Single Photon Time Resolution Research Articles

A Novel Segmented SiPM Combined With Amplifiers on One Chip With Improved Single-Photon Timing Resolution in 0.35-μm CMOS

A Novel Segmented SiPM Combined With Amplifiers on One Chip With Improved Single-Photon Timing Resolution in 0.35-<i>μ</i>m CMOS

LinoSPAD2: an FPGA-based, hardware-reconfigurable 512×1 single-photon camera system.

We report on LinoSPAD2, a single-photon camera system, comprising a 512×1 single-photon avalanche diode (SPAD) front-end and one or two FPGA-based back-ends. Digital signals generated by the SPADs are processed by the FPGA in real time, whereas the FPGA offers full reconfigurability at a very high level of granularity both in time and space domains. The LinoSPAD2 camera system can process 512 SPADs simultaneously through 256 channels, duplicated on each FPGA-based back-end, with a bank of 64 time-to-digital converters (TDCs) operating at 133 MSa/s, whereas each TDC has a time resolution of 20 ps (LSB). To the best of our knowledge, LinoSPAD2 is the first fully reconfigurable SPAD camera system of large format. The SPAD front-end features a pitch of 26.2 μm, a native fill factor of 25.1%, and a microlens array achieving 2.3× concentration factor. At room temperature, the median dark count rate (DCR) is 80 cps at 7 V excess bias, the peak photon detection probability (PDP) is 53% at 520 nm wavelength, and the single-photon timing resolution (SPTR) is 50 ps FWHM. The instrument response function (IRF) is around 100 ps FWHM at system level. The LinoSPAD2 camera system is suitable for numerous applications, including LiDAR imaging, heralded spectroscopy, compressive Raman sensing, and other computational imaging techniques.

The time resolution improvement of Cherenkov-Radiator-Window Photomultiplier tube

The improvement of time resolution in time-of-flight positron emission tomography (TOF-PET) relies on the development of scintillation materials and photodetectors. With the introduction of Cherenkov TOF-PET, higher requirements have been placed on the intrinsic timing performance of photodetectors. Our team has proposed a Cherenkov Radiator Window Photomultiplier tube (CRW-FPMT) that uses the Cherenkov radiator directly as the light window, which eliminates the boundary between the scintillator and the photodetector for fast time resolution. This paper mainly discusses the factors influencing its time resolution and optimizes it to achieve a single photon time resolution of 27.2 ps.

Super-resolution non-line-of-sight imaging based on temporal encoding.

Non-line-of-sight (NLOS) imaging techniques have the ability to reconstruct objects beyond line-of-sight view, which would be useful in a variety of applications. In transient NLOS techniques, a fundamental problem is that the time resolution of imaging depends on the single-photon timing resolution (SPTR) of a detector. In this paper, a temporal super-resolution method named temporal encoding non-line-of-sight (TE-NLOS) is proposed. Specifically, by exploiting the spatial-temporal correlation among transient images, high-resolution transient images can be reconstructed through modulator encoding. We have demonstrated that the proposed method is capable of reconstructing transient images with a time resolution of 20 picoseconds from a detector with a limited SPTR of approximately nanoseconds. In systems with low time jitter, this method exhibits superior accuracy in reconstructing objects compared to direct detection, and it also demonstrates robustness against miscoding. Utilizing high-frequency modulation, our framework can reconstruct accurate objects with coarse-SPTR detectors, which provides an enlightening reference for solving the problem of hardware defects.

