In-vitro Eletrochemical-stablity Evaluation Of A Flexible Microelectrode Array And Manufacture Of Silicon-based C-MEMS Microelectrode

More than70%information for the humans to recognize the outsidesurroundings comes from vision, thus scientists have proposed a method torestore the visual function of blind person by implanting visual prosthesis.A visual prosthesis can electrically activate exciting neural cells byelectrical stimulation from an implanted neural stimulator. Amicroelectrode directly interfaces with the stimulating neural tissue, and isone key component of a visual prosthesis. Consequently, theelectrochemical characteristic evaluation of the microelectrode isnecessary to achieve the in-vivo safety and effectiveness.Carbon-Microeletromechanical System(C-MEMS), combined withtraditional lithography and pyrolytic process, can manufacture carbonmicro-structure that has good chemical stability, biocompatibility andmechanical properties. C-MEMS technology is compatible with MEMSfabrication process, thus a new method to manufacture silicon-basedC-MEMS microelectrode array is proposed in this thesis.The contents of this thesis include:(1) In-vitro electrochemical-stability evaluation of a flexible MEMSmicroelectrode. Three-electrode testing method was used to investigate theeffect of temperature on electrode impedance, experiments in PBS(phosphate buffered solution) solution showed that the electrodeimpedance was almost invariable at35°C~40°C (the human bodytemperature range). (2) pH shifts in saline solution resulting from the electricalstimulation. Experiments in unbuffered saline solution showed that pHshifts decreased when the frequency of biphasic charged-balanced pulsesincreased. Even stimulated by monophasic pulses, the stimulus-induced pHshift of electrode only varies0.15(with both anodic pulse current andcathodic pulse current).(3) An implantable penetrating electrode array that based onC-MEMS technology was designed. The stimulating site was arranged by8*2or4*1, a single eletrode was70m in diameter, the width of guideline was30m, bonding pad was a300m square. Photosensitivepolyimide (PSPI) was served as the conducting material through pyrolysisby C-MEMS techology. Silicon dioxide that deposited by PECVD(Plasma-enhanced-chemical-vapor deposion, PEVCD) was choosen to bethe insulating material. Finally, the microelectrode was released bydouble-side lithography and silicon etching.