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This paper presents the measurements on first very thin Ultra-Fast Silicon Detectors (UFSDs) produced by Fondazione Bruno Kessler; the data have been collected in a beam test setup at the CERN PS, using beam with a momentum of 12 GeV/c. UFSDs with a nominal thickness of 25 and 35 $$\mu$$ μ m and an area of 1 $$\times$$ × 1 $$\text {mm}^2$$ mm 2 have been considered, together with an additional HPK 50-$$\mu$$ μ m thick sensor, taken as reference. Their timing performances have been studied as a function of the applied voltage and gain. A time resolution of about 25 ps and of 22 ps at a voltage of 120 and 240 V has been obtained for the 25 and 35 $$\mu$$ μ m thick UFSDs, respectively.

The challenging demands of the ATLAS High Luminosity (HL-LHC) Upgrade aim for a complete swap of new generation sensors that should cope with the ultimate radiation hardness. FBK has been one of the prime foundries to develop and fabricate such radiation-hard 3D silicon (Si) sensors. These sensors are chosen to be deployed into the innermost layer of the ATLAS Inner Tracker (ITk). Recently, a pre-production batch of 3D Si sensors of 50x50 um2 pixel geometry, compatible with the full-size ITKPix (RD53B) readout chip, was fabricated. Two wafers holding temporary metal were diced at IZM, Germany, and a systematic QC test campaign was carried out at the University of Trento electronics laboratory. The paper briefly describes the 3D Si sensor design for ATLAS ITk and the required QC characterization setups. It comprises electrical tests (i.e., I-V, C-V, and I-T) of non-irradiated RD53B sensors. In addition, the study of several parametric analyses, i.e., oxide charge density, oxide thickness, inter-pixel resistance, inter-pixel capacitance, etc., are reported with the aid of Process Control Monitor (PCM) structures., 8 pages, prepared for iWoRiD 2022 Proceeding

In this work, we introduce a new design concept: the DC-Coupled Resistive Silicon Detectors, based on the LGAD technology. This new approach intends to address a few known features of the first generation of AC-Coupled Resistive Silicon Detectors (RSD). Our simulation exploits a fast hybrid approach based on a combination of two packages, Weightfield2 and LTSpice. It demonstrates that the key features of the RSD design are maintained, yielding excellent timing and spatial resolutions: a few tens of ps and a few microns. In the presentation, we will outline the optimization methodology and the results of the simulation. We will present detailed studies on the effect of changing the ratio between the n+ layer resistivity and the low-resistivity ring and on the achievable temporal and spatial resolution.

ITk detector, the new ATLAS tracking system at High Luminosity LHC, will be equipped with 3D pixel sensor modules in the innermost layer (L0). The pixel cell dimensions will be either 25 × 100 μm2 (barrel) or 50 × 50 μm2 (endcap), with one read-out electrode at the centre of a pixel and four bias electrodes at the corners. Sensors from pre-production wafers (50 × 50 μm2) produced by FBK have been bump bonded to ITkPixV1.1 chips at IZM. Bare modules have been assembled in Genoa on Single Chip Cards and characterized in laboratory and on beam.

The ARCADIA collaboration is developing fully-depleted (FD) Monolithic Active Pixel Sensors (MAPS) in a 110 nm CMOS process in collaboration with LFoundry. The sensor design incorporates an n+ collection node within a n-type epi-layer on top of a high-resistivity n-type substrate and p+ backside. Thus, the pn-junction sits on the backside and through an applied backside bias, the full substrate gets depleted. The targeted applications of this technology range from future high energy physics experiments to space applications, and medical and industrial scanners. Together, these applications set the minimum requirements on the detector: data collection at hit rates of (10–100) MHz/cm2, full signal processing within (1–10) μs, maximum power consumption (5–20) mW/cm2 and radiation tolerances of up to 3.4 Mrad or 6.2 × 1012 1 MeV neutron equivalent fluence. In order to proof the performance of the technology, a demonstrator chip of 512 × 512 pixels with 25 μm pitch was designed and fabricated in a first engineering run in 2021, together with additional test structures of pixel and strip arrays with different pitches and sensor geometries. The production run has produced functional passive and active pixel matrices. Earlier studies have shown that positive oxide charges and traps at the Si-SiO2 interface, introduced by ionising radiation, affect the depletion region around the collection electrode, increasing the pixel capacitance. By varying the gap size between collection node and pwells, the geometry can be optimised to keep the capacitance low also after irradiation. To study the performance after irradiation, of the optimised diode designs, the passive pixel matrices were irradiated with doses up to 10 Mrad (SiO2) using a X-ray tube with a Tungsten anode. The measurements are complemented by TCAD simulations. The maximum capacitance increase after irradiation was found to reach 6 and 12 fF/pixel for pixel pitches of 25 and 50 μm, respectively. The relative capacitance increase after irradiation has hereby been found to reach up to 250% after a dose of 10 Mrad.

