This Small Business Technology Transfer Phase I project proposes development of Novel Ultra-Flexible Integrated Packaging for Intraocular Retinal Stimulators. In these flexible retinal implants ultra-thin silicon chips (<30 mm thick) are fully embedded in thin polyimide flex cables protecting interconnects, connections pads, and cables/leads between chip and flex substrate from the corrosive effects of the biological fluids, a major problem with long-term flexible chronic implants. The ultra-thin CMOS microstimulator chips will be flexible enough to fully implant through a minimal incision, and enable high density retinal stimulation. In Phase I of the project we will demonstrate the fabrication approach and extremely high flexibility of fully encapsulated, ultra-thin Si chips. In our approach, we bond ultra-thin and extremely flexible Si chips directly on a flexible polyimide substrate mounted temporarily on a standard Si carrier wafer. All around encapsulation is achieved by microfabricating a second polyimide layer(s) directly on top of the Si chip / flex cable, thus embedding the chip completely between polyimide layers. This approach eliminates many potentially weak connection points. No solder bumps or underfill materials are used in this process, improving overall biocompatibility and allowing extremely high mechanical flexibility of the structure. The use of a standard carrier wafer during processing allows the fabrication of high density interconnects between the microstimulator and the retinal array using standard microfabrication procedures. The use of ultra-thin Si die (<30 mm thick) provides the whole structure with enough flexibility after release of the carrier wafer to allow the device to be folded/rolled to a radius of < 1 mm. By applying Premitec's proprietary PECVD/polyimide barrier coatings to the outer surfaces, long-term protection of the device and biocompatibility are further improved. The use of a monolithically fabricated structure, including microfabricated interconnects, stimulating array and a fully function CMOS microstimulator can enable the ultimate vision of a fully intra-ocular system with high spatial resolution.Project Narrative ? ? Efforts to develop retinal prostheses are motivated by the need to treat incurable diseases of the outer retina that blind 100,000s of individuals around the world. Age- related macular degeneration (AMD) and retinitis pigmentosa (RP) are leading causes of blindness in the developed world and expected to increase dramatically with aging of the population. Retinal prostheses provide a sense of sight. The prototypes under test only provide crude sensations as of yet, but multiple efforts that are directed at more sophisticated devices hold the promise of providing more visual function. The progress made by us so far with support from NIH and the proposed work have the potential to lead to a successful commercialization of a fully implantable intraocular retinal stimulator and make a real impact on public health. ? ? ?
