Donor-Acceptor Oligoimides for Application in High-Performance Electrical Memory Devices

Improving Memory Performances by Adjusting the Symmetry and Polarity of O-Fluoroazobenzene-Based Molecules

Three O-fluoroazobenzene-based molecules were chosen as memory-active molecules: FAZO-1 with a D-A2-D symmetric structure, FAZO-2 with an A1-A2-A1 symmetric structure, and FAZO-3 with a D-A2-A1 asymmetric structure. Both FAZO-1 and FAZO-2 had a lower molecular polarity, whereas FAZO-3 had a higher polarity. The fabricated indium-tin oxide (ITO)/FAZO-1/Al (Au) and ITO/FAZO-2/Al (Au) memory devices both exhibited volatile static random access memory (SRAM) behavior, whereas the ITO/FAZO-3/Al (Au) device showed nonvolatile ternary write-once-read-many-times (WORM) behavior. It should be noted that the reproducibility of these devices was considerably high, which is significant for practical application in memory devices. In addition, the different memory performances of the three active materials were determined to be attributable to the stability of electric-field-induced charge-transfer complexes. Therefore, the switching memory behavior could be tuned by adjusting the molecular polarity.

Synthesis of imidazole derivatives and study of the ON-based different memory performances

We report the synthesis of two imidazole-based small molecules with different planarity of terminal aromatic rings and their application in memory devices with a sandwich configuration. The optical, electric, and the on-based device performances were systematically investigated. Surprisingly, the device based on BT-PMZ exhibited volatile static random access memory (SRAM) behavior, whereas that based on BT-BMZ showed nonvolatile write-once-read-many-times (WORM) behavior. Further studies on the film morphology and the molecular electronic structure were carried out to investigate the underlying mechanism for the large difference in their performance. Moreover, the performance of the device that incorporates a LiF buffer layer (5 nm) embedded at the interface between the BT-BMZ active layer and the Al top electrode as well as that of the device with a cold-deposited top electrode of mercury droplet was further investigated. At that point a dramatic change in memory performance of the devices from the WORM to SRAM type was observed. The intrinsic volatile SRAM performance for the two molecules results from the moderate electron-withdrawing strength of the acceptor moieties and thus weak trapping of the charge carriers.

Electronic effect of terminal acceptor groups on different organic donor–acceptor small-molecule based memory devices

Three conjugated organic donor–acceptor small-molecules BCZ-BT, BCZ-NO2 and BCZ-CN with different electronic effects in their terminal acceptors were designed and synthesized and their application in memory devices with a sandwich configuration was tested.