Understanding the effects of charge diffusion in next-generation soft x-ray imagers

Eric D. Miller; Gregory Y. Prigozhin; Beverly J. LaMarr; Marshall W. Bautz; Richard F. Foster; Catherine E. Grant; Craig S. Lage; Christopher Leitz; Andrew Malonis

doi:10.1117/12.2628929

31 August 2022 Understanding the effects of charge diffusion in next-generation soft x-ray imagers

Eric D. Miller, Gregory Y. Prigozhin, Beverly J. LaMarr, Marshall W. Bautz, Richard F. Foster, Catherine E. Grant, Craig S. Lage, Christopher Leitz, Andrew Malonis

Author Affiliations +

Proceedings Volume 12181, Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray; 121816R (2022) https://doi.org/10.1117/12.2628929
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

To take advantage of high-resolution optics sensitive to a broad energy range, future x-ray imaging instruments will require thick detectors with small pixels. This pixel aspect ratio affects spectral response in the soft x-ray band, vital for many science goals, as charge produced by the photon interaction near the entrance window diffuses across multiple pixels by the time it is collected, and is potentially lost below the imposed noise threshold. In an effort to understand these subtle but significant effects and inform the design and requirements of future detectors, we present simulations of charge diffusion using a variety of detector characteristics and operational settings, assessing spectral response at a range of x-ray energies. We validate the simulations by comparing the performance to that of real CCD detectors tested in the lab and deployed in space, spanning a range of thickness, pixel size, and other characteristics. The simulations show that while larger pixels, higher bias voltage, and optimal backside passivation improve performance, reducing the readout noise has a dominant effect in all cases. We finally show how high-pixel-aspect-ratio devices present challenges for measuring the backside passivation performance due to the magnitude of other processes that degrade spectral response, and present a method for utilizing the simulations to qualitatively assess this performance. Since compelling science requirements often compete technically with each other (high spatial resolution, soft x-ray response, hard x-ray response), these results can be used to find the proper balance for a future high-spatial-resolution x-ray instrument.

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Eric D. Miller, Gregory Y. Prigozhin, Beverly J. LaMarr, Marshall W. Bautz, Richard F. Foster, Catherine E. Grant, Craig S. Lage, Christopher Leitz, and Andrew Malonis "Understanding the effects of charge diffusion in next-generation soft x-ray imagers", Proc. SPIE 12181, Space Telescopes and Instrumentation 2022: Ultraviolet to Gamma Ray, 121816R (31 August 2022); https://doi.org/10.1117/12.2628929

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