TechFront Research and Development in Manufacturing and Technology
Graphene-Based Light Detectors Add Thermal Vision to Contact Lenses
N
ew research into graphene-based light detectors that can use the full infrared spectrum has the potential to put heat-vision technology into a contact lens or other devices. And unlike the mid- and far-infrared detectors currently on the market, the detector developed by University of Michigan (Ann Arbor, MI) engineering researchers doesn’t require bulky cooling equipment to work. Thermal imaging is widely used today in military applications for night-vision goggles and cameras, and it’s even made some headway into high-end automotive systems, like the night-vision technology from BMW and other carmakers. Infrared light starts at wavelengths just longer than those of visible red light and stretches to wavelengths up to a millimeter long. “We can make the entire design super- thin,” said Zhaohui Zhong, University of Michigan assistant professor of electrical and computer engineering. “It can be stacked on a contact lens or integrated with a cell phone.” Defense applications for the technology include communications, IR imaging and de- tectors for heat-seeking missiles, said Zhong. “Currently, we are working on making an imaging camera using the graphene photodetector array, and I estimate a prototype camera within the next three years.” Infrared vision may be best known for spotting people and animals in the dark and heat leaks in houses, but it can be used by doctors to monitor blood flow, to identify chemicals in the environment, or to allow seeing an artist’s original sketch under layers of paint.
single layer of carbon atoms, could sense the whole infrared spectrum—plus visible and ultraviolet light—but until now, it hasn’t been viable for infrared detection because it can’t capture enough light to generate a detectable electrical signal. With one-atom thickness, it only absorbs about 2.3% of the light that hits it, and if the light can’t produce an electrical signal, graphene can’t be used as a sensor.
A schematic of the new graphene photodetector device that could add infrared detection to military applications or in contact lenses, cell phones and imaging cameras.
Unlike the visible spectrum, which conventional cameras capture with a single chip, infrared imaging requires a com- bination of technologies to see near-, mid- and far-infrared radiation all at once. The mid-infrared and far-infrared sensors typically need to be at very cold temperatures. Graphene, a
“The challenge for the current generation of graphene- based detectors is that their sensitivity is typically very poor,” Zhong said. “It’s a hundred to a thousand times lower than what a commercial device would require.” Zhong and Ted Norris, the Gerard A. Mourou Professor of Electrical Engineering and Computer Science, worked with graduate students to design a new way of generating the electrical signal. Rather than trying to directly measure the electrons that are freed when light hits the graphene, they am- plified the signal by looking instead at how the light-induced electrical charges in the graphene affect a nearby current. The device is described in a paper titled “Graphene photo- detectors with ultra-broadband and high responsivity at room
May 2014 |
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Image courtesy Zhaohui Zhong/University of Michigan
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