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Quantitative Analysis and Optimization of Gravure Printed Metal Ink, Dielectric, and Organic Semiconductor Films
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† †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
*E-mail: [email protected]
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ACS Applied Materials & Interfaces

Cite this: ACS Appl. Mater. Interfaces 2015, 7, 9, 5045–5050
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https://doi.org/10.1021/am508316f
Published February 3, 2015

Copyright © 2015 American Chemical Society. This publication is licensed under CC-BY.

Abstract

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Here we demonstrate the optimization of gravure printed metal ink, dielectric, and semiconductor formulations. We present a technique for nondestructively imaging printed films using a commercially available flatbed scanner, combined with image analysis to quantify print behavior. Print speed, cliché screen density, nip pressure, the orientation of print structures, and doctor blade extension were found to have a significant impact on the quality of printed films, as characterized by the spreading of printed structures and variation in print homogeneity. Organic semiconductor prints were observed to exhibit multiple periodic modulations, which are correlated to the underlying cell structure.

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Organic electronics have been widely demonstrated as viable alternatives to silicon-based devices as organic field-effect transistors (OFETs), organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), and other structures. (1-3) By combining soluble metal inks, polymer dielectrics, and organic semiconductors with print technologies such as inkjet, flexographic, and gravure, (4, 5) these devices have the potential to be manufactured inexpensively on mass, facilitating technological advances in areas such as lighting, displays, and much more. (6-9)
Gravure printing is of particular interest as it allows high throughput (>10 ms–1) and large area (>1 m wide, and up to 1 km long) parallel manufacturing, with an inherent speed advantage over serial technologies. (5, 10) However, to facilitate wider adoption of gravure printing, a greater understanding of the interaction between organic electronic materials and print parameters is required. This includes metal inks for the patterning of conductive electrodes; (11) dielectrics for capacitors, OFETs, and as device encapsulation; (12) and organic semiconductors for the design and operation of solid-state devices. (10, 13)
The optimization of printed layers is challenging task, in part because of the complexity of the dynamic print process. In the case of intaglio methods such as gravure, printing is influenced by multiple parameters including print speed, nip pressure, doctor blade pressure, and cliché cell geometry. This problem is further compounded by the desire to print large-area structures, where even prints of modest dimensions (15 cm × 20 cm) are already too large for most lab-based microscopy techniques without destruction of the underlying sample. Here, we present how an affordable flatbed scanner can be combined with image processing techniques to quantitatively analyze and optimize gravure printed films. We demonstrate this technique by optimizing gravure printed silver nanoparticle ink, a commercially available dielectric ink, and a variety of organic semiconductor formulations. From this, we are able to infer underlying relationships between print quality and print parameters.

Figure 1

Figure 1. Gravure print process. (a) Illustration of gravure print mechanism, showing key parameters investigated here; (b) photograph of printer used.

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Figure 1 shows an illustration and photograph of the gravure printer used in this work, along with key parameters. The cliché is doctored with ink by the doctor blade, which then contacts the substrate in the nip region under pressure from the impression roller. Post print ink droplets may coalesce on the substrate, depending on solvent evaporation rate and relative interfacial energies. Spatial definition is achieved by selectively patterning the cliché with cells, typically by mechanical scribing or an electrochemical etching process. (14) The cell spacing (lcell) is more commonly referred to by the reciprocal parameter screen density (lSD), where lSD = lcell–1, quoted in lines cm–1.
For the work here, silver nanoparticle inks, a commercially available dielectric GSID 13447–1 (BASF), (12, 15) and ink formulations of the organic semiconductors poly{[N,N′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} P(NDI2OD-T2) (ActivInk N2200, Polyera); (16) diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT, Flexink); (17) and an indacenodithiophene-benzothiadiazole (C16IDT-BT) (18) were prepared (see Supporting Information, Note S1, for further details). An electrochemically etched gravure cliché was used with a sheet fed gravure printer (Labratester, Norbert Schläfli Maschinen). The clichés contain features aligned at 0, 45, and 90° to the print direction, as well as seven different screen densities to facilitate optimization. Further details of the printer setup are discussed in the Supporting Information, Note S2.
Prints were scanned using a commercially available flatbed scanner; see the Supporting Information, Note S3, for details. A binary reference image was created from the cliché design data, representing a perfect print. The scanned images were transformed and registered to this reference, to provide equivalent scaling and accounting for differences in x- and y-calibration observed in the scanner. Images were processed using an image analysis tool (ImageJ, NIH) (19) and purpose-written analysis scripts (implemented in MATLAB 2013a, MathWorks). For metal inks, a constant binary luminance threshold of 0.95 was applied to all scanned images and each compared to the reference image. A composite image was generated, where black pixels indicates correct ink placement (Σx = total number of black pixels), red incorrect (y), and green missing ink (z). A parameter “spreading” was defined as Δ = (Σx + Σy)Σx–1, where values Δ > 1 indicate that the printed feature is larger than intended. For dielectric inks the mean (μ) and standard deviation (σ) of pixel intensity within each region of interest recorded, and the coefficient of variation (cv = σ/μ) calculated. For semiconductor inks each region of interest in the image was isolated, a fast Fourier transform performed, and the corresponding wavelength (λ) and the angle of modulation relative to the print direction (ω) extracted.

Figure 2

Figure 2. Impact of print parameters on the spreading of printed metal ink. (a) Print speed versus spreading for multiple screen densities. (b) Nip pressure versus spreading. (c) Orientation to print direction versus spreading. (d) Doctor blade extension versus spreading. (e) Scanned images of gate structure printed at varying screen densities. (f) Scanned image of optimized OFET source-drain structure. Each inset represents a single printed structure for illustration; the data points in a–d represent the average of 30, 120, 15, and 120 identical printed structures, respectively.

