Counting Hybrid Pixel Detector Research Articles

Characterization results of the first small pixel high rate (SPHIRD) pixel detector prototypes

This work presents a summary of the experimental results and the performance obtained from a first set of p-type silicon SPHIRD prototypes. The SPHIRD project (Small Pixel High Rate photon counting Detector) targets a new generation of X-ray photon counting hybrid pixel detectors for synchrotron radiation applications, with small pixels and operating between 10 and 30 keV. The readout ASIC is designed to explore techniques that boost the count rate capabilities of the detector and methods to manage, or in some cases exploit, the effects of charge sharing that are unavoidable with small pixels in this type of detector.The achievement of high photon rates relies on the implementation of a fast charge-sensitive amplifier in the pixelin combination with pile-up compensation techniques, which have been compared experimentally. The obtained results show and quantify their effectiveness in increasing the count-rate handled by the detector.The readout chip also includes dedicated circuitry for the relocation of photon hits, a functionality necessary to reduce the photon losses that are observed in photon counting detectors due to charge sharing when the discrimination threshold is set to 50% of the photon energy. The circuitry is however not limited to full pixel relocation: it also implements resources to reassign X-ray hits within regions smaller than the physical pixel. All these operation modes were experimentally evaluated with a pencil beam and with full field images.

Study of neutron-rich isotopes near N=152 shell closure using Timepix type detectors integrated into the mass separator MASHA

The MASHA facility [1–3] was developed as a high precision mass-spectrometer for heavy and super heavy elements with masses up to 450 a.m.u. It uses ISOL (Isotope Separation On-Line) method. Its unique properties opens great prospective for the investigation of neutron-rich nuclei produced in multinucleon transfer reactions. Mainly nuclei near the neutron N = 126 and N = 152 shell closures are of great interest. This region of nuclei is not so far thoroughly enough investigated while its research has direct relation to the synthesis of super heavy elements. As is known the island of stability close to super heavy elements (Z = 112–118) exists due to the shell effects in nuclei. More detailed investigation of these shell effects can greatly help in the synthesis of next super heavy elements. Heavy neutron rich radon isotopes were produced in the multinucleon transfer reaction 40Ar + 232Th at Flerov Laboratory of Nuclear Reactions, Dubna. Radon isotopes with given masses were detected using two types of detectors: a multi-strip well-type detector (made in Canberra) and a position-sensitive quantum counting hybrid pixel detector of the Timepix type [1]. The latter detector has an array of 256×256 square pixels each with a pitch size of 55 μm for the full sensitive area 14×14 mm2. Radon isotopes implanted into the detector emit then alpha and beta particles until they reach the stable or long-lived isotopes at the end of their decay chains. The positions of radon isotopes, the tracks, times and energies of the beta particles were measured and analyzed. New software for the particle recognition and data analysis of the results obtained from the experiment was developed and used. It has been proven that MASHA + Timepix setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

High rate proton detection with single photon counting hybrid pixel detector

We present the design and measurements of a proton detection system built using a single photon counting hybrid pixel array detector. The system uses the UFXC detector designed for operating with very high photon fluxes. We demonstrate, that with appropriately modified data acquisition firmware, the UFXC detector is capable of operating in the frame-triggered zero dead-time mode, which captures every frame containing desired information, at a rate of up to 50 kfps. The detector consists of a 128 x 256 matrix of square-shaped pixels with a pitch of 75 μm, which makes it suitable for particle tracking applications in test beam environments. We estimate the position resolution achieved with a single layer of the UFXC detector to be around 40 μm.

High speed systems for time-resolved experiments with synchrotron radiation

The UFXC32k is a single photon counting hybrid pixel detector with 75 μm pixel pitch. It was designed to cope with high X-ray intensities and therefore it is a very good candiate for synchrotron applications. In order to use this detector in an application, a dedicated setup must be designed and built allowing proper operation of the detector within the experiment. The paper presents two setups built for the purpose of Pump-Probe-Probe experiments at the Synchrotron SOLEIL and XPCS experiments at the APS.

Spatial resolution and detection efficiency of algorithms for charge sharing compensation in single photon counting hybrid pixel detectors

This paper presents a new method for charge sharing compensation in hybrid pixel semiconductor detectors. The presented solution is based on pattern recognition and allows to significantly reduce circuit complexity, while maintaining allocation accuracy of other, more complex algorithms. The proposed method is evaluated and compared to the existing solutions in terms of missed/false hit probability and allocation accuracy, based on simulation results of a pixel readout circuit model.

