Florian Aschauer

Development and Characterization of New 256

DEPFET detectors are silicon (Si) active pixel sensors designed and manufactured in the Max-Planck-Institut semiconductor lab. Their high spatial resolution and high energy resolution in X-rays make them attractive for particle tracking in colliders and for X-ray astronomy. This technology is foreseen for the Wide Field Imager of the International X-ray Observatory currently in study with ESA, NASA, and JAXA. New DEPFET matrixes with 256 × 256 pixels of 75-μm pitch have been produced, mounted on ceramic boards with dedicated front-end electronics and integrated in a new setup able to acquire large-format images and spectra. Excellent homogeneity has been observed. Energy resolution as low as 127 eV FWHM at 5.9 keV has been obtained including all single events of the matrix back illuminated at -45<;°C and read out at a 300-frames/s rate. This paper presents experimental methods and results.

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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 telescopes expected 5 arcsec point spread function. The WFIs 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.

256 Pixel DEPFET Detectors for X-Ray Astronomy

The eROSITA space telescope is presently developed for the determination of cosmological parameters and the equation of state of dark energy via evolution of galaxy clusters. It will perform in addition a census of the obscured black hole growth in the Universe. The instrument development was also strongly motivated by the intention of a first imaging X-ray all-sky survey above an energy of 2 keV. eROSITA is scientific payload on the Russian research satellite SRG and the mission duration is scheduled for 7.5 years. The instrument comprises an array of seven identical and parallel-aligned telescopes. The mirror system is of Wolter-I type and the focal plane is equipped with a PNCCD camera for each of the telescopes. This instrumentation permits spectroscopy and imaging of X-rays in the energy band from 0.3 keV to 10 keV with a field of view of 1.0 degree. The camera development is done at the Max-Planck-Institute for Extraterrestrial Physics and in particular the key component, the PNCCD sensor, has been designed and fabricated at the semiconductor laboratory of the Max-Planck Society. All produced devices have been tested and the best selected for the eROSITA project. Based on calculations, simulations, and experimental testing of prototype systems, the flight cameras have been configured. We describe the detector and its performance, the camera design and electronics, the thermal system, and report on the latest estimates of the expected radiation damage taking into account the generation of secondary neutrons. The most recent test results will be presented as well as the status of the instrument development.

The wide-field imager for IXO: status and future activities

The combined Detector/Amplifier structure DePFET (Depleted P-channel Field Effect Transistor) features excellent energy resolution, low noise readout at high speed and low power consumption. This is combined with the possibility of random acessibility of pixels and on-demand readout. In addition it possesses all advantages of a sideways depleted device, i.e. 100% fill factor and very good quantum efficiency. Combining the DePFET structure with a silicon drift detector (SDD) like drift ring structure forms a so-called macropixel device which allows for large flexibility in terms of pixel size. All this makes DePFET macropixels a promising new building block for large area silicon radiation detector devices. In this paper, first results of qualifying measurements performed with a macropixel prototype are presented. The detector shows good linearity over the investigated energy range and no significant charge loss within the pixel area.

Progress of the x-ray CCD camera development for the eROSITA telescope

Focal plane instrumentation based on the combined Detector-Amplifier structure DEPFET (Depleted P-channel FET) are being considered for the application in a large variety of experiments in X-ray astronomy and high energy physics. DEPFET based detectors show excellent energy resolution and can be read out at high speed. In addition, they combine low power consumption with the attractive features of random accessibility of pixels and on-demand readout. They feature all advantages of a sideways depleted device in terms of fill factor and quantum efficiency, and so-called macropixel devices, being a combination of a DEPFET with a drift ring structure, allow for large flexibility in terms of pixel size. Presently, DEPFET based focal plane instrumentation for X-ray imaging spectroscopy is being developed for a variety of space experiments with very different requirements. The payload of the French-Italian X-ray Astronomy mission SIMBOL-X includes a focal plane array based on DEPFET macropixels, and one of the instruments on board the European Mercury exploration mission BepiColombo, the so-called MIXS (Mercury Imaging X-ray Spectrometer) instrument, also uses DEPFET macropixel based focal plane arrays for the detection of X-rays. In both cases, the performance of the respective X-ray optics demands the use of macropixel matrices due to the large required pixel sizes. The MPI semiconductor laboratory in Munich has produced prototype devices for SIMBOL-X with a large sensitive area as well as the first flight grade devices for the MIXS instrument; and the first large-area detectors have been tested. The devices show excellent performance in terms of energy resolution, peak-to-background ratio and homogeneity. Here, the requirements of the respective experiments on their detectors are outlined, together with the strategies to comply with the requirements by choosing a suitable readout strategy and an appropriate design of the focal plane instrumentation. Finally, the first test results of the large area macropixel prototype devices are shown.

Performance and spectroscopic behaviour of DePFET macropixels

DEPFET detectors are silicon active pixel sensors for X-ray imaging spectroscopy. They will be used for the MIXS instrument of BepiColombo planetary mission and they are foreseen for the Wide Field Imager of the International X-ray Observatory currently in study with ESA, NASA and JAXA. New DEPFET matrixes with 256 × 256 pixels of 75 μm pitch have been produced, mounted on ceramic boards with dedicated front-end electronics and integrated in a new set-up able to acquire large-format images and spectra. Excellent homogeneity has been observed on two samples. Energy resolution as low as 129 eV FWHM at 5.9 keV has been obtained including all single events of the matrix back illuminated at −40°C and read out at a 300 frames per second rate. Experimental methods and results are reported.

DEPFET macropixel arrays as focal plane instrumentation for SIMBOL-X and MIXS on BepiColombo

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 ESAs 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 Mercurys 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.

Development and characterization of new 256 × 256 pixel DEPFET detectors for X-ray astronomy

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 DEPFET-based focal plane detectors for MIXS on BepiColombo

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 telescopes expected 5 arcsec point spread function. The WFIs 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.

Design and performance of the eROSITA focal plane instrumentation

BepiColombo, ESAs fifth cornerstone mission, is a planetary exploration mission to Mercury. On board of BepiColombos Mercury Planetary Orbiter (MPO), the MIXS instrument will perform a complete X-ray fluorescence analysis of Mercurys 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.