X-ray Pixel Detectors Research Articles

Results from a synthetic model of the ITER XRCS-Core diagnostic based on high-fidelity x-ray ray tracing.

A high-fidelity synthetic diagnostic has been developed for the ITER core x-ray crystal spectrometer diagnostic based on x-ray ray tracing. This synthetic diagnostic has been used to model expected performance of the diagnostic, to aid in diagnostic design, and to develop engineering tolerances. The synthetic model is based on x-ray ray tracing using the recently developed xicsrt ray tracing code and includes a fully three-dimensional representation of the diagnostic based on the computer aided design. The modeled components are: plasma geometry and emission profiles, highly oriented pyrolytic graphite pre-reflectors, spherically bent crystals, and pixelated x-ray detectors. Plasma emission profiles have been calculated for Xe44+, Xe47+, and Xe51+, based on an ITER operational scenario available through the Integrated Modelling & Analysis Suite database, and modeled within the ray tracing code as a volumetric x-ray source; the shape of the plasma source is determined by equilibrium geometry and an appropriate wavelength distribution to match the expected ion temperature profile. All individual components of the x-ray optical system have been modeled with high-fidelity producing a synthetic detector image that is expected to closely match what will be seen in the final as-built system. Particular care is taken to maintain preservation of photon statistics throughout the ray tracing allowing for quantitative estimates of diagnostic performance.

Perspective of perovskite-based X-ray hybrid pixel array detectors

Compound semiconductors are playing a major role in the production of X-ray pixel detectors for the application in laboratories and beamlines at photon sources. The performance of these detectors has constantly been improved for the last decades but experiments are still limited by the properties of the detector material, especially under high flux illumination. The fast development of perovskite crystals opens the possibility for new materials to be used as highly efficient X-ray pixel detectors. The published data until now, of the transport properties, demonstrate the large potential of perovskite semiconductors. The achieved values are comparable with the ones of CdTe-based detectors. This paper presents potential perovskite-based detector materials and compares their performance with the state-of-the-art CdTe-based detectors. The perspectives of perovskite semiconductors are promising for the production of large area X-ray detectors but still some challenges remain.

An 11-bit SAR ADC for high frame rate and high-dynamic X-ray imaging at future XFELs

The paper presents the design and test results of an 11-bit successive approximation register (SAR) ADC, suitable for massive on-chip integration in a pixel readout chip. The objective is to establish new digital readout architectures for X-ray pixel detectors at future X-ray free electron laser (XFEL) facilities, enabling high frame rates and a high dynamic range simultaneously. The prototype chip has been designed and fabricated in a 130 nm CMOS process, with the core circuit occupying an area of ~ 0.034 mm2. The measured differential nonlinearity (DNL) and integral nonlinearity (INL) are +0.78/-0.78 LSB and +0.58/-0.52 LSB, respectively. The signal-to-noise-and-distortion ratio (SINAD) is 61.6 dB at 2 MS/s, achieving an effective number of bit (ENOB) of ~ 9.94-bit. The core circuit power consumption is 47 μW at 2 MS/s with a 1.2 V supply.

Efficient Direct X-ray Detection and Imaging Based on a Lead-Free Electron Donor-Acceptor MOF.

Metal-organic frameworks (MOFs) have recently gained extensive attention as potential materials for direct radiation detection due to their strong radiation absorption, long-range order, and chemical tunability. However, it remains challenging to develop a practical MOF-based X-ray direct detector that possesses high X-ray detection efficiency, radiation stability, and environmental friendliness. The integration of donor-acceptor (D-A) pairs into crystalline MOFs is a powerful strategy for the precise fabrication of multifunctional materials with unique optoelectronic properties. Herein, a new lead-free MOF, Cu2I2(TPPA) (CuI-TPPA, TPPA = tris[4-(pyridine-4-yl)phenyl]amine), with a 6-fold interpenetrated structure is designed and synthesized based on the electron donor-acceptor strategy. CuI-TPPA has a large mobility-lifetime (μτ) product of 5.8 × 10-4 cm2 V-1 and a high detection sensitivity of 73.1 μC Gyair-1 cm-2, surpassing that of commercial α-Se detectors. Moreover, the detector remains fairly stable with only a 2% reduction in photocurrent under continuous bias irradiation conditions with a total dose of over 42.83 Gyair. The CuI-TPPA/poly(vinylidene fluoride) flexible composite X-ray detector films are successfully manufactured with different thicknesses. Through multifaceted assessments, the optimal thickness is found with a high detection sensitivity of up to 143.6 μC Gyair-1 cm-2. As proof-of-concept, 11 × 9 pixelated X-ray detectors are fabricated on the same composite film to realize X-ray direct imaging. This work opens up potential applications of MOFs in environmentally friendly and wearable devices for direct X-ray detection and imaging.