Real-time control of the beam attenuation with XPAD hybrid pixel detector

In order to fully benefit from a beam produced by modern synchrotron light sources, characterised by a wide and continuous energy spectrum, high brightness and a very high intensity, advancement in detector technology has been made over the last decades. However, one of the main limitations of the state-of-the-art counting hybrid pixel detectors is the maximum count-rate that is very often few orders of magnitudes lower than of the incident, reflected or diffracted beam flux. Therefore, direct beam attenuation is mandatory in order to perform the measurements according to the detector's characteristics. In this work we present a major upgrade of a fast attenuation system developed at Synchrotron SOLEIL, which allows for a dynamical change of the beam attenuation as a function of the photon flux received by XPAD S140 photon counting detector. The system performs a cyclic real-time estimation of the flux received by every pixel during acquisition of an image and searches for clusters of at least two pixels that exceed user defined levels of counts/s. The beam attenuation is immediately and automatically changed in order to guarantee that the detector will always operate in its linear range even during a long continuous scan, by acting on the direct attenuators.

Similarities and differences of recent hybrid pixel detectors for X-ray and high energy physics developed at the Paul Scherrer Institut

Hybrid pixel detectors are being developed for both photon science and high energy physics. The article will cover similarities and differences in pixel detectors for both applications using two of the pixel detectors developed at the Paul Scherrer Institute (Switzerland) as examples: the EIGER photon counting detector and the psi46dig chip, which has been developed for the Compact Muon Solenoid (CMS) tracking pixel detector upgrade.EIGER is a single photon counting hybrid pixel detector for applications at synchrotron light sources in the energy range from a few to 25 keV. It is characterized by a small pixel size (75 × 75 μm2), high count rate capability (106 counts/pixel/s) and very high data rate, which reaches 6 Gb/s for a 256 × 256 pixel chip. The CMS pixel detector is designed to provide charge information from the pixels in the harsh radiation environment at the Large Hadron Collider. The short time between bunches of 25 ns and the high event rate at luminosity up to 2 × 1034cm−2s−1 require a detector with high hit efficiency, with good timing resolution and the ability to retain timestamp information for the hits. The readout architecture is based on the transfer of hits from the pixels to the periphery, where the trigger validation is performed before data transfer. The data rates of the digitized output reach 160 Mb/s for a 52×80 pixel chip.The specific timing and rate requirements for the detectors, the analog performances (minimum threshold and noise), the power consumption and the radiation hardness will be compared. An overview on future developments based on mutual learning and common solutions will be discussed.

Performance of the EIGER single photon counting detector

EIGER is a single photon counting hybrid pixel detector being developed at Paul Scherrer Institute (PSI), Switzerland, for applications at synchrotron light sources in an energy range from a few to 25 keV. EIGER is characterized by a small pixel size (75 × 75 μm2), a frame rate up to 22 kHz and a small dead time between frames (4 μs).An EIGER module is a hybrid detector composed of a ≈ 8 × 4 cm2 monolithic silicon sensor bump bonded to 4 × 2 readout chips, for a total of 500 kpixels. Each pixel has a configurable depth (up to 12 bits) counter and records the number of photons impinging. Custom designed module electronics reads out the bits in the pixel counter and processes the data in the module before transferring them to a PC. A large dynamic range (32 bits) for the pixel counter can be obtained through on-board image summation. Rate corrections can be applied on-board to compensate for inefficiencies when the pixel counting rates approach pile-up levels around a million counts per second. The EIGER modules are the building blocks of large area detectors: a 1.5 and a 9 Mpixel systems are under development for the cSAXS beamline at the Swiss Light Source (SLS) at PSI. The very high frame rate capabilities are equally fast for multi-module systems due to the fully parallel data processing.The module calibration will be discussed, with emphasis on the choice of the optimal operation settings as a function of photon energy. The performance regarding threshold dispersion and minimum achievable threshold will be presented. In addition, the progress towards the production of larger multi-module systems will be discussed.

