Dresden 2009 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: Organic Thin Films I

DS 21.2: Talk

Wednesday, March 25, 2009, 09:45–10:00, GER 38

Potential mapping in the channel of organic thin film transistors. — Peter Bakalov, •Torsten Balster, and Veit Wagner — Jacobs University Bremen, Bremen, Germany

For the analysis of transport properties of organic semiconductors additional information about the potential distribution within the channel of organic thin film transistor (OTFT) would be extremely helpful, which is not easily accessible by integral IV measurement.

For this purpose we have patterned sense fingers in the channel of a transistor in bottom gate geometry by lithographic means on a silicon substrate with 58 nm silicon oxide as insulator. Therefore, the potential within the conducting channel can be directly accessed by high impedance electrometers attached to the sense fingers. As organic semiconductors thiophene oligomers and polymers have been investigated.

The measured current and potential data are evaluated using a combined model of contact resistance and charge carrier density dependent mobility. P3HT devices with and without an additional protection layer of PMMA were analyzed this way. The latter shows superior performance and stability, e.g. the mobility increases almost by a factor of 2, while the threshold voltage shifts by +15 V. The potential data recorded allow to reveal laterally inhomogeneous trapping efficiencies in the device, e.g. resulting in hysteresis.