We present a cost-effective, fully reconfigurable time-resolved single-photon detection system in which the active quenching circuit (AQC) is implemented using the tri-state gates of a field-programmable gate array (FTG-SPAD). By embedding the AQC within the FPGA, interfacing with discrete avalanche photodiodes (APDs), this design decouples the detector front end from the quenching and data processing circuits, enabling a rapid initialization of APDs into Geiger-mode single-photon detection. It has the advantages of firmware-level reconfigurability at fine temporal and spatial granularity, and flexibility to interchange APDs with different structures or operation wavelength for diverse applications. In addition to the quenching circuit, the FPGA back end implemented a time-to-digital converter (86.2 ps least significant bit), a 32-bit counter, and communication modules, forming a complete reconfigurable system for time-correlated single-photon counting. The FTG-SPAD with APDs of 23 µm diameter demonstrates a dark count rate of ∼12.2 cps at 3.2 V excess bias, a peak photon detection probability of 29.9% at 460 nm, and a single-photon time resolution of ∼234.6ps (FWHM) at 475 nm. These results verify that promising time-resolved single-photon detection can be achieved within this FPGA-based architecture, aiming to be a cost-effective, compact, flexible single-photon detection platform.

This study presents a high-performance photon counting detector (PCD) for photon-counting computed tomography (PCCT) applications, addressing the critical challenge of pulse pile-up at high X-ray photon fluxes. The PCD is composed of a fast Lu1.8Y0.2SiO5:Ce (LYSO) scintillator with an epitaxial quenching resistor type silicon photomultiplier (EQR SiPM), which features a small microcell pitch of 10 & micro;m, a small active area of 0.52 & times; 0.52 mm(2) and high fill factor of 49%. It exhibits a rapid recovery time of 1.85 ns and high photon detection efficiency (PDE) greater than 30%, thus is able to achieve a high photon counting rate while retaining adequate high energy resolution (ER). In order to further mitigate pile-up effects, a pole-zero cancellation (PZC) circuit was implemented to narrow pulse width from 46.1 ns to 19.5 ns (FWHM) along with a pileup recovery algorithm (PRA) for pileup pulse discrimination. Experimental results demonstrate an ER of 37.7%(FWHM) at 59.5 keV (Am-241, 24 kBq) and a maximum count rate (CR) of 102.7 Mcps/mm(2) under 80 kV X-ray irradiation. This CR was twice as high as that obtained without using PRA methods. These preliminary results indicate the feasibility of EQR-silicon photomultiplier (SiPM)-based scintillation PCDs in clinical PCCT. The results demonstrate the PRA method's efficacy in improving spectral performance under high flux conditions in a laboratory setting, though its clinical scalability remains challenging due to high computational demands.

To address the limitations of count rate and inter-pixel optical crosstalk in scintillator-based photon-counting CT, we present a high-count-rate X-ray photon-counting detector (PCD) composed of a fast LYSO scintillator array directly coupled to a custom epitaxial-quenching-resistor (EQR) silicon photomultiplier (SiPM) array. Each EQR SiPM element matches the 0.5 mm pitch of the pixelated scintillator and features a 10-mu m microcell pitch together with a fast recovery time of approximately 1.3 ns. By using readout electronics with a pole-zero cancellation (PZC) network, an X-ray scintillation pulse width of 17.8 ns was achieved. To further mitigate pulse pile-up at high photon fluxes, a digital pile-up recovery algorithm (PRA) was implemented. With the PRA, the detector reached a maximum count rate of 112 Mcps/mm2 under 80 kV X-ray irradiation-nearly double the performance without the PRA. The system also showed acceptable energy resolutions of 39.6% at 59.5 keV and 24.5% at 140 keV. Moreover, experiments revealed that inter-pixel optical crosstalk could be reduced from 26.6% to 6.6% by omitting the conventional resin coating on the EQR SiPM surface. These results demonstrate that the EQR-SiPM-based scintillation PCD offers a feasible and cost-effective alternative for clinical photon-counting CT detectors.

