A vision for Printed Electronics is to “Create value by adding functionality to everyday products”. There are, however, several challenges in realizing this vision. One of the most important one is to be able to integrate different components into functional systems. Usually this involves a large number of processing steps that has to be compatible with each other and show very high yield. If a R2R process is considered, ink drying time is critical. There must also be electrical compatibility of the printed components to be integrated. Standard Si circuits should be used where high memory and processor capacity are needed. From an environmental perspective there should be a sustainable cradle to cradle design of the products and the materials and processes must be environmentally friendly. Acreo has developed Printed Electronics platform that can meet some of these challenges The major advantage of the platform is that the manufacturing can be performed by using standard printing tools, outside the clean room facility that typically is used for most other transistor and display technologies. The reason for this is that no critical dimensions are required, and the resulting devices are operated at low voltages, less than 3 V, and are thereby compatible with energy sources like printed batteries. The device manufacturing is further simplified by that only a small set of materials is employed, that is, the very same conducting polymer is utilized as the active material in for example both transistors and displays. In the presentation we will describe this platform in detail and also a number of product demonstrators at different levels of integration.

Metallic patterns comprising high electrical conductivities are indispensable components of many organic electronic devices, e.g. light emitting diodes (OLEDs), photovoltaic cells (OPVs), and thin film transistors. Furthermore, they find widespread use in RFID tags, smart labels and a variety of other applications. Screen printing of metal containing pastes on flexible plastic foils is a convenient deposition method for these structures, especially since it is roll-to-roll (R2R) compatible and allows very high processing speeds. However, in order to achieve the high electrical conductivities which are necessary for appropriate device performance, a fast post-deposition sintering step is also required. We have developed photonic flash sintering as a processing technology that allows to improve the conductivities of printed silver structures on foils within fractions of a second without substrate deformation. The combination of high velocities and mild processing conditions enabled us to construct a R2R tool that comprises a rotary screen printer with a photonic flash sintering unit. In this presentation, we demonstrate the applicability of this approach to the R2R fabrication of functional, highly conductive structures on PET substrates. Screen printed silver structures with line widths down to 70 µm and sheet resistances down to 4.2 m#8486;/sq/mil (corresponding to a conductivity of 15 % of the value of bulk silver) can be produced at a speed of 6 m/min on this R2R tool. These structures have a promising potential to be integrated in ITO-free organic devices such as OLEDs and OPVs on a large scale and at low production costs.

Recently, the life paradigm of human being has been dynamically transformed into the one that is heavily dependent on mobile devices like smart mobile phones and computers. These devices are required to be lighter, more flexible, and cheaper than ever. Roll-to-roll printed electronics are being thought as an emerging counterproposal to these requirements for mobile devices. However there are many issues related to the roll-to-roll printed electronics including web handling, drying, register control, patterning, inks, substrates, roll-to-roll control systems etc. But one of most important issues in the roll-to-roll printed electronics might be the matching technology among the ink, the pattern, the substrate, and the roll-to-roll system itself. In this presentation, several technologies for matching will be suggested. Mathematical models and experimental approaches are introduced in order to develop matching logics which will define inter-relationships among parameters in ink transfer, pattern geometry, surface conditions of substrates, and operating conditions in the roll-to-roll printing systems. Matching logics to print micro-fine patterns on the flexible film using roll-to-roll systems are being developed in the FDRC(Flexible Display Roll-to-Roll Research Center in Konkuk Univ.). A design concept of roll-to-roll systems for printed electronics is also being developed including necessary subsystems of the roll-to-roll printing system like air-floatation rolls, suctions rolls, and rolls with crack minimization design. Matching logics were validated through simulations and experiments by using roll-to-roll printing systems which are in the FDRC. Simple devices like RLC circuit were manufactured through the roll-to-roll printing and coating systems to validate these matching logics. Some examples of these validation processes of matching logics will be presented in the talk.

Over the past decade, printed electronics evolved into an interdisciplinary research area incorporating the physical and chemical materials sciences, as well as mechanical and electrical engineering. The vast majority of publications covering manufacturing concepts employ a “roll-to-roll” process, in which a mechanically flexible substrate (plastic foil, metal foil, or paper) is guided through the individual manufacturing steps between an unwinding and a winding cylinder (“roll-to-roll”). As seen in the title of this MRS Symposium, the term “roll-to-roll” became a synonym for high-throughput production of organic electronics. The focus on web-fed processing in the scientific community remains ambiguous, as a variety of other forms of substrate transport is established in printing science and industry. The method of substrate transport is currently not considered in the move towards upscaling of printed electronics production. This paper introduces four different substrate transport technologies and reflects on their applicability to printed electronics. Besides the classical substrate technology concepts -- “roll-to-roll” and “sheet-to-sheet” -- we introduce two new technologies: “shuttle-transport” and the hybrid transport concept “roll-to-sheet”. Basic working principles, chances and limitations of each concept are discussed. In a further step, the perspective is broadened to the entire process from substrate-production until the assembly of the final product. We show that a second question is directly linked to the selection of a substrate transport technology: what is the optimal point for cutting the substrate web to individual sheets? This problem is more complicated than simply choosing between “roll-to-roll” or “sheet-to-sheet”. Therefore, a model for the cutting point of printed electronics manufacturing has been developed. We present one possible solution for the optimal point and offer an outlook on an expanded version, which incorporates parallelized sheet-fed printing machines.

Flexible electronics is considered an indispensible force that will drive future electronics applications ranging from displays, lighting and communication to sensing, renewable energy and biomedicine. The challenges in realizing the flexible electronics revolution lie not only in developing new materials and new processes that enable roll-to-roll (R2R) processes for manufacturing electronics with desirable performance at a low cost, but also in focusing on particular applications uniquely suitable for large scale and flexible format electronic devices. I will discuss the possible roles of flexible electronics in civil and energy infrastructures, on which most activities of the modern society heavily rely. As current civil and energy infrastructures are rigid, bulky and expected to last without much attention until failures occur, the future infrastructures are expected to be intelligent, efficient, self-monitoring and self-repairing with the help of ubiquitous sensors. Using examples from our recent effort in developing flexible sensor arrays, I will illustrate unique constraints and opportunities of flexible devices for civil and energy infrastructures.

