Elimination of Space Charge Effects in Passivation Films: The Key to Substantially Enhancing the Dielectric Properties of Tantalum Oxide Films

Abstract

Tantalum (Ta) electrolytic capacitors have been in widespread use for over half a century, yet the breakdown of the dielectric layer (Ta oxide film, Ta2O5) remains a challenging issue today. This study, for the first time, determines that the natural passivation film is a critical factor in inducing the breakdown of Ta oxide. Furthermore, a comprehensive explanation of its induction mechanism is presented. Our findings reveal that a built-in electric field, which is generated by the PN junction, exists within the natural passivation film. Therefore, performing anodization on the Ta foil with the natural passivation film retained is equivalent to applying a reverse bias voltage to the PN junction. When the reverse voltage exceeds 0.5 V, the passivation film will be broken down, resulting in the deterioration of the dielectric properties of the subsequently grown oxide film. Significantly, removal of the natural passivation film eliminates the PN junction configuration, leaving a reformed passivation film exhibiting exclusive p-type semiconductor characteristics. This modification yields dual technological advancements: (1) The anodization duration is remarkably reduced to 10% of conventional processing time, and (2) The fabricated Ta oxide films demonstrate three orders of magnitude reduction in leakage current at 10 V bias. These findings provide critical insights for optimizing dielectric performance in tantalum capacitor fabrication.