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 interferometry and atomic force microscopy. The dielectric film is characterised electrically by impedance spectroscopy and current-voltage measurements. Films with thickness around 100 nm are gravure printed on 50×50 mm² substrates and incorporated in TFT structures. The TFT configuration is bottom-gate bottom-contact with TIPS-pentacene (6,13-bis(triisopropyl-silylethynyl)pentacene) as the semiconductor. For optimal semiconductor performance the surface of the dielectric is modified with ultra-thin layer of poly(α-methylstyrene) (PαMS). The charge-carrier mobility is of the order of 0.2 cm²/Vs which is comparable to the best values reported for this semiconductor in bottom-contact TFTs[1,2]. The dielectric thickness is about 15-fold lower than the present state-of-the-art gravure printed dielectrics[3] and approaches the electrical performance of thin cross-linked dielectrics on rigid substrates[4]. The low dielectric thickness affords operational voltage below 10 V which is essential for low-power and portable electronic applications. [1] X. Li, W.T.T. Smaal, C. Kjellander, B. van der Putten, K. Gualandris, E.C.P. Smits, J. Anthony, D.J. Broer, P.W.M. Blom, J. Genoe and G. Gelinck, Org. Electron. 12, 1319-1327 (2011). [2] B.K.C. Kjellander, W.T.T. Smaal, J.E. Anthony and G.H. Gelinck, Adv. Mater. 22, 4612-4616 (2010). [3] J. Noh, S. Kim, K. Jung, J. Kim, S. Cho and G. Cho, IEEE Electr. Device L. 32, 1555-1557 (2011). [4] X. Cheng, M. Caironi, Y.-Y. Noh, J. Wang, C. Newman, H. Yan, A. Facchetti and H. Sirringhaus, Chem. Mater. 22, 1559-1566 (2010).

Transferring inorganic electronic devices on flexible substrate is one of the most promising candidates to fabricate flexible electronics. Comparing with the conventional fabrication process by which organic devices are directly printed on flexible substrates, it is possible to fabricate the flexible electronics with high performance since the transfer process has benefits to utilize the devices that are fabricated on silicon substrate under high temperature process. In addition, the continuous fabrication process with high productivity can be easily realized by transferring the devices by roll stamp. The roll transfer process is more suitable for scale-up of transfer process than the transfer process based on flat stamps due to alignment issue. We developed the transfer process machine with the roll stamp, and transferred inorganic thin films to investigate wrinkle and crack generation during the process. The failures such as wrinkle and crack are caused by the contact mechanics of roll stamp. Main elements to decide the deformation of the roll stamp are nip pressure of contacted roll stamp, synchronization between angular velocity of the roll stamp and translational velocity of the sample stage, and design of the roll stamp and the devices. To manifest how the failure mechanism is affected by the elements in the roll transfer process, the experiments are performed with various settings, i.e. contact pressure controlled by feedback systems, ratio of velocities between the roll stamp and the stage, and the design of the hybrid roll stamp. After transferring thin films on flexible substrates, the wrinkles and crack formation are observed optical microscope and surface profiler. Finally we compared the experimental observation with numerical simulation using finite element method to develop how to control the damages during the roll transfer process.

Development of low cost, time effective, scalable transfer method for oxides based thin film transistors (TFTs) together with the integration to nonconventional substrates can be of great significance for realizing the large area flexible, stretchable electronics in real life. Transfer method is required in order to avoid the direct fabrication on nonconventional substrates as it restricts the high temperature processing which improves the quality of TFT active layers: gate dielectric, channel layer, electrode contact and interface between channel and gate dielectric. In-Ga-ZnO (IGZO) based TFTs attracted much attention due to their higher current driving capability than the hydrogenated amorphous silicon (a-Si:H), superior scalability and high optical transparency for an active matrix in OLED displays. Here, we developed an automated roller system for transferring the IGZO TFTs from high temperature endured rigid Si substrate to stretchable rubber like substrate. IGZO TFT showed good electrical performance after transferring by developed automated roller system. Fabricated TFTs are designed to encapsulate in such a way that after transferring, wrinkles can form which can provides the stretchability to the TFT circuitry. TFT also showed the good electrical performance under stretching and repeated cyclic tests. Strain values experienced by device active layers during the transfer are simulated and its effect on device performance is investigated. The proposed transferring method opens a way for realizing the large area fabrication of oxides based systems in flexible electronics.

Ultraviolet photodetectors with high detectivities and fast response times are required for many applications. We will present low-cost organic photodiodes that absorb into the deep UV, with responsivities of 0.1 A/W at 300 nm [1]. These photodiodes have a P3HT:PCBM active layer and an inverted device structure with illumination through the top electrode. The device structure prevents blocking of UV light by glass and commonly used ITO electrodes and allows for easier integration with other semiconductor components. All devices are free of ITO and PEDOT:PSS. Recent work using low-temperature, solution processed ZnO layers to increase UV absorption and to act as hole blocking layers will be reported. We will discuss design considerations for the photodiodes, using a transfer matrix model to optimize their performance with particular consideration of the transparent electrode. We will show that single layer graphene is beneficial relative to conventional electrodes in these devices, leading to high detectivity and responsivity over a wide spectral range. A comparison of the optical response of devices with organic materials having different band gaps will be presented. Finally, the devices can be fabricated on a flexible substrate and still function under bending, allowing for the possibility of novel applications. [1] Burkhardt, M.; Liu, W.; Shuttle, C. G.; Banerjee, K.; Chabinyc, M. L. Applied Physics Letters 2012 accepted.

Roll-to-roll (R2R) gravure printing is a promising method for the manufacture of thin film transistors (TFTs) for the flexible and low cost electronics. To obtain printed stable and high performance TFTs using R2R gravure printing process, R2R gravure printer should provide fine patterns and smooth surface morphology of gate electrode and dielectric layer. Furthermore, among a couple of extra key issues in R2R gravure systems, the degree of the registration accuracy between gate electrodes and drain-source electrodes are one of the most important one to provide reliable and constant printed TFTs. In this study, the registration accuracy of R2R gravure was controlled between 100 mu;m to 20 mu;m while printing TFTs with the channel length of 200 mu;m on PET foils while printing speed, web tension, impression roll pressure, drying temperature and groove cell structures were all kept constant to figure out the role of registration accuracy on the electrical fluctuation of printed TFTs. The detail results to achieve narrower distribution of threshold voltages for printed TFTs will be reported.

The most common materials of choice for printed flexible electronics are currently organic semiconductors. However, the issue concerning these materials is the low charge carrier mobility, limited to only few cm2/Vs. Nanomaterials such as inorganic semiconducting nanowires are offering significantly higher charge carriers mobilities due to their single-crystal nature. High length/diameter ratio allows to achieve two-fold advantage: 10-20 micron nanowire length is sufficient to bridge realistic device channel gaps, whereas few tens of nanometer diameters can be efficiently depleted in field-effect devices. Importantly, these nanomaterials can be dispersed in a variety of solvents to form functional ‘inks&’, opening up possibilities for low-temperature deposition envisioned for printed electronics. Applications for such materials extend to electronic circuits, photovoltaic energy conversion, sensor elements, light emitting structures, nano-structured electrodes for batteries, and miniature piezo elements converting movement into electric energy. In this work we focus on nanowire applications as semiconducting elements in solution processable field-effect transistors for large area electronics. To realise high performance printed field-effect transistors with effective channel mobility of few hundred cm2/Vs we address several main challenges, including nanowires deposition and alignment, contact metallisation and effects of surface states. Here we introduce two new dispersion deposition methods allowing one-step coating and alignment of nanowire arrays on host substrates, explore ink-jet printing of metal nanoparticles inks for device electrodes, investigate formation of ohmic metal/semiconductor contacts on nanowires by varying metal work function, and reduce electrical hysteresis effects caused by surface states by using hybrid organic/inorganic device structures with organic gate dielectric layers. Finally, we compare performance of solution-processed nanowire transistors with similar devices based on organic semiconductors, discuss a transition from a waver-scale fabrication to roll-to-roll processing and offer a perspective on application of nanowires for printed electronics.

A novel screen-printable conductive silver ink that can be sintered at low temperatures (< 120 °C (248 °F)) is presented. The low processing temperature renders these inks suitable for printing conductive patterns on temperature-sensitive flexible substrates such as PET films. The ink ingredients include silver flakes (particle size in the range of 0.6 - 8.0 mu;m), an organometallic silver salt, an accelerator and a propriety solvent system. This binderless silver ink can be thermally converted into pure metallic patterns containing without any binder and less than 1% organic residue. The organometallic silver salt thermally decomposes with the aid of an accelerator to produce reactive silver. The reactive silver thus generated chemically welds the silver flakes. The silver traces having an electrical conductivity within two orders of magnitude of elemental silver can be formed using these inks. Thermogravimetric analysis was used to determine the role of accelerator in lowering the degradation temperature of the organometallic silver from 122 °C (248 °F) to about 90 °C (194 °F). Several factors influence the conductivity, cohesion (particle-to-particle) and adhesion (particle-to-substrate) of the conductive traces. These factors were optimized using orthogonal experimental design. In order to assess the suitability of the ink for commercial roll-to-roll manufacturing processes such as screen, flexographic or gravure printing, the rheological properties were also studied. The inks show shear thinning behavior and the viscosity is in the range of 5.0-6.6 Pa`s at 1000 s^-1. These inks can be used in a wide variety of applications ranging from interconnects in organic photovoltaic solar cells (OPV) and organic light emitting diodes (OLED) to printed radio frequency identification devices (RFID) antennae and membrane switches.

