Conventional CMOS cameras
Optics and the capture system are key to digital camera image quality. Today’s CMOS cameras only capture 25% of the incoming light, reducing the quality of the picture (see the figure). Half the loss is in the filter and metal layers, and the other 50% is due to a lack of quantum efficiency.
InVisage looks to capture almost 100% of the incoming light, enabling the CMOS sensor to be significantly more efficient. The company places its QuantumFilm just under the color filter found on camera chips. The film contains quantum dots that are sensitive to light. The design of the dots can be tuned to a particular range of wavelengths.
What Are Quantum Dots?
Alexel Ekimov discovered quantum dots in the early 1980s. Quantum dots are semiconductors whose excitons are confined in three spatial dimensions. The semiconductor properties of quantum dots are based on the size and shape of the crystalline structure of the material.
Quantum dots are very small, allowing higher-resolution cameras that are also more sensitive. The current approach uses a single layer of QuantumFilm that is sensitive to the viewable bandwidth. A multiple-sensor system might have multiple films designed for different bandwidths, with the final image constructed from the combination of sensor input. Quantum dots can handle infrared radiation as well as visible light. A multiple-sensor approach is more efficient in terms of light gathering, but it’s more complex physically.
InVisage’s approach uses a continuous QuantumFilm layer. It surrounds each pixel by using a checkerboard pattern of voltage-biased metal rings. The underlying silicon then detects the voltage changes. Unlike other sensors, the base silicon is not used to detect the light.
InVisage created the technology and has prototype cameras now. The company expects samples in the fourth quarter, so your distributor won’t have these chips yet.