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We realize single-mode, waveguide-coupled, electrically driven silicon light emitting diodes in commercial, unmodified silicon photonics foundry processes and develop a model of both the electrical and optical behavior to understand the performance limitations. We measure a center wavelength of 1130 nm, a 90 nm 3 dB optical bandwidth, and 200 pW of optical power propagating in each direction. We show on-chip modulation and detection of the generated light using native resonant photodetectors integrated in the same chip. Our work unveils a new native light source available in silicon photonics processes, which can find applications ranging from device screening and fabrication quality assessment to imaging, refractive index sensing, or intra-chip communication. [ABSTRACT FROM AUTHOR]

CMOS single-photon avalanche diode (SPAD) array is a high-timing-resolution photon-counting image sensor. Pixel size shrinkage for high image resolution is highly desirable but hindered by the lowered photon-detection-probability (PDP) as the edge area becomes significant. We propose and demonstrate a parameter-free method for simulating PDP with the edge effect. Considering the doping profile, electric field, photon generation, and trigger probability distributions in two dimensions, the PDP reduction at the device edge is analyzed in a quantitative way. Besides, a novel guard-ring design for enhancing PDP of small SPAD has been proposed and simulated by our method. A threefold enhancement was obtained with the newly designed guard-ring structure compared with the original one. Our work is useful for developing small-pitch SPAD array for high-resolution imaging applications. [ABSTRACT FROM AUTHOR]

Fast active quenching of single-photon avalanche diodes (SPADs) is important to reduce the afterpulsing probability (APP). An option to reduce the reaction time of electronics to a SPAD's avalanche is to design a quencher exploiting bipolar transistors. A quencher in a 0.35 μm CMOS technology with a nominal supply voltage of 3.3 V, which operated with excess bias voltages up to 6.6 V, was re-designed accordingly. In the new 0.35 μm pure-silicon BiCMOS quencher, the comparator takes advantage of a bipolar differential amplifier, which additionally gives the head room to increase the width of some CMOS transistors as well. The proposed BiCMOS quencher is able to drive the load of a wire-bonded 184 μm-diameter SPAD, while the CMOS design fails. A comparison, where both chips are measured with a wire-bonded, 34 μm-diameter SPAD, shows that the BiCMOS quencher has a reaction time, which is 330 ps to 1.1 ns faster than that of the CMOS quencher. [ABSTRACT FROM AUTHOR]

SPADs (Single-Photon Avalanche Diodes) are important detectors for a wide range of applications including positron emission tomography, Raman spectroscopy, light detection and ranging, and quantum key distribution. For some applications, custom image sensor technologies are used, but at a higher cost and lower performance imagers when compared to implementation in a standard planar CMOS technology. In this paper, we explore time-gating and multi-junction techniques to improve the SPAD’s performance in smaller standard planar CMOS processes to take advantage of their potential for monolithic integration with other advanced, mixed-signal circuitry for simple, low-cost, high-performance imaging solutions. A passively quenched, unbuffered, triple-junction SPAD structure was designed in a standard 65 nm CMOS process from TSMC. The characterization of the SPAD junctions in this process is the first in literature and proves useful for SPAD designers aiming for advanced CMOS technology nodes. The time-gated (TG) pixel design used the top shallow junction. The potential for improved photon detection efficiency and wavelength distinction through a multi-junction design was investigated. Our testing demonstrated that the proposed implementation of the triple-junction SPAD in this technology node is not suitable for wavelength distinction. The TG design achieved a fill-factor of 28.6%, and at an excess voltage of 300 mV, it achieved a peak photon detection efficiency of ~2.1% at 440 nm, <1% afterpulsing probability for hold-off times >22 ns, and <200 ps timing jitter. [ABSTRACT FROM AUTHOR]

