Compact model for forward subthreshold characteristics in polymer semiconductor transistors

Abstract

We present a compact model for polymer thin film transistors (TFTs) operating in forward subthreshold region. Due to the threshold voltage shift in these devices, the bias point of a device operating for a sufficiently long time moves toward the subthreshold region. Therefore, modeling subthreshold operation in polymer semiconductor based TFTs is important. We particularly address two areas where polymer TFTs are different from other disordered materials such as amorphous silicon. Firstly, the shape of the density of deep states cannot be assumed to be purely exponential. Such an assumption does not provide fine modeling of the subthreshold slope. Secondly, for subthreshold operation particularly under high drain-source bias, we need to include PooleFrenkel type transport mechanisms such as variable range hopping and space charge limited current. This paper includes these features and develops a compact closed form model.