Online program Overview Session: NSS-08

Abstract

The DEPFET Sensor with Signal Compression (DSSC) is a 1-megapixel, 2D X-ray detector designed for the European XFEL, capable of operating at MHz frame rates. This work presents the characterization results of the second-generation DSSC focal-plane modules (FPMs), which incorporate active DEPFET sensors to improve dynamic range and performance compared to the first-generation mini-SDD-based camera. Each FPM—the smallest independent unit of the camera—comprises two sensors read by eight ASICs and underwent rigorous geometric characterization, with sensor-to-sensor systematic deviation of 32.9 ± 68.9 µm and −48.6 ± 66.9 µm in the x- and y-direction, respectively. Functional tests were run under vacuum at 18°C. Key metrics demonstrated excellent reproducibility of prototype characterization, with tight distributions in sensitivity (199.4 ± 5.4 eV/ADU), equivalent-noise charge (23.2 ± 1.2 e- rms), first gain-compression energy (74.9 ± 4.3 keV) and in-pixel leakage current (1.3 ± 0.3 pA/pixel). The results validate the reliability of the DEPFET FPMs for integration into the 1-megapixel camera, ensuring uniform performance.

Abstract

The fourth generation of synchrotron light sources brings unprecedented brightness to the experimental stations of the x-ray science community. As light sources improve their performance, detector instrumentation requirements become more demanding. Among these, readout electronics should be capable of achieving zero dead-time, handling an inter-bunch spacing of just a few nanoseconds, and including a digital backend able to deal with the expected data stream. In this context, a prototype readout channel has been developed in a commercial 65 nm CMOS technology and assembled in a 16-pixel matrix, named pFREYA16. Each pixel features a low-noise Charge-Sensitive Amplifier, a semi-Gaussian unipolar RC-CR shaper with four selectable peaking times, a pseudo-differential discrimination chain to enable zero-suppression, and an A/D chain with a differential S/H and a differential 10-bit SAR ADC, along with a basic digital backend to shift data out and configure the matrix. The prototype has been fully characterised at each stage of the signal processing chain. It exhibits a linear input-output transfer characteristic over a full-well capacity of 256 photons at 5, 9, 15, and 25 keV, single-photon resolution with a measured ENC of 380 e- rms at 9 keV at a frame rate of 1 MHz, and a power consumption of approximately 220 uW per pixel.

Abstract

Soft X-ray detection is essential for synchrotron and free-electron laser science, but existing detector technologies remain limited in quantum efficiency, signal-to-noise ratio, and readout performance at low photon energies. In this work, we present DIANA, a Low-Gain Avalanche Diode (LGAD)-based detector architecture optimized for soft X-ray applications. The device employs a p-type entrance window for high transparency and places the gain layer on the readout side, allowing charge carriers generated near the entrance surface to drift through the full silicon thickness before undergoing controlled internal amplification. An additional n-type buffer layer is introduced between the gain layer and segmented readout electrodes to mitigate electric field non-uniformities and improve stability. TCAD simulations and first prototype fabrication at Brookhaven National Laboratory demonstrate stable operation above full depletion and confirm the effectiveness of the buffer layer in shaping the electric field.  Electrical characterization shows clear charge multiplication with gains up to approximately 3, while spectroscopic measurements demonstrate stable and nearly energy-independent amplification across the investigated photon-energy range. These results validate the DIANA concept as a promising candidate for next-generation soft X-ray detectors.

Abstract

The upgrade of synchrotron facilities, such as Swiss Light Source 2.0 (SLS 2.0), will provide significantly higher brilliance and photon flux than current-generation sources. These operating conditions will exceed the count-rate capability of many existing single-photon-counting detectors. Although higher photon flux improves acquisition capability, synchrotron experiments still often rely on detecting weak features where only a few photons contain important information. Preserving sensitivity while operating at very high photon flux therefore becomes a major challenge. To address these limitations, Matterhorn, a single photon counting hybrid pixel detector, is developed at the Paul Scherrer Institute for future high-flux synchrotron experiments. The detector implements a multi-threshold photon-counting architecture with four independently adjustable thresholds in each pixel to improve count-rate performance under high-flux condi- tions. The detector targets count rate up to 20 Mcounts/pixel/s through the implementation of multi-threshold circuitry in each pixel. The ASIC consists of a 256 × 256 pixel matrix with a pixel pitch of 75 × 75 μm 2 and is implemented in UMC 110 nm technology. Single-chip assemblies (i.e. a single chip bump- bonded to a single-chip sensor) are characterized using both a laboratory X-ray source and measurements at the SLS beamline. Preliminary measurements demonstrate stable operation of the full-size ASIC and reproduce the performance from the prototype studies. This contribution presents the current characterization status and summarizes the main performance results obtained so far, while a more detailed discussion of the detector architecture will be presented in a separate contribution.

