Phase‐Change and Ovonic Materials (Fourth Edition)

Once again, it is our great pleasure to continue the E\PCOS tradition by presenting this fourth edition of special issue on Phase-Change and Ovonic Materials that published each year as part European Symposium Sciences (E\PCOS). We have admit 2022 had a spirit marked long-awaited return face-to-face on-site symposium after two-year hiatus due Covid crisis. Last September, was most successful in terms attendance history E\PCOS. This no coincidence once editorial, Harish Bhaskaran, Luci Bywater Oxford team are sincerely thanked behalf entire community for making success possible even if unfortunately, some major actors could not join us at Wolfson College year. As three previous editions, again aims summarize recent innovative scientific technological achievements field phase-change materials, well their new fields application. In addition advances field, objective also present emerging interests neuromorphic computing, nonlinear photonics or plasmonics. thus provides an overview state art, both experimental theoretical, experienced young researchers interested these topics. usual, let first recall, younger newer members ever-evolving community, born Switzerland 2001, with aim provide platform discuss promote fundamental science materials (PCM). goal included applications rewritable optical discs (e.g., CDs later successfully developed DVD Blu-ray Disc formats) initially PCOS referred storage (which diversified 2005 ovonic science). fact, from held Japan 1990, thanks Professor Masahiro Okuda, who advisor during its early years. years, has considerably. While fingerprints field's founding father, late Stanford Ovshinsky, still very recognizable, number topics covered continued grow significantly including non-volatile electronic memories, optoelectronics, photonics, computing. The confirmed premier international conference exciting evergreen topic. edition, which follows 2021 virtual somewhat challenge community. However, unprecedented close ties between key players academic industrial. By covering rich variety beyond will mark paper Park et al. use Sb2Te3/TiTe2 heterostructure replace conventional canonical GST (Ge2Sb2Te5) alloy class memory computing hardware illustration [pssr.202200451]. Indeed, recently introduced novel (PCM) applications, faster SET speed lower RESET energy than those obtained usual GST225 required. study, PCM devices based multilayers made amorphous Sb2Te3 TiTe2 nanolayers deposited sputtering exhibit fast (≈30 ns), reduction more 80% compared GST-based reference resistance drift high state. These promising results deserve future work example evaluate endurance type programming cycles. A similar motivated presented Kashem [pssr.202200419] they proposed finite element simulation framework combining amorphization–crystallization dynamics electro-thermal effects better describe RESET–SET–READ operations nanoscale devices. They concluded alloy-based model account impacts dynamic changes crystallinity device operation were consistent observations, providing understanding dynamics. would allow any geometry be studied explore effect pulse material engineering, architecture performance. For example, predict impact thermoelectric current requirements significant role heater height heat loss current. One other challenges technology storage-class related improving density using multilevel cells (MLCs), shown Zhao [pssr.202200463]. Although design aspect ratio confined-structure PCMs enables controllable MLC operation, negatively affects power consumption, becomes too large operate PCM. Therefore, investigated trade-off different sizes nanowire COMSOL experiments. Their conclusion best much consumption enhancement can length below 1.5 μm about 10:1. Increased enabled vertical 3D integration cross-point arrays. achieved adding cross point cell array Threshold Switching (OTS) selector. latter chalcogenide OTS behavior under electrical-field two-terminal selector allowing program read selected but same time limiting suppressing unavoidable leakage paths through adjacent unselected cells. Performance characterized threshold voltage (Vth) required switch into metastable highly conductive subthreshold Vth directly defines size achievable array. context, Ravsher [pssr.202200417] investigate one selectors instability. To end, studied, electrical characterization devices, polarity-induced shift quaternary SiGeAs(Te/Se) binary GexSe1−x compounds case polarity, bipolar cycling, thickness, interface oxidation, stoichiometry conduction. magnitude depends composition increases up nearly order when going SiGeAsTe, SiGeAsSe GeSe. showed families reversed direction dependence operating From theoretical point-of-view Perego [pssr.202200433] answer