Crystallization kinetics in antimony and tellurium alloys used for phase change recording
Modern computers usually employ several types of data storage devices. Most frequently, magnetic and optical storage media are used. The latter have become of great importance throughout the last decade: nowadays a significant amount of data is stored on compact discs (CDs) and digital versatile discs (DVDs). A few years ago, rewritable CDs and DVDs have become commercially available and are widely used these days. In these storage media, a thin film of an antimony (Sb) or tellurium (Te) alloy is locally and reversibly switched by laser heating between the amorphous and the crystalline state. These states can be distinguished optically by their difference in reflectivity. Due to the reversibility of the phase transformation, rewritable CDs and DVDs are also called phase change media. The corresponding Sb and Te alloys are frequently termed phase change materials. Recently, phase change materials have also shown high potential for the development of non-volatile electronic phase change random access memories. In this application, a current pulse provides the heat that is necessary to induce the phase transformation between the amorphous and the crystalline state, which can be distinguished by their difference in electrical conductivity. First prototypes of this memory type are currently developed by the industry and demonstrate fast non-volatile data storage. There are good prospects that these memories finally replace current data storage devices in modern computers. In order to accomplish this, however, it is highly necessary to understand the phase transformation between the amorphous and the crystalline phase for Sb and Te alloys. This thesis makes a contribution to a fundamental understanding of the crystallization kinetics of amorphous and liquid phase change materials. The results should help to optimize both optical and electronic phase change media in terms of data transfer rates and scalability.
info:eu-repo/classification/ddc/530, Physik, Kinetik des Phasenwechsels, Kristallisierung, Glasübergang, Transmissions-Elektronenmikroskopie, Kalorimetrie, kinetics of phase transformations, crystallization, glass transition, transmission electron microscopy, calorimetry
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