JUNGFRAU 0.2: prototype characterization of a gain-switching, high dynamic range imaging system for photon science at SwissFEL and synchrotrons

JUNGFRAU (adJUstiNg Gain detector FoR the Aramis User station) is a two-dimensional pixel detector for photon science applications at free electron lasers and synchrotron light sources. It is developed for the SwissFEL currently under construction at the Paul Scherrer Institute, Switzerland. Characteristics of this application-specific integrating circuit readout chip include single photon sensitivity and low noise over a dynamic range of over four orders of magnitude of photon input signal. These characteristics are achieved by a three-fold gain-switching preamplifier in each pixel, which automatically adjusts its gain to the amount of charge deposited on the pixel. The final JUNGFRAU chip comprises 256 × 256 pixels of 75 × 75 μm2 each. Arrays of 2 × 4 chips are bump-bonded to monolithic detector modules of about 4 × 8 cm2. Multi-module systems up to 16 Mpixels are planned for the end stations at SwissFEL. A readout rate in excess of 2 kHz is anticipated, which serves the readout requirements of SwissFEL and enables high count rate synchrotron experiments with a linear count rate capability of > 20 MHz/pixel. Promising characterization results from a 3.6 × 3.6 mm2 prototype (JUNGFRAU 0.2) with fluorescence X-ray, infrared laser and synchrotron irradiation are shown. The results include an electronic noise as low as 100 electrons root-mean-square, which enables single photon detection down to X-ray energies of about 2 keV. Noise below the Poisson fluctuation of the photon number and a linearity error of the pixel response of about 1% are demonstrated. First imaging experiments successfully show automatic gain switching. The edge spread function of the imaging system proves to be comparable in quality to single photon counting hybrid pixel detectors.

Sampling function of single-X-ray-photon counting hybrid pixel detectors: combining an analytical approach to Monte-Carlo simulations and Finite-Element-Modeling

Spectroscopic and imaging performance parameters of hybrid pixel detectors operated in single-X-ray photon-counting mode can be inferred from the dependence of their sampling function (or aperture function) on the detection energy threshold. In a previous paper, it was shown that this dependence could be modelled using a simple analytical method. Measurements were performed on typical synchrotron X-ray detectors and fitted to the analytical formulas in order to obtain detector parameters such as charge-sharing width, energy dispersion and fill-factor at 50% threshold. In the present paper, we use Monte-Carlo (MC) and Finite-Element-Modeling (FEM) software tools to perform a more detailed simulation of image formation processes taking place in photon-counting hybrid pixel detectors of various pixel sizes associated to standard silicon sensor thickness and exposed to 15 keV monochromatic X-rays. We show that the MC/FEM simulation results can be used to produce detector parameters required in the analytical expressions of the sampling function of these detectors.

Detective quantum efficiency model of single-X-ray-photon counting hybrid pixel detectors

A Detective Quantum Efficiency (DQE) model of single-X-ray-Photon Counting Hybrid Pixel Detectors (PC-HPDs) is presented. It applies to PC-HPDs based on semiconductor sensors such as silicon and CdTe pixel sensors. Charge-sharing effects are introduced in the expressions of imaging performance parameters such as large-area gain factor, presampling modulation transfer function and digital noise power spectrum, using the concept of threshold-dependent effective fill-factor. A simple X-ray induced charge distribution approximation is used to derive a practical formula for the threshold-dependent large-area gain factor, i.e. the integral X-ray spectrum which can be indirectly measured with a PC-HPD. This detector model was applied to standard synchrotron X-ray PC-HPDs: MEDIPIX3, PILATUS and XPAD detectors.

EIGER: Next generation single photon counting detector for X-ray applications

EIGER is an advanced family of single photon counting hybrid pixel detectors, primarily aimed at diffraction experiments at synchrotrons . Optimization of maximal functionality and minimal pixel size (using a 0.25 μ m process and conserving the radiation tolerant design) has resulted in 75 × 75 μ m 2 pixels. Every pixel comprises a preamplifier , shaper, discriminator (with a 6 bit DAC for threshold trimming), a configurable 4/8/12 bit counter with double buffering, as well as readout, control and test circuitry. A novel feature of this chip is its double buffered counter, meaning a next frame can be acquired while the previous one is being readout. An array of 256×256 pixels fits on a ∼ 2 × 2 cm 2 chip and a sensor of ∼ 8 × 4 cm 2 will be equipped with eight readout chips to form a module containing 0.5 Mpixel. Several modules can then be tiled to form larger area detectors. Detectors up to 4×8 modules (16 Mpixel) are planned. To achieve frame rates of up to 24 kHz the readout architecture is highly parallel, and the chip readout happens in parallel on 32 readout lines with a 100 MHz Double Data Rate clock. Several chips and singles (i.e. a single chip bump-bonded to a single chip silicon sensor) were tested both with a lab X-ray source and at Swiss Light Source (SLS) beamlines . These tests demonstrate the full functionality of the chip and provide a first assessment of its performance. High resolution X-ray images and “high speed movies” were produced, even without threshold trimming, at the target system frame rates (up to ∼ 24 kHz in 4 bit mode). In parallel, dedicated hardware, firmware and software had to be developed to comply with the enormous data rate the chip is capable of delivering. Details of the chip design and tests will be given, as well as highlights of both test and final readout systems.

