Optimization of Device Clocking Schemes to Minimize the Effects of Radiation Damage in Charge-Coupled Devices

Abstract

The European Space Agency Euclid mission aims to answer the question of how the universe originated through the mapping of the dark Universe. One method to investigate this geometry is to measure subtle changes in ellipticity using image sensors such as the charge-coupled device (CCD). However, the radiation environment in space plays a major part in the performance of CCD-based camera systems. When placed in space, a CCD becomes damaged by the radiation environment, and this can lead to a “smearing” of the charge, acting to change the ellipticity, and therefore, one must be able to separate the changes in ellipticity caused by radiation damage from those the mission aims to measure. To this end, the radiation-damage-induced shape changes require an in-depth investigation such that optimized operation can be achieved. A Monte Carlo simulation is being used to predict this impact, backed by experimental data from a detector formerly baselined for the mission. During the experimental study, an investigation was undertaken into the serial readout of the CCD to demonstrate an approach toward performance optimization through a consideration of the trap species involved. A change in the clocking scheme was found to result in a factor of 3 reduction in charge transfer inefficiency.