The Silicon Photomultiplier (SiPM) is a mature photodetector concept that is applied in a variety of applications ranging from medical imaging to automotive LiDAR systems. Over the last few years, improvements of the sensor performance are gradually approaching to a saturation. In this work we present our new concept to overcome the intrinsic limitations of planar configurations of electrodes. Our non-planar technology is based on focusing and enhancing the electric fields by tip-like electrodes. The shape of the electric field and the lack of typical micro-cell edges, allows us to exclude cell separation boundaries and eliminate dead space around active cell areas. Our design provides a high-density micro-cell layout with a high geometric efficiency. It resolves the well-known trade-off between the detection efficiency and the dynamic range. The first “Tip Avalanche Photodiode” (TAPD) prototypes show a remarkable geometric efficiency above 80% for a micro-cell pitch of 15 $\mu \text{m}$. This directly translates into a photon detection efficiency (PDE) record peak value of 73% at 600nm with respect to the state-of-the-art SiPMs. Moreover, the PDE remains above a value of 45% up to a wavelength of 800nm with another record value of 22% at 905nm. The reduced micro-cell capacity allows for a fast recovery time below 4ns, which improves the operation at high photon rates. Overall, the TAPD is anticipated to be a very promising SiPM generation for various wide-spectral and high-dynamic-range applications in health science, biophysics, particle physics and LiDARs. [ABSTRACT FROM AUTHOR]

This article reports the design and characterization of a 32 $\times $ 32 single-photon avalanche diode (SPAD) time-resolved image sensor for quantum imaging applications fabricated in a 150-nm CMOS standard technology. A per-SPAD time-to-digital converter (TDC) records the spatial cross correlation functions of a flux of entangled photons. Each 44.64- $\mu \text{m}$ pixel with 19.48% fill-factor features a 210.2-ps resolution, 50-ns (8-bit) range TDC with 1.28-LSB differential and 1.92-LSB integral nonlinearity (DNL/INL). The sensor achieves an observation rate of up to 1 MHz through a current-based mechanism that avoids reading empty frames when the photon rates are low. A row-skipping mechanism detects the absence of SPAD activity in a row to increase the duty cycle. These two features require only three transistors in each pixel. The sensor functionality is demonstrated in a quantum imaging experiment that achieves super-resolution. [ABSTRACT FROM AUTHOR]

A monolithic resistorless circuit has been designed for active reset of the N+P single-ended (common anode) single-photon avalanche diode (SPAD). This type of SPAD has enhanced the photon detection efficiency in the near-infrared (NIR) region relatively to the P+N (two-ended) SPAD. Due to this fact, the N+P SPAD is a better candidate for the light detection and range (LiDAR) working in the NIR region. The circuit is fabricated in a standard 0.18-μm CMOS image sensor process. The dead time after each photon detection is adjustable; the minimum measured value is 4 ns. The maximum photon count rate corresponding to this dead time is 2.5 ⋅ 108 photons/s. This circuit guarantees precise repeatable response, short and well-controlled dead time, and after-pulsing effect reduction. All these are essential for many SPAD applications and crucial for increasing the saturation level of the silicon photo multiplier (SiPM)-based LiDAR systems working in strong background light conditions on sunny day. [ABSTRACT FROM AUTHOR]

We present a novel silicon photomultiplier based on a shallow junction obtained within a standard 0.35 ${\mu }\text{m}$ complementary metal oxide semiconductor process. The sensitive structure is equipped with a dedicated optical window as well as an optimized antireflective coating. The device exhibits performances comparable to custom-based commercial technologies: an unprecedented photon detection efficiency of 43% at 420 nm, a breakdown voltage temperature dependence of (27.9 ± 0.9) mV/K, a dark count rate of 480 kHz/mm2, a gain of ${3\times 10^{6}}$ , and a single photon time resolution of (78 ± 2) ps (FWHM). The process proposed in this letter can be applied to new generation single photon sensors with on-chip integrated intelligent electronics. [ABSTRACT FROM AUTHOR]

