Acute skin toxicity after radiation treatments highlights the need for improved dose monitoring and measurement, as the treatment planning system does not accurately estimate skin dose. Wearable radiation detectors may be the solution for mostin vivodosimetry needs, but they require innovative materials. The purpose of this work is to overcome the challenges that limit accurate skin dosimetry by exploring the use of hydrogenated amorphous silicon (a-Si:H) fabricated on a flexible polyimide substrate for direct radiation detection. The a-Si:H detector was fabricated on a 125μm polyimide substrate with a thickness of 3.6-10μm. The detector's response to the build-up region of the percentage depth dose (PDD) of the MV photon beam was compared to Geant4 radiation transport simulations and benchmarked to Attix ionization chamber measurements. Angular dependency and surface field factors at the phantom surface were compared to Attix IC. The PDD measurement is within 2% of Geant4's simulation and the Attix chamber's response from 150m to 25 mm in a plastic water phantom. All samples showed linear dose responses with 0.37% reproducibility. The a-Si:H device matches the Attix chamber for surface field factor measurements (6-10 MV photon beams, for 5 to 25 cm field sizes). The angular dependence (-60° to +60°) compared to the Attix IC confirms the sensor's WED of 150 ± 5µm. This study demonstrates that a-Si:H sensors on flexible plastic substrates have a potential for accurate surface dose measurements and agree with reference detectors. This thin, flexible detector provides real time measurements and is stable under high radiation doses. The possibility to assemble with ease an array of a-Si:H pixels over large areas with different sizes and shapes, makes this technology attractive forin vivodosimetry.

The objective of the Photo-HASPIDE experiment is the construction and test of an indirect a-Si:H (Hydrogenated Amorphous Silicon) photo-detector plus scintillator device on a flexible substrate for the detection and measurement of particles fluxes (X-rays, electrons and protons) and for dosimetric measurements. The idea behind this experimental project lies in the utilization of Hydrogenated Amorphous Silicon (a-Si:H) as photodiode material; owing to its notable attributes of radiation hardness, light detection capability and mechanical flexibility. After the implementation of the HASPIDE experiment, which explored direct radiation detection using a-Si:H devices on a polyimide (PI) substrate, we aim to delve into indirect detection by employing these devices in conjunction with flexible and rad-hard scintillators like polysiloxane. The indirect detector design holds promise for improved responsiveness to low radiation fluxes compared to direct detection methods. The indirect a-Si:H detector should be composed of arrays of small (about 5 x 5 mm2) scintillator crystals read by a-Si:H photodiodes. Through optimization of the scintillator and detector thicknesses, we expect to achieve a better performance for low minimum detectable fluxes compared to direct detection methodologies. This new detector will find application in in-vivo dosimetry during radiotherapy or hadron-therapy and also, due to its expected fast response, in FLASH therapy. Another important application will be also in Solar Physics using these devices to measure particle fluxes in solar energetic particle events.

The paper reports on the timing resolution achieved with Low-Gain Avalanche Diodes (LGADs), optimised for extreme-fluence conditions, at the DESY Test Beam Facility using 4 GeV/c electrons. The LGADs adopt an n-in-p technology with a p+-type boron gain implant, co-implanted with carbon to mitigate acceptor deactivation due to irradiation. The substrate thickness of the sensors varies from 20 to 45 & micro;m, with an active area spanning from 0.75 & times; 0.75 to 1.28 & times; 1.28 mm2. The experimental setup consisted of a 45 & micro;m-thick trigger sensor with an active area of 3.6 & times; 3.6 mm2, two device-under-test (DUT) planes, and a Photonis micro-channel plate photomultiplier tube (MCP) as a time reference. Data taking was performed at the ambient temperature of the facility, at 18 degrees C. The gain was measured between 7 and 40 across all non-irradiated sensors in the study. The timing resolution was calculated from a Gaussian fitting of the difference in times of arrival of a particle at the DUT and the MCP, using the constant fraction discriminator technique. A timing resolution of 26.4 ps was achieved in 45 & micro;m-thick sensors, down to 16.6 ps in 20 & micro;m-thick sensors, in the non-irradiation study. The combination of two 20 & micro;m-thick LGADs reached a timing resolution of 12.2 ps. A set of 30 & micro;m-thick sensors irradiated with neutrons at fluences between 0.4 & times; 1015 and 2.5 & times; 1015 neqcm-2 were tested in the beam. These irradiated sensors achieved a gain between 7 and 30 using a similar apparatus but cooled with solidified CO2 to-42 degrees C. A timing resolution of 20 ps was obtained in these irradiated sensors.

