Silicon Sensors Research Articles

Implementation of the diagnostic capabilities of the CMOS sensor in the NIR environment, using 1070 nm interference filter and a conventional IR-pass filters set

NIR reflectography with silicon sensors (CMOS) is commonly acquired with 780 nm band-pass filters that allow the acquisition of clear images and high shutter speeds, while maintaining a low equipment cost. In this way, however, acquisition between 1000 nm and 1150nm-where the silicon sensor is still formally infrared sensitive-is in fact overhelmed by the stronger sensitivity in the infrared spectrum portion between 780 nm and 980 nm. Coupling a 1070 nm (± 5 nm) interferencial filter to an 87C nm IR pass filter (FHWH 850 nm) acquisitions in this portion of the NIR spectrum were carried out, witnessing a outstanding increase in visibility of underdrawings and pentimenti. A practical test of the effectiveness of the filters system mounted on the Nikon D800 IRUV was made, comparing the results with those obtained by the “Osiris” InGaAs detector by Opus Instruments. The comparison was performed on the “Deposition” (oil on panel) by Antonio Semino (1485–1555) in the collection of the Accademia Ligustica of Genoa, highlighting a significant qualitative proximity between the results obtained with the interference system and those with InGaAs detector, compared to the conventional acquisition with single IR long-pass filter.In addition, the 1070nm+87C filter system was used to increase the recognition capability of azurite pigments. This procedure widens the possibilities of first-impact diagnostics by means of low-cost and market available imaging systems based on commercial CMOS IRUV cameras..

Characterizing novel Indium Phosphide pad detectors with focused X-ray beams and laboratory tests

Future tracking systems in High Energy Physics experiments will require large instrumented areas with low radiation length. Crystalline silicon sensors have been used in tracking systems for decades, but are difficult to manufacture and costly to produce for large areas. We are exploring alternative sensor materials that are amenable to fast fabrication techniques used for thin film devices. Indium Phosphide pad sensors were fabricated at Argonne National Lab using commercially available InP:Fe 2-inch mono-crystal substrates. Current-voltage and capacitance-voltage characterizations were performed to study the basic operating characteristics of a group of sensors. Micro-focused X-ray beams at Canadian Light Source and Diamond Light Source were used to study the response to ionizing radiation, and characterize the uniformity of the response for several devices. Electrical test results showed a high degree of performance uniformity between the 48 tested devices. X-ray test beam results showed good performance uniformity within tested devices after accounting for spatially-local defects and edge fields. This motivates further studies into thin film devices for future tracking detectors.

High-count-rate particle tracking in proton and carbon radiotherapy with Timepix2 operated in ultra-short acquisition time

This work investigates the operational acquisition time limits of Timepix3 and Timepix2 detectors operated in frame mode for high-count rate of high deposited energy transfer particles. Measurements were performed using alpha particles from a 241Am laboratory source and proton and carbon ion beams from a synchrotron accelerator. The particle count rate upper limit is determined by overlapping per-pixel particle signals, identifiable by the hits per pixel counter > 2, indicating the need to decrease acquisition time. On the other hand, the lower limit is the time required to collect the particle deposited charge while maintaining spectral properties. Different acquisition times were evaluated for an AdvaPIX Timepix3 detector (500 μm Silicon sensor) with standard per-pixelDigital to Analog Converter (DAC)settings and a Minipix Timepix2 detector (300 μm Silicon sensor) with standard and customized settings the pulse shaping parameter and threshold. For AdvaPIX Timepix3, spectra remained accurate down to 100 μs frame acquisition time; at 10 μs, loss of collected charge occurred, suggesting either avoiding this acquisition time or applying a correction. Timepix2 allowed acquisition times down to 100 ns for single particle track measurements even for high energy loss, enabled by a new Timepix2 feature delaying shutter closure until full particle charge collection. This work represents the first measurement utilizing Timepix-chips pixel detectors in an accelerator beam of clinical energy and intensity without the need to decrease the beam current. This is made possible by exploiting the short shutter feature in Timepix2 and a customized per-pixel energy calibration of the Timepix2 detector with a larger discharging signal value which allowed for shorterTime-over-Threshold (ToT)signal. These customized settings extend the operation of the pixel detectors to higher event rates up to 109 particles/cm2/s.