The performance of 4 × 4 array of one-dimensional position sensitive SiPM, intrinsic continuous Cap Resistive Layer Silicon Photomultipliers, with each element in size of 6.14 × 6.14 mm 2 , and total area of 24.6 × 24.6 mm 2 is reported in this paper. By using a specular anode-cathode signal multiplexing configuration, the number of readout channels is greatly reduced from 32 to 4 while retaining adequate high space and time resolution simultaneously. Under condition of a mean photoelectron number around 130 and the reverse bias voltage of 32 V, the position measurement error was 54.8 ± 38.3 μm, which accounted for 0.2% of the length of the CRL SiPM array. The position resolution was 392.9 ± 58.3 μm, and the time resolution was 205.3 ± 22.3 ps. A 10 × 10 LYSO array, with each element of 0.52 × 0.52 × 20 mm 3 , was clearly resolved in 1D by utilizing the natural radioactive radiation of lutetium element.

A Compton camera prototype was developed and characterized, utilizing a novel epitaxial-quenching-resistor Silicon Photomultiplier (EQR SiPM). The SiPM, with dimensions of 3.75 × 3.55 mm 2 and an effective area of 3.00 × 3.00 mm 2 , was configured into a 6 × 6 array. The array, with horizontal and vertical spacings of 0.58 mm and 0.82 mm respectively, formed a total size of 25.4 × 25.4 mm 2 . Both the scatterer and absorber were constructed from identical Lutetium-yttrium oxyorthosilicate (LYSO) crystal arrays, each comprising 24 × 24 crystals with dimensions of 0.98 × 0.98 × 10 mm 3 in 1.0 mm pitch. Coincidence events were acquired using an 8-channel data acquisition card (DAQ). Image reconstruction was performed using a filtered back-projection (FBP) algorithm with a Shepp-Logan filter, optimized for multi-graphics processing units (GPUs) processing. Calibration results demonstrated an energy resolution (Full Width at Half Maximum, FWHM) of 11.89% at 662 keV. Imaging experiments with a point source yielded an angular resolution of 8.95° (FWHM) at a scatterer-to-absorber distance of 50 mm. Additionally, successful imaging of a V-shaped tubing phantom confirmed the system's ability to accurately image distributed sources. The study also investigated how angular resolution and detection efficiency change with varying distances between the two detector layers. The results from Monte Carlo simulations demonstrated the system's ability to simultaneously image two distinct sources. Furthermore, the findings suggest that the current system's energy resolution is the main factor constraining the overall angular resolution. Future work will focus on optimizing the system design, including studying the effects of temperature and bias on SiPM gain, to enhance the camera's performance for various applications.

Position sensitive silicon photomultipliers that utilize an intrinsic continuous resistive layer (CRL SiPMs) for charge division are reviewed, and new developments of one-dimensional (1D) CRL SiPMs are reported. This study compares and analyzes the position and timing characteristics of three 1D CRL SiPM configurations: square ring (SR) electrodes with microcell sizes of 15 μm and 20 μm, and a dual parallel side strip (DPSS) electrode with a 10 μm microcell size. The position resolution degrades as microcell size increases, whereas the position measurement error remains independent of microcell size. The larger measurement error observed in the 10 μm device is caused by reversed pulses rather than microcell size. At the mean photoelectron numbers of 230 for the 10 μm and 15 μm devices and 240 for the 20 μm device, the average position resolutions are 72.6 ± 13.6 μm, 128.7 ± 20.1 μm, and 196.2 ± 20.2 μm, position measurement errors are 79.8 ± 57.0 μm, 32.0 ± 24.0 μm, and 31.6 ± 26.4 μm, the time resolutions are 165.8 ± 111.2 ps, 96.0 ± 33.2 ps, and 198.0 ± 112.3 ps, respectively. Moreover, the SR structure exhibited better time resolution due to the shortest charge transmition path. Compared to the tetra lateral and SR structure 2D CRL SiPM, the orthogonal configuration of two 1D CRL SiPMs can eliminate electrode-induced barrel distortion in scintillation imaging detection, and acquire depth information of interaction (DOI). As a result, the 1D CRL SiPM with SR collection electrodes has an advantage for application in scintillation detection where high 3D space and timing resolution are needed.

