Ni full-filling into Al₂ O₃ /Al film with etched tunnels using a polyethylene glycol solution bath in electroless-plating

Ni/ Al₂ O₃ /Al film was fabricated for a high performance capacitor using electrochemical etching, anodizing, and electroless-plating. The focus of this study was to form seamless and void-free Ni electrodes on Al₂ O₃ /Al with etched tunnels. The conventional deposition method of metal was limited to full-fill for the Al tunnel pits with a high aspect ratio, a depth of about 40 μm, and diameters of about 0.5-1 μm. Nevertheless, Ni filling in tunnel pits was achieved through electroless-plating for the first time, producing a seamless and void-free electrode. The authors used a polyethylene glycol solution bath to block the Pd on top of the tunnel prior to electroless-plating, which enabled the Ni to deposit preferentially at the bottom, leading to a filling from the bottom to the top. Finally, the capacitance density for the etched and Ni electroless plated films was 220 nF/cm² while that for a film without any etch tunnel was 12.5 nF/cm².