Dinuclear aluminum complex as an active material for RRAM switching devices

Abstract

In this study, we report the synthesis and structural characterization of dinuclear aluminum complex 1, containing redox-active bis-catecholaldimine ligand 6,6′-{[ethane-1,2-diylbis(azanylidene)]bis(methanylidene)}-bis(3,5-di-tert-butyl-1,2-dihydroxybenzene) (LH₄). Complex 1 was readily obtained by refluxing LH₄ and Al(NO₃)₃·9H₂O in 3 : 2 molar ratio in the presence of triethylamine in a methanolic solution. Single-crystal X-ray diffraction analysis of complex 1 showed that catecholaldimine ligands bound via octahedral coordination to each of the two Al(III) centers. Out of three, two ligands coordinated in a salen N₂O₂ fashion, providing four coordinating sites, while the third ligand acted as a bridged ligand, binding through its two catecholate oxygen atoms to each of the two Al(III) centers. Complex 1 was also further characterized using various techniques, such as HRMS, FTIR spectroscopy, TGA and CHN analysis. Electrochemical characterization of complex 1 was performed using cyclic voltammetry in a DCM solution, which showed several quasi-reversible and irreversible oxidation–reduction peaks. The lipophilic aluminum complex 1 was further employed as an active material to fabricate a resistive switching memory device, ITO/complex 1/Ag, and it was characterized using a write-read-erase-read cycle. Interestingly, the device showed stable current–voltage characteristics, excellent endurance stability and analog switching between two different resistance states for 5000 s, making it a viable option for long-term data storage applications. The frontier molecular orbital energy of complex 1 was calculated using density functional theory, where it was observed that the hole injection was favourable during the conduction mechanism of the memory device.