Material World Network: Understanding and Exploiting Mixed-Mode Ultra-Fast Optical-Electrical Behavior in Nanoscale Phase Change Materials

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

TECHNICAL SUMMARY The objective of this Materials World Network project is to investigate comprehensively the material properties of phase change materials in mixed optical-electrical phase transitions. The underlying principle of memory storage in Ge-Sb-Te alloys is reversible crystalline to amorphous phase transitions that are associated with significant changes in optical reflectivity and electrical resistivity. Although the optical and electrical mechanisms have been independently investigated, there is no work done on the mixed-mode operation, i.e. switching the material optically while probing it electrically and vice-versa. This is however extremely important for a host of potentially game-changing applications ranging from optically gated ultra-fast transistors to non-von-Neumann arithmetic processing. This collaboration between PIs in US, UK and Germany will focus on investigating fundamental phase switching properties in mixed-mode, elucidating phase change mechanisms via dynamic optical probing of electrical phase transitions, and exploring the materials best suited for unconventional future arithmetic processors. The work will involve growth and characterization of new compositions of phase change nanowires, optical pulse induced switching which will be probed electrically, and detailed size- and composition-dependent studies of mixed mode operation in nanowires. NON-TECHNICAL SUMMARY The von Neumann model of computing, which is currently used in computer architecture, utilizes designs with separate divisions for processing, logic and memory. Although this design has been highly successful for today's computers, there is clearly a need to go beyond von Neumann's model to keep up with the ever-increasing demand for faster computers with unprecedented capabilities. Combining arithmetic processing capabilities via optical excitation with electronic memory on a common platform is one possible solution to go beyond the conventional computer architecture and phase change materials are very promising in this regard. This Materials World Network project plans to study for the first time the optical-electrical mixed mode behaviour of phase change materials. Although the remarkable properties of these materials have made them commercially successful in memory devices, the fundamental material properties that govern their phase transitions between crystalline and amorphous states are still quite unknown. The project will provide fundamental and novel insights into how the electrical behaviour of these materials is influenced by optical excitation and vice versa. The research seeks to transfer best practises between PIs in three participating countries. The results of this work will greatly impact the development of non-von Neumann computing using arithmetic processing techniques that can revolutionize computing as we know it. Research and educational activities will be integrated by the involvement of undergraduates in the research program; incorporating new research results in the teaching module, and training high school teachers from the local school districts in three countries. In addition, international collaborative opportunities will give students opportunities to spend time in another laboratory and will provide a unique opportunity to pursue cutting edge research across national boundaries. This project is supported by the Electronic and Photonic Materials program and Office of Special Programs, Division of Materials Research.