This paper reports the Trento test setup and the cold test procedure for three triplets (ID: R4, R5, and R6) assembled with RD53A readout cheap and planar sensors. The trim and tuning of Front Ends (FE), as well as sensor I-V measurements, were made for a cold temperature (−25 °C) for an applied voltage (−30 V for R4, −10 V for R5 and R6). As a part of QC, initially, several test scans: analog, digital, threshold, ToT, noise, etc., were performed to evaluate the module response at −25 °C before applying a necessary tuning script to find a spatially uniform threshold distribution over the pixel matrix. Later, the crosstalk-based disconnected-bump and X-ray scans were made to check modules’ bump bonding quality and hits per pixel. Results reported here show a good agreement to a qualified triplet module, assuring the Trento cold test setup capacity for the ATLAS ITk QA/QC process.

Dark count rate (DCR) increase in CMOS single-photon avalanche diodes (SPADs) exposed to a nonmonochromatic neutron source is modeled, taking into account the source spectrum and the geometry of the device under test. Experimental results from the characterization of SPADs fabricated in a 150-nm technology and irradiated with 1-MeV neutron equivalent fluences up to $10^{\textsf {11}}$ cm $^{-\textsf {2}}$ are found to be in good agreement with the theoretically calculated distribution of the nonionizing energy deposited in the device substrate.

3D type of pixel sensors is a promising option for the innermost pixel layer at the High-Luminosity LHC. However, the required very high hit-rate capabilities, finer pixel granularity, extreme radiation hardness and reduced material budget call for a downscale of the pixel size as compared to existing 3D sensors, involving smaller pitch (e.g. 50 × 50 or 25 × 100 μ m 2 ), shorter inter-electrode spacing ( ∼ 30 μ m ), narrower electrodes ( ∼ 6 μ m diameter), and reduced active thickness ( ∼ 100 – 150 μ m ). Within a joint R&D effort with INFN, FBK has produced a new generation of 3D pixel sensors with these challenging features. In this talk preliminary results from the electrical and functional characterisation of the first prototypes are reported, included their behaviour after large radiation fluence, close to the ones expected in the High Luminosity LHC environment. Prospects for the next prototypes are also presented.

Fondazione Bruno Kessler (FBK, Trento, Italy) has recently delivered its first 50 μ m thick production of Ultra-Fast Silicon Detectors (UFSD), based on the Low-Gain Avalanche Diode design. These sensors use high resistivity Si-on-Si substrates, and have a variety of gain layer doping profiles and designs based on Boron, Gallium , Carbonated Boron and Carbonated Gallium to obtain a controlled multiplication mechanism. Such variety of gain layers will allow identifying the most radiation hard technology to be employed in the production of UFSD, to extend their radiation resistance beyond the current limit of ϕ ∼ 1015 n e q /cm 2 . In this paper, we present the characterisation, the timing performance, and the results on radiation damage tolerance of this new FBK production.

The growing interest on the use of colloidal Quantum Dots (QDs) in scintillation and dosimetry applications in comparison with organic fluorophores relies in their narrower and tunable photoluminescence (PL) emission, easier chemical processability and higher cross-section for ionizing radiation. In this context, a deep understanding of the role of the embedding medium on the QD optical properties in unirradiated and irradiated samples represents an important issue. In this paper, we present the optical characterization of colloidal core-shell CdSe/ZnS QDs embedded in polyvinyl alcohol (PVOH) and irradiated with 2 MeV protons at different fluences. The characterization of the samples, performed by both steady-state and time-resolved PL measurements, indicates a damage of the QDs at the lowest fluence (1013 H+cm−2), demonstrated by a quenching of the QD PL intensity and by a shortening of the QD lifetime. At the middle fluence (5 × 1013 H+cm−2) a partial recovering of the QD optical properties are observed, due to energy transfer phenomena between radiation-induced PL defects in the PVOH, acting as donors, and the QDs, acting as acceptors. The higher concentration of PVOH PL defects in the most irradiated sample (1014 H+cm−2) led to an enhancement of the QD PL intensity in comparison with the unirradiated sample, highlighting the crucial role of the embedding medium in the post-irradiation QD optical response.

Semiconductor sensors for neutron detection have been initially proposed as direct replacement of 3He detectors but have recently raised interest in imaging systems. We have developed a monolithic sensor with high spatial granularity in SOIPIX technology for the detection of alpha particles of energy compatible with the reaction products of neutrons with typical converter materials. The chipset is composed by the main pixel matrix and the test structures needed for a better understanding of the chip functionality and for studying the electronic tuning strategies. The fabricated prototypes have been recently delivered and the first tests under alpha source have been performed. In this paper we will present the proposed devices and the results of the experimental characterization.