The EXFLU batches of thin LGAD sensors with substrates of thickness between 20 and 45 & micro;m were tested for timing performance at the DESY Test Beam Facility. The sensor designs are optimised for excellent timing resolution, and are manufactured by Fondazione Bruno Kessler. The timing performance is reported for both non-irradiated LGAD sensors and a set of 30 & micro;m sensors irradiated up to 2.5 & times; 10(15 )n1 (MeV eq.) cm(-2). In addition, a new approach to the analysis of thin sensors is considered using differential programming to optimise a signal probability model. The results using the conventional method and this approach using machine learning are presented.

Silicon carbide is a promising material for radiation-hard detectors due to its wide bandgap, low leakage current, high critical electric field, and high saturation velocity. A key obstacle for its use in high-radiation environments is the incomplete understanding of surface damage at the 4H-SiC/SiO_2 interface.In this work, we present a combined experimental and TCAD simulation study of X-ray radiation-induced surface damage on n-type 4H-SiC MOS capacitors fabricated at CNM (Centro Nacional de Microelectronica, Barcelona), irradiated up to 10 Mrad. High-frequency (100 kHz) and quasi-static capacitance-voltage (C–V) measurements are used to evaluate the evolution of fixed oxide charge density and interface trap density as a function of dose.A dose-dependent TCAD surface model is developed and validated against the full set of measurements. The optimized model reproduces the measured C–V characteristics across the entire irradiation range and provides a physically grounded baseline for simulations of n-type 4H-SiC-based detectors. It can be used as a starting point for predictive modeling of irradiated detectors.

A new gain implant design has recently been introduced to enhance the radiation resistance of low-gain avalanche diodes (LGADs) to the extreme fluences anticipated in future hadron colliders like FCC-hh. This design utilises an engineered compensation of two opposing types of doping implants, requiring a thorough analysis of their evolution due to irradiation. To this end, the experimental measurements of their initial test structures have been compared with Technology CAD simulations both before and after irradiation. From the measurement-simulation comparison regarding C-V characteristics, the donor removal at high initial donor concentrations (>10^16 at/cm^3) used in Compensated LGADs has been studied, along with how donor co-implantation influences the beneficial effect of carbon to slow acceptor removal. Furthermore, an innovative application of van der Pauw test structures, typically employed by foundries to monitor process quality, has been implemented. The doping removal of the single implants used in Compensated LGADs has been estimated by examining the variation in sheet resistance with irradiation through these structures.

Future high-energy physics experiments require a paradigm shift in radiation detector design. In response to this challenge, resistive LGADs that combine Low Gain Avalanche Diode technology with resistive readout have been developed. The prototypes created so far, employing AC-coupled contacts, have demonstrated impressive performance, achieving a temporal resolution of 38 ps and a spatial resolution of 15 µm with a pixel pitch of 450 µm. To tackle some of the issues encountered up to this point, particularly the non-uniform response across the entire surface of the detector, a new version with DC-coupled contacts has recently been developed. The Synopsys ® Sentaurus TCAD simulations that have guided the design of their first production, released by the Fondazione Bruno Kessler in November 2024, will be presented below along with a concise summary of the history of the prototypes with AC-coupled contacts.

Recent advancements in Low-Gain Avalanche Diode (LGAD) architectures, including resistive and compensated designs, highlight the need for a precise understanding of donor removal at high donor concentrations to optimize their performance after irradiation. A method based on the variation of sheet resistance with fluence, measured through van der Pauw test structures, has been introduced to extract doping-removal coefficients. This approach was applied to resistive LGAD samples to quantify donor removal in the donor-doped resistive collection layer (NPLUS). Test structures from the RSD2 batch, manufactured by Fondazione Bruno Kessler with varying NPLUS doses, were irradiated up to 5.0 $\times$ 10$^{15}$ 1 MeV n$_{\text{eq}}$/cm$^2$ at the JSI TRIGA reactor, and donor removal coefficients were experimentally determined using this method. In this contribution, TCAD simulations are used to validate the experimental results and to confirm the reliability of the van der Pauw-based extraction method.

