PN-CCD detector for the European photon imaging camera on XMM

The pn-Charge Coupled Device (pn-CCD) detector system was developed as the focal plane instrument of an X-ray telescope for the European Photon Imaging Camera (EPIC) on the X-ray Multi Mirror (XMM) Mission. The second cornerstone mission of the European Space Agency's Horizon 2000 plan performs high throughput imaging and spectroscopy of the X-ray sky in the domain of 0.1 keV - 15 keV. The pn-Charge Coupled Device will also be used for a German X-ray astronomy satellite mission, called ABRIXAS (A Broad-Band Imaging X-ray All-Sky Survey). While XMM will perform pointed observations, ABRIXAS will carry out an all sky survey with imaging telescopes. Both projects are planned to be launched in 1999. The homogeneous coherent sensitive area of the detector consists of a 6 cm x 6 cm large array of 12 pn-CCDs which are monolithically integrated on a single silicon wafer together with the first stage of amplification. The pn-CCD detector has been optimized for high-resolution X-ray spectroscopy and its performance is close to the theoretical limits given by the Fano noise. High quantum efficiency essential for the investigation of faint objects is accomplished over the whole energy range by a thin photon entrance window and a full sensitive detector thickness. A fast readout achieves excellent time resolution for the observation of pulsed X-ray sources and avoids pile-up for bright objects. The relevant performance parameters reflecting the state of the detector development are presented. The radiation hardness of the pn-CCD was verified for the ten year satellite mission. No significant increases in the thermally generated current, charge transfer losses and transfer noise occurred in the temperature range planned for detector operation. A correction of the signal charge losses, which occur already before irradiation in all types of Charge Coupled Devices during the charge transfer to the anodes, is necessary to achieve the highest energy resolution of the detector. Methods to reduce the signal charge losses which were successfully tested, are described.