Graphene sensor claim broadest light spectrum detection

A graphene-based sensor claims to be the first to be able to detect a broad spectrum of light. The device, developed by Assistant Professor Wang Qijie, from Nanyang Technological University's (NTU) School of Electrical & Electronic Engineering, has high photoresponse or sensitivity and can sense visible to mid-infrared light.

These properties make the sensor suitable for different camera types, such as infrared cameras, traffic speed cameras, satellite imaging, etc.

The study said the graphene sensor is 1,000 times more sensitive to light than current low-cost imaging sensors found in today's compact cameras and also uses 10 times less energy as it operates at lower voltages. When mass produced, graphene sensors are estimated to cost at least five times cheaper, the research noted. Graphene is a million times smaller than the thickest human hair (only one-atom thick) and is made of pure carbon atoms arranged in a honeycomb structure. It is known to have a high electrical conductivity among other properties such as durability and flexibility.

Graphene nanostructure explained
Wang came up with the innovative idea to create nanostructures on graphene that will "trap" light-generated electron particles for a much longer time, resulting in a much stronger electric signal. Such electric signals can then be processed into an image, such as a photograph captured by a digital camera.

The "trapped electrons" is the key to achieving high photoresponse in graphene, which makes it far more effective than the normal CMOS or charge-coupled device (CCD) image sensors, explained 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," Wang added.

First of its class
It is believed to be the first time that a broad-spectrum, high photosensitive sensor has been developed using pure graphene, Wang noted. His breakthrough, made by fabricating a graphene sheet into novel nano structures, was published this month in Nature Communications.

"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," said Wang.

While designing this sensor, we have kept current manufacturing practises in mind. This means the industry can in principle continue producing camera sensors using the CMOS (complementary metal-oxide-semiconductor) 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 nano-structured graphene material," Wang noted.

If the technology is adopted by the industry, Wang expects the cost of manufacturing imaging sensors to decrease, eventually leading to cheaper cameras with longer battery life.

The research costs Rs.1.08 crore ($200,000) and was funded by the Nanyang Assistant Professorship start-up grant and supported partially by the Ministry of Education Tier 2 and 3 research grants. It took Wang two years to complete the research. His team consisted of two research fellows, Zhang Yongzhe and Li Xiaohui, and four doctoral students Liu Tao, Meng Bo, Liang Guozhen and Hu Xiaonan, from EEE, NTU. Two undergraduate students were also involved in this ground-breaking work. Wang has filed a patent through NTU's Nanyang Innovation and Enterprise Office for his invention.

The next step is to work with industry collaborators to develop the graphene sensor into a commercial product.