1 rthogonal Processing: A New Strategy for Patterning rganic Electronics ERC Teleconference 3/September/2009 Jin-Kyun Lee and Christopher K. ber* Materials Science & Engineering Cornell University
2 rganic Electronics Will enable simple, low cost electronics and photonics Will make dumb object smart Will complement Si-based electronics (+) Ease of processing TTs (+) Tunability of electronic properties (+) Integration with biological systems (-) Low-end performance LEDs DuPont PVs (-) Lifetime Kodak Siemens
utline Patterning issues in organic electronics? rthogonal Processing employing - Supercritical carbon dioxide - Hydrofluoroethers and tuned fluorinated materials Applications and possibilities
5 verview on Patterning of Solution Processable rganic Materials technique resolution materials compatibility photolithography 30 nm photoresists, functional organics inkjet printing 10-20 μm soft printing 0.1-2 μm organic conductors, low molecular weight polymers, wax, others SAMs, thin metals, organic and inorganic semiconductors imprint lithography <10 nm moldable resists, functional organics capillary molding laser imaging 2-5 μm 5 μm resists, low-viscosity inks, functional organics organic conductors, semiconductors and electroluminescent materials embossing 1 nm moldable resists, functional organics E. Menard, et al., Chem. Rev. 2007, 107, 1117. J. R. Sheats, J. Mater. Res. 2004, 19, 1974.
6 Patterning by Photolithography Advantages of photolithography Long history in Si industry ptimized Process Experienced operators Cheaper depreciated equipment Parallel process Large area High Resolution Good registration (alignment between layers) But Chemical compatibility issues between process chemicals and organic electronic materials!
7 Problems in Photolithographic Patterning of rganic Materials Etching method? UV etchant?? photoresist deposition Lift-off method UV exposure development pattern transfer by etching UV - UV exposed photoresist - photoresist - active material - clean substrate?? resist removal Photoresist deposition UV exposure development active material deposition lift off Development of lithographic conditions in chemically non-damaging solvent system
8 rthogonal Patterning Research bjectives To develop processes and materials for the fabrication of organic/flexible electronic devices employing chemically benign, environmentally-friendly process solvents rthogonal solvents (scc 2 & fluorous liquids) Hydroxylic solvents Non-polar organic solvents
9 Patterning rganic Electronic Materials employing luorinated Photoresists in Hydrofluoroethers
10 Supercritical Carbon Dioxide (scc 2 ) Below critical point - separate liquid and gas phases Near critical point - meniscus begins to fade (T c = 31.1 ºC, P c = 72.8 bar) J. Mater. Chem. 2000, 10. 207. - Most non-fluorinated materials are stable in scc 2 - Environmentally safe - Cheap and readily available Above critical point - no meniscus, homogeneous phase J. Chem. Soc., Perkin Trans. 1, 2001, 917. scc 2 is promising to develop photoresist patterns!
11 Photoresist Processable in scc 2 Mechanism CH 2 CH 3 C m CH 2 CH 3 C n PAG H + UV CH 2 CH 3 C m CH 2 CH 3 C n Si N H Si CH 2 CH 3 C m CH 2 CH 3 C n (CH 2 ) 2 H 3 C CH 3 (CH 2 ) 2 H scc 2 insoluble (CH 2 ) 2 H 3 C Si CH 3 (C 2 ) 7 CH 3 (C 2 ) 7 (C 2 ) 7 CH 3 C 3 scc 2 soluble P(DMA-TBMA) Imaging C 3 P(DMA-MA) Strip off C 3 scc 2 soluble Acid generation from PAG 3 C S N 365 nm H 2 3 C S H + HN + C 2 Chemical Physics Letters, 2007, 443, 323. H. S. Hwang, et al., J. Mater. Chem., 2008, 18, 3087.
12 Lithographic Evaluation of Resist Good adhesion and pattern development on PEDT:PSS film Glass Aluminum PEDT:PSS S 3 H S 3 H S 3 H S 3 H S 3 - S 3 H S 3 H S 3 H S S S S S + S S * S
13 Acid-Diffusion from PEDT:PSS ilm Unexpected decomposition of acid-labile photoresist was resolved through a careful selection of photoacid generator S + TPS-Nf I - - + S (C 2 ) 3 C 3 S (C 2 ) 3 C 3 Iod-Nf Ionic PAGs N S (C 2 ) 3 C 3 Nor-Nf N S NI-Nf (C 2 ) 3 C 3 Non-ionic PAGs J.-K. Lee, et al., J. Mater. Chem., 2009, 19, 2986.
