Humidity Effects on Reverse Bias Testing of Ta Film Capacitors

Reverse bias testing of Ta thin film capacitors under accelerated conditions showed higher failure rates at 45 and 65°C than at 85°C. TWo distinct failure modes occurred: area dependent point failures and non-area dependent failures along the counterelectrode/dielectric edge. The work reported here shows that the edge failures are moisture dent, while the point failures are not. The product limit method of statistical analysis was used to separate the two failure modes. The edge breakdowns occur only in the presence of moisture and the rate at which they occur is a function of the humidity level present. Low voltage leakage current studies indicate that there is a threshold bias value below which there is no observable moisture effect.