Digital silicon photomultipliers (dSiPMs) and single-photon avalanche diode (SPAD) imagers are optical sensing systems formed from the integration of time-to-digital converters (TDCs) with arrays of highly sensitive photodetectors known as SPADs. TDCs are high-performance mixed-signal circuits capable of timestamping events with picosecond level resolution. The digital operation mechanisms of SPADs allow for their outputs to be sent to TDCs, where the timestamps of individual photon detections are recorded. In recent years, time-resolved SPAD-based sensors have been a heavily studied topic due to their exceptional performance potential in biomedical imaging applications, including time-of-flight (ToF) positron emission tomography (PET), fluorescence lifetime imaging microscopy (FLIM), and diffuse optical tomography (DOT). This work targets the optimization of these sensors in low-cost standard complementary metal-oxide-semiconductor (CMOS) processes. Firstly, this thesis provides a detailed review of the work accomplished in CMOS TDCs and their integration in SPAD-based sensors. Next, a feedback time amplification TDC was designed and tested in the TSMC 65 nm process that can achieve < 5 ps timing resolution in a very compact area of 0.016 mm2. The design is then described for a multi-time-gated array of p+/n-well SPADs that aims to mitigate SPAD dark noise while providing high-speed imaging by applying shifted gate windows simultaneously to an array of SPADs. The p+/n-well SPAD is first characterized in a passive quench configuration where it demonstrated a maximum dark count rate of 44.9 kHz, 18.1% peak PDP at 420 nm, and 0.82 ns timing jitter at a 0.7 V excess bias. While the current multi-time-gated prototype is not fully functional, the measurement results for individual pixels of the multi-time-gated array showed a 3.25 ns median gate window with a 2.2x 10-4 dark count probability for a 0.7 V excess bias, with 440 ps timing resolution and ~1 LSBrms timing jitter. Based on the results, limitations of the current design and sources for future improvement are then discussed in detail. / Thesis / Master of Applied Science (MASc) / Medical imaging plays a key role in the diagnosis of diseases like cancer, and as such, the optimized performance of medical imaging systems is a large area of research. Recently, highly sensitive photodetectors known as single-photon avalanche diodes (SPADs) were integrated with high-performance timing circuits known as time-to-digital converters (TDCs) to form digital silicon photomultipliers (dSiPMs) and SPAD imagers. DSiPMs and SPAD imagers are capable of timestamping the detection of individual photons with a very high level of accuracy in order to generate biomedical images. This thesis focuses on the design and measurement of these sensors using standard fabrication processes with the aim of working towards high-performance medical imaging sensors at a low cost. Firstly, we review the results achieved in TDCs and SPAD-based sensors within the recent literature. Following that, we present the design and performance results of a custom-designed TDC that aims to achieve state-of-the-art performance within a small area in order to maintain low-cost and optimal integration with SPADs. Next, the design is described for an array of custom time-gated SPADs with integrated TDCs. Finally, the SPAD is characterized in two different configurations to identify sources of improvement for future design iterations.

Single-photon avalanche diodes (SPADs) capable of single photon detection are promising optical sensors for use as receivers in optical wireless communication (OWC) systems. In SPAD-based receivers, the intersymbol interference (ISI) effect caused by dead time is an important drawback that limits performance. In this thesis, we propose two novel SPAD operation receivers to reduce the ISI effect in SPAD-based OWC. To validate the feasibility of these two modes, we design a free-running SPAD front-end circuit with post-layout transient simulation results. This SPAD circuit is improved by a novel mixed passive-active quench and reset front-end circuit that achieves a very short dead time. Based on the traditional free-running mode, we design the clock-driven mode and time-gated mode to reduce the ISI effect through time-controlled operating signals. In this work, we develop a new simulation system to assess the ISI effect in On-Off Keying (OOK) modulated communication and pulse position modulated (PPM) communication. To accurately evaluate these three modes, we build a OWC platform to test our proposed SPAD receiver manufactured by TSMC 65 nm process. The Test results demonstrate that the clock-driven mode and time-gated mode receivers can improve the bit error rate (BER) performance in low data rate communication and high data rate high optical power communication, respectively. Moreover, compared to the free-running mode, the two proposed time-controlled modes achieve higher data rate communication and better noise tolerance ability in SPAD-based OWC. / Thesis / Master of Applied Science (MASc) / Optical communication involves using light as a signal to transmit information, and it is currently a highly popular field of research. However, optical receivers used in this type of communication often require specific conditions, which can limit the overall performance of the communication system. To address this issue, we have developed an optical sensor tailored for optical communication. This sensor boasts exceptional sensitivity, allowing it to detect individual particles of light, thereby substantially reducing the demand for signal intensity in the optical communication system. Moreover, we have devised three operational circuits that enhance the sensor's responsiveness to signals under specific communication conditions. We have created a mathematical model to evaluate the proposed optical sensor and the designed circuits, and subsequently manufactured the optical sensor. Both the simulation results and the actual test outcomes unequivocally demonstrate that our proposed sensor has the potential to enhance the performance of optical communication systems.

