Unprotected sidewalls of implantable silicon-based neural probes and conformal coating as a solution

Abstract

Silicon-based implantable neural devices have great translational potential as a means to deliver various treatments for neurological disorders. However, they are currently held back by uncertain longevity following chronic exposure to body fluids. Conventional deposition techniques cover only the horizontal surfaces which contain active electronics, electrode sites, and conducting traces. As a result, a vast majority of today’s silicon devices leave their vertical sidewalls exposed without protection. In this work, we investigated two batch-process silicon dioxide deposition methods separately and in combination: atomic layer deposition and inductively-coupled plasma chemical vapor deposition. We then utilized a rapid soak test involving potassium hydroxide to evaluate the coverage quality of each protection strategy. Focused ion beam cross sectioning, scanning electron microscopy, and 3D extrapolation enabled us to characterize and quantify the effectiveness of the deposition methods. Results showed that bare silicon sidewalls suffered the most dissolution whereas ALD silicon dioxide provided the best protection, demonstrating its effectiveness as a promising batch process technique to mitigate silicon sidewall corrosion in chronic applications.

Configuring intracortical microelectrode arrays and stimulus parameters to minimize neuron loss during prolonged intracortical electrical stimulation

“…A related issue is the electrical conductivity of the materials that come in contact with the tissues. The majority of multisite silicon devices leave their sidewalls and backside uninsulated, exposing silicon which is typically electrically-conductive [27]. Coating these regions with insulating material such as silicon dioxide could potentially yield a different tissue response following long-term stimulation.…”

A nanoscale inorganic coating strategy for stabilizing hydrogel neural probes in vivo

“…15 Given PVA's relatively low decomposition temperature (315 °C), 16 ALD is chosen over conventional chemical vapor deposition due to its lower processing temperatures (lower than 200 °C). 17 The ALD coating approach offers multiple advantages, including precise control over coating thickness and uniformity, and it operates below the decomposition temperature of PVA. The deposition process under high temperature (175 °C) also promotes nanocrystalline growth and enhances the stability of PVA hydrogel fibers without negatively impacting their optical properties.…”