In the case of graphene, there is no energy gap for converting valence electrons into free electrons. Therefore, in principle, it can absorb light with any wavelength to turn valence electrons into free electrons. When optical sensors utilizing the properties of graphene are arranged in an array like existing CMOS image sensors, it is possible to realize a multi-spectrum image sensor that can take images on the same optical axis.
Low-cost, high-performance sensor might replace everything
The Advanced Technology R&D Center considers that it is possible to realize a multi-spectrum image sensor having a lower cost and higher performance than existing multi-spectrum image sensors because (1) the material for graphene is carbon, which is inexpensive, and (2) electrons move fast in graphene.
In the case of far-infrared sensors used for thermography, elements called "quantum type" have a high performance. But graphene may have an even higher performance than that in terms of response speed and sensitivity.
The quantum type generally uses special materials and is cooled to several hundred degrees C below zero to reduce the influence of noise. On the other hand, the graphene-based sensor does not need to be cooled.
The Advanced Technology R&D Center expects that the graphene-based sensor will replace all kinds of far-infrared sensors because of multiple excellent properties in the future. Though carbon, which is not used for common CMOS processes, is used for the production of the sensor, the manufacturing process of the sensor itself is a commonly-used process.
The filtering for taking in only light with a specific wavelength can be structurally realized without using an optical method, according to the Advanced Technology R&D Center. Specifically, a bandgap is artificially generated by making graphene have a regular pattern so that the sensor becomes sensitive only to desired wavelengths. Also, there is a method of forming a resonance structure so that the sensor becomes highly sensitive only to lights having specific wavelengths corresponding to resonance frequencies.