Study experimental time resolution limits of recent ASICs at Weeroc with different SiPMs and scintillators

Medical applications, such as Positron Emission Tomography (PET), and space applications, such as Light Detection and Ranging (LIDAR), are in need of highly specialized ASICs. Weeroc, in collaboration with different partners, is highly involved in developing a new generation of front-end ASICs. In the context of a joined LIDAR project among Weeroc, CNES, and Airbus, Weeroc is working on the development of Liroc, an ASIC for space LIDAR application. Weeroc is also working on advancing ASICs for medical applications with Radioroc under development and intended to be used for PET applications. This study experimentally evaluates the time resolution limits of these ASICs in different configurations, with some of the most recent silicon photomultiplier (SiPM) technologies available on the market, coupled to different scintillation crystals. The best single-photon time resolution (SPTR) was achieved using FBK NUV-HD SiPMs with an FWHM of 90 ps with Liroc and 73 ps with Radioroc. Furthermore, the coincidence time resolution (CTR) of Radioroc was studied with different crystal sizes. Using a large LYSO:Ce,Ca crystal of (3 × 3 × 20 mm3) with Broadcom Near UltraViolet-Metal in Trench (NUV-MT) yields a CTR of 127 ps (FWHM). The best CTR of Radioroc was determined to 83 ps (FWHM) with Broadcom NUV-MT SiPMs coupled to LYSO:Ce,Ca (2 × 2 × 3 mm3)) from Taiwan Applied Crystal (TAC).

Photo-Trap: A low-cost and low-noise large-area SiPM-based pixel

The small sensitive area of commercial silicon photomultipliers (SiPMs) is often the main limitation for their use in experiments and applications that require large detection areas. Since capacitance, dark count rate and cost increase with the SiPM size, they are rarely found in sizes larger than 6 × 6 mm2. Photo-Trap combines a wavelength-shifter plastic, a dichroic filter and a standard commercial SiPM to build pixels of a few cm2. With this approach it can collect light over an area that can be ∼10–100 times larger than the area of a commercial SiPM, while keeping the noise, single-photoelectron resolution, power consumption and likely the cost of a single small SiPM. We developed four different proof-of concept pixels sensitive in the near UV band, the largest one being of 40 × 40 mm2. We characterized them through laboratory measurements and Geant4 simulations. The optical gain we measured with the prototypes went from ∼5 to ∼15, while the single-photon time resolution was of ∼3–5 ns FWHM. With the achieved performance Photo-Trap could be a competitive low-cost alternative for applications that require photosensors with large collection areas and low noise, such as dark matter experiments and optical wireless communication.

On timing-optimized SiPMs for Cherenkov detection to boost low cost time-of-flight PET

Objective. Recent SiPM developments and improved front-end electronics have opened new doors in TOF-PET with a focus on prompt photon detection. For instance, the relatively high Cherenkov yield of bismuth-germanate (BGO) upon 511 keV gamma interaction has triggered a lot of interest, especially for its use in total body positron emission tomography (PET) scanners due to the crystal’s relatively low material and production costs. However, the electronic readout and timing optimization of the SiPMs still poses many questions. Lab experiments have shown the prospect of Cherenkov detection, with coincidence time resolutions (CTRs) of 200 ps FWHM achieved with small pixels, but lack system integration due to an unacceptable high power uptake of the used amplifiers. Approach. Following recent studies the most practical circuits with lower power uptake (<30 mW) have been implemented and the CTR performance with BGO of newly developed SiPMs from Fondazione Bruno Kessler tested. These novel SiPMs are optimized for highest single photon time resolution (SPTR). Main results. We achieved a best CTR FWHM of 123 ps for 2 × 2 × 3 mm3 and 243 ps for 3 × 3 × 20 mm3 BGO crystals. We further show that with these devices a CTR of 106 ps is possible using commercially available 3 × 3 × 20 mm3 LYSO:Ce,Mg crystals. To give an insight in the timing properties of these SiPMs, we measured the SPTR with black coated PbF2 of 2 × 2 × 3 mm3 size. We confirmed an SPTR of 68 ps FWHM published in literature for standard devices and show that the optimized SiPMs can improve this value to 42 ps. Pushing the SiPM bias and using 1 × 1 mm2 area devices we measured an SPTR of 28 ps FWHM. Significance. We have shown that advancements in readout electronics and SiPMs can lead to improved CTR with Cherenkov emitting crystals. Enabling time-of-flight with BGO will trigger a high interest for its use in low-cost and total-body PET scanners. Furthermore, owing to the prompt nature of Cherenkov emission, future CTR improvements are conceivable, for which a low-power electronic implementation is indispensable. In an extended discussion we will give a roadmap to best timing with prompt photons.

