Paul P. Budenstein

On the Mechanism of Dielectric Breakdown of Solids

The mechanism of dielectric breakdown in solids, according to recent experimental evidence, involves the creation of a gaseous channel through the dielectric. The high conductance of breakdown appears to be associated with this channel, not with conduction through the solid itself. The central problem in the theory of dielectric breakdown in solids is thus to explain the development, in a strong electric field, of a macroscopic gaseous channel through the dielectric before the large change of conductance characteristic of dielectric breakdown. Recent experimental results will be reviewed and a gaseous model of breakdown in solids will be described in terms of four stages: Formative, Tree Initiation, Tree Growth and Return Streamer. The model is still in the stage of phenomenological development.

Breakdown Conduction in Al‐SiO‐Al Capacitors

Destructive breakdown has been studied in Al‐SiO‐Al capacitors using transmission electron microscopy and electron diffraction, while the capacitors were subjected to controlled electrical stresses. Extensive electrical measurements were made outside the electron microscope on other capacitors. The purpose is to describe destructive breakdown and to relate it to prebreakdown conduction, conditions of fabrication, and capacitor structure.It is found that breakdowns originate at inhomogeneities in the dielectric which appear in electron micrographs as irregularly shaped dark spots about 0.5 μ in diameter. The structure of these dark spots has not been determined. Breakdowns are not concentrated at pinholes, dust spots, or fissures. Breakdown is accompanied by the growth of crystalline silicon. Electrical measurements with a given capacitor reveal two well‐defined polarity‐sensitive threshold voltages, one for the onset of breakdown and one for the cessation of breakdown. Both are virtually independent of te...

Dielectric Breakdown in Thin Evaporated Films of CaF2, MgF2, NaF, and LiF

Prebreakdown dc conduction and breakdown properties have been studied in thin‐film capacitors with dielectrics of CaF2, MgF2, NaF, and LiF. The results are compared mostly with theory developed for electronic breakdown in ionic crystals due to Frohlich, Callen, and Forlani and Minnaja. Capacitors were formed on glass substrates with dielectric thicknesses from 700 to 30 000 A and electrodes of Al. Between −200° and 100°C prebreakdown and breakdown conduction appear to be independent. The transition time between prebreakdown and breakdown conduction is 10−8–10−7 sec. Except for some cases where the breakdown field Fmax (≈106 V/cm) displays an initial rise, an increase in temperature from −200 to 100 C is accompanied by a decrease in Fmax. Only the initial rise can be interpreted in terms of theoretical developments by Frohlich and Callen. An increase in Fmax is observed as the rate of voltage rise varies from 15 to 15 000 V/sec. The breakdown field also varies in most cases as w1/2, where w is dielectric t...

Impulse Breakdown in PMMA under Miegavolt, Nanosecond Excitation

Single impulse dielectric breakdown tests were performed on thick (0.16 to 1.91 cm) polymethylmethacrylate (PMMA) specimens using a uniform field geometry with 7.5 cm diameter Bruce contour electrodes. The applied voltage rose within 20 ns to 2 MV, remained there about 30 ns and decayed in about 65 ns. In some cases, specimens were deliberately altered by surface scribing, pin pricking, drilling small dimples, drilling holes in portions of laminated specimens, and combinations of these. Light emission during the breakdown pulse and damage morphology were studied. Results of these experiments include the following: Each specimen contained many partial channels as well as a main breakdown path. The number varied greatly with overvoltage. Specimens 0.16 cm thick (peak field 12 MV/cm) contained about 2000 partial tree-like channels in various stages of growth, while 1.91 cm thick specimens (peak field 1.1 MV/cm) contained about 20 partial channels. In all unaltered specimens, the channels originated at the anode surface. However, when deep cavities were intentionally introduced into the cathode surface, channels originated at these artificially produced defects as well as on the defect-free anode surface. Intense light emission occurred from both the partial channels and the main discharge channel. The main discharge path is formed only after one of the partial discharge channels has grown completely across the specimen.

