Composants Passifs Intégrés en Technologie CMOS pour la Miniaturisation des Circuits RF

Une démarche originale pour le développement de composants passifs dans une filière industrielle consiste à effectuer un report des contraintes en performances sur les caractéristiques électriques des matériaux utilisés en couches minces. Nous présentons dans cet article la démarche adoptée à travers trois phases clés du développement d’une technologie faibles coûts de composants passifs intégrés en filière CMOS. Le développement et la caractérisation de films minces d’oxyde de titane et de tantale. L’intégration de films résistifs d’oxynitrure de titane en filière industrielle et la modélisation électrique d’inductances spirales intégrées en CMOS

Effect of the bainitic and martensitic microstructures on the hardening and embrittlement under neutron irradiation of a reactor pressure vessel steel

International audienceThe hardening and the embrittlement under neutron irradiation of a RPV steel considering three different coarse grained microstructures (bainite, bainite-martensite and martensite) have been investigated. Bainite and martensite have a comparable irradiation induced temperature transition shifts but hardening is smaller for martensite than for bainite. Bainite appears to be less sensitive to non-hardening embrittlement (NHE) than martensite. The onset of brittle intergranular fracture after irradiation for the martensitic microstructure is likely the origin of this difference of sensitivity to NHE. However, the bainitic-martensitic microstructure has the largest irradiation induced shift and is the most sensitive to NHE amongst all the tested microstructures. These results show that the microstructure is an important parameter to control the irradiation induced non hardening embrittlement and the enhancement of the brittle intergranular fracture in reactor pressure vessel steels

Bending tests on T91 samples implanted with 0.25 at.% helium: Experiments and mechanical analysis

In order to investigate helium effects on the fracture properties of martensitic mod 9Cr-1Mo (T91) steel, miniature Charpy specimens were implanted at 250 degrees C in the notch region to 0.25 at.% helium using a degraded 34 MeV He-3 ion beam and subsequently submitted to static bending tests at room temperature. For the six implanted specimens, a 'pop-in' phenomenon, which is an arrested unstable crack extension, was systematically recorded during testing. In the implanted zones of the samples, the fracture mode was fully brittle with both intergranular and cleavage fracture, whereas for unimplanted samples tested at -170 degrees C, the fracture mode was found to be 100% cleavage. Finite element simulations of the tests performed on unimplanted and implanted specimens were also carried out to determine stress and strain fields at the onset of crack propagation. Based on these computations, the fracture toughness of implanted T91 was tentatively evaluated using the Beremin model of the local approach to brittle fracture. (c) 2006 Elsevier B.V. All rights reserved

Effect of a high helium content on the flow and fracture properties of a 9Cr martensitic steel

An experimental characterization was conducted of helium effects on the mechanical properties of a 9Cr martensitic steel. Six sub-size Charpy samples were implanted in the notch region at 250 degrees C with 0.25 at.% helium and subsequently tested in 3-point bending at room temperature. Brittle fracture mode (cleavage and intergranular fracture) was systematically observed in the implanted zones of the samples. Finite element calculations of the tests, using as input the tensile properties measured on a helium loaded sample, were performed in order to determine the fracture stress at the onset of brittle crack propagation. Preliminary TEM investigations of the implantation-induced microstructure revealed a high density of small helium bubbles. (c) 2007 Elsevier B.V. All rights reserved

Comparative study on Charpy specimen reconstitution techniques

International audienceReconstitution techniques are often used to allow material from previously fractured Charpy-V specimens to be reused for additional experiments. This paper presents a comparative experimental study of various reconstitution techniques and evaluates the feasibility of these methods for future use in shielded cells. The following techniques were investigated: arc stud welding, 6.0 kW CO2 continuous wave laser welding, 4.5 kW YAG continuous wave laser welding and friction welding. Subsize Charpy specimens were reconstituted using a 400 W YAG pulsed wave laser. The best result was obtained with arc stud welding; the resilience of the reconstituted specimens and the load-displacement curves agreed well with the reference specimens, and the temperature elevation caused by the welding process was limited to the vicinity of the weld. Good results were also obtained with friction welding; this process led to the best quality welds. Laser welding seems to have affected the central part of the specimens, thus leading to different resilience values and load-displacement curves

Mechanical properties of zircaloy-4 PWR fuel cladding with burnup 54-64MWd/kgU and implications for RIA behavior

The PROMETRA material testing program is a support program related to the study of high burnup fuel rod behavior under Reactivity Initiated Accidents (RIA) and to the interpretation of the CABRI REP-Na RIA test results. Hoop and axial tensile tests have been performed on fresh and irradiated Zircaloy-4 cladding alloy first at CEA Grenoble hot labs and now at CEA Saclay in order to assess the cladding mechanical behavior during RIA transients. Efforts have been continuously carried out in order to improve the prototipicallity of the tests for RIA studies involving new specimens and new testing techniques. The corrosion level of irradiated specimens reached up to 130 μm of oxide layer thickness. The influence of in-pile oxide layer spallation has also been addressed. High strain-rate material properties of irradiated Zircaloy-4 and the consequences of hydride embrittlement can be derived from the PROMETRA program. Copyright © 2005 by ASTM International

Cardiovascular parameters for mental workload detection of air traffic controllers

In our study, we focused on air traffic controller’s working position for arrival management. Our aim was to evaluate cardiovascular parameters regarding their ability to distinguish between conditions with different traffic volumes and between conditions with and without the occurrence of an extraordinary event. Our sample consisted of 21 subjects. During an interactive simulation, we varied the load situations with two independent variables: the traffic volume and the occurrence of a priority-flight request. Dependent variables for registering mental workload were cardiovascular parameters, i.e., the heart rate, relative low-frequency and high-frequency band powers, and bandpower ratio of the low- and high-frequency bands. Heart rate was the only parameter able to differentiate significantly between simulations with minimal and high air-traffic volume, while the effect of the priority-flight request remained doubtful. No significant interaction between traffic volume and priority request could be identified for any of the cardiovascular parameter

Thermal conductivity of aluminium nitride thin films prepared by reactive magnetron sputtering

International audienceThe relationship between thermal conductivity and microstructures of aluminium nitride films is reported. Films were deposited on silicon substrates by magnetron sputtering of a pure Al target in nitrogen argon plasma at low temperatures (<300 °C) with thickness ranging from 150 to 3500 nm. Balanced and unbalanced magnetron configurations were used for different nitrogen contents in the gas phase. Various microstructures were thus created and their thermal conductivity was measured with the transient hot strip technique. Depending on the crystalline structure of the films, the bulk thermal conductivity of the AlN films at room temperature varied between 2 and 170 W m−1 K−1. Unbalanced magnetron allowed achieving highly dense (0 0 2) oriented AlN films with a grain size in the 100 nm range, a low oxygen content close to 0.5 at% and a resulting bulk thermal conductivity as high as 170 W m−1 K−1. Such a crystalline quality resulted from the ion energy involved in the growth process. In contrast, balanced magnetron led to weakly textured AlN films containing 5 at% oxygen with a grain size in the 30 nm range and a resulting thermal conductivity ranging from 2 to 100 W m−1 K−1 depending on the microstructure. Otherwise, the thermal boundary resistance between AlN films deposited by unbalanced magnetron and the silicon substrate was found to be as low as 1.0 × 10−8 K m2 W−1. Such a value was in good agreement with the thickness of the interfacial amorphous layer determined in the 2 nm range by high resolution transmission electron microscopy