Characterization results of MAPS digital prototypes for the ALICE ITS3

The three innermost layers of the ALICE Inner Tracking System (ITS2) will be replaced by a truly cylindrical tracker, the ITS3, to be ready for LHC Run 4 (2029-2032). The ITS3 will be composed of three layers, each made by two self-supporting, ultra-thin (≤50μm) flexible Monolithic Active Pixel silicon Sensors (MAPS) of large area (O(10 × 26 cm2)). The final sensor will be realized using the 65 nm CMOS imaging process and stitching technology. Multiple small-scale test structures were included in the first production run (Multiple Layer Reticle 1 - MLR1) to validate the 65 nm CMOS imaging technology. First large-scale stitched MAPS were included in the second production run (Engineering Run 1 - ER1). The pixel cell performance has been qualified on the MLR1 Digital Pixel Test Structures (DPTS) in laboratory and with in-beam measurements. The large-area (1.4 × 25.9 cm2) ER1 MOnolithic Stitched Sensor (MOSS) prototype has been used to prove the stitching principle and evaluate the detection efficiency and spatial resolution. This contribution will give an overview of the most recent results of the digital prototype tests.

Optimizing charge transport simulation for hybrid pixel detectors

To enhance the spatial resolution of the MÖNCH 25 µm pitch hybrid pixel detector, deep learning models have been trained using both simulation and measurement data. Challenges arise when comparing simulation-based deep learning models to measurement-based models for electrons, as the spatial resolution achieved through simulations is notably inferior to that from measurements. Discrepancies are also observed when directly comparing X-ray simulations with measurements, particularly in the spectral output of single pixels. These observations collectively suggest that current simulations require optimization. To address this, the dynamics of charge carriers within the silicon sensor have been studied using Monte Carlo simulations, aiming to refine the charge transport modeling. The simulation encompasses the initial generation of the charge cloud, charge cloud drift, charge diffusion and repulsion, and electronic noise. The simulation results were validated with measurements from the MÖNCH detector for X-rays, and the agreement between measurements and simulations was significantly improved by accounting for the charge repulsion.

ATLAS ITk pixel detector overview

In the high-luminosity era of the Large Hadron Collider, the instantaneous luminosity is expected to reach unprecedented values, resulting in up to 200 proton–proton interactions in a typical bunch crossing. To cope with the resulting increase in occupancy, bandwidth and radiation damage, the ATLAS Inner Detector will be replaced by an all-silicon system, the Inner Tracker (ITk). The innermost part of the ITk will consist of a pixel detector, with an active area of about 13 m2. To deal with the changing requirements in terms of radiation hardness, power dissipation and production yield, several silicon sensor technologies equipped with novel ASICs connecting by bump-bonding technique will be employed in the five barrel and endcap layers. As a timeline, it is facing to pre-production of components, sensor, building modules, mechanical structures and services. This contribution presents the status of the ITk-pixel project focusing on the lessons learned and the biggest challenges towards production, from mechanics structures to sensors, and it will summarize the latest results on closest-to-real demonstrators built using module, electric and cooling services prototypes.

Beam test performance studies of CMS Phase-2 Outer Tracker module prototypes

A new tracking detector will be installed as part of the Phase-2 upgrade of the CMS detector for the high-luminosity LHC era. This tracking detector includes the Inner Tracker, equipped with silicon pixel sensor modules, and the Outer Tracker, consisting of modules with two parallel stacked silicon sensors. The Outer Tracker front-end ASICs will be able to correlate hits from charged particles in these two sensors to perform on-module discrimination of transverse momenta (p T). The p T information is generated at a frequency of 40 MHz and will be used in the Level-1 trigger decision of CMS. Prototypes of the so-called 2S modules were tested at the Test Beam Facility at DESY Hamburg between 2019 and 2020. These modules use the final front-end ASIC, the CMS Binary Chip (CBC), and for the first time the Concentrator Integrated Circuit (CIC), optical readout and on-module power conversion. In total, seven modules were tested, one of which was assembled with sensors irradiated with protons. An important aspect was to show that it is possible to read out modules synchronously. A cluster hit efficiency of about 99.75 % was achieved for all modules. The CBC p T discrimination mechanism has been verified to work together with the CIC and optical readout. The measured module performance meets the requirements for operation in the upgraded CMS tracking detector.

