Phase-change materials: Empowered by an unconventional bonding mechanism
- PDF / 597,330 Bytes
- 6 Pages / 585 x 783 pts Page_size
- 29 Downloads / 244 Views
Introduction
PCMs and switching speeds
Phase-change materials (PCMs) have attracted significant interest in the last few years. There are two major reasons for this attention. PCMs have a wide range of present and potential applications, ranging from rewriteable optical data storage to novel electronic memories and switchable photonic devices.1–3 For these applications, it is crucial to understand the source of the unconventional properties of PCMs,4,5 and how the properties can be tailored. Yet, PCMs are also stimulating from the perspective of fundamental sciences. What are the origins of the unconventional properties that characterize these remarkable solids? In this article, we attempt to address both perspectives. We first summarize the properties portfolio that is desirable for different applications of PCMs, in particular, where improvements of materials properties promise significant gains in the application arena. Subsequently, we briefly address how material properties can be explained utilizing fundamental concepts of the relationship between bonding, structure, and properties. The emerging insights are then employed to address an aspect of significant application interest—the origin of the high switching speeds.6,7 Finally, the potential of the approach presented is critically evaluated.
PCMs are presently employed for rewritable optical and electronic data storage. Both means of storage utilize the fact that PCMs can exist at room temperature in both a metastable amorphous phase and a (more stable) crystalline state.8 The coexistence of two such states can be realized in many materials, including Si and SiO2 (glass and crystal). What makes PCMs stand out are the potentially high switching speeds from the amorphous to the crystalline state at elevated temperatures, which can be as short as 1 ns, or less,9–11 while the amorphous phase can be stable for more than 10 years at room temperature. The switching speed exhibits an extraordinary temperature dependence in these materials, with an increase in temperature of about 300 K leading to an increase in switching speed by 16–17 orders of magnitude. The second highly remarkable feature of this material class is the pronounced difference in properties between the amorphous and the crystalline states. While the optical properties of SiO2 such as the optical reflectivity hardly differ in the amorphous (glassy) and crystalline states. This is very different for PCMs, where the amorphous and crystalline phase show a pronounced difference in refractive index and optical polarizability ε∞, leading to applications such as their use in Blu-ray discs.2
J. Pries, Institute of Physics IA, RWTH Aachen University, Germany; [email protected] O. Cojocaru-Mirédin, Institute of Physics IA, RWTH Aachen University, Germany; [email protected] M. Wuttig, Institute of Physics IA, RWTH Aachen University; and JARA-Institute, Energy-Efficient Information Technology (Green IT), Germany; [email protected] doi:10.1557/mrs.2019.204
• VOLUMECo
Data Loading...