In the past few years, the need of measuring accurately the spatial and temporal coordinates of the particles generated in high-energy physics experiments has spurred a strong R\&D in the field of silicon sensors. Within these research activities, the so-called Ultra-Fast Silicon Detectors (UFSDs), silicon sensors optimized for timing based on the Low-Gain Avalanche Diode (LGAD) design, have been proposed and adopted by the CMS and ATLAS collaborations for their respective timing layers. The defining feature of the Ultra-Fast Silicon Detectors (UFSDs) is the internal multiplication mechanism, determined by the gain layer design. In this paper, the performances of several types of gain layers, measured with a telescope instrumented with a $^{90}$Sr $\beta$-source, are reported and compared. The measured sensors are produced by Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics (HPK). The sensor yielding the best performance, both when new and irradiated, is an FBK 45\mum-thick sensor with a carbonated deep gain implant, where the carbon and the boron implants are annealed concurrently with a low thermal load. This sensor is able to achieve a time resolution of 40~ps up to a radiation fluence of~\fluence{2.5}{15}, delivering at least 5~fC of charge., Comment: v3 revised version as requested by Editor

This paper presents the detailed simulation of a double-pixel structure for charged particle detection based on the 3D-trench silicon sensor developed for the TIMESPOT project and a comparison of the simulation results with measurements performed at $\pi-$M1 beam at PSI laboratory. The simulation is based on the combined use of several software tools (TCAD, GEANT4, TCoDe and TFBoost) which allow to fully design and simulate the device physics response in very short computational time, O(1-100 s) per simulated signal, by exploiting parallel computation using single or multi-thread processors. This allowed to produce large samples of simulated signals, perform detailed studies of the sensor characteristics and make precise comparisons with experimental results., Comment: 23 pages, 18 figures

Fully Depleted Monolithic Active Pixels (FD-MAPS) represent a state-of-the-art detector technology and profit from a low material budget and cost for high energy physics experiments and other fields of research like medical imaging and astro-particle physics. Compared to the MAPS currently in use, fully depleted pixel sensors have the advantage of charge collection by drift, which enables a fast and uniform response overall the pixel matrix. The functionality of these devices has been shown in previous proof-of-concept productions. In this article we describe the optimization of the test pixel designs, that will be implemented in the first engineering run of the demonstrator chip of the ARCADIA project. These optimization procedures include radiation damage models, that have been employed in Technology Computer Aided Design simulations to predict the sensors behavior in different working environments., 16 pages, 13 figures, submitted to Frontiers in Physics

This paper presents the procedure developed and used within the TimeSPOT (for Time and Space real time Operating Tracker) project to design and characterise 3D silicon sensors with enhanced timing capabilities. Such procedure is based on the combined use of commercial (TCAD), semi-custom (GEANT4) and custom (TCoDe) software tools which allow to fully design and simulate the device, from the definition of doping profiles and concentrations to the description of the charge carriers transportation mechanisms and the calculation of the induced current signals, which are input to the front-end electronics. A very important feature of the procedure is its speed in the most time-consuming part, that is the calculation of the carriers transportation phenomena inside the sensor volume. This allows to routinely perform analyses based on several thousand of signals, thus giving a statistically significant description of the detection mechanisms and the possibility to compare simulation and experimental results. The design study has been decisive to obtain a 3D silicon sensor with time resolutions well below 30 ps. The procedure is in principle extendable to any kind of solid state sensors.

International audience; In view of the LHC upgrade phase towards the High Luminosity LHC (HL-LHC), the ATLAS experiment plans to upgrade the Inner Detector with an all-silicon system. The n-on-p silicon technology is a promising candidate to achieve a large area instrumented with pixel sensors, since it is radiation hard and cost effective. This paper reports on the last n-on-p pixel productions made by a collaboration between the FBK-CMM and the LPNHE in Paris, with some focus on the latest designs of thin sensors bump-bonded to the RD53A prototype chip, featuring a 100 × 25 and 50 × 50 µm^2 pixel cells. An overview of 2019–2020 test-beam results for the produced devices will be given, with a special perspective to the sensor design for the ATLAS ITk pixel construction. Preliminary results for new 50 µm thick n-on-p pixel sensors, still produced by LPNHE at FBK-CMM will be also presented.

