Trends in Optical Storage - University of Exeter...

The Microelectronics Training Center, IMEC v.z.w.www.imec.be/mtc

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MTC 2008 : PCM Memories: An overviewIMEC© 2008

Stephan Knappmann

Trends in Optical Storage

Deutsche Thomson OHGCorporate Research VillingenOptical Storage LaboratoryStephan Knappmann (VOS)

WINDWINDIMST 2008 - EU Memory Projects Workshop & Tutorials

Date: Wednesday 26-Friday 28 November 2008Venue: IMEC, Kapeldreef 75, 3001 Leuven, Belgium

2

Outline

• Motivation• Storage & application trends

• Optical storage technology • R&D @ Thomson

• Solution for content distribution (“sub-TeraByte”)• Solution for archiving (> 1 TeraByte)


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Why do we need optical storage for the next decade?

• The storage demand is continuing to grow exponentially• Economy is more and more driven by content and leveraged by

high performance, cost-effective hardware and storage.• People collect more and more digital information

– personal collections built with published titles, own creations and shared content

– high-definition, social networking are fueling the storage demand further

Source: Coughlin Associates, 2008

Accumulated digital content per average

household

4

Digital data capacity forecast

Annual capacity projections for creation of professional moving image content

Source: Coughlin Associates, 2008


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Super Hi-Vision (SHV) - Ultra High Definition Video

Super Hi-Vision's main specifications:Resolution: 7,680 × 4,320 pixels (16:9) (appr. 33 megapixels) Bits depth: 10 bit per channel Frame rate: 60 frame/s. (progressive) Audio: 22.2 channels

• 9 — above ear level (top layer), 10 — ear level (middle layer), 3 — below ear level (bottom layer), 2 — low frequency effects

Bandwidth: 21 GHz frequency band • 600 MHz, 500~6600 Mbit/s bandwidth

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Requirements for HDTV, Ultra High Definition Video

July 2008

Bandwidth requirement for advanced A/V quality:

> 100 Mbps


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Can download replace physical media distribution?

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Advertised download

speed

Rank 15 regarding number of

subscribers per 100 people

November 2007


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Measured download speed in the United States

August 2008

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July 2008

Expected average

speed for the USA in 2012


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Consumer study by the Digital Entertainment Group (DEG)

Los Angeles, November 2008A new consumer study by the DEG indicates HDTV and Blu-ray Disc (BD) player owners still find packaged media — such as Blu-ray Discs —preferable to alternative internet streaming and download servicesto play premium HD movie and video content.

• > 1,100 HDTV owners in the US, 500 HDTV owners each in the UK & Japan• 96 % of BD users said they are familiar with downloading and streaming

services, with two-thirds stating “Watching a movie on Blu-ray is a better overall entertainment experience.”

• HDTV owners familiar with BD favor the format over downloading and streaming by a nearly 10-to-1 margin, with ~ 70 % citing the key factor: “you actually have a physical disc that you can keep”.

• Blu-ray Disc was preferred to internet streaming and downloads even by younger audiences that are very familiar with internet platforms.

• The study found that 96 % of BD owners said they had experienceddownloading or streaming video over the internet, but when they compared them the majority sided with BD while only 3 % said downloading or streaming was better than BD.

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Vision for content distribution

Optical disc will stay the dominant medium• Low cost per GB, “better experience”

Download provides an additional distribution stream for standard definition video & highly compressed HD video

Download to HDD or Download to Disc


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Optical storage success factors

• Optical storage success factors and key differentiators compared with e.g. HDD and solid-state:• Media removability & exchangeability

– expandable capacity– tangibility – privacy & security

• Media longevity • Low-cost read-only and recordable media

Any successor standard and product has to maintain these features!

