Non-invasive iridium oxide biopotential electrodes

Abstract

Biopotential recording electrodes have been used to monitor non-invasively electroencephalogram (EEG), electromyogram (EMG) and electrocardiogram (ECG) by means of electrolyte pastes that improve electrode-skin interface. However, the skin preparation of 32 EEG electrodes may take up to 45 min. Despite the low skin-contact impedance and reasonable stability of the standard Ag/AgCl electrodes, several authors have been suggesting iridium oxide (IrO) as a promising biopotential recording and stimulation material. Hence, IrO thin-films were reactively DC-sputtered onto silicon substrates and electrochemically compared to the Ag/AgCl recording electrodes. The IS results observed for the IrO coatings were comparable to the results observed for the standard Ag/AgCl electrodes. The present work introduces a new IrO electrode with microtip structures that penetrate the outer skin layer (i.e. stratum corneum) that is 10 μm thick. The tip structures (100-200 μm high) were micromachined through a wet etching process with undercut in a KOH solution. The proposed dry electrode needs no paste application for signal quality improvement since it is in direct contact with the electrolytic fluids of the inner skin layers. A physiological experiment suggests that the IrO electrodes with microtips perform equally to the standard Ag/AgCl biopotential electrodes. The new dry IrO electrode is suggested to reduce the preparation period before the biopotential acquisition and for surface stimulation of excitable tissues.