Study on the time resolution limits of FPMT and SiPM under femtosecond laser

In the past decade, a type of micro-channel-plate based photomultiplier tubes (MCP-PMT) with fast-timing resolution, also called fast-timing PMT(FPMT), has attracted considerable attention in many fields for its single-photon detection capability, good timing performance and magnetic insensitivity. The Silicon Photo-multiplier (SiPM) is another kind of newly developed photodetector with comparable performance to the FPMT. More attention was paid to the single photon time resolution of the photodetectors. However, with the improvement of the temporal performance requirements of photodetectors, the time resolution limit of photodetectors determine the limits of time performance improvement, which worth investigating. In this manuscript, a femtosecond laser is used to calibrate the time resolution limit of FPMT and SiPM. The time resolution limit of FPMT is measured to be 480.4 fs. In addition, the temporal performance of FPMT from single photon to multi-photons under femtosecond laser is also investigated. The time resolution limit of SiPM is measured to be 2.68 ps.

Demonstration of a 25-picosecond single-photon time resolution with gaseous photomultiplication

Photosensitive gaseous detectors with a simple photoelectron multiplication mechanism of resistive plate chambers (RPCs) are expected to have both a large photocoverage and an excellent time resolution and to be low-cost. To demonstrate the time resolution of the RPC-based photodetectors, we built a prototype detector with a LaB6 photocathode. It was tested with a picosecond pulse laser and the intrinsic time resolution for single photons was measured to be 25.0±1.1 ps at a gain of 3.3×106.

NUV-HD SiPMs with metal-filled trenches

In this paper we present the performance of a new SiPM that is sensitive to blue light and features narrow metal-filled trenches placed in the area around the single-photon avalanche diodes (SPADs) that allow an almost complete suppression the internal optical crosstalk. In particular, we show the benefits of this technological upgrade in terms of electro-optical SiPM performance when compared to the previous technology which had only a partial optical screening between the SPADs. The most relevant effect is the much higher bias voltage that can be applied to the new device before the noise diverges. This allows to optimize and improve both the photon-detection efficiency and the single-photon time resolution. We also coupled the SiPMs to LYSO scintillators to verify the performance for possible application in Positron-Emission Tomography. Thanks to the better electro-optical features we were able to measure an improved coincidence time resolution. Furthermore, the optimal voltage operation region is substantially larger, making this SiPM more suitable for real system application where thousands of channels have to provide stable and reproducible performance.

Quenching Circuit Discriminator Architecture Impact on a Sub-10 ps FWHM Single-Photon Timing Resolution SPAD

In the field of radiation instrumentation, there is a desire to reach a sub-10 ps FWHM timing resolution for applications such as time-of-flight positron emission tomography, time-of-flight positron computed tomography and time-resolved calorimetry. One of the key parts of the detection chain for these applications is a single-photon detector and, in recent years, the first single-photon avalanche diode (SPAD) with a sub-10 ps timing resolution was presented. To reach such a timing resolution, the SPAD was read out by an operational amplifier operated in open-loop as a comparator. This paper presents a comparison between comparators and inverters to determine which type of leading-edge discriminator can obtain the best single-photon timing resolution. Six different quenching circuits (QCs) implemented in TSMC 65 nm are tested with SPADs of the same architecture and in the same operation conditions. This allows us to compare experimental results between the different QCs. This paper also presents a method to measure the SPAD signal slope, the SPAD excess voltage variation and simulations to determine the added jitter of different leading-edge discriminators. For some discriminator architectures, a cascode transistor was required to increase the maximum excess voltage of the QC. This paper also presents the impact on the single-photon timing resolution of adding a cascode transistor for a comparator or an inverter-based discriminator. This paper reports a 6.3 ps FWHM SPTR for a SPAD read out by a low-threshold comparator and a 6.8 ps FWHM SPTR for an optimized 1 V inverter using a cascode transistor for a higher excess voltage.

