Different methods to alter surface morphology of high aspect ratio structures.

Area of Science:

• Materials Science
• Biomedical Engineering
• Neuroscience

Background:

• Altering surface morphology of high aspect ratio structures increases real surface area, enhancing device functionality in applications like neural prostheses and solar cells.
• Neural implants, such as the Utah electrode array (UEA), require specific electrode surface area and impedance for effective single-neuron communication, balancing high selectivity with good signal-to-noise ratios.
• Traditional methods for increasing electrode surface area, like roughening metallization or using alternative materials, involve complex deposition processes and can negatively impact mechanical properties.

Purpose of the Study:

• To engineer the surface of silicon micro-needles for neural electrodes by creating defined microstructures.
• To enhance electrode surface area without altering the geometrical dimensions, thereby improving functionality for neural recording and stimulation.
• To optimize surface modification techniques for high aspect ratio silicon structures used in neural implants.

Main Methods:

• Engineered silicon micro-needle surfaces using methods including laser ablation, focused ion beam, sputter etching, reactive ion etching (RIE), and deep reactive ion etching (DRIE).
• Optimized surface modification processes specifically for the high aspect ratio silicon structures of the Utah electrode array (UEA).
• Verified the increase in real surface area and assessed impedance changes using scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS).

Main Results:

• Successfully created defined microstructures on silicon micro-needles, increasing the real surface area while maintaining geometrical dimensions.
• Achieved the most significant improvements in surface morphology and impedance reduction using deep reactive ion etching (DRIE).
• Demonstrated up to a 76% decrease in electrode impedance values, indicating successful surface engineering.

Conclusions:

• Surface modification of silicon micro-needles via DRIE is a viable method to increase real surface area and reduce impedance in neural electrodes.
• This approach allows for enhanced neural recording (improved SNR) and stimulation (higher charge injection/transfer) by optimizing electrode properties.
• The developed technique maintains standard metal deposition processes, overcoming limitations of traditional surface enhancement methods.