JUNGFRAU is a state-of-the-art charge-integrating X-ray detector widely used for imaging, diffraction and spectroscopy experiments at synchrotrons and free electron lasers. The current frame rate is 2.2 kHz, limited by analog signal integrity due to the number of available output pads. With the goal of increasing the frame rate of the detector to over 10 kHz, we have designed a digital 3.125 Gbps high-speed serial readout. Consequently, the development of a fast Analog-To-Digital Converter ADC has become our primary goal to overcome the aforementioned constraints. In addition, on-chip digitization reduces noise pickup and signal distortion caused by wirebonds,traces, and other off-chip components. The ADC has been submitted in June 2024 and arrived at PSI for testing in October 2024. This contribution presents the first characterization results of the new ADC prototype, using standard ADC characterization techniques including statistical histogram testing.

With the evolution of synchrotron light sources to fourth generation (diffraction-limited storage rings), the brilliance is increased by several orders of magnitude compared to third generation facilities. For example, the Swiss Light Source (SLS) has been upgraded to SLS 2.0, promising a horizontal emittance reduced by a factor of 40, and a brilliance up to two orders of magnitude (three at higher energies). A key challenge arising from the increased flux is the heightened accumulated dose in silicon sensors, which leads to a significant increase in radiation damage. This translates into an increase of both noise and dark current, as well as a reduction in the dynamic range for long exposure times, thus affecting the performance of the detector, in particular, for charge-integrating detectors. We have designed sensors with a 4 × 4 mm2 pixel array featuring 16 design variations of 25 µm pitch pixels with different implant and metal sizes and tested them bump-bonded to MÖNCH 0.3, a charge integrating hybrid pixel detector readout ASIC. Following a first assessment of the functionality and performance of the different pixel designs, the assembly has been irradiated with X-rays. The variation in the tested parameters was characterized at different accumulated doses up to 100 kGy at the sensor entrance window side. The annealing dynamics at room temperature have also been measured. The results show that the default pixel design is currently not optimal and can benefit from layout changes (reduction in the inter-pixel gap area with full metal coverage of the implant). Further studies on the metal coverage over large implants could be conducted. The layout changes are, however, not sufficient for future full-sized sensors, requiring improved radiation hardness and long-term stability, and additional strategies such as focusing on detector cooling and changes in sensor technologies would be required.

Soft X-ray experiments at synchrotron light sources are essential for a wide range of research fields. However, commercially available detectors for this energy range often cannot deliver the necessary combination of quantum efficiency, signal-to-noise ratio, dynamic range, speed, and radiation hardness within a single system. While hybrid detectors have addressed these challenges effectively in the hard X-ray regime, specifically with single photon counting pixel detectors extensively used in high-performance synchrotron applications, similar solutions are desired for energies below 2 keV. In this work, we introduce a single photon counting hybrid pixel detector capable of detecting X-ray energies as low as 550 eV, utilizing the internal amplification of Low Gain Avalanche Diode (LGAD) sensors. This detector is thoroughly characterized in terms of Signal-to-Noise Ratio and Detective Quantum Efficiency. We demonstrate its capabilities through ptychographic imaging at MAX IV 4th-generation synchrotron light source at the Fe L3-edge (707 eV), showcasing the enhanced detection performance of the system. This development sets a benchmark for soft X-ray applications at synchrotrons, paving the way for significant advancements in imaging and analysis at lower photon energies. The internal amplification of Low-Gain Avalanche Diode sensors can enhance the signal-to-noise ratio, improving the detection of low-energy X-rays. In this work, the authors demonstrate a single photon counting hybrid pixel detector detecting X-ray energies down to 550 eV, and test it in ptychographic imaging at the Fe L3-edge.

Abstract Gotthard-II is a charge-integrating silicon microstrip detector developed for energy-dispersive experiments and X-ray photon beam diagnostics at the European X-ray Free-Electron Laser (EuXFEL). Its one-dimensional geometry, featuring fewer readout channels than pixel detectors, and its fast readout capability make it the only segmented detector able to perform experiments at a 4.5 MHz frame rate while capturing all 2700 X-ray pulses in a bunch train produced by the EuXFEL machine. The Gotthard-II detector was tested for single-photon sensitivity and dynamic range, meeting all specifications. In addition to FEL applications operating at a 4.5 MHz frame rate in burst mode, the detector supports continuous acquisition at up to 400 kHz and counting mode at ≤4.5 MHz for synchrotron applications. Experimental tests with standard samples using X-ray diffraction and X-ray emission spectroscopy were conducted at several beamlines of the Swiss Light Source (SLS) and EuXFEL. The measurement results were compared with those obtained using established detectors at these beamlines, demonstrating the performance of the detector in energy-dispersive experiments.

