roll-to-roll printed electronics on paper

Roll-to-roll printed electronics on paper

Roger Bollström1, Daniel Tobjörk2, Peter Dolietis1, Tommi Remonen2,3, Carl-Johan Wikman3, Sari Viljanen4, Jawad Sarfraz5, Pekka Salminen6, Mika Lindén5, Carl-Eric Wilén3, Johan Bobacka4, Ronald Österbacka2 and Martti Toivakka1 Center for Functional Materials, Turku, Finland 1 Paper Coating and Converting, Department of Chemical Engineering, Åbo Akademi University, Turku, Finland 2Physics, Department of Natural Sciences, Åbo Akademi University, Turku, Finland 3Laboratory of Polymer Technology, Department of Chemical Engineering Åbo Akademi University, Turku, Finland 4Laboratory of Analytical Chemistry, Department of Chemical Engineering Åbo Akademi University, Turku, Finland 5Laboratory of Physical Chemistry, Department of Natural Sciences, Åbo Akademi University, Turku, Finland 6Styron Europe GmbH, CH 8833 Samstagern, Switzerland

ABSTRACT

New low cost, intelligent products with novel functionalities, e.g., sensors and simple displays have recently received much attention in the research community. For these types of products to come into everyday use, devices with reasonable electrical performance and negligible production cost are required. One way to reduce the manufacturing cost is to fabricate the electronics on inexpensive paper substrates by using roll-to-roll techniques (“Paper Electronics”), as an alternative to conventional electronics manufactured with batch processes on glass or polymer film substrates. The current work discusses printing of electronics on paper and demonstrates, as a proof-of-concept, a hygroscopic insulator field effect transistor device, a hydrogen sulfide sensor, ion selective electrodes and electrochemical pixels printed on paper with a custom-built roll-to-roll hybrid printer.

INTRODUCTION

New, value-added products with novel functionalities, e.g., paper- or board-based printed devices (sensors, displays etc.) are currently drawing much attention [1,2]. Low-cost paper and paper-like substrates have been considered for various printed applications outside the conventional graphic arts industry [1-4]. Electronic devices such as transistors, capacitors and batteries have been fabricated on paper or paper-like substrates by using functional inks containing, e.g., conducting and semiconducting materials, such as silver, organic polymers as well as carbon nanotubes [5-11]. Organic photodiodes and photovoltaic cells, electronic paper displays, foldable thermochromic displays and high-performance organic thin film transistor arrays on paper have also been demonstrated [11-16]. Different sensor applications are also drawing increasing attention, for example for product quality analysis on packages or as home diagnostics for medical purposes [15-21]. For these products to come into everyday use, devices with reasonable electrical performance and negligible production cost are required. The low cost can be achieved with manufacturing techniques such as printing or coating, which enable large scale production in a roll-to-roll process.

The authors have previously developed a multilayer-coated, paper-based substrate that is suitable for printed electronics and functionality [22-24]. In this multilayer structure a thin top-coating consisting of mineral pigments is coated on top of a dispersion-coated barrier layer. The combination of the two layers allows for controlling the absorption of ink solvents. By adjusting the thickness and porosity of the top coating the printability can be tuned for the functional ink in use. The penetration of ink solvents and functional materials stops at the barrier layer, which not only improves the performance of the functional material but also eliminates potential fiber swelling and de-bonding that can occur if the solvents are allowed to penetrate into the base paper [25]. Additionally, the heat stability of the coated paper enables online infrared sintering where high temperatures may be temporarily reached [26]. Manufacturing of such a multilayer structure can be coated in steps [27], sequentially layer by layer, but a cost competitive method for industrial scale production is the curtain coating technique, which enables coating of all the layers in one pass [28-32].

The objective of this study was to understand how properties of the top-coating affect flexographic and inkjet printability of functional materials with the focus on a roll-to-roll process. As a proof of concept, transistors [22, 33-37], hydrogen sulfide sensors [17], ion selective electrodes [18-20] and electrochemical pixels [12,16] were printed roll-to-roll with a custom-built hybrid printer on the multilayer coated paper.

MATERIALS AND METHODS

Coating procedure and formulation

A precoated woodfree base paper (GCC precoating, total grammage 107 g/m2) was blade coated with a smoothening layer (10 g/m2, Barrisurf FX, Imerys Minerals Ltd., UK). On top of this base a barrier layer, combined with various top-coatings, was coated with a laboratory-scale multi-layer curtain coater (speed 600m/min, curtain height 30 cm, gap 0.3mm, vacuum deaeration, Styron R&D Center, Samstagern, Switzerland). The barrier layer consisted of high aspect ratio kaolin (Barrisurf HX, Imerys Minerals Ltd., UK) combined with 50 pph ethylene acrylic acid copolymer latex (Tecseal E799-35, Trüb Emulsions Chemie AG, CH) coated to a coat weight of 10 g/m2 for all the papers. The top-coating formulation and coat weight was varied (Table 1) by using kaolin (Barrisurf FX, Imerys Minerals Ltd., UK), precipitated calcium carbonate (PCC) (Opacarb 3000, Specialty Minerals Nordic Oy, FI) and Silica (Syloid C807, Grace GmbH, DE) with styrene-butadiene (SB) latex (DL920, Styron Europe GmbH, CH) as binder. Carboxymethyl cellulose (0.84 pph, Finnfix 30, CPKelco Oy, FI) was used as thickener in the barrier layer and in the top-coatings a synthetic thickener (HPV 56, DOW Chemical Company, CH) was used at required amounts given in Table 1. The relatively high amounts of thickener for the thin top-coatings, which were coated at low solids content, were required to ensure problem free runnability on the curtain coater. The papers were calendered with a single soft nip laboratory calender (DT Paper Science Oy, FI).

Table 1. Top-coating formulation for the multilayer curtain coated substrates.

