Laser Sharpening of Carbon Fiber Microelectrode Arrays for Brain Recording

Microwire microelectrode arrays (MEAs) are implanted in the brain for recording neuron activities to study the brain functioning mechanism. Among various microwire materials that had been applied, carbon fiber is outstanding due to its small footprint (6–7 μm), relatively high Young’s modulus, and low electrical resistance. Tips of microwire in MEAs are often sharpened to reduce insertion force. Currently, carbon fiber MEAs are sharpened with either torch burning, which can only give a uniform length of wires in an array, or electrical discharge machining (EDM), which requires circuit connection with each single carbon fiber. The sharp tip results from intense burning induced by a flame or spark, leading to poor repeatability and controllability of the sharp tip geometry. In this paper, a laser-based, non-contact carbon fiber sharpening method is proposed, which enables controllable and repeatable production of carbon fiber MEAs of custom electrode lengths, insulation stripping lengths, and sharpened tips. Path of laser movement is designed according to desired array pattern. Variation in tip geometry can be accomplished by changing laser output power and moving speed. Test with different laser parameters (output power and moving speed) were conducted. Tip sharpening results were evaluated and analyzed in terms of tip geometry and insulation stripping length. Results showed that to achieve the desired MEA with sharper tip and shorter insulation stripping length, a higher laser power with faster moving speed is preferred.