gmr read head - ucsdx-ray.ucsd.edu/mediawiki/images/9/9d/gmrreadheads-fullerton.pdf · recording...
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UCT)
ATE
GMR Read headGMR Read headEric Fullerton
ECE, CMRR
Introduction to recordingBasic GMR sensorNext generation heads TMR, CPP-GMRChallenges
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Product scalingProduct scaling
2 kbits/in2
70 kbits/s50x 24 in dia disks$10,000/Mbyte
Microdrive78 Gbits/in2
1 x 1” dia disk
8 Gbyte
5 Mbyte 100 Gbytemobile drive
RAMAC 1956
130 Gbits/in2
630 Mb/s2 x 2.5”glass disks<$0.01/Mbyte
UCT)
ATE
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ArealAreal density trendsdensity trends
0.01
0.1
1
10
100
1000
10000
1980 1990 2000 2010
Are
al D
ensi
ty (G
b/sq
.in.)
100% / yr
30% / yr
60% / yr
Standard FFMR headPRML channel Thin film disk
GMR head
Demos Perpendicular
40% / yr230 Gb/in2 demo
Products
}20%-40%
• IBM / Hitachi, highest AD productsCompetitors, mobile
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19751975
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Recording basicsRecording basics
Suspension
DiskActuator
Spindle / Motor
Slider
Data trackTrackwidth
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Magnetic recording componentsMagnetic recording components
Direction of Disk Motion
Inductive Write Element
GMR Read Sensor
Track of Recording Media
Grain Structure andMagnetic Transitiont
W
B
B = 25 nm (σ<3 nm), W=140 nm, t = 14 nm~ GHz data rates / 10 year retention
~8 nm
Head-media 10 nm
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Magnetic recording componentsMagnetic recording components
Copper Write Coils
Pole WidthInductive Write HeadP2 Layer
Throat Height
Write Gap
Width
Inductive Write HeadP1 Layer &Top Shield
GMR Contacts& Hard Bias GMR Read Sensor
Bottom Shield
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Magnetic recording componentsMagnetic recording components
B = 25 nm (σ<3 nm), W=150 nm, t = 14 nmdata rate ~ GHz
Direction of Disk Motion
Inductive Write Element
GMR Read Sensor
t
W
B
“Compass” that responds to local magnetic field and varies the resistance
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“0” “1” “0”
3 0 0 0 0 3 0 1 0 0 3 0 2 0 0 3 0 3 0 0 3 0 4 0 0 3 0 5 0 0
- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
sign
al
t i m e [ n s ]
“1”
Recording basicsRecording basics
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103 0 0 0 0 3 0 1 0 0 3 0 2 0 0 3 0 3 0 0 3 0 4 0 0 3 0 5 0 0
- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
sign
al
t i m e [ n s ]
“0” “0” “0” “1”
Recording basicsRecording basics
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110 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0- 8 0
- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
8 0
t i m e [ n s ]
sign
al
3 0 0 0 0 3 0 1 0 0 3 0 2 0 0 3 0 3 0 0 3 0 4 0 0 3 0 5 0 0
- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
sign
al
t i m e [ n s ]
PW50
PW50/T = 3
Magnetic resolutionMagnetic resolution
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Anisotropic MagnetoAnisotropic Magneto--resistance (AMR)resistance (AMR)
M I
M I
high resistance
low resistance
Bulk property of magnetic materials
0 90 180 270 360
resi
stan
ce
1-2 % effects
angle between I and M
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AMR SensorAMR Sensor
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Giant MagnetoGiant Magneto--resistance (GMR)resistance (GMR)
M I
high resistance
low resistanceInterface property of magnetic materials
0 90 180 270 360
resi
stan
ceangle between M1 and M2
M I
10-20 % effects
Baibich et al. Phys. Rev. Lett. 61 2472 (1988)Binasch et al. Phys. Rev. B 39, 4828 (1989); P. Grunberg, U.S. patent # 4,949,039
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GMR sensorGMR sensor
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GMR sensors and scalingGMR sensors and scalingMR and GMR/Spin Valve Head
Characteristics
Spin dependent scattering in a single alloyGrochowski/Gurney
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GMR sensorsGMR sensors
Pinned layer
Spacer layer
Free layer
Track of data
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GMR sensorsGMR sensors
Trackwidth
Fringe field frombits rotates free layermagnetization
