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Roll-to-Roll Manufacturing of Flexible Displays

Carl Taussig, Bob Cobene, Rich Elder, Warren Jackson, Mehrban Jam, Albert

Jeans, Hao Luo, Ping Mei, Craig Perlov, Hewlett-Packard Company, Palo Alto, CA

Frank Jeffrey, Marcia Almanza-Workman, Kelly Beacom, Steve Braymen, Bob

Garcia, Jason Hauschildt, Han-Jun Kim, Ohseung Kwon, Don Larson, Phicot Inc, Ames, IA

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Introduction•Why we need paper-like displays

Self-Aligned Imprint Lithography (SAIL)• Benefits and challenges of roll-to-roll (R2R) manufacturing• SAIL basics• green manufacturing for green products• toolset for 1/3m wide line• world’s first R2R active matrix displays

Outline

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Sustainability

Millions of tons/year

US Paper & board disposal, 2005

US EPA

1/3 waste is paper… of which 43% is print

36m tons/yr

Newspapers 12

Commercial print 7.35

Office 6.6

Magazines 2.5

Books 1.15

Packaging & other 47.7

Standard mail 5.8

Directories 0.65

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Macro-Trends Are Helping to Drive Electronic Paper

Clean Technology

Mobile Internet

Printed Electronics Digital Media

*courtesy of Mike McCreary, E Ink

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Electronic Publishing is a Multi-$B Addressable Market

• $100B- $300B annual publishing industry today, about the same as the whole current display industry*

• Mobile electronic books have not previously succeeded because they lacked the attributes of paper: low cost, outdoor readability, light weight (low power), &mechanical toughness.

A library in your hands

*courtesy of Mike McCreary, E Ink

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Newspapers Need an Alternative to Paper• Paper newspaper subscriptions are dropping sharply

– 12 hour delay in receiving news– newest generations of people are on-line much more– increased sensitivity to ecology issues

• Newspaper profitability is under pressure as a result– increasing energy costs– On-line subscriptions are growing but it takes 50-100 on-line

subscribers to make up for one lost paper subscription*

• Digital distribution enables personalization– Geographic localization enhanced– Individually targeted content and advertising

• A paper-like reader appliance is needed – Low cost, portable, daylight readable, mechanically tough

*courtesy of Mike McCreary, E Ink

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Paper Newspapers and the Environment

1/5 ton per subscription

per year

OIL

OIL

OIL

OIL

OIL

OIL

OIL

OIL

OIL

OIL

OIL

OIL

*courtesy of Mike McCreary, E Ink

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Economic Reasons to Move From Paper Newspapers Printing$6.7M

Circulation $10.1M

Ink and paper $10.4M

Newroom $9.9M

Advertising $7.3M

Building, G&A $27.6M

Composite Newspaper Business Profile*

*Published by Bill Richards (former NY Times and Washington Post reporter)

100,000 Circulation$83.9M Revenue $72.1M Total Cost

~10% Profit

• Newspapers could eliminate $27M (~38%) from its variable budget by moving away from printed newspapers

• But it will be critical to keep subscriptions and advertising rates high with electronic newspapers

*courtesy of Mike McCreary, E Ink

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Introduction•Why we need paper-like displays

Self-Aligned Imprint Lithography (SAIL)• Benefits and challenges of roll-to-roll (R2R) manufacturing• SAIL basics• green manufacturing for green products• toolset for 1/3m wide line• world’s first R2R active matrix displays

Outline

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Challenges & Benefits of R2R Electronics Fabrication

Benefits Challenges

Lower substrate cost Lower process temperature

Steady state processing: high-throughput, high-yield

Defect repair

Lower cleanroom requirements patterning

Cheaper equipment - better scaling?

