We developed and tested X-ray PNCCD focal plane detectors for the eROSITA (extended ROentgen Survey with an
Imaging Telescope Array) space telescope. General scientific goal of the eROSITA project is the exploration of the X-ray
universe in the energy band from about 0.2 keV up to 10 keV with excellent energy, time, and spatial resolution in
combination with large effective telescope areas. The observational program divides into an all-sky survey and pointed
observations. The mission duration is scheduled for 7.5 years. The German instrument will be launched in near future to
the Lagrange point L2 on the Russian satellite SRG. The detection of single X-ray photons with precise information
about their energy, angle of incidence and time is accomplished for eROSITA by an array of seven identical and
independent PNCCD cameras. Each camera is assigned to a dedicated mirror system of Wolter-I type. The key
component of the camera is a 5 cm • 3 cm large, back-illuminated, 450 μm thick and fully depleted frame store PNCCD
chip. This chip is a further development of the sensor type that is in operation as focal plane detector on the XMMNewton
satellite since launch in 1999 to date. Development and production of the CCDs for the eROSITA project were
performed by the MPI Halbleiterlabor, as already in the past for the XMM-Newton project. According to the status of
the project, a complete design of the seven flight cameras including the camera electronics and the filter wheel has been
developed. Various functional and performance tests have been accomplished for a detailed characterization of the
eROSITA camera system. We focus here especially on the focal plane detector design and the performance of the
detectors, which are essential for the success of the X-ray astronomy space project.
The approved German X-ray telescope eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the
core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission. After satellite launch to Lagrangian point
L2 in near future, eROSITA will perform a survey of the entire X-ray sky. In the soft band (0.5 keV - 2 keV), it will be
about 30 times more sensitive than ROSAT, while in the hard band (2 keV - 8 keV) it will provide the first complete
imaging survey of the sky. The design driving science is the detection of 100,000 clusters of galaxies up to redshift
z ~ 1.3 in order to study the large scale structure in the Universe and test cosmological models including Dark Energy.
Detection of single X-ray photons with information about their energy, arrival angle and time is accomplished by an
array of seven identical and independent PNCCD cameras. Each camera is assigned to a dedicated mirror system of
Wolter-I type. The key component of the camera is a 5 cm • 3 cm large, back-illuminated, 450 μm thick and fully
depleted frame store PNCCD chip. It is a further development of the sensor type which is in operation aboard the
XMM-Newton satellite since 1999. Development and production of the CCDs for the eROSITA project were performed
in the semiconductor laboratory of the Max-Planck-Institutes for Physics and Extraterrestrial Physics, the MPI
Halbleiterlabor. By means of a unique so-called 'cold-chuck probe station', we have characterized the performance of
each PNCCD sensor on chip-level. Various tests were carried out for a detailed characterization of the CCD and its
custom-made analog readout ASIC. This includes in particular the evaluation of the optimum detector operating
conditions in terms of operating sequence, supply voltages and operating temperature in order to achieve optimum
performance.
In the course of the eROSITA camera development, an engineering model of the eROSITA flight detector was
assembled and is used for tests since 2010. Based on these results and on the extensive tests with lab model detectors,
the design of the front-end electronics has meanwhile been finalized for the flight cameras. Furthermore, the
specifications for the other supply and control electronics were precisely concluded on the basis of the experimental
tests.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian
Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in 2013. eROSITA will perform an all-sky
survey lasting four years, followed by a phase of three years for pointed observations. eROSITA consists of seven
identical Mirror Modules, each equipped with 54 Wolter-I shells with an outer diameter of 360 mm. This would provide
an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular
resolution of 28 arcsec averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD
provides a field of view of 1°in diameter. In this paper we report on the instrument development and its status only.
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The instrument development is in phase C/D since fall 2009. The design driving science is the detection 100.000 Clusters of Galaxies up to redshift z ~1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular resolution of 28 - 30 arcsec, averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD provides a field of view of 1° in diameter.
The new X-ray telescope eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the main
instrument on the Russian new Spectrum-RG satellite, scheduled for launch in 2012. The primary scientific goal
of eROSITA is the detection of about 100,000 clusters of galaxies in an all sky survey. This allows a systematic
study on the large scale structures in the universe and will give new information about the nature of dark energy.
The focal plane detector is a 5 cm × 3 cm framestore PNCCD, an advanced successor of the XMM-Newton
PNCCD, designed and fabricated at the MPI Halbleiterlabor. It has 384 × 384 pixels of 75 μm × 75 μm in the
image area and will provide high position, time and spectral resolution as well as a high quantum efficiency for
X-ray photons in the energy range from 0.2 keV up to 10 keV. The first flight-like CCDs have been finished in
2008. In order to extensively test these new PNCCDs we developed an electronic test-setup. It is very versatile,
allowing us to test the CCDs under many different conditions and is appropriate to show at the same time
excellent performance of the detector. In this contribution we present in detail the electronic test-setup, some
test results and the conclusions which can be drawn for the eROSITA flight modules.
For the eROSITA X-ray telescope, which is planned to be launched in 2012, detectors were developed and
fabricated at the MPI Semiconductor Laboratory. The fully depleted, back-illuminated pnCCDs have an ultrathin
pn-junction to improve the low-energy X-ray response function and quantum efficiency. The device thickness of
450 μm is fully sensitive to X-ray photons yielding high quantum efficiency of more than 90% at photon energies of
10 keV. An on-chip filter is deposited on top of the entrance window to suppress visible and UV light which would
interfere with the X-ray observations. The pnCCD type developed for the eROSITA telescope was characterized
in terms of quantum efficiency and spectral response function. The described measurements were performed in
2009 at the synchrotron radiation sources BESSY II and MLS as cooperation between the MPI Semiconductor
Laboratory and the Physikalisch-Technische Bundesanstalt (PTB). Quantum efficiency measurements over a
wide range of photon energies from 3 eV to 11 keV as well as spectral response measurements are presented. For
X-ray energies from 3 keV to 10 keV the quantum efficiency of the CCD including on-chip filter is shown to be
above 90% with an attenuation of visible light of more than five orders of magnitude. A detector response model
is described and compared to the measurements.
A special type of CCD, the so-called PNCCD, was originally developed for the focal plane camera of the XMMNewton
space telescope. After the satellite launch in 1999, the MPI Halbleiterlabor continued the detector development
for various ground-based applications. Finally, a new X-ray PNCCD was designed again for a space telescope named
eROSITA. The space telescope will be equipped with an array of seven parallel oriented X-ray mirror systems of
Wolter-I type and seven cameras, placed in their foci. This instrumentation will permit the exploration of the X-ray
universe in the energy band from 0.3 keV up to 10 keV with a time resolution of 50 ms for a full image comprising
384 x 384 pixels. eROSITA will be accommodated on the new Russian Spectrum-RG satellite. The mission was already
approved by the responsible German and Russian space agencies. The detector development is focussed to fulfil the
scientific specifications for detector performance under the constraints of all the mechanical, power, thermal and
radiation hardness issues for space instrumentation. This considers also the recent change of the satellite's orbit. The
Lagrange point L2 was decided as new destination of the satellite instead of a low-Earth orbit (LEO). We present a
detailed description of the detector system and the current development status. The most recent test results are reported
here. Essential steps for completion of the seven focal plane detectors until satellite launch in 2012 will be itemized.
KEYWORDS: Electronics, Digital signal processing, Cameras, Sensors, X-rays, CCD cameras, Space telescopes, Signal processing, Charge-coupled devices, CCD image sensors
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.
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