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Imaging Applications and Systems

Session chair: Bertuccio , Giuseppe (Politecnico di Milano, Department of Electronics, Information and Bioengineering, Como, Italy); Aoki , Toru (Shizuoka University, Research Institute of Electronics, Hamamatsu, Japan)
Shortcut: R-07
Date: Wednesday, 20 October, 2021, 11:45 AM - 1:45 PM
Room: RTSD
Session type: RTSD Session


Click on an contribution to preview the abstract content.

11:45 AM R-07-01

Low leakage currents contacts for High-Flux CdZnTe (#475)

M. Bettelli1, S. Zanettini3, N. Sarzi Amadè3, F. Casoli1, C. Ponchut2, S. Tsigaridas2, D. Calestani1, A. Zappettini1

1 CNR, IMEM, Parma, Italy
2 ESRF, Grenoble, France
3 Due2Lab s.r.l., Reggio Emilia, Italy


Recently, sensors made from high-Z compound semiconductors have attracted attention for use in applications which require the direct detection of X-rays in the energy range 30–100 keV. Cadmium zinc telluride (CdZnTe or CZT) is one of the candidates with promising properties. However, under high photon flux, standard CZT is affected by a strong polarization due to hole trapping that leads to poor performance. Redlen has developed a novel CZT material for high flux applications where holes transport properties have been improved. Since detectors for high-flux applications must be strongly biased (>500V/mm), blocking contacts are mandatory in order to minimize the leakage current and to enhance detector performances. Platinum and gold are promising candidates for the realization of blocking contacts on CZT.

However, the novel high-flux CdZnTe material proposed by Redlen showed a different behavior in respect to the standard grade. Gold electroless contacts, which allow to obtain very low leakage current on standard CZT, lead instead to too high leakage current also at low biasing. In this work a detailed study on the behavior of various combinations of electric contacts is shown. Current-voltage characteristics have been achieved on all fabricated samples, a deeper characterization comprising low- and high-flux measurements has been carried out. Results of this study will be presented in this work.
Keywords: CdZnTe, High-Flux, Platinum, Blocking Contacts, Low Leakage Current
12:00 PM R-07-02

Perovskite Semiconductor X-ray Detectors for Medical and Synchrotron Applications (#1116)

K. Hansen1, A. Datta1, S. Motakef1

1 CapeSym, Inc., R&D, Natick, Massachusetts, United States of America


X-ray imaging has applications in several key areas of science, medicine, and security. The detectors that are currently available either lack the efficiency to work with higher X-ray energies or the spatial resolution to detect micron-scale features. As a new generation of direct X-ray detectors, we are developing a perovskite semiconductors based sensor material that has enough stopping power to compete with a-Se detectors and the capability to produce high spatial resolution exceeding the microcolumnar CsI:Tl detectors. The methylammonium lead iodide (MAPbI3) based detectors are highly scalable and radiation hard. The high-Z semiconductor and the charge limiting layers are deposited by a low-temperature and low-cost process. The deposition of this semiconductor on high spatial resolution pixel arrays doesn’t require the high-cost pitch-limiting bump bonding process and hence can produce high spatial resolution detectors only limited by the grain-size. To mitigate the challenge of poor repeatability and improve the film smoothness we have tailored the solvent system allowing for large scale film processing. Additionally, we introduced a solvent annealing step to improve the crystallinity and increase the grain size, thereby increasing the X-ray sensitivity of the MAPbI3 films. These detectors not only demonstrate low dark current and high X-ray sensitivity but also can be repeatedly manufactured over large area active pixel backplanes.

Keywords: Semiconductor detectors, Dark current, X-ray Detectors, X-ray Sensitivity
12:15 PM R-07-03

Brass material analysis result with X-Ray fluorescence (XRF) system based on the Deep Learning method (#737)

A. Jo1, W. Lee2, 3

1 Korea University, Department of Bio-convergence Engineering, Seoul, Republic of Korea
2 Korea University, School of Health and Environmental Science, Seoul, Republic of Korea
3 Korea University, Transdisciplinary Major in Learning Health Systems, Graduate School, Seoul, Republic of Korea


X-ray fluorescence (XRF) systems use the characteristic X-rays emitted from the atoms when photons interact with materials to analyze materials. XRF systems use the silicon drift detectors (SDD) which have high energy resolution for the XRF systems. SDD detectors, however, have difficulty in detecting high-energy photons because the low atomic number of Si and their thicknesses. In this study, we used the CdTe semiconductor detector array and deep learning method to improve the XRF system performance. It is expected that K-series characteristic X-rays can be used for the high-Z material analysis attributed to the high atomic number of CdTe and deep learning models can improve the accuracy of material analysis by learning the patterns of various energy spectrums even though the energy resolution of CdTe detectors are lower than that of SDDs. Brass was analyzed in this study due to its small Kα characteristic X-ray energy difference between its components. The overall performance of the XRF system based on deep learning method can be estimated.

