On the size dependence of the dielectric breakdown strength of solid insulators at room temperature

The dielectric breakdown strength of solid insulators is usually dependent on the dimensions of the sample. In particular, for "thick" insulating sheets, the dielectric breakdown strength is often found to be roughly proportional to the inverse of the square root of the sample thickness. In this contribution, the hypothesis is examined that the latter type of size dependence is related to electric field inhomogeneities associated with the geometrical electrode configuration. In order to test the hypothesis, DC dielectric breakdown experiments have been performed for alumina ceramic sheets of different thicknesses ranging from 0.25 mm to 2 mm for both polarities and voltage ramp rates in the range between 0.1 and 5.8 kV/s. An electrode configuration has been used which allows for an analysis of the local electric field enhancement at the electrode edge in terms of fracture mechanics concepts. It is concluded from a comparison of experimental and theoretical results that the mentioned dependence of the dielectric breakdown strength on sample thickness is likely related to electrode edge effects.