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Figure 2 shows the optimization of gravure printed metal ink structures on plastic for various print parameters. This is also illustrated by the composite images shown in Figures 2a–d, (note: the intended design is effectively superimposed on top of the analyzed image).
Clear correlations are observed between print speed and ink spreading (Figure 2a). Faster print speeds were observed to reduce spreading, consistent with reduced ink transferred for a given print area. (20) Similarly increasing cliché screen density, which decreases the cell volume for a given area, was also observed to reduce spreading. Smaller cells have a reduced surface area to volume ratio, increasing the influence of ink adhesion to the cell walls, and reducing the relative proportion of ink transferred. (21, 22)
Figure 2e shows a nominally identical structure printed with various line spacing. At lSD = 40 lines cm–1 not only is greater spreading visible in the print, but also the cell structure of the cliché. Although common and often desirable in gravure halftone printing, (14) this effect must be minimized for printed electronics, as such structuring impacts the performance of the layer. This is a major difference between graphic arts and plastic electronic printing, demonstrating the need for a context-specific optimization approach.
Increasing the nip pressure was found to decrease spreading, as indicated in Figure 2b. The exact cause of this behavior is unclear, and interestingly contrasts with other reports. Nguyen et al. observed that the width of a printed silver nanoparticle line increased with nip pressure. (23) They attributed this to deformation of the plastic substrate under greater nip pressure, resulting in the filling of additional smaller cells at the edge of their main cliché cell structures. This mechanism is not possible here—these features are not present in our clichés because of the better line edge definition achieved by electrochemically etching the cells. (14) Instead, we suggest that increasing the nip pressure results in instability in the ink due to a greater pressure differential across the nip region. (24) This could potentially impede cell emptying, reducing ink transfer and hence spreading.
Ink spreading was observed to be dependent on print direction. Evenly spaced printed lines (inset in Figure 2c) illustrate how ink spreading was greater parallel to the print direction. Similar behavior has previously been attributed to the orientation of cell sidewalls, whereby rotating a structure can yield cells with narrower effective aspect ratios in the print direction, resulting in greater spreading. (25) The impact of such spreading is to short circuit adjacent device electrodes, and hence this effect must be taken into account when designing circuit layouts.
Figure 2d shows the impact of increasing the effective length of the doctor blade, lDB (Figure 1) where lDB = 0 mm represents the doctor blade just touching the cliché during printing. Increasing lDB increases the pressure with which the doctor blade contacts the cliché. At low extensions, ink is not doctored but spread across the cliché, resulting in ink transfer from unpatterned areas of the cliché (as indicated by the high spreading value). With increasing extension, spreading decreases as ink is properly removed from these regions with a minima observed at lDB = 1 mm. However, despite this, the low doctoring pressure also fails to fill the cliché cells, resulting in missing printed structures (as indicated by green pixels in the inset image). Increasing the blade extension to lDB ≥ 2 mm was observed to yield the required doctoring, and optimum results as shown in Figure 2f.

Figure 3

Figure 3. Impact of print speed and screen density on variation in printed films. (a) Screen density versus coefficient of variation for increasing print speed. (b) Scanned images of 5 × 6 arrays of printed dielectric at 100 lines cm–1 for the same increasing print speeds, also (c) at 200 lines cm–1. (d) Cliché design data and (e) scanned image of corresponding cliché region for comparison. (f) Summary plot of analysis data for print speed versus coefficient of variation for b and c, where each data point represents 120 devices. (g) Optical micrograph of optimized printed dielectric pad on top of a photolithographically defined gate, on a flexible plastic substrate.

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Variation in semitransparent dielectric films was also investigated as a function of print parameters. Figure 3a shows the impact of screen density and print speed upon film variation for a given dielectric ink formulation. Here the coefficient of variation quantifies the relative variation in pixel intensity for each region of interest. This represents a combination of both the average film thickness (and hence a change in the mean observed pixel intensity) as well as any inhomogeneity within each region, as indicated by the spread of data.
For print speeds s > 0.17 ms–1, an inverse relationship is observed between screen density and the coefficient of variation, indicating that higher screen densities yield thinner films with less variation. At a print speed of s = 0.17 ms–1, this relationship breaks down because of the high ink volume transferred to the substrate, causing the coalescence of adjacent structures, as shown in the corresponding array in Figure 3b. To understand the impact of this behavior in a manufacturing context, we made prints of 5 × 6 arrays of printed dielectric squares at both 100 and 200 lines cm–1, designed for the manufacture of OFETs. The combined numerical results are summarized in Figure 3f. Behavior at 100 lines cm–1 is inconsistent because of a high volume of ink transferred; however, at 200 lines cm–1, a clear reduction in variation is observed with increasing speed and screen density, consistent with the reduction in spreading observed for the metal ink above. Kang et al. observed similar behavior for gravure printed metal inks and the dielectric poly(4-vinylphenol), (11) where better pattern definition and less variation occurs when viscous forces dominate the print transfer process, rather than the relative interfacial energy of ink and substrate. This agrees well with the uncontrolled wetting/spreading behavior observed at s = 0.17 ms–1.
Overall, a print speed of s = 0.73 ms–1 and a screen density of lSD = 200 lines cm–1 yielded arrays with minimal variation and spreading, important for reducing device-to-device differences in the layer capacitance. (12, 26) The outcome of the optimization process is shown in Figure 3g, with an optical micrograph of the optimized dielectric layer printed on top of a photolithographically patterned transistor gate. The film is printed without pinhole defects, and with good separation of dielectric between adjacent devices, allowing for interconnects to be patterned between layers.

