Instead of using a flat microchip as the light sensor for their new camera,
a team of engineers has developed a sensor that is a flexible mesh of wire-connected
pixels.
The mesh is made from many of the same materials as a standard digital-camera
sensor, but has the unique ability to conform to convoluted, irregular surfaces.
The technology is already showing promise for photography, as the researchers
conformed the array to a hemispherical shape and incorporated the device into
a working eye-like camera. The new system eliminates some of the aberrations
caused by current camera designs and improves the quality of captured images.
Researchers are testing the same design principles in a range of other applications,
including as a thin, conformable monitor to detect electrical signals traveling
across the undulating surface of the human brain.
Led by John Rogers of the University of Illinois at Urbana-Champaign and Yonggang
Huang of Northwestern University in Evanston, Ill., the researchers announced
their findings Aug. 7, 2008, in the journal Nature.
"This research is truly transformative," said Ken Chong, advisor
in the National Science Foundation
(NSF) Engineering Directorate, who is one of the officers overseeing the
researchers' NSF grant. "Using simple mechanics principles, the researchers
have produced, for the first time, electronic devices on a hemispherical surface
so that they can take images much like those captured by the human eye."
The technology breakthrough is a novel approach that bypasses a traditional
planar sensor of adjacent pixels and instead relies upon an array of pixels
interconnected by small wires. Using a flexible, temporary backing, the researchers
can form the array into a curved shape and then transfer the array to its permanent
location affixed to a glass lens.
Over the last 20 years, many researchers have tried to manufacture such electronic
eye systems, but until now, none were able to create a working camera.
"This strategy opens up exciting, new engineering design possibilities
by eliminating the two dimensional, planar constraints of conventional, semiconductor
wafer-based optoelectronics," said John Rogers, Flory-Founder Chair Professor
of Materials Science and Engineering at University of Illinois at Urbana/Champaign.
While a flat, planar sensor cannot flex without damaging its light-sensitive
pixels, the new technology puts the strain on the wires, each flexing as much
as 40 percent. Since the wires absorb the strain, the pixels are barely stressed,
even when affixed to the retina-shaped housing of the new experimental camera.
Conventional digital cameras use planar chips based on rigid, brittle semiconductor
wafer substrates that fracture at strains of less than 1 percent.
"Mechanics helps to reduce the stresses and strain in components, and
guide and optimize the system design," said Yonggang Huang, Joseph Cummings
Professor of Civil and Environmental Engineering and Mechanical Engineering,
Northwestern University, who worked with his team to model the mechanical properties
of the design so that it could be manufactured.
The current sensor array includes only 256 pixels, but because the technology
is based on established materials and manufacturing processes, the researchers
ultimately expect more sophisticated sensors in higher density arrays. The same
approaches can be used for nearly any class of semiconductor electronic device
for a range of functions such as sensing, actuating and computing.
"We believe that some of the most compelling areas of future application
involve the intimate, conformal integration of electronics with the human body,
in ways that are inconceivable using established technologies," said Rogers,
who is also affiliated with the Beckman Institute for Advanced Science and Technology
and the Frederick Seitz Materials Research Laboratory. "We are working
actively with collaborators to explore possibilities in advanced health monitors,
prosthetic devices and therapeutic systems.