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The Future of Magnetic
Recording Technology
April 11, 2008
Richard New
Director of Research
© 2008 Hitachi Global Storage Technologies
Agenda
„
Overview of Hitachi GST & San Jose Research Center
„
Technology Challenges for Magnetic Recording
„
Future Recording Directions
Patterned Media
„ Thermally Assisted Recording
„
© 2008 Hitachi Global Storage Technologies
4/11/2008
2
Hitachi Ltd. Overview
Revenue
US$ 86,847 million
Operating Income
US$ 1,547 million
Number of Employees
384,444
Consolidated Subsidiaries
934
Consolidated figures for FY 2006, ended March, 2007
Information & Telecommunication Systems
Power & Industrial Systems
24%
Financial Services
5%
12%
Logistics, Services
and Others
High Functional Materials
© 2008 Hitachi Global Storage Technologies
13%
US$ 86.8
billion
29%
日立の事業
18%
Electronic Devices
15%
Digital Media & Consumer Products
4/11/2008
3
Hitachi Global Storage Technologies Overview
„
Hitachi Global Storage Technologies (GST) was formed when Hitachi Ltd.
purchased the Storage Technology Division from IBM.
The hard disk drive operations from IBM and Hitachi Ltd. were combined and
launched as a new company on January 1, 2003.
„
Revenues in 2006 of $4.9 billion, 33K employees worldwide.
„
US headquarters in San Jose, California.
WW operations in 9 countries (R&D in US & Japan, manufacturing in China,
Phillipines, Thailand, Singapore, Japan and US).
„
1.5K R&D employees, with industry’s largest patent portfolio.
Enterprise
3.5-inch
2.5-inch
√
√
√
√
√
√
√
√
√
√
√
√
© 2008 Hitachi Global Storage Technologies
√
4/11/2008
4
Hitachi GST Headquarters in San Jose, CA
© 2008 Hitachi Global Storage Technologies
4/11/2008
5
Hitachi San Jose Research Center : Our People
San Jose Research Center Staff
„
„
„
Technical Disciplines
~100 permanent research staff
>70% hold PhD degree
Geographically diverse
50% NA; 25% EMEA; 25% Asia
„
„
15 Fellows of professional societies
Wide range of technical disciplines
Educational Institution
Educational Institution
10
9
8
7
6
5
4
3
2
1
UC
St
an
f
or
d
UC
Be SD
rk
el
ey
UC
LA
Sa
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Jo t e
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St
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eo
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ia
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ar
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Un W
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iv
H
I
Un er s Aa T
iv it y che
er
o
si f B n
ty
a
of se
To l
ky
o
0
© 2008 Hitachi Global Storage Technologies
4/11/2008
6
Hitachi San Jose Research Center : Our Facilities
Expose / Develop
Plating / Etching
Resist Apply / Strip / Bake
San Jose Research Center Facilities
„
„
„
„
„
„
58,000 sq ft of lab space
15,000 sq ft of clean room space
Recording head prototyping line
Full nano-fabrication facility
E-beam, optical litho, deposition, RIE,
mill, characterization, SEM.
MEMS lab, model making / machining shop
© 2008 Hitachi Global Storage Technologies
CMP
Vacuum
E-beam Photo
MEMS
4/11/2008
7
Agenda
„
Overview of Hitachi GST & San Jose Research Center
„
Technology Challenges for Magnetic Recording
„
Future Recording Directions
Patterned Media
„ Thermally Assisted Recording
„
© 2008 Hitachi Global Storage Technologies
4/11/2008
8
Areal Density Trend
10000
Hitachi/HGST
20~60% CGR
Areal Density (Gb/in2)
IBM/HGST
1000
Quantum/Seagate
60% CGR
Toshiba
GMR heads
MEPRML channel
etc.
Fujitsu
100
Samsung
90% CGR
10
1
MR head
thin film m edia
PRML channel
etc.
25% CGR
AFC-LMR
TMR
Advanced PMR?
DTM
BPM
TAR
PMR
TFC
etc.
