Product / Technology Interview “SWIR Image Sensor”
October 27 2021
Sony publishes an interview with its SWIR InGaAs stacked sensor designers. Few quotes:
“…the miniaturization of SWIR image sensors had been hindered by the use of bump connection. We already knew that this problem could possibly be solved using the Cu-Cu connection*2, which is the stacking technology Sony had developed for years for image sensors. This technology would make it possible to align pixels at a micro-pitch. Meanwhile, conventional image sensors use silicon as a photoelectric conversion layer, but this material does not absorb the SWIR range of light. So, we needed to use indium gallium arsenide (InGaAs) as the photodiode material that can absorb the SWIR spectrum and convert the light energy into electric signals. This material was never used in Sony’s image sensors before, but however, Another division of Sony had the compound semiconductor technology to produce InGaAs.
Another point was that conventional SWIR image sensors had many defects. White patches would appear in the dark image due to the quality issues particular to InGaAs. We had the technology to make compound semiconductors based on our years of expertise in developing laser technology, so we aimed to leverage it in creating defect-free, high-quality products.
As it was the Group’s first-ever SWIR image sensor to be developed using InGaAs, we thoroughly reviewed challenges to be addressed, which resulted in more than 300 in the early stages of the development. As we proceeded further into the development, we found more issues to deal with. There turned out to be so many challenges awaiting.”