High Speed-Low Loss Micromachined Coplanar Waveguides in GaAs Technology

High speed-low loss micromachined transmission lines were fabricated in coplanar waveguide configuration. They make use of polyimide dielectric membranes deposited on a GaAs substrate with subsequent back-side bulk micromachining. On-wafer measurements of scattering parameters up to 110 GHz for different characteristic impedance lines (50, 75, 100 ¿) show a constant phase velocity of 2.9×108 m/s and a low-loss regime limited by metallic losses with a square root frequency dependence. Also, special attention was paid to the transition between the probing and propagation regions with the proposal of a novel tapering section making use of anisotropic etching profile.