Pulse Anodization of Tantalum Oxide/Polypyrrole Film on Nanoporous Tantalum Anode for Solid Electrolytic Capacitors

Abstract

Under a pulse anodization mode, a dielectric Ta₂O₅ film and a conducting polypyrrole film were formed on a nanoporous Ta pellet anode (average pore size: 250 nm, specific surface area: 4,000 cm² g^－1, capacitance: 50,000μFV g^－1). At a first pulse, Ta metal was anodized to form dielectric Ta₂O₅ nano film (1.6~ 14 nm in thickness) on nano-porous Ta pellet. With subsequent pulses, the polypyrrole film was deposited uniformly and compactly (average thickness: 70~230 nm) on the Ta₂O₅/Ta nano-porous layer. The thickness of polypyrrole film was controlled by tuning current and charge of the pulse. The polypyrrole film on the Ta₂O₅/Ta nano-porous layer showed low resistivity of 2×10^－1Ω persquare. By AC impedance analysis, low equivalent series resistance (400 mΩ at 100 kHz) was demonstrated for a sample electrolytic capacitor with nano-porous Ta₂O₅/Ta anode with polypyrrole coating layer.