Search

The first DSSC 1-Mpixel camera became available at the European XFEL (EuXFEL) in the Hamburg area in February 2019. It was successfully tested, installed, and commissioned at the Spectroscopy and Coherent Scattering Instrument. DSSC is a high-speed, large-area, 2-D imaging detector system optimized for photon science applications in the energy range between 0.25 and 6 keV. The camera is based on direct conversion Si sensors and is composed of 1024 × 1024 pixels of hexagonal shape with a side length of 136 μm. The 256 application-specific integrated circuits (ASICs) provide full parallel readout, comprising analog filtering, digitization, and in-pixel data storage. In order to cope with the demanding X-ray pulse time structure of the EuXFEL, the DSSC provides a peak frame rate of 4.5 MHz. The first Mpixel camera is equipped with miniaturized silicon drift detector (MiniSDD) pixel arrays. The intrinsic response of the pixels and the linear readout limit the dynamic range but allow one to achieve noise values of about 60 electrons r.m.s. at the highest frame rate. The challenge of providing high-dynamic range (~104 photons/pixel/pulse) and single-photon detection simultaneously requires a nonlinear system front end, which will be obtained with the DEPFET active pixel technology foreseen for the advanced version of the camera. This technology will provide lower noise and a nonlinear response at the sensor level. This article describes the architecture of the whole detector system together with the main experimental results achieved up to now. [ABSTRACT FROM AUTHOR]

Depleted field effect transistors (DEPFET) are used to achieve very low noise signal charge readout with sub-electron measurement precision. This is accomplished by repeatedly reading an identical charge, thereby suppressing not only the white serial noise but also the usually constant 1/f noise. The repetitive non-destructive readout (RNDR) DEPFET is an ideal central element for an active pixel sensor (APS) pixel. The theory has been derived thoroughly and results have been verified on RNDR-DEPFET prototypes. A charge measurement precision of 0.18 electrons has been achieved. The device is well-suited for spectroscopic X-ray imaging and for optical photon counting in pixel sensors, even at high photon numbers in the same cell. [ABSTRACT FROM AUTHOR]

This work presents the experimental results from the characterization of the second prototype of a high accuracy (in terms of linearity, mismatch and noise) injection circuit to be used for in-pixel calibration of a large sensor matrix. The circuit was designed for the calibration of the pixel cell unit of a hybrid pixel device, the DEPFET Sensor with Signal Compression (DSSC) chip, for the large format imager at the European X-ray Free Electron Laser (XFEL), but, in principle, it can be used also for other kinds of detectors, e.g., deep N-well monolithic CMOS sensors. In the case of hybrid pixels, the injection circuit is particularly useful to test the functionality of the readout electronics already at the chip level, when no sensor is connected to the chip. Two injection techniques have been investigated: one for a charge sensitive amplification and the other for a transresistance readout channel. The aim of the paper is to describe the architecture of the calibration circuit, which has been implemented in a 130-nm CMOS technology, and to present the results from the characterization of the second prototype. [ABSTRACT FROM AUTHOR]

The Mercury imaging X-ray spectrometer (MIXS) on board of ESA's 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. [ABSTRACT FROM PUBLISHER]

The European X-ray Free Electron Laser (XFEL) under construction in Hamburg (Germany) will be able to deliver high intensity X-ray pulses of few tens of femto seconds of duration, at 5 MHz pulse repetition rate. Thanks to its characteristics, this instrument will open up new research opportunities for experiments in femto chemistry, structural biology and material research. A high speed focal plane detector system has been presented, based on a novel non-linear DEPFET as a detector. DEPFETs have been chosen since they can provide excellent energy resolution and high speed readout, a fundamental property to cope with the very demanding pulse time structure of XFEL. Full parallel readout is required, with every channel comprising analog filtering, data conversion and memory storage. In this paper we show results for the first prototype of the analog front end that implements the current readout of the DEPFET pixel. The circuit is based on the Flip Capacitor Filter technique, here briefly presented, and has been designed in 130 nm 1.2 V CMOS technology from IBM. Careful characterization of the individual circuit alone and also connected to a single pixel linear detector has been carried out and the measured performance is summarized. [ABSTRACT FROM AUTHOR]

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\,\times\,256 pixels of 75-\mum 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\,^\circC and read out at a 300-frames/s rate. This paper presents experimental methods and results. [ABSTRACT FROM AUTHOR]