CPP-GMR
60% CGR
0.1
1990
1995
2000
2005
2010
2015
Year product available (mobile)
© 2008 Hitachi Global Storage Technologies
4/11/2008
9
HDD Technology Challenges
Head/Disk Spacing
Recording System
Requirements:
Center the recording head above
the data track.
Fly the head very close to the
recording medium.
Magnetic
Element
Servo Mechanics
Data
TMR
Write Head
Magnetic Spacing Physical Spacing
Magnetic
Overcoat
Film
Disk Substrate
Data
Servo
Servo
Servo
Write sharp transitions in the
recording medium.
Store the data reliably for more
than 10 years.
Read the data back with high SNR
and high resolution.
Decode the signal with very few
readback errors (~10-11 Sector
Failure Rate).
All with high reliability, high
performance, low power, and for
pennies per GB.
© 2008 Hitachi Global Storage Technologies
01010100101101
10101010101010
01010101110101
10101101010010
01010101010101
I
Disk
Signal Processing
Read Head
4/11/2008
10
Servo Mechanics Challenges
FDB Motors
Airflow
Modeling
1000 kTPI Æ Track pitch = 25 nm Æ NRRO Sigma = 0.6 nm
1000
Large TPI jump
with BPM
kTPI
• Reduce Disturbances
– Motor Vibration
– Airflow Management
• Increase Disturbance Rejection
– Increased Mechanical BW
– External Vibration Feed
Forward
– Adaptive Servo Algorithms
– Dual Stage Actuation
(milli or micro−actuator)
• Shock Resilience
25% TPI CAGR
Patterned Media
Continuous Media
100
2005 2006
2007 2008
2009 2010
2011
2012 2013
Year
Micro Actuator
Suspension
Slider
Microactuator
G Shock
Recording
Head
© 2008 Hitachi Global Storage Technologies
4/11/2008
11
Magnetic Spacing Challenges
1000
Design Constraint(s)
Recession
Slider Process
Slider Overcoat
Scratch resistance
Clearance
Lube Transfer
Take Off Height
Disk Roughness
Lubricant
Scratch resistance
Media Overcoat
Corrosion, Scratch resistance
Mag Spacing (nm)
Magnetic Spacing
Component
10
1
0.1
Surface Topology & Overcoats
Magnetic
Element
100
1
10
100
Areal Density (Gb/in2 )
1000
Thermal Fly Height Control
Slider
Recession
Slider
Overcoat
Lube
Magnetic Spacing
Clearance
TOH
Media Overcoat
Magnetic Film
Disk Substrate
© 2008 Hitachi Global Storage Technologies
4/11/2008
12
The Recording Mechanism
Write
Head
Current
Read
Head
Write
Flux
Magnetization into the plane
Magnetization out of the plane
Disk Rotates
This Way
Track
Width
Hard Magnetic
Recording Layer
(CoCrX granular alloy)
Fly
Height
Exchange Break Layer
Soft Underlayer
Old Data
New Data
Media
Top
View
Skew
Angle
Read
Width
Pole Tip
1 0 111 0 0 1 1 0 1 0 0 0 0 1 0 0 11 0
Readback
Signal
Voltagel
© 2008 Hitachi Global Storage Technologies
Write
Width
Detected
Data
time
4/11/2008
13
Writeability, Thermal Stability, and SNR
Magnetic
Grain
Single Grain
Magnetostatic Energy
CONVENTIONAL
MEDIA
50
50 nm
nm
Energy
Barrier
-90
0
90
Magnetization Angle
Magnetic Stability:
energy barrier
Problem:
thermal energy
∝
• To increase SNR, need small grains.
• Smaller grains are thermally unstable.
• To avoid thermal instability, increase
grain anisotropy Ku.
• This increases the medium coercivity and
makes the medium difficult to write.
© 2008 Hitachi Global Storage Technologies
anisotropy x volume
kB x temperature
=
K uV
k BT
Solutions:
• Capped and exchange spring media.
• Work with larger ‘grains’: patterned media.
• Work with higher anisotropy: thermally
assisted recording (TAR).
