future materials research in data storage nsf workshop on cyberinfrastructure for materials science...

Future Materials Research in Data Storage

NSF Workshop on Cyberinfrastructure for Materials Science

Mark H. KryderCTO and Sr. Vice President, Research, Seagate TechnologyUniversity Professor, Carnegie Mellon University

Mark H. KryderNSF Workshop 08-06

Outline

Recording Overview

Materials Problems in Future Recording Technologies

Perpendicular Recording

Heat Assisted Magnetic Recording

Bit Patterned Media

TGMR/GMR Readers

Multiferroics

Discussion of Modeling Needs


Disc Drives Today Cover the Widest Range of Users and Systems Ever

Handheld Gaming DVR Notebook Desktop Enterprise

12 GB12 GB 750 GB750 GB 160 GB160 GB 73 GB73 GB 300 GB300 GB750 GB750 GB 750 GB750 GB

Low-cost, high-capcity, disk drives are enabling new devices, resulting in rapid growth of the storage industry and the emergence of new industries. e.g. Apple iPod, PVR’s, X-Box, automobile navigation systems, digital video cameras, etc.


Areal Density Growth

0.1

1

10

100

1000

10000

100000

year

gig

ab

it / in2

Single particle superparamagnetic limit (estimated)

Charap’s limit (broken)

• Late 1990s – super paramagnetic limit demonstrated through modeling

• Longitudinal recording reaching areal density limits

• Perpendicular expected to extend to 0.5-1 Tb/in2

• Additional innovations required at that point• heat-assisted

recording (HAMR)• bit patterned

media (BPM) recording

• Areal Density CAGR 40%

• Transfer Rate CAGR 20%

Perpendicular

HAMR

HAMR+BPM


Magnetic domains oriented in the direction of travel of the head.

Longitudinal Recording

Perpendicular Recording

Soft underlayer “mirrors” write head and makes it possible to write domains much closer together.


Magnetic Media EvolutionMagnetic Media Evolution

0

0.05

0.1

0.15

0.2

0.25

0 5 10 15 20 25 30 35

grain size (nm)

no

rmal

ized

fre

qu

ency

24 Gbit/in2

10 nm mean size

16 Gbit/in2

11 nm mean size

10 Gbit/in2

12 nm mean size

6 Gbit/in2

15 nm mean size

100 Gbit/in2

9.1 nm mean sizeStd. Dev. 1.7nm

45 Gbit/in2

9 nm mean sizeStd. Dev. 2.2nm

20nm20nm20nm

Physical grain size below 10 nm


HAMR can theoretically extend areal density beyond 10 Tbpsi


YCo5

HAMR Potential Ability to record on media

with anisotropy beyond writability with current perpendicular recording technology

Increased resolution with cross- and in-track thermal gradient recording

HAMR freezing dynamics allowing more intergranular exchange and unique composite media designs.

10× AD gain potential with FePt

10 n

m

Dieter Weller

SmCo5


HAMR Head Disc Interface Material Needs• Media Overcoat (< 2 nm) and Lubricant must be able to

withstand the repeated exposure to the high writing temperature.

• New media overcoat materials will be needed.

• Carbon overcoat can be damaged and/or graphitized at much lower temperature than its 560°C oxidation temperature.

• New Disc Lubricant materials will be required.

120mJ/cm2

Media DLC is removed

0 100 200 300 400 500 600 700 800 900

0

20

40

60

80

100

We

igh

t (%

)

Temperature (Degree C)

Zdol 2000 Lubricant 1 Lubricant 2

In Air10 K/min heating rate

0.0

1.0

2.0

3.0

4.0

5.0

400 500 600 700 800

Curie Temperature (K)

Ani

sotr

opy

(10^

7 er

g/cc

)

HDI


Bit Patterned MediaLithography vs. Self Organization

Lithographically Defined

Major obstacle is finding low cost means of making media• At 1 Tbpsi, assuming a square bit cell and

equal lines and spaces, 12.5 nm lithography would be required

• Semiconductor Industry Association roadmap does not provide such linewidths within the next decade

Direct E-Beam Write or Di-Block Co-Polymer

Idea:Use Pattern Assisted Assembly to establish circumferential tracks on discs

FePt Self-Organizing Media

130 nm

6 nm FePt particles

“9 Tb/in2“

~mm


Di-Block Co-polymer Template

A B

Lo

Guiding patterns can provide long

range order

• controlled 2D alignment to guiding patterns

• balance polymer-interface vs polymer-substrate interactions

Block-copolymers form naturally ordered nano-structures

A-B block copolymerprecursorsubstrate

• control of vertical orientation on any substrate• improve long-range order and uniformity• selective removability of one component• reduce L0 without losing uniformity, order• use of “environmentally safe” chemicals

Use as a template for pattern transfer• additive process (fill in holes by plating):

