First double-layer transistor: Sony introduces new stacked CMOS image sensor technology

Sony Semiconductor Solutions has successfully developed the world’s first stacked CMOS image sensor using double-layer transistor pixel technology. It is reported that the traditional solution requires the photodiode and the pixel transistor to be placed on the same substrate, while Sony’s new technology separates the two on different substrate layers. Thanks to the almost doubled saturation signal level and the increase in dynamic range/decrease in noise, the new solution can significantly improve imaging performance.

In the pixel chip, the diode responsible for photoelectric signal conversion and the pixel transistor for controlling the signal are located on the same layer. In traditional stacked CMOS image sensors, photodiodes and pixel transistors are arranged on the same substrate.

In the same or smaller pixel size, the new technology pixel structure (located on the logic chip of the signal processing circuit) can maintain or improve the existing characteristics.

In addition, manufacturers are allowed to optimize the two-layer structure of the photodiode and the pixel transistor respectively, so that the saturation signal level is approximately doubled compared with the traditional image sensor, and the dynamic range is further improved.

The increased saturation signal level plays an important role in realizing high-quality images with a wide dynamic range.

The pixel transistors outside the transmission gate (TRG)-including reset (RST), select (SEL) and amplifier (AMP) transistors-are arranged on the photodiode layer.

Thanks to the increase in the size of the amplifier transistor, Sony has also successfully reduced the noise that is easily generated at night and other darker scenes, while preventing overexposure or underexposure under strong sensitive contrast conditions.

Finally, Sony will push the dual-layer transistor pixel technology with higher image quality to many areas, such as mobile image sensors on smartphones.