arXiv subjects

M. Centis Vignali

Publications and source records attributed to M. Centis Vignali.

11 recordsLinked to original sources

arXiv2025

Measurements and TCAD simulations of innovative RSD and DC-RSD LGAD devices for future 4D tracking

This paper summarizes the beam test results obtained with a Resistive Silicon Detector (RSD) (also called AC-Low Gain Avalanche Diode, AC-LGAD) pixel array tested at the DESY beam test facility with a 5 GeV/c electron beam. Furthermore, it describes in detail the simulation results of DC-RSD, an evolution of the RSD design. The simulations campaign described in this paper has been instrumental in the definition of the structures implemented in the Fondazione Bruno Kessler FBK first DC-RSD production. The RSD matrix used in this study is part of the second FBK RSD production, RSD2. The best position resolution reached in this test is sigma_x = 15 micron, about 3.4% of the pitch. DC-RSD LGAD, are an evolution of the AC-coupled design, eliminating the dielectric and using a DC-coupling to the electronics. The concept of DC-RSD has been finalized using full 3D Technology-CAD simulations of the sensor behavior. TCAD simulations are an excellent tool for designing this innovative class of detectors, enabling the evaluation of different technology options (e.g., the resistivity of the n+ layer, contact materials) and geometrical layouts (shape and distance of the read-out pads).

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arXiv2025

Innovative DC-coupled Resistive Silicon Detector for 4D tracking

In the past 10 years, two design innovations, the introduction of low internal gain (LGAD) and of resistive read-out (RSD), have radically changed the performance of silicon detectors. The LGAD mechanism, increasing the signal-to-noise ratio by about a factor of 20, leads to improved time resolution (typically 30 ps for a 50-$\mu$m thick sensor), while resistive read-out, sharing the collected charge among read-out electrodes, leads to excellent spatial resolution even using large pixels (about 15 $\mu$m for 450-$\mu$m pixel size). This contribution outlines the design strategy and presents the first performance results of the latest evolution of silicon sensors for 4D tracking, the DC-coupled Resistive Silicon Detector (DC-RSD). The DC-RSD is a thin LGAD with a DC-coupled resistive read-out. This design leads to signal containment within a predetermined number of electrodes using isolating trenches (TI technology). Several test structures and application-oriented devices have been implemented in the wafer layout. The sensors, produced at Fondazione Bruno Kessler (FBK) in the framework of the 4DSHARE project, have been characterized with a laser TCT system and recently tested at DESY with an electron beam. The study of this first prototype production will provide us with immediate feedback on the soundness of the DC-RSD concepts.

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arXiv2022

High-Precision 4D Tracking with Large Pixels using Thin Resistive Silicon Detectors

The basic principle of operation of silicon sensors with resistive read-out is built-in charge sharing. Resistive Silicon Detectors (RSD, also known as AC-LGAD), exploiting the signals seen on the electrodes surrounding the impact point, achieve excellent space and time resolutions even with very large pixels. In this paper, a TCT system using a 1064 nm picosecond laser is used to characterize sensors from the second RSD production at the Fondazione Bruno Kessler. The paper first introduces the parametrization of the errors in the determination of the position and time coordinates in RSD, then outlines the reconstruction method, and finally presents the results. Three different pixel sizes are used in the analysis: 200 x 340, 450 x 450, and 1300 x 1300 microns^2. At gain = 30, the 450 x 450 microns^2 pixel achieves a time jitter of 20 ps and a spatial resolution of 15 microns concurrently, while the 1300 x 1300 microns^2 pixel achieves 30 ps and 30 micron, respectively. The implementation of cross-shaped electrodes improves considerably the response uniformity over the pixel surface.

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arXiv2022

Beam test results of 25 $μ$m and 35 $μ$m thick FBK UFSD]{Beam test results of 25 $μ$m and 35 $μ$m thick FBK ultra fast silicon detectors

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 $μ$m and 35 $μ$m and an area of 1 $\times$ 1 $\text{mm}^2$ have been considered, together with an additional HPK 50-$μ$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 V and 240 V has been obtained for the 25 and 35 $μ$m thick UFSDs, respectively.

