TEM nano-structural investigation of Ag conductive filaments in polycrystalline ZnO-based resistive switching devices.

Memristive devices based on resistive switching mechanism are considered very promising for non-volatile memory and unconventional computing applications, even though many details of the switching mechanisms are not yet fully understood. Here we report a nano-structural study by means of high resolution transmission electron microscopy and spectroscopy techniques of a Ag/ZnO/Pt memristive device. In order to ease the localization of the filament position for its characterisation, we propose to use the guiding effect of regular perturbation arrays obtained by FIB technology to assist the filament formation. HRTEM and EDX were used to identify the composition and crystalline structure of the so obtained conductive filaments and the surrounding regions. It was determined that the conducting paths are composed mainly of mono-crystalline Ag, which remains polycrystalline in some circumstances, including the zone where the switching occurs and at secondary filaments created at the grain boundaries of the poly-crystalline ZnO matrix. We also observed that the ZnO matrix shows a degraded quality in the switching zone, while it remains unaltered in the rest of the memristive device.