KEYWORDS: Field effect transistors, Electrons, Sensors, Transistors, Signal processing, X-ray imaging, Imaging systems, Analog electronics, Active sensors, Imaging spectroscopy
Since many years DEPFETs have been developed for space and ground based X-ray imaging and spectroscopy experiments. Prototypes have been successfully tested and qualified. Over the past years, the DEPFET technology was improved and additional features of DEPFETs were developed: increase of dynamic range, improvement of radiation hardness, implementation of electronic shutters, integration of an analog storage, reduction of readout noise and improvement of the low energy performance. This paper will present two novel DEPFET concepts which are able to fulfill the demanding requirements of the proposed ATHENA Wide Field Imager. It will summarize the most important DEPFET characteristics on the basis of measurements and device simulations, taking into account the given boundary conditions of the mission.
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.
Petra Majewski, Florian Aschauer, Alexander Bähr, Giulio de Vita, Bettina Günther, Kathrin Hermenau, Sven Herrmann, Martin Hilchenbach, Thomas Lauf, Peter Lechner, Gerhard Lutz, Danilo Miessner, Matteo Porro, Jonas Reiffers, Gerhard Schaller, Florian Schopper, Heike Soltau, Alexander Stefanescu, Rafael Strecker, Lothar Strüder, Johannes Treis
The Mercury Imaging X-ray Spectrometer (MIXS) is an instrument on board of the 5th ESA cornerstone mission
BepiColombo. This Spectrometer comprises two instruments for imaging x-ray spectroscopy of the Mercury
surface. The detector plane arrays (DPA) for the energy and spatial resolved detection of x-rays are based on
DEPFET (Depleted P-channel FET) macropixel detectors with 64×64 pixel each and 300×300 μm2 pixel
size. The MIXS target energy band is from 0.5 to 7 keV with an energy resolution better than 200 eV at 1 keV
at mission end. This allows to access the Fe-L line at about 0.7 keV, which was not accessible to previous
instruments, and to separate the x-ray lines of the elements of interest.
Before a detector chip is integrated into a detector module, it is electrically pre-characterized in order to select
only the best chips for the complex and time-consuming integration. The high degree of complexity of the
integration process comes from the need to thermally decouple the detector chip from its readout and steering
ASICs by a sophisticated mechanical structure, due to the limited amount of cooling power available for the
instrument. After the spectroscopic characterization of the detector modules, the flight and flight spare detectors
were calibrated at the PTB (Physikalisch-Technische Bundesanstalt) beamlines at the BESSY-II synchrotron.
We report on the pre-characterization, integration, qualification and calibration of MIXS flight and flight spare
detectors, which is now successfully completed.
To improve the signal to noise level, devices for optical and x-ray astronomy use techniques to suppress background
events. Well known examples are e.g. shutters or frame-store Charge Coupled Devices (CCDs). Based
on the DEpleted P-channel Field Effect Transistor (DEPFET) principle a so-called Gatebale DEPFET detector
can be built. Those devices combine the DEPFET principle with a fast built-in electronic shutter usable for
optical and x-ray applications. The DEPFET itself is the basic cell of an active pixel sensor build on a fully
depleted bulk. It combines internal amplification, readout on demand, analog storage of the signal charge and a
low readout noise with full sensitivity over the whole bulk thickness. A Gatebale DEPFET has all these benefits
and obviates the need for an external shutter.
Two concepts of Gatebale DEPFET layouts providing a built-in shutter will be introduced. Furthermore proof
of principle measurements for both concepts are presented. Using recently produced prototypes a shielding of
the collection anode up to 1 • 10−4 was achieved. Predicted by simulations, an optimized geometry should result
in values of 1 • 10−5 and better. With the switching electronic currently in use a timing evaluation of the shutter
opening and closing resulted in rise and fall times of 100ns.
The Wide Field Imager (WFI) of the International X-ray Observatory (IXO) is an X-ray imaging spectrometer based on a
large monolithic DePFET (Depleted P-channel Field Effect Transistor) Active Pixel Sensor. Filling an area of
10 x 10 cm2 with a format of 1024 x 1024 pixels it will cover a field of view of 18 arcmin. The pixel size of
100 x 100 μm2 corresponds to a fivefold oversampling of the telescope's expected 5 arcsec point spread function. The
WFI's basic DePFET structure combines the functionalities of sensor and integrated amplifier with nearly Fano-limited
energy resolution and high efficiency from 100 eV to 15 keV. The development of dedicated control and amplifier
ASICs allows for high frame rates up to 1 kHz and flexible readout modes. Results obtained with representative
prototypes with a format of 256 x 256 pixels are presented.
