Detectors with high energy and position resolution over a wide energy range are required for space telescopes in high energy astrophysics missions. By combining a low noise fully depleted pnCCD detector with a columnar CsI(Tl) scintillator, an energy dispersive spatially resolving detector can be realized with high quantum efficiency in the range from below 0.5 keV to above 150 keV. The detector is exposed to the photon source such that the X-rays first traverse the 450 μm sensitive pnCCD. If they are stopped through the photoelectric effect in the silicon detector, Fano-noiselimited energy resolution is achieved. This is true for X-rays from a few hundred eV up to approximately 15 keV. Above this energy the probability that the photon penetrates the pnCCD and converts in the CsI(Tl) scintillator is becoming higher. Due to the high atomic number of Cs (Z=55) and I (Z=53) hard X-rays are stopped efficiently in a 0.7 mm thick CsI(Tl) scintillator for photon energies up to 150 keV. The light from the scintillator is recorded with the same backilluminated pnCCD. For X-rays from a 57Co source with an energy of 122 keV and 136 keV we achieve an energy resolution of 0.7% (FWHM=850 eV) for the direct conversion in the silicon while the energy resolution for the conversion in the CsI(Tl) is 10% (12 keV). We have performed a knife-edge experiment at 122 keV and achieved a position precision of 27 μm at that energy. Monte Carlo simulations were showing similar, fully compatible results. In case the X-rays are converted directly in the silicon the position precision is better than 10 μm. This is close to the theoretical limit of the spatial resolution in such a system, which is given by the length of the tracks of the secondary electrons in the ionizing process in silicon and CsI. Spectra, images and the results of the GEANT4 simulations will be shown.
In a semiconductor tracking detector, a single X-ray photon can create signals in a cluster of adjacent pixels. We present a novel technique to reconstruct the points of entry (PoEs) of X-ray photons from these clusters based on a convolutional neural network (CNN). The new method allows improving the spatial resolution into subpixel regime. Beside the improved accuracy of the reconstruction, the method is much less computational intensive than conventional event analyses and therefore can be run even on less powerful machines in realtime. Due to its special architecture, the CNN can handle different frame sizes without adjustments or retraining processes.
pnCCDs are a special type of charge coupled device (CCD) which were originally developed for applications in X-ray astronomy. At X-ray Free Electron Lasers (XFEL) pnCCDs are used as imaging X-ray spectrometers due to their outstanding characteristics like high readout speed, high and homogenous quantum efficiency, low readout noise, radiation hardness and a high pixel charge handling capacity. With pnCCDs it is possible to separate one photon from no photon and two photons as well as being able to measure up to up to 104 photons per pixel per frame. However, extremely high photon intensities can result in pixel saturation and charge spilling into neighboring pixels. Because of this charge blooming effect, spatial information is reduced. Due to the deep understanding of the internal potential distribution we can enhance the pixel full well capacity even more and improve the quality of the image. This paper describes the influence of the operation voltages and space charge distribution of the pnCCD on the electric potential profile by using 2D numerical device simulations. Experimental results with signal injection from an optical laser confirm the simulation models.
N. Loh, Dmitri Starodub, Lukas Lomb, Christina Hampton, Andrew Martin, Raymond Sierra, Anton Barty, Andrew Aquila, Joachim Schulz, Jan Steinbrener, Robert Shoeman, Stephan Kassemeyer, Christoph Bostedt, John Bozek, Sascha Epp, Benjamin Erk, Robert Hartmann, Daniel Rolles, Artem Rudenko, Benedikt Rudek, Lutz Foucar, Nils Kimmel, Georg Weidenspointner, Günther Hauser, Peter Holl, Emanuele Pedersoli, MengNing Liang, Mark Hunter, Lars Gumprecht, Nicola Coppola, Cornelia Wunderer, Heinz Graafsman, Filipe R. N. Maia, Tomas Ekeberg, Max Hantke, Holger Fleckenstein, Helmut Hirsemann, Karol Nass, Thomas White, Herbert Tobias, George Farquar, W. Henry Benner, Stefan Hau-Riege, Christian Reich, Andreas Hartmann, Heike Soltau, Stefano Marchesini, Sasa Bajt, Miriam Barthelmess, Lothar Strueder, Joachim Ullrich, Philip Bucksbaum, Keith Hodgson, Mathias Frank, Ilme Schlichting, Henry Chapman, Michael Bogan
Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
We developed a camera with a 264 × 264 pixel pnCCD of 48 μm size (thickness 450 μm) for X-ray and optical
applications. It has a high quantum efficiency and can be operated up to 400 / 1000 Hz (noise≈ 2:5 ē ENC
/ ≈4:0 ē ENC). High-speed astronomical observations can be performed with low light levels. Results of test
measurements will be presented. The camera is well suitable for ground based preparation measurements for
future X-ray missions. For X-ray single photons, the spatial position can be determined with significant sub-pixel
resolution.