The single photon counting microstrip detector MYTHEN III was developed at the Paul Scherrer Institute to satisfy the increasing demands in detector performance of synchrotron radiation experiments, focusing on time-resolved and on-edge powder diffraction measurements. Similar to MYTHEN II, the detector installed on the Material Science beamline covers 120° in 2θ. It is based on the MYTHEN III.0 readout chip wire-bonded to silicon strip sensors with a pitch of 50 µm, and it provides improved performance and features with respect to the previous version. Taking advantage of the three independent comparators of MYTHEN III, it is possible to obtain an improvement in the maximum count rate capability of the detector at 90% efficiency from 2.9 ± 0.8 Mphotons s−1 strip−1 to 11 ± 2 Mphotons s−1 strip−1 thanks to the detection of pile-up at high photon flux. The readout chip offers additional operation modes such as pump–probe and digital on-chip interpolation. The maximum frame rate is up to 360 kHz in 8-bit mode with dead-time-free readout. The minimum detectable energy of MYTHEN III is 4.3 ± 0.3 keV with a minimum equivalent noise charge (ENC) of 121 ± 8 electrons and a threshold dispersion below 33 ± 10 eV. The energy calibration is affected by temperature by less than 0.5% °C−1. This paper presents a comprehensive overview of the MYTHEN III detector system with performance benchmarks, and highlights the improvements reached in powder diffraction experiments compared with the previous detector generation.

High-Z compound semiconductors aim to replace silicon as sensor material for X-ray energies above 15 keV thanks to their superior absorption efficiency. However, compared to silicon, high-Z sensors still lack in several aspects such as homogeneity, charge transport properties, charge trapping (leading to polarization and afterglow effects), long ranged fluorescence photons, and others.The aim of this study is to identify sensor materials that can widen the usable energy range of our detector systems at synchrotron sources and free electron lasers (FELs) towards higher photon energies. The main characterization tool was the 75 μm pitch JUNGFRAU charge integrating detector in combination with various high-Z sensors. As charge integrating detectors allow the direct measurement of the collected charge of every single photon with a high spatial resolution, these detectors offer interesting insights into temporal as well as spatial sensor effects which affect the charge collection.As one of the major challenges of the upcoming 4 th generation of synchrotrons or FELs are very intense and potentially pulsed photon beams, the sensors needs to be able to reliably measure highly intense signals and to have no afterglow phenomena after illumination. Measurements performed at the Material Science (MS) beamline of the SLS using photon fluxes up to 5×10 10 ph/(mm 2 • s) and at the FXE beamline of the EuXFEL focused on understanding the dynamic behavior (like signal stability, polarization and afterglow effects) of various high-Z sensor materials like GaAs:Cr (from different suppliers), as well as CdTe (Ohmic and Schottky type) and CdZnTe.The presentation will give an overview of the specific needs of the sensors for the different photon sources and will show how the results obtained fulfill these requirements.

JUNGFRAU is a state-of-the-art charge-integrating detector for high performance experiments at synchrotrons and free-electron lasers. It is currently limited to a frame rate of 2.2 kHz. With the goal to increase the frame rate of the detector to $\gt10 \mathrm{kHz}$, we have designed a 3.125 Gbps high speed serial readout. Thus, the development of a fast Analog-To-Digital Converter (ADC) has become a priority. The design of the current rail-to-rail, fully differential ADC prototype will be presented along simulation results and laboratory evaluation. The prototype targets a sampling rate of $20 \mathrm{MS} / \mathrm{s}$ together with an effective number of bits (ENOB) of equal to or greater than 11 bits. Power and area requirements to reach this goal are currently under evaluation. To meet these demands, a 12-bit Successive Approximation Register (SAR) ADC has been developed and fabricated in the 110 nm UMC CMOS process. We present laboratory characterization results, verifying the design requirements together with a comparison to other ADCs targeting similar use cases.

Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n+ region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

MoNCH is a hybrid pixel detector featuring 25 pm pixel pitch and analogue readout for X-ray imaging at synchrotron radiation (SR) facilities. Sub -pixel spatial resolution has been demonstrated using charge sharing and interpolation algorithms. The current prototype version, MoNCH0.4, features 19 different pixel architectures to assess the design choices and components for an optimised architecture to be used at SR facilities, and to explore the potential use of dynamic gain switching in fine pitch pixels for applications at X-ray free electron lasers (XFELs). Previous characterisation results of the pixel architectures without dynamic gain switching have shown noise levels as low as 21.7 e- r.m.s., which have now been pushed to sub -20 e- r.m.s at room temperature using standard 300 pm -thick silicon sensors. Achieving low noise values however requires high conversion gain and necessitates design choices such as the simplification of the pixel architecture (e.g. by limiting the available choice of in -pixel gains). These compromises ultimately restrain the available dynamic range and prevent the use of MoNCH with low -gain avalanche diodes (LGADs) or high -Z sensors because of the large signals (internal amplification and high photon energies, respectively) and of large leakage currents. In this paper, we will introduce the MoNCH project followed by a description of the current prototype along with characterisation results of the pixel architectures without dynamic gain switching for synchrotron applications with an emphasis on noise and dynamic range. These experimental results will be used to fine-tune the design of MoNCH0.5 to validate the final pixel design. This small prototype should also include additional features from the continuous developments of the PSD detector group towards a full-scale 2 x 3 cm2 MoNCH1.0.

Due to their high frame rates and dynamic range, large area coverage, and high signal-to-noise ratio, hybrid silicon pixel detectors are an established standard for photon science applications at X-ray energies between 2 keV and 20 keV. These properties also make hybrid detectors interesting for experiments with soft X-rays between 200 eV and 2 keV. In this energy range, however, standard hybrid detectors are limited by the quantum efficiency of the sensor and the noise of the readout electronics. These limitations can be overcome by utilizing inverse Low-Gain Avalanche Diode (iLGAD) sensors with an optimized X-ray entrance window. We have developed and characterized a prototype soft X-ray iLGAD sensor bonded to the charge integrating 75 µm pixel JUNGFRAU chip. Cooled to −22°C, the system multiplication factor of the signal generated by an impinging photon is ≥ 11. With this gain, the effective equivalent noise charge of the system is ≤5.5 electrons root-mean-square at a 5 µs integration time. We show that by cooling the system below −50°C, single photon resolution at 200 eV becomes feasible with a signal-to-noise ratio better than 5.

To enhance the spatial resolution of the M & Ouml;NCH 25 mu m pitch hybrid pixel detector, deep learning models have been trained using both simulation and measurement data. Challenges arise when comparing simulation-based deep learning models to measurement-based models for electrons, as the spatial resolution achieved through simulations is notably inferior to that from measurements. Discrepancies are also observed when directly comparing X-ray simulations with measurements, particularly in the spectral output of single pixels. These observations collectively suggest that current simulations require optimization. To address this, the dynamics of charge carriers within the silicon sensor have been studied using Monte Carlo simulations, aiming to refine the charge transport modeling. The simulation encompasses the initial generation of the charge cloud, charge cloud drift, charge diffusion and repulsion, and electronic noise. The simulation results were validated with measurements from the M & Ouml;NCH detector for X-rays, and the agreement between measurements and simulations was significantly improved by accounting for the charge repulsion.

Experiments at synchrotron radiation sources and X-ray Free-Electron Lasers in the soft X-ray energy range (250 eV–2 keV) stand to benefit from the adaptation of the hybrid silicon detector technology for low energy photons. Inverse Low Gain Avalanche Diode (iLGAD) sensors provide an internal gain, enhancing the signal-to-noise ratio and allowing single photon detection below 1 keV using hybrid detectors. In addition, an optimization of the entrance window of these sensors enhances their quantum efficiency (QE). In this work, the QE and the gain of a batch of different iLGAD diodes with optimized entrance windows were characterized using soft X-rays at the Surface/Interface:Microscopy beamline of the Swiss Light Source synchrotron. Above 250 eV, the QE is larger than 55% for all sensor variations, while the charge collection efficiency is close to 100%. The average gain depends on the gain layer design of the iLGADs and increases with photon energy. A fitting procedure is introduced to extract the multiplication factor as a function of the absorption depth of X-ray photons inside the sensors. In particular, the multiplication factors for electron- and hole-triggered avalanches are estimated, corresponding to photon absorption beyond or before the gain layer, respectively.