We report on the first results from a new setup for electrical qualification measurements of DEPFET pixel detector
matrices. In order to measure the transistor properties of all pixels, the DEPFET device is placed into
a benchtest setup and electrically contacted via a probecard. Using a switch matrix, each pixel of the detector
array can be addressed individually for characterization.
These measurements facilitate to pre-select the best DEPFET matrices as detector device prior to the mounting
of the matrix and allow to investigate topics like the homogeneity of transistor parameters on device, wafer
and batch level in order to learn about the stability and reproducibility of the production process. Especially
with regard to the detector development for the IXO Wide Field Imager (WFI), this yield learning will be an
important tool.
The first electrical qualification measurements with this setup were done on DEPFET macropixel detector flight
hardware, which will form the FPAs of the Mercury Imaging X-ray Spectrometer (MIXS) on board of the 5th
ESA cornerstone mission BepiColombo. The DEPFET array consists of 64×64 macropixel for which the transfer,
output and clear characteristics were measured.
The Wide Field Imager (WFI) of the International X-ray Observatory (IXO) is an X-ray imaging spectrometer based on a
large monolithic DePFET (Depleted P-channel Field Effect Transistor) Active Pixel Sensor. Filling an area of
10 × 10 cm² with a format of 1024 × 1024 pixels it will cover a field of view of 18 arcmin. The pixel size of
100 × 100 μm² corresponds to a fivefold oversampling of the telescope's expected 5 arcsec point spread function. The
WFI's basic DePFET structure combines the functionalities of sensor and integrated amplifier with nearly Fano-limited
energy resolution and high efficiency from 100 eV to 15 keV. The development of dedicated control and amplifier
ASICs allows for high frame rates up to 1 kHz and flexible readout modes. Results obtained with representative
prototypes with a format of 256 × 256 pixels are presented.
J. Treis, L. Andricek, F. Aschauer, K. Heinzinger, S. Herrmann, T. Lauf, P. Lechner, G. Lutz, P. Majewski, M. Porro, J. Reiffers, R. Richter, G. Schaller, M. Schnecke, F. Schopper, H. Soltau, A. Stefanescu, L. Strüder, G. de Vita
X-ray detectors based on arrays of DEPFET macropixels, which consist of a silicon drift detector combined with
a detector/amplifier structure DEPFET as readout node, provide a convenient and flexible way to adapt the pixel
size of a focal plane detector to the resolving power of any given X-ray optical system. Macropixels combine the
traditional benefits of an SDD, like scalability, arbitrary geometry and excellent QE even in the low energy range,
with the advantages of DEPFET structures: Charge storage capability, near Fano-limited energy resolution, low
power consumption and high speed readout. Being part of the scientific payload of ESA's BepiColombo mission,
the MIXS instrument will be the first instrument to make use of DEPFET macropixel based FPA detectors in
space. MIXS will perform a complete planetary X-ray fluorescence analysis of Mercury's crust with high spectral
and spatial resolution. MIXS will contain two focal plane detectors consisting of a 64 × 64 macropixel matrix
with 300 × 300 μm2 pixel size. The main challenges for the instrument are the difficult radiation and thermal
environment around Mercury, requiring high speed readout and sophisticated thermal management to reduce
the impact of thermally generated leakage current within an irradiated detector. Dedicated VLSI integrated
readout electronics has been developed for MIXS: a fast, radiation hard, low power, high voltage switch circuit
to control the device, and a low noise, high speed amplifier/shaper IC. Detector assemblies have been built,
electrical screening tests for the flight models and spectroscopical qualification tests are in progress.
J. Treis, L. Andricek, F. Aschauer, S. Herrmann, K. Heinzinger, M. Hilchenbach, T. Lauf, P. Lechner, G. Lutz, P. Majewski, M. Porro, R. Richter, G. Schaller, M. Schnecke, F. Schopper, H. Soltau, A. Stefanescu, L. Strüder, G. de Vita
BepiColombo, ESA's fifth cornerstone mission, is a planetary exploration mission to Mercury. On board of
BepiColombo's Mercury Planetary Orbiter (MPO), the MIXS instrument will perform a complete X-ray fluorescence
analysis of Mercury's crust with unprecedented spectral and spatial resolution. This is achieved by
using a lightweight X-ray mirror system and by using of DEPFET based Macropixel devices as X-ray detectors.
