Flexible Pentacene/PMMA Thin-Film Transistors Fabricated on Aluminium Foil Substrates
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Flexible Pentacene/PMMA Thin-Film Transistors Fabricated On Aluminum Foil Substrates J. Puigdollers, C. Voz, M. Fonrodona, I. Martín, A. Orpella, M. Vetter, R. Alcubilla MNT, Universitat Politècnica de Catalunya, C/ Jordi Girona 1-3. Mòdul C4. Barcelona-08034. Spain ABSTRACT Pentacene thin-film transistors (TFT) were fabricated on aluminum foils using polymethyl methacrylate (PMMA) as gate dielectric. In such structure, the aluminum substrate acts as the gate electrode itself. A bottom gate inverted structure was used to study the influence of the dielectric and the aluminum substrate on the device performance. Pentacene thin-films were deposited by thermal evaporation in high-vacuum at deposition rates around 3 Ås-1 and three different substrate temperatures (30, 60 and 90ºC). The maximum process temperature achieved was 170 ºC, corresponding to the baking of polymethyl methacrylate. The TFTs exhibit field-effect mobility values of ~ 10-3 cm2V-1s-1 and threshold voltage values around –15 V. The influence of the dielectric and the substrate temperature on the pentacene structure and device field-effect mobility is discussed. INTRODUCTION Over the last years, the use of organic semiconductors in field-effect transistors has been envisioned as a viable alternative to traditional technologies based on inorganic materials. A key advantage of organic field-effect transistors (OTFTs) over those based on inorganic semiconductors is their ease of fabrication and low temperature processing. Therefore, OTFTs could be competitive for applications requiring large area coverage on inexpensive substrates. Such applications include smart cards, radio frequency identification tags and displays. The electrical performance of OTFTs has improved considerably during the last decade. Among the variety of organic semiconductors, OTFTs based on conjugated p-type semiconductors have reached the highest electrical performance [1]. Pentacene has been used in the OTFTs showing very good performances, with field-effect mobility values higher than those achieved with the mature amorphous silicon technology. Furthermore, integrated circuits incorporating more than 1800 pentacene TFTs have been recently fabricated [2] Although OTFTs are usually fabricated on non-flexible flat substrates such as crystalline silicon or glass, the use of flexible substrates is more challenging, as its use and that of less carefully controlled conditions could open the possibility of roll-to-roll fabrication, similar to the continuous printing processes used in publishing technology. Additionally, some flexible substrates could not be compatible with the medium-high process temperatures used to obtain standard inorganic dielectrics. Therefore, the use of alternative polymeric dielectrics which can be spin cast or dip coated on inexpensive substrates would also be more desirable. Pentacene based OTFTs have been reported on glass [3], plastic substrates (polyimide [4], polyethylene naphtalate (PEN) [5], polyethylene terephtalate (PET) [6, 7], paper [8] and, eve
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