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Design and Characterization of a Biocompatible Packaging Concept for Implantable Electronic Devices
Keywords: miniaturized implantable packaging, bi-directional diffusion barrier, biocompatible metallization
A biocompatible packaging process for implantable electronic systems is under development at imec, combining biocompatibility and hermeticity with extreme miniaturization. Also cost aspects are taken into account, an important aspect since precious metals such as gold, platinum and IrOx are used. In a first phase of the total packaging sequence, all chips are encapsulated in order to realize a bi-directional diffusion barrier 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. For cost effectiveness, this hermetic chip sealing is performed as post-processing at wafer level, using modifications of standard clean room (CR) fabrication techniques such as partial dicing and die rounding prior to diffusion barrier deposition, in order to ensure very good step coverage of these layers. To avoid CR cross contamination, well known conductive and insulating CR materials are investigated with respect to their biocompatibility, diffusion barrier properties and sensitivity to corrosion. A series of tests are performed: various types of cell cultures using both cell lines and primary cells, TXRF analysis of extracts, corrosion tests at 37C and at elevated temperatures. In a second phase of the packaging process, all chips of the final device should be electrically connected, applying a biocompatible metallization scheme using eg. gold or platinum. For electrodes being in direct contact with the tissue after implantation, improved performance is expected when IrOx metallization is used. Device assembly is the third packaging step, during which all system components such as electronics, passives, a battery,... will be interconnected. To provide sufficient mechanical support, all components are finally embedded using a biocompatible elastomer such as PDMS. A soft elastomer will also reduce the body reaction upon implantation due to its biomimetic nature (flex, soft material cfr. tissue).
Maaike Op de Beeck, Program Manager HUMAN++
IMEC
Heverlee, Leuven B-3001,
Beligium


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