Online program Overview Session: NSS-28

Abstract

Abstract — Metal halide perovskites are promising for direct X‑ray detection, but phase impurity in conventional quasi‑2D systems limit device performance. Here we report a methylpiperazinium (MPZ) based quasi‑2D perovskitoid, (mpz)₅Pb₈Br₂₆·2H₂O. The crystal features a unique segmented architecture: four corner‑sharing PbBr₆ octahedra form 3D‑like conduction blocks, separated by 2D spacer regions where MPZ²⁺. This design simultaneously achieves a high mobility‑lifetime (μτ) product of 6.1×10^-3 cm² V^-1. A direct X‑ray detector fabricated in the out‑of‑plane configuration exhibits a sensitivity of 33.18 μC Gy^-1 cm^-2 and a detection limit of 6.2 nGy s^-1, representing a record among lead‑based quasi‑2D perovskites. The successful construction of quasi-2D single crystals provides a versatile platform for high-performance optoelectronics, proving its efficacy for applications spanning photodetection, solar energy conversion, and light-emitting devices even under the most rigorous material requirements

Abstract

Graphene has emerged as a promising material for next-generation sensing systems due to its exceptional carrier mobility, low electronic noise, mechanical flexibility, and high electrical conductivity. In this work, we present the design and evaluation of graphene strip arrays for radiation detection applications. The detector architecture employs segmented graphene sensing strips integrated connected to low-noise front-end electronics to investigate radiation-induced signal generation, spatial sensitivity, and charge transport characteristics. Conventional semiconductor radiation detectors often face challenges associated with fabrication complexity, radiation damage, and limitations in scaling toward lightweight and flexible detection systems. Graphene-based detectors provide an alternative approach with potential advantages in fast signal response, compact integration, and scalable fabrication.

The proposed detector consists of patterned graphene strip arrays fabricated on an silicon substrate with optimized strip geometry and differential signal readout. Radiation-induced charge variations are detected through low-noise charge amplification and signal conditioning electronics. Preliminary experimental characterization demonstrates measurable detector response under controlled irradiation conditions and stable electrical operation across multiple bias configurations. The segmented strip geometry enables position-sensitive radiation detection and supports scalability toward larger-area detector systems. The presented work demonstrates the feasibility of graphene strip arrays as compact, low-noise radiation detectors for advanced nuclear science and charged-particle instrumentation.

Abstract

A silicon electron multiplier (SiEM) that achieves internal multiplication without a dedicated doped gain layer is demonstrated. The device employs a two-stage mesa-type architecture in which impact ionization occurs in a localized high-field region formed by geometric field crowding within a cylindrical mesa. A buried gate electrode independently controls carrier injection into the multiplication region. Devices were fabricated in a sub-micron CMOS process line. The structure consists of an injection stage and a multiplication stage. The injection stage uses a buried polysilicon gate to electrostatically steer carriers toward the center of the pixel, while the multiplication stage confines the high electric field within a constricted cylindrical mesa. Three-terminal operation enables independent control of multiplication through the gate bias. Electro-optical measurements were performed using 905 nm illumination with an absorption depth of approximately 30–35 µm in silicon. The devices exhibit a multiplication factor exceeding 100 for |Vgate| < 50 V. Scaling of the cylindrical mesa geometry shows that smaller diameters and reduced mesa height lower the bias required for multiplication. For example, reducing the mesa diameter from 3.0 µm to 1.6 µm increases the multiplication factor from approximately 1.5 to greater than 3 at |Vgate| = 40 V, and gains exceeding 400 are obtained at |Vgate| ≈ 50 V. Temperature measurements from −40 °C to 40 °C show a multiplication sensitivity of dVgate/dT = 24–30 mV/°C at constant gain (M = 10). This value is significantly smaller than those typically reported for gain-layer detectors. These results demonstrate geometry-defined impact ionization with electrostatically controlled carrier injection. The proposed SiEM provides a design framework for radiation-tolerant silicon detectors with internal multiplication.

Abstract

Thin segmented silicon sensors have attracted increasing interest for beam monitoring and microdosimetry in emerging radiotherapy modalities such as FLASH and spatially fractionated radiotherapy, owing to their excellent temporal response, high spatial precision, and robustness. In this study, thin planar silicon sensor manufactured by Fondazione Bruno Kessler and implementing different electrode-isolation strategies were investigated through electrical characterization and irradiation tests under ultra-high dose rate electron beams. The investigated devices included sensors with two different trench technologies, which were compared with segmented silicon detectors based on p-stop and Junction Termination Extension isolation techniques. Electric characterization was performed through current-voltage and capacitance-voltage measurements to extract relevant operational parameters. In addition, the detectors were exposed to electron beams delivered by a LINAC at dose-per-pulse values of 2.2 Gy in a 4µs pulse. Preliminary results showed comparable electrical performance for all detector technologies, with leakage currents in the nanoampere range and stable operation up to 200 V bias voltage. Nevertheless, segmented sensor without trench isolation exhibited  deviations between collected charge and pad areas ratios, suggesting geometry-dependent contributions to charge collection, likely related to perimeter effects. Ongoing studies aim to evaluate whether trench isolation mitigates these effects and improves sensitive volume definition, as well as to assess the radiation hardness of the proposed detector technologies.

