Good Radiation Hardness Research Articles

HASPIDE: a project for the development of hydrogenated amorphous silicon radiation sensors on a flexible substrate

Hydrogenated amorphous silicon (a-Si:H) is a material with a very good radiation hardness and with the possibility of deposition on flexible substrates like Polyimide (PI). Exploiting these properties, the HASPIDE (Hydrogenated Amorphous Silicon PIxels DEtectors) project has the goal of developing a-Si:H detectors on flexible substrates for beam dosimetry and profile monitoring, neutron detection and space experiments. The detectors for this experiment will be developed in two different structures: the n-i-p diode structure, which has been used up to now for the construction of the planar a-Si:H detectors, and the recently developed charge selective contact structure. In the latter the doped layers (n or p) are replaced with charge selective materials namely electron-selective conductive metal-oxides (TiO2 or Al:ZnO) and hole-selective conductive metal oxides (MoO x ). In this paper preliminary data on the capabilities of these detectors to measure X-ray and electron fluxes will be presented. In particular, the linearity, the sensitivity, the stability and dark current in various conditions will be discussed.

Enhancing spatial resolution in MÖNCH for electron microscopy via deep learning

Hybrid Pixel Detectors (HPDs) are highly suitable in diffraction-based electron microscopy due to their high frame rates (> 1 kHz), high dynamic range, and good radiation hardness. However, their use in imaging applications has been limited by their relatively large pixel size (≥ 55 μm) and high-energy (>80 keV) electrons scattering over multiple pixels in the sensor layer. To realize the full potential of fast, radiation-hard HPDs across electron microscopy modalities, we developed deep learning techniques to precisely localize the impact point of incident electrons in MÖNCH, a charge integrating HPD with 25 μm pixel size. With neural network models trained using labeled data via simulations and experimental measurements, the best spatial resolution obtained, defined in terms of the root mean squared error, was 0.60 pixels for 200 keV electrons, a three-fold improvement over a simple charge centroid method. This article presents the training sample generation, deep learning model design, training results, and imaging outcomes for a sample containing gold nanoparticles.

Intense radioluminescence from transparent CsGd2F7: Ce3+ nano-glass scintillator

Nano-glasses are next-generation scintillators combining favorably the merits of both scintillator crystals and glasses. Here, a new nano-glass scintillator is prepared embedding CsGd2F7:Ce3+ nanocrystals (NCs). The microscopic morphology, particle size, and distribution of the NCs are studied by high resolution transmission electron microscopy. Significantly enhanced radioluminescence efficiency is obtained in the nano-glasses. The largest integrable intensity of X-ray excited luminescence is 316% of the standard Bi4Ge3O12 (BGO) crystal. A well-resolved full-energy peak with an energy resolution of 17.4% is registered for the 662 keV gamma rays, and the light yield is determined to be 827 ± 8 ph/MeV. The nano-glass scintillators exhibit good radiation hardness and thermal stability. As a proof of concept, an X-ray imaging system of a good resolution is built on the nano-glass scintillators.

Development of a SiC semiconductor-based dosimeter for evaluating clinical dose distribution in carbon ion cancer therapy fields

Dosimeters with excellent energy resolution are required to improve quality control and assurance (QA/QC) for heavy-ion cancer therapy, in which multiple species of ions are expected to be used. The conventional ionization chamber that is widely used for QA/QC generally does not support quality discrimination for different radiation species, and several types of energy-dispersive dosimeters are being studied for this application, including silicon semiconductors on insulator devices. Other wide bandgap semiconductors with good radiation hardness, including SiC and diamond, are being studied for use in cancer therapy ion fields. In this study, a 4H-SiC Schottky barrier diode was used for energy-dispersive dosimetry in the clinical carbon therapy field at Gunma University Medical Center for Heavy Ion Beam Medicine. The relative biological effectiveness was estimated from the linear energy transfer spectra for a pristine carbon beam with an energy of 290 MeV/n and a spread-out Bragg peak beam using the linear-quadratic model. The results showed that the SiC-based dosimeter could be used in the detailed characterization of the clinical dose distribution of carbon ion cancer therapy fields.

