Effects of electron donating and accepting moieties on electrical memory behaviors of polymers

Abstract

In this study, three different series of vinyl copolymers bearing electron donating and accepting moieties in various compositions and their homopolymers were synthesized by reversible addition-fragmentation chain transfer polymerizations. They all were soluble in conventional organic solvents and gave good quality nanoscale films via conventional coating and drying processes. They were thermally stable up to 242 °C or higher temperatures. Their optical and electrochemical properties as well as electron densities and mass densities were measured. The nanoscale film morphologies were further examined by synchrotron grazing incidence X-ray scattering analysis; they were confirmed as amorphous or structurally-featureless films. All polymers exhibited various electrical properties depending on the polymers and film thicknesses. In particular, only p-type digital memory characteristics were observed within certain film thickness windows, regardless of electron-donating polymers, electron-accepting polymers, and their copolymers. Moreover, all polymers revealed high memory performances with low switching-ON voltages, high ON/OFF current ratios and high reliabilities even in air ambient conditions. The memory behaviors followed a combination of hopping conduction and trap-limited space charge limited conduction in the OFF-state and hopping conduction in the ON-state. However, the film thickness window showing digital memory characteristics was significantly dependent upon the compositions of electron donating and accepting moieties. Higher fraction of electron-donating moieties provided wider film thickness window for digital memory. For this aspect, the electron-accepting polymers could gain great benefits by incorporating electron-donating moieties, whereas the electron-donating polymers could attain only negative impacts via the addition of electron-accepting moieties. Overall, all polymers of this study are suitable for the low-cost mass production of high-performance programmable memory devices.