Impact of dark current on pinned photo-diode capacitance of CMOS image sensor in low illumination regime

Abstract

Applications for quanta and space sensing both depend on efficient low-light imaging. To precisely optimize and design image sensor pixels for these applications, it is crucial to analyze the mechanisms behind dark current generation, considering factors such as temperature, trap cross-section and trap concentration. The thresholds for these generating effects are computed using optoelectrical technology computer aided design (TCAD) simulations, and the ensuing changes in pinned photo-diode (PPD) dynamic capacitance are observed. Various generation models along with an interfacial trap model are used to compare PPD capacitance fluctuations during light and dark environments. With the use of this comparison study, current compact models of complementary metal oxide semiconductor (CMOS) image sensors can be modified to accurately capture the impacts of dark current in low-light conditions. The model developed through this study demonstrates a deviation of only 6.85% from the behavior observed in physical devices. These results not only enhance our understanding of dark current generation mechanisms but also offer practical applications by improving the performance and accuracy of image sensors.

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