Influence of interfaces on impedance response and breakdown of oxide–metal multilayer structures

We report on the enhancement in impedance and the break-down behavior of room temperature deposited single and multi-layer metal/oxide films of comparable thicknesses. Aluminum–alumina and chromium–chrome oxide thin film structures grown by sputtering were explored as model systems in this study. Electrochemical impedance spectroscopy measurements showed that the resistance of the structure increases with an increase in the number of metal/oxide bi-layers while the total thickness was kept constant. The resistance of the multi-layer system was over an order of magnitude higher than the single bi-layer for an equivalent total thickness for the case of thin film Al–Al2O3. In addition, potentiodynamic polarization measurements exhibited a consistent and reproducible improvement in the break-down potential with an increase in the number of layers. Similar results are obtained for the case of the chromium–chromium oxide bi-layer system as well. Combination of interfaces and lateral current spreading in the multi-layer structure leads to superior overall break-down resistance suggesting the concept of in-situ sacrificial layers for corrosion protection.