Simone Tisa

Politecnico di Milano, Milano, Lombardy, Italy

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Publications (80)85.4 Total impact

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    ABSTRACT: 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 μm CMOS technology, with about 1 mm × 1 mm total area and different kinds of microcells, based on single-photon avalanche diodes with 30 μm diameter reaching 21.0% fill-factor (FF), 50 μm diameter (FF = 58.3%) or 50 μm square active area with rounded corner of 5 μm 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.
    Journal of Modern Optics 06/2015; DOI:10.1080/09500340.2015.1049572 · 1.17 Impact Factor
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    ABSTRACT: Optical quantum random number generators (QRNGs) are a special class of physical random data sources, whose randomness is established on elementary quantum optics processes. We present a QRNG based on a CMOS chip which overcomes the limitations of the commonly used optical QRNG and which achieves a random bit generation rate up to 200 Mb/s. The CMOS chip is based on an array of single-photon avalanche diodes (SPADs) and digital counters. We prove the absolute randomness of the generated random data through statistical test suites and even more stringent correlation and bias tests applied to 32 Gbit streams. The QRNG passes all tests; hence, it proves to be one of the fastest and more reliable CMOS optical QRNGs currently available.
    IEEE Journal of Selected Topics in Quantum Electronics 05/2015; 21(3):1-7. DOI:10.1109/JSTQE.2014.2375132 · 3.47 Impact Factor
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    ABSTRACT: Silicon Photomultipliers (SiPMs) are emerging single photon detectors used in many applications requiring large active area, photon-number resolving capability and immunity to magnetic fields. We present three families of analog SiPM fabricated in a reliable and cost-effective fully standard planar CMOS technology with a total photosensitive area of 1×1 mm2. These three families have different active areas with fill-factors (21%, 58.3%, 73.7%) comparable to those of commercial SiPM, which are developed in vertical (current flow) custom technologies. The peak photon detection efficiency in the near-UV tops at 38% (fill-factor included) comparable to commercial custom-process ones and dark count rate density is just a little higher than the best-in-class commercial analog SiPMs. Thanks to the CMOS processing, these new SiPMs can be integrated together with active components and electronics both within the microcell and on-chip, in order to act at the microcell level or to perform global pre-processing. We also report CMOS digital SiPMs in the same standard CMOS technology, based on microcells with digitalized processing, all integrated on-chip. This CMOS digital SiPMs has four 32×1 cells (128 microcells), each consisting of SPAD, active quenching circuit with adjustable dead time, digital control (to switch off noisy SPADs and readout position of detected photons), and fast trigger output signal. The achieved 20% fill-factor is still very good.
    SPIE Photonics West 2015, San Francisco; 04/2015
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    ABSTRACT: Advanced Driver Assistance Systems (ADAS) are the most advanced technologies to fight road accidents. Within ADAS, an important role is played by radar- and lidar-based sensors, which are mostly employed for collision avoidance and adaptive cruise control. Nonetheless, they have a narrow field-of-view and a limited ability to detect and differentiate objects. Standard camera-based technologies (e.g. stereovision) could balance these weaknesses, but they are currently not able to fulfill all automotive requirements (distance range, accuracy, acquisition speed, and frame-rate). To this purpose, we developed an automotive-oriented CMOS single-photon camera for optical 3D ranging based on indirect time-of-flight (iTOF) measurements. Imagers based on Single-photon avalanche diode (SPAD) arrays offer higher sensitivity with respect to CCD/CMOS rangefinders, have inherent better time resolution, higher accuracy and better linearity. Moreover, iTOF requires neither high bandwidth electronics nor short-pulsed lasers, hence allowing the development of cost-effective systems. The CMOS SPAD sensor is based on 64 × 32 pixels, each able to process both 2D intensity-data and 3D depth-ranging information, with background suppression. Pixel-level memories allow fully parallel imaging and prevents motion artefacts (skew, wobble, motion blur) and partial exposure effects, which otherwise would hinder the detection of fast moving objects. The camera is housed in an aluminum case supporting a 12 mm F/1.4 C-mount imaging lens, with a 40°×20° field-of-view. The whole system is very rugged and compact and a perfect solution for vehicle’s cockpit, with dimensions of 80 mm × 45 mm × 70 mm, and less that 1 W consumption. To provide the required optical power (1.5 W, eye safe) and to allow fast (up to 25 MHz) modulation of the active illumination, we developed a modular laser source, based on five laser driver cards, with three 808 nm lasers each. We present the full characterization of the 3D automotive system, operated both at night and during daytime, in both indoor and outdoor, in real traffic, scenario. The achieved long-range (up to 45m), high dynamic-range (118 dB), highspeed (over 200 fps) 3D depth measurement, and high precision (better than 90 cm at 45 m), highlight the excellent performance of this CMOS SPAD camera for automotive applications.