Abstract

In this work, a novel 3D column-trench detector based on a 30 $\mu $m thick high-resistivity P-type epitaxial silicon is proposed and experimentally validated. The detector is fabricated on the standard CMOS process platform of the Institute of Microelectronics, Chinese Academy of Sciences (IMECAS), featuring a hybrid 3D configuration that combines N-type column electrodes and P-type strip trench electrodes. Electrical characterizations performed on single-pixel device with central N-type electrode demonstrate that the proposed detector achieves a low leakage current of 0.3 nA and a small capacitance of 0.3 pF under a reverse bias voltage of 30 V. According to the analysis of current-voltage (IV) and capacitance-voltage (CV) characteristics, the device exhibits a full depletion voltage of approximately 3 V and a high breakdown voltage up to 130 V. In addition, the device design, layout, and electrical performance of the 3DCTS are systematically elaborated in this paper. The electrical test results indicate that the proposed device possesses promising application prospects in high-energy physics experiments, medical imaging, and space radiation detection.

Abstract

The transition from 6-inch to 8-inch high-resistivity silicon wafer processing has been implemented for the fabrication of large-area pixel sensors for photon-counting applications. The upgraded production line enables a doubling of usable wafer area compared to conventional 6-inch wafers, allowing either larger sensor formats or increased number of sensors per wafer. Prototype 8- inch wafers were processed using stepper lithography with stitching to realize multiple sensor layouts compatible with Medipix3, Timepix3 and Timepix4 readout ASICs. Electrical characterization was performed prior to under-bump metallization (UBM) and flip-chip assembly. Leakage currents at a reverse bias of -300 V were compared with reference data from 6-inch production batches of 500 μm thick sensors. An approximately 60% increase in leakage current for sensors fabricated on 8-inch wafers is attributed to a non-uniform radial resistivity distribution observed in the prototype 8-inch material.

8-inch wafer processing has been successfully demonstrated for silicon pixel sensor fabrication. The process is compatible with existing 6-inch technology and supports large-area sensor production. Although an increased leakage current was observed due to resistivity non-uniformity, the results confirm the feasibility of the approach. Future 8-inch production wafers are expected to have an improved resistivity profile, which is anticipated to reduce the leakage current and improve sensor uniformity.

Abstract

This contribution will present the first results on the radiation resistance of p-in-n Low-Gain Avalanche Diodes (nLGAD) produced at Fondazione Bruno Kessler (FBK), where signal multiplication is achieved through a high-concentration n-type dopant implant. The sensors are fabricated on thin epitaxial n-type substrates with an active thickness of 55 µm and incorporate a redesigned p⁺⁺ ohmic contact and n⁺ gain layer, optimized to account for dopant activation and diffusion effects. Fourteen wafers were produced, exploring different implant depths, diffusion profiles, and employing two n-type dopants, Phosphorus and Arsenic. These devices provide a unique platform to study the donor removal mechanism at concentrations of ~10¹⁶ atoms/cm³, offering key input for the development of radiation-hard p⁺–n⁺ compensated LGADs for operation at extreme fluences. We will present the first results on nLGAD sensors irradiated with neutrons in the fluence range 10¹⁴–10¹⁵ n_eq/cm². The characterization pre- and post-irradiation focuses on the evolution of gain and charge collection, providing a first direct assessment of the radiation hardness of nLGAD in this fluence regime. The study of the radiation resistance of the gain layer will be further supported by the characterization of the n⁺ implant, through the characterization of irradiated Van der Pauw structures.

Abstract

Recent progress in sensor technology has paved the way for high-resolution 4D-tracking silicon detectors capable of simultaneously measuring position and time of passage of charged particles. This is achieved through the innovative concepts of Low Gain Avalanche Diodes (LGAD) and Resistive Silicon Detectors (RSD). While standard LGADs aim at excellent temporal resolution, the RSD design also achieves high spatial resolution through signal sharing. This contribution presents the latest advancements in the DC-coupled RSD (DC-RSD) design, which utilizes trenches for cell isolation and signal sharing control. A major milestone of the 2026 campaign is the integration of the FAST3 ASIC, a custom-designed chip specifically optimized for high-precision timing measurements with LGAD-based sensors. For the first time, this readout electronics is employed to characterize the performance of DC-RSD sensors in a test beam environment before and after radiation exposure. We will present the results of an experimental campaign conducted on DC-RSD sensors irradiated at fluences 2×10¹⁴ and 4×10¹⁴ neq/cm². These measurements will represent the first test beam characterization performed on irradiated DC-RSD sensors. The analysis focuses on the evolution of timing and spatial resolution as a function of fluence, comparing the performance of the FAST3 chip with previous readout solutions. The results, obtained at the DESY and CERN test beam facilities, offer insights into the radiation hardness and robustness of the DC-RSD principle.