arXiv subjects

Tomoka Imamura

Publications and source records attributed to Tomoka Imamura.

4 recordsLinked to original sources

arXiv2026

Systematic Investigation of Acceptor Removal in HPK LGADs with Modified Gain Layers

Low-Gain Avalanche Diodes (LGADs) are fast silicon sensors with internal charge multiplication and are key candidates for precision timing layers in future high-energy hadron colliders. Their operation in harsh radiation environments, however, is limited by acceptor removal in the gain layer, which reduces the active acceptor concentration and degrades the internal electric field required for avalanche multiplication. Improving the radiation tolerance of the gain layer is therefore essential for future 4D tracking applications. In this work, we investigated several LGAD prototypes produced in collaboration with Hamamatsu Photonics K.K. (HPK), featuring modified gain-layer designs, including oxygen-modified, carbon-implanted, and boron--phosphorus compensated structures. The sensors were studied after proton and reactor-neutron irradiation. Radiation tolerance was characterized using the acceptor-removal coefficient extracted from IV measurements and the operation voltage required to recover the timing performance after irradiation. The results show that carbon implantation is the only approach among those studied here that provides a clear improvement in radiation tolerance. In contrast, neither oxygen-related modification, including the Partially Activated Boron (PAB) approach, nor gain-layer compensation alone yields a significant improvement, and the compensated carbon-implanted structure shows no clear advantage over the carbon-only case. In addition, the acceptor-removal coefficient is found to depend on the irradiation particle type and energy.

physics.ins-det↗

arXiv2025

Results for pixel and strip centimeter-scale AC-LGAD sensors with a 120 GeV proton beam

We present the results of an extensive evaluation of strip and pixel AC-LGAD sensors tested with a 120 GeV proton beam, focusing on the influence of design parameters on the sensor temporal and spatial resolutions. Results show that reducing the thickness of pixel sensors significantly enhances their time resolution, with 20 $μ$m-thick sensors achieving around 20 ps. Uniform performance is attainable with optimized sheet resistance, making these sensors ideal for future timing detectors. Conversely, 20 $μ$m-thick strip sensors exhibit higher jitter than similar pixel sensors, negatively impacting time resolution, despite reduced Landau fluctuations with respect to the 50 $μ$m-thick versions. Additionally, it is observed that a low resistivity in strip sensors limits signal size and time resolution, whereas higher resistivity improves performance. This study highlights the importance of tuning the n$^{+}$ sheet resistance and suggests that further improvements should target specific applications like the Electron-Ion Collider or other future collider experiments. In addition, the detailed performance of four AC-LGADs sensor designs is reported as examples of possible candidates for specific detector applications. These advancements position AC-LGADs as promising candidates for future 4D tracking systems, pending the development of specialized readout electronics.

physics.ins-det↗

arXiv2024

Development of HPK Capacitive Coupled LGAD (AC-LGAD) detectors

The detectors with $\mathcal{O}$(10) $μ$m spatial resolution and $\mathcal{O}$(10) ps timing resolution construct powerful particle trackers for future hadron or lepton collider experiments. LGAD: Low-Gain-Avalanche-Diode is a semiconductor detector technology to improve timing resolution. Capacitive Coupled LGAD (AC-LGAD) detectors have been developed with HPK in order to meet both spatial and timing resolution requirements. Prototype samples with finely segmented electrodes have been produced and tested with various sensor fabrication parameters: doping concentrations, active thickness and electrode coupling capacitance. Timing resolution and signal height were evaluated with beta-ray. As a result, 100 $μ$m pitch pixel detector has been successfully developed achieving a good signal to noise ratio and 30 ps timing resolution for beta-ray. The detectors have to meet radiation hardness requirements as well. Radiation hardness of LGAD detectors has to be improved to use the detectors as inner trackers for hadron colliders. One of the major mechanisms of radiation damage of LGAD detectors is acceptor removal: shallow dopants in the gain layer of LGAD detectors are reduced by radiation damage. Two novel ideas are tested on effectiveness of delaying the acceptor removal.

physics.ins-det↗

arXiv2023

Development of AC-LGAD detector with finer pitch electrodes for high energy physics experiments

Low-Gain Avalanche Diode (LGAD) sensor is one of candidate sensors for the tracker at future hadron collider experiments. To use this sensor as a tracking detector, AC-LGAD sensor is being developed which has both timing and spatial resolutions. In high luminosity environments, good timing resolution (typically 30 ps) together with $\mathcal{O}$(10) ${\mathrmμ}$m spatial resolution helps to reduce pileup effect and reconstruct tracks correctly. By optimizing fabrication parameters, 80 ${\mathrmμ}$m pitch strip and 100 ${\mathrmμ}$m pitch pixel sensors are successfully produced. The signal height (MPV) was 39.26$\pm$0.08 mV and 128.9$\pm$3.3 mV, respectively, for penetrating $β$ particles. The observed 60% of signal reduction of the strip sensor is explained by a larger inter-electrode capacitance compared with the pixel sensor. In this paper, we present the performance of fine electrode pitch AC-LGAD sensors including the pulse height and cross-talk of pixel and strip type sensors evaluated using a $β$-ray source and the detection efficiency measured in an 800 MeV electron beam.

physics.ins-det↗