Reassessment of degradation mechanisms in anodic tantalum oxide capacitors under high electric fields

High-voltage Ta capacitors have broad applications in various electric systems. Anodically grown, amorphous tantalum oxide (ATO) serves as the dielectric in these capacitors. A detailed understanding of the behavior of ATO exposed to high electric fields is highly desirable and is reflected in a number of prior investigations into this subject. In the conventional view, the electric field promotes the growth of crystalline oxide, which is electrically more conductive and thus leads to the degradation of the dielectric. This interpretation is re-examined using several advanced characterization techniques. The results indicate that oxidation of the ATO and underlying Ta occurs preferentially at specific locations. Subsequent crystallization at these sites was only observed in specimens where this enhanced oxidation led to cracking in the ATO. The results with different Ta materials indicate that these cracks are more prevalent with rougher surfaces. The reported sequence of mechanisms that leads to crystallization provides new insight that can potentially be employed to improve the reliability and stability of Ta capacitors.