Limited equipment available – no previous generation

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  Photolithography Imprint lithography

Inkjet Physical mask

Laser ablation

Throughput Moderate: limited by step & repeat / stitching

High: > 5 meters/min

Low Limited only by deposition

Low

Resolution Limited by substrate flatness ~10μ

100nm demonstrated

>10μ 10μ -100μ ~10μ

Alignment Limited by substrate flatness ~10μ

Self alignment possible

External sensor required

poor ~10μ

Issues Scaling to large areas costly

New technology

Materials must be jettable

Cleaning, particles

Thermal effects, selectivity

Imprint Lithography is the Best Choice for R2R Patterning

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a R2R Process for Manufacturing Active Matrix BackplanesBased on Plasma Processing and Self-Aligned Imprint Lithography

Vacuum deposition of metals, dielectrics, & semiconductors

5μ

Multiple mask levels imprinted as single 3D structure

Patterning completed w/ wet & dry processes

deposition imprint etch

deposit

spin resist

align/expose

develop

strip/clean

etch

deposit etchimprint

etchmask

Conventional Photo-Lith SAIL

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Iowa Thin Film Technologies is now PowerFilm Solar

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Basic Imprint Lithography Process

~40nm lines on 50μ polyimide

Multilevel structures on flex at 5m/min

Pixel speed depends linearly on mobility but inversely with the square of channel length

6: etch

5: release

3: emboss

4: cure with UV

1: coated substrate

2: coat with polymer

1μm

4 levels in 0.5 μ step heights

20 m

0123

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SAIL encodes multiple patterns and alignments into thickness modulations of a

monolithic masking structure

SAIL: Self-Aligned Imprint Lithography

Photolithograph

yS

AIL

Multiple masking and alignment steps required

Different mask used to pattern each layer

Single mask used to pattern all the layers multiple times

Process induced distortion of 200ppm results in 20μ

misalignment over 10cm

No misalignment because mask distorts with substrate

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Imprint mask on TFT stack consisting of•Top metal•Contact layer (optional)•Semiconductor•Dielectric•Bottom metalProcess produces complete backplane:TFTPixel electrodeData lineCrossoverGate line

Etch exposed stack all the way to the substrate undercutting the bottom metal in the thin regions to isolate the gate lines and the TFTs

Etch the polymer down to expose the layers covering the gate lines

Etch through top metal and (optionally) other layers to form crossovers

Etch polymer a second time to expose area covering TFT channel

Etch top metal and contact layer to define TFT channel

Remove remaining polymer to expose completed backplane

Disassemble array one layer at a time to expose structure. Begin by removing top metal

Next remove contact layer to expose channel semiconductor

Then remove semiconductor to expose gate dielectric

Finally remove gate dielectric to expose gate lines that were isolated by the undercut

SAIL backplane: patterning process flow

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$0.0 $0.5 $1.0 $1.5 $2.0 $2.5 $3.0

Web preparation

Sputter Gate 1 Metal

Align and Expose

SiN, a-Si, N+ dep

Align and Expose

Si RIE & Resist Strip

Ultrasonic Clean

Align and Expose

Sputter Dep/ ITO

Align and Expose

Sputter Dep Interconnect

Align and Expose

Web cost

SAIL solves alignment problem & saves money

$0.0 $0.5 $1.0 $1.5 $2.0 $2.5

Condition web (de-hydro)Gate metal deposition (Al)

PECVD oxide/nitride/Si/N+ depositionSD metal deposition (Cr)

Imprint SAIL structureWet etch Cr

RIE etch n+&Si&SINRIE etch oxide

Plasma etch Al

Thin down 2P (clear gate-pad)Pre-Cr-etch CleaningRIE etch n+&Si&SIN

Thin down 2P (clear gate-pad)Wet etch CrRIE etch n+

Under-cut Al (1-3 um)RIE etch oxide

Strip-off 2PWeb cost

cost

per

ft2

$0.00

$2.00

$4.00

$6.00

$8.00

$10.00

$12.00

$14.00

$16.00

$18.00

Photolithography SAIL

Cost of Patterning

Backplane materials costs for R2R photolith & SAIL

R2R

SA

ILR

2R photolith (A

GI)

Multiple photoresist applications

dominate photolithography process materials costs

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Green manufacturing for a green product