Figure 4

Figure 4. Impact of screen density on gravure printed semiconductor films, showing periodic modulation. Scanned images of printed semiconductor films and corresponding 2D frequency power spectra for: (a) P(NDI2OD-T2), 15 mg mL–1 in Indane:tetralin 1:1 v/v solvent blend; (b) P(NDI2OD-T2), 5 mg mL–1 in mesitylene; (c) DPPT-TT, 5 mg mL–1 in mesitylene; (d) C16IDT-BT, 5 mg mL–1 in chlorobenzene. (e) Optical micrographs of corresponding cliché regions (note a difference in scales due to the limited field of view of the microscope). (f) Summary of screen density versus modulation wavelength and (g) angle of modulation to print direction versus screen density, extracted from images.

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Figure 4 shows the impact of screen density on printed film variation for various semiconductor ink formulations. Unlike dielectrics, which are generally viscous because of the presence of high-molecular-weight polymer modifiers, (12, 27) state-of-the-art organic semiconductor formulations are normally constrained by the expense of producing large quantities of high concentration inks. (28) Consequently, it was observed that lower viscosity semiconductor formulations were more susceptible to high film variation than either the printed metal ink or dielectric presented above.
At low screen densities, periodic film modulation was observed parallel to the print direction. Figure 4f shows how the modulation wavelength (λ) decreases as a function of increasing screen density, consistent with the corresponding decrease in cell width and spacing. For low viscosity inks, this modulation can occur as a consequence of two immiscible fluids (in this case ink and air) mixing during the ink transfer process, referred to as “viscous fingering”. (29, 30) Of particular interest, however, is the emergence of a secondary modulation mode at higher screen densities, as seen by the diagonal lines in the scanned images. Here we define ω as the angle of this modulation relative to the print direction. Figure 4g shows screen density versus ω as a function of different semiconductor formulations. All films tend to the same value (ω ≈ 35°); however, the onset is ink-dependent, suggesting that the viscosity of each formulation impacts this behavior. This was confirmed by analyzing prints of the same semiconductor, but in a less viscous ink formulation (compare Figure 4a, b).
To understand the origin of the secondary modulation, we made optical micrographs of each cliché cell structure, as shown in Figure 4e. For all screen densities the cells are orientated at a constant angle of ω ≈ 52° to the print direction, indicating that cell geometry is the probable cause of film modulation. The dependence on screen density seen in Figure 4g suggests that this effect is dominant only for higher screen densities, which is in contrast to the general trend observed above (namely that higher screen density is preferable). It is important to consider the impact of this modulation while designing cliché geometries that are to be used with multiple material systems.
In conclusion, our technique has demonstrated that print speed and cliché screen density have a significant impact on the morphology of solution-processable materials for organic electronics. Spreading of silver nanoparticle inks is reduced at higher print speeds and, in contrast to previous results, also by increased impression pressure, most likely as a result of incomplete ink transfer due to ink instabilities in the nip region. By reducing variation and spreading in printed dielectric films, we have demonstrated the optimized printing of large arrays of dielectric pads. Periodic film modulations were observed both parallel and at an angle to the print direction in low concentration semiconductor formulations. This was observed to be both formulation dependent, as well as related to the underlying cliché structure. These findings imply that our analysis techniques are a powerful tool for analyzing printed films, and for providing insight into appropriate print and design parameters. Traditional graphics arts approaches to cliché design are unlikely to be sufficient to accommodate the demands for printed electronic films, namely homogeneous, noncontiguous structures.

Supporting Information

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Additional details about the ink formulations, printer setup, and scan parameters. This material is available free of charge via the Internet at http://pubs.acs.org.

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Author Information

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  • Corresponding Author
    • Beinn V. O. Muir - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom;  Email: [email protected]
  • Authors
    • Stuart G. Higgins - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
    • Francesca L. Boughey - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
    • Russell Hills - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
    • Joachim H. G. Steinke - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
    • Alasdair J. Campbell - †Department of Physics and Centre for Plastic Electronics and ‡Department of Chemistry, Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
  • Author Contributions

    The authors S.G.H. and F.L.B. contributed equally. S.G.H. performed dielectric and semiconductor printing, created the analysis technique and scripts, performed analysis, and wrote the manuscript. F.L.B. performed metal ink printing, wrote analysis scripts, and performed analysis on metal inks. R.H. performed metal ink printing and performed analysis. B.V.O.M. performed metal ink printing, supervised, and set the scientific aims. J.H.G.S. and A.J.C. supervised and set the scientific aims.

  • Notes
    The authors declare no competing financial interest.

Acknowledgment

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This work has been supported by the European Commission’s 7th Framework Programme (FP7/2007-2013) under grant agreement 247978 (POLARIC). S.G.H. was supported by the Engineering and Physical Sciences Research Council (EPSRC) under grant number EP/P505550/1.

