Critical currents, flux-creep activation energy and potential barriers for the vortex motion from the flux creep experiments

We present an experimental study of thermally activated flux creep in a superconducting ring-shaped epitaxial YBCO film as well as a new way of analyzing the experimental data. The measurements were made in a wide range of temperatures between 10 and 83 K. The upper temperature limit was dictated by our experimental technique and at low temperatures we were limited by a crossover to quantum tunneling of vortices. It is shown that the experimental data can very well be described by assuming a simple thermally activated hopping of vortices or vortex bundles over potential barriers, whereby the hopping flux objects remain the same for all currents and temperatures. The new procedure of data analysis also allows to establish the current and temperature dependencies of the flux-creep activation energy U, as well as the temperature dependence of the critical current Ic, from the flux-creep rates measured at different temperatures. The variation of the activation energy with current, U(I/Ic), is then used to reconstruct the profile of the potential barriers in real space.Comment: 12 pages, 13 Postscript figures, Submitted to Physical Review

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d)

Magnetic flux jumps in textured Bi2Sr2CaCu2O(8+d) have been studied by means of magnetization measurements in the temperature range between 1.95 K and Tc, in an external magnetic field up to 9 T. Flux jumps were found in the temperature range 1.95 K - 6 K, with the external magnetic field parallel to the c axis of the investigated sample. The effect of sample history on magnetic flux jumping was studied and it was found to be well accounted for by the available theoretical models. The magnetic field sweep rate strongly influences the flux jumping and this effect was interpreted in terms of the influence of both flux creep and the thermal environment of the sample. Strong flux creep was found in the temperature and magnetic field range where flux jumps occur suggesting a relationship between the two. The heat exchange conditions between the sample and the experimental environment also influence the flux jumping behavior. Both these effects stabilize the sample against flux instabilities, and this stabilizing effect increases with decreasing magnetic field sweep rate. Demagnetizing effects are also shown to have a significant influence on flux jumping.Comment: 10 pages, 6 figures, RevTeX4, submitted to Phys. Rev.

Characterization of partial discharge performance of die attach adhesives

In this paper, the suitability of two types of die attach (DA) material within an isolating system is compared: non-conductive and antistatic epoxy adhesives, respectively. The electrical conductivity of second material has been adjusted by density, size, and shape of carbon filler particles incorporated into the resin matrix. The study shows that micro-voids inside die attach layers of a semiconductor package can lead to partial discharges (PD). Such discharges are reduced by a design-in of carbon filled glues into the device. The experimental verification of the simulation shows increased partial discharge immunity, improved by conductivity tuning of the adhesive materials

Assessment of a lasersingulation process for Si-wafers with metallized back side and small die size

We report on the development of a dry lasersingulation process for Si-wafers with back side metallization targeting small die sizes below 0.07 mm2. The dicing technology aims at improved manufacturing of diodes with thicknesses ranging from approx. 100 µm to 150 µm, die sizes down to 230 x 230 µm2 and metallized back side metallization layers used for solder die attach. We discuss the impact of the laser process on subsequent assembly processes as well as on the die itself. Particular emphasis is set on the laser induced modification of the mechanical properties within the wafer, e. g. the reduction of the die strength. For the wafer technology under evaluation, the laser process is considered to be superior to standard blade dicing approaches

Lifetime modeling based on anodic oxidation failure for packages with internal galvanic isolation

In More-than-Moore technologies, the number and complexity of micro and nano devices, that are directly integrated into control units of power electronics and mechatronics systems, increase. These systems typically operate at working voltages in the range of 220–1000 VRMS

Magnetische Untersuchungen an einkristallinen und gesinterten Hochtemperatursupraleitern nach verschiedenen Herstellungsbedingungen und nach Elektronenbestrahlung

Bi_2Sr_2CaCu_2O_8_+_#delta# and (RE)Ba_2Cu_3O_7_-_#delta#-samples (RE=Y, Gd, Dy; single crystals, ceramic crystals, melt processed samples and thin films) were investigated after different preparation procedures and electron irradiation. Magnetization measurements (SQUID-magnetometer) allow the determination of critical current densities and pinning potentials. From AC-susceptibility measurements carried out on electron-irradiated YBa_2Cu_3O_7_-_#delta#-samples (annealing experiments) displacement-energies, corresponding mainly to oxygen displacements, have been evaluated. Using the AC-susceptometer introduced by Chen a geometry dependence of the irreversibility line was found. The dependence of the critical current density on sample geometry, grain size, and additional chemical phases was investigated by means of transport current measurements. Using the newly installed low temperature Faraday microscope local and dynamical determinations of flux density and critical current density were performed. (orig.)Untersucht wurden Bi_2Sr_2CaCu_3O_8_+_#delta# und (RE)Ba_2Cu_3O_7_-_#delta#-Proben (RE=Y, Gd, Dy; Einkristalle, Sinterproben, aufgeschmolzene Proben und duenne Schichten) nach verschiedenen Herstellungsbedingungen und Elektronenbestrahlung. Magnetisierungsmessungen (SQUID-Magnetometer) ermoeglichten die Bestimmung von kritischen Stromdichten und Haftkraftpotentialen. Aus AC-Suszeptibilitaetsmessungen wurden an elektronenbestrahlten YBa_2Cu_3O_7_-_#delta#-Sinterproben (Ausheilexperimente) Verlagerungsenergien ermittelt, die vor allem Sauerstoffverlagerungen zugeordnet werden konnten. Mit der nach Chen verbesserten AC-Suszeptibilitaetsapparatur konnte eine Geometrieabhaengigkeit der Irreversibilitaetslinie nachgewiesen werden. Mittels Transportstrommessungen an YBa_2Cu_3O_7_-_#delta#-Sinterproben wurde die Abhaengigkeit der kritischen Stromdichte von der Geometrie, der Korngroesse sowie von Fremdphasenzusaetzen untersucht. Das erfolgreich aufgebaute Faraday-Tieftemperaturmikroskop ermoeglicht lokale und dynamische Bestimmungen der Fluss- und Stromdichteverteilungen. (orig.)Available from TIB Hannover: F94B0166+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman

Induced Voltage Measurements on a YBa2Cu3O7−δ Superconducting Thin Film Due to a Pair of Rotating Magnets

[[abstract]]In this study, the induced voltages due to the rotation of a pair of magnets on an YBCO superconducting thin film sample (SS) with and without bias current were measured. It was found that the induced root mean square voltage (Vrms) was a constant (V0) at temperatures higher than the critical temperature (Tc) of the SS, as expected from Faraday’s law. At a temperature in the superconducting transition region, the induced Vrms is a sensitive function of both the motion of the magnet and the bias current applied to the SS. These results can be understood by considering the superposition of the two kinds of induced voltages. One is induced according to Faraday’s law, and the other one is induced by the vortex movements inside the SS which is caused by the bias current. At temperatures below the transition region, the induced Vrms had a value equal to V0 and remained unchanged as the temperature further decreased. An explanation based on the distribution of the magnetic flux inside the SS was given, and it was concluded that the superconductor-normal conductor loop acted like a normal-normal conductor loop to the moving magnetic fields in this low temperature region.[[notice]]補正完