Experimentally observed frequency variation of the attenuation of millimeter-wave coplanar transmission lines with thin metallization.

The attenuation of small coplanar transmission lines on insulating InP and GaAs has been investigated experimentally over the frequency range 0-60 GHz by on-wafer probing. The ground to ground spacing d, the center line width w, and the metal thickness t were varied. For thin (0.25-1 Mym) gold metallization, the variation of the attenuation with frequency was found to be dependent on the geometry of the line. A good fit to the experimental data was obtained when the attenuation a was modeled as a is equal to asub0fhighn, where asub0 and n are geometry dependent. The exponent n was found to be in the range 0.15-0.35, and to increase with increasing w/d ratio, which is interpreted to be due to a correspondingly varying frequency dependent resistance and current distribution.