Substrate K 0.5 K 1 K 3 K 5 KP 0.5 KP 1 KP 3 KP 5 S 0.5 S 1 S 3

Top-coating Grammage [g/m²] 0.5 1 3 5 0.5 1 3 5 0.5 1 3

Coating formulation Silica [pph] 100 100 100

PCC [pph] 30 30 30 30

Kaolin [pph] 100 100 100 100 70 70 70 70

SB latex [pph] 4 4 4 4 4 4 4 4 20 20 20

Thickener [pph] 16.7 9.0 0.5 0.5 17.3 6.8 0.6 0.6 16.8 5.9 0.7

Coating color parameters Solids [%] 5.0 10.0 40.0 40.0 5.2 10.2 40.0 40.0 5.1 10.2 19.4

Brookfield visc. 20 rpm [mPas]

980 1270 1420 1420 850 970 1460 1460 680 830 560

Brookfield visc. 100 rpm [mPas] 400 520 390 390 410 390 410 410 382 460 510

Calendering parameters Line load [kN/m] 122 122 122 122 122 122 122 122 122 122 122

Temperature [°C] 70 70 70 70 70 70 70 70 30 30 30

Functional inks

Two commercial conducting inks were used, Creative Materials 125-06 (Creative Materials Inc., US) micrometer particle size flexography silver ink and Creative Materials 110-04 micrometer particle size flexography carbon ink. Regioregular poly(3-hexylthiophene) (P3HT) (Plexcore OS-1100, Plextronics Inc., US) dissolved (0.25 weight-%) in a solvent mixture (1:1:2) of xylene:chlorobenzene:ortho-dichlorobenzene was used as the semiconductor ink and poly(4-vinylphenol) (PVP) (PHS-XE-HP, DuPont Electronic Polymers, US) in ethylene acetate as insulator. A water based ink of the conducting polymer poly(3,4-ethylene dioxythiophene) with poly(styrene sulfonate) (PEDOT:PSS) (Clevios P HC V4, Heraeus Clevios GmbH, DE) was used for the gate electrode in the transistor and as electrodes in the electrochemical pixels.

Printing methods

Flexographic printing was carried out using a custom-built roll-to-roll mini pilot scale printer. Commercial ASAHI DSH® (Shore A 69°) photopolymer plate was used. The ceramic anilox cylinder (Cheshire Engraving Cervices Ltd., UK) used with the silver ink had a cell angle of 60° with 120 lines/cm and a cell volume of 12 cm3/m2, while the one used with the carbon ink had a cell angle of 60° with 70 lines/cm and a cell volume of 30 cm3/m2. The printing speed was 10 m/min and eight 500 W infrared sintering units (HQE 500, Ceramicx, IRL) (700 °C) were mounted online. The inkjet printhead (Xaar 128/80, Xaarjet Ab, SE) consisted of 128 nozzles with a nominal drop volume of 80 pl and was operated by an Imaje 4400 controller and software and fed by a custom-built ink-feed setup. Alignment of inkjet printing was controlled with the help of an optical sensor that was coupled to the inkjet control unit. Flexography register control was carried out manually with stepmotors. The online reverse gravure coating unit is also custom-built.

Figure. 1. A: The custom-built roll-to-roll printer. All printing units are exchangeable and the setup can be varied depending on the materials being printed. B: Schematic image of the setup on the printer used for printing transistors.

Substrate and surface energy characterization

A JEOL JSM-6335F field emission scanning electron microscope (SEM) was used for cross-section imaging. An NTEGRA Prima (NT-MDT) atomic force microscopy (AFM) was used to analyze the topography of the samples. A Pascal 140/440 (Thermo Fisher Scientific Inc., GER) mercury porosimeter was used for analyzing the porosity. A DeWetPres (DT Paper Science) tablet press was used for pressing tablets of the coating colors for the mercury porosimetry measurements. The contact angles were measured in ambient conditions (RH = 22 ± 3%, T = 22 ± 2°C) using a CAM 200 contact angle goniometer (KSV Instruments Ltd).

A B

RESULTS

Paper properties

The multilayer coating structure consisting of a thin mineral pigment coating layer on top of a barrier layer was produced using curtain coating technique in a single pass. The precoating and smoothening layers underneath were coated using the blade coating technique. The cross-section SEM image (Figure 2) shows the multilayer coating structure. This structure provides adequate barrier properties, limiting the penetration of functional materials and solvents. Measured according to the ASTM standard [38], the barrier against water vapor is 37 g/m²/day at 85 % relative humidity and 23 °C temperature. Important parameters of top-coating, which affect the printability of various functional inks, are thickness, porosity, pore volume, surface energy and surface roughness. These can be adjusted by the choice of pigment size, shape and their distributions.

Figure 2. Cross-section SEM image showing the layer structure of the coating: topcoating, barrier layer, smoothing layer, precoating and basepaper.

Surface topography

The surface roughness of the substrates was measured by AFM (100 × 100 μm²) (Table 2). Higher coat weights resulted in smoother surfaces for both the pure kaolin coatings as well as for the kaolin/PCC blends. The silica coatings had drastically higher roughness because of the significantly larger particle size of the silica pigments compared to kaolin and PCC (1-2 μm, respectively 0.05-0.15 μm). All substrates were calendered in a single soft nip calender at a line load of 122 kN/m, but the temperature used was higher (70° C) for the kaolin and kaolin/PCC coatings compared to 30° C for the silica coatings. The lower temperature for the silica coatings was necessary because of the high amount (20 pph) SB latex which caused picking at higher temperatures. The smoothness could potentially have been further enhanced by multi-nip calendering.

Topcoating Barrier layer

Smoothing layer

Basepaper

Precoating

Figure 3. A. Contact angles for water, ethylene glycol (EG), and diiodomethane (DIM). B. Surface energy, divided into polar (p) and dispersive (d) components for each substrate.

Surface chemistry

The partial absorption of test liquids into the porous top coatings complicates the measurement of the true surface energy. The measured values should be considered as apparent surface energies, which still are useful to measure, since the ink spreading is controlled by it. The surface energy increased along with the higher coat weight for all the coatings. For the kaolin and kaolin/PCC coatings the dispersive component remained constant whereas the polar component increased. The most probable reason for this is the higher total amount of polar dispersing agent present at higher coat weights, which significantly lowered the water contact angles. The total surface energy of the barrier layer is in the same range as for the thin (0.5 g/m²) top-coatings, but the polarity is lower (Figure 3).

