A Low Dark Leakage Current High-Sensitivity CMOS Image Sensor With STI-Less Shared Pixel Design

Abstract

A CMOS image sensor with a low dark current and high sensitivity is developed with shallow trench isolation (STI) less shared pixel. By sharing in-pixel transistors, such as the reset transistor, select transistor, and source follower amplifier, each pixel achieves a high fill factor of 43% and a high sensitivity of 144.6 ke <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> /lx · s. In addition, compared with a conventional image sensor which has the STI structure in the pixel for isolation, the developed image sensor achieves a relatively low dark current of 104.5 e <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> /s/pixel (median), corresponding to a current density J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dark</sub> of approximately 30 pA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 60 °C. This is a low value and the consequence of not using STI as pixel isolation. Both types of pixels, namely the conventional and the proposed active pixel sensor have the same pixel size of 7.5 × 7.5 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and are fabricated by the same process. The developed imager with STI-less shared pixel obtains sufficiently good responses at 400 to 900 nm, and, particularly, a peak QE of 68% at 600 nm. This is suitable for scientific applications.