Mechanical stresses upon crystallization in phase change materials

Crystallization processes in different Te alloys, employed in phase change materials for optical data storage, have been investigated by in situ mecha nical stress measurements. Upon crystallization a considerable stress build up is observed, which scales with the volume change upon crystallization. N evertheless the observed stress change only corresponds to approximately 9% of the stress estimated for a purely elastic transformation. Further evide nce of stress relief phenomena comes from the temperature dependence of the stress in the crystalline and amorphous states. Ultrathin dielectric layer s have a profound influence on the crystallization process as evidenced by simultaneous optical reflectance and mechanical stress measurements. This o bservation can be explained by heterogeneous nucleation of crystallites at the interface between the dielectric layer and the phase change film. (C) 2 001 American Institute of Physics.