- ensure open contact to metal substrate- ensure all pores get filled equally

• subtractive process (transfer down by RIE):- etching requires high etch-resistive resist

lines dots


Examples of some h=20nm h=10nm

Uniaxial Ferromagnetic Materials Cube Sphere Cylinder Cylinder

Kux107 Ms Tc Hk Vp Dp Dp Dp Dp

Material (ergs/cc) (emu/cc) (K) (kOe) (nm3) (nm) (nm) (nm) (nm)

Co hcp alloy

CoCrPt 0.3 330 18.2 966 9.9 12.3 7.8 11.1

Co3Pt 2 1100 36.4 145 5.3 6.5 3.0 4.3

CoPt3 0.5 300 600 33.3 580 8.3 10.3 6.1 8.6

Co 0.45 1422 1393 6.3 644 8.6 10.7 6.4 9.1

Multilayer #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

Co2/Pt9 1 360 500 55.6 290 6.6 8.2 4.3 6.1

Co2/Pd9 0.6 360 500 33.3 483 7.8 9.7 5.5 7.8

L10 #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

FePd 1.8 1100 760 32.7 161 5.4 6.7 3.2 4.5

FePt 6.6 1140 750 115.8 44 3.5 4.4 1.7 2.4

CoPt 4.9 800 840 122.5 59 3.9 4.8 1.9 2.7

Rare Earth #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0! #DIV/0!

Fe14Nd2B 4.6 1270 585 72.4 63 4.0 4.9 2.0 2.8

SmCo5 20 910 1000 439.6 14 2.4 3.0 1.0 1.4

Self Organized Magnetic Array Media

Important Research Topics:• Particle Size and Distribution Control• Eliminate Sintering / Coarsening during anneal e.g. FCC-FCT (A1 – L10) Phase Transformation • Magnetic Easy Axis Orientation • Registered Large Scale Assembly• Packing density• Tribology

Dp: smallest possible thermally stable magnetic grain core size!

S. Sun, Ch. Murray, D. Weller, L. Folks, A. Moser, Science 287, 1989 (2000).

Solvent Evaporation

130 nm

e.g. 6 nm FePt particles

1 particle/bit~“9 Tb/in2“

~m


TGMR/GMR Reader Materials

To

p S

hie

ld

Magnet MagnetFL

AFM/SAF/RL

Bottom ShieldInsulator

CurrentFlow

ElectronFlow

FL

RL

TunnelingBarrier

Flux from the media rotates reader free layer magnetization thus changing spin polarized electron tunneling conduction.

MediaField

OutputVoltage

FL-RL

FL-RL

FL

LinearRange

Operate in the linear range of transfer function.

Sensitivity (slope)is determined by TMR

Alternate Barrier TGMR (MgO)

Improved amplitude, and lower RA

Potential to extend TGMR reader to area density

Current problem – Maintaining soft magnetic property of free layer, while keeping high DR/R and low RA.

CCP Design (current confined path)

A discontinuous oxide buried in metal

Higher DR/R and RA as compared to CPP Spin Value

Potential to use for area density of 400~ 600Gb/In2.

Current problem – Reducing variation of RA, and DR/R, and increasing DR/R.

CPP Spin Valve With Metal or Half Metal Spacer

Could offer better reliability, and SNR at very high KTPI

Potential to use for area density of 600Gb/In2 and behind

Current problem – Concept not proven, and processing half metals at temperature magnetic head can tolerate difficult

AFMPinned Layer

RuRef. Layer

Free Layer

AFMPinned Layer

RuRef. Layer

CuFree Layer

AFMPinned Layer

RuRef. Layer

MgOFree Layer

Reader Development Approaches


Multiferroic Data Storage System Readback is difficult from PE media, due to free charges, but not from FM media.

Generating enough magnetic field to write to thermally stable FM media is difficult.

An electric field can be used to assist writing by by using a media that is both PE and FM (Multiferroic). The data could then be read back using an MR head.

Both single phase and multiferroic materials exist, but composite materials are most interesting due to their higher transition temperatures (both PE & FM above RT).

• A composite material is achieved by combining MS and PE materials [ex. BiFeO3-CoFe2O4 or BaTiO3-CoFe2O4]. An electric field applied to the composite will induce strain in the PE constituent which is passed along to the MS constituent, where it induces a change in the magnetic anisotropy.

V+

V-

V+

V-

I

Diagram of an Example Recording System

P PM

P PM

P PM

P PM


Computing Needs in Magnetic Recording Technology

Micromagnetic models of media structure with 3-10 nm grain size and variable exchange coupling at the grain boundaries that allow us to understand the recording of 10’s to 1000’s of bits involving 50-100 grains each.

Models which enable prediction of magnetic materials properties and processes for making them that enable growth of materials with variable grain sizes, variable magnetic parameters, and variable exchange coupling across grain boundaries.

Models of tribological properties of thin film (<2 nm) materials. Models of self organization in diblock copolymers and in magnetic

nanoparticle arrays. Predictions of improved giant and tunneling magnetoresistive

materials. Predictions and understanding of multiferroic materials. NUMEROUS OTHERS!!

future materials research in data storage nsf workshop on cyberinfrastructure for materials science...

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