High frequency design and characterization of SU-8 based conductor backed coplanar waveguide transmission lines

The epoxy-based negative photoresist SU8 is widely, used within the MEMS (microelectromechanical systems) community, and is well known for its ability to form thick layers with high aspect ratios and for its chemical resistance. However, only a few papers have investigated the electrical properties of this material and mostly within the MEMS area or at lower frequency ranges. This paper presents the design and characterization of conductor-backed coplanar waveguide (CBCPW) transmission lines using SU-8 dielectric material. The coplanar transmission lines are carefully designed using EDA tools, and fabricated on a metallized glass substrate coated with SU-8 material. S-parameter measurements are performed from 45 MHz to 50 GHz using a vector network analyzer and a probe station. From these measurements, transmission line parameters such as characteristic impedance, attenuation constant, effective dielectric constant, loss tangent, etc, are determined. The design procedure, fabrication process and measurement results are described in this paper. To our knowledge, this is the first time the SU-8 material is characterized in microelectronics using CBCPW transmission lines.