Neural prosthetics based on microelectrode arrays

This thesis presents a comprehensive analysis of various passivation layers for interdigitated electrodes (IDEs), focusing on their fabrication, behavior under varying environmental conditions, and their influence on performance and longevity. The primary aim is to determine the most effective passivation techniques to enhance the stability and reliability of IDEs in biomedical applications, particularly in neuroprosthetic devices. IDEs are fabricated using photolithographic techniques in a controlled cleanroom environment, both with and without passivation layers such as SU-8, Silicon dioxide, and Silicon nitride of varying thicknesses. The experimental setup involves electrochemical impedance spectroscopy (EIS) to measure impedance in different media, such as air, deionized water, tap water, and saline solutions, to assess the effectiveness of these passivation layers. Impedance data from experiments is utilized to characterize key parameters like geometric capacitance (Cg), double-layer capacitance (Cdl), capacitance due to the solution (Csol), and solution resistance (Rsol). COMSOL Multiphysics, a finite element analysis (FEA) software, is used to model and simulate the impedance of IDEs under different conditions to validate experimental results. Theoretical models employing Finite Element Method (FEM) and conformal mapping techniques provide insights into IDE capacitance under ideal conditions, validating experimental findings. A comparative study examines the performance differences between passivated and non-passivated IDEs, focusing on the impact of different passivation materials and thicknesses. Longevity tests assess IDE performance pre- and post-aging, highlighting significant differences between passivated and non-passivated IDEs. IDEs lacking passivation layers show increased impedance post-aging, indicative of potential corrosion and damage, while passivated IDEs demonstrate reduced impedance, suggesting degradation of the passivation layer. The study underscores the critical role of passivation layers—SU-8, silicon dioxide, and silicon nitride—in mitigating environmental degradation and ensuring long-term functionality in biomedical applications. In conclusion, this research advances the understanding of the effectiveness of various passivation layers in protecting Interdigitated Electrodes and optimizing their design for improved performance and reliability in biosensing and biomedical device applications. Future directions include refining theoretical models to account for real-world imperfections and further experimental validation in clinical settings.