All-organic field effect transistors
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H3.2.1
All-organic field effect transistors. R. Parashkov1, E. Becker1, G. Ginev1, D. Schneider1, D. Metzdorf1, T. Dobbertin1, H-H. Johannes1, W. Kowalsky1 1
Institut für Hochfrequenztechnik, Technische Universität Braunschweig, PO Box 33 29, D-38092 Braunschweig, Germany e-mail: [email protected].
ABSTRACT In this work we present fully patterned organic transistors based on selective electropolymerization of conducting polymers that enables simple fabrication of micron scale features. It involves fabrication of pentacene field effect transistors in which the conducting, insulating parts as well as the substrate are all made of polymers. We have fabricated drain and source electrodes by electropolymerization of 3,4- ethylenedioxythiophene and gate by spin coating of commercially available poly( 3,4- ethylenedioxythiophene) (PEDOT:PSS) aqueous dispersion, polyvinylalcohol for the gate dielectric layer, and pentacene for the organic active layer. We have built a top-gate structure with gate dielectric layer and gate placed on the top of the pentacene layer, and in a such way obtained protection of the active layer could permit enhancement of the operating time of devices. Carrier mobility as large as 0,01 cm2/V s was measured. Functional all- organic transistors have been realised using a simple and potentially inexpensive technology. INTRODUCTION Since the first demonstration of an organic based field-effect transistor (OFET) by Tsumura and Koezuka [1], considerable improvements in device characteristics have been obtained. Most of the work has concentrated on the improvement of field- effect mobility in the active organic layers. To date, field effect mobilities of 1.5 cm2/Vs, comparable to those in hydrogenated amorphous silicon TFTs, have been measured in pentacene OFETs [2]. Although this value is usually at least one order of magnitude lower for OFETs comprising polymeric organic semiconductors like polythiophenes, several examples of polymer integrated circuits have been reported [3-5]. One important aspect of so- called “plastic electronics” is the prospect of simple and cheap mass production by solution processing. Screen printing of conductive inks achieves resolution in the range of 100 µm, which is not satisfactory for patterning source and drain electrodes of organic TFTs [6]. Inkjet printing on pre- patterned substrates yields an enhanced resolution down to a few microns [7], but involves an additional high- resolution process step. Methods based on change of conductivity in photosensitized conducting PANI- layers induced by UV- exposure through a mask and PEDOT or PANI UV photocrosslinking have already proven to be useful for making polymeric integrated circuits with hundreds of transistors [8,10]. Fully patterned all- organic thin films transistors and integrated circuits have been produced [35]. The aim of this paper is to present fully patterned all- organic thin film transistors based on selective electropolymerization and printing of conducting polymers that enables simple
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