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Optical storage technology alternatives

• 4th generation “sub-TByte” optical storage will likely be provided by a mixture of today’s evolving technologies:

• Smaller spot size – Optical near-field (objective lens NA >1)– Non-linear masking layer on the disc (referred to as Super-RENS)

• Multilayer based e.g. on– Blu-ray Disc based technology– 2-photon absorption– Micro-holograms

• Holographic data storage shall aim at TByte+ capacities • Professional archiving applications first• Consumer home archival applications will follow


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Concept for Near-Field Recording (NFR)

Two main streams of SIL based NFR

• 1st surface NFR

• Cover layer incident NFR

Picture from CISD, Korea

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Feasibility of Multilayer NFR

Concept demonstrated by Philips and others

data layer 1

cover layer (3 µm)

substrate

intermediate layer (3 µm)

data layer 2

n1 ~2.1

n2 ~2.1

NA = 1.45 = 2.1 * sin(44°) 1matched refractive

index:n1 = n2


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data layer 1

cover layer (3 µm)

substrate


data layer 2

n1 ~2.1

n2 ~1.6

NA = 1.45 = 2.1 * sin(44°) 2realistic

refractive index:

NA < n2 < n1

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data layer 1

cover layer (3 µm)

substrate


data layer 2

n1 ~2.1

n2 ~1.4

NA = 1.45 = 2.1 * sin(44°) 3n2 < NA

total internal

reflection


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Super-RENS

• Super-resolution based on masking layers is considered as a promising technology to increase the storage capacity beyond BD

• Referred to as Super-RENS (Tominaga et al.)– Super REsolution Near-field Structure

• Resolution limit determined by “effective aperture size”due to mask layer

• Conventional far-field optics can be used

• Not sensitive to dust & fingerprints

• Backward compatible with BD• Main technical challenges

• Material development for read-only, recordable and RW discs• Advanced equalization, signal processing and ECC • Track pitch reduction

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Variety of Super-RENS concepts and materials

Mask layer materials:• Sb• PtOx, AgOx• Phase change materials

(GST, AIST, etc.)• Semiconductor

(ZnO, InSb)Applicable for ROM & recordable media


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Blu-ray Disc with higher capacity per layer

Samsung showed 40GB per layer and 5 layers 200 GB with Blu-ray Optics

• New data detection schemePre-equalizer, LMS equalizerViterbi decoderWaveform detection PLL

• OpticsAdvanced spherical aberration compensation needed

Substrate2.3%Layer 0

15 µm spacer2.3%Layer 1




Reflectance60 µm Cover Layer

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Blu-ray Disc with more than 10 layers

Pioneer showed 25GB per layer and 16 layers400 GB with Blu-ray Optics

• OpticsAdvanced spherical aberration compensation neededPin hole forsuppression of interlayer X-talk

Even 20 layers have been

tested.


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Multilayer based on 2-photon absorption

Different proposals, e.g. Call/Recall, Mempile• Demonstration of full recording

by Call/Recall: 1TB on 12cm disc– 200 layers with 5GB each– Thickness: 1mm– High NA optics used: NA = 1.0– Recording with green laser:

12W at 532nm(75MHz repetition & 6.5ps pulses)

– Readout with red laser: 635nm

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Multilayer based on Micro-holograms

Different proposals, e.g Sony, GE, University of Berlin– Recording with counter propagating

beams– Readout with single sided beam– Disadvantage: low data rate– PU with 2 wavelengths (Sony)

405nm

660nm

Refractive index modulation


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Holographic Data Storage Concept of InPhase

• Recording Readout

• Product: tapestry™• 300GB – 1.6TB Capacities

20MB/s-120 MB/s transfer rate & milliseconds data access time

Polytopic multiplexing

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Coaxial Holographic Data Recording (Sony)

• Concept overview• Coaxial signal beam and

reference beam• External Cavity Diode Laser (ECDL)

407 nm, up to 80 mW CW

• Focusing and tracking is similar to conventional optical disc systems

• Image stabilizing allows continuous rotating disc

• Recording data rate ~100 Mbit/s• Recording density

• Demonstrated density: 270 Gbit/in²Error rate < 10%Material: Photopolymer with 600µm

• Coherent addition technique (homodyne detection) allows further capacity increase by 3 to 4