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arXiv2022

The second production of RSD (AC-LGAD) at FBK

In this contribution we describe the second run of RSD (Resistive AC-Coupled Silicon Detectors) designed at INFN Torino and produced by Fondazione Bruno Kessler (FBK), Trento. RSD are n-in-p detectors intended for 4D particle tracking based on the LGAD technology that get rid of any segmentation implant in order to achieve the 100% fill-factor. They are characterized by three key-elements, (i) a continuous gain implant, (ii) a resistive n-cathode and (iii) a dielectric coupling layer deposited on top, guaranteeing a good spatial reconstruction of the hit position while benefiting from the good timing properties of LGADs. We will start from the very promising results of our RSD1 batch in terms of tracking performances and then we will move to the description of the design of the RSD2 run. In particular, the principles driving the sensor design and the specific AC-electrode layout adopted to optimize the signal confinement will be addressed.

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arXiv2022

DC-coupled resistive silicon detectors for 4-D tracking

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.

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arXiv2020

A novel hybrid microdosimeter for radiation field characterization based on TEPC detector and LGADs tracker: a feasibility study

In microdosimetry, lineal energies y are calculated from energy depositions $ε$ inside the microdosimeter divided by the mean chord length, whose value is based on geometrical assumptions on both the detector and the radiation field. This work presents an innovative two-stages hybrid detector (HDM: hybrid detector for microdosimetry) composed by a Tissue Equivalent Proportional Counter (TEPC) and a silicon tracker made of 4 Low Gain Avalanche Diode (LGAD). This design provides a direct measurement of energy deposition in tissue as well as particles tracking with a submillimeter spatial resolution. The data collected by the detector allow to obtain the real track length traversed by each particle in the TEPC and thus estimates microdosimetry spectra without the mean chord length approximation. Using Geant4 toolkit, we investigated HDM performances in terms of detection and tracking efficiencies when placed in water and exposed to protons and carbon ions in the therapeutic energy range. The results indicate that the mean chord length approximation underestimate particles with short track, which often are characterized by a high energy deposition and thus can be biologically relevant. Tracking efficiency depends on the LGAD configurations: 34 strips sensors have a higher detection efficiency but lower spatial resolution than 71 strips sensors. Further studies will be performed both with Geant4 and experimentally to optimize the detector design on the bases of the radiation field of interest. The main purpose of HDM is to improve the assessment of the radiation biological effectiveness via microdosimetric measurements, exploiting a new definition of the lineal energy ($y_{T}$), defined as the energy deposition $ε$ inside the microdosimeter divided by the real track length of the particle.

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arXiv2019

Deep Diffused APDs for Charged Particle Timing Applications: Performance after Neutron Irradiation

Recent interest in pile-up mitigation through fast timing at the HL-LHC has focused attention on technologies that now achieve minimum ionising particle (MIP) time resolution of 30 picoseconds or less. The constraints of technical maturity and radiation tolerance narrowed the options in this rapidly developing field for the ATLAS and CMS upgrades to low gain avalanche detectors and silicon photomultipliers. In a variety of applications where occupancies and doses are lower, devices with pixel elements of order 1 cm$^2$, nevertheless achieving 30 ps, would be attractive. In this paper, deep diffused Avalanche Photo Diodes (APDs) are examined as candidate timing detectors for HL-LHC applications. Devices with an active area of $8 \times 8$ mm$^2$ are characterised using a pulsed infrared laser and, in some cases, high energy particle beams.The timing performance as well as the uniformity of response are examined. The effects of radiation damage on current, signal amplitude, noise, and timing of the APDs are evaluated using detectors with an active area of $2 \times 2$ mm$^2$. These detectors were irradiated with neutrons up to a a 1-MeV neutrons fluence $Φ_{eq} = 10^{15}$ cm$^{-2}$. Their timing performance was characterised using a pulsed infrared laser. While a time resolution of $27 \pm 1$ ps was obtained in a beam test using an $8 \times 8$ mm$^2$ sensor, the present study only demonstrates that gain loss can be compensated by increased detector bias up to fluences of $Φ_{eq} = 6 \cdot 10^{13}$ cm$^{-2}$. So it possibly falls short of the $Φ_{eq} = 10^{14}$ cm$^{-2}$ requirement for the CMS barrel over the lifetime of the HL-LHC.

