Cochlear electrode array employing tantalum metal

An implantable tissue-stimulating prosthesis comprising

• implanted stimulus-forming electronic circuitry hermetically sealed in a package, said package including a plurality of tantalum feedthroughs which provide an electrical path to the stimulus-forming circuitry hermetically sealed in said package, and at least one noble metal feedthrough that provides a return electrical path to the stimulus-forming circuitry hermetically sealed in said package;
• a plurality of electrode contacts made from sintered, anodized tantalum;
• a plurality of tantalum wire leads, each connecting one of the plurality of electrode contacts to a respective one of the plurality of tantalum feedthroughs, whereby each of the plurality of electrode contacts is electrically connected to one of the plurality of tantalum feedthroughs;
• at least one counterelectrode contact made from activated iridium;
• and
• at least one lead made from a noble metal connecting the at least one counterelectrode to the at least one noble metal feedthrough;
• wherein said implanted stimulus-forming electronic circuitry comprises:
• means for deriving a single source of operating potential V.sub.s and applying said potential V.sub.s to maintain an anodic polarization between the tantalum feedthrough and the noble metal feedthrough when stimulation is not desired, and
• means for generating a biphasic stimulus between a selected one of said anodized tantalum electrode contacts and said at least one counterelectrode when stimulation is desired, including means for controlling a cathodal phase of the biphasic stimulus by discharging electrical charge stored by a capacitance formed by said anodized tantalum electrode contact, said activated iridium electrode contact and intervening tissues and fluids.

A cochlear prosthesis comprising:

• an hermetically sealed package wherein stimulus pulse-forming electronic circuitry is housed;
• a multiplicity of tantalum feedthroughs, each of which provides electrical contact with the pulse-forming electronic circuitry within the hermetically sealed package;
• a multiplicity of electrode contacts, each electrode contact being connected to a respective one of said multiplicity of tantalum feedthroughs via a respective tantalum wire lead, whereby each electrode contact is electrically connected to the pulse-forming electronic circuitry;
• at least one iridium counterelectrode outside of said hermetically sealed package;
• at least one noble metal feedthrough connected to said at least one iridium counterelectrode via a respective noble metal lead outside of said hermetically sealed package, and connected to said pulse-forming electronic circuitry within said hermetically sealed package;
• potential means within said hermetically sealed package for maintaining a first anodic voltage between each of the multiplicity of tantalum feedthroughs and the at least one noble metal feedthrough, with each tantalum feedthrough being maintained positive relative to the at least one noble metal feedthrough;
• and
• means for causing a balanced biphasic current pulse to flow between at least one of the electrodes connected to a respective tantalum feedthrough and the iridium counterelectrode by varying said first anodic voltage by a predetermined amount.