Field dependent conductivity and threshold switching in amorphous chalcogenides—Modeling and simulations of ovonic threshold switches and phase change memory devices

Abstract

We model electrical conductivity in metastable amorphous Ge2Sb2Te5 (GST) using independent contributions from temperature and electric field to simulate phase change memory devices and ovonic threshold switches. 3D, 2D-rotational, and 2D finite element simulations of pillar cells capture threshold switching and show filamentary conduction in the on-state. The model can be tuned to capture switching fields from ∼5 to 40 MV/m at room temperature using the temperature dependent electrical conductivity measured for metastable amorphous GST; lower and higher fields are obtainable using different temperature dependent electrical conductivities. We use a 2D fixed out-of-plane-depth simulation to simulate an ovonic threshold switch in series with a Ge2Sb2Te5 phase change memory cell to emulate a crossbar memory element. The simulation reproduces the pre-switching current and voltage characteristics found experimentally for the switch + memory cell, the isolated switch, and the isolated memory cell.