Multichannel integrated circuit for time-based measurements in 28 nm CMOS

This paper discusses the application-specific integrated circuit prototype dedicated to readout of hybrid pixel X-ray detectors. The circuit is fabricated in 28 nm CMOS technology and occupies 1.1 × 1.1 mm2 of silicon area. Each of 8 × 4 pixels present in the prototype includes an analog front-end and a digital block with two ring oscillators and their supporting circuits. The circuit can operate in single-photon counting mode or time-based measurement mode. The paper discusses in detail the design decisions that influenced the final in-pixel ring oscillator architecture and layout. Measurement results are presented which demonstrate the performance of ring oscillators as well as regular operating modes of the chip: single photon counting and time-over-threshold measurement.

Simulation study on improving the spatial resolution of photon-counting hybrid pixel X-ray detectors

Simulation study on improving the spatial resolution of photon-counting hybrid pixel X-ray detectors

In-pixel AI for lossy data compression at source for X-ray detectors

Integrating neural networks for data compression directly in the Read-Out Integrated Circuits (ROICs), i.e. the pixelated front-end, would result in a significant reduction in off-chip data transfer, overcoming the I/O bottleneck. Our ROIC test chip (AI-In-Pixel-65) is designed in a 65 nm Low Power CMOS process for the readout of pixelated X-ray detectors. Each pixel consists of an analog front-end for signal processing and a 10b analog-to-digital converter operating at 100KSPS. We compare two non-reconfigurable techniques, Principal Component Analysis (PCA) and an AutoEncoder (AE) as lossy data compression engines implemented within the pixelated area. The PCA algorithm achieves 50× compression, adds one clock cycle latency, and results in a 21% increase in the pixel area. The AE achieves 70× compression, adds 30 clock cycle latency, and results in a similar area increase.

A Python package based on robust statistical analysis for serial crystallography data processing.

The term robustness in statistics refers to methods that are generally insensitive to deviations from model assumptions. In other words, robust methods are able to preserve their accuracy even when the data do not perfectly fit the statistical models. Robust statistical analyses are particularly effective when analysing mixtures of probability distributions. Therefore, these methods enable the discretization of X-ray serial crystallography data into two probability distributions: a group comprising true data points (for example the background intensities) and another group comprising outliers (for example Bragg peaks or bad pixels on an X-ray detector). These characteristics of robust statistical analysis are beneficial for the ever-increasing volume of serial crystallography (SX) data sets produced at synchrotron and X-ray free-electron laser (XFEL) sources. The key advantage of the use of robust statistics for some applications in SX data analysis is that it requires minimal parameter tuning because of its insensitivity to the input parameters. In this paper, a software package called Robust Gaussian Fitting library (RGFlib) is introduced that is based on the concept of robust statistics. Two methods are presented based on the concept of robust statistics and RGFlib for two SX data-analysis tasks: (i) a robust peak-finding algorithm and (ii) an automated robust method to detect bad pixels on X-ray pixel detectors.

Corrections for Fluorescence and Charge-Sharing Effects to Bremsstrahlung Spectra for a Hyperspectral Pixelated CZT X-Ray Detector

A Monte-Carlo model was developed to simulate the response of a pixelated hyperspectral CZT X-ray detector. The first part of the simulation was carried out using Geant4 to obtain a list of energy depositions inside the CZT crystal. The second part of the simulation used charge transport equations to calculate the size of the electron charge cloud, as it drifts under the influence of an electric field to be read out. Experimentally acquired data from an Am-241 source with the HEXITEC detector were compared to simulated data, and good agreement was found. The model was used to investigate the energy dependence of fluorescence and charge sharing effects. The probability of producing an escaped fluorescence photon was quantified as a function of primary photon energy. As expected, at primary photon energies just above the K-edge of Cd, there was a greater chance of producing an escaped fluorescence photon, and this probability decreased as the primary photon energy increased. The probability of an event being shared across multiple pixels as a function of primary photon energy was quantified. It was found that as the primary photon energy was increased, there was a greater chance of producing an event shared across multiple pixels. The detector response to a Bremsstrahlung spectrum was simulated. Using previous results, fluorescence and charge sharing effects were corrected for, giving a corrected spectrum in good agreement with the input spectrum.

