WORKSHOP PAPER
A High QE, Fast Shuttered CMOS Image Sensor with a Vertical Overflow Drain Shutter Mechanism
Abstract
This paper presents a prototype CMOS image sensor with a fast global shutter based on the Vertical Overflow Drain (VOD) shutter mechanism. The imager presents several novel features: First, the adaptation of the VOD shutter mechanism previously used exclusively in CCDs into a 0.18-µm CMOS image sensor process. Second, the application of the VOD shutter for purposes of fast gating with several nanosecond pulse widths. Measurement results of the novel imager show fast shutter efficiency of 1:100 which to an unprecedented measured modulation contrast (MC) of 98%. The measured rise and fall times of 2ns and minimal measured shutter width of 5ns are in line with the state of the art for indirect Time-of-Flight (TOF) image sensors. These fast gating times, equivalent to modulation frequency higher than 100MHz, can be reached without reduction in the modulation contrast due to the novel shutter mechanism. The prototype pixel was designed and fabricated with special emphasis on high IR QE, featuring a deep photodiode with simulated internal QE of up to 19% for 850nm illumination. In this work the device structure and special mode of operation, that enables fast shutter operation, are studied through TCAD simulations and experimental results. Important design features that influence the pixel performance are illustrated in detail.Keywords
CMOS image sensor, Vertical Overflow Drain, Time-of-Flight,References
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