Transparent conductors are mainly used in organic electronic devices, such as organic solar cells and organic light emitting diodes. The most widely used transparent conductor is indium tin oxide (ITO). However, increasing indium price, low flexibility and low chemical stability are seem the main disadvantages of ITO. Hence investigation of alternative transparent conducting materials have become quite attractive. Among offered alternatives, Ag nanowire networks seem to be one of the most promising candidates. Transparency and sheet resistance values of Ag NW networks are very close to that of ITO. In this study, Ag nanowires synthesized through a simple solution based polyol process [1]. Then, these nanowires were purified through multiple centrifuge process. Following purification, nanowires were suspended in ethanol and spray coated onto glass substrates. A post annealing process was applied in order to decrease nanowire-nanowire junction resistance and remove residual capping agent. The electrical and optical properties of the Ag nanowire networks are then investigated. The networks are found to be highly transparent (87% at 550 nm) and conducting (11 ohms/square) with values comparable to ITO. Furthermore, in order to decrease surface roughness of Ag NW networks, a parametric study on spin coating of PEDOT:PSS was investigated. Finally, Ag NW networks were used as anode in polymer light emitting diodes (PLEDs). We will present a detailed analysis of optpelectronic properties of Ag NW networks and as fabricated PLEDs. [1] Coskun S, Aksoy B, Unalan H.E, “Polyol Synthesis of Silver Nanowires: An Extensive Parametric Study” Cryst. Growth Des. 2011, 11, 4963-4969.

Roll-to-roll manufacturing holds the potential to rapidly and cheaply produce electronic devices in a flexible format as well as to effectively scale up production of emerging nanotechnologies. Developing scalable techniques for the efficient and effective use of solution-processed functional material is a significant factor in realizing the potential of roll-to-roll manufacturing. We present a novel inkjet deposition process developed to rapidly deposit arrays of micron-wide lines of silver nanoparticles for use as an optically transparent and electrically conducting film. The technique involves jetting a controlled number of space-overlapped drops of a dilute nanoparticle silver ink onto a substrate to form a long stable ink rivulet with two parallel and pinned edges. Subsequently, nanoparticles deposit preferentially at the two parallel rivulet edges due to edge-enhanced evaporation of the solvent. The final result is a twin-deposit of parallel continuous nanoparticle lines, each with a characteristic width less than 5mu;m and height less than 200nm. The twin lines are separated by a predominantly particle-free region with the spacing between the lines ranging from 50mu;m to 500mu;m, where the spacing is a function of ink, substrate, and printing conditions. The effect of ink composition, substrate, and jetting parameters on nanoparticle line morphology and electrical conductivity is presented. Arrays of such lines have been printed and evaluated as potential transparent conducting films. This edge-enhanced twin-deposition technique has the potential for rapid, material-efficient, and lithography-free patterned deposition of functional material for use in roll-to-roll manufacturing.

Optoelectronic devices require at least one electrode to be transparent. Indium tin oxide (ITO) is the traditional material for the transparent electrode of optoelectronic devices. But ITO has problems of scarce indium on earth and poor mechanical flexibility. A conductive polymer, PEDOT:PSS, is regarded as the next-generation transparent electrode materials, because it can be dispersed in water and high-quality PEDOT:PSS films in a large area can be prepared by the solution processing techniques. However, as-prepared PEDOT:PSS films have a problem of low conductivity of about 1 S/cm. In this paper, we will report novel methods to significantly enhance the conductivity of PEDOT:PSS films through a treatment with various acids. The conductivity can be more than 3000 S/cm, which is higher than that of ITO on plastic and comparable to ITO on glass. The relationship between the conductivity enhancement and the structure and properties of acids will be elucidated.

A novel manufacturing process for large area flexible devices has been developed. The process consists of continuously high-speed coating for functional film materials, 3-dimensional (3-D) nano/micro-machining of the films on fibers, and weaving the functional fibers into large-area integration. In the coating process, functional materials, e.g., organic semiconductor, piezoelectric, conductor and insulator films could be formed on fibers with a speed of 20 m/min. In the 3-D nano/micro-machining, a compound reel-to-reel process system including both thermal roller imprint and photolithography functions was developed. In addition, the microfabrication of the 3-D exposure module and the spray deposition of thin resist films on the fibers were demonstrated. Using the process, a round-projection microspring contact structure was developed for the electrical contact between weft and warp fibers in a large area of woven textile. Evaluation of the durability showed that the microspring contact structures made of silicon elastomer and PEDOT:PSS are applicable to a movable contact.

Organic photovoltaic (OPV) devices for harvesting solar energy have the potential to be a widely adopted source of sustainable electricity for a range of applications. The devices can be solution processed; therefore inexpensive reel-to-reel printing and coating techniques are being investigated as a means of mass-producing OPV devices. This work aims to demonstrate the successful production of large-area devices using a novel coating technique. The coating technique employed in this work may be described simply as a draw-bar coating method, whereby a substrate is passed by a cylindrical rod held at some distance from the surface. The coating fluid is introduced between the rod and substrate and the resulting meniscus is dragged along by movement of either the substrate or rod, depositing a trail of fluid. The coating follows the Landau & Levich regime, hence coating thickness is able to be theoretically predicted based on the coating speed and meniscus shape. Experimentally, the coating thickness was controlled by varying the coating speed, rod diameter, gap height, amount of solution injected, rod diameter, rod composition material and number of layers. Substrate patterning in one dimension was able to be achieved by modification of the rod. In this work the devices were fabricated on 0.1 x 0.1 m substrates and consisted of six device fingers each with dimensions of 0.1 x 0.01 m. The draw-bar coating method was used to firstly deposit a layer of PEDOT onto the ITO coated PET substrate, followed by the active solution of P3HT:PCBM dissolved in chloroform, and finally an aluminium cathode was evaporated. Devices were tested under AM1.5 conditions. The film thickness was correlated to the variation in each coating parameter outlined above. A smaller rod diameter and smaller gap height both independently resulted in thicker films. Similarly, injecting a greater amount of fluid produced thicker films. These observations may be due to a greater meniscus contact length on the substrate in all cases. The number of layers deposited had the greatest impact on final film thickness and allowed the largest range of thicknesses to be achieved. Devices with active layer thicknesses ranging from 35 to 475 nm were produced, with the optimum thickness found to be around 160 nm. Devices produced at this thickness achieved typical efficiencies of 0.4 %. The thicker devices performed almost as well, achieving efficiencies around 0.35 %, however the devices below 85 nm thickness did not function due to short-circuiting. This work demonstrates that the draw-bar coating method allows controlled deposition of a wide range of film thickness and can successfully be used to manufacture large-area devices. Further work to improve efficiencies is ongoing.

Ultrathin membrane-type flexible electronic devices enable cloth-type computers, metamorphic cellular phones, and biomedical conformably implantable devices. Such applications require generating printable formats of the devices and developing the related transfer printing technology. In particular, when the thickness of a device including a substrate is tens of micrometers or less, high flexibility itself does not provide mechanical stability during all fabrication processes so using a supportive substrate is highly desired. After device fabrication, the final device should be transferred from the handling substrate onto a target surface in controllable manner. Here, this research describes a new method to guarantee the both stability in fabrication and high efficient transfer printing by employing a sacrificial layer and concave/convex structure with optimized depth, pitch, and lateral shape at the interface between a handling substrate and a flexible polymer substrate. The key idea is to hold the bellies of the convexities inside the narrow necks of concavities after etching the sacrificial layer to reduce the adhesion in the interface between the two substrates in deterministic way: Larger depth, smaller pitch, more complex shapes increased the adhesion. To demonstrate the efficacy of new method, we transferred various sizes and shapes of SU-8 pattern onto various planar and curvilinear substrates using flat, cylindrical roller-type, or hemispherical membrane-type rubber stamps. Finally, we successfully developed printable highly flexible ultrathin electrodes that can be printed onto various substrates such as a sheet of paper, column-like surface of a laser pointer, and a stretchable adhesive tape. Ref] Y. Hwang, H. A Cho, S. H. Kim, H. S. Jang, Y. Hyun, J.-Y. Chun, S.-J. Park, H. C. Ko, Soft Matter, in press.

Emergence of the rapid development of flexible electronics requires research contributions from 3 aspects: materials (both substrate materials and functional materials), fabrication and post- treatment. To realize roll-to-roll (R2R) large scale manufacturing, many solution-based fabrication methods have already been widely studied and adopted (such as inkjet printing, slot die coating, gravure printing, etc.). However, challenges still exist in the post-treatment step. For instance, consider metal nanoparticle suspensions. To carry out its functionality (electrical conductivity), usually a sintering step is necessary to turn the deposited material structure into a continuous phase. It is always difficult to prevent substrates from degradation during sintering due to conditions of high temperature, harsh chemical environments etc. Although advanced substrate materials (such as polyimides) have shown compatibility to some specific sintering environments, to lower the manufacturing cost and maintain R2R compatibility, less-costly and hence less-tolerant substrates such as Polyethylene terephthalate (PET) should be emphasized. In our recent efforts, radio frequency plasma is demonstrated to enable sintering of silver nanoparticle films at low processing temperature. To carefully investigate the silver nanoparticles sintering behavior, we control the particle sizes as well as the thickness of their organic capping layers (which are incorporated during the synthesis steps to stabilize the particles in the suspension format). The relationship between plasma parameters (such as power, working pressure, gas component, and treatment time) versus sintering results (sintered structure depth, film continuity and electrical resistivity) will be reported. According to our efforts so far, we have achieved the electrical resistivity of the sintered film at about 20 times greater than the value of bulk silver using a process compatible with the low temperature requirements of common flexible polymer substrates.

The first nanoparticle inks developed for printable electronics have been gold and silver based inks. These inks provide good conductivity but the bulk metal price is high. In large scale manufacturing the ink prices and bulk price of the metal become significant. To attract the interest of manufacturers, ink developers have been recently developing copper nanoparticle inks. Some inks are available commercially and some can be acquired for research use as they are still in development phase. Along with cost-related issues there are also other challenges with silver based nanoparticle inks, which drive the need for copper nanoparticle inks. As fully printed electronic circuits still lie in the future, compatibility with existing technologies is crucial considering the commercialization of printable electronics. Silver nanoparticle inks are not compatible with soldering processes due to silver leeching and require conductive adhesives for component interconnections. Soldering processes have been developed to be used with components on copper circuits. The use of copper nanoparticle inks might bridge the gap between inkjet-printed circuits and soldering processes. Currently only few types of nanoparticle copper inks are available commercially or for research use. One type of copper nanoparticle ink consists of copper nanoparticles covered with a dispersion agent, which prevents the particles from oxidizing and agglomerating. The sintering time for inks of this type needs to be very short due to copper nanoparticle oxidation. The viable solutions for processing inks of this sort are photonic sintering methods (laser sintering, flash sintering). Another type of copper nanoparticle ink consists of oxidized nanoparticles in solvent. These oxidized nanoparticles can be chemically reduced by gas or liquid processes to form a conductive copper layer. In this paper we focus on sintering of inkjet-printed copper nanoparticle ink structures using a continuous wave 808nm diode laser. Laser sintering is a rapid sintering method which can be applied with or without a nitrogen athmosphere around the sintering area. The advantages of laser sintering are processing speed and localized sintering. The used ink(s) consist of copper nanoparticles covered with a dispersion agent. Photonic sintering is needed to speed up the sintering process to prevent oxidation during sintering. Electrical and mechanical performance of the printed structures will be analyzed.

