Stacked Sensor

A stacked sensor bonds a dedicated memory and processing layer directly to the back of the image sensor die. This is distinct from a standard BSI sensor, where the wiring sits behind the photodiodes but no additional processing layer is present. By placing high-speed DRAM or logic circuitry in direct contact with the sensor, a stacked design allows the sensor to read out its data far faster than a standard sensor that must transfer data through a slower interface to a separate processor.

The primary benefit of faster readout is reduced rolling shutter distortion. In electronic shutter mode, a sensor reads pixel data line by line from top to bottom. If this process is slow relative to subject or camera movement, the top and bottom of the frame are captured at different moments, causing vertical lines to lean and fast-moving subjects to appear distorted. A stacked sensor reads so quickly that there is little time for movement between the first and last lines, dramatically reducing this effect.

In M43, the OM System OM-1 and OM-1 Mark II use stacked BSI sensors. The OM-1 Mark II's stacked sensor enables up to 120fps electronic shutter burst, 50MP handheld high-res shooting, and the fast readout required for Pro Capture at high frame rates. The Panasonic G9 II and GH7 also use stacked sensor designs, enabling their phase-detect AF systems and high-speed burst capabilities. Stacked sensors are more expensive to produce than standard BSI sensors, which is reflected in the higher price of cameras that use them.