14 Acid-Diffusion in Conventional Resist The same result was observed in case of ESCAP resist Baking at 120 C
15 Acid-Diffusion: Proposed mechanism Ion exchange in the interfacial region has been suspected J.-K. Lee, et al., J. Mater. Chem., 2009, 19, 2986.
16 Patterning LED in scc 2 patterned device UV exposure & LEP deposition cathode deposition development in scc 2 - Cs/Al cathode - light emitting polymer - exposed resist - unexposed resist - PEDT:PSS - IT glass -5 μm fine features were realized - luminous efficiency of ca. 22 cd/a H. S. Hwang, et al., J. Mater. Chem., 2008, 18, 3087.
17 Hydrofluoroethers (HEs) H 3 CC 2 C 2 C 2 C 3 + C 3 H 3 CCC 2 C 3 H 3 CCH 2 C 2 C 2 C 2 C 3 C 3 + C C 3 CCC 2 C 2 C 3 3 CH H 3 CCH 2 CC 2 C 2 CH 3 3 HE-7100 (bp 61 o C) HE-7200 (bp 76 o C) HE-7500 (bp 130 o C) - Commercialized by 3M - Benign to non-fluorinated organic electronic materials - Environmentally safe (zero-ozone depletion potential) - acile recycling EL device with Ru(bpy) 3 (P 6 ) 2 EL device with poly(dioctylfluorene) HEs are orthogonal solvents for organic electronic devices A. A. Zakhidov, J.-K. Lee, H. H. ong et al., Adv. Mater., 2008, 20, 3481.
18 Molecular Resist Processable in HEs Chemically amplified molecular resist processable in HEs (C 2 ) 7 C 3 3 C( 2 C) 7 R R R R UV PAG H + R -Calix-H (R =H) R R (C 2 ) 7 C 3 R R 3 C( 2 C) 7 R -Calix-tBoc (R = ) PAG = N S (C 2 ) 3 C 3 NI-Nf J.-K. Lee, et al., J. Am. Chem. Soc., 2008, 130, 11564.
19 Lithographic Performance Evaluation Spin-coated from HE-7500 (4 parts) + PGMEA (1 part) mixture Pattern developed in HE-7200 J. Photopolym. Sci. Technol., 2003, 16, 91. (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).
20 Patterning Materials by Lift-off Patterning of various electronic materials was successful i-line UV exposure Development In HE-7200 Active material deposition Lift-off resist in HE-7200+IPA (5wt%) PEDT:PSS (80 nm) Gold (30 nm) Ru(bpy) 3 (P 6 ) 2 (100 nm) P3HT (30 nm)
21 Patterning Materials by Lift-off Patterning of various electronic materials was successful i-line UV exposure Development In HE-7200 Active material deposition Lift-off resist in HE-7200+IPA (5wt%) 1 st layer: polyfluorene (P8) 2 nd layer: Ru(bpy) 3 (P 6 ) 2 50 m 50 m
22 High Voltage Polymer Solar Cell P3HT/PCBM solar cell patterned by orthogonal patterning IT P3HT/PCBM IT glass P3HT/PCBM IT Resist patterning in HEs R -Calix glass 50 μm Etch and stripping urs Lit. 1 Voc (V) 89.6 880 glass Angled Al deposition # cells 300 24,000 Voc/cell (V) 0.3 0.04 Jsc/cell (ma/cm 2 ) 4.2 0.34 Al 0.24 0.25 PCE (%) 0.31 0.008 glass 1. M. Niggemann et al., Adv. Mater., 2008, 20, 4055. Y.-. Lim, et. al., J. Mater. Chem., 2009, 19, 5394.
