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Vitali M.,Omicron Energy Solutions GmbH | Bronzi D.,Polytechnic of Milan | Krmpot A.J.,University of Belgrade | Nikolic S.N.,University of Belgrade | And 8 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

Confocal laser scanning microscopy (CLSM) is commonly used to observe molecules of biological relevance in their native environment, the live cell, and study their spatial distribution and interactions nondestructively. CLSM can be easily extended to measure the lifetime of the excited state, the concentration and the diffusion properties of fluorescently labeled molecules, using fluorescence lifetime imaging microscopy (FLIM) and fluorescence correlation spectroscopy (FCS), respectively, in order to provide information about the local environment and the kinetics of molecular interaction in live cells. However, these parameters cannot be measured simultaneously using conventional CLSM due to damaging effects that are associated with strong illumination, including phototoxicity, photobleaching, and saturation of the fluorescence signal. To overcome these limitations, we have developed a new camera consisting of 1024 single-photon avalanche diodes that is optimized for multifocal microscopy, FLIM and FCS. We show proof-of-principle measurements of fluorescence intensity distribution and lifetime of the enhanced green fluorescent protein expressed in live cells and measurement of quantum dot diffusion in solution by FCS using the same detector. © 1995-2012 IEEE.

Villa F.,Polytechnic of Milan | Lussana R.,Polytechnic of Milan | Bronzi D.,Polytechnic of Milan | Tisa S.,Micro Photon Device SRL | And 7 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

We present a CMOS imager consisting of 32 × 32 smart pixels, each one able to detect single photons in the 300. 900 nm wavelength range and to perform both photon-counting and photon-timing operations on very fast optical events with faint intensities. In photon-counting mode, the imager provides photonnumber (i.e., intensity) resolvedmovies of the scene under observation, up to 100 000 frames/s. In photon-timing, the imager provides photon arrival times with 312 ps resolution. The result are videos with either time-resolved (e.g., fluorescence) maps of a sample, or 3-D depth-resolvedmaps of a target scene. The imager is fabricated in a cost-effective 0.35-μm CMOS technology, automotive certified. Each pixel consists of a single-photon avalanche diode with 30 μm photoactive diameter, coupled to an in-pixel 10-bit time-to-digital converter with 320-ns full-scale range, an INL of 10% LSB and a DNL of 2% LSB. The chip operates in global shutter mode, with full frame times down to 10 μs and just 1-ns conversion time. The reconfigurable imager design enables a broad set of applications, like time-resolved spectroscopy, fluorescence lifetime imaging, diffusive optical tomography, molecular imaging, time-of-flight 3-D ranging and atmospheric layer sensing through LIDAR. © 2014 IEEE.

Bronzi D.,Polytechnic of Milan | Villa F.,Polytechnic of Milan | Bellisai S.,Polytechnic of Milan | Tisa S.,Micro Photon Device S.r.l. | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

SPADs (Single Photon Avalanche Diodes) are emerging as most suitable photodetectors for both single-photon counting (Fluorescence Correlation Spectroscopy, Lock-in 3D Ranging) and single-photon timing (Lidar, Fluorescence Lifetime Imaging, Diffuse Optical Imaging) applications. Different complementary metal-oxide semiconductor (CMOS) implementations have been reported in literature. We present some figure of merit able to summarize the typical SPAD performances (i.e. Dark Counting Rate, Photo Detection Efficiency, afterpulsing probability, hold-off time, timing jitter) and to identify a proper metric for SPAD comparison, both as single detectors and also as imaging arrays. The goal is to define a practical framework within which it is possible to rank detectors based on their performances in specific experimental conditions, for either photon-counting or photon-timing applications. Furthermore we review the performances of some CMOS and custom-made SPADs. Results show that CMOS SPADs performances improve as the technology scales down; moreover, miniaturization of SPADs and new solutions adopted to counteract issues related with the SPAD design (electric field uniformity, premature edge breakdown, tunneling effects, defect-rich STI interface) along with advances in standard CMOS processes led to a general improvement in all fabricated photodetectors; therefore, CMOS SPADs can be suitable for very dense and cost-effective many-pixels imagers with high performances. © 2013 SPIE.

