Inter-diffusion between NiCuZn-ferrite and LTCC and its influence on magnetic performance

The present study investigated inter-diffusion between NiCuZn-ferrite and low-temperature-cofired ceramic (LTCC) during co-firing. The copper (Cu) ions in ferrite can diffuse into LTCC at a distance of 120 μm after sintering at 900 °C for 2 h, yielding a diffusion coefficient around 10−9 cm2/s. The magnesium (Mg) and aluminum (Al) ions from LTCC also diffuse into ferrite for a shorter distance. Several new phases form through such inter-diffusion. For example, the inter-diffusion between alumina and ferrite induces the formation of hematite whose presence is detrimental to the saturation magnetization and permeability of ferrite. Additionally, inter-diffusion also induces changes in the lattice parameters of ferrite. We note a linear relationship between the lattice constant of ferrite and saturation magnetization, which demonstrates that magnetic properties are strongly tied to the crystalline structure of ferrite.