Latest Developments In Polyester Film For Flexible …people.ccmr.cornell.edu/~cober/mse542/page2/files/Barriers.pdf · Latest Developments In Polyester Film For Flexible Electronics

Latest Developments In Polyester Film For Flexible Electronics

W MacDonald, K Rollins, D MacKerron, R Eveson, R Rustin, R Adam, K Looney, K Rakos and K Hashimoto- DuPont Teijin Films

2

Agenda

• Factors influencing film choice– Introduction to DTF family of films for flexible displays

• Characterisation of polyester films for flexible electronics– Surface quality– Mechanical properties of multilayer strucures– Control of dimensional reproducibility

• Influence of planarising coating on barrier performance• Examples of DTF film in flex electronic application

3

Key Challenges for Engineered Substrates into Flexible Display applications

• Low Coefficient of Thermal Expansion• Low Shrinkage• Upper Temperature for Processing• Surface smoothness• Barrier• Solvent Resistance• Moisture Resistance• Clarity• Rigidity• Conductive layers• Commercial availability

• Substrates for the more demanding applications are likely to be multilayer structures containing both organic and inorganic layers

4

Factors Influencing Film Choice-Property Set

“Simple” organic circuitry

Organic AM backplanes

Inorganic AM backplanes

OLED displays Increasing complexity of substrate structure

More demanding property set

5

Factors Influencing Film Choice-Physical Form/Manufacturing Route

• Physical form of display and type of usage will influence film choice particularly with respect to thickness– Flat but exploiting light weight, ruggedness– Conformable, one time fit to uneven surface– Flexible– Rollable

• Batch, fast sheet and R2R processing– Rigidity

6

Rigidity

• Rigidity (D) of Teonex of different thickness calculated below and compared relative to 25 micron film

• Thickness has a significant effect on rigidity

Teonex Thickness Microns

Rigidity Nm x 10-4

Rigidity relative to 25 micron film

25 0.1 150 1 1075 3 30

125 15 140175 40 390200 60 580

D = E t3

12(1-ν)

E is the tensile or Youngs Modulut is the thickness, ν is Poissons ratio (0.3-0.4).

7

Structure of PET and PEN Films

Biaxially oriented, semicrystalline films

Tetoron® and Melinex®

Polyethylene Terephthalate(PET)

Teonex®

Polyethylene Naphthalate(PEN)

C

O

O CH2CH2 O

C

O

n

CC

O O

n

PET Tm 255C Tg 78C

PEN Tm 263C Tg 120 C

O CH2CH2 O Tetoron® and Melinex®

Polyethylene Terephthalate(PET)

Teonex®

Polyethylene Naphthalate(PEN)

C

O

O CH2CH2 O

C

O

n

CC

O O

n

PET Tm 255C Tg 78C

PEN Tm 263C Tg 120 C

O CH2CH2 O

n

8

DTF Grades for Flexible Electronics

• Teonex® Q65FA– One side pretreated, heat stabilised PEN film– “Thick” grade (>75 micron) with high clarity– Emerging as a leading material for OLED displays and AM

backplanes• Teonex® Q83

– “Thin” (25 and 50 micron), lightly filled,heat stabilised grade of PEN to give handleability

• Melinex® ST506– 2 side pretreat, heat stabilised PET film– “Thick” grade

• Melinex® ST504– 1 side pretreat, heat stabilised PET film– “Thick” grade

9

Key properties of Teonex® Q65FA compared with heat stabilised PET (eg Melinex® ST506)

Glass transition, oC

Haze %

Moisture pickupat 20oC, 40%RH

Youngs Modulusat 20oC, GPa

Youngs Modulus at 150oC, GPa

Shrinkage in MD at 150o C after 30 mins (%)

Upper temperature for processing, oC

78oC

120oC

180-220oC

18-20ppm/oC

0.05%

1000ppm

0.7%

150oC 4GPa

0.1%

1000ppm

0.7%

5GPa

3GPa20-25ppm/oC 1GPa

Heat stabilised PET

Teonex® Q65A

CTE ppm/oC

10

Surface Quality-Surface Smoothness

• Micro roughness which is dictated by whether film is unfilled, filled, pretreat coated

• Characterised by – AFM

1-50 micron field of view with lateral resolution down to nm’s

– White Light Interferometry Micron to cm field of view with lateral resolution down to ca

0.2 micron

11

Teonex Family

Teonex®Q83Sample size 600x400um

Teonex®Q65 “raw”Sample size 600x400micron

Teonex®Q65 pretreatSample size 2x2 micron(NB AFM-different scale)

