Compact modeling and contact effects in thin film transistors

A compact model for the current-voltage characteristics of organic thin-film transistors (OTFTs), which includes the effects of the contact regions, is proposed. Different physical and morphological aspects of contacts with organic or other emerging materials such as graphene, semiconducting dichalcogenides such as {\rm MoS}₂, or NW devices are described. The electrical behavior of the contacts is studied in OTFTs, and circuit models that describe them are reviewed. Two trends are observed in the current-voltage curves of the contacts of different OTFTs: linear and nonlinear, and different models are used to explain them. A unified model for the contact region that reproduces both trends and gathers the different physical and structural features of the contacts is developed. It is described by a single parameter and introduced in a generic analytical model for TFTs. The variability in OTFT structures, materials, and fabrication approaches gives rise to a strong variability in the values of the parameters of the model. In this regard, a characterization technique to determine the value of the parameters of the model from experimental data is also developed. Different physical tests are proposed to validate the results of the technique. The procedure is applied to recent experimental data for different pentacene-based transistors. The good agreement between the experimental data and our analytical results provides a way to relate the parameters of the model with the physical or geometrical origin of the contact effects in OTFTs.