DEPFET based Macropixel detectors combine the advantages of the DEPFETs, like flexible readout modes,
Fano-limited energy resolution and low power consumption, with the properties of the drift detectors, like arbitrary
scalable pixel size and geometry. In addition, the excellent properties of the entrance window, like good
QE even in the low energy range and 100% fill factor, are preserved. An energy resolution better than 200 eV
FWHM @ 1 keV and an energy range from 0.5 keV to 10 keV, for a pixel size of 300 x 300 square micron, is
required. To be sensitive to the Iron-L energy, the quantum efficiency at 0.5 keV is required to be larger than
80%. Main challenges for the instrument are the difficult radiation and thermal environment in the mercury
orbit. The production of the first batch of flight devices has been finished at the MPI semiconductor laboratory,
and first laboratory modules have been built. The properties of the sensors have been evaluated at the BESSY
facility, and the devices have been used for XRF measurements at the ELETTRA synchrotron facility in Trieste.
The results of the first tests will be presented here.
The observation of astrophysical objects in the mid-infrared requires Blocked Impurity Band (BIB) detectors
based on n-doped Silicon. It is desirable to observe faint astronomical objects with such a detector, which can
be achieved with a high Signal to Noise ratio. One possibility is an implemented Depleted P-channel Field Effect
Transistor (DEPFET) Active Pixel Sensor (APS)1 on the BIB detector in order to be free of interconnection
stray capacitance. A noise of 2 e- ENC and a current amplification of 300 pA per e- can be obtained at room temperature.
These detectors operate at a temperature range from 6 K to 12 K. The DEPFET is operated under these
conditions to investigate the functional principle of the detector. We show results of characteristic and dynamic
measurements of the single pixel DEPFET at low temperature. We irradiate the DEPFET single pixel with
x-rays originating from the nuclear decay of Fe55 and take a spectrum of the Kα- and Kβ-line. Uncomplete clear
is identified with freeze-out of the signal charge into ionized shallow donor states in the heavily doped internal
Gate of the DEPFET due to low thermal energy. We found a solution to emit the localized signal charges into
the conduction band in order to ensure the transport from the internal Gate to the Clear contact.
KEYWORDS: Sensors, Field effect transistors, X-rays, Analog electronics, Field programmable gate arrays, Silicon, X-ray imaging, Prototyping, Space operations, Quantum efficiency
The large collecting area of the X-ray optics on the International X-ray Observatory (IXO), their good angular
resolution, the wide bandwidth of X-ray energies and the high radiation tolerance required for the X-ray detectors
in the focal plane have stimulated a new development of devices which unify all those science driven specifications
in one single detector. The concept of a monolithic, back-illuminated silicon active pixel sensor (APS) based on
the DEPFET structure is proposed for the IXO mission, being a fully depleted, back-illuminated 450 μm thick
detector with a physical size of about 10 × 10 cm2 corresponding to the 18 arcmin field of view. The backside
will be covered with an integrated optical light and UV-filter. Corresponding to the 5 arcsec angular resolution
of the X-ray optics, 100 x 100 cm2 large pixels in a format of approximately 1024 x 1024 are envisaged, matching
the point spread function of approximately 500 μm HEW of the optics. The energy range from 100 eV to 15 keV
is achieved by an ultra thin radiation entrance window for the low energies and 450 μm depleted silicon thickness
for higher energies. The fast readout of 1.000 full frames per second is realized by a dedicated analog CMOS
front end amplifier IC. The detector device is intrinsically radiation hard. The leakage current from the bulk
damage is controlled through the operation temperature around -60 °C and by the high readout speed. Results
of various prototype measurements will be shown.
DEPFET Macropixel detectors, based on the fusion of the combined Detector-Amplifier structure DEPFET with
a silicon drift chamber (SDD) like drift ring structure, combine the excellent properties of the DEPFETs with
the advantages of the drift detectors. As both device concepts rely on the principle of sideways depletion, a
device entrance window with excellent properties is obtained at full depletion of the detector volume.
DEPFET based focal plane arrays have been proposed for the Focal Plane Detectors for the MIXS (Mercury
Imaging X-ray Spectrometer) instrument on BepiColombo, ESAs fifth cornerstone mission, with destination
Mercury. MIXS uses a lightweight Wolter Type 1 mirror system to focus fluorescent radiation from the Mercury
surface on the FPA detector, which yields the spatially resolved relative element abundance in Mercurys crust.
In combination with the reference information from the Solar Intensity X-ray Spectrometer (SIXS), the element
abundance can be measured quantitatively as well. The FPA needs to have an energy resolution better than
200 eV FWHM @ 1 keV and is required to cover an energy range from 0.5 keV to 10 keV, for a pixel size of
300 x 300 μm2. Main challenges for the instrument are the increase in leakage current due to a high level of
radiation damage, and the limited cooling resources due to the difficult thermal environment in the mercury
orbit. By applying an advanced cooling concept, using all available cooling power for the detector itself, and
very high speed readout, the energy resolution requirement can be kept during the entire mission lifetime up to
an end-of-life dose of ~ 3 × 1010 10 MeV p / cm2. The production of the first batch of flight devices has been
finished at the MPI semiconductor laboratory, and first prototype modules have been built. The results of the
first tests will be presented here.
