The role of defects in resistively switching chalcogenides

Abstract

This overview describes the present Understanding of resistive switching phenomena encountered in chalcogenide-based cells which may be utilized in energy-efficient nonvolatile memory devices and in array-based logic applications. We introduce the basic operation principle of the phase change mechanism, the thermochemical mechanism, and the valence change mechanism and we discuss the crucial role of structural defects in the switching processes. We show how this role is determined by the atomic Structure of the defects, the electronic defect states, and/or the ion transport properties of the defects. The electronic structure of the systems in different resistance states is described in the light of the chemical bonds involved. While for phase change alloys the interplay of ionicity and hybridization in the crystalline and ill the amorphous phase determine the resistances, the local redox reaction at the site of extended defects, the change in the oxygen stoichiometry. and the resulting change ill the occupancy of relevant orbitals play the major role in transition metal oxides which switch by the thermochemical and the valence change mechanism. Phase transformations are not only discussed for phase change alloys but also for redox-related switching processes. The switching kinetics as well as the ultimate scalability of switching cells are related to structural defects in the materials