AcknowledgmentThis work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MIST) (No. 2020R1A2C1005924) and by the Nuclear Safety Research Program thjrough the Korea Foundation of Nuclear Safety (KoFONS) using the financial resource granted by the Nuclear Safety and Security Commission (NSSC) of the Republic of Korea (No. 1903006).
Keywords: X-ray Fluorescence imaging, Deep Learning, Material analysis
12:30 PM R-07-04

High-Z sensors for synchrotron sources and FELs (#561)

D. Greiffenberg1, M. Andrae1, R. Barten1, A. Bergamaschi1, S. Chiriotti1, R. Dinapoli1, M. Brueckner1, V. Hinger1, T. King1, E. Froejdh1, S. Hasanaj1, P. Kozlowski1, D. Mezza1, A. Mozzanica1, C. Lopez1, K. Moustakas1, C. Ruder1, B. Schmitt1, D. Thattil1, J. Zhang1

1 Paul Scherrer Institute (PSI), SLS Detector Group, Villigen, Aargau, Switzerland


High-Z compound semiconductor aim at replacing silicon as sensor material for X-ray energies above 15 keV thanks to their superior absorption efficiency. However, compared to silicon, high-Z sensors such as GaAs:Cr, CdTe or CZT still lack in several aspects such as homogeneity, charge transport properties, charge trapping (leading to polarization 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 as well as free electron lasers (FELs) towards higher photon energies. Promising results have been obtained using the 75 µm pitch JUNGFRAU charge integrating detector in combination with various high-Z sensors (GaAs:Cr, Ohmic/Schottky type CdTe and CZT). 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 (e.g. fluorescence, dislocation lines, detrapping of charge carriers etc.).

As one of the major challenges at the advanced light sources (like the upcoming 4th generation of synchrotrons or FELs) are high (potentially pulsed) photon fluxes, the dynamic behavior (like signal stability, polarization, afterglow) of the different high-Z sensors has been investigated using photon fluxes up to 1010 ph/(mm2·s). The imaging capabilities of different sensors with 75 × 75 µm2 pixel pitch will be presented together with an interpolation method to improve the spatial resolution by comparing the signal of the adjacent pixels, allowing virtual pixel pitches down to 5 × 5 µm2.

Keywords: Charge-integrating, Pixel detector, CZT, CdTe, GaAs:Cr
12:45 PM R-07-05

Improving the Real-Time Sub-Millimeter Contaminants Detection Capability of XSpectra® (#276)

B. Garavelli1, D. Macera1, D. Rizzo1, M. Sammartini1

1 Xnext s.r.l., Milano, Italy


A challenging requirement in the field of real-time quality-controls on industrial production lines is the ability to detect smaller and smaller foreign bodies inside products. Xnext patented technology XSpectra® has already successfully entered the food market sector, overcoming the existing conventional  inspection technologies owing to its multi-spectral approach. To further upgrade our detection system, the detector geometry can be modified by shrinking the  pixel area from 0.8 × 0.8 mm2 to 0.4 × 0.4 mm2, which ensures an higher spatial resolution, essential to distinguish even smaller contaminants. A proprietary  simulator has been developed in-house in order to compare the main capabilities of the new 0.4 mm pitch detector with the previous 0.8 mm one. We report the  successful result of the simulation of a typical inspection case of a contaminated brick of milk with two copper spheres, with diameters of 5 mm and 0.5  mm: the 0.4 mm pitch detector is able to resolve both foreign bodies, while the 0.8 mm only sees the bigger one. The simulations allowed also to demonstrate  the improvements in the charge transport and collection mechanisms achievable with the 0.4 mm detector, which is a consequence of an enhanced small pixel effect. To this purpose, we provide a comparison between the signals induced by equal-energy photons absorbed at the same spatial coordinate of the bulk for  both the detector geometries and their respective weighting fields. Moreover, the comparison between the simulated radiation spectra acquired by both the  detectors showed a slight worsening in energy resolution for the 0.4 mm detector, which is caused by an increase in charge-sharing and cross-talk events due  to the reduction of the pixel area. All these promising simulation results will be verified with experimental tests on our first prototypes of 0.4 mm detector,  expected in the very next months.

Keywords: Non-Destructive-Test X-ray equipment, CdTe detectors, Small-pixel effect, Multi-spectral analysis
1:00 PM R-07-06

Temperature dependence of α-particle detection characteristics of GaN radiation detectors (#688)

H. Nakagawa1, K. Hayashi2, A. Miyazawa2, Y. Honda3, H. Amano3, 4, T. Aoki1, T. Nakano1, 2

1 Shizuoka University, Research Insutitute of Electronics, Hamamatsu, Japan
2 Shizuoka University, Department of Electronics and Materials Science, Hamamatsu, Japan
3 Nagoya University, Institute of Materials and Systems for Sustainability, Nagoya, Japan
4 Nagoya University, Akasaki Research Center, Nagoya, Japan


Gallium nitride (GaN) is a promising semiconductor for radiation detection at room temperature. Based on this concept, we have previously suggested a BGaN detector for neutron detection. In this study, the radiation-detection properties of GaN pin-diode detectors, fabricated on the base material of BGaN, were evaluated under high-temperature conditions (~573 K). GaN pin-diodes were fabricated by metal-organic vaper phase epitaxy (MOVPE). In the radiation-detection measurement, the fabricated GaN pin-diode detectors were measured and evaluated by a multi-channel analyzer, which enables measurements of both pulse height and rise time from the output signal pulse, irradiated from 241Am radio-isotope as the source of alpha-particles. The alpha-particle detection measurements were carried out under an applied reverse voltage of 5 V and a distance between the 241Am alpha-particles source and GaN pin-diode detector of 19 mm. Temperature was varied by heating the atmosphere around the shield box containing the GaN pin-diodes with a heater from about 293 K (room temperature) to 573 K. From the energy spectra obtained from the alpha-particles detection measurements, it was confirmed that the GaN pin-diode detector can detect at any temperature below 573 K. The temperature dependence of the peak position and energy resolution obtained from the alpha-particle energy spectra were analyzed. The peak position was observed to shift to lower energies with temperature increase. This result indicates that the sensitive layer of alpha-particles was reduced due to the temperature increase. On the other hand, the energy resolution was improved with temperature increasing. This result means that the carrier-collection efficiency improved as temperature is increased. From these results, it was confirmed that the GaN pin-diode semiconductor detector can be enabled to operate under high-temperature conditions.

Keywords: GaN, radiation detector, temperature dependence

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