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

Outline Introduction Self-Aligned Imprint Lithography (SAIL) 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

Sustainability 1/3 waste is paper… of which 43% is print 36m tons/yr Newspapers 12 Commercial Packaging & other 47.7 print 7.35 And we waste more if we print. Current and targetted printing markets generate millions of tons of waste in the US alone landfill paper is a major greenhouse gas source, and paper is one of the most water-intensive industries. We must do better than this. Reflective color ePrint will be part of the solution. Office 6.6 36m tons/yr Standard mail 5.8 Millions of tons/year US Paper & board disposal, 2005 US EPA Magazines 2.5 Books 1.15 Directories 0.65

Macro-Trends Are Helping to Drive Electronic Paper Mobile Internet Clean Technology Printed Electronics Digital Media *courtesy of Mike McCreary, E Ink

Electronic Publishing is a Multi-$B Addressable Market A library in your hands $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. *courtesy of Mike McCreary, E Ink

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

Paper Newspapers and the Environment OIL OIL OIL OIL OIL OIL OIL OIL OIL ½ ton of trees are required to produce the 1/5 ton of paper per subscription per year Paper accounts for about 1/5 of the worldwide harvest of trees very energy intensive process---plup and paper are the 5th largest industrial consumer of energy more water to produce a ton of product than any other industry accounts for 40% of our municipal waste (only ½ is paper packaging) and paper use has grown 6X in the last 50 years and double in the last 30 years Germany and Europe are leading efforts for recycled paper, US uses 1/3 of paper in the world 1/5 ton per subscription per year OIL *courtesy of Mike McCreary, E Ink

Economic Reasons to Move From Paper Newspapers 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 Composite Newspaper Business Profile* revenue includes 15.8M paid circulation plus $3.9 online ad revenue 100,000 Circulation $83.9M Revenue $72.1M Total Cost ~10% Profit *Published by Bill Richards (former NY Times and Washington Post reporter) *courtesy of Mike McCreary, E Ink

Outline Introduction Self-Aligned Imprint Lithography (SAIL) 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

Challenges & Benefits of R2R Electronics Fabrication 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

Imprint Lithography is the Best Choice for R2R Patterning   Photolithography Imprint lithography Inkjet Physical mask Laser ablation Throughput Moderate: limited by step & repeat / stitching High: > 5 meters/min Low Limited only by deposition Resolution Limited by substrate flatness ~10μ 100nm demonstrated >10μ 10μ -100μ ~10μ Alignment Self alignment possible External sensor required poor Issues Scaling to large areas costly New technology Materials must be jettable Cleaning, particles Thermal effects, selectivity

Conventional Photo-Lith a R2R Process for Manufacturing Active Matrix Backplanes Based 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 Conventional Photo-Lith SAIL deposit spin resist align/expose develop strip/clean etch deposit etch imprint mask

Iowa Thin Film Technologies is now PowerFilm Solar

Basic Imprint Lithography Process 1: coated substrate 1μm Pixel speed depends linearly on mobility but inversely with the square of channel length 2: coat with polymer 3: emboss ~40nm lines on 50μ polyimide 4: cure with UV 20 m 1 2 3 5: release Multilevel structures on flex at 5m/min 6: etch 4 levels in 0.5 μ step heights

SAIL: Self-Aligned Imprint Lithography Photolithography SAIL Process induced distortion of 200ppm results in 20μ misalignment over 10cm Multiple masking and alignment steps required Different mask used to pattern each layer SAIL encodes multiple patterns and alignments into thickness modulations of a monolithic masking structure Single mask used to pattern all the layers multiple times No misalignment because mask distorts with substrate

SAIL backplane: patterning process flow Disassemble array one layer at a time to expose structure. Begin by removing top metal Next remove contact layer to expose channel semiconductor Finally remove gate dielectric to expose gate lines that were isolated by the undercut Remove remaining polymer to expose completed backplane Then remove semiconductor to expose gate dielectric Etch top metal and contact layer to define TFT channel 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 Imprint mask on TFT stack consisting of Top metal Contact layer (optional) Semiconductor Dielectric Bottom metal Process produces complete backplane: TFT Pixel electrode Data line Crossover Gate line

SAIL solves alignment problem & saves money R2R SAIL R2R photolith (AGI) Multiple photoresist applications dominate photolithography process materials costs cost per ft2 Cost of Patterning Backplane materials costs for R2R photolith & SAIL

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

The web rolled on the core is its own clean room HEPA filter Ambient Process Vacuum Process

Equipment footprint comparison between R2R and flat panel Gen10 cluster tool 330mm imprint system

Patterning scaling: R2R imprinter compared to panel stepper comparison made at equal throughput Scaling similar for R2R and panel; cost much lower for R2R

PECVD Scaling: R2R photovoltaic compared to panel comparison made at equal throughput Again; scaling similar for R2R and panel; cost much lower for R2R

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] Mobility [cm2/V/S] 1.E 0 1.E-3 1.E-2 1.E-1 1.E 1 1.E 2 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 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] is shown as a function L in Figure 4.1.3.

SAIL Backplane on flexible substrate Initial display demonstrators World’s first active matrix display made exclusively with R2R processes (including E Ink Front Plane) SAIL Backplane on flexible substrate

Yield Improvements: Pareto process at work Process Step Severity Thin film deposition Shunt defects 1/mm2 Stress control unstable Particle generation low Imprinting Master defects Stamp defects med Imprint process Etching Endpoint control Process design Device test Contact liquefaction Probing errors/damage Process flow A bubble defect, voids are formed by insufficient volume of photopolymer to fill mold pinhole defect in metal caused by etchant diffusing through pinhole in oxide A crack defect typically results from imbalanced deposition stress Tenting defect formed by particle between stamp and substrate at imprinting time or by void in stamp Nonuniform imprinting results in premature mask erosion and feature loss Bridging caused by breakage of imprint stamp in narrow (~2u) regions

13” production solar cell deposition R2R tool development 13” production solar cell deposition 13” wet etcher 13” imprinter 4” imprinter 10” drum PECVD 13” RIE 2005 2008 2007 2006 2009

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

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 Corporation ASU Flexible Display Center