Porosity

Since it is not possible to measure reliably the porosity in the top-coating of the multilayer structure directly with the mercury porosimetry, pressure-filtrated tablets of the top-coating formulations were measured instead. Detailed porosity and pore size distribution could thereby be studied without influence from the basepaper and coated layers underneath. Table 2 shows how the total pore volume and porosity can be controlled by either changing the coat weight or the coating pigments. The smallest pore volumes were obtained for thin kaolin and kaolin/PCC top-coating while a higher coat weight or the use of larger particle size silica pigments provided higher total pore volumes. When comparing the coating colors containing the same pigments, it can be seen that the coating color formulated for the thin coatings provided significantly lower porosity. This can be explained by the high amount of synthetic thickener which had to be used in order to adjust the viscosity and meet the coater runnability window (Table 1). As shown in several previous studies, the pore size distribution and network structure of the coating layer determine how quickly ink penetrates into the available pore volume [39-42]. In the multilayer coating structure it is the pore volume of the top-coating layer that provides the region where the ink particles and vehicle are held during the ink setting process. The pore size modal values indicate the peak values in the pore size distribution, i.e. the dominant pore sizes. While kaolin and kaolin/PCC lead to monomodal pore size distributions that can be characterized by a single pore size modal value (Pore size modal value 1), the use of nanoporous silica particles results in a bimodal distribution and thereby two modal values. Pore size modal value 2 is related to the pore size within the porous silica pigments themselves.

0

20

40

60

80

100

120 Ba

rrie

r

K 0.

5

K 1

K 3

K 5

KP 0

.5

KP 1

KP 3

KP 5

S 0.

5

S 1

S 3

[°] Water EG DIM

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ier

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[mN/m] p d

B A

Table 2. Porosity, roughness and conductor printability properties.


Porosity

Pore volume [nl/cm²] 6 19 76 126 4 25 86 144 52 110 390

Porosity [%] 19 30 39 39 13 37 42 42 68 72 76

Pore size modal value 1 [nm] 49.0 69.2 60.3 60.3 13.2 85.2 74.2 74.2 350.8 375.8 803.5

Pore size modal value 2 [nm]

20.7 10.4 10.4

RMS Roughness [nm] 256 236 160 136 217 187 122 140 517 710 738

Flexography (line width on plate 350 μm)

Silver Line width including squeeze [μm] 568 511 416 421 474 511 432 484 374 400 411

Surface resistance [Ω/sq] 27 19 3 3 27 8 3 3 54 5 3

Carbon Line width including squeeze [μm] 489 463 421 421 468 458 432 421 432 405 379

Surface resistance [kΩ/sq] 183 129 67 65 207 100 62 43 108 43 30

Conductor printability For the flexographic silver and carbon prints, squeeze and ink spreading was studied, i.e. line width on substrate compared to line width on plate. The more porous silica top-coating minimizes the squeeze effect due to rapid absorption of ink vehicle as shown in Table 2. On all the papers the squeeze effect could be reduced by increasing the thickness and porosity of the top-coating. The trend was the same when using carbon ink with MEK as the solvent. When using the polar solvents PM acetate or MEK on polar surfaces of the thick top-coatings, the fine line printability was improved. The conductivity of the printed lines also increased as a function of top-coating thickness, perhaps due to an improved alignment of the flaky ink particles. Less spreading of the ink results in a thicker printed layer and also explains the lower surface resistivity. Additionally, the lower roughness of the thicker coating layers may further enhance the conductivity. Semiconductor printability

Semiconductor, regioregular poly(3-hexylthiophene) (P3HT) dissolved in a mixture (1:1:2) of xylene:chlorobenzene:ortho-dichlorobenzene, was printed with inkjet in a roll-to-roll process. This means the drop spacing is constant and nonadjustable in cross direction while in machine direction the drop spacing is controlled by adjusting firing frequency relative to the web speed. P3HT was printed at a solids content of 0.25 weight -%. at three different amounts, giving equal theoretical uniform dry thicknesses of 20 nm, 40 nm and 80 nm. This corresponds to applied P3HT-volumes of 2, 4 and 8 nl/cm² and to total printed volumes of 800, 1600 and 3200 nl/cm² respectively. These volumes were compared to the pore volumes in the top-coatings, which were in the range of 4 to 400 nl/cm². P3HT was naturally doped in air, which resulted in measurable values of the surface resistivity. The obtained surface resistivity values (corresponding to the off-currents in a transistor structure) are a help in finding the amount of semiconductor that is required in order to fabricate functioning transistors on the substrates with different pore volumes.

Figure 4. Surface resistivity as function of pore volume for 2 nl/cm2 (left), 4 nl/cm2 (middle) and 8 nl/cm2 (right) total printed (roll-to-roll) semiconductor amounts. Surface resistivity was measured for all the printed amounts and was correlated with the pore volume. As is shown in Figure 4, the relationship between the surface resistivity and the pore volume is almost linear for the small pore volumes (< 100 nl/cm²) and small amount of semiconductor (2 nl/cm²), while the impact of pore volume decreases along with a higher amount applied. It is likely that for small applied volumes the semiconductor penetrates fully into the coating structure and surrounds the mineral particles, thereby creating a connected network. Once the pores are filled, with both semiconductor and evaporating solvent, the rest of the applied amount will be on the surface and evaporation continues resulting in an irregular film. This may be a disadvantage in a transistor, causing for example high off-currents and poor modulation, which can be seen from the relatively low surface resistivities of the high applied amounts (GΩ/sq vs. TΩ/sq). Ideally the semiconductor is a homogenous film at the aimed theoretical thickness, but since the surfaces are at least partly absorbing this will not be the case. Printing the semiconductor at higher solids content makes it possible to lower the total applied amount solvent and is thereby preferable. However, already at a concentration of 0.5 weight-% there was a tendency for inkjet nozzle clogging resulting in inadequate runnability. Similar trends in inksetting behavior, i.e. the dependence on pore volume, could also be observed for the copper chloride in the hydrogen sulfide sensor as well as for the electrolyte in the electrochemical pixel.

