Impedance characterization of the degradation of insulating layer patterned on interdigitated microelectrode

Life-time and functionality of planar microelectrode-based devices are determined by not only the corrosion-resistance of the electrode, but also the durability of the insulation layer coated on the transmission lines. Degradation of the insulating layer exposed to a humid environment or solution may cause leakage current or signal loss, and a decrease in measurement sensitivity. In this study, degradation of SU-8, an epoxy-based negative photoresist and insulating material, patterned on Au interdigitated microelectrode (IDE) for long-term (>30 days) immersion in an electrolyte at 37°C was investigated by electrical impedance spectroscopy and theoretical equivalent circuit modeling. From the experiment and simulation results, it was found that the degradation level of the insulating layer of the IDE electrode can be characterized by monitoring the resistance of the insulating layer among the circuit parameters of the designed equivalent circuit modeling.