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.