High-transconductance insulating-gate InP/InGaAs buried p-bufferDH-MODFETs grown by MOVPE

Buried p-buffer double heterostructure modulation-doped field-effect transistors (BP DH-MODFETs) with an InGaAs quantum-well channel were fabricated with high transconductance and good breakdown voltage, by placing the metal gate directly on Fe-doped InP insulating layer. Excellent extrinsic DC transconductance of 560 mS/mm and a high gate-to-drain diode breakdown voltage (greater than 20 V) were achieved at room temperature with FETs of 1.2-μm gate length. Unity currently gain cutoff frequency f_T of 24 GHz and maximum oscillation frequency f_max of 60 GHz were demonstrated for a drain to source voltage V_DS=4 V, which corresponds to an average electron velocity of 2.2×10⁷ cm/s in the quantum well     

Optimization of the test method for determining the bonding quality of core plywood (blockboard)

Over the last few decades, thanks mainly to their specific technological features and their stability of dimension and shape, wood-based panels have seen flourishing industrial and commercial development. Of these, blockboard consists of a central layer (core) made up of solid wood strips which is stiffened and bound together by glued, hot-pressed rotary cut veneers overlaid with grain (main wood fibre direction) perpendicular one to another. The panel made in this way is considered a distinct type of plywood. Although blockboard is widely used in furniture-making and carpentry in general, and plays an important role in the production of some EU countries, its physicalmechanical properties are largely unknown and the combination of wood components having very different thickness (strips and veneers) makes it difficult to precisely determine the bonding quality. The aim of this work is to contribute to setting up a testing method to objectively assess the above property as well as to achieve more efficient production process control. To this end the main testing methodologies, and in particular those on solid wood panels (prEN 13354), glulam (EN 392) and plywood (EN 314) were evaluated. The tension shear test seemed to be the most significant for assessing the actual resistance of the pair of glue lines bonding the wooden elements that make up the blockboard. In order to obtain symmetrical test pieces, the determination of the bonding quality also made it necessary to further glue two portions of the panel realizing a compound (5 layers) specimen whose core layer consisted of two overlaid veneers with parallel grain. Because of the encouraging results obtained, the method proposed has been included in the recent revision of the standard EN 314, the contents of which is also going to be adopted by ISO.

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Résumé Au cours des dernières décennies, grace surtout à leurs intéressantes caractéristiques technologiques et leur stabilité en matière de dimensions et de formes, les panneaux à base de bois ont enregistré un croissant développment industriel et commercial. L'un d'entre eux, le panneau latté, est constitué d'une couche centrale (ame) d'éléments en bois massif qui est rendue solidaire par la superposition, par collage et pressage à chaud, d'un placage avec direction des fibres perpendiculaires. Pour la composition susmentionnée, le panneau qui en dérive est considéré comme étant un type particulier de contre-plaqué. Bien que le panneau latté utilisé largement dans le secteur de l'ameublement et de la menuiserie en général, et qu'il occupe une place capitale dans le cadre de la production de plusieurs pays de l'UE, ses propriétés mécaniques sont peu connues, alors que la présence actuelle de composants en bois d'épaisseur très différente (liteaux et placages) rend difficile une détermination correcte de la qualité du collage. à ce propos, les principales méthodologies d'essai sur cet aspect ont été soigneusement évaluées, en particulier celles qui concernent les panneaux de bois massif (prEN 13354), le bois lamellé collé (EN 392) et le contre-plaqué (EN 314). L'essai de cisaillement par traction s'est révélé être le plus significatif pour évaluer la résistance effective des deux lignes de colle qui relient les éléments en bois composant le panneau. Toutefois, pour obtenir des éprouvettes symétriques, la détermination recherchée nécessite le collage de deux portions de panneau ce qui permet de réaliser une éprouvette composée (à cinq couches) dans laquelle la couche centrale est constituée par deux placages superposés avec direction des fibres parallèles. En considération des résultats obtenus, la méthodologie proposée a été introduite dans la révision de la norme EN 314, dont le contenu sera aussi adopté par l'ISO.

     

Thermally and plastically induced residual strains in textured Zircaloy-2 plate

The residual intergranular strains in textured Zircaloy-2 plate samples induced by cooling from 823 K to ambient temperatures, by cold-rolling by 1.5% and 25% and by deforming in tension by 1.5% were measured by neutron diffraction. The strong rolling texture, which gives rise to two ideal orientations, permitted the interpretation of much of the data in terms of strain tensors for the two orientations. The experimental results were compared with calculations based on the elasto-plastic self-consistent model with no adjustable parameters. Close agreement was obtained for samples in the as-cooled state and deformation in tension by 1.5% but the agreement is less satisfactory for cold-rolling.     

Experimental study on optically band-limited 40-Gb/s RZ signals with optically time-division demultiplexing receiver

The impact of optical filtering on 40-Gb/s return-to-zero (RZ) signals was experimentally investigated with an optically time-division multiplexing (OTDM) receiver. Through the evaluation of the signal performance by changing the interpulse-phase conditions of the symmetrically band-limited 40-Gb/s signals, we have confirmed that similar performance was obtained regardless of the interpulse-phase condition, owing to the pulse-reshaping capability of an OTDM receiver. A performance comparison was also conducted between symmetrically and asymmetrically filtered 40-Gb/s RZ signals. It was found that the symmetrically filtered signal was more tolerant for the dispersion-compensation error, while the asymmetrically filtered signal was more tolerant for fiber nonlinearity with optical filters that have a 3-dB bandwidth of 45 GHz.     

Effects of Sc2O3 and MgO passivation layerson the output power of AlGaN/GaN HEMTs

The low temperature (100°C) deposition of Sc₂O₃ or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm² HEMTs for both types of oxide passivation layers. Both Sc₂ O₃ and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN_x passivation which typically showed ⩽2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc₂O₃ or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs     

Performance enhancement of an induction motor by secondaryimpedance control

The paper demonstrates the use of nonresistive secondary control of an induction motor to improve efficiency, power factor and torque. A mathematical algorithm is presented to predict the control requirements in terms of secondary capacitance. The required secondary capacitance is implemented by a novel electronic switching technique that effectively increases the value of the used capacitor. This overcomes the high-capacitance demand and provides a feasible solution. Experimental verification is presented in the results obtained from a small induction motor drive     

Theoretical comparison of SiC PiN and Schottky diodes based on power dissipation considerations

In order to select the optimal device for a particular application, designers must carefully analyze the tradeoffs between competing devices. Recent progress in SiC power rectifiers has resulted in the demonstration of high-voltage PiN and Schottky barrier diodes (SBDs). With both technologies maturing, power electronics engineers will soon face the task of selecting between these two devices. Until recently, the choice was simple, since silicon SBDs are only available for relatively low voltage applications. The choice is not as clear when considering SiC diodes, and guidelines for determining the proper application of each are needed. The purpose of this paper is to provide such guidelines, based on an analysis of the most significant tradeoffs involved.