The ANIMMA conferences offer a unique opportunity to discover research carried out in all fields of nuclear measurements and instrumentation with applications extending from fundamental physics to fission and fusion reactors, medical imaging, environmental protection and homeland security. After four successful editions of the Conference, it was decided to prepare a review based to a large extent but not exclusively on the papers presented during the first four editions of the conference. This review is organized according to the measurement methodologies: neutronic, photonic, thermal, acoustic and optical measurements, as well as medical imaging and specific challenges linked to data acquisition and electronic hardening. The paper describes the main challenges justifying research in these different areas, and summarizes the recent progress reported. It offers researchers and engineers a way to quickly and efficiently access knowledge in highly specialized areas. [ABSTRACT FROM AUTHOR]

We present and discuss a comprehensive electrical model for Silicon Photomultipliers (SiPMs) based on a microcell able to accurately simulate the avalanche current build-up and the self-quenching of its Single-Photon Avalanche Diode (SPAD) “pixel” with series-connected quenching resistor. The entire SiPM is modeled either as an array of microcells, each one individually triggered by independent incoming photons, or as two macrocells, one with microcells all firing concurrently while the other one with all quiescent microcells; the most suitable approach depends on the light excitation conditions and on the dimension (i.e. number of microcells) of the overall SiPM. We validated both models by studying the behavior of SiPMs in different operating conditions, in order to study the effect of photons pile-up, the deterministic and statistical mismatches between microcells, the impact of the number of firing microcells vs. the total one, and the role of different microcell parameters on the overall SiPM performance. The electrical models were developed in SPICE and can simulate both custom-process and CMOS-compatible SiPMs, with either vertical or horizontal current-flow. The proposed simulation tools can benefit both SiPM users, e.g. for designing the best readout electronics, and SiPM designers, for assessing the impact of each parameter on the overall detection performance and electrical behavior. [ABSTRACT FROM AUTHOR]

In this paper, we present the characteristics and performances of new silicon photomultipliers (SiPMs), produced at FBK, for the near-ultraviolet (NUV) light detection, with reduced afterpulsing and delayed optical crosstalk. To study these components of the correlated noise, we manufactured SiPMs on silicon wafers featuring different substrate minority-carrier lifetime. This parameter proved to be crucial in determining the amount of delayed optical crosstalk and afterpulsing caused by photo-generated carriers diffusing from the substrate to the cell active region. With a very low substrate lifetime, we were able to minimize this correlated noise component to few percent at room temperature. Besides reducing the excess noise factor, the lower delayed correlated noise allows biasing the SiPM at higher voltages, reaching higher values of photon detection efficiency. [ABSTRACT FROM PUBLISHER]

In this paper, we report on the characterization of the single-photon time resolution (SPTR) of the RGB (Red-Green-Blue) type silicon photomultipliers (SiPM) produced at FBK. We measured and compared single-photon timing jitter of 1 \times 1~\mm^2 and 3 \times 3~\mm^2 SiPMs, and also of square SPADs with integrated passive quenching, identical to the cells composing the SiPMs. We reached a single-photon time resolution of about 180 ps full-width at half-maximum for 3 \times 3~\mm^2 SiPM, 80 ps for 1 \times 1~\mm^2 SiPM and less than 50 ps for single cells. From measurements with pinholes placed in front of 1 \times 1~\mm^2 detector we see a very good cell-to-cell uniformity: it is not a limiting factor for time resolution. We also characterized the timing jitter of SiPMs as a function of the number of photons per laser pulse (N) finding that it does not decrease exactly with the square root of N because of the optical crosstalk between cells. [ABSTRACT FROM PUBLISHER]

This paper presents a digital silicon photomultiplier (SiPM) partitioned in columns, whereas each column is connected to a column-parallel time-to-digital converter (TDC), in order to improve the timing resolution of single-photon detection. By reducing the number of pixels per TDC using a sharing scheme with three TDCs per column, the pixel-to-pixel skew is reduced. We report the basic characterization of the SiPM, comprising 416 single-photon avalanche diodes (SPADs); the characterization includes photon detection probability, dark count rate, afterpulsing, and crosstalk. We achieved 264-ps full-width at half maximum timing resolution of single-photon detection using a 48-fold column-parallel TDC with a temporal resolution of 51.8 ps (least significant bit), fully integrated in standard complementary metal–oxide semiconductor technology. [ABSTRACT FROM PUBLISHER]

