Abstract
The rapid development of Internet of Things devices requires real time processing of a huge amount of digital data, creating a new demand for computing technology. Phase change memory technology based on chalcogenide phase change materials meets many requirements of the emerging memory applications since it is fast, scalable and non-volatile. In addition, phase change memory offers multilevel data storage and can be applied both in neuro-inspired and all-photonic in-memory computing. Furthermore, phase change alloys represent an outstanding class of functional materials having a tremendous variety of industrially relevant characteristics and exceptional material properties. Many efforts have been devoted to understanding these properties with the particular aim to design universal memory. This paper reviews materials science aspects of chalcogenide-based phase change thin films relevant for non-volatile memory applications. Particular emphasis is put on local structure, control of disorder and its impact on material properties, order–disorder transitions and interfacial transformations.
Highlights
The rapid development and increasing number of Internet of Things devices require storage and on-line processing of a huge amount of data
This review focuses on materials science aspects of Ge–Sb–Te based phase change thin lm materials, focusing on atomic structure, impact of disorder on material properties, control of disorder, order–disorder transitions and interfacial transformations
Ge–Sb–Te based phase change alloys represent an outstanding class of functional materials having a tremendous variety of industrially relevant properties
Summary
The rapid development and increasing number of Internet of Things devices require storage and on-line processing of a huge amount of data. The atomic structure of the crystalline phase is stabilized by a unique type of bonding (in the past called resonant bonding while a new interpretation calls it metavalent bonding).[35,36,43,47,48,49] This type of bonding is responsible for the high electronic polarizability and optical dielectric constants reported for crystalline phase change materials.[35,50] this type of bonding requires long-range order Since this order vanishes in the amorphous state, the phase shows an ordinary covalent type of bonding with lower polarizability.[37,51] More interestingly, many phase change materials undergo order–disorder transitions within their crystalline phases.[52,53,54,55,56] This is attributed to the presence of a huge amount of structural vacancies in the materials, which are responsible for the p-type conductivity of phase change alloys.[57] Depending on the composition, the number of structural vacancies in the cation sublattice can be up to 29% (e.g. for GeSb4Te7).[58,59] In the crystalline phase the vacancies can be found randomly distributed or they can be ordered into vacancy layers. The fourth part discusses order– disorder transitions and interfacial transformations in Ge–Sb– Te materials with special emphasis on vacancy ordering processes, the cubic–trigonal phase transition, interlayer exchanges in layered Ge–Sb–Te crystal structures and ultrafast interface-controlled crystallisation processes in Ge–Sb–Te materials
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