Printed Electronics: from fundamentals to advanced processing techniques

Transcription

1 1 Printed Electronics: from fundamentals to advanced processing techniques Mario Caironi Center for Nano Science and Istituto Italiano di Tecnologia

2 Outline 2 Graphic Arts Printing Techniques Surface Tension Introduction to Inkjet Printing Continuous vs. Drop-on-Demand (DOD) Thermal DOD Piezoelectric DOD Acoustic DOD E-jet DOD Fundamentals of Piezoelectric DOD Inkjet Printing Tools and Materials Applications in the Field of Organic Electronics

3 Graphic Arts Printing Pad printing 3 Gravure Printing* *images from Wikipedia Flexography Offset Printing* Inkjet Printing Screen printing* MicroFab Technote 99-01

4 Mass Produced Printed Film prelonic technologies nanosolar

5 Overview of Printing Techniques 5

6 Surface Tension For solids and more general: Surface Energy 6 It is a force for unit length (1N/m = 1000 dyne/cm) or equivalently energy per area (J/m 2 ) It is caused by cohesive forces It develops at the interface between two different immiscible fluids or at the interface between a fluid and a gas Young-Laplace Equation Δp = γ(r x -1 + R y -1 ) Δp: pressure difference γ: surface tension R x and R y : principal curvature radii

7 7 Contact Angle γ LG θ C γ SL γ SG Young equation γ SG γ SL γ LG cosθ = 0 Results of the interplay between adhesion and cohesion forces The higher the surface tension of the liquid, the higher the contact angle The higher the surface energy of the solid, the lower the contact angle

8 Introduction to Inkjet Printing 8

9 Jets instability 9 Surface tension triggered phenomenon Observation of uniform drop formation from a stream of liquid issuing from an orifice Savart, 1833 Instability of Newtonian jets to disturbances whose exceeds the diameter of the jet Rayleigh instability, 1878

10 Continuous mode 10 Water jet, 20kHz 50 m 100 m High ink velocity: 50 m / s Typical droplet diameter: 150 m Typical rate: kHz, up to 1MHz Industrial market applications, product labeling high throughput MicroFab Technote 99-01

11 Drop-On-Demand (DOD) mode 11 Drops produced by electromechanically induced pressure waves Hansell 1950 MicroFab Technote m Less complex system, no recirculation More energy to produce a droplet Typical rate: tens of khz Baytron PH water based ink Smaller drop size, higher placement accuracy Low-end printer market

12 Thermal DOD technology 12 H. P. Le, J. Imaging Sci. Technol. 42 (1998) 49 Bubble jet - Endo and Hara Canon, 1979 Simple design, low cost - dominates low-end color printer market Restricted to fluids that can be vaporized practically limited to aqueous inks

13 Piezoelectric DOD technology 13 MicroFab Technote H. P. Le, J. Imaging Sci. Technol. 42 (1998) 49 Suited to a variety of solvents Miniaturization has been an issue for many years Epson Stylus 800 (1993) microdrop

14 Principle of operation of piezoelectric printheads 14 The deflection of a piezoelectric transducer generates an acoustic wave in the printhead cavity, which causes the break off of a drop from the nozzle Minimum internal diameter of the nozzle: 10 μm (1pl) Susceptible to clogging

15 Acoustic DOD Printing 15 free liquid surface RR-PT FETs 0.1 cm 2 V -1 s -1 Nozzleless printheads An acoustic beam (5-300 MHz) is focused by a high-frequency acoustic lens on a free liquid surface Stable formation of drops with volume down to 65 fl (5 μm diameter) Scalability not demonstrated so far S. A. Elrod, B. et al. J. Appl. Phys. 65 (1989) K. E. Paul et. al., Appl. Phys. Lett. 83 (2003) 2070

16 Electrohydrodynamic-jet Printing 16 Gold coating with hydrophobic SAM An electric field combined with very fine glass capillaries is used to eject sub-femtoliter droplets. Internal diameter um The field accumulates mobile ions near the surface of the pendent meniscus. At a certain field the electrostatic stress overcomes the capillary tension. Printed lines with widths as small as 700 nm can be achieved (polyethyleneglycol). J. U. Park et al. Nat. Mater. 6 (2007)

17 DOD inkjet technologies comparison 17

18 18 Piezoelectric DOD Inkjet Printing: Fundamentals

19 Main Physical Parameters 19 Step Droplet formation Ink viscosity Key parameters Ink surface tension Pattern definition Ink surface tension Substrate surface energy Ink boiling temperature Duineveld, J. Fluid. Mech. 477 (2003) 175