GEANT4 simulation and spectrum restoration of a pixelated X-ray detector

We perform a detailed simulation of a pixelated CdTe detector using the GEANT4 toolkit completed with a custom code emulating the detector's electronic response. We demonstrate that a measured tungsten X-ray spectrum can be majorly restored back to the original incident spectrum using the developed model, without requiring the dedicated hardware charge sharing correction.

An integrated system for user-friendly X-ray intensity attenuation in a wide energy range

For undulator hard X-ray beamlines of a wide energy range, the beam intensity control is often needed to regulate the photon flux impinging on delicate detectors. Despite the capability of state-of-the-art X-ray pixel detectors being greatly advanced recently, the frontier undulator beamlines in synchrotron facilities often carry outstanding photon fluxes that are sometimes too high for certain measurements. Here, we report a developed protocol that allows intensity attenuation of an X-ray beam in the 4-23 keV energy range with flexible attenuation factors; a prototype is installed and tested on the 13A biological small-angle X-ray scattering beamline of the 3 GeV Taiwan Photon Source (TPS) of the National Synchrotron Radiation Research Center, Hsinchu, Taiwan. The intensity attenuation system is modified from a commercially available pneumatically actuated, vacuum-type precision X-ray attenuator of ADC ABS-300; the system provides beam attenuation factors covering 8 orders of intensity attenuation for an X-ray beam in 4-23 keV. This was achieved with selected combinations of 10 sets of metal foils comprising different thicknesses of Al, Ti, Cu, and Ta foils. A user-friendly protocol is established to automatically compare a subscribed attenuation factor with all the possible attenuation factors from the 1024 combinations of the 10 sets of foils in the X-ray energy used, and determine a set of the metal foils having a best-matched attenuation factor. Calculation of beam intensity attenuations with the selected foils is coded with Python and integrated into the Experimental Physics and Industrial Control System (EPICS). The input of an attenuation factor is done through a graphical display of the attenuator system based on the Control System Studio (CSS). The developed X-ray beam attenuation system provides a convenient and intuitive beam intensity control and has the potential to be adopted in future beamlines.

XIDER: a novel X-ray detector for the next generation of high-energy synchrotron radiation sources

Next-generation sources of synchrotron radiation pose significant challenges for 2D pixelated X-ray detectors, such as at the ESRF Extremely Brilliant Source (EBS), the first fourth-generation high-energy synchrotron facility. In particular, scattering and diffraction experiments require fast detectors with a high dynamic range, from single photon sensitivity to pile-up conditions under very high photon fluxes. Furthermore, in the case of high-energy applications, the high-Z sensor materials needed for efficient photon detection introduce other difficulties. Leakage current, bias- and flux-induced polarisation, and afterglow all must be carefully managed for the detector system to reach the required specifications. The XIDER project aims to fulfil the needs of the above-mentioned applications by implementing a novel incremental digital integration readout scheme. XIDER detectors seek to operate efficiently under the high-flux EBS beam of up to 100 keV photons, with a time resolution that can cope with near-continuous and pulsed beams. Simultaneously, non-constant leakage current contributions can be removed for noise-free single photon detection, resulting in a very high dynamic range. This contribution presents the recent developments of the XIDER project, including the first characterisation measurements with cadmium telluride sensors.

Automatic bad-pixel mask maker for X-ray pixel detectors with application to serial crystallography.

X-ray crystallography has witnessed a massive development over the past decade, driven by large increases in the intensity and brightness of X-ray sources and enabled by employing high-frame-rate X-ray detectors. The analysis of large data sets is done via automatic algorithms that are vulnerable to imperfections in the detector and noise inherent with the detection process. By improving the model of the behaviour of the detector, data can be analysed more reliably and data storage costs can be significantly reduced. One major requirement is a software mask that identifies defective pixels in diffraction frames. This paper introduces a methodology and program based upon concepts of machine learning, called robust mask maker (RMM), for the generation of bad-pixel masks for large-area X-ray pixel detectors based on modern robust statistics. It is proposed to discriminate normally behaving pixels from abnormal pixels by analysing routine measurements made with and without X-ray illumination. Analysis software typically uses a Bragg peak finder to detect Bragg peaks and an indexing method to detect crystal lattices among those peaks. Without proper masking of the bad pixels, peak finding methods often confuse the abnormal values of bad pixels in a pattern with true Bragg peaks and flag such patterns as useful regardless, leading to storage of enormous uninformative data sets. Also, it is computationally very expensive for indexing methods to search for crystal lattices among false peaks and the solution may be biased. This paper shows how RMM vastly improves peak finders and prevents them from labelling bad pixels as Bragg peaks, by demonstrating its effectiveness on several serial crystallography data sets.

