Silicon detectors have been a cornerstone of high-energy physics experiments for decades. Standard LGAD technology provides excellent time resolution, but as pixel size shrinks, the number of readout channels grows, increasing power consumption and material budget. Resistive LGADs solve this by allowing large pixels without sacrificing spatial resolution. This work aligns with active development of radiation-hard detectors for future colliders: related studies in our archive also cover silicon detectors, nuclear clocks on a chip, and gravitational wave searches, but this paper stands out for its focus on confining the signal to a single pixel using a novel electrode geometry and oxide trenches.
The new detector design was developed using full three-dimensional TCAD (Technology Computer-Aided Design) simulations in the Synopsys® Sentaurus package. Structures with DC-coupled electrodes of various geometries were modeled: cross-shaped electrodes with long arms and small circular contacts, supplemented by oxide trenches that interrupt the resistive layer between electrodes. The influence of trench length and contact resistance on signal confinement was investigated. To assess post-irradiation behavior, the latest radiation damage model developed in Perugia was used. As a test, the passage of a minimum ionizing particle (MIP) through the central pixel was simulated, after which the current distribution in the resistive plane and the charge collected by each electrode were analyzed.
Simulations showed that cross-shaped electrodes with long arms confine up to 97% of the signal to a single pixel, but when a particle hits the tip of an electrode, the coordinate reconstruction error reaches hundreds of micrometers. Using small circular electrodes minimizes this error but does not confine the signal by itself. The solution was to add oxide trenches connecting adjacent electrodes: they interrupt the resistive layer and prevent the signal from spreading to neighboring pixels. A key condition is that the trenches must run from electrode to electrode; otherwise, the signal leaks through. With high contact resistance, the signal also bypasses the electrodes and leaks into neighboring pixels, so low contact resistance is critical. Simulations after irradiation with fluences up to several units of $10^{15}$ neutron equivalents per square centimeter showed that the fraction of charge collected by each electrode remains nearly constant, although the total charge decreases due to carrier trapping. This indicates that the resistive layer is weakly affected by radiation, thanks to its high peak doping concentration and shallow depth.
This work demonstrates that DC-coupled resistive LGADs with oxide trenches can provide a uniform response across the entire detector area, eliminating the main drawback of previous AC-coupled versions. Unlike related studies that focus on general silicon detector characteristics or other technologies, this work proposes a specific engineering solution for confining the signal to a single pixel, validated by full 3D simulations. This paves the way for large-pixel detectors with high spatial and temporal resolution for future experiments, such as tracker upgrades at the Large Hadron Collider.
The first batch of DC-RSDs was produced by Fondazione Bruno Kessler in November 2024, and characterization has already begun: laboratory tests and a test beam at DESY in December 2024, with another scheduled for March 2025. These results will validate the simulation predictions and, if necessary, refine the trench and electrode geometry. Future work may also optimize contact resistance and study detector behavior at even higher fluences, up to levels expected at future high-luminosity colliders.
DC-coupled resistive LGAD technology will directly impact the development of trackers for future high-energy physics experiments, especially in high-radiation environments such as the HL-LHC or future electron-positron colliders. It may also find applications in medical imaging and detectors for space experiments, where high spatial resolution is required with a limited number of channels.
Immediate next steps include completing the characterization of the first DC-RSD batch on test beams, comparing experimental data with TCAD simulation results, and, if necessary, adjusting the design to achieve an optimal balance between signal confinement and coordinate reconstruction accuracy.
For detector physics, a key unresolved problem remains achieving high spatial and temporal resolution simultaneously with minimal material budget and power consumption under extreme radiation. This work contributes to solving this problem by showing that DC-coupled resistive LGADs with oxide trenches can maintain response uniformity after irradiation, which is critical for long-term detector operation.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This paper presents results from 3D TCAD simulations of resistive LGADs with DC coupling, aimed at confining the signal within a single pixel. Electrode geometries and oxide trenches were studied, showing that round electrodes with trenches between them confine the signal, and that irradiation has little effect on the resistive layer.
Where its strength is
The strength of this work lies in combining full 3D simulation with a concrete engineering solution (oxide trenches connecting electrodes) that preserves timing resolution and limits signal leakage, which is important for radiation-hard detectors.
Where it could go next
Worth trying
Why this may matter
Resistive LGADs with improved signal confinement could become a key component of tracking systems at future colliders, providing high spatial and temporal resolution with fewer readout channels and, consequently, lower power consumption and material budget.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.52, against a usual 0.64. It looks like few have drilled nearby.
A spatial resolution of 15 μm with a pixel pitch of 450 μm means the detector determines a particle's position 30 times more precisely than the pixel size itself. That's like being able to pinpoint where a ball lands on a tennis court using only a grid with cells the size of a car.