Digital memory behaviors of aromatic polyimides bearing bis(trifluoromethyl)- and bithiophenyl-triphenylamine units

Two thermally, dimensionally stable aromatic polyimides (PIs) of triphenylamine derivatives bearing electron-accepting bis(trifluoromethyl)phenyl group and electron-donating bithiophene group were synthesized with reasonably high molecular weights. These PIs in nanoscale thin films were investigated in aspects of morphological structure and interfaces in contact with substrates and metal electrodes as well as optical and electrochemical properties. The PIs in memory devices initially exhibited a high resistance (OFF-state). When positive and negative voltages were applied, the PIs demonstrated two different types of unipolar memory behaviors (volatile static dynamic random access memory and nonvolatile write-once-read-many-times memory) with a high ON/OFF current ratio up to 108, depending on the electron-accepting and donating substituents of the TPA units. All of the memory behaviors were found to be governed by a mechanism involving field-enhanced thermal emission of trapped charges and filament formation. Overall, this study has demonstrated that the thermally, dimensionally stable PIs are highly suitable active materials for the low-cost mass production of high performance, polarity-free programmable memory devices that can be operated with very low power consumption.