sakhrat khizroev - center for nanoscale information devices next generation memory devices florida...

Sakhrat Khizroev - Center for Nanoscale Information Devices

Next Generation Memory Devices

Florida International University Miami, Florida, U.S.A.

Center for Nanoscale Magnetic Devices

Sakhrat Khizroev


Outline

Background

Perpendicular Magnetic Recording

Three-dimensional Magnetic Recording

Protein-based memory

Summary


BackgroundTraditionally, Scaling Laws were followed to advance data storage technologies

S N N S N SS N S NN S

Inductive“Ring” Writer

MR Reader

MagnetizingCoil

Write field Recording Media

S N N S N SS N S NN SScaling

At 1 Gbit/in2 information density, bit sizes are: 400 x 1600 nm2

At 100 Gbit/in2 : 40 x 160 nm2

At 1 Tbit/in2 : 13 x 52 nm2


Scaling: Smaller Transducers and Media

Flying Height 5 nm

Head Smoke Particle

Fingerprint

Human Hair 75,000nm

Media 10-100nm Disk Substrate

At 1 Tbit/in2 information density, Bit Sizes are: 13 x 52 nm2


Superparamagnetic Limit

Magneticgrains

Bit transitionSNR ~ log(N), N - number of grains per bit

While scaling, need to preserve number of grains per bit to preserve SNR

Grain size is reduced for higher areal densities:

DensityAreala

1~


-45 0 45 90 135 180 225

-0.5

0.0

0.5

1.0

1.5

2.0

E+

E-

Ene

rgy,

eVMagnetization angle

H

megrain volu

energy anisotropy

E ,10-10~

k

Eexp

1290

B0

V

K

VKf

Tff

U

U

Probability of magnetization reversal due to thermal fluctuations:

6040kB

T

VKUThermally stable media:

Relaxation time = = 72 sec for KuV/kT=40 = 3.6x109 years for KuV/kT = 60

Media Stability


SuperparamagnetismSuperparamagnetism

U

U

K

TaV

T

VK B3

B

k606040

k

3B

minimum

k60

1~

UK

Ta

DensityAreala

If a<aminimum, medium becomes thermally unstable leading to severe deterioration of recorded data over time.Approaches to avoid superparamagnetic instabilities:

• Decrease aminimum by increasing KU

• Increase a by decreasing the number of grains per bit• Demagnetization fields in transitions shorten the

relaxation timePerpendicular Recording*

Patterned Media

HAMR

*S. Khizroev and D. Litvinov, Perpendicular Magnetic Recording, Kluwer Academic Publishers, 2004; ISBN 1-4020-2662-5.


In a typical longitudinal recording layer the magnetic anisotropy axes of individual grains are randomly oriented in the plane of the film

In perpendicular recording layer the anisotropy axis is relatively well aligned (<2-4 degrees) perpendicular to the plane of the film

Magneticgrains

2D random medium

oriented medium

Substantially relaxes the requirements for write field gradientsCan use thicker recording layer - better thermal stability !!!

(increased V in KUV/kBT ratio)

Perpendicular Recording*: Well-defined Anisotropy



Nanoscale Device: Tbit/in2 Recording Transducer*

S N N S N SS N S NN S

Inductive“Ring” Writer

MR Reader

MagnetizingCoil

Write field Recording Media

Inductive“SPH” Writer

MR Reader

MagnetizingCoil

Recordinglayer

SUL

Writefield

Longitudinal

Perpendicular

Bit Sizes: 13 x 52 nm2

*S. Khizroev, D. Litvinov, “Physics of perpendicular recording: writing process,” Appl. Phys. Reviews – Focused Review, JAP 95 (9), 4521 (2004).


In perpendicular recording the write process effectively occurs in the gap (Write Field < 4MS)

In longitudinal recording the write process is done with the fringing fields (Write Field < 2MS)

Gap Versus Fringing Field Writing2/3

30 ~1

~2

DensityAreala

MNM

KHH Seff

S

Uwrite Higher areal density media requires higher write fields !!!



FIB to Trim Regular Transducers into Nanoscale Devices*

Z

X

Ionbeam

Permalloy

Diffusionregion

ProbeTrench

FIB Etch to Define a Nanoprobe

Permalloy

Diffusionregion

ProbeFIB-deposited region

TungstenTungsten

FIB Deposition

The most critical step is to make a probe with Nanoscale dimensions

*S. Khizroev, D. Litvinov, FIB Review in Nanotechnology 14, R7-15 (2004).


