Definition and Use of a Specific Value to Characterize the Dielectric Breakdown of Thin Insulating Layers

Starting from the assumption that "conditioning" is necessary to trigger a breakdown and that its duration can be seen as the delay time before breakdown, a new approach to the problem of the dielectric stress of solid insulators is proposed. It is founded on the relationship existing between the delay time which is determined statistically, and the amplitude of the electrical field. The experiments deal with a few hundred nm thick layers of silicon oxide, alumina, and polystyrene, coated with self-healing electrodes to which successive voltages of different amplitudes are applied. The delay time is determined either by τ
_I
, i.e. the lag time between two consecutive breakdowns, or by t
_{I<.sub>, time during which the material has been under stress before the ith breakdown. The variations, as a function of field G, of the mean value τm of τI, or of tτ inferred from Weibull statistical model applied to ti, yield an asymptotic value Gc for which the "conditioning" duration tends to infinity. By identifying the curve τm(G) with an expression such as τm = a/(G-Gc)^α, the three constants a, α and Gc are calculated, the latter representing a "specific breakdown field"; tw(G) may give a similar definition. An example of the use of such a criterion is its variation as function of the sample thickness.}