A Flexible High-density Microelectrode Array For Retinal Prosthesis Based On MEMS Technology

Vision is the most important part of senses of human being. Having acomplete and effective visual pathway is the only way to gain normalvision. Researches show that the vision pathway of the blind was notdamaged totally. By stimulating function-remained part of visual pathway,visual prosthesis provides some degree of artificial sight for visual disabledpatients. As the neural interface between the visual prosthesis and biologicaltissue, the MEA(micro electrode arrays) is the key part of the device and thegateway of all the information. According to the different parts ofMEA-implant positions, there are three kinds of prosthesises, they arevisual cortex prosthesis, optic nerve prosthesis and retina prosthesis.Retina prosthesis with a good topological correspondence between thestimulating site and the visual field, doing less harm to tissues, and keepingmost functions of the visual path is becoming the most practical andprospective one of prosthesises.To enhance the artificial sight of the blind who receives prosthesisimplant, resolution is one of the key factors of prosthesises. Therefore, itrequires MEA a density high enough of stimulating sites. Based on MEMStechnology we designed and fabricated two kinds of MEAs with differentdensities of stimulating sites. They were both made of photosensitivepolyimide(PI) as the base and platinum as the material of conducting metallayer. Titanium layer was placed between the base and the conductingmetal layer to get better adhesion. With traditional craft we made the1stvision of MEA which has30channels and350μm diameter of stimulatingpoint. The stimulating sites was arranged by65with1optional returnelectrodes. Width of the interconnect line is30μm and the minimum width between interconnect lines is40μm.To amend the disadvantages of Lift-Off method and improve theproperty of MEA, we introduced Ion Beam method to develop a newprocess of fabrication. With the new way, we made the2nd vision of MEAwith121channels. It was made by single-layer process technology, thediameter of stimulating site is280μm, and the whole stimulating sites areawas arranged by1210with1optional return electrode whose diameterbeing700μm. Width of the interconnect lines and the minimum widthinter-lines is both10μm. We tested the MEAs exteriorly, mechanically andelectrically, performances in electrochemistry analysts and biocompatibilit-y comparison are similar, but the120channels MEA had a higher densityof stimulating sites, which was a good guarantee for prosthesis to improvethe artificial sight.