INTEGRATED SINGLE-PHOTON SENSING AND PROCESSING PLATFORM IN STANDARD CMOS

Practical implementation of large SPAD-based sensor arrays in the standard CMOS process has been fraught with challenges due to the many performance trade-offs existing at both the device and the system level [1]. At the device level the performance challenge stems from the suboptimal optical characteristics associated with the standard CMOS fabrication process. The challenge at the system level is the development of monolithic readout architecture capable of supporting the large volume of dynamic traffic, associated with multiple single-photon pixels, without limiting the dynamic range and throughput of the sensor. Due to trade-offs in both functionality and performance, no general solution currently exists for an integrated single-photon sensor in standard CMOS single photon sensing and multi-photon resolution. The research described herein is directed towards the development of a versatile high performance integrated SPAD sensor in the standard CMOS process. Towards this purpose a SPAD device with elongated junction geometry and a perimeter field gate that features a large detection area and a highly reduced dark noise has been presented and characterized. Additionally, a novel front-end system for optimizing the dynamic range and after-pulsing noise of the pixel has been developed. The pixel is also equipped with an output interface with an adjustable pulse width response. In order to further enhance the effective dynamic range of the pixel a theoretical model for accurate dead time related loss compensation has been developed and verified. This thesis also introduces a new paradigm for electrical generation and encoding of the SPAD array response that supports fully digital operation at the pixel level while enabling dynamic discrete time amplitude encoding of the array response. Thus offering a first ever system solution to simultaneously exploit both the dynamic nature and the digital profile of the SPAD response. The array interface, comprising of multiple digital inputs capacitively coupled onto a shared quasi-floating sense node, in conjunction with the integrated digital decoding and readout electronics represents the first ever solid state single-photon sensor capable of both photon counting and photon number resolution. The viability of the readout architecture is demonstrated through simulations and preliminary proof of concept measurements

EndoTOFPET-US a Novel Multimodal Tool for Endoscopy and Positron Emission Tomography

The EndoTOFPET-US project aims to jointly exploit Time-Of-Flight Positron Emission Tomography (TOFPET) and ultrasound endoscopy with a multi-modal instrument for the development of new biomarkers for pancreas and prostate oncology. The paper outlines the functionality of the proposed instrument and the challenges for its realization. The high level of miniaturization and integration poses strong demands to the fields of scintillating crystallography, ultra-fast photon detection, highly integrated electronics and system integration. Solutions are presented to obtain a coincidence time resolution better than 200 ps and a spatial resolution of ~1 mm with an asymmetric TOFPET detector. A tracking system with better than 1 mm spatial resolution precision enables the online alignment of the system. The detector design, the production and test status of the single detecto

Time-to-digital converters and histogram builders in SPAD arrays for pulsed-LiDAR

Light Detection and Ranging (LiDAR) is a 3D imaging technique widely used in many applications such as augmented reality, automotive, machine vision, spacecraft navigation and landing. Pulsed-LiDAR is one of the most diffused LiDAR techniques which relies on the measurement of the round-trip travel time of an optical pulse back-scattered from a distant target. Besides the light source and the detector, Time-to-Digital Converters (TDCs) are fundamental components in pulsed-LiDAR systems, since they allow to measure the back-scattered photon arrival times and their performance directly impact on LiDAR system requirements (i.e., range, precision, and measurements rate). In this work, we present a review of recent TDC architectures suitable to be integrated in SPAD-based CMOS arrays and a review of data processing solutions to derive the TOF information. Furthermore, main TDC parameters and processing techniques are described and analyzed considering pulsed-LiDAR requirements

A portable device for time-resolved fluorescence based on an array of CMOS SPADs with integrated microfluidics

