J. Treis

Design and technology of DEPFET pixel sensors for linear collider applications

The performance requirements of vertex detectors for future linear collider experiments is very challenging especially for the detectors innermost sensor layers. The DEPleted Field Effect Transistor (DEPFET) combining detector and amplifier operation is capable to meet these requirements. A silicon technology is presented which allows production of large sensor arrays consisting of linear DEPFET detector structures. The envisaged pixel array offers a low noise and low power operation. To ensure a high radiation length a thinning technology based on direct wafer bonding is proposed.

DEPMOSFET active pixel sensor prototypes for the XEUS wide field imager

Active pixel sensors (APS) based on the DEPMOSFET (depleted p-channel MOSFET) recently produced at the MPI semiconductor laboratory are a promising new type of sensor to cope with the advanced requirements of the XEUS wide field imager. DEPMOSFET APS combine high energy resolution and random accessibility of pixels providing for highly flexible readout modes with fast readout speed. In the first prototype production, several design variants of 64 /spl times/ 64 pixel DEPMOSFET matrices with a pixel size of 75 /spl times/ 75 /spl mu/m/sup 2/ have been realized. A data acquisition system (DAQ) for evaluation of sensor prototypes has been developed, which allows for a performance characterization of the different designs. For operation, DEPMOSFET device, front-end IC and control ICs are integrated onto a readout hybrid. Device readout is done row by row, addressing and resetting one single matrix row at a time and processing the signals with a 64 channel parallel CMOS amplifier / multiplexer IC of the CAMEX type applying 8-fold correlated double sampling. Addressing and resetting of the matrix rows is done by two control ICs of the SWITCHER type fabricated in a high voltage CMOS technology. A number of readout hybrids has been built, the characterization of the different devices in terms of noise, spectral resolution and charge collection efficiency is in progress. The most promising DEPMOSFET matrix design variants, the DAQ system and measured key performance parameters of the devices are presented.

New results on DEPFET pixel detectors for radiation imaging and high energy particle detection

DEPFET pixel detectors are unique devices in terms of energy and spatial resolution because very low noise (ENC = 2.2e at room temperature) operation can be obtained by implementing the amplifying transistor in the pixel cell itself. Full DEPFET pixel matrices have been built and operated for autoradiographical imaging with imaging resolutions of 4.3 /spl plusmn/ 0.7 lp/mm at 22 keV. For applications in low energy X-ray astronomy the high energy resolution of DEPFET detectors is attractive. For particle physics, DEPFET pixels are interesting as low material detectors with high spatial resolution. For a Linear Collider detector the readout must be very fast. New readout chips have been designed and produced for the development of a DEPFET module for a pixel detector at the proposed TESLA collider (520 /spl times/ 4000 pixels) with 50 MHz line rate and 25 kHz frame rate. The circuitry contains current memory cells and current hit scanners for fast pedestal subtraction and sparsified readout. The imaging performance of DEPFET devices as well as present achievements towards a DEPFET vertex detector for a Linear Collider are presented.

First results of DEPFET based Active Pixel Sensor prototypes for the XEUS Wide Field Imager

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.

DEPFET based focal plane instrumentation for X-ray imaging spectroscopy in space

The combined Detector-Amplifier structure DEPFET (Depleted P-channel FET) is a promising new building block for large area silicon detector devices, e.g. in X-ray astronomy and high energy physics. The DEPFET structure combines excellent energy resolution, high speed readout and low power consumption with the attractive features of random accessibility of pixels and on-demand readout. In addition, it features all advantages of a sideways depleted device in terms of fill factor and quantum efficiency. Finally, the newly introduced combination of a DEPFET structure and a silicon drift diode (SDD) like drift ring structure to form a so-called macropixel device allows for large flexibility in terms of pixel size. Presently, focal plane instrumentation for X-ray imaging spectroscopy based on DEPFET arrays is being developed for a variety of space experiments with very different requirements. The next European X-ray Observatory XEUS is going to have a wide field imager covering the full FOV, which consists of a large-area DEPFET array. The concept for the French-Italian X-ray Astronomy mission SIMBOL-X includes a focal plane array based on DEPFET macropixels, and, finally, the MIXS (Mercury Imaging X-ray Spectrometer) instrument on the European Mercury exploration mission BepiColombo also contains two DEPFET macropixel based focal plane arrays. While for XEUS and SIMBOL-X excellent energy resolution and quantum efficiency in the low energy range are mandatory, radiation hardness is imperative for MIXS. A first production of DEPFET prototype arrays showed very promising results. More sophisticated prototype devices for SIMBOL-X and XEUS with a large sensitive area as well as flight grade devices for the MIXS instrument have been produced at the MPI semiconductor laboratory in Munich/Germany. The strategies to meet the respective requirements by an appropriate design of the focal plane instrumentation are shown as well as first results of the new production.

