The Microwave Barium Ferrite Thick Films, And Performance

Microwave ferrite circulators are indispensable components in communication, radar, microwave / millimeter-wave circuits and systems. With the development of microwave / millimeter-wave circuits and systems, microwave ferrite circulators will be planar, self-biased. So thick or thin ferrite films with high saturation magnetization (Ms), high remanence ratio, high coercivity (Hc) and high C-axis preferred orientation become the key material of next generation circulators.Barium ferrite thick films are prepared by screen printing. The influence of glass content, sintering temperature, sintering time, pressing pressure, cold isostatic pressure (CIP) and orientation magnetic field to the microstructure and magnetic properties of barium ferrite thick film are studied. Self-biased circulators are prepared on barium ferrite thick films.The results show that, the remanence ratio of barium ferrite thick film increase with the glass content, but too much or too little glass will lead to low saturation magnetization and low coercivity, 8wt.% glass content have the best magnetic properties where the Ms is about 1.8kGs, Hc is about 3.8kOe,and remanence ratio is about 0.54. When the sintering temperature is too high or too low, the magnetic properties will be low, the optimal sintering temperature is about 1150℃where the Ms is about 1.9kGs, Hc is about 3.8kOe, remanence ratio is about 0.66. The best sintering time is about 8 hour where the Ms is about 1.8kGs, Hc is about 3.7kOe, remanence ratio is about 0.66. Hot-press sintering can improve the magnetic properties of barium ferrite thick film obviously, when the pressure is 10MPa, the Ms is about 2.8kGs, Hc is about 3.9kOe, remanence ratio is about 0.63. The magnetic properties can also improved by CIP treatment, when the pressure is 120MPa, the Ms is about 2.5kGs, Hc is about 3.5kOe, remanence ratio is about 0.5. The C-axis preferred orientation of the barium ferrite thick film increase with the magnetic field, when the magnetic field is 8.0kOe, the Ms is about 2.8kGs, Hc is about 3.8kOe, remanence ratio is about 0.78.The test results show that, the fabricated circulator has an insertion loss of 19 dB and an isolation of 39 dB at 38.6 GHz, and a non-reciprocity of 20 dB.