Electrical properties of ferrite-dielectrics multi-layer EMI filters using buffer layer

Co-firing compatibility between ferrite and dielectric materials with silver electrode is the key issue in the production process of multi-layer chip EMI filters. We have used Ni-Zn-Cu ferrite inductor and BaO-Nd2O3-TiO2 dielectric capacitor to sinter at the temperature lower than 900 degreesC Direct contact in the ferrite/dielectric multi-layer chip filters generates delamination and inter-diffusion between the ferrite and dielectric layers. This problem could be solved inserting the buffer layer. The buffer was modified changing Bi2O3 and glass content. Organic compositions and sintering conditions of the buffer-inserted multi-layer EMI filters were also optimized to obtain the defect-free microstructure and the high strength. The EMI filter incorporating ferrite/dielectric multi-layer showed a 3dB-cutoff-frequency at 50 Mhz, and a maximum attenuation value of 45 dB at 1.2 Ghz.