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15 May 2001 Active pixel sensors fabricated in a standard 0.18-μm CMOS technology
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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.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Hui Tian, Xinqiao Liu, SukHwan Lim, Stuart Kleinfelder, and Abbas El Gamal "Active pixel sensors fabricated in a standard 0.18-μm CMOS technology", Proc. SPIE 4306, Sensors and Camera Systems for Scientific, Industrial, and Digital Photography Applications II, (15 May 2001);

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