Phase-Change Memory Material in Periodic Mesoporous Silica: Structure and Phase-Transition Behavior under One-Dimensional Confinement

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).NON-TECHNICAL DESCRIPTION:Non-volatile memories such as those used in DVDs retain stored information even when power is not supplied. Phase-change memories (PCM), due to their high-speed phase transitions used for information storage, have attracted tremendous interest as a highly promising candidate for next-generation non-volatile memories. A major challenge needs to be overcome -- that is, phase changes usually demand high power consumption making PCM less power efficient than their low-speed counterparts. The goal of this project is to resolve this issue by testing the hypothesis that PCM materials confined in nanosized cylindrical pores with unusual structures and thermodynamic behaviors could exhibit enhanced material properties that lead to reduced power consumption. State-of-the-art characterization tools will be employed including synchrotron X-ray techniques. Work on the nanoscale confinement of PCM materials is also closely collaborated with a leading theoretical research group at Ohio University (OU) to further investigate the mechanisms of phase transitions in the confined PCM. This project offers abundant opportunities for students at all levels to be trained in a cross-disciplinary setting. In addition to supporting graduate students at OU, internships are provided for underrepresented undergraduate students to conduct research at both OU and Argonne National Laboratory. Students will have the opportunity to access a variety of world-class synchrotron facilities at the Advanced Photon Source.TECHNICAL DETAILS:PCM materials are very promising candidates for applications in next-generation non-volatile memory devices because they exhibit high-speed phase transitions under electrical pulse excitation. An outstanding issue lies in the fact that fast phase transitions also demand high power usage. This research aims to address this problem by exploring the nanoscale confinement of PCM materials which could result enhanced properties that lead to reduced power consumptions. The PCM material chosen for this study is a PCM prototype, Ge2Sb2Te5. Periodic mesoporous silica glasses with cylindrical pores and various pore sizes (2 - 30 nm) that are synthesized through a sol-gel process act as the confining media. Subsequently, magnetron sputtering is used to finish the confining process by filling the pores with Ge2Sb2Te5. The characterization part employs a variety of techniques including synchrotron-based X-ray absorption fine structure, small/wide-angle X-ray scattering, and X-ray microdiffraction. As a computational aspect of this project, molecular dynamic simulations are also performed to help further understand the relationship between the engineered structures and the phase-transition mechanisms as well as other material properties such as electronic and transport properties. This research project is expected to provide a general approach to significantly advance both the understanding and applications of existing PCM materials. Students, including those from underrepresented groups, will be trained on an extensive series of topics such as glass science, semiconductor materials and devices, self-assembly-based nanotechnology, and advanced X-ray characterization techniques.