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Trends in Magnetic Information Data Storage Trends in Magnetic Information Data Storage and Magnetic Random Access Memory (MRAM)and Magnetic Random Access Memory (MRAM)
YangYang--KiKi Hong Hong Professor and DirectorProfessor and Director
Magnetic and Electronic Materials LaboratoryMagnetic and Electronic Materials LaboratoryDepartment of Materials Science and Engineering, Department of Materials Science and Engineering,
University of IdahoUniversity of Idaho
November 20, 2003November 20, 2003
Yang-Ki Hong
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Information to store Temporary Storage Permanent Storage
Audio Tape Tape
Photo Floppy disk Floppy disk
Video CDR CDR
DVDR DVDR
HDD Internet
Solid State Devices (MRAM, Flash, OUM, FRAM)
Information Data and Storage MediaInformation Data and Storage Media
$$ Internet and networks to download software, consumer video storage, storage of HDTV program 40 ~ 50 GB
$$ Winning technology power, capacity, robustness, and cost
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3Yang-Ki HongSource: WTEC Panel Report on The Future of Data Storage Technologies, June 1999
Trend in Storage Capacity DemandTrend in Storage Capacity Demand
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MAGNETIC RECORDING
Particulate Recording Media
Thin Film Recording Media
MAGNETIC RECORDING
Particulate Recording Media
Thin Film Recording Media
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Magnetic Recording SystemMagnetic Recording System
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PerpendicularLongitudinal
Carbon overcoat
Seed layer
Recording Media
Soft magnetic underlayer
Ring Type Head Single Pole Type Head
OR
SubstrateSubstrate
GMR laser
write coils
heat spot
Source: Dr. Eric Fullerton, Hitachi San Jose Research Center
Thermally assisted recording (HAMR)
Lubricant
Magnetic layerUnderlayer
Soft magnetic underlayer
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M a g n e t i c & E le c t r o n i c M a t e r ia ls R e s e a r c h L a b .
B a F e a n d /o r C o C r a l lo y
Magnetic & Electronic Materials Research Lab.
Longitudinal and Perpendicular ModesLongitudinal and Perpendicular Modes
Magnetic & Electronic Materials Research Lab.
Perpendicular Longitudinal
Thin Film
Particulate
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Trend in Areal Density of Particulate Recording Media
Trend in Areal Density of Particulate Recording Media
Yang-Ki HongYang-Ki Hong
Helical scan
Narrow track longitudinal
Traditional longitudinal
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Trend in Areal Density of Thin Film Recording MediaTrend in Areal Density of Thin Film Recording Media
60 Gbits/in2 (2003)in market
80 Gbits/in2 (2004)product
130 Gbits/in2 (2003)deomonstrated
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Longitudinal: 130 Gbits/in2 (Mrt = 0.35 memu/cm2, 300 emu/cc, D = 6 ~ 8 nm, Hc = 4040 Oe, Linear density: 610 Kbpi, Track density: 213 Ktpi)
demonstrated in 2003Recording media limit 200 Gbits/in2 (Mrt = 0.35)Recording head limit < 200 Gbits/in2
(due to magnetization of writing head material < 2.35 Tesla)
Perpendicular: 130 Gbits/in2 (Hc = 4500 Oe, 550 ~ 600 emu/cc, D= 6 ~ 8 nm)demonstrated in 2003; Storage limit 0.6 Terabits/ in2 by 2009?
Thermally Assisted Recording (HAMR; heat-assisted perpendicular recording):
~ 1 Terabits/ in2 (1.5 x 1015 bits/m2) by 2013??Optical spot size < 50 nmKu = 106 ~ 107 erg/cm3 for tetragonal L10 FePt or CoPt
Discrete bit technology: Nanoimprinting; array of self-ordered magnetic nanoparticles
Beyond 1 Terabits/ in2 by 2020???