The Max Planck Advanced Study Group (ASG) at the Center for Free Electron Laser Science (CFEL) has
designed the CFEL-ASG MultiPurpose (CAMP) instrument, which provides a unique combination of particle
and photon detectors for experiments at 4th generation light sources. In particular, CAMP includes two sets
of newly developed 1024 × 1024 pixel pnCCD imaging detector systems. The CAMP instrument has now been
successfully employed during the first three beam times at LCLS, and we report here on practical experience
gained for the operation of imaging pnCCD detectors at FEL facilities. We address a wide range of topics:
pnCCD gain and energy calibration during experiments; suppression of optical light contamination in pumpprobe
experiments; contamination of the pnCCD entrance window with sample material; effects of accidental
direct impact on the pnCCDs of particles generated by the FEL beam impinging on the experimental setup; and
the effect of accidental direct exposure of a pnCCD to the focused and unattenuated X-ray beam. These lessons
learned will help us to further improve operation of pnCCDs in future FEL experiments.
Andrew Martin, Jakob Andreasson, Andrew Aquila, Saša Bajt, Thomas R. Barends, Miriam Barthelmess, Anton Barty, W. Henry Benner, Christoph Bostedt, John Bozek, Phillip Bucksbaum, Carl Caleman, Nicola Coppola, Daniel DePonte, Tomas Ekeberg, Sascha Epp, Benjamin Erk, George Farquar, Holger Fleckenstein, Lutz Foucar, Matthias Frank, Lars Gumprecht, Christina Hampton, Max Hantke, Andreas Hartmann, Elisabeth Hartmann, Robert Hartmann, Stephan Hau-Riege, Günther Hauser, Peter Holl, André Hoemke, Olof Jönsson, Stephan Kassemeyer, Nils Kimmel, Maya Kiskinova, Faton Krasniqi, Jacek Krzywinski, Mengning Liang, Ne-Te Duane Loh, Lukas Lomb, Filipe R. N. Maia, Stefano Marchesini, Marc Messerschmidt, Karol Nass, Duško Odic, Emanuele Pedersoli, Christian Reich, Daniel Rolles, Benedikt Rudek, Artem Rudenko, Carlo Schmidt, Joachim Schultz, M. Marvin Seibert, Robert Shoeman, Raymond Sierra, Heike Soltau, Dmitri Starodub, Jan Steinbrener, Francesco Stellato, Lothar Strüder, Martin Svenda, Herbert Tobias, Joachim Ullrich, Georg Weidenspointner, Daniel Westphal, Thomas White, Garth Williams, Janos Hajdu, Ilme Schlichting, Michael Bogan, Henry Chapman
Results of coherent diffractive imaging experiments performed with soft X-rays (1-2 keV) at the Linac Coherent
Light Source are presented. Both organic and inorganic nano-sized objects were injected into the XFEL beam
as an aerosol focused with an aerodynamic lens. The high intensity and femtosecond duration of X-ray pulses
produced by the Linac Coherent Light Source allow structural information to be recorded by X-ray diffraction
before the particle is destroyed. Images were formed by using iterative methods to phase single shot diffraction
patterns. Strategies for improving the reconstruction methods have been developed. This technique opens
up exciting opportunities for biological imaging, allowing structure determination without freezing, staining or
crystallization.
Measurement campaigns of the Max-Planck Advanced Study Group (ASG) in cooperation with the Center for
Free Electron Laser Science (CFEL) at DESY-FLASH and SLAC-LCLS have established pnCCDs as universal
photon imaging spectrometers in the energy range from 90 eV to 2 keV. In the CFEL-ASG multi purpose
chamber (CAMP), pnCCD detector modules are an integral part of the design with the ability to detect photons
at very small scattering angles. In order to fully exploit the spectroscopic and intensity imaging capability of
pnCCDs, it is essentially important to translate the unprocessed raw data into units of photon counts for any
given position on the detection area.
We have studied the performance of pnCCDs in FEL experiments and laboratory test setups for the range
of signal intensities from a few X-ray photons per signal frame to 100 or more photons with an energy of 2 keV
per pixel. Based on these measurement results, we were able to characterize the response of pnCCDs over the
experimentally relevant photon energy and intensity range. The obtained calibration results are directly relevant
for the physics data analysis. The accumulated knowledge of the detector performance was implemented in
guidelines for detector calibration methods which are suitable for the specific requirements in photon science
experiments at Free Electron Lasers.
We discuss the achievable accuracy of photon energy and photon count measurements before and after the
application of calibration data. Charge spreading due to illumination of small spots with high photon rates is
discussed with respect to the charge handling capacity of a pixel and the effect of the charge spreading process
on the resulting signal patterns.
New generation synchrotron light sources, the X-ray free electron lasers, require a two dimensional focal plane
instrumentation to perform X-ray imaging from below 100eV up to 25keV. The instruments have to face the accelerator
bunch structure and energy bandwidth which is different for existing (FLASH, Hamburg and LCLS, Menlo Park) and
future photon sources (SACLA, Harima and XFEL, Hamburg). Within the frame of the Center for Free Electron Laser
Science (CFEL), a joint effort of the Max-Planck Society, DESY and the University of Hamburg, the MPI
semiconductor laboratory developed, produced and operated large area X-ray CCD detectors with a format of nearly
60cm2 image area. They show outstanding characteristics: a high readout speed due to a complete parallel signal
processing, high and homogeneous quantum efficiency, low signal noise, radiation hardness and a high pixel charge
handling capacitance. We will present measurement results which demonstrate the X-ray spectroscopic and imaging
capabilities of the fabricated devices.
