A tabletop prototype of a roll-to-roll (R2R) direct stamping apparatus has been developed. The prototype is about 100 cm long, 30 cm wide and 40 cm high and is operational up to the web speed of 1 m/min. While upper rolls carry a web with a patterned stamp on it clockwise, a sprayer on top of the R2R apparatus dispenses the nano-ink to fill in the stamp. Two other rolls with adhesive films completely remove the residual layer on the stamp. Final products remain on the substrate after de-stamping in which the web rolls up and the substrate moves to the further right. This roll-to-roll direct stamping apparatus demonstrates high throughput and material efficiency for fabrication of flexible micro- and nano-electronic 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). 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 is able to model these effects. The technique has been successfully validated against published experimental data from two different roller-NIL processes: one involving an ultraviolet-curing resist film on a glass plate, and another involving a flexible thermoplastic web softened at its surface.

Scaling contact lithography (microcontact printing, microflexography, and nanoimprint lithography) to large roll-to-roll platforms will enable high speed, low cost lithographic patterning of surfaces. However, many details of robust implementations at the roll-to-roll scale remain an engineering challenge, including precise regulation of printing pressures and the stamp-substrate interaction. This paper introduces a method for precise control of contact pressure that can accommodate large dimensional variations, i.e. varying stamp and substrate thicknesses. This control algorithm is implemented on a simply supported roll positioning stage. Experimental results for microcontact printing and microflexography are shown both with in situ contact measurements on a pseudo substrate and with 5 um silver nanoparticle prints. Ultimately, this approach enables robust printing despite sensitive stamp patterns and large dimensional variations (> 10 μm) in substrates, stamps, and roll equipment.

Organic photovoltaic (OPV) devices were fabricated using a novel draw bar premetered coating technique, whereby a meniscus of fluid is dragged across a substrate to leave a trailing wet film. The results showed that coating thickness could be controlled by varying the coating speed, rod diameter, gap height, amount of solution injected, rod diameter, rod composition material and number of layers. Devices on PET with active areas of 10 cm2 and active layer thicknesses ranging from 35 to 475 nm were produced using the technique. Active layers of 160 nm were the optimum of thicknesses trialled, achieving typical best efficiencies around 0.4 %. Devices with films thinner than 90 nm did not function due to short-circuiting. The draw-bar coating method has the advantage of allowing controlled deposition of a wide range of film thicknesses with no solution wastage.

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 5μm and height less than 300 nm. The twin lines are separated by a predominantly particle-free region with the spacing between the lines ranging from 100 μm to 600 μm, where the spacing is a function of ink, substrate, and printing conditions. The effect of substrate surface and jetting parameters on nanoparticle line morphology is presented. Arrays of such lines have been printed and evaluated as potential transparent conducting films, showing an effective sheet resistance of ∼5 Ω/□. 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.

Deposition of solution-processed functional materials generally requires additional post-processing to optimize the functionality of the material. We study sintering of Ag nanoparticle (NP) (with average diameter 77nm) deposits for improved electrical conductivity, with emphasis on Argon plasma methods compatible with the low temperature requirements of regular low-cost flexible polymer substrates. The relationship between plasma parameters (such as power and treatment time) versus sintering results (sintered structure depth, film continuity and electrical sheet resistance) 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.

Uniformly uni-axially aligned electrodes are formed by uniaxially cracking an indium tin oxide, ITO, film vacuum deposited on a polyester substrate. The cracks are produced by bending the film around a small radius of curvature, producing narrow, parallel cracks in the ITO separated by 5-10 μm. The cracks are enhanced by etching or uniaxial stretching. Heating and stretching is the most effective, producing a crack width of about 0.05 μm 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 substrates 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 μm 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 polymers to produce the line electrodes required for flexible, passive matrix displays and related electronic applications. Un-axially cracking can be easily integrated into a roll-to-roll manufacturing process.

Electroless copper films 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 during the deposition of the films from the electroless plating bath as well as afterwards. These tests were carried out for three chemical formulations and the results from both techniques agree qualitatively. For one bath, the substrate bending method detects a 60 nm region of local stress at the film-surface interface.

In this paper, we focused on sintering of inkjet-printed copper nanoparticle ink structures using a continuous wave 808nm diode laser. Laser sintering in printed electronics is a rapid sintering method which enables localized sintering. Sintering of Cu inks is usually done in nitrogen atmosphere but the novelty of this study is that successful sintering of Cu ink was done under ambient conditions. The used ink consists 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 was analyzed. Resistivity of 10-12 μΩcm with good repeatability as well as excellent adhesion, were achieved.