Transcript Magnetic Storage at Nano

Patterned Media Recording:
the future technology for
magnetic storage industry
Xiaojun Zhang (Mechanical Engineering)
Jie Wu
(Physics)
Final project of EE 235 course
Information Storage
Hard disk drive (HDD) is one of the most important
data storage media for electronics.
Main advantage:
1. Big capacity.
2. Economical in terms of cost per bit.
3. Permanent (no power consuming to maintain data).
HDD is NOT replaceable in modern life.
The market of HDD
In 1999, sales of hard drives reaches US $32 billion.
In 2007, the 2 biggest HD oems - Seagate and Western Digital
collectively reported an annual HD revenue of nearly $17 billion.
An a substantial improvement of magnetic storage could enable entirely
new computing applications, with spillovers across the computer industry
and every industry that uses magnetic recording to store data.
Example of how fast a new technology is adopted by this industry:
The dramatic advance of HDD
Time:
September 4, 1956
Name:
IBM 305 RAMAC
Capacity: 5 million 8-bit characters.
Size:
fifty 24-inch diameter disks
Areal density:
2,000 bit/in2
In 2005, the areal density is
Commercial HD: 100~150 Gbit/in2
Toshiba (perpendicular recording): 179 Gbit/in2
Toshiba's experimental systems: 277 Gbit/in2
Seagate Technology demonstrates: 421 Gbit/in2
Maximum of perpendicular recording technology: 1 Tbit/in2
Moore’s law
Price of HDD, DRAM and Flash
The price/performance ratio in terms of cost per bit:
1965: $10,000/MB
1989: $36/MB
1994: $1/MB
2000: 2¢/MB
2004: 0.1¢/MB
2009: 0.01 ¢/MB
Trends dominated by technology
The future of record media
Our focus today
Hard Disk Drive
http://news.bbc.co.uk/1/hi/technology/6677545.stm
Magnetic Recording Fundamentals
Magnetic field
http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm
Two Problems in Magnetic Recording
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Thermal Stability Issue
Transition Jitter Noise
Thermal Stability Issue
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Average Thermal Energy is
kBT (KB is the Boltzmann’s constant)
T normally is room temperature, ~ 300K
Energy barrier to switch a domain is
KuV
(V is the volume of the domain;
Ku is the anisotropy constant of the material.
Higher Ku means higher writing magnetic field)
KuV/kBT demtermines the thermal stability.
Normally it should be larger than 60.
Thermal Fluctuation Induced
Magnetization Switch
Magnetic Domain
Magnetic Domain
Transition Jitter Noise
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Transition boundary
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Transitions meanders
between random
grains.
This transition jitter
causes noise.
More grains at the
boundary can make
the transition
smoother, and thus
reduce noise.
Normally, for each bit
cell, there must be
100 or more grains to
get good signal-tonoise ratio (SNR).
Longitudinal Media Recording
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Before 2005, HDDs were made by longitudinal recording. However,
as the bit size becomes smaller and smaller, thermal instability
becomes a problem. (KuV/kBT)
The magnetization of each bit is directed along the disk surface.
This head-to-head or tail-to-tail structure makes them unstable
against thermal fluctuation.
Since it uses fringing field, which is normally smaller than gap field.
Materials with high Ku can not be used.
Perpendicular Media Recording
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The first commercially available disk drive with a
diameter of 1.8" was produced by Toshiba in
2005.
Soon after that in January 2006, Seagate
Technology began its first laptop sized 2.5-inch
hard drive.
Most recently in February 2009 Seagate
Technology announced the first 7200 rpm 2.0
Terabyte Hard Drive using PMR technology.
Perpendicular Media Recording
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The bits in perpendicular recording are magnetized
up or down perpendicular to the disk surface.
With the combination of soft magnetic underneath,
perpendicular recording technology realized the use
of gap field.
Materials with higher Ku can be used to circumvent
the thermal instability problem. (KuV/kBT)
Recording Layer
Soft Magnetic Layer
Patterned Media Recording
Comparison of conventional media recording with patterned media recording (from Hitachi)
Patterned Media Recording
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In conventional recording techniques, if we increase
grain volume V, the noise due to transition jitter will
increase accordingly.
In patterned media recording, the magnetic bits are
perfectly patterned and isolated from each other.
Therefore the jitter problem can be reduced.
Each island is a single magnetic domain. Patterned
media is therefore thermally stable.
Since we only need one grain for each bit instead of
100 grains, the areal density can be increased
roughly by 100 times with the same thermal stability.
Patterned Media Recording
For the same areal density, we can get better thermal
stability with patterned media recording.
Typical design for a patterned media recording
Nano-fabrication approaches
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Optical lithography
poor spatial resolution
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Focused Iron Beam
not suitable for massive production
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E-beam lithography
low throughput
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Block copolymer lithography
not uniform in big scale
A candidate approach:
E-beam lithography
+block copolymer assembly
Encouraging result:
improved uniformity
& 4 times density multiplication
A key step towards massive
production
Patterns obtained after pattern transfer
A. Cr patterns
B. Si patterns
Summary
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HDD experience dramatic development for the last
50 years and will keep this trend as Moore’s law
requires.
The development of HDD is generated by the
emerging and adoption of new technologies.
Patterned Media Record is the future technique to
replace longitudinal and perpendicular media
recording.
Nano-fabrication technique is the key to realize our
goal.