A New Fabrication Process for Low-Loss Millimeter-Wave Transmission Lines on Silicon

The new type of coplanar waveguide for millimeter-wave transmission was fabricated on silicon by chemical mechanical polishing and selective electroplating processes based on silicon technology. The thick interconnections obtained using these processes have less conductor loss than the conventional interconnections, and the deep grooves on both sides of a signal line in this new waveguide reduce the dielectric loss caused by the high permittivity of the silicon substrate. The electro-optic sampling technique confirmed that the new waveguide has excellent millimeter-wave propagation characteristics, low effective permittivity and low attenuation, at frequencies up to 300 GHz. The new fabrication processes should be useful in combining millimeter-wave systems with ultralarge-scale integrated circuits on silicon.