relevant question, structure crystallization kinetics GeTe films. perform molecular simulations 8000 atoms. compare atomic arrangement melt-quenched samples as-deposited conclude similar, least atoms sufficiently particle energies. important since difficult create macroscopic often unravel glassy phase PCMs. Finally, films contain larger Ge-Ge bonds Ge-atoms tetrahedral geometries. nature defects, ab initio dynamics, discussed Konstantinou Elliott [pssr.202200496]. four GeSbTe compounds, i.e. GeTe, Sb2Te3, GeTe4 Ge2Sb2Te5 find charge-trapping centers. trapping centers ranges over- under-coordinated atoms, distorted octahedral sites, four-fold rings homopolar bonds. intrinsic property, localizes electrons holes should operation. van-der-Waals (vdW) gaps play various Strepanov [pssr.202200430] focus GaSe employed functional theory (DFT) analyze influence uniaxial compressive stress perpendicular vdW gaps. It levels (up 30 GPa) do gaps, 2D 3D, contrary generates quasi-1D chains oriented along applied pressure. structural change course strongly alters structure. authors think generic currently test occur Sb2Te3. Ge-rich alloys attractive embedded fulfill tough temperature specifications automotive applications. challenging tendency separate. Petroni [pssr.202200458], advanced statistics methodology quantifies segregation clustering multiple chemical species processing, highlighting specific correlations elements evolves. uses here elemental maps STEM focused ion beam prepared cross-sectional actual integrated only demonstrates strong capabilities methodology, optimization BEOL process causing improved less undesirable clustering. Ge addressed study multistep (GST) compounds. Rahier employing in-situ synchrotron radiation scanning transmission electron microscopy (STEM) [pssr.202200450]. next generation digital memories offer increased thermal stability phase. Upon crystallization, incongruent formation observed. Initially, already starts undergo separation leading regions content. Subsequently, grains start crystallize, trigger cubic Cubic formed higher temperatures upon incorporation Sb grains. Humphreys [pssr.202200474] highlights added value metamaterials. Here, periodic arrays sub-wavelength-scale plasmonic metal generate resonant peaks via extraordinary (EOT) effect. Adding GST, switching crystalline phases, allows active control, particular shifting spectral position such whole cycle design, fabrication, EOT targeted spectrum terahertz infrared presented. conclusion, please enjoy latest research science. we hope help strengthen preparation meeting Rome September 18-20, 2023. many countries, there saying: “All roads lead Rome”, so look forward welcoming you celebrate together 22 years following last 2022, thriving ever. Pierre Noé, Bart J. Kooi Matthias Wuttig Guest editors B.J.K. P.N. acknowledge funding Union's Horizon 2020 innovation programme grant agreement No.824957 ('BeforeHand': Boosting Phase Change Devices Hetero- Nano-structure Material Design). support ANR projects MAPS ANR–20–CE05 OCTANE ANR–20–CE24–0019, Auvergne-Rhône-Alpes region “Pack Ambition Recherche 2019”-NanoCHARME project Europe No.101070238 (‘NEUROPULS’: Neuromorphic Energy-Efficient Secure Accelerators Based On Augmented Silicon Photonics). thank French group “GdR CHALCO”, created (https://gdrchalco.cnrs.fr/). M.W. acknowledges Deutsche Forschungs-Gemeinschaft (DFG) collaborative center Nanoswitches (SFB 917). At last, appreciate efforts all contributors Focus Issue. Noé began his career CEA's Basic Research Directorate 2000 engineer working Si-based nanostructured microelectronics, spintronics. 2011, he became permanent researcher CEA-Leti PhD physics 2013 University Grenoble-Alpes. Since then, own within Leti's Technologies division. His focuses development frontier knowledge (memories, thermoelectricity, etc.). He involved two Agency projects, HORIZON projects; six committee Groupement de (GdR) CHALCO guest editor 2019 Special Issue annually journal pssRRL. received "Habilitation à Diriger des Recherches" Obtained degree 1995 Delft Technology, Netherlands. Worked then Groningen (Netherlands) assistant, associate full professor, starting 2009 Nanostructured Interfaces Zernike Institute Advanced Materials. main nanostructure-property relations, microscopy, interfaces, transformations tellurium antimony Ph.D. 1988 RWTH Aachen/Forschungszentrum Jülich. visiting professor several institutions Lawrence Berkeley Laboratory, CINaM (Marseille), University, Hangzhou IBM Almaden, Bell Labs, DSI Singapore Chinese Academy Shanghai. 1997, appointed Full Aachen. been heading resistively chalcogenides 917), funded German Science Foundation (DFG). [pssr.202200451] [pssr.202200463] [pssr.202200496] [pssr.202200458] [pssr.202200450]