50nm

-25nm

0nm

12

Surface Quality-Surface Smoothness

• Within micro roughness possible to also see sporadic surface peaks up to 10’s microns lateral dimensions, 100’s nm height-illustrative examples below

• Due to internal particulate burden both organic and inorganic

• Largely controlled via polymer recipe, plant hygiene

13

Surface Quality- Surface Cleanliness

• Surface Cleanliness, extent of which depends upon the 'external'contaminants such as air-borne debris, scratches, etc. Up to 10micron high, 10’s of microns long-illustrative examples shown below

• Control through– surface cleaning eg tacky roller– planarising coating in clean room

Dust-40 microns long10 microns high

Scratch 150 microns long0.5 microns high at ridge

14

Planarised Films

• DTF is developing a family of planarising coatings that– Give glass smooth surfaces– Meet product requirements

hardness vs smoothness vs ability to withstand stress/strain adhesion, solvent resistance, environmental resistance etc

15

Melinex ® ST506-Benefit of Planarisation

Pretreat on Melinex ® ST506 gives good adhesion to subsequent coatingsBut at expense of surface roughnessRa 1.53nmSample size 594micron

Planarised Melinex ® ST506Very smooth surface-on a par withPolished glass mirrorRa 0.6nmSample size 608 microns

16

Effect of Planarising Coating on Reducing Surface Peaks

Extreme Surface Peak 'Rp' (All high points > 25nm) - Frequency Distribution comparison, for Melinex ST504 non pre treated surface and hardcoat upon it's pre treated surface.

0

100

200

300

400

500

600

700

800

900

1000

40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400

< Rp height (nm)

Rp

coun

t

MELINEX ST504

HARDCOAT

PeakCount

Peak Size

17

Surface Quality

• DTF at leading edge of surface metrology • DTF’s surface metrology allows characterisation of

nanometer to centimeters (lateral scale) and heights from nm to 10’s of microns

• DTF are developing techniques to characterise surface cleanliness

• Currently using a combination of techniques to – understand what surface defects dominate electronic product

manufacture and performance– develop film grades that meet product requirements

18

Mechanical Behaviour

• Component layers in flexible displays embrace a wide range of mechanical behaviour– Polymeric layers are flexible and tough– Conductive and barrier layers are stiff and brittle inorganics

• Structures may be subjected to residual stresses– Manufacture– Differential thermal expansion– Bending during handling

• Spreadsheet model has been developed to apply beam theory to laminate structures

• Inputs-material properties, stack geometry, mode of mechanical stress

19

Hypothetical Example

• 5 layer laminate based on – PET (substrate)– ITO (mimic inorganic layer)– Acrylic (organic coating)– Active layer eg PEDOT

• Laminate bent to a radius of 50mm

Layer Material

Thickness

Young’s Modulus

Poisson’s Ratio

Outer stress

Inner stress

µm GPa MPa MPaAcrylic 0.5 5 0.38 4.3 4.3ITO 0.03 145 0.2 110 110Active 0.1 0.1* 0.4* 0.09 0.09ITO 0.03 145 0.2 109 109PET 75 4 0.3 3.2 -3.4

20

Modelling Studies

• Tensile or compressive strength through the thickness of the 5 layer laminate

– High modulus ITO layers carry high stress and displace the neutral axis for bending from 37.5 to >40micron

– Neutral axis is still far removed from layers developing high stress– Control via base layer thickness / modulus or different product structure

21

Mechancial Behaviour

• Further work is required to build up data on “active”layers and to further validate the model

• Model is useful for predicting and rationalising failure behaviour

• Models can be used as design tools to optimise structure to minimise risk of failure

22

Dimensional reproducibilityEffect of RH on Moisture Pickup at 20C

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14 16Time(hrs)

Moi

stur

e(pp

m)

RH 20%

RH 40%

RH 60%

486 ppm

957 ppm

1440 ppm

23

Hypothetical Processing Examples

Moisture Pick-Up in Humid Air at Elevated Temperatures

0

5

10

15

20

25

30

35

0 3 6 9 12 15Time (min)

Moi

stur

e C

onte

nt (p

pm)

100C & 0.6% AH

150C & 0.6% AH

150C & 1% AH

0.6% absolute humidity equivalent to 41% RH at 20°C1% absolute humidity equivalent to 68% RH at 20°C

24

Conclusions

• Moisture pickup will have a significant effect on dimensional change-ca 45ppm in a given direction per 100ppm moisture

• Critical to understand how equilibrium level of moisture will change through device manufacturing process to obtain registration and to maximise dimensional reproducibility– this will vary depending upon a given set of processing

conditions and film type• Optimise dimensional reproducibility via control of

– inherent shrinkage of base film – processing environment

25

Barrier

101

100

10-1

10-2

10-3

10-4

10-5

10-6

Moi

stur

e Pe

rmea

bilit

y(g

/m2 /d

ay/a

tm)

Several Plastic Films

Target for OLED

Substrate for Plastic LCDPCTFELimit of Mocon Test

10-12 Glass

PEN is a factor of 5 better barrier than PET butadditional barrier technologywill be required to meet OLED Display requirements(water vapour transmission rates of <10-6 g/m2/day and oxygen transmission rates of <10-5 mL/m2/day).

