Tutorial EL09—Phase-Change Memory—Materials Fundamentals and Advanced Applications

Instructors: Matthias Wuttig, RWTH Aachen University; Wolfram Pernice, University of Münster;  Riccardo Mazzarello, RWTH Aachen University; Fabio Pellizzer, Micron Technology, Inc.

The rapidly growing demand for data storage and processing, driven by artificial intelligence (AI) and other data-intensive applications, is posing a serious challenge for current computing devices based on the von Neumann architecture. For every calculation, data sets need to be shuffled sequentially between the processor, and multiple memory and storage units through bandwidth-limited and energy-inefficient interconnects, typically causing 40% power wastage. Phase-change materials (PCMs) show great promise to break this bottleneck by enabling nonvolatile memory devices that can optimize the complex memory hierarchy, and neuro-inspired computing devices that can unify computing with storage in memory cells. In this tutorial session, four comprehensive talks are scheduled to highlight recent breakthroughs in the fundamental materials science, as well as electronic and photonic implementations of these novel devices based on PCMs. More details can be found in "Phase-change materials in electronics and photonics" [MRS Bull. 44 (9), 686 (2019)]. The instructors are senior researchers working in the area of phase-change materials from RWTH Aachen University, University of Münster and Micron Technology, Inc.

8:30 am
Phase-Change Materials—Empowered by an Unconventional Bonding Mechanism
Matthias Wuttig, RWTH Aachen University

Phase-change materials (PCMs) have demonstrated a wide range of potential applications ranging from electronic memories to photonic devices. These applications are enabled by the unconventional portfolio of properties that characterizes crystalline PCMs. Here, I address the origin of these unusual properties and how they are related to the application potential of these materials. Evidence will be presented that the properties are related to an unconventional bonding mechanism. Employing a novel map, which separates solids according to the number of electrons transferred and shared between adjacent atoms, it is shown that PCMs occupy a well-defined region. Depicting physical properties such as the optical dielectric constant as the third dimension in the map reveals systematic property trends. Such trends can be utilized to unravel the origins of the unconventional materials properties or alternatively, as a means to optimize them.

10:00 am BREAK

10:30 am
Evolution and Challenges of Phase-Change Memory
Fabio Pellizzer, Micron Technology, Inc.

The aim of this tutorial will be to describe the evolution and the residual challenges of phase-change memory technology from the point of view of the device operation. The speed of the phase transitions and their stability will be discussed, together with their implications for the possible applications. Moreover, the architectural challenges of a 3D Cross-Point array will be reviewed, highlighting the boundary conditions posed to the technology.

1:30 pm
Integrated Phase-Change Photonic Devices and Systems
Wolfram Pernice, University of Münster

Driven by the rapid rise of silicon photonics, optical signaling is moving from the realm of long-distance communications to chip-to-chip, and even on-chip domains. If on-chip signaling becomes optical, we should consider what more we might do with light than just communicate. We might, for example, set goals for the storing and processing of information directly in the optical domain. Doing this might enable us to supplement, or even surpass, the performance of electronic processors, by exploiting the ultrahigh bandwidth and wavelength division multiplexing capabilities offered by optics. Here, I show how, by using an integrated photonics platform that embeds chalcogenide phase-change materials into standard silicon photonics circuits, we can achieve some of these goals. Specifically, I show that a phase-change integrated photonics platform can deliver binary and multilevel memory, arithmetic and logic processing, as well as synaptic and neuronal mimics for use in neuromorphic, or brain-like, computing – all working directly in the optical domain.

2:30 pm BREAK

3:00 pm
Atomistic Simulations of Phase-Change Material
Riccardo Mazzarello, RWTH Aachen University

Phase-change materials (PCMs) are used in optical devices and electronic nonvolatile memories, and are promising candidates for neuro-inspired computing applications. These technologies exploit the ability of PCMs to switch rapidly between amorphous and crystalline states with pronounced optical and electrical contrast. In this tutorial, an overview is given of recent computational work on PCMs based on density functional theory and machine learning potentials. It will be shown that simulations have enabled the elucidation of fundamental links between structure and dynamics. Such links have shed light on technologically relevant properties of PCMs, including the ultrafast crystallization at high temperature, the behaviour of the liquid phase in the deep undercooling regime and the relaxation of the amorphous state.