Today, Wednesday, the conference part on Cameras and Sensors started. Several interesting papers were presented, but I would like to highlight two of them :
1) Paper from NHK, presented by Ryohei Funatsu, entitled : “Single-chip color imaging for UHDTV camera with a 33M-pixel CMOS image sensor”.
In bullet form, the following key items were mentioned :
– In het ultra-HD project, NHK went from 4 x 8 Mpixels CCD sensors, to 4 x 8 Mpixels CMOS sensors, to 3 x 33 Mpixel CMOS imagers to now 1 x 33 Mpixel CMOS imager,
– The theoretical MTF of a single chip camera is larger than the MTF of a 4 chips solution (nothing was mentioned about the aliasing),
– A new demosaicing algorithm was illustrated (based on directional correlation in G and correlation with green in B and R), based on a 1D 8-taps filter. The results shown were quite impressive compared to other demosaicing algorithms,
– Pixels were still 3T, 3.8 x 3.8 mm2,
– Noise figures and speed were mentioned as well, but I missed them in my notes,
– Camera has 16 output channels,
– The coefficients of the CCM were shown : some large negative numbers off-diagonal.
Nice presentation, but I think that there is still room to improve for this impressive camera : switching to a more advanced pixel structure with pinned photodiodes as well as an improvement of the color filters. Probably some interesting stuff for next year’s conference or for the International Image Sensor Workshop ?
2) Paper entitled : “Optimizing quantum efficiency in a stacked CMOS sensor”, by Lumiense Photonics, HanVision Co., and Alternative Vision Corp. Presentation was done by Dave Gilblom of Alternative Vision Corp.
The basic idea of the sensor is not new : the photodiodes are made in a top layer of Si, the in-pixel transistors in a second layer, and the third layer of silicon contains the last part of the circuitry. What actually surprised me is that 3 small companies took on this very challenging technology, and by the way, are realizing these devices. Within a couple of days, the first silicon is expected. If the predictions can be realized, this is something to watch ! The quantum efficiency was boosted by two actions : an optimized AR layer on top of the diodes to increase the transmission of the incoming light and an optimized coating below the diodes to reflect the light (that is not absorbed in the photodiode) as much as possible back into the diode. Looks all straight forward, but you still have to make it.
Pixels are 7 T (no problem to put a lot of transistors below the actual photo sensitive part), 12 e– noise, 180 ke– full well, 0.18 mm technology, huge quantum efficiency close to 100 % across a wide spectral range, 5 x 5 mm2 pixels and a dark current at room temperature of less than 1 e–/s/pixel. To be honest, this last number I cannot believe. At the end of the talk I deliberately asked to the speaker to confirm this number and he did. But a photodiode lying in the top layer absolutely needs an electric contact to the second layer and this will kill the dark current. Wait and (literally !) see.
Albert, 26-1-2011.