An 8\,\times\,16 pixel array based on CMOS small-area silicon photomultipliers (mini-SiPMs) detectors for PET applications is reported. Each pixel is 570 \,\times\,610 \mum ^2 in size and contains four digital mini-SiPMs, for a total of 720 SPADs, resulting in a full chip fill-factor of 35.7%. For each gamma detection, the pixel provides the total detected energy and a timestamp, obtained through two 7-b counters and two 12-b 64-ps TDCs. An adder tree overlaid on top of the pixel array sums the sensor total counts at up to 100 Msamples/s, which are then used for detecting the asynchronous gamma events on-chip, while also being output in real-time. Characterization of gamma detection performance with an 3\,\times\,3\,\times\,5 mm ^3 LYSO scintillator at 20 ^\circC is reported, showing a 511-keV gamma energy resolution of 10.9% and a coincidence timing resolution of 399 ps. [ABSTRACT FROM AUTHOR]

We report on the electrical and optical characterization, in continuous wave regime, of a novel class of silicon photomultipliers fabricated in standard planar technology on a silicon p-type substrate. Responsivity measurements, performed with an incident optical power down to tenths of picowatts, at different reverse bias voltages and on a broad (340–820 nm) spectrum, will be shown and discussed. The device temperature was monitored, allowing us to give a physical interpretation of the measurements. The obtained results demonstrate that such novel silicon photomultipliers are suitable as sensitive power meters for low photon fluxes. [ABSTRACT FROM PUBLISHER]

In this paper, we describe current trends in data path topologies for Positron Emission Tomography (PET) data acquisition (DAQ) systems which is used to capture signals from the detector modules and generate coincidence data for a image reconstruction computer. First, the requirements of DAQ systems in PET, such as event throughput, timing resolution, and energy resolution, are analyzed. Then, design issues related to DAQ designs are discussed including multiplexing schemes, DAQ boards interconnection topologies, and transmission protocols to transfer data to the image reconstruction computer. We also discuss how new trends in PET systems, such as time-of-flight (TOF) PET, depth-of-interaction (DOI) information, and PET/MRI, can affect the design of PET DAQ systems. [ABSTRACT FROM AUTHOR]

In this paper, we present the results of the characterization of the first high-density (HD) cell silicon photomultipliers produced at FBK. The most advanced prototype manufactured with this technology has a cell size of 15\,\times\,15 \mum^2 featuring a nominal fill factor of 48%. To reach this high area coverage, we developed a new border structure to confine the high electric-field region of each single-photon avalanche diode. The measured detection efficiency approaches 30% in the green part of the light spectrum and it is above 20% from 400 to 650 nm. At these efficiency values, the correlated noise is very low, giving an excess charge factor below 1.1. We coupled a 2\,\times\,2\,\times\,10-mm^3 LYSO scintillator crystal to a 2.2\,\times\,2.2-mm^2 silicon photomultiplier, obtaining very promising results for PET application: energy resolution of less than 11% full-width at half maximum (FWHM) with negligible loss of linearity and coincidence resolving time of 200-ps FWHM at 20^\circC. [ABSTRACT FROM AUTHOR]

Interventional radiologists and staff members, during all their professional activities, are frequently exposed to protracted and fractionated low doses of ionizing radiation. Due to skin tissues and peripheral blood irradiation, these exposures can result in deterministic effects (radiodermatitis, aged skin, and hand depilation) or stochastic ones (skin and non-solid cancer incidence). The authors present a novel approach to perform online monitoring of the staff during their interventions by using a device based on an Active Pixel Sensor. The performance of the sensor as an X-ray radiation detector has been evaluated with a proper experimental setup: the number of photons and the generated charge have been assessed as dosimetric observables from the frames acquired by the sensor using a two-threshold clustering algorithm, the efficiency of which has been evaluated as well. The correlation of these observables with passive dosimeter dose measurements has been analyzed: a good linearity has been demonstrated, and the response difference between pulsed and continuous operational modes is reduced to less than 10%, marking a distinct improvement with respect to commercial Active Personal Dosimeters. [ABSTRACT FROM AUTHOR]

