Memory switching in In Te glasses: results of heat-transport measurements

Abstract

Even 33 years after the discovery of electrical switching in chalcogenide glasses, a complete understanding of the mechanisms responsible for this phenomenon is lacking. It is believed that threshold switching in chalcogenide glasses is electronic in origin whereas memory switching is of thermal origin. According to the thermal model, the ON state during memory switching is caused by a thermal breakdown of the steady state of the material when the heat generated by Joule heating cannot be removed fast enough by thermal conduction. Joule heating causes crystallization of the glass into fine filaments resulting in excess carrier concentration in the current path due to the large electric field present. Even though electrical conductivity and related properties of a number of materials have been investigated during and after switching, no measurements seem to have been done to determine the variation in thermal conductivity and related properties during switching. In this paper we report the results of our measurements of thermal conductivity and heat capacity of In–Te glasses, which exhibit clear memory type electrical switching at threshold fields in 80–140 V cm−1 range. Measurements have been made on bulk samples using an improved photothermal technique. Results show that thermal conductivity of the samples increase considerably during electrical switching, whereas heat capacity remains more or less constant. The results are discussed in the light of the thermal model for memory switching applicable to Te-based chalcogenide glasses.