– Potential for >1 Tbit/in²


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R&D activities @ THOMSON

• Super-resolution based on masking layers• Holographic data storage

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Semiconductor material for Super-RENS: InSb

InSb show non-thermal effect in contrast to phase-change material: “Free Carrier Reflectivity” (Drude Model)

• Laser photons generate free electrons in conduction band• For higher electron concentration the semi-conductor becomes

“metallic” high reflectivity• Local change of optical properties allows pit detection below the

optical resolution limit

B. Hyot et al. ODS 2006

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Experimental details

• Disc format• Pre-embossed pits • Single tone with 80 nm pits & 80 nm land• Track pitch 320 nm • Mask layer: InSb or AgInSbTe (AIST)

• Test conditions• Blu-ray optics (λ=405nm, NA=0.85)• linear speed 4.92 m/s

mask layer (20-25 nm)ZnS:SiO2 (50 nm)

cover layer (0.1mm)

ZnS:SiO2(70 nm)

substrate

Laser

1.0µm


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0.5 1.0 1.5 2.0 2.5 3.00

10

20

30

40

50

0

5

10

15

20

25

30

35

CNR (InSb)

CN

R (d

B)

laser power (mW)

Ref

lect

ivity

(%)

R (InSb)

0.5 1.0 1.5 2.0 2.5 3.00

10

20

30

40

50

0

5

10

15

20

25

30

35

CNR (InSb) CNR (AIST)

CN

R (d

B)

laser power (mW)

Ref

lect

ivity

(%)

R (InSb) R (AIST)

Comparison of mask layer materials

CNR and low pass filtered reflectivity measured for 80nm single tone pits at increasing laser power

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Investigation on random patterns

Disc format• Pre-embossed pits

– Multi-tone with RLL (1,9) and 2T=80nm• Track pitch = 320nm• Same layer stack & test conditions as before

Measured spectrum is limited by Modulation

Transfer Function (MTF)due to spot size of focused

laser beam


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0 10 20 30 40 50 60

-10

0

10

20

30

40

50

2.6mW 0.8mW

pow

er (d

Bm

)

frequency (MHz)

Power spectrum of the read-out signal

0 10 20 30 40 50 60

-10

0

10

20

30

40

50 0.8mW 2.0mW

pow

er (d

Bm)

f (MHz)

InSb• Bit error rate measurements

were successful: bER = 5*10-4

– Measured after PRML detector– See also ISOM/ODS presentation

ThA02 [TD05-42]

AIST• Impossible to calculate bER

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1200 1500 1800 2100 2400 2700-0.4

-0.2

0.0

0.2

0.4

ampl

itude

(a.u

.)

time (ns)

InSb (1.8 mW)

1200 1500 1800 2100 2400 2700-0.4

-0.2

0.0

0.2

0.4

ampl

itude

(a.u

.)

time (ns)

InSb (1.8 mW) AIST (2.6 mW)

Analysis of multi-tone patterns

20 x 2T19T 20T

Shortest pit length: 2T = 100nm

Inverted signal


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Overview and conclusion

• Continuous spectrum• Addition of diffractive part

and SR part

• Dip in the spectrum• Cancellation of diffractive

part and SR part close to the cut-off frequency

• Consistent SR signal• Inverted SR signal• Good CNR for single tone• Good CNR for single tone

• Increase of reflectivity with laser power

• Reflection type

• Decrease of reflectivity with laser power

• Aperture type

Semiconductor - InSbPhase change - AIST

Conclusion for ROM type super-resolution discs:• Tuning of the layer stack needed to get strong reflectivity

increase in the center of the focused beam

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Summary – material comparison

Super-resolution ROM discs with 3 layer stack have been studied with AIST or InSb as mask layer

• For single tone pattern, the same signal quality was found for both materials• With InSb bER= 5*10-4 was found for 40nm CBL (after PRML)• It was impossible to decode the HF signal with AIST mask layer

Correlation between reflectivity change and SR detection • InSb: Data signal increases on land

– Consistent with diffraction allows the bER calculation– Diffractive process enhanced

