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Orthogonal Processing: A New Strategy for Patterning

Organic Electronics

Orthogonal Processing: A New Strategy for Patterning

Organic Electronics

Jin-Kyun Lee and Christopher K. Ober*

Materials Science & Engineering Cornell University

ERC Teleconference3/September/2009

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OLEDs

Kodak

Organic Electronics

(+) Ease of processing

(+) Tunability of electronic properties

(+) Integration with biological systems

(-) Low-end performance

(-) Lifetime

OTFTs

DuPont

OPVs

Siemens

Will enable simple, low cost electronics and photonicsWill make dumb object smartWill complement Si-based electronics

Outline

Patterning issues in organic electronics?

Orthogonal Processing employing

- Supercritical carbon dioxide

- Hydrofluoroethers and tuned fluorinated materials

Applications and possibilities

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Overview on Patterning of Solution Processable Organic Materials

E. Menard, et al., Chem. Rev. 2007, 107, 1117. J. R. Sheats, J. Mater. Res. 2004, 19, 1974.

technique resolution materials compatibilityphotolithography 30 nm photoresists, functional organics

inkjet printing 10-20 μm organic conductors, low molecular weight polymers, wax, others

soft printing 0.1-2 μm SAMs, thin metals, organic and inorganic semiconductors

imprint lithography <10 nm moldable resists, functional organics

capillary molding 2-5 μm resists, low-viscosity inks, functional organics

laser imaging 5 μm organic conductors, semiconductors and electroluminescent materials

embossing 1 nm moldable resists, functional organics

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Patterning by Photolithography

• Long history in Si industryOptimized ProcessExperienced operatorsCheaper depreciated equipment

• Parallel process• Large area• High Resolution• Good registration (alignment

between layers)

But… Chemical compatibility issues between process chemicals and organic electronic materials!

Advantages of photolithography

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Problems in Photolithographic Patterning of Organic Materials

Etching method

Lift-off method

Photoresist deposition

UV exposure development active material deposition

lift off

UVetchant

UV ? ?

Development of lithographic conditions in chemically non-damaging solvent system

photoresist deposition

UV exposure development pattern transfer by etching

resist removal

- clean substrate- active material- photoresist- UV exposed photoresist

? ??

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Orthogonal Patterning

To develop processes and materials for the fabrication of organic/flexible electronic devices employing chemically benign, environmentally-friendly process solvents

Research Objectives

Orthogonal solvents (scCO2 & fluorous liquids)

Hydroxylic solvents

Non-polar organic solvents

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Patterning Organic Electronic Materials employing Fluorinated Photoresists in Hydrofluoroethers

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Supercritical Carbon Dioxide (scCO2 )

- Most non-fluorinated materials are stable in scCO2

- Environmentally safe- Cheap and readily available

Below critical point - separate liquid and

gas phases

Near critical point - meniscus begins to

fade

Above critical point - no meniscus,

homogeneous phase

(Tc = 31.1 ºC, Pc = 72.8 bar)

J. Mater. Chem. 2000, 10. 207.

J. Chem. Soc., Perkin Trans. 1, 2001, 917.

scCO2 is promising to develop photoresist patterns!scCO2 is promising to develop photoresist patterns!

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Photoresist Processable in scCO2

Strip offImaging

Mechanism

scCO2 soluble

C

CH3

O

O

(CH2)2

(CF2)7CF3

CH2 C

CH3

O

O

CH2m n

P(FDMA-TBMA)

PAG H+

UV

scCO2 soluble

scCO2 insolubleCH3

C

CH3

O

O

(CH2)2

(CF2)7CF3

CH2 C

CH3

O

OH

CH2m n

P(FDMA-MA)

CH3H3C

SiNH

Si

C

CH3

O

O

(CH2)2(CF2)7

CF3

CH2 C

CH3

O

O

CH2m n

SiH3C CH3

CH3

N

O

O

OS

O

O

F3C365 nm

OHS

O

O

F3C +HN

O

+H2O

CO2

Chemical Physics Letters, 2007, 443, 323.

Acid generation from PAG

H. S. Hwang, et al., J. Mater. Chem., 2008, 18, 3087.

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Lithographic Evaluation of Resist

PEDOT:PSS

Aluminum

Good adhesion and pattern development on PEDOT:PSS film

Glass

SO3H SO3H SO3H SO3H SO3- SO3H SO3H SO3H

S

O O

S

O O

S

O O

S

O O

S

O O

S

O O

S

O O

S

O O

+ *

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Acid-Diffusion from PEDOT:PSS FilmUnexpected decomposition of acid-labile photoresist was resolved through a careful selection of photoacid generator

J.-K. Lee, et al., J. Mater. Chem., 2009, 19, 2986.