26

Approach to Barrier Films for OLED Displays

• Multilayer organic/inorganic coatings eg Vitex Systems inc– Polymer layer planarises and fills defects in inorganic layers– Provide tortuous path for molecules

Barrier“Stack”

SEM Photo courtesy of Vitex Systems

Teonex®PEN Substrate

Barrier“Stack”

SEM Photo courtesy of Vitex Systems

Teonex®PEN Substrate

• Single layer of dense inorganic coating eg Symmorphix– Requires very low defect area

• Several other companies actively developing barrier technology based on variations of the above

27

Barrier

• In principle a perfect layer of SiOx of only a few nm would give adequate water and oxygen barrier

• Reality– Surface defects on substrate lead to pinhole damage– Vacuum deposited thin films often show columnar growth and have

densities less than bulk material

1000nm

20nm

RF sputtered multilayer Pulsed DC sputtered multilayer

28

Barrier

• Investigating the impact of substrate on barrier performance– The deposition of thin films via microwave assisted pulsed DC

reactive magnetron sputtering (high energy) on planarised film (minimised defects)

• 120nm SiOx has been deposited on – Teonex® Q65– Planarised Teonex ® Q65

• Comparison sample of lower energy RF process on planarised® Teonex Q65 also run

29

Ca Button Test Results-Change in OD with Time

0

20

40

60

80

100

120

0 200 400 600 800 1000

Hours

% o

f Orig

ina

Teonex Q65 withplanariser coating(microwaveassisteddeposition)Teonex Q65 withplanariser (RF)

Teonex Q65(microwaveassisteddeposition)

30

Density of SiOx coating

• The density of thin silica films on different substrates was calculated from refractive index measurements

• SiOx via microwave assisted pulsed DC reactive magnetron sputtering on planarised Teonex Q65 is unusually dense

• Correlates with good Ca button test performance

Density g/cm3 Crystalline Quartz 2.65Bulk fused silica 2.2SiO2 on planarised Teonex Q65 2.52

31

R2R Coater

• DTF is currently commissioning R2R sputter coater in clean room

• Designed for flexibility• Conductive / inorganic

coatings on prototype scale

32

Polymer Vision

• Approach- organic based TFTs• Combine AM polymer driving

electronics with a reflective “electronic ink” front plane on extremely thin sheet of plastic

• Only 100 mµ thick• Bending radius: ~0.75 cm• Weight: 1.5g• Using engineered substrates

supplied by DTF

Slide courtesy of Polymer Visionhttp://polymervision.nl/

33

Plastic Logic

• The worlds largest flexible organic AM display

• 10" diagonal SVGA (600 by 800) with 100ppi resolution and 4 levels of greyscale

• Thickness less than 0.4mm• Using engineered substrates

supplied by DTF

Slide courtesy of Plastic Logichttp://www.plasticlogic.com/

34

A-Si TFT Backplanes

• Exciting progress reported by PARC, Honeywell on successfully building a-Si TFTs on Teonex Q65 using low temperature process

• Dimensional reproducibility of <100ppm at 150C reported

• By careful control of processing environment it appears that one can push Teonex beyond DTF data sheet spec

35

Summary

• Choice of film type and thickness is crucial– Important to pick the right film for the application

• Control of surface quality is critical– DTF at leading edge of surface metrology– Critical to understand what type of surface defect impacts on

device manufacture and performance

• Modelling studies are important for– Optimising device architecture– Minimising the effects of environment on processing

• Preliminary results indicate improvement in barrier performance achieved on planarised film

36

Summary

• DTF are developing a family of engineered substrates for different flexible electronic applications

• DTF substrates evaluated in a wide set of application spaces including– e-paper– Organic TFTs– a-Si flexible TFTs– Flexible OLEDs

• Positive feedback from the market• DTF can advise on which films are suitable for a given

application/process

Lexan® for Organic ElectronicsMin (Martin) Yan, Ahmet Gün Erlat, Larry Turner, Brian Scherer, Cheryl Jones, Ri-an Zhao, TaeWon Kim, Lifeng Zhang, Paul A. McConnelee, Thomas Feist, Anil Duggal

GE Global Research / GE Plastics5th Annual Flexible Displays & Microelectronics Conference 2006

Outline• Introduction

• GE batch mode graded ultra-high barrier substrate development

• GE R2R graded ultra-high barrier substrate development

• Summary

2 /Lexan® for Organic Electronics/

February, 2006

Monetization Path for Plastic SubstrateNOW FUTURE

“Roll-Up Displays”

Glass Substrate

Plastic Advantages

• Rugged.• Thinner.• Lighter.• Enable flexible display.• Enable R2R processing.

