Charge transfer inefficiency mitigation in a CCD by trap pumping

Abstract

The issue of radiation induced Charge Transfer Inefficiency (CTI) is the main disadvantage of using a Charge Coupled Device (CCD) in hostile radiation environments. The formation of defects within the silicon lattice, arising from displacement damage from incident radiation, can capture and hold charge for a period of time dependant on the operating temperature and the type of defect. The location and type of these defects can be investigated using the CCD and a technique called trap pumping, where charge is shuffled forwards and backwards between pixels using different transfer times and temperatures to determine the defects emission time constant and activation energy. It is also possible to move the charge forwards and backwards using the clocking scheme used to perform normal CCD readout, in this case producing a trap map of the defects which will likely impact charge loss when the device is readout. This paper describes an analytical algorithm created to investigate the ability to recover lost charge in X-ray images from a p channel CCD204, irradiated at 153 K, and assess the ability to add charge back into the X-ray event from which it was lost.