Indole and triazole containing ferrocene-based two-terminal resistive memory devices

Abstract

Metal complexes have emerged as promising candidates for next-generation resistive switching memory elements owing to their structural tunability, flexible geometry, ligand–metal coordination, thermal stability, redox activity, and molecular-level precision. Among them, ferrocene (Fc) derivatives are particularly attractive as molecular memory elements due to their excellent solution processability, well-defined redox characteristics, and structural tunability via terminal ligand architectures. Their relatively low threshold voltages for ON/OFF current switching and less power requirement further enhance their potential as alternatives to conventional complementary metal–oxide–semiconductor (CMOS) technology. In this study, we investigate the resistive switching behavior of two ferrocene derivatives that differ in their terminal groups—an electron-rich indole, which is connected through an ethylene spacer, and an electron-deficient triazole conjugated to a cyclopentadiene (Cp) moiety. The terminal functionality and the extent of conjugation strongly influence the switching characteristics of ITO/Fc/Al two-terminal digital memory features. The Fc derivatives exhibit stable bipolar, non-volatile resistive switching, with switching voltages of +1.42 V and +0.52 V, and ON/OFF current ratios of 10³ and 10⁴ for the non-conjugated and conjugated ferrocene derivatives, respectively. A comparison of the memory characteristics of two ferrocene derivatives highlights their underlying structure–property relationships. These results highlight a molecular design pathway toward high-performance, tunable, and energy-efficient digital memory applications.