Trend in Magnetic Data Storage DensityTrend in Magnetic Data Storage Density
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CoCrPtB-based granular thin film: low SQ, small negative HN low thermal stability
Co-Pd or Co-Pt multilayered (> 20 layers) film: large grain size lower SNR than granular film
CoCrPt-oxide thin film: Wide coercivity distribution (SFD), High σ Hkof magnetic grains
For 0.6 Terabits/in2
SNR ∝ √N (N = the number of grains/bit; D < 5 nm)
Thermal stability (KuV/kT > 60; Ku > 3~4 x 106 erg/cm3)
Hk > 20 kOe, HN > - 2 kOe, SQ ~ 1.00, Slope ~ 1.2 to 2.0
Well-isolated fine grain (D < 5 nm)
Trend in Perpendicular Recording FilmTrend in Perpendicular Recording Film
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Hexa-ferrite Particle (BaFe)
Hc(Tape) = 1750 Oe, Br (Tape) = 1300 GSQ (Tape) = 0.76, SFD (Tape) = 0.09Aspect ratio = 4
BaFe+
40 nm
Hc(Tape) = 2000 - 5000 Oe, Br (Tape) = 1350 G, Aspect ratio = 3SQ (Tape) = 0.73, SFD (Tape) = 0.12
BaFe++
33 nm
Hc(Tape) = 2000-2500 Oe,
Br (Tape) = 1200 GSQ (Tape) = 0.59, SFD (Tape) = 0.33Aspect ratio = 3
BaFe+++
22 nm
Metal Particles (MP)
MP
Ceramic layer
Hc (Tape) = 1550 Oe, Br (Tape) = 2400GSQ (Tape) = 0.82, SFD (Tape) = 0.35Aspect ratio = 12
180 nm
MP+
Double coating layer
130 nmHc (Tape) = 1700 Oe, Br (Tape) = 2750GSQ (Tape) = 0.88, SFD (Tape) = 0.32Aspect ratio = 9
65 nmMP+++
Hc (Tape) = 2500 Oe, Br (Tape) = 3400GSQ (Tape) = 0.85, Aspect ratio = 6, σs = 145 emu/g
Coating layer
MP++
80 nmHc (Tape) = 1875 Oe, Br (Tape) = 3200GSQ (Tape) = 0.8, SFD (Tape) = 0.34Aspect ratio = 6, σs = 130 emu/g
Coating layer
Co
Nd
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Trend in Recording Magnetic ParticlesTrend in Recording Magnetic Particles
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Barium Ferrite Unit Cell –MagneticStructure
Barium Ferrite Unit Cell –MagneticStructure
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Barium Ferrite CrystalBarium Ferrite Crystal
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Roadmap for Particulate Recording Density and Coating Technologies Proposed by Fuji film
Source: Fuji film Recording Media Yang-Ki Hong
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Let: τ = 100 sec (required time to measure the remanence of specimen)
Vp = Superparamagnetic volume
kTKV
kTKV
eef−−
== 90 101
τ25=
kTKVp
3
234
=
DVp π ( ) nmCoDp 6.7=
M-D = multi-domainS-D = single-domainSP = superparamagnetic
0 Dp Ds
Hci
Unstable
Stable
M-DS-D
SP
Particle Diameter D
fo = 109/sec
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Hexagonal Platelet Barium Ferrite (H-BaFe) Nanoparticles
D = 50 nm
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Magnetic layer
Non-magnetic under layer
Substrate
S-BaFe or S-MP (CoPt or FePt) nanoparticles
α-Fe2O3 or TiO2 or other non-magnetic particles
PET or any substrate
UI’s Proposed particulate recording media with barium ferrite nanoparticles
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Grain Structure of CoCrPt Perpendicular Thin Film Media for 130 ~ 170 Gbits/in2(?)
