Synthesis Of Push-pull Structural Organic Conjugate Molecules And Study The Memory Performances

The requirements of materials and based memory devices which employed in the ultra-high density data storage are higher and higher as the rapid development of science and technology.Possessed many advantages such as low-cost,rich structure flexibility,light-weight and super-high data storage density,organic materials based memory devices could play an important role in the ultra-high density data storage.In order to explore the relationships of the molecular structures and memory performances,designed the material structures to optimize the performances of memory device is effective approach,and this is very important for electrical memory devices applied in the ultra-high density data storage in the future.In this paper,the relationships between the molecular structures and memory performances had been studied through molecular framework designed.The main contents as below:（1）In order to study the electronic effect of terminal acceptors on the memory properties,three donor-acceptor organic conjugated small-molecules with different terminal acceptor groups,BCz-BT,BCz-NO₂ and BCz-CN,were synthesized.The as-fabricated devices based on BCz-BT showed volatile SRAM switch behaviour,while that based on BCz-NO₂ and BCz-CN exhibited stable non-volatile WORM and flash memory characteristics,respectively.The results indicated that i)device based on the molecule with weak electronic effect between donor and acceptor（BCz-BT）induced volatile memory SRAM behaviour,ii)strong inductive effect but weak conjugative effect（BCz-NO₂）induced non-volatile WORM characteristic,iii)strong inductive effect and conjugative effect（BCz-CN）caused non-volatile flash switch behaviour which arises from the formation of CT complex.（2）Two imidazole-based small molecules（BT-PMZ,BT-BMZ）with different planarity of terminal aromatic rings and their application in memory devices with a sandwich configuration.The device based on BT-PMZ with a rigid planar structure exhibited the volatile static random access memory（SRAM）behavior while that based on BT-BMZ showed the non-volatile 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 their large difference in performance.When a LiF buffer layer（5 nm）embedded at the interface between BT-BMZ active layer and the Al top electrode,a dramatic change in memory performance of the devices from WORM to SRAM type was observed.The thin-film morphology was adjusted by molecular planarity and the model of memory device was changed by optimized the device fabrication process,which offered the new approach to molecular framework design and fabrication process of device in the future.（3）Based on our groups had been reported works of the multilevel data storage,two different electron-withdrawing groups,benzothiazole unit and nitryl,were introduced simultaneously into the bi-carbazole skeleton,and studied the effect of the different charge trapping groups on the multilevel memory performances.The results showed that the memory device based on molecule with different electron-withdrawing groups exhibited ternary switch characteristic.Furthermore,the relationship between the ternary memory performances and thickness of the active layer was systematically studied.The results showed that the operating voltage of the device would be gradually increased as the increase of film thickness,while the current of OFF state would be decreased gradually,which indicated the ON/OFF current ratio of the neighboring conductive state would be increased.Besides,according to the statistical data of different thin-film thickness based devices,the relationship between the effective switching rate of multilevel storage devices and the thickness of the thin film belong to the normal distribution.This provides the experimental basis for the optimization of the device fabrication to control stability and performances of the multilevel storage devices.（4）Based on the switch mechanism of different charge traps to achieve ternary data storage,in this section,a novel molecule which contained redox active ferrocene unit and electron-withdrawing group simultaneously was synthesized.The as-fabricated memory device exhibited ternary non-volatile WORM characteristic.The results of the UV-vis absorption spectrum,cyclic voltammetry curve and theoretical simulation showed that the intramolecular charge transfer and oxidation-reduction reaction governed together the ternary switch.The multilevel switch governed by two memory mechanisms not only provides the novel idea to design multilevel switch materials but also provides the theoretical basis of the various approach to achieve the multilevel data storage.