Implantable microelectronic device and method of manufacture
An implantable hermetically sealed microelectronic device and method of manufacture are disclosed. The microelectronic device of the present invention is hermetically encased in a insulator, such as alumina formed by ion bean assisted deposition (“IBAD”), with a stack of biocompatible conductive layers extending from a contact pad on the device to an aperture in the hermetic layer. In a preferred embodiment, one or more patterned titanium layers are formed over the device contact pad, and one or more platinum layers are formed over the titanium layers, such that the top surface of the upper platinum layer defines an external, biocompatible electrical contact for the device. Preferably, the bottom conductive layer is larger than the contact pad on the device, and a layer in the stack defines a shoulder.
1. A method of making a device having an electrical contact, comprising the steps of:
providing an electrical device having a non-biocompatible contact pad,
forming at least one first patterned conductive layer over said contact pad, having a first layer formed on said contact pad;
forming at least one second patterned conductive layer over said first pattered conductive layer, said second patterned conductive layer having a biocompatible top electrical contact surface,
encasing the resulting structure in biocompatible electrical insulator, wherein said biocompatible electrical insulator, said first patterned conductive layer and said second patterned conductive layer from a hermetic seal around the electrical device,
forming an aperture in said electrical insulator to expose said biocompatible top electrical contact surface.
2. The method of claim 1 wherein said step of hermetically encasing the structure in a biocompatible insulator comprises ion beam assisted deposition of a ceramic material.
3. The method of claim 1 wherein the step of forming at least one first patterned conductive layer comprises ion beam assisted deposition of at least one metal.
4. The method of claim 1 wherein at least one of said first patterned conductive layers is titanium or titanium alloy.
5. The method of claim 1 wherein at least one of said second patterned conductive layers is platinum or platinum alloy.
6. The method of claim 1 wherein at least one first patterned layer of titanium and at least one second patterned layer of platinum are formed by beam assisted deposition.
7. The method of claim 1 wherein said first patterned conductive layer is larger than said contact pad such that it extends beyond the edge of said contact pad.
8. The method of claim 1 wherein the step of forming an aperture comprises laser machining.
9. The method of claim 1 further comprising the steps of forming a sacrificial layer over said top electrical contact surface, such that the top electrical contact surface is protected during subsequent processing and, thereafter, removing said sacrificial layer.
10. The method of claim 1 wherein one of said conductive layers defines a shoulder.
11. The method of claim 1 further comprising filling said aperture with metal.
12. The method of claim 1 , wherein the first patterned conductive layer is larger than said second patterned conductive layer.
13. The method of claim 7 , wherein the first patterned conductive layer is larger than said second patterned conductive layer.