Atomic layer deposition (ALD) is known for its outstanding ability to growing dense conformal thin films with monolayer control. ALD has been evidenced to yield superior gas permeation barriers for organic electronic devices [1, 2]. Low processing temperatures, render them highly attractive for the use on sensitive substrates, e.g. PET foils or organic electronic devices. Substantial drawbacks of classical ALD is the requirement for vacuum processing equipment and the related long processing times, which were often seen as main obstacle to use ALD in high-throughput manufacturing. This paradigm changed with the first demonstration of high-speed ALD at atmospheric pressure [3]. The processing speed of 1.2 nm/s seeds the prospect of ALD as part of roll-to-roll or in-line production [4, 5]. For precursor systems where thermal ALD is not applicable or too slow, plasma assisted ALD (PA-ALD) may be favorable. However, reports on atmospheric pressure plasma ALD (APP-ALD) are very limited today [6]. Here, we present the first report on APP-ALD for the deposition of TiOx, which is a functional oxide in a plethora of applications (catalysis, optics, photovoltaics, etc.). We will show the use of the TiOx prepared by APP-ALD as electron extraction layer in solution processed inverted organic solar cells. Titanium isopropoxide (TIP) is used as metal precursor in sequence with a plasma generated by an isolated surface barrier discharge typically excited at 6.5 kV and 3.5 kHz using a process gas of Ar/O2 at atmospheric pressure. At room temperature, the TiOx growth rate is 1.1 Å/cycle, in agreement with conventional PA-ALD, and about an order of magnitude larger than that of thermal ALD using TIP/H2O. XPS analysis indicates predominantly Ti4+ and a stoichiometry of Ti/O close to 1:2. 25 nm thick TiOx layers are used as electron selective charge extraction layers in efficient inverted organic solar cells. The device characteristics are comparable to that of OSCs with solution processed TiOx layers. Contrary to the porous and permeable solution processed TiOx, the APP-ALD TiOx is intended to concomitantly serve as gas diffusion barrier to protect the moisture sensitive OSCs. [1] J. Meyer, P. Görrn, F. Bertram, S. Hamwi, T. Winkler, H.-H. Johannes, T. Weimann, P. Hinze, T. Riedl, and W. Kowalsky, Adv. Mater. 21, 1845 (2009). [2] J. Meyer, D. Schneidenbach, T. Winkler, S. Hamwi, T. Weimann, P. Hinze, S. Ammermann, H.-H. Johannes, T. Riedl, and W. Kowalsky, Appl. Phys. Lett. 94, 233305 (2009). [3] D. H. Levy, D. Freeman, S. F. Nelson, P. J. Cowdery-Corvan, and L. M. Irving, Appl. Phys. Lett. 92, 192101 (2008). [4] W.M.M. (Erwin) Kessels and M. Putkonen, MRS Bulletin 36, 907 (2011). [5] P. Poodt, D. C. Cameron, E. Dickey, S. M. George, V. Kuznetsov, G. N. Parsons, F. Roozeboom, G. Sundaram, and A. Vermeer , J. Vac. Sci. Technol. A 30, 010802 (2012). [6] P. Poodt , B. Kniknie , A. Branca , H. Winands , F. Roozeboom , Phys. Status Solidi RRL 5 , 165 (2011).

The last few years have seen important developments regarding spatial atomic layer deposition, making it possible to do ALD with high deposition rates (> 1 nm/s) [1]. Whereas in conventional ALD, precursors are dosed separated in time using a purge or pump step, in spatial ALD, precursors are dosed simultaneously and continuously at different physical locations. As purge steps are no longer required, the spatial ALD process can be operated at much higher speeds, limited by the reaction kinetics rather than pumping times. As a result, deposition rates exceeding 1 nm/s have been reported for spatial atmospheric ALD of Al2O3 [2]. This has led to the launch of high throughput, industrial scale ALD tools for surface passivation of crystalline silicon solar cells. The combination of ALD-quality thin films with high deposition rates opened up new application fields for spatial ALD, such as flexible electronics, flexible displays, OLEDs and thin-film solar cells. Examples of such applications are transparent oxide (semi)conductors (e.g. ZnO), gate dielectrics for thin-film transistors and moisture permeation barriers (e.g. Al2O3). These applications however require high-throughput and low-cost processing schemes. A new type of atmospheric pressure operated spatial ALD reactor for deposition on flexible substrates that we designed will be discussed. In this reactor, a rotating drum is used to supply the precursor gases to slots at the peripheral surface of the drum, parallel to its rotation axis. The foil substrate is transported around the drum surface, where gas bearings are used to keep the foil and the drum separated, as well as separate the different precursors. The foil being contactless enables the drum to rotate at high speed while the foil is slowly advancing. Thus every part of the foil surface will come into contact with a predefined number of precursor cycles. Each individual precursor pair cycle will deposit one monolayer of e.g. Al2O3. In our current design, the drum has six precursor slot pairs at its outer surface. Thus, when the drum rotates at a frequency of 5 Hz, the number of precursor pairs per second is approximately 30, for low foil traversing speeds. When the foil covers 50% of the drum surface, a ~100 nm thick layer can be applied in a continuous roll-to-roll process. For deposition on temperature-sensitive substrates, such as polymer films, a low temperature (~100 oC) ALD process for making Al2O3 from trimethyl-aluminum and water has been developed, showing excellent barrier properties (WVTR = le;1e-5 g/m^2/day for 20-50 nm Al2O3 single films). Combined with our roll-to-roll spatial ALD reactor, the large-scale production of cost-effective, high-performance encapsulation foils becomes feasible. [1] Poodt et al. JVST-A 30 (2012) 0108021 [2] P. Poodt, A. Lankhorst, F. Roozeboom, K. Spee, D. Maas, A. Vermeer, Adv. Mater. 22 (2010) 3564

