Etude et mise au point de transformateurs large bande radiofréquence

This work concern the integration of inductive components used in radiofrequency range (1 to 600 MHz). The decrease of the component size can be achieved thanks to a reduction of the core loss. It was therefore decided to study the various parameters controlling the temperature dependence of core loss of the Ni-Zn-Cu-Co ferrites. The decrease of the core loss was obtained thanks to cobalt substitution. These substitutions lead to a magneto-crystalline compensation and also to a pinning of the domain walls. The stability versus temperature could be improved by adjusting the Ni/Zn ratio and by reducing the copper concentration. The ferrites developed in this study exhibit 4 to 5 times less loss compared to conventional ferrites, in a wide range of temperature (-50 to 100°C). Studies were also carried out in order to make Ni-Zn-Cu ferrites compatible with the multilayer technology. The addition of Bi2O3 enabled to densify Ni-Zn-Cu-Co ferrites after firing at 880°C, while keeping their good magnetic properties. Co-sintering with conductive and dielectric materials was achieved. The use of Ni-Zn-Cu-Co ferrites in multilayer technology had finally been validated through the realisation of co-fired transformers with electromagnetic coupling coefficient of 97%.