Microwave and magnetic properties of self-biased barium hexaferrite screen printed thick films

The interest in barium hexaferrite thick films, particularly with high remanent magnetization, is driven by the development of small planar ferrite microwave devices. We report here processing and microwave characterization of BaFe12O19 ferrite thick films (100-400 mu m). The films were deposited on silicon and alumina substrates by screen printing, oriented under a magnetic field of 8 kOe, then annealed at 250 degrees C and sintered at temperatures ranging from 850 to 1300 degrees C. Scanning electron microscopy and x-ray diffraction exhibited strong crystallographic alignment of c-axis crystals perpendicular to the film plane. The magnetization measurement indicated that a typical dense film with 270 mu m thickness yielded a high squareness (M-r/M-s) of 0.93. Ferrimagnetic resonance (FMR) measurements were performed in the frequency range of 40-55 GHz. From the linear dependence of FMR frequency on the external field, a g factor of 2.03 +/- 0.08 was deduced, while the smallest linewidth was obtained to be 1.2 kOe at 40 GHz. The broadening of the FMR linewidth arises predominantly from magnetic inhomogeneities in the polycrystalline films. The thick films have great potential for use in future microwave and millimeter wave monolithic integrated circuits. (C) 2006 American Institute of Physics.