Bronzi D.,Polytechnic of Milan | Villa F.,Polytechnic of Milan | Bellisai S.,Polytechnic of Milan | Tisa S.,Micro Photon Device S.r.l. | And 8 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

We designed and characterized Silicon Single-Photon Avalanche Diodes (SPADs) fabricated in a high-voltage 0.35 μm CMOS technology, achieving state-of-the-art low Dark Counting Rate (DCR), very large diameter, and extended Photon Detection Efficiency (PDE) in the Near Ultraviolet. So far, different groups fabricated CMOS SPADs in scaled technologies, but with many drawbacks in active area dimensions (just a few micrometers), excess bias (just few Volts), DCR (many hundreds of counts per second, cps, for small 10 μm devices) and PDE (just few tens % in the visible range). The novel CMOS SPAD structures with 50 μm, 100 μm, 200 μm and 500 μm diameters can be operated at room temperature and show DCR of 100 cps, 2 kcps, 20 kcps and 100 kcps, respectively, even when operated at 6 V excess bias. Thanks to the excellent performances, these large CMOS SPADs are exploitable in monolithic SPAD-based arrays with on-chip CMOS electronics, e.g. for time-resolved spectrometers with no need of microlenses (thanks to high fillfactor). Instead the smaller CMOS SPADs, e.g. the 10 μm devices with just 3 cps at room temperature and 6 V excess bias, are the viable candidates for dense 2D CMOS SPAD imagers and 3D Time-of-Flight ranging chips. © 2013 SPIE.

Zou Y.,Polytechnic of Milan | Villa F.,Polytechnic of Milan | Bronzi D.,Polytechnic of Milan | Tisa S.,Micro Photon Device S.r.l. | And 2 more authors.
Journal of Modern Optics | Year: 2015

Silicon photomultipliers (SiPMs) are large area detectors consisting of an array of single-photon-sensitive microcells, which make SiPMs extremely attractive to substitute the photomultiplier tubes in many applications. We present the design, fabrication, and characterization of analog SiPMs in standard planar 0.35 m CMOS technology, with about 1 mm × 1 mm total area and different kinds of microcells, based on single-photon avalanche diodes with 30 m diameter reaching 21.0% fill-factor (FF), 50 m diameter (FF = 58.3%) or 50 m square active area with rounded corner of 5 m radius (FF = 73.7%). We also developed the electrical SPICE model for CMOS SiPMs. Our CMOS SiPMs have 25 V breakdown voltage, in line with most commercial SiPMs and higher gain (8.8 × 106, 13.2 × 106, and 15.0 × 106, respectively). Although dark count rate density is slightly higher than state-of-the-art analog SiPMs, the proposed standard CMOS processing opens the feasibility of integration with active electronics, for switching hot pixels off, drastically reducing the overall dark count rate, or for further on-chip processing. © 2015 Taylor and Francis.

Villa F.,Polytechnic of Milan | Bronzi D.,Polytechnic of Milan | Zou Y.,Polytechnic of Milan | Scarcella C.,Polytechnic of Milan | And 8 more authors.
Journal of Modern Optics | Year: 2014

Many demanding applications require single-photon detectors with very large active area, very low noise, high detection efficiency, and precise time response. Single-photon avalanche diodes (SPADs) provide all the advantages of solid-state devices, but in many applications other single-photon detectors, like photomultiplier tubes, have been preferred so far due to their larger active area. We developed silicon SPADs with active area diameters as large as 500 m in a fully standard CMOS process. The 500 m SPAD exhibits 55% peak photon detection efficiency at 420 nm, 8 kcps of dark counting rate at 0°C, and high uniformity of the sensitivity in the active area. These devices can be used with on-chip integrated quenching circuitry, which reduces the afterpulsing probability, or with external circuits to achieve even better photon-timing performances, as good as 92 ps FWHM for a 100 m diameter SPAD. Owing to the state-of-the-art performance, not only compared to CMOS SPADs but also SPADs developed in custom technologies, very high uniformity and low crosstalk probability, these CMOS SPADs can be successfully employed in detector arrays and single-chip imagers for single-photon counting and timing applications. © 2014 Taylor & Francis.