We will also report on the concept and the anticipated properties of the full, large scale system. The implementation of
the detector into an experimental chamber to perform measurements e.g. of macromolecules in order to determine their
structure at atomic resolutions will be shown.
KEYWORDS: Sensors, Charge-coupled devices, Cameras, X-rays, Electronics, CCD cameras, Digital signal processing, Signal processing, CCD image sensors, Space telescopes
The German X-ray observatory eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the prime
instrument of the new Spectrum-RG mission. Launch of the Russian satellite is planned for the year 2011. The scientific
goal of eROSITA is primarily the detection and analysis of 100 thousand clusters of galaxies in order to study the large
scale structures in the Universe and to test cosmological models. The therefore required large effective area is obtained
by an array of seven identical and parallel aligned Wolter-I telescopes. In the focus of each mirror module, there is a
large frame store pnCCD detector, providing a field of view of 1° in diameter. The same X-ray detector type will also be
applied for ART-XC, another grazing-incidence telescope system aboard Spectrum-RG, which permits the detection of
heavily obscured X-ray sources. These scientific instruments allow the exploration of the X-ray Universe in the energy
band from 0.3 keV to 11 keV. During a mission time of at least five years, an all-sky survey, wide as well as deep
surveys and pointed observations will be performed. Approval and funding for eROSITA were granted by the German
space agency DLR in April 2007.
The conceptual design of the X-ray focal plane cameras is presented here comprising electrical, thermal, and mechanical
aspects. Key part of the camera is the pnCCD detector chip, which is developed and produced in our semiconductor
laboratory, the MPI Halbleiterlabor. The CCD was designed according to the specifications given by the scientific goals
of eROSITA. The eROSITA CCD differs apparently from all previously produced frame store pnCCDs by its larger
size and format. The CCD image area of the seven eROSITA cameras is in total 58 cm2 large and their number of pixels
is about seven times higher than that of the XMM-Newton pnCCD camera. First pnCCD devices were recently
produced and tested. Their performance measurements and results are of most importance for eROSITA because the
tested CCDs are the control sample of the flight detector production.
A pnCCD detector fulfils all typical requirement specifications to an X-ray detector optimally: The energy of the X-ray
photon is precisely measured, incidence position is determined even more accurate than the pixel size, and the arrival
time of the photon is very well defined by the high frame rate due to complete parallel signal processing. The
probability for detection of an X-ray photon is from 0.3 keV to 10 keV close to 100% and homogeneous over the image
area.
Such a detector has been developed for application in X-ray astronomy. The XMM-Newton space observatory is already
equipped with a pnCCD camera which performs since commissioning in 2000 till this day excellent measurements. For
the upcoming eROSITA telescope on the Spectrum-Roentgen-Gamma satellite, an advanced pnCCD detector system is
presently developed. Seven pnCCD cameras are placed in the foci of seven X-ray mirror systems researching the X-ray
sky during a mission time of 5 years.
For ground based instrumentation the X-ray fluxes can be extremely high, as it is the case in X-ray free electron lasers
(XFELs). The evolving XFELs will make it possible to capture three-dimensional images of the nanocosmos. Here the
focus is set on the measurement of X-ray intensities instead of spectroscopy, i.e. the number of monochromatic photons
per pixel (up to > 1000 photons) is counted at very high frame rates ( > 100/s).
Both projects have again in common the request for large image areas: in case of eROSITA seven times an image area
of 8 cm2 and for the XFEL experiment at LCLS we provide in a first step a 59 cm2 large image area. In a second step it
will be enlarged to even 236 cm2. We performed recently promising tests with the prototype detectors. Therefore we
started the production of the final devices for both applications in the MPI semiconductor laboratory.
An advanced pnCCD type has been developed, based on the concept of the XMM-Newton detector, which has been
performing spectroscopy and imaging since 2000. This new detector is designed according to the requirements of
eROSITA, a new X-ray astronomy mission, to be launched in 2010. The focal plane for each of the seven individual
Wolter telescopes will be equipped with one of these new-type X-ray pnCCDs. In addition to the eROSITA chips, we
have developed CCDs for other applications, e.g. for projects which require smaller pixel sizes. The devices that have
been produced in the semiconductor laboratory (MPI Halbleiterlabor) of the Max-Planck-Institut fur extraterrestrische
Physik are currently subject of systematic quality checks and spectroscopic tests. These tests are performed under
standardized conditions on a representative subset of the many devices we have produced. The aim of these tests is to
extract the key performance parameters of the individual CCDs like readout noise, energy resolution and the occurrence
of bad pixels. The analysis includes the CAMEX analog signal processor, which has been developed for the readout of
the CCD signals. After an introduction, we present the motivation for the detector development and give an overview
about our CCD design and production, as well as about the CAMEX ASIC. Then device tests, test setups and data
analysis are described. We report in detail about the performance of the tested devices. Failures that occurred during
device tests are subsequently discussed. Finally, we give a review of the results.