Comparative Single Photon Time Resolution Measurements of Commercial Silicon-Photomultipliers and a Specially Designed SiPM with High Accuracy in 0.35 µm Technology

In this study, we present highly accurate single photon time resolution (SPTR) measurements of proved commercial Silicon-Photomultiplier (SiPM) from Broadcom (AFBR-S4N44C013), KETEK (PM3350), OnSemi (FJ30035) and Hamamatsu (S13360-3050V) with similar dimensions for highly precise SPTR measurements. The principal objective of this project was to investigate the timing precision of SiPM, since they play a key role for users in application areas like time of flight positron emission tomography (TOF-PED). For the SPTR comparative measurements in this research, we used a high-precision measurement setup including a femtosecond laser (λ = 400 nm, pulse width = 70 fs) and an oscilloscope with a 10 GHz bandwidth and a sampling rate of 50 GS/s to keep the influence of the measurement setup on the SPTR as small as possible, so that we are able to measure the true SPTR of commercial SiPM. In order to filter out external noise, we present an offline analysis to get as close as possible to the intrinsic SPTR of each SiPM. Furthermore, this study presents a special designed 4 x 4 SiPM integrated into a 0.35 µm CMOS process. The CMOS SiPM consists of a moderately selected diode capacitance combined with a low grid capacitance leading to very short pulses with a peak width below 2 ns and a peak height of 30 mV at an excess bias voltage of 8 V, facilitating the acquisition without the requirement of a pre-amplifier. The final obtained SPTR results of the commercial SiPM showed values between 191 ps to 104 ps. For the 4 x 4 CMOS SiPM a SPTR of 40 ps was achieved. We also show that SPTR values can be improved by filtering out external noise by a subsequent offline analysis up to 55.5%.

A novel multi-anode MCP-PMT with Cherenkov radiator window

With the proposal of the road map of Time-of-Flight positron emission tomography (TOF-PET) with a Coincidence Time Resolution (CTR) of 10 ps by Paul Lecoq et al. in 2020, the technology based on TOF puts forward higher requirements on the performance of its core optical devices. In this manuscript, we developed a kind of Multi-Anode micro channel plate photomultiplier tube (MCP-PMT) based on Cherenkov radiator window. By using the Cherenkov radiator as the optical window of Multi-Anode MCP-PMT directly, the optical interface between the scintillator and the PMT window in conventional TOF-PET is eliminated, reducing light loss and further improve the time resolution of TOF-PET. The anode of this MCP-PMT can be split into a finely spaced array of collecting electrodes to achieve good positional sensitivity. In this paper, the single photon detection capability and time resolution of this kind of MCP-PMT are evaluated. The transit time spread (TTS) at single photon mode can reach 42.9 ps, and the TTS at multi photon mode is less than 10 ps. The CTR based on this kind of MCP-PMT is 156.7 ± 10.6 ps FWHM, which is equivalent to a position resolution of 23.5 ± 1.6 mm along a line of response (LOR). The performance uniformity of this kind MCP-PMT has also been calibrated.

Design improvement and characterization of SOI-based silicon-photomultiplier prototype

We designed and fabricated six new silicon-on-insulator silicon-photomultiplier (SOI-SiPM) prototypes with a SOI CMOS using 200-nm integrated-process technology. Each prototype consisted of sixty-four 30-μm microcells but had a different combination of quenching resistance (100 or 200 kΩ), cathode size, and guard-ring size. The observed breakdown voltage was 20.5–21.9 V with an operation range of 2.6–3.8 V; the measured gain was approximately 1–3 × 105. The measured time resolution with full excitation was 22.7 ps (FWHM); the single-photon time resolution was 246.3 ps. The photon spectrum showed clear photon-counting capability and the photo-detection efficiency was 8.1% (a four-fold improvement from the previous prototype). These results suggest that SOI-SiPM can be employed in a fully integrated monolithic pixel photon detector, which would be a useful sensor for positron emission tomography, Compton camera, or photon-timing applications.

