CMOS active pixel sensor with improved dark current and sensitivity

摘要

An active pixel sensor which provides reduced dark current, improved sensitivity, and improved modulation transfer function. An N well, surrounded by a P well is formed in a P type epitaxial substrate. A P⁺ region is formed extending from within the P well into the substrate leaving a gap between the P⁺ region and the N well. A gate dielectric is formed covering at least the gap, part of the P⁺ region, and part of the N well. A gate electrode is formed on the gate dielectric over the gap, part of the P⁺ region, and part of the N well. The gate electrode is biased so that the region of the substrate under the gate electrode is accumulated with holes and the region of the N well under the gate electrode is depleted of electrons. This will reduce the dark current and improve the sensitivity of the active pixel sensor. In a second embodiment the P type epitaxial substrate is replaced by an N type epitaxial substrate, the N well is replaced by a P well, N⁺ regions are replaced by P⁺ regions, and P⁺ regions are replaced by N⁺ regions. In this second embodiment the gate electrode is biased so that the region of the substrate under the gate electrode is depleted of electrons and the region of the P well under the gate electrode is accumulated with holes.