Development of a gaseous Xe scintillator for particle identification of high-intensity and heavy ion beams

We have developed a gaseous Xe scintillator as a new ΔE detector which is expected to have good radiation hardness and fast response. In this research, we made a new version of the detector whose thickness is comparable to that of an ion chamber which is the current standard ΔE detector in RIBF. We carried out a performance test of the detector in RIBF. The root-mean-square (rms) resolutions of the atomic number Z around Z=35 and Z=55 are found to be about 0.2 and 0.3, respectively. In addition, it has a good timing resolution for a 238U beam of 74.4(6)ps in rms.

Radiation hardness of a wide spectral range SiPM with quasi-spherical junction

New pixel geometries are on the rise to achieve high sensitivity in near-infrared wavelengths with silicon photomultipliers (SiPMs). We test prototypes of the tip avalanche photo-diodes, which feature a quasi-spherical p-n junction and a high photodetection efficiency over a wide spectral range, and analyze the performance after neutron irradiation. The observed increase in dark count rate is significantly smaller than for a SiPM with a conventional design, indicating a good radiation hardness of the pixel geometry.

A Low Noise Readout System for Diamond Microstrip Detectors

Diamond is widely adopted in physics experiments owing to its good radiation hardness. In this paper, a low noise electronics system based on charge sensitive amplifier (CSA) is designed to read out diamond microstrip detectors. Up to 40 channels are implemented in the system, each containing a CSA, a CR — RC 2 shaper, an analog to digital convertor (ADC) and a discriminator used for trigger generation. After calibration and joint test with prototype detector with a size of 4×4×0.5 mm 3, a noise level of less than 845 electrons is realized in all 40 channels. Furthermore, the result with 90 Sr radiation source is consistent with the theory, and a position resolution of 13 um is obtained in laser test which indicates the readout system meets the demand of the future experiment.

Characterization of Heavily Irradiated Dielectrics for Pixel Sensors Coupling Insulator Applications

An increase in the radiation levels during the high-luminosity operation of the Large Hadron Collider calls for the development of silicon-based pixel detectors that are used for particle tracking and vertex reconstruction. Unlike the conventionally used conductively coupled (DC-coupled) detectors that are prone to an increment in leakage currents due to radiation, capacitively coupled (AC-coupled) detectors are anticipated to be in operation in future collider experiments suitable for tracking purposes. The implementation of AC-coupling to micro-scale pixel sensor areas enables one to provide an enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of new generation capacitively coupled (AC-coupled) pixel sensors with coupling insulators having good dielectric strength and radiation hardness simultaneously. The AC-coupling insulator thin films were aluminum oxide (Al2O3) and hafnium oxide (HfO2) grown by the atomic layer deposition (ALD) method. A comparison study was performed based on the dielectric material used in MOS, MOSFET, and AC-coupled pixel prototypes processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates. Post-irradiation studies with 10 MeV protons up to a fluence of 1015 protons/cm2 suggest HfO2 to be a better candidate as it provides higher sensitivity with negative charge accumulation on irradiation. Furthermore, even though the nature of the dielectric does not affect the electric field within the AC-coupled pixel sensor, samples with HfO2 are comparatively less susceptible to undergo an early breakdown due to irradiation. Edge-transient current technique (e-TCT) measurements show a prominent double-junction effect as expected in heavily irradiated p-type detectors, in accordance with the simulation studies.

Determination of Position Resolution for LYSO Scintillation Crystals Using Geant4 Monte Carlo Code

LYSO scintillation crystals, due to their significant characteristics such as high light yield, fast decay time, small Moliére radius, and good radiation hardness, are proposed to be used for the electromagnetic calorimeter section of the Turkish Accelerator Center Particle Factory (TAC-PF) detector. In this work, the center of gravity technique was used to determine the impact coordinates of an electron initiating an electromagnetic shower in a LYSO array, in a calorimeter module containing nine crystals, each 25 mm × 25 mm in cross-section and 200 mm in length. The response of the calorimeter module has been studied with electrons having energies in the range 0.1 GeV-2 GeV. By using the Monte Carlo simulation based on Geant4, the two-dimensional position resolution of the module is obtained as σ R mm = 3.95 ± 0.08 / E ⊕ 1.91 ± 0.11 at the center of the crystal.

