arXiv subjects

Alessandro Fondacci

Publications and source records attributed to Alessandro Fondacci.

5 recordsLinked to original sources

arXiv2026

Measurements and simulations of X-ray radiation damage effects on CNM n-type 4H-SiC MOS capacitors

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.

physics.ins-det↗

arXiv2025

Timing resolution from beam tests on thin LGADs down to 16.6 ps

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~\micron, with an active area spanning from 0.75~$\times$~0.75 to 1.28~$\times$~1.28~mm$^{2}$. The experimental setup consisted of a 45~\micron-thick trigger sensor with an active area of 3.6~$\times$~3.6~mm$^{2}$, 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$^{\circ}$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~\micron-thick sensors, down to 16.6~\ps in 20~\micron-thick sensors, in the non-irradiation study. The combination of two 20~\micron-thick LGADs reached a timing resolution of 12.2~\ps. A set of 30~\micron-thick sensors irradiated with neutrons at fluences between 0.4~$\times$~10$^{15}$ and 2.5~$\times$~10$^{15}$~\mevneut were tested in the beam. These irradiated sensors achieved a gain between 7 and 30 using a similar apparatus but cooled with solidified CO$_{2}$ to -42$^{\circ}$C. A timing resolution of 20~\ps was obtained in these irradiated sensors.

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arXiv2025

Compensated LGAD optimisation through van der Pauw test structures

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.

physics.ins-det↗

arXiv2025

Design and optimisation of radiation resistant AC- and DC-coupled resistive LGADs

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 $\mu$m with a pixel pitch of 450 $\mu$m. 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.

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arXiv2022

A Compensated Design of the LGAD Gain Layer

In this contribution, we present an innovative design of the Low-Gain Avalanche Diode (LGAD) gain layer, the p$^+$ implant responsible for the local and controlled signal multiplication. In the standard LGAD design, the gain layer is obtained by implanting $\sim$ 5E16/cm$^3$ atoms of an acceptor material, typically Boron or Gallium, in the region below the n$^{++}$ electrode. In our design, we aim at designing a gain layer resulting from the overlap of a p$^+$ and an n$^+$ implants: the difference between acceptor and donor doping will result in an effective concentration of about 5E16/cm$^3$, similar to standard LGADs. At present, the gain mechanism of LGAD sensors under irradiation is maintained up to a fluence of $\sim$ 1-2E15/cm$^2$, and then it is lost due to the acceptor removal mechanism. The new design will be more resilient to radiation, as both acceptor and donor atoms will undergo removal with irradiation, but their difference will maintain constant. The compensated design will empower the 4D tracking ability typical of the LGAD sensors well above 1E16/cm$^2$.

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