The Effect of Annealing Thin Film Parylene C-Platinum Interfaces Characterized by Broadband Dielectric Spectroscopy

Thin film Parylene C has increasingly been employed as a substrate material with metals like platinum (Pt), especially in MEMS implantable devices. To assist in device design, broadband dielectric spectroscopy (up to 110 GHz) can characterize such materials with unique advantages unavailable in more-commonly used electrochemical impedance spectroscopy (up to 1 MHz). In this work, coplanar waveguides (CPWs) fabricated from electron-beam evaporated Pt coated with Parylene C were measured with broadband dielectric spectroscopy to characterize the effect of thermal annealing. We confirmed that annealing caused no significant changes in Parylene C permittivity $(2.85\pm 0.13$ and $2.80\pm 0.18$ before and after annealing; respectively) and extended the upper frequency limit to 110 GHz for the known permittivity value. Pt resistivity was unexpectedly reduced by 20% from annealing. Results and implications herein may inform fabrication-related design considerations of implantable devices using thin film Parylene C and Pt metal with radio frequency (RF) applications such as wireless power and data transfer.