Filamentation in silicon‐on‐sapphire homogeneous thin films

Dynamic temperature configuration and current filamentation in single‐crystal silicon films on sapphire substrates were studied with high‐amplitude constant‐current pulse excitation using Sunshines stroboscopic technique. Temperature configurations vary greatly depending upon the pulse duration and amplitude, electrode geometry magnitude of heat flow into the substrate, and magnitude of transverse heat flow. Filamentation occurs in two steps, each accompanied by a voltage drop. An initial broad filament forms as local regions rise in temperature beyond the peak of the resistivity‐temperature curve of the silicon. The second filamentation is a narrow melt channel that forms interior to the initial filament. A time‐dependent computer simulation is presented that includes both the heat flow into the substrate and transverse heat conduction. The model shows that a stable‐current filament can exist without a melt transition, but only for a very restricted range of current levels.

Interpretation of Destructive Breakdown in Thin Dielectric Films

Klein and Gafni have phenomenologically classified breakdown in thin-film capacitors as “single hole,” “propagating,” and “maximum voltage.” Maximum-voltage breakdown, which is supposed to yield the ultimate dielectric strength of the bulk dielectric, is here investigated by adding to the test circuit of Klein and Gafni, a silicon-controlled rectifier that removes the applied voltage within a few microseconds of the occurrence of breakdown. It is shown that maximum-voltage breakdown is initiated as a single-hole breakdown and that total destruction occurs through a series of consecutive breakdowns, each of which is localized and similar to other single-hole breakdowns. The negative resistance region that precedes maximum-voltage breakdown is believed incidental, not causative.

Failure analysis of a composite insulation system under impulse excitation

Breakdown occurred in an impulsively excited, composite insulation system in the region of the output spark gap and peaking capacitor of a Marx bank generator, The spark gap system contained 8 gaps in parallel operating in pressurized SFG. Systematic differences were observed in the damage morphology from module to module of the spark gap insulating system. These data were supplemented with voltage waveforms and a knowledge of the history of the system, The analysis yields a reconstruction of the sequence of events associated with growth of breakdown paths, an explanation of distinctive features of the damage configuration, and an estimate of average conduction properties of the gaseous breakdown plasma during two stages of channel development.

Time correlation of light intensity, voltage and current waveforms in breakdown of transformer oil under steep-fronted impulse excitation

Time-correlated specimen voltage, current, and light-intensity waveforms are related to tree initiation, onset of conduction, and tree propagation. Results on breakdown voltage and time of initiation relative to waveforms are also given. It is demonstrated that the breakdown phenomena in polymethylmethacrylate, as indicated by waveforms and self-luminosity, are similar to those described for breakdown in transformer oil.<<ETX>>

A model of electric breakdown in solids

When a solid dielectric is subjected to a sufficiently high electrical stress, breakdown occurs with an abrupt increase in conductance. The signature of the breakdown includes a rapid transition from nonlocalized to localized conduction at a field of about 106 V/cm, a high breakdown current density, creation of hollow channels through the dielectric, and intense light emission from the damage channels.

Dielectric breakdown in solids

Breakdown in solids and over surfaces of solids continues to be an area of great technological interest. Understanding has improved in high field conduction of very thin, high-quality films, laser-induced damage, and in aspects of relatively low-field, long-time deterioration of dielectrics. In comparisons of breakdown properties of structurally similar materials, certain consistencies have been pointed out, but the often-sought general relationships between mechanical, thermal, and breakdown properties remain elusive. The anticipation of greater utilization of electrical energy has spurred research in cryogenic cables. Studies of deterioration and failure of insulation systems in cables, transformers, and polluted insulators continue because of their economic importance. Reviews during 1974 treated thin film breakdown (50) and laser-induced damage (55, 56), A symposium on treeing phenomena was held during the 1973 Conference on Electrical Insulation and Dielectric Phenomena.