Integration of High‐Frequency M‐Type Hexagonal Ferrite Inductors in LTCC Multilayer Modules

Monolithic hexagonal BaCo _1,3 Ti _1,3 Fe _9,4 O ₁₉ ferrite multilayers sintered at 900°C exhibit a fine‐grained microstructure with permeability of μ′ = 16 and a resonance frequency f _r ≥ 1 GH z. Co‐firing of hetero‐laminates of ferrite with CT 700 glass–ceramic LTCC tapes and with polycrystalline zinc titanate ( ZT ) LTCC tapes was studied. Co‐firing at 900°C of ferrite/ CT 700 leads to multilayers with cracks caused by substantial thermal expansion mismatch. Co‐fired ferrite/ ZT multilayer laminates exhibit a permeability of μ′ = 16 and do not show any defects. Hexagonal ferrite multilayer inductor elements were integrated into ZT ‐based multilayer LTCC modules and co‐fired at 900°C with Ag metallization.