The design and fabrication of backside-illuminated photodetectors still face challenges in achieving full-spectrum detection ranging from ultraviolet to near-infrared wavelengths, a low leakage current, and mass- and cost-effective production. To overcome these difficulties, we present the first backside-illuminated ferroelectric-induced avalanche photodiode in which the silicon substrate is completely removed from the incident surface and a transparent organic ferroelectric-induced carrier accumulation layer for passivation is processed with a fixed charge density of - 3.75 × 1011 cm-2. This device demonstrates high external quantum efficiency exceeding 45% over the range of 300-950 nm, reaching 70% at 905 nm, while maintaining an ultralow leakage current of approximately 10 pA. The organic ferroelectric passivation method employed is compatible with low-cost chip-on-board packaging, offering a superior solution for broadband photodetector applications.

ACTIVE 7 MAX is a compact benchtop preclinical PET scanner dedicated to high sensitivity and high-resolution imaging of small animals. This study evaluated the performance of the ACTIVE 7 MAX system using the National Electrical Manufacturers Association NU 4-2008 standard protocol. The scanner consists of four rings, each containing 14 detector modules. Each detector module is made up of a 16 × 16 array of lutetium yttrium orthosilicate (LYSO) scintillation crystals, with each crystal measuring 1.47 × 1.47 × 10.0 mm3. The crystal array was coupled to a novel 6 × 6 epitaxial-quenching-resistor silicon photomultiplier (EQR SiPM) array. Flood images and energy resolution were obtained by irradiating each detector module with a 18F source. The average energy resolution for the 56 detector modules in the system was found to be 11.46

The characteristics of one-dimensional (1D) position sensitive SiPM with an intrinsic continuous cap resistive layer (CRL) and its performance in acquiring two-dimensional (2D) radiation imaging are reported in this paper. The device, with an active size of 6.14 mm x 6.14 mm, demonstrated the position measurement error of 32.0 +/- 24.0 mu m without correction, which accounted for 0.5% of the length of the SiPM at a mean response photoelectron number around 230 and the reverse bias voltage of 40 V. Under the same condition, it demonstrated a position resolution of 128.7 +/- 20.1 mu m and a time resolution of 96.0 +/- 33.2 ps. A 3D scintillation detector for acquiring 2D radiation imaging with depth information of interaction (DOI) is proposed by implementing two 1D CRL SiPMs in a perpendicular orientation on the two ends of a scintillator. Using this configuration, the 2D imaging of a pixelated 10 x 10 lutetium yttrium orthosilicate (LYSO) array, with each element having a volume of 0.52 mm x 0.52 mm x 20 mm, was successfully resolved by utilizing the natural radioactive radiation of lutetium element in LYSO without distortions at the edges and corners.

Low-gain avalanche detectors (LGADs) are promising candidates for 4-D tracking detectors in future high-energy physics (HEP) experiments, offering high position and time resolution. However, conventional pixel array LGADs suffer from large dead areas between pixels and require a large number of readout channels, resulting in poor spatial resolution and high cost. In this article, we present a 1-D position-sensitive LGAD (1-D PS-LGAD) based on dc coupling and a resistive charge division mechanism. The 1-D PS-LGAD features two cathodes and one anode, with 2-D position coordinates obtained by cross-placing two 1-D PS-LGADs. With an active thickness of 50 $\mu \text{m}$ and an active area of $2.7\times2.7$ mm, a 1-D PS-LGAD demonstrated an average position measurement error (PME) of 32.2 ± 35.4 $\mu \text{m}$ , accounting for 1.2% of the side length of the active area with a 100% fill factor. The coincidence time resolution and position resolutions were 8.8 ps and 22.5 $\mu \text{m}$ , respectively, at the center of the device for incident 532 nm light with a spot diameter of approximately 25 $\mu \text{m}$ and a mean photoelectron number (MPEN) of 6000 when the reverse voltage was 620 V.