Plastic Film Substrate

Goal: Replace glass for OLED industry.


February, 2006

Plastic Substrate for OLED- Development Need

Plastic substrate enables flexible device and R2R fabricationProvide new functions, high volume manufacturing, lower cost

OLED manufacturers need high heat plastic with ultra-high barrierNeed high T process compatibility, impermeability to moisture.

GE has the unique Ability to Combine New TechnologiesGE has high Tg Materials, optimized processes, ultra high barriers

Material Process Barrier Application

High T PolycarbonateHigh T Crystalline MaterHigh T material from external vendors.

Solvent Cast / Extrude GRC Batch


February, 2006

Organic Electronics (OE) AT Program at GRC

Flexible substrate

Transparent contact

Metal contactV Organic Active Layers

“Newspaper-Like”Roll-to-Roll Fabrication

VTechnologies:• OLED Devices• Low Cost Manufacturing• High Barrier Substrate


February, 2006

High barrier substrate enables R2R OLED manufacturing.

Challenges for flexible OLED substrate

The Problem

Plastic

OLEDBarrier

H2O O2

The Solution


February, 2006

Plastic

Plastic

OLEDBarrier

H2O O2

The Solution

Proved in batch that high barrier substrate is possible

Substrate Development- Overview

Plastic Substrate

Film

Ultra-high Barrier Coating

Chemical Resistant Coating

Transparent Conductor

Coating

Technology Development at GE

Enable

Integrated Plastic OLED Substrate

Chem resist layer

High heat polycarbonate

Graded ultra high barrier

Chem resist layer

Transparent electrode


February, 2006

Ultra-high Barrier- GE’s Approach


February, 2006

XPS Spectrum of Graded UHBGE’s Graded Ultra High Barrier

Inorganic Organiczone

Continuous composition transition

Cross-sectional TEM of Graded UHB (made in batch mode)

Key USDC Specifications* GEGR Performance• Moisture Barrier 10-6 g/m2/day low 10-5~mid 10-6 (at 23°C 50 %

RH)• Chemical Resistance acid, solvent, alkali Pass• Electrical Conductivity ≤40 Ω/Sq 40.3 Ω/Sq• Optical Transparency >80% 82 %• Mechanical Flexibility bend around 1” radius Pass.• Thermo-Mechanical Stability 2000C for 1hour Pass • Adhesion ≥4B 4B• Dimension stability <20 ppm/hr at 150°C 4 ppm/hr• Average surface roughness <5 nm 0.6 nm

15 cm square flexible OLED lighting Device on high heat polycarbonate substratewith graded UHB

Plastic Substrate Development- Performance Summary

* Subset of complete USDC specification list


February, 2006

GE plastic substrate meets key USDC specifications

Barrier Development- GE Internal Test

Ca Test @ 60°C 90% RH

Polycarbonate

EpoxyCa

Barrier Coating

Glass0 hr 500 hrs

OLED Shelf Lifetime Test @ 23°C 40% RHAfter 3,530 hrs


February, 2006

Demonstrated ultra-high barrier performance.

Barrier Development- External Test

Ultra-high barrier performance confirmed by Tritium test.

General Atomics Tritium Test


February, 2006


February, 2006

Need to transfer batch PECVD barrier process to R2R.

Substrate Fabrication- Process Overview

Roll-to-roll Ultra-high Barrier- Process development


February, 2006

Develop single layer SiOxNy and SiOxCy processes.Develop plasma cleaning process.

• Develop and optimize R2R graded ultra-high barrier process.

• Test compatibility with OLED device fabrication processes.

Transfer processes from batch reactor to R2R reactor

Achieve graded ultra-high barrierCFD Simulation

Roll-to-roll Ultra-high Barrier- Graded Structure

SiOxNySiOxCySiOxNy


February, 2006

X-ray Photoelectron Spectroscopy (XPS)

Achieved graded coating structure.

