In this report, the development of conventional, mass-printing strategies into high-resolution, alternative patterning techniques is reviewed with the focus on large-area patterning of flexible thin-film transistors (TFTs) for display applications. In the first part, conventional and digital printing techniques are introduced and categorized as far as their development is relevant for this application area. The limitations of conventional printing guides the reader to the second part of the progress report: alternative-lithographic patterning on low-cost flexible foils for the fabrication of flexible TFTs. Soft and nanoimprint lithography-based patterning techniques and their limitations are surveyed with respect to patterning on low-cost flexible foils. These show a shift from fabricating simple microlense structures to more complicated, high-resolution electronic devices. The development of alternative, low-temperature processable materials and the introduction of high-resolution patterning strategies will lead to the low-cost, self-aligned fabrication of flexible displays and solar cells from cheaper but better performing organic materials.

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Room temperature-sintering, poly(acrylic acid)-capped silver nanoparticles (Ag-PAA NPs) were used in a wide range of nanofabrication methods to form metallic silver microstructures on flexible poly(ethylene terephthalate) (PET) substrates. Silver wires on top of PET foil were patterned by micromolding in capillaries (MIMIC), and silver wires embedded in SU8 on PET foil were fabricated by wetting-controlled deposition in open microchannels. One hundred mm-wide Ag microwires with lengths of 5-15 mm, heights of 0.6-2.5 mm, and a maximum conductivity of a factor 7.3 lower than bulk Ag were obtained. Methanol was studied as an alternative dispersing solvent. It sped up MIMIC drastically, but the low particle packing quality and pre-coalescence in solution resulted in a higher resistivity. The sintering depth was found to be limited to around 100 nm for HCl-vapor induced sintering. Aqueous NaCl, added in a concentration below 50 mM to the Ag-PAA NP ink, was investigated as self-sintering agent. It resulted mainly in strong particle clustering and formation of numerous non-connected grains upon the evaporation of water. A hydrogel reservoir stamping system was used as an alternative printing technique for the transfer of the Ag-PAA NP ink on a PDMS substrate to yield the repetitive printing of arrays of 144 three-micron-wide Ag dots.

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In this paper, a thermal imprint technique, double-layer nanoimprint lithography (dlNIL), is introduced, allowing complete filling of features in the dimensional range of submicrometer to millimeter. The imprinting and filling quality of dlNIL was studied on Si substrates as a model system and compared to results obtained with regular NIL (NIL) and reverse NIL (rNIL). Wavy foils were imprinted with NIL, rNIL and dlNIL and the patterning results compared and discussed. With dlNIL, a new application possibility was introduced in which two different resists having, for example, a different etch resistance to a certain plasma were combined within one imprint step. dlNIL allows extension to many resist combinations for tailored nanostructure fabrication.