Effects of ZrO₂ sol concentration on microstructure and electrical properties of ZrO₂-Al₂O₃ dielectrics formed on Al foils

The effects of ZrO₂ sol concentration on the microstructure and electrical properties of ZrO₂-Al₂O₃ dielectrics on etched Al foils are studied. The experiment is carried out by coating the surface of etched Al foils with ZrO₂ sol with a series of concentrations and anodizing in the 2-methyl-1,3-propanediol (MPD)-boric acid electrolyte at 700, 800, and 900 V. The increase in the thickness of the ZrO₂-coated layer with increasing ZrO₂ sol concentration causes a reduction in the total thickness of dielectrics. The tetragonal-to-monoclinic ZrO₂ phase change can be induced by anodization and the increase in the crystalline size of tetragonal ZrO₂. The Zr-Al-O composite layer after anodization exhibits a microstructure that is a combination of the microstructures of separated high-permittivity crystalline ZrO₂ and amorphous high-resistivity Al₂O₃. The optimal ZrO₂ sol concentration is 1.3 M, and the specific capacitances increased by 38% for 700 V, 40% for 800 V, and 66% for 900 V compared with those of non-coated samples.