Etude du ferrite NiZnCu nanostructuré produit par SPS : des propriétés physiques à la réalisation de composants monolithiques intégrés

The work presented in this thesis is part of the theme «power integration». It covers the study of the nanostructured NiZnCu ferrite material sintered by SPS (simple and reactive sintering) and the realization of monolithic integrated components.The objectives set for the thesis have been achieved. We have shown that nanostructured ferrites with good properties can be obtained by SPS. For a simple sintering, the principal structural, dielectric and magnetic characteristics were determined for different temperatures and densification duration. These sintered samples after decarburization exhibit high electrical resistivity, low dielectric permittivity, high initial magnetic permeability and merit factor.These characteristics can be controlled by sintering time and temperature. The in-situ synthesis by SPS also shows similar properties than those obtained by simple sintering. We have also shown that the starting from oxides of nanometric size, the milling conditions and the in-situ synthesis by SPS can lead to design ferrites with interesting properties with constant losses up to 3 MHz, at 15 mT and up to a temperature of 60 °C.Other the last objectives were also achieved. The co-sintering of ferrites with conductives and dielectric materials show that is possible to produce monolithic integrated electromagnetic components. These experiments show that the co-sintering ferrite is compatible with copper, barrium titanate and dielectric green tape. Inductive components and transformers were designed and fabricated. The frequency characteristics of inductive components show that the insertion of a dielectric increases the performance of components. Indeed, with dielectric, losses are lower and there is less variation in series resistance and inductance with bias current. For transformers with a dielectric layer, the results aren't satisfactory because the dielectric between the primary and secondary melts, during the fabrication creating a short-circuit. The low values of the coupling coefficient and efficiency of the transformer fabricated without a dielectric were predictable because of the large leakage inductance associated with the presence of a magnetic layer between the two windings of the transformer.