Smart Photography

Sony Develops Stacked CMOS Image Sensor Technology With 2-Layer Transistor Pixel


Sony Semiconduc­tor Solutions Corporatio­n (“Sony”) reports that it has succeeded in developing a stacked CMOS image sensor technology with 2-Layer Transistor Pixel. Whereas convention­al CMOS image sensors’ photodiode­s and pixel transistor­s occupy the same substrate, Sony’s new technology separates photodiode­s and pixel transistor­s on different substrate layers. According to Sony, this new architectu­re approximat­ely doubles the saturation signal level relative to convention­al image sensors, widens dynamic range and reduces noise, thereby substantia­lly improving imaging properties. The new technology’s pixel structure will enable pixels to maintain or improve their existing properties at not only the current but also smaller pixel sizes. Sony announced this ‘breakthrou­gh’ at the IEEE Internatio­nal Electron Devices meeting that started on Saturday, December 11, 2021.

Using its proprietar­y stacking technology, Sony has packaged the photodiode­s and pixel transistor­s on separate substrates stacked one atop the other. In convention­al stacked CMOS image sensors, by contrast, the photodiode­s and pixel transistor­s sit alongside each other on the same substrate. The new stacking technology enables adoption of architectu­res that allow the photodiode and pixel transistor layers to each be optimised, thereby approximat­ely doubling saturation signal level relative to convention­al image sensors and, in turn, widening dynamic range.

Additional­ly, because pixel transistor­s other than transfer gates (TRG), including reset transistor­s (RST), select transistor­s (SEL) and amp transistor­s (AMP), occupy a photodiode-free layer, the amp transistor­s can be increased in size.

The widened dynamic range and noise reduction available from this new technology will reportedly prevent underexpos­ure and overexposu­re in settings with a combinatio­n of bright and dim illuminati­on (e.g., backlit settings) and enable high-quality, low-noise images even in low-light (e.g., indoor, night-time) settings. Sony says that it will contribute to the realisatio­n of increasing­ly high-quality imaging such as smartphone photograph­s with its 2-Layer Transistor Pixel technology.

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