Honeywell Confidential 1

Transparent Organic Planarizing Films for Low Temperature Display Applications

Edward W. Rutter, Jr., Ahila Krishnamoorthy, Joseph T. KennedyHoneywell Electronic Materials, 1349 Moffett Park Drive, Sunnyvale CA 94089

Jeremy Burroughes, Sharmil Ghouse, Jonathan Halls and Chris NewsomeCambridge Display Technology Ltd, Unit 12, Cardinal Business Park, Godmanchester,

6Cambridgeshire, PE29 2XG, UK

June 4, 2009

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Material Characteristics:• Completely organic film • Low temperature cure:

- Single hotplate bake: 120-200°C, 60-120 s• Film thickness covers a wide range (up to 3 µm single coat, >12

µm multiple coats)• Excellent gap-fill and planarization• High optical transmittance • Readily etched using oxygen-based plasma (for pattern transfer)• Thermally stable, low outgassing

Integration Requirements:• Process temperature (for OTFT must be below 150°C) • Must withstand subsequent processes (SED, dry/wet etch, strip,

clean)

Many existing materials cure >200°C, so cannot be used for OTFT or plastic substrates

ACCUFLO®T-31

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0%

20%

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80%

100%

80 130 180 230Bake Temperature (°C/60 s)

% F

ilm R

eten

tion

ABDC

Low Temperature Curing

• Several variations made from “C” that differ in cure temperature

• Curing measured by film retention after exposure to PGMEA (60 s puddle) –aggressive test

• Multiple bakes may be performed to enhance reflow (planarization) prior to cure

• Crosslinking temperature lowered ~ 110°C to 130°C

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0

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40

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250 450 650 850 1050Wavelength (nm)

%T

Glass BlankANext Gen

Optical Transmittance

• Very high optical transmission from 400 nm to 1100 nm (Formulation A shown)

• At 550 nm, optical transmittance is 97% relative to glass substrate

• Next Gen formulation permits high transmittance to be extended into the UV

n = 1.62, k= 0.0001 at 633 nm 150°C bake

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Fieldarea

Dense trenches0.22 µm to 6 µm

Substrate

• Coat (4000Å)• Two stage bake

Semiglobal PlanarizationTrench to field height differential

Film thickness difference between field and array areas measured by high resolutionprofilometry (over the entire array of different features)

Low, medium and high temperature versions of T31:A and B are improvements relative to D

300

1600

850

400

0

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1200

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C D A BFormulation

Ste

p he

ight

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ce (Å

)

original (CDT) improved

Planarization

9000Å

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Before

• Effective via fill – polymer reflows faster than crosslinking

Excellent via fill properties Film thickness ~270 nm

Via CD: 0.28 μmVia depth: 0.6 μm

Coat & Bake Process:Single coatSS: 1500 rpmBake: 200°C/60 s

Excellent via fill properties Film thickness ~270 nm

Via CD: 0.28 μmVia depth: 0.6 μm

Coat & Bake Process:Single coatSS: 1500 rpmBake: 200°C/60 s

Aftercoating

Via Fill (Formulation D)

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Transparent CathodeOLED Layers

Planarization

Polymer Dielectric

Gate: Metal eg. Al

Channel length 5 – 200 μm

Source & Drain:Metal eg. AuGlass substrate

Semiconductor

500 nm

OLED contact

Via

Cross-sectional Device Architecture

• OTFTs potentially provide a route to low cost, lightweight flexible backplanes for OLED displays• A planarization layer is required to protect the OTFTs and planarize the surface on which to

build the OLEDs• Top emitting OLED using glass instead of flexible substrate in order to demonstrate proof of

concept using ACCUFLO®T-31 as TFT planarizing layer• Film hotplate baked at 120°C for 120 s using 60°C/60 s pre- and post cure bakes (2.25 µm film

spin coated at 1000 rpm)

ACCUFLO®T-31

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OTFT Device Characteristics with ACCUFLO®T-31

• I-V characteristics were measured before and after planarization under two different voltage conditions

• The planarization process does not negatively impact the performance of the device• Process optimization is required to improve the consistency of Ioff• Additional work required to understand how well ACCUFLO®T-31 protects the underlying

OTFT circuitry• ACCUFLO®T-31 is a strong candidate for OTFT circuit planarization

TFT 1Blue BeforeRed After

Vds = -3V

Vds = -40V

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0.9

0.95

1

1.05

1.1

0 50 100 150 200Storage Time (Days)

Nor

mal

ized

Mw

A at 40°C

B at 21°C

• Formulation D must be stored refrigerated or the molecular weight grows. Aging is more pronounced at higher temperatures

• Formulations A shows no change in molecular weight when stored at high temperature (40°C) over 190 days (accelerated aging)

• The average normalized Mw is constant with low variation (~ 2% relative) within the error of the GPC method used to measure

• Improved formulations (A and B) are more convenient for use since they can be stored without refrigeration and do not require equilibration times associated with warming up for use

0

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0 100 200 300 400Storage Time (Days @ 40°C)

Nor

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Mw

ADB at 21°C

0.0220.987B

0.0200.968A

StDevAverageFormulation

Comparative Formulation Stability

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Thank You for your Attention

ACCUFLO®T-31 demonstrates low temperature curing, excellent gap-fill/planarization and high optical transmittance with outstanding formulation shelf-life

This combination of properties is enabling for use in temperature-sensitive materials such as Organic TFTs and plastic substrates

This material has demonstrated integration as a permanent dielectric layer into an OTFT with no degradation of device performance

Summary

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Although all statements and information contained herein are believed to be accurate and reliable, they are presented without guarantee or warranty of any kind, express or implied. Information provided herein does not relieve the user from the responsibility of carrying out its own tests and experiments, and the user assumes all risks and liability for use of the information and results obtained. Statements or suggestions concerning the use of materials and processes are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe any patent. The user should not assume that all toxicity data and safety measures are indicated herein or that other measures may not be required.