This paper presents the principles of operation of Resistive AC-Coupled Silicon Detectors (RSDs) and measurements of the temporal and spatial resolutions using a combined analysis of laser and beam test data. RSDs are a new type of n-in-p silicon sensor based on the Low-Gain Avalanche Diode (LGAD) technology, where the $n^+$ implant has been designed to be resistive, and the read-out is obtained via AC-coupling. The truly innovative feature of RSD is that the signal generated by an impinging particle is shared isotropically among multiple read-out pads without the need for floating electrodes or an external magnetic field. Careful tuning of the coupling oxide thickness and the $n^+$ doping profile is at the basis of the successful functioning of this device. Several RSD matrices with different pad width-pitch geometries have been extensively tested with a laser setup in the Laboratory for Innovative Silicon Sensors in Torino, while a smaller set of devices have been tested at the Fermilab Test Beam Facility with a 120 GeV/c proton beam. The measured spatial resolution ranges between $2.5\; \mu m$ for 70-100 pad-pitch geometry and $17\; \mu m$ with 200-500 matrices, a factor of 10 better than what is achievable in binary read-out ($bin\; size/ \sqrt{12}$). Beam test data show a temporal resolution of $\sim 40\; ps$ for 200-$\mu m$ pitch devices, in line with the best performances of LGAD sensors at the same gain., Comment: 34 pages, 33 figures

Semiconductor quantum dots (QDs) are receiving increasing interest for the production of scintillator detectors and dosimeters. For this reason, the investigation of the effects of ionizing radiation on the optical properties of QDs has become of great importance. In this paper, we present the optical characterization of colloidal CdSeS/ZnS core-shell quantum dots (QDs) embedded in a polyvinyl alcohol (PVA) matrix and irradiated with 2 MeV H+ and He+ ions at different fluences. With steady-state luminescence measurements, we investigate the ion irradiation effects on the luminescence spectrum of the irradiated samples. With time-resolved luminescence measurements, acquired with a Time Correlated Single Photon Counting (TCSPC) system, we evaluate the radiation-induced change in the QD charge carrier dynamics. Luminescence spectra show the appearance of new features related to damage of the PVA host. Time-resolved measurements highlight a shortening of the QD luminescence time constants as the ion fluence increases.

In scintillation and dosimetry applications, the increasing interest on the use of colloidal quantum dots (QDs) in comparison with organic fluorophores is mainly due to their easier chemical proces...

Solid-state sensors fabricated with 3D technologies and coupled to different neutron converter materials have been developed by several groups as direct replacement of 3 H e gas detectors, mainly for homeland security applications. Results so far achieved in terms of detection efficiency are quite good (up to ≃ 50%) and, combined with the intrinsic excellent position resolution of silicon sensors, could lead to high performance neutron imaging systems. In this paper, we review the state of the art in three-dimensional silicon sensors for thermal-neutron detection, addressing the most promising solutions for neutron imaging. Moreover, selected results from the developments at the University of Trento on 3D pixelated detectors having relatively low fabrication complexity and expected high neutron detection efficiency up to 30% will be reported.

Small-pitch, thin 3D Si sensors have been developed for the ATLAS and CMS experiment upgrades at the High Luminosity LHC. The pixel sizes are 50 × 50 µm2 with 1 readout column, and 25 × 100 µm2 with 1 or 2 readout columns (1E and 2E). Owing to the small inter-electrode distance, ranging from ∼28 µm to ∼51 µm in the considered layouts, these devices are expected to be extremely radiation hard. TCAD simulations by Synopsys Sentaurus, incorporating advanced radiation damage models, have been used for the design/optimization of these new 3D pixel sensors. In this study, we have compared the accuracy of different bulk damage models in predicting the signal efficiency of small-pitch 3D sensors irradiated at large fluences and its evolution with the bias voltage at different positions within the 3D cell. Selected simulation results will be reported in comparison to experimental data.

In this paper we present a position-sensitive detector based on the vertical integration of pairs of aligned pixels operating in Geiger-mode regime and designed for charged particle detection. This novel device exploits the coincidence between two simultaneous avalanche events to discriminate between particle-triggered detections and dark counts. This concept allows to have a reduced material budget and low power consumption in spite of a high granularity and fast timing response. A proof-of-principle prototype was designed and fabricated in a 150 nm CMOS process and vertically integrated through bump bonding. This first demonstrator has been characterized and tested with a high energy particle beams at CERN SPS/PS facilities, in different configurations, featuring a reduction of the dark-count rate (DCR) at room temperature from ∼ 100 kHz/mm 2 to about 24 Hz/mm 2 a particle detection efficiency limited only by the geometric factor. The device radiation tolerance has been investigated, via irradiation of single tiers with 10 keV X-rays up to a dose of 1 Mrad (SiO2) and with neutrons up to a fluence of 1011 cm−2. A second prototype, addressing the goal to improve the present fill-factor, has been designed, manufactured and approaches now the characterization phase. Potential applications of this sensor include high spatial resolution tracking in high-energy experiments, radiation monitoring in space and radiation imaging in nuclear medicine. A small hand-held demonstrator is under construction for radio-guided surgery.

