C-AFM study on multi - resistive switching modes observed in metal–organic frameworks thin films

Metal-organic framework (MOF) materials have recently attracted much attention for use in resistive random-access memory due to the advantages of having high insulative properties, well-defined structures, a large specific surface area, and an adjustable pore size. In this study, the memory device based on zirconium (IV)-carboxylate MOF (UiO-66) nanoparticles exhibits the low operation voltage (V < 0.5 V), high ON/OFF ratio (~104), excellent endurance (5 × 102 cycles), and longtime retention (104 s). To clarify the resistive switching mechanism of the Ag/PVA-MOF/FTO device, conductive atomic force microscopy (C-AFM) was used. The results indicate that all of the electrode, Zr6 clusters of UiO-66, PVA, and UiO-66 conjugation have simultaneous contributions to the resistance switching behavior. The resistive switching can be controlled either by the electron hopping process between Ag+ ions and Zr6 nodes in threshold mode or the formation/rupture of the metal filaments in the bipolar switching mode. Interestingly, inherent characteristics of MOF materials, such as high porosity and large size cages (octahedral, tetrahedral), strongly influence the transport properties and switching mechanism of the device which is also discussed in detail. These resistive switching characteristics and mechanisms of UiO-66 could provide a thorough understanding for future research and application not just for UiO-66 but also for the general MOFs materials.