The performance of an active-quenching single-photon avalanche diode (SPAD) array that is based on the tri-state gates of a field programmable gate array (FPGA) is presented. The array is implemented by stacking a bare 4 × 4 N-on-P SPAD array on a bare FPGA die, and the electrodes of the SPAD pixels and the I/O ports of the FPGA are connected through wire bonding within the same package. The active quenching action on each SPAD pixel is performed by using the properties of the tri-state gates of the FPGA. Digital signal processing, such as pulse counters, data encoders, and command interactions, is also performed by using the same FPGA. The breakdown voltage of the SPAD pixels, with an active area of 60 μm × 60 μm, is 47.2–48.0 V. When the device is reverse biased at a voltage of ~50.4 V, a response delay of ~50 ns, a dead time of 157 ns, a dark count rate of 2.44 kHz, and an afterpulsing probability of 6.9% are obtained. Its peak photon detection probability (PDP) reaches 17.0% at a peak wavelength of 760 nm and remains above 10% at 900 nm. This hybrid integrated SPAD array is reconfigurable and cost effective.

Silicon photomultiplier (SiPM) is one of the best choices for Positron Emission Computed Tomography (PET) detectors due to its excellent properties. In order to achieve high fill factor of SiPM tile for PET detector, we have developed a small “dead zones” packaging technology based on lithography, SU-8 photoresist and conductive silver paste rather than Au wire bonding. It was simple, cost-effective to form a small “dead” zone as small as 60 µm of packaging SiPMs for mass production, the ratio of chip area to packaged device area is as high as 0.9037. The preliminary yield reached 49.8%.

北京师范大学新器件实验室（NDL）一直致力于研制结构紧凑、工艺相对简单的外延电阻淬灭型硅光电倍增器（silicon photomultiplier with epitaxial quenching resistor, EQR SiPM）。近期为了满足硅光电倍增器（silicon photomultiplier, SiPM）在核医学成像方面的需要，NDL通过优化器件设计和制作工艺，成功研制出微单元尺寸为15μm、有效面积为9 mm~2的EQR SiPM。相较以往同类型器件，实现了器件暗计数率（dark count rate, DCR）的进一步降低同时保持了较高的光子探测效率（photon detection efficiency, PDE），在环境温度为20℃、过偏压为7 V时，DCR的典型值为226 kHz/mm~2、峰值PDE为46%。另外，为了进一步提升EQR SiPM的动态范围，NDL还研制出微单元尺寸为6μm、有效面积为9 mm~2、微单元数目为244 720的EQR SiPM，在环境温度为20℃、过偏压为7 V时，DCR的典型值为240 kHz/mm~2、峰值PDE为28%，其较大的动态范围特别适合高能宇宙射线的测量、强子量能器等应用。

We study the radiation effects of the Low Gain Avalanche Detector (LGAD) sensors developed by the Institute of High Energy Physics (IHEP) and the Novel Device Laboratory (NDL) of Beijing Normal University in China. These sensors have been irradiated at the China Institute of Atomic Energy (CIAE) using 100 MeV proton beam with five different fluences from 7x10(14) n(eq)/cm(2) up to 4.5x10(15) n(eq)/cm(2). The result indicates that the effective doping concentration in the gain layer decreases with the increase of irradiation fluence, as expected by the acceptor removal mechanism. By comparing data and model gives the acceptor removal coefficient c(A)=(5.52 +/- 0.58)x10(-16) cm(2), which shows the NDL sensor has fairly good radiation resistance. The time resolution of the sensors after irradiation was measured at (-30 +/- 2) degrees C.

Conventional isothermal annealing is helpful to performance recovery of radiated silicon detector; but it is hard to be applied in vast well-installed detectors in high energy physics experiments. This summary investigated an in-situ annealing technique that employs joule heat of the intrinsic p-n junction to mitigate radiation damage effect on low gain avalanche detector (LGAD). The LGADs are 2 × 2 array with each pad of 1.3 mm × 1.3mm active area and were irradiated by 2 MeV proton to an equivalent fluence of 5×10 14 neq/cm 2 . After being applied a forward current of 1 A lasting for 27 s, which reached a peak annealing temperature around 180°C, the leakage current, the full depletion voltage and the gain of the radiated LGADs were restored partially. The leakage current was decreased about an order of magnitude, the full depletion voltage increased from 20 V to 85 V, and the gain increased from about 6 to 11 at 400 V. This simple in-situ annealing method is possible to implement during the service period of the detectors, thus prolongs their lifetime in harsh irradiation environment.

