arXiv subjects

Yajun He

Publications and source records attributed to Yajun He.

8 recordsLinked to original sources

arXiv2026

Review of prototypes developed in a 65 nm CMOS imaging technology in view of vertexing applications at a future lepton collider

The OCTOPUS project addresses the development and characterization of monolithic active pixel sensors in the TPSCo 65 nm ISC technology in view of vertexing applications at a future lepton collider. Meeting the corresponding requirements -- outlined in the ECFA detector road map -- will necessitate the simulation, design, and testing of prototypes and a demonstrator chip in this very process. This work reviews the literature on existing prototypes, summarizing their design characteristics, properties, and performance in charged-particle detection, and provides an overview of previous simulation efforts. The presented results suggest the feasibility of the endeavor while showcasing challenges, the need for further investigations, and providing a foundation for imminent design choices.

physics.ins-det↗

arXiv2026

Impact of Cold Noise on the tracking performance of ATLAS ITk short strip barrel modules using a charged particle beam

The inner tracking system of the ATLAS experiment will be upgraded to a full silicon detector in 2030 for HL-LHC. The new tracking system is called ITk, the Inner Tracker. It is required to be operable with efficiency higher than 99\% and noise hit occupancy smaller than 0.1\%. During the pre-production phase of the ITk project, many short-strip modules were observed to exhibit so-called "Cold Noise (CN)", wherein clusters of strips displayed very high noise when the modules were operated at temperatures below~$-35\degree$C. To investigate the CN impact and ensure the quality of module production, huge amount of effort have been put in by the collaboration. This paper focuses on the impact of CN on the tracking performance by examining two short strip modules that exhibit CN: one is non-irradiated, while the other one has been irradiated to the maximum expected end-of-lifetime fluence. For each module, the global and single strip tracking performance are evaluated.

physics.ins-det↗

arXiv2025

Characterization of the H2M Monolithic CMOS Sensor

The H2M (Hybrid-to-Monolithic) is a monolithic pixel sensor manufactured in a modified \SI{65}{\nano\meter}~CMOS imaging process with a small collection electrode. Its design addresses the challenges of porting an existing hybrid pixel detector architecture into a monolithic chip, using a digital-on-top design methodology, and developing a compact digital cell library. Each square pixel integrates an analog front-end and digital pulse processing with an 8-bit counter within a \SI{35}{\micro\meter}~pitch. This contribution presents the performance of H2M based on laboratory and test beam measurements, including a comparison with analog front-end simulations in terms of gain and noise. A particular emphasis is placed on backside thinning in order to reduce material budget, down to a total chip thickness of \SI{21}{\micro\meter} for which no degradation in MIP detection performance is observed. For all investigated samples, a MIP detection efficiency above \SI{99}{\%} is achieved below a threshold of approximately 205 electrons. At this threshold, the fake-hit rate corresponds to a matrix occupancy of fewer than one pixel per the \SI{500}{\nano\second}~frame. Measurements reveal a non-uniform in-pixel response, attributed to the formation of local potential wells in regions with low electric field. A simulation flow combining technology computer-aided design, Monte Carlo, and circuit simulations is used to investigate and describe this behavior, and is applied to develop mitigation strategies for future chip submissions with similar features.

physics.ins-det↗

arXiv2025

Test beam measurements and computer simulations of the ATLAS ITk R2 silicon strip detector

The ATLAS Inner Tracker, the future innermost part of the ATLAS detector, is an all-silicon tracker composed of pixel and strip modules, designed to cope with the extreme conditions expected during High-Luminosity LHC runs. Thorough testing of modules during the individual phases of their development is critical to ensure the required performance level of the whole tracker. This document presents results obtained from electron beam measurements of the ATLAS ITk R2 end-cap strip module. Key performance metrics are presented and discussed for both perpendicular and angled beam incidence. Computer simulations of the module were performed in the Allpix-Squared framework and the results were compared to experimental data.

physics.ins-det↗

arXiv2025

Impact of the circuit layout on the charge collection in a monolithic pixel sensor

