Low Gr/Gb sensitivity imbalance 3.2M CMOS image sensor with 2.2μm pixel

For CMOS image sensors with pixel size under 3μm pixel, the pixel architecture in which several photodiodes share floating diffusion and transistors tends to be adopted in order to improve full well capacity and sensitivity. In spite even in the aforementioned advantage, adoption of the architecture may result in sensitivity imbalance between the shared photodiodes. On reproduced images obtained by the shared pixel architecture, sensitivity imbalance between Gr and Gb photodiodes in Bayer CFA is often conspicuous, because the imbalance results in horizontal pattern noise. We developed a low Gr/Gb sensitivity imbalance 3.2M CMOS Image Sensor with 2.2μm pixel. The pixel has the structure which is optically designed carefully in order to prevent light diffraction in pixel. According to a simulation result, read transistor gate for pixels with red color filter has an edgeless layout, because longer wave length light incident to the red pixels. For the optical design, electromagnetic analytical simulation was used because wave-optical effect cannot be ignored for the small pixel below 3μm. Gr/Gb sensitivity imbalance was measured for both the developed sensor and conventional sensor in visible light range. It was measured that the Gr/Gb sensitivity imbalance is below measurement limit.