Effect of the Relative Area of Exposed Electrode to the Insulating Area on the Impedance Measurement of Electrolyte

Abstract

Precise characterization of the electrical properties of the microelectrode system is necessary to optimize the neural recording/ stimulation or the sensitivity of bioimpedance measurement. This article reports on the dependency of the electrical characteristics of the planar microelectrode on the relative area of exposed electrode to the insulating area. Based on the finite element method analysis employing the thin-layer approximation, the impedance spectra of the electrode were simulated with respect to the structural factor. For the experiment, indium tin oxide disk electrodes with a radius of 7.5 mu m to 795 mu m exposed from an insulating layer of parylene-C with a thickness of 550 nm were fabricated. The impedance spectra of the fabricated electrodes were measured with 0.9% NaCl electrolyte. The decrease in the relative area of exposed electrode to the insulating area caused an increase in the contribution of the impedance of the insulator to the total impedance.