Fabrication of Self-Biased Circulators with Integrated Hexagonal Microwave Ferrites Using LTCC Technology

Next-generation magnetic microwave devices for satellite communication technologies require passive components including circulators that manipulate electromagnetic signals at high frequency. For this, circulators have to be integrated into LTCC microwave communication modules. Substituted M-type hexagonal ferrites represent a class of microwave magnetic materials with self-biasing ability and ferromagnetic resonance frequencies in the range of 25-50 GHz. The authors report on different options for integration of self-biased ferrites into LTCC multilayer devices, including drop-in sintered ferrites, and cofiring of screen-printed ferrite layers or ferrite tapes. Sintered substituted hexagonal microwave ferrites with preferential orientation were fabricated by compaction of powders in a magnetic field and sintering, whereas ferrite thick films were prepared by screen-printing, drying in an external magnetic field, and sintering at 900 °C. The magnetic texture of the ferrites is characterised using XRD, EBSD, and magnetic measurements. The substituted ferrites exhibit a ferromagnetic resonance frequency at about 30 GHz with nonreciprocal properties, and were integrated in a LTCC Y-junction circulator. Test results indicate that hexagonal ferrites are promising materials for self-biased circulators fabricated in LTCC technology for microwave components at Ka-band frequencies around 30 GHz.