    SPIE Photonics West 2015, San Francisco; 02/2015
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    ABSTRACT: We present a Time-to-Digital Converter (TDC) card with a compact form factor, suitable for multichannel timing instruments or for integration into more complex systems. The TDC Card provides 10 ps timing resolution over the whole measurement range, which is selectable from 160 ns up to 10 μs, reaching 21 ps rms precision, 1.25% LSB rms differential nonlinearity, up to 3 Mconversion/s with 400 mW power consumption. The I/O edge card connector provides timing data readout through either a parallel bus or a 100 MHz serial interface and further measurement information like input signal rate and valid conversion rate (typically useful for time-correlated single-photon counting application) through an independent serial link.
    Review of Scientific Instruments 11/2014; 85(11):114703. DOI:10.1063/1.4900863 · 1.58 Impact Factor
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    ABSTRACT: We report on the design and characterization of a multipurpose 64x32CMOS single-photon avalanche diode (SPAD) array. The chip is fabricated in a high-voltage 0.35-μm CMOS technology and consists of 2048 pixels, each combining a very low noise (100 cps at 5-V excess bias) 30-μm SPAD, a prompt avalanche sensing circuit, and digital processing electronics. The array not only delivers two-dimensional intensity information through photon counting in either free-running (down to 10-μs integration time) or time-gated mode, but can also perform smart light demodulation with in-pixel background suppression. The latter feature enables phase-resolved imaging for extracting either three-dimensional depth-resolved images or decay lifetime maps, by measuring the phase shift between a modulated excitation light and the reflected photons. Pixel-level memories enable fully parallel processing and global-shutter readout, preventing motion artifacts (e.g., skew, wobble, motion blur) and partial exposure effects. The array is able to acquire very fast optical events at high frame-rate (up to 100 000 fps) and at single-photon level. Low-noise SPADs ensure high dynamic range (up to 110 dB at 100 fps) with peak photon detection efficiency of almost 50% at 410 nm. The SPAD imager provides different operating modes, thus, enabling both time-domain applications, like fluorescence lifetime imaging (FLIM) and fluorescence correlation spectroscopy, as well as frequency-domain FLIM and lock-in 3-D ranging for automotive vision and lidar.
    IEEE Journal of Selected Topics in Quantum Electronics 11/2014; 20(6). DOI:10.1109/JSTQE.2014.2341562 · 3.47 Impact Factor
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    ABSTRACT: 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. CLSM can be easily extended to measure the lifetime of the excited state of fluorescent molecules and their diffusion properties, with Fluorescence Life7 time Imaging Microscopy (FLIM) and Fluorescence Correlation Spectroscopy (FCS), in order to provide additional information about the cell biochemistry. However, these physical parameters cannot be measured simultaneously using conventional CLSM at very high scanning speeds due to photodamage and saturation of the fluorescence signal of the excited molecules or induced phototoxicity to the observed biosystems. To overcome these limitations, we developed a new camera that consists of 1024 Single-Photon Avalanche Diodes (SPADs) which is optimized for multifocal microscopy, FLIM and FCS. We show proof17 of-principle measurements of fluorescence intensity distribution and lifetime of the enhanced Green Fluorescent Protein (eGFP) expressed in live cells and measurement of Quantum Dots (QD) diffusion in solution by FCS using the same detector.
