Biophysicochemical evaluation of passivation layers for the packaging of silicon microsystems in medical devices

This paper is dedicated to the research and development of hermetic and biocompatible packaging of microelectronic devices for medical applications. Materials such as Al₂O₃, HfO₂, TiO₂, ZnO, SiN, SiO₂, SiOC, SiC, a-CH, and BN which had been reported as biocompatible and compatible with fabrication in standard clean rooms were studied. As there were many candidate materials, a method for selecting the best passivation layers was implemented. Our methodology consisted of screening materials by accelerated aging tests in Phosphate-Buffer Saline (PBS, a saline solution that resembles the human blood serum), gas permeability tests and in-vitro cytotoxicity tests. To quantify the stability of each material in PBS, the corrosion rate (defined as the amount of corrosion loss in thickness over time) of each packaging layer was monitored over time by Variable Angle Spectroscopic Ellipsometry (VASE). Helium gas permeability measurements of selected packaging layers are also provided. Finally, candidate layers were confirmed to be non-cytotoxic according to the norm for in-vitro evaluation of medical devices ISO10993-5.