• AIST: Data signal decreases on land– Inverted SR signal– Position of the smallest pits and lands mistaken

Experimental and theoretical findings are consistent

For layer stack optimization it is not sufficient to look only at the CNR of single tone signals


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Signal processing for super-resolution

• Super-RENS discs show lower signal to noise ratio (compared to BD/HD-DVD)

– To keep the code rate, higher error correction capability is required

• Turbo-Codes (concatenated codes): • Low-Density-Parity-Check (LDPC) • Turbo Product Code (TPC)

• Advantage of Turbo-Codes– … come closest to approaching the Shannon limit, the theoretical

limit of maximum information transfer rate over a noisy channel.

Timing Recovery Detector Demodulator LDPC decoder

Super-Trellis

Turbo detectionIterative TimingRecovery

RS decoderTiming Recovery Detector Demodulator LDPC decoder

Super-Trellis


RS decoder

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Timing Recovery Detector Demodulator LDPC decoder

Super-Trellis


RS decoderTiming Recovery Detector Demodulator LDPC decoder

Super-Trellis


RS decoder

Data detection with increased linear density

5·10-35.2·10-4bER

after PRML detector

63 GB46.6 GBCapacity

(using BD mod.)

DPDDPDTracking method

60nm80nmMin. pit length

bER

80nm 60nm

320nm track pitch


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German / French project on 4th gen. Optical Storage

• 4GOOD – "4th-Generation Omni-purpose Optical Disc-system" • Technology

– Higher storage density by using super-resolution– Material study based on semiconductor material– Demonstration of 2.5 x density gain compared to

Blu-ray Disc– Miniaturized pickup & drive components

• Funding June 2005 – September 2008Federal Ministry of Economy and Technology in Germany (Bundesministerium für Wirtschaft und Technologie, BMWi)Ministry of Economy, Finance and Industry in France (Ministère de l'Économie, des Finances et de l'Industrie, MINÉFI)

• http://www.4goodtechnology.org/

4GOOD4th-Generation, Omni-purpose Optical Disc-system

10010100

111010

010

0

3

2

1

0

3

2

14GOOD4th-Generation, Omni-purpose Optical Disc-system

10010100

111010

010

10010100

111010

010

0

3

2

1

0

3

2

1

LaserMonitor diode Detector

LaserMonitor diode Detector

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Capacity estimation for Super-RENS & SIL

400 (??)

200

100 – 200

4 – 8.6

72 – 155

190 – 130

47 – 32

31 – 21

1.5 – 2.2

405

SIL

(???)320 (??)1004 layers (GB)

360 (*)160502 layers (GB)

200 – 400 (*)80251 layer (GB)

8 – 17 (*)~3.31Gain factor

140 – 30059.418Gbit/in²

150 – 100240320Track Pitch (nm)

30 – 2145111.75Data bit (nm)

20 – 143074.5Channel bit (nm)

1.5 – 2.20.850.85Num. Aperture

405405405λ (nm)

SIL + Super-RENSSuper-RENSBD

(reference)

* capacities estimated with reduced gain factors


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Funded project SURPASS

SURPASS =SUper-Resolution Photonics for Advanced Storage Systems

R&D Challenges• Decrease of Laser Spot Size• Combination of Super-RENS

& Near-Field Recording (SIL)• Mastering & replicaton of

pits < 80nm• Track Distance Reduction• Multilayer Structures• Modulation & Coding

Project start: June 2008

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Common aperture holography

objective lens

storage layer

focal plane

object beams2 reference beams (filling whole aperture)

image plane

focus of reference beams

r r

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Disc structure for common aperture HDS

• Pre-grooved substrates for tracking • groove geometry designed for high tracking/addressing

signal amplitude and minimum interaction with blue laser • Blue-sensitive polymer (thickness typ. 0.3mm)

Servo layer Polycarbonate substrate

Objective lens

Fourier plane blue laser

Holographic Layer

Separation Layer Servo Mark

Disc

GG LGGL

GGL

Red laser


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Drive concept for common aperture HDS