ASTEROID: A new 64 channel ASIC for source follower based readout of the MIXS DEPFET arrays on BepiColombo

ASTEROID is a new 64 channel ASIC developed to read out a DEPFET macropixel array. This sensor will be part of the MIXS instrument that will be used in the ESAs BepiColombo Mercury exploration mission. The detector will operate in an environment with high density of solar proton flux that will cause severe radiation damage and an increase of leakage current during mission lifetime. Given the relatively high value of the leakage current, a high speed readout and a proper cooling of the detector is needed in order to achieve the required energy resolution. The contribution of the readout electronics to the noise should be smaller than 10 electrons r.m.s. The foreseen pixel arrays are optimized for source follower readout. In this operating mode of the DEPFETs, the readout electronics is AC-coupled. This allows easy coping with non homogeneity of the pixel matrix and - most of all - an easy compensation of threshold voltage shifts of the DEPFET devices due to radiation damage. In order to achieve the low noise value required at short processing time, ASTEROID implements a trapezoidal weighting function, which represents the time-limited optimum filter for white series noise. This is the major electronics noise source at the foreseen readout speed. Measurements on a first prototype of the ASIC have shown the very satisfactory resolution of 147 eV on Mn-Kalphapeak of 55Fe with a readout time of approximately 1.2 mus, that would lead, considering the settling time of the DEPFET, to a total processing time of 4.2 mus. We present the experimental results of a first prototype that includes 4 analog channels and a new digital section for the generation of the timing signals of the circuit. This digital section is based on radiation- hardened dual-port memory cells and registers and has already been implemented to serve all the 64 channels foreseen for the final version of the ASIC.

Performance of ASTEROID: A 64 channel ASIC for source follower readout of DEPFET matrices for X-ray astronomy

We present the complete 64 channel version of the ASTEROID ASIC, developed to readout DEPFET Macro-Pixel Arrays operated in source follower mode. These sensors have been designed for the X-Ray Astronomy applications Simbol-X and BepiColombo. Both are satellite based missions that require a detector system with high speed readout, high energy resolution and radiation hardness properties. The foreseen baseline pixel arrays are optimized for source follower readout. In this operating mode of the DEPFETs, the readout electronics is AC-coupled. This allows easy coping with non homogeneity of the pixel matrix and an easy compensation of threshold voltage shifts of the DEPFET devices due to radiation damage. In order to achieve the low noise value required at short processing time, ASTEROID implements a trapezoidal weighting function. This filtering scheme substitutes the Multi-Correlated-Double-Sampling used so far by CAMEX ASICs and represents the time-limited optimum filter for white series noise, which is dominant at the foreseen readout speed. Measurements on single pixels had shown that an electronics noise as low as of about 8 electrons r.m.s. is achievable at room temperature with a total processing time of 4µs. In this work, preliminary measurements on the complete 64 channel readout ASIC coupled with a 64×64 DEPFET matrix have confirmed this noise performance. This result fits the requirements both of BepiColombo and Simbol-X. Also the other parameters of the ASIC have been tested on the 64 channel version. In order to fully operate the 64 channels in parallel, the ASIC contains a digital section that generates the timing signals for the analog circuits. This digital section is based on SEU-immune dual port memory cells. The outputs of the 64 analog channels are multiplexed to one serial output with a speed up to 20MHz. Thanks to the new multiplexer architecture adopted, ASTEROID will be the only ASIC that allows window-mode readout of the pixel matrices, i.e. that allows to address selectively arbitrary sub-areas of the pixel array or even to readout different sub-areas at different speeds.

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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Pixelated semiconductor detectors for X-ray imaging spectroscopy are foreseen as key components of the payload of various future space missions exploring the x-ray sky. Located on the platform of the new Spectrum-Roentgen-Gamma satellite, the eROSITA (extended Roentgen Survey with an Imaging Telescope Array) instrument will perform an imaging all-sky survey up to an X-ray energy of 10 keV with unprecedented spectral and angular resolution. The instrument will consist of seven parallel oriented mirror modules each having its own pnCCD camera in the focus. The satellite born X-ray observatory SIMBOL-X will be the first mission to use formation-flying techniques to implement an X-ray telescope with an unprecedented focal length of around 20 m. The detector instrumentation consists of separate high- and low energy detectors, a monolithic 128 × 128 DEPFET macropixel array and a pixellated CdZTe detector respectively, making energy band between 0.5 to 80 keV accessible. A similar concept is proposed for the next generation X-ray observatory IXO. Finally, the MIXS (Mercury Imaging X-ray Spectrometer) instrument on the European Mercury exploration mission BepiColombo will use DEPFET macropixel arrays together with a small X-ray telescope to perform a spatially resolved planetary XRF analysis of Mercurys crust. Here, the mission concepts and their scientific targets are briefly discussed, and the resulting requirements on the detector devices together with the implementation strategies are shown.

256 Pixel DEPFET Detectors for X-Ray Astronomy

The Mercury imaging X-ray spectrometer (MIXS) on board of ESAs fifth cornerstone mission BepiColombo will be the first space instrument using DEpleted P-channel FET (DEPFET) based detectors. The MIXS spectrometer comprises two channels with identical focal plane detectors and is dedicated to energy resolved imaging of X-ray fluorescence from the mercurial surface. We report on the characterization, integration, and spectroscopic qualification of MIXS flight detectors. Detector chips were precharacterized at die level in order to select the best dies for integration and to do homogeneity and yield studies. Then, the detector chips were integrated to MIXS Detector Plane Arrays (DPAs), a complicated process due to the sophisticated mechanical structure, which allows the thermal decoupling of the detector from its readout and control chips. After integration, spectroscopic qualification measurements were done in order to analyze the detector performance and to prove the excellent spectroscopic performance of the DEPFET Macropixel detectors over a wide temperature range. The integration and spectroscopic qualification of all flight grade modules is now successfully completed.