Prebreakdown current and noise in insulators

Haworth and Bozorth, as well as von Hippel, many years ago observed that the prebreakdown current in dielectrics may be accompanied by characteristic noise phenomena of a not clearly established origino Lately, several scientists have ascribed this noise to impact ionization in the dielectric and deduced the number and height of these avalanches from it. This interpretation appears very doubtful, because the onset of impact ionization in the presence of field emission should normally lead to breakdown(l). To clarify the situation, the present authors have investigated the origin of the noise and its frequency spectrum in some detail.