Thin silicon sensors for extreme fluences: A doping compensation strategy

The CompleX project aims at extending the operation range of silicon detectors as 4D trackers up to 5 × 1017 neqcm−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 1017 neqcm−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.

Monitoring electron and proton beam profiles with segmented silicon sensors

The FRIDA INFN project characterized thin silicon sensors for monitoring electron FLASH beams, showing a response linearity up to ∼10 Gy/pulse on 9 MeV electrons. The use of segmented silicon configurations could provide the spatial resolution useful in Spatially Fractionated Radiotherapy (SFRT). Within the MIRO INFN project, a strip sensor integrated with a multichannel readout chip is being developed and tested for monitoring FLASH and SFRT electron and proton beams. One hundred and twenty-eight strips are independently read by two front-end TERA chips. Preliminary tests were performed on 6–10 MeV electron beams at the LINAC at Physics Department of the University of Torino, with and without using a tungsten minibeam collimator, and on 62–226 MeV proton beams at CNAO (Pavia). The capability to spatially resolve electron and proton beams at conventional dose-rates has been proved.

Italian-cluster technical solutions for the Quality-Control tests to the pixel-modules of the ATLAS Inner Tracker for High Luminosity LHC

In the era of high-luminosity LHC the instantaneous luminosity will achieve unprecedented levels, leading to the occurrence of up to 200 proton–proton interactions during a typical bunch crossing. In response to the resulting surge in occupancy, bandwidth demand, and radiation damage, the ATLAS Inner Detector is slated for replacement by an all-silicon system known as the Inner Tracker (ITk). The innermost segment of the ITk will be comprised of a pixel detector, featuring an active area spanning approximately 13 square meters. To address evolving requirements related to radiation hardness, power dissipation, and production yield, multiple silicon sensor technologies will be incorporated across the five barrel and end-cap layers. The ITk detector will be built in different laboratories all around the world. Several institutes are actively involved in the ITk project assembling and testing pre-production modules, that have been constructed to assess their production efficiency. Testing sites perform the so-called quality control (QC) tests. The ITk community defines requirements for QC testing both prototypes and modules, and provides common software tools as well as possible technical solutions. Each laboratory must qualify for the QC activity by demonstrating the chosen solutions are compliant with requirements. In this contribution the relevance of the QC procedures will be outlined, focusing on the custom structures and items developed by the Italian laboratories to improve the quality of the tests and to satisfy the requirements imposed by the Collaboration.

A 4D-tracker demonstrator based on the Timespot1, a CMOS 28-nm ASIC

The Timespot1 ASIC was developed using 28-nm CMOS technology within the TimeSPOT/IGNITE collaborations and aimed to bridge the gap between available fast-timing ASICs and those required for high-luminosity applications. We present results of the performance of the Timespot1 hybrid, where 3D trench silicon and 3D columnar diamond sensors have been bump-bonded to the Timespot1 ASIC.

Measurements and TCAD simulations of guard-ring structures of thin silicon sensors before and after irradiation

The developing of high performing silicon detectors for particle tracking in the next generation of high-energy physics experiments at future colliders (e.g., HL-LHC, FCC) able to operate efficiently up to very high fluence (∼1⋅10171MeVneq/cm2) is of the utmost importance. In order to sustain high voltage values with minimum leakage current injection into the core region of the sensor, the design and optimisation of the Guard-Ring (GR) protection structure is crucial, especially when small substrate thicknesses are used. In a recent R&D batch produced at Fondazione Bruno Kessler (FBK) in the framework of the “eXFlu” project - INFN CSN5 grant for Young Researchers, different optimisation studies of GR structures for thin substrates (45, 30, 20 and 15μm) up to high fluence (2.5⋅10151MeVneq/cm2) have been addressed. These have been enabled thanks to ad-hoc advanced Technology CAD (TCAD) modelling of different GR design strategies, accounting for the comprehensive bulk and surface radiation-induced damage effects, and an extensive test campaign on such GR structures, both before and after irradiation. In this paper the validation of the development framework of the various GR design options before and after irradiation is presented.