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GMR sensorsGMR sensorsThe reference ferromagnetic layer magnetization is pinned by an
antiferromagnetic layer and does not rotate in small magnetic fields
Mom
ent
ΔR
/R
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GMR sensorsGMR sensorsPinned layer is AP pinned to obtain flux closure to minimize magneto-static coupling to free layer
Utilize AP coupling property of Ru, Ir…
5 10 15
J (a
rb. u
nits
)
thickness (Ru)
F coupling
AF coupling
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GMR sensorsGMR sensors
X XHapplied
External hardmagnet bias
reference
free
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GMR sensorsGMR sensors1) Produce undercut resist structure
(193nm photolithography)
2) Ion Mill, then IBD HB/leads
3) Lift-off Resist
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GMR sensors and scalingGMR sensors and scaling
Total gap
shield
shieldCurrent-in-plane
(CIP)
downtrack direction
Total gap
shield
shieldCurrent-in-plane
(CIP)
downtrack direction
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GMR sensorsGMR sensors
70 nm Critical lithography feature
NiFeCoFeCuCoFeRuCoFe
IrMn
State-of-the-art magnetic hard disk drivesI. R. McFadyen, E. E. Fullerton and M. J. Carey, MRS Bulletin 31, 379 (2006).
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GMR sensorsGMR sensorsThe height of the sensor is controlled by lapping (polishing) not by lithography.
The smallest feature in a thin film head is determined mechanically
sensor
lapped air bearing surface
DiskSide
Shield 1
Shield 2
Sensor width = 160 nm
Sensor height = 100 nm100 nm
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GMR read headGMR read headWorks great, what’s the problem
ΔR not increasingR increasingShorting to the shieldsEdge damage for small features
11
10
9
8
7
GM
R R
atio
(%)
25020015010050Width (nm)
Model Data
J. A. Katine, et al., Appl. Phys. Lett., 83, 401 (2003).
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New sensor geometryNew sensor geometry
I
CPP-Tunnel Magnetoresistance (high R)(Current-perpendicular-to-plane)I
CIP-GMR(Current-in-plane)
CPP-GMR (low R)(Current-perpendicular-to-plane)
I
GMR spin-valve
Magnetic tunnel-valve
GMR spin-valve
Tunnel-valve head
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CPP sensorCPP sensor
xbottom lead and shield
Insulator/hard bias deposition/Insulator deposition
Sensor deposition
Photo/Ion mill
Top lead and shield
x
current
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TMR sensorTMR sensor
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TMR sensorTMR sensor
Underlayer(s)
Magnetic electrode 1Barrier material
oxidation
Tunnel barrier
Magnetic electrode 2
Overlayer(s)
Shield S1
2) Thickness of given barrier materialDetermines RA= Resistance x Area
3) TMR is independent of specific materials in sensor stack
Sensor design is highly flexible
1) Barrier + magnetic electrode interfaces determine maximum TMRAlOx 70%TMR and MgO >500% TMR
Key goals: - Smooth substrate+underlayers- continuous ultrathin barrier growth- Stable chemistry @ barrier interfaces- No shunting of barrier during lithography
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TMR sensorTMR sensorThe resistance of the device depends on RA product
R (per unit area) depends exponentially on the barrier thickness
A is set by size of the bits (decreases with time).
To keep the resistance of the device constant you need to thin the barrier over time (or find lower R barrier materials).
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TMR sensorTMR sensor
1
10
100
0.001 0.01 0.1 1 10 100 1000
26.5 dB head S/ N15% ut i l izat ion
Vop = 180 mV
CPPtunnel-valves
CPPspin-valvesCPPSpin-valves
CPPTunnel valves
35 Gb/in2
31 MB/s
300 Gb/in265 MB/s
150 Gb/in2
50 MB/s 70 Gb/in2
40 MB/s
ΔR/R
(%)
RA (Ω-μm2)Low RA (high current):+Amplifier noise+Ampere curling field+ Thermal/electromigration[+spin-torque]
High RA (low current):+Shot noise+Voltage bias limit+RC time constant
Johnson noise
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TMR sensorTMR sensor
Y. Nagamine et al. (Anelva corp.)Intermag ‘06
CoFeB/MgO/CoFeB
0 1 2 3 4 5 6
TMR
(%)
RA (Ω-μm2)
Typical behavior
"knee"
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CPP GMR SensorCPP GMR SensorIn absence of low RA tunnel barrier move to metal devices.