In the past few years, there has been growing interest in the development of silicon sensors able to simultaneously measure accurately the time of passage and the position of impinging charged particles. In this contribution, a review of the progresses in the design of UFSD (Ultra-Fast Silicon Detectors) sensors, manufactured at the FBK (Fondazione Bruno Kessler) Foundry, aiming at tracking charged particles in 4 dimensions, is presented. The state-of-the-art UFSD sensors, with excellent timing capability, are planned to be used in both ATLAS and CMS experiments detector upgrade, in order to reduce the background due to the presence of overlapping events in the same bunch crossing. The latest results on sensors characterization including time resolution, radiation resistance and uniformity of the response are here summarized, pointing out the interplay between the design of the gain layer and the UFSD performances. The research is now focusing on the maximization of the sensor fill factor, to be able to reduce the pixel size, exploring the implementation of shallow trenches for the pixel isolation and the development of resistive AC-coupled UFSD sensors. In conclusion, a brief review on research paths tailored for detection of low energy X-rays or for low material budget applications is given.

In this paper we present the numerical simulation of silicon detectors with internal gain as the main tool for 4-dimensional (4D) particle trackers design and optimization. The Low-Gain Avalanche Diode (LGAD) technology and its present limitations are reviewed with the aim of introducing the Resistive AC-Coupled Silicon Detectors (RSD) paradigm as a case study of our investigation. Authors here present Spice-like and 2D/3D Technological Computer-Aided Design (TCAD) simulations to characterize sensors in terms of both their electrostatic behavior, capacitive (dynamic) coupling and radiation-hardness performances, showing the methodological approach used in order to extract the set of layout rules allowing the release of RSD1, the incoming production run at Fondazione Bruno Kessler (FBK) of next-generation silicon detectors for 4D tracking with intrinsic 100% fill-factor.

The TIMESPOT project aims at the construction of a mini-tracker demonstrator implementing both high space and time resolutions at the single pixel level. The pixels have a pitch of 55 × 55 μ m2. Specified time resolution is equal or better than 50 ps. Developed sensors are based both on 3D silicon and diamond technologies, whose layout and fabrication process have been suitably optimized for best time resolution. Read-out pixel electronics is being developed in 28-nm CMOS technology. The first batch of 3D silicon sensors, containing several test structures based on different geometries of the electrodes, has been delivered in June 2019 and has been tested against its timing performance both under laser and minimum ionizing particle beams. In the present paper, the output of these starting measurements is presented. The sensors show very good timing performance, having σ i30 ps (sigma), although operated with non-optimized front-end electronics and in noisy environment. These results represent an important step forward in the development of pixels with timing operating at extremely high interaction rates and fluences, as required in the next generation of upgraded colliders.

An extensive R\&D program aiming at radiation hard, small pitch, 3D pixel sensors has been put in place % in CMS between Istituto Nazionale di Fisica Nucleare (INFN, Italy) and FBK Foundry (Trento, Italy). The CMS experiment is supporting % profiting of these developments the R\&D in the scope of the Inner Tracker upgrade for the High Luminosity phase of the CERN Large Hadron Collider (HL-LHC). In the HL-LHC the Inner Tracker will have to withstand an integrated fluence up to $2.3 \times 10^{16} \, \mathrm{n_{eq}/cm^2}$. % (1 MeV equivalent neutrons). A small number of 3D sensors were interconnected with the RD53A readout chip, which is the first prototype of 65 nm CMOS pixel readout chip designed for the HL-LHC pixel trackers. In this paper results obtained in beam tests before and after irradiation are reported. Irradiation of a single chip %interconnected module was performed up to a maximum equivalent fluence of about $1 \times 10^{16} \, \mathrm{n_{eq}/cm^2}$. Analysis of the collected data shows excellent performance: spatial resolution in not irradiated (fresh) sensors is about 3 to 5 $\mathrm{ \mu }$m depending on the pixel pitch. Hit detection efficiencies are close to 99\% measured both before and after the above mentioned irradiation fluence.

