Characterization and correction of serial deferred charge in LSST camera ITL CCDs

Abstract

Electro-optical testing and characterization of the Vera C. Rubin Observatory Legacy Survey of Space and Time Camera has shown that the focal plane charge-coupled devices developed by Imaging Technology Laboratory exhibit serial deferred charge signal in excess of the expected proportional deferred charge loss from global charge transfer inefficiency. We model the additional deferred charge as resulting from localized charge trapping in the serial register and from a signal-dependent electronic offset effect. A physically motivated forward deferred charge simulation algorithm and a reverse deferred charge correction algorithm were developed in order to correct for deferred charge during data reduction and reduce the possible impacts on Rubin Observatory project science goals. We apply the correction algorithm to calibration data and demonstrate the ability to reduce deferred charge signal measured in the overscan pixel regions and remove the serial pixel correlations resulting from the redistribution of charge between pixel neighbors during readout.