David Stoppa

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

A Time-Resolved, Low-Noise Single-Photon Image Sensor Fabricated in Deep-Submicron CMOS Technology

We report on the design and characterization of a novel time-resolved image sensor fabricated in a 130 nm CMOS process. Each pixel within the 3232 pixel array contains a low-noise single-photon detector and a high-precision time-to-digital converter (TDC). The 10-bit TDC exhibits a timing resolution of 119 ps with a timing uniformity across the entire array of less than 2 LSBs. The differential non-linearity (DNL) and integral non-linearity (INL) were measured at ±0.4 and ±1.2 LSBs, respectively. The pixel array was fabricated with a pitch of 50 μm in both directions and with a total TDC area of less than 2000 μm2. The target application for this sensor is time-resolved imaging, in particular fluorescence lifetime imaging microscopy and 3D imaging. The characterization shows the suitability of the proposed sensor technology for these applications.

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.

A Fully Digital 8

An 8 × 16 pixel array based on CMOS small-area silicon photomultipliers (mini-SiPMs) detectors for PET applications is reported. Each pixel is 570 × 610 μm2 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 × 3 × 5 mm3 LYSO scintillator at 20°C is reported, showing a 511-keV gamma energy resolution of 10.9% and a coincidence timing resolution of 399 ps.

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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

16 SiPM Array for PET Applications With Per-Pixel TDCs and Real-Time Energy Output

Today the cost of solid-state two-dimensional imagers has dramatically dropped, introducing low cost systems on the market suitable for a variety of applications, including both industrial and consumer products. However, these systems can capture only a two-dimensional projection (2D), or intensity map, of the scene under observation, losing a variable of paramount importance, i.e., the arrival time of the impinging photons. Time-Of-Flight (TOF) Range-Imaging (TOF) is an emerging sensor technology able to deliver, at the same time, depth and intensity maps of the scene under observation. Featuring different sensor resolutions, RIM cameras serve a wide community with a lot of applications like monitoring, architecture, life sciences, robotics, etc. This book will bring together experts from the sensor and metrology side in order to collect the state-of-art researchers in these fields working with RIM cameras. All the aspects in the acquisition and processing chain will be addressed, from recent updates concerning the photo-detectors, to the analysis of the calibration techniques, giving also a perspective onto new applications domains.

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

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.

TOF Range-Imaging Cameras

A Time-to-Amplitude Converter (TAC) with embedded analog-to-digital conversion is implemented in a 130-nm CMOS imaging technology. The proposed module is conceived for Single-Photon Avalanche Diode imagers and can operate both as a TAC or as an analog counter, thus allowing both time-correlated or time-uncorrelated imaging operation. A single-ramp, 8-bit ADC with two memory banks to allow high-speed, time-interleaved operation is also included within each module. A 32x32-TACs array has been fabricated with a 50-µm pitch in order prove the highly parallel operation and to test uniformity and power consumption issues. The measured time resolution (LSB) is of 160 ps on a 20-ns time range with a uniformity across the array within ±2LSBs, while DNL and INL are 0.7LSB and 1.9LSB respectively. The average power consumption is below 300µW/pixel when running at 500k measurements per second.

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

A high-speed and hardware-only algorithm using a center of mass method has been proposed for single-detector fluorescence lifetime sensing applications. This algorithm is now implemented on a field programmable gate array to provide fast lifetime estimates from a 32 × 32 low dark count 0.13 μm complementary metal-oxide-semiconductor single-photon avalanche diode (SPAD) plus time-to-digital converter array. A simple look-up table is included to enhance the lifetime resolvability range and photon economics, making it comparable to the commonly used least-square method and maximum-likelihood estimation based software. To demonstrate its performance, a widefield microscope was adapted to accommodate the SPAD array and image different test samples. Fluorescence lifetime imaging microscopy on fluorescent beads in Rhodamine 6G at a frame rate of 50 fps is also shown.

A 32x32-pixel array with in-pixel photon counting and arrival time measurement in the analog domain

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.