SEGR Study on Power MOSFETs: Multiple Impacts Assumption

Expérience GANILInternational audienceThis paper presents experimental data showing heavy ions inducing gate degradation in power MOSFETs. In the experiments, backside and front-side irradiations are performed. During backside irradiation, the heavy ion ranges are tuned in such way to control whether they hit the gate or not. Gate-to-source current Igss ( ) is measured versus heavy ions (H.I.) fluence . Post-irradiation- gate-stress-test (PGST) allows measurement of gate breakdown voltage VBD( ) which is observed to decrease with (H.I.) fluence. Based on these experimental results, a hypothesis of substrate- generated carriers impact overlap of multiple strikes may explain gate degradation until SEGR triggering. This last hypothesis is supported by a statistical model approach of heavy ions multiple impacts

Uranium sorption to organic matter and long-term accumulation in a pristine alpine wetland

Understanding the controls on uranium (U) mobility in the environment is key to improve the management of sites contaminated by U mining activities. Previous research has shown that natural or engineered wetlands are particularly able to scavenge high amounts of U(VI) and U(IV) under noncrystalline forms. However, questions remain on the respective roles of sorption and reduction processes in the removal of U from running waters in wetlands, as well as on the long-term stability of U storage. Here, we performed a series of geochemical, isotopic (δ238U, (234U/238U)), microscopic (SEM-EDXS, EPMA) and spectroscopic (µ-XRF, µ-XAS, XANES and EXAFS at the U L3 and M4-edges and Fe K-edge) investigations to determine the modes of U accumulation and assess U mobility in a natural exceptionally U-enriched (up to 5000 µg/g) wetland on the shore of Lake Nègre (Mediterranean Alps, France). Uranium (VI) was largely dominant in the two studied soil cores, except a few samples containing as much as ∼50 % U(IV). At the particle scale, U is associated to a variety of organic constituents of the soil matrix with a homogenous oxidation state. Bulk EXAFS spectroscopy at the U L3-edge shows that U is mostly mononuclear, with dominant monodentate binding to organic moieties (C neighbors at ∼3.45 Å). An additional minor fraction of U under polymeric forms is inferred from wavelet (CCWT) analysis of the EXAFS data. These observations are reinforced by 1 M bicarbonate extractions that result in the dissolution of 82–96 % of total U, including putative polymeric species. At the wetland scale, similar or slightly fractionated isotopic ratios (δ238U) between the wetland-feeding creek waters and the wetland soils are observed, supporting the idea that U(VI) sorption on organic matter is the primary U scavenging mechanism. Furthermore, it indicates that partial U(VI) reduction to U(IV) occurs as a second step, after sorption. Analysis of U decay chain disequilibria in the cores as a function of depth suggests that U accumulation in this wetland has lasted for several thousand years. We propose that the wetland acts as an active reactor where U has been massively accumulating for ∼14500 years, especially as U(VI) forms associated to organic matter, and is further partly exported to the lake through soil erosion

SEGR Study on Power MOSFETs: Multiple Impacts Assumption

This paper presents experimental data showing heavy ions inducing gate degradation in power MOSFETs. In the experiments, backside and front-side irradiations are performed. During backside irradiation, the heavy ion ranges are tuned in such way to control whether they hit the gate or not. Gate-to-source current Igss (Phi) is measured versus heavy ions (H.I.) fluence Phi. Post-irradiation-gate-stress-test (PGST) allows measurement of gate breakdown voltage V-BD (Phi) which is observed to decrease with (H.I.) fluence. Based on these experimental results, a hypothesis of substrate-generated carriers impact overlap of multiple strikes may explain gate degradation until SEGR triggering. This last hypothesis is supported by a statistical model approach of heavy ions multiple impacts