Influence of humidity on AC electrical breakdown in plasma-polymerized thin films

The ac electrical breakdown has been measured in plasma-polymerized thin films. The breakdown strength is on the order of 8-10 MV/cm under a dry condition; however, it decreases drastically with humidity. Leakage current increases with humidity, while dielectric loss does not show significant increase with it. Results have been explained in terms of thermal breakdown based on Joule heating due to an enhanced leakage current through a localized narrow channel.