Improvement Of Memory Device Performance Via Introducing Bridges Between Electron Acceptors And Donors

Nowadays,our society is undergoing rapid development.Scientific information storage technology must follow the steps with such fast and great progress.Among all the novel information storage manners,organic memory devices based on typical sandwiched-structure has obtained more and more attention for the following advantages,low cost,tunable material structures,simple fabrication process,low power consumption,multi-stimulus response and so on.With the increase of storage density,organic multilevel memory devices may be one of the best choices for information storage technology application.In this paper,the effects of the introduction of conjugated bridges,heteroatoms and external light conditions on the improvement of organic multilevel memory device performance has been explored and discussed,which has been shown in details as follows:?1?Two acceptor-donor-acceptor?A-D-A?type organic conjugated small molecules,NTPA₂BT and NTPA₂EBT,were designed and synthesized.Two molecules have the same electron-rich?TPA moiety?and electron-deficient?benzothiadiazole and nitro groups?moieties.Compared with NTPA₂BT molecule,in NTPA₂EBT,alknyl group was introduced into molecular backbone by Sonogashira coupling.Compared with aromatic rings,alkynyl has no side atoms that cause steric hindrance or atom repulsions.Both devices show typical WORM?Write-Once-Read-Many?memory behaviors.Compared with NTPA₂BT,the memory device based on NTPA₂EBT presents better nonvolatile ternary memory performance with higher reproducibility of tri-stable conductance states and lower average threshold voltages.Such superior performance of NTPA₂EBT based devices is ascribed to the introduction of alkynyl as conjugated bridge,which significantly improves the planarity of the conjugation backbone and facilitates the molecular stacking.Thus better crystallinity and lower threshold voltages are achieved.These results show that alkynyl is an important group to tailor organic molecules for achieving excellent data storage devices.?2?On the basis of our previous synthesized molecule NTPA₂BT,a comparative study was performed to demonstrate two novel effective molecular design strategies:incorporation of thiophene ring as conjugation linkage between electron acceptors and donors or substitution of benzothiadiazole hydrogens by fluorine atoms.Compared with NTPA₂BT,both the two new molecules based devices show typical ternary WORM?Write-Once-Read-Many?memory behaviors with lower threshold voltages,higher reproducibility and better stability.However,the reasons for memory performance enhancement were distinct.On one hand,the addition of 3-hexylthiophene bridges significantly promotes the planarity of the conjugation backbone and facilitates the molecular stacking,which is beneficial for intramolecular charge transfer.On the other hand,the insertion of fluorine atoms also enhances the film crystallinity,decreases the distance of molecular layers,and thus induces an ordered molecular stacking.Results show that both insertion of 3-hexylthiophene bridges and substitution of fluorine atoms are effective strategies in designing conjugated organic molecules to achieve superior organic memory performances.?3?One organic small molecule BNH with acylhydrazone group as bridge was designed and synthesized.One feature of this kind of molecules is trans-cis isomerization around the imine-like C?N double bond via ultraviolet light illumination,which could change the configuration.Before UV light illumination,the device shows DRAM memory behavior,while after UV light illumination,it exhibits WORM memory behavior.According to the results of series of tests,after UV light illumination,closer stacking in molecular thin film,enhanced intermolecular interaction,rougher thin film and larger intramolecular twist were triggered.These factors can make the recovery of intermolecular and intramolecular charge transfer harder,thus the device performance changes from DRAM to WORM type memory behavior.Therefore,we could successfully regulate the type of memory device by external UV light illumination.