The control and rational design of redox‐based memristive devices, which are highly attractive candidates for next‐generation nonvolatile memory and logic applications, is complicated by competing ...and poorly understood switching mechanisms, which can result in two coexisting resistance hystereses that have opposite voltage polarity. These competing processes can be defined as regular and anomalous resistive switching. Despite significant characterization efforts, the complex nanoscale redox processes that drive anomalous resistive switching and their implications for current transport remain poorly understood. Here, lateral and vertical mapping of O vacancy concentrations is used during the operation of such devices in situ in an aberration corrected transmission electron microscope to explain the anomalous switching mechanism. It is found that an increase (decrease) in the overall O vacancy concentration within the device after positive (negative) biasing of the Schottky‐type electrode is associated with the electrocatalytic release and reincorporation of oxygen at the electrode/oxide interface and is responsible for the resistance change. This fundamental insight presents a novel perspective on resistive switching processes and opens up new technological opportunities for the implementation of memristive devices, as anomalous switching can now be suppressed selectively or used deliberately to achieve the desirable so‐called deep Reset.
In situ transmission electron microscopy of memristive devices—a highly attractive candidate for next‐generation nonvolatile memory—reveals a previously unknown anomalous resistive switching mechanism. The resistance change is caused by an increase (decrease) in the overall concentration of oxygen vacancies within the device after positive (negative) biasing due to electrocatalytic release and reincorporation of oxygen at the electrode/oxide interface.
Van der Waals layered GeTe/Sb2Te3 superlattices (SLs) have demonstrated outstanding performances for use in resistive memories in so‐called interfacial phase‐change memory (iPCM) devices. GeTe/Sb2Te3 ...SLs are made by periodically stacking ultrathin GeTe and Sb2Te3 crystalline layers. The mechanism of the resistance change in iPCM devices is still highly debated. Recent experimental studies on SLs grown by molecular beam epitaxy or pulsed laser deposition indicate that the local structure does not correspond to any of the previously proposed structural models. Here, a new insight is given into the complex structure of prototypical GeTe/Sb2Te3 SLs deposited by magnetron sputtering, which is the used industrial technique for SL growth in iPCM devices. X‐ray diffraction analysis shows that the structural quality of the SL depends critically on its stoichiometry. Moreover, high‐angle annular dark‐field‐scanning transmission electron microscopy analysis of the local atomic order in a perfectly stoichiometric SL reveals the absence of GeTe layers, and that Ge atoms intermix with Sb atoms in, for instance, Ge2Sb2Te5 blocks. This result shows that an alternative structural model is required to explain the origin of the electrical contrast and the nature of the resistive switching mechanism observed in iPCM devices.
The impact of stoichiometry on the structure of van der Waals layered GeTe/Sb2Te3 superlattices (SLs) is revealed here. Advanced X‐ray diffraction, and transmission electron microscopy analysis of the optimized and stoichiometric SLs, rule out the most used structural models to explain the electrical contrast and the resistive switching of such SLs when incorporated in interfacial phase‐change memory devices.
Seven pairs of macrocyclic/cryptand polyamines, differing only in the added dimensionality, were selected and evaluated as receptors for anions in aqueous solution. The main differences on binding ...properties of protonated macrocycles and protonated cryptands as receptors for anions were analyzed through the association constants and structural data from the literature. Reported stepwise association constant values were critically evaluated on the basis of diagrams of log
K
eff in function of pH, being
K
eff the effective constant values.
The present study analyzes the representation of the anomalyin Oscar de profundis by Catherine Mavrikakis. This inexplicableevent is paradoxically ever-present and completely absent in endof world ...literature. In particular, we will examine the role of ruinsin the portrayal of the post-catastrophe scenario. This paper arguesthat the anomaly invites the reader to investigate further. However,they will only find ruins which are a constant reminder of what waslost and not an explanation of how these memories were erasedfrom the collective conscience. The concept of depicting the anomalythrough ruins will allow us to better understand how end of worldliterature may propose a critique of contemporary society.
The ancient city of Vieux-Poitiers in the community of Naintré (Vienne) is located 3 km from the confluence of the Clain river and the Vienne river, about 25 km north-east of the city of ...Poitiers/Limonum (Vienne), capital of the territory of the Pictones. Although the layout of the antique city and its theatre were known for several decades, remains of its ports were only discovered recently in 2012, during an underwater survey. This bank development is located on the right bank of the Clain river, in the continuation of a road originating from the ancient city. Geophysical surveys carried out in the adjacent sector have revealed potential storage buildings, parts of which had already been identified by previous aerial surveys. The initial embankment was reinforced by an alignment of piles at the beginning of the 1st c. AD enabling access to the river. Maintenance apparently took place over several years as indicated by piles attributed to successive felling phases between 15-16 and 18-22 AD. This initial development was then replaced at the end of the 1st c. AD. by a construction of wooden caissons, filled in by a succession of backfills and connected to a pavement the use of which is still uncertain (ramp?). This more monumental construction and its maintenance can be dated to the apogee of Vieux-Poitiers. The port structure seems to have been in use until a period of decline of the antique city of Vieux-Poitiers dated to the 3rd-4th c. AD. The settlement was progressively displaced to the confluence zone at Cenon-sur-Vienne (Vienne). The site is located at the crossroads of waterways and overland roads, a strategic position for human settlement, but also a place of prime importance for trade between the Loire basin and the territory of the Pictones.
