Ferrimagnetic garnets for Low Temperature Co-fired Ceramics microwave circulators

Yttrium Iron Garnet based ferrites are used in nonreciprocal devices like microwave circulators and isolators. The low dielectric and magnetic losses of those materials provide the required properties. The main drawbacks of circulators are their size and cost, due to complex mechanical assembling of the different materials. Adapting the different materials to a common LTCC (Low Temperature Co-fired Ceramics) process should be a possible solution to simplify the complex manufacturing process. We showed that cationic substitutions (bismuth and copper) enable a considerable decrease of the sintering temperature, from about 1450°C to down to 950°C. Furthermore, due to bismuth cations, a high permittivity is achieved allowing the reduction of the circulator core size. Assemblies of ferrite and dielectric tapes metallized with silver or gold are studied. The first results of circulators in LTCC-technology with gold and silver screen printing are presented and the compatibility of the different elements is analyzed.