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20 February 2007 Leakage characteristics for the buried photodiode structure on vertical CMOS image sensors
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Proceedings Volume 6502, Digital Photography III; 650206 (2007)
Event: Electronic Imaging 2007, 2007, San Jose, CA, United States
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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Sang-Gi Lee, Su Lim, Chang-Eun Lee, Jeong-Su Park, Sun-Kyung Bang, Sung-Hyun Kang, Russel A. Martin, Sanghoon Bae, and Jin Won Park "Leakage characteristics for the buried photodiode structure on vertical CMOS image sensors", Proc. SPIE 6502, Digital Photography III, 650206 (20 February 2007);

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