[eng] Traditionally, molecular analysis is performed in laboratories equipped with desktop instruments operated by specialized technicians. This paradigm has been changing in recent decades, as biosensor technology has become as accurate as desktop instruments, providing results in much shorter periods and miniaturizing the instrumentation, moving the diagnostic tests gradually out of the central laboratory. However, despite the inherent advantages of time-resolved fluorescence spectroscopy applied to molecular diagnosis, it is only in the last decade that POC (Point Of Care) devices have begun to be developed based on the detection of fluorescence, due to the challenge of developing high-performance, portable and low-cost spectroscopic sensors. This thesis presents the development of a compact, robust and low-cost system for molecular diagnosis based on time-resolved fluorescence spectroscopy, which serves as a general-purpose platform for the optical detection of a variety of biomarkers, bridging the gap between the laboratory and the POC of the fluorescence lifetime based bioassays. In particular, two systems with different levels of integration have been developed that combine a one-dimensional array of SPAD (Single-Photon Avalanch Diode) pixels capable of detecting a single photon, with an interchangeable microfluidic cartridge used to insert the sample and a laser diode Pulsed low-cost UV as a source of excitation. The contact-oriented design of the binomial formed by the sensor and the microfluidic, together with the timed operation of the sensors, makes it possible to dispense with the use of lenses and filters. In turn, custom packaging of the sensor chip allows the microfluidic cartridge to be positioned directly on the sensor array without any alignment procedure. Both systems have been validated, determining the decomposition time of quantum dots in 20 nl of solution for different concentrations, emulating a molecular test in a POC device.[cat] Tradicionalment, l'anàlisi molecular es realitza en laboratoris equipats amb instruments de sobretaula operats per tècnics especialitzats. Aquest paradigma ha anat canviant en les últimes dècades, a mesura que la tecnologia de biosensor s'ha tornat tan precisa com els instruments de sobretaula, proporcionant resultats en períodes molt més curts de temps i miniaturitzant la instrumentació, permetent així, traslladar gradualment les proves de diagnòstic fora de laboratori central. No obstant això i malgrat els avantatges inherents de l'espectroscòpia de fluorescència resolta en el temps aplicada a la diagnosi molecular, no ha estat fins a l'última dècada que s'han començat a desenvolupar dispositius POC (Point Of Care) basats en la detecció de la fluorescència, degut al desafiament que suposa el desenvolupament de sensors espectroscòpics d'alt rendiment, portàtils i de baix cost. Aquesta tesi presenta el desenvolupament d'un sistema compacte, robust i de baix cost per al diagnòstic molecular basat en l'espectroscòpia de fluorescència resolta en el temps, que serveixi com a plataforma d'ús general per a la detecció òptica d'una varietat de biomarcadors, tancant la bretxa entre el laboratori i el POC dels bioassaigs basats en l'anàlisi de la pèrdua de la fluorescència. En particular, s'han desenvolupat dos sistemes amb diferents nivells d'integració que combinen una matriu unidimensional de píxels SPAD (Single-Photon Avalanch Diode) capaços de detectar un sol fotó, amb un cartutx microfluídic intercanviable emprat per inserir la mostra, així com un díode làser UV premut de baix cost com a font d'excitació. El disseny orientat a la detecció per contacte de l'binomi format pel sensor i la microfluídica, juntament amb l'operació temporitzada dels sensors, permet prescindir de l'ús de lents i filtres. Al seu torn, l'empaquetat a mida de l'xip sensor permet posicionar el cartutx microfluídic directament sobre la matriu de sensors sense cap procediment d'alineament. Tots dos sistemes han estat validats determinant el temps de descomposició de "quantum dots" en 20 nl de solució per a diferents concentracions, emulant així un assaig molecular en un dispositiu POC

High linearity SPAD and TDC array for TCSPC and 3D ranging applications

An array of 32x32 Single-Photon Avalanche-Diodes (SPADs) and Time-to-Digital Converters (TDCs) has been fabricated in a 0.35 mu m automotive-certified CMOS technology. The overall dimension of the chip is 9x9 mm(2). Each pixel is able to detect photons in the 300 nm - 900 nm wavelength range with a fill-factor of 3.14% and either to count them or to time stamp their arrival time. In photon-counting mode an in-pixel 6-bit counter provides photon-number-resolved intensity movies at 100 kfps, whereas in photon-timing mode the 10-bit in-pixel TDC provides time-resolved maps (Time-Correlated Single-Photon Counting measurements) or 3D depth-resolved (through direct time-of-flight technique) images and movies, with 312 ps resolution. The photodetector is a 30 mu m diameter SPAD with low Dark Count Rate (120 cps at room temperature, 3% hot-pixels) and 55% peak Photon Detection Efficiency (PDE) at 450 nm. The TDC has a 6-bit counter and a 4-bit fine interpolator, based on a Delay Locked Loop (DLL) line, which makes the TDC insensitive to process, voltage, and temperature drifts. The implemented sliding-scale technique improves linearity, giving 2% LSB DNL and 10% LSB INL. The single-shot precision is 260 ps rms, comprising SPAD, TDC and driving board jitter. Both optical and electrical crosstalk among SPADs and TDCs are negligible. 2D fast movies and 3D reconstructions with centimeter resolution are reported

A CMOS Imager for Time-of-Flight and Photon Counting Based on Single Photon Avalanche Diodes and In-Pixel Time-to-Digital Converters

The design of a CMOS image sensor based on single-photon avalanche-diode (SPAD) array with in-pixel time-to-digital converter (TDC) is presented. The architecture of the imager is thoroughly described with emphasis on the characterization of the TDCs array. It is targeted for 3D image reconstruction. Several techniques as fast quenching/recharge circuit with tunable dead-time and time gated-operation are applied to reduce the noise and the power consumption. The chip was fabricated in a 0.18 m standard CMOS process and implements a double functionality: time-of-flight (ToF) estimation and photon counting. The imager features a programmable time resolution of the array of TDCs down to 145 ps. The measured accuracy of the minimum time bin is lower than 1LSB DNL and 1.7 LSB INL. The TDC jitter over the full dynamic range is less than 1 LSB.Peer reviewe

A CMOS Imager for Time-of-Flight and Photon Counting Based on Single Photon Avalanche Diodes and In-Pixel Time-to-Digital Converters

The design of a CMOS image sensor based on single-photon avalanche-diode (SPAD) array with in-pixel time-to-digital converter (TDC) is presented. The architecture of the imager is thoroughly described with emphasis on the characterization of the TDCs array. It is targeted for 3D image reconstruction. Several techniques as fast quenching/recharge circuit with tunable dead-time and time gated-operation are applied to reduce the noise and the power consumption. The chip was fabricated in a 0.18 m standard CMOS process and implements a double functionality: time-of-flight (ToF) estimation and photon counting. The imager features a programmable time resolution of the array of TDCs down to 145 ps. The measured accuracy of the minimum time bin is lower than 1LSB DNL and 1.7 LSB INL. The TDC jitter over the full dynamic range is less than 1 LSB.Office of Naval Research (USA) N000141410355Ministerio de Economía y Competitividad TEC2012-38921- C02, IPT-2011-1625-430000, IPC- 20111009 CDTIJunta de Andalucía TIC 2012-233