Predicting the performance benefit of multi-level clocking in CCDs using the active trap model

Buggey, T. W.; Hall, D. J.; Soman, M. R.; Verhoeve, P. and Holland, A. D. (2022). Predicting the performance benefit of multi-level clocking in CCDs using the active trap model. In: SPIE Astronomical Telescopes and Instrumentation, SPIE, 12191(12191J).



Charge-coupled devices have been the detector of choice for soft X-ray astronomy missions for many decades due to excellent energy resolution, noise performance, and longevity in space. Newer CCD-based missions require everincreasing performance which is made challenging by radiation damage inherent to the space environment. Missions such as ESA’s upcoming EUCLID observatory is aiming to measure tiny changes in the shape of distant galaxies, created by the presence of dark matter. Such high precision (not only specific to EUCLID) necessitates significant mitigation against radiation damage effects, one of which is utilising different detector operation modes such as multilevel clocking. Multi-level clocking uses three electrode voltage levels (compared to the standard two) to encourage traps within the damaged silicon to emit their charge such that they do not contribute to charge transfer losses, improving charge transfer efficiency and overall detector performance. However, multi-level clocking requires bespoke hardware to implement, followed by significant amount of testing to show that the benefit is significant.

A recent CCD optimisation technique, called the Active Trap Model, utilises knowledge of the radiation-induced defects within a CCD to optimise charge transfer performance across a wide range of variables including temperature, clocking speeds and device operation modes. This paper presents development of the Active Trap Model to predict the performance of multi-level clocking in CCDs. The performance of the model is compared to the experimental data available, namely from ESA’s PLATO1 mission, and shows good agreement between model and experimental data. The results show the versatility of the Active Trap Model and uses of the technique in potential future CCD-based space missions such as HabEx2 and LUVIOR3.

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