What is a stacked sensor –and do you actually need one in your camera?

Illustrative image of a stacked image sensor from Canon, with pixels erupting through the lens mount of a Canon EOS R7.

Image sensor design has come a long way in just a few years. Some improvements have been slow, quiet and evolutionary. Others have brought a clear step forward in sensor performance. The latest innovation is ‘stacked sensors’, which have brought a big increase in continuous shooting and video performance. So what is a stacked sensor and how does it work?

Let’s start briefly with BSI, or back-side illuminated sensors. In the old days, all the associated circuitry for sensors ran in and around the light-sensitive photosites that actually captured the light values.