High sensitivity dynamic range enhanced complementary metal-oxide- semiconductor imager with noise suppression

Satoru Adachi, Woonghee Lee, Nana Akahane, Hiromichi Oshikubo, Koichi Mizobuchi, Shigetoshi Sugawa

Research output: Contribution to journalArticle

Abstract

In a high sensitivity complementary metal-oxide-semiconductor (CMOS) image sensor featuring a high conversion gain floating diffusion (FD) with a lateral overflow integration capacitor (LOFIC) in a pixel, the methods of the feedback noise suppression and the FD dark current reduction are discussed. The noise floor is found to be suppressed by introducing a small FD capacitance with the reduced feedback capacitance of a pixel source follower in accordance with a noise feedback theory. The reduction of the full well capacity due to the small FD capacitance causes the reduced tolerance for the FD dark current at the switching point from a low light signal (SI) to a bright light signal (S2). However it is solved by the reduction of the electric field concentrations at the FD in conjunction with the LOFIC capacitance optimization. A 1/4in. video graphics array (VGA) format CMOS image sensor fabricated through 0.18 μm two-poly three-metal process demonstrates both 2.2e- rms noise floor and an invisible signal-to-noise (S/N) ratio degradation at the S1/S2 switching point under 2s integration time while the full well capacity is extended up to 100ke-.

Original languageEnglish
Pages (from-to)2761-2766
Number of pages6
JournalJapanese journal of applied physics
Volume47
Issue number4 PART 2
DOIs
Publication statusPublished - 2008 Apr 25

Keywords

  • CMOS image sensor
  • Dark current
  • High conversion gain
  • High sensitivity
  • Noise reduction
  • Wide dynamic range

ASJC Scopus subject areas

  • Engineering(all)
  • Physics and Astronomy(all)

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