At MPI Halbleiterlabor, pnCCDs have been continuously developed to improve readout noise, readout speed, charge transfer efficiency and energy resolution. Pixel sizes of 75μm, 51μm and 36μm were realized in addition to the original 150μm pixel design. Reduction of the pixel size evidently changes the electric fields in the pixel structure. This leads to the question of how scaling of the pixel size affects the charge collection at subpixel dimensions. We used the "mesh-method" to measure the amount of signal charge deposited in a pixel depending on the position of X-Ray photon incidence within the pixel. In this experiment, a mesh with a rectangular hole pattern was mounted above the entrance window or structured front side of the detector. A slight rotation of the mesh ensures that every hole has a different position relative to the pixel below. It corresponds to scanning of a single pixel. Measurements were done with pnCCDs of 150μm, 75μm and 51μm pixel size at photon energies from 0.7keV to 5.4keV. We also used a setup with front side illumination of a pnCCD with 75μm pixel size to investigate the absorption of X-ray photons in the register structure of the device. Numerical simulations delivered results for signal charge distribution into pixels along the charge transfer direction. We analyzed the charge collection in a pixel and the absorption properties of the register structure with a spatial resolution below 5μm and could investigate the accuracy of numerical device simulations.
A new generation of pnCCDs has been developed for the proposed X-ray astronomy missions, DUO and ROSITA. The DUO/ROSITA CCD is a frame store pnCCD based on the concept of the XMM-Newton pnCCD and has both, improved performance and new features. This detector permits accurate spectroscopy of X-rays as well as imaging and high time resolution with high quantum efficiency in the energy band from 0.3 keV to 10 keV. Interfering electron-hole pair generation due to optical and UV light is prevented by a deposition of an on-chip filter. We describe the frame store pnCCDs developed and fabricated for the DUO and ROSITA missions in the semiconductor laboratory of the Max-Planck-Institut fuer extraterrestrische Physik. An overview about the CCD concept and design is given along with some details about the fabrication of the devices. In addition, we introduce a new analog signal processor which has been developed specifically for the readout of the frame store pnCCD signals. The main focus of this paper is to present the very first measurements with this CCD type and its analog signal processor. Towards this aim we report the operation of this new sensor and its key performance parameters. Finally we discuss ongoing and future tests with the DUO/ROSITA CCDs.
DUO and ROSITA are two future X-ray astronomy missions observing in the energy band from about 0.3 keV to 10 keV. While the NASA satellite DUO will scan selected areas of the X-ray sky with high sensitivity, the German ROSITA mission shall perform an all-sky survey. Both missions apply an array of seven Wolter telescopes with separated field of views and seven dedicated PN-CCD focal plane detectors. The focal plane detectors are a further development of the flight-proven PN-CCD applied for the XMM-Newton observatory. The advanced device, called 'frame store PN-CCD', is designed and fabricated in the semiconductor laboratory of the Max-Planck-Institute for extraterrestrial physics. An introduction into the detector concept and design are presented as well as the promising results which have been achieved with the prototype devices. This includes an overview about the performance of the PN-CCD and in detail the recent measurements with the detector. An example is the low energy response of the optimized photon entrance window with integrated optical light filter. As the CAMEX analog signal processor chip is a main component of the detector module, we describe its development status. Furthermore, we report about the application of the mesh experiment to the PN-CCD which allows for a study of the electric potential characteristics in the detector bulk, in particular in the charge transfer depth. The information is of great importance for an accurate knowledge about the drift of the generated signal electrons into the potential wells of the pixels.
A new type of Active Pixel Sensor is proposed which will be capable to meet the requirements of the wide field imager of ESA's future X-ray mission XEUS: the simultaneous energy and position resolved detection of X-rays at high count rate on a large format sensor. The Active Pixel Sensor is based on the integrated detector-amplifier structure DEpleted P-channel Field Effect Transistor (DEPFET). The device operates on a fully depleted bulk and provides internal signal amplification at the position of the charge generation. A very low value of the overall output capacitance leads to extremely low read noise. In the matrix arrangement of an Active Pixel Sensor the single DEPFET pixels can be randomly accessed for readout, and various flexible readout modes are possible. In contrast to CCDs the DEPFET-based Active Pixel Sensor avoids the transfer of signal charges over long distances within the detector bulk, and related problems of transfer loss or out-of-time-events cannot occur. An interesting feature is the non-destructive nature of the DEPFET readout which can be used for the reduction of the low-frequency noise contribution by repetitive readings of the signal information. The device principle of the DEPFET based pixel sensor is explained. First results of single DEPFET measurements are presented.
The fully depleted PN-CCD detector is meanwhile field-tested in several experiments on ground and in space. Its application as focal plane detector aboard ESA's XMM-Newton observatory can be considered as the most impressive one. The further development of this detector type including its readout chip in the MPI semiconductor laboratory is presented here. The new device, called frame store PN-CCD, shows substantial improvement of performance, in particular concerning the energy resolution and the probability of out of time event occurrence. Moreover, the detector offers features which are of great importance for its application in space. This is, besides the radiation hardness of the CCD, the variety of feasible pixel sizes and the high frame rates in combination with the small power consumption of the detector. Because of the thin radiation entrance window and the full depletion of the chip, the detector provides a high quantum efficiency for soft X-rays as well as for optical light and the near infrared. The frame store PN-CCD detector will be applied for the proposed X-ray astronomy missions DUO and ROSITA.
