Ternary resistive switching memory of copper–organic complex/iodocuprate/sulfur hybrid enabled by π–π interactions and S8 relaxation

Abstract

A multi-level memristor, implemented with inexpensive precursors and well-defined mechanisms, will be significant for the development of high-density memory in the coming big data era. Sulfur, a cheap element extracted from petroleum and natural gas, holds fascinating potential for use in information memory. In this work, a three-component hybrid, [Cu(Phen)₂I]₂·Cu₂I₄·S₈ (Phen = 1,10-phenanthroline), was synthesized. In this structure, strong π–π stacking interactions among Phen ligands, cuprophilic interactions in (Cu₂I₄)²⁻ anions, and C–H⋯I/S hydrogen bonds contributed to the formation of a quasi-3D network. A FTO/hybrid/Ag memristor was fabricated, exhibiting ternary memory performance with a high ON2/ON1/OFF current ratio (10^4.50/10^1.47/1) and a ternary yield of 68%. The memristor could operate at a high temperature of 185 °C. Based on the structural characteristics of the hybrid, FIB-SEM measurements on the Ag/hybrid/Ag model device, double logarithm analysis of the I–V curve, memory performance of the three individual precursors, and external voltage-dependent PXRD, its ternary resistive switching performance could be explained as follows: upon continuous external voltages, the transition OFF → ON1 was driven by enhanced π–π stacking interactions among the Phen ligands, and the current jump ON1 → ON2 resulted from the formation of a conductive S₈/(Cu₂I₄)²⁻ layer bearing cuprophilic interactions via S₈ relaxation. This works extends the strategy of sulfur relaxation in multi-level memories from coordinated polysulfides to uncoordinated ones. The use of inexpensive precursors, combined with the distinct structure–property correlation, provides a promising avenue for implementing novel high-density memristors.