Dresden 2011 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 67: OLEDs and OFETs

HL 67.5: Talk

Wednesday, March 16, 2011, 19:00–19:15, FOE Anorg

Electrolyte-gated organic thin-film transistors for sensing applications — •Felix Buth, Deepu Kumar, Martin Stutzmann, and José Antonio Garrido — Walter Schottky Institut, Technische Universität München, Garching, Germany

Organic thin films can potentially be used in low-cost, disposable devices for chemical or bio-sensing. However, operating organic sensor devices in an aqueous environment raises difficulties when it comes to necessary operation voltages or device stability. One approach to reduce the gate voltage is increasing the capacitance of the gate dielectric. Electrolytic gates offer extraordinarily large capacitances, up to several µ F/cm² at low frequencies. This high capacitance, which is the result of the formation of an electrical double layer at the electrolyte/semiconductor interface makes low-voltage operation possible, without high production costs. In this contribution, we investigate the behavior of polycrystalline α-sexithiophene (α6T) thin-film transistors with an aqueous electrolyte gate. Electrochemical impedance spectroscopy and CV measurements indicate a nearly perfectly polarizable interface with negligible parasitic Faradaic currents. For gate voltages below 1 V, a conductive channel is induced at the α6T/electrolyte interface via an electrical field effect. The transistor is stable for several hours and sensitive to changes in the pH or the ionic strength of the solution. The pH sensitivity arises from a shift in the threshold voltage of the transistor, and is not due to changes of the carrier mobility. The pH-dependent threshold voltage shift, in the range of 10 mV/pH, is caused by a change in the surface charge of the thin film.