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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。非技术说明：非易失性存储器，如DVD中使用的存储器，即使在断电时也能保留存储的信息。相变存储器（PCM）由于其用于信息存储的高速相变而作为下一代非易失性存储器的非常有前途的候选者吸引了巨大的兴趣。需要克服的一个主要挑战是，相位变化通常需要高功耗，这使得PCM的功率效率低于其低速对应物。该项目的目标是通过测试以下假设来解决这一问题：限制在具有不寻常结构和热力学行为的纳米级圆柱形孔中的PCM材料可以表现出增强的材料特性，从而降低功耗。将采用最先进的表征工具，包括同步加速器X射线技术。PCM材料的纳米级限制的工作也与俄亥俄州大学（俄亥俄州）的一个领先的理论研究小组密切合作，以进一步研究限制PCM中的相变机制。该项目为各级学生提供了丰富的机会，在跨学科的环境中接受培训。除了支持研究生在斯坦福大学，实习提供了代表性不足的本科生在斯坦福大学和阿贡国家实验室进行研究。学生将有机会访问先进光子源的各种世界一流的同步加速器设施。技术优势：PCM材料在下一代非易失性存储器件中的应用是非常有前途的候选者，因为它们在电脉冲激发下表现出高速相变。一个突出的问题在于快速相变也需要高功率使用的事实。 本研究旨在通过探索PCM材料的纳米级限制来解决这个问题，这可能会导致性能增强，从而降低功耗。本研究选择的PCM材料是PCM原型Ge 2Sb 2 Te 5。通过溶胶-凝胶工艺合成的具有圆柱形孔和各种孔径（2 - 30 nm）的周期性介孔二氧化硅玻璃充当限制介质。随后，使用磁控溅射通过用Ge 2Sb 2 Te 5填充孔来完成限制过程。表征部分采用了多种技术，包括基于同步辐射的X射线吸收精细结构，小/广角X射线散射和X射线微衍射。作为该项目的计算方面，还进行了分子动力学模拟，以帮助进一步了解工程结构和相变机制之间的关系，以及其他材料特性，如电子和传输特性。该研究项目预计将提供一种通用方法，以显着推进现有PCM材料的理解和应用。学生，包括那些来自代表性不足的群体，将在广泛的一系列主题，如玻璃科学，半导体材料和器件，自组装为基础的纳米技术，和先进的X射线表征技术的培训。

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.