Common threads in printed electronics today are high materials usage and high throughput (low cost), wide substrate latitude (electronics everywhere), and the use of digital patterning (low-volume manufacturing and custom designs). Typical printed electronics efforts employ processes wherein the active layers of an electronic device are digitally printed. Using additive printing processes for fabricating printed electronics requires that semiconductors, dielectrics, and electrode materials have ink-like as well as electronic properties. This need for active materials to be “printable” greatly restricts the materials available for use in the formation of printed electronics, and has to date limited device performance. Here we explore an alternative approach to printed electronics where the patterning is achieved by printing, but the active material is deposited via atomic layer deposition (ALD). We thus separate the ink-like requirements from the active materials requirements. In this “patterned by printing” approach to printed electronics, a director material is printed that inhibits the deposition of the functional material. The active material is globally applied but only deposits in the areas where the director is not present—and as such is patterned at the time of deposition. In our work, the active materials are deposited by an atmospheric pressure, roll-compatible spatial ALD (SALD) process. In addition to removing the formulation constraint from the active materials, the “patterned by printing” approach also relaxes the constraints on required print quality. In additive printed systems, the active materials interfaces are formed in the printing steps and layer uniformity is critical. As we will demonstrate, a relatively non-uniform printed director does not influence the ability of the director to direct, and since the active materials are grown via spatial atomic layer deposition (SALD) the functional layers are uniform and have low defect interfaces. Additionally, a single director ink formulation can be used to pattern all active material layers further simplifying the printing processes. There are three key elements in our “patterned by printing” approach: 1) spatial ALD (SALD), 2) director materials and mechanisms, and 3) printing methods. We will walk through the important aspects of each element, and link them into a process flow for ZnO thin film transistors (TFTs). New performance data from representative TFTs made using this methodology will be presented that show the potential to form high quality devices and ultimately circuits via roll compatible processes.

Micro-structured riblet surfaces mimicking the skin of sharks are well known for reducing the viscous drag, thus being highly interesting for energy saving topics in fluid dynamical applications. In this study, riblet patterns have been produced on large-area flexible polymer foils by roll-to-roll (r2r) UV-imprinting. These foils show a potential of up to 4-6 % viscous drag reduction and are easily applied on wind turbines, aircrafts or surf boards. The main challenge is the right choice of the substrate and the imprint resist. They have to show the combination of several major qualities, due to harsh outdoor conditions and a broad number of crucial r2r processing parameters. High flexibility, excellent weather- and UV-stability, scratch resistance have to come along with favorable r2r-processing parameters such as high curing speed and clean demolding from the Nickel imprint stamp. Therefore, polyethylene terephtalate (PET) foils have been selected and an UV-curable polyurethane acrylate (PUA) imprint resist has been developed. The coating of a 25 cm wide PET substrate web with the PUA-based imprint resist and the micro-structuring of the riblets has been performed on a custom made roll-to-roll coating and UV-imprint pilot machine. The riblet structures with dimensions of 10-80 microns have been created by interference lithography and then electroformed into a Nickel-roller-stamp (shim) having the size of ca. 27cm x 63 cm. This Nickel-shim is magnetically fixed onto the imprint cylinder and the UV-curing occurs from the backside through the substrate web. First successful r2r-imprints of exemplary riblet-type test patterns into UA-resist with high reproduction fidelity have been performed and shown to be homogeneous over more than 100m web length. UV-curable surface active molecules that are chemically bonded to the surface of the imprinted riblets provide durable water and dirt repellence to the drag reducing foils. Depending on the riblet orientation water contact angles of 100° and 145° are found on the r2r-imprinted riblet foils.

Micro- and nano-scale structures patterning is essential technologies for the successful miniaturization of functional electrical and biochemical devices. Among the many types of micro- or nano-patterning processes, microcontact printing (µCP) provides a powerful method for creating sub-micron-scale features on target substrates. In this study, we presented a novel vacuum-assisted microcontact printing (µCP) process that presents a method for patterning functional materials with precise alignment. The printing pressure of the vacuum-assisted µCP was applied using the pressure difference between the inside of an elastomeric printing stamp and the atmospheric pressure. A double exposure microfabrication process was adopted for manufacturing different height protrusions on the elastomeric printing stamps. The outer protrusion was fabricated to be higher than the printing patterns, thereby acting as a vacuum sealing wall. The printing pressure was easily applied and controlled using syringes and motorized syringe controllers. Precision alignment was realized using a common optical alignment system. During the alignment process, damage to the previously patterned material and undesired printing patterns due to stamp dragging was avoided by imposing a separation distance between the printed pattern and the substrate. Several functional materials, including proteins (FITC-streptavidin and Alexa Flour 594-goat anti-human IgG) and nanostructures (ZnO nanowires), could be successively patterned. For the proteins patterning, proteins were diluted in phosphate buffered saline (PBS) as 100 mu;g/ml. After loading the protein onto the PDMS stamp, the stamp surface was gently rinsed with PBS and DI water, and dried under a nitrogen stream. Contact between the protein-loaded PDMS stamp and the glass substrate lasted about 3 min at a 0.5 psi printing pressure. The nano-structures were fabricated by patterning ZnO nanoparticles(NPs) onto the substrate. The NPs subsequently grew as ZnO NWs via hydrothermal synthesis. The ZnO precursor for hydrothermal growth was prepared in an aqueous solution containing 25 mM zinc nitrate hexahydrate (Zn(NO₃)₂#9679;6H₂O), 5-7 mM polyethylenimine (C₂H₅N), and 25 mM hexamethylenetetramine (C₆H₁₂N₄). The solution was heated to 95°C and cooled to room temperature. The patterned ZnO NWs were obtained via µCP of the patterned ZnO NPs, which provided seeds, using a 1 min contact time and a 0.8-1 psi printing pressure. The ZnO NPs patterned substrates were then immersed in the precursor solution, and NWs were synthesized over 5-8 hours at 95°C. As a result, protein-protein, protein-nanowire, and three-dimensionally patterned nanowires are described. This versatile vacuum-assisted µCP process gives a practical means for implementing the large-area and continuous fabrication based on roll-to-roll process of bio- and nano-technologies and related applications.

The application of lasers for the deposition of thin films has been developed over the last decade to a variety of mature and robust techniques which are utilized for the deposition of a wide range of materials for different applications. For the deposition, or better direct writing of materials, with a lateral resolution from the micron to mm range an alternative, laser based approach has been developed, i.e. laser-induced forward transfer (LIFT). In this approach thin films (nm to µm) with a well defined geometry are transferred from a target onto a receiver which may even have a structure on its own, e.g. a electrode structure for sensors. The transfer of thin films with defined geometries has been first reported in 1969, and became known in 1986 under the name of laser-induced forward transfer (LIFT), but also several other names have been used for fundamental very similar processes, such as LAT, LITI, MAPLE- DW etc. One of the further developments of the LIFT process has been the application of laser light absorbing layers between the substrate and the layer to be transferred. These absorbing layers, also named dynamic release layers (DRL) or sacrificial layers protect the transfer layer from the laser, which may cause thermal or photochemical reactions, and allow therefore the transfer at lower laser fluences and also of sensitive materials. A large number of sensitive materials, e.g. bio-materials and polymers, has been transferred by this approach in liquid or solid form. Selected examples, e.g. of light emitting polymers (OLEDs) and sensor materials (ranging from biomaterials to oxides), will be shown to suggest that LIFT may be a possible alternative to other non-laser based direct writing techniques, such as ink-jet printing, which require solvents and nozzles.

