Insights into the breakdown mechanism of anodic oxide film

The breakdown mechanism of the anodic-oxide-film--electrolyte system has been studied for a long time, but there are still very few experimental studies that can summarize its physical image. Here, we report a finding on the breakdown mechanism of the tantalum ($\mathrm{Ta}$) oxide-electrolyte system. We observe the evolution process of oxygen bubbles in $\mathrm{Ta}$ oxide films and demonstrate that oxygen generation is a cause of breakdown. The oxygen evolution reaction not only provides the initial electron injection for avalanche breakdown, but the resulting oxygen bubbles also lead to a concentration of stress and electric field. Further studies have shown that oxygen vacancies in oxide films are key to driving oxygen evolution and electron-current formation. Based on these findings, we attenuated oxygen evolution by the addition of a reducing agent, and the crystallization of the $\mathrm{Ta}$ oxide films was consequently drastically reduced, with the leakage current density of the dielectric being only 12.6% of the original. Therefore, this study not only contributes to an in-depth understanding of the breakdown mechanism of anodic oxide films, but also provides a promising prospect for the fabrication of high-quality $\mathrm{Ta}$ capacitors.