    IEEE Journal of Selected Topics in Quantum Electronics 11/2014; 20(6). DOI:10.1109/JSTQE.2014.2333238 · 3.47 Impact Factor
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    ABSTRACT: 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 photon-number (i.e, intensity) resolved movies 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-resolved maps 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.
    IEEE Journal of Selected Topics in Quantum Electronics 09/2014; 20(6). DOI:10.1109/JSTQE.2014.2342197 · 3.47 Impact Factor
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    ABSTRACT: We present our latest results concerning CMOS Single-Photon Avalanche Diode (SPAD) arrays for high-throughput parallel single-photon counting. We exploited a high-voltage 0.35 μm CMOS technology in order to develop low-noise CMOS SPADs. The Dark Count Rate is 30 cps at room temperature for 30 μm devices, increases to 2 kcps for 100 μm SPADs and just to 100 kcps for 500 μm ones. Afterpulsing is less than 1% for hold-off time longer than 50 ns, thus allowing to reach high count rates. Photon Detection Efficiency is > 50% at 420 nm, > 40% below 500 nm and is still 5% at 850 nm. Timing jitter is less than 100 ps (FWHM) in SPADs with active area diameter up to 50 μm. We developed CMOS SPAD imagers with 150 μm pixel pitch and 30 μm SPADs. A 64×32 SPAD array is based on pixels including three 9-bit counters for smart phase-resolved photon counting up to 100 kfps. A 32x32 SPAD array includes 1024 10-bit Time-to-Digital Converters (TDC) with 300 ps resolution and 450 ps single-shot precision, for 3D ranging and FLIM. We developed also linear arrays with up to 60 pixels (with 100 μm SPAD, 150 μm pitch and in-pixel 250 ps TDC) for time-resolved parallel spectroscopy with high fill factor.
    SPIE Sensing Technology+ Applications; 05/2014
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    ABSTRACT: 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 photon's 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.
    Scientific Reports 04/2014; 4:4685. DOI:10.1038/srep04685 · 5.58 Impact Factor
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    ABSTRACT: 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 μm in a fully standard CMOS process. The 500 μm 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 μm 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.
    Journal of Modern Optics 12/2013; 61(2). DOI:10.1080/09500340.2013.864425 · 1.17 Impact Factor
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    ABSTRACT: We present a compact time-resolved spectrometer suitable for optical spectroscopy from 400 nm to 1 μm wavelengths. The detector consists of a monolithic array of 16 high-precision Time-to-Digital Converters (TDC) and Single-Photon Avalanche Diodes (SPAD). The instrument has 10 ps resolution and reaches 70 ps (FWHM) timing precision over a 160 ns full-scale range with a Differential Non-Linearity (DNL) better than 1.5 % LSB. The core of the spectrometer is the application-specific integrated chip composed of 16 pixels with 250 μm pitch, containing a 20 μm diameter SPAD and an independent TDC each, fabricated in a 0.35 μm CMOS technology. In front of this array a monochromator is used to focus different wavelengths into different pixels. The spectrometer has been used for fluorescence lifetime spectroscopy: 5 nm spectral resolution over an 80 nm bandwidth is achieved. Lifetime spectroscopy of Nile blue is demonstrated.
    12/2013
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    ABSTRACT: We developed a single-photon counting multichannel detection system, based on a monolithic linear array of 32 CMOS SPADs (Complementary Metal-Oxide-Semiconductor Single-Photon Avalanche Diodes). All channels achieve a timing resolution of 100 ps (full-width at half maximum) and a photon detection efficiency of 50% at 400 nm. Dark count rate is very low even at room temperature, being about 125 counts/s for 50 μm active area diameter SPADs. Detection performance and microelectronic compactness of this CMOS SPAD array make it the best candidate for ultra-compact time-resolved spectrometers with single-photon sensitivity from 300 nm to 900 nm.
