Collision ionization

Collision ionization model The common collision ionization model of the electric breakdown as summarized by O Dwyer [156] requires a sufficiently high probabihty for the ionization process. Later this model was extended by Ikonopisov [150]. If the ionization cross section, film thickness and energy dissipation are large enough, an ionic avalanching will finally destroy the passive film. 

Tunnel model forthin films In some cases, the validity of the collision ionization model is limited. For ultrathin films with d < 10 nm the number of ions is too small for an establishment of the avalanche and a different model was proposed. In Fig. 27, the breakdown voltage /bd was determined as a function of d or the film formation potential f/porm- A straight line with a slope of bd = 6, 25 MV cm is obtained. This value is just the reciprocal of the film formation factor k (Chapter 3.2.3.2.3). This identity of porm BD in Fig. 28 demonstrates the... 

In early studies, it was natural to seek explanations of the processes in terms of the already well-confirmed mechanisms of gas breakdown such as collision ionization and streamer propagation. Since that time, the very considerable advance in understanding the electronic properties of the amorphous solid state offers opportunity for a much wider appraisal of the breakdown mechanisms of liquids. They are, as condensed phases, in many ways closer to the solid than to the gaseous state, at least through the initiatory stages of breakdown if not at the onset of final dielectric collapse. An important feature of the improved understanding is the possibility to consider in detail the electronic processes of an electro-chemical nature which are likely to occur at metal electrode-dielectric liquid interfaces. As will be discussed below, the processes at these interfaces play a vital role in breakdown initiation ... 

Fig. 10. Energy states for an insulating micro-region on a metal cathode under an applied field (after Latham, 1982). Electrons tunnel from cathode to conduction band of insulator through Schottky barrier, A. Electron traps become filled, B. Electrons accumulate at electron-affinity barrier at insulation-vacuum interface, C. Holes produced by collision ionization drift to A and enhance electron tunnelling. Electrons with enhanced kinetic energy emitted over barrier C into liquid conduction band, D. Positive hole states of liquid E, ...

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