arXiv subjects

Miljenko Šuljić

Publications and source records attributed to Miljenko Šuljić.

6 recordsLinked to original sources

arXiv2026

Charge sharing and alignment performance of bent ALPIDEs measured with low-energy protons

The upgrade of the ALICE experiments Inner Tracking System (ITS3) aims to replace its innermost detection layers with bent wafer-scale CMOS MAPS sensors. This study examines the performance of ALPIDE chips, currently used in the ALICE ITS2, when operated in a bent configuration under realistic experimental conditions. Proton beams with energies of 80 MeV, 120 MeV and 200 MeV were used to study proton-proton elastic scattering on a polypropylene fiber target reconstructed using two opposing arms of trackers with sensors bent to radii of 18 mm, 24 mm and 30 mm. The measured low-momentum protons provided a testbed for investigating clustering behavior in high-energy loss events, where no significant impact of bending was observed on cluster size. Additionally, alignment strategies for bent detectors were evaluated using the distance of closest approach (DCA) and opening angle between scattered proton tracks as benchmarks. The achieved resolution matches expectations from simulations, confirming the suitability of bent MAPS sensors for future high-energy and nuclear physics applications.

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arXiv2026

A Novel Approach for Fault Detection and Failure Analysis of CMOS Copper Metal Stacks

For the Inner Tracking System 3 (ITS3) upgrade, the ALICE experiment at CERN requires monolithic active pixel sensors of dimensions up to 97~mm$\,\times\,$266~mm, occupying a large fraction of a 300 mm wafer. To manufacture such a wafer-scale device, larger than the single design reticle size, stitching is employed. The MOnolithic Stitched Sensor (MOSS) is a prototype silicon pixel sensor of 14~mm$\,\times\,$259~mm size with the primary goal of understanding the stitching technique and yield. Given the large size, high yield is paramount for the ITS3 sensors, and an in-depth yield characterization was performed on these MOSS sensors. In a collaborative effort, the foundry adapted the metal stack to the requirements of the project, but recurrent fault signatures were discovered with various frequencies across all 20 wafers tested, and correlated through dedicated measurements and analyses. Following these findings, the foundry implemented a mitigation strategy to avoid the issue in the future. This article does not describe process details but concentrates on the measurements and analysis method.

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arXiv2025

Further Characterisation of Digital Pixel Test Structures Implemented in a 65 nm CMOS Process

The next generation of MAPS for future tracking detectors will have to meet stringent requirements placed on them. One such detector is the ALICE ITS3 that aims to be very light at 0.07% X/X$_{0}$ per layer and have a low power consumption in the active area of 40 mW/cm$^{2}$ by implementing wafer-scale MAPS bent into cylindrical half layers. To address these challenging requirements, the ALICE ITS3 project, in conjunction with the CERN EP R&D on monolithic pixel sensors, proposed the Tower Partners Semiconductor Co. 65 nm CMOS process as the starting point for the sensor. After the initial results confirmed the detection efficiency and radiation hardness, the choice of the technology was solidified by demonstrating the feasibility of operating MAPS in low-power consumption regimes, < 50 mW/cm$^{2}$, while maintaining high-quality performance. This was shown through a detailed characterisation of the Digital Pixel Test Structure (DPTS) prototype exposed to X-rays and ionising beams, and the results are presented in this article. Additionally, the sensor was further investigated through studies of the fake-hit rate, the linearity of the front-end in the range 1.7-28 keV, the performance after ionising irradiation, and the detection efficiency of inclined tracks in the range 0-45$^\circ$.

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arXiv2025

Detection efficiency and spatial resolution of Monolithic Active Pixel Sensors bent to different radii

Bent monolithic active pixel sensors are the basis for the planned fully cylindrical ultra low material budget tracking detector ITS3 of the ALICE experiment. This paper presents results from testbeam campaigns using high-energy particles to verify the performance of 50 um thick bent ALPIDE chips in terms of efficiency and spatial resolution. The sensors were bent to radii of 18, 24 and 30 mm, slightly smaller than the foreseen bending radii of the future ALICE ITS3 layers. An efficiency larger than $99.9\%$ and a spatial resolution of approximately 5 um, in line with the nominal operation of flat ALPIDE sensors, is obtained at nominal operating conditions. These values are found to be independent of the bending radius and thus constitute an additional milestone in the demonstration of the feasibility of the planned ITS3 detector. In addition, a special geometry in which the beam particles graze the chip and traverse it laterally over distances of up to 3 mm is investigated.

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arXiv2024

Characterisation of analogue Monolithic Active Pixel Sensor test structures implemented in a 65 nm CMOS imaging process

Analogue test structures were fabricated using the Tower Partners Semiconductor Co. CMOS 65 nm ISC process. The purpose was to characterise and qualify this process and to optimise the sensor for the next generation of Monolithic Active Pixels Sensors for high-energy physics. The technology was explored in several variants which differed by: doping levels, pixel geometries and pixel pitches (10-25 $μ$m). These variants have been tested following exposure to varying levels of irradiation up to 3 MGy and $10^{16}$ 1 MeV n$_\text{eq}$ cm$^{-2}$. Here the results from prototypes that feature direct analogue output of a 4$\times$4 pixel matrix are reported, allowing the systematic and detailed study of charge collection properties. Measurements were taken both using $^{55}$Fe X-ray sources and in beam tests using minimum ionizing particles. The results not only demonstrate the feasibility of using this technology for particle detection but also serve as a reference for future applications and optimisations.

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arXiv2023

Digital Pixel Test Structures implemented in a 65 nm CMOS process

The ALICE ITS3 (Inner Tracking System 3) upgrade project and the CERN EP R&D on monolithic pixel sensors are investigating the feasibility of the Tower Partners Semiconductor Co. 65 nm process for use in the next generation of vertex detectors. The ITS3 aims to employ wafer-scale Monolithic Active Pixel Sensors thinned down to 20 to 40 um and bent to form truly cylindrical half barrels. Among the first critical steps towards the realisation of this detector is to validate the sensor technology through extensive characterisation both in the laboratory and with in-beam measurements. The Digital Pixel Test Structure (DPTS) is one of the prototypes produced in the first sensor submission in this technology and has undergone a systematic measurement campaign whose details are presented in this article. The results confirm the goals of detection efficiency and non-ionising and ionising radiation hardness up to the expected levels for ALICE ITS3 and also demonstrate operation at +20 C and a detection efficiency of 99% for a DPTS irradiated with a dose of $10^{15}$ 1 MeV n$_{\mathrm{eq}}/$cm$^2$. Furthermore, spatial, timing and energy resolutions were measured at various settings and irradiation levels.

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