Numerical Calculations*

*Jointly with Integrated Inc. ,a group at Durham University, UK, and groups at Carnegie Mellon University

Longitudinal

Perpendicular

Modeled Fields (Quantum-mechanical) Gallium Ion Implantation

0 50 1000

5

10

15

20

25

Dose = 2 x 106 Ions/cm2

Lateral

Normal

Diff

usio

n Le

ngth

(nm

)

I = 100 pA

Accelaration Energy (keV)

0 50 1000

2

4

6

8

10

Max

imum

Cav

ity S

ize

(nm

)Ion Current (pA)


Longitudinal Transducerwith a 30 nm Width

Perpendicular Transducerwith a 60 nm Width

FIB-fabricated Nanoscale Transducers*

Note: It takes ~ 10 minutes to make one such device in the University environment



Control of Gallium Diffusion*

AFM MFM

3 x 105 Ions/cm2

2 x 106 Ions/cm2

Ion Dose

NOTE: Although NO texture change is observed through AFM, substantial magnetic grain change is seen through MFM

dose

increase

*D. Litvinov, E. Svedberg, T. Ambrose, F. Chen, E. Schlesinger, J. Bain, and S. Khizroev, “Ion implantation of magnetic thin-films and nanostructures,” JMMM 277 (3-4), xxx (2004).


The process how to make Nano-precision patterns with FIB wasshared with a few companies and successfully implemented by:Carnegie Mellon University, IBM, Seagate, and others

500 nm500 nm

Sidewall

A Part of a Device made in the Industry before the

process was implemented

Same Device made withthe process implemented

Nanoscale FIB Process*



0 nsec 0.5 0.75

1 nsec 1.5 2 nsec

P2GapP1

Dynamic Kerr Measurement of the Field from a Nanoscale Transducer*Characterization

Kerr-Image Snap-Shots for a SPH Transducer (Near-field Kerr Microscopy)

Glass SubstrateMedia Stack

Microscope

Writer

*These experiments were repeated at Seagate, CMU, and IBM

*D. Litvinov, J. Wolfson, J. Bain, R. White, R. Chomko, R. Chantrell, and S. Khizroev, “Dynamics of perpendicular recording,” IEEE Trans. Magn. 37 (4), 1376-8 ( 2001).


Characterization

3nm Feature

(a) (b)

3nm Feature

(a) (b)

Ion image of a FIB-fabricated and

magnetically active 3-nm-long feature MFM image of recorded

nanoscale magnetic "dots"


Perpendicular Recording with Bit Widths of less than 65 nm*

130 nm

~400 ktpiCoB/Pd multilayer

CoCrPtTa alloy~190 ktpi

Current “state-of-the-art” longitudinal recording is <100ktpi

400 nm

Writer

Reader

MFM Images of Nanoscale Size Information

*S. Khizroev, D. A. Thompson, M. H. Kryder, and D. Litvinov, Appl. Phys. Lett. 81 (12), 2256 (2002); Editor's choice for the Virtual Journal of Nanoscale Science & Technology, Sep 23rd 2002.

The FIB-made transducer


• Perpendicular Recording promises to defer the superparamagnetic limit to ~ 1 Terabit/in2

• Heat-Assisted and Patterned Media are still 2-D limited and relatively slow

It is expected that Moore’s law will inevitably reach its limit between 2010 and 2020

Time to stack multiple active layers on top of each other

3-D Magnetic Recording is a data storage form of 3-D integration

Conventional and 3-D Recording Media

(a) (b)

~2 to 10

~ 2 nmN sub-layers

Magnetization “up” and “down”

Note: Each cell is 50 x 50 nm2

Three-dimensional Magnetic Recording


3-D Magnetic Recording

The development of 3-D magnetic recording is divided into two phases:

1. Multi-level Recording: not optimally utilized 3-D space

Note: Effective areal density increase is by a factor of Log2L (where L is the number of signal levels)

2. 3-D Recording: each magnetic layer is separately addressed

Note: Effective areal density increase is by a factor of N (where N is the number of recording layers)

N layerscontributingtogether to one level

n-th layer addressing

Note: Each cell is 50 x 50 nm2

Note: These are not active layers

Lead Ph.D. Graduate Student: Yazan Hijazi, Sakhrat Khizroev


Recording Head

The current in the single pole head is varied to vary the recording field

Each recording is performed via two pulses: 1) a cell is saturated and 2) the information is recorded

Realhead

Imagehead

3D Recording medium

“Soft” underlayer

Schematics of a TransducerSimulated Recording Field


Playback Head

The playback head is designed to preferably read the vertical field component which is dominant in this case

