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X-ray Measurement of the subpixel structure of the XMM EPIC MOS CCD

H. Tsunemi·K. Yoshita·A. D. Short·P. J. Bennie·M. J. L. Turner·A. F. Abbey
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Abstract

We report here the results of a mesh experiment to measure the subpixel structure of the EPIC MOS CCDs on board the XMM X-ray observatory. The pixel size is 40$μ$m square while the mesh hole spacing is 48$μ$m, a combination quite different from our standard mesh experiment. We have verified that this combination functions properly and have analyzed the CCD structure with sub-pixel resolution. The EPIC MOS CCD has an open electrode structure to improve detection efficiency at low energies. We obtained the distribution of various grades of X-ray events inside the pixel. A horizontally split two-pixel event is generated near the channel stop which forms a straight vertical pixel boundary whereas a vertically split two-pixel event is generated where the potential due to the thinned gate structure forms a wavy horizontal pixel boundary. Therefore, the effective pixel shape is not a square but is distorted. The distribution of X-ray events clearly shows that the two etched regions in each pixel, separated by the bridging finger of the enlarged (open) electrode. We measured the difference in X-ray transmission between the conventional and open regions of the pixel using O-K and Cu-L X-ray emission lines, and found it to be consistent with an electrode thickness comprising $0.2\pm0.1μ$m of Si and $0.6\pm0.2μ$m of SiO2.

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H. Tsunemi, K. Yoshita, A. D. Short, P. J. Bennie, M. J. L. Turner, A. F. Abbey. 1999-10-02. X-ray Measurement of the subpixel structure of the XMM EPIC MOS CCD. https://doi.org/10.1016/s0168-9002(99)00762-7

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