Analysis of the contact resistance in staggered, top-gate organic field-effect transistors

Contact resistance effects are significant in many organic field-effect transistors. Here, we present a detailed analysis of the contact resistance in staggered, top-gate conjugated polymer field-effect transistors. A compact physical model based on the current crowding formalism has been developed. It includes gate modulation of the bulk resistivity of the semiconductor to explain the experimentally observed gate voltage dependence of the contact resistance for different thicknesses of the semiconducting film. The contact resistance is found to be Ohmic. For thick semiconducting films, we have observed a significant asymmetry between source and drain contact resistances with the drain resistances increasing more rapidly with thickness than the source resistance, reflecting the importance of diffusion at the drain contact.(C) 2007 American Institute of Physics.