There is a pressing need to develop alternative communications links due to a number of physical phenomena, limiting the bandwidth and energy efficiency of wire-based systems or economic factors such as cost, material-supply reliability and environmental costs. Networks have moved to optical connections to reduce costs, energy use and to supply high data rates. A primary concern is that current optical-detection devices require high optical power to achieve fast data rates with high signal quality. The energy required therefore, quickly becomes a problem. In this thesis, advances in single-photon avalanche diodes (SPADs) are utilised to reduce the amount of light needed and to reduce the overall energy budget. Current high performance receivers often use exotic materials, many of which have severe environmental impact and have cost, supply and political restrictions. These present a problem when it comes to integration; hence silicon technology is used, allowing small, mass-producible, low power receivers. A reconfigurable SPAD-based integrating receiver in standard 130nm imaging CMOS is presented for links with a readout bandwidth of 100MHz. A maximum count rate of 58G photon/s is observed, with a dynamic range of ≈ 79dB, a sensitivity of ≈ −31.7dBm at 100MHz and a BER of ≈ 1x10−9. We investigate the properties of the receiver for optical communications in the visible spectrum, using its added functionality and reconfigurability to experimentally explore non-ideal influences. The all-digital 32x32 SPAD array, achieves a minimum dead time of 5.9ns, and a median dark count rate (DCR) of 2.5kHz per SPAD. High noise devices can be weighted or removed to optimise the SNR. The power requirements, transient response and received data are explored and limiting factors similar to those of photodiode receivers are observed. The thesis concludes that data can be captured well with such a device but more electrical energy is needed at the receiver due to its fundamental operation. Overall, optical power can be reduced, allowing significant savings in either transmitter power or the transmission length, along with the advantages of an integrated digital chip.

With data throughput increasing exponentially in wireless communication networks, the limited radio frequency (RF) spectrum is unable to meet the future data rate demand. As a promising complementary approach, optical wireless communication (OWC) has gained significant attention since its licence-free light spectrum provides a considerable amount of communication bandwidth. In conventional OWC systems, the information-carried signal has to be real-valued and non-negative due to the incoherent light output of the conventional optical transmitter, light emitting diode (LED). Therefore, an intensity modulation and direct detection (IM/DD) system is used for establishing the OWC link. Some modified orthogonal frequency division multiplexing (OFDM) schemes have been proposed to achieve suitable optical signals. In previous research, three OFDM-based schemes have been presented, including DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and unipolar orthogonal frequency division multiplexing (U-OFDM). Basic concepts of SPAD receivers are studied and a novel application in OWC is proposed for a permanent downhole monitoring (PDM) system in the gas and oil industry. In this thesis, a complete model of the SPAD-based OWC system is presented, including some related SPAD metrics, the photon counting process in SPAD and a specific nonlinear distortion caused by passive quenching (PQ) and active quenching (AQ) recharged circuits. Moreover, a practical SPAD-based visible light communication (VLC) system and its theoretical analysis are presented in a long-distance gas pipe with a battery-powered LED and a basic on-off keying (OOK) modulation scheme. In this thesis, two novel optical orthogonal frequency division multiplexing (O-OFDM) technologies are proposed: non-DC-biased orthogonal frequency division multiplexing (NDCOFDM) and OFDM with single-photon avalanche diode (SPAD). The former is designed for optical multiple-input multiple-output (O-MIMO) systems based on the optical spatial modulation (OSM) technique. In NDC-OFDM, signs of modulated O-OFDM symbols and absolute values of the symbols are separately transmitted by different information carrying units. This scheme can eliminate clipping distortion in DCO-OFDM and achieve high power efficiency. Furthermore, as the indices of transmitters carry extra information bits, NDC-OFDM gives a significant improvement in spectral efficiency over ACO-OFDM and U-OFDM. In this thesis, SPAD-based OFDM systems with DCO-OFDM and ACO-OFDM are presented and analysed by considering the nonlinear distortion effect of PQ SPAD and AQ SPAD. A comprehensive digital signal processing of SPAD-based OFDM is shown and theoretical functions of the photon counting distribution in PQ SPAD and AQ SPAD are given. Moreover, based on Bussgang theorem, a conventional method for analysing memoryless distortion, close-formed bit-error rate (BER) expressions of SPAD-based OFDM are derived. Furthermore, SPAD-based OFDM is compared with conventional photo-diode (PD) based OFDM systems, and a gain of 40 dB in power efficiency is observed.

