Canon working on a three-layer sensor - The world of photography

Reminder: light penetrates slightly opaque materials before being absorbed. The depth of penetration varies with the wavelength, for example, silicon, blue penetrates less than half a micron while red happens to two to three microns below the surface. Placing photodiodes different depths, so they capture different wavelengths.

long known, this principle is operated since 2002 by the Foveon sensors fitted to cameras Sigma. Each photosite three diodes are stacked, the surface capturing a rather bluish light, that of absorbing green areas and background receiving only red. The main interest is to remove the demosaicing, causing various artifacts (moire in particular), and low-pass blurs the details to mitigate these adverse effects filter.

Sony diagram showing the depths of capture for blue, green and red.

There are however two drawbacks: the dispersion of the red wire penetration into the silicon, which makes them particularly sensitive to this little color sensors, and the complexity of the electronics, which complicates the capture of light and increases digital noise. Sigma devices are well known to lose as quickly past 800 Iso despite APS-C sensors.

Sony and Canon to attack

This does not prevent other manufacturers work on the subject. If the multi-layer came to the sensitivity of ordinary sensors, the benefits would indeed important, especially in the rendering of textures and materials.

Sony has introduced in the end of 2012 a patent system combining three layers and etching BSI, the firm control particularly well to improve overall sensitivity.

Now it’s time for Canon to patent tri-layer sensor. Canon’s solution is not BSI category diodes remain below the readout electronics, which can in principle the same problems as the Foveon sensors. However, an irregular crystal placed on the red layer would reduce the dispersion and thus maintain a good capture warm tones.

First Experience

patent attracts more attention than the Sony, probably for one simple reason: it is more likely to be the subject of a real application one day. Large companies settle indeed thousands of patents every year, and only a small fraction of them actually happens in sales. However, Canon makes and already uses multi-layer sensors …

cell iFCL Canon EOS 5D Mk III Document:. Canon

There is no CMOS imagers, but cell light measurement: the iFCL sensor appeared in the EOS 7D and again since on many cameras, until recent EOS 700D and EOS 100D. This is a bi-layer, separating the red-green and light blue-green light in order to reduce the hyper-sensitivity of conventional red cells. The experience of Canon in the industrialization of light sensors multilayer therefore makes plausible the arrival on the market of competitors Foveon imagers.

course, it is time for that speculation. But after the onset of X-trans matrix at Fujifilm, the limits of Bayer are obvious and probably the manufacturers they work hard to more satisfactory solutions …