Thermal effects on switching of solids from an insulating to a conductive state

Electrical switching in solids has been observed in semiconductors and insulators and often controversy has appeared in the literature over the interpretation of such events. The major reason for the disagreements is the complexity of the switching events, involving a number of separate steps, with possibly different mechanisms at these steps. General properties which are common to most switching events are discussed. Events are shown to start a) by an initiating step increasing the electrical conductivity, followed by b) the current runaway step due to instability, c) the voltage collapse step including the discharge of stored electrostatic energy, and d) the settling-down step with establishment of a low-voltage steady state. The usual mechanisms for initiation are thermal, or electronic. Thermally initiated events continue to develop by thermal effects. Thermal effects may govern also the continuation of the development of electronically initiated events. The influence of the thermal effects will be discussed in detail, emphasizing that the interpretation of a switching process requires the investigation of each switching step separately.