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Proceedings Paper

Active pixel sensors fabricated in a standard 0.18-um CMOS technology
Author(s): Hui Tian; Xinqiao Liu; SukHwan Lim; Stuart Kleinfelder; Abbas El Gamal
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Paper Abstract

CMOS image sensors have benefitted from technology scaling down to 0.35 micrometers with only minor process modifications. Several studies have predicted that below 0.25 micrometers , it will become difficult, if not impossible to implement CMOS image sensors with acceptable performance without more significant process modifications. To explore the imaging performance of CMOS Image sensors fabricated in standard 0.18 micrometers technology, we designed a set of single pixel photodiode and photogate APS test structures. The test structures include pixels with different size n+/pwell and nwell/psub photodiodes and nMOS photogates. To reduce the leakages due to the in-pixel transistors, the follower, photogate, and transfer devices all use 3.3V thick oxide transistors. The paper reports on the key imaging parameters measured from these test structures including conversion gain, dark current and spectral response. We find that dark current density decreases super-linearly in reverse bias voltage, which suggest that it is desirable to run the photodetectors at low bias voltages. We find that QE is quite low due to high pwell doping concentration. Finally we find that the photogate circuit suffered from high transfer gate off current. QE is not significantly affected by this problem, however.

Paper Details

Date Published: 15 May 2001
PDF: 9 pages
Proc. SPIE 4306, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications II, (15 May 2001); doi: 10.1117/12.426982
Show Author Affiliations
Hui Tian, Stanford Univ. (United States)
Xinqiao Liu, Stanford Univ. (United States)
SukHwan Lim, Stanford Univ. (United States)
Stuart Kleinfelder, Stanford Univ. (United States)
Abbas El Gamal, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 4306:
Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications II
Nitin Sampat; Morley M. Blouke; John Canosa; John Canosa; Nitin Sampat, Editor(s)

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