Phase change materials and their application to nonvolatile memories

Phase change materials and their application to nonvolatile memories have been reported. Phase change materials are materials that exist in at least two structurally distinct solid phases, an amorphous and one crystalline phase. Optical data storage based on phase change materials started with the discovery of a certain family of phase change materials (semiconductor alloys containing Ge, Sb, and Te) that showed the required fast crystallization times that limit the data rate in optical storage. They exhibit large differences in physical properties such as reflectivity and electrical resistivity between the amorphous and crystalline phases which are due to structural differences between the phases. The most successful phase change materials are characterized by a simple cubic structure with atoms on random locations in the lattice, often with large numbers of vacancies and distortions. Phase change materials are the crucial element of the mature rewritable optical storage technology and the emerging PCRAM technology.