Sony to showcase stacked CMOS image sensor technology with 2-layer transistor pixels
[10:46 Sun,19.December 2021 by Rudi Schmidts]
At the IEEE International Electron Devices Meeting from Dec. 13-15, 2021 in San Francisco, Sony announced that it will be able to almost double the saturation value (FullWell) of a sensor compared to conventional sensors with a new Stacked CMOS image sensor technology. For this purpose, in Sony&s new technology, photodiodes and the associated transistors are no longer arranged next to each other but on top of each other on separate substrates (quasi "chip layers"). At the same time, this separation is also supposed to reduce noise, which together allows a theoretical increase of more than one f-stop to be expected.
In previous stacked sensors, there was already a lot of signal electronics in a layer under the photodiodes and the associated transistors, but the fact that the transistors of the sensor itself now also move one layer deeper seems to bring a lot more, according to Sony.
A doubling of the full well speaks for the fact that up to now about half of the available sensel area consisted of transistors. This could also be advantageous for aliasing, because it should significantly reduce the gaps between the sensors.
Sony explains the significant reduction of the noise as follows:
"Since the pixel transistors (except the transfer gates) (TRG) - reset transistors (RST), select transistors (SEL) and amplifier transistors (AMP) - occupy a photodiode-free layer, the amplifier transistors can be enlarged. By enlarging the amplifier transistors in this way, Sony has been able to significantly reduce noise, which is often a problem, especially when shooting at night or in dark environments."
According to Sony, the pixel structure of this new technology should make it possible to maintain or improve the existing properties of pixels not only at current pixel sizes, but also at smaller ones. Sony also emphasizes elsewhere that it primarily sees the advantages of this new technology in the smartphone sector. Thus, Sony should first use the increased dynamics to let smartphones catch up even closer to large sensors. Which is not incomprehensible, since the smartphone market is certainly at least a power of ten higher in terms of units. But what is not yet in the large sensor sector can (also) still come.
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