Nonvolatile electrical switching behavior and mechanism of functional polyimides bearing a pyrrole unit: influence of different side groups†
To better understand the structure–property relationships and the mechanisms of the electronic switching behavior of functional polyimides, a new series of diamines containing a pyrrole core with different side groups were designed and synthesized. Three novel, thermally stable and aromatic polyimides (Py6FPIs) containing the as-designed diamines were prepared. They were fabricated into memory devices sandwiched between an Al top electrode and an indium-tin oxide (ITO) bottom electrode by spin-coating. The polyimides exhibited high thermal stability with glass transition temperatures (Tg) around 300 °C as determined by DMA. The memory devices were found to show nonvolatile bistable write-once-read-many (WORM) memory characteristics with diverse switching threshold voltages and ON/OFF ratios, depending on the electron affinity of the pendent groups. The low-conductivity state and the high-conductivity state could be sustained under a constant bias or a refreshing voltage pulse of 1.0 V. The switching mechanism and the memory effects were finely demonstrated with the aid of molecular simulations and electronic absorption spectra of these Py6FPIs.