Simbol-X is a French-Italian-German hard energy X-ray mission with a projected launch in 2014. Being sensitive in the
energy range from 500 eV to 80 keV it will cover the sensitivity gap beyond the energy interval of today's telescopes
XMM-Newton and Chandra. Simbol-X will use an imaging telescope of nested Wolter-I mirrors. To provide a focal
length of 20 m it will be the first mission of two independent mirror and detector spacecrafts in autonomous formation
flight.
The detector spacecraft's payload is composed of an imaging silicon low energy detector in front of a pixelated
cadmium-telluride hard energy detector. Both have a sensitive area of 8 × 8 cm2 to cover a 12 arcmin field of view and a pixel size of 625 × 625 μm2 adapted to the telescope's resolution of 20 arcsec. The additional LED specifications are:
high energy resolution, high quantum efficiency, fast readout and optional window mode, monolithic device with 100 %
fill factor and suspension mounting, and operation at warm temperature.
To match these requirements the low energy detector is composed of 'active macro pixels', combining the large, scalable
area of a Silicon Drift Detector and the low-noise, on-demand readout of an integrated DEPFET amplifier. Flight
representative prototypes have been processed at the MPI semiconductor laboratory, and the prototype's measured
performance demonstrates the technology readiness.
Two new DEPFET concepts are presented motivated by potential applications in adaptive optics and
in synchrotron radiation experiments at the future Free Electron
X-ray Laser (XFEL) in Hamburg.
The gatable DEPFET structure allows the selection of signal charges arriving in a predefined time
interval. Charges produced outside this gate interval are lead to a sink electrode while charge
collected already is protected and kept for later delayed readout.
In synchrotron radiation experiments one faces the challenge of being sensitive enough for single X-ray
photons in some parts of the detector while on other regions a very large charge due to the
superposition of many X-rays has to be measured. A DEPFET with strongly non-linear
characteristics combines naturally excellent energy resolution with high dynamic range, large charge
handling capability and high read out speed.
DEPMOSFET based Active Pixel Sensor (APS) matrices are a new detector concept for X-ray imaging spectroscopy missions. They can cope with the challenging requirements of the XEUS Wide Field Imager and combine excellent energy resolution, high speed readout and low power consumption with the attractive feature of random accessibility of pixels. From the evaluation of first prototypes, new concepts have been developed to overcome the minor drawbacks and problems encountered for the older devices. The new devices will have a pixel size of 75 μm × 75 μm. Besides 64 × 64 pixel arrays, prototypes with a sizes of 256 × 256 pixels and 128 × 512 pixels and
an active area of about 3.6 cm2 will be produced, a milestone on the way towards the fully grown XEUS WFI device. The production of these improved devices is currently on the way. At the same time, the development of the next generation of front-end electronics has been started, which will permit to operate the sensor devices with the readout speed required by XEUS. Here, a summary of the DEPFET capabilities, the concept of the sensors of the next generation and the new front-end electronics will be given. Additionally, prospects of new device developments using the DEPFET as a sensitive element are shown, e.g. so-called RNDR-pixels, which feature repetitive non-destructive readout to lower the readout noise below the 1 e- ENC limit.
The CAST experiment at CERN (European Organization of Nuclear Research) searches for axions from the sun. The axion is a pseudoscalar particle that was motivated by theory thirty years ago, with the intention to solve the strong CP problem. Together with the neutralino, the axion is one of the most promising dark matter candidates. The CAST experiment has been taking data during the last two years, setting an upper limit on the coupling of axions to photons more restrictive than from any other solar axion search in the mass range below 10-1 eV. In 2005 CAST will enter a new experimental phase extending the sensitivity of the experiment to higher axion masses. The CAST experiment strongly profits from technology developed for high energy physics and for X-ray astronomy:
A superconducting prototype LHC magnet is used to convert potential axions to detectable X-rays in the 1-10 keV range via the inverse Primakoff effect. The most sensitive detector system of CAST is a spin-off from space technology, aWolter I type X-ray optics in combination with a prototype pn-CCD developed for ESA's XMM-Newton mission. As in other rare event searches, background suppression and a thorough shielding concept is essential to improve the sensitivity of the experiment to the best possible. In this context CAST offers the opportunity to study the background of pn-CCDs and its long term behavior in a terrestrial environment with possible implications for future space applications. We will present a systematic study of the detector background of the pn-CCD of CAST based on the data acquired since 2002 including preliminary results of our background simulations.
