Phase-change thin films: resistance switching and isothermal crystallization studies

Phase-change materials are identified as promising candidates for the future non-volatile memory applications. It is crucial to develop potential methods and technologies for the materials to meet the future data storage requirements such as high data storage density and high data transfer rate. A part of the present work is about electrical data recording studies with GeSbTe phase-change thin films, where two types of resistive switching mechanisms have been addressed. One is based on amorphous-crystalline phase transformation and the other on the solid-state electrolytic behaviour of the films. Using atomic force microscopy technique, both the mechanisms were demonstrated at nanoscales. Moreover, an extensive investigation was carried-out on the switching characteristics such as reversibility, cyclability and response-time of the second switching mechanism using prototype capacitor-like memory cells. Another major part of the work is the material characterization. From the point of view of data transfer rate, crystallization of the phase-change layer is the rate-limiting process. Therefore, studying the crystallization process and exploring the underlying mechanisms are crucial to improve the switching performance of the existing materials and develop new materials with superior properties. Determining the factors affecting the crystallization plays also a role of equal importance from application point of view. Therefore in this work, the crystallization kinetics Ge-doped Sb-Te thin films was investigated by isothermal annealing experiments using a transmission electron microscope and the various factors influencing the crystallization such as the film composition, protective/capping layer type and electron beam of the microscope were also determined.