Single-photon detection of X-rays in the energy range of 250 eV to 1 keV is difficult for hybrid detectors because of the low quantum efficiency and low signal-to-noise ratio. The low quantum efficiency is caused by the absorption of soft X-rays in the entrance window of the silicon sensors. The entrance window consists of an insensitive layer on the surface and a highly doped layer, which is typically from a few hundred nanometers to a couple of micrometers thick and is comparable to the absorption depth of soft X-ray photons (e.g. the attenuation length of 250 eV X-ray photons is ∼100 nm in silicon). The low signal-to-noise ratio is mainly caused by the small signal amplitude (e.g. ca. 70 electrons for 250 eV X-ray photons in silicon) with respect to the electronic noise. To improve the quantum efficiency, the entrance window must be optimized by minimizing the absorption of soft X-rays in the insensitive layer, and reducing charge recombination at the Si-SiO2 interface and in the highly doped region. Low gain avalanche diodes (LGADs) with a multiplication factor between 5 and 10 increase the signal amplitude and therefore improve the signal-to-noise ratio for soft X-rays, enabling single-photon detection down to 250 eV. Combining LGAD technology with an optimized entrance window technology can thus allow hybrid detectors to become a useful tool also for soft X-ray detection. In this work we present the optimization of the entrance window by studying the internal quantum efficiency of eight different process technology variations. The sensors are characterized using light emitting diodes with a wavelength of 405 nm. At this wavelength, the light has an absorption depth of 125 nm, equivalent to that of 276 eV X-rays. The best variation achieves an internal quantum efficiency of 0.992 for 405 nm UV light. Based on this study, further optimization of the quantum efficiency for soft X-rays detection is planned.

The new fourth-generation storage rings (diffraction-limited storage rings, e.g., MAXIV, ESRF EBS, SLS2.0) will have a much higher brilliance than the third-generation sources increasing the photon flux at the pixel level. This will exceed the count rate capabilities of many of the single photon-counting detectors currently used, making them unsuitable to be used in future experiments at these machines. Matterhorn is a 2-D hybrid pixel detector developed by the PSD detector group of the Paul Scherrer Institut (PSI, Switzerland) to be used at SLS2.0. The main goal of this detector is to extend the count rate capability (target 20 Mcounts/pixel/s) by means of multi-threshold circuitry in the pixels.The final Matterhorn ASIC will have 256 x 256 pixels with 75 μm pitch, will be designed in UMC 110nm technology, and will be highly configurable. Each pixel will have a charge-sensitive amplifier and a shaper connected to four comparators. Each comparator will have an adjustable threshold that can be set to a value higher than the photon energy allowing to extend the count rate capability. Each comparator is connected to a 16-bit independently gateable counter. The target frame rate for reading out one 16-bit counter of all pixels is 10 kHz. Therefore, each ASIC will be equipped with four serial links operating at the clock frequency of 3.125 GHz provided by an on-chip PLL.The first prototype of the ASIC with 48 x 48 pixels was submitted in January 2023 and is expected back by June 2023. The pixels already include the four comparators and counters. In the periphery, two serial links working at a clock frequency of 1.6 GHz provided by an on-chip PLL are included. Moreover, the digital periphery can be configured to read one (selectable), two, three, or all the counters.In this contribution, we will show the working principle of this detector and all its foreseen functionalities. Moreover, the experimental results of the first prototype will also be shown.

Despite being used in many X-ray applications, hybrid single photon counting detectors are limited in spatial resolution due to the diffusion of the charge produced by single photons between neighboring electronic channels, also called charge sharing. In this work, we demonstrate that on-chip interpolation can be used to improve the effective spatial resolution in a single photon counting detector without increasing the number and density of interconnects between the sensor and the readout electronics. We describe a digital communication scheme between neighboring channels exploiting charge sharing to obtain a spatial resolution better than the channel pitch, which has been implemented for the first time in the MYTHEN III microstrip detector. The interpolation is achieved directly on-chip at the time the photons are absorbed, limiting the data throughput and the computational effort and allowing a higher photon flux compared to interpolation using analog detectors. Here we show the first results obtained with this interpolation mechanism, characterizing the spatial resolution in terms of modulation transfer function. The spatial resolution of the 50 μm pitch MYTHEN III microstrip detector can be improved from the 20 lp/mm given by the physical strip pitch to an average resolution of approximately 30 lp/mm using the interpolation method.