Terahertz wave (frequency range: 0.1-10 THz) has been attracting a great deal of attention in recent years due to its ability to achieve innovative sensing systems. Growing research activities using THz wave is driven by scientific and industrial applications such as defense, security, biology, or medical care. However, manufacturing THz sensing/imaging devices with low cost has been a difficult subject. We therefore propose utilization of organic field-effect transistors (OFETs) for this purpose owing to their applicability to flexible electronics with low fabrication cost. Our previous works revealed that the HOMO-band edge of a pentacene thin film is randomly fluctuated [1] due to the existence of crystallite boundaries [2]. The maximum amplitude of the fluctuations is around 30 meVp-p and the local barrier height against carrier transportation is 0.5not;-10 meV, which corresponds well with the photon energy of THz wave (0.41-41 meV). It is therefore highly probable that the irradiation of THz wave enhances the carrier transport in OFETs with pentacene thin films. In this presentation, we will report on the THz absorption in pentacene OFETs and its modulation by the gate electric field as the first stage of the study aiming at the THz sensing devices. Pentacene OFETs were fabricated on n-type silicon substrates covered with 300-nm-thick oxide layers. The substrate was served as a gate electrode to bias against interdigital-type source/drain electrodes on the oxide layer and the absorption spectra of the OFET were measured with THz time-domain spectroscopy (THz-TDS). Counter experiments were performed using a dummy sample where a very thin Au layer was deposited instead of the pentacene active layer. Transmission spectra were measured under ON-state gate bias (-30 V) of OFETs and they were normalized by OFF-state (+30 V) ones of the same sample. For the dummy sample, the gate-bias modulation of THz absorption exhibited a broad absorption due to the accumulated free carriers in Si. The absorption spectrum was consistent with a Drude model[3] in the range of 0.5-2.0THz. On the other hand, the OFET sample exhibited larger absorption than the dummy sample did. The difference in the absorption between those with and without the organic layer is, therefore, counted as the absorption by the accumulated holes in pentacene. The difference is smaller in the lower frequency range, while larger in the range of 1.5-2.0 THz. This must be due to the motion of holes that are weakly confined to the local minima of the HOMO band edge. The absorption by the holes in pentacene increased with the accumulation gate bias. This would be clear evidence that shows the energy transfer from THz photons to accumulated holes in an OFET. [1] N. Ohashi et al., Appl. Phys. Lett. 91, 162105 (2007). [2] R. Matsubara et al., Org. Electron. 12, 195 (2011). [3] T.-I Jeon et al., Appl. Phys. Lett. 72, 3032 (1998).

NFC (near field communication) technology using 13.56 MHz has been considered as a key step for the realization of ubiquitous society. However, the cost of NFC tag has been deteriorated all the advantages of the NFC technology because all of items cannot have their own NFC tags. In this presentation, we would like to first report fully roll-to-roll printed inexpensive NFC-QR code to replace current expensive NFC tag especially for item tracking. The fully printed NFC-QR code is operated at 13.56 MHz and compatible with current smart phone. The printed NFC-QR code is consisted by rectenna (antenna, diode and capacitor) and electrochromic display based QR code. By simply closing by the smart phone to the printed NFC-QR code, the AC power (13.56 MHz) is transmitted wirelessly to the antenna and then converted into DC power by passing through a diode and a capacitor, printed in the NFC-QR code, to turn on QR code which will be red automatically by the smart phone. During the presentation, the operation of fully printed NFC-QR code will be demonstrated.

Roll-to-roll technology is a natural progression of nano imprint lithography (NIL), and roll-based imprinting is considered as a next generation manufacturing platform for the functional surfaces such as subwavelength antireflective structure, highly efficient reflective structure, front plane architecture for displays, and biomedical nanostructures. Making the technology commercially viable requires systematic development of the roll-to-roll processing tools and the proper conditions such as resin, pressure, rolling speed, etc.. In a laboratory, critical process conditions for roll-based UV nanoimprinting can be optimized in more flexible roll-to-plate (R2P) process tool and then potentially transferred to a roll-to-roll (R2R) system. In this paper, we are focused on finding the novel resin that is suited for a roll-to-roll process. Polymerization can be categorized into two groups, that is, radical polymerization and cationic polymerization. While the radical polymerization is conventionally used as a resin with its fast curing and its readily available silicone containing acrylate, cationic polymerization resin is pursued for the roll-to-roll process to overcome the problem of oxygen inhibition. The performance of epoxy resin has been researched previously but other cationic polymerization based vinyl etherprovides a low viscosity, five times higher tensile strength, and fast curing speed than acrylate have not been sufficiently investigated for R2R applications. Conventional SAM coating that helps resin to be easily separated from a mold by reducing the surface energy can be substituted by fluorine monomer. For a R2R application where we use imprinted structure directly, rather than as a transfer mask that needs to endure the process such as reactive ion etching, we do not need to consider siloxane in choosing a proper vinyl ether resin. There are several considerable features to find a proper resin, such as the time of the contact, rolling speed, curing time, and intensity of UV source. We control and find the proper condition of the curing time and intensity of UV source using UV exposure equipment. Surface energy of cured resin is evaluated by measuring contact angle, and the replication performance of this resin is charaterized by using FE-SEM.

The low thermal conductivity substrates typical of flexible electronics necessitate the development of low power circuit architectures for reasonable electronic system sizes. CMOS based circuit architectures offer a natural solution but require the development of both n and p type materials and, ideally, an ability to match the threshold voltage of n and p type devices. While considerable research effort has resulted in high electron mobility inorganic materials such as ZnO and GaInZnOx, little success has been reported for high hole mobility devices. Pyrite (FeS2) is a promising earth abundant absorber layer for photovoltaic applications with relatively large hole mobility. In this work, we examine the electrical and physical properties of thin film pyrite produced using pulsed laser deposition (PLD) on Si substrates from an FeS2 target at temperatures ranging from 25 oC to 300 oC. For the substrate temperatures and laser fluences (1-3 J/cm2) explored, the lower band gap monosulfide, pyrrhotite was mainly produced. The complete transformation of FeS into FeS2 was enabled through sulfidation annealing at 400 oC. Pyrite films, produced by annealing FeS films in sulfur atmosphere at 80Kpa for 15 minutes were found to have uniform microstructure and stoichiometry. Hall mobility in these materials and bottom gate thin film transistor performance will be discussed.

Metacapacitors are solid state ceramic/polymer composite capacitors designed for close integration with large scale power conversion devices. The qualities of a metacapacitor include low cost, high frequency operation, a moderate dielectric constant and low leakage. The development of this technology has many industrial applications, such as integration into LED drivers. Current research efforts include the scale up of the fabrication with roll-to-roll compatible processes. One major obstacle to this scale up is the controlling the quality of the printed film. Consistent microscale structure of the film is necessary for creating repeatable, high quality capacitors. Additionally, uneven or patchy films can trap solvent and/or allow breaks in the dielectric film, destroying the capacitor. An automated spray printing process has been developed to deposit the composite solution, a mixture of ceramic nanoparticles and polymer precursor, in a continuous repeatable fashion. The deposition occurs at room temperature and in air. The film is cured under low heat and does not require a high heat step to achieve a useful dielectric constant. Printing parameters such as flow rate, distance to the substrate, and ink composition can effect the quality of the film in complex ways. This work aims to investigate these effects, and to work towards full targeted control of film composition, thickness, and roughness over areas large enough to be suitable for high throughput production.

Printed electronic devices consist of multiple layers, which are applied in several manufacturing steps. The majority of publications employ individual roll-to-roll processes. Each production step is often carried out on separate printing machines, thus requiring up to six machines for a complete manufacturing process. In comparison, newspaper printing incorporates all necessary processing steps in one fully automated manufacturing system. While roll-to-roll became a synonym for high-throughput production of organic electronics, the optimal number of manufacturing-steps per machine is currently not considered in the discussion about upscaling printed electronics production. Pursuing production at optimal costs, we introduce a theory for the manufacturing process of printed electronics, which determines the cost and the optimal number of production steps per machine. We find that the most important variables are the set-up time and the process time for each production step including the drying time.

Nanoparticle polymer composite capacitors have been examined for some time as a way to achieve high performance, printable capacitors. One approach to creating these composites is to use vapor deposited polymers, which can yield high performance, but also a structurally asymmetric device. The low temperature process is applicable to flexible substrates in which roll-to-roll fabrication can be realized. The performance of a nanoparticle BST/parylene-C composite capacitor is compared to that of a nanoparticle BST capacitor without the polymer layer under both directions of bias. The composite device shows four orders of magnitude improvement in the leakage current under positive bias of the top electrode compared to the particle-only device, and five orders of magnitude improvement when the bottom electrode is positively biased. The voltage tolerance of the capacitor also shows a similar improvement and asymmetrical pattern (28 V vs. 44 V in top and bottom positive bias, respectively). This study not only shows the advantage of this class of composite device construction, but also demonstrates that proper application of the device bias in this type of asymmetrical system can yield additional benefit.

