gms | German Medical Science

Objective: In the present paper the development of a three dimensional micro electrode array with an iridium oxide coating is described. The electrode arrays are optimized for insertion into retinal tissue. The array allows to stimulate neurons or to record neuronal activity and by this to acquire spatially resolved data. In addition local changes of pH values can be measured with the electrodes, too.

Materials and methods: A fork like structure serves as a carrier for the electrodes. These structures have four shafts with a length of up to 1mm, a width of 50 µm to 100 µm and a thickness of 20 µm, which can penetrate the retina. Four electrodes with sizes varying from 100 square micrometers to 1600 square micrometers are placed on every shaft. The shape of the carriers is etched into an oxidized silicon wafer by reactive ion etching. The carriers are separated from the wafer by backside etching. Signal lines are micro structured sputtered gold films. The electrodes are made by micro electroplating of gold and then coated with iridium oxide. Polyimide serves as a protection layer. To arrange the electrodes in a 3-D array the structures are glued together to a stack. The shafts and their tips were optimized to allow penetration and to minimize the damage to the retina and to be still stable enough to endure the mechanical stress during implantation. Because of the small width of the shafts, the electrode size is limited. The small size leads to high impedance. Measurements show that the electrode impedance is significantly reduced by coating with iridium oxide due to its electro chemical behavior and its porosity.

Acknowledgment: This work is funded by the German Research Foundation (DFG) within the research project “BiMEAs”.