Design and synthesis of ferrocene-terminated hyperbranched polyimide for memory devices

In this work, a novel tetra-amine, bis (4-(3, 5-bis (4-amino-2-(trifluoromethyl) phenoxy) phenoxy) phenyl) methanone, was synthesized and then utilized to produce hyperbranched polyamic acids via polycondensation with 4, 4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA). The resulting hyperbranched polyamic acids underwent termination by (4-amino) phenyl ferrocene and imidization, leading to ferrocene-terminated hyperbranched polyimide (HBPI-Fc). The resulting HBPI-Fc displayed superior solubility in conventional organic solvents and excellent thermal stability. A memory device with a configuration of indium tin oxide (ITO)/HBPI-Fc/Al was fabricated, in which the HBPI-Fc acted as the active layer. The device exhibited bistable electrical conductivity switching and nonvolatile bipolar write-once-read-many-times memory character with two threshold voltages of 2.2 V and −2.6 V, respectively, during positive and negative voltage sweep. The device exhibited an ON/OFF current ratio of 10 4 under a constant bias of −1.0 V and good stability in both ON- and OFF-state during the test period of 10 4  s. The revealed electrical bistability of the HBPI-Fc was found mainly due to the effective charge trapping effect of the electroactive terminal ferrocene groups.