++

charges in the transition

++

+ + + + + + + + - - - - - - - - - -

- - - - - - - - - - + + + + + + +

Hstray

Hstray

+ + + + + + + + - - - - - - - - - -

- - - - - - - - - - + + + + + + + Underlayerboundary

Mediumimage

M(a)

(b)

(c)

Stray Field from 3D Medium

Recording MediumRecording Medium

MR

Sen

sor

MR

Sen

sor

(c) (d)

shield shield

Recording MediumRecording MediumM

R S

enso

r

MR

Sen

sor

(a) (b)

shield shield

MR

Sen

sor

MR

Sen

sor

Differential Reader Configuration

FIB-defined Writer(50 nm wide)

Zoomed View of FIB-defined Reader(40 nm wide)

Electronic Images of FIB-fabricated Transducer


Multi-level Recording on a Continuous Medium

Hz> Hc2

SinglePoleHead

Hz= Hc2

Magnetized “up” state

No definedMagnetization

Hz< Hc2

SinglePoleHead

Hz= Hc1



“down” state



“down” state

Overlapping Side Region

Major Disadvantages:

•Every time a track is recorded into the bottom layer, there are side regions in the top layer in which the earlier recorded information is lost because of the overlapping side region

•The superparamagnetic limit

Recording Step 1: Recording Step 2:

Recording Step 3:


Multi-level Recording on a Patterned Medium

+ + + +

+ + + +

- - - -- - - -

M+ + + +

+ + + +

- - - -- - - -

M

+ + + +

+ + + +

- - - -

- - - -

M

tb

tt

Playback Signal

Vertical Pattern Optimized Pattern

Patterned Media by Toh-Ming Lu

Note 1: The tilt angle can be controlled via deposition condition

Note 2: The inter-layer separation should be sufficient to break the quantum-mechanical “exchange” coupling

FIB-etched Patterned Medium

Note: Each cell is ~50 x 50 nm2


Multi-level Recording on a Patterned Medium: Writing

Note 2: The inter-layer separation should be sufficient to break the quantum-mechanical “exchange” coupling

Micromagnetic Simulation Illustrating Two Cases of Interlayer Separation:

a) < 1 nm and b) > 2 nm

Recording Field Profile

M up

M down

e.a.


Multi-level Recording on a Patterned Medium: Writing

H= - H1>Hc >H2

H4>Hc >H5

1

2

3

4

5

1

2

3

4

5

1

2

3

4

5

1

2

3

4

5

1

2

3

4

5

H3>Hc >H4H2>Hc >H3

-200 -100 0 100 200

0.0

0.2

0.4

0.6

0.8

1.0

Layer 3

Layer 2

Layer 1

Hz /2

Ms

Distance along the track (nm)

Recording Field Profiles in Individual Layers at a Given

Current Value

Hc


Multi-level Recording on a Patterned Medium: Playback

+ + + + + + +

- - - - - - - - - -

+ + + + + + +

- - - - - - - - - -

+ + + + + + +- - - - - - - - - -

... + + + + + + +- - - - - - - - - -

+ + + + + + +

- - - - - - - - - -

HH

H

Magnetic “Charge” Representation of the Playback Process

“10” “9” “5”

0 10 20 30 40 50

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Level 4: digital "7"Level 5: digital "6"

Level 3: digital "8"



Hz

stra

y (au

)

Distance in the medium (nm)

Simulated Stray Field from a 3-D Medium at different levels of

recording


Section lines

Three-layer Co/Pt multilayer with a net thickness of 30 nm

One-layer Co/Pt multilayer with a thickness of 40 nm

10 mA

100 mA

100 mA

10 mA

0 100 200 300 400

-0.2

0.0

0.2

0.4

0.6

0.8

1.0 10 mA100 mA

MF

M p

hase

cha

nge

(/M

axim

um s

igna

l)


0 100 200 300 400

0.00

0.25

0.50

0.75

1.00

10 mA

MF

M p

hase

cha

nge

(/M

axim

um s

igna

l)

100 mA


MFM Images of Two Types of Media

Each cell is ~ 60 x 60 nm2


Note 2: The demagnetization field could be fairly large for some configuration. Special bit encoding should be considered to avoid the unfavorable bit configuration.

Hdemag >> 4Ms

SNR Limitations

1 2 3 4 5

4

6

8

10

12

14

16

18

20

22

SN

R (

dB

)

Number of Layers

Patterned Media (ideally, fabrication technique limited)

Electronic noise sources are 10 Ohm GMR Sensor and 0.2 nV/sqrt(Hz) preamp noise over a 500 MHz CTF bandwidth at 1 Gbit/sec

Note 1: Special encoding channels should be used to reduce BER


Soft Underlayer

Magneticsub-layers

Decouplinginterlayers

Magnetization directions

Magnetoresistive elementsI Word lines

I1

I2

I3

In

...