The NSF Center for Hierarchical Manufacturing (CHM) at the University of Massachusetts Amherst is developing materials and processing approaches for the fabrication of nanotechnology enabled devices on a R2R platform. Specifically we employ additive-drive self-assembly to produce well-ordered polymer/nanoparticle hybrid materials that can serve as active layers in a device, have developed simple and effective routes towards substrate planarization, and employ R2R nanoimprint lithography for device scale patterning. Our newly constructed R2R processing facility includes a custom designed, precision R2R UV-assisted nanoimprint lithography (NIL) system and hybrid materials coaters operating on 6" webs. Here we illustrate the capabilities of self-assembly and NIL by the fabrication of floating gate field effect transistor memory devices. The charge trapping layer is comprised of well-ordered polymer/gold NP composites prepared via additive-driven self-assembly; the addition of gold nanoparticles that selectively hydrogen bond with pyridine in poly(styrene-b-2-vinyl pyridine) copolymers yields well-ordered hybrid materials at gold nanoparticle loadings of more than 40 wt%. The charge trapping layer is sandwiched between a dielectric layer and a poly(3-hexylthiophene) semiconductor layer. We can achieve facile control of the memory windows by changing the density of gold nanoparticles. The devices show high carrier mobility (> 0.1 cm2/Vs), controllable memory windows (0~50V), high on/off ratio (>105) between memory states and long retention Strategies for extending the fabrication of these devices to R2R including microgravure coating of the active layer, the incorporation of solution coat-able high-k layers for low voltage operation, and patterning of the device using NIL will be discussed. For the latter we use a solution etch through a NIL mold to pattern Cu top contacts.

Direct stamping of functional nano-inks has been developed for cost-effective and process-effective manufacturing of functional nano/micro structures of semiconductors and conductors. We have demonstrated facile fabrication of flexible strain sensors that have micro-scale thick interdigitated capacitors with no residual layer by the direct stamping. Every step of the direct stamping is simple to be adapted for a roll-to-roll process combined with spraying of nano-inks. A tabletop prototype of the roll-to-roll direct stamping apparatus has been developed to include all the features like filling the stamp with the nano-ink, removing the residual layer, stamping, UV-curing and de-stamping while the apparatus is run by rollers and motors.. The fabricated prototype&’s size is about 100cm long, 30cm wide and 40cm high. While upper rollers carry a web with a patterned stamp on it counterclockwise, a sprayer on top of the roll-to-roll apparatus dispenses the nano-ink to fill the stamp. Another roller with an adhesive film completely removes the residual layer on the stamp rolling over the stamp on the web. A substrate with adhesive layer moves under the web to the right and contacts the stamp. Both stamping and UV-curing occur where the substrate and the stamp on the web make contact. Final products remain on the substrate after de-molding in which the web rolls up and the substrate moves to the further right. The roll-to-roll direct stamping apparatus demonstrates high throughput and material efficiency for fabrication of micro- and nano-electronic devices. 1. J. Kim, P. Lin, W. S. Kim, “Mechanically robust super-oleophobic for direct stamping of silver nanoparticle ink,” Thin Solid Films, 520 (2012), 4339 2. J. Kim, K. Wubs, B. S. Bae, W. S. Kim, “Direct stamping of silver nanoparticles toward residue-free thick electrode,” Sci. Technol. Adv. Mater., 13 (2012), 035004

Adapting soft lithography to roll-based printing processes is a promising technique for large area, high rate patterning of micron and sub-micron features. In particular, microcontact printing offers a viable means of patterning metallic conductors on photovoltaic or flexible electronic devices. Precise control of the stamp contact region in rolling machinery is a significant engineering challenge. This paper reviews the sensitivity of the stamp contact behavior, presents a machine and control algorithm designed for sub-micron contact manipulation, and highlights progress in printing patterns with single micron length scales. The elastomeric stamps used in soft lithography (typically polydimethylsiloxane, PDMS) deform or collapse at moderate contact pressures. A study of stamp feature behavior [1] provides design guidelines for robust stamp design (e.g. feature aspect ratio). Even optimally designed feature collapse under pressures that are only a fraction of the stamp modulus. Analytical and experimental approaches show that these pressures can occur at single microns of roll displacement in roll-to-roll printing [2,3]. This collapse displacement represents a very narrow process window and requires high precision in printing machinery. A two degree-of-freedom lab scale rolling stage has been constructed for roll-to-plate printing of 100 mm wide substrates with 180 nm position resolution [4,5]. This paper presents an impedance control strategy that provides good disturbance rejection for high-fidelity printing, even when roll, stamp, or substrate dimensional errors are much larger than the process window. Experiments using in-situ contact measurement show that this machine and control strategy can maintain contact fidelity (i.e. full stamp contact with no feature collapse). Ultimately, the utility of this machine and control strategy are demonstrated by highlighting recent results in printing sparse conductive traces with silver nanoparticle inks. Sparse patterns (e.g. thin film transistor interconnects or transparent conductor traces) are very difficult to print without feature collapse. Using this machine and control strategy with PDMS stamps for high resolution flexography, line widths of 5 um or less can be printed on glass or polymer substrates. Results will be shown from a sparse pattern with a fill factor less than 10%. [1] Petrzelka & Hardt, JMM 2012 (accepted) [2] Petrzelka & Hardt, MRS Fall 2011 [3] Petrzelka & Hardt, ASME JMSE (in draft) [4] Petrzelka & Hardt, ASPE 2011 [5] Petrzelka & Hardt, Prec. Engr. (submitted)

Transfer printing has proven to be a versatile tool for deterministic assembly of two and three dimensional structures of diverse materials, with feature sizes from the cm to the nm range. Some of the most compelling application opportunities are in electronic and optoelectronic devices that combine high performance inorganic semiconductor materials in the form of nanomembranes/ribbons/wires with unusual substrates, such as sheets of plastic or slabs of rubber. In these and other cases, advanced designs in stamps for transfer printing are critically important. This talk will describe two such designs: (1) pneumatically controlled structures in stamps with programmable configurations for improved versatility in the printing, and (2) anisotropic relief features in stamps with direction-dependent adhesion for continuous, roll-to-roll operation.

