A new photodiode structure with optical window for high-sensitivity complementary metal oxide semiconductor (CMOS) imagers

A new photodiode structure with optical windows fabricated using the 0.35 mum standard logic complementary metal oxide semiconductor (CMOS) process is reported. To enhance the sensitivity of the photodiode covered by the optically opaque silicide layer, optical windows are formed by oxide spacers between polysilicon fingers, which are deposited at the same time as the transistors' polysilicon gate, Cell sensitivity up to 1.6 times higher than that of the control cell has been measured under normal operation conditions, Further sensitivity enhancement can be obtained by optimization of the window area/pixel area ratio. The dynamic range of the imagers can also be improved through the application of positive bias voltage on the polysilicon finger structure.