Soft Lithography Fabrication of Fully Flexible and Transparent all Organic FETs for Large Area Applications
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Soft Lithography Fabrication of Fully Flexible and Transparent all Organic FETs for Large Area Applications Piero Cosseddu1,2, Emanuele Orgiu1,2, and Annalisa Bonfiglio1,2 1 Department of Electrical and Electronic Engineering, University of Cagliari, Piazza d'Armi, Cagliari, 09123, Italy 2 S3-Nanostructures and BioSystems at Surfaces, INFM-CNR, via campi 213/A, Modena, 41100, Italy ABSTRACT Fully flexible and transparent all organic field effect transistors were fabricated by means of an innovative and inexpensive technique. A 1.8µm thick polyethylenetetherephtalate sheet, Mylar® (Du Pont), was used as gate dielectric and at the same time as mechanical support for the whole structure. We used pentacene, deposited by thermal sublimation, as semiconducting layer, whereas poly(ethylene-dioxythiophene)/polystyrene sulfonate (PEDOT/PSS) was used for the realization of the electrodes. Gate electrodes were realized by spin coating, while source and drain electrodes were patterned by micro-contact printing. We fabricated typical p-type field effect transistors, with mobilities up to 2 x 10-1cm2/Vs and Ion/Ioff up to 105, in a very simple and inexpensive way. It is worth to note that this technique allows the realization of bottom contact and top contact transistors. We realized both bottom contact and top contact devices on the same substrate and with the same active layer and we investigated how the structure itself and the active layer morphology influence the electrical properties in terms of hole mobility, Series Contact Resistance and parasitic capacitance effects. The comparison between top-contact and bottom-contact devices shows interesting marked differences that can be mainly attributed to a different PEDOT:PSS/semiconductor interface quality, influencing the most meaningful parameters. The flexibility of the obtained structure and the easy scalability of the technological process, suitable for roll to roll mass production processes, open the way for economic production of high-resolution organic devices INTRODUCTION Much attention has been paid over the past years to the field of organic electronics. Electrical devices made out of plastic materials, such as Organic Light Emitting Diodes (OLEDs), Plastic Solar Cells (PSCs) or Organic Field Effect Transistors (OFETs), have been extensively studied due to the advantageous chemical and electrical properties of the employed materials[1]. The reason for focused interest in the field of “plastic electronics” is the opportunity to produce low cost devices on plastic substrates on large areas, opening, indeed, an entire new market segment. Organic transistors have a great potential for the fabrication of flexible electronics, such as active matrix displays, electronic papers, smart identification tags and sensors [1, 2, 3, 4]. A fundamental issue in device fabrication concerns the availability of suitable materials not only for the active semiconductor layer, but also for contacts that, so far, have been mainly fabricated with metals. In these past years a lo
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