Cherbourg-Octeville, France
Cherbourg-Octeville, France

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Berthet F.,Site University | Guhel Y.,Site University | Gualous H.,Site University | Boudart B.,Site University | And 5 more authors.
Solid-State Electronics | Year: 2012

In this paper we show the creation of electrical traps in AlGaN/GaN HEMTs during electrical stress. In fact we highlight that an ageing test carried out for V DS = 20 V and V GS = -5 V (OFF-state stress) or for V DS = 20 V and V GS = 0 V (ON-state stress) induces a decrease in the drain current and an increase of the access resistance (R k). The degradation of these electrical performances observed after ageing tests are reversible, contrary to the majority of the results found in the literature. We have demonstrated, by using simple methods, that the observed phenomena are explained by the creation of electrical traps, which can be considered as donors and acceptors, and not by degradation of the ohmic contacts and/or of the Schottky contact and/or the appearance of cracks in the passivation layer. Moreover, this paper shows that the two ageing tests are also responsible for the creation of two kinds of electrical traps in the gate-drain region of the devices, particularly in the top of the device structure. However, the creation of electrical traps at the AlGaN/GaN buffer interface has been observed for an OFF-state stress though not for an ON-state stress. © 2012 Elsevier Ltd. All rights reserved.

Nivot C.,Site University | Bernard J.,Site University | Lelievre C.,Site University | Haussonne J.-M.,Site University | Houivet D.,Site University
Ceramics International | Year: 2010

This work deals with the sensitivity to moisture rate in air of perovskite with general formula YCr(1-x)MnxO3 with x ranging from 0 to 0.8. The combined sensitivity to moisture and temperature let us think the possibility of realizing composite sensors temperature/moisture. This study clearly shows the influence of the Mn content on moisture which affects the working frequency of sensors. Capacitance variation of the most sensitive compositions increases from 100 pF to 1 nF for relative humidity between 20 and 80%. The influence of porosity is also demonstrated. © 2009 Elsevier Ltd and Techna Group S.r.l.

Marion M.,GTE | Marion M.,Site University | Tiffonnet A.L.,GTE | Tiffonnet A.L.,Site University | And 4 more authors.
Building and Environment | Year: 2011

The main parameters which control the emission of volatile organic compounds between wall materials and indoor air were examined. A physically based model considers that the global emission phenomenon results from three elementary physical phenomena: diffusion through the boundary layer separating the wall from environment, diffusion within the porous network of the materials, and sorption of the gas molecules on the active sites of the materials. The pollutant transfer between porous material and air is therefore subjected to two complementary resistances and we identify first the resistance which controls the transfer. Then, we predict the global emission time constant from the mass transfer coefficient of convection and the thickness of the material. Experimental results from a small scale chamber are compared to predicted values in the case of acetone emission from chipboard in humid air and for high initial acetone concentration. Good agreement is obtained at the beginning of emission but an acetone retention effect by chipboard is observed, showing that it will be necessary to take into account the interactions of water vapor with materials and the pollutants to achieve accurate modeling of the material VOC emission process. © 2010 Elsevier Ltd.

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