Method and apparatus for visual neural stimulation
The present invention is a flexible circuit electrode array for stimulating neurons where the electrode are less than 20 μm in size and less than 60 μm apart. The array is preferably arranged in a hexagonal pattern to maximize electrode density, and longer in the horizontal direction to correspond to a normal visual scene. The array includes a polymer base layer, metal traces deposited on the polymer base layer, including electrodes suitable to stimulate neural tissue, and a polymer top layer deposited on the polymer base layer and the metal traces defining openings for the electrodes smaller than the electrodes to overlap the electrodes.
1. A method of making a flexible electrode array for retinal stimulation comprising:
depositing a polymer base layer on a flat substrate forming bond pad portion, a cable portion, and an array portion;
depositing metal on the polymer base layer;
patterning the metal to form metal bond pads in the bond pad portion at an end, metal electrodes in the array portion at an opposite end and metal traces in the cable portion between the metal bond pads and metal electrode connecting the metal bond pads to the metal electrodes, the electrodes being less than 20 μm in diameter and less than 60 μm apart and wherein adjacent electrodes are arranged in a hexagon around a single adjacent central electrode;
depositing a polymer top layer on the polymer base layer, the metal electrodes and the metal traces forming the flexible circuit electrode array;
forming microwells in the polymer top layer and plating platinum in the microwells;
removing the flexible circuit electrode array from the flat substrate;
molding the flexible circuit electrode array portion in an approximately concave spherical mold to form the array portion in an approximately convex spherical shape to approximate the curvature of target retinal tissue and make the curved surface suitable to contact the retinal tissue; and
forming a second polymer, softer than said polymer top layer, over said polymer top layer; and
wherein the cable portion is suitable to pass through a sclera and the bond pad portion connect to an electronics package and receiver coil outside the eye and mounted to a lateral side of the eye.
2. The method according to claim 1 , wherein the step of depositing the polymer base layer and the polymer top layer is depositing polyimide.
3. The method according to claim 1 , wherein the step of depositing the polymer base layer and the polymer top layer is depositing silicone.
4. The method according to claim 1 , wherein the step of depositing the polymer base layer and the polymer top layer is depositing fluoropolymer.
5. The method according to claim 1 , further comprising bonding at least one bumper to a peripheral edge of the flexible circuit electrode array.
6. The flexible circuit electrode array according to claim 5 , where the bumper is a continuous skirt covering at least of portion of the flexible circuit electrode array.
7. The method according to claim 1 , further comprising bonding a stress relief membrane, suitable for attachment to neural tissue, to the flexible circuit electrode array, wherein the stress relief membrane is a more compliant material than the polymer base layer.
8. The method according to claim 1 , wherein the step of patterning is patterning the electrodes in a hexagonal pattern.
9. The flexible circuit electrode array according to claim 1 , wherein the adjacent electrodes arranged in a hexagon around a single adjacent central electrode are equally spaced.