D. Mezza

Prototype characterization of the JUNGFRAU pixel detector for SwissFEL

The SwissFEL, a free electron laser (FEL) based next generation X-ray source, is being built at PSI. An XFEL poses several challenges to the detector development: in particular the single photon counting readout, a successful scheme in case of synchrotron sources, can not be used. At the same time the data quality of photon counting systems, i.e. the low noise and the high dynamic range, is essential from an experimental point of view. Detectors with these features are under development for the EU-XFEL in Hamburg, with the PSI SLS Detector group being involved in one of these efforts (AGIPD). The pulse train time structure of the EU-XFEL machine forces the need of in pixel image storage, resulting in pixel pitches in the 200 μm range. Since the SwissFEL is a 100 Hz repetition rate machine, this constrain is relaxed. For this reason, PSI is developing a 75 μm pitch pixel detector that, thanks to its automatic gain switching technique, will achieve single photon resolution and a high dynamic range. The detector is modular, with each module consisting of a 4 × 8 cm2 active sensor bump bonded to 8 readout ASICs (Application Specific Integrated Circuit), connected to a single printed circuit readout board with 10GbE link capabilities for data download. We have designed and tested a 48 × 48 pixel prototype produced in UMC110 nm technology. In this paper we present the general detector and ASIC design as well as the results of the prototype characterization measurements.

Eiger: a single-photon counting x-ray detector

Eiger is a single-photon counting x-ray pixel detector being developed at the Paul Scherrer Institut (PSI) for applications at synchrotron light sources. It follows the widely utilized and successful Pilatus detector. The main features of Eiger are a pixel size of 75 × 75 μm2, high frame rate capability of 22 kHz and negligible dead time between frames of 4 μs. This article contains a detailed description of Eiger detector systems, from the 500 kpixel single-module detector to large-area multi-modules systems. The calibration and performance of the first 500 kpixel system that is in routine user operation are also presented. Furthermore, a method of calibrating the energy of single-photon counting detectors along the detector gain axis is introduced. This approach has the advantage that the detector settings can be optimized at all energies for count rate capabilities. Rate capabilities of the system are reported for energies between 6 and 16 keV.

AGIPD, a high dynamic range fast detector for the European XFEL

AGIPD—(Adaptive Gain Integrating Pixel Detector) is a hybrid pixel X-ray detector developed by a collaboration between Deutsches Elektronen-Synchrotron (DESY), Paul-Scherrer-Institut (PSI), University of Hamburg and the University of Bonn. The detector is designed to comply with the requirements of the European XFEL. The radiation tolerant Application Specific Integrated Circuit (ASIC) is designed with the following highlights: high dynamic range, spanning from single photon sensitivity up to 104 12.5keV photons, achieved by the use of the dynamic gain switching technique using 3 possible gains of the charge sensitive preamplifier. In order to store the image data, the ASIC incorporates 352 analog memory cells per pixel, allowing also to store 3 voltage levels corresponding to the selected gain. It is operated in random-access mode at 4.5MHz frame rate. The data acquisition is done during the 99.4ms between the bunch trains. The AGIPD has a pixel area of 200× 200 μ m2 and a 500μ m thick silicon sensor is used. The architecture principles were proven in different experiments and the ASIC characterization was done with a series of development prototypes. The mechanical concept was developed in the close contact with the XFEL beamline scientists and is now being manufactured. A first single module system was successfully tested at APS.

MÖNCH, a small pitch, integrating hybrid pixel detector for X-ray applications

PSI is developing several new detector families based on charge integration and analog readout (CI) to respond to the needs of X-ray free electron lasers (XFELs), where a signal up to ~ 104 photons impinging simultaneously on a pixel make single photon counting detectors unusable. MONCH is a novel hybrid silicon pixel detector where CI is combined with a challengingly small pixel size of 25 × 25 μm2. CI enables the detector to process several incoming photon simultaneously in XFEL applications. Moreover, due to the small pixel size, the charge produced by an impinging photon is often shared. In low flux experiments the analog information provided by single photons can be used either to obtain spectral information or to improve the position resolution by interpolation. Possible applications are resonant and non-resonant inelastic X-ray scattering or X-ray tomography with X-ray tubes. Two prototype ASICs were designed in UMC 110 nm technology. MONCH01 contains only some test cells used to assess technology performance and make basic design choices. MONCH02 is a fully functional, small scale prototype of 4 × 4 mm2, containing an array of 160 × 160 pixels. This array is subdivided in five blocks, each featuring a different pixel architecture. Two blocks have statically selectable preamplifier gains and target synchrotron applications. In low gain mode they should provide single photon sensitivity (at 6-12 keV) as well as a reasonable dynamic range for such a small area ( > 120 photons). In high gain they target high resolution, low flux experiments where charge sharing can be exploited to reach μm resolution. Three other architectures address possible uses at XFELs and implement automatic switching between two gains to increase the dynamic range, as well as input overvoltage control. The paper presents the MONCH project and first results obtained with the MONCH02 prototype.

