Preparation and properties of Y₂O₃-Doped ZrO₂ films on etched al foil by sol-gel process

The oxide films formed on etched aluminum foils play an important role as dielectric layers in aluminum electrolytic capacitors. Y₂O₃-doped ZrO₂ (YZ) films were coated on the etched aluminum foils by sol-gel dip coating, and the electrical properties of YZ-coated Al foils were characterized. YZ films annealed at 450°C were crystallized into a cubic phase, and as the Y₂O₃ doping content increased, the unit cell of ZrO₂ expanded and the grain size decreased. The etch pits of Al foils were filled by YZ sol when it dried at atmospheric pressure after repeating for several times, but this step could essentially be avoided when being dried in a vacuum. YZ-coated foils indicated that the specific capacitance and dissipation factor were 2-2.5 μF/cm² and 2-4 at 1 kHz, respectively, and the leakage current and withstanding voltage of films approximately 200 nm thick were 5 × 10^-4A at 21 V and 22 V, respectively. After being anodized at 500 V, the foils exhibited a specific capacitance and dissipation factor of 0.6-0.7 μF/cm² and 0.1-0.2, respectively, at 1 kHz, while the leakage current and withstanding voltage were 2 × 10^-4 - 3 × 10^-5 A at 400 V and 420-450 V, respectively. This suggests that YZ film is a promising dielectric that can be used in high voltage Al electrolytic capacitors.