The pn-CCD camera on board of XMM-Newton as well as the Wide Field Imager (WFI) currently being designed for the XEUS mission can be read out in special fast timing modes, providing spectroscopy at very high time resolution. The two fast modes, Timing and Burst mode, of the pn-CCD camera on board XMM-Newton provide a time resolution of 30 μs, respectively. However, this fast timing is only possible at the expense of spatial resolution in readout direction. In contrast, the current baseline design of the WFI for XEUS will provide 25 μs timing at full spatial resolution. We describe the basic principles of the fast readout schemes of the pn-CCD and the SFI, discuss the potential of XEUS for high time resolution spectroscopy and present first results of pulse phase resolved spectroscopy of the Crab pulsar with the pn-CCD in Timing mode.
The pn-CCD was developed as focal plane detector for the XMM-Newton mission and operates successfully for more than 30 months in orbit without performance degradation. In order to match the new requirements of the future ROSITA mission which will perform a broad band X-ray all-sky survey, we propose an advanced type of pn-CCD. The concept and the new features of this frame store pn-CCD as part of the imaging X-ray spectrometer of ROSITA are described. First
measurements with prototype devices show the improvement of detector performance in comparison to the pn-CCD on XMM-Newton. We suggest as optical filter for the observations of the X-ray sky, a thin aluminum layer deposited on the photon entrance window of the device.
Active Pixel Sensors (APS) offer high-resolution imaging in combination with a fast and flexible readout. The MPI Halbleiterlabor develops and produces DEPFET (Depleted Field Effect Transistor) based APS devices. They are additionally characterized by enhanced sensitivity for X-ray photons in the range from 0.1 keV to 25 keV, spectroscopic energy resolution (below 1 electron r.m.s.) and radiation hardness. Moreover, the production process on high-ohmic silicon allows incorporating additional high-speed spectrometers based on silicon drift detectors. Such a detector system is proposed as a wide field imager for the XEUS (X-ray Evolving Universe Spectroscopy) mission. XEUS is a planned project within the European Space Agency's Horizon 2000+ program. We will present a focal plane concept for XEUS and measurement results from DEPFET-APS prototypes and high speed drift detectors.
Based on the operational experience with the EPIC pn-CCD system on board of XMM-Newton, new imaging X-ray spectroscopic detector systems for future X-ray missions will be introduced in terms of energy, position and time resolving detectors. As the readout speed requirement in the case of single photon coating detectors increases drastically with the collecting area and improved angular resolution, but noise figures have to be on the lowest possible level, new detector schemes must be developed: Active pixel sensors (APS) for X-ray detection have the capability to randomly select areas of interest and to operate at noise levels below 1 electron (rms). About 1000 frames per second can be read out with a relatively low level of electric power with the proposed DEPFET arrays. One prominent candidate for the use of an APS is ESA's XEUS 0 the X-ray Evolving Universe Spectroscopy mission. It represents a potential follow-on mission to the cornerstone XMM-Newton, currently in orbit. The XEUS mission is considered as part of ESA's Horizon 2000+ program within the context of the International Space Station (ISS).
The pn-CCD camera on EPIC-XMM is the most advanced imaging X-ray spectrometer, as it combines high quantum efficiency, high speed readout and high energy resolution. The camera operates for almost two years as calibrated prior to launch. Future missions, like ESA's XEUS (X-ray Evolving Universe Spectroscopy) mission require higher spatial resolution, higher response at energies above 20 keV and most important a full frame readout rate increased by at least a factor of 20 for the first operational phase. XEUS represents a potential follow-on mission to the cornerstone XMM-Newton, currently in orbit. The XEUS mission is considered as part of ESA's Horizon 2000+ program within the context of the International Space Station (ISS.) In order to match the above requirements for the wide field imager of XEUS, we propose a frame store pn-CCD camera system based on the technology development of the EPIC (European Photon Imaging Camera) camera on XMM-Newton. Our goal is readout rate of 250 complete frames per second for 1024 x 1024 pixels with a pixel size of 75x75micrometers 2, monolithically integrated on a 6 inch wafer. The concept and the new features of the frame store pn-CCD camera will be described. The focal plane layout, the readout concept and the expected scientific performance will be introduced. The implementation of thin aluminum filters, monolithically grown on the pn-CCD entrance window, will be discussed as well as the integration of a very fast spectroscopic detector being able to record 106 counts per second with a FWHM of about 250 eV.
An integrating solid state detector with segmentation has been developed that addresses the needs in scanning transmission x-ray microscopy below 1 keV photon energy. The detector is not cooled and can be operated without an entrance window which leads to a total photon detection efficiency close to 100%. The chosen segmentation with 8 independent segments is matched to the geometry of the STXM to maximize image mode flexibility. In the bright field configuration for 1 ms integration time and 520 eV x-rays the rms noise is 8 photons per integration.