CIP-GMR Shunting effect limits maximum signal
Spin-diffusion length lsf
(100-300A)
Pinned layer
Free layer
Underlayer
Cap
SpacerGMR
Parasitic resistance
Parasitic resistance
CPP-GMRShield 2
Shield 1
Pinned layer
Free layer
Underlayer
Cap
Spacer
Shunting
GMR
Shunting
Shunting
Electron mean-free path λ(10-100A)
Gap 1
Gap 2Parasitic resistance
Lead
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CPP GMR SensorCPP GMR Sensor
Spacer
Cap layer
S2
Ru
AFM
Underlayer
S1
Free layer(M=30-50A NiFe)
CoFe/Cu interfaces
Spin mixing layersAP-pinned layers(ΔM = 0)
Antiferromagnet(Jex > 0.3 erg.cm2)
Total gap < 500AJ.Y. Gu et al., JAP 87, 4831 (2000)
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CPP GMR SensorCPP GMR SensorWant high resistance high spin polarized materials
0 20 400.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
CoFeAl in FL CoFeAl in FL and AP2
75 nm Hex
40.9 at.% Al
36.4 at.% Al
30.7 at.% Al
24.9 at.% Al17.8 at.% Al
ΔR/R
(%)
x (at.%)
0 at.% Al
(Co45.5Fe54.5)(1-x)Alx
Maat et al., JAPHirohata et al.,Current Opinion in Solid State and Mat. Sci. 10, 93 (2006).
Heusler alloys
e.g. NiMnSb, CrFeAl, …
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CPP GMR SensorCPP GMR SensorCompared to TMR, CPP GMR has lower R, ΔR & ΔR/R
So how to get a signal?
Current: > 108 A/cm2
HeatingElectromigrationSpin – transfer torques
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R ~ R0 + ΔR (1-cos(θ))GMR metallicTMR insulator
Spin transportSpin transport
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• Current polarized by F1• Transfer of spin angular
momentum to M• J ∼107 A/cm2
J. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996)L. Berger, Phys. Rev. B 54, 9353 (1996)
Spin transfer effectSpin transfer effect
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Magnetization dynamicsMagnetization dynamics
mHm×= 0γdt
d
Field torque (precession)
Damping torque (dissipation)
⎟⎠⎞
⎜⎝⎛ ×+
dtdmmα
Spin torque (negative friction )
( )( )pmm xμ
−teM
gIP
s
Bi
m
H
××
x
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Magnetization dynamicsMagnetization dynamics
J.A. Katine et al., Phys. Rev. Lett. 84, 3149 (2000)
nano-pillar
F2
F1e- GMR
Nanocontact
F2
F1e-
H
M. Tsoi et al., Phys. Rev. Lett. 80, 4281-4284 (1998)W. H. Rippard et al., Phys. Rev. Lett. 92, 027201 (2004)
( )SKdipSAPP
C MHHHpgVMA
I πα
2)0( // +++≈−
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GMR sensorGMR sensor
Thermal fluctuationsfluctuation-dissipation theorem
S kBT / M Vfree
Smith and Arnett, APL 78, 1448 (2001).
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SensorsSensors
Sensors need a lot of properties not just ΔR/R
Opportunities for new materials and new phenomena
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NonNon--magnetic magnetic sensorsmagnetic magnetic sensors
Solin, APL 80, 4012 (2001)Metal dot embedded in high mobilitylow carrier density semiconductor (i.e. InSb).
At low field E is _|_ to metal/SC boundary and j follows E low R.
At high fields because of the Lorentz force theangle between j and E can approach 90 degreeswith little current flowing through metal high R.
• Attractive because immune from magnoise, spin-torque• However geometry is challenging for a slider-type sensor
High-mobility SC
Metal shunt