Abstract
The paper reports on an investigation of two chalcogenide films that both show bipolar resistance switching, i.e., Ag/Ge~0.25~Se~0.75~ and Ge~2~Sb~3~Te~5~. Changes occurring in the chalcogenide films during switching were analyzed by conductiveβatomic force microscopy (CβAFM). All the findings in the first Ag/Ge~0.25~Se~0.75~ 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 Ge~2~Sb~3~Te~5~ 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 Sbβrich phase would exist in between Ge~2~Sb~2~Te~5~ crystallites. This would create conductive paths when a bias is applied, paths that would break when the polarity is reversed.