4/11/2008
14
Media Technology
History of Media Innovations
Media Technology Challenges
• Thin film media (early 1990’s)
• Reduce grain size (8-9nm -> 6-7 nm).
• Increase anisotropy (to maintain stability).
• Maintain high quality growth:
– Uniform grain size
– Narrow switching field distributions.
• Reduce media layer thicknesses:
– Reduce head to media spacing
– Reduce head to SUL spacing
• AFC longitudinal media (pixie dust) (2000)
• PMR capped media (2005)
• Exchange spring media (2008)
Capped Media Exchange Spring Layer
(ESL) Media
Soft Cap Layer
Soft Cap Layer
Mag Layer
Coupling Layer
Mag Layer
Media Stack
Mag Layer Granular Structure
COC
Mag Layers
H=0
H
H
H
Underlayer
Seed Layer
Soft Underlayer
(SUL)
Exchange
Break Layer
(EBL)
Adhesion
Substrate
© 2008 Hitachi Global Storage Technologies
4/11/2008
15
Read Head Sensor Technologies
Year
1979
Areal
Density
10
Mb/in2
(LMR)
Sensor
Technology
Structure
Thin-film
Inductive
1991
Lead
MR Sensor
(LMR)
1997
2
Gb/in2
NiFe Free
Layer
Hard Bias
Lead
Hard Bias
Spacer
NiFeX SAL
Lead
N/A
N/A
Barkhausen
Johnson
Anisotropic
MR
Hard Bias
Cu Spacer
NiFe Free Layer
2006
Tunnel Valve
(PMR)
Johnson
Lead
Spacer
Hard Bias
Insulator
Johnson
Bottom Shield
Shield
CoFe/NiFe Free Layer
Spacer
Hard Bias
Insulator
Lead
Giant
MR
Shield
100
Gb/in2
CIP
(Current In Plane)
Shield
Lead
Hard Bias
(LMR)
Major Noise
Sources
Shield
Insulator
AP Pinned
Co Layer
Spin Valve
Current
Geometry
Shield
Insulator
100
Mb/in2
MR
Effect
Tunneling
MR
MgO Tunnel Barrier
AP Pinned CoFeB Layer
Shield
CPP (Current
Perpendicular
to the Plane)
Johnson
Shot Noise
Mag Noise
Shield
Shield
2011
1 Tb/in2
(PMR)
CPP GMR
High spin-scattering Free Layer
Spacer
Spacer
Hard Bias
Hard Bias
Insulator
Insulator
High spin-scattering
Pinned Layer
© 2008 Hitachi Global Storage Technologies
Cu Spacer
Shield
Giant
MR
Shield
Johnson
Mag Noise
Spin Torque
4/11/2008
16
Read Head Sensor Challenges
Migration to Low RA Sensors
Read Head Challenges
500
– Track width
– Shield spacing
• High Sensitivity (mV/Oe)
∆V = i η (∆R/R) R
• Low Noise
– Johnson Noise
– Shot Noise (TMR)
– Mag Noise
2
0.4 Ω - μ m
400
2
1 Ω- μm
(RA Product)
2
0.15 Ω - μ m
300
2
0.1 Ω - μ m
TMR
Current Screen
CPP-GMR
All Metal
CPP- GMR
200
Migration to
Low RA Sensors
~TW
2
0.05 Ω - μ m
TW
100
• Design Constraints
–
–
–
–
–
Sensor resistance (Ω)
• Small Geomerty
50 Ω < R < 500 Ω
Temperature Rise
Breakdown Voltage
Spin Torque Instability
Magnetic Self-Field
Sensor Resistance
R = (RA / TW 2 )
0
0
10
20
30
40
50
60
70
80
Track Width (nm) (~ Stripe Height)
Read Head Requirements
Requirement
300 Gbit/in2
500 Gbit/in2
750 Gbit/in2
1000 Gb/in2
2000 Gb/in2
Track Width
60 nm
45 nm
35 nm
27 nm
20 nm
Shield Spacing
35nm
32nm
30nm
22nm
20nm
SNR
33 dB
32 dB
31 dB
30 dB
30 dB
© 2008 Hitachi Global Storage Technologies
4/11/2008
17
AMR, GMR and TMR Physical Mechanisms
1991
AMR (CIP)
ΔR/R ~ 2%
t ~ 100 nm
NiFe
e−
M
Mechanism : Spin orbit scattering.