Amorphous oxide semiconductors (AOS) that are based on indium oxide include amorphous In-Zn-O (IZO) and In-Ga-Zn-O (IGZO) are of great interest for use as thin film transistor (TFT) channel material in next generation active-matrix liquid crystal (AM-LCD) and active-matrix organic light emitting diode (AM-OLED) displays. The high field effect mobility of In2O3-based AOS devices (10-25 cm2/Vsec)[1] offers significant performance improvements over present-day a-Si TFTs (<1 cm2/Vsec) technology. Additional advantages of AOS materials include room temperature processing, isotropic wet etch characteristics, and high optical transparency (>85 % in the visible regime) all of which make this material suitable for large area, flexible, and transparent devices on inexpensive polymer substrates. In previous work, we reported[2] high performance long-channel a-IZO n-MOSFETs which operate in depletion-mode (Vth~ -3.21 V) and have saturation field effect mobility of (mu;sat) of ~20 cm2/Vsec and on/off ratio of >10⁶. These demonstration devices were fabricated on glass and Si substrates that used the conducting a-IZO and Si as a bottom-gate, respectively, SiO2 as the gate dielectric, semiconducting a-IZO as the channel and conducting a-IZO as the source/drain metallization. We have also deposited TFTs with sputtered dielectric layers to demonstrate an all-room temperature TFT fabrication process. For most applications, these AOS materials may be deposited at room temperature and are then typically exposed to only relatively low (100 °C

For flexible printed circuit board (FPCB), especially, high peel strength is one of the crucial factors because induced stress during bending, twisting and stretching is concentrated on the interface between metal lines and polyimide (PI) substrate. Until now, although monel (NiCu) and nikel-chromium (NiCr) have been used as typical adhesion layers, they have showed limitation in peel strength. To solve this problem, we recently developed a new adhesion thin film, NiMoX having high peel strength at the fresh state and even aged state held at 150 °C for 7 days. In this study, NiMoX thin film was deposited on PI substrate with two different methods by roll to roll magnetron sputtering; one is plasma pre-treated PI, the other is plasma untreated PI. The peel strength made from plasma pre-treated and untreated flexible copper clad laminate (FCCL) is 0.66 kgf/cm and 0.49 kgf/cm, respectively. Moreover, the peel strength remained still high at aged state compared to that of conventional adhesion layers. The characteristics of morphology and chemical bonding state on peeled PI for plasma pre- treated and untreated FCCLs were comparatively studied by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM).

The structural degradations of indium tin oxide (ITO)/PET films based on various PET films with different hard coating layer in hot and humid environments were investigated in relation to the surface resistance of ITO films at the same sputtering condition of ITO. The roughness and energy on the surface of hard coating layer of PET films were analyzed by atomic force microscopy (AFM) and contact angle analyzer. The ITO/PET films, which were held at 85^oC and in relative humidity (RH) of 85% for 10 days or 60^oC/95% for 10 days, experienced a sharp increase of the surface resistance, respectively. The surface analysis of ITO/PET films were executed with field-emission scanning electron microscopy (FESEM) and the cross-sectional microstructures were analyzed by transmission electron microscopy (TEM) using focused ion beam (FIB) technique for specimen preparation. And the cross-cut tests were carried out for the adhesive force of ITO/PET films. The increase of the surface resistance is attributable to the peel-off resulting from poor adhesion between ITO and hard coating layer of PET film. The high roughness and low energy on the surface of hard coating layer of PET film promote the degradation of ITO/PET films in hot and humid environments.

We developed meter-scale large area touch sensors where organic conductive polymer and passivation-polymer-coated fibers were woven as wefts and warps. The coating method of die-coating for fibers and weaving machine were reported by our group, but the resultant sensor was not characterized nor optimized. The sensing mechanism was based on the measurement of the capacitance between fiber and human body. The capacitance between 500 um-diameter fiber and 2 cm-wide finger or foot was measured with conventional capacitance meter in standard microcontroller, resulting 1-2 pF. If the length of the fiber increased, electric resistance of the conductive polymer electrode increased, resulting in small signal and high noise. The optimal resistance of 5 kohm/meter was measured. Finally after the 1.2 m wide touch sensors were connected to the capacitance meters, human motion was monitored.

Printed electronics have been considered as a way of manufacturing inexpensive, roll-able and disposable electronic devices. However, the lower operation frequency (< 1 KHz) and higher power consumption (> 20 V) of the printed electronic devices would deteriorate the advantages of the printed electronics and retard the all the applications in IT market. In this presentation, we would like to first demonstrate all printed CMOS based ring oscillator with the operation frequency of 100 KHz using the power of 5 V. The CMOS based ring oscillator has been printed using gravure and inkjet on PET film with silver ink for gate and drain-source electrodes, BaTiO3 ink for dielectric layer and SWNT ink for active layer.

We reported on the experimental study of silver micro-sized electrode by the inkjet printing of silver nanoparticle ink. The inkjet method promises many advantages over conventional lithography. However, there are some barriers to be applicable to industrial products by inkjet. One of them is that metal electrode fabricated by inkjet may have nano- or micro-sized pores which are trapped in metal line when metal nanoparticles are agglomerated with the evaporation of ink solvents at the sintering process. These pores decrease the uniformity and electrical properties of electrode. To analyze sintering characteristics and remove pores, drop volume (0.01~1pl) and drop spacing for ink-jetting and the material and structure of substrate were controlled at the printing process, and sintering source and profile (temperature and time) were also controlled. The surface and cross-section of printed silver lines were observed using scanning electron microscopy (SEM) by focused ion beam (FIB) and the electrical resistivity of lines was measured. From this study, 3mu;m-width, 3mu;m-thick silver lines with lower electrical resistivity (<3mu;Omega;.cm) were printed without micropores. These results are helpful to understand the sintering mechanism of metal nanoparticles and are expected to be applicable to the next generation of printed electrode for display, solar cell and memory by the substitution of other manufacturing processes.

Stretchable electronics has emerged as a new class of soft electronics, which is considered potential and intriguing in applications such as biomedicine and sensing system. In the present study, we try to combine the aerosol jet printing process with deformable elastomers, polydimethylsiloxane (PDMS), to simplify the conventional microlithography process for fabricating metal interconnects and active devices. By using silver nanoparticles solution (<1 µm) as ink, we utilize aerosol jet printing process to generate serpentine conductive interconnects on polyimide (PI) substrate with line width of 60~120 µm and thickness of 150~250 nm. After transfer printing onto a pre-strained PDMS elastomer, the thin circuit sheet was adhered strongly to the surface of PDMS elastomer only at the nodes through O-Si-O bonding between deposited silica on the backside of PI substrate and the surface of PDMS. Taking advantages of the store energy by releasing the pre-strain of PDMS elastomer, stretchable silver interconnects can be formed. The aerosol jet printing process provides simple and direct patterning of metal interconnects and adhesive layer on the substrate, and therefore facilitate the fabrication process of stretchable electronics. Furthermore, by direct deposition under ambient condition, the integration of active devices such as Pt based temperature and communication antenna may be integrated easily.

Indium-tin-oxide (ITO) is considered the most promising candidate for the transparent conducting materials. Solution-based deposition of ITO films is increasing significantly because this method is a low cost, simple, and atmospheric process compared to sputter deposition. Among the fabrication solution, two main types are used: metal-organic deposition (MOD) solutions and nanoparticle suspension. Nanoparticle ITO films have the advantages of controlling thickness and being pre-synthesized, however they showed much lower electrical conductivity (10^-2 ~ 10⁰ Omega;^-1cm^-1) than sputtered films (10⁴ Omega;^-1cm^-1) as well as the MOD films (10² ~ 10³ Omega;^-1cm^-1). In this research, highly conductive and transparent nanoparticle ITO films which are comparable to MOD and even sputtered ones are fabricated by applying new post treatment process; oxygen partial pressure annealing. Conductivity of ITO is determined by carrier concentration and mobility. Nanoparticle ITO has low mobility and carrier concentration due to high amount of organic impurity and lack of the oxygen vacancy. We design the effective annealing process improving conductivity and it is scientifically confirmed by carrier concentration and mobility change with variation of the annealing parameters. ITO nanoparticle ink had a solid loading of 20 wt % with an average particle diameter of 50 nm. The nanoparticles were dispersed in ethanol. ITO nanoparticulate film was deposited on glass substrate by spin coater. After deposition, films were dried in oven and annealed in furnace with various temperature (250 ~ 550 °C), time (1 ~ 3 h), and ambient(Air, vacuum: 10^-6 ~ 10^-1 Torr). Microstructure, conductivity, and transmittance of ITO films were characterized. From microstructure analysis (X-ray diffraction, scanning electron microscopy), the fabricated samples were identified as highly crystalline nano-sized ITO particles films. Measured electrical conductivity of nanoparticle ITO was changed significantly by annealing temperature and ambient. Optimum conductivity (3 × 10² Omega;^-1cm^-1) can be obtained at 550 °C and the specific level of vacuum ambient (10^-2 Torr). This result can be explained the relationship between annealing parameter and electrical properties, carrier concentration and mobility which can be separated by Hall measurement. And we can find why nanoparticle ITO had poor conductivity and how much these factors have to be improved. It is concluded that the burning of organic ligand and the change of oxygen vacancy concentration were the main factors for this conductivity change. Samples except in the case annealed in vacuum at high temperature, had the excellent the optical transmittance (T > 95 %, 300 nm thick). Maximum figure of merit is 5.4 × 10^-3 Omega;^-1 which is comparable to sputtered ITO thin films.

Uniform electrodes are formed by uni-axially cracking an indium tin oxide, ITO film vacuum deposited on a polyester substrate. The cracks are produced by bending the film around a tight radius of curvature, producing narrow, parallel cracks in the ITO separated by 5-10 microns. The cracks are enhanced by etching or uni-axial stretching. Heating and stretching is the most effective, producing a crack width of about 0.05 microns and a differential conductivity (measured parallel and perpendicular to the cracks) several orders of magnitude or greater. A passive matrix bistable cholesteric display is fabricated using top and bottom electrodes with perpendicularly aligned electrodes. The addressed lines on each substrate are defined by the contact electrode, which contacts multiple cracked ITO lines. Because of the small dimension of the cracks (much less than the thickness of the active layer) they are not visible in the display. The separation between the contact electrodes must be great than 20 microns in order to include at least one crack and electrically isolate each individual line. The resulting display demonstrates how controlled cracking of ITO can replace photolithographic etching of ITO or printing of conducting polymer to produce the line electrodes required for flexible, passive matrix displays and related electronic applications. Un-iaxially cracking can be easily integrated into a roll-to-roll manufacturing process.