Low Gain Avalanche Detectors (LGAD) are silicon particle sensors with intrinsic gain through a thin p-type multiplication layer inserted between n-type implant and p-type bulk. The first prototype of LGAD sensors in China have been developed at the Institute of High Energy Physics (IHEP) of Chinese Academic Sciences and the Novel Device Laboratory (NDL) of Beijing Normal University. With an active thickness of 33 μm, good breakdown performance, gain > 10, these sensors have reached jitter contribution of 10 ps to timing resolution with laser tests.

The performances of Low Gain Avalanche diode (LGAD) sensors from a neutron irradiation campaign with fluences of 0.8 x 10^15, 15 x 10^15 and 2.5 x 10^15 neq/cm2 are reported in this article. These LGAD sensors are developed by the Institute of High Energy Physics, Chinese Academy of Sciences and the Novel Device Laboratory for the High Granularity Timing Detector of the High Luminosity Large Hadron Collider. The timing resolution and collected charge of the LGAD sensors were measured with electrons from a beta source. After irradiation with a fluence of 2.5 x 10^15 neq/cm2, the collected charge decreases from 40 fC to 7 fC, the signal-to-noise ratio deteriorates from 48 to 12, and the timing resolution increases from 29 ps to 39 ps.

A High-Granularity Timing Detector (HGTD) is proposed based on the Low-Gain Avalanche Detector (LGAD) for the ATLAS experiment to satisfy the time resolution requirement for the up-coming High Luminosity at LHC (HL-LHC). We report on beam test results for two proto-types LGADs (BV60 and BV170) developed for the HGTD. Such modules were manufactured by the Institute of High Energy Physics (IHEP) of Chinese Academy of Sciences (CAS) collaborated with Novel Device Laboratory (NDL) of the Beijing Normal University. The beam tests were performed with 5 GeV electron beam at DESY. The timing performance of the LGADs was compared to a trigger counter consisting of a quartz bar coupled to a SiPM readout while extracting reference SiPM by fitting with a Gaussian function. The time resolution was obtained as 41 ps and 63 ps for the BV60 and the BV170, respectively.

The thickness of the high-resistivity layer (activelayer) is a crucial factor affecting the timing resolution oflow gain avalanche diodes (LGADs). We studied the poten-tial improvement of the timing resolution of charge particlesbased on LGADs with different active layer thicknesses. TheInstitute of High Energy Physics (IHEP) and the Novel DeviceLaboratory (NDL) jointly designed two types of LGAD sensorswith active layer thicknesses of 33 and 50μm. The timingresolution is given by contributions from the time walk, jitter,and nonuniform charge deposition (Landau term). The jitterand the Landau term contributions in the timing resolution areextracted by the combination of the90Srbeta source test andthe picosecond laser test. The Landau contribution is found tobe the dominant contribution for both types of LGAD sensors,and the Landau contribution of the 33μm sensor is lowerthan that of the 50μm sensor. Based on the experimentalresults, we perform the simulation for thinner active layer LGADwith the WeightField2 program. The timing resolution can befurther improved by reducing the active layer thickness from33 to 20μm.

A two-dimensional (2D) square-bordered position-sensitive (PS) silicon photomultiplier (SiPM) toward distortion-free performance with high spatial resolution is reported in this letter. The device, based on SiPM technology of an epitaxial quenching resistor, contains a central cap resistive region enclosed by a narrow square-shaped metal ring contact located at the surface periphery. Four small output metal pads are connected to the metal ring at each corner to read out signal charges. With an active area of 6.14 mm x 6.14 mm, the PS-SiPM demonstrated an average position measurement error (PME) of 86.9 μm without correction, which accounted for 1.4% of the side length of the active area. The average position resolutions were demonstrated to be ~130.7 μm and ~135.6 μm in the X and Y directions, respectively, for incident light with a spot diameter of 80 μm and a mean photoelectron number (MPEN) of ~600. In addition, an intrinsic radioactive-light image of a pixelated 12 × 12 lutetium-yttrium oxyorthosilicate (LYSO) array with each element volume of 0.475 × 0.475 × 6 mm 3 was clearly resolved by the 2D square-bordered PS-SiPM.