Surface treatment is a key technological parameter in the microelectronics technology and especially for SiC devices since high temperatures must be used for implanted impurities annealing and crystal damage recovery. In this work we take profit of a novel fine polishing process developed by NOVASIC to improve the electrical characteristics of Boron and Aluminium implanted Schottky diodes, which are surface quality highly sensitive devices. The mentioned fine polishing process allows to remove a layer thickness of 100nm to 3000nm on the surface of a processed SiC wafer, reducing the surface roughness to RMS of 1Å. The impact of this process on the electrical properties of the samples shows a general improvement of characteristics reproducibility, reduction of leakage current and improvement of breakdown of Boron implanted diodes.

The local critical current (Ic) at 77 K measured at the mm scale in a 60 mm long sample of YBa2Cu3O7−δ prepared by a melting zone process is correlated to the microstructure. Lower values of Ic (<20 A) were obtained in a part of the sample which optical microscope examination showed to be generally polycrystalline. In contrast, the rest of the sample, consisting mostly of large textured domains, gave values for Ic of 120 A and above. Transmission electron microscope observations revealed that the textured domains contain internal boundaries. Depending on the scale of observation, the misorientation angles across the boundaries could vary from a few tenths of a degree up to a few degrees. This seems characteristic for boundaries in textured material which allow strong coupling of the superconducting current across themselves.

We study the limitation possibilities of bulk Bi high Tc materials. For this we test these materials with a.c. or d.c. currents above their critical currents. We study particularly the evolution of the voltage with time or with current. The material, the value of the current and the time duration play important parts. For sintered Bi samples the voltage depends only on the current even for values much larger than the critical current. With textured samples the V(I) curves shows an hysteretic behaviour due to a warming up. The textured materials are more interesting than sintered ones in terms of required volume for the current limitation. In both cases the superconductors are in a dissipative state but not in the normal state. This state is nevertheless reached if the dissipated energy inside the sample is sufficient. We have tried to apply a magnetic field on the samples in order to trigger a more effective limitation. The voltage increases but with a limited effect for currents much higher (3–4 times) than the critical zero field current. We think that the dissipative state is due mainly to the grain boundaries which become resistive above the critical current.

Industrial applications of the bulk superconducting YBa2Cu3O7 material imply to control the growth of large oriented monodomains in samples of big size (several centimeters). The laboratory EPM-Matformag is committed to produce such materials according to three different methods (zone melting, solidification controlled by a magnetic field, crystal growth from a seed). The results obtained show that it is possible by such methods to elaborate a material with high performances at the centimeter scale and to produce it in series. The availability of such materials allows the measure of physical properties on a large scale and the testing of prototypes for cryo-electrotechnical applications (magnetic bearing, flywheel, coupling device, current lead...).

La densité de courant critique selon l'axe c (Jc) est mesurée à 77 K en transport et par des mesures magnétiques sur les mêmes échantillons texturés monodomaines d'YBaCuO. L'influence des plans de macles (TP) sur Jc et sur la ligne d'irréversibilité $B(T^*$) est étudiée en faisant tourner le champ dans les plans ab, perpendiculairement à l'axe c. Les résultats montrent que dans ces composés, Jc et $B(T^*$) sont fortement influencés par le piégeage par les TP. Divers comportements des lignes de flux résultant de l'influence de ces défauts corrélés sont proposés selon les gammes de température et de champ étudiées.

Un limiteur de courant supraconducteur pourrait être utilisé en haute tension. La plupart des matériaux à haute température critique existants actuels ont été testés en situation de limitation du courant. Les matériaux massifs sont classés par densité de courant critique croissante qui correspondent à des comportements différents. Le champ critique lors des transitions semble être de l'ordre de 1 kV/m.

Afin de déterminer la capacité à limiter le courant du composé ${\rm Y}_1{\rm Ba}_2{\rm Cu}_3{\rm O}_{7-\delta}$ texturé, des études en courants de transport élevés, en régime pulsé et en régime permanent alternatif, ont été menées. Il en résulte que YBaCuO possède une forte capacité de transport du courant en régime pulsé (9000 A soit 23 000 $\ {\rm A} / {\rm cm}^2$ dans un barreau de 4 cm de long) et en régime permanent alternatif (3000 A soit 7800 $\ {\rm A} / {\rm cm}^2$) et que le retour à l'état normal par dépassement du courant critique est très abrupt.

Des forts courants pulsés d'une durée comprise entre 1,25 et 20 ms ont été appliqués à T = 77 K à des conducteurs Bi:2223 texturés par forgeage à chaud ou frittés. Pour des pulses de courant ${I>I_{\rm c}}$, deux comportements sont observés : quand la température moyenne de l'échantillon est inférieur à ${T_{\rm c}}$, le matériau retourne dans l'état supraconducteur avant la fin du pulse de courant. Au dessus de ${T_{\rm c}}$, l'échantillon transite dans l'état normal après le pulse de courant à cause de l'élévation de température. Ceci induit une puissance instantanée importante appliquée au conducteur de 182 GW/m3. À I = 15Ic, des champs électriques de 400 à 1000 V/m sont obtenus sur des éléments frittés et texturés.

We discuss the magnetic properties of lead doped Bi-2223 bulk samples obtained through combined magnetic melt texturing and hot pressing (MMTHP). The ac complex susceptibility measurements are achieved over a broad ac field range (1 Oe < hac < 100 Oe) and show highly anisotropic properties. The intergranular coupling is improved in the direction perpendicular to the applied stress and magnetic field direction, and an intragranular loss peak is observed for the first time. A comparison is made with other bismuth-based compounds and it is shown that the MMTHP process shifts the ac irreversibility line (ac IL) toward higher fields. It is also shown that all the ac IL's for quasi 2D bismuth-based compounds show a nearly quadratic temperature dependence and deviate therefore strongly from the linear behavior observed in quasi 3D compounds and expected from a critical state model.