As displays and electronics evolve to become lighter, thinner, and more flexible, the substrate choice continues to be critical to their overall optimization. The substrate directly affects improvements in the designs, materials, fabrication processes, and performance of advanced electronics. With their inherent benefits such as surface quality, optical transmission, hermeticity, and thermal and dimensional stability, glass substrates enable high-quality and long-life devices. As substrate thicknesses are reduced below 200um, ultra-slim flexible glass continues to provide these inherent benefits to high-performance flexible electronics. In addition, the reduction in glass thickness also allows for new device designs and high-throughput, continuous manufacturing enabled by roll-to-roll processes. This invited paper provides an overview of WillowTM glass substrates and how they enable flexible electronic device optimization. Specific focus is put on flexible glass&’ mechanical reliability. For this, a combination of substrate design and process optimizations has been demonstrated that enable both sheet-based and roll-to-roll device fabrication on flexible glass. Demonstrations of roll-to-roll flexible glass processes such as ITO deposition, photolithography, laser patterning, screen printing, and lamination will be described. These basic capabilities enable continuous manufacturing methods for high-quality devices on flexible glass substrates.

Recently, surface wrinkling has been largely studied due to its versatile applications; stretchable electronics, photonics, tissue engineering, biosensors, and regenerative biology. It can be normally generated in a variety of systems including thermally or mechanically stressed rigid thin film supported on elastomeric substrates, and solvent-swelled polymeric surfaces. However, only a few studies on the control of wrinkling and surface stress have been reported, where either modulated physical topography of the elastomeric substrate [1] or chemical patterning [2] was used. Even though controlled wrinkling was implemented, the important technical issue of surface stress has been overlooked. The surface typically suffered from external strain although wrinkles were not generated. In order to overcome these limits, in this paper, we fabricated the stretchable film with controlled wrinkling and surface stress in which the rigid island structures were embedded. Previously, rigid islands have been fabricated by either deposition of inorganic materials [3] or ultraviolet (UV) patterning of polymeric materials [4] only for the formation of stress-released rigid area. In addition, these processes were relatively complicated for scalable and large area applications. We solved these problems through inkjet-printing the UV-curable polymer. Using the hydrophobic property of polydimethylsiloxane (PDMS) and hydrophilic property of UV-curable polymer, we could fabricate hemisphere-shaped transparent rigid island array embedded in PDMS with simple UV exposure. Since the polymer we used is highly cross-linkable under UV exposure, these rigid islands exhibited crack-free properties different from the deposited inorganic rigid islands. Furthermore, simply varying the pattern size or using repeated printing we could obtain the size-tunable, reproducible, and large-area rigid island arrays. After the rigid island arrays were formed, the PDMS film was pre-stretched and then UV-ozone treated. When the PDMS film was released, wrinkling morphology has been obtained on the PDMS surface. We successfully controlled the surface stress and wrinkling by modulating the size and inter-distance between islands. The experimental results were consistent with the finite element method simulation on the controlled wrinkling phenomenon under the various island array structures. This work was supported by the Converging Research Center Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education, Science and Technology (No. 2009-0082824). References [1] T. R. Hendricks et al., Nano Lett., 7, 372 (2007). [2] A. Malachias et al., ACS Nano, 2, 1715 (2008). [3] J. Y. Sun et al., J. Mater. Res., 24, 3338 (2009). [4] I. M. Graz et al., Appl. Phys. Lett., 98, 124101 (2011).

The significance of interfacial adhesion between ultra-thin functional films in the success of roll-to-roll printing of large area of flexible electronics and functional surfaces cannot be overstated, as it plays a pivotal role in many key enabling technologies of roll-to-roll processing, such as additive and subtractive manufacturing, multilayer registration and device structural stability. However, direct measurement of adhesion properties of ultra-thin films can be challenging, as the traditional metrology of adhesion at macroscopic scales becomes unsuitable in dealing with samples of extremely small dimension. Here, we present a feasible and robust approach combining nano-transfer printing (nTP) experiments and mechanics modeling to quantitatively determine the interfacial adhesion of submicron thin films. We show that, the measurements of the interfacial adhesion of a submicron polycarbonate (PC) thin film on a PC substrate at multiple locations in multiple samples agree within 7.3%, demonstrating the accuracy and robustness of our approach. Given the versatility of the nTP process, the approach demonstrated in this paper is expected to be generally applicable to measure the adhesion of interfaces of other material combinations. In this sense, the present study sheds light on better understanding of the adhesive properties of functional interfaces between ultra-thin films, a crucial issue toward the success of roll-to-roll processing of flexible electronics and advanced functionalities.

For many energy and electronic applications, single-crystal-like materials offer the best performance. However in almost all cases, the single crystal form of the relevant material is too expensive. In addition, for many applications, very long or wide materials are required, a regime not accessible by conventional single crystal growth. This necessitates the use of flexible, large-area, long-length, single-crystal-like substrates for epitaxial growth of the relevant device layer for the electronic or energy application in question. Details of substrate fabrication, the texture quality of the substrates, the nature of grain boundaries, and the range of materials that can be epitaxially grown on such substrates will be discussed. The substrate technology employs simple and industrially scalable thermomechanical processing routes to obtain long lengths of near single-crystal-like substrates. Epitaxial buffer layers of various buffer layers (of rock salt, flourite, perovskite and pyrochlore crystal structures) are then deposited in a roll-to-roll configuration using web-coating employing electron-beam evaporation, sputtering, MOCVD and/or chemical solution deposition. Addressing tension and web-handling issues particularly for deposition at high temperatures (600-800°C) as well as entering and existing vacuum deposition systems in series has been key to the success of the technology. As an example of a material for energy and electronic applications, results will be presented for growth of superconductors on such substrates. Kilometer long, single-crystal-like high-temperature superconducting wires are now routinely fabricated using these substrate technologies. Roll-to-roll depositions have also been used to create self-assembled nanostructures in long-lengths. This technology is presently also being used for low-cost, high-performance semiconductor devices such as photovoltaics, ferroelectrics, multiferroics, and ultra-high density storage. Examples will be given for all of these cases with greater emphasis on integration of semiconductors on single-crystal-like substrates.

A versatile technique that realizes a variety of functional ceramic thin films on plastics is proposed. The technique is innovative in that the crystalline state of films, which is essential for a number of functionalities, is guaranteed by a firing process. Any kinds of ceramic thin films can be prepared on plastics by this technique, with smooth surface, optically transparency, and thickness of 50 - 600 nm. The ceramic thin films achieved on plastics include highly reflective TiO₂, electrically conductive ITO, and crystallographically oriented ZnO thin films. Patterned ITO and ZnO thin films can also be achieved on plastic substrates. The technique comprises (i) the sol-gel preparation of precursor gel films on silicon substrates by dip- or spin-coating, (ii) the conversion of the gel films into ceramic thin films by firing, and (iii) the transfer of the ceramic thin films onto plastic substrates. Prior to the gel film deposition the silicon substrates are coated with an organic polymer layer, which helps the ceramic thin film to be released from the silicon substrate on the transfer step. The ceramic thin films thus prepared are transferred onto plastic substrates either by two methods; one is to use adhesives [1,2] and the other is to melt the surface of the plastic substrates [3]. In the latter case, ceramic thin films are directly bonded to plastic substrates. Although ceramic thin films are brittle in general, they are not cracked even on the transfer process under designed conditions. And the ceramic thin films thus transferred to plastic substrates are somehow flexible, being not cracked on substrate bending. In spite of the mechanically severe transfer process, the surface as well as the interface is smooth in SEM scale. The conditions for the successful transfer will be presented, and the application of the technique to roll-to-roll processing will also be addressed. [1] H. Kozuka, A. Yamano, T. Fukui, H. Uchiyama, M. Takahashi, M. Yoki, T. Akase, J. Appl. Phys., 111, 016106 (2012). [2] H. Kozuka, H. Uchiyama, T. Fukui, M. Takahashi, Japanese Patent Application, No. 2011-022986. [3] H. Kozuka, H. Uchiyama, T. Fukui, M. Takahashi, Japanese Patent Application No. 2011-285428.

During the fabrication process (such as roll-to-roll process) or the usage of flexible electronics, a metal electrode on the flexible substrate should undergo various deformations such as bending, sliding, or stretching. These repeated mechanical deformations would result in the degradation of mechanical and electrical properties. Even though the relationship between such mechanical deformations and the electrical properties is essential to develop highly stable flexible devices, little effort has been made to correlate such properties. Hence, we suggested a universal scaling relationship between the electrical resistance and bending cycle which is associated with the fundamental mechanical damage evolution process: fatigue crack nucleation, propagation, and stress field overlap. Tensile fatigue damage of the metal electrode was applied by bending of the flexible substrate at a fixed curvature along with the repeated bending and linear motion of one end of the sample. Cyclic tensile bending test was performed in 1.1 ~ 2.0% strain range at 5 Hz frequency, and sliding distance was varied from 10 to 30 mm under 1.1% bending strain. The resistance changes during cyclic bending were measured simultaneously. The electrical resistance begins to increase upon crack nucleation caused by the collective dislocation motion during the repeated deformation, and then continues to increase with crack propagation. Systematic investigation also shows the relationship of electrical resistance change with an increase of fatigue damaged area and bending strain. As the fatigue damaged area increases, the crack nucleation cycle decreases due to the increase of the crack nucleation probability. The bending strain affects the crack nucleation cycle with the well-known Coffin-Manson relationship. Furthermore, a universal scaling relationship for the electrical resistivity change after the crack nucleation stage with respect to fatigue cycle is extracted using a dimensional analysis. It demonstrated that the nucleation cycle of crack, which can be identified by the in-situ monitoring of electrical resistance during cycling, is a critical parameter to predict the electrical resistance change during mechanical fatigue cycles. Furthermore, the effect of film thickness and bending strain on electrical stability will be discussed.