Proof of concept devices

Hygroscopic Field Effect Transistor

As a proof of concept, hygroscopic field effect transistors (HIFET) were printed with the roll-to-roll hybrid printer on the multilayer coated substrate. In order to ensure adequate printability of both the silver electrodes and the semiconductor, a substrate with a 3 g/m² kaolin top-coating (K3) was used as a compromise. The source and drain silver electrodes were printed using flexography. The finger width was ca 350 μm, the channel length was ca 300 μm and the total channel width of the interdigitated electrodes was 10 mm. The semiconductor (P3HT) was roll-to-roll inkjet-printed to an approximate amount of 4 nl/cm². The insulator (PVP dissolved in ethyl acetate combined with 10 weight-% kaolin) was coated using the reverse gravure technique. The gate electrode (PEDOT:PSS) was printed using either flexography or inkjet in combination with oven and hot air drying, of which inkjet enabled for thicker printed layer and thereby lower surface resistivity. Furthermore the risk for causing short circuits by breaking the insulator layer was reduced when using non-impact inkjet printing. In order to ensure adequate wettability the surface tension of the water based PEDOT:PSS ink was lowered just before printing by addition of a surfactant (Triton X-100, 0.1 volume-%). Figure 5A shows a schematic image of the top gate bottom contact FET geometry and an optical top view image of the gate electrode in blue, printed on top of the transparent insulator layer. Underneath is the purple semiconductor printed on top of the silver electrodes. The output and transfer characteristics of the transistor are shown in Figure 5 B and C, respectively. Compared to transistors manufactured in batch process, especially on plastic substrates, the current throughput is rather low. Poor semiconductor ordering and impurities of the paper surface might degrade the charge transport [33-37]. While the hysteresis is only slightly poorer compared to batch manufactured transistors, problems with short circuits and gate leakage are common. The overall yield is thereby still on an unsatisfactory level, mostly due to challenges in alignment control.

R² = 0.9348

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Pore volume [nl/cm²]

P3HT volume 2 nl/cm²Total printed volume 800 nl/cm²

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Figure 5. A: Schematic and optical image of a roll-to-roll printed HIFET. Output (B) and transfer (C) characteristics of the transistor on the multilayer curtain coated paper.

Modified atmosphere sensor

Manufacturing of sensors for hydrogen sulfide detection was also demonstrated in a roll-to-roll process. The sensor consists of two electrodes of silver printed with flexography. The same interdigitated finger structure as for the transistor (with a finger width of 350 μm and gap of 300 μm) was used. Copper chloride and polyaniline (CuCl2/PANI) can be applied by spray coating or inkjet printing on top of the silver electrodes. In the presence of trace amounts (5-10ppm) of hydrogen sulfide, the increase in the conductivity and color change of the sensing film (pani/copper chloride) can be explained by the formation of copper sulfide with the subsequent protonation of polyaniline [17]. Figure 6 shows the change in resistance measured as function of the exposure to hydrogen sulfide.

Figure 6. The resistance of the sensor is shown as a function of the exposure time to hydrogen sulfide.

Ion-selective electrodes

Another sensor application demonstrated on the multilayer coated paper is ion-selective electrodes. In earlier work ion-selective electrodes and reference electrodes have been produced by screen printing on a plastic substrate [18, 19]. The paper-based electrode substrates consist of flexography printed carbon as electronic conductor and flexography printed UV-curable lacquering as an insulating layer. The ion-selective membranes dissolved in tetrahydrofuran are added by drop casting and the slowly evaporating tetrahydrofuran sets high demands on the barrier properties. Since ion-selective electrodes are used to determine ion activities in aqueous solutions, the barrier properties against water were also evaluated and found to last for at least one hour in a 1 M KCl solution. The requirement of the barrier properties of the substrate were

A B C

therefore higher compared to the other demonstrated devices. The multilayer coated substrate used for the ion selective electrodes had a barrier structure consisting of two 10 g/m2 platy kaolin/ethylene latex layers with one 10 g/m2 polyolefin latex layer in between. As top coating a 5 g/m2 kaolin (similar to K 5) layer was used to ensure adequate printability.

A potassium-selective membrane containing valinomycin as ionophore was deposited on one printed carbon electrode and a reference-electrode membrane containing tetrabutylammonium tetrabutylborate as equitransferent salt [20] was deposited on the adjacent printed carbon electrode. This resulted in an all-solid-state K+ selective electrode and a reference electrode adjacent to each other on the paper substrate. The potentiometric response of the sensor to K+ ions at concentrations from 10-6 to 10-1 M at a constant ionic background of 0.1 M NaCl is shown in Figure 7. The sensor responds to K+ ions in a selective manner, which is regarded as a proof of concept. As can be seen in Figure 7 (top) the sensor shows sub-Nernstian behaviour (slope < 59 mV/decade) when the potential is recorded after 5 min in each solution. This is related to potential drift illustrated in Figure 7 (bottom), so if the potential value is taken immediately after changing the KCl concentration the response will be close to Nernstian.

Figure 7. Potentiometric response of the all-solid-state sensor to potassium ions. Calibration plot (top) and potential vs. time curves (bottom) are shown for KCl concentrations from 10-6 to 10-1 M at a background electrolyte of 0.1 M NaCl. Electrochemical pixels

To further demonstrate the barrier properties of the multilayer coated paper, and its usefulness as a printed electronics substrate, we fabricated electrochromical (EC) displays onto it. By flexo-printing PEDOT/PSS electrodes and coating electrolyte, we were able to demonstrate low voltage (1.5V) driven EC displays (Figure 8). By making the display unsymmetrical (i.e. different electrode areas) we have been able to enhance display performance and decrease the over-oxidation degradation that is known to happen in PEDOT/PSS at high voltages (>1.2V).

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Figure 8. Shown on the left are one printed EC display at three different biases – In the middle an un-switched display is shown and to the left and right the pixel at -1.5V and +1.5V, respectively is shown. On the right side a voltamogram when switching the pixel is shown. Note that the asymmetry in the electrode areas makes this curve also unsymmetrical.