Abstract: Tip based lithography was used to print large, regular arrays of 200 nm cobalt oxide nanoclusters over millimeter areas onto silicon dioxide substrates. Carbon nanotubes (CNT) were grown from each cobalt oxide nanocluster by introducing the sample into a furnace and exposing it to acetylene at 700 °C. The result is tunable arrays of carbon nanotubes positioned accurately onto a surface. This method is capable of printing single metal particles to a surface and growing single carbon nanotubes from each location. The cobalt oxide arrays are formed by first mixing Co(NO3)2 into a P2VP-PEO block co-polymer aqueous solution. The polymer acts as a transfer agent to print sub micron sized droplets using parallel printing from multiple cantilever based pens. The substrate is then heat treated to decompose the polymer leaving behind nanoclusters of Co3O4 (XRD analysis) in arrays defined by the software. These features proved to be excellent catalysts for growing multi-walled CNTs from each printed position. Arrays as covering a square millimeter containing over 65,000 features can be printed within 2 hours. Single features can also be easily deposited onto specific surface structures like electrodes or sensors. The morphology of the nanoclusters and carbon nanotubes were examined with SEM and AFM microscopy. The Carbon structures were interrogated with Raman spectroscopy. This can be an excellent technique to create carbon nanotube sensors as the cobalt oxide nanoclusters can be placed with nanometer scale precision onto existing features.

Commercialization of materials utilizing patterned carbon nanotube (CNT) forests, such as hierarchical composite structures, dry adhesives, and contact probe arrays, will require catalyst patterning techniques that do not rely on cleanroom photolithography. We demonstrate the large scale patterning of CNT growth catalyst via a laser printing process that uses magnetic ink character recognition (MICR) toner. The MICR toner contains iron oxide nanoparticles that serve as the catalyst for CNT growth, which are printed onto a flexible polymer (polyimide), and then transferred to a rigid substrate (silicon or alumina) under heat and mechanical pressure. Then, the substrate is processed for CNT growth under a normal C2H4-based chemical vapor deposition (CVD) recipe. We show that CNT density can be controlled by the laser intensity or grayscale pixilation, that the minimum feature size with a standard office printer is 40 µm (one grayscale dot), and that virtually any pattern can be designed using standard software (e.g. MS Word, AutoCAD, etc.) and printed on demand. Based on SAXS, SEM and TEM analysis, forests grown from laser printed catalyst are shown to have comparable CNT diameter, alignment, and density to those grown with standard thin-film catalysts. This novel process shows promise to enable high-speed micro patterning of catalyst thin films under ambient conditions.

In the rapid development of nanotechnology, the demand for low cost high-through-put technologies of fabricating micro and nanometer structures which can be used in micro-electro-mechanical systems and biophysics is increasing. There are many techniques like injection molding, (roll-to-roll) nano-imprinting and PDMS casting which enable low cost and high- through-put replication of polymer structures with features on the micro- as well as on the nano-scale. In order to improve these techniques, we need a strong and stress free Ni mold. Electroplating is an attractive technique to fabricate micro and nanostructures in Ni. Here we discuss suitable photoresists that can be patterned with proton beam writing (PBW) down to the sub-100 nanometer level. These resist can be removed after Ni plating to yield high quality Ni molds with 3D nanofeatures. PBW is a new direct-write technique which uses a focused MeV proton beam to pattern photoresist. This process is similar to electron beam writing, however, because of the large mass of the proton, it has several advantages compared with electrons used for lithography in electron beam writing. A proton can penetrate to a very large depth while maintaining a straight path. Since the proton mainly scatters from electrons in the substrate it shows no proximity effects. This allows PBW to fabricate three-dimensional, high density and high aspect ratio structures with vertical, smooth sidewalls and low edge roughness (~2.5 nm RMS). For very small and high aspect ratio structures negative resist removal can be challenging after Ni electroplating. In order to overcome this problem, we test several resists for PBW and mold fabrication. For the negative photoresist-ma-N 2401 and positive photoresist-PMMA, we have obtained 60 nm wide structures. However, after electroplating ma-N 2401 is very difficult to remove, while the PMMA can be removed easily. For ARP series resist and ma-N 2410 photoresists, removal is challenging for feature sizes below 150 nm and aspect ratio higher than 2. The Ni molds have been used in both injection molding and nano-imprinting experiments. Structures down to 500 nm in width (1 µm height) and 200 nm in width (270 nm height) have been replicated into PMMA through injection molding and nano-imprinting respectively. We are developing these Ni molds as a tool for nanofluidic lab on chip fabrication for single molecule study via nano imprint lithographies. Important here is the reduction of stress in the Ni molds for high quality reproduction of high aspect ratio nanofeatures.

To address the vast market potential that is foreseen for thin film transistors (TFTs) on polymeric substrates in the fields ranging from radio frequency identification (RFID) tags to solar cells, displays and sensor arrays, faster and much cheaper routes for production have to be developed. Precise lateral alignment of the source and drain electrodes of the TFT with respect to its gate electrode are of particular relevance to the performance. On the way to roll-to-roll mass production we have developed a process that eliminates costly and time consuming alignment steps and is compatible with the use of flexible polymeric substrates. Our approach consists of four steps[1] starting with the application of a multi-material continuous stack onto a flexible polymeric substrate. Partially anodized aluminum is included to construct the gate electrode (aluminum) and gate dielectric (aluminum oxide) of the transistors while gold is added to provide the source and drain electrodes. Subsequently a layer of thermal imprint resist is applied and a multilevel pattern having the gate, source and drain structures intrinsically aligned, is applied in a single imprinting step. From this point on all structures conform coherently to any possible deformations of the substrate making sure that alignment is maintained throughout the process. One by one the patterned levels are removed and transposed into the underlying functional layers by series of selective etching steps. Finally the obtained structures are completed into functional devices by applying the semiconductor using ink jet printing. Transistors fabricated by this method show mobility values around 0.5 cm2V-1s-1 as can be expected using tips-pentacene as a semi-conductor. Taking the non-patterned continuous stack of materials as a point of departure allows us to use the aluminum gate layer as an electrode to grow anodized aluminum oxide as a gate dielectric material. Its dielectric properties combined with the low concentration of conductive defects that is inherent to the nature of the anodization process are major advantages contributing to the high yield ratios (220 out of 220 for 20µm structures) and the high on/off ratios (>106) that are obtained. Acknowledgement This work has been carried out within the ORICLA project which is funded by the European Union (FP7-ICT No. 247798) [1] Qin et. al. Adv. Func. Mat. 2012, vol22, p1209-1214

