Eur. Phys. J. Appl. Phys. 48, 30401 (2009)
https://doi.org/10.1051/epjap/2009163

Analytic model for organic thin film transistors (OTFTs): effect of contact resistances application to the octithiophene

¹ Laboratoire de Physique des Matériaux : Structure et Propriétés, Groupe Physique des Composants et Dispositifs Nanométriques, Faculté des Sciences de Bizerte, 7021 Jarzouna-Bizerte, Tunisia
² ITODYS, CNRS-UMR 7086, University Denis-Diderot, 1 rue Guy de la Brosse, 75005 Paris, France

Corresponding author: mansourislah@yahoo.fr

Received: 26 July 2008
Revised: 6 July 2009
Accepted: 10 August 2009
Published online: 30 October 2009

Abstract

Thin film organic field-effect transistors were grown with vapor-deposited polycrystalline-octithiophene on silicon oxide insulating layers. This component requires an ohmic source and drain contacts for ideal operation. The performance of organic electronic-devices is often limited by injection. In many real situations, however and specifically in organic devices, the injection of charge carriers from metals into semiconductors is non-linear. This has an adverse impact on the performance of thin film transistors, and makes the analysis of electrical measurements a complex task because contact effects need to be disentangled from transistor properties. This paper deals with the effects of non-ohmic contacts on the modeling of organic transistors and gives specific rules on how to extract the real transistor parameters using only electrical measurements. Several methods are used in order to study the influence of the contact resistance on the performance of organic transistors. This influence appears especially on the current-voltage characteristics of organic field effect transistor. We present a first method used to extract the key parameters of OFET such as; mobility, threshold voltage and contact resistances using the fit of the transfer characteristic of the devices. The second method has been used to exploit the different functional dependences of current on gate voltage which is induced by the presence of contact resistances in the linear and in the saturation regimes. All electrical key parameters of OFETs based on octithiophene have been extracted and we demonstrate that both mobility and contact resistance depend on gate voltage and temperature.