Research Of Parylene-Based Flexible Microelectrode Arrays

Neuroengineering is an interdiscipline which relates to neuroscience, microelectronic technique, material Science, information science, etc, which is helpful for investigating the operating mechanism of the neural system and solving the problems related to neural disorders and neural rehabilitation. The microelectrode is the interface between nervous system and circuit, which is the most critical component in neuroengineering systems.A MEMS-based flexible microelectrode array (MEA) is studied in this thesis, which is fabricated by photoresist thermal melting technology, chemical vapor deposition Parylene C. The main contents and conclusion are stated as follows: The coupling capacitance between interconnect lines are analyzed by Ansys, and the current density of different surface area is analyzed by Comsol. Some key questions for the fabrication of MEA are discussed, accounting for electrode packaging materials, interconnect lines and electrode material, electrode geometry. Based on the analyzing result, the flexible MEA is fabricated. The key processes during the fabricating MEA is researched, include photoresist melting and etching Parylene films by RIE. The electrochemical impedance spectroscopy of a single electrode is tested in 0.9% NaCl solution. The testing data are analyzed, and some advices are put forward for further improving the electrode performances.The fabricated electrode is 5×5 grid, covering an area of 3 mm×3 mm. The width of the interconnect lines is 50μm and the space is 100μm. The space of two electrodes is 600μm. Each electrode is 60μm diameter and the height is about 24μm, which have an approximately hemispherical surface profile. The electrode typically exhibit an impedance of 54.12k? and the phase shift of -61.6°at 1 kHz, respectively, which indicates that the microelectrode is more dominated by its capacitive component. Compared to plane microelectrode, the electrode with hemispherical geometry increases the surface of the electrode, allows electrode sites to be close to target neurons and reduces electrode impedance, which is helpful to neural stimulation.