Pyramidal Shaped 3–Dimensional 8 x 8 Electrode Array for Retinal Prostheses

Abstract

Purpose: : Pyramidal shaped 3–dimensional 8 x 8 electrode array is developed for retinal prostheses. Its novel 3–dimensional structure having a highly sharp tip can contact with ganglion cells, which is impossible to planar electrode array used at most retinal prostheses researches.

Methods: : Pyramidal shaped 3–dimensional electrode array is fabricated using MEMS (MicroElectroMechanical Systems) technology, which can make electrical and mechanical systems in the range from micrometers to millimeters. Its main substrate is silicon conventionally used for semiconductor fabrication. The triangular base of the electrode array is defined by the two successive photolithography patterning steps. The deep silicon RIE defines the vertical dimension of electrode array. Due to previous deposited mask film, triangular column structure has passivation films on the selected surface planes. Then, the triangular column structure is dipped into an aqueous alkaline solution to perform pyramidal shaped structure formation. After electrical isolation layer is deposited on the pyramidal shaped structure and the substrate, titanium film and gold film is sputtered sequentially and patterned. Finally, the oxide/nitride/oxide triple films are deposited as electrical and chemical isolation layers.

Results: : Fabricated device size is 4 mm x 4 mm. The electrode height is about 50 um. The height of single electrode can be controlled by the wet etch time within the range of 30∼60 um, which is the depth length from inner limiting layer to ganglion cells. The cone angle of electrode tip is about 15 degrees, and the tip radius is less than 1 um.

Conclusions: : The fabricated 3–dimensional multi–electrode array can communicate with retinal neurons under the inner limiting membrane with 120 µm spacing pitch. We have a long term project to develop epiretinal prostheses using the developed 3–dimensional electrode array.

Keywords: retina • retinal development