We have recently introduced a fullerene-derivative [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) based device geometry where the active single-layer devices are composed by incorporating the PCBM loadings into an insulating polymer polystyrene (PS) matrix to yield a PCBM/PS thin-film, which is then sandwiched between two aluminum (Al) electrodes. When the applied bias reaches a certain threshold voltage (Vth), the device makes an abrupt transition from the low-conductivity (OFF) state to the high-conductivity (ON) state and exhibits NDR thereafter. The current-voltage curves are N-shaped in the ON state, i.e. the current decreases with increasing voltage, having a local current maximum at Vmax and a local current minimum at Vmin. The current density ratio at Vmax and Vmin in the NDR regime is more than or equal to ten, which is comparable to the performance of Esaki or tunnel diodes in terms of application. The memory phenomenon in terms of NDR in our Al/PCBM:PS/Al devices is explained by a suggestive mechanism called “tunneling” between the individual PCBM nanoparticles, which is supported with temperature independent NDR down to 240 K. The entire process has been reported in Nanotechnology. The NDR effect in these PCBM/PS films can be easy to control under rugged printable memory electronics point of view, since it is not so sensitive to variations in the processing.
This work is a collaboration between the Department of Physics, Åbo Akademi University, Turku, Finland and the Department of Engineering Physics and Mathematics, Helsinki University of Technology, Espoo, Finland. Future work will include the better understanding of these types of devices, mechanism(s) of bistable switching at Vth and NDR. Our main focus will be to concentrate on establishing a connection between the device morphology and the underlying electrical characteristics by investigating a series of devices fabricated from different materials. The author wishes to thank Prof Ronald Österbacka, Prof Olli Ikkala, Dr Himadri S Majumdar, Ari Laiho, Dr Robin HA Ras and Prof Janne Ruokolainen for their outstanding contribution for this research work published in Nanotechnology.
