Most attempts to improve the quality of image sensors have focused on making them more sensitive to low light. A newly-developed organic CMOS sensor from Fuji and Panasonic goes in the other direction. It increases the sensor’s saturation level — while at the same time reducing noise. The result is a ground-breaking 88dB of signal-to-noise (s/n), about 12dB above the typical value for conventional silicon sensors.
Higher signal-to-noise means improved dynamic range. The 12dB increase is expected to mean that the new sensor design is capable of gathering four times the light of a traditional design, or about 2 f-stops more dynamic range. That means that a single frame captured using this new sensor design could contain essentially all the same information as a bracket of three images shot at -1, 0 and +1 f-stop exposures. Best of all, of course, that data would be captured in a single instant, making HDR-quality images of action scenes a reality.
Organic sensors explained
Typical camera sensors rely on silicon to trap photons and turn them into electrons. Fujifilm has pioneered the use of organic (carbon-based) compounds to do the same job. It was first granted a patent on the process in 2011, but the partnership with Panasonic is designed to bring the technology to life in a complete sensor implementation. By placing the photosensitive layer on top of the electronics, the organic sensor design is expected to reach a nearly 100% fill factor — the percentage of the surface area sensitive to light — resulting in increased low-light sensitivity.
The increased absorption capability of the organic compounds also results in thinner sensors. The light-sensing layer can shrink from around 3 microns to 0.5 micron. This allows the sensor to capture light from a larger angle of incidence, as shown by the illustration above, providing yet more light sensitivity. The thinner photosites will also make it easier to design lenses, as the need to send light directly down into the photosites of current sensors is one factor driving up the cost of lenses for digital cameras.
In addition to the increased dynamic range shown in this sample image, this image shows that the new sensor also has the potential reducing noise. Its designers are claiming reset noise as low as 3 electrons, well below the typical level for current designs. The combination of higher saturation and lower noise could make organic sensors a clear winner over current silicon-based versions.
Sensor developers from Fujifilm and Panasonic are just presenting their research this week at VLSI 2013 in Kyoto so we’re short on potential product specifics so far. However, if the two companies can deliver on all they are promising this week, it could mark quite an upgrade for future cameras.
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