Picosecond Timing Electronics for a DIRC-Like Detector at the Super Tau-Charm Facility

The DIRC-like time-of-flight detector (DTOF) at the Super Tau-Charm Facility (STCF) in China is a Cherenkov light detector that uses the TOF technique to identify charged particles. To achieve the expected target that provides a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\sigma \pi $ </tex-math></inline-formula> /K separation at 2-Ge/c momentum, a single-photon time resolution of better than 50 ps is required, while the contribution from electronics should be lower than 15 ps. To meet the requirements with high channel count integration, the timing electronics using leading-edge discrimination and field-programmable gate array (FPGA)-based time-to-digital converters (TDCs) are employed in the DTOF detector. This article reports the results of the first phase of project where the timing electronics with 128 channels has been constructed and its performance has been evaluated. Including the uncertainty of system clock distribution and synchronization, the intrinsic timing resolution of the electronics is better than 10-ps rms. Taking fast microchannel plate photomultiplier tubes (MCP-PMTs) as Cherenkov photodetectors and adopting time-over-threshold (TOT) measurement for time walk correction, the measured single-photon time resolutions are better than 40-ps rms. The test results confirm that the proposed timing electronics has advantages of high precision and high integration, which is highly demanded in future picosecond timing detectors.

Low power implementation of high frequency SiPM readout for Cherenkov and scintillation detectors in TOF-PET

State-of-the-art (SoA) electronic readout for silicon photomultiplier (SiPM)-based scintillation detectors that demonstrate experimental limits in achievable coincidence time resolution (CTR) leverage low noise, high frequency signal processing to facilitate a single photon time response that is near the limit of the SiPMs architecture. This readout strategy can optimally exploit fast luminescence and prompt photon populations, and promising measurements show detector concepts employing this readout can greatly advance PET detector CTR, relative to SoA in clinical systems. However, the technique employs power hungry components which make the electronics chain impractical for channel-dense time-of-flight (TOF)-PET detectors. We have developed and tested a low noise and high frequency readout circuit which is performant at low power and consists of discrete elements with small footprints, making it feasible for integration into TOF-PET detector prototypes. A 3 × 3 mm2 Broadcom SiPM with this readout chain exhibited sub-100 ps single photon time resolution at 10 mW of power consumption, with a relatively minor performance degradation to 120 ± 2 ps FWHM at 5 mW. CTR measurements with 3 × 3 × 20 mm3 LYSO and fast LGSO scintillators demonstrated 127 ± 3 ps and 113 ± 2 ps FWHM at optimal power operation and 133 ± 2 ps and 121 ± 3 ps CTR at 5 mW. BGO crystals 3 × 3 × 20 mm3 in size show 271 ± 5 ps FWHM CTR (1174 ± 14 ps full-width-at-tenth-maximum (FWTM)) at optimal power dissipation and 289 ± 8 ps (1296 ± 33 ps FWTM) at 5 mW. The compact and low power readout topology that achieves this performance thereby offers a platform to greatly advance PET system CTR and also opportunities to provide high performance TOF-PET at reduced material cost.

Monte Carlo simulation of SiPMs with GATE

Silicon photomultipliers (SiPMs) replace photomultiplier tubes (PMTs) for the detection of light in many applications, particularly in high energy physics and medical imaging. We describe a flexible implementation of a SiPM model for the GATE Monte Carlo simulation platform, which is based on the SiPM noise description proposed by Rosado and Hidalgo, and describe an easy and effective method to determine and instantiate the SiPM noise model with simple measurements. We also simulate the micro-cell Single Photon Time Resolution (SPTR) and describe its measurement.

