KEYWORDS: Sensors, X-rays, Analog electronics, Electronics, Monte Carlo methods, Aluminum, Silicon, Staring arrays, Field programmable gate arrays, Quantum efficiency
The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments of the International
X-ray Observatory (IXO). The HTRS is the only instrument matching the top level mission requirement of
handling a one Crab X-ray source with an efficiency greater than 10%. It will provide IXO with the capability
of observing the brightest X-ray sources of the sky, with sub-millisecond time resolution, low deadtime, low
pile-up (less than 2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6 keV). The HTRS
is a non-imaging instrument, based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a
circular envelope and a X-ray sensitive volume of 4.5 cm2 x 450 μm. As part of the assessment study carried
out by ESA on IXO, the HTRS is currently undergoing a phase A study, led by CNES and CESR. In this
paper, we present the current mechanical, thermal and electrical design of the HTRS, and describe the expected
performance assessed through Monte Carlo simulations.
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.
NHXM, under study by ASI (Agenzia Spaziale Italiana), is an X-ray observatory in the energy band between 0.5 and
80 keV and will have 3 telescopes dedicated to X-ray imaging with a field of view diameter of 12 arcmin and a focal
length of 10 m. We report on the development of high-speed and low-noise readout of a monolithic array of DEPFET
detector. The DEPFET based detectors, thanks to an intrinsic low anode capacitance, are suitable as low-energy
detectors (from 0.5 to 10 keV) of the new NHXM telescope.
The challenging requirements of the NHXM cameras regard the necessity to obtain images and spectra with
nearly Fano-limited energy resolution with an absolute time resolution of about 100 μs. In order to exploit the speed
capability of the DEPFET array, it has been developed a readout architecture based on the VELA circuit: a drain
current readout configuration to implement an extremely fast readout (2 μs/row) and preserve the excellent noise
performance of the detector.
In the paper the foreseen maximum achievable frame-rate and the best energy resolution will be presented in
order to assert the VELA suitability for X-ray imaging and spectroscopy.
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.
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.
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.
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