Testing radiation, non-rectangular conductor profiles and edge roughness as source of additional losses in transmission lines

Losses in mmWave transmission lines often exceed first-principles predictions based on measurements of dc resistivity and the nominal conductor geometry. In our case, we observed an additional distributed resistance of coplanar waveguides on DyScO3 substrates. Here, we test three hypotheses on the additional resistance: radiation, non-rectangular conductor profiles, and conductor edge roughness. We present measurements on metallic and dielectric chucks to test radiation and atomic force microscopy measurements of the conductor to test non-rectangular conductor profiles and edge roughness. Our findings suggest that none of the above approaches is sufficient by themselves to explain the observed additional resistance. Still, we expect our findings to impact industrial processes especially when considering the trend from stepper lithography to microlens array (MLA) lithography for rapid prototyping and multiproject wafers.