Magnetic texturing of self-biasing hexagonal ferrite tapes for integration in LTCC microwave modules

Next-generation microwave LTCC modules for satellite communication systems require the integration of passive components including circulators to manipulate high frequency signals. Self-biasing oriented M-type hexagonal ferrites (Ba/Sr)ScxFe12-xO19 with high ferromagnetic resonance frequency are key materials for microwave circuits. The ferrites are integrated into LTCC multilayer devices as sintered drop-in bulk samples or printed films. Tape casting of ferrite tapes and subsequent drying in an external magnetic field is another option to fabricate oriented ferrite films which can be cofired with LTCC tapes at 900 °C. We report on the fabrication of non- and Sc-substituted M-type ferrite tapes with high degree of ferrite particle orientation. M-type ferrites without and with sintering additives were used and the laminated textured ferrite multilayer stacks were sintered at 1200 °C or 900 °C, respectively. Textured ferrite tapes were also combined with low-k dielectric LTCC tapes and cofired at 900 °C. The magnetic texture of the ferrite multilayer samples is characterized using XRD pole figures, EBSD and magnetic measurements. The results indicate that tape casting of magnetically textured hexagonal ferrites is a promising technology for the integration of self-biasing circulators in LTCC microwave modules operating at Ka-band frequencies at around 30 GHz.