Measuring dielectric changes at the solid-liquid interface of Parylene films with microwave microfluidic spectroscopy

Implantable MEMS-based devices enable wireless RF sensing and power transmission within the body. These devices often incorporate a polymer interface, such as Parylene-C, to serve as a substrate or coating for electronics. However, the solid-liquid interface is poorly understood, and the dielectric response is largely unknown at RF frequencies. Moreover, recent research suggests that Parylene-C can delaminate over time, compromising lifetime. Understanding the solid-liquid interface of Parylene-C layers will be essential for ensuring device performance and longevity. We have developed a microwave spectroscopy technique that captures the dielectric response of liquid media over a broad frequency range (100 kHz – 110 GHz). In this work, we use microwave microfluidic spectroscopy to analyze the interface between Parylene-C films and aqueous salt solutions. Our initial results suggest that water can permeate into Parylene-C within hours of soaking, changing the film’s electrical properties. Here we present the time-dependent electrical properties of Parylene devices as they are exposed to aqueous environments. More broadly, we will demonstrate the utility of microwave microfluidics for characterizing dielectric changes at solid-liquid interfaces over time.