Highly Efficient and Tunable Emission of Lead‐Free Manganese Halides toward White Light‐Emitting Diode and X‐Ray Scintillation Applications

AbstractEnvironmental friendly metal halides have become emerging candidates as energy downconverting emitters for lighting and X‐ray imaging applications. Herein, luminescent single crystals of tetramethylammonium manganese chloride (C4H12NMnCl3) and tetraethylammonium bromide ((C8H20N)2MnBr4) are synthesized via a facile room‐temperature evaporation method. C4H12NMnCl3 and (C8H20N)2MnBr4 with octahedrally and tetrahedrally coordinated Mn2+ have correspondingly exhibited red and green emission peaking at 635 and 515 nm both originating from 4T1–6A1 transition of Mn2+ with high photoluminescence quantum yield (PLQY) of 91.8% and 85.1% benefiting from their specific crystal structures. Thanks to their strong photoexcitation under blue light, high PLQY, tunable emission spectra, good environmental stability, the white light‐emitting diode based on blending of C4H12NMnCl3 and (C8H20N)2MnBr4 delivers an outstanding luminous efficacy of 96 lm W−1, approaching commercial level, and shows no obvious photoluminescence intensity degradation after 3000 h under operation. In addition, manganese halides also demonstrate interesting characteristics under X‐ray excitation, C4H12NMnCl3 and (C8H20N)2MnBr4 exhibit steady‐state X‐ray light yields of 50 500 and 24 400 photons MeV−1, low detectable limits of 36.9 and 24.2 nGyair s−1, good radiation hardness, and X‐ray imaging demonstration with high‐resolution of 5 lp mm−1. This work presents a new avenue for luminescent Mn‐based metal halides toward multifunctional light‐emitting applications.

A reconfigurable CMOS sensor for tracking, pre-shower and digital electromagnetic calorimetry

Recent advances in CMOS imaging sensor technology have led to designs able to withstand much higher radiation levels, up to those required at hadron colliders for all but the innermost layers. Also, with stitching, wafer scale devices have been fabricated on the same process as used for the prototypes described in this submission, for applications such as, for example, direct electron detection in transmission electron microscopy. A small sensor prototype has been designed and fabricated in the TowerJazz 180 nm CMOS imaging process. The prototype has a pixel matrix of 64x64 pixels with a pitch of 55 x 55μm and reads out using fast logic at 40 MHz. Each pixel contains four collection electrodes, trimming logic, pre-amplifier, shaper and discriminator with digital output. It can be reconfigured to function as either a binary short strip sensor, for particle tracking including as a pre-shower, or as a pad sensor, counting the number of pixels above threshold for digital calorimetry. As well as providing a seamless transition from outer tracking to EM calorimetry, for optimal use of particle flow algorithms, digital calorimetry also can give excellent energy resolution. This concept is proposed as a possible option for future digital calorimeters able to read-out at LHC collision rates with good radiation hardness and realisable in low cost commercial technologies for equipping large areas. Results on physics performance simulation in a FCC-hh context and the characterisation of the prototype sensor are presented. The summing logic is demonstrated and the analogue pixel performance is validated by illuminating a test pixel within the matrix with a laser of wavelength of 1064 nm. The absolute laser intensity is calibrated such that the injected charge is similar to that expected for a minimum ionising particle. The measured pre-amplifier and shaper signals are compared to Cadence simulations. Laser illuminations in the digital pixel area and the response measured using a threshold scan confirm successful digital functionality in strip and pad operation modes.

