Threshold switching mechanism by high-field energy gain in the hopping transport of chalcogenide glasses

Abstract

Chalcogenide glasses are widely used in phase-change nonvolatile memories and in optical recording media\ud for their ability to rapidly change their structure to crystalline, thus obtaining different electrical resistance and\ud optical reflectivity. Chalcogenide glasses universally display threshold switching, that is a sudden, reversible\ud transition from a high-resistivity state to a low-resistivity state observed in the current-voltage I-V characteristic.\ud Since threshold switching controls the operating voltage and speed of phase-change memories, the\ud predictability of the switching voltage, current, and speed is of critical importance for selecting the proper\ud chalcogenide material for memory applications. Although threshold switching has long been recognized to be\ud an electronic process with an intimate relation to localized states, its detailed physical mechanism is still not\ud clear. In this work, threshold switching is explained by the field-induced energy increase in electrons in their\ud hopping transport, moderated by the energy relaxation due to phonon-electron interaction. The energy increase\ud leads to an enhancement of conductivity and a collapse of the electric field within the amorphous chalcogenide\ud layer, accounting for the observed negative differential resistance at switching. Threshold switching is found to\ud obey to a constant electrical-power condition. The proposed model generally applies to low-mobility semiconductors\ud featuring a deep Fermi level and hopping-type conduction, and can predict the thickness, temperature,\ud and material dependence of threshold voltage and current

Transient phases during fast crystallization of organic thin films from solution

“…Adler et al 23 suggested the double injection model with narrow barriers forming at both electrodes. Ielmini 24 proposed a trap-hopping model in which the high electric fields lead to non-equilibrium distribution of trapped electrons that causes a sudden increase in the conductivity. The model features a critical power-density at which threshold switching can initiate.…”

Microstructure-dependent DC set switching behaviors of Ge–Sb–Te-based phase-change random access memory devices accessed by in situ TEM

“…29 The detection of conductive filaments by TEM is very challenging in such an embedded cell geometry because of the two-dimensional projection nature of TEM images. Considering the spatial resolution (δ) of TEM diffraction contrast imaging, δ≈0.61λ/α = 0.8 nm, where λ and α are the wavelength (0.00251 nm) and the convergent angle (3.125 mrad) of the electron beam, respectively, critical nuclei or conductive filaments are in principle detectable (the radius of a critical nucleus is typically 1-3 nm 30,31 ).…”

Ion Implantation in Phase Change Ge2Sb2Te5 Thin Films for Non Volatile Memory Applications

“…The threshold switching occurs at a certain threshold field, on the order of 10-100 V/m (Krebs et al, 2009), depending on the material composition, and it is characterized by a sudden decrease of resistivity, with negative differential resistance, as schematically shown in figure 1. Several models have been suggested to explain this effect, such as thermal runaway caused by Joule heating (Owen et al 1979) or energy gain of electrons in a high electric field, leading to a voltage-current instability (Ielmini, 2008). However, detailed experimental validations of the proposed models are further required to better understand the physical mechanisms.…”