Si

12345

EDS Spectra taken fromthese 5 locations.See next slide.

glue

Si substrate

Transmission Electron Microscopy (TEM)


February, 2006

Continuous change of carbon concentration through thickness.

Roll-to-roll Ultra-high Barrier- Graded Structure

Energy Dispersive X-ray Spectroscopy (EDS)


February, 2006

Summary

GE CONFIDENTIAL 16

Positioned to transfer batch process to R2R process- Built proof of concept R2R PECVD reactor. - Developed R2R PECVD processes for inorganic and organic coatings. - Developing R2R graded ultra-high barrier coating process.

Acknowledgements– GE Plastics – Marketing & Technology.– USDC / ARL - grant MDA972-93-2-0014.– USDC Member Companies:

UDC, Dupont Displays, GAT, Kodak, Philips Research and CDT.

1

Flexible Stainless Steel Substrates for Displays

V. Cannella, M. Izu, and S. Jones Energy Conversion Devices

S. Wagner and I-C. ChengPrinceton University

2

Background

Substantial recent efforts to develop flexible displays and microelectronics

various military displayswearable displays, direct view screens, curved dashboard displays, rollaway displays

Heavy focus on plastic substratesPET, polycarbonate (PC), PEN, and polyimide (Kapton)Thin, light, flexible, transparent, conformable,Roll-to-roll processing compatible

3

Problems with Plastic Substrates

Limited process temperature ranges (<<300 C) limits TFT devices processes and backplane performance

Poor dimensional stability with varying process temperatures, stress, and relative humidity

limits pattern resolution for multi-step photolithographyvery difficult to make high resolution display circuits

Permeable to diffusion of oxygen & water vapor major problem for OLEDs displays that degrade even in low levels of oxygen & waterrequire complex and costly multilayer barrier coatings to limit diffusion to less than 10-5 gm/cm2/day.

4

Attractive Alternative -Stainless Steel Substrates

For flexible emissive or reflective displays where transparency is not required

Stainless Steel (SS) <5 mils thick, 125 µmprovides a durable flexible substrate tolerates high temperature processesmuch better dimensional stability than plasticperfect diffusion barrier to oxygen & water vaporproven device compatibilityroll-to-roll manufacturing compatibility

5

Stainless Steel SubstratesStable up to 1000 °C

Allow high quality a-Si and gate insulator (>300 °C )Allow growth of large grain poly-Si (500-900 °C)

Perfect Diffusion BarrierImpermeable to oxygen or water vapor

Not degraded by UV, ozone or organic solvents Dimensional stability much better than plastic

Much higher elastic modulusLower coefficient of thermal expansionZero coefficient of hydrolytic expansionNegligible mechanical hysteresisAllows excellent multi-photostep microprocessing

resolutions comparable to Corning 1737 glassResistant to curling due to stress in films

a problem that needs special control with plastic

6

Comparison of SS & Flexible Other Substrates

Thickness (µm) 100 100 100

Weight g/m2) 800 120 220

Safe bending radius (cm) 4 4 40

RTR processable? yes likely unlikely

Visually transparent? no some yes

Max process temp (ºC) 1000 180, 300 600

TCE (ppm/ºC) 10 16 5

Elastic Modulus (GPa) 200 5 70Permeable O2, H2O? no yes no

Coeff Hydrolytic Exp (ppm/%RH) none 11, 11 none

Pre-bake required? no yes maybe

Planarization necessary? yes maybe no

Buffer layer necessary? yes yes maybe

Electrical conductivity high none none

Thermal conductivity (W/m·ºC) 16 0.1-0.2 1Plastic encapsulation substrate thickness for TFTs in neutral plane 8x 1x 5xDeform after device fabrication no yes no

PropertyStainless-

Steel GlassPlastics

(PEN, PI)

7

TFT Circuits on SS Well Proven

Both a-Si and poly-Si display circuits on SS substrates demonstrated on R&D scale

High quality poly-Si TFTs on flexible SiO2 coated SSby Wu et.al. (Princeton) at 600-950°C

µe >greater than 60 cm2/V-spoly-Si AMOLEDs on SS demonstrated

by Afentakis et. al. (Lehigh)a-Si AMOLEDs on SS demonstrated

by Wu et.al. (Princeton)by Troccoli et. al. (Lehigh) with 2-TFT & 4-TFT arrays

a-Si active matrix EPD on SS by E-Inkdemonstrated product prototypes

8

Flexible Large-scale SS Substrates in Semiconductor Manufacturing

SS well established as semiconductor substrateLarge area photovoltaic (PV) modules - up to 16 ft2

Both a-Si & CIGS (Copper Indium Gallium Diselenide)