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  1. Yan-Long Tai and Zhen-Guo Yang . Facile and Scalable Preparation of Solid Silver Nanoparticles (<10 nm) for Flexible Electronics. ACS Applied Materials & Interfaces 2015, 7 (31) , 17104-17111. https://doi.org/10.1021/acsami.5b03775
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  5. I. Burda, C. Baechler, S. Gardin, A. Verma, G.P. Terrasi, G. Kovacs. Low-cost scalable printing of carbon nanotube electrodes on elastomeric substrates: Towards the industrial production of EAP transducers. Sensors and Actuators A: Physical 2018, 279 , 712-724. https://doi.org/10.1016/j.sna.2018.07.021
  6. Kee-Hyun Shin, Ho Anh Duc Nguyen, Janghoon Park, Dongjun Shin, Dongjin Lee. Roll-to-roll gravure printing of thick-film silver electrode micropatterns for flexible printed circuit board. Journal of Coatings Technology and Research 2017, 14 (1) , 95-106. https://doi.org/10.1007/s11998-016-9844-y
  7. Sanha Kim, Hossein Sojoudi, Hangbo Zhao, Dhanushkodi Mariappan, Gareth H. McKinley, Karen K. Gleason, A. John Hart. Ultrathin high-resolution flexographic printing using nanoporous stamps. Science Advances 2016, 2 (12) https://doi.org/10.1126/sciadv.1601660
  8. Jongsu Lee, Janghoon Park, Hakyung Jeong, Kee-Hyun Shin, Dongjin Lee. Optimization of printing conditions for microscale multiline printing in continuous roll-to-roll gravure printing. Journal of Industrial and Engineering Chemistry 2016, 42 , 131-141. https://doi.org/10.1016/j.jiec.2016.07.031
  9. Gerd Grau, Jialiang Cen, Hongki Kang, Rungrot Kitsomboonloha, William J Scheideler, Vivek Subramanian. Gravure-printed electronics: recent progress in tooling development, understanding of printing physics, and realization of printed devices. Flexible and Printed Electronics 2016, 1 (2) , 023002. https://doi.org/10.1088/2058-8585/1/2/023002
  10. Tatsuhiko Sasaki, Masatoshi Sakai, Tokuyuki Ko, Yugo Okada, Hiroshi Yamauchi, Kazuhiro Kudo, Yuichi Sadamitsu, Shoji Shinamura. Solvent‐Free Printing of Flexible Organic Thin Film Transistors by Ultrasonic Welding. Advanced Electronic Materials 2016, 2 (3) https://doi.org/10.1002/aelm.201500221
  11. Stuart G. Higgins, Beinn V. O. Muir, Giorgio Dell'Erba, Andrea Perinot, Mario Caironi, Alasdair J. Campbell. Complementary Organic Logic Gates on Plastic Formed by Self‐Aligned Transistors with Gravure and Inkjet Printed Dielectric and Semiconductors. Advanced Electronic Materials 2016, 2 (2) https://doi.org/10.1002/aelm.201500272
  12. S. G. Higgins, B. V. O. Muir, G. Dell'Erba, A. Perinot, M. Caironi, A. J. Campbell. Self-aligned organic field-effect transistors on plastic with picofarad overlap capacitances and megahertz operating frequencies. Applied Physics Letters 2016, 108 (2) https://doi.org/10.1063/1.4939045
  13. William J. Scheideler, Jeremy Smith, Igal Deckman, Seungjun Chung, Ana Claudia Arias, Vivek Subramanian. A robust, gravure-printed, silver nanowire/metal oxide hybrid electrode for high-throughput patterned transparent conductors. Journal of Materials Chemistry C 2016, 4 (15) , 3248-3255. https://doi.org/10.1039/C5TC04364F
  14. Stuart G. Higgins, Beinn V. O. Muir, Martin Heeney, Alasdair J. Campbell. Indacenodithiophene-benzothiadiazole organic field-effect transistors with gravure-printed semiconductor and dielectric on plastic. MRS Communications 2015, 5 (4) , 599-603. https://doi.org/10.1557/mrc.2015.66
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  • Abstract

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    Figure 1

    Figure 1. Gravure print process. (a) Illustration of gravure print mechanism, showing key parameters investigated here; (b) photograph of printer used.

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    Figure 2

    Figure 2. Impact of print parameters on the spreading of printed metal ink. (a) Print speed versus spreading for multiple screen densities. (b) Nip pressure versus spreading. (c) Orientation to print direction versus spreading. (d) Doctor blade extension versus spreading. (e) Scanned images of gate structure printed at varying screen densities. (f) Scanned image of optimized OFET source-drain structure. Each inset represents a single printed structure for illustration; the data points in a–d represent the average of 30, 120, 15, and 120 identical printed structures, respectively.

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    Figure 3

    Figure 3. Impact of print speed and screen density on variation in printed films. (a) Screen density versus coefficient of variation for increasing print speed. (b) Scanned images of 5 × 6 arrays of printed dielectric at 100 lines cm–1 for the same increasing print speeds, also (c) at 200 lines cm–1. (d) Cliché design data and (e) scanned image of corresponding cliché region for comparison. (f) Summary plot of analysis data for print speed versus coefficient of variation for b and c, where each data point represents 120 devices. (g) Optical micrograph of optimized printed dielectric pad on top of a photolithographically defined gate, on a flexible plastic substrate.

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    Figure 4

    Figure 4. Impact of screen density on gravure printed semiconductor films, showing periodic modulation. Scanned images of printed semiconductor films and corresponding 2D frequency power spectra for: (a) P(NDI2OD-T2), 15 mg mL–1 in Indane:tetralin 1:1 v/v solvent blend; (b) P(NDI2OD-T2), 5 mg mL–1 in mesitylene; (c) DPPT-TT, 5 mg mL–1 in mesitylene; (d) C16IDT-BT, 5 mg mL–1 in chlorobenzene. (e) Optical micrographs of corresponding cliché regions (note a difference in scales due to the limited field of view of the microscope). (f) Summary of screen density versus modulation wavelength and (g) angle of modulation to print direction versus screen density, extracted from images.

