Thickness-dependence of the breakdown strength: Analysis of the dielectric and mechanical failure

Abstract

The breakdown strength as well as the mechanical strength of ceramic materials decreases with increasing volume. The volume-effect of the mechanical strength can be explained by the Weibull theory. For the breakdown strength the same explanation has been often assumed.In order to validate this assumption breakdown strength and mechanical strength of alumina samples with defined porosities were compared. Differences in the Weibull moduli of breakdown and mechanical strength distributions indicate that the volume-effect cannot explain the thickness-dependence of the breakdown strength. In particular, the thicknessdependence of the breakdown strength always leads to a Weibull modulus of two which is not 2 in agreement with the measured Weibull moduli for samples with constant thickness. It can be concluded that the thickness-dependence of the breakdown strength cannot be explained by the Weibull concept. A recently developed breakdown model which is based on space charge injection is able to explain the experimental results.

Influence of test procedure on dielectric breakdown strength of alumina

“…This is already a relative difference of 20.2% related to the large value, and 25.3% related to the small value, respectively. As described in the introduction, dielectric strength is indirectly proportional to the square root of the sample thickness [6,8]. Based on this relationship, a normalized dielectric strength E d,n with respect to a normalized thickness t n can be calculated according to Eq.…”

“…A noteworthy characteristic of dielectric strength, especially with respect to test conditions, is its thickness dependence. In contrast to common mechanical strength concepts, dielectric strength shows a 1/ d dependence, where d is the sample thickness [6,8,15]. Neusel and Schneider [15] concluded that the thickness dependence cannot be explained by the Weibull concept.…”

“…They concluded that high breakdown strength generally involves weak wear, although their data does not invariably follow this tendency. A proportionality of dielectric strength to the −0.5 power of relative permittivity is shown by different groups of researchers [8,9]. Trapping of charges [10,11] and space charge limited conductivity [12][13][14] are recently discussed to be decisive for breakdown channel formation in ceramics.…”

Dielectric Losses in Dry-Type Insulation of Medium-Voltage Power Electronic Converters

“…Non-pottable and/or non-polymeric insulation materials, such as mica, ceramic (e.g., AlN and AlSiC), aramid (e.g., Nomex), polyimide (e.g., Kapton) also feature interesting properties, i.e. high breakdown strength (especially for thin layers), good resistance to partial discharges, and low losses [43], [62]. These materials are typically combined with potted polymeric materials or oils, in order to avoid the presence of air near the electric field hot spots, which can lead to partial discharges [56].…”

Electrical conduction mechanism in bulk ceramic insulators at high voltages until dielectric breakdown

“…33 For thin films, the breakdown process can be described by an intrinsic, electric breakdown model originally proposed by von Hippel. [34][35][36] Bulk samples show a dependence of the breakdown strength on the sample thickness, 33,[37][38][39] which cannot be explained by the intrinsic, electric breakdown model. Different breakdown mechanisms of bulk samples and thin films might also be associated with different conduction mechanisms.…”