• Less is better: 50μm thick plastic vs. 0.7mm thick glass

• Less process materials: removal of photolith reduces process consumables

• Energy costs: – transients involved in batch consume energy; steady

state is more efficient– Reduced clean room requirements:

• Smaller equipment footprint

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HEPA filter

The web rolled on the core is its own clean room

Ambient Process Vacuum Process

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330mm imprint system Gen10 cluster tool

Equipment footprint comparison between R2R and flat panel

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2 3 4 5 6 7 8 9 1010

-3

10-2

10-1

100

eq

uip

men

t co

st [

M$]

/ th

rou

gh

pu

t [c

m2 /

S]

generation

equipment cost scaling comparison: panel stepper vs R2R imprinter

100 mm R2R imprinter 330 mm R2R imprinter

Patterning scaling: R2R imprinter compared to panel steppercomparison made at equal throughput

Scaling similar for R2R and panel; cost much lower for R2R

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PECVD Scaling: R2R photovoltaic compared to panelcomparison made at equal throughput

Again; scaling similar for R2R and panel; cost much lower for R2R

1 2 3 4 5 6 7 8 9 1010

-2

10-1

100

eq

uip

men

t co

st [

M$]

/ th

rou

gh

pu

t [c

m2 /

S]

generation

equipment cost scaling comparison: panel CVD vs R2R CVD

330 mm R2R PECVD

1 m R2R PECVD

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W=100um Vsd=10.1V

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

-10 0 10 20 30 40

Vg(V)

Isd

/(W

/L)

(A)

100.0 1.0

100.0 2.0

100.0 5.0

100.0 10.0

100.0 20.0

100.0 50.0

100.0 100.0

W [μm] L [μm]

Performance of Full-SAIL a-Si TFTs

Full SAIL TFTs with thinner dielectrics have greatly improved performance• on-off ratio > 107

• 100μA on-current• mobility from linear portion of transfer curve as high as 0.8 cm2/V/S• near linear scaling of Ion vs 1/L to L~2μm

Channel Length [μm]

Mo

bil

ity

[c

m2/V

/S]

100

101

102

10-3

10-2

10-1

100

101

1161F15-02Array1-41C

x

y

q1 =11.3663p1 =0.83471R2=0.96302

1.E 01.E-3

1.E-2

1.E-1

1.E 0

1.E 1

1.E 1 1.E 2

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Initial display demonstrators

SAIL Backplane on flexible substrate

World’s first active matrix display made exclusively with R2R

processes (including E Ink Front Plane)

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Yield Improvements: Pareto process at work

Pro

ce

ss

flow

Process Step SeverityThin film deposition

Shunt defects 1/mm2

Stress control unstableParticle generation low

Imprinting Master defects lowStamp defects medImprint process low

Etching Endpoint control medProcess design med

Device test Contact liquefaction lowProbing errors/damage

low

A bubble defect, voids are formed by insufficient volume of photopolymer to fill mold

A crack defect typically results from imbalanced deposition stress

Nonuniform imprinting results in premature mask erosion and feature loss

Tenting defect formed by particle between stamp and substrate at imprinting time or by void in stamp

pinhole defect in metal caused by etchant diffusing through pinhole in oxide

Bridging caused by breakage of imprint stamp in narrow (~2u) regions

R2R tool development

2005 200820072006 2009

13” production solar cell deposition

4” imprinter

13” RIE

13” imprinter

13” wet etcher

10” drum PECVD

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Next steps towards commercialization

• September 22, 2008 PowerFilm announced that it has taken a license to the SAIL technology• October 6th, 2008 PowerFilm announced it has won a $1.4M / year cooperative agreement from the U.S. Army for development of a 'self powered flexible display' . HP Labs and PowerFilm will collaborate on the contract.• PowerFilm Solar has created Phicot as a subsidiary to commercialize the technology

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Acknowledgements

The authors gratefully acknowledge the support of their collaborators and sponsors

--FlexTech Alliance - contract RFP04-112F

ARL contract W911NF-08-2-0063--

E Ink CorporationASU Flexible Display Center