Broadband permittivity characterization of polymers up to 110GHz using co-planar waveguides

Abstract

This work presents a method to characterize the complex permittivity of dielectric materials on top of co-planar waveguides (CPW). CPW lines made of aluminum are patterned on a 200mm quartz wafer and coated with a material under test (MUT). The S-parameters of the transmission lines are measured from 5GHz to 110GHz, and the propagation constant is calculated using the multiline TRL de-embedding technique. An analysis of the influence of the electrical properties of the MUT on the propagation constant shows that the attenuation constant depends on the complex permittivity, while the phase constant depends only on the relative permittivity. These relationships are exploited to extract the complex permittivity of the MUT with a 2D field solver by optimizing the MUT complex permittivity to match the measured propagation constant. For the purpose of this experiment, four materials are coated on separated wafers, and their complex permittivity values are extracted from 5GHz to 110GHz. Out of the four materials analyzed in this study, one exhibits a low dielectric constant of 2.5 and a loss tangent below 0.005 above 15GHz.