Integration of Ni-Cu-Zn and Hexagonal Ferrites into LTCC Modules: Cofiring Strategies and Magnetic Properties

Abstract

We have studied the integration of Ni-Cu-Zn ferrite spinels as well as substituted hexagonal Co₂Y-and M-type ferrites into LTCC (Low Temperature Ceramic Co-firing) modules. The cofiring behavior and the magnetic properties of these materials were investigated and evaluated for multilayer applications. Ni-Cu-Zn ferrites exhibit permeabilities of μ=300–500 for operating frequencies in the MHz range. Cu-substituted Y-type ferrites Ba₂Co_2-x-yZn_xCu_yFe₁₂O₂₂ in combination with sintering additives display sufficient shrinkage and densification at 900°C. A permeability of μ=10 is observed; however, substituted Co₂Y-type ferrites do not exhibit long-term stability at 900°C. Co/Ti-substituted M-type ferrites BaFe_12-2yCo_yTi_yO₁₉ (y=1.2) with planar magneto-crystalline anisotropy exhibit excellent soft magnetic behavior. Using sintering additives, complete densification is reached at 900°C and a permeability of μ=15 and a resonance frequency of larger than 1 GHz are observed. Integration of ferrite multilayer inductor components into LTCC modules using free and constrained cofiring technologies is demonstrated.