Silicon photomultipliers (SiPMs) are fabricated in two different configurations: p-on-n and n-on-p junctions. p-on-n SiPMs turn out to be more suitable for application in positron emission tomography (PET), due to their higher sensitivity in blue wavelength range where common PET scintillators have their emission spectrum. In this paper, we report on the electro-optical performances of the first p-on-n SiPMs manufactured at STMicroelectronics, Catania. The results obtained on these devices are compared with those measured on the standard n-on-p technology. [ABSTRACT FROM AUTHOR]

We are developing a technique to fabricate high spatial resolution and cost-effective photon counting detectors using silicon photomultipliers (SiPMs) and microcolumnar structured scintillator. Photon counting detectors using SiPMs are of much interest to the gamma- and X-ray detector community, but they have limitations at low energy due to their dark noise. In this paper, we report on vapor deposition of CsI:Tl directly onto a SiPM, a technique that improves optical coupling and allows for detection of low energy gamma- and X-rays. It simultaneously addresses related issues of light loss and light spread in the scintillator, thereby improving the performance of the detector. Devices made by this technique may be used for both photon counting and gamma- and X-ray imaging. [ABSTRACT FROM PUBLISHER]

We present a novel structure for the back-side readout silicon photomultiplier (SiPM). Current SiPMs are front-illuminated structures with front-side readout, which have relatively small geometric fill factor leading to degradation in their photon detection efficiency (PDE). Back-side readout devices will provide an advantageous solution to achieve high PDE. We designed and investigated a novel structure that would allow back-side readout while creating a region of high electric field optimized for avalanche breakdown. In addition, this structure has relatively high fill factor and also allows the direct coupling of the individual microcell of the SiPM to application-specific integrated circuits. We will discuss the performance that can be attained with this structure through device simulation and the process flow that can be used to fabricate this structure through process simulation. [ABSTRACT FROM AUTHOR]

Solid-state photomultiplier (SSPM) arrays are a new technology that shows great promise to be used in PET detector modules. To reduce the number of channels in a PET scanner, it is attractive to use resistor dividers, which multiplex the number of channels in each module down to four analog output channels. It is also attractive to have SSPMs with large pixels (3\,\times\,3 or 4\,\times\,4 mm^2). However, large area SSPMs have correspondingly large capacitances (up to 1 nF) and directly coupling them to a resistive network will create a low-pass filter with a high RC time constant. In order to overcome this, we have developed an application specific integrated circuit (ASIC) that “hides” the intrinsic capacitance of the SSPM array from a resistive network with current buffers, significantly improving the rise time of the SSPM signals when connected to the resistive network. The ASIC is designed for a wide range of SSPM sizes, up to 1 nF (equivalent to 4\,\times\,4 mm^2), and for input currents of 1 to 20 mA per channel. To accommodate various sizes of SSPM pixels, the ASIC uses adjustable current sources (to keep the feedback loop stable). A test ASIC has been fabricated that has 16 input channels, an internal resistor divider array that produces four analog outputs, 16 buffers that isolate the SSPM capacitance from the resistor array, and four output buffers that can drive 100 ohm loads. Thus, detector modules based on SSPMs and this ASIC should be compatible with the block detector readout electronics found in many PET cameras. Tests of this ASIC show that its rise time is <2 ns (and it will thus not significantly degrade the \sim \ 7 ns rise time of the SSPM pixels) and that the analog decoding circuitry functions properly. [ABSTRACT FROM PUBLISHER]