Comparing EC displays fabricated onto ordinary coated finepaper to ones fabricated on our multilayer coated paper, we see much less spreading and penetration of the electrolyte leading to more stable operation on the latter. Also the flexo-printed PEDOT/PSS wets more uniformly and is more conducting on the multilayer coated paper than on ordinary coated finepaper. This type of display can be used in simple display applications, e.g. indicator displays. In a more elaborate approach, the EC pixels can be combined with transistors to make matrix addressed, pixelated displays [15,16]

CONCLUSIONS

Curtain coating is a suitable method for producing a multilayer coating structure in pilot or full industrial scale. The curtain coating method allowed for extremely thin top-coatings to be applied onto the closed and sealed barrier layer, thereby enabling the combination of adequate printability of functional materials with high barrier properties. Among the top-coating parameters, thickness, porosity, surface energy and absorptivity can be adjusted by use of different mineral pigments. Suitable top-coatings can be produced depending on the materials to be printed. However, when printing multilayer functional devices, such as a transistor, which consists of several printed layers, compromises have to be made. While a thicker and more porous top-coating is preferable for printing of source and drain electrodes from a silver or carbon particle ink, a thinner and less absorbing top-coating is required to form a functional semiconducting layer. As proof of concept, simple structure devices such as a transistor, hydrogen sulfide sensor, ion-selective electrode and electrochemical pixel were demonstrated by manufacturing them in a laboratory scale roll-to-roll process. While in the current study, the first steps towards fully roll-to-roll printed devices with the custom-built printing press were taken, challenges still remain. Especially the alignment (register) control needs improvements in order to improve the overall yield of produced components. There is also much room for optimization of the runnability through selection of best performing materials, solvent mixtures, solids contents and printing methods.

ACKNOWLEDGEMENTS

Marco Ahtinen and the laboratory personnel at Styron Europe Samstagern are acknowledged for carrying out the curtain coatings. Mikael Ek is acknowledged for assistance in laboratory work. The authors would also like to thank Imerys Minerals Ltd., Specialty Minerals Nordic Oy, Grace GmbH, Trüb Emulsions Chemie AG , Paramelt B.V., DOW Chemical Company and DuPont Electronic Polymers for supplying the materials as well as Xaarjet Ab Sweden for supplying the inkjet print heads. The Academy of Finland is acknowledged for financial support.

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[15] N. Kaihovirta, C. Wikman, T. Mäkelä, C. Wilén, and R. Österbacka “Self-Supported Ion-Conductive Membrane-Based Transistors”; Adv. Mater. 2009, 21, 2520–2523

[16] P. Andersson, D. Nilsson, P. O. Svensson, M. X. Chen, A. Malmstrom, T. Remonen, T. Kugler, M. Berggren, “Active matrix displays based on all-organic electrochemical smart pixels printed on paper”, Advanced Materials 2002, 14, 1460

[17] J. Sarfraz, D. Tobjörk, R. Österbacka, M. Lindén, ”Low-Cost Hydrogen Sulfide Gas Sensor on Paper Substrates; Fabrication and Demonstration”, IEEE sensors conference, Limerick 2011 [18] D. Cicmil, S. Anastasova, A. Kavanagh, D. Diamond, U. Mattinen, J. Bobacka, A. Lewenstam, A. Radu, “Ionic Liquid-Based, Liquid-Junction-Free Reference Electrode”, Electroanalysis 2011, 23, No. 8, 1881 – 1890 [19] S. Anastasova, A. Radu, G. Matzeu, C. Zuliani, D. Diamond, U. Mattinen, J. Bobacka, Disposable solid-contact ion-selective electrodes for environmental monitoring of lead with ppb limit-of-detection, Electrochim. Acta (2011) doi:10.1016/j.electacta.2011.10.089.

[20] U. Mattinen, J. Bobacka, A. Lewenstam, Solid-contact reference electrode based on lipophilic salts, Electroanalysis, 21 (2009) 1955–1969.

[21] J. Olkkonen, K. Lehtinen and T. Erho, Flexographically printed fluidic structures in paper. Anal. Chem., 82 (2010), pp. 10246–10250

[22] R. Bollström, A. Määttänen, D. Tobjörk, P. Ihalainen, N. Kaihovirta, R. Österbacka, J. Peltonen, M. Toivakka, A multilayer coated fiber-based substrate suitable for printed functionality, Org. Electron. 10 (2009) 1020–1023.

[23] R. Bollström, A. Määttänen, P. Ihalainen, J. Peltonen, M. Toivakka, Method for creating a substrate for printed or coated functionality, substrate, functional device and its use, PCT/FI2010/050056, WO 2010/086511.

[24] A. Määttänen, P. Ihalainen, R. Bollström, M. Toivakka, J. Peltonen, Wetting and print quality study of an inkjet-printed poly(3-hexylthiophene) on pigment coated papers, Colloids Surf. A: Physicochem. Eng. Aspects 367 (2010) 76–84.

[25] R. Bollström, J.J. Saarinen, J. Räty, M. Toivakka, Measuring solvent barrier properties of paper, Measurement Science and Technology, Meas. Sci. Technol. 23 (2012) 015601

[26] D. Tobjörk, H. Aarnio, P. Pulkkinen R. Bollström, A. Määttänen, P. Ihalainen, T. Mäkelä, J. Peltonen, M. Toivakka, H. Tenhu, R. Österbacka, IR-sintering of ink-jet printed metal-nanoparticles on paper, Thin Solid Film (2011), doi: 10.1016/j.tsf.2011.10.017.

[27] R. Bollström, M. Tuominen, A. Määttänen, J. Peltonen, M. Toivakka, Top layer coatability on barrier coatings, Progress in Organic Coatings 73 (2012) 26– 32

[28] D.J. Hughes, Method for simultaneously applying a plurality of coated layers by forming a stable multilayer free falling vertical curtain, US Patent 3,508,947 (1970).

[29] G. Gugler, R. Beer, M. Mauron, Operative limits of curtain coating due to edge, Chemical Engineering and Processing 50 (2011) 462-465.

