Low-loss thin film microstrip lines and filters based on magnetorheological finishing

This paper presents a surface finishing method based on magnetorheological fluid to obtain low-loss high-frequency transmission lines and filters on CMOS-grade silicon. As specimens for the magnetorheological finishing, high-Z₀ and low-Z₀ thin film microstrip lines with a 20 μm-thick polyimide interface above the ground plane that is patterned on the silicon substrate are evaluated. In all cases, thin film microstrip lines treated with the magnetorheological finishing scheme reveal much lower losses compared to original lines owing to reduced conductor roughness. In addition, low-pass filters with 0.5 dB Chebyshev responses based on high-Z₀ and low-Z₀ thin film microstrip lines are designed and characterized before and after applying the magnetorheological finishing treatment, exhibiting a roughly 1.0-dB insertion loss improvement for the entire pass band range. The proposed magnetorheological finishing scheme can be applied to smoothen any 3-D high-frequency structures, and it can significantly improve conductor roughness.