October 14, 2015
At Dartmouth’s Thayer School of Engineering, Professor Eric Fossum and doctoral student Jiaju Ma have developed a new pixel with dramatically improved low-light sensitivity. Fossum, who invented the CMOS image sensor used in most cellphones and digital cameras, worked with Ma for more than three years before publishing results of their new Quanta Image Sensor (QIS) in an IEEE publication. Among the applications for the new sensor are security cameras, astronomy and life science imaging.
Phys.org suggests the sensor could be used for other low-light applications in photography or the Internet of Things.
“The photons go into the semiconductor [the sensor chip] and break the chemical bonds between silicon atoms and, when they break the bond, an electron is released,” explains Fossum. “Almost every photon that comes in makes one electron free inside the silicon crystal. The brighter the light, the more electrons are released.”
The new kind of pixel is so sensitive that it can see one electron above all the background noise, without “resorting to extreme measures such as cooling the sensor to -60 C and/or avalanche multiplication,” says Fossum, who notes that one challenge in QIS is to count “how many electrons are set free by photons and thus effectively count photons.”
The new pixel is much smaller than those that are standard today, since each one is designed to sense only one photon. The goal is to have 1 billion pixels on the sensor in the same form factor, according to Ma.
Fossum also thought about backwards compatibility for the new pixel (and hence the new sensor). “We deliberately wanted to invent it in way that is almost completely compatible with today’s CMOS image sensor technology so it’s easy for industry to adopt it,” he says.
Fossum is also intent on figuring out how to “build this in a current, commercially accessible, not-too-expensive CMOS process.” Fossum and Ma are working out other issues, and consider QIS at a “proof of concept” stage.