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New Hermetic Packaging Concept for Implantable Medical Devices
Keywords: implantable packaging, biocompatible materials, biocompatible metallization
For implantable devices, a biocompatible packaging process is under development at imec, combining biocompatibility with extreme miniaturization, taking cost aspects into account. In a first phase, encapsulation of chips is essential, to realize a bi-directional diffusion barrier around each die preventing body fluids to leach into the package causing corrosion, and preventing IC materials such as Cu to diffuse into the body, causing various adverse effects. Realizing a hermetic chip sealing is not straightforward. For cost effectiveness, all corresponding fabrication is performed as post-processing at wafer level in a standard clean room (CR). Adjusted fabrication techniques are explored, such as wafer level based die rounding in order to ensure very good step coverage of the diffusion barriers. In order to ensure CR compatibility of the final process, known insulating materials used for conventional chip passivation and conductive barriers such as Ti, TiN, Ta, TaN are investigated with respect to biocompatibility, diffusion properties and corrosion prevention. Various tests are performed: cell cultures using various primary cells, TXRF analysis of extracts, corrosion tests at 37C and at elevated temperatures. In a second phase, all chips of the final device should be electrically connected, applying a biocompatible metallization scheme using eg. gold or platinum. Various deposition processes of platinum are compared related to cost and to cleaning possibilities to avoid cross-contamination towards other CR processes. Finally, all system components, such as electronics, passives, a battery,... need to be interconnected during device assembly. A biocompatible embedding using PDMS will provide sufficient mechanical support to the components, while the body reaction upon implantation will be limited due to the biomimetic nature of PDMS (flex, soft material cfr. tissue). During the workshop, our biocompatible packaging proposal and the ongoing investigations will be discussed, including dedicated test procedures as well as results.
Karen Qian, Dr.
IMEC
Heverlee, Leuven B-3001,
Belgium


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