The Packaging of Implantable Integrated Sensors

Integrated sensors are being designed for long-term implantation for physiological research using animal models and for permanent implantation for various types of prostheses in clinical applications. The problem of packaging these implantable integrated sensors outside of hermetically sealed hybrid packages is described. The electrolytic corrosion of cable conductors and integrated circuit metallizations is the principal danger. The published performance of the materials which have been used to date to encapsulate nonintegrated sensors and conductors is evaluated, and found to be unreliable for these applications. So, too, are the metals which have been used as electrical conductors. New techniques being developed in the attempt to achieve "hermeticity on a chip" are described. Finally, a critical, residual aspect of the overall problem is identified: how to make a mechanically rugged and inherently noncorrodible connection between a cable and a thin film on a silicon chip. No solution to this problem has been demonstrated.