Resistance lower when current flow
is parallel to the magnetization M.
Limitation : Surface scattering limits
film thickness to > 100 nm.
GMR (CPP)
M2
M1
e−
FM1
Cu
FM2
2010?
ΔR/R ~ 10%
Mechanism : Same as CIP GMR.
No parasitic resistance problem.
Low noise, but lower ΔR/R than TMR.
Limitation : Spin torque, and “mag
noise” due to thermal fluctuations in M.
© 2008 Hitachi Global Storage Technologies
GMR (CIP)
FM1
Cu
FM2
M2
M1
1997
ΔR/R ~ 10-15%
e−
Mechanism : Spin dependent scattering.
With M1||M2, half the electrons (the majority
electrons) have low scattering in both films.
With M1 anti || M2, all electrons have high
scattering in one of the films.
It turns out that M1||M2.has lower resistance.
Limitation : CIP lead parasitic resistance.
TMR (CPP)
M2
M1
e−
E
low
scattering
high
scattering
EF
majority
electrons
minority
electrons
D(E)
D(E)
2006
FM1
MgO
FM2
ΔR/R >= 100% (room temp)
Mechanism : Spin dependent tunneling.
FM1 imparts a spin polarization : more min conduction e−.
When M1||M2, these min e− have more states to tunnel into.
So M1||M2 is the lower resistance state.
Limitation : High resistance as sensor size shrinks.
4/11/2008
18
Future Readback Sensor Candidates
Extraordinary
Magnetoresistance
Magnetic Tunnel
Transistor
Spin Accumulation
Sensor
Physics:
Lorentz force +
electrostatics in
semiconductor
/metal
heterostructures
Solin et al,
JVST B 21,
3002 (2003)
Coulomb Blockade
Magnetoresistance
Physics:
Hot electron transport
+ spin dependent
transmission
Park et al,
JAP 98,
103701 (2005)
Spin FET
Jedema et al,
APL 81,
5162 (2002)
Tunneling Anisotropic
Magnetoresistance
Physics:
Single electron
transport +
spin dependent
chemical
potential
Wunderlich
et al, PRL 97,
077201 (2006)
© 2008 Hitachi Global Storage Technologies
Physics:
Spin polarized injection
and extraction +
Hall et al,
Rashba effect
APL 83,
2937 (2003)
Giddings et al,
PRL 94,
127202 (2006))
4/11/2008
19
Extraordinary Magnetoresistance (EMR) Sensor
2 DEG
Current Density
×
Applied
Field
Linear Response with ΔR/R ~ CIP GMR
External Field
2005 EMR Device
Electrons
0.13
Metal Shunt
y = 6.2e-006*x
+ 0.13
ΔV
EMR~ 6 mV @ 650 Oe
ΔVEMR/ΔH ~ 6 μV/Oe
0.129
2 DEG
V2-4 [V]
0.128
0.127
0.126
Applied
Current
Measured
Voltage
+
0.125
0.124
-500
2006
Device
© 2008 Hitachi Global Storage Technologies
-400
-300
-200
-100
0
100
BApplied [Gauss]
200
300
400
500
Noise still a problem : lower SNR than TMR.
4/11/2008
20
Iterative Decoding (LDPC Decoding)
Iterative Decoding
Issues
Parity Check Nodes
LDPC
Decoder
Bit Nodes
• Implementation complexity,
speed and latency.
• Decoding error floors.
• Miscorrection detection.