Hydrogenated amorphous silicon (a-Si:H) devices on flexible substrates are currently being studied for application in dosimetry and beam flux measurements. The necessity of in vivo dosimetry requires thin devices with maximal transparency and flexibility. For this reason, a thin (<10 µm) a-Si:H device deposited on a thin polyimide sheet is a very valid option for this application. Furthermore, a-Si:H is a material that has an intrinsically high radiation hardness. In order to develop these devices, the HASPIDE (Hydrogenated Amorphous Silicon Pixel Detectors) collaboration has implemented two different device configurations: n-i-p type diodes and charge-selective contact devices.Charge-selective contact-based devices have been studied for solar cell applications and, recently, the above-mentioned collaboration has tested these devices for X-ray dose measurements. In this paper, the HASPIDE collaboration has studied the X-ray and proton response of charge-selective contact devices deposited on Polyimide. The linearity of the photocurrent response to X-ray versus dose-rate has been assessed at various bias voltages. The sensitivity to protons has also been studied at various bias voltages and the wide range linearity has been tested for fluxes in the range from 8.3 × 107 to 2.49 × 1010 p/(cm2 s).

Radiation damage tests in hydrogenated amorphous silicon (a-Si:H) flexible flux and dose-measuring devices have been performed with a 3-MeV proton beam, to evaluate combined displacement and total ionizing dose damage. The tested devices had two different configurations and thicknesses. The first device was a 2-mu m-thick n-i-p diode having a 5 x 5 mm area. The second device was a 5-mu m-thick charge-selective contact (CSC) detector having the same area. Both the devices were deposited on a flexible polyimide substrate and were irradiated up to the fluence of 1016 neq/cm(2). The response to different proton fluxes has been measured before irradiation and after irradiation at 1016 neq/cm(2) for CSCs and n-i-p devices. The effect of annealing for partial performance recovery at 100 degrees C for 12 h was also studied, and a final characterization on annealed devices was performed. This test is the first combined displacement and total ionizing dose test on flexible a-Si:H devices.

Precise tracking in space and time is becoming a more and more pivotal ingredient in designing high-energy physics experiments. Low-Gain Avalanche Diodes (LGADs) with an active thickness of ∼ 50 μm have proved the ability of silicon sensors to provide precise timing down to about 30 ps. At present, this timing performance is maintained almost unchanged up to a fluence of 2.5 × 10 15 n 1MeV eq. /cm 2 . Thinner substrates can further improve the timing resolution and the radiation tolerance of the LGAD sensors. At the end of 2022, FBK released a batch of thin LGAD sensors with an active thickness between 15 and 45 μm to investigate the effect of the thickness in improving sensor performances. A new design of the sensor layout and periphery has been studied and manufactured, optimised for the sensor thickness and the requirement to withstand high electric fields up to very high fluences. The state-of-the-art design of the LGAD gain implant from FBK has been used on thin substrates, exploiting the concurrent implantation of boron and carbon atoms in the multiplication region typical of LGAD sensors. This resulted in the most radiation-tolerant LGADs ever produced by FBK. The electrical characterisation of sensors before and after irradiation, together with the analysis of the signals from laser stimulus and charged particles, will be presented. The impact of the sensor thickness on the collected charge and the timing resolution will be explored and discussed.

