The capability to perceive light was among the first senses to develop in animals and, many species use eyes as their primary sense organs. Blindness continues to be a severe handicap for which there is currently no cure. Researchers from the University of Illinois and Northwestern University, US have now accomplished an important step towards the development of artificial eyes. By combining biologically inspired design and photoelectronic technology, John Rogers and his group have created a spherical camera, based on size, shape, and layout of the human eye, (Ko et al., Nature 454, 748-753, 2008).
The spherical camera simply combines a hemispherical detector with a single imaging lens. To manufacture the detector, scientists have moulded a thin elastomer membrane in the shape of a hemisphere which is then stretched flat, like a drumhead. On this flattened membrane, a matrix focal plane array, formed by conventional planar processing, is applied. The individual pixel elements are single crystalline silicon photodetectors with thin, flexible metal interconnects. When the tension is gradually released, the membrane relaxes back to its initial hemispherical shape, bending the applied array with it. The emerging strain is taken by the thin connecting lines, which delaminate locally from the membrane, forming arcs between the pixel elements, thus leaving them without any significant deformation. The whole arrangement is then transferred to a matching hemispherical glass carrier. This relatively simple manufacturing procedure should allow mass production at costs comparable to those associated with conventional detectors.
“In terms of resolution, the devices that we report have a modest number (i.e. hundreds) of pixels, due only to limitations associated with our academic facilities. Theoretical analysis of the mechanics and initial feasibility tests show that the same approaches can be used with much higher resolution arrays,” says Rogers.