Radiation damage effects at High Luminosity LHC (HL-LHC) expected fluences and total ionizing doses (TID) will impose very stringent constraints in terms of radiation resistance of silicon detectors. In this work, we address the effects of surface damage on detectors fabricated on p-type substrates by two different foundries. Starting from standard test structure measurements, the interface trap state density and the oxide charge can be extracted for each specific foundry before and after irradiation with X-rays with doses ranging from 0.05 to 100 Mrad(SiO2). These parameters are then used as inputs to the Technology-CAD simulation tools, aiming at evaluating the effects of oxide charge density and interface trap density variation with the dose on MOS capacitor capacitances and interstrip resistances. The good agreement between simulation results and measurements would support the use of the model as a predictive tool to optimize the design and the operation of novel silicon detectors in the HL-LHC scenario.

Single-photon avalanche diodes (SPADs) fabricated using two different CMOS technologies were exposed to a neutron source up to a maximum fluence of $3\times 10^{11}\,\,1$ -MeV neutron equivalent cm−2. Significant changes in the dark count rate (DCR), with a strong dependence on the fluence and the device active area, were detected after irradiation. A model for the probability of DCR degradation, accounting for the source spectrum and the geometry of the device under test (DUT), was proposed and proved to be in good agreement with experimental data. The model may be helpful in performing worst-case analysis of SPAD-based detection systems under neutron irradiation.

In the last years, high-resolution time tagging has emerged as the tool to tackle the problem of high-track density in the detectors of the next generation of experiments at particle colliders. Time resolutions below 50ps and event average repetition rates of tens of MHz on sensor pixels having a pitch of 50$\mu$m are typical minimum requirements. This poses an important scientific and technological challenge on the development of particle sensors and processing electronics. The TIMESPOT initiative (which stands for TIME and SPace real-time Operating Tracker) aims at the development of a full prototype detection system suitable for the particle trackers of the next-to-come particle physics experiments. This paper describes the results obtained on the first batch of TIMESPOT silicon sensors, based on a novel 3D MEMS (micro electro-mechanical systems) design. Following this approach, the performance of other ongoing silicon sensor developments has been matched and overcome, while using a technology which is known to be robust against radiation degradation. A time resolution of the order of 20ps has been measured at room temperature suggesting also possible improvements after further optimisations of the front-end electronics processing stage., Comment: This version was accepted to be published on JINST on 21/07/2020

Resistive AC-Coupled Silicon Detectors (RSD) represent a new frontier in 4D particle tracking through silicon detectors with intrinsic gain. In this work we present the experimental characterization done on the first run of sensors, RSD1, produced at Fondazione Bruno Kessler (FBK) in Trento, Italy.

We designed, produced, and tested RSD (Resistive AC-Coupled Silicon Detectors) devices, an evolution of the standard LGAD (Low-Gain Avalanche Diode) technology where a resistive ${n}$ -type implant and a coupling dielectric layer have been implemented. The first feature works as a resistive sheet, freezing the multiplied charges, while the second one acts as a capacitive coupling for readout pads. We succeeded in the challenging goal of obtaining very fine pitch (50, 100, and $200~\mu \text{m}$ ) while maintaining the signal waveforms suitable for high timing and 4D-tracking performances, as in the standard LGAD-based devices.

International audience; We report on the ATLAS and CMS joint research activity, which is aiming at the development of new, thin silicon pixel detectors for the Large Hadron Collider Phase-2 detector upgrades. This R&D; is performed under special agreement between Istituto Nazionale di Fisica Nucleare and FBK foundation (Trento, Italy). New generations of 3D and planar pixel sensors with active edges are being developed in the R&D; project, and will be fabricated at FBK. A first planar pixel batch, which was produced by the end of year 2014, will be described in this paper. First clean room measurement results on planar sensors obtained before and after neutron irradiation will be presented.

Low Gain Avalanche Diodes (LGADs) are now considered a viable solution for 4D-tracking thanks to their excellent time resolution and good resistance to high radiation fluence. However, the currently available LGAD technology is well suited only for applications that require coarse space precision, pixels with pitch in the range 500 µm–1 mm, due to the presence of a no-gain region between adjacent pixels of about 50 μ m , in which the gain is completely suppressed. In this paper, we will discuss the segmentation issues in the LGAD technology and we will present two new segmentation strategies aimed at producing LGADs with high spatial resolution and high fill factor. The first presented design is the so-called Trench-Isolated LGAD (TI-LGAD). Here, the pixel isolation is provided by trenches, physically etched in the silicon and then filled with silicon oxide. The second design is the Resistive AC-coupled Silicon Detector (RSD), an evolution of LGADs, where the segmentation is obtained by means of AC-coupled electrodes. Prototypes of both designs have been produced at FBK and characterized at the Laboratories for Innovative Silicon Sensors (INFN and University of Turin) by means of a laser setup to estimate the space resolution and the fill factor. The functional characterization shows that both the technologies yield fully working small pixel LGADs (down to 50 µm), providing the first examples of sensors able to concurrently measure space and time with excellent precision.

