The role of C and N dopants incorporation in phase change materials

Phase change memory (PCM) technology is considered to be among the most promising alternatives to conventional technologies in embedded memories [1]. To allow operation at relatively high temperatures in embedded applications, it is crucial to improve the stability of the amorphous phase. Carbon and nitrogen doping have been shown to significantly increase the crystallization temperature [1-3]. Moreover, the high RESET current requirement [2], which is a limit to the scalability of GeTe and GST, can be reduced by the incorporation of a dopant element [4]. In this presentation we focus on correlating experimental results and ab initio simulations to understand the effect of C and N incorporation in GeTe and GST PCM devices. Understanding the effect of dopants on the change of electronic properties and the mechanisms of the phase transformation requires analysis of the local order and structure of the amorphous to crystalline phases. In this context, we demonstrate that carbon and nitrogen deeply affects the structure and the dynamical properties of the amorphous phase of GeTe. In particular, the inclusion of N and C dopant elements in GeTe has a drastic effect on the vibrational modes of GeTe therefore improving the stability of the glass. This effect goes with an increased mechanical rigidity explaining why these doped GeTe compounds have a higher crystallization temperature than the undoped ones. Finally we will explore, mainly by FTIR and XRD measurements, the effect of C and N dopants during the annealing of amorphous PCMaterials towards their crystalline phases. These results will be discussed in order to understand the origin of the differences of the doped PCMaterials amorphous phase stability (data retention) observed between full sheet materials and the materials integrated in PCM devices. [1] A. Fantini et al., 2010 IEEE International Electron Devices Meeting (IEDM), 2010, pp. 29.21.21-29.21.24. [2] G. Betti Beneventi et al., Solid-State Electronics, 65-66 (2011) 197-204. [3] V. Sousa et al., EPCOS 2011. [4] Q. Hubert et al., IMW 2012.A.R.C. Themoter

Chemical state of Ag in Conducting Bridge Random Access Memory cells: a depth resolved X-ray Absorption Spectroscopy investigation

International audienceConducting Bridge Random Access Memories (CBRAM) are a promising substitute for FLASH technology but problems with limited retention of the low resistance ON state still hamper their massive deployment. Depth resolved X-ray Absorption Spectroscopy has been used to describe the chemical state of the atoms of the active electrode (in this case Ag) and to reveal the role of Sb as stabilizer of the metallic stat

Electrical characterizations of resistive random access memory devices based on GaV4S8 thin layers

International audienceThe Mott insulator compound GaV4S8 exhibits resistive switching (RS) properties under electric pulses which could be used in the domain of data storage for future replacement of Flash technology. In this work, we present the characterization and the resistive switching performances of three devices containing GaV4S8 thin films with various electrode sizes and geometries, i.e. planar interdigit electrodes and Metal/Insulator/Metal Au/GaV4S8/Au structures. First, we evidence the good quality of the interfaces between GaV4S8 layers and gold electrodes through transmission electron microscopy observations which allows reliable electrical characterizations. Then, we demonstrate a downscaling effect as the resistive switching amplitude ΔR/R = (Rhigh − Rlow) / Rlow increases from a few percents to more than 600% as the electrode size decreases from 50 × 50 μm2 to 2 × 2 μm2. Finally we show that other performances such as cycling endurance, reaching more than 65,000 RS cycles, data retention time till 10 years or writing speed below 100 ns confirm the high potential of GaV4S8 as active material in future resistive random access memories or Mott memories

Web Communication of French Geoparks in Education: The Expression of Their Legitimacy

International audienceIn France seven areas are labeled “UNESCO World Geoparks”: the Haute-Provence national nature reserve, the Luberon massif, the Bauges Mountains, the Chablais Alps, the Ardèche Mountains, the causses du Quercy and the Beaujolais. To obtain the label, the geopark must be able to justify its active participation in school education for sustainable development, which addresses socioenvironmental issues related to the territory and heritage. French geoparks are thus faced with a dual problem of public recognition, sometimes in a context of hyper-patrimonialization, and a demand for deployment to formal educational environments. To open a web page of a site related to a geopark is to immerse yourself in a (geo)graphic environment. The analysis of the statements on the education of the websites of French geoparks according to the different dimensions of a unified educational theory for each territory shows that, beyond the specific territorial features advanced, convergence with education for sustainable school development is preponderant