Coupling of MnZn-ferrite films onto electronic components by a novel solution process for high frequency applications

A novel approach for the preparation of "coupling-type noise suppressors" in which ferrite films are directly deposited onto the components of the printed circuit board is reported. Crystalline Mn _xZn_yFe_3-x-yO₄ films were fabricated on IC chips and polyimide substrates by a soft-chemistry route at temperatures below 100 °C. A "reaction-solution" comprising MCl₂ (M = Mn, Zn, Fe) and an "oxidizing-solution" (pH buffer + oxidizing agent) were sprayed simultaneously onto a substrate maintained at 90 °C on a rotating disk. The as-prepared films were highly crystalline and hence do not require any post annealing. The magnetic and electrical properties of the films were studied. The films exhibited a large magnetic loss (imaginary permeability ″) in GHz range and also exhibited high resistivity in accordance to overcome the heat treatment during the reflow soldering process. Resistivity of 2 × 10⁵ Ω sq^-1 was found to be the lower limit for the coupling-type noise suppressors. Noise suppression of above 50% at 10 GHz was obtained for a 6.7 m thick MnZn-ferrite film and was equivalent to that of commercialized composite sheet noise suppressors of 50 m thickness.