Thin oxide films gained a high interest for renewable energy applications. Process cost efficiency pushed the development of nanoparticle thin films forward, but the electrical properties of such layers prepared from nanoparticle dispersions are highly sensitive to impurities. To prohibit aggregation of the nanoparticles during the processing steps and to ensure proper film formation properties, wetting agents or chemical functionalization of the particles are often necessary for economically interesting coating processes of thin nanoparticle films. This inherently results in entrainment of organic and inorganic impurities into the conducting layer leading to largely varying electrical conductivity, especially when low-temperature processing is needed for flexible devices, where no heat treatment is possible to remove the organic materials (sensitive polymer substrates). This study [1] provides a systematic investigation showing how insulating shells, as surfactants, small organic molecules or silica, on transparent conducting oxide nanoparticles influence the overall resistivity of assembled nanoparticle thin films. Antimony-doped tin oxide, derived by flame spray synthesis, was organically (different dispersing agents) respectively inorganically (in-situ SiO₂ deposition) coated. A systematic study on pressure dependent resistance revealed the accurate role of shell thickness and mean conducting core distance between nanoparticles on the overall resistivity in the nanoparticle assembly. Insulating impurities or shells presented a dominant influence of the tunneling effect on the overall layer resistance. Mechanical relaxation phenomena were found for 2 nm insulating shells for both large polymer surfactants and (inorganic) SiO₂ shells. Understanding the role of surfactants, adsorbates or processing aids in thin film preparation will assist the development of improved film preparation methods as urgently required in photovoltaics and classical electronics. [1] S.B. Bubenhofer, C.M. Schumacher, F.M. Koehler, N.A. Luechinger, G. A. Sotiriou, R.N. Grass, W.J. Stark, ACS Appl. Mater. Interfaces, 4 (5), 2664-2671, 2012.

Over the past 10 years solution-process materials have been used in several applications as they have the potential to create a new manufacturing paradigm for electronics. We are developing technology to demonstrate reliable deposition of solution processed electronic materials over large areas in order to obtain stable device performance and allow integration of components of sensing systems that are mechanically flexible. We are investigating methods of obtaining stability at every step of device fabrication: ink formulation, ink deposition, solvent removal, thin film morphology and device electrical stability. We will discuss the use of printed flexible devices in the fabrication of receiving coils for Magnetic Resonance Imaging (MRI) and other medical applications. The quality of images produced during a MRI scan is dependent on the distance between the person/subject and the coil. Therefore if a traditional and rigid coil is used on an area/body that it was not designed for, the image quality suffers since the distance is changed. We use screen printing methods to deposit conductors and insulators, along with non-traditional flexible mesh substrates to design and fabricate flexible MRI coils and tuning capacitors. The most common MRI systems used in industry today are 1.5T and 3.0T and they require the receiver coils to have a resonant frequency of 63.86 MHz and 127.72 MHz respectively. We have fabricated coils that meet the requirements of these two systems (resonance at 63.86 and 127.72 MHz respectively) while maintaining body noise dominance to improve imagine quality. The coils exhibit resistances of 2-5 ohms for a single layer print, 1 ohm for multiple layers printed on a mesh screen. The capacitors created on these devices have shown capacitances between 1-50pF. We will discuss design, fabrication, and imaging techniques.

During the past decade, great research interest on efficient, low-cost solution-processed organic photovoltaic devices has led to certified efficiencies of 10 %. For an efficient organic bulk heterojunction solar cell, good control of morphology is a key aspect, which is mainly influenced by the components&’ solubility during processing and the formation of the resulting film. In order to fully exploit the capacity and the potential of high volume, large area production, a careful design of the inks is mandatory. Solubility is the key phenomenon with regard towards the design of inks and solvent systems with mutual multi-component solubility regimes. Since formulation of organic inks is one of the determining factors for processing of the active layer in organic solar cells, several approaches are under investigation to predict solubility of the materials in question and their influence on the device performance. In general chlorinated solvents are commonly used for processing in laboratories, which have restricted application in industrial operation due to safety risks and processing costs. Environmentally friendly inks are therefore one decisive criterion for mass production which should provide full functionality. The concept of Hansen solubility parameters (HSP) is applied to organic semiconductors in order to determine and predict their solubility behavior, which is essential for the design of functional and environmentally friendly ink formulations for organic photovoltaics. The method for determining the solubility parameters is discussed as well as their suitability for designing of organic electronic devices. We discuss a novel method based on solvent blends and demonstrate the potential for organic semiconductor processing at the hand of P3HT and PCBM. Comparing the solubility studies with device investigations allows identifying the processing limits of solvent systems. In order to challenge the predictions from the HSP theory we investigated a solvent system around the solubility limits for P3HT/PCBM. Here binary solvent mixtures of chlorobenzene and acetone were used, which show a dramatically solubility decrease for already small additions of acetone. At 60 °C addition of more than 30 vol.-% acetone is critical for the maximum P3HT solubility which is in agreement with Hansen theory. The addition of up to 30 vol.-% acetone in the solvent mixture does not dramatically reduce the device performance. By surpassing the solubility limit of P3HT and PCBM with 40 vol.-% acetone no processing is possible, again as predicted by Hansen theory. Therefore predictions from HSP and their implication on processing were found to be correct, also at the limitations of the solubility regime. Furthermore these new method is also expanded for high performance polymers.

In this work we study the gravure printing process of the poly-phenylvinylene derivative light emitting polymer colloquially named “super yellow” (SY) on Poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) surfaces and apply the results to the fabrication of flexible organic light-emitting diodes (OLEDs). SY can be easily dissolved in toluene and has been commonly used to fabricate high performance OLEDs by spin coating. However, when gravure printed this formulation yields thin films unsuitable for devices with high surface modulation due to process-induced viscous fingering effects. Therefore, in order to prepare SY ink formulations suitable for gravure printing, solvent mixtures formed by toluene and benzothiazole are used. Benzothiazole is a high boiling point solvent and should be expected to delay the drying time of the film contributing to surface demodulation. The rheological properties of the formulations are systematically investigated by changing the SY concentration and the solvent volume fraction while keeping the surface tension within a suitable window to allow wetting of the substrate. We observe that upon increase of benzothiazole volume fraction, the film drying time increases although favorable film conformation is only permitted within a range of solvent ratios. To explain these results we make use of a physical model that takes into consideration the viscosity and surface tension of the ink to estimate the surface demodulation time. As expected, a homogeneous printed layer, suitable for device fabrication, will be achieved when the demodulation time is shorter than a critical time, at which the film has lost its mobility due to solvent evaporation. As a final part of this work, we apply the knowledge obtained from the printing process to fabricate SY based flexible OLEDs with homogenous layers yielding a luminance of ~5000 cd m^-2.

Organic optoelectronic devices - organic photovoltaics (OPV), organic light emitting diodes (OLE) - provide a huge market potential for energy harvesting, lighting and display applications. Cost efficient manufacturing of these components on different flexible substrates is under heavy investigation. R2R process development requires active investments to machinery and novel deposition, drying/curing, pre- and post-processing techniques. In this abstract VTT&’s R2R manufacturing process capabilities for printing of OPV and OLED components are presented. In both devices the manufacturing process starts with transparent electrode patterning which is typically ITO-PET substrate. Alternatively ITO free structures based silver nanowires or metal grid with highly conductive PEDOT can be processed. After the transparent electrode patterning a hole transport layer which is some PEDOT:PSS grade depending on the component is gravure printed on top of the transparent electrode. For printing the polymer thin films a gravure printing technique is used in VTT&’s R2R manufacturing process. On top of the hole transport layer a photoactive polymer layer is also gravure printed. In case of OLED it is a light emitting polymer and in case of OPV is a light absorbing polymer blend, typically P3HT:PCBM. Cathode electrode on top of the photoactive layer is thermally evaporated or rotary screen printed using a suitable conductive paste. Finally the device stack is encapsulated using a commercial gas barrier foil. Besides polymer substrates OPV R2R printing on a flexible glass substrate is presented. In case of printed OLEDs following application demonstrators will be presented: 1) RFID driven 6 number 7 segment OLED display integrated in to a smart card, 2) printed OLED lighting panel where light emissive area is 35 cm2 and 3) printed transparent signage element In case of printed OPV application demonstrators includes: 1) OPV driven electrochrome display under room lighting and 2) an autonomous energy storage system utilizing printed OPV panel as energy harvesting component for low power sensor platform

We report about roll-to-roll processing of polymer solar modules applying and combining slot-die coating and laser ablation. For the semitransparent electrode, a highly conductive aqueous dispersion of PEDOT:PSS was used. The active layer was cast from a common solution of PCDTBT and PC70BM. The device architecture was non-inverted, which was fashioned by realizing the electron extracting electrode by a combination of solution processed TiOx and a vacuum processed aluminum back electrode. The semitransparent electrode and the photo-active layer have been laser-structured, whereas the metal back electrode was realized through a shadow mask. All devices were characterized for their performance and analyzed in detail by various imaging methods.

Numerous techniques have been demonstrated to grow organic semiconductor thin films, such as vacuum thermal evaporation (VTE) and organic vapor phase deposition (OVPD). In addition, roll-to-roll (R2R) processing provides a potential pathway to cost effective production of thin film electronics. In OVPD, small molecular weight organic molecules are transported by a hot inert gas to a cold substrate where they are physisorbed. Since OVPD is a low-pressure process, it is particularly adaptable to R2R deposition environments. For practical implementation, these techniques require a means to reproducibly and precisely monitor and control the growth rate and thin film thickness in real-time. We describe such a technique called laser-induced fluorescence (LIF) monitoring of growth via OVPD. In LIF, an ultra-violet or deep blue laser beam intersects the gas stream containing fluorescent “marker” molecules. The incident light is absorbed by the molecules, resulting in light emission whose photoluminescence intensity is proportional to the concentration of the markers. The time-dependence and intensity of PL is then used to determine concentrations, molar flow rates, and other transport properties of the molecular stream. LIF is adaptable to separately monitoring multiple luminescent materials using spectrally resolved detection, making the technique useful for controlling deposition of doped films in OLED displays and lighting. In this talk, we describe a variety of transient and steady state studies to demonstrate the ability of LIF to characterize physical mechanisms and optimize growth parameters. Specifically, the green fluorescent tris(8-hydroxyquinolinato)aluminum (Alq3) is deposited in our large scale OVPD system [1]. In particular, we probe the gas boundary layer to determine how concentration of organic in gas phase varies at the growth interface on the wafer surface. Finally, using short bursts of Alq3 from the source cell, transient conditions were measured, and the effects of varying system parameters on transport phenomena were determined. Taylor-Aris dispersion theory, as well as fitting methods used in chromatography, are required to properly describe transient molecular flows in the OVPD environment [2],[3]. Using these theories, material diffusivity and retention in the OVPD system can be understood, and are useful for characterizing growth in dynamic environments employed in R2R deposition. [1] R. Lunt, B. Lassiter, J. Benziger, S. Forrest, Appl. Phys. Lett. 95, 233305 (2009). [2] R. Aris, Proc. R. Soc. Lond. A, 235, 1200, 67-77 (1956). [3] J. Foley, J. Dorsey, J. Chromat. Sci., 22, 40-46 (1984).

