Digital BW, The Print

> From: Austin Franklin [mailto:darkroom@...]
>
> I'm not sure about what sensors you are specifically talking
> about, but the
> sensor arrays I've designed and designed with, are purely monochromatic
> sensors, and the Bayer pattern filter of the same "pitch" is simply placed
> on top of the sensor array (and affixed by a mechanical means, or
> adhesive).
>
> It certainly does make sense that the manufacturing process be done as you
> say for sensors that have any decent volume, since the primary
> use today is
> color w/ a Bayer pattern filter, so I don't doubt what you say
> about *some*
> sensors, I've just not physically seen one.
>
> Here is a decent overview of the color filter array:
>
> http://www.fillfactory.com/htm/technology/htm/rgbfaq.htm
>
> and they do clearly say:
>
> "The most widespread method to give RGB color sensitivity to image sensors
> is the application of a color filter mosaic array (CFA) on top of a
> black&white imager."
>
> Now, how the color filter mosaic array is "applied" to the top of the
> black&white imager is left to question.

I'm not denying that the underlying sensor is monochrome, and that the color
sensitivity is achieved with filters. I'm only skeptical that the filters
aren't built as part of the chip. For sensors with big pixels, the filter
may be separate, but the pixel pitch on a pro digicam is about 7 microns,
and on a typical consumer camera, it's much smaller. I don't see how they
could possibly build a separate filter, and then stick it to the IC with
micron-level alignment. The filter would have to be thinner than the pixel
pitch, which would make it a fraction of the thickness of ordinary plastic
wrap.

The link you provided (which is very interesting) mentions the use of
polymers for filters. I would think they'd be deposited right on the chip,
and then photo-etched away, because this would be an extension to the normal
semiconductor processing. If this is true, they might still be removable, if
you could find the right solvent.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...