Memristive Characteristics of Composite Hafnium/Tantalum Anodic Oxides

A composite anodic oxide film is formed by electrochemical treatment of an ultra-thin Hf film superimposed on Ta, due to the growth of Ta2O5 columns through HfO2. The oxidation dynamic is governed by an electrical version of the Rayleigh–Taylor effect, the current preferring the more conductive path via Ta during anodization of the superimposed Hf film. Memristive devices obtained by patterning Pt top electrodes are investigated and their electrical behavior is reported. The effect of electrolyte species incorporation on the memristive behavior is analyzed by anodization in different solutions. The influence of citrate-buffered (CB) and phosphate-buffered (PB) electrolytes is studied, and the presence of P in the composite anodic oxides is evidenced in the latter case leading to early device failure. Composite memristors grown in citrate electrolytes show both unipolar and bipolar switching, high stability, very good retention, and endurance. The coexistence of both switching mechanisms is related to the special composite oxide nanostructuring.