Electroless copper films, with thickness typically below 1 mu;m, are usually the first conducting layer on the insulating substrates of printed circuit boards. For this and other emerging applications, the internal stress of the copper layer is an important consideration both for film adhesion and film-substrate interaction. We have combined stress/strain analysis based on X-ray diffraction, which is sensitive to the strain of the copper crystallites, with a conventionally used technique that analyses the bending of the substrate (Deposit Stress Analyzer). Both techniques were implemented in such a way that the stress could be monitored continuously both during the deposition of the films from the electroless plating bath as well as afterwards. These tests were carried out for a variety of different chemical formulations of the electroless baths, with the deposit thickness as a variable parameter. For a group of baths, we find that the results from both techniques agree quantitatively. In the other cases, the sign of the stress (compressive/tensile) and the direction of the time evolution agree, while the magnitudes differ. Some features, such as voids and pinholes, may be a mechanism through which the stress and strain of the copper crystallites and the substrate can be affected to different degrees. We are currently trying to correlate these features with the stress data.

The area of printed electronics has seen a tremendous development over the past ten years, mainly driven by the introduction of new materials that enable new functionalities or improved properties. This development is expected to last for the coming years, similar to the evolution of silicon-based electronics. Silicon electronics has proven suitable to produce highly complex electronic devices, but in turn has established a highly sophisticated and energy consumptive production environment. Hence there are at least two development strategies: first, a further improvement of the material performance and the existing technologies and second, the development and adaptation of materials that can be applied in novel, low-cost and energy-saving manufacturing feasible for the target applications. As a customization of the to-date available materials to completely new process technologies is very limited, flexibility in the processing techniques must be used to circumvent. Printing techniques such as gravure and rotary screen are often used as a reference for the future of printed electronics. However, printing of electronic devices requires a large degree of freedom with respect to the applied techniques and a perfect control of the environmental conditions. This is a particular challenge as this degree of complexity and stringency of environmental control has never been realized in classical “graphical” printing. Based on the long-lasting experience of our company in the semiconductor industry, we report about a flexible, modular production platform for printed electronics - “MicroFLEX”. In a comparable complexity, such tools have been realized only on a lab-scale level before (e.g. change from gravure to rotary screen). The platform is compliant with a variety of requirements, beginning with its easy accessibility and usability to controlled environment conditions and process tolerances, making it capable of pilot and large-scale production volumes. The platform consists of production modules carrying a moving web which enables the creation of a flexible production line for flexible substrates from R2R in which the process chain can be designed according to the requirements of the target materials and products. This includes the capability to simply change the order of the process steps, the adaptation of and the substitution of available technologies with new or better suited approaches or finally to extend the capabilities of a R2R tool to enhance its functionality or throughput. As the scale of such a system can easily achieve a level of complexity which can hardly be managed 3D-Micromac AG has developed a manufacturing execution system which leads to a significant reduction in the development efforts. , With this software solution, the user is capable of measuring process conditions and allocating them to the posteriori characterized devices.

As produced, raw carbon nanotubes are not soluble in many solvents necessary for printing applications. Standard methods for circumventing this problem involve sidewall functionalization and surfactants. Sidewall functionalization invariably destroys the π-network that gives carbon nanotubes their useful electronic properties, while surfactants deposit an insulating layer onto the carbon nanotube surface that must be washed off to regain the desired properties. Non-covalent functionalization offers the possibility to achieve solubility without the destruction of the π-network, but published methods have resulted in relatively low concentrations or substandard electronic performance. We have developed a scalable method to non-covalently functionalize long (> 3 mu;m) carbon nanotubes with simple pyrene derivatives. This method produces highly dispersed solutions with concentrations as high as 2.5 g/L that can be used to produce conductive coatings with sheet resistance as low as 350 Omega;/square with 85% transmittance at 550 nm without post-deposition washing or doping treatments. The functionalized carbon nanotubes can be formulated into solutions that can be printed by ink-jet deposition, Aerosol-Jet® deposition, screen printing, and spray coating for printed electronics fabrication, and the solutions are stable for months without signs of bundling.

Effective stabilization and dispersion of carbon nanotubes (CNTs) in solvents and polymer matrices remains a major challenge for both fundamental research and practical applications. The common strategies to disperse CNTs fall into two general categories: chemical functionalization and noncovalent surface modification. Chemical treatment inevitably involves disruption of the long range π conjugation of the nanotube, leading to partial loss of electronic properties and mechanical strength. Therefore the noncovalent approach is considered advantageous in that it maintains the sp2-conjugated structures of CNTs and therefore preserves their intrinsic properties and performances. We report a new chemistry for CNT dispersion, using nonconjugated organometallic polymers like polyvinylferrocene (PVF). PVF contains none of the previously reported chemical structures (such as pyrene, porphyrins, nucleotide bases, and conjugated polymeric structures) that are known to have strong noncovalent interactions with CNTs. The aim of the present work is threefold: (1) to evaluate the efficiency of using PVF to stabilize and disperse pristine SWCNTs and MWCNTs, (2) to provide evidence of a strong noncovalent interaction between the nonconjugated organometallic polymer and the carbon nanotubes, and (3) to investigate the quality of dispersion of CNTs by PVF in polymer matrices. This work has clear technological implications in the field of CNT dispersion because the ferrocene moiety can be easily introduced to a wide range of surfactants and polymers, enabling the development of new types of CNT dispersants based on noncovalent interactions without using any conjugated components. This chemistry offers new opportunities to extend applications of pristine carbon nanotubes in a greater variety of media.

Semiconducting Single-walled carbon nanotubes (s-SWNTs) are thought to be an ideal candidate for the next generation printable semiconductor. s-SWNTs have been shown to have field-effect mobility which is much than those of other contenders such as polymers and they are also thermally and mechanically stable and robust. The mobility of semiconducting nanotubes has been calculated to be extremely high and hence SWNTs are thought to be promising candidates for the active material in printable transistors [1]. However, in most as-synthesized single-walled carbon nanotube (SWNT) samples, about one-third of the nanotubes have metallic electronic properties and two-thirds are semiconducting. The metallic species short the circuits and are undesired for applications in transistor and associated electronic devices. Dispersion and separation of s-SWNTs are key issues in the application of nanotubes in electronic applications. We have demonstrated that polymers can effectively debundle and disperse SWNTs. There are two main categories of polymers used for dispersion and separation of SWNTs and they are the polyaromatics [2-5] and the polysaccharides [6-9]. Our group has pioneered the application of polysaccharides in the effective dispersion and separation of SWNTs. We have investigated chitosan, various neutral pH water-soluble chitosan derivatives and heparin sodium salt as dispersants of SWNTs. Chitosan (CS) can disperse SWNTs well, but only in acidic pH condition. Our two novel derivatives, O-carboxymethylchitosan (OC) and OC modified by poly(ethylene glycol) at the -COOH position (OPEG), were able to produce highly effective debundling and dispersion of SWNTs in neutral pH aqueous solution. We have also shown the chondroitin sulfate A isomer (CSA) is a highly effective and removable dispersant of Single-Walled Carbon Nanotubes. We report our gel electrophoresis method based on the CSA selective polymer which produces high purity (95%) semiconducting SWNTs with high yield (25%). Semiconducting nanotubes purified with this method were successfully employed in the fabrication of high performance network-based field effect transistors.

Solubilization of the single-walled carbon nanotubes (SWCNTs) is important for fundamental studies and industrial applications of SWCNTs. Especially, precise tuning of the dispersibility of the SWCNTs is necessary in many applications including switching devices, sensors, and drug delivery systems. Herein, we describe water-soluble stilbene derivatives having several numbers of aryl groups that act as excellent dispersants. Moreover, one of them showed photochemically tunable dispersibility for SWCNTs, based on photocyclization of a stilbene unit in an aqueous solution. The nearly coplanar structure of the stilbene dispersant should be important to interact with surface of the SWCNTs via π-π interactions, resulting in a stable dispersion of the SWCNTs with individual debundling confirmed by several spectroscopic techniques. Photoinduced cyclization of the dispersant triggered re-precipitation of the SWCNTs due to detachment of the dispersant from SWCNTs surfaces. It is expected that the photochemical dispersibility control of the SWCNTs produces an advantage for creating novel smart stimuli-responsive systems, such as purification, separation, and CNT composites.

Due to their nanoscale dimensions and outstanding electrical and mechanical properties single walled carbon nanotubes (SWNTs) devices are of intense research especially in the rapidly emerging field of flexible electronics. Here, we demonstrate integration of highly ordered SWNTs on a lithographically patterned flexible Polyethylene naphthalate (PEN) films employing fluidic assembly with excellent electrical characteristics. PEN plastic films feature low coefficient of thermal expansion, high resistance to most solvents, and heat stabilized material so that it is compatible with conventional CMOS process. Optical lithography is employed to generate these micron scale patterns on the PEN substrate. Various factors influencing the assembly yield such as humidity and template surface energy are also studied. A controllable drying process has been developed to increase the yield of highly dense SWNT assembly over large arrays. Oxygen plasma treatment process was used to clean organic residues off substrates and to hydroxylate the surfaces making them hydrophilic. The exposed hydrophilic surface in the PEN template has hydroxide chemical groups enabling anchoring of SWNTs. Subsequently, metal electrodes were fabricated onto the assembled SWNTs and electrical characterization were carried out. These highly aligned SWCNTs exhibited resistivity of the order of 10^4 ohm-cm suitable for a variety of applications including solar cells and EMI shielding.

In this talk, the use of carbon nanotubes as the active and passive components of various flexible electronic and sensor systems will be discussed. Specifically, multifunctional flexible systems capable of detecting and responding to external stimuli will be discussed. The work sets the stage for the development of user-interactive systems with advanced functionalities that can be readily attached to any surface. The stimuli could include pressure (e.g., touch), temperature, strain (e.g., crack formation), humidity and chemicals, and more. The enabled “electronic-skin” presents a new class of smart materials, which provides interfacing of a system to the external ambient with high fidelity.