J1 J2 J3 Jk. . .

Three-dimensional Recording

Schematic Diagrams of a 3-D Memory Device

Biasing Conductor for Layer Identification during Writing

2-D Recording/Reading Grid (similar to MRAM)


Magnetically-induced Writing

Note: The current in the biasing conductor is continuously decreased from the maximum to zero to identify individual layers starting from the top to the bottom

K-th layer is identified

(K-1)-th layer is identified


Thermally-induced Writing

Magneticsub-layers




I1

I2

I3

In

...

J1 J2 J3 Jk. . .

Simulation by Roman Chomko

(jointly with Seagate Research)


3-D Reading

Active layers: MRAM devices stacked together

Different Implementations

Magneticsub-layers




I1

I2

I3

In

...

J1 J2 J3 Jk. . .

Magneticsub-layers




I1

I2

I3

In

...

J1 J2 J3 Jk. . .

Magnetic Resonance FM

CoCrPtTa alloyMagnetic Resonance FM


CoCrPtTa alloy

Apex: 40 x 40 x 10 nm3

Electron Image of “Smart”

Nano-probe (made via FIB)

Comparative MFM Images of Atomic-size Information obtained by the Conventional State-of-the-art MFM (left) and the FIU-developed “Smart”

Nano-probe

3-D Reading: Magnetic Resonance Force Microscopy

rf-coil


3-D Reading: Magnetically-induced Reading*

Note 1: Through the variation of the “softness” of the SUL, one can vary the sensitivity field of each cell

-0.10 -0.05 0.00 0.05 0.10

0

50

100

150

Hz (

au)

Distance along X, m

Sensitivity Field with a “Free” SUL (red) and “Saturated” SUL (black)

rrMrrHS zz

)()(~According to the Reciprocity principle, the signal in each cell is given by Expression

Note 2: Effective physical scanning in the vertical direction is produced via the variation of the “softness” of the SUL. Thus, each layer could be independently addressed

*Provisional patent filed with US PTO on August 4th 2004


Recorded Pattern in Layer 6Parallel Set of Signals at Ibias = 0 (A turn)


Recorded Pattern in Layer 4Parallel Set of Signals at

Ibias = 1.56 (A turn)


Recorded Pattern in Layer 2

Parallel Set of Signals at Ibias = 5.85 (A turn)


Summary on 3-D Magnetic Recording

The study of 3-D magnetic recording has been initiated

During the last year, the PIs have authored 8 peer-review papers on the underlying physics of magnetic and magneto-thermal recording

Specific designs of 3-D magnetic devices have been proposed

The university is in the process of filing a patent on the proposed mechanism.

CommitmentWithin two years, demonstrate an experimental prototype of a stable (for at least 50 years at room temperature) 3-D magnetic memory with at least ten recording layers with an effective areal density of at least 1 Terabit/in2 and a data rate faster than 2 Gbit/sec


Protein-based Memory

Why Protein?• Naturally occurring residues of proteins (Bacteriorhodopsin (bR) mutants) in the form of molecules with a diameter of less than 3 nm (more than 100 times smaller than polymeric material used to DVDs) demonstrate unprecedented thermal stability at room temperature (critical advantage over magnetic storage, correspond to areal densities of much beyond 10 Terabit/in2 • Unprecedented recyclablity of protein medium: it can be rewritten more than 10 million times (more than 1000 times better than CD/DVD) • The light-sensitive properties of proteins integrated with the modern semiconductor laser technology provide a relatively straightforward control of recording and retrieving information from the protein media. • Much faster time response of protein media (as compared to magnetic media): the time response in the protein media is in the picosecond region (as compared to the nanosecond region in magnetic media) • Economical• Non-volatile


*R. R. Birge, Scientific American, 90-95, March 1995

Schematics of a halobacterial cell and its functional devices

Salinos del Rio on Lanzarote Island

Wild-life Bacteriorhodopsine (bR) produced by Halobacteria


Goal is to demonstrate the feasibility of recording/storing/retrieving information on/from photochromic proteins at areal densities of above 1 Terabit/in2 and data rates of above 10 Gigahertz.

