High resistive ferrite films by a solution process for electromagnetic compatible (EMC) devices

Mn-Zn ferrite films with high resistivity and good noise suppressing ability for use as ‘coupling-type noise suppressors’ have been prepared by the spin-spray ferrite plating. The as-prepared films were crystalline and exhibited single-phase spinel structure. The films had an ‘integrated nano-columnar’ morphology that resulted in a very high resistivity. Further, by varying the chemical composition, films with varying resistivity were prepared and then heat treated at 260 °C for 3 min, similar to that of the reflow soldering process. The reflection and transmission coefficients, S₁₁ and S₂₁ parameters, on coplanar micro-strip line (50 Ω) were measured for the as-prepared and heat-treated films in order to study the effect of heat treatment. When the resistivity was above 2×10⁵ Ω/sq, S₁₁ and S₂₁ exhibited uniform profiles throughout the measurement frequency (50 MHz-10 GHz), which is ideal for the ‘coupling-type’ noise suppressor. These films retain a moderately high resistivity and hence do not show the downshift in the stopband frequency even after the heat treatment (reflow soldering process).