• Burst correction.
readback
samples
readback
samples
PR
equalizer
PR
equalizer
bit probabilities
SISO
Detector
Parity
Post Proc
Viterbi Plus
Error Filters
SISO
detector
iteration
LDPC
decoder
RS ECC
decoder
RS ECC
decoder
detected
data
detected
data
soft decisions (bit probabilities)
hard decisions (bits)
© 2008 Hitachi Global Storage Technologies
4/11/2008
21
Agenda
„
Overview of Hitachi GST & San Jose Research Center
„
Technology Challenges for Magnetic Recording
„
Future Recording Directions
Patterned Media
„ Thermally Assisted Recording
„
© 2008 Hitachi Global Storage Technologies
4/11/2008
22
Patterned Media
Conventional PMR Media
• Continuous granular
recording layer.
• Multiple grains per bit.
• Boundaries between bits
determined by grains.
• Thermal stability unit is
one grain.
© 2008 Hitachi Global Storage Technologies
Bit Patterned Media
• Highly exchange coupled granular media.
• Multiple grains per island, but each island
is a single domain particle.
• Bit locations determined by lithography.
• Thermal stability unit is one island.
Discrete Track Media
• Conventional PMR media,
with patterned tracks.
• Multiple grains per bit.
• Eliminates track edge
noise and increases
tolerance to TMR.
• Thermal stability unit is
still one grain.
4/11/2008
23
Patterned Media Fabrication Process
Template Fabrication
Media Fabrication Process
PMR Media Deposition
Template Replication
Rotary Stage E-Beam
Patterning
Nanoimprint
Master Template
Fabrication
Template
Replication
Pattern Transfer
(i.e. etch/mill into
recording layer)
Planarization
One e-beam
master template
10,000 replica
nanoimprint molds
Existing Processes
New Processes
Lube and Burnish
100,000,000 imprinted
disk substrates
Inspection
© 2008 Hitachi Global Storage Technologies
4/11/2008
24
Thermally Assisted Recording (TAR)
• Using new magnetic media, heat is
applied for ease of writing data
• Heat media to record data but store and
read data at normal temperature
• Enables use of very difficult to write highenergy media, which is more stable for
writing data
• May allow areal density in the
terabit/square inch range, similar to
patterned media
GMR
laser
write coils
heat spot
© 2008 Hitachi Global Storage Technologies
4/11/2008
25
Thermally Assisted Recording (TAR) Challenges
• Development of new small grain high coercivity
media with correct thermal properties.
• Recording head writer design with optical
waveguide and near field source.
• Head-disk interface & contamination.
• Light coupling efficiency from laser, through
waveguide and near field source.
• Spot size converter, polarization rotator.
• Power dissipation and thermal
management in the recording head.
• Cost of laser and assembly per slider.
• Thermal timing and side writing on neighboring
tracks.
© 2008 Hitachi Global Storage Technologies
4/11/2008
26
HDD Future Technology Roadmap
HDD Future Technology
• Conventional PMR technology likely extendable to 1 Tb/in2 or more.
• Magnetic storage technology extendable to very high areal densities.
20,000?
Areal Density
Thermally Assisted Recording (TAR)
Possibly combined with PM
5,000?
Patterned Media (PM)
(DTR & BPM)
1000?
Perpendicular Recording
130
Longitudinal
Recording
• 50 Years
• >50 Million increase in areal density
Time
© 2008 Hitachi Global Storage Technologies
4/11/2008
27
Changing Markets and Usage Requirements
„
New Applications
•
•
•
•
„
Portable storage
Near line storage
Set Top Boxes/PVR
Gaming
Emerging Technical Requirements
• Security Features (bulk encryption)
• Reduced power consumption for data
centers
„
New Storage Interfaces
„
New Competing Technologies
„
Continued Growth in Capacity
Requirements
© 2008 Hitachi Global Storage Technologies
4/11/2008
28
Summary
„
The HDD industry is at a technology
crossroads.
„
Transition to future technologies will be
more difficult than transition from
longitudinal to perpendicular recording.
„
Faster rate of technology introduction.
• Many new technologies required to reach
1 Tb/in2 in ~2011.
„
Technologies must be introduced while
reducing cost (average prices declining
about 5% per year).
„
Magnetic recording technology
continues to be very extendable, but
investing in the R&D and in new
technology introduction is challenging.
© 2008 Hitachi Global Storage Technologies
4/11/2008
29