Materials World Network: Ordered Ge/Si Core-Shell Nanostructures for Nonvolatile Memory Applications

来自加州大学滨江分校（UCR）的两个研究小组和中国南京大学的一个研究小组的研究人员开发了必要的材料技术，以实现闪存技术向CMOS极限的可扩展性，并使用有序的Ge/Si核壳量子点。闪存是许多便携式电子产品中的关键部件，当要求更高的存储容量和更低的功耗时，它将不能正常工作。作为一种替代器件，硅基半导体存储器虽然正在被存储器行业广泛研究以实现商业化，但对于超过32 nm的技术节点来说也将失败。关键问题是由于浮点密度变化引起的不均匀写入和擦除以及由于较薄的隧道氧化物用于较低电压操作而导致的不可接受的短保持。在这个项目中，Ge/Si核壳量子点通过合作自组装成一维阵列的工程与当前CMOS向一维结构的缩放趋势是协同的，预计将导致额外的性能改善。采用全原子模型、半经验模型和第一性原理模型研究了标度效应对Ge/Si核壳量子点电子性质的影响。实验制造和表征提供了理论和实验数据之间的紧密耦合。夏季交流活动和研究演示的小型研讨会允许参与的博士生和本科生在各种专业领域接受培训。以研究为基础的课程开发，研究成果的网络传播，出版物和会议演示，并通过视频传播到当地学区将影响更多的学生，包括那些在大学预科水平。考虑到UCR及其周边地区学生的背景非常多样化，许多参与和受影响的学生来自传统上在科学和工程领域代表性不足的群体。这种国际学生交流使美国学生接触到中国式的研究网络和南京的中国文化，也使中国学生接触到美国-风格研究和文化。如果成功演示，这项工作将对非易失性存储器行业产生广泛的影响。该项目由材料研究部，国际科学与工程办公室和MPS多学科活动办公室共同资助。

Investigators from two groups at the University of California at Riverside (UCR) and one group at Nanjing University, China, develop materials technologies necessary for realizing the scalability of flash memory technology toward the CMOS ultimate limit and beyond using ordered Ge/Si core-shell quantum dots. Flash memory, which is a key component in many portable electronics, will not operate properly when higher storage capacity and lower power consumption are requested. As an alternative device, silicon nanocrystal memory, although being extensively investigated by the memory industry for commercialization, will also fail for technology nodes beyond 32nm. The key issues are non-uniform writing and erasing due to floating dot density variation and unacceptable short retention as a result of thinner tunnel oxide for lower voltage operation. In this project, engineering of Ge/Si core-shell quantum dots into one-dimensional arrays through cooperative self-assembly is synergistic with the current CMOS scaling trend toward one-dimensional structures and is expected to result in additional performance improvement. The effect of scaling on the electronic properties of the Ge/Si core-shell quantum dots is theoretically investigated using fully atomistic models and both semi-empirical and first-principle models. Experimental fabrication and characterization provide close coupling between the theory and experimental data.Summer exchange activities and small workshops of research presentations allow participating PhD students and undergraduate students to be trained in a wide variety of areas of expertise. Research-based curriculum development, web-based dissemination of research results, publications and conference presentations, and dissemination to local school districts through videos will impact more students including those at the pre-college level. Considering the very diverse background of student body in UCR and its surrounding area, many of the students involved and affected come from groups traditionally underrepresented in science and engineering. This international exchange of students exposes U.S. students to the Chinese style of networking in research and Chinese culture in Nanjing, and it also exposes Chinese students to U.S.-style research and culture. If successfully demonstrated, the work will have broad impact on the nonvolatile memory industry. This project is co-funded by the Division of Materials Research, the Office of International Science and Engineering, and the MPS Directorate Office of Multidisciplinary activities.