S

S

O

O

O (CF2)3CF3

TPS-Nf

I

S

O

O

O (CF2)3CF3

Iod-Nf

N

O

O

O S

O

O

(CF2)3CF3

NI-Nf

Ionic PAGs Non-ionic PAGs

-

+

-+

N

O

O

O SO

O(CF2)3CF3

Nor-Nf

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Acid-Diffusion in Conventional ResistThe same result was observed in case of ESCAP resist

Baking at 120 °C

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Acid-Diffusion: Proposed mechanismIon exchange in the interfacial region has been suspected

J.-K. Lee, et al., J. Mater. Chem., 2009, 19, 2986.

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Patterning OLED in scCO2

- ITO glass- PEDOT:PSS- unexposed resist- exposed resist- light emitting polymer- CsF/Al cathode

UV exposure &development in scCO2

LEP deposition cathode deposition

patterned device

- 5 μm fine features were realized- luminous efficiency of ca. 22 cd/A

H. S. Hwang, et al., J. Mater. Chem., 2008, 18, 3087.

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Hydrofluoroethers (HFEs)

HFEs are orthogonal solvents for organic electronic devicesHFEs are orthogonal solvents for organic electronic devices

H3COCF2CF2CF2CF3

HFE-7100 (bp 61 oC) HFE-7200 (bp 76 oC) HFE-7500 (bp 130 oC)

+

H3COCFCF2CF3

CF3

H3CCH2OCF2CF2CF2CF3+

H3CCH2OCFCF2CF3

CF3CF3CFCFCF2CF2CF3

CF3

OCH2CH3

EL device with Ru(bpy)3 (PF6 )2 EL device with poly(dioctylfluorene)

A. A. Zakhidov, J.-K. Lee, H. H. Fong et al., Adv. Mater., 2008, 20, 3481.

- Commercialized by 3M - Benign to non-fluorinated organic electronic materials - Environmentally safe (zero-ozone depletion potential) - Facile recycling

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Molecular Resist Processable in HFEs

Chemically amplified molecular resist processable in HFEs

J.-K. Lee, et al., J. Am. Chem. Soc., 2008, 130, 11564.

O

O O

O

O

OO

O

O

O

O

O

(CF2)7CF3

(CF2)7CF3

F3C(F2C)7

F3C(F2C)7

(R =H)

RF-Calix-tBoc

(R = )

R

R

R

RR

R

R

R

O

O

PAG H+

RF-Calix-HUV

N

O

O

O S

O

O

(CF2)3CF3

NI-Nf

PAG =

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Lithographic Performance Evaluation

Spin-coated from HFE-7500 (4 parts) + PGMEA (1 part) mixture Pattern developed in HFE-7200

(a) Structure of a PAG. (b) Glass. (c) Polyimide-coated wafer (scale bars are 10 m). (d) SEM image on Si under e-beam exposure (80 nm features).

J. Photopolym. Sci. Technol., 2003, 16, 91.

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Patterning Materials by Lift-off

i-line UVexposure

DevelopmentIn HFE-7200

Active material deposition

Lift-off resist in HFE-7200+IPA (5wt%)

PEDOT:PSS (80 nm) Gold (30 nm)

Ru(bpy)3 (PF6 )2 (100 nm) P3HT (30 nm)

Patterning of various electronic materials was successful

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Patterning Materials by Lift-off

i-line UVexposure

DevelopmentIn HFE-7200

Active material deposition

Lift-off resist in HFE-7200+IPA (5wt%)

Patterning of various electronic materials was successful

50 m50 m

1st layer: polyfluorene (PF8)2nd layer: Ru(bpy)3 (PF6 )2

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P3HT/PCBM solar cell patterned by orthogonal patterning

Ours Lit.1

Voc (V) 89.6 880# cells 300 24,000Voc/cell (V) 0.3 0.04Jsc/cell (mA/cm2) 4.2 0.34FF 0.24 0.25PCE (%) 0.31 0.008

1. M. Niggemann et al., Adv. Mater., 2008, 20, 4055.

High Voltage Polymer Solar Cell

Y.-F. Lim, et. al., J. Mater. Chem., 2009, 19, 5394.

glass

glass

glass

glass

ITO ITOP3HT/PCBM

RF -Calix

Al

Resist patterning in HFEs

Etch and stripping

Angled Al deposition

P3HT/PCBMITO

50 μm

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Application to Device FabricationOrganic FETs having top-contact source-drain geometry

Mobility: µSAT = 0.01 cm2V-1s-1

(0.45 for pentacene)

L = 1 m

Deposit Au contacts without using shadow masks

Au AuP3HT (60 nm)SiO2 (300 nm)

