  The traditional characterization of charge transfer inefficiency (CTI) in
charge-coupled devices (CCDs) can suffer from a number of deficiencies: CTI is
often only calculated for a limited number of signal levels, CTI is calculated
from a limited number of pixels, and the sources of CTI are usually assumed to
occur at every pixel-to-pixel transfer. A number of serial CTI effects have
been identified during preliminary testing of CCDs developed by Imaging
Technology Laboratory (ITL) for use in the Large Synoptic Survey Telescope
(LSST) camera focal plane that motivate additional study beyond the traditional
CTI characterization. This study describes a more detailed examination of the
serial deferred charge effects in order to fully characterize the deferred
charge measured in the serial overscan pixels of these sensors. The results
indicate that in addition to proportional CTI loss that occurs at each pixel
transfer, ITL CCDs have additional contributions to the deferred charge
measured in serial overscan pixels, likely caused by fixed CTI loss due to
charge trapping, and an electronic offset drift at high signal.