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      Baeg, Kang-Jun; Caironi, Mario; Noh, Yong-Young
      Advanced Materials (Weinheim, Germany) (2013), 25 (31), 4210-4244CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. For at least the past ten years printed electronics has promised to revolutionize the authors' daily life by making cost-effective electronic circuits and sensors available through mass prodn. techniques, for their ubiquitous applications in wearable components, rollable and conformable devices, and point-of-care applications. While passive components, such as conductors, resistors and capacitors, had already been fabricated by printing techniques at industrial scale, printing processes were struggling to meet the requirements for mass-produced electronics and optoelectronics applications despite their great potential. In the case of logic integrated circuits (ICs), which constitute the focus of this Progress Report, the main limitations were represented by the need of suitable functional inks, mainly high-mobility printable semiconductors and low sintering temp. conducting inks, and evoluted printing tools capable of higher resoln., registration and uniformity than needed in the conventional graphic arts printing sector. Soln.-processable polymeric semiconductors are the best candidates to fulfill the requirements for printed logic ICs on flexible substrates, due to their superior processability, ease of tuning of their rheol. parameters, and mech. properties. One of the strongest limitations was mainly represented by the low charge carrier mobility (μ) achievable with polymeric, org. field-effect transistors (OFETs). However, recently unprecedented values of μ ∼ 10 cm2/Vs were achieved with soln.-processed polymer based OFETs, a value competing with mobilities reported in org. single-crystals and exceeding the performances enabled by amorphous silicon (a-Si). These values were achieved thanks to the design and synthesis of donor-acceptor copolymers, showing limited degree of order when processed in thin films and therefore fostering further studies on the reason leading to such improved charge transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary CMOS-like logic for the design of digital ICs, easing the scaling down of crit. geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, the authors review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-vol. micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices to achieve the operation frequencies needed for applications, such as flexible radiofrequency identification (RFID) tags, near-field communication (NFC) devices, ambient electronics, and portable flexible displays.
    7. 7
      Kopola, P.; Tuomikoski, M.; Suhonen, R.; Maaninen, A. Gravure Printed Organic Light Emitting Diodes for Lighting Applications Thin Solid Films 2009, 517, 5757– 5762
      7
      Gravure printed organic light emitting diodes for lighting applications
      Kopola, P.; Tuomikoski, M.; Suhonen, R.; Maaninen, A.
      Thin Solid Films (2009), 517 (19), 5757-5762CODEN: THSFAP; ISSN:0040-6090. (Elsevier B.V.)
      A major advantage of polymer based org. light emitting diodes (OLED) is the capability to be manufg. them with low cost, high-throughput printing techniques. In this paper, we report on double layer gravure printed polymer based OLED light sources with an active area of 0.16 cm2 on glass substrate. The devices exhibit brightness of 100 cd/m2 and 1000 cd/m2 at 4.2 V and 5.4 V, resp. Furthermore, a large area OLED of 30 cm2 in which both polymer layers are gravure printed is demonstrated for lighting applications. Based on the results presented in this paper, the feasibility of the gravure printing technique for the fabrication of large area OLEDs in large-scale prodn. is proved.
    8. 8
      Lee, T.-M.; Noh, J.-H.; Kim, C. H.; Jo, J.; Kim, D.-S. Development of a Gravure Offset Printing System for the Printing Electrodes of Flat Panel Display Thin Solid Films 2010, 518, 3355– 3359
      There is no corresponding record for this reference.
    9. 9
      Forrest, S. R. The Path to Ubiquitous and Low-Cost Organic Electronic Appliances on Plastic Nature 2004, 428, 911– 918
      9
      The path to ubiquitous and low-cost organic electronic appliances on plastic
      Forrest, Stephen R.
      Nature (London, United Kingdom) (2004), 428 (6986), 911-918CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      A review. Org. electronics are beginning to make significant inroads into the com. world, and if the field continues to progress at its current, rapid pace, electronics based on org. thin-film materials will soon become a mainstay of technol. existence. Already products based on active thin-film org. devices are in the market place, most notably the displays of several mobile electronic appliances. Yet the future holds even greater promise for this technol., with an entirely new generation of ultralow-cost, lightwt. and even flexible electronic devices in the offing, which will perform functions traditionally accomplished using much more expensive components based on conventional semiconductor materials such as Si.
    10. 10
      Voigt, M. M.; Guite, A.; Chung, D.-Y.; Khan, R. U. A.; Campbell, A. J.; Bradley, D. D. C.; Meng, F.; Steinke, J. H. G.; Tierney, S.; McCulloch, I.; Penxten, H.; Lutsen, L.; Douherent, O.; Manca, J.; Brokmann, U.; Sönnichsen, K.; Hülsenberg, D.; Bock, W.; Barron, C.; Blanckaert, N.; Springer, S.; Grupp, J.; Mosley, A. Polymer Field-Effect Transistors Fabricated by the Sequential Gravure Printing of Polythiophene, Two Insulator Layers, and a Metal Ink Gate Adv. Funct. Mater. 2010, 20, 239– 246
      There is no corresponding record for this reference.
    11. 11
