Surface Passivation of an Implantable Semiconductor Multielectrode Array

摘要

An effective passivation material was needed for the protection of a semiconductor multielectrode array during long-term bio-implantations. The following properties were required of the material: a large electrical resistivity, a small relative dielectric constant, good adhesion to silicon dioxide and aluminum, impermeability to water and ionic contaminants, chemical stability in water, and a thermal coefficient of expansion compatible with those of aluminum and silicon dioxide. Three materials were initially evaluated with respect to these properties: Du Pont PI-2555, Accuglass 407, and Diffusion Technology U-1A. The first is a polyimide, and the latter two are polysiloxanes. The polysiloxanes were found to be permeable to ionic contaminants and were eliminated from further consideration. The polyimide possesses all of the desired properties. Several multielectrode arrays were passivated with polyimide using conventional photolithography and wet etching techniques. These arrays were tested in vitro in a saline solution for thirty days. The aluminum metallization on the multielectrode array was heavily corroded by the saline solution, resulting in changes in the integrated circuit's electrical parameters.