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H. Uwazumi, et al., IEEE Trans. Mag., 39, 1914 (2003)
M. Zheng, et al., IEEE Trans. Mag., 39, 1919 (2003)
D = 7 ~ 8 nm
D = ~ 7 nm
20Grain size, Hc, Ms ∝ f (δAlN,,δBaM, and Ts-BaM)
Si
T. Ox., SiO2
AlN
BaM
Si
T. Ox., SiO2
amorphous-BaM
BaM
Grain size ∝ f (TS-BaM)Yang-Ki Hong
J. Magn. Magn., Mater., 242-245, 304 (2002)
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21AFM image of BaM (50nm thickness)Yang-Ki HongSource: Professor A. Morisako, Shinshu University, Japan
Structure and Grains of Barium Ferrite Thin Film
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(111) MgO
α
a1
a2
a3 (000l) BaFeaBaM = 5.893 Å, cBaM = 23.215 Å [110] in MgO (111) α = 60 oaMgO(111) = aMgO*√2 = 5.958 Å
(000l) BaFe normal to (111) MgO substrate α = 60 oaMgO(111) = 5.958 Å
α a1
a2
a3
c
5.958Å
Proposed Hexaferrite Thin Film Media for Perpendicular Recording
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NONVOLATILE MEMORY
Magnetic Random Access Memory (MRAM)
NONVOLATILE MEMORY
Magnetic Random Access Memory (MRAM)
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New Memory That Doesn't ForgetBy Elliot Borin |02:00 AM Jul. 09, 2003 PTWith both Motorola and IBM firmly lined up behind a single contender, the five-year search for a "universal RAM" technology offering a combination of non-volatility and high-speed random access appears to be all but over. According to Motorola, samples of the new magnetoresistive random access memory, or MRAM, chips will be distributed to developers by the end of 2003, and cell phones and PDAs incorporating MRAM should be on sale by mid-2004. Though IBM had previously announced plans to release its MRAM chips in 2005, Elke Eckstein, new CEO of Altis Semiconductor, a joint venture of IBM and Infineon Technologies charged with developing MRAM, indicated that a vastly accelerated timetable is being implemented.
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Nonvolatile Memory Comparison (2003)Nonvolatile Memory Comparison (2003)
• OUM: Ovonics Unified Memory
• MRAM: Magnetic Random Access Memory
• FRAM: Ferroelectric Random Access Memory Yang-Ki Hong
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N-MOSFET
Digit line (Easy axis)
N-MOSFET N-MOSFET
Bit line (Hard axis)
Word line(For reading)
1MTJ and 1 n-MOSFET for 1bit
Reading:
Word+Bit lines Writing:
Digit + Bit lines
MRAM element (MTJ)
FM-I: NiFe, etc.Insulator: Al2O3, etc.
PFM: Co etc.
P-AFM: IrMn, etc.
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MRAM Architecture with UI’s New Element DesignMRAM Architecture with UI’s New Element Design
Reading:Word+Bit lines
Writing: Digit + Bit lines
Digit line
MTJ Memory element
Word line
Digit line
Low k Insulator
Electrode
Bit line
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Minimum feature size: F = 0.13 µm
Cell size: 16 F2 = 0.27 µm2
(= 0.52 µm × 0.52 µm)Array size: 0.692 cm2
Chip size: 2.31 cm2
for array efficiency of 30 %
Hexagonal element size: 0.2 × 0.4 µm2
Space between neighboring elements
0.32 µm for width direction0.12 µm for length direction
Width of metal pitch: 0.3 µm
( = 150% of the width of element)
Space between neighboring metal pitches = 0.22 µm
A possible array of 256 Mbit with 0.13 µm process
We have estimated:
Metal pitchOne Cell area
Elliptical MRAMelement
Metal pitch
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Free ferromagnetic layer: NiFe, etc.
Insulating barrier layer: Al2O3, etc.
Pinned ferromagnetic layer: Co, etc.
Pinning antiferromagnetic layer: IrMn, etc.