20 Ink Viscosity Accepatable range: mpa s (1 mpa s = 1 cp) Higher the viscosity, higher acoustic waves dampening water: 0.89 mpa s xylene: 0.93 mpa s ethanol: 1.07 mpa s mercury: 1.53 mpa s olive oil: 81.x mpa s 20 Higher the viscosity, less satellites formation Ethylene glycol, 18 mpa s Isopropanol, 2 mpa s MicroFab Technote 99-02

21 Ink surface tension and boiling point 21 Surface Tension Acceptable Range: mn m -1 ethanol: 22.3 mn m -1 xylene: mn m -1 olive oil: 32 mn m -1 water: 72.8 mn m -1 mercury: 465 mn m -1 Solvent volatility, sufficiently low Bp: 132 C 66 C 144 C TU/e U.S. Schubert, TU/e MEH-PPV, 2.5 mg/ml, M n = 40k-70k g/mol

22 22 Surface energy and line stability Substrate surface energy vs. ink surface tension: wettability, line width, line stability Ag metallic ink on perfluorinated polymer Droplet ejection rate / substrate velocity Whiting et al., APL 95 (2009) mm s -1 2 mm s -1 Duineveld, J. Fluid. Mech. 477 (2003) 175

23 23 Surface energy and line stability Substrate surface energy vs. ink surface tension: wettability, line width, line stability Ag metallic ink on perfluorinated polymer Droplet ejection rate / substrate velocity Whiting et al., APL 95 (2009) mm s -1 2 mm s -1 Duineveld, J. Fluid. Mech. 477 (2003) 175

24 Coffee stain effect 24 Coffee stain effects lead to inhomogeneous thickness R.D. Deegan et al., Nature 389 (1997) E. Tekin et al., Adv. Funct. Mat. 17 (2007) 227 Pinning of the line due to surface imperfections / impurities

25 25 Marangoni Flow Caused by a gradient in surface tensions Molecules of a liquid with higher surface tensions pull stronger than molecules of a liquid with lower surface tension E.g.: wine tears

26 Controlling Flows 26 CB Hex DCB Dod TIPS-pentacene a+e : 100% CB b+f : 75% CB + 25% Hex c+g : 75% CB + 25% DCB d : 75% CB + 25% Dod K. Cho, Adv. Funct. Mater. 19 (2009) 1515

27 27 Piezoelectric DOD Inkjet Printing: Tools

28 Desktop Printers 28 availability low cost Epson Stylus Color 670 compatibility of cartridges/print heads with solvents cameras are not available accuracy could be insufficient substrate T.-F. Guo et al., Langmuir 18 (2002) 8142

29 Research and Commercial Printers 29 Custom Lab Printers Prototyping and Ink Testing Printers Dimatix Materials Printer Development Printers Production Printers LITREX 120L LITREX M-Series Generation 8 (2400 mm X 2400 mm)

30 Single and multi-nozzle printheads µm Single nozzle printhead (MicroFab Technologies) Multi nozzle printhead (Fujifilm-Dimatix SX3-128 nozzles printhead)

31 Single nozzle inkjet printers Printer developed by Plastic Logic, based on MicroFab Technologies nozzles and waveform generator Printhead x-y positioning Custom printer, based on Microdrop Technologies nozzles and droplet generator

32 Litrex 120 multi-nozzle inkjet printer Printhead control hardware 32 Y motion stage supporting the printhead mount and hardware Ink and solvent reservoirs with electronic regulation of nozzle meniscus pressure to achieve a precise control and reproducibility of process conditions X motion stage with Heated Vacuum Chuck (substrate temperature up to 70 degc) Control terminal Printing Industry-standard development system conceived for inkjet printing of LEP for OLEDs and filters for LCDs System designed for process development, based on the Litrex 140P production system

33 33 Piezoelectric DOD Inkjet Printing: Inks

34 Polymer inks 34 Polymer solutions elongational viscosity Maximum viscosity cp Newtonian fluid Small amount of high M w polymer PPV-derivatives case: if M w > , no separate drops form (0.5-2% by weight) B.-J. de Gans et al., Adv. Mat. 16 (2004) 205

35 Highly conductive metallic inks 35 R R R R S S S S S S S S R R R Colloidal gold nanoparticles : R = C 4 H 9 Particle size < 5 nm R Silver ink based on Ag-containing organic complex: Less susceptible to nozzle clogging Lower sintering temperature Ph. Buffat and J-P. Borel, Phys. Rev. A, 13, 1976, 2287

36 Inkjet Printing Applications 36

37 37 Main applications LCDs Alignment layers for the liquid crystals Color filters Spacers OLEDs Organic Field-Effect Transistors (OFETs) Flexible Sensors RFID Tags

38 Multicolor OLED displays /1 Fabrication of multicolor displays requires micropatterning 38 CDT Dupont Ink-jet printing technique offers: PLUS possibility to deposit very small and controlled amounts of materials not sensible to substrate defects MINUS restriction to low viscosity inks, meaning low polymer concentration

