Analytical modeling and parameter extraction of top and bottom contact structures of organic thin film transistors

This paper proposes a structure based model of an organic thin film transistor (OTFT) and analyzes its device physics. The analytical model is developed for the top contact structure by mapping the overlap region to the resistance (in the vertical direction) that includes the contact and the bulk sheet resistances. Total device resistance includes the vertical resistance per unit area of the contact region and the sheet resistance of the channel. In addition, the drain and the gate voltages take into account the potential drop across the respective contacts. The gate bias dependent mobility is considered in place of constant mobility, since; it is more realistic and relevant to the organic TFTs. The proposed analytical model is also applied to the bottom contact structure and the current-voltage (I-V) characteristics are obtained. Furthermore, a differential method is employed to extract the parameters, such as, mobility enhancement factor γ, threshold voltage VT, mobility µB, characteristic length LC, vertical resistance RV and contact resistance RC. Finally, the model is validated in terms of electrical characteristics and performance parameters for both top and bottom contact structures. The analytical model results are in close agreement with the experimental results.