1

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

2

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

Yang-Ki Hong

2

3Yang-Ki HongSource: WTEC Panel Report on The Future of Data Storage Technologies, June 1999

Trend in Storage Capacity DemandTrend in Storage Capacity Demand

4

MAGNETIC RECORDING

Particulate Recording Media

Thin Film Recording Media

MAGNETIC RECORDING

Particulate Recording Media

Thin Film Recording Media

Yang-Ki Hong

3

5

Magnetic Recording SystemMagnetic Recording System

Yang-Ki Hong

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

6Yang-Ki Hong

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

4

7Yang-Ki Hong

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

8Yang-Ki Hong

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

5

9Yang-Ki Hong

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

10Yang-Ki Hong

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

6

11

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

Yang-Ki Hong

Trend in Recording Magnetic ParticlesTrend in Recording Magnetic Particles

12

Barium Ferrite Unit Cell –MagneticStructure

Barium Ferrite Unit Cell –MagneticStructure

Yang-Ki Hong

7

13Yang-Ki Hong

Barium Ferrite CrystalBarium Ferrite Crystal

14

Roadmap for Particulate Recording Density and Coating Technologies Proposed by Fuji film

Source: Fuji film Recording Media Yang-Ki Hong

8

15Yang-Ki Hong

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

16Yang-Ki Hong

Hexagonal Platelet Barium Ferrite (H-BaFe) Nanoparticles

D = 50 nm

9

17Yang-Ki Hong

18Yang-Ki Hong

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

10

19

Grain Structure of CoCrPt Perpendicular Thin Film Media for 130 ~ 170 Gbits/in2(?)

Yang-Ki Hong

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)

11

21AFM image of BaM (50nm thickness)Yang-Ki HongSource: Professor A. Morisako, Shinshu University, Japan

Structure and Grains of Barium Ferrite Thin Film

22

(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

Yang-Ki Hong

12

23

NONVOLATILE MEMORY

Magnetic Random Access Memory (MRAM)

NONVOLATILE MEMORY

Magnetic Random Access Memory (MRAM)

Yang-Ki Hong

24Yang-Ki Hong

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.

13

25

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

26Yang-Ki Hong

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.

14

27

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

Yang-Ki Hong

28

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

Yang-Ki Hong

15

29

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

Yang-Ki Hong

30

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

Yang-Ki Hong

16

31

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

Yang-Ki Hong

32

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

Yang-Ki Hong

Magnetic Element ShapeMagnetic Element Shape

17

33May 15, 2002

Yang-Ki Hong

34

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

18

35

(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)

Yang-Ki Hong

Table 1 The detail dimensions of ring element

36

(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

Yang-Ki Hong

19

37

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

Yang-Ki Hong

38

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

Yang-Ki Hong

Anisotropy Magnetoresistance Measurement of Ring Element

20

39

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

Yang-Ki Hong

Or

Onion state-HTH

Vortex state

40

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

Yang-Ki Hong

21

41

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)

42

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

Yang-Ki Hong

22

43

135o150o

165o180o

Yang-Ki Hong

PM-I (SEM)PM-I (SEM)

44

Si//Ta(5nm)NiFe(40nm)/Ta(5nm)

Pac-man Type II

Pac-man Type I

Magnetization configuration of various PM Elements (as-patterned elements)

Yang-Ki Hong

MFM ImagesMFM Images

23

45

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)

Yang-Ki Hong

46

-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)

24

47

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

48Yang-Ki Hong

Results of Pac-Man Element Studies

25

49

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

50

Comparison of MFM images in as-patterned state< PM 1 > < PM 2 >

< EPM 1 > < EPM 2 >

Yang-Ki Hong

26

51

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)

Yang-Ki Hong

20 nm

Micromagnetic Simulation Results