Adjustment Of Interface In Memory Devices Based On Organic Conjugated Molecules

With the rapid development of information storage technology, inorganic semiconductor materials have been unable to meet the requirement of information storage. Recently, organic storage materials have attracted more interest than inorganic semiconductor materials due to their simple synthesis process, low cost, structure designability. On the one hand, however, it is limited to improve the performance of memory devices only through adjusting the structure of molecule. As the current means can not meet the requirements of practical application, a variety of means need to be comprehensive used to improving the performance of devices. On the other hand, in the field of organic optoelectronics, interface control has been widely studied to improve the performance of devices and achieved significant breakthrough. Unfortunately, this technology has not been applied in the field of organic memory devices. In this article, in order to investigate the effect on the performance of the memory devices through interface adjustment, the method that the electrode/function layer interface, function domain/domain interface have been adjusted, respectively, which is the first time to use in the field of organic memory devices. Our study is performed in the following three aspects.(1) The interface between the ITO substrate and organic molecular layer which affect the performance of organic storage devices. A new Donor-Accepter-Accepter structure molecule, which establishes ternary memory performance, has been designed and successfully synthesized. To improve the property of the devices, the influence of the property of the devices through modification of the Indium tin oxide(ITO) substrate were investigated. Two phosphonic acid derivatives have been used to modify the ITO substrate, octylphosphonic acid for ITO-C8 and phenylphosphonic acid for ITO-Ph. Both the devices based the unmodified and modified substrate have established ternary memory performance, however compared with ITO based device, the ratio of the effective ternary unit in the modified ITO based device have raised from 28% to 39%. The results from the XRD and GISAX demonstrate that the modification of the ITO leads to different surface on the ITO and thus to varied intermolecular stacking style in the active layer. This work illustrated that altering the surface of the ITO substrate could improve the intermolecular stacking which leads to save power consumption and raise rate of effective products, which is good for the rational design and application of future advanced organic memory devices(OMDs).(2) The domain interface of molecule in the functions layer has been adjusted, which affect the performance of organic storage devices. Two structural isomers α-PBT and β-PBT, which only differ in the phenyl substituent position on the quinolinechromophore, have been designed and successfully synthesized. The influences of substituent position on the film morphology and the devices storage performances were investigated. Both molecules employed in the memory devices exhibited same nonvolatile binary(WORM, write-once-read-many-times) characteristics, but the switch threshold voltage(Vth) of β-PBT based device was obviously lower than that of α-PBT based. Simulation results demonstrate that the variation of phenyl substituent position lead to different intermolecular stacking style and thus tovaried grain sizes for each film morphology. This work illustrated that altering the phenyl substituent position in the molecular backbone could improve film morphology quality and save power consumption, which is good for the rational design of future advanced organic memory devices(OMDs).(3) It has also been proved that the adjusting of the interface between functions layer and top electrode would affect the property of memory device. We designed and synthesized two organic conjugated molecules with donor-accepter-donor(D-A-D) structure, which both contains phenothiazine and triphenylamine groups. As the sulfur atom in phenothiazine groups to different oxidation degree, the morphology of the film has been changed. This phenomenon mainly explored that as the oxidation degree of sulfur atom in two molecules is different, whether the morphology of the film and the properties of the devices would change. The results of the experiments implied that as the oxidation degree increased, either the devices based on TPA-PTO or TPA-PTD exhibited same binary SRAM characteristic. However the TPA-PTO has a shorter recover time, the TPA-PTD has a lower switch threshold voltage.This work illustrated that altering the morphology of the active layer can improve the interface between active layer and top electrode, which will reduce the injected energy barrier of carriers and save power consumption. The result is good for the rational design of future advanced organic memory devices(OMDs).