X-ray analysis of fully depleted CCDs with small pixel size

Abstract

X-ray frames offer a lot of information about CCD. 55Fe sources are traditionally being used for CCD gain and charge transfer efficiency (CTE) measurements. In addition X-rays can be used for the system linearity test. We demonstrate how spectral lines of 55Fe and 241Am rad. sources are used for system linearity measurements. The pixel size of modern scientific CCDs is getting smaller. The charge diffusion causes the charge spread among neighboring pixels especially in thick fully depleted sensors. This enables measurement of the charge diffusion using 55Fe X-rays. On the other hand, the usual CTE characterization method based on single pixel X-ray events becomes statistically deficient. A new way of measuring CTE using shape and amplitude analysis of X-ray clusters is presented and discussed. This method requires high statistical samples. Advances in test automation and express analysis technique allow for acquiring such statistical samples in a short period of time. The lateral diffusion measured using e2v CCD250 is presented and implications for X-ray cluster size and expected cluster shape are discussed. The CTE analysis using total X-ray cluster amplitude is presented. This analysis can reveal CTE problems for certain conditions. The statistical analysis of average X-ray cluster shape is presented. The details of our measurement procedure are presented.