Applications at the High Luminosity LHC (HL-LHC) have required the development of a new generation of 3D pixel sensors with increased pixel granularity, extreme radiation hardness and low material budget. To this purpose, new 3D pixels have small pitch (e.g., 50×50 or 25×100 μm2) and reduced active thickness (∼100 μm). Owing to the small inter-electrode spacing (∼28 μm in the most aggressive designs). These 3D pixels are expected to be radiation hard even after irradiation at the hadron fluences. Indeed, they are of interest for the innermost tracking layers of ATLAS and CMS (∼2×1016 neq cm−2), and beyond. In order to estimate the charge collection efficiency (CCE) after irradiation, TCAD simulations can be conveniently used, providing useful information for the optimization of sensor design and fabrication technology. Within the AIDA-2020 project, with reference to the new single-sided 3D technology from FBK (Trento, Italy), we have simulated the CCE of pixel sensors with different inter-electrode spacing irradiated at different fluences. For these simulations, a 2D domain was used, consisting of a horizontal slice taken at half the depth of a 3D sensor. Simulations consider the hit of a minimum ionizing particle, described by the Heavy Ion model at different points within the active area. In addition, bulk radiation damage is accounted by using advanced deep-level trap models. This paper reports a comprehensive description of the simulation results based on a radiation model validated by comparison to experimental results from n-in-p strip detectors at 248 K and 900 V bias.

Single-photon avalanche diode (SPAD) arrays fabricated in a 180-nm CMOS technology with a high-voltage option have been exposed to calibrated neutron and X-ray sources to evaluate their radiation tolerance. The technology is being investigated in view of the design of low material budget detectors for charged particle tracking based on the coincidence of the signals coming from two or more overlapping layers of SPAD sensors. Each element in the array is a monolithic detector including the processing electronics together with the diode in the same substrate. Different sensor dimensions and structures have been implemented in the test chip to thoroughly explore the technology features. This paper will present and discuss the results from the characterization, in terms of dark count rate, of SPAD arrays irradiated with X-ray doses reaching 1 Mrad(SiO2) and with neutron fluences up to $10^{11}~1$ -MeV neutron equivalent cm $^{-2}$ .

Radiation damage effects at High Luminosity LHC (HL-LHC) fluences greater than 2 . 2 × 1 0 16 n ∕ cm 2 1 MeV equivalent and total ionizing doses (TID) greater than 1 Grad will impose very stringent constraints in terms of radiation resistance of solid-state detectors. To cope with this design challenge, TCAD tools can be used to study different technology and design options, in order to optimize the performance of silicon detectors in terms of inter-electrode isolation and charge collection properties. A comprehensive modeling approach based on combined bulk and surface damage effects accounting for a limited number of measurable parameters needs therefore to be developed and validated over different technology options. In this work, we mainly focus on the effects of surface damage on detectors fabricated on p-type substrates by different providers. Actually, starting from standard test structure measurements (i.e. MOS capacitors, gated diodes), the integrated interface trap state density ( N IT ) and the oxide charge ( Q OX ) can be extracted for different vendors and used as input parameter to the simulation tools. Test structures under study include MOS capacitors, gated-diodes, fabricated both at Hamamatsu Photonics (Japan) and at Infineon (Austria). Using High-Frequency (HF) and Quasi-Static (QS) C–V characteristics and current–voltage (I–V) measurements, the effective oxide charge density ( N EFF ), the surface generation velocity ( s 0 ) and the interface trap density ( D IT ) have been determined and compared for the two technologies before and after irradiation with X-rays with doses ranging from 0.05 to 20 Mrad(SiO2). A detailed simulation analysis on MOS capacitor capacitances and gated diode currents has been carried out, varying the previously mentioned parameters, with the aim to evaluate the effects of oxide charge density and interface trap density increase with the dose. The separate effects of different types of interface trap states have been considered as well, by varying one by one the total density of donor- and acceptor-type trap states, respectively. The effects of different trap energy distributions and capture cross sections have been evaluated within Synopsys Sentaurus TCAD device simulator by means of steady-state, AC and transient analyses. The good agreement obtained for both vendors would support the use of the model as a predictive tool to optimize the design and the operation of novel solid-state detectors in the HL-LHC scenario.

International audience; In view of the LHC upgrade for the High Luminosity phase (HL-LHC), the ATLAS experiment plans to replace the Inner Detector with an all-silicon system. The n-on-p silicon technology is a promising candidate to achieve a large area instrumented with pixel sensors, since it is radiation hard and cost effective. The paper reports on the performance of thin 100 and 130μm n-in-p planar pixel sensors produced by FBK-CMM with active-edge technology in collaboration with LPNHE and INFN. Beam-test results are presented, with focus on the hit efficiency at the detector edge of a novel design consisting of a staggered deep trench.

