On the nature of conduction and switching in SiO2

Further experimental results are presented concerning high conduction and switching in Al–SiO2–Si sandwich structures. The high-conduction state is filamentary and is governed mainly by the voltage across the sandwich. It is relatively insensitive to variations in device geometry. Periodic current oscillations are observed for certain combinations of series load resistance and applied voltage. Once the high-conduction state is achieved, it can be maintained at applied voltages below the one required to cause the transition but larger than a minimum voltage, which may be related to the minimum ionization energy in SiO2. Fluctuations are observed that depend on external circuit configuration, i.e., the load line, and on the ambient temperature. It is shown that a two-branched current-voltage characteristic can account for the observed behavior. A physical model is presented in an attempt to provide a qualitative explanation of the origin of this form of characteristic. Local damage is evident whenever the high-conduction state is seen (even with a single 50-nsec pulse). Electron microscopic analysis of a damaged region is presented.