Ruth Männer

Power Inductors in Ceramic Multilayer Circuit Boards

Power electronic inductors, with values of several μH, have been integrated into thermally stable ceramic multilayer circuit boards by the use of NiZnCu and MnZn ferrite tapes in low temperature cofired ceramic (LTCC) technology. These ferrites are particularly attractive for switched mode power supplies in automation, drives, and consumer applications, where the miniaturization of modules is triggered by advances in transistor technology and switching frequencies. The small signal analysis of embedded individual inductors and coupled transformer coils reveals the generic design rules for these components and additional materials properties beyond those accessible by ring core measurements. In the process of adapting the materials to LTCC, the distinct differences between the two materials become blurred, for example, they can be engineered to exhibit similar cutoff frequencies. NiZnCu ferrite, which is sinterable in air, may even achieve higher permeability than MnZn ferrite. The latter, however, shows h...

Ceramic Multilayer Integration of Power Electronic Inductors

New MnZn and NiZnCu ferrites for low temperature co-fired ceramics technology are driving investigations on design rules of integrated power electronic inductors and transformers. Their magnetic properties and impact on device performance are described in the following with particular emphasis on MnZn ferrite and basic transformer structures comprising a pure ferrite multilayer, a dielectric multilayer with ferrite cladding, and a dielectric multilayer with closed ferrite core. While the monolithic embedded version exhibits low magnetic coupling and power capacity, the gap and the core design achieve more than 100 W transmitted power per cm 3 device volume at 90% efficiency.

Investigations on stoichiometric and substoichiometric La1-x-γSrxMnO3-δ used as cathode material in the sold oxide fuel cellused as cathode material in the sold oxide fuel cell

The influence of A-site deficiency in perovskite materials of the system La0.8-γSr0.2MnO3-δ on the rate of oxygen reduction at the cathode of the SOFC were investigated. Cathode layers with the compositions La0.8Sr0.2MnO3-δ and La0.75Sr0.2MnO3-δ were prepared by screenprinting and were sintered onto thin sheets of cubic Y-stabilized zirconia. The time dependent response of the cell voltage to changes in current density was found to be different for these two cathode composititons. During cell operation the performance of the La0.8Sr0.2MnO3-δ layer improved slowly and eventually attained values identical to those of the La0.75Sr0.2MnO3-δ layer which reached its final performance comparatively fast. Furthermore, for the La0.8Sr0.2MnO3-δ layer, degradation in the performance was observed, if subsequently the applied current density was lowered, i.e. the improvement is reversible. Similar effects were seen for the A-site deficient composition, but to a much smaller degree. The difference in electrochemical performance of these two compositions is attributed to a different reactivity between the electrolyte and the cathode material, a change of the morphology of the La0.8Sr0.2MnO3-δ layer during operation and/or a change of the electrochemically effective area in the vicinity of the three phase boundary.

Design of Compact Transmission Line Transformers in LTCC Technology

Concepts for ceramic integrated transmission line transformers (TLT) to conduct powers up to some kW and currents up to 10 A with an impedance ratio of 4:1 are presented. In this power range, a TLT usually consists of coaxial cables. To optimize size, improve integrability and enhance electric performance, our work pursues the integration into a planar multilayer board with electroplated conductors using Low Temperature Cofired Ceramics Technology (LTCC). The methodical design approach is presented, using complementary simulation tools for circuit, multilayer and FEM analysis to reach the aforementioned application-specific performance. Size is reduced further using specific ferrites and optimizing their position. The correlation between measured characteristics of various transmission line transformers produced and underlying design considerations are given in detail. Minimum sizes of 10 to 15 mm squared have been realized using single sided metallisation, which is also well suited for electroplating.