Residual bulk image characterization and management in CCD image sensors

Residual Bulk Image ("RBI") was evaluated in a recently manufactured large format CCD (KAF09000). Operating at -20 C, RBI was observed more than four hours after an image exposure. A number of parameters were measured in an engineering grade CCD including charge trap capacity, filled trap leakout rate, and total trap exhaustion time for temperatures ranging from +10 C to -30 C. A NIR Flood/Flush/Integrate protocol was tested as a candidate to eliminate the RBI by pre-filling the traps and it was found effective at eliminating the RBI as well as the amplifier luminescence observed in non-flooded test exposures. It was also found that the leakage from the pre-filled traps greatly exceeded the thermal dark current over the tested temperature range leading to an increase in the overall dark shot noise. Deep cooling is required to suppress this additional dark noise component. An Arrhenius plot was used to project the required cooling levels as a function of exposure time for various read noise limits. For half hour exposures with a target 5 e- read noise limit, an operating temperature of -87.8 C was indicated. A plot of the maximum operating temperature as a function of exposure time was created from the data.