Study of the charge sharing effect in the photon-counting pixel detector XPAD3-S

The charge sharing effect in the single photon counting hybrid pixel detector XPAD3-S is studied. Several figures of merit are measured, both in the case of Si and CdTe sensors. Data are compared to a Monte Carlo simulation that models the main sources of charge migration.

Spectroscopic X-ray imaging with photon counting pixel detectors

Single particle counting hybrid pixel detectors simultaneously provide low noise, high granularity and high readout speed and make it possible to build detector systems offering high spatial resolution paired with good energy resolution. A limiting factor for the spectroscopic performance of such detector systems is charge sharing between neighbouring pixels in the sensor part of the detector. The signal spectrum at the collection electrodes of the readout electronics deviates significantly from the photonic spectrum when planar segmented sensor geometries are used. The Medipix3 implements a novel, distributed signal processing architecture linking neighbouring pixels and aims at eliminating the spectral distortion produced in the sensor by charge sharing and at reducing the impact of fluorescence photons generated in the sensor itself. Preliminary results from the very first Medipix3 readouts bump bonded to 300 μ m Si sensor are presented. Material reconstruction is a possible future application of spectroscopic imaging detectors and an example of material reconstruction in small animal imaging is given.

Imaging performance of the hybrid pixel detectors XPAD3-S

Hybrid pixel detectors, originally developed for tracking particles in high-energy physics experiments, have recently been used in material sciences and macromolecular crystallography. Their capability to count single photons and to apply a threshold on the photon energy suggests that they could be optimal digital x-ray detectors in low energy beams such as for small animal computed tomography (CT). To investigate this issue, we have studied the imaging performance of photon counting hybrid pixel detectors based on the XPAD3-S chip. Two detectors are considered, connected either to a Si or to a CdTe sensor, the latter being of interest for its higher efficiency. Both a standard ‘International Electrotechnical Commission’ (IEC) mammography beam and a beam used for mouse CT results published in the literature are employed. The detector stability, linearity and noise are investigated as a function of the dose for several imaging exposures (∼0.1–400 µGy). The perfect linearity of both detectors is confirmed, but an increase in internal noise for counting statistics higher than ∼5000 photons has been found, corresponding to exposures above ∼110 µGy and ∼50 µGy for the Si and CdTe sensors, respectively. The noise power spectrum (NPS), the modulation transfer function (MTF) and the detective quantum efficiency (DQE) are then measured for two energy threshold configurations (5 keV and 18 keV) and three doses (∼3, 30 and 300 µGy), in order to obtain a complete estimation of the detector performances. In general, the CdTe sensor shows a clear superiority with a maximal DQE(0) of ∼1, thanks to its high efficiency (∼100%). The DQE of the Si sensor is more dependent on the radiation quality, due to the energy dependence of its efficiency its maximum is ∼0.4 with respect to the softer radiation. Finally, we compare the XPAD3-S DQE with published curves of other digital devices in a similar radiation condition. The XPAD3-S/CdTe detector appears to be the best with the highest DQE at low frequency, although some improvements are expected to reduce the increase of noise with the counts statistics and to guarantee a better stability of the detector response.

Photon counting hybrid pixel detector for X-ray imaging

We have designed and built prototype modules of a large area photon counting hybrid pixel detector. The detector consists of modules each with seven Aladin readout chips solder bump bonded to a silicon pixel detector. Each Aladin chip has 64×64 pixels together with logic to readout the whole array in 400 μs. It is intended to tile an area of 2000×2000 pixels, each of 150 μm×150 μm and capable of up to 1 MHz count rate per pixel. This paper describes the design and operation of the detector and the performance of the existing modules. The measurements demonstrate that the detector can image 19 keV photons at 200 kHz photons per pixel with 3 keV FWHM noise. The detector is intended for X-ray diffraction studies with data capture speeds up to 1000 images per second, independent of the image size.