23 Application to Device abrication rganic ETs having top-contact source-drain geometry C 6 H 13 Au Au P3HT (60 nm) Deposit Au contacts without using shadow masks S Si 2 (300 nm) Si ++ n L = 1 m Mobility: µ SAT = 0.01 cm 2 V -1 s -1 (0.45 for pentacene) unpublished result
24 rthogonal Patterning of PEDT:PSS Synthesis of acid-inert photoresist system specially designed for PEDT:PSS patterning CH 2 CH 3 r m CH 2 CH 3 n UV CH 2 CH 3 r m CH 2 CH 3 n H (CH 2 ) 2 CH 2 N 2 N (CH 2 ) 2 (C 2 ) 7 (C 2 ) 7 C 3 P(DMA-NBMA) C 3 P(DMA-MA) soluble in HEs insoluble in HEs 2 plasma etch SEM image of P(DMA-MA) on top of PEDT:PSS film ptical image of patterned PEDT:PSS film P. G. Taylor, et al., Adv. Mater., 2009, 21, 2314.
0.00 14.94 X[µm] 25 rthogonal Patterning of PEDT:PSS Application to TT fabrication: PEDT:PSS electrodes and pentacene active layer were patterned photolithographically (a) PEDT:PSS on Si 2 /Si Apply Photoresist Pattern Photoresist Etch PEDT:PSS Remove Photoresist Apply Photoresist Pattern Photoresist Deposit Pentacene Lift-off Photoresist (b) 5 m 200 nm (c) 1 m (d) 10-6 sat = 0.029 cm 2 V -1 s -1 10-7 I DS (A) 10-8 10-9 V DS =-100 V 10-10 Z[nm] 0.00 112.48 0 nm 0-20 -40-60 -80-100 V G (V) PEDT:PSS/Pentacene bottom-contact TT (a) Schematic illustration of device fabrication, (b) AM images of a 5μm (width) x 50μm (length) Pentacene channel between PEDT:PSS electrodes (c) optical image of TT, (d) device performance plots
26 Patternable Low-k Materials in HEs Molecular precursors for low-k Materials processable in HEs - Solution processable - Thermally stable (>400 o Cby TGA) - Cross-linkable by H + - Low dielectric constant Dielectric constant A R B R = (A) k = 2.65 ~ 2.75 C (CH 2 ) 4 (C 2 ) 7 C 3 (B) C 2 CHC 2 C(C 2 ) 2 C 3 C 3 (C) E. Murotani, et al., ACS Appl. Mater. Interfaces, 2009, Accepted.
27 Patternable Low-k Materials in HEs Photolithographic Patterning in HEs Crosslinking reaction - Robust film formation - Patternability To prove patternability in HEs Spin coat material/pag Expose with 365nm 1) PAG H + UV 2) Bake Bake at 50 C Develop in HEs Successful patterning in HE-7100
28 Patterning luorinated Electronic Materials employing Conventional Photoresists in rganic Solvents
29 Semi-Perfluoroalkyl Polyfluorenes Perfluoroalkyl polyfluorenes as blue light-emitting polymers 3 C( 2 C) 7 (C 2 ) 7 C 3 y X 1 m ca. 60% content by weight unpublished result
30 Application to Patterning RGB patterning using conventional photoresists and organic solvents
31 Potential of rthogonal Processing LEDs TTs Low-k materials rthogonal processing Green processing of inorganic semiconductors Photovoltaics Bio-related application
The rthogonal 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 rthogonal Processing for the patterning of organic electronic materials has been proposed HEs have been identified as environmentally-friendly, chemically non-damaging solvents for orthogonal processing Acid-sensitive perfluoroalkyl resorsinarene has been developed and employed successfully in TT and LED fabrication Semi-perfluoroalkyl polyfluorenes have been synthesized and patterned with conventional photoresist and organic solvents
34 Acknowledgement Materials World Network Team at Cornell Alex Zakhidov, Priscilla Taylor, Hon Hang ong, Eisuke Murotani, John Deranco, Margarita Chatzichristidi, Ha Soo Hwang Prof. George Malliaras Materials World Network Team at Melbourne, Australia Georgia McCluskey, Wallace Wong Prof. Andrew Holmes (Melbourne, Australia) National Science oundation/australian Research Council (Materials World Network, DMR-0602821) National Science oundation IGERT program New York State oundation for Science, Technology and Innovation (NYSTAR) Cornell NanoScale acility (Photolithography) 3M (HE series solvents) Asahi Glass (GPC in fluorous solvents)
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