Parasitic resistance in bottom-contact pentacene thin-film transistors that use water- dispersible polyaniline electrodes

Introduction Organic thin-film transistors (TFT) have received considerable attention due to promises of low manufacturing costs, ease of processibility, and extendibility to flexible circuits. The feasibility of organic TFTs has largely been demonstrated with devices that use metal source and drain electrodes, such as gold and palladium. Such devices, when fabricated in the bottom-contact (BC) configuration, exhibit pronounced non-linear current-voltage (I-V) characteristics in the low source-drain voltage regime [1]. This phenomenon has been attributed to the presence of a large dipole barrier at the organic semiconductor/metal interface [2]. It has also been hypothesized that this dipole barrier can be decreased through the incorporation of organic, rather than metallic, conductors as electrodes. For example, Koch et al. found that organic semiconductor/conducting polymer interfaces, e.g. pentacene/poly(3,4ethylenedioxythiopene)-poly(styrenesulfonate), significantly reduce the hole injection barrier and the interfacial dipole barrier [3]. Lefenfeld et al. also showed that BC pentacene TFTs that use polyaniline (PANI)/single-wall carbon nanotube electrodes exhibit decreased contact resistance at the interface [4]. This paper presents an experimental study of parasitic resistance in BC pentacene TFTs that use water-dispersible PANI electrodes. PANI electrodes were fabricated using our recent stamp-and-spin-cast technique [5]. Thermal evaporation of pentacene directly onto the channel region completes the circuit. We extracted the parasitic resistance using the TFTs with different channel lengths. Quantitative comparison between the contribution of the PANI electrode bulk resistance and the contact resistance at the pentacene/PANI electrode interface to the parasitic resistance indicates negligible contact resistance at the pentacene/PANI interface.