Nonvolatile polymer memory device based on bistable electrical switching in a thin film of poly(N-vinylcarbazole) with covalently bonded C60

A functional polymer (PVK-C60), containing carbazole moieties (electron donors) and fullerene moieties (electron-acceptors) in a molar ratio of about 100:1, was synthesized via covalent tethering of C60 to poly(N-vinylcarbazole) (PVK). The molecular structure and composition of PVK-C60 were characterized by FTIR, Raman, and UV-vis absorption spectroscopy, gel permeation chromatography (GPC), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CyV). The C60-modified PVK exhibited an enhanced glass-transition temperature (Tg = 226 degrees C) and good solubility in organic solvents such as toluene, tetrahydrofuran, chloroform, and N,N-dimethylformamide (DMF). It could be cast into transparent films from solutions. For a thin film of PVK-C60 sandwiched between an indium tin oxide (ITO) electrode and an Al electrode (ITO/PVK-C60/Al), the device behaved as nonvolatile flash (rewritable) memory with accessible electronic states that could be written, read, and erased. The polymer memory exhibited an ON/OFF current ratio of more than 105 and write/erase voltages around -2.8 V/+3.0 V. Both the ON and OFF states were stable under a constant voltage stress of -1 V for 12 h and survived up to 108 read cycles at -1 V under ambient conditions.