A High Fill-Factor Low Dark Leakage CMOS Image Sensor with Shared-Pixel Design

摘要

We have developed and evaluated the high responsivity and low dark leakage CMOS image sensor with the ring-gate shared-pixel design. A ring-gate shared-pixel design with a high fill factor makes it possible to achieve the low-light imaging. As eliminating the shallow trench isolation in the proposed pixel, the dark leakage current is significantly decreased because one of major dark leakage sources is removed. By sharing the in-pixel transistors such as a reset transistor, a select transistor, and a source follower amplifier, each pixel has a high fill-factor of 43 % and high sensitivity of 144.6 ke~-/lx·sec. In addition, the effective number of transistors per pixel is 1.75. The proposed imager achieved the relatively low dark leakage current of about 104.5 e~-/s (median at 60°C), corresponding to a dark current density J_(dark_proposed) of about 30 pA/cm~2. In contrast, the conventional type test pixel has a large dark leakage current of 2450 e~-/s (median at 60°C), corresponding to J_(dark_conventional) of about 700 pA/cm~2. Both pixels have a same pixel size of 7.5×7.5 μm~2 and are fabricated in same process.