United-Solar Ovonic photovoltaic products on flexible stainless steel

5-mil flexible SS substrate forPV semiconductor devices

9

Roll-to-Roll Ovonic PV Manufacturing Line

ECD subsidiary United Solar Ovonicmanufactures triple-junction a-SiGe solar cells on 5 mil SS

nine semiconductor layers, ~ 1µm totalroll-to-roll manufacturing processessimultaneous processing on six 1.5-mile-long SS rolls

300 ft-long roll-to-roll PV manufacturing line on SS substrates

10

Program Scope

Initial development phase for flexible SS substrates

Integrate ECD SS substrate expertise with work at Princeton to planarize, passivate SS, build TFTsDevelop processes for 6” x 6” substrates Characterize substrates Demonstrate a-Si TFT compatibilityProvide sample substrates to USDC team to verify compatibility with OLED and a-Si backplanes

Anticipated follow-up – Scale up to larger areasProcesses compatible with roll-to-roll processing

11

Specific SS Substrate Issues - Planarization

Vendor A Sample 500X Vendor B Sample 500X

Bare SS substrates have rougher surfaces than glass or plasticSS foils come with rolling mill marks that have sharp profiles

can cause device degradation or failureSteel foils must either be polished or planarized with a film

for production we planarize with a spin-on-glass-type layer

12

Bare SS Smoothness Parameters Ra of SS Substrates for Various Vendors

0

0.01

0.02

0.03

0.04

0.05

0.06

0 2 4 6 8 10 12 14 16 18

Sample Number

Ra

(mic

rom

eter

s)

Vendor 2

Vendor 3

Vendor 6

Ry Rz Ra Rq V2 Average 0.2626 0.1654 0.0378 0.0513 V3 Average 0.0551 0.0381 0.0085 0.0111 V6 Average 0.1939 0.1281 0.0291 0.0393

Ra- Av. roughness

Ry- max change peak-to-valley

Rz- ten-point roughness height

Rq- rms roughness

13

Planarization and Passivation LayersOLEDs require surface roughness < 5-nm rmsPlanarization available layers - organic, inorganic or a mix

Higher organic % allows thicker crack-free filmOrganic % impose temperature limit for later processes

We used planarization thicknesses 1.5 µ and 2.5 µ------------------------------------------------------------------------------

Passivation layer for SS substrates provides:electrical insulation adhesion to the subsequent device layers barrier against process chemicals.

SiNx is standard insulator in a-Si TFTsalso an excellent diffusion barrier

SiO2 has lower dielectric constantreduced capacitive coupling to substrate

14

Schematic cross section (not to scale) of a passivated back-channel a-Si TFT and three

substrates types: (a) glass, (b) plastic,(c) stainless steel

substrate

n+ a-Si:H

Cr

SiNx

i a-Si:HSiNx

(c) stainless steel

passivation planarization

(a) glass

passivation

(b) plastic

passivation

passivation

Specific SS Issues – Electrical Isolation

SS substrates are electrically conductive:

must be coated to provide excellent electrical insulationvideo scan rates require low capacitive coupling of device to substrate

These requirements can be met by combining :

planarization layer followed by electrically insulating capping layer

15

Planarization & Passivation Materials for Various Subsequent Processes

Subsequent Device Process

methyl siloxane silicatespin-on-

glassspin-on-

glasslow temperature process <250°C √ √ √ > 0.2 µm > 0.2 µm

conventional a-Si:H TFT <400°C √ √ > 0.2 µm > 0.2 µm

conventional poly-Si TFT process

>450°C √ > 0.2 µm

laser-annealing √ √ √ > 0.2 µm*

Planarization Layer Passivation Layer

organic polymer

deposited SiO2

deposited SiNx

16

Planarized & Passivated SS Substrate Type A

Without metal With metal

17

Planarized & Passivated SS Substrate Type B

Without metal With metal

18

050603-03 (1.5 µm + SiOx + Mo) 050603-12 (2.5 µm + SiOx + Mo)

Typical Inclusion Defects

19

SS Substrate Sample SmoothnessSample Planarization

ThicknessSiOx Mo Slide # Graph TypMag. X-res. Y-res. Baseline ∆h ∆h (peak)

050603-03 1.5 µm 200 nm N/A 5 optical low

(no Mo region) 6 optical high7 profilometry 0.4 µm 10 µm √ < 100 nm8 profilometry ~ 273 nm

050603-03 1.5 µm 200 nm 100 nm 10 optical low

(Mo region) 11 optical high12 profilometry 0.4 µm 10 µm √ < 80 nm13 profilometry ~ 51 nm14 profilometry ~ 193 nm15 profilometry 2 µm ~ 212 nm