Characterization of a Modified Clinical Linear Accelerator for Ultra-High Dose Rate Beam Delivery

Irradiations at Ultra-High Dose Rate (UHDR) regimes, exceeding 40 Gy/s in single fractions lasting less than 200 ms, have shown an equivalent antitumor effect compared to conventional radiotherapy with reduced harm to normal tissues. This work details the hardware and software modifications implemented to deliver 10 MeV UHDR electron beams with a linear accelerator Elekta SL 18 MV and the beam characteristics obtained. GafChromic EBT XD films and an Advanced Markus chamber were used for dosimetry characterization, while a silicon sensor assessed the machine’s beam pulses stability and repeatability. The dose per pulse, average dose rate and instantaneous dose rate in the pulse were evaluated for four experimental settings, varying the source-to-surface distance and the beam collimation, i.e., with and without the use of a cylindrical applicator. The results showed a dose per pulse from 0.6 Gy to a few tens of Gy and an average dose rate up to 300 Gy/s. The obtained results demonstrate the possibility to perform in vitro radiobiology experiments and test new technologies for beam monitoring and dosimetry at the upgraded LINAC, thus contributing to the electron UHDR research field.

40 MHz readout of CMS silicon modules in a high intensity beam

In order to maintain its outstanding performance under the challenging conditions brought by the high-luminosity LHC, the CMS collaboration is preparing the production of a new outer tracker detector. The upgraded detector modules will feature two silicon sensors and the ability of reading out correlated clusters, or stubs, compatible with high transverse momentum particles at the full 40 MHz collision rate. With the detector design being finalised and mass production planned to start during the second half of 2024, the scalability of the readout system and the study of the commissioning and characterisation of the detector in realistic conditions are ever-more pressing.In this context, a joint beam-test was organised in collaboration with the MUonE collaboration where twelve modules were placed in an asynchronous muon beam line reaching particle rates of about 50 MHz, with the full stub stream being recorded to disk triggerless. The experiment and read-out chain is outlined, the commissioning procedures and operational challenges discussed and resulting system performance are presented.

A novel detector for 4D tracking in particle therapy

An innovative beam monitor for particle therapy applications was developed to count protons and carbon ions in clinical beams and was integrated with a Time-to-Digital Converter (TDC) to add the measurement of particles’ crossing time. The detector exploits strip-segmented planar silicon sensors with an active thickness of a few tens of μm and the front-end electronics is based on a 24-channel ASIC (named ABACUS) for the discrimination of the particles’ signals. The proton counting efficiency shows a dependence on the beam energy because of transversal dimension and pile-up effects, whereas an efficiency between 94 and 98 % with lower energy dependence is found for carbon ions. The time measurements with the TDC allow for the study of the time interval between consecutive particles in one strip, which appears to be compatible with the radio-frequency period of the synchrotron. These results indicate that thin silicon sensors and custom front-end readout with high counting rate capability allow for a full 4D tracking of clinical ion beams, opening the way to future technologies for online monitoring systems.

Characterization of Tracking Modules Based on DSSD Sensors at the SC-1000 Accelerator for the BM@N Project

The results of studying characteristics of modules based on double-sided microstrip silicon sensors, which are designed to create the wide-aperture Silicon Tracking System for the BM@N facility, are presented. The main module features are the use of fast readout electronics based on the STS-XYTER chip and the application of ultralight (0.23% X0) aluminum microcables for transmitting analog signals from the sensor strips to the input channels of the readout electronics. The results of testing different configurations of tracking modules on the extracted beam of protons at the SC-1000 accelerator in the PNPI are presented. The stable operation of readout electronics is demonstrated at loads close to the maximum values of 360 kHz s–1 cm–2. The signal-to-noise ratio was no less than 23. The measured coordinate resolution of the modules within the beam telescope was 17 ± 0.4 μm, and the detector efficiency of recording for protons with energy of 1 GeV was no less than 99%.