GeTe/Sb2Te3 superlattices (SLs) obtained by sputtering are integrated in phase‐change memory (PCM) devices with a “wall structure”. The high structural quality of SLs deposited on TiN or SiNx layers, ...used as metallic bottom heater and dielectric bottom layer in PCM devices, is established by X‐ray diffraction, for as‐grown SLs and after an annealing corresponding to the maximum thermal budget during the integration process. Scanning transmission electron microscopy (STEM) images of SLs within PCM cells confirm that the SL structure is kept after integration. A robust statistical analysis on a large number of devices demonstrates unambiguously that the RESET current is lower in SL devices than in GeTe reference devices and decreases when the Sb2Te3 layer thickness in the SL increases from 2 to 8 nm. STEM imaging of a PCM cell incorporating an SL demonstrates that switching from the low‐ to the high‐resistance state occurs through a melting–quenching process and is not due to crystal–crystal transition or defect reorganization in the SL, in contrast to what is commonly stated in the literature on interfacial phase‐change memories (iPCMs). The origin of the improved switching performance of SL‐based PCM devices is discussed, linked with the impact of swapped bilayers.
GeTe/Sb2Te3 superlattices are successfully integrated in phase‐change memory (PCM) devices. Superlattice devices require lower RESET current than standard PCM ones. Electron microscopy imaging of a superlattice device evidences its amorphization in the RESET state. A novel explanation of the origin of the decrease in the RESET current in superlattice devices when increasing the thickness of Sb2Te3 layers is proposed.
Innovative Low-Power Self-Nanoconfined Phase-Change Memory Serra, Anna Lisa; Lefevre, Gauthier; Bourgeois, Guillaume ...
I.E.E.E. transactions on electron devices/IEEE transactions on electron devices,
02/2021, Letnik:
68, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In this article, we demonstrate at array level and in industrial-like devices, the extreme scaling down to nanometric dimensions of the phase-change memory (PCM) technology due to an innovative ...self-nanoconfined PCM (SNC PCM) device. We show how such solution based on an optimized GeN/GeSbTe stack enables programming down to 50 <inline-formula> <tex-math notation="LaTeX">\mu \text{A} </tex-math></inline-formula> and endurance up to more than <inline-formula> <tex-math notation="LaTeX">10^{{8}} </tex-math></inline-formula> cycles in 4-kb arrays, with the huge advantage of having no dependence on the critical lithography dimension used. We further demonstrate that the high thermal confinement achieved in such extremely confined PCM makes the engineering of the SET pulse becoming fundamental in order to ensure a reduced SET resistance drift. Moreover, due to physicochemical analyses and 3-D TCAD electrothermal simulations, we demonstrate the SNC phenomenon, revealing an effective scaling of the PCM down to around 12 nm and how it improves the thermal efficiency of the device due to a reduced current density and thermal stress in the system.
•Mull and Moder are two different ways of life or life “strategies”.•Agroecosystems exhibit a poorly known humus form that is neither Mull nor Moder.•Humus forms must be considered as solving the ...soil diversity puzzle.
Most scientific papers dealing with soil biota do not describe the humus form or even mention the humus type, although it’s the habitat of micro- and macro-organisms, and the environment they contribute to create. Traditionally, and to a large extent, even today research into the topic of soil biology is rooted in agroecosystems. The humus context is neither a Mull nor a Moder but is more closely related to the former. In consequence, advance knowledge is poorly suited to the natural humus profile, notably to the Moder way of life, despite the number of studies concerning biodiversity. In this paper, Mull and Moder are taken as examples of contrasting life-styles. These two humus forms exhibit such dramatic differences that they support two different food webs enclosing high levels of unshared species diversity. A spectrum between Mull and Moder can be interpreted as a juxtaposition of hotspots coming from the two humus forms. Such an additive effect may explain much of the soil diversity enigma irrespectively of any other ecological determinants (soil, climate and vegetation).
Founded in 2016 at Université de Montréal, Ensemble d’oscillateurs (French for “Oscillator Ensemble”) brings together 10 musicians around old analog test equipment oscillators that produce audio sine ...waves. The ensemble performs new compositions while also arranging early electronic pieces. In parallel, the project has developed itself as a space to gather information and reflect on sine wave–based music. In this article, the author presents some of the key considerations and challenges in the formation of Ensemble d’oscillateurs. Based on observations made throughout the development of a body of work using these audio oscillators, he then aims to open a discussion on some aspects of the historical trajectory of the use of sine waves in modern music.
The molecular recognition of five targeted amino acids differing in the nature of the side (R)- group and in the size of the aliphatic chain, glycine (Hgly), phenylalanine (Hphe), glutamic acid ...(Hglu−), 4-aminobutyric acid (Hgaba), and 6-aminohexanoic acid (Heahx), has been studied with a new heteroditopic receptor based in two distinct macrocycles, a cyclen and a crown ether moiety. The bismacrocycle L was synthesized via the bis-aminal route allowing to obtain the designed compound in gram scale and in good yield. Protonation constants of L and its binding constants with amino acids were determined by potentiometry in H2O/MeOH (1:1 v/v) solutions at 298.2 K and I=0.10 mol dm−3 in NMe4NO3. Stronger binding ability of the HnLn+ receptor for α-amino acids, Hgly and Hphen, than for the other studied substrates were found. Structural data derived from NMR studies showed that the binding of α-amino acids result from the cooperative participation of hydrogen bonds between the carboxylate group of amino acids and the polyammonium sites of cyclen, and the ion-dipole interactions between the ammonium group of the amino acids and the oxygen atoms of the crown ether.
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