CERN's strategic R&D programme on technologies for future experiments recently started investigating the TPSCo 65nm ISC CMOS imaging process for monolithic active pixels sensors for application in high energy physics. In collaboration with the ALICE experiment and other institutes, several prototypes demonstrated excellent performance, qualifying the technology. The Hybrid-to-Monolithic (H2M), a new test-chip produced in the same process but with a larger pixel pitch than previous prototypes, exhibits an unexpected asymmetric efficiency pattern. This contribution describes a simulation procedure combining TCAD, Monte Carlo and circuit simulations to model and understand this effect. It proved able to reproduce measurement results and attribute the asymmetric efficiency drop to a slow charge collection due to low amplitude potential wells created by the circuitry layout and impacting efficiency via ballistic deficit.

physics.ins-det↗

arXiv2025

TelePix2: Full scale fast region of interest trigger and timing for the EUDET-style telescopes at the DESY II Test Beam Facility

With increasing demands by future and current upgrades of particle physics experiments on rate capabilities and time resolution, the requirements on test beams are also increasing. The current infrastructure at the DESY II test beam facility includes particle tracking telescopes with long integration times, no additional timing but excellent spatial resolution. This results in readouts with multiple particles per trigger, causing ambiguities in tracking and assigning particles to triggers. Also, it is likely not to trigger on particles that pass through a small device under test, leading to inefficient data taking. These issues can be solved by adding TelePix2 as a timing and flexible region of interest trigger layer. TelePix2 is a full scale HV-CMOS chip based on the successful small scale prototype TelePix. The DAQ system and the sensors performance featuring efficiencies above 99 % and a time resolution of 3.844(2) ns are presented. The integration into EUDAQ2 and the AIDA-TLU to seamlessly work in the test beam environment as well as into the analysis chain is described. First successful use cases are highlighted to conclude that TelePix2 is a well-suited timing and trigger layer for test beams

hep-ex↗

arXiv2025

The H2M Monolithic Active Pixel Sensor -- characterizing non-uniform in-pixel response in a 65 nm CMOS imaging technology

The high energy physics community recently gained access to the TPSCo 65 nm ISC (Image Sensor CMOS), which enables a higher in-pixel logic density in monolithic active pixel sensors (MAPS) compared to processes with larger feature sizes. To explore this novel technology, the Hybrid-to-Monolithic (H2M) test chip has been designed and manufactured. The design followed a digital-on-top design workflow and ports a hybrid pixel-detector architecture, with digital pulse processing in each pixel, into a monolithic chip. The chip matrix consists of 64$\times$16 square pixels with a size of 35$\times$35 um2, and a total active area of approximately 1.25 um2. The chip has been successfully integrated into the Caribou DAQ system. It is fully functional, and the measured threshold dispersion and noise agree with the expectation from front-end simulations. However, a non-uniform in-pixel response related to the size and location of the n-wells in the analog circuitry has been observed in test beam measurements and will be discussed in this contribution. This asymmetry in the pixel response, enhanced by the 35 um pixel pitch - larger than in other prototypes - and certain features of the readout circuit, has not been observed in prototypes with smaller pixel pitches in this technology.

physics.ins-det↗

arXiv2025

Transient studies using a TCAD and Allpix Squared combination approach

The goal of the TANGERINE project is to develop the next generation of monolithic silicon pixel detectors using a 65 nm CMOS imaging process, which offers a higher logic density and overall lower power consumption compared to previously used processes. A combination of Technology Computer-Aided Design (TCAD) and Monte Carlo (MC) simulations is used to understand the physical processes within the sensing element and thus the overall performance of the pixel detector. The response of the sensors can then be tested in laboratory and test beam facilities and compared to simulation results. Transient simulations allow for studying the response of the sensor as a function of time, such as the signal produced after a charged particle passes through the sensor. The study of these signals is important to understand the magnitude and timing of the response from the sensors and improve upon them. While TCAD simulations are accurate, the time required to produce a single pulse is large compared to a combination of MC and TCAD simulations. In this work, a validation of the transient simulation approach and studies on charge collection are presented.

physics.ins-det↗