Results on radiation hardness of black silicon induced junction photodetectors from proton and electron radiation

The stability of black silicon induced junction photodetectors under high-energy irradiation was tested with 11 MeV protons and 12 MeV electrons using fluence of 1⋅1010 protons/cm2 and dose of 67 krad(Si) for protons and electrons, respectively. The energies and dose levels were selected to test radiation levels relevant for space applications. The degradation was evaluated through dark current and external quantum efficiency changes during (within 1 h after each step) and after (some days after) full irradiation sequences. Furthermore, the black silicon photodetectors were compared to planar silicon induced junction and planar silicon pn-junction photodetectors to assess the contribution from both black silicon and semiconductor junction characteristics. The calculated radiation damage factors of all types of studied detectors were in agreement with values previously published in literature. The external quantum efficiency results demonstrated that the combination of black silicon surface and aluminum oxide induced junction provides a good radiation hardness against the used proton and electron doses showing degradation only in the near infrared region due to bulk damage. The pn-junction photodetectors with silicon dioxide passivation exhibited significant degradation also in the ultraviolet responsivity after electron irradiation.

Study of Underlapped Finfets Behavior for a Radiation Sensing Purpose

The use of MOSFET transistors as radiation sensors has been intensively studied in recent years. Since the main effects caused by the total ionization dose (TID) are well known, the application of this technology as a dosimeter for many applications has greatly increased. One example is the application of MOSFETs as dosimeter of Radiotherapy (1). Knowing that SOI FinFETs have high immunity to soft errors and thin FinFET devices also presents a good radiation hardness for TID effects, the Underlapped FinFET structure can be applied as an accurate radiation sensor since only the oxide in the underlap region will be responsible for the drain current (ID) variation.The experimental behavior of self-aligned FinFET transistor with fin width (WFIN) of 20nm before and after proton irradiation are presented in figure 1. As already reported in (2, 3), the FinFET with WFIN=20 nm shows a high immunity to TID effects of proton radiation even considering the accumulated charges in the front and buried oxides due to the high coupling between gates.From now on, it was considered the underlap regions for both source and drain (S/D) sides. The simulation was calibrated with experimental FinFET behavior for self-aligned structure and it was extrapolated for other underlapped structures varying the underlap lengths (LSP). The underlap region was varied from 0nm (self-aligned structure) to 50nm and the permittivity (k) of the oxide in the underlap region was varied from 1 (no oxide in the underlap region) to 25 (hafnium oxide – HfO2). Figure 2 presents the drain current as a function of gate voltage (VG) for underlapped FinFETs, varying the underlap length and the permittivity of the oxide in the underlap region. The increase of the LSP results in a strong degradation of ID due to the loss charge control over the underlap, caused by lower electric field effect (fringing field), which increases the series resistance and the current spreading in the spacer.Besides the underlap length, the impact of permittivity on the on-state current level (ION) can also be observed in figure 2. The permittivity increase results in a higher fringing fields from the gate to the source/drain regions and consequently a higher current density, that in turns, causes the improvement on ION. The electric field and the electron density were extracted from numerical simulations for devices with k=1 and k=25 and a higher fringing field and consequently the higher electron density over the underlap region, for devices with k=25, can be observed in figure 3.The sensitivity (S), that was calculated by ID (k=X)/ID (k=1), was evaluated in order to select the better oxide and length to the underlap region. From figure 4, it is possible to observe that the greater the LSP and permittivity, the better is the sensitivity of the device. Although devices with longer underlap present a high series resistance and consequently a smaller drain current level, the ION enhancement caused by the higher influence of fringing field becomes more pronounced when using the higher permittivity, resulting in a more sensitive device. However, for high drain bias (VDS=1V) the underlap length plays a hole until LSP=30 nm, for longer underlap no significant sensitivity variation was obtained.Considering that the device with longer underlap region (LSP=50nm) and higher k (HfO2 – k=25) presents a better sensitivity, it was considered to evaluate its charges sensing ability.Aiming to analyze the underlapped FinFET as a radiation sensor (TID), fixed charges density (Qox) with carrier concentration of 0, 1011, 5x1011 and 1012 cm-2 were considered in the underlap region, where Qox=0 cm-2 characterizes the pre-radiated transistor. Figure 5 shows that despite the low on-state current caused by the high series resistance, when the oxide charges are considered, there is an increase of the potential in the underlap region causing an enhancement of ION. The radiation sensitivity was calculated by post-radiated ION over pre-radiated ION ratio.Although narrow FinFETs are well known as a radiation hardness transistor, from figure 6 it is possible to notice that a long underlap region with a high k dielectric allows this device to have a good sensing behavior. When considering a relatively low trapped charge density (Qox= 5x1011cm-2), the drain current increases about 60%, i.e., sensitivity equal 1.6. Increasing the trapped charge density to Qox=1x1012 cm-2, the obtained sensitivity values are still higher, reaching an increment of 140% on the ION current level (S=2.4), confirming the excellent characteristic of the device working as a radiation sensor. Figure 1

