Nanostructured polymer transistors for volatile organic compound detection

In this paper, we show that the chemical sensing responses of organic thin film transistors (OTFTs) based on nanostructured regioregular polythiophene are strongly dependent upon the gate biasing field and the operation mode. With different applied gate voltages the source-drain current response can be different both in sign and magnitude for the same analyte. Using swept gate voltages, sensors show larger response than when operated with a constant gate voltage. These results imply that multiple, competing sensing mechanisms exist. We propose that the sensing mechanisms for polycrystalline semiconducting polymer thin films are mainly an intragrain effect, which yields a positive response, and a grain boundary effect, which yields a negative response. Noise properties of the OTFT sensors were also investigated. For the typical sensor operation frequency range these results show that low frequency noise is the dominant noise source.