39 39 Multicolor OLED displays /2 Patterning of the charge injection layer (aqueous PEDOT/PSS solution), MEH-PPV spun on top J. Bharathan et al., Appl. Phys. Lett. 72 (1998) 2660 RGB multicolor displays H. Kobayashi et al., Synth. Metals (2000) 125

40 40 Upscaling 37 inches inkjet printed OLED TV Seiko Epson 2009

41 Fabrication of OFETs 41 by Inkjet Printing Low cost processing thanks to simplification and reduced material consumption thanks to the additive approach Lower equipment investment Low temperature process, compatible with flexible substrates Compatible with roll-to-roll and wide area processing A more environmental friendly process, much smaller amounts of waste solvents compared to subtractive processes

42 Some examples 42 All-inkjet-printed flexible FETs by high-resolution laser sintering S. H. Ko et. al., Nanotechnol. 18 (2007)

43 Some examples 43 Tunable SWCNT Transistors = cm 2 /Vs Y. Iwasa, Adv. Funct. Mater. 2010

44 Some examples 44 Semiconductor nanowires embedded in an insulating polymer P3HT/PS (20:80) in CB/CHN K. Cho, Adv. Funct. Mater. 2010

45 Minemawari et al., Nature 475 (2011) 364 Some examples 45 = 16 cm 2 /Vs antisolvent

46 Integrated Circuits Manufacturing by Graphic Arts Printing? 46 Solution-processable organic conjugated polymers and molecules are low mobility semiconductors Graphic arts printing technologies offer insufficient resolution and linewidth capability Very slow switching speed in the order of 1-100Hz and high operating voltages A. Huebler, ICCG 2006 PolyIC, JAP 96, 2286 (2004)

47 Increasing the resolution: E-jet printing 47 T. Sekitani, et al. Proceedings of the National Academy of Sciences 105 (2008)

48 Increasing the resolution: surface energy assisted printing 48 hydrophilic hydrophobic 5 m resolution thanks to surface energy pre-patterning with: Standard lithography Soft lithography Direct-write laser patterning Down to 200 nm with E-beam lithography H. Sirringhaus et al., Science 290 (2000) 2123 J. Z. Wang, et al. Nat. Mater. 3 (2004)

49 Self-Aligned Printing (SAP) 49 2 nd 1 st L: critical feature is self-defined C.W. Sele et al., Adv. Mat. 17 (2005) m PEDOT:PSS PEDOT:PSS

50 Single-droplet Contacts st 2 nd 2 1 st Electrode 1 st Electrode 37 μm 2 nd Electrode Single droplet 2 nd Electrode

51 Drying Time of Ink is a Critical Factor s (a) 240 s (b) 300 s (c) 310 s (d) 320 s (e) 330 s (f) 340 s (g) sintered (h) Extra force exerted by evaporation of the solvent Reliable dewetting, tolerant to surface defects 50 μm Process window >> 10 μm

52 High Yield Electrodes Array % yield possible Very low leakage, < 2 pa at 10 V Breakdown voltage > 2 MVcm -1 leakage Caironi et al., ACS Nano 4 (2010) 1452

53 Printed Gate Contacts and Interconnects 53 Room temperature cross-linking Y. Y. Noh et al. Org. Electron. 10 (2009) 174 dielectric SC glass Ag 50nm Au TEC-IJ-010 (InkTec Co., Ltd.) Ag-organic complex Ag Organic Ligands Viscosity 9-15 cps (mpa s) Surf. Tension dynes/cm (mn/m) 5-10 x 10-8 Ωm Low sintering temperature Compatible with semiconductor and dielectric layers

54 Caironi et al., ACS Nano 4 (2010) 1452 Fully Solution Processed SAP-FET μm Ag gate Au source Au drain

55 High yield SAP FETs array 55 Chip current mapping I D at V G = -10 V TIPS-pentacene Yield > 94 % Good currents uniformity

56 56 Some References H. P. Le, Progress and trends in ink-jet printing technology", The Journal of Imaging Science and Technology 42 (1998) MRS Bulletin 8 (2003) Inkjet Printing of Functional Materials B.-J. de Gans, P. C. Duineveld and U. S. Schubert, Inkjet Printing of Polymers: State of the Art and Future Developments, Adv. Mater. 16 (2004) 203 H. Sirringhaus, C. W. Sele, T. von Werne, and C. Ramsdale, Manufacturing of organic transistor circuits by solution-based printing", in Organic Electronics, Materials, Manufacturing and Applications, edited by WILEY-VCH, pp , 2006 E. Gili, M. Caironi and H. Sirringhaus, Picoliter Printing, in Handbook of Nanofabrication, 2010, Edited by Gary Wiederrecht, Elsevier, ISBN: