Dielectric layers for organic field effect transistors as gate dielectric and surface passivation

Organic field effect transistors with the organic semiconductor pentacene, using silicon substrates, were successfully built on conventional inorganic dielectrics like silicon dioxide or silicon nitride. They can drive drain currents up to 15 mA. Beyond that, polymer films were investigated as gate dielectrics in order to achieve transistors on plastic films. On polyester substrates with an inorganic-organic gate dielectric, devices reach drain currents comparable to transistors on silicon dioxide and charge carrier mobilities of up to 0.35 cm(2)/V s. Analysis of the pentacene surface by atomic force microscopy showed pentacene crystallites achieving dimensions of more than 1.5 mu m. The unprotected organic devices suffer from degradation due to water and oxygen incorporation. Therefore, the application of a hydrophobic polytetrafluoroethylene layer as capping layer is studied. Because of the reduced influence of water, a shift to positive threshold voltages is caused. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.