Stretchable silicon camera a step closer to artificial retina

Washington, Aug 7 : The human eye has inspired a new technology that is likely to push the limits of photography by producing vastly better images over a wider field of view.

The remarkable imaging device has been made possible by combining stretchable optoelectronics and biologically inspired design like the layout of the eye.

University of Illinois and Northwestern University researchers have developed a high-performance, hemispherical "eye" camera using an array of single-crystalline silicon detectors and electronics, configured in a stretchable, interconnected mesh.

The work opens new possibilities for advanced camera design. It also foreshadows artificial retinas for bionic eyes similar in concept to those in the movie "Terminator" and other popular science fiction.

"Conformally wrapping surfaces with stretchable sheets of optoelectronics provides a practical route for integrating well-developed planar device technologies onto complex curvilinear objects," said John Rogers, professor of materials science and engineering at Illinois, and co-author of the paper.

"This approach allows us to put electronics in places where we couldn't before," Rogers said. "We can now, for the first time, move device design beyond the flatland constraints of conventional wafer-based systems."

The camera's design is based on that of the human eye, which has a simple, single-element lens and a hemispherical detector. The camera integrates such a detector with a hemispherical cap and imaging lens, to yield a system with the overall size, shape and layout of the human eye.

Next, a prefabricated focal plane array and associated electronics - created by conventional planar processing - are transferred from a silicon wafer to the tensioned, drumhead membrane.

When the tension is released, the membrane returns to its original shape. This process compresses the focal plane array, causing specially designed electrical interconnects to delaminate from the rubber surface and form arcs, pinned on the ends by detector pixels.

These deformations accommodate strains associated with the planar to hemispherical transformation, without stressing the silicon, as confirmed by mechanics modelling performed by researchers at Northwestern.

The array package is then transfer printed to a matching hemispherical glass substrate. Attaching a lens and connecting the camera to external electronics completes the assembly. The camera has the size and shape of a human eye.

Over the last 20 years, many research groups have pursued electronic eye systems of this general type, but none has achieved a working camera.

"Optics simulations and imaging studies show that these systems provide a much broader field of view, improved illumination uniformity and fewer aberrations than flat cameras with similar imaging lenses," said Rogers, who also is a researcher at the Beckman Institute and at the university's Frederick Seitz Materials Research Laboratory.

These findings have been reported in Thursday's issue of Nature.