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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
2
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
5
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
6
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
7
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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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.
12
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
15
Acid-Diffusion: Proposed mechanismIon exchange in the interfacial region has been suspected
J.-K. Lee, et al., J. Mater. Chem., 2009, 19, 2986.
16
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
18
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
21
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
22
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
23
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
24
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
26
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.
27
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
28
Patterning Fluorinated Electronic Materials employing Conventional Photoresists in Organic Solvents
29
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
31
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
33
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
34
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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