Spin-sprayed ferrite films with high resistivity and high-frequency magnetic loss for GHz conducted noise suppressors

In the present study, crystallized ferrite (an intermediate between Fe3O4 and γ-Fe2O3) films prepared by spin-spray technique exhibited strong magnetic losses at high frequencies and are applicable as GHz conducted noise suppressors. The reaction (metal ions) and oxidizing (pH buffers and oxidizing agent) solutions were separately sprayed onto the substrates (90 °C) mounted on a rotating disc. Two types of films were prepared on the basis of the different oxidizing solutions; CH3COONa + NaNO2 in the case of film-A and CH3COONa + (NH4)2CO3 + NaNO2 + NaOH for film-B. The as-prepared films were heat-treated under a condition similar to that of the reflow soldering process (265 °C). The effects of the preparation conditions and film morphology on the electrical and magnetic properties before and after the heat treatment were studied. The results revealed that film-B had a relatively smaller initial permeability (μ′) compared to film-A. However, it had a high-imaginary permeability (μ″), resonance frequency (fr) and surface resistivity (ρs) even after heat treatment. Also, the noise suppressing properties of film-B were relatively good, hence ideal for use as conducted noise suppressors.