Abstract
The paper reports on an investigation of two chalcogenide films that both show bipolar resistance switching, i.e., Ag/Ge0.25Se0.75 and Ge2Sb3Te5. Changes occurring in the chalcogenide films during switching were analyzed by conductive atomic force microscopy (C-AFM). All the findings in the first Ag/Ge0.25Se0.75 family are in agreement with the proposal of a migration of Ag from the electrode throughout the film, creating random conductive paths when a bias is applied and their rupture when the bias is reversed. Reversible bipolar resistance switching with bias in the range of few volts was clearly demonstrated in Ge2Sb3Te5 films, even though its nature is not so well understood. Clear enough is the fact that a primary and irreversible contraction of the film along with an increase in its conductivity occurred when a bias was applied to the film. It was related to a crystallization of the film. Further write/erase cycles induced resistance switching but no change in the contraction/expansion of the films. Our findings corroborated a mechanism where an amorphous Sb-rich phase would exist in between Ge2Sb2Te5 crystallites. This would create conductive paths when a bias is applied, paths that would break when the polarity is reversed.