In this work, we presented the development of a simulation methodology for a-Si:H devices in a commercial state-of-the-art simulation environment. Hydrogenated amorphous silicon (a-Si:H) has emerged as an attractive material for particle detectors, driven by its high bandgap, which translates to minimal leakage current, and the potential for cost-effective large-area deposition on diverse substrates. The adoption of Technology Computer Aided Design (TCAD) simulation represents a powerful mean for the design and optimization of particle detectors, fostering the evaluation of the electrical properties of the material and the interaction with a particle at device level. We included within the Synopsys Sentaurus TCAD a new material featuring the main parameters of a-Si:H (e.g. band-gap, density of states, e/h creation energy) and an articulated picture of energy of states of defects. Moreover, a brand-new mobility model, derived from the Pool-Frenkel one, has been developed and included as external add-on, accounting for the influence on the mobility of the potential/electric field distribution inside the device and of the temperature. Simulation findings have been compared with measurements carried out on different p-i-n samples for model validation purposes.

The recently developed Low -Gain Avalanche Diode (LGAD) technology has gained growing interest within the high-energy physics (HEP) community, thanks to its capability of internal signal amplification that improves the particle detection. Since the next generation of HEP experiments will require tracking detectors able to efficiently operate in environments where expected fluences will exceed 1 x 1017 1 MeV neq/cm2, the design of radiation -resistant particle detectors becomes of utmost importance. To this purpose, Technology Computer -Aided Design (TCAD) simulations are a relevant part of the current detector R&D, not only to support the sensor design and optimization, but also for a better understanding and modelling of radiation damage. In this contribution, the recent advances in the TCAD modelling of non -irradiated and irradiated LGAD sensors are presented, whose validation relies on the agreement between the simulated and experimental data - in terms of current -voltage (I -V), capacitance -voltage (C -V), and gain -voltage (G -V) characteristics, coming from devices manufactured by Hamamatsu Photonics (HPK), and accounting for different irradiation levels and temperatures.

Two design innovations, low-gain avalanche (Low-Gain Avalance Diode, LGAD) and resistive read-out (Resistive Silicon Detector, RSD), have brought strong performance improvements to silicon sensors. Large signals, due to the added gain mechanism, lead to improved temporal precision, while charge sharing, introduced by resistive read-out, allows for achieving excellent spatial resolution even with large pixels. LGAD- and RSD- based silicon sensors are now adopted, or considered, in several future experiments and are the basis for almost every next 4D-trackers. New results obtained with sensors belonging to the second FBK production of RSD (RSD2) demonstrate how a combined resolution of 30 ps and 30 \microns can be obtained with pixels as large as $1 \times 1 $ mm$^2$.

A new gain layer design, whose effective doping profile results from the difference between two overlapping implants of opposite dopant species (e.g. boron and phosphorus), is conceived to extend the operational life of Low-Gain Avalanche Diodes (LGADs) to fluences significantly above the present limit of 2.5.10(15) 1 MeV neq/cm(2). Both acceptor and donor atoms will experience doping removal due to irradiation, but their difference will remain fairly constant. The implementation of this ambitious goal necessitates a meticulous process of optimizing the two implants that constitute the gain layer of the Compensated LGADs. To this end, the Synopsys (R) Sentaurus TCAD toolkit, with the most up-to-date release of the Perugia radiation damage model, was employed, enabling a comprehensive investigation of these new sensors. This level of scrutiny is crucial for understanding the behaviour of the first Compensated LGAD production (2022 by FBK) and designing the subsequent batches of Compensated LGADs.

Recent advancements in sensor technology have paved the way for the development of high-resolution 4D-tracking detectors capable of simultaneously measuring the position and time of passage of charged particles within a single sensitive device. The key point is the use of resistive read-out in thin Low Gain Avalanche Diode (LGAD) sensors, which introduces combined intrinsic signal sharing and internal gain. This contribution focuses on the development of a thin LGAD with a DC-coupled resistive read-out (DC-coupled Resistive Silicon Detector - DC-RSD). The aim is to achieve a spatial resolution of a few micrometers and an excellent time resolution of approximately 30 ps, using relatively large pixels (150-200 micrometers), which enables detectors with low channel density and low power consumption. A strong effort has been put into the simulation of the device, supported by experimental measurements of the AC-coupled resistive read-out sensors, which can be used to extrapolate the DC-RSD performance. This contribution describes the design and implementation strategy of the first DC-RSD production, presently in progress at Fondazione Bruno Kessler. Several test structures and application-oriented devices have been designed, which will enable detailed studies of the charge sharing optimization. The production is expected to be completed in early Fall 2024. The initial characterization of the production in the laboratory will provide us with immediate feedback on the soundness of the DC-RSD concepts.