    The Review of scientific instruments 12/2013; 84(12):123112. DOI:10.1063/1.4850677 · 1.58 Impact Factor
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    ABSTRACT: An estimation and remote state preparation for qubits are demonstrated by implementing a 28 element quantum measurement using an array of detectors and carefully designed imaging optics.
    CLEO: QELS_Fundamental Science; 06/2013
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    ABSTRACT: We experimentally demonstrate a quantum state estimation and tomography for qubits encoded in a single photon's spatial degree of freedom. The experimental setup depicted in Fig. 1 consists of: 1) polarization entangled photon pairs source; 2) spatial encoder allowing to map a polarization state into spatial state; 3) polarization analyzer and 4) spatial state analyzer. The 28 element spatial quantum state measurement set was implemented using imaging optics and a linear array of 28 single photon avalanche diodes (SPAD). The timing information from all the detectors was acquired using custom made FPGA electronics.
    International Quantum Electronics Conference; 05/2013
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    ABSTRACT: 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.
    Proceedings of SPIE - The International Society for Optical Engineering 05/2013; DOI:10.1117/12.2017357 · 0.20 Impact Factor
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    ABSTRACT: We present a single-photon avalanche diode (SPAD) front-end circuitry, in a cost-effective 0.35 $mu{rm m}$ 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.
    IEEE Photonics Technology Letters 04/2013; 25(8):776-779. DOI:10.1109/LPT.2013.2251621 · 2.18 Impact Factor
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    ABSTRACT: This paper presents a time-to-digital converter (TDC) architecture capable of reaching high-precision and high-linearity with moderate area occupation per measurement channel. The architecture is based on a coarse counter and a couple of two-stage interpolators that exploit the cyclic sliding scale technique in order to improve the conversion linearity. The interpolators are based on a new coarse-fine synchronization circuit and a new single-stage Vernier delay loop fine interpolation. In a standard cost-effective 0.35 μm CMOS technology the TDC reaches a dynamic range of 160 ns, 17.2 ps precision and differential non-linearity better than 0.9% LSB rms. The TDC building block was designed in order to be easily assembled in a multi-channel monolithic TDC chip. Coupled with a SPAD photodetector it is aimed for TCSPC applications (like FLIM, FCS, FRET) and direct ToF 3-D ranging.
    Circuits and Systems I: Regular Papers, IEEE Transactions on 03/2013; 60(3):557-569. DOI:10.1109/TCSI.2012.2215737 · 2.30 Impact Factor
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    ABSTRACT: "Indirect" time-of-flight is one technique to obtain depth-resolved images through active illumination that is becoming more popular in the recent years. Several methods and light timing patterns are used nowadays, aimed at improving measurement precision with smarter algorithms, while using less and less light power. Purpose of this work is to present an indirect time-of-flight imaging camera based on pulsed-light active illumination and a 32 × 32 single-photon avalanche diode array with an improved illumination timing pattern, able to increase depth resolution and to reach single-photon level sensitivity.
    Optics Express 02/2013; 21(4):5086-5098. DOI:10.1364/OE.21.005086 · 3.53 Impact Factor
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    ABSTRACT: A CMOS imager that combines single photon sensitivity with photon timing capabilities has been developed for Time-Of-Flight (TOF) measurements and for Time-Correlated Single-Photon Counting (TCSPC) applications. A test structure with 32×4 pixels is presented in this paper. Each pixel is based on a 30 μm diameter Single-Photon Avalanche Diode (SPAD) with low Dark Counting Rate (60 cps at room temperature) and a Time-to-Digital Converter (TDC) with 400 ps resolution. Some preliminary measurements confirm the possibility to use this SPAD array in a 3D TOF scanning system.
    Time-to-Digital Converters (NoMe TDC), 2013 IEEE Nordic-Mediterranean Workshop on; 01/2013