Characterization of SINTEF 3D diodes with trenched-electrode geometry before and after neutron irradiation

We report on the characterization of 3D diodes with trenched electrodes and active edges manufactured by SINTEF MiNaLab (Oslo, Norway), and irradiated with reactor neutrons up to a maximum fluence of 2 × 1016 neq cm−2. The charge collection performance of these test structures is investigated by using a position resolved pulsed laser system, and discussed with the aid of TCAD simulations. In spite of the non-idealities of the test setup, whose spatial resolution is not fine enough for the small-pitch geometries of the considered samples, results confirm the good radiation hardness of 3D sensors with trenched electrodes.

Effects of proton and ion beam radiation on magnetic tunnel junctions

Conventional semiconductor-based electronic devices can cause errors when they are exposed to cosmic rays. Magnetic memory has been proposed as an alternative because it consists of a metal structure free from radiation-induced errors in principle. In this study, we investigated the effects of proton and Cr ion irradiations on the magnetic and electric properties of a magnetic tunnel junction (MTJ). We observed that the magnetic hysteresis and magnetoresistance of MTJ were not affected by proton irradiation of an energy of 20 MeV and dose levels up to 1 × 1018/m2, thus demonstrating good radiation hardness in response to the proton beam. On the other hand, when a MTJ was irradiated by a Cr ion beam of an energy of 20 keV and dose levels up to 1 × 1018/m2, its magnetic properties or magnetoresistance deteriorated, depending on the layer structure of the MTJ. A simulation study shows that this degradation may stem from radiation-energy dependent displacement damage in the magnetic layers, which can be avoided by the introduction of a proper protective layer.

Development of 3D trenched-electrode pixel sensors with improved timing performance

The high luminosities expected at collider experiments over the coming years will put stringent requirements on the vertex detectors used in these experiments. The increased pile up will require improved spatial and timing resolution to distinguish between particle tracks while also requiring the devices to have an increased radiation hardness. 3D sensors have already been proven as a viable technology with good radiation hardness due to the short distance between electrodes and are also capable of achieving the desired spatial resolution. 3D sensors have so far not been fully exploited to achieve good timing resolution due to the non-uniformity of the electric field in the sensors. The TIMESPOT project aims to develop a complete integrated system for tracking with high precision in both space and time. Novel 3D sensors are being developed for this purpose, providing the normal advantages of this technology (such as radiation hardness and low depletion voltage), with the trench geometry also providing more uniform electric and weighting fields, optimized for timing. TCAD simulations have been carried out to optimize the design of these sensors and to estimate their performance, finding a compromise between the capacitance and the intrinsic speed. Technological tests have also been carried out at FBK to determine the manufacturing constraints of these sensors. A first layout including pixel sensors compatible with the TIMEPIX read-out chip and several test structures has been prepared and production of the first batch of sensors is underway.