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arXiv2019

Deep Diffused Avalanche Photodiodes for Charged Particles Timing

The upgrades of ATLAS and CMS for the High Luminosity LHC (HL-LHC) highlighted physics objects timing as a tool to resolve primary interactions within a bunch crossing. Since the expected pile-up is around 200, with an r.m.s. time spread of 180 ps, a time resolution of about 30 ps is needed. The timing detectors will experience a 1-MeV neutron equivalent fluence of about $Φ_{eq}=10^{14}$ and $10^{15}$ cm$^{-2}$ for the barrel and end-cap regions, respectively. In this contribution, deep diffused Avalanche Photo Diodes (APDs) produced by Radiation Monitoring Devices are examined as candidate timing detectors for HL-LHC applications. To improve the detector's timing performance, the APDs are used to directly detect the traversing particles, without a radiator medium where light is produced. Devices with an active area of $8\times8$ mm$^2$ were characterized in beam tests. The timing performance and signal properties were measured as a function of position on the detector using a beam telescope and a microchannel plate photomultiplier (MCP-PMT). Devices with an active area of $2\times2$ mm$^2$ were used to determine the effects of radiation damage and characterized using a ps pulsed laser. These detectors were irradiated with neutrons up to $Φ_{eq}=10^{15}$ cm$^{-2}$.

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arXiv2019

Inverse Low Gain Avalanche Detectors (iLGADs) for precise tracking and timing applications

Low Gain Avalanche Detector (LGAD) is the baseline sensing technology of the recently proposed Minimum Ionizing Particle (MIP) end-cap timing detectors (MTD) at the Atlas and CMS experiments. The current MTD sensor is designed as a multi-pad matrix detector delivering a poor position resolution, due to the relatively large pad area, around 1 $mm^2$; and a good timing resolution, around 20-30 ps. Besides, in his current technological incarnation, the timing resolution of the MTD LGAD sensors is severely degraded once the MIP particle hits the inter-pad region since the signal amplification is missing for this region. This limitation is named as the LGAD fill-factor problem. To overcome the fill factor problem and the poor position resolution of the MTD LGAD sensors, a p-in-p LGAD (iLGAD) was introduced. Contrary to the conventional LGAD, the iLGAD has a non-segmented deep p-well (the multiplication layer). Therefore, iLGADs should ideally present a constant gain value over all the sensitive region of the device without gain drops between the signal collecting electrodes; in other words, iLGADs should have a 100${\%}$ fill-factor by design. In this paper, tracking and timing performance of the first iLGAD prototypes is presented.

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arXiv2017

Neutron irradiation effect on SiPMs up to $Φ_{neq}$ = 5 $\times$ 10$^{14}$ cm$^{-2}$

Silicon Photo-Multipliers (SiPM) are becoming the photo-detector of choice for increasingly more particle detection applications, from fundamental physics to medical and societal applications. One major consideration for their use at high-luminosity colliders is the radiation damage induced by hadrons, which leads to a dramatic increase of the dark count rate. KETEK SiPMs have been exposed to various fluences of reactor neutrons up to $Φ_{neq}$ = 5$\times$10$^{14}$ cm$^{-2}$ (1 MeV equivalent neutrons). Results from the I-V, and C-V measurements for temperatures between $-$30$^\circ$C and $+$30$^\circ$C are presented. We propose a new method to quantify the effect of radiation damage on the SiPM performance. Using the measured dark current the single pixel occupation probability as a function of temperature and excess voltage is determined. From the pixel occupation probability the operating conditions for given requirements can be optimized. The method is qualitatively verified using current measurements with the SiPM illuminated by blue LED light.

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