Structural and Chemical Changes due to Electrical Stress in Phase-Change Nanowires: An In-Situ Electron Microscopy Study

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Nontechnical Description: Almost all electronic products utilize memory devices to store and access information. The requirements for these memory devices include high-density information storage capacity, fast read/write speed and low power consumption. There is a need to continuously discover new materials for memory devices with superior properties to meet the increasing demand of the information technology. Amongst many types of materials, phase change materials are a very promising system as they can switch very rapidly and reversibly between high and low resistance states when electrical current pulses are applied. However, many challenges remain to be overcome in order to make the technology commercially viable. A major one is that a large electrical current is required to change the resistance states. The large current reduces power efficiency and leads to material's degradation. This research project tackles this materials science challenge and studies the degradation mechanisms via advanced microscopy techniques. The research findings can be used to design better materials for future electronic memory devices. In this project, research, training and educational activities are tightly integrated. The latters include (1) the involvement of undergraduates in the research laboratory, (2) incorporation of the latest research results in the teaching module, and (3) training of high-school and college teachers in the Philadelphia district with a high minority student population. Technical Description: This research project studies the effect of electric field on the structural and chemical changes in phase change nanowires made of germanium-antimony-tellurium (Ge-Sb-Te) alloys. The research team utilizes a unique lateral configuration of nanowire devices to directly investigate the changes in Ge-Sb-Te nanowire structure, morphology and chemical composition via in-situ electron microscopy measurements while operating the device under an electrical bias. The goal is to understand the fundamental mechanisms operative behind the functioning of phase change materials, especially the effect of electric field and current on atomic migration and recrystallization. The research provides insights into the atomic processes that are responsible for the functioning of phase change memory devices and their failure mechanisms. The insights obtained will impact the development of novel materials for non-volatile, ultra-dense, ultrafast and energy efficient memory devices .