[show abstract][hide abstract] ABSTRACT: A special type of charge-coupled device, the pnCCD, has been developed in the nineties as focal-plane detector for the X-ray astronomy mission XMM-Newton of the European Space Agency. The pnCCD detector has been in operation since the satellite launch in 1999. It is performing up to date spectroscopy of X-rays in combination with imaging and high time resolution. The excellent performance of the flight camera is still maintained; in particular, the energy resolution has been nearly constant since launch. In order to satisfy the requirements of future X-ray astronomy missions as well as those of ground-based experiments, a new type of pnCCD has been developed. The 'frame store pnCCD' shows various optimizations in device design and fabrication process. Devices with up to 256 Â 512 pixels have been fabricated in 2004 and recently tested. Simultaneously, a programmable analog signal processor for the readout of the CCD signals, the DUO CAMEX, has been developed. The readout noise of the new detector has a value of 2 electrons ENC which is less than half of the figure of the XMM-Newton pnCCD. We measured an energy resolution that is close to the theoretical limit given by the Fano noise. In particular the low-energy response of the new devices was substantially improved. The quantum efficiency for X-rays is at least 90% in the entire energy band from 0.3 keV up to 11 keV. This is due to the ultra-thin photon entrance window as well as the full depletion of the 450 mm thick back-illuminated pnCCD. The position resolution is better than the pixel sizes of 75 mm Â 75 mm or 51 mm Â 51 mm because the signal charge is spread over up to four pixels which allows a more accurate event position determination. 'Out of time' events are substantially reduced to the order of 0.1% by operating the pnCCD in frame store mode. Higher operating temperatures, e.g. À20 1C, are possible due to the smaller thermally generated dark-current level of the new devices and the operation at higher frame rates. Low power consumption applications like for the ROSITA X-ray astronomy mission with low frame rates of, e.g. 20 images/s, as well as high frame rate applications, e.g. 200 images/s, are possible with the same device.
Nuclear Instruments and Methods in Physics Research A30.Kv. 01/2006; 568(29).
[show abstract][hide abstract] ABSTRACT: In the MPI-Halbleiterlabor (MPI-HLL) we are developing fully depleted pn-type Charge Coupled Devices (pnCCD) with a thick radiation-sensitive region. Since 1997, the mesh experiment has been established as an unique technique to determine an X-ray interaction position with subpixel resolution. In order to investigate the signal charge behavior in pnCCDs, we performed the mesh experiment using various characteristic X-ray lines. Cu-L (0.9 keV), Al-K (1.5 keV) and Ti-K (4.5 keV) were used and the device operated under various conditions, e.g. register voltages. We obtained the restored pixel images for various X-ray event patterns. The photon entrance window of the back illuminated pnCCD shows highly uniform detection efficiency within a pixel. We measured the charge cloud size generated by an X-ray photon inside the CCD. The measured charge cloud sizes are around 6 mm (rms) depending on the X-ray energy. The operation with different register conditions revealed asymmetries and regions with a weaker electric field around pixel boundaries. r 2006 Published by Elsevier B.V.
Nuclear Instruments and Methods in Physics Research A60.Gz. 01/2006; 568(95).