Silicon Drift Detectors (SDDs) with integrated readout transistors combine a large sensitive area with a small total readnode capacitance and are therefore well suited for high resolution, high count rate X-ray spectroscopy. The low leakage current level obtained by elaborated process technology makes it possible to operate them at room temperature or with moderate thermo-electric cooling. The monolithic combination of several SDDs to a multichannel drift detector solves the limited of size and allows for the realization of new physics experiments and systems. Up to 3 cm2 large SDDs for spectroscopic applications were fabricated and tested. Position sensitive X-ray systems are introduced. The description of the device principle is followed by the introduction of the multichannel drift detector concept. Layout, performance and examples of current and future applications are presented.
Fully depleted silicon pn-CCDs with an active thickness of 300 micrometers exhibit a quantum efficiency of 90 percent at a wavelength of 1 micrometers in the near IR. The multi-parallel readout architecture allows for a frame time shorter than 2 ms for a device having a format of 256 by 256 pixel. It can be operated in a full frame mode and in a frame store mode. The pixel size is 50 micrometers by 50 micrometers . The active area is then 12.8 by 12.8 mm2. Cooled down to -90 degrees C the electronic noise floor is below 5 electrons at 50 Megapixel per second. Quantum efficiency measurements will be shown as well as the physical models of the radiation entrance window. A camera system with comparable specifications - except for the pixel size - was already fabricated for ESA's XMM-NEWTON satellite mission, which was launched in early December 1999. The active size of the detector is 60 by 60 mm2 with a readout time of 4 ms. Future work includes the extension of the active area to 1000 by 1000 pixel, monolithically fabricated on a high resistivity 6 inch silicon wafer. The main driver for this development is ESA's planned XEUS mission, to be launched at the end of the next decade.
Peter Klein, P. Buchholz, Peter Fischer, N. Hoernel, Peter Holl, Josef Kemmer, M. Loecker, Gerhard Lutz, W. Neeser, Diana Stoetter, Lothar Strueder, M. Trimpl, J. Ulrici, J. Vocht, Norbert Wermes
A 64 X 64 pixel matrix prototype has been produced at the HLL. We will describe the test system setup and present measurements which characterize the performance.
Large format arrays covering a wide bandwidth from 1 eV to 25 keV will be used in the focal plane of X-ray telescopes as well as in adaptive optics systems. As the readout speed requirements increase drastically with the collecting area, but noise figures have to be on the lowest possible level, CCD-type detectors do not seem to be able to fulfill the experiment expectations. Active pixel sensors (APS) have the capability to randomly select areas of interest and to operate at noise levels below 1 electron (rms). One prominent candidate for the use of an APS is XEUS: The X-ray Evolving Universe Spectroscopy mission. It represents a potential follow-on mission to the ESA cornerstone XMM currently in orbit. The XEUS mission was considered as part of ESA's Horizon 2000+ within the context of the International Space Station.
XMM-Newton, the most powerful X-ray telescope ever built was launched from the european space port Kourou on december 10 last year. Three large X-ray Wolter type mirror systems are focusing the incoming X-rays from 100 eV up to 15,000 eV onto the focal instruments: fully depleted backside illuminated pn-CCDs and frontside illuminated MOS-CCDs. The concept of the pn-CCD camera will be briefly described and its performance on ground and in orbit will be shown. Special emphasis will be given to the radiation hardening of the devices, to the instrument background and to the experience of charged particle background in space. A comparison of the performance on ground and after 5 months in space will be shown.
On 10th December 1999, the European X-ray satellite XMM, now called XMM-Newton, was successfully put into orbit. After initial commissioning of the satellite's subsystems, the EPIC-pn camera was switched on and tested thoroughly in the period Jan./Febr. 2000. After refining of some of the parameter settings and the on-board pn-computer programs, we started the Calibration and Performance Verification Phase, which will last until the end of May 2000. In this paper we report on the results of the EPIC-pn Commissioning Phase with respect to the in-orbit performance of the camera. We also show some of the early results with the pn-camera, the first light image of a region in the Large Magellanic Cloud, and an observation of the Crab Nebular.
The concept of fully depleted, backside illuminated pn-CCD's with an integrated frame store area for high-speed applications will be presented. The device with a format of 128 by 256 pixel exhibits a readout time faster than 1000 frames per second with an electronic noise of less than 5 electrons. Due to the large sensitive volume of the detector and the development of an ultra-thin radiation entrance window, near theoretical quantum efficiencies are achieved from the ultra violet to the near infrared region. The high speed, low noise and high quantum efficiency makes these devices especially suited for the use as wavefront sensors in adaptive optics systems.
In the near future the European x-ray satellite XMM will be launched into orbit. The satellite is equipped with a PN-CCD camera with a sensitive area of 60 mm X 60 mm, integrated on a single silicon wafer. The same camera is on board of the German x-ray satellite ABRIXAS. The main feature of this camera type is the very good quantum efficiency of more than 90 percent in the energy range from 0.3 to 10 keV and the high time resolution, selectable between 7 microsecond(s) ec and 280 msec. All flight cameras are extensively calibrated, utilizing the long beam test facility Panter in Muenchen, the Synchrotron Radiation Facility beam lines at the Institut d'Astrophysique Spatiale in Orsay, and the PTB beam line at the Bessy Synchrotron in Berlin. We will give an overview of all the calibrations and calibration methods as well as some global results.