FLIM is branch of microscopy mainly used in biology which is quickly improving thanks to a rapid enhancement of instrumentation and techniques enabled by new sensors. In FLIM, the most precise method of measuring fluorescent decays is called TCSPC. High voltage PMT detection devices together with costly and bulky optical setups which scan the sample are usually required in TCSPC instrumentation. SPADs have enabled a big improvement in TCSPC measurement setup, providing a CMOS compatible device which can be designed in wide arrays format. However, sensors providing in-pixel TCSPC do not scale in size and in large array like the time-gated SPAD pixel sensors do. Time-gated pixels offer a less precise lifetime estimation, discarding any photon information outside a given time window, but this loss in photon-efficiency is offset by gains in pixel size. This work is aimed at the development of a wide field TCSPC sensor with a pixel size and fill factor able to reduce the cost of such devices and to obtain a high resolution time-resolved fluorescence image in the shortest time possible. The study focuses on SPAD and pixel design required to maximise the fill factor in sub 10 μm pixel pitch. Multiple pixel designs are proposed in order to reduce pixel area and so enable affordable wide array TCSPC systems. The first proposed pixel performs the CMM lifetime estimation in order to reduce the frame rate needed to stream the data out of the SPAD array. This pixel is designed in a 10 μm pitch and attains with the most aggressive design a fill factor of 10:17 %. A second design proposes an analogue TCSPC which consists in a S/H TAC circuitry. This simpler pixel can achieve a higher fill factor of 19:63% as well as smaller pitch of 8 μm thanks to the adoption of SPAD n-well and electronics area sharing. This last design is implemented in a 320 x 256 SPAD array in which is included part of a novel ADC aimed at reduction of the processing time required to build a TCSPC histogram. A more conventional analogue readout is used to evaluate the pixel performance as well as a more fine TCSPC histogram. The device was used to measure the fluorescence lifetime of green micro-spheres while the 2b flash ADC is used to demonstrate rapid resolution and separation of two different fluorescence decays.

Single-photon avalanche diodes’ (SPADs) capabilities of detecting even a single photon with excellent timing resolution and compatibility with strong magnetic fields make them the most promising sensor for positron emission tomography imaging systems. With the advancements of silicon fabrication techniques, SPADs designed in standard planar complementary metal-oxide-semiconductor (CMOS) processes show competitive performance and a lower manufacturing cost. Additionally, CMOS SPADs have the potential for monolithic integration with other CMOS signal conditioning and processing circuits to achieve simple, low-cost, and high-performance imaging solutions. This work targets the design and optimization of SPAD sensors to improve their performance using low-cost standard CMOS technologies. Firstly, a detailed review on the SPADs in recent literature is presented. Then, the random telegraph signal (RTS) noise is investigated based on n+/p-well SPADs fabricated in a standard 130 nm CMOS process. Through the measurements and analysis, the RTS noise of a SPAD is found to correlate with its dark count rate and afterpulsing. Next, we design n+/p-well SPADs with field poly gates to improve the noise performance. Furthermore, a SPAD pixel, consisting of a p+/n-well SPAD and a compact and high-speed active quench and reset circuit is designed and fabricated in a standard TSMC 65 nm CMOS process. The post-layout simulations show that this pixel achieves a short 0.1 ns quenching time and a 3.35 ns minimum dead time. The measurement results show that the SPAD pixel has a dark count rate of 21 kHz, a peak photon detection probability of 23.8% at a 420 nm wavelength and a timing jitter of 139 ps using a 405 nm pulsed laser when the excess voltage is set to 0.5 V. Due to the short quenching time, almost no afterpulsing is observed even at a low operating temperature of -35 °C. Finally, a new differential quench and reset (QR) circuit consisting of two QR circuits on both the cathode and anode to quench and reset the SPAD through both terminals is proposed to reduce the reset time, to increase the count rate, to reduce the afterpulsing and to reject the common-mode noise. / Thesis / Doctor of Philosophy (PhD) / Positron emission tomography (PET) imaging is a powerful tool for diagnosis and assessment of cancers and tumors in the clinical field. Due to their capabilities of detecting even a single photon, excellent timing resolution, and their compatibility with magnetic fields to build PET/MRI (magnetic resonance imaging) multimodal imaging systems; single-photon avalanche diodes (SPADs) become the most promising sensor technology for PET imaging applications. SPADs fabricated in standard complementary metal-oxide-semiconductor (CMOS) technologies allow for a lower manufacturing cost and present the potential to integrate with other CMOS circuits to form a complete imaging system. In this thesis, random telegraph signal noise in SPADs is investigated first. Then, the poly gate is used in the design of an n+/p-well SPAD to improve the noise performance. In addition, a compact and high-speed SPAD pixel is designed and fabricated using an advanced standard CMOS process. Thanks to the fast quench and reset circuit, the SPAD pixel achieves a very short quenching time and a high-count rate. Finally, a differential quench and reset (QR) circuit consisting of two QR circuits on both the cathode and anode to quench and reset the SPAD through both terminals is proposed and studied.