      Kang, H.; Kitsomboonloha, R.; Jang, J.; Subramanian, V. High-Performance Printed Transistors Realized Using Femtoliter Gravure-Printed Sub-10 Mm Metallic Nanoparticle Patterns and Highly Uniform Polymer Dielectric and Semiconductor Layers Adv. Mater. 2012, 24, 3065– 3069
      There is no corresponding record for this reference.
    12. 12
      Vaklev, N. L.; Müller, R.; Muir, B. V. O.; James, D. T.; Pretot, R.; van der Schaaf, P.; Genoe, J.; Kim, J.-S.; Steinke, J. H. G.; Campbell, A. J. High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric Adv. Mater. Interfaces 2014, 1, 1300123
      12
      High-Performance Flexible Bottom-Gate Organic Field-Effect Transistors with Gravure Printed Thin Organic Dielectric
      Vaklev, Nikolay L.; Mueller, Robert; Muir, Beinn V. O.; James, David T.; Pretot, Roger; van der Schaaf, Paul; Genoe, Jan; Kim, Ji-Seon; Steinke, Joachim H. G.; Campbell, Alasdair J.
      Advanced Materials Interfaces (2014), 1 (3), 1300123/1-1300123/6CODEN: AMIDD2; ISSN:2196-7350. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A flexible and photopatternable polymer dielec. has been demonstrated which can be gravure printed and spin-cast, gives low leakage current, high breakdown voltage, and low surface roughness.
    13. 13
      Chung, D.; Huang, J.; Bradley, D. High Performance, Flexible Polymer Light-Emitting Diodes (PLEDs) with Gravure Contact Printed Hole Injection and Light Emitting Layers Org. Electron. 2010, 11, 1088– 1095
      13
      High performance, flexible polymer light-emitting diodes (PLEDs) with gravure contact printed hole injection and light emitting layers
      Chung, Dae-Young; Huang, Jingsong; Bradley, Donal D. C.; Campbell, Alasdair J.
      Organic Electronics (2010), 11 (6), 1088-1095CODEN: OERLAU; ISSN:1566-1199. (Elsevier B.V.)
      The ultimate approach to org. semiconductor device fabrication is expected to be via high-speed, large area, roll-to-roll (R2R) printing. Gravure contact printing is one of the highest vol. potential techniques, operating at speeds of over 35 m/min. Here we report high performance, flexible polymer light-emitting diodes (PLEDs) with gravure contact printed hole injection and emissive layers. We are able to successfully print highly uniform layers of optimum thickness of poly (3,4-ethylene dioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) and the light emitting polymer (LEP) LUMATION Green 1300. All the optimized formulations dry rapidly and evenly without solute aggregation and are compatible with fast processing on plastic substrates. PLEDs with the gravure printed layers have an identical performance to conventional spin-coated devices on the same substrate, achieving, at a display brightness of 100 cd/m2, luminosity, efficiency and drive bias values of 5.4 lm/W, 5.2 cd/A and 3 V, resp. The devices achieve a max. luminosity of 8.8 lm/W and a max. luminance of 66,000 cd/m2, comparable to the performance range found for conventionally fabricated state-of-the-art green-emitting flexible PLEDs.
    14. 14
      Kipphan, H. Handbook of Print Media, 1st ed; Springer-Verlag: Heidelberg, Germany, 2001.
      There is no corresponding record for this reference.
    15. 15
      Kastler, M.; Köhler, S. Crosslinkable Dielectrics and Methods of Preparation and Use Thereof. U.S. Patent 8,853,820, Oct 7, 2014.
      There is no corresponding record for this reference.
    16. 16
      Yan, H.; Chen, Z.; Zheng, Y.; Newman, C.; Quinn, J. R.; Dötz, F.; Kastler, M.; Facchetti, A. A High-Mobility Electron-Transporting Polymer for Printed Transistors Nature 2009, 457, 679– 686
      16
      A high-mobility electron-transporting polymer for printed transistors
      Yan, He; Chen, Zhihua; Zheng, Yan; Newman, Christopher; Quinn, Jordan R.; Dotz, Florian; Kastler, Marcel; Facchetti, Antonio
      Nature (London, United Kingdom) (2009), 457 (7230), 679-686CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Printed electronics is a revolutionary technol. aimed at unconventional electronic device manuf. on plastic foils, and will probably rely on polymeric semiconductors for org. thin-film transistor (OTFT) fabrication. In addn. to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chem. stability, large soly. in common solvents, and inexpensive soln. and/or low-temp. processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielec. and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly sol. (∼60 g l-1) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to ∼0.45-0.85 cm2 V-1 s-1) under ambient conditions in combination with Au contacts and various polymeric dielecs. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielec. layers deposited by spin-coating as well as by gravure, flexog. and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.
    17. 17
      Chen, Z.; Lee, M. J.; Shahid Ashraf, R.; Gu, Y.; Albert-Seifried, S.; Meedom Nielsen, M.; Schroeder, B.; Anthopoulos, T. D.; Heeney, M.; McCulloch, I.; Sirringhaus, H. High-Performance Ambipolar Diketopyrrolopyrrole-thieno[3,2-B]thiophene Copolymer Field-Effect Transistors with Balanced Hole and Electron Mobilities Adv. Mater. 2012, 24, 647– 652
      17
      High-Performance Ambipolar Diketopyrrolopyrrole-Thieno[3,2-b]thiophene Copolymer Field-Effect Transistors with Balanced Hole and Electron Mobilities
      Chen, Zhuoying; Lee, Mi Jung; Ashraf, Raja Shahid; Gu, Yun; Albert-Seifried, Sebastian; Nielsen, Martin Meedom; Schroeder, Bob; Anthopoulos, Thomas D.; Heeney, Martin; McCulloch, Iain; Sirringhaus, Henning
