Field-induced nucleation switching in binary ovonic threshold switches

Abstract

In this study, we investigate the initial electroforming and electrically driven threshold switching characteristics of a binary boron-tellurium-based ovonic threshold switch (OTS) device using field-induced nucleation theory and related material parameters. First, an analysis of the current-voltage characteristics of devices with various electrode areas shows that the OTS device exhibits filamentary switching, consistent with the field-induced nucleation framework. Further, we find that the OFF-state current depends on the device area, whereas the hold current remains constant regardless of the device area, indicating that the ON-state current flows through a local conduction path. For verifying field-induced nucleation phenomena in the forming and subsequent switching of the OTS device, we apply constant voltage pulses and measure the delay time required for electrical switching of the device. During both forming and switching processes, the switching time is exponential in inverse voltage with different nucleation energy (W0) values; W0 for forming is larger than that for switching. To verify this analysis, incremental voltage pulses with various pulse widths are also applied to confirm the relation between the threshold voltage and time. The W0 values for the two types of switching in this analysis are consistent, solidifying our understanding of the critical contribution of nucleation phenomena in OTS. The smaller W0 for switching can be explained by the generation of clusterlike nucleation sites during forming with lower nucleation energy than in the surrounding matrix.