Suspended Slow-Wave transmission lines for mm-wave applications

This paper presents and validate the concept of a suspended, slow-wave microstrip transmission line that uses air as a substrate. The lines are fabricated on a low-cost interposer technology, the metallic nanowire membrane (MnM), that allows selective growth of copper nanowires, enabling transmission lines with a wide range of Z
_c
. Lines with widths of 35 μm, 25 μm and 15 μm were designed and fabricated with 1, 2 or 4 suspended segments of 250 μm or 500 μm of length. Parametric extraction from the measured S-parameters showed ε
_eff
ranging from 5 to 7.5, α smaller than 0.8 dB/mm at 70 GHz and Q as high as 55. Z
_c
varied between 65 Ω and 90 Ω.