Desired switching zone
HDigit-easy
HBit-hard
Digit line (Easy axis)
InsulatorConductor to Transistor
Bit line (Hard axis)
MTJ
Magnetic Tunneling Junction (MTJ) Structure
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Comparison of magnetization mode Comparison of magnetization mode
• Stable vortex, but existence of vortex core• Limited disk size for a stable vortex
Asymmetric disk (Regensburge,
Germany)
• No edge domain effect but high switching field and its wide distribution• Unstable vortex in deep submicron size (< 0.1µm)• Low SNR and unrepeatable output signal caused by vortex core
Symmetric disk (Univ. of Cambridge,
UK)
Circular m
agnetization mode
Linear magnetization mode
• No edge domain effect and stable vortex in deep submicron size• Require complex reversal field• Low manufacturing tolerance (double mask process required)
Symmetric ring(Naval Research Lab &
CMU, USA)
Predict:
• Narrow switching field distribution
• High selectivity (C-state domain configuration)
• Easy to fabricate
Asymmetric Pac-man type
(University of Idaho, USA)
• Less complex reversal field than symmetric ring• Low manufacturing tolerance (double mask process required)• Domain wall motion: low switching speed
Asymmetric ring
(Univ. of Cambridge, UK)
• Edge domain effectwide switching distribution
• For deep sub-micron, unstable reversal process, high switching field, and wide switching field distribution
• For tapered end element, small variation of end shape large change in the switching field.
Most of microelectronics companies
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Two stable vortex states at the remanent stateNo edge domain and no 360 o domain wallNo magnetostatic interaction between neighboring elements No magnetic charge at remanent state
Linear and Circular Magnetization ModesLinear and Circular Magnetization Modes
M
H
Linier Magnetization Mode
M
H
Circular Magnetization Mode
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Scanned domain configuration of elements by MFM
Counted the number of unswitched elements among 100 patterned elements after successive applied field.Applied field:
+ 440 Oe remanence state (0 Oe) desired negative field remanent state (0Oe)
Dimension:
Pac-man TypeHexagonRectangle
0.75 µm
0.25 µm
0.75 µm
0.25 µm
0.25 µm 0.75 µm
0.375µm
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Magnetic Element ShapeMagnetic Element Shape
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Remanent state of various elements (saturated at - 440 Oe)
0 Oe
120 Oe
160 Oe
220 Oe
260 Oe
380 Oe
Happ
Rec.: 0.5 µm x 1.5 µm Yang-Ki Hong
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(a) RO = 2.0 µmC1
C2 C3 C4 C5 C6 C7
(b) RO = 1.6 µmC1
C2 C3 C4 C5 C6 C7
(c) RO = 1.1 µmC1
C2 C3 C4 C5 C6 C7
Dimension of ring element (Si/Ta/NiFe/Ta)
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Table 1 The detail dimensions of ring element
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(a) RO = 2.0 µm, t = 40 nm
(b) RO = 1.6, t = 40 nm
(c) RO = 1.1, t = 40 nm
Happ = 5000 O
e
* Background noise from electric source and environment
(d) RO = 2.0 µm, t = 65 nm
(e) RO = 1.6 µm, t = 65 nm
(f) RO = 1.1 µm, t = 65 nm
Ring Size Dependence of Onion State
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Head-to-head domain wall in onion state ring element
Thickness = 40 nmRin/Rout=0.8 µm/2.0 µm
Thickness = 40 nmRin/Rout=1.0 µm/2.0 µm
Thickness = 40 nmRin/Rout=1.2 µm/2.0 µm
Thickness = 65 nmRin/Rout=1.2 µm/2.0 µm
Thickness = 65 nmRin/Rout=1.6 µm/2.0 µm
Happ = 5000 O
e
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Fig. 5 SEM images of NiFe ring elements with 30 nm thickness and an outer diameter of 2.2 µm aligned with Al pads for AMR measurements. The ratios of inner to outer diameter of ring elements shown in (b) are 0, 0.16, 0.27, 0.39, 0.5, and 0.61 for a, b, c, d, e and f, respectively.
