Mater. Res. Soc. Symp. Proc. Vol. 1435 © 2012 Materials Research Society DOI: 10.1557/opl.2012. Reliability studies of pentacene based thin film transistors R. Ledru 1 , S. Pleutin 1,2 , B. Grouiez 1 , D. Zander 1 , H. Bejbouji 1,2 , K. Lmimouni 2 , and D. Vuillaume 2 . 1 CReSTIC, University of Reims, Moulin de la Housse, 51687 Reims Cedex 2 (France). 2 IEMN UMR CNRS, University of Lille, BP 60069, Avenue Poincaré, 59652 Villeneuve d’Ascq Cedex (France). ABSTRACT The complex admittance of the Si + /SiO 2 /Pentacene/Au (metal/oxide/pentacene) thin film junctions is investigated under ambient conditions. The results are compared with the ones obtained for the corresponding Si + /SiO 2 /Au junctions (i.e. a small part of the surface left free from pentacene) which constitutes the “reference” of our samples. This allows us to extract the “organic” part of the dielectric response from the whole spectrum. Our data clearly show that the admittance is decomposed in three main contributions. At low frequencies, a contribution attributed to proton diffusion through the oxide is seen. This diffusion is shown to be anomalous and is believed to be also at the origin of the bias stress effect observed in organic field effect transistors. At higher frequencies, two dipolar contributions are evidenced, attributed to defects located one at the organic/oxide interface or within the organic, and the other in the bulk of the oxide. These two dipolar responses show different dynamic properties that manifest themselves in the admittance in the form of a Debye contribution for the defects located in the oxide, and of a Cole-Cole contribution for the defects related to the organic. INTRODUCTION As Organic Field-Effect Transistors (OFET) are now close to applications questions about their reliability under realistic atmospheric conditions become more and more important [1] . Electrical instabilities are evidenced, for instance, in the bias stress effect where under a prolonged application of a gate potential the device characteristics, such as the threshold voltage, evolve with time. Several mechanisms were proposed to understand these degradations of the device properties. Some are intrinsic mechanisms such as trapping of charges, in the organic film or at the organic/oxide interface, or pairing of mobile charges to heavier bipolarons. Some others are extrinsic mechanisms needed especially when the measurements are done in the air since humidity was shown to amplify these instabilities. An example of such mechanism was proposed recently based on proton production by electrochemical reactions involving water molecules adsorbed at the organic/oxide interface, followed by proton diffusion through the oxide [2,3] . In this work, we have considered the Si/SiO 2 /Pentacene/Au junctions that are the two terminal pendants of thin film transistors with the same layer structure. We study the dynamic electrical response of these junctions under ambient conditions over a large frequency window as function of a superimposed dc voltage. The complex admittance, Y(ω), was measured using a frequency response analyzer (Solartron 1260) coupled with an interface dielectric (Solartron 1296) that provides directly the parallel conductance and capacitance. 1248