050603-12 2.5 µm 200 nm N/A 18 optical low

(no Mo region) 19 optical high20 profilometry 0.4 µm 10 µm √ < 40 nm21 profilometry 2 µm ~ 38 nm

050603-12 2.5 µm 200 nm 100 23 optical low

(Mo region) nm 24 optical high25 optical high26 profilometry 0.4 µm 10 µm √ < 35 nm27 profilometry ~ 63 nm28 profilometry ~ 69 nm29 profilometry ~ 1030 nm30 profilometry 2 µm ~ 60 nm

20

SS Substrate Smoothness SummaryOptical micrograph of sample without Mo:

looks rough but actual surface is smoothimage reflects the surface roughness of the steel substratedifficult to locate the defects (image interfered by the substrate roughness)

Baseline area surface is very smooth surface roughness (peak-to-peak) over 300 µm square:

050603-03 (w/ Mo) 1.5 µm < 80 nmRa (AFM) ~ 5 -10 nm

050603-12 (w/ Mo) 2.5 µm < 35 nmRa (AFM) < 5 nm

Defect types:050603-03 1.5 µm point defects050603-12 2.5 µm point defects & line defects

21

Electrical Isolation

050603_04 Formatted Map 050603_05 Formatted Map 050603_06 Formatted Map

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 676195 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07





5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 397955 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07




1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07


050603_07 Formatted Map 050603_08 Formatted Map 050603_09 Formatted Map




5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5720048 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 285024 2.6E+07 5.1E+07 5.1E+07 5.1E+07


5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5147940 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 2.6E+07 1.7E+07 1.3E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1.3E+07 1E+07 1.3E+07 1.3E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 1E+07 1.3E+07 1E+07 1E+07 1E+07 8580587 1E+07 1E+07 1E+07 1E+07 1E+07 1E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 1.3E+07 1E+07 1.3E+07 1E+07 1E+07 1.3E+07 1E+07 1E+07 1E+07 1E+07 1E+07 1E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 1E+07 1E+07 3959716 1E+07 8580587 1E+07 1E+07 1E+07 1E+07 1E+07 1E+07 1E+07

5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 5.1E+07 1E+07 1E+07 1E+07 1E+07 1.7E+07 1.7E+07 1.7E+07 1.7E+07 1.7E+07 1.7E+07 1.7E+07 1.7E+07

Electrical Resistance measurements on 3mm x 3mm MIM squares

Green=high resistance, Yellow=partial shunting, Red=short

22

pF 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 161 246

2 226

3 221

4 221

5 225 221 222 217 222

6 218 214 212 208 215

7 221

8 222 220

9 255 226 231 241 218 222 221 222 220 215 213 220 221 222 223 230

10 218

11 223 220 219 214 217

12 226 224 222 212 214

13 235

14 222

15 221

16 284 284 288

Capacitance (pF) of 3mm x 3mm MIM squaresSample 050603-07 2.5µ Planarization

23

TFT Compatibility

To verify TFT compatibility we fabricated common gate TFT structures SS substrates proved compatible with all a-Si processes

300 C processes for a-Si, Si3N4, SiO2, plasma etching, etc.

Substrate planarity compatible with 4 µm photopatterningOnly one common gate device out of 20 showed shuntingEastman Kodak Company and Princeton University also collaborated to fabricate a-Si TFTs on these stainless steel substrates

device performance was similar to TFTs made on glass

24

Commercial Availability & EconomicsSS foil is currently available commercially with a surface finish compatible with planarization layers at <$10/m2

< equivalent polyimide, ~ same as high quality PENProduction planarization will use high utilization coating processes (not “spin-on”)SS substrates need only one PECVD insulator coatMaterials cost for planarization & passivation ~ $20/m2

Planarized passivated SS substrates will be economically attractive vs. plastic substrates

Plastic substrates for OLEDs require multilayer barrier coatings estimated to cost >$50/m2

25

Outlook for Flexible SS SubstratesPlanarized & passivated SS substrates can provide functional substrates for flexible electronics & displaysSS is attractive vs. plastics for flexible displays:

thermal stability compatible with both a-Si & poly-Si TFTsexcellent mechanical stability for multi-photostep processingperfect barrier against diffusion of O2 & H2O more rugged and robust than plastics, suited to applications that require mechanical strength, flexibility, & resiliencechemical stability to organic solvents, to UV radiation, and ozone

Active matrix circuits on SS substrates are provenboth a-Si and high-temperature poly-Si TFTs

Planarized passivated SS will be economically very attractive compared to plastic with barrier layers

