On the performance of pyrolytic MnO2/tantalum capacitors: Columnar vs. nanocrystalline cathodic layers

MnO2 cathodic layers of solid tantalum capacitors have been manufactured under standard and low convective flow conditions. MnO2 layers formed by low convective flow pyrolysis display lower resistance in the 1 kHz–10 MHz frequency range. The cathodic materials present both highly faulted pyrolusite with a columnar morphology and nanocrystalline structures. The proportion of the latter regions is higher for pyrolyses carried out under lower convective flow. It is proposed that the improved performance of capacitors produced under lower convective flow is related to the electrical conductivity anisotropy of semiconductors with rutile-type structures and results from the absence of the columnar texture as well as from the formation of an essentially nanocrystalline cathodic layer.