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

来自加州大学河滨分校（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，利用有序的Ge/Si核壳量子点，开发了实现闪存技术向CMOS极限扩展和超越CMOS极限所需的材料技术。闪存是许多便携式电子产品的关键部件，当要求更高的存储容量和更低的功耗时，它将无法正常工作。作为一种替代器件，硅纳米晶存储器虽然被存储器行业广泛研究用于商业化，但在32nm以上的技术节点上也将失败。关键问题是由于浮动点密度变化导致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留。在本项目中，通过协同自组装将Ge/Si核壳量子点工程成一维阵列，与当前CMOS向一维结构的缩放趋势相协同，有望带来额外的性能提升。利用全原子模型、半经验模型和第一性原理模型从理论上研究了尺度对Ge/Si核壳量子点电子特性的影响。实验制作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报告的小型研讨会使参与的博士生和本科生在各种专业领域得到培训。以研究为基础的课程开发、在网上传播研究成果、出版物和会议报告，以及通过视频向当地学区传播，将影响更多的学生，包括大学预科学生。考虑到UCR及其周边地区的学生群体背景非常多样化，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。这项国际学生交流活动使美国学生在南京接触到中国式的研究网络和中国文化，也使中国学生接触到美国式的研究和文化。如果成功证明，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理事会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.