2-Aminobenzazolium Chlorocuprate(II) Complexes for Memristive Devices: Structural Studies, Synaptic Plasticity, and Random Number Generation

Abstract

In this work, we investigate a family of organic-inorganic hybrid compounds for their potential application in memristors.Specifically, we study a series of three chlorocuprate(II) complexes incorporating 2-aminobenzazole derivatives with changing geometry from square planar in 2-aminobenzothiazole (containing a sulfur heteroatom), to tetrahedral in 2aminobenzoxazole (containing an oxygen heteroatom), to triangle bypiramid in 2-aminobenzimidazole (containing an additional nitrogen atom in the heterocyclic ring). These structural variations allow for systematic evaluation of the influence of heteroatom identity on the electronic and switching properties of the resulting hybrid materials. Based on these compounds, two-terminal stack-up thin-film devices were fabricated on indium tin oxide (ITO) glass substrates with copper top electrodes. It is demonstrated that the studied devices show hysteretic current-voltage behaviour and offer repeatable switching between high-and low-resistance states. Pulse measurements with controlled amplitude, duration, and interval, induce switching between resistance states (potentiation and depression), a fundamental feature of biological learning and memory. Comprehensive spectroscopic characterisation of the complexes was carried out across a broad energy range, from near-infrared to visible, ultraviolet, soft, and tender X-ray regions. To complement the experimental findings, density functional theory (DFT) calculations were performed to gain deeper insight into the nature of bare cations, as well as the electronic structure of crystal materials. The scan-rate independent hysteresis loops indicate an interfacial resistive switching mechanism involving charge trapping at the metal/semiconductor interface. Resistive switching is attributed to an interfacial, electronically driven mechanism involving charge trapping at the metal/semiconductor interface, modulated by the heteroatom-dependent electronic structure and hydrogen-bonding networks of the organic cations. The interfacial, noise-dominated switching dynamics give rise to stochastic conductance fluctuations that can be harnessed for hardware random number generation.