On Analog Silicon Photomultipliers in Standard 55-nm BCD Technology for LiDAR Applications

We present an analog silicon photomultiplier (SiPM) based on a standard 55-nm Bipolar-CMOS-DMOS (BCD) technology. The SiPM is composed of 16 × 16 single-photon avalanche diodes (SPADs) and measures 0.29 × 0.32 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{2}$</tex-math></inline-formula> . Each SPAD cell is passively quenched by a monolithically integrated 3.3 V thick oxide transistor. The measured gain is 3.4 × 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{5}$</tex-math></inline-formula> at 5 V excess bias voltage. The single-photon timing resolution (SPTR) is 185 ps and the multi-photon timing resolution (MPTR) is 120 ps at 3.3 V excess bias voltage. We integrate the SiPM into a co-axial light detection and ranging (LiDAR) system with a time-correlated single-photon counting (TCSPC) module in FPGA. The depth measurement up to 25 m achieves an accuracy of 2 cm and precision of 2 mm under the room ambient light condition. With co-axial scanning, the intensity and depth images of complex scenes with resolutions of 128 × 256 and 256 × 512 are demonstrated. The presented SiPM enables the development of cost-effective LiDAR system-on-chip (SoC) in the advanced technology.

Picosecond timing of charged particles using the TORCH detector

TORCH is a large-area, high-precision time-of-flight (ToF) detector designed to provide charged-particle identification in the 2–20 GeV/c momentum range. Prompt Cherenkov photons emitted by charged hadrons as they traverse a 10 mm quartz radiator are propagated to the periphery of the detector, where they are focused onto an array of micro-channel plate photomultiplier tubes (MCP-PMTs). The position and arrival times of the photons are used to infer the particles’ time of entry in the radiator, to identify hadrons based on their ToF. The MCP-PMTs were developed with an industrial partner to satisfy the stringent requirements of the TORCH detector. The requirements include a finely segmented anode, excellent time resolution, and a long lifetime. Over an approximately 10 m flight distance, the difference in ToF between a kaon and a pion with 10 GeV/c momentum is 35 ps, leading to a 10–15 ps per track timing resolution requirement. On average 30 photons per hadron are detected, which translates to a single-photon time resolution of 70 ps. The TORCH R&D program aims to demonstrate the validity of the detector concept through laboratory and beam tests, results from which are presented. A timing resolution of 70–100 ps was reached in beam tests, approaching the TORCH design goal. Laboratory timing tests consist of operating the MCP-PMTs coupled to the TORCH readout electronics. A time resolution of 50 ps was measured, meeting the TORCH target timing resolution.

Front-End Design for SiPM-Based Monolithic Neutron Double Scatter Imagers.

Neutron double scatter imaging exploits the kinematics of neutron elastic scattering to enable emission imaging of neutron sources. Due to the relatively low coincidence detection efficiency of fast neutrons in organic scintillator arrays, imaging efficiency for double scatter cameras can also be low. One method to realize significant gains in neutron coincidence detection efficiency is to develop neutron double scatter detectors which employ monolithic blocks of organic scintillator, instrumented with photosensor arrays on multiple faces to enable 3D position and multi-interaction time pickoff. Silicon photomultipliers (SiPMs) have several advantageous characteristics for this approach, including high photon detection efficiency (PDE), good single photon time resolution (SPTR), high gain that translates to single photon counting capabilities, and ability to be tiled into large arrays with high packing fraction and photosensitive area fill factor. However, they also have a tradeoff in high uncorrelated and correlated noise rates (dark counts from thermionic emissions and optical photon crosstalk generated during avalanche) which may complicate event positioning algorithms. We have evaluated the noise characteristics and SPTR of Hamamatsu S13360-6075 SiPMs with low noise, fast electronic readout for integration into a monolithic neutron scatter camera prototype. The sensors and electronic readout were implemented in a small-scale prototype detector in order to estimate expected noise performance for a monolithic neutron scatter camera and perform proof-of-concept measurements for scintillation photon counting and three-dimensional event positioning.