Compact model for sub-threshold operation in polymer semiconductor thin film transistors

Abstract

We present a compact model for polymer thin lm transistors (TFTs) operating in the forward sub-threshold region. Due to the threshold voltage shift in these devices, the bias point of a device operating for a sufficiently long time moves towards 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 like amorphous silicon. Firstly, the shape of the density of deep states cannot be assumed to be purely exponential. Such an assumption does not provide new modeling of the subthreshold slope. Secondly, for subthreshold operation particularly under high drain-source bias, we need to include Poole-Frenkel 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.