Si++

S

C6H13

n

unpublished result

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Orthogonal Patterning of PEDOT:PSS Synthesis of acid-inert photoresist system specially designed for PEDOT:PSS patterning

SEM image of P(FDMA-MA) on top of PEDOT:PSS film

CH2

CH3

O

O

(CH2)2

(CF2)7

CF3

CH2

CH3

O

O

CH2

NO2

rm n

CH2

CH3

O

O

(CH2)2

(CF2)7

CF3

CH2

CH3

O

OH

rm n

NO

O

soluble in HFEs insoluble in HFEs

P(FDMA-NBMA) P(FDMA-MA)

UV

Optical image of patterned PEDOT:PSS film

O2 plasma etch

P. G. Taylor, et al., Adv. Mater., 2009, 21, 2314.

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X[µm]0.00 14.94

Z[nm

]0.

0011

2.48

0 nm

(b)5m

Application to OTFT fabrication: PEDOT:PSS electrodes and pentacene active layer were patterned photolithographically

PEDOT:PSS/Pentacene bottom-contact OTFT (a) Schematic illustration of device fabrication, (b) AFM images of a 5μm (width) x 50μm (length) Pentacene channel between PEDOT:PSS electrodes (c) optical image of OTFT, (d) device performance plots

(a)PEDOT:PSS on SiO2 /Si

Apply Photoresist Pattern Photoresist Etch PEDOT:PSS Remove Photoresist

Apply Photoresist Pattern Photoresist Deposit Pentacene Lift-off Photoresist

0 -20 -40 -60 -80 -100

10-10

10-9

10-8

10-7

10-6

I DS(A

)VG (V)

sat= 0.029 cm2V-1s-1

VDS=-100 V

(c) (d)1m

200 nm

Orthogonal Patterning of PEDOT:PSS

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Patternable Low-k Materials in HFEs Molecular precursors for low-k Materials processable in HFEs

OO

O

R

F

F

F

FF

F

F

F

OO F

FF

F

F

F

F

F

FF

F F

F

F

F

O

F

R = (A)

(CH2)4(CF2)7CF3

CF2CFHOCF2CFO(CF2)2CF3

CF3

(B)

(C)

- Solution processable- Thermally stable (>400 oC by TGA)- Cross-linkable by H+

- Low dielectric constant

Dielectric constant

k = 2.65 ~ 2.75

A

B

C

E. Murotani, et al., ACS Appl. Mater. Interfaces, 2009, Accepted.

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1)

2) Bake

PAG H+

UV

Photolithographic Patterning in HFEs

Successful patterning in HFE-7100

Spin coat material/PAG Expose with 365nm

Bake at 50 °C Develop in HFEs

To prove patternability in HFEs- Robust film formation- Patternability

Crosslinking reaction

Patternable Low-k Materials in HFEs

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Patterning Fluorinated Electronic Materials employing Conventional Photoresists in Organic Solvents

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Semi-Perfluoroalkyl Polyfluorenes

Perfluoroalkyl polyfluorenes as blue light-emitting polymers

ca. 60% F content by weight

F3C(F2C)7 (CF2)7CF3

y1 mX

unpublished result

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Application to PatterningRGB patterning using conventional photoresists and organic solvents

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Potential of Orthogonal Processing

OLEDs

OTFTs

Bio-related application

PhotovoltaicsGreen processing

of inorganic semiconductors

Low-k materials

Orthogonal processing

The Orthogonal Solution

• Patent-pending photoresist & process to manufacture organic electronics– Change photoresist chemistry to be compatible with

sensitive organic systems– Enabling photolithography infrastructure to produce

organic electronics

www.orthogonalinc.com

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Summary

Concept of Orthogonal Processing for the patterning of organic electronic materials has been proposed

HFEs have been identified as environmentally-friendly, chemically non-damaging solvents for orthogonal processing

Acid-sensitive perfluoroalkyl resorsinarene has been developed and employed successfully in OTFT and OLED fabrication

Semi-perfluoroalkyl polyfluorenes have been synthesized and patterned with conventional photoresist and organic solvents

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Acknowledgement

Materials World Network Team at CornellAlex Zakhidov, Priscilla Taylor, Hon Hang Fong, Eisuke Murotani,

John DeFranco, Margarita Chatzichristidi, Ha Soo Hwang Prof. George Malliaras

Materials World Network Team at Melbourne, AustraliaGeorgia McCluskey, Wallace Wong

Prof. Andrew Holmes (Melbourne, Australia)

National Science Foundation/Australian Research Council (Materials World Network, DMR-0602821)

National Science Foundation IGERT program New York State Foundation for Science, Technology and Innovation

(NYSTAR)

Cornell NanoScale Facility (Photolithography) 3M (HFE series solvents)

Asahi Glass (GPC in fluorous solvents)

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