All about hard drives
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All About Hard Drives. Lili Ji 2005. 4. 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. Outlines. 1956, IBM, RAMAC 5Mb Storage

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All about hard drives

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 Drive Reading Heads

Hard Drive Limits

What’s next?

Summary

Outlines

EE666 Advanced Semiconductor Devices


Hard drive history

1956, IBM, RAMAC

5Mb Storage

50 disks, 24 inch in diameter

Hard Drive History

EE666 Advanced Semiconductor Devices


Hard drive history1

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 history2

Hard Drive History

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Hard drive structures

Hard Drive Structures

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Hard drive disk media

Hard Drive Disk Media

  • The gap between the head and the disk surface is 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 media1

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

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


All about hard drives

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

EE666 Advanced Semiconductor Devices


Hard drive reading heads amr reading heads

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!

AMR Origin

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

EE666 Advanced Semiconductor Devices


Hard drive reading heads gmr reading heads

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.

GMR Origin

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

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Hard drive bit size

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

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

Sadamichi, Spin Dependent Transport in Magnetic Nanostructure

EE666 Advanced Semiconductor Devices


What s the problem

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

Super Paramagnetic

  • Definition:

    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

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

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

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!

Summary

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