Analysis of incomplete charge transfer effects in a CMOS image sensor

A method to judge complete charger transfer is proposed for a four-transistor CMOS image sensor with a large pixel size. Based on the emission current theory, a qualitative photoresponse model is established to the preliminary prediction. Further analysis of noise for incomplete charge transfer predicts the noise variation. The test pixels were fabricated in a specialized 0.18 μm CMOS image sensor process and two different processes of buried N layer implantation are compared. The trend prediction corresponds with the test results, especially as it can distinguish an unobvious incomplete charge transfer. The method helps us judge whether the charge transfer time satisfies the requirements of the readout circuit for the given process especially for pixels of a large size.