Contact effects in Cu(TCNQ) memory devices

Reversible electrical switching and memory effects have been reported for a range of organic materials and device configurations. The underlying mechanism is still not clarified and subject of investigations. We present a detailed summary of our experiments on the influence of the contacts on the switching properties of bistable Cu(TCNQ) devices. We have electrically characterized devices with a number of different contact metals as well as different contact and device configurations. In the case of noble metal top contacts, switching was only observed when the contact area was small or when an oxide interlayer was used. These devices reversibly lost there switching properties when no oxygen was present in the ambience. We observed a dependence of the switching polarity on the work function of the contact met al. While devices in the commonly used stacked configuration have an asymmetric electrical characteristic, we were able to produce symmetric, planar devices with symmetric switching behaviour. A device structure comprising three electrodes allowed us to localize the switching process in the vicinity of the metal electrode with the lower work function. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)