Single-photon avalanche diodes (SPADs) have become the sensor of choice in many applications whenever high sensitivity, low noise, and sharp timing performance are required, simultaneously. Recently, SPADs designed in CMOS technology, have yielded moderately good performance in these parameters, but never equaling their counterparts fabricated in highly customized, non-standard technologies. The arguments in favor of CMOS-compatible SPADs were miniaturization, cost and scalability. In this paper, we present the first CMOS SPAD with performance comparable or better than that of the best custom SPADs, to date. The SPAD-based design, fully integrated in 180 nm CMOS technology, achieves a peak photon detection probability (PDP) of 55% at 480 nm with a very broad spectrum spanning from near ultraviolet (NUV) to near infrared (NIR) and a normalized dark count rate (DCR) of 0.2 cps/ $\mu$ m $^2$ , both at 6 V of excess bias. Thanks to a dedicated CMOS pixel circuit front-end, an afterpulsing probability of about 0.1% at a dead time of $\sim$ 3 ns were achieved. We designed three SPADs with a diameter of 25, 50, and 100 $\mu$ m to study the impact of size on the timing jitter and to create a scaling law for SPADs. For these SPADs, a single-photon time resolution (SPTR) of 12.1 ps, 16 ps, and 27 ps (FWHM) was achieved at 6 V of excess bias, respectively. The SPADs operate in a wide range of temperatures, from −65 $^{\circ }$ C to 40 $^{\circ }$ C, reaching a normalized DCR of 1.6 mcps/ $\mu$ m $^2$ at 6 V of excess bias for the 25 $\mu$ m at −65 $^{\circ }$ C. The proposed SPADs are ideal for a wide range of applications, including (quantum) LiDAR, super-resolution microscopy, quantum random number generators, quantum key distribution, fluorescence lifetime imaging, time-resolved Raman spectroscopy, to name a few. All these applications can take advantage of the vastly improved performance of our detectors, while enjoying the opportunities of megapixel resolutions promised by the economy of scale that is offered by CMOS technologies.

The radiation hardness of 180 nm complementary metal–oxide–semiconductor (CMOS) and 55 nm bipolar–CMOS–double-diffused MOS single-photon avalanche diodes (SPADs) is studied using 10 MeV and 100 MeV protons up to a displacement damage dose of 1 PeV/g. It is found that the dark count rate (DCR) levels are dependent on the number and the type of defects created. A new stepwise increase in the DCR is presented. Afterpulsing was found to be a significant contributor to the observed DCR increase. A new model for DCR increase prediction is proposed considering afterpulsing. Most of the samples under test retain reasonable DCR levels after irradiation, showing high tolerance to ionizing and displacement damage caused by protons. Following irradiation, self-healing was observed at room temperature. Furthermore, high-temperature annealing shows potential for accelerating recovery. Overall, the results show the suitability of SPADs as optical detectors for long-term space missions or as detectors for high-energy particles.

Advances in high-speed imaging techniques have opened new possibilities for capturing ultrafast phenomena such as light propagation in air or through media. Capturing light in flight in three-dimensional $xyt$ space has been reported based on various types of imaging systems, whereas reconstruction of light-in-flight information in the fourth dimension $z$ has been a challenge. We demonstrate the four-dimensional light-in-flight imaging based on the observation of a superluminal motion captured by a new time-gated megapixel single-photon avalanche diode camera. A high-resolution light-in-flight video is generated without laser scanning, camera translation, interpolation, or dark noise subtraction. An unsupervised machine-learning technique is applied to analyze the measured spatiotemporal data set. A theoretical formula is introduced to perform least-square regression for numerically solving a nonlinear inverse problem, and extra-dimensional information is recovered without prior knowledge. The algorithm relies on the mathematical formulation equivalent to the superluminal motion in astrophysics, which is scaled by a factor of a quadrillionth. The reconstructed light-in-flight trajectory shows good agreement with the actual geometry of the light path. Applicability of the reconstruction approach to more complex scenes with multiple overlapped light trajectories is verified based on a data set generated by Monte Carlo simulations. Our approach could potentially provide novel functionalities to high-speed imaging applications such as non-line-of-sight imaging and time-resolved optical tomography.

The proposed next generation of particle physics experiments utilizing ring imaging Cherenkov detectors (RICH) will require photodetectors with 100ps timing, mm² granularity, large active area and the ability to operate in increasingly harsh environments. Due to increased luminosity, any detector will be required to demonstrate a neutron radiation hardness of order 10¹³ n_eq/cm² by the end of the experimental run time. Digital silicon photomultipliers (dSiPMs), based on single-photon avalanche diodes (SPADs), have emerged as an attractive proposition for RICH detectors due to their high timing precision and architectural flexibility. Digital implementations in standard CMOS allow the introduction of advanced functionalities directly on chip, including gating, pixel masking and precise timestamping. Neutron radiation hardness, however, remains an ongoing challenge, as irradiation results in an increased dark count rate (DCR), proportional to the fluence. Reduction of the SPAD active volume lowers the increase in DCR for a given dose, so the addition of microlens structures to recover fill factor on small-volume SPADs promises an encouraging route towards radiation-hard dSiPMs. In this work we present a study of multiple SPAD designs, in a variety of technology nodes, to determine the optimal configuration for neutron radiation hardness. We report on testing of optical microlens structures in multiple materials, to determine the effects of neutron radiation up to 10¹⁴ n_eq/cm².