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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
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