Graphene-based image sensor to enhance low-light photography
A team of scientists at Nanyang Technological University (NTU) in Singapore has developed a new image sensor from graphene that promises to improve the quality of images captured in low light conditions. In tests, NTU claims it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy.
The new sensor is able to detect broad spectrum light, from the visible to mid-infrared, with great sensitivity. This will make it ideal for use in all types of cameras, including infrared cameras, traffic safety cameras, satellite imaging, and more. According to NTU, this technology will allow photographers to take much clearer images in harsh lighting conditions and, when mass produced, estimates are that graphene sensors will be up to five times cheaper than camera sensors today.
The research was led by Assistant Professor Wang Qijie from NTU’s School of Electrical & Electronic Engineering and has been ongoing for two years. “We have shown that it is now possible to create cheap, sensitive and flexible photo sensors from graphene alone. We expect our innovation will have great impact not only on the consumer imaging industry, but also in satellite imaging and communication industries, as well as the mid-infrared applications,” says Wang,
What is clearly exciting for the camera industry is how little needs to be done to introduce graphene to existing CMOS sensors.
“While designing this sensor, we have kept current manufacturing practices in mind," explains Asst. Prof Wang. "This means the industry can in principle continue producing camera sensors using the CMOS process, which is the prevailing technology used by the majority of factories in the electronics industry. Therefore manufacturers can easily replace the current base material of photo sensors with our new nanostructured graphene material.”
Graphene is a material composed of pure carbon with atoms arranged in a regular hexagonal pattern. It is a one-atom thick layer of the mineral graphite, a million times smaller than the thickest human hair and is known to have a high electrical conductivity and is very light, with a 1-square-meter sheet weighing only 0.77 milligrams.
Asst. Prof Wang has devised a novel way to create nanostructures on graphene which "trap" light-generated electron particles for a longer period of time, translating into a stronger electrical signal. These electrical signals are then processed into an image, such as a photograph captured by a digital camera.
The "trapped electrons" are the key to achieving high photoresponse in graphene, which makes it far more effective than the normal CMOS or CCD image sensors, said Asst Prof Wang. Essentially, the stronger the electric signals generated, the clearer and sharper the photos.
"The performance of our graphene sensor can be further improved, such as the response speed, through nanostructure engineering of graphene, and preliminary results already verified the feasibility of our concept," Asst. Prof Wang says.
Why is this so exciting for the photography industry? Camera ISO is one of the three pillars of photography (the other two being aperture and shutter speed). In simple terms, ISO is the level of sensitivity of your camera’s image sensor to available light. The majority of people taking pictures have probably never adjusted the ISO setting on their cameras so here is an explanation. Essentially, a lower ISO setting reduces your cameras sensitivity to light creating higher quality images, while a higher ISO number increases sensitivity and your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at a cost – it adds grain or “noise” to the pictures.
Of course, not all grain is bad and we often see creative uses of it in black and white photography. But if you are a sports photographer shooting in a poorly lit indoor stadium, in order to freeze action, you have to shoot with a wide aperture (f 2.8 or lower) and try to keep your shutter speed above 500. The only way to do this is to increase ISO and live with the resulting grainy pictures. Asst. Professor Wang’s graphene sensor, being more sensitive, will negate the need to increase ISO in low light settings.
Canon and Nikon in particular, have been battling each other to develop the highest ISO levels with the least grain since the beginning of digital photography and no doubt “wires are buzzing" with these new developments. Asst. Prof Wang has already filed a patent through NTU’s Nanyang Innovation and Enterprise Office for his invention and plans to find industry partners to develop the graphene sensor into a commercial product. Our senses tell us that he won't have to look too far.
The NTU team's paper appears in the journal Nature Communications.