A lightweight, user-configurable detector ASIC digital architecture with on-chip data compression for MHz X-ray coherent diffraction imaging

Today, most X-ray pixel detectors used at light sources transmit raw pixel data off the detector ASIC. With the availability of more advanced ASIC technology nodes for scientific application, more digital functionalities from the computing domains (e.g., compression) can be integrated directly into a detector ASIC to increase data velocity. In this paper, we describe a lightweight, user-configurable detector ASIC digital architecture with on-chip compression which can be implemented in 130 nm technologies in a reasonable area on the ASIC periphery. In addition, we present a design to efficiently handle the variable data from the stream of parallel compressors. The architecture includes user-selectable lossy and lossless compression blocks. The impact of lossy compression algorithms is evaluated on simulated and experimental X-ray ptychography datasets. This architecture is a practical approach to increase pixel detector frame rates towards the continuous 1 MHz regime for not only coherent imaging techniques such as ptychography, but also for other diffraction techniques at X-ray light sources.

The Radon transform as a tool for 3D reciprocal-space mapping of epitaxial microcrystals.

This work presents a new approach suitable for mapping reciprocal space in three dimensions with standard laboratory equipment and a typical X-ray diffraction setup. The method is based on symmetric and coplanar high-resolution X-ray diffraction, ideally realized using 2D X-ray pixel detectors. The processing of experimental data exploits the Radon transform commonly used in medical and materials science. It is shown that this technique can also be used for diffraction mapping in reciprocal space even if a highly collimated beam is not available. The application of the method is demonstrated for various types of epitaxial microcrystals on Si substrates. These comprise partially fused SiGe microcrystals that are tens of micrometres high, multiple-quantum-well structures grown on SiGe microcrystals and pyramid-shaped GaAs/Ge microcrystals on top of Si micropillars.

Research advances on X-ray pixel detectors

<p indent="0mm">Advanced light sources, represented by synchrotron radiation facilities, are important platforms for multi-discipline research. Several large-scale scientific facilities are under construction or being scheduled, including the High Energy Photon Source (HEPS), Shanghai high repetition rate XFEL and extreme light facility (SHINE), Hefei Light Source, and so on. This shows that they are the strategic directions from the national demands. However, detector technologies of the light source beamlines became the bottleneck problem for a long time. Among them, the X-ray pixel detector is a typical representative. Unfortunately, systematic studies were fully blank in this field in China before, and products were totally foreign-monopolized. To break through the dilemma, Wei Wei and his team made pioneer studies in the X-ray pixel detector field in China, and achieved two stages of key results through long-term research. (1) Realized the breakthrough and filled in the blanks in the field of high-end detectors for synchrotron radiation: Brought out the first domestic silicon pixel detector prototype machine, while the performance of the full system reached the level of advanced international products; the sub-project successfully passed the national acceptance inspection of HEPS-TF (High Energy Photon Source-Test Facility); the detector has been delivered for customer applications, while customers’ achievements have already begun to emerge. During the development work, key techniques of pixel detectors have been broken through, especially the techniques of pixel IC chips, sensors, and advanced packaging. Meanwhile, key technology localization has also been achieved and various innovations have been made. This proved the work generally solved the problem of “being strangled” in the field of pixel detectors. (2) Aiming at the international frontier: Led the development of the fine pitch pixel detector. Its spatial resolution reached the same level as the state-of-the-art research of the world, and filled in the blanks in the domestic field; Wei Wei proposed a novel 4-D detection mode and implemented it in the field of synchrotron radiation for the first time; a series of prototype chips were successfully developed for large-scale scientific facilities including vertex detectors for particle physics experiments, free-electron lasers, and so on. The work preliminarily realized “paralleling” with international studies while promoted from “pursuing”. The breakthrough of those key technologies can make beamlines in future light sources capable to realize customized detector design. Therefore, the restrictions from foreign products can be freed and a large number of national funds can be saved. Moreover, it also makes it possible to promote the beamline capabilities, or even explore brand new experimental methodologies to realize original innovations.

Design of Prototype Readout Integrated Circuit for Time-of- Arrival and Time-over-Threshold Measurement for Hybrid Pixel X-ray Detectors in 28 nm CMOS

Wydawnictwo SIGMA-NOT wydaje czasopisma fachowe informujące swoich czytelników o najnowszych osiągnięciach naukowych i nowoczesnych rozwiązaniach technicznych w Polsce i na świecie, popularyzuje problemy techniczne oraz poszerza wiedzę i kulturę techniczną.