A 6 cm X 6 cm large monolithic charge coupled device has been developed and fabricated as focal plane x-ray detector for the European XMM satellite mission and the German ABRIXAS mission. This spectroscopic silicon detector is denominated pn-CCD because of its use of reverse biased pn- junctions as charge transfer registers, as ultra-thin homogeneous photon entrance window and for the on-chip electronics. Due tot he pn-CCD concept, the whole wafer thickness of 300 micrometers is sensitive to ionizing radiation. The read-out is performed in parallel and needs only 73 ms for the 36 cm2 large detector area. A uniform low noise performance is realized by on-chip integrated JFET electronics. The two best pn-CCDs have been integrated in the flight cameras for XMM and abrixas and extensively tested for the long term operation in space. The presentation comprises the basic concept of the detector, a short description of the flight device and its fabrication, test and operating as well as the key performance parameters. The concluding outlook describes methods of further development of the pn-CCD.
The pn-Charge Coupled Device (pn-CCD) camera was developed as one of the focal plane instruments for the European Photon Imaging Camera on board the x-ray multi mirror mission. An identical camera was foreseen on board ABRIXAS, a German x-ray satellite. The pn-CCD camera is an imaging x- ray detector for single photon counting, operating at a temperature below -80 degrees C. Due to a 0.3 mm depletion depth of the CCDs, the detector has a high quantum efficiency up to 15 keV. The effective area of the instrument is 6 cm X 6 cm with 12 CCDs monolithically integrated on a single silicon wafer. The camera includes a filter wheel with different filters for suppression of optical and UV light. A radioactive source provides an in- orbit calibration. In this paper we give an overview of the mechanical, thermal and electrical design of the instrument and a description of different readout and test modes. More detailed information about the performance and calibration of the instrument can be found in companion papers.
ESA's future x-ray mission, the x-ray evolving ESA's future x-ray mission, the x-ray evolving universe spectroscopy mission (XEUS) is actually under study as a potential successor of the XMM satellite. Its collecting area for x- rays form 100 eV up to 20 eV will be about 200 times larger than compared to XMM. The angular resolution will be improved by a factor of five. The field of view will eventually be as large as 10 arcmin. Novel wide field images are needed to overcome the limitations by the state-of-the- art CCD type detectors, limited due to the high number of x- rays focused into the focal plane. To face the problem of high count rate and large formats with simultaneous good energy resolution and high quantum efficiency we have proposed two new focal plane x-ray detectors: (a) a back illuminated active pixel sensor and (b) a 200 readout channel back illuminated frame store pn-CCD. Both will be fabricated at the MPI semiconductor lab on 500 micrometers high resistivity silicon.
The x-ray multi mirror (XMM) mission, the second cornerstone of the European Space Agency's Horizon 2000 program, will be launched in August 1999 and will perform high throughput imaging and spectroscopy in the energy range form 0.1 to 15 keV. One of the focal plane instruments is the EPIC pn CCD camera with a sensitive area of 60 mm by 60 mm, integrated on a single silicon wafer. The camera is divided into 4 redundant quadrants of three 10 mm by 30 mm CCDs with 64 by 200 pixels each. The thin entrance window in combination with a depletion depth out modes give the flexibility to observe targets of different source strength up to several Grab with some reduction in spectral and spatial performance. We will report on the calibration of the flight unit of the EPIC pm camera, performed at the long beam test facility Panter in Muenchen and at the Synchrotron Radiation Facility beam lines at the Istitute d'Astrophysique Spatiale in Orsay. In this paper we describe the preliminary results of the calibration of the imaging modes.
The pm-CCD camera is one of the three focal plane instruments of the European Photon Imaging Camera (EPIC) on board the x-ray multi mirror (XMM) mission scheduled for launch in August 1999. The detector consists of four quadrants of three pn-CCDs each, which are integrate don one 4 inch silicon wafer. Each CCD has 200 by 64 pixels with 280 micrometers depletion depth. One CCD of a quadrant is readout at a time, while the four quadrants can be processed independently of each other. Observations of point sources brighter than 11 mCrab in imaging mode will be effected by photon pile-up. However, special operating modes can be used to observe bright sources up to 150 mCrab in Timing Mode with 30 microsecond(s) time resolution and very bright sources up to several Crab in Burst Mode with 7 microsecond(s) time resolution. We have tested and calibrate the flight model FM of the EPIC pn-CCD camera at the long beam test facility Panter near Munich and at the synchrotron monochromators of the Institut d'Astrophysique Spatiale in Orsay, France. In this paper describe the calibration of the pn-CCD detector in high time resolution/bright source operating modes and present preliminary results on the performance in these modes.