Abstract

In X-Ray Fluorescence Microscopy, where the analyses can take up to several hours, optimizing the solid angle of the spectrometer is critical. Moreover, the use of multichannel spectrometers is now a necessity due to the high throughput required from the incread brilliance achieved by modern, 4^th generation synchrotrons.
ORBIS is a 16-channel monolithic SDD array optimized for backscattering configurations, with a geometry that can guarantee an uncollimated total solid angle coverage of 2.35 sr while ensuring uniform irradiation of all the pixels.
The project, supported by Ruhr University Bochum (RUB) and Deutsches Elektronen-Synchrotron (DESY) aims to develop a novel, vacuum compatible spectrometer to be used for biological experiments.
A preliminary characterization of the SDD array shows promising results, with FWHM resolutions as low as 131 eV measured at the Mn-kα line at 800 ns peaking time, and 171 eV FWHM at 32 ns peaking time.
The first tests in P06 beamline are planned in June 2026, during which the instrument performance will be evaluated. The results of this campaign will be reported at the conference.

Abstract

The evolving requirements of X-ray Free Electron Laser (XFEL) applications in terms of speed, dynamic range, and noise motivate the development of new X-ray pixel detectors. The next generation of detectors must provide a high dynamic range while maintaining low-noise performance to ensure single-photon detection at low energies. In this work, we present a front-end architecture employing a Charge Sensitive Amplifier (CSA) with predictive gain switching and a Flip-Capacitor filter. The CSA is designed to achieve both a high dynamic range up to 10⁴ photons and single-photon resolution by means of active gain control. The novel predictive gain switching circuit sets the optimal gain by measuring the time required for the CSA output signal to exceed a fixed threshold. The trapezoidal filter, by reducing the electronic noise, enables single-photon resolution at low energies when the CSA operates in its highest gain configuration. A dedicated voltage-to-current converter has been designed to couple the CSA and the filter. The proposed front-end is implemented in 65 nm CMOS technology, and preliminary characterization has been performed to evaluate gain switching and noise performance. The ASIC has been coupled to a Silicon Drift Detector (SDD), and an Equivalent Noise Charge of 35 e⁻ has been measured. Further measurements, including tests with a mini-SDD, are planned. This front-end architecture will be proposed for the XSTREAM (Xray detector System with high-Throughput REadout Architecture and Modularity) Pathfinder.

Abstract

We performed the mesh experiment to map the charge collection function of hexagonal DEPFET pixels of the DSSC camera, a 1024x1024 hybrid pixel detector targeted at soft X-ray imaging experiments at the European XFEL with stringent requirements on noise, speed and dynamic range. With a read noise of few electrons rms, the measurement of the pixel charge collection function and its correlation to pixel layout and operating conditions are essential to assess the spectroscopic performance of the camera and detect possible optimizations. The obtained virtual scan of the hexagonal pixel of one DSSC sensor (256x128 pixels) highlights a non-uniform charge collection that can affect the camera spectroscopic performance, proving the effectiveness of this technique to optimize the performance of large, low-noise detectors.

Abstract

High-resolution particle detectors based on microchannel plates (MCPs) provide unique capabilities for applications requiring detection of photons, electrons, ions, and neutrons with high spatial and temporal resolution. Recent advances in readout technologies have substantially increased the counting-rate capabilities of these detectors, with rates exceeding 10⁸ particles/s/cm². However, experiments with even higher incident fluxes remain limited by the number of particles that MCP detectors can process.

In some high-flux applications, only a small fraction of the incident particles needs to be recorded, while the total flux can be extremely high. In such cases, fast gating of the detector can prevent unnecessary charge extraction and allow MCP-based detectors to operate under otherwise unsustainable flux conditions. For soft X-ray, gamma photons, electron, neutron and ion detection, the primary particle conversion occurs at the front surface of the MCP itself. In this case, the MCP itself must be gated directly, which is challenging because of the MCP’s large capacitance and high operating bias.

In this paper, we present results from gated MCP detectors that can be switched on and off on a time scale of approximately 5 ns. We demonstrate this capability using an MCP detector with a Timepix readout, selectively detecting chosen synchrotron pulses while suppressing detection of the remaining bunches. Without gating, the detector is oversaturated and cannot operate under the same incident flux. This gating approach is applicable to a broad range of MCP readout configurations, not only Timepix-based systems, and enables high-resolution MCP detectors to be used in applications where the total input flux would otherwise exceed their sustainable operating range.