[30] S. Renvall, T. Nurmiainen, J. Haavisto, I. Endres, R. Urscheler, K. Tano, New cost-efficient concept for coated white top liner with on-machine multilayer curtain coating, General Review (2009), 276-280. Publisher: (Kami Parupu Gijutsu Kyokai, ) CODEN:NTKKFN

[31] T. Lamminmäki, J. Kettle, H. Rautkoski, A. Kokko, and P.A.C. Gane, Limitations of Current Formulations when Decreasing the Coating Layer Thickness of Papers for Inkjet Printing, Ind. Eng. Chem. Res. 50 (2011) 7251–7263.

[32] R. Bollström, D. Tobjörk, P. Dolietis, P. Salminen, J. Preston, R. Österbacka and M. Toivakka, Printability of functional inks on multilayer curtain coated paper, Chemical Engineering and Processing (Submitted) [33] H. Sirringhaus, Physics of Solution Processed Organic Field Effect Transistors, Adv. Mater. Device, 17, 2411 (2005) [34] R. Bollström, A. Määttänen, D. Tobjörk, P. Ihalainen, N. Kaihovirta, R. Österbacka, J. Peltonen, M. Toivakka, A, A recyclable paper substrate suitable for printed functionality, In Proceedings of NEXT, Shanghai, 87-94 (2009)

[35] H. G. O. Sandberg, T. G. Bäcklund, R. Österbacka, H. Stubb, A high performance all-polymer transistor utilizing a hygroscopic insulator, Adv. Mater. 16 1112-1115, (2004)

[36] D. Tobjörk, N.J. Kaihovirta, T. Mäkelä, F.S. Pettersson, R. Österbacka, All-printed low-voltage organic transistors, Org. Electron. 9 931-935, (2008)

[37] D. Tobjörk, R. Bollström, P. Dolietis, A. Määttänen, P. Ihalainen, T. Mäkelä, J. Peltonen, M. Toivakka and R. Österbacka, Printed low-voltage organic transistors on plastic and paper, In Proceedings of European Coating Symposium, 62-65. (2011)

[38] Standard Test Methods for Water Vapor Transmission of Material, E 96/E96M-10, ASTM International, Reapproved 2010

[39] C.M. Gribble, G.P. Matthews, G.M. Laudone, A. Turner, C. J. Ridgway, J. Schoelkopf, P. A.C. Gane, Porometry, porosimetry, image analysis and void network modelling in the study of the pore-level properties of filters, Chem. Eng. Sci. 66 (2011) 3701-3709.

[40] C. Ridgway, P.A.C. Gane, J. Schoelkopf, Effect of Capillary Element Aspect Ratio on the Dynamic Imbibition within Porous Networks J. Colloid Interface Sci. 252 (2002) 373.

[41] C. Ridgway, P.A.C. Gane, Controlling the Absorption Dynamic of Water-Based Ink into Porous Pigmented Coating Structures to Enhance Print Performance Nord. Pulp Pap. Res. J. 17 (2002) 119.

[42] R. Olsson, J. van Stam, M. Lestelius, Effects on Ink Setting in Flexographic Printing: Coating Polarity and Dot Gain Nord. Pulp Pap. Res. J. 21 (2006) 569.

Roll-to-roll printed electronics on paper

Roger Bollström

D. Tobjörk, P. Dolietis, T. Remonen, C-J. Wikman, S. Viljanen, J. Sarfraz, P. Salminen, M. Lindén,

C-E. Wilén, J. Bobacka, R. Österbacka, M. Toivakka

Åbo Akademi University, Turku, Finland

Electronics on paper • Potential for numerous

value-added product concepts • Disposable

electronics • Smart packaging • Sensor applications • Home diagnostics • Simple displays

Paper electronics platform

• Novel device concepts needed: - Solution processable

• Preferably without clean-room - Simple design - Linewidths of >10 µm

• To avoid critical alignments etc. - Low-voltage operation needed - Recyclable or disposable substrate

Graphical vs. Functional printing • Printing is

• a fast process for transferring of material (ink) to substrate

• developed for graphical printing with visual properties in focus

• an excellent choice for fabricating multilayer devices

“You can cheat the human eye but not the conductivity”

Graphical printing Printed device

P3HT Ag Ag

Substrate

PEDOT:PSS PVP

Omya

Basepaper: 80 g/m2 woodfree 250 µm

Basepaper

Precoating Smoothing layer

Barrier layer Topcoating

Barrier layer (Latex)

RMS 260 nm

Calandered topcoating (Kaolin)

RMS 55 nm

Precoating (GCC)

RMS 580 nm

Smoothing layer (Kaolin)

RMS 300 nm

Mylar® A RMS 30 nm

Multilayer coating structure

R. Bollström et al. A multilayer coated fiber-based substrate suitable for printed functionality, Org. Electronics, 10, 1020 (2009) WO 2010/086511, PCT/FI2010/050056, Method for creating a substrate for printed functionality, substrate, and printed functional device Bollström Roger, Määttänen Anni, Ihalainen Petri, Toivakka Martti, Peltonen Jouko

Precoating (GCC)

RMS 580 nm

Smoothing layer (Kaolin)

RMS 300 nm

Mylar® A RMS 30 nm

Multilayer coating structure

R. Bollström et al. A multilayer coated fiber-based substrate suitable for printed functionality, Org. Electronics, 10, 1020 (2009) WO 2010/086511, PCT/FI2010/050056, Method for creating a substrate for printed functionality, substrate, and printed functional device Bollström Roger, Määttänen Anni, Ihalainen Petri, Toivakka Martti, Peltonen Jouko

Topcoating 0.5-5µm

Barrier layer 5-20µm

Smoothing layer

Precoating layer

Basepaper

Printers • Batch inkjet printing with

Dimatix Materials Printer (DMP 2800)

• Spin coating • IGT AIC2 (Flexography)

• Custom built roll to roll printer - Flexography - Inkjet - Reverse gravure - Spray

Printed transistors on paper (batch) • Output and transfer characteristics

Logic circuits • Inverter • Ring oscillator:

Odd number of inverters in parallel

0.0 -0.5 -1.0 -1.5 -2.00

-2

-4

-6

-8

-10

-12On paperInkjetted PQTW = 2.5 cm

-0.8 V

-0.4 V

Drain

curre

nt (µ

A)

