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

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。非技术描述：非易失性存储器，如DVD中使用的存储器，即使在没有电力供应的情况下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引起了人们的极大兴趣，成为下一代非易失性存储器的候选材料。需要克服的一个主要挑战是，相变通常需要高功耗，使PCM的能效低于低速相变。这个项目的目标是通过测试这样一个假设来解决这个问题：限制在具有不同结构和热力学行为的纳米圆柱孔中的PCM材料可以表现出更好的材料性能，从而降低功耗。将使用最先进的表征工具，包括同步加速器X射线技术。我们还与俄亥俄大学(OU)的一个领先的理论研究小组密切合作，研究PCM材料的纳米尺度限制，以进一步研究受限PCM中的相变机制。该项目为所有级别的学生提供了在跨学科环境中接受培训的大量机会。除了支持俄亥俄州立大学的研究生外，还为代表不足的本科生提供实习机会，让他们在俄亥俄州立大学和阿贡国家实验室进行研究。学生们将有机会参观先进光子源的各种世界级同步加速器设施。技术细节：PCM材料是非常有希望应用于下一代非易失性存储器件的候选材料，因为它们在电脉冲激励下表现出高速相变。一个突出的问题在于，快速相变也需要高功率使用。这项研究旨在通过探索PCM材料的纳米级限制来解决这个问题，这种限制可以提高性能，从而降低功耗。本研究选用的相变材料为相变材料原型Ge2Sb2Te5。以溶胶-凝胶法合成的具有圆柱孔和不同孔径(2-30 nm)的周期性介孔二氧化硅玻璃为约束介质。随后，用磁控溅射的方法在气孔中填充Ge2Sb2Te5来完成限制过程。表征部分采用了多种技术，包括基于同步加速器的X射线吸收精细结构、小角/广角X射线散射和X射线显微衍射。作为本项目的计算方面，还进行了分子动力学模拟，以帮助进一步了解工程结构与相变机制以及其他材料性质(如电子和输运性质)之间的关系。这一研究项目有望提供一种普遍的方法，大大促进对现有相变材料的理解和应用。学生，包括那些来自代表性不足的群体的学生，将接受一系列广泛的主题的培训，如玻璃科学、半导体材料和器件、基于自组装的纳米技术和先进的X射线表征技术。

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.