Electrical Characterization of Defects Created by γ-Radiation in HfO2-Based MIS Structures for RRAM Applications

The γ-radiation effects on the electrical characteristics of metal–insulator-semiconductor capacitors based on HfO2, and on the resistive switching characteristics of the structures have been studied. The HfO2 was grown directly on silicon substrates by atomic layer deposition. Some of the capacitors were submitted to a γ ray irradiation using three different doses (16 kGy, 96 kGy and 386 kGy). We studied the electrical characteristics in the pristine state of the capacitors. The radiation increased the interfacial state densities at the insulator/semiconductor interface, and the slow traps inside the insulator near the interface. However, the leakage current is not increased by the irradiation, and the conduction mechanism is Poole–Frenkel for all the samples. The switching characteristics were also studied, and no significant differences were obtained in the performance of the devices after having been irradiated, indicating that the fabricated capacitors present good radiation hardness for its use as a RS element.

Performances of Crystal Scintillators in a Severe Radiation Environment Caused by Gamma Rays

Because of their superb energy resolution and detection efficiency crystal scintillators are widely used in high energy and nuclear physics experiments. A crucial issue is radiation damage. We report an investigation on γ-ray induced radiation damage in crystal scintillators of large size, including BaF2, BGO, CeF3, pure CsI, LSO/LYSO/LFS and PWO with an integrated dose up to 340 Mrad at a dose rate up to 1 Mrad/h. Optical and scintillation properties of these crystal samples were measured before and after irradiations. The result shows that pure CsI crystals have good radiation hardness below 100 krad. BaF2, BGO and LYSO crystals show good radiation hardness beyond 1 Mrad. In terms of light output degradation LSO/LYSO/LFS is clearly the best among all scintillation crystals.

Diamond Based Schottky Photodiode for Radiation Therapy <i>In Vivo</i> Dosimetry

Diamond has long been considered as a suitable material for the fabrication of radiation detectors due to its outstanding physical properties. Even more so in the specific case of radiation therapy dosimetry applications, where the near-tissue equivalence radiation absorption, good spatial resolution and radiation hardness are required. Recently, a synthetic single crystal diamond dosimeter was developed at “Tor Vergata” University in cooperation with PTW-Freiburg, showing excellent dosimetric properties. Such a device was thus commercialized (microDiamondTM, PTW-type 60019) and widely accepted by the medical physics community, due to its reproducibility, reliability, accuracy and versatility. In this work, a novel diamond based dosimeter for in vivo application developed in our laboratories is presented. A basic dosimetric characterization of detector performances was performed under irradiation with 60Co and 6 MV photon beams. Response stability, short and long term reproducibility, fading effect, linearity with dose, dose rate dependence, and temperature dependence were investigated. The detector response was found to be reproducible and dose rate independent in the range between 0.5 and 5 Gy/min. Its temperature dependence was within 0.5% between 25 and 38 ◦C, and negligible fading effect was observed. The obtained results indicate the proposed novel diamond device as a promising candidate for in vivo dosimetry in radiation therapy application.

Test beam results of a high granularity LuAG fibre calorimeter prototype

The progresses in the micropulling-down technique allow heavy scintillating crystals to be grown directly into a fibre geometry of variable shape, length and diameter. Examples of materials that can be grown with this technique are Lutetium Aluminum Garnets (LuAG, Lu3Al5O12) and Yttrium Aluminum Garnets (YAG, Y3Al5O12). Thanks to the flexibility of this approach, combined with the high density and good radiation hardness of the materials, such a technology represents a powerful tool for the development of future calorimeters. As an important proof of concept of the application of crystal fibres in future experiments, a small calorimeter prototype was built and tested on beam. A grooved brass absorber (dimensions 26cm×7cm×16cm) was instrumented with 64 LuAG fibres, 56 of which were doped with Cerium, while the remaining 8 were undoped. Each fibre was readout individually using 8 eightfold Silicon Photomultiplier arrays, thus providing a highly granular description of the shower development inside the module as well as good tracking capabilities. The module was tested at the Fermilab Test Beam Facility using electrons and pions in the 2–16 GeV energy range. The module performance as well as fibre characterization results from this beam test are presented.