the grain KuV---Magnetic anisotropy energy of the grainKuV---Magnetic anisotropy energy of the grain To save information more than 10 years, To save information more than 10 years,

KuV>40~50kTKuV>40~50kT As V decreasing, Ku need to be increased to As V decreasing, Ku need to be increased to

avoid super paramagnetic!avoid super paramagnetic! Hc ----Switching field, Hc=2Ku/Hc ----Switching field, Hc=2Ku/00Ms, so a larger Ms, so a larger

field is needed to write information.field is needed to write information.

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Possible SolutionsPossible Solutions

Engineering media with narrower grain size distribution, Engineering media with narrower grain size distribution, so magnetic anisotropy Ku can be increased.so magnetic anisotropy Ku can be increased.

Perpendicular writing will have larger writing field, and Perpendicular writing will have larger writing field, and supporting smaller bit size while at the same time allows supporting smaller bit size while at the same time allows more amount of grains in each bit.more amount of grains in each bit.

Thermally assisted writing is to use laser to locally heat Thermally assisted writing is to use laser to locally heat the media, to lower the coercivity Hc in that spot. the media, to lower the coercivity Hc in that spot.

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What’s nextWhat’s next??------Patterned Magnetic MediaPatterned Magnetic Media

Bit size is decided Bit size is decided by lithography.by lithography.

Information is Information is stored in a single stored in a single domain magnet domain magnet particle.particle.

A 50 nm-period A 50 nm-period square dot array square dot array gives 250 Gb gives 250 Gb /sq.inch/sq.inch

http://eltweb.mit.edu/3.063/lecturenotes/Lec.16.4.5.05.pdf

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What’s Next?What’s Next?--BMR Reading Heads--BMR Reading Heads

Ballistic Magnetoresistive can provide a Ballistic Magnetoresistive can provide a ∆R/R∆R/R of more than 300%. of more than 300%.

Edward Price, CMRR& UCSD Physics.

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SummarySummary

Smaller Bit Size +More sensitive reading headsSmaller Bit Size +More sensitive reading heads

Larger Hard Drive!Larger Hard Drive! Now let's have some fun!Now let's have some fun!