Resistive memory materials based on transition-metal complexes

A resistive memory operates as an electrical switch between high and low conductivity states (or multistates) in response to an external electric field. Due to the high capacity, high flexibility, good scalability, low cost, and low power consumption, resistive memory is promising for the next-generation high-density data storage. In addition to inorganic metal oxides, carbon nanomaterials, organic small molecular and polymeric semiconductor materials, transition-metal complexes have recently received much attention as active materials for resistive memory. In this contribution, the applications of transition-metal complexes in resistive memory reported to date are summarized and discussed, mainly including group VIII [Fe(II), Ru(II), Co(III), Rh(III), Ir(III), and Pt(II) complexes], group IB and IIB [Cu(II), Au(III), and Zn(II) complexes], and lanthanide complexes [mainly Eu(III) complexes]. The memory behavior and mechanism of these materials will be discussed. Transition-metal complexes often possess well-defined and reversible redox processes. The frontier energy levels and gaps can be easily modulated by changing the structures of ligands and metal species, which is beneficial for generating electrical bistates or multistates when they are used in resistive memory devices. These features make transition-metal complexes potentially useful as memory materials in practical applications.