Drain voltage (V)

0 V

VG= -1.2 V

0.5 0.0 -0.5 -1.0 -1.5 -2.01E-3

0.01

0.1

1

10

ID IS IG

VD= -1.5 V

Curre

nts (µA

)

Gate voltage (V)

R. Bollström et al. A multilayer coated fiber-based substrate suitable for printed functionality, Org. Electronics, 10, 1020 (2009) D. Tobjörk, et al. All-printed low-voltage organic transistors, Organic Electronics 9, 931-935 (2008)

Multilayer structure -Combined printability and barrier properties

Mylar® A

References

Topcoating added Stora Enso Lumiart 150

Copypaper

Precoating Smoothing layer

(Kaolin) PCC Kaolin

Frontside

Backside

Frontside

Backside

10 mm

Barrier layer (Latex)

P3HT in DCB

Drop size 5μl

R. Bollström et al. A multilayer coated fiber-based substrate suitable for printed functionality, Organic Electronics, 10, 1020 (2009)

Barrier layer

Topcoating

Precoating

Smoothing layer

Roll to roll infrared sintering

D. Tobjörk, H. Aarnio, P. Pulkkinen R. Bollström, A. Määttänen, P. Ihalainen, T. Mäkelä, J. Peltonen, M. Toivakka, H. Tenhu, R. Österbacka, IR-sintering of ink-jet printed metal-nanoparticles on paper, Thin Solid Film (2011), doi: 10.1016/j.tsf.2011.10.017. I. Reinhold, W. Voit, M. Thielen, M. Müller, M. Müller, S. Farnsworth, I. Rawson, R. Bollström, W. Zapka, Inkjet Printing of Electrical Connections in Electronic Packaging, Proceedings of the NIP 27 and Digital Fabrication 2011 Conference, 445-451

0 5 10 15 200

5

10

15

20

25

30 Inkjetted AgNPs on paper Bulk resistivity of Ag

Volu

me

resi

stiv

ity (µΩ

cm)

Irradiation time (s)

Applications and references

• Transistor - R. Bollström, A. Määttänen, D. Tobjörk, P. Ihalainen, N. Kaihovirta, R. Österbacka, J. Peltonen and M.

Toivakka, 2009, A multilayer coated fiber-based substrate suitable for printed functionality, Organic Electronics 10, 1020

- R. Bollström, A. Määttänen, D. Tobjörk, P. Ihalainen, N. Kaihovirta, R. Österbacka, J. Peltonen, M. Toivakka, A recyclable paper substrate suitable for printed functionality, In Proceedings of NEXT, Shanghai, 87-94 (2009)

- D. Tobjörk, R. Bollström, P. Dolietis, A. Määttänen, P. Ihalainen, T. Mäkelä, J. Peltonen, M. Toivakka and R. Österbacka, Printed low-voltage organic transistors on plastic and paper, In Proceedings of European Coating Symposium 2011, 62-65

• Electrowetting and UV sensor

- J.J. Saarinen, P. Ihalainen, A. Määttänen, R. Bollström and J. Peltonen, 2011, Printed sensor and electric field assisted wetting on a natural fibre based substrate, Nordic Pulp and Paper Research Journal, 25

• Electrochemical polymerization

- P. Ihalainen, A. Määttänen, U. Mattinen, M. Stepien, R. Bollström, M. Toivakka, J. Bobacka and J. Peltonen, 2011, Electrodeposition of PEDOT-Cl film on a fully printed Ag/polyaniline electrode, Thin Solid Films, 2172-2175

Objectives • Manufacture multilayer coating structure for printed

electronics applications utilizing pilot scale curtain coater • Understand which topcoating parameters are important for

functional printing - Inkjet / flexography - Silver (nano / micron), P3HT

• Demonstrate roll to roll printed devices

Curtain coated papers • Basepaper

• Precoated woodfree (Coarse GCC) • Smoothing layer (Imerys Barrisurf FX)

• Barrier layer • Imerys Barrisurf HX+ 50 pph ethylene

acrylic latex (Trüb Emulsions Chemie AG)

• PCC: Specialty Minerals Opacarb 3000 • Kaolin: Imerys Barrisurf FX • Silica: Grace Syloid C807


Top-coating Grammage [g/m²] 0.5 1 3 5 0.5 1 3 5 0.5 1 3

Coating formulation

Silica [pph] 100 100 100

PCC [pph] 30 30 30 30

Kaolin [pph] 100 100 100 100 70 70 70 70

SB latex [pph] 4 4 4 4 4 4 4 4 20 20 20

Thickener [pph] 16.7 9.0 0.5 0.5 17.3 6.8 0.6 0.6 16.8 5.9 0.7

R. Bollström, D. Tobjörk, P. Dolietis, P. Salminen, J. Preston, R. Österbacka and M. Toivakka, Printability of functional inks on multilayer curtain coated paper, Chemical Engineering and Processing (Submitted)

Barrier layer

Topcoating

Precoating

Smoothing layer

Barrier layer

Topcoating

Precoating

Smoothing layer

0.5 g/m2 kaolin topcoating, uncalendered

10 g/m2 hyper platy kaolin + 50 pph latex

10 g/m2 kaolin smoothing layer

Adequate barrier properties (WVTR @ 23° C 85% RH: 37 g/m2/day)

0.5 g/m2 kaolin topcoating, uncalendered

10 g/m2 hyper platy kaolin + 50 pph latex

Coating structure


AFM Roughness - RMS at different cut off lengths

0

100

200

300

400

500

600

700

800

900

0.5 1 3 5 0.5 1 3 5 0.5 1 3

100 Silica 100 Silica 100 Silica

100 Kaolin 100 Kaolin 100 Kaolin 100 Kaolin 70 Kaolin 70 Kaolin 70 Kaolin 70 Kaolin

30 PCC 30 PCC 30 PCC 30 PCC

RMS [nm] 100 um 50 um 25 um 12.5 um


Barrier layer

Topcoating

Precoating

Smoothing layer

Analysing the printability of functional materials

• Surface energy • Porosity

• Pore size • Pore volume

• Laboratory scale test printing

• Inkjet (Nanoparticle silver ink) • Flexography (Micron-size silver ink)