DEPMOSFET based Active Pixel Sensor (APS) matrix devices, originally
developed to cope with the challenging requirements of the XEUS Wide
Field Imager, have proven to be a promising new imager concept for a
variety of future X-ray imaging and spectroscopy missions like Simbol-X. The devices combine excellent energy resolution, high speed readout and low power consumption with the attractive feature of random accessibility of pixels. A production of sensor prototypes with 64 x 64 pixels with a size of 75 μm x 75 μm each has recently been finished at the MPI semiconductor laboratory in Munich. The devices are built for row-wise readout and require dedicated control and signal processing electronics of the CAMEX type, which is integrated together with the sensor onto a readout hybrid. A number of hybrids incorporating the most promising sensor design variants has been built, and their performance has been studied in detail. A spectroscopic resolution of 131 eV has been measured, the readout noise is as low as 3.5 e- ENC. Here, the dependence of readout noise and spectroscopic resolution on the device temperature is presented.
KEYWORDS: Field effect transistors, Sensors, Prototyping, Transistors, Signal processing, Analog electronics, Electrons, Cadmium sulfide, Field programmable gate arrays, Imaging systems
The concept of an Active Pixel Sensor (APS) based on the
integrated detector/amplifier structure DEPFET (DEpleted P-channel
Field Effect Transistor) has been developed to cope with the
challenging requirements of the XEUS Wide Field Imager. The
DEPFET-APS combines high energy resolution, fast readout, and random accessible pixels allowing the application of flexible readout modes. First prototypes of DEPFET-based Active Pixel Sensors with a 64 x 64 pixel format and 75 μm x 75 μm pixel area have been produced at the MPI semiconductor laboratory. The APS is read out row by row, i.e. the pixel signals of one row are processed in parallel by a 64 channel CMOS amplifier/multiplexer chip of the CAMEX type. The addressing of one row of pixels for readout and reset is done by two control chips of the SWITCHER type fabricated in a high-voltage CMOS technology. The processing time for one row is of the order of a few micro-seconds. APS operation, the control and data acquisition system are described, and first experimental results are presented.
The Cern Axion Solar Telescope - CAST - uses a prototype 9 Tesla LHC superconducting dipole magnet to search for a hypothetical pseudoscalar particle, the axion, which was proposed by theory in the 1980s to solve the strong CP problem and which could be a dark matter candidate. In CAST a strong magnetic field is used to convert the solar axions to detectable photons via inverse Primakoff effect. The resulting X-rays are thermally distributed in the energy range of 1-7 keV and can be observed with conventional X-ray detectors. The most sensitive detector system of CAST is a pn-CCD detector originally developed for XMM-Newton combined with a Wolter I type X-ray mirror system. The combination of a focusing X-ray optics and a state of the art pn-CCD detector which combines high quantum efficiency, good spacial and energy resolution, and low background improves the sensitivity of the CAST experiment such that for the first time the axion photon coupling constant can be probed beyond the best astrophysical constraints. In this paper we report on the performance and status of the X-ray telescope and pn-CCD detector of CAST.
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.
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.
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.
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.
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.
For future x-ray satellite missions and other applications we propose a novel sensor which is based on the `DEPleted Field Effect Transistor (DEPFET)'. MOS-type DEPFETs (DEPMOS) are employed in prototype designs of pixel detectors ready for production. The device operated on a fully depleted silicon wafer allows an internal charge amplification directly above the position where the signal conversion takes place. A very low gate capacitance of the DEPMOS transistor leads to low noise amplification. In contrast to CCDs neither transfer loss nor `out of time events' can occur in a DEPFET-array. Fast imaging and low power consumption can be achieved by a row by row selection mode. The signal charge stored in a potential minimum below the transistor channel can be read out non destructively and repeatedly. By shifting the charge between two neighboring DEPMOS amplifiers the repeated signal readout leads to significant noise reduction. Concept, design and device simulations are presented and consequences of the expected properties for applications in x-ray imaging are discussed.
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.
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.
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.
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 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.
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.
The capabilities of the European Photon Imaging Camera (EPIC), the main instrument of ESA's 'Cornerstone' mission in X-ray astronomy with multiple mirrors (XMM), are discussed. The CCD characteristics, spatial resolution, energy bandpass and faint source sensitivity, spectral resolution and sensitivity, and timing capability are addressed, and the scientific rationale of the EPIC is summarized. The EPIC instrument system concept is briefly described.
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.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.