Monday, October 05, 2009

Fujifilm Organic CMOS Sensor

MuTaka has brought to my attention a DPNet article in Chinese on organic image sensors - see comments to Tessera post. Unfortunately, I'm unable to understand most of the article, other than seeing that Fuji is making a good progress in the organic sensors.

Potentially, multi-layered organic sensors can over-perform BSI by a big margin. Their biggest advantage is that the dye absorption could be tuned to have very high QE in each of three colors, crosstalk can be minimized and each pixel location can detect and process all three color signals. Bayer sensors, on the other hand, get only one color per pixel, effectively discarding 2/3 of the incoming signal.

Said all this there are few challenges that organic sensors should overcome on their way to the mass market:
  • Process reproducibility and reliability. So far thin film organic photodiodes experience large variation, in comparison with silicon photodiodes.
  • Large dark current, orders of magnitude higher than Si photodiodes of the same size
  • Noise, primarily kTC noise. It appears that generic 4T pixel architecture used for kTC noise suppression is not applicable for organic sensors. Other techniques for the noise reduction should be developed for them.
If these challenges are solved, multilayered organic sensors would enjoy a bright future.

4 comments:

  1. Thanks image sensor world,
    unfortunately I'm not an Chinese speaker, so I'm not able to translate, but Charlie has a informative comment below Tessera post.
    As far as I understood it, Fuji had succeeded in producing a color picture from the organic sensor. Their test sensor was 1/15" with a 3 micron pixel. The effective image 320*240 pixels. QE is 65%, and with antireflective film surpaces 80%. For a 550nm wave length
    Fuji design is not sensitive to IR so doesn't need IR cut filter.
    The main chalenge is stacking the three layers and the electrodes together. Fuji “needs to make the improvement to the nanometer stamping installment” .
    Hope that someone more knowledgeable can help translating.
    Image sensor world, thanks for the great blog.

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  2. Actually, the previous version of Fujifilm sensor featured in the blog some time ago:

    http://image-sensors-world.blogspot.com/2006/04/fujifilms-organic-image-sensor.html

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  3. Not a sensor professional here, but some more details, hope it helps

    Engineering sample specs

    Pixel pitch: 3.0um
    Optical size: 1/15" (1.2mm diagonal)
    Total array size: 360 x 256 pixels
    Usable array size: 320 x 240 pixels
    Frame Rate: 50 frames/sec
    Full well capacity: 40000e
    Dynamic Range: 60dB
    Dark current: 7e at 60 degrees centigrade, 50fps
    Quantum efficiency: 65% at 550nm
    electron to voltage conversion: 56uV/e
    Pixel fogging?: none
    Image ghosting: cannot be detected using current apparatus
    Organic Layers: - (unknown?, does not include AR film on pixel)
    Pixel fill factor: 85%
    metal layer Structure: 2 polysilicon layers, 4 "wire routing" layers
    1 pixel uses 3 transistors
    Process node: 180nm
    Micro Lens: None

    Some more details of the article. Fuji thinks it would be possible to perform nanoimprint lithography with an additional AR layer to raise the quantum efficiency to 80%

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  4. Thank you for the translation. The table with parameters you translated is a picture, so the automatic translation engines ignore it.
    40Ke full well and 60db DR numbers translate to 40e noise. I think that most of this noise is kTC - the result of 3T pixel architecture.
    Generally, there are quite a few techniques to reduce kTC noise in 3T pixels. All of them assume that the photodiode is a well conducting plane. I'm not sure this assumption is correct in case of organic photodiode. It would be great if somebody can clarify this.

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