Approach (2-D Single Molecule Level instead of 3-D) is 1) to take advantage of the 2-D stability of BR media to record on one surface at

a single-molecule level or/and use a stack of layers to record in 3-D and 2) take advantage of the most advanced nanoscale recording system – so called

heat-assisted magnetic recording (HAMR) based on the near-field optical recording transducer

Protein-based Memory

Problems with Protein Media:• Early proteins were unstable (Solved with discovery of bacteriorhodopsin)• Polymers, on which protein structures are made, are less stable than proteins themselves• It is not trivial to immobilize proteins in 3-D• Holographic methods are not perfected for ultra-high densities (far from competing with magnetic)


Data Recording/Retrieval in Protein-Based Storage

Thermal Cycle with Two Stable States


Fig. Writing digital 1. Transition A B.Two photon absorption causes transition to intermediate state, which then relax to the second stable state B.

Cascade two photon absorption.

h1

State A State B

Intermediate 1

h2 h2

State A State B

Intermediate 2

h1

Note: Using two photon and other nonlinear processes makes possible remote writing digital information inside optical media volume. It is applicable for nonvolatile multi-layered optical memory.

Recording Mechanism: Two photon processes


Earlier Proposed Protein Memory*

*R. R. Birge, Scientific American, 90-95, March 1995

Parallel Data Access (page by page via positioning of the green light)

Issues:•Optics never could record high densities

•3-D media are not trivial to immobilize


All the above-described methods of recording/retrieving data are quite complicated and it is hard to see whether they will be implemented and if yes, when. In fact, so far no physical demonstration of ultra-high density recording has been made!

The PIs propose first, to use a bit-by-bit 2-D type of recording to demonstrate the feasibility

of the protein-based storage (it is trivial to immobilize 2-D media); then, to apply one of the available parallel data recording/retrieving mechanism (e.g. holographic).

To accomplish this goal, the PIs use the transducer design earlier developed for heat-assisted magnetic recording (HAMR)*. HAMR is the most advanced recording mechanism proposed so far. The PIs have pioneered one of the most efficient design of the transducer for HAMR

The Proposed Solution to Demonstrate the Feasibility of Protein Based Storage

*T. McDaniel, W. Challener, “Issues in heat-assisted perpendicular recording,” IEEE Trans. Magn. 39 (4), 1972-9 (2003).


Air-bearing-surface (ABS) view of laser diode with a thin layer of Al

with FIB-etched "C" shape aperture

Novel Recording Transducer for Areal Densities Above 1 Terabit/in2

Electron Image of FIB-fabricated Apertureless Transducer

Note: Focused ion beam (FIB) is used to fabricate “apertureless” transducers (with aperture dimensions of less than 100 nm << than the wavelength)*

< 90 nm

In-house made

*F. Chen, A. Itagi, J. A. Bain, D. D. Stancil, and T. E. Schlesinger, “Imaging of optical field confinement in ridge waveguides fabricated on very-small-aperture laser,” Appl. Phys. Lett. 83 (16), 3245 (2003).


Two-Dimensional Protein Media • Easy to fabricate*

• Naturally stable Optical spectra of a gelatin-mixed BR film in two states, the ground state and one of the intermediate

M states*

*The spectra were recorded with a Varian CARY 50 spectrophotometer.

The decay absorption signal in the excited M-state measured at a wavelength of 410 nm

*A gelatin-mixed bR film under study was fabricated by Lars Lindvold

Note: Patented approach to immobilize proteins Into stable thin-film recording media (H. Arjomandi, V. Renugopalakrishnan)

AFM Image of a 2-D Pattern with a 2.4-nm Period


Custom-made Near-field System built around Aurora-3 by DI

Experimental setup to record and read information on/from proteins

Schematic Diagram

Note: The modular structure of the system allows simultaneously using more than one (currently, up to four) sources (red to blue lasers, UV lamps) to conduct photons through a fiber to the sample in the near-field regime. In addition, as described below, the system will allow implementing diode lasers assembled right at the air bearing surfaces (ABS) of the recording probes attached to the SPM’s cantilever.


Early Results: Reading Tracks from Photochromic BR Media

* The signal is the absorbed power in the detector system in the reflection mode

Near-field Optical Readback Signal

Narrowest track is ~ 100 nm


1 Tbit/in2

10 Tbit/in2

50 Tbit/in2

100 Gbit/in2

1. Perpendicular Recording

2. Use smaller Grains&Deal with Write Field Problem (~10x gain)

• Heat Assisted Magnetic Recording (HAMR)

• E.g. high anisotropy 3 nm FePt grains3. Single Grain per Bit Recording combined with HAMR (~5x gain)

• Patterned Media4. 3-D Magnetic Recording5. Protein-based Memory (Single-Molecule Recording)

Ultimate Recording Density > 50 Tbit/in2 conceivable

Summary

0. End to Longitudinal Recording

sakhrat khizroev - center for nanoscale information devices next generation memory devices florida...

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