Unravelling the Correlation Between Moisture and TDDB in Galvanic Isolators Based on Polymeric Dielectrics

In this paper, the impact of moisture on the time-dependent dielectric breakdown (TDDB) in polymeric dielectrics for galvanic isolators is investigated experimentally. Through ad hoc test schemes, device lifetime under electrical stress is quantitatively correlated to the moisture concentration in the samples by monitoring the latter via the permittivity of the dielectric material. Experimental data reveal that TDDB shows a strongly nonlinear dependence on moisture concentration, with device lifetime displaying, first, a strong decrease with the increase in it and, then, a net saturation. This behaviour is observed for different temperatures of the stress phase and the temperature activation of device lifetime appears to be independent of the moisture concentration. Finally, a sound physical picture is proposed to explain all the experimental evidence, allowing to get insights into the role of moisture in the TDDB of galvanic isolators based on polymeric dielectrics.