All About Hard Drives

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30 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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EE 666 Advanced Semiconductor Devices

All About Hard
Drives


Lili Ji


2005. 4

EE666 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

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


ƒ
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
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

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


Introduced by IBM in 1991.


∆R/R=2~5%,providing areal density 1~5Gb/sq.inch


R=R
0
+

∆Rcos
2
θ






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 85
Å


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:


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/

0
Ms, 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 Dr楶e!


Now let's have some fun!