PHASE CHANGE MATERIALS: CHEMICAL BONDING AND STRUCTURAL PROPERTIES

The phase change materials are the most important materials in the class of chalcogenides (combination of chalcogens (S, Se and Te) with metalloids or metals). The outstanding property of these materials is the switching from a high electrical resistivity state to low electrical resistivity state and back under a moderate voltage. The thin film materials are used in computer memories, CD and DVD devices with performing speed and storage capacity. We have studied several thin solid films made of Ge-Sb-Te in order to assess the switching quality of different compositions. In order to systemize the whole class of chalcogenide phase change materials we have investigated the correlation between different crystallo-chemical parameters and the ionicity of the elements. Binary and ternary compounds are distributed into several distinct groups. The most favorable phase change materials are situated in a specific range of mean ionicity and mean glass formation ability. The results give the possibility to design new compositions with better switching properties.