Influence of sintering temperature on complex permeability of ferritic LTCC in wide frequency range

The complex permeability values of commercially available ferrite LTCC tapes (Low Temperature Cofired Ceramics) in dependence on firing peak temperature have been for the first time determined in the high-frequency range (300 kHz - 1 GHz). Grain size growth due to higher firing peak temperature is compared to the change of the complex permeability. Permeability values have been calculated from S-parameters measured with a vector network analyzer and a short coaxial sample holder into which ferritic LTCC toroids have been placed. The toroids were realized by stacking and laminating 62 layers of green tape and then sintered at peak temperatures of 885°C, 1000°C and 1100°C, respectively. The maximum relative permeability values increase up to 900 (at 1100°C firing peak temperature) and show a shift to lower frequency values.