DePMOS based Active Pixel Sensor (APS) matrix is a new detector concept for X-ray imaging and spectroscopy applications. This type of X-ray detector can provide excellent energy resolution and high-speed readout. Both these features and the advantage of random pixel accessibility can fulfill the requirements of new space applications, like the XEUS Wide Field Imager. In a matrix arrangement, each pixel must be read out by a time variant filter, so a new readout mechanism and a proper multi-channel integrated shaping amplifier are needed. To operate at the required fast processing time (e.g., 4 µs per line) DePMOS transistor cannot be operated in the classical source follower configuration, because this results in a long settling time. So a new design for multi-channel readout of the DePMOS matrix has to be considered. We propose a new fast readout concept, which is based on the DePMOS drain current readout and processing. [ABSTRACT FROM AUTHOR]

In this work we demonstrate theoretically and experimentally the capability to reduce the readout noise of an optical and X-ray photon detector based on the semiconductor DEPFET device below a level of only 0.3e- ENC (equivalent noise charge). The readout method used is called "Repetitive Non Destructive Readout" (RNDR) and was realized by placing two single DEPFET-devices next to each other and by coupling their charge storing region by an additional gate. By transferring the stored charge from one DEPFET to the other and vice versa the same charge can be measured non-destructively and arbitrarily often. Taking the average value of a large number n of these measurements, the noise is reduced by 1/√n The main advantage of such a detector is to greatly reduce the contribution of the 1/f noise to the readout noise. The theoretically and experimentally achievable resolution for different operating parameters (leakage current, readout noise, number and duration of readouts) was investigated by Monte-Carlo simulations and verified on a real RNDR minimatrix (pixelarray). Single optical photon detection with high quantum efficiency and, even more fascinating, the possibility to distinguish between different numbers of photons, e.g., 100 from 101 are demonstrated in measurements. [ABSTRACT FROM AUTHOR]

A modified Depleted P-Channel Field Effect Transistor (DEPFET) is the key feature of the DEPFET Sensor with Signal Compression (DSSC), a 1 Mpixel X-ray camera aiming at ultra-fast imaging of soft X-rays at the European XFEL. Operation of large-area devices with a large number of DSSC-type DEPFET pixels requires the accurate knowledge of the sensitivity of the response to the relevant DEPFET parameters. The paper presents the experimental qualification of the response of DSSC-type DEPFET pixels in the space of 4 relevant parameters: drain current, source voltage, drain voltage and back side voltage. The obtained results allow estimation of the impact of the inevitable parameter fluctuations in large monolithic sensors and of the actual trimming range of the shape of signal compression in view of the pixelwise calibration of the 1 Mpixel DSSC camera. [ABSTRACT FROM AUTHOR]

Abstract: Depleted P-channel Field Effect Transistor (DEPFET) Macropixel detectors have been designed for X-ray applications and the prototypes with 1×1mm2 pixel size have been fabricated. The prototype applies a newly designed DEPFET structure with drain-clear-gate (DCG) as the readout element of a silicon drift detector. Therefore, the size of Macropixel detectors can be adjusted to match the requirement of the instrument on spatial resolution from about 50×50μm2 to several square millimeters. The measured energy resolution for Mn-Kα peak at room temperature is 191eV with a prototype single pixel. In this paper we present the DEPFET Macropixel detector concept as well as the static and dynamic test results. [Copyright &y& Elsevier]

Abstract: We demonstrate the use of a silicon detector based on a DEPFET device, with sub-electron readout noise ( ENC). The so-called repetitive non-destructive readout (RNDR) detector was realised by putting two single DEPFETs next to each other, and connecting their charge storing region by an additional gate. By every transfer from gate 1 to 2 and vice versa the signal charge can be measured non-destructively. By taking the average value of a large number of these measurements the serial noise is reduced by . This way of readout does not only reduce the white noise, but also averages out the noise. Because the whole readout time is times longer than the time for one readout, the device is interesting for low-noise and low-flux applications. The main advantage of such a detector is the ability to reduce the influence of noise to the readout noise. The theoretically and experimentally achievable resolution for different operating parameters (leakage current, readout noise, number and duration of readouts) were investigated by Monte-Carlo simulations and measured on single pixel RNDR devices. [Copyright &y& Elsevier]