Organic field-effect transistors for biosensing applications

Organic field-effect transistors (OFETs) with regioregular poly(3-hexylthiophene) (P3HT) have been designed and fabricated aiming at the lowest possible working point (i.e. the adjusted values of gate voltage and drain–source voltage) for the use as sensor in electrolytes. Using thermally grown silicondioxide with a thickness of 45 nm it has been possible to dramatically lower the gate potential. Even around one volt the channel current and its modulation are still large enough for detection with simple operational amplifiers.The experimental results indicate a strong dependence of the transistor performance on the solvent used for spin coating the organic film. A theoretical analysis based on an analytical model allowed us to relate the different behavior of the transistor to their mobility, which is in turn dependent on the density of traps. In the context of this paper the leakage currents – as a non-zero gate current – have been analyzed. The observed gate leakage currents of the electrode structures themselves as well as of the complete transistors can be well described by Fowler’s and Nordheim’s field enhanced tunneling.