With the shift from the development of processes for silicon wafer platforms to the development of manufacturing platforms for fabrication of low-cost, large-area nano-materials and devices using roll-to-roll processing technology, new opportunities and challenges are presented. We have built a roll-to-roll nanoimprint (R2RNIL) facility to address the challenge of fabricating nanostructured thin films on a high-speed, high-reliability platform. The goal of our work is to enable commercialization of R2RNIL by any number of entities for a wide variety of end-applications ranging from sensors, water purification, batteries and thin film organic electronic devices. Fast R2R processes have several stringent requirements in terms of the selection of materials for imprint. First, liquid resists having good coating properties are preferred because they can be continuously and uniformly coated onto plastic substrates and be easily imprinted with low pressure - imprinting will be done under web tension only. Second, such liquid resists should have low viscosity before curing for fast imprinting. Third, resists used in R2RNIL need to be quickly cured and with minimum shrinkage after curing. We initially pursued UV-curable compositions as thermoplastic materials used in NIL processes require very high pressures and relatively long processing times to complete the imprinting. We note that UV curing can be accomplished in seconds. The proper choice of mold material and surface chemistry is a critical component of the successful implementation of this R2RNIL. We report the use of a range of different silicones and fluoropolymers in the NIL process. Our initial focus has been to generate molds of optical gratings of periodicities and aspect ratios. We will report our results, including the fabrication of 70nm grating arrays and demonstration of applications of R2R-fabricated sensors and detectors. Key challenges and findings will be outlined in the selection of mold-materials, resists and amelioration of defects.

The ability to pattern materials at the nanoscale can enable a variety of applications ranging from ultra-high density data storage, nanoelectronics, displays, photonic devices and CMOS integrated circuits to emerging applications in the biomedical and energy sectors. These applications require varying levels of pattern control, short and long range order, and have varying cost tolerances. Extremely large area R2R manufacturing on flexible substrates is ubiquitous for applications such as paper and plastic processing. It combines the benefits of high speed processing and inexpensive substrates to deliver a commodity product at low cost. The challenge is to extend this approach to the realm of nanopatterning and realize similar benefits. The cost of manufacturing is typically driven by speed (or throughput), tool complexity, cost of consumables (materials used, mold or master cost, etc.), substrate cost, and the downstream processing required (annealing, deposition, etching, etc.). In order to achieve low cost nanopatterning, it is imperative to move towards high speed imprinting, less complex tools, near zero waste of consumables and low cost substrates. The Jet and Flash Imprint Lithography (J-FIL) process uses drop dispensing of UV curable resists to assist high resolution patterning for subsequent dry etch pattern transfer. The technology - including tools, materials and templates - have been developed for ultra-high denisty data storage including semiconductor memory and patterned media for hard disk drives. Here, the key challenges for roll based nanopatterning is discussed by introducing a novel concept: Ink Jet based Roll-to-Roll Nanopatterning. To address this challenge, we have introduced a J-FIL based demonstrator tool. Topics that are discussed in the paper include tool design, process innovation and process performance including process reliability. In addition, we have used this tool to fabricate high performance wire grid polarizers (WGP) on flexible polycarbonate (PC) films. Transmission of better than 80% and extinction ratios on the order of 4500 have been achieved. WGPs are used as exemplary devices to study the robustness of the tool and process technologies to create > 1,000 devices.

We contribute a fast numerical approach to simulating the roller-imprinting of complex patterns. The technique predicts the extent to which imprinted patterns are fully formed, as well as variation of the imprinted material&’s residual layer thickness (RLT). Process development for roller imprint is often done experimentally, which is laborious and wasteful of materials. Some use has been made of analytical squeeze-flow models, which predict average RLTs but take no account of material flow at the scale of nanofeatures. Our new technique builds upon a simulation system for wafer-scale nanoimprint that we have previously developed and validated experimentally with several thermoplastic resists (SPIE 764129). Our technique describes the deformation of the imprinted material using the response of its surface topography to a normal mechanical impulse applied to a small region. The elastic deformation of the roller(s) and substrate are described by point-load responses. The technique finds the evolving pressure distribution experienced by the web as it moves in contact with the roller. The approach can be used for roll-to-roll and roll-to-plate configurations, and for rollers with or without elastomeric coatings. If patterns vary in pitch, shape or areal density across the roller, RLT and the completeness of pattern transfer can vary with position as well as with processing parameters, and our technique captures these effects. A typical imprinting process can be simulated within two minutes using a standard personal computer. When the resist is a UV-curing resin, we employ a purely viscous resist model, and our technique reproduces the inverse-square-root relationship between roller pressure and RLT, and the square-root relationship between web speed and RLT observed by Ahn and Guo (ACS Nano 3, 2304). When the imprinted material is thermoplastic, meanwhile, a viscoelastic model is needed, particularly if the material is a high-molecular-weight, highly entangled network that constitutes the web itself. We show that a Voigt model—with a viscous component and a limiting elasticity—can explain the relationship that Mäkelä et al. found between the depths of imprinted nanostructures and the speed of a cellulose acetate web softened only at its surface (Microelectron Eng 88, 2045). We also predict that there exists an optimal web speed if there is a fixed distance between the place where pressure is applied and that where the imprinted material is cooled or cured. While slower web speeds allow nanostructures to be more fully formed by the patterned roller, longer delays before resist solidification permit shape recovery driven by material stresses or by surface tension. We argue that pattern formation and dissipation compete to give an optimal processing rate that maximizes pattern fidelity. This insight could inform machine design as well as process development.

The structure resolution of mass printing processes such as flexographic printing, gravure printing, screen printing or offset printing is typically found in the range of 100µm. There are patterning techniques compatible with roll-to-roll manufacturing such as laser ablation and ink jet printing that have been shown to be capable of producing features with dimensions down to 10µm. However, since there is always a trade-off between throughput and minimum feature size these serial patterning techniques are not compatible with industrial and low cost production. Contrary, roller-based imprinting processes such as UV-nanoimprint lithography and hot embossing are capable of patterning on the nanoscale with production-fit throughput thus paving the way for high-resolution patterning on large flexible areas. In this paper an overview is given on the worldwide activities in R2R-nanoimprinting including an introduction to the versatile rotary imprinting techniques. It will be shown that substantial effort is necessary to optimize the imprint resist, the material and fabrication of the stamps as well as the surface treatment of the imprint tools. Applications ranging from large area surface functionalization via micro- and nanopatterns to first steps in electronic device manufacturing will be presented.