Low gain avalanche diodes for photon science applications

Low Gain Avalanche Diodes (LGADs) are silicon sensors designed to achieve an internal gain in the order of 10 through the impact ionization process. The development of LGADs was pushed forward by their application in High Energy Physics (HEP) experiments, where they will be employed to provide measurements of the time of arrival of minimum ionizing particles with a resolution of around 30 ps. The initial technological implementation of the sensors constrains their minimum channel size to be larger than 1 mm2, in order to reduce inefficiencies due to the segmentation of the gain structure. The gain of the sensors is kept in the order of 10 to limit the sensor shot noise and their power consumption. In photon science, the gain provided by the sensor can boost the signal-to-noise ratio of the detector system, effectively reducing the x-ray energy threshold of photon counting detectors and the minimum x-ray energy where single photon resolution is achieved in charge integrating detectors. This can improve the hybrid pixel and strip detectors for soft and tender x-rays by simply changing the sensor element of the detector system. Photon science applications in the soft and tender energy range require improvements over the LGADs developed for HEP, in particular the presence of a thin entrance window to provide a satisfactory quantum efficiency and channel size with a pitch of less than 100 μm. In this review, the fundamental aspects of the LGAD technology are presented, discussing also the ongoing and future developments that are of interest for photon science applications.

From 3D to 5D tracking: SMX ASIC-based double-sided micro-strip detectors for comprehensive space, time, and energy measurements

We present the recent development of a lightweight detector capable of accurate spatial, timing, and amplitude resolution of charged particles. The technology is based on double-sided double-metal p+ – n – n+ micro-strip silicon sensors, ultra-light long aluminum-polyimide micro-cables for the analogue signal transfer, and a custom-developed SMX read-out ASIC capable of measurement of the time (Δt ≲ 5 ns) and amplitude. Dense detector integration enables a material budget > 0.3 % X 0. A sophisticated powering and grounding scheme keeps the noise under control.In addition to its primary application in Silicon Tracking System of the future CBM experiment in Darmstadt, our detector will be utilized in other research applications.

Towards precise LET measurements based on energy deposition of therapeutic ions in Timepix3 detectors

Objective. There is an increasing interest in calculating and measuring linear energy transfer (LET) spectra in particle therapy in order to assess their impact in biological terms. As such, the accuracy of the particle fluence energy spectra becomes paramount. This study focuses on quantifying energy depositions of distinct proton, helium, carbon, and oxygen ion beams using a silicon pixel detector developed at CERN to determine LET spectra in silicon. Approach. While detection systems have been investigated in this pursuit, the scarcity of detectors capable of providing per-ion data with high spatial and temporal resolution remains an issue. This gap is where silicon pixel detector technology steps in, enabling online tracking of single-ion energy deposition. The used detector consisted of a 300 µm thick silicon sensor operated in partial depletion. Main results. During post-processing, artifacts in the acquired signals were identified and methods for their corrections were developed. Subsequently, a correlation between measured and Monte Carlo-based simulated energy deposition distributions was performed, relying on a two-step recalibration approach based on linear and saturating exponential models. Despite the observed saturation effects, deviations were confined below 7% across the entire investigated range of track-averaged LET values in silicon from 0.77 keV µm−1 to 93.16 keV µm−1. Significance. Simulated and measured mean energy depositions were found to be aligned within 7%, after applying artifact corrections. This extends the range of accessible LET spectra in silicon to clinically relevant values and validates the accuracy and reliability of the measurements. These findings pave the way towards LET-based dosimetry through an approach to translate these measurements to LET spectra in water. This will be addressed in a future study, extending functionality of treatment planning systems into clinical routine, with the potential of providing ion-beam therapy of utmost precision to cancer patients.

Conversion of fast neutrons for neutron radiography with TPX2 detector

Abstract The Timepix2-based hybrid-pixel detector with a 500 μm thick silicon sensor was employed for fast-neutrons registration to be applied in neutron radiography of metallic printed circuit heat exchanger (PCHE). Two energies of neutrons were experimentally tested. The detection of 3.55 MeV neutrons from the deuteron–deuteron (DD) reaction was compared to 15.7 MeV neutrons from the deuteron–tritium (DT) neutron generator. In order to distinguish the signal induced by the registered neutrons from the accelerator background, filtration of the recorded particle spectral tracks was applied. The benefit of applying hydrogen-based converter layer for 3.55 MeV neutrons was observable. On the other hand, in the case of 15.7 MeV neutrons, the direct registration by interaction with the sensor Si significantly dominates the conversion.