No description available.

Fluorescence based analysis is a fundamental research technique used in the life sciences. However, conventional fluorescence intensity measurements are prone to misinterpretation due to illumination and fluorophore concentration non-uniformities. Thus, there is a growing interest in time-resolved fluorescence detection, whereby the characteristic fluorescence decay time-constant (or lifetime) in response to an impulse excitation source is measured. The sensitivity of a sample’s lifetime properties to the micro-environment provides an extremely powerful analysis tool. However, current fluorescence lifetime analysis equipment tends to be bulky, delicate and expensive, thereby restricting its use to research laboratories. Progress in miniaturisation of biological and chemical analysis instrumentation is creating low-cost, robust and portable diagnostic tools capable of high-throughput, with reduced reagent quantities and analysis times. Such devices will enable point-of-care or in-the-field diagnostics. It was the ultimate aim of this project to produce an integrated fluorescence lifetime analysis system capable of sub-nano second precision with an instrument measuring less than 1cm3, something hitherto impossible with existing approaches. To accomplish this, advances in the development of AlInGaN micro-LEDs and high sensitivity CMOS detectors have been exploited. CMOS allows electronic circuitry to be integrated alongside the photodetectors and LED drivers to produce a highly integrated system capable of processing detector data directly without the need for additional external hardware. In this work, a 16x4 array of single-photon avalanche diodes (SPADs) integrated in a 0.35μm high-voltage CMOS technology has been implemented which incorporates two 9-bit, in-pixel time-gated counter circuits, with a resolution of 400ps and on-chip timing generation, in order to directly process fluorescence decay data. The SPAD detector can accurately capture fluorescence lifetime data for samples with concentrations down to 10nM, demonstrated using colloidal quantum dot and conventional fluorophores. The lifetimes captured using the on-chip time gated counters are shown to be equivalent to those processed using commercially available external time-correlated single-photon counting (TCSPC) hardware. A compact excitation source, capable of producing sub-nano second optical pulses, was designed using AlInGaN micro-LEDs bump-bonded to a CMOS driver backplane. A series of driver array designs are presented which are electrically contacted to an equivalent array of micro-LEDs emitting at a wavelength of 370nm. The final micro-LED driver design is capable of producing optical pulses of 300ps in width (full width half maximum, FWHM) and a maximum DC optical output power of 550μW, this is, to the best of our knowledge, the shortest reported optical pulse from a CMOS driven micro-LED device. By integrating an array of CMOS SPAD detectors and an array of CMOS driven AlInGaN micro-LEDs, a complete micro-system for time-resolved fluorescence analysis has been realised. Two different system configurations are evaluated and the ability of both topologies to accurately capture lifetime data is demonstrated. By making use of standard CMOS foundry technologies, this work opens up the possibility of a low-cost, portable chemical/bio-diagnostic device. These first-generation prototypes described herein demonstrate the first time-resolved fluorescence lifetime analysis using an integrated micro-system approach. A number of possible design improvements have been identified which could significantly enhance future device performance resulting in increased detector and micro-LED array density, improved time-gate resolution, shorter excitation pulse widths with increased optical output power and improved excitation light filtering. The integration of sample handling elements has also been proposed, allowing the sample of interest to be accurately manipulated within the micro-environment during investigation.

