Lucio Pancheri

A CMOS 3-D Imager Based on Single Photon Avalanche Diode

A 64-pixel linear array aimed at 3-D vision applications is implemented in a high-voltage 0.8 mum CMOS technology. The detection of the incident light signals is performed using photodiodes biased above breakdown voltage so that an extremely high sensitivity can be achieved exploiting the intrinsic multiplication effect of the avalanche phenomenon. Each 38times180-mum2 pixel includes, besides the single photon avalanche diode, a dedicated read-out circuit for the arrival-time estimation of incident light pulses. To increase the distance measurement resolution a multiple pulse measurement is used, extracting the mean value of the light pulse arrival-time directly in each pixel; this innovative approach dramatically reduces the dead-time of the pixel read-out, allowing a high frame rate imaging to be achieved. The sensor array provides a range map from 2 m to 5 m with a precision better than plusmn0.75% without any external averaging operation. Moreover, with the same chip, we have explored for the first time the implementation of an indirect time-of-flight measurement by operating the proposed active pixel in the photon counting mode

Single-Photon Avalanche Diode CMOS Sensor for Time-Resolved Fluorescence Measurements

A single-photon avalanche diode-based pixel array for the analysis of fluorescence phenomena is presented. Each 180 times 150 - mum2 pixel integrates a single photon detector combined with an active quenching circuit and a 17-bit digital events counter. On-chip master logic provides the digital control phases required by the pixel array with a full programmability of the main timing synchronisms. The pixel exhibits an average dark count rate of 3 kcps and a dynamic range of over 120-dB in time uncorrelated operation. A complete characterization of the single photon avalanche diode characteristics is reported. Time-resolved fluorescence measurements have been demonstrated by detecting the fluorescence decay of quantum-dot samples without the aid of any optical filters for excitation laser light cutoff.

CMOS Single-Photon Avalanche Diode Array for Time-Resolved Fluorescence Detection

A single photon avalanche diode detector for the analysis of fluorescence phenomena is presented. The 14-pixels array, fabricated in a conventional high voltage 0.35-mum CMOS technology, allows measuring photon densities as low as 108 photons/cm2s. Each 180times150-mum2 pixel integrates a single photon avalanche diode combined with an active quenching circuit and a 17-bit digital events counter. On chip master logic provides the digital control phases required by the pixel array with a full programmability of the main timing synchronisms. Time-resolved measurements has been demonstrated by detecting a 10ns, 10pW (peak-power on the pixel) light pulse with a typical resolution of 80ps

A hybrid CMOS-imager with a solution-processable polymer as photoactive layer

The solution-processability of organic photodetectors allows a straightforward combination with other materials, including inorganic ones, without increasing cost and process complexity significantly compared with conventional crystalline semiconductors. Although the optoelectronic performance of these organic devices does not outmatch their inorganic counterparts, there are certain applications exploiting the benefit of the solution-processability. Here we demonstrate that the small pixel fill factor of present complementary metal oxide semiconductor-imagers, decreasing the light sensitivity, can be increased up to 100% by replacing silicon photodiodes with an organic photoactive layer deposited with a simple low-cost spray-coating process. By performing a full optoelectronic characterization on this first solution-processable hybrid complementary metal oxide semiconductor-imager, including the first reported observation of different noise types in organic photodiodes, we demonstrate the suitability of this novel device for imaging. Furthermore, by integrating monolithically different organic materials to the chip, we show the cost-effective portability of the hybrid concept to different wavelength regions.

A Range Image Sensor Based on 10-

This paper presents the design and characterization of a lock-in pixel array based on a buried channel photo-detector aimed at time-of-flight range imaging. The proposed photo-demodulator has been integrated in a 10-μm pixel pitch with a fill factor of 24%, and is capable of a maximum demodulation frequency of 50 MHz with a contrast of 29.5%. The sensor has been fabricated in a 0.18-μm CMOS imaging technology and assembled in a range camera system setup. The system provides a stream of three-dimensional images at 5-20 fps on a 3-6 m range, with a linearity error lower than 0.7% and a repeatability of 5-16 cm, while the best achievable precision is 2.7 cm at a 50-MHz modulation frequency.

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The implementation of single-photon avalanche diode detectors (SPAD) in a standard high voltage 0.7-mum CMOS technology is presented. Two different device structures, combined with integrated quenching circuits, have been fabricated and successfully tested. A novel biasing scheme is proposed allowing the reduction of afterpulsing effect and the decrease of minimum device-to-device distance. Good noise performance is obtained for the 100 mum2 active area device where over 50% of the population has a dark count rate below lOOcps and afterpulsing lower than 0.3% with a 4-V excess bias and a 32-ns dead time. The peak photon detection probability is about 30%, while the overall system, upper limit, for the time resolution is 144 ps.

Lock-In Pixels in 0.18-

A monolithic 64-pixel linear array for Fluorescence Lifetime Imaging applications is presented. Each pixel includes four actively quenched Single Photon Avalanche Diodes, four gated 8-bit counters and is capable of measuring single and double exponential decays. The array has a 34% fill factor, a maximum throughput rate of 320 Mbps, and has been tested up to 40 MHz laser repetition rate. Preliminary fluorescence measurements have been performed obtaining a 6% lifetime precision in 660 µs accumulation time and a very good uniformity among the pixels.

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This paper presents the design and electro-optical test of a 160 × 120-pixels CMOS sensor specifically conceived for Time-Of-Flight 3D imaging. The in-pixel processing allows the implementation of Indirect Time-Of-Flight technique for distance measurement with reset noise removal through Correlated Double Sampling and embedded fixed-pattern noise reduction, whereas a fast readout operation allows the pixels values to be streamed out at a maximum rate of 10 MSample/s. The imager can operate as a fast 2D camera up to 458 fps, as a 3D camera up to 80 fps, or even coupling both operation modes. The chip has been fabricated using a standard 0.18 μm 1P4M 1.8 V CMOS technology with MIM capacitors. The resulting pixel has a pitch of 29.1 μm with a fill-factor of 34% and includes 66 transistors. Distance measurements up to 4.5 m have been performed with pulsed laser light, achieving a best precision of 10 cm at 1 m in real-time at 55 fps and 175 mA current consumption.

m CMOS Imaging Technology

In this paper, we report on an avalanche photodiode (APD) fabricated in a standard 0.35-mum CMOS technology. The main electrooptical characteristics of the device are presented, showing a remarkably low-noise factor if compared to other CMOS APDs. An estimation of the noise properties of a pixel based on the proposed photodiode with charge-amplifier readout is performed, showing that it could have an improved noise performance with respect to a standard photodiode-based pixel.

Low-Noise CMOS single-photon avalanche diodes with 32 ns dead time

This paper presents a 32 × 32 pixel image sensor for time-gated fluorescence lifetime detection based on single-photon avalanche diodes. The sensor, fabricated in a high-voltage 0.35- μm CMOS technology, uses an analog counting approach to minimize the area occupation of pixel electronics while maintaining a nanosecond timing resolution and shot-noise-limited operation. The all nMOS pixel is formed by 12 transistors and features 25- μm pitch and 20.8% fill factor. The chip includes a phase-locked loop circuit for gating window generation, working at a maximum repetition frequency of 40 MHz, while the sensor can be gated at frequency up to 80 MHz using an external delay generator. Optical characterization with a picosecond-pulsed laser showed a minimum gating window width of 1.1 ns. Example images acquired in both continuous and time-gated mode are presented, together with a lifetime image obtained with the sensor mounted on a fluorescence microscope.