Three related thin-film stamping techniques recently enabled development of pixelated quantum dot LEDs, patterned molecular LEDs, and large-area MEMS arrays. The additive stamp-printing of patterned single layers of colloidal quantum dots (QDs) led to development of high-efficiency QD-LEDs. The subtractive stamp-printing of molecular multilayer films generated the highest resolution printed molecular LED patterns. The print-transfer of macroscopic metal films of nanoscale thickness dramatically simplified fabrication of macroscopic MEMS arrays. The talk will quantify the nano-scale mechanisms behind the above thin-film stamping techniques, enumerate the device technology advancements that these new nano-scale manufacturing processes already brought, and project on how will they further extend the state of the art of large-area nano-scale fabrication.

We report chemically-coupled chlorosilane-terminated polystyrene (PS-brush) layer for high-performance all-inkjet-printed inverter using two p-type organic thin-film transistors (OTFTs) on a flexible poly-arylate substrate. Inkjet-printing technology is one of the most promising methods for OTFT fabrication due to its easy and low-cost process. However, all-inkjet-printed OTFTs, thus corresponding circuits typically show poor electrical performance and high-voltage operation because of difficulty in full integration of surface treatment process, access to high-performance materials. Although in order to achieve better OTFT electrical performance, surface treatments between gate dielectric layer and organic semiconductor layer has been adopted by using self-assembly monolayer (SAM), they require the immersion process for a long time, thus are not suitable in inkjet-printing process. In addition, source/drain (S/D) metal surface has been additionally treated for better contact behavior with organic semiconductor layer. Therefore, we applied the coil-like PS-brush layer on surface of both S/D electrodes and dielectric layer simultaneously for high-performance all-inkjet-printed flexible inverter by using inkjet-printing process. PS-brush layer not only removes the hydroxyl group at the gate dielectric, but produces chemically coupled PS-chains at S/D electrodes resulting in excellent electrical performance and physical contact property with organic semiconductor layer. For inverter fabrication, Ag ink and PVP solution were printed to form a gate electrode and gate dielectric layer on poly-arylite substrate, respectively. For S/D electrodes fabrication, interdigitated Ag S/D electrodes were defined by inkjet-printing which had channel width / length of 250 mu;m / 90 mu;m and 14000 mu;m / 100 mu;m for load and drive OTFT, respectively. After PS-brush layer were formed using inkjet-printing process, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) layer was printed. The fabricated inverter showed a full up-down switching performance with a gain of -8.2 V/V at supply voltage of -20 V and a maximum gain as high as -20 V/V at supply voltage of -40 V. In addition, even after 1000-time bending stress test with speed of 10 mm/sec and bending radius of 5 mm, frequency response up to 50 kHz and an excellent stable performance with gain of -5.5 V/V at -20 V were sustained. In addition, contact property improvement was also verified by scanning kelvin probe microscopy. These better performances came from PS-brush layer on PVP dielectric and inkjet-printed Ag S/D electrodes. From these results and analysis, we believe that the PS-brush layer can improve the electrical performance of inkjet-printed electronics. This work was supported by the Industrial Strategic Technology Development Program (KI002104, Development of Fundamental Technologies for Flexible Combined-Function Organic Electronic Device) funded by the Ministry of Knowledge Economy (MKE, Korea).

The improvement of organic electronics materials has offered the possibility to manufacture a variety of devices in different fields of electronics, including OLEDs, solar-cells, sensors and transistors, and to integrate these into circuits. However, many of these devices have been produced using low throughput processes like vacuum evaporation, lithography or spin-coating. Here, we present three different rectifying circuits for high-frequency applications which are manufactured using only scalable printing processes. Due to the characteristics of the printed devices, the circuit operation may differ from the silicon based solid state circuits. Therefore, we also present a consistent performance comparison between the different circuit architectures. A half-wave rectifier, consisting only one rectifying diode and a filtering capacitor, is the simplest rectifying circuit and has been studied by many research groups. Important information about the diode AC operation can be obtained by studying the half-wave rectifier circuit. We present a gravure printed rectifying diode with high yield, high rectification ratio and good AC performance at 13.56 MHz. In addition, a full-wave bridge rectifier circuit is monolithically gravure printed using a similar diode structure. The output voltages of the half-wave and the full-wave rectifier are limited by the input signal amplitude. However, the DC supply voltage required for organic thin film transistors, for example, is generally higher than the available AC signal amplitude in wireless applications. Therefore, a printed AC-DC type charge pump circuit is presented for DC output voltages that exceed the input signal amplitude. The charge pump output characteristics are studied using different number of stages and different loading of the circuits. The operation of the printed rectifier is dependent on the input signal magnitude and the output load properties. Therefore, suitability of the circuit architectures for different applications is discussed. The benefits and drawbacks of the circuits are presented and the development prospects are estimated for each circuit.

We have manufactured printed organic thin-film transistors with floating gate structures on 13-mu;m thin-film plastics and applied for ultraflexible active matrix organic LED pixel circuits. It is demonstrated that printed floating-gate organic transistors can compensate LED brightness variations and degradation for more than 6 months. The 230×230 mm² printed active matrix circuit comprises 64×64 screen-printed organic 2-transistor-1-capacitor cells. The feasibility of ultra-flexible floating gate transistors for applications to medical sensors and other applications will be also demonstrated.