Bronzi D.,Polytechnic of Milan | Villa F.,Polytechnic of Milan | Tisa S.,Micro Photon Device S.r.l. | Tosi A.,Polytechnic of Milan | Zappa F.,Polytechnic of Milan
IEEE Sensors Journal | Year: 2016

Single-photon avalanche diodes (SPADs) emerged as the most suitable photodetectors for both single-photon counting and photon-timing applications. Different complementary metal-oxide-semiconductor (CMOS) devices have been reported in the literature, with quite different performance and some excelling in just few of them, but often at different operating conditions. In order to provide proper criteria for performance assessment, we present some figures of merit (FoMs) able to summarize the typical SPAD performance (i.e., photon detection efficiency, dark counting rate, afterpulsing probability, hold-off time, and timing jitter) and to identify a proper metric for SPAD comparisons, when used either as single-pixel detectors or in imaging arrays. The ultimate goal is not to define a ranking list of best-in-class detectors, but to quantitatively help the end-user to state the overall performance of different SPADs in either photon-counting, timing, or imaging applications. We review many CMOS SPADs from different research groups and companies, we compute the proposed FoMs for all them and, eventually, we provide an insight on present CMOS SPAD technologies and future trends. © 2016 IEEE.

Villa F.,Polytechnic of Milan | Markovic B.,Polytechnic of Milan | Bellisai S.,Polytechnic of Milan | Bronzi D.,Polytechnic of Milan | And 7 more authors.
IEEE Photonics Journal | Year: 2012

We present a smart pixel based on a single-photon avalanche diode (SPAD) for advanced time-of-flight (TOF) and time-correlated single photon counting (TCSPC) applications, fabricated in a cost-effective 0.35-μ CMOS technology. The large CMOS detector (30-μ active area diameter) shows very low noise (12 counts per second at room temperature at 5-V excess bias) and high efficiency in a wide wavelength range (about 50% at 410 nm and still 5% at 800 nm). The analog front-end electronics promptly senses and quenches the avalanche, thus leading to an almost negligible afterpulsing effect. The in-pixel 10-bit time-to-digital converter (TDC) provides 312-ps resolution and 320-ns full-scale range (FSR), i.e., 10-cm single-shot spatial resolution within 50-m depth range in a TOF system. The in-pixel 10-bit memory and output buffers make this smart pixel the viable building block for advanced single-photon imager arrays for 3-D depth ranging in safety and security applications and for 2-D fluorescence lifetime decays in biomedical imaging. © 2012 IEEE.

Bronzi D.,Polytechnic of Milan | Tisa S.,Micro Photon Device Srl | Villa F.,Polytechnic of Milan | Bellisai S.,Polytechnic of Milan | And 2 more authors.
IEEE Photonics Technology Letters | Year: 2013

We present a single-photon avalanche diode (SPAD) front-end circuitry, in a cost-effective 0.35 μ m CMOS technology, for single-photon detection in the visible wavelength range, aimed at speeding up the sensing of detector ignition and at promptly quenching the avalanche current buildup. The circuit allows the reduction in detrimental effects of afterpulsing through reducing any delays in the electronics intervention on the detector and through a proper time-varying action of the MOS transistors on the different SPAD's operating conditions. The sensing time is reduced down to a few hundreds of picoseconds, with an active quenching transition of about 1 ns for 6 V excess bias, and a final reset in just 3 ns. © 1989-2012 IEEE.

PubMed | U.S. National Institute of Standards and Technology, Nicolaus Copernicus University, Polytechnic of Milan, University of Waterloo and Micro Photon Device S.r.l.
Type: | Journal: Scientific reports | Year: 2014

The double-slit experiment strikingly demonstrates the wave-particle duality of quantum objects. In this famous experiment, particles pass one-by-one through a pair of slits and are detected on a distant screen. A distinct wave-like pattern emerges after many discrete particle impacts as if each particle is passing through both slits and interfering with itself. Here we present a temporally- and spatially-resolved measurement of the double-slit interference pattern using single photons. We send single photons through a birefringent double-slit apparatus and use a linear array of single-photon detectors to observe the developing interference pattern. The analysis of the buildup allows us to compare quantum mechanics and the corpuscular model, which aims to explain the mystery of single-particle interference. Finally, we send one photon from an entangled pair through our double-slit setup and show the dependence of the resulting interference pattern on the twin photons measured state. Our results provide new insight into the dynamics of the buildup process in the double-slit experiment, and can be used as a valuable resource in quantum information applications.

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