Electrons are emerging as a strong complement to X-rays for diffraction based studies. In this paper we investigate the performance of a JUNGFRAU detector with 320 um thick silicon sensor at a pulsed electron source. Originally developed for X-ray detection at free electron lasers, JUNGFRAU features a dynamic range of 120 MeV/pixel (implemented with in-pixel gain switching) which translated to about 1200 incident electrons per pixel and frame in the MeV region. We preset basic characteristics such as energy deposited per incident particle, resulting cluster size and spatial resolution along with dynamic (intensity) range scans. Measurements were performed at 4, 10 and 20 MeV/c. We compare the measurements with GEANT4 based simulations and extrapolate the results to different sensor thicknesses using these simulations.

Since the introduction of the extremely intense X-ray free electron lasers, the need for low noise, high dynamic range and potentially fast charge integrating detectors has increased significantly. Among all the problems that research and development groups have to face in the development of such detectors, their calibration represents one of the most challenging and the collaboration between the detector development and user groups is of fundamental importance. The main challenge is to develop a calibration suite that is capable to test the detector over a wide dynamic range, with a high granularity and a very high linearity, together with a certain radiation tolerance and the possibility to well define the timings and the synchronization with the detector. Practical considerations have also to be made like the possibility to calibrate the detector in a reasonable time, the availability of the calibration source at the experimental place and so on. Such a calibration test suite is often not represented by a single source but by several sources that can cover different parts of the dynamic range and that need to be cross calibrated to have a final calibration curve. In this respect an essential part of the calibration is also to develop a mathematical model that allows calibrating the entire dynamic range, taking into account features that are calibration source and/or detector specific. The aim of this contribution is to compare the calibration for the AGIPD detector using several calibration sources such as internal current source, backside pulsing, IR pulsed laser, LED light and mono-energetic protons. The mathematical procedure used to calibrate the different sources will be discussed in great detail showing how to take into account a few shortcomings (like pixel coupling) that are common for many charge integrating detectors. This work has been carried out in the frame of the AGIPD project for the European X-ray Free Electron Laser.

The polarization characteristics of ohmic and (Al-)Schottky type CdTe sensors supplied by Acrorad have been characterized with the low noise, charge integrating readout chip JUNGFRAU, revealing defined areas in the Schottky type sensors, which were irradiated with 20 keV photons in previous experiments more than one year ago. These areas, which have absorbed doses of up to 1079 kGy, show a more robust charge collection compared to unirradiated areas. In contrast to this, no alteration of the polarization characteristics could be found in ohmic type CdTe sensors after irradiation. The polarization behavior of the sensors has been characterized in-situ over time and at different temperatures by using an homogeneous, low flux molybdenum fluorescence illumination. An increase of the leakage current in the irradiated areas was found and quantified as a function of absorbed dose as well as its influence on the stability on the number of photon counts. In addition to the influence of X-ray irradiation, the effect of thermal annealing on the polarization characteristics of Schottky type CdTe sensors has been studied. Possible routes for the usage of Schottky type CdTe sensors in synchrotron applications are outlined in this publication.

The charge-integrating hybrid silicon pixel detector JUNGFRAU has found widespread use at free-electron laser and synchrotron facilities. The detector was designed for use with hard X-rays; yet, because of its low noise, high dynamic range, position resolution, and scalable size, JUNGFRAU is of high interest for soft X-ray applications. We discuss improvements of the readout chip and alterations of the entrance window at the back of the sensor that facilitate low-energy X-ray detection. The first use case of the improved system at a low-energy beamline demonstrates single photon sensitivity down to 800 eV. At lower energies, the readout noise of the hybrid detector hinders the resolution of single photons. We propose to couple the JUNGFRAU readout chip with charge-multiplying low-gain avalanche diode (LGAD) sensors to resolve X-ray photons with a minimum energy of 250 eV.

We show the developments carried out to improve the silicon sensor technology for the detection of soft X-rays with hybrid X-ray detectors. An optimization of the entrance window technology is required to improve the quantum efficiency. The LGAD technology can be used to amplify the signal generated by the X-rays and to increase the signal-to-noise ratio, making single photon resolution in the soft X-ray energy range possible. In this paper, we report first results obtained from an LGAD sensor production with an optimized thin entrance window. Single photon detection of soft X-rays down to 452 eV has been demonstrated from measurements, with a signal-to-noise ratio better than 20.