Synthesis and memory properties of a conjugated copolymer of fluorene and benzoate with chelated europium complex

Abstract

A conjugated copolymer of diethylhexylfluorene and europium complex-chelated benzoate (PF8Eu) was synthesized. The device based on an Al/PF8Eu/indium-tin-oxide sandwich structure exhibited nonvolatile, write-once read-many-times (WORM) memory behavior. The fluorene moiety served as the backbone and electron donor, while the europium complex served as the electron acceptor. The as-fabricated device was in its low conductivity state. After applying a voltage of ∼3V, the device underwent a transition to the high conductivity state, which could not be erased by a reverse bias. In the initial low conductivity state, the device showed a charge injection controlled current. At the high conductivity state, the current-voltage characteristics were dominated by a space-charge-limited current. The device had a switching time of ∼1μs and an on/off current ratio as high as 106. No degradation in device performance was observed after 107 read cycles at a read voltage of 1V under ambient conditions. The device also exhibited good stability under a constant 1V stress. Thus, the device based on PF8Eu is potentially useful as a WORM memory.