Per-Pixel Dark Current Spectroscopy Measurement and Analysis in CMOS Image Sensors

Eric A. G. Webster, Robert L. Nicol, Lindsay Grant, David Renshaw

Research output: Contribution to journalArticlepeer-review


A per-pixel dark current spectroscopy measurement and analysis technique for identifying deep-level traps in CMOS imagers is presented. The short integration time transfer gate subtraction experimental technique used to obtain accurate results is described and discussed. The activation energies obtained for molybdenum (approximate to 0.3 eV), tungsten (approximate to 0.37 eV), and the phosphorus-vacancy (E-center) (approximate to 0.44 eV) trap levels in silicon match published results measured with other techniques. The Meyer-Neldel Relationship (MNR) was observed between the Arrhenius preexponential frequency factor and activation energy. The trap capture cross-sectional calculation methodology using the MNR is presented. The cross sections of molybdenum, tungsten, and the E-center were calculated as approximate to 1 x 10(-16) cm(2), approximate to 1.5 x 10(-16) cm(2), and approximate to 2.5 x 10(-16) cm(2), respectively, at 318 K. The data obtained suggest electric field enhanced emission, and Poole-Frenkel barrier force lowering of E-center defects occurs in the pinning implant regions. It is proposed that a changing Fermi level results in the correct activation energies being obtained below half the band gap and that the dark current measurement process is affected by the measurement time result of statistical mechanics. It is also tentatively suggested that, in this case, the observed MNR is a geometric relationship and not due to a physical process.

Original languageEnglish
Pages (from-to)2176-2182
Number of pages7
JournalIEEE Transactions on Electron Devices
Issue number9
Publication statusPublished - Sep 2010

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