Technical: The objective of the project is to explore fundamental materials behavior in ultra-scaled low-dimensional binary/ternary phase-change chalcogenide nanostructures. Aiming at generating in-depth knowledge for developing future-generation information technologies using nanoscale phase-change systems, the project is composed of two major parts: (i) exploitation of multi-level phase transition behavior in one-dimensional chalcogenide nanowires, discovering mechanism and technology pathway towards ultra-high-density information processing in future electronic systems, and (ii) investigation of ultimate materials scalability and energy efficiency in binary/ternary chalcogenides with deeply-scaled physical dimensions. Combining multiple Co-PI's different technical expertise, the team plans to build up comprehensive understandings of phase-change phenomena in aggressively scaled materials systems using both experimental and computational approaches with strong support from industry partner. The concept of information technology based of phase-change behavior in materials is recognized as one of the most successful innovations in microelectronics industry in this decade, leading to a prospective main-stream post-silicon technology. If successful, the proposed research would bring in substantial impact in this important technology by generating largely demanded knowledge to break through the well recognized technical barriers: power-efficiency and scalability.
The research opens opportunities for graduate and undergraduate students to acquire interdisciplinary research experience in nanoscale sciences, material engineering, nanofabrication, and computational nanotechnology. The efforts broaden participation of under-represented groups in research programs at the two universities. Outreach activities comprise on-site demonstration of nanoscale scientific and engineering techniques for K-12 students in the Tech Valley of upstate New York and the greater Seattle Area. The dissemination of research results by journal publications and presentations at international conferences, and its inclusion in new curriculum development at both universities will ensure broad impacts to scientific, educational, and general public communities.
Key aspects of phase change memory technology are size of memory, energy or power requirements, and speed of reading and writing memory states. The amorphous and crystalline phases of the phase change material represent the two logic states 0 and 1, as they have different resistances. Driving electrical current causes a reversible transformation between the crystalline and amorphous phases. This project studied the (i) energy requirements as a function of the size of the phase change material, using the heat equation, and (ii) electrical resistance in both crystalline and amorphous phases as a function of the system size, using first principle calculations and molecular dynamics simulations. We find that metal contacts limit the scaling of phase change memory to the smallest of sizes. As a result, using materials with a large bandgap may be useful in scaling to the smallest possible physical dimensions. We also find that the elastic energy plays an important role in determining the energy required to transform the material between the crystalline and amorphous phases. This project involved the training of both graduate and undergraduate students. Three undergraduate students had the opportunity to model heat transport in nanowire based phase change memory and learn about an emerging topic. This NSF Collaborative Project also involved extensive collaboration between our group which focused on theory and modeling, and Prof. Bin Yu’s group which focused on experiments.
