High-Density Implantable Microelectrode Arrays for Brain-Machine Interface Applications

Abstract

Microelectrode arrays (MEAs) act as an interface between electronic circuits and neural tissues of implantable devices. Biological response to chronic implantation of MEAs is an essential factor in determining a successful electrode design. Finding appropriate coating materials which are biocompatible and improve electrical properties of MEAs are among the main challenges. In this paper, we propose a novel, three-dimensional (3D), high-density, silicon-based MEAs for both neural recording and stimulation. Electrodes were fabricated using micromachining techniques. Geometrical features of these electrodes not only cause less tissue damage during insertion but also provide more contacts between the electrodes and targeted neural tissues. In order to achieve the proposed geometry, we introduce a novel masking method to coat variable-height electrodes with uniform and small tip-exposure. More importantly, compared to conventional techniques, the new masking method significantly improves process time and costs. This technique needs only one step masking and reduces the conventional masking steps from ten to three. In the next step, the active sites of the electrodes were coated with thin-films of molybdenum (Mo) and platinum (Pt) due to their ability to transfer between ionic and electronic current and to resist corrosion. Electrodes were characterized by scanning electron microscopy and impedance measurements. The average impedance of Mo and Pt electrodes at 1 kHz was 350 ± 50 kΩ and 150 ± 10 kΩ, respectively.