• Conductivity • Silver, carbon, doped semiconductor

• Optical print quality

Barrier layer

Topcoating

Precoating

Smoothing layer

Apparent surface energy

Polarity increases with increased grammage

0

10

20

30

40

50

60

Barrier 0.5 1 3 5 0.5 1 3 5 0.5 1 3




[mN/m] polar dispersive

Barrier layer

Topcoating

Precoating

Smoothing layer

Pore size vs. ink penetration (silver)

49 69 60 60 13

85 74 74

351 (21) 376 (10)

0

100

200

300

400

500

0.5 1 3 5 0.5 1 3 5 0.5 1 3




[nm]

(Bimodal porosity)

Kaolin Kaolin/PCC Silica Kaolin Kaolin/PCC Silica

Flexography (micron size flaky particles) Inkjet (nanoparticles)

804 (10)

Flexography silver print quality Ink: Silver, Creative Materials (125-06) Speed: 10 m/min Plate material: Asahi DSH (Shore A 65-67) Anilox: 120 l/cm and 12 cm3/m2

Line width: 350 μm Line gap: 350 μm Line length: 11 mm Resistance: 1 finger Sintering: Online infrared (8 * ~800°C)

300

350

400

450

500

550

600

0.5 1 3 5 0.5 1 3 5 0.5 1 3




27 19 3 3 27 8 3 3 54 5 3

wid

th (μ

m)

Width including squeeze

Line width analysis, flexo printed silver

A thicker and more porous topcoating preferable

Ω/sq

Line width analysis, flexo printed carbon

300

350

400

450

500

0.5 1 3 5 0.5 1 3 5 0.5 1 3




wid

th (μ

m)

Width Width including squeeze

A thicker and more porous topcoating preferable

Semiconductor amount vs. pore volume

R² = 0.9348

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 20 40 60 80 100

TΩ/s

q



0

20

40

60

80

100

120

140

0 50 100 150 200

GΩ

/sq



0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 50 100 150

TΩ/s

q



• Surface resistivity of inkjet printed P3HT layer

- Naturally doped (air) • A thinner and less porous topcoating preferable


R² = 0.9348

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 20 40 60 80 100

TΩ/s

q



Semiconductor performance vs. top coating

0

1000

2000

3000

4000

5000

6000

7000

0 1 2 3 4 5 6

GΩ/sq

Topcoating (g/m²)

Kaolin2 nl/cm² (20 nm) 80 pl drops

4 nl/cm² (40 nm) 80 pl drops




0 1 2 3 4 5 6Topcoating (g/m²)

Kaolin/PCC

0 1 2 3 4 5 6Topcoating (g/m²)

Silica8000 - 18000 GΩ/sq


6 19

76 126

4 25

86

144

52

110

390

0

100

200

300

400

0.5 1 3 5 0.5 1 3 5 0.5 1 3




nl/c

m²

Roll to roll printed devices -proof of concept

•Transistor •Hydrogen sulfide sensor •Ion-selective electrode •Electrochromic pixel

Custom built hybrid printer

• UVA/UVC lamps • Spray coating unit • Gravure unit • Laminator/embossing unit

Camera

Alignment

Inkjet

Flexography Rewinder Unwinder

Reverse Gravure

Infrared Ovens

Fans

Flexography + infrared sintering and inkjet

Reverse gravure and spray coating

Roll to roll printed transistor

Inkjet (semiconductor)

Flexography (source & drain)

Unwinder

Reverse gravure (insulator)

Inkjet (gate)

Rewinder

Infrared sintering

Semiconductor (P3HT)

Source (Ag) Drain (Ag)

Insulator (PVP)

Gate (Pedot:PSS)

Multilayer coated paper


Roll to roll printed hydrogen sulfide sensors

Polyaniline with copper salt E.g. CuCl2 + H2S → CuxS + HCl

=> protonation of polyaniline-EB

J. Sarfraz, D. Tobjörk, R. Österbacka, M. Lindén, ”Low-Cost Hydrogen Sulfide Gas Sensor on Paper Substrates; Fabrication and Demonstration”, IEEE sensors conference, Limerick 2011

Roll to roll printed ion-selective electrodes

300

350

400

450

500

-7 -6 -5 -4 -3 -2 -1 0

Pote

ntia

l [m

V]

log a(K)

300

350

400

450

500

550

0 300 600 900 1200 1500 1800 2100

Pote

ntia

l [m

V]

Time [s]

• Carbon electrodes • Membrane added by drop cast • Extremely high barrier properties required

• 10 minutes against tetrahydrofuran • 1 hour against 1M KCl

•

Roll to roll printed electrochromic pixels

P. Andersson, D. Nilsson, P. O. Svensson, M. X. Chen, A. Malmstrom, T. Remonen, T. Kugler, M. Berggren, “Active matrix displays based on all-organic electrochemical smart pixels printed on paper”, Advanced Materials 2002, 14, 1460 P. Andersson, R. Forchheimer, P. Tehrani, M. Berggren, Printable all-organic electrochromic active-matrix displays, Adv. Funct. Mater. 17 (2007) 3074–3082.

-1.5 V 0 V +1.5 V -2 V -1 V 0 V 1 V 2 V -4

00nA

0

nA

400

nA

Conclusions • Curtain coating a suitable method for manufacturing

the multilayer structure • Printability controlled by top coating

- Thickness, surface energy, porosity, roughness • Functional printing requires a compromise

- Optimum parameters for silver and semiconductor are partly the opposite

• Combination of suitable coating and printing methods enables for roll to roll manufacturing of functional devices

Acknowledgements • Marco Ahtinen • Janet Preston • Jani Kniivilä

• Imerys Minerals Ltd. • Specialty Minerals Nordic Oy • Grace GmbH • Trüb Emulsions Chemie AG • Paramelt B.V. • DOW Chemical Company • DuPont Electronic Polymers • Xaarjet Ab Sweden

• Academy of Finland

roll-to-roll printed electronics on paper

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