Sony's Partially Stacked Sensor Utilizes New CoW-BI Technology

According to Sony Alpha Rumors, Sony Semiconductor has officially announced its 24-megapixel partially stacked sensor on its website. This sensor is used in the Panasonic LUMIX S1ii and Nikon Z63 cameras. Sony did not list the 33-megapixel partially stacked sensor used in the Sony A7M5, as it is exclusive to the Alpha product line. Sources indicate this exclusivity will continue until 2027, after which Nikon and other companies are expected to be able to use the same sensor.

Interestingly, this is the only listed sensor employing "CoWBl" (Chip on Wafer Back-illuminated CMOS Image Sensor) technology. Unsurprisingly, the 33-megapixel sensor in the Sony A7M5 also uses this new technology.

Typically, manufacturers use WoW (Wafer-to-Wafer) bonding technology. They permanently bonded a complete silicon wafer containing the pixel array to a complete silicon wafer containing the logic circuitry, and then diced them into individual sensors. CoW (Chip-to-Wafer) technology changed this. Instead of bonding two huge, uncut wafers together, Sony first diced one wafer into individual chips. These pre-diced individual chips were then bonded to the larger, uncut wafer.

Why is CoW BI technology important? Size mismatch: In large sensors (such as full-frame or medium-format cameras), the physical pixel array is very large. If standard wafer-to-wafer bonding were used, the logic chip bonded underneath would also have to be equally large to match its physical size, wasting extremely expensive silicon. CoW technology allows Sony to attach a small logic/memory chip to a large pixel sensor.