26

Program ResultsInitial P&P processes developedBaseline smoothness is very promising, <5nm

Work to eliminated inclusions must be continued

Compatibility with TFT processes verifiedPlanarized & passivated SS substrates delivered to team

For processing with OLEDs and backplanes

Next program phase will include scale-up to larger areas

27

Acknowledgements

USDC and ARL for partial funding of this workDave Beglau and Bud Dotter who did all the hands-on work for this program

1Method of measuring ultra-low water vapor permeation for OLED displays

Method of measuring ultra-low water vapor permeation for

OLED displays

General Atomics

Display Products Group

Dr. Ralf Dunkel

3550 General Atomics Court

San Diego California 92121

Phone 858-455-2751

Email: [email protected]


General Atomics• GA specializes in diversified research and development

in energy, defense and other advanced technologies• GA was founded as a division of General Dynamics in

1955, later owned by Gulf Oil and Chevron and is privately owned since 1986

• It has a staff in San Diego that currently numbers about 2,100.

• GA has activities in military and commercial thin film coatings

• Commercial activities include R&D on roll-to-roll barrier coatings and transparent conductive coatings and prototypical work for OLED on flexible substrates


Why is the topic water permeation important for OLED’s on glass or

plastic?

Then take a look at my picture gallery:


Selected Water Vapor Permeation Testing Methods

• Gravimetric (loss of water or gain of water on P2O5)

• Capacitive or Resistive (humidity sensor)

• Spectroscopy (mass spectroscopy, fluorescence quenching)

• Calcium degradation (optically1 or change in resistance2)

• Radioactive (tritium or 14CO)

1 G. Nisato, P.C.P. Bouten, P.J. Slikkerveer, W.D. Bennett, G.L. Graff, N. Rutherford, L. Wiese, Proc. Asia Display, 1435 (2001).2 R. Paetzold, A. Winnacker, D. Henseler, V. Cesari, and K. Heuser, Review of Scientific Instruments Vol 74(12) pp. 5147-5150.

December 2003.


Our Approach and its Capabilities

• We choose a radioactive method using tritiated water (HTO) to measure permeation directly

• Detection limit of 1e-8 grams/m2 day• Can either measure permeation through

barrier coatings on plastic or epoxy seal on glass

• Oxygen measurement also possible


Comparison of techniques

~1e-8 g/m2 day~1e-6 g/m2 dayDetection Limit

YesNoDifferentiates direction of permeation

NoYesCharacterizes spatial defects

NoYesSample preparation required

Week(s)Week(s)Measurement time

DirectIndirectMeasurement mode

RadioactiveCalcium


Setup: x,y and z directional testingCH4 CH4 + H2O

100 % RH

CH4 CH4 + H2O

100 % RH

Mode 1: z-directional (plastic) Mode 2: x,y-directional (glass)


Required: Licensed Radioactive Lab

Licensed for 10 Curie Tritium


Experimental Setup


1 cm3 HTO

50 cm3 volume under ball valve (saturated with HTO vapor)

Methane in Methane out

Ball Valve

Square O-rings

Round O-ring

Sample

Lower Purge SystemInner Purge System


Experimental Setup

• 1cm3 of HTO, radioactivity 1 Curie• Sample 10cm x 10cm square• Conditions: room temperature and 100% RH• Test cell volume ~ 9.8 cm3

• Saturation time < 5 minutes• Baseline mode and measurement mode• Detection limit 0.1 µCi (2.e-7 g/m2 day)


Z-directional test Results – Example Graph



X,y-directional test Results and Repeatability

Epoxy Edge seal on glass


Comparison of results of AlxOy barrier coatings on plastic

0.0008864

0.00276

0.00050.003± 0.001

Result

0.003122C/100RHRadioactive (tritium water)

0.0027638C/90RHCalcium (resistance change)

0.003522C/50RHCalcium (optical density)

0.00338C/90RHMocon

Corrected to 38C/90RH

(estimated*)

ConditionMethod

* Assumes activation energy 58 kJ/mol, Arrhenius behavior for temperature and linear behavior for relative humidity

1. Thin Solid Films 382 (2001) 194-201

2. Polymer Testing 19 (2000) 673-691


Current work (USDC contract)

• Build 2 new systems• Heating capability 38 – 60 degree C• Full automation (e.g. add computer

controlled valves)• Measure NIST Standard• Process validation


Future work

• Offer testing service• Test optimization• Measure oxygen permeation

Documents

Latest Developments In Polyester Film For Flexible …people.ccmr.cornell.edu/~cober/mse542/page2/files/Barriers.pdf · Latest Developments In Polyester Film For Flexible Electronics