The leakage characteristics of the buried photodiode structure have been investigated in direct color CMOS image
sensor with a stacked photodiode (PD) structure tailored for detecting red, green and blue light. Image quality was
investigated showing that the blue photodiode has surface related effects while the red and green PDs do not. From
these experiments, it is found that the activation energy of PDs display dependence on area, periphery, and corners and
the corner component dominants. Leakage characteristic of PDs show similar behavior to normal n+pwell diode of
similar structure. Also the separate contribution from the area, periphery and corners, and their relationship to STI was
analyzed by TCAD.
For the first time, we have analyzed the vertical buried photodiode structure and found that corner components on red
and green PD can be source of leakage current. We also found that surface contact of blue PD can be a noise source,
reducing image quality. Therefore, to maintain high image quality, the blue photo diode of a CIS has to be designed as
a buried structure and the connections to the buried red and green PDs has to be free from STI sidewall contact.
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