In order to improve the sensitivity of an optical receiver, the gain and the collection area of the photo-detectors within the receiver should be increased. Detectors with internal gain such as avalanche photodiodes (APD) are usually used to increase the sensitivity of the receiver. One problem with APDs is the sensitivity of their gain to their bias voltage, which makes them challenging to be fabricated in a standard CMOS process due to variations in their gain. However, when an APD is biased over its breakdown voltage, it is sensitive to a single photon, hence, referred to as a single photon avalanche diodes (SPAD). The SPADs are photon-counting detectors, which are less sensitive to their bias voltage, and can be integrated with rest of the electronic circuitry that form an optical receiver. An avalanche diode requires dedicated circuits to be operated in the SPAD mode. These circuits make the diode insensitive to an incident photon for a duration that is known as deadtime. Unfortunately, The collection area of the PD, APD, and SPADs are limited to their capacitance. Hence, a large photo-detector leads to a larger capacitance, which reduces the bandwidth of the receiver. In this thesis, a photon counting optical receiver based on an array of SPADs is proposed which increases the collection area with a low output capacitance. The avalanche diode and peripheral circuits which operate and readout-out the SPAD array are fabricated in the commercially available UMC 0.18 μm CMOS process. Initially, the avalanche diode is tested and characterised. A high performance circuit is then designed and tested which is able to achieve short deadtimes up to 4 ns. Once the photon counting operation of the SPAD is verified, a numerical model is developed to investigate the influence of several factors, including the deadtime, on the performance of the photon-counting detector in a communication link. Based on the simulation results, which show the advantages of an array over a single detector, a prototype detector array of 64 asynchronous SPADs is designed and tested. This array uses a high-speed readout mechanism which is inspired by the current steering digital-to-analogue converters. Bit error ratio tests (BERT) verify the photon counting capability of the proposed detector, and a bit error rate of 1E-3 has been achieved at data rate of 100 Mbps. In addition, the array of SPAD is compatible with a front-end of conventional optical receiver which uses a photodiode as a photo detector.

De nombreuses applications en sciences nucléaires bénéficieraient d’un détecteur possédant une précision temporelle de 10 ps largeur à mi-hauteur à la mesure d’un photon unique. Par exemple, le projet de Time-Imaging Calorimeter en cours de conception au CERN requiert un détecteur possédant une telle précision temporelle afin de mesurer le temps de vol (TDV) et la trajectoire des particules émises lors des collisions dans les expériences du Large Hadron Collider (LHC), ce qui permet d’identifier ces dites particules. De plus, un détecteur possédant une précision temporelle de l’ordre de 10 ps permettra la mitigation de l’empilement des événements. Un second exemple est la tomographie d’émission par positrons (TEP), une modalité d’imagerie médicale non-invasive qui mesure la distribution d’un traceur radioactif afin d’étudier et détecter le cancer. Dans le but de développer un scanner TEP temps réel, le groupe de recherche en appareillage médical de Sherbrooke (GRAMS) travaille sur l’intégration de la mesure du TDV de l’interaction TEP. Les meilleures performances actuelles des détecteurs TEP se situent aux alentours de 150 ps, ce qui n’est pas suffisant pour intégrer le TDV dans un scanner TEP préclinique. Cette mesure exige une résolution temporelle TEP de l’ordre de 10 ps. La solution proposée par le GRAMS est de développer un module de comptage monophotonique (MCMP) 3D qui est composé d’une matrice de photodiodes avalanches monophotoniques (PAMP) reliée par des interconnexions verticales (TSV) à une matrice de circuits de lecture composée d’un circuit d’étouffement et d’un convertisseur temps-numérique. Ce détecteur permet donc de mesurer précisément le temps d’arrivée de chaque photon détecté. Ce document présente la conception du circuit d’étouffement réalisé en technologie CMOS 65 nm de TSMC (Taiwan Semiconductor Manufacturing Company) intégré à chaque pixel de 50 × 50 µm2 dans un MCMP 3D. Afin de répondre au besoin de précision temporelle de 10 ps dans un détecteur 3D, le circuit proposé est un circuit d’étouffement passif avec une recharge active possédant un amplificateur opérationnel en boucle ouverte à titre de comparateur de tension. L’amplificateur opérationnel utilisé possède un seuil ajustable de 0 à 2,5 V afin d’être en mesure d’évaluer le seuil optimal pour la mesure de gigue temporelle avec une PAMP. La taille finale du circuit d’étouffement est de 18 × 30 µm2 incluant l’amplificateur qui est d’une taille de 13 × 8 µm2, ce qui représente respectivement environ 22% et 4% de la taille totale du pixel. Le circuit d’étouffement possède une gigue temporelle de 4 ps largeur à mi-hauteur (LMH). Les résultats obtenus prouvent qu’il est possible d’intégrer de l’électronique de lecture de PAMP dans un MCMP 3D possédant des performances temporelles sous les 10 ps.