Abstract
Fundamental limits for photon counting and photon energy measurement are reviewed for CCD and CMOS imagers. The challenges to extend photon counting into the visible/nIR wavelengths and achieve energy measurement in the UV with specific read noise requirements are discussed. Pixel flicker and random telegraph noise sources are highlighted along with various methods used in reducing their contribution on the sensor’s read noise floor. Practical requirements for quantum efficiency, charge collection efficiency, and charge transfer efficiency that interfere with photon counting performance are discussed. Lastly we will review current efforts in reducing flicker noise head-on, in hopes to drive read noise substantially below 1 carrier rms.
Highlights
Silicon CCD and CMOS imagers have been demonstrated to be exceptional detectors for particle counting and energy measurement for some time
The technology coined floating gate “Skipper” long ago Nondestructive floating gate readout schemes have worked in a straightforward fashion in can theoretical achieve any desired noise level as the read noise decreases by the square-root of the producing sub carrier noise performance assuming there are no restrictions involving frame time number of samples taken for each pixel [2]
It could be tough going in lowering the “average” read noise substantially below 1 carrier rms because of the 1/f noise wall
Summary
Silicon CCD and CMOS imagers have been demonstrated to be exceptional detectors for particle counting and energy measurement for some time. The spectral range where photon counting is possible covers an extensive wavelength range from 0.1 to 1000 nm (1.24 to 12,400 eV), i.e., nIR, visible, UV, EUV and soft X-ray. Where 3.65 is an experimentally determined constant for silicon (eV/carriers) and ni is measured quantum yield (carriers generated/interacting photon). The formula is not useful for energies less than this because the constant 3.65 wildly fluctuates Besides photons, this equation is useful for any particle that ionizes silicon atoms (electrons, protons, muons, etc.). The uncertainty in energy measurement is limited by the detector’s read floor and Fano noise. 22 of of 17 showing be covered by an imager for aa given read noise floor.
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