International audience; An array of Single Photon Avalanche Diodes (SPAD), fabricated in a 180 nm CMOS technology featuring a high voltage (HV) option, has been investigated in terms of radiation tolerance, in view of the design of low material budget dual-tier detectors for charged particle tracking based on the coincidence of signals coming from pairs of vertically aligned pixels. Each pixel in the array includes both the processing electronics and the sensing element in a monolithic structure. The test vehicles were irradiated with 10 keV X-rays up to a dose of 1 Mrad (SiO 2 ) and with neutrons up to a fluence of 10 11 n eq cm −2 . A selection of the characterization results are presented together with the main features of a new large scale SPAD array to be fabricated in a 150 nm CMOS technology and ready for vertical interconnection in a dual layer structure.

The recent development in the design of Ultra Fast Silicon Detector (UFSD), aimed at combining radiation resistance up to fluences of 1015 neq/cm2 and fine read-out segmentation, makes these sensors suitable for high energy physics applications. UFSD is an evolution of standard silicon sensor, optimized to achieve excellent timing resolution (~30 ps), thanks to an internal low gain (~20). UFSD sensors are n in p Low Gain Avalanche Diode (LGAD) with an active thickness of ~5 μm. The internal gain in LGAD is obtained by implanting an appropriate density of acceptors (of the order of ~ 1016/cm3) close to the p-n junction, that, when depleted, locally generates an electric field high enough to activate the avalanche multiplication; this layer of acceptors is called gain layer. The two challenges in the development of UFSD for high energy physics detectors are the radiation hardness and the fine segmentation of large area sensors. Irradiation fluences of the order of 1015 neq/cm2 have a dramatic effect on the UFSD: neutrons and charged hadrons reduce the active acceptor density forming the gain layer; this mechanism, called initial acceptor removal, causes the complete disappearance of the internal gain above fluence of 1015 neq/ cm2. For the segmentation of UFSDs, the crucial point is the electrical insulation of pads and the extension of the inactive area between pads. In this paper we present the latest results on radiation resistance of LGADs with different gain layer designs, irradiated up to 3⋅1015 neq/ cm2. Three different segmentation technologies, developed by Fondazione Bruno Kessler in Trento, will also be discussed in detail in the second part of the paper.

The High Luminosity upgrade of the CERN Large Hadron Collider (HL-LHC) calls for new high radiation-tolerant solid-state pixel sensors, capable of surviving irradiation fluences up to a few 1 0 16 n eq /cm 2 at ∼ 3 cm from the interaction point. The INFN ATLAS-CMS joint research activity, in collaboration with Fondazione Bruno Kessler, is aiming at the development of thin n + on p type pixel sensors to be operated at the HL-LHC. The R&D covers both planar and 3D pixel devices made on substrates obtained by the Direct Wafer Bonding technique. The active thickness of the planar sensors studied in this paper is 100 μ m or 130 μ m , that of 3D sensors 130 μ m . First prototypes of hybrid modules, bump-bonded to the present CMS readout chips (PSI46 digital), have been characterized in beam tests. First results on their performance before and after irradiation up to a maximum fluence of ∼ 5 × 1 0 15 n eq /cm 2 are reported in this article.

International audience; In view of the LHC upgrade phase towards the High Luminosity LHC (HL-LHC), the ATLAS experiment plans to upgrade the Inner Detector with an all-silicon system.The n-on-p silicon technology is a promising candidate to achieve a large area instrumented with pixel sensors, since it is radiation hard and cost effective. The paper reports on the performance of thin (100 and 130 μm thick) and edgeless n-on-p planar pixel sensors produced by FBK-CMM. The production featured standard 50 μm × 250 μm pixel-pitch modules, compatible with the ATLAS FE-I4B readout chip, and small 50 μm × 50 μm and 25 μm × 100 μm pixel-pitch modules, compatible with the RD53A readout chip prototype. After discussing the sensor technology, an overview of 2018 testbeam results of the produced devices will be given, before and after irradiation, with a special focus on the hit efficiency at the detector edge.

Several sensor technologies are currently under development to define a new generation of time and space (4D) tracking detectors [1] , [2] able to operate at high luminosity conditions [3] . One of those technologies is the 3D silicon sensor. This kind of sensor is characterized by a particular configuration of its electrodes which are built vertically to the wafer surface by digging columnar or trenched structure hundreds of micrometers deep through the silicon wafer using specific etching techniques [4] . This approach decouples the interelectrode distance from the wafer thickness, achieving lower depletion voltage, higher radiation hardness and also faster charge collection times, typically smaller than 500 ps.