Analysis of dielectric constant behavior of thermally treated SU-8 polymer up to 18 GHz

Abstract

Su-8 polymer has excellent potential for application in process manufacturing. This paper presents the effects of thermal stress on the electromagnetic properties of SU-8 polymer, showing the frequency-dependent microwave response of the material. The procedure follows the international standard method for assessing the quality of components and devices for space qualification as thermal stress simulates the aging process. The polymer has been used as a base layer to fabricate passive devices in the coplanar waveguide (CPW) configuration. Resonating structures and delay lines, with different sizes, have been manufactured on a SU-8 layer spun on a high resistivity silicon wafer. The material's dielectric constant has been calculated by measuring the microwave response of the devices before and after the thermal processes. We have recorded data in a broadband range, from 2 GHz to 18 GHz, and the conclusive comparison allows us to identify a frequency dependence of the electromagnetic performances of SU-8 polymer and confirms the possibility to use it for medium- and long-term microwave space applications. Specifically, minor changes of the electrical matching have been recorded in the Ku-band, from 12 GHz to 18 GHz, making the polymer reliable for current space communications.