Micron resolution of MÖNCH and GOTTHARD, small pitch charge integrating detectors with single photon sensitivity

MONCH, a charge integrating readout ASIC (Application Specific Integrated Circuit) prototype with a pixel pitch of 25 μm developed at PSI, allows new imaging applications in the field of micron resolution and spectral imaging. The small pixel size of this system facilitates charge sharing between pixels, which then can be exploited to gain additional information about the photon absorption position and photon energy. However, for reconstructing complete images from this information, sufficient hits need to be recorded and therefore acquisition times are potentially long. We present a fast read-out system, that is capable of acquiring enough statistics for an image in a few hours in combination with a position reconstruction algorithm, which has the potential to run in a similar amount of time on a fast computing node. We further present results of experiments with a comparable strip detector (small-pitch GOTTHARD system) showing that with the aid of single photon interpolation algorithms micron resolution is achievable. Additionally, we show that a similar position reconstruction algorithm works in the two dimensional case for MONCH.

Towards hybrid pixel detectors for energy-dispersive or soft X-ray photon science

A novel hybrid pixel detector is evaluated and its potential for low-noise/low-energy detection and energy-dispersive photon science is highlighted.

Micrometer-resolution imaging using MÖNCH: towards G2-less grating interferometry

The MÖNCH 25 µm-pitch hybrid pixel detector is described in detail and characterized. The interpolation algorithm developed to achieve micrometer-level resolution is applied to grating interferometry measurements.

Characterization results of the JUNGFRAU full scale readout ASIC

The two-dimensional pixel detector JUNGFRAU is designed for high performance photon science applications at free electron lasers and synchrotron light sources. It is developed for the SwissFEL currently under construction at the Paul Scherrer Institut, Switzerland. The detector is a hybrid pixel detector with a charge integration readout ASIC characterized by single photon sensitivity and a low noise performance over a dynamic range of 104 12 keV photons. Geometrically, a JUNGFRAU readout chip consists of 256×256 pixels of 75×75 μm2. The chips are bump bonded to 320 μm thick silicon sensors. Arrays of 2×4 chips are tiled to form modules of 4×8 cm2 area. Several multi-module systems with up to 16 Mpixels per system will be delivered to the two end stations at SwissFEL. The JUNGFRAU full scale readout ASIC and module design are presented along with characterization results of the first systems. Experiments from fluorescence X-ray, visible light illumination, and synchrotron irradiation are shown. The results include an electronic noise of ~50 electrons r.m.s., which enables single photon detection energies below 2 keV and a noise well below the Poisson statistical limit over the entire dynamic range. First imaging experiments are also shown.

Calibration status and plans for the charge integrating JUNGFRAU pixel detector for SwissFEL

JUNGFRAU (adJUstiNg Gain detector FoR the Aramis User station) is a two-dimensional hybrid pixel detector under development for photon science applications at free electron laser and synchrotron facilities. In particular, JUNGFRAU detectors will equip the Aramis end stations of SwissFEL, an X-ray free electron laser currently under construction at the Paul Scherrer Institut in Villigen, Switzerland. JUNGFRAU has been designed specifically to meet the challenges of photon science at XFELs, including high frame rates, single photon sensitivity in combination with a high dynamic range, vacuum compatibility and tilable modules. This has resulted in a charge integrating detector with three dynamically adjusting gains, a low noise of 55 ENC RMS, readout speeds in excess of 2 kHz, single photon sensitivity down to 2 keV (with a signal to noise ratio of 10) and a dynamic range covering four orders of magnitude at 12 keV. Each JUNGFRAU module consists of eight chips of 256 × 256 pixels, each 75 × 75 μm2 in size. The chips are arranged in 2 × 4 formation and bump-bonded to a single silicon sensor 320 μm thick, resulting in an active area of approximately 4 × 8 cm2 per module. Multi-module vacuum compatible systems comprising up to 16 Mpixels (32 modules) will be used at SwissFEL. The design of SwissFEL and the JUNGFRAU system for the Aramis end station A will be introduced, together with results from early prototypes and a characterisation using the first batch of final JUNGFRAU modules. Plans and first results of the pixel-by-pixel calibration will also be shown. The vacuum compatibility of the JUNGFRAU module is demonstrated for the first time.

Looking at single photons using hybrid detectors

The SLS detector group develops silicon hybrid detectors for X-ray applications used in synchrotron facilities all over the world. Both microstrip and pixel detectors with either single photon counting or charge integrating read out are being developed. Low noise charge integrating detectors can be operated in single photon regime, i.e. with low fluxes and high frame rates in order to detect on average less than one photon per cluster of 2×2 pixels. In this case, the analog signal read out for each single X-ray provides information about the energy of the photon. Moreover the signal from neighboring channels can be correlated in order to overcome or even take advantage of charge sharing. The linear charge collection model describing microstrip detectors and large pixels is unsuitable for the calibration of small pitch pixel detectors due to the large amount of charge sharing occurring also in the corner region. For this reason, the linear charge collection model is extended to the case of small pixels and tested with monochromatic X-ray data acquired using the 25 μm pitch MONCH and the 75 μm pitch JUNGFRAU detectors. The successful outcome of the calibration of the MONCH detector is proven by the high energy resolution of the spectrum obtained by accumulating the counts from more than 6000 channels after the correction of the gain mismatches using the proposed model.