The concept and performance of the fully depleted pn- junction CCD system, developed for the European XMM- and the German ABRIXAS-satellite missions for soft x-ray imaging and spectroscopy in the 0.1 keV to 15 keV photon range, is presented. The 58 mm X 60 mm large pn-CCD array uses pn- junctions for registers and for the backside instead of MOS registers. This concept naturally allows to fully deplete the detector volume to make it an efficient detector to photons with energies up to 15 keV. For high detection efficiency in the soft x-ray region down to 100 eV, an ultrathin pn-CCD backside deadlayer has been realized. Each pn-CCD-channel is equipped with an on-chip JFET amplifier which, in combination with the CAMEX-amplifier and multiplexing chip, facilitates parallel readout with a pixel read rate of 3 MHz and an electronic noise floor of ENC < e-. With the complete parallel readout, very fast pn-CCD readout modi can be implemented in the system which allow for high resolution photon spectroscopy of even the brightest x-ray sources in the sky.
Monolithic arrays of 12 CCDs, 3 by 1 cm2 each, have been developed and produced for the focal plane instrumentation of the European photon imaging camera (EPIC) on XMM and the German ABRIXAS x-ray satellite mission. The design parameters have been optimized to match the properties of the x-ray imaging optics as well as the x-ray intensity, energy bandwidth and characteristic time constants of the objects to observe. The pixel size is 150 by 150 micrometer2; readout is performed in parallel; low noise, spectroscopic performance is realized by on-chip integrated JFET electronics; highohmic, ultrapure bulk material allows full depletion and enhances the efficiency for higher energy x-ray detection. The fabrication process, the layout topology and the operating conditions guarantee for a ten year operation in space without performance degradation.
The pn-charge coupled device (pn-CCD) camera was developed as one of the focal plane instruments for the European photon imaging camera (EPIC) on board the x-ray multi mirror (XMM) mission. The homogeneously sensitive detector consists of four quadrants of three pn-CCDs each, which are integrated on a single silicon wafer. Each CCD has an area of 10 mm by 30 mm divided into 64 by 200 pixels with a depletion depth of 280 micrometers. Altogether the sensitive area is 60 mm by 60 mm. In the standard imaging mode (full frame mode) the CCDs are read out sequentially every 70 ms. In addition, different window modes allow imaging of brighter sources by restricting the detector area and reducing the integration time down to 6 ms. We have tested one quadrant of the EPIC pn-CCD camera at line energies from 0.52 keV to 17.4 keV at the long beam test facility PANTER in focus of the qualification mirror module for XMM as well as in a homogeneous x-ray beam. In this paper we describe the tests in the different imaging modes and report on the performance.
The pn-CCD camera is developed as one of the focal plane instruments for the European photon imaging camera (EPIC) on board the x-ray multi mirror (XMM) mission to be launched in 1999. The detector consists of four quadrants of three pn-CCDs each, which are integrated on one silicon wafer. Each CCD has 200 by 64 pixels (150 micrometer by 150 micrometers) with 280 micrometers depletion depth. One CCD of a quadrant is read out at a time, while the four quadrants can be processed independently of each other. In standard imaging mode the CCDs are read out sequentially every 70 ms. Observations of point sources brighter than 1 mCrab will be effected by photon pile- up. However, special operating modes can be used to observe bright sources up to 150 mCrab in timing mode with 30 microseconds time resolution and very bright sources up to several crab in burst mode with 7 microseconds time resolution. We have tested one quadrant of the EPIC pn-CCD camera at line energies from 0.52 keV to 17.4 keV at the long beam test facility Panter in the focus of the qualification mirror module for XMM. In order to test the time resolution of the system, a mechanical chopper was used to periodically modulate the beam intensity. Pulse periods down to 0.7 ms were generated. This paper describes the performance of the pn-CCD detector in timing and burst readout modes with special emphasis on energy and time resolution.
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 by 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.
PN-CCDs are being developed as focal plane detectors for ESA's X-ray Multi-Mirror satellite mission (XMM), to be launched at the end of this century. As a part of the European Photon Imaging Camera (EPIC) the pn-CCDs will convert the incoming X-ray radiation with high quantum efficiency, low readout noise, excellent background rejection, timing in the microsec regime, radiation tolerance up to several hundreds of krads and a position resolution tailored according to the angular resolution of the telescope. The goal of our laboratorial efforts for this mission is to fabricate a monolithic pn-CCD of an active area of 6 x 6 sq cm having 768 on-chip JFET amplifiers located at the end of each CCD line. It is the aim of this contribution to report on the ongoing work of the pn-CCD system. This article focuses on the position resolution capabilities of fully depleted pn-CCDs, some recent results in the noise analysis and preliminary results on 10 MeV proton damage.
Recent results on the on-chip electronics, transfer properties, and radiation entrance window of pn-CCDs are presented. With recently fabricated devices, an improved charge transfer efficiency per pixel of 0.9995 and an energy resolution of the CCD output stage of 5 e(-) rms have been measured. This performance is achieved without a degradation of other characteristics of the devices, such as an X-ray efficiency of 90 percent at 10 keV, more than a factor of 1000 better time resolution in the full frame mode in comparison with all other CCD concepts, and a one-dimensional spatial resolution of 24 microsec in the timing mode. The use of pn-junctions instead of MOS structures makes the devices intrinsically radiation resistant.
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