Dark current saturation in CMOS image sensors

The dark current in a photodiode limits the use of CMOS image sensor in low noise applications. The dark current is due to the generation-recombination centers present on the surface, space charge region and the bulk. The generation-recombination current depends on the number of active traps present, capture cross-section area of the traps and the operating temperature. In this work we show that the generation-recombination current due to increase in depletion width under transfer gate (TG) does not increase indefinitely and saturates. The saturation of the generation-recombination current is useful in estimating the deep level trap concentration in a CMOS pinned photodiode.