• 408nm ECL diode for holographic data page recording • Reference and object beam share the same objective lens (NA=0.6)• 650nm servo optics for focus and track• Shift multiplexing

CCD

650nm servo optics

SLM

reference beam

object beam

mirror with pinhole

λ/4 platelaserdiode408nm

objective lens

reflective disc

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Counter-propagating approach - Basic idea

• Reference beam is converted into signal beam after transmission of medium

• Transmission of 500µm thick holographic material = 90% • Signal beam power = 16% of reference beam power• Best beam overlap compared to other concepts

• most efficient use of medium in a small volume

reflective spatial light modulator

reference beam

signal beam

holographicmaterial


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Schematic of the optical set-up

• Reflective 4f-set-up • Holographic material at Fourier plane • L1 & L2 improve overlap• L1 & L2 have no influence on intensity distribution on image plane• Reference focus is shifted away from Fourier plane• Focal lengths FL2 = -2*FL1

conjugate image planes

L1

f1 f1 f1 f1

OL OL L2

SLMreference

signal

H

Δf

48

Experimental set-up with random phase mask

• Blue diode laser with external cavity• Max. power at reference beam focus 1mW

• Photopolymer with thickness 100 to 500µm • Improve shift selectivity with phase mask

• Standard binary phase masks require pixel-to-pixel alignment• Alignment through optics extremely difficult• Less alignment sensitive phase mask needed

blue diodelaser

L1 OL1 L2

non-polarizingbeam splitter

SLM

spatial filter

CCD camera

OL2

storagemedium

phase mask


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Reflective set-up with random phase mask

New random phase mask with improved alignment tolerance• data area on data page uses blocks with 4*4 SLM pixels • data blocks are separated by single pixel width blank zone (no data) • 1 phase mask pixel == 5*5 SLM pixels• alignment tolerance == SLM pixel width• use blank grid instead of sync marks (data capacity)

1 pixel of phase maskdata page

nodata

50

Reflective set-up with random phase mask

• Material thickness 500µm, fL1 = 150mm, fL2 = -300mm• Pixel-size of random phase mask: 5x10.7µm = 53.5µm

-40 -30 -20 -10 0 10 20 30 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

ηno

rm

x [μm]

reflective set-up, z-shiftsel.

shift-selectivity with & without phase mask

random-phase mask improves shift selectivity in all 3 directions

z-10 -5 0 5 10

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

ηno

rm

x [μm]

reflective set-up, x-shiftsel.


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Counter-propagating system with 2 beams

Concept based on reflection-type holograms

beams superimposedin Fourier plane (most effective)

data pagefilling full aperture

multiplexing in z-direction

possible

spherical reference beam:lateral shift-multiplexing

reference beam

object beam

drawback:second objective lens(reading with one lens)

nearly perfect ref-obj beam

overlap

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Counter-propagating set-up

• Use separate reference and signal beams to avoid reflections• Block part of the reference beam that causes biggest part of

reflections• More details at IWHM 2008 (paper submitted)

SER = 0.012

SLM

laser 405nm

CCD camera

storage medium

spatial filter

phase mask 1

phase mask 2OL1 OL2central stop


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Summary for holographic data storage

We investigated 2 counter-propagating holographic systems:

• Reflective set-up• Dual beam set-up

The main results are:High energy efficiencyIntroduced new alignment tolerant phase mask & data pagePhase mask improves shift selectivity

System with separate reference & signal beams preferred

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Conclusion

Storage applications are increasing in capacity demand, driving all digital storage technologiesOptical storage capacity will increase to meet the future needs for content distribution and archiving

• Packaged media will continue to be highly profitable– Blu-ray Disc is ramping up

• Content is very valuable and archiving becomes increasingly important

Products with 300-500 GByte capacity per disc are expected beyond 2012

Semiconductor material for super resolution readout has high technological potential

Holography is considered as a promising technology for archiving application in the TByte domain


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Trends in Optical Storage - University of Exeter...

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