Fe-Si-Cr Alloy–Ni-Cu-Zn Ferrite Composite Multilayer Inductors: Fabrication, Co-firing, and Magnetic Performance

Abstract Fe-Si-Cr alloy powders exhibit higher saturation magnetization than Ni-Cu-Zn ferrites and have gradually replaced Ni-Cu-Zn ferrites in power inductors. However, the low resistivity of Fe-Si-Cr alloys results in a lower component breakdown voltage. Furthermore, during the sintering process, the surface of the Fe-Si-Cr alloy powders will form a dense chromium oxide layer and interact with the silver internal electrodes, resulting in the discontinuity of the internal electrodes. In this study, a new type of multilayer power inductor based on a Fe-Si-Cr alloy/Ni-Cu-Zn ferrite composite design is proposed. The effect of co-firing temperature and uniaxial pressure during pressure-assisted constrained sintering of the multilayer composite power inductors on the densification and microstructures of the Fe-Si-Cr and Ni-Cu-Zn ferrite layers was investigated. The composite inductors were sintered at about 900°C and 1 MPa in a nitrogen atmosphere, resulting in significant Ag migration. It was found that silver diffusion could be effectively prevented by reducing the sintering temperature to 800°C. Inductance at 1 MHz of about 0.25 μH, a quality factor of about 9, and rated current of about 2.25 A were obtained for a multilayer power inductor with dimensions of 10 x 10 x 2.8 mm 3 sintered at 800°C and 3 MPa in a nitrogen atmosphere. Graphical Abstract