Surface-Micromachined Rectangular Micro-Coaxial Lines for Sub-Millimeter-Wave Applications

This letter describes the design, fabrication and characterization of surface micro-machined micro-coaxial transmission lines. The fabrication process relies on successive deposition of sacrificial polymer layers and metal electroplating. Transmission lines with a cross-section of $88\,\,\mu \text {m}\,\,\times 42\,\,\mu \text {m}$ have been fabricated on a fused silica substrate, with various shapes. These lines are very well suited for applications above 50 GHz, where propagation in air minimizes both loss and dispersion. The measured lines have good performances with measured insertion losses of −0.33 dB/mm @ 127 GHz and return loss better than −15 dB.