      Advanced Materials (Weinheim, Germany) (2012), 24 (5), 647-652CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The authors we have demonstrated ambipolar OFETs based on a single soln.-processed conjugated polymer, DPPT-TT, with balanced hole and electron field-effect mobilities both exceeding 1 cm2 V-1s-1. The low bandgap and the position of the HOMO and LUMO energy levels were designed to enable efficient ambipolar charge injection and transport, but a careful optimization of the device architecture, charge injection and polymer processing was also required to observe such high, balanced electron and hole mobilities in this polymer system. These values are larger by an order of magnitude than the highest ones previously reported for ambipolar conjugated polymer OFETs. High-performance ambipolar DPPT-TT OFETs are promising candidates for applications in ambipolar devices and integrated circuits, as well as model systems for fundamental studies of ambipolar charge transport in conjugated systems.
    18. 18
      Zhang, W.; Smith, J.; Watkins, S. E.; Gysel, R.; McGehee, M.; Salleo, A.; Kirkpatrick, J.; Ashraf, S.; Anthopoulos, T.; Heeney, M.; McCulloch, I. Indacenodithiophene Semiconducting Polymers for High-Performance, Air-Stable Transistors J. Am. Chem. Soc. 2010, 132, 11437– 11439
      18
      Indacenodithiophene Semiconducting Polymers for High-Performance, Air-Stable Transistors
      Zhang, Weimin; Smith, Jeremy; Watkins, Scott E.; Gysel, Roman; McGehee, Michael; Salleo, Alberto; Kirkpatrick, James; Ashraf, Shahid; Anthopoulos, Thomas; Heeney, Martin; McCulloch, Iain
      Journal of the American Chemical Society (2010), 132 (33), 11437-11439CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      High-performance, soln.-processed transistors fabricated from semiconducting polymers contg. indacenodithiohene repeat units are described. The bridging functions on the backbone contribute to suppressing large-scale crystn. in thin films. However, charge carrier mobilities of up to 1 cm2/(V s) for a benzothiadiazole copolymer are reported and, coupled with both ambient stability and long-wavelength absorption, make this family of polymers particularly attractive for application in next-generation org. optoelectronics.
    19. 19
      Schneider, C. a; Rasband, W. S.; Eliceiri, K. W. NIH Image to ImageJ: 25 Years of Image Analysis Nat. Methods 2012, 9, 671– 675
      19
      NIH Image to ImageJ: 25 years of image analysis
      Schneider, Caroline A.; Rasband, Wayne S.; Eliceiri, Kevin W.
      Nature Methods (2012), 9 (7_part1), 671-675CODEN: NMAEA3; ISSN:1548-7091. (Nature Publishing Group)
      For the past 25 years NIH Image and ImageJ software have been pioneers as open tools for the anal. of scientific images. We discuss the origins, challenges and solns. of these two programs, and how their history can serve to advise and inform other software projects.
    20. 20
      Elsayad, S.; Morsy, F.; El-Sherbiny, S.; Abdou, E. Some Factors Affecting Ink Transfer in Gravure Printing Pigm, Resin Technol. 2002, 31, 234– 240
      There is no corresponding record for this reference.
    21. 21
      Yin, X.; Kumar, S. Flow Visualization of the Liquid Emptying Process in Scaled-up Gravure Grooves and Cells Chem. Eng. Sci. 2006, 61, 1146– 1156
      21
      Flow visualization of the liquid emptying process in scaled-up gravure grooves and cells
      Yin, Xiuyan; Kumar, Satish
      Chemical Engineering Science (2006), 61 (4), 1146-1156CODEN: CESCAC; ISSN:0009-2509. (Elsevier Ltd.)
      The liq.-emptying process in scaled-up gravure grooves and cells is studied using flow visualization in order to better understand gravure coating and printing processes. Water and two different glycerin/water mixts. serve as the test liqs., and the emptying process is initiated by moving over the groove or cell a rotating roller or a glass top with a curved surface. For the scaled-up groove, a region of recirculating flow is obsd. to attach to the moving glass top. When the glass top is used to drive flow in the scaled-up cell, an air bubble may appear inside the cell when the gap between the bottom of the curved surface and the top of the cell is zero. When this gap is pos., a liq. bridge is formed, dragged across the cell, and then broken, leaving some liq. inside the cell. The amt. of liq. remaining in the cell, Vr, is measured for different liqs., surface speeds, and gap distances for both the glass top and the rotating roller. The effect of using a soft elastomeric covering on the glass top and roller is also explored. For each liq., Vr increases as the speed of the glass top or roller increases. The data are correlated by multiplying Vr by a liq.-dependent shift factor, which leads to a power-law relationship between the shifted Vr and the capillary no. These exptl. observations and measurements can be used to benchmark theor. calcns., which can then be applied to design gravure grooves and cells that empty in a controlled way.
    22. 22
      Sung, D.; de la Fuente Vornbrock, A.; Subramanian, V. Scaling and Optimization of Gravure-Printed Silver Nanoparticle Lines for Printed Electronics IEEE Trans. Compon., Packag., Technol. 2010, 33, 105– 114
      22
      Scaling and optimization of gravure-printed silver nanoparticle lines for printed electronics
      Sung, Donovan; de la Fuente Vornbrock, Alejandro; Subramanian, Vivek
      IEEE Transactions on Components and Packaging Technologies (2010), 33 (1), 105-114CODEN: ITCPFB; ISSN:1521-3331. (Institute of Electrical and Electronics Engineers)
      Printed electronics promises to enable new applications such as RFID tags, displays and various types of sensors. Crit. to the development of printed electronics is the establishment of a manufacturable printing technique with high resoln. and throughput. Gravure is a high-speed roll-to-roll printing technique that has many of the characteristics necessary for a viable printed electronics process. We present the first systematic study on the scaling and optimization of conductive lines for printed electronics, esp. with high viscosity nanoparticle inks. We demonstrate gravure-printed nanoparticle lines, which are potentially suitable for use in thin-film transistor (TFT) based circuits as well as passive components. We present several trends obsd. by varying cell and ink parameters, and compare two different techniques for printing lines. We examine current limits to scaling printed lines and demonstrate the potential viability and scalability of gravure for printed electronics.