The EXFLU1 batch of LGAD sensors on substrates of thickness between 15 and 45 mu m were exposed to various radiation grades between 1 x 10(14) and 5 x 10(15) n(eq)cm(-2) using the TRIGA Mark II research nuclear reactor at the Jozef Stefan Institute. The sensor designs are optimised to preserve characteristics at high fluences. These sensors are manufactured by Fondazione Bruno Kessler. The latest studies of the effects of radiation have been performed, with particular focus on acceptor removal and gain evolution.

The CompleX project aims at extending the operation range of silicon detectors as 4D trackers up to 5 x 10(17) n(eq)cm(-2). The project envisions achieving this unprecedented radiation tolerance through a novel comprehension of radiation damage saturation, and an innovative design for the Low-Gain Avalanche Diodes (LGADs) gain layer with compensated implants. This innovative LGAD design, featuring a co-implantation of acceptor and donor dopants, represents a paradigm shift in radiation-resistant sensor technology. It potentially enables compensated LGADs to maintain functionality at fluences exceeding 10(17) n(eq)cm(-2), significantly extending the operational lifetime of conventional LGAD sensors under extreme fluence conditions. This advantage is further enhanced by the inherent radiation tolerance of thin substrates. This work presents simulations and measurements from the first compensated LGAD production (late 2022, FBK foundry) before and after neutrons irradiation. Numerical modeling strategies using state-of-the-art Technology-CAD tools quantify the reduction in acceptor removal rate due to carbon co-implantation and investigate the behavior of donor removal under irradiation. This comprehensive approach paves the way for the development of highly efficient tracking detectors for future collider experiments.

This paper presents a comprehensive study of hydrogenated amorphous silicon (a-Si)-based detectors, utilizing electrical characterization, Raman spectroscopy, photoemission, and inverse photoemission techniques. The unique properties of a-Si have sparked interest in its application for radiation detection in both physics and medicine. Although amorphous silicon (a-Si) is inherently a highly defective material, hydrogenation significantly reduces defect density, enabling its use in radiation detector devices. Spectroscopic measurements provide insights into the intricate relationship between the structure and electronic properties of a-Si, enhancing our understanding of how specific configurations, such as the choice of substrate, can markedly influence detector performance. In this study, we compare the performance of a-Si detectors deposited on two different substrates: crystalline silicon (c-Si) and flexible Kapton. Our findings suggest that detectors deposited on Kapton exhibit reduced sensitivity, despite having comparable noise and leakage current levels to those on crystalline silicon. We hypothesize that this discrepancy may be attributed to the substrate material, differences in film morphology, and/or the alignment of energy levels. Further measurements are planned to substantiate these hypotheses.

The DC-coupled resistive silicon detectors (DC-RSD) are the evolution of the AC-coupled RSD (RSD) design, both based on the low-gain avalanche diode (LGAD) technology. The DC-RSD design concept intends to address a few known issues present in RSDs (e.g., baseline fluctuation and long tail-bipolar signals) while maintaining their advantages (e.g., signal spreading and 100% fill factor). The simulation of DC-RSD presents several unique challenges linked to the complex nature of its design and the large pixel size. The defining feature of DC-RSD, charge sharing over distances that can be as large as a millimeter, represents a formidable challenge for technology CAD (TCAD), the standard simulation tool. To circumvent this problem, we have developed a mixed-mode approach to the DC-RSD simulation, which exploits a combination of two simulation tools: TCAD and SPICE. Thanks to this hybrid approach, it has been possible to demonstrate that, according to the simulation, the key features of the RSD—excellent timing and spatial resolutions (few tens of picoseconds and few microns)—are maintained in the DC-RSD design. In this work, we present the developed models and methodology, mainly showing the results of device-level numerical simulation, which have been obtained with the state-of-the-art Synopsys Sentaurus TCAD suite of tools. Such results will provide all the necessary information for the first batch of DC-RSD produced by the Fondazione Bruno Kessler (FBK) foundry in Trento, Italy.