Measurement of partial charge collection in a soft X-ray optimised backside illuminated CMOS image sensor

Abstract The measurement of the charge collection properties at the back surface of a backside illuminated CMOS image sensor optimised for soft X-ray detection is presented. Further investigation of the CIS221-X at the BESSY-II synchrotron has enabled the properties of the back surface partial charge collection layer to be determined. There is agreement between the measured properties and both existing models inferred from quantum efficiency testing conducted on the detector and other detectors with similar back surface processing. The partial charge collection region, close to the back surface of the detector, has a large impact on the behaviour exhibited by the X-ray detector when observing very soft X-rays. Determination of these effects is an important step towards the use of the CIS221-X for scientific applications.