    23. 23
      Nguyen, H. A. D.; Lee, J.; Kim, C. H.; Shin, K.-H.; Lee, D. An Approach for Controlling Printed Line-Width in High Resolution Roll-to-Roll Gravure Printing J. Micromech. Microeng. 2013, 23, 095010
      There is no corresponding record for this reference.
    24. 24
      Bohan, M. F. J.; Lim, C. H.; Korochkina, T. V.; Claypole, T. C.; Gethin, D. T.; Roylance, B. J. An Investigation of the Hydrodynamic and Mechanical Behaviour of a Soft Nip Rolling Contact Proc. Inst. Mech. Eng., Part J. 1997, 211, 37– 49
      There is no corresponding record for this reference.
    25. 25
      Lee, T.-M.; Lee, S.-H.; Noh, J.-H.; Kim, D.-S.; Chun, S. The Effect of Shear Force on Ink Transfer in Gravure Offset Printing J. Micromech. Microeng. 2010, 20, 125026
      25
      The effect of shear force on ink transfer in gravure offset printing
      Lee, Taik-Min; Lee, Seung-Hyun; Noh, Jae-Ho; Kim, Dong-Soo; Chun, Sangki
      Journal of Micromechanics and Microengineering (2010), 20 (12), 125026/1-125026/8CODEN: JMMIEZ; ISSN:1361-6439. (Institute of Physics Publishing)
      This paper asserts that shear force plays an important role in the printing mechanism of gravure offset line printing. To that end, a theor. printing model showing shear force dependence on the printing angle is proposed. The decrement of the internal angle between the printing direction and the pattern-line direction increases shear force, thereby enhancing the amt. of transferred ink in the off stage. A printing expt. using pattern-line widths of 80 μm and 20 μm shows the angle dependence of the line width, thickness and amt. of transferred ink, reflecting the effect of shear force. The effect of the internal angle on cross-sectional differences in lines with a width of 20 μm and with angle variation is greater than that in lines with a width of 80 μm, which corresponds with the theor. prediction that shear force has greater influence on a narrower line. The strong correlation between the exptl. data and the theor. model supports the validation of the theor. model.
    26. 26
      Hambsch, M.; Reuter, K.; Stanel, M.; Schmidt, G.; Kempa, H.; Fügmann, U.; Hahn, U.; Hübler, A. C. Uniformity of Fully Gravure Printed Organic Field-Effect Transistors Mater. Sci. Eng., B 2010, 170, 93– 98
      26
      Uniformity of fully gravure printed organic field-effect transistors
      Hambsch, M.; Reuter, K.; Stanel, M.; Schmidt, G.; Kempa, H.; Fuegmann, U.; Hahn, U.; Huebler, A. C.
      Materials Science & Engineering, B: Advanced Functional Solid-State Materials (2010), 170 (1-3), 93-98CODEN: MSBTEK; ISSN:0921-5107. (Elsevier B.V.)
      Fully mass-printed org. field-effect transistors were made completely by gravure printing. Therefore a special printing layout was developed to avoid register problems in print direction. Upon using this layout, contact pads for source-drain electrodes of the transistors are printed together with the gate electrodes in one and the same printing run. More than 50,000 transistors were produced and by random tests a yield of ∼75% was detd. The principle suitability of the gravure printed transistors for integrated circuits was shown by the realization of ring oscillators.
    27. 27
      Maliakal, A. In Organic Field-Effect Transistors; Bao, Z.; Locklin, J., Eds.; Taylor & Francis Group: Boca Raton, FL, 2007; Chapter 3, pp 229– 251.
      There is no corresponding record for this reference.
    28. 28
      Berggren, M.; Nilsson, D.; Robinson, N. D. Organic Materials for Printed Electronics Nat. Mater. 2007, 6, 3– 5
      28
      Organic materials for printed electronics
      Berggren, M.; Nilsson, D.; Robinson, N. D.
      Nature Materials (2007), 6 (1), 3-5CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Org. materials can offer a low-cost alternative for printer electronics and flexible displays. However, research in these systems must exploit the differences-via mol.-level control of functionality-compared with inorg. electronics if they are to become com. viable.
    29. 29
      Hernandez-Sosa, G.; Bornemann, N.; Ringle, I.; Agari, M.; Dörsam, E.; Mechau, N.; Lemmer, U. Rheological and Drying Considerations for Uniformly Gravure-Printed Layers: Towards Large-Area Flexible Organic Light-Emitting Diodes Adv. Funct. Mater. 2013, 23, 3164– 3171
      There is no corresponding record for this reference.
    30. 30
      Reuter, K.; Kempa, H.; Brandt, N.; Bartzsch, M.; Huebler, A. C. Influence of Process Parameters on the Electrical Properties of Offset Printed Conductive Polymer Layers Prog. Org. Coat. 2007, 58, 312– 315
      30
      Influence of process parameters on the electrical properties of offset printed conductive polymer layers
      Reuter, K.; Kempa, H.; Brandt, N.; Bartzsch, M.; Huebler, A. C.
      Progress in Organic Coatings (2007), 58 (4), 312-315CODEN: POGCAT; ISSN:0300-9440. (Elsevier B.V.)
      We report on results of investigating the material-process interaction for the case of offset printed conductive polymers. We interpret the characteristic branched morphol. of printed layers of Poly(3,4-ethylenedioxythiophene) doped with Poly(4-styrenesulfonate) in terms of the phenomenon of "viscous fingering". A comprehensive study of the relevant process parameters reveals that the cond. of the printed layers results from an interplay between the characteristic wavelength of the fingered structure and the deposited amt. of material. Furthermore, optimization of the process parameters allows for significant redn. of the sheet resistance for about 1 order of magnitude to 0.5 kΩ.

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