Next Generation Phase Change Memory Materials: Nanostructure, Electronic Properties and Thermal Transformations

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Technical: This project is to conduct fundamental study of phase change memory materials, including doped binary and exploratory ternary compositions of chalcogenide thin films. The objective is to achieve a detailed understanding of the phase-changing mechanism and the following properties of these materials: the nanoscale structure of the amorphous phase; thermal heat release during phase transitions; incorporation site, possible electrical activation, and structural effects of dopants; composition dependence of the valence band density of states; and the modifications resulting from alloy composition, conditions of synthesis including doping, and post-deposition thermal or optical processing. Scanning transmission electron microscopy, coupled with statistical data processing, will be used to characterize the effect of thermal history and composition on nanoscale structural order. Key objectives include determination of change induced by laser priming or melt-quenching and examination of structural changes associated with write/erase cycles. Nanocalorimetry will be used to study the heat capacity of each phase. Valence band density of states, including band tails and states in the gap, relationships to crystal structure, and switching mechanism, will be probed by measurements of the electrical conductivity and its temperature dependence; optical spectroscopy of the band gap absorption edge; and X-ray and UV photoemission. Pump-probe laser-induced phase transformations and in-situ measurements of the reflectivity will be carried out as a function of time. Phenomena to be studied during the transformations include atomic force microscopy of crystallites in a partially crystallized thin film sample and crystallinity and directionality of the crystallites using electron backscattered diffraction.Non-technical: Future development of chalcogenide materials for advanced data storage applications requires mastery of the relationship between composition, structure, thermal transformation, and electronic properties. This project, focusing on the fundamental materials research, will generate a deep scientific understanding of the nanoscale structure, thermal properties, electronic properties, and kinetics of the phase transformation of the phase change memory materials, enabling rapid development of optical memory and non-volatile memory based on phase change materials. The project will support two graduate students. One or two undergraduates will carry out portions of this project as their senior theses. To broaden the participation of underrepresented groups, qualified students will be identified through the SURGE (Support of Under-represented Groups in Engineering) and WISE (Women in Science and Engineering) programs at the University of Illinois - Urbana Champaign.