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Monolithic CMOS cameras for direct imaging in electron microscopy and other radiation imaging applications have been developed and have been used to capture images with high signal to noise and resolution. Based on CMOS Active Pixel Sensor (APS) technology, the arrays use an 8 to 20 mum epitaxial layer that acts as a thicker sensitive region for the liberation and collection of ionization electrons resulting from impinging charged particles. This results in a 100% fill factor and a far larger signal per incident charged particle than a typical CMOS photodiode could provide. The per-pixel CDS scheme discussed in this paper has demonstrated reductions in kT/C noise by a factor of four, to 11 electrons RMS at room temperature. The CDS scheme requires only one read instead of the two reads plus pre- and post-integration subtraction required by traditional CDS, and is hence faster than alternate schemes. In addition, the test device was used in the observation of Random Telegraph Signal noise (RTS) in small-capacitance pixels under different V gs conditions.
Date of Publication: June 2009