Design And Synthesis Of Electric Memory Materials Based On Quinoxaline And Nitrogen-containing Conjugated Backbones For Multilevel Electronic Memory Applications

With the rapid growth of information, study of multilevel data storage information materials and nano devices are of great significance. In 2010, our research group first reported a small organic molecule-based ternary memory device via adjusting the molecular structures, demonstrating the "zero" breakthrough of organic-based multilevel memory materials. In recent years, throughout the research status of the small organic molecular storage, the ternay storage is closer to the future requirements of ultrahigh density information storage(~ 1015 bits/cm2) in theory, but the current research states is still far from meeting the requirements of practical application with the characters of effectiveness, stability, simple process, convenience and flexibility. Therefore, the optimizations on device performace is still a long way to go via designing the molecular structures,opportunity and challenge are all coexistence. According to the optimization strategies for the performance of organic electronics devices, the related reports on the regulation of the properties of small organic molecular electric storage devices such as the isomeric effect, the aromatic spacer variation and electronic effects, etc are still rare.This paper carried out the study from the following aspects:(1) Investigation of the isomeric effect on electrical memory device performance: Two quinoxaline-based small organic molecules, which are conjugated and mutual isomers in vertical and horizontal directions, were successfully synthesized. By exploring isomers with identical functional groups, the impact from changing in molecular composition on the observed different performance can be minimized. Their photoelectrical properties, thin-film morphology and the electrical memory performance were comparatively investigated. The devices based on these two small molecules both showed ternary WORM storage performances. Compared with vertical direction, horizontal molecule had a lower threshold voltage and higher current ratio. The results of AFM and XRD showed that horizontal molecule has better thin-film morphology and layered accumulation, which are conducive to the migration of carriers. We hope this study can provide a new reference to the future elaborate design and synthesis of novel small-molecule electrical memory materials.(2) Investigation of electrical the terminal doner strength on multilevel device data storage performance: Two small organic molecules based on quinoxaline and carbazole, Qu-Ph and Qu-Oct were synthesized. The only difference between them was the substituents at N atom, one was benzene ring(Qu-Ph), and the other was 2-ethylhexyl(Qu-Oct). Sandwich devices based on ITO/organic small molecule/Al had ternary WORM-type. Comparing to Qu-Oct, Qu-Ph owned more advantages, such as closer packing, more regular surface morphology and lower turn-on voltage. The results showed that the turn-on voltage of the device could be reduced effectively when the alkyl chain of small organic molecules was adjusted to benzene ring. The study could provide an effective strategy for the design of low power memory device in the future.(3) Investigation of the aromatic spacer variation on electrical storage devise performance: Two triphenylamine-quinoxaline-π-methylenemalononitrile derivatives TPAQPh and TPAQFu with different π aromatic spacers(i.e., phenyl or furyl) were synthesized. The two molecules have the same donor and acceptors and the only difference between them was the aromatic spacers, one was benzene ring(TPAQPh), and the other was furyl(TPAQFu). Sandwich devices based on ITO/organic molecule/Al had ternary WORM-type. The substitution of phenyl with thienyl leads to closer packing, more regular surface morphology and lower turn-on voltage which was attributed to effectively reduce the distortion angle between the quinoxaline group and methylenemalononitrile unit. This comparative study of regulating the properties of organic molecures via aromatic π-spacers may be an available approach for the future design and study of ultrahigh-performance memory devices.(4) Investigation of the number of conjugated branches on a triphenylamine core on electrical memory device performance: To study the influence of the number of branches mounting on molecular backbones on the thin-film morphology and performance of their memory devices, we successfully synthesized three conjugated small molecules containing triphenylamine and benzothiazole moieties(TPA-nBBT, n=1, 2, 3) and studied their memory performances. Binary static random access memory(SRAM) characteristics could be achieved for the three compounds-based devices with sandwich-like configuration of ITO/molecule/Al. The device based on TPA-3BBT exhibited best device performance with the lowest threshold voltage and best thermal stability which is related to the temperature insensitive thin-film morphology and film crystallinity. Our results demonstrate that increasing the number of branches in D-A conjugated molecules to adjust film morphology and intermolecular accumulation may be an effective strategy to improve the stability of the device performances.