S. Capraro

Magnetic properties of sputtered barium ferrite thick films

The development of devices that combine a magnetic material with a semiconductor chip is a major focus of current research. Barium hexaferrite (BaFe12O19 or BaM) thick films are deposited here using a rf sputtering system. The films are amorphous and nonmagnetic after deposition. Postdeposition thermal annealings are employed to obtain magnetic properties. The effects of the substrate, thermal annealing and thickness of BaM on the magnetic properties are studied using a vibrating sample magnetometer. The initial results show good magnetic properties for the two subtrates studied and after thermal annealing above 800 °C. The magnetic properties of the thick films are close to the bulk (BaM) ones.

Fabrication and characterization of a planar interleaved micro-transformer with magnetic core

This paper presents the design, the fabrication and the characterization of a planar interleaved micro-transformer with an Yttrium Iron Garnet (YIG) core. The design of this micro-transformer and the manufacturing steps are presented. HFSS software is used for the conception and the simulation of the interleaved magnetic micro-transformer. It is composed of two identical windings. A bottom magnetic core is used to improve the integrated transformer performances. To form the windings, we have used a surface micromachining process. We have also used a negative photoresist (SU-8) as an insulating layer and as support for the fabrication of a bridge to connect the central end of the coils to the ground shield. The micro-transformer have been characterized with impedance meter up to 100 MHz, and completed to 1 GHz using vector network analyzer.

Design and Study of Interleaved and Face to Face Magnetic Microtransformers

The aim of this paper is to compare two types of microtransformers using the High Frequency Structural Simulation simulator. Interleaved and face to face transformers were studied for applications in dc/dc converters and variable speed drive. These transformers have a magnetic material core (yttrium iron garnet) and square spiral windings. The main purpose of the use of magnetic material is to increase the magnetizing inductance LF and the coupling factor k. For this, LF and k were studied by simulation as a function of turn spacing, magnetic, and insulating layer thicknesses. The results presented were compared with recently published works. An important improvement of the main properties was observed in the frequency range (10-100 MHz). The interleaved transformer properties are equal to 0.95 and 0.80 μH for k and LF parameters, which corresponds to an 0.05 μH/mm2 inductance area ratio (LF/A), whereas for the face to face transformer k and LF are equal to 0.9 and 0.78 μH for an 0.08 μH/mm 2 inductance area ratio. Interleaved transformers were manufactured and characterized. Results show close agreement between simulation and measurement results.