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Hermetic Packages and Feedthroughs for Neural Prostheses


Principal InvestigatorAffiliationContract NumberLink
Khalil Najafi, Ph.D.University of MichiganN01-NS8-2387

ProjectTitle: Hermetic Packages and Feedthroughs for Neural Prostheses, 1997



The Neural Prosthesis Program (NPP) of the National Institute of Neurological Disorders and Stroke (NINDS) supports the development of implants for the purpose of forming in-going and out-going connections with the nervous system. Such implants are needed for the development of neural prostheses for individuals with sensory and motor disabilities. The implanted elements of these prostheses include electrodes that interface with the biological tissue, a power and telemetry receiver, control electronics, and a biocompatible package for the implanted electronics. The development of a microsized, biocompatible package for neural prosthetic implants is the focus of this work.

Implanted electronic circuitry must function reliably for the lifetime of the recipient. Experience in the pacemaker industry suggests that hermetic packaging of electronic components is needed to achieve such reliability. The goal of this project is to develop hermetic packaging techniques that can be used to protect the electronic circuitry needed for telemetry and powering of microelectrodes, as might be used in the central nervous system, and macroelectrodes, such as cuff or intramuscular electrodes for peripheral prostheses. Compared to cardiac pacemakers, the required packages are 100 to 1,000 times smaller in volume and require a greater number of feedthroughs.

Research has demonstrated that feedthroughs can be fabricated on planar silicon substrates at a linear density of a feedthrough every 4 microns using batch fabrication techniques. Several of these feedthroughs can be tied in parallel if a low resistance path is required. A glass capsule has been anodically bonded to the silicon base to produce a microhermetic package. In-vitro testing of these packages at accelerated temperatures suggests that they will function reliably at body temperature for over 40 years.

Hermetic packages for specific neural prosthesis applications will now be designed and developed. The mean-time-to-failure for the packages will be determined by means of accelerated testing. In-vivo testing of the packages will also be conducted using hermetic packages that include a telemetry system and moisture sensors to permit monitoring of package integrity in an animal model. Based on the results of accelerated and in-vivo testing, failure mechanisms for hermetic seals will be studied. New materials and process methods will be devised to eliminate these failures. The investigators will also cooperate with other neural prosthesis investigators to develop complete implant systems for specific applications utilizing either micro or macroelectrodes.

This Request for Proposals represents a competitive renewal of an ongoing research contract (N01 NS4-2319, The University of Michigan). Copies of progress reports from this contract and other current contracts related to this work and a bibliography of Neural Prosthesis Program publications are available from the Neural Prosthesis Program, Room 916 Federal Bldg., Bethesda, MD 20892-9170.


Independently and not as an agent of the Government, the contractor shall exert its best efforts to develop and demonstrate the reliability of implantable, microsized, hermetic packages and feedthroughs for use in neural prostheses.

Specifically, the contractor shall:

A. Develop a microsized hermetic package with multiple feedthroughs for use with implantable micro and/or macroelectrodes.

1. The packaging method shall be compatible with package volumes ranging from 10 to 100 cubic millimeters.

2. The package sealing techniques shall not harm electronic components that cannot tolerate temperatures greater than 360 degrees C.

3. At least 12 feedthroughs on a pitch of 125 microns or less shall be provided.

4. Feedthrough terminations shall be suitable for making connections to integrated and discrete microelectrodes utilizing wirebonding or other techniques.

5. Strain relief of wires as they leave the package shall be incorporated into the package design.

6. The package shall permit coupling of power and information to the implant by an electromagnetic link.

7. The package design shall incorporate remote monitoring of package integrity by electronic or other means.

8. The packaging method shall be compatible with volume production.

9. Consideration shall be given to including a micromachined microelectrode as an integral part of the package.

B. Develop a telemetry system that permits remote monitoring of the internal package humidity in implants in unrestrained animals.

C. Test the package and feedthroughs by accelerated in-vitro testing and also by in-vivo testing in a nonprimate animal model for at least 1 year.

D Based on the testing results redesign the package as needed to eliminate failure modes.

E. Identify a collaborating group involved in chronic stimulating or recording in the central or peripheral nervous system and cooperate with them in the development of a suitable microhermetic package and the supporting electronics needed to provide chronic in-going or out-going connections.

Last Modified November 24, 2008