The ubiquitous society will be fully realized when costless and flexible electronics are available. However, current Si based electronics have reached the limit of cost and flexibility. In other words, the photolithography based process would not be a manufacturing process for producing those costless and flexible electronics anymore. Recently, that&’s why roll to roll (R2R) printing process has been considered as an alternative manufacturing process for the production of the costless and flexible electronics. As a consequence of developing R2R printing process as a manufacturing process for the costless and flexible electronics, this dissertation has been pioneered in employing R2R gravure for fabricating 13.56 MHz passive RFID tags as a reference sample for the costless and flexible electronics. For developing the R2R gravure process in printing 13.56 MHz passive RFID tags, first, all of inks (conducting, semiconducting and dielectric) have been developed respectively using silver nanoparticles, single walled carbon nanotubes (SWNTs) and BaTiO3 nanoparticles. Second, all printed thin films transistors (TFTs) on plastic foils using the developed inks were fully characterized and simulated to further integrate into 1 bit to 96 bit 13.56 MHz RFID tags on plastic foils. Finally, using all gravure printed transistor, we have made 1 bit to 96 bit RFID tag and NFC tag using electro chromic displayer and smog sensor on 1 bit RFID tag.

The compressive behavior of nominally vertically aligned carbon nanotube (VACNT) patterned into pillars, typically resembles that of an open cell foam. Such stress-strain data usually exhibits 3 distinct regimes: (1) short initial elastic section followed by (2) an extended stress plateau up to 70-80 % strain, and (3) densification characterized by a rapid stress increase with subsequent strain. In contrast to foams, the plateau regions of VACNTs are not flat but have a strengthening slope, which ranges from a flat plateau (slope ~ 0) to a strong positive slope (~ 11 MPa). The mechanisms for such a stress plateau strengthening have not been understood, although it has been suggested that a linear non-uniformity in the yield strength along the sample height scaled with the plateau slope (Hutchens, S. B., A. Needleman and J. R. Greer, 2011. Journal of the Mechanics and Physics of Solids 59(10): 2227-2237, Bedewy,M. et al. J. Phys. Chem. C 2009, 113, 20576-20582). We present the results of in-situ micro-mechanical experiments, image analysis, and mechanics modeling, all of which suggest a correlation between the density gradient along the bundle height and the strengthening slope of the plateau region. Two sets of VACNT micro-pillars with either square (40 µm ×25 µm, height × width) or circular (40 µm ×30 µm, height × diameter) cross-sections were grown on the same Si substrate by chemical vapor deposition. Uniaxial compression experiments were performed in-situ, in a custom-built nano-mechanical deformation instrument, SEMentor. Two distinct compressive signatures were observed: (1) square pillars deformed via a bottom-to-top localized buckling sequence and had sloped stress plateau (slope ~ 0.5 MPa) and (2) in circular pillars the bottom buckles always formed last, with no observable strengthening slope in the stress plateau (slope ~ 0). Image analysis of the scanning electron micrographs taken along the heights of each sample type revealed distinct gradients in the relative CNT number density as a function of sample height. A compressible elastic-viscoplastic constitutive relation, previously developed to model the inelastic behavior of VACNTs (Hutchens, S. B., A. Needleman and J. R. Greer, 2011. Journal of the Mechanics and Physics of Solids 59(10): 2227-2237), is used in finite deformation, finite element analyses to explore the stress-strain response of VACNTs as a function of varying yield gradient. The results of these experiments, image analysis, and modeling are interpreted in concert in the framework of foam-like deformation and suggest that density is a key parameter, which governs compressive response of VACNTs.

Carbon nanotubes (CNTs) have been the focus of significant research since Iijma&’s 1991 Nature article. Due to their superior mechanical, electrical and thermal properties CNTs may prove beneficial for a wide range of potential applications. Most research efforts have primarily been directed toward growing CNTs on flat substrates. In this study, dense, aligned CNTs were grown on 3-dimensional open cell reticulated carbon foam. The CNTs were realized using floating catalyst chemical vapor deposition with xylene and ferrocene as the carbon and catalyst sources, respectively. The best results were achieved when a thin layer of Al2O3 was deposited on the foam via atomic layer deposition (ALD) prior to CNT growth. The foam samples were 1 cm x 0.5 cm x 0.5 cm, yet CNTs were found throughout the volume of the sample and not just the outer layers of the foam. Growing CNTs on a 3-Dimension foam structure dramatically increases the available surface area, potentially enhancing mechanical and thermal performance characteristics of the foam. The nanotube/foam composite could make an ideal packaging material for power electronics modules. Namely, the composite would help remove heat from high power devices and possibly address concerns about coefficient of thermal expansion mismatch (CTE) between materials. In order to effectively utilize the nanotube/foam in a package stacking configuration, however, it is necessary to braze or bond the composite to the other materials in the stack. Hence, after formation the nanotube/foams were coated with a layer of nickel. Two different nickel coating techniques were explored-electroless plating and electroplating. The results of this study will be presented, including growth details, microscopy at various stages of processing, and thermal property analysis.

While carbon nanotube (CNT) forests have been shown to have outstanding thermal, electrical and mechanical properties, devices and interfaces that utilize these characteristics cannot bear the cost of batch-style processing on silicon wafers. Moreover, growth of the flexible electronics and composites markets has created demand for efficient chemical vapor deposition (CVD) equipment for continuous processing. Lessons learned from our previous work with continuous manufacturing of CNT forests on rigid substrates drove the design specifications for the continuous manufacturing process and machine that is presented here. The machine utilizes a novel concentric tube design, where a thin foil substrate, wrapped in a helical path around the inner tube, continuously translates and is exposed to the gas atmosphere in the small uniform gap between the concentric tubes. Radial holes in the inner tube sidewall allows for a carbon precursor gas to be introduced to the foil at a specific location in the heated region. This decoupled, multi-zone reaction chamber enables reducing and growth atmospheres to be seamlessly combined in a controlled thermal environment, as validated by 3D computational fluid dynamics (CFD) simulations. We present the design and construction of a bench-scale prototype machine, along with a characterization study of the system illustrating the control of forest height and density via the substrate feed-rate and the concentric tube gap. Finally, we summarize an analysis of gas utilization and throughput that facilitates the adoption of this machine design for different substrate sizes and applications, which when compared to lab scale systems, enables a feed gas volume savings of over 90%. This work, in combination with continuous feed evaporative deposition of catalyst particles, enables a continuous manufacturing process and device for low-cost and scalable production of VA-CNT forests on flexible substrates.

An industrial mass production process of graphene is one of the most important technologies for graphene electronics and optoelectronics. The thermal CVD on metal catalysts [1] and the reduction of graphene oxide [2] were reported for the syntheses of graphene films on large area. However, higher temperature and long process time are remaining problems for the industrial mass productions. In our previous study, the relatively low deposition temperature had been realized by using microwave plasma CVD [3]. Recently, we developed a roll-to-roll graphene synthesis based on a linear antenna type microwave plasma CVD and demonstrated the continuous deposition of graphene with A4 (297 mm) width [4]. In order to develop the practical mass production system of graphene, it is necessary to widen the substrate width and to increase the deposition rate. However, it is difficult to achieve above two problems using the linear antenna type system. A slot antenna type microwave plasma CVD system is expected to be solved the above problems since the slot antenna type plasma CVD enabled us to arrange coat diamond films on large area by controlling arrangement of slots. By modulating the antenna structure in CVD apparatus, we succeeded the increasing of the deposition area and the flow speed. Four slot antennas were prepared to form plasma in the area of 650x650 mm2. Each slot antenna was controlled one microwave generator with maximum power of 5 kW, which indicated that total microwave power was 20 kW. To control the film temperature, sample holder was equipped with a heating system. A roll-to-roll system consists of an unwnder and a roll up mechanism. Roll-up process had a motor to dominate the film flow speed. The unreeling process had a decelerator to keep the appropriate tension of Cu film. The flow speed of foils was 60 mm/s, which was one order faster than the previous our process. The film temperature was about 400 C. Total microwave power is 18 kW. The pressure of CH4, H2 and Ar atmosphere was 5 Pa. A rolled 33µm-thick cupper film with 594 mm in width was used as substrate. It was confirmed by Raman spectroscopy that a continuous graphene film with 594 mm width was successfully deposited on Cu foil. By using the slot antenna type microwave plasma CVD, both of increasing the deposition area and the flow speed were realized for the graphene mass production. [1]S. Bae et al., Nature Nanotechnol. 5 (2011) 574. [2] H. Yamaguchi et al., ASC Nano 4 (2010) 524. [3] J. Kim et al., Appl. Phys. Lett. 98 (2011) 091502. [4] T. Yamada et al., Carbon 50 (2012) 2515.

Carbon nanotubes have been actively studied since its first observation in 1991. Various methods of fabricating CNT patterns have been researched. Chemical vapor deposition (CVD) can grow CNT patterns with micro-level resolution. However, CVD is limited to be used on thermally durable growth substrates. Other method, such as polydimethylsiloxane stamps based transfer printing method, can achieve a CNT pattern resolution of 50 um, but requires various stamps for specific patterns. Electrophoresis deposition of CNT has also been researched, but has difficulties making defined micro-level patterns. Ink-jet printing is a method capable of printing CNT patterns with a resolution of 20um. In this work, ink-jet printing is used to define single-walled carbon nanotubes (SWNTs) patterns. Sodium dodecyl sulfate (SDS) is used as surfactant to facilitate SWNT to disperse in DI water. This dispersion is used as ink for inkjet printing. Printed CNT pattern has a micro-level feature size. The as printed pattern is electroplated with indium sulfamate plating bath. Instead of being plating on top of the CNT pattern, indium fills in the CNT mesh and a composite of SWNT and indium is formed. This composite of SWNT and indium display higher durability compared with pure indium and high electrical conductivity. This indium coated CNT has potential of being used as interconnect. Indium bumps can be used as interconnect. However, indium bumps are not reworkable. By adding CNT into indium bumps, indium bumps are stronger and reworkablity becomes possible. Reworkablity test has been performed. To further research its potential of being used as interconnects, these interconnects have to be useful at high frequency. Using ink-jet printing as a patterning method, coplanar waveguides with indium plated CNT as interconnect material are fabricated and their high frequency performance has been researched.