Curiosity: Sony now lists the partially stacked sensor of the Nikon Z6III on their website
Sony officially listed the Nikon Z6III 24MP sensor on their website. We should soon be able to download the PDF file containing all detailed specs. What’s interesting is that this is the only sensor listed that has “CoW BI” technology.
This is an explanation of the tech using Gemini AI:
Usually, manufacturers use WoW (Wafer-on-Wafer) bonding. They take an entire silicon wafer full of pixel arrays and permanently press it against an entire silicon wafer full of logic circuits, and then cut them into individual sensors-
CoW (Chip-on-Wafer) changes this. Instead of pressing two giant, uncut wafers together, Sony dices one of the wafers into individual chips first. They then bond those individual, pre-cut chips onto the larger, uncut wafer[5][6].
Why is CoW BI important?
Moving to a Chip-on-Wafer approach provides Sony with several massive advantages for modern cameras:
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Size Mismatching: In large sensors (like Full-Frame or Medium Format cameras), the physical pixel array is massive. If you use standard Wafer-on-Wafer bonding, the logic chip bonded beneath it also has to be massive to match its physical footprint, which wastes incredibly expensive silicon. CoW allows Sony to attach a small logic/memory chip to a large pixel sensor[7].
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Higher Yields (Known Good Die): With Wafer-on-Wafer, if a logic chip on the bottom wafer is defective, it ruins the perfectly good pixel sensor bonded above it. With CoW, Sony can test the individual chips first and only bond the “Known Good Dies” to the expensive pixel wafer, drastically reducing manufacturing waste and lowering costs[5].
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Insane Readout Speeds & Global Shutters: CoW allows Sony to optimally position specific functional chips (like Advanced A/D converters or DRAM memory) directly on top of the pixel wafer using microscopic Copper-to-Copper (Cu-Cu) hybrid bonding This allows for massive parallel data transfer, which is how Sony achieves features like completely distortion-free Global Shutters (such as their 127-megapixel IMX661 industrial sensor) and the hyper-fast readout speeds required for 8K and 120fps+ video.
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Adding Edge AI: Because they are stacking individual chips, Sony can stack specialized processors—like dedicated AI edge-processing chips—directly onto the sensor to analyze images before the data even reaches the camera’s main processor.
In short, CoW BI is an advanced 3D packaging technique that allows Sony to build smarter, faster, and more complex stacked sensors while keeping manufacturing defects and costs under control.