Monte Carlo simulations for XIDer, a novel digital integration X-ray detector for the next generation of synchrotron radiation sources

This work presents the first simulation results of the incremental digital integration readout, a charge-integrating front-end scheme with in-pixel digitisation and accumulation. This novel readout concept is at the core of the XIDer (X-ray Integrating Detector) project, which aims to design 2D pixelated X-ray detectors optimised for high energy scattering and diffraction applications for the next generation of synchrotron radiation sources such as the ESRF Extremely Brilliant Source (EBS). The digital integration readout and the XIDer detector open the possibilities for high-duty-cycle operation under very high photon flux, fast frame-rate and high dynamic range with single-photon sensitivity in the 30–100 keV energy range. The readout method allows for noise-free effective X-ray detection. The digital integration concept is currently under investigation to evaluate the impact of main critical design parameters to identify the strengths and weaknesses of the readout scheme and consequently to propose refinements in the final implementation. Simulations have been performed with a dedicated Monte Carlo simulation tool, X-DECIMO, a modular Python package designed to recreate the complete detection chain of X-ray detectors for synchrotron radiation experiments. Losses and non-linearities of the readout scheme are simulated and quantified. In addition to presenting simulation results for this novel readout scheme, this work underlines the potential of the approach and some of its limitations.

Optical design and performance of the biological small-angle X-ray scattering beamline at the Taiwan Photon Source.

The optical design and performance of the recently opened 13A biological small-angle X-ray scattering (SAXS) beamline at the 3.0 GeV Taiwan Photon Source of the National Synchrotron Radiation Research Center are reported. The beamline is designed for studies of biological structures and kinetics in a wide range of length and time scales, from angstrom to micrometre and from microsecond to minutes. A 4 m IU24 undulator of the beamline provides high-flux X-rays in the energy range 4.0-23.0 keV. MoB4C double-multilayer and Si(111) double-crystal monochromators (DMM/DCM) are combined on the same rotating platform for a smooth rotation transition from a high-flux beam of ∼4 × 1014 photons s-1 to a high-energy-resolution beam of ΔE/E ≃ 1.5 × 10-4; both modes share a constant beam exit. With a set of Kirkpatrick-Baez (KB) mirrors, the X-ray beam is focused to the farthest SAXS detector position, 52 m from the source. A downstream four-bounce crystal collimator, comprising two sets of Si(311) double crystals arranged in a dispersive configuration, optionally collimate the DCM (vertically diffracted) beam in the horizontal direction for ultra-SAXS with a minimum scattering vector q down to 0.0004 Å-1, which allows resolving ordered d-spacing up to 1 µm. A microbeam, of 10-50 µm beam size, is tailored by a combined set of high-heat-load slits followed by micrometre-precision slits situated at the front-end 15.5 m position. The second set of KB mirrors then focus the beam to the 40 m sample position, with a demagnification ratio of ∼1.5. A detecting system comprising two in-vacuum X-ray pixel detectors is installed to perform synchronized small- and wide-angle X-ray scattering data collections. The observed beamline performance proves the feasibility of having compound features of high flux, microbeam and ultra-SAXS in one beamline.

Pixelated Photoinduced Discharge Readout X-Ray Detector Using 450-nm LED Line Beam

This paper describes a study on a novel X-ray detector with photoinduced discharge (PID) readout devices. Especially, we demonstrated optical scanning X-ray imaging devices based on intrinsic hydrogenated amorphous silicon (i-a-Si:H) PID readout layer, on which a pixelated metal layer, molybdenum, is formed as a charge accumulation layer of 200 μm pitch for clearly defining the pixel in the lateral and longitudinal directions. We decided to use i-a-Si:H as a readout layer instead of amorphous selenium(a-Se) layer because the material of a-Se does not withstand standard wet fabrication processes like lift-off wet process. An X-ray absorption layer of 500 μm thick a-Se is formed by a thermal evaporation process. To optically switch on the i-a-Si:H PID readout layer, we use a narrow line-beam with a beam width of 50 μm consisting of a blue LED array, optical films, and GRIN lens array. The pixelated PID readout X-ray detector is 512×512 image resolutions with a 200 μm pitch, and the overall active dimension is 10.24 cm ×10.24 cm. The sensitivity of the pixelated PID readout X-ray detector is 302 pC/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·mR at Normal X-ray Tube conditions (IEC66220-1). According to MTF measurement results, the value of MTF0.1(10%) is measured at near 2.5 1/mm in the column direction scanning while the value is measured at 1.9-2.5 1/mm in the row direction scanning.