A Fast-Gated CMOS Image Sensor With a Vertical Overflow Drain Shutter Mechanism

Abstract

This paper presents a fast-gated CMOS image sensor (CIS) with a vertical overflow drain (VOD) shutter mechanism. The prototype imager includes two novel features: 1) the adaptation of the VOD shutter structure into a 0.18- $\mu \text{m}$ CIS process and 2) the application of the VOD shutter for the purposes of time-resolved imaging with down to 5-ns pulsewidth. A 360-pixel $\times $ 180-pixel array with several 5.4- $\mu \text{m} \times 5.4$ - $\mu \text{m}$ pixel types was implemented and tested, demonstrating 2-ns shutter rise/fall times and the 1:20 shutter contrast ratio for 850-nm pulsed illumination. These parameters, together with the uniformity of the shutter and the large full-well capacity of the pixel, are on par with the state-of-the-art of indirect time-of-flight and time-resolved imagers. The device structure and the special mode of operation that enables a fast gating are studied through the TCAD simulations and experimental results. Important design features that affect the pixel performance are illustrated in detail.