(a) (b)
a b c
d e f
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Anisotropy Magnetoresistance Measurement of Ring Element
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Anisotropy magnetoresistance of ring elementStructure: Si/Ta(5nm)/NiFe(30nm)/Ta(5nm)Dimensions: ROD = 2 µm, RID= 0.8 µm
Magnetic Field
-400 -200 0 200 400253.47
253.48
253.49
253.50
253.51
253.52
253.53
253.54
Res
ista
nce
(Ω)
Magentic field (Oe)
Current
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Or
Onion state-HTH
Vortex state
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Magnetic Element Shapes for MTJ of MRAM Magnetic Element Shapes for MTJ of MRAM
• Edge domain
• End shape variation
• Vortex core• Complex wiring
required
• Fabrication• Complex wiring
required
• Vortex core• Bi-domain
• Fabrication• Domain wall
motion
• Low selectivity• Complex domain
• Low selectivity• Complex domain
• Vortex core• Bi-domain
• High selectivity• Low end shapevariation
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Definition of Pac-man (PM) ElementDefinition of Pac-man (PM) Element
Design: disk or ring with an open slot toward its center or near the center
PM type I: Sharp slot end (imaginary inner circle = 0) (PM-I)PM type II: Round slot end (imaginary inner circle ≠ 0) (PM-II)
Yang-Ki HongM. H. Park, Y. K. Hong, S. H. Gee, D. W. Erickson, and B. C. Choi, Applied Physics Letters, vol 83, July 14 (2003)
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Si//Ta(5nm)/NiFe(40nm)/Ta(5nm)High proximity effect at the center of
the element with a low angle slot of PM 1
45 o
60 o
75 o
90 o
105 o
120 o
135 o
150 o
165 o
180 o
45 o
60 o
75 o
90 o
105 o
120 o
135 o
150 o
165 o
180 o
PM type IPM type I PM type IIPM type II
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135o150o
165o180o
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PM-I (SEM)PM-I (SEM)
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Si//Ta(5nm)NiFe(40nm)/Ta(5nm)
Pac-man Type II
Pac-man Type I
Magnetization configuration of various PM Elements (as-patterned elements)
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MFM ImagesMFM Images
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Slot Angle Dependence of As-patterned Pac-man Submicron Magnets
Slot Angle Dependence of As-patterned Pac-man Submicron Magnets
40 60 80 100 120 140 160 180 200
0.0
0.2
0.4
0.6
0.8
1.0
Pac-man type I Pac-man type II
Slot angle (o)
Sing
le d
omai
n (n
orm
aliz
ed)
Si//Ta(5nm)NiFe(40nm)/Ta(5nm)
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-400 -300 -200 -100 0
0.0
0.2
0.4
0.6
0.8
1.0 Rectangle Hexagon Pac-man
Applied field (Oe)
Nor
mal
ized
125 Oe (PM)
165 Oe (H)
195 Oe (R)
Summary of Remanent CurvesSummary of Remanent Curves
Yang-Ki HongM. H. Park, et al., Applied Physics Letters, vol. 83, July 15 (2003)
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AA
B
B
C
C
D
D
E
E
Micromagnetic Simulation for Pac-man Type I*
NiFe element
Slot angle: 90 o
Diameter: 0.75 µm
Temperature: 0 K
Yang-Ki Hong*To be submitted for publication
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Results of Pac-Man Element Studies
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Advanced Design: Elongated Pac-Man (EPM) element (EPM-I and EPM-II)Providing a higher shape anisotropy
Magnetization Configuration
Switching Properties
Definition of Elongated Pac-Man Element(Advanced Design)
Definition of Elongated Pac-Man Element(Advanced Design)
Yang-Ki Hongsubmitted to Journal of Applied Physics, October 2003
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Comparison of MFM images in as-patterned state< PM 1 > < PM 2 >
< EPM 1 > < EPM 2 >
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Magnet field (Oe)
-200 -150 -100 -50 0 50 100 150 200
M/M
s
-1.0
-0.5
0.0
0.5
1.0
L=1.55 µm (elongated)L=1.05 µm (elongated)L = 0.75 µm (PM-I)
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20 nm
Micromagnetic Simulation Results