Printed electronics with functional liquid inks is an attractive approach for achieving flexible and low-cost back-planes for bendable, large area displays and other electronic applications. Challenges remain in printed electronics however, which concern the development of high-performance and low-cost TFTs backplanes for flat panel displays (FPDs). To achieve working products, it is important to systems that are easy to process must be fabricated on desired surfaces, with high integration levels. In particular, even though active-matrix displays with printable, novel semiconductors are attractive among FPDs, it is difficult to routinely fabricate working prototypes because soft materials that have electrical and mechanical properties comparable to conventional semiconductors such as a-Si/poly-Si are not available. However, the combination of already existing printable high-mobility semiconductors with suitable device architectures is anticipated to be a potential solution. Here, we demonstrate flexible displays such as e-paper and polymer dispersed liquid-crystal (PDLC), where inkjet-printed organic thin-film transistor (OTFT) arrays are used to drive the panels. For the production of well-defined and very uniform printed OTFT arrays, we have molecularly designed ambient processable functionalized conjugated copolymers with a liquid-crystalline nature, which result in high-performance OTFTs once integrated as the active layer. Morphological and structural studies reveal that the polymer chains are well ordered in the nanoscopic and macroscopic level, which is extremely beneficial for the enhancement of TFT performance in terms of charge carrier mobility and subthreshold swing. In addition, we have conducted post-treatment processes of the inkjet-printed OTFTs to improve their stability with respect to the environment and electrical bias stress.The treatments resulted in the reduction of deep trap states in the channel layer and hence rendered the material more resistant to the ambient and bias stress. Also, we briefly intend to show all-printed TFTs for next generation electronics. Our approaches are expected to enable the realization of a new-concept of displays, and offer a promising solution for the advancement of future displays.

Applications of electrochromic (EC) technology in the field of embedded displays are attracting widespread attention in both academic and industrial community. Examples of these applications include transparent displays, smart windows, smart packaging, electronic paper and flexible displays. We are demonstrating an effective and scalable to mass production strategy for creating high performance EC devices that meets the demands of each of those applications. In this study, all-solid-state planar structure EC devices consisting of two TCO coated substrates, dual-phase a-WO3/TiO2/WOX EC film and new class of thermosetting solid state electrolyte were assembled and successfully operated. An innovative approach involves application of Printing Technologies (inkjet-, screen-printing) to deposit inorganic EC materials based on sol-gel technique, in which additionally the film crystallinity can be controlled in a low T process by addition of nanoparticles into liquid precursor. The grain size, crystallinity and stoichiometry of those particles are dependent only on the origin of crystals and are defined at the ink formulation stage. Those optically active films outperform their amorphous or nanocrystalline analogues presented in the state-of-the-art, owing to their superior switching time (<3s) optical density (0.7) and extremely low power consumption. Novel, solid state electrolytes were drop casted or screen printed and cured in-situ, using Succinonitrile as a solvent for lithium salt, thermosetting resin as a matrix and metal oxide nanoparticles as filler. We are also presenting experimental data related to ionic conductivity (10-6-10-4 Scm-1@RT), spectral response, mechanical strength and various structural characterizations. The combination of both components conveys excellent mechanical, electrical and optical properties of prototype displays and EC windows, which overall performance is also discussed.

Newer and better capacitors will be required to allow switched capacitor DC-DC converters to transition to higher-power applications including drivers for LED lighting and voltage conversion for photovoltaic panels. These improved capacitors must combine high frequency performance with low leakage, and low loss. Continuous fabrication on flexible substrates will drive down cost and enable novel form factors and applications. We have developed a method for fabricating capacitors using printed nanoparticle dielectrics for power conversion applications. Whereas standard ceramic capacitor manufacture requires a high-temperature firing step, our printed capacitors are fabricated using only low-temperature processing, and thus enable flexible, configurable high-throughput deposition onto a polymer substrate at low cost. We demonstrate a new class of printed high-frequency capacitors for power conversion applications, using a dielectric ink comprised of barium strontium titanate (BST) nanocrystals in suspension. The nanocrystals are synthesized using a low-temperature solution process, and are deposited on both glass and flexible polymer substrates. Deposition methods include a roll-to-roll compatible spray coating process, as well as spin-coating. These capacitors exhibit single-layer capacitance density in excess of 0.5 nF/mm^2, and have been fabricated in areas as large as 800 mm^2 and multilayer stacks of up to 4 dielectric layers. Dissipation factor at 1 MHz is below 0.05, and operating voltage up to 20 V has been shown. Both spray-coated and spin-coated capacitors were integrated to an off-the-shelf 1 MHz charge-pump LED driver circuit, configured as the power-handling flying capacitors. Circuit performance was comparable to that obtained using industry-standard multilayer ceramic capacitors.

Gravure printing has emerged as one of the most attractive techniques for the realization of printed electronic circuits due to its high throughput, excellent scalability, and superb pattern fidelity. In recent years, gravure printing has been used to realize high performance printed transistors, and has further, been deployed to realize RFID tag circuitry of varying degrees of complexity. To ensure the viability and continued scalability of gravure printing, it is crucial that the various fluid mechanical effects present during gravure printing be understood and modeled. Here, we review our work developing models to describe the effect observed during gravure printing during inking and wiping of the gravure cylinder, as well as during transfer and subsequent drying. We observe the competition during capillary effects and the doctor blade speed during filling, and describe the impact of ink and printing parameters on subsequent wiping. By coupling these results to ink transfer mechanisms, we are able to establish parametric relationships between ink and printing parameters and final pattern features. Based on this understanding, we next describe the realization of highly-scaled gravure printed organic transistors with >1MHz switching speed, realized using femtoliter-scale gravure printing to achieve sub-10um feature sizes. The transistors are realized at printing speeds of ~1m/s, attesting to the attractiveness of gravure printing for viable printed electronics applications.

Recent advances in printed electronics have led to the all printed central processing unit (CPU) to fabricate microprocessor which consists of arithmetic and logic unit (ALU), memory, data bus, etc. by all printing processes directly onto flexible substrate. The fundamental block of the printed CPU is the printed arithmetic unit which performs arithmetic operation such as addition, subtraction, multiplication and division. In this research, 4 bits adder/subtracter arithmetic unit is formed on flexible plastic substrates by fully gravure printing process. Based on our formal research results, nanoparticle-based silver inks for conductive ink, the network structure of single walled carbon nanotubes (SWNTs) for semiconductive inks and BaTiO3 nanopoweder hybrid ink for dielectric ink have been employed to print the 4 bits adder/subtracter arithmetic unit.

Printing techniques promise low-cost high-volume fabrication of flexible electronics. In particular, gravure printing is a very promising method for high throughput device fabrication on a batch or roll-to-roll format. This talk will present results from gravure printing of thin-film dielectrics using proprietary research formulations of BASF for organic thin-film transistors (TFTs). The work demonstrates a formulation which is not only suitable for gravure printing but can be also cross-linked via UV exposure for additional patterning, robustness and insolubility. Good printing uniformity over large areas and low surface roughness, ca. 1 nm, are shown via optical inter