Transfer gate effects on the dark current in pinned photodiode image sensors

In this work, we investigate a mechanism of dark current generation under the transfer gate (TRA) in pinned photodiode (PPD) image sensors for science and space applications. It was established that the dark current could change by an order of magnitude depending on the biasing conditions of the TRA and the sense node during integration. This was observed in three sensors with different pixel sizes, made by two different foundries. The results from the characterization work to investigate the source of the dark current are presented. It was discovered that the effect strongly depends on the interplay between the timing and the biasing of the transfer gate and the sense node during reset. Two methods for the reduction of this dark current are proposed and evaluated. The results could help to find the optimal operating conditions of PPD image sensors used in applications where the dark current performance is paramount.