New Donor–Acceptor Oligoimides for High-Performance Nonvolatile Memory Devices

We report the synthesis, optoelectronic properties, and electrical switching memory characteristics of three new donor–acceptor oligoimides consisting of the electron-donating moieties (triphenylamine or carbazole) and electron-withdrawing phthalimide moieties. The influence of different donor (D)–acceptor (A) arrangements, including D-A-D and A-D-A structures, on the electrical properties was explored. Devices based on D-A-D oligoimides revealed a reversible nonvolatile negative-differential-resistance (NDR) characteristic and excellent stability during operation. Without applying voltage stress, the on and off states of the devices showed no obvious degradation for an operation time of 10 s and 108 read pulses. However, the devices prepared from the A-D-A oligoimide showed only the insulating properties. The different memory characteristic was probably because the terminal donor moieties in the D-A-D structure might facilitate the injection and transporting of the holes. Besides, the D-A-D oligoimide with triphenylamine groups exhibited an on/off ratio of 104, 2 orders of magnitude higher than that with carbazole groups. The mechanism related to electrical switching properties was elucidated through molecular simulation. Thus the significance of D-A-D structure on tuning memory characteristics for memory device applications was revealed.