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In some cases the megapixel count has gone up in Sony CMOS sensors but the pixel size is actually larger.
This is due to CMOS sensors having circuitry surrounding each pixel unlike CCDs. So putting them upside down and thinning them and having the circuitry on the underside saves 40% of space. Also thinner copper wiring
(its typically been aluminium wiring due to reactions in the process)
allows the sensor "stack" (microlenses, pixel light well shaft, cover glass etc) to be thinner allowing more light to be angled in to each pixel.
Other advancements were analogue to digital converters actually on the sensor and not a separate piece of electronics (reduces read noise and why Sony sensors are so good at lifting shadows with no noise). I think there are other tricks to do with a 2nd capacitor with a gate that opens when full well is achieved to increase capacity (and dynamic range) a 2 stage ISO amplification that gives a boost at certain points in the ISO range that increases Dynamic Range at those points. It seems like there is a continual flow of new improvements over the last few years.
For example I read recently that the read noise of my Sony A7r2 42.4mp sensor at one ISO is .8 electrons. No CCD camera matches that. So perhaps CMOS may play a part in future astro cameras?? Are they coming of age?
Greg.
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