Low-power CMOS digital-pixel Imagers for high-speed uncooled PbSe IR applications

This PhD dissertation describes the research and development of a new low-cost medium wavelength infrared MWIR monolithic imager technology for high-speed uncooled industrial applications. It takes the baton on the latest technological advances in the field of vapour phase deposition (VPD) PbSe-based medium wavelength IR (MWIR) detection accomplished by the industrial partner NIT S.L., adding fundamental knowledge on the investigation of novel VLSI analog and mixed-signal design techniques at circuit and system levels for the development of the readout integrated device attached to the detector. The work supports on the hypothesis that, by the use of the preceding design techniques, current standard inexpensive CMOS technologies fulfill all operational requirements of the VPD PbSe detector in terms of connectivity, reliability, functionality and scalability to integrate the device. The resulting monolithic PbSe-CMOS camera must consume very low power, operate at kHz frequencies, exhibit good uniformity and fit the CMOS read-out active pixels in the compact pitch of the focal plane, all while addressing the particular characteristics of the MWIR detector: high dark-to-signal ratios, large input parasitic capacitance values and remarkable mismatching in PbSe integration. In order to achieve these demands, this thesis proposes null inter-pixel crosstalk vision sensor architectures based on a digital-only focal plane array (FPA) of configurable pixel sensors. Each digital pixel sensor (DPS) cell is equipped with fast communication modules, self-biasing, offset cancellation, analog-to-digital converter (ADC) and fixed pattern noise (FPN) correction. In-pixel power consumption is minimized by the use of comprehensive MOSFET subthreshold operation. The main aim is to potentiate the integration of PbSe-based infra-red (IR)-image sensing technologies so as to widen its use, not only in distinct scenarios, but also at different stages of PbSe-CMOS integration maturity. For this purpose, we posit to investigate a comprehensive set of functional blocks distributed in two parallel approaches: • Frame-based “Smart” MWIR imaging based on new DPS circuit topologies with gain and offset FPN correction capabilities. This research line exploits the detector pitch to offer fully-digital programmability at pixel level and complete functionality with input parasitic capacitance compensation and internal frame memory. • Frame-free “Compact”-pitch MWIR vision based on a novel DPS lossless analog integrator and configurable temporal difference, combined with asynchronous communication protocols inside the focal plane. This strategy is conceived to allow extensive pitch compaction and readout speed increase by the suppression of in-pixel digital filtering, and the use of dynamic bandwidth allocation in each pixel of the FPA. In order make the electrical validation of first prototypes independent of the expensive PbSe deposition processes at wafer level, investigation is extended as well to the development of affordable sensor emulation strategies and integrated test platforms specifically oriented to image read-out integrated circuits. DPS cells, imagers and test chips have been fabricated and characterized in standard 0.15μm 1P6M, 0.35μm 2P4M and 2.5μm 2P1M CMOS technologies, all as part of research projects with industrial partnership. The research has led to the first high-speed uncooled frame-based IR quantum imager monolithically fabricated in a standard VLSI CMOS technology, and has given rise to the Tachyon series [1], a new line of commercial IR cameras used in real-time industrial, environmental and transportation control systems. The frame-free architectures investigated in this work represent a firm step forward to push further pixel pitch and system bandwidth up to the limits imposed by the evolving PbSe detector in future generations of the device.La present tesi doctoral descriu la recerca i el desenvolupament d'una nova tecnologia monolítica d'imatgeria infraroja de longitud d'ona mitja (MWIR), no refrigerada i de baix cost, per a usos industrials d'alta velocitat. El treball pren el relleu dels últims avenços assolits pel soci industrial NIT S.L. en el camp dels detectors MWIR de PbSe depositats en fase vapor (VPD), afegint-hi coneixement fonamental en la investigació de noves tècniques de disseny de circuits VLSI analògics i mixtes pel desenvolupament del dispositiu integrat de lectura unit al detector pixelat. Es parteix de la hipòtesi que, mitjançant l'ús de les esmentades tècniques de disseny, les tecnologies CMOS estàndard satisfan tots els requeriments operacionals del detector VPD PbSe respecte a connectivitat, fiabilitat, funcionalitat i escalabilitat per integrar de forma econòmica el dispositiu. La càmera PbSe-CMOS resultant ha de consumir molt baixa potència, operar a freqüències de kHz, exhibir bona uniformitat, i encabir els píxels actius CMOS de lectura en el pitch compacte del pla focal de la imatge, tot atenent a les particulars característiques del detector: altes relacions de corrent d'obscuritat a senyal, elevats valors de capacitat paràsita a l'entrada i dispersions importants en el procés de fabricació. Amb la finalitat de complir amb els requisits previs, es proposen arquitectures de sensors de visió de molt baix acoblament interpíxel basades en l'ús d'una matriu de pla focal (FPA) de píxels actius exclusivament digitals. Cada píxel sensor digital (DPS) està equipat amb mòduls de comunicació d'alta velocitat, autopolarització, cancel·lació de l'offset, conversió analògica-digital (ADC) i correcció del soroll de patró fixe (FPN). El consum en cada cel·la es minimitza fent un ús exhaustiu del MOSFET operant en subllindar. L'objectiu últim és potenciar la integració de les tecnologies de sensat d'imatge infraroja (IR) basades en PbSe per expandir-ne el seu ús, no només a diferents escenaris, sinó també en diferents estadis de maduresa de la integració PbSe-CMOS. En aquest sentit, es proposa investigar un conjunt complet de blocs funcionals distribuïts en dos enfocs paral·lels: - Dispositius d'imatgeria MWIR "Smart" basats en frames utilitzant noves topologies de circuit DPS amb correcció de l'FPN en guany i offset. Aquesta línia de recerca exprimeix el pitch del detector per oferir una programabilitat completament digital a nivell de píxel i plena funcionalitat amb compensació de la capacitat paràsita d'entrada i memòria interna de fotograma. - Dispositius de visió MWIR "Compact"-pitch "frame-free" en base a un novedós esquema d'integració analògica en el DPS i diferenciació temporal configurable, combinats amb protocols de comunicació asíncrons dins del pla focal. Aquesta estratègia es concep per permetre una alta compactació del pitch i un increment de la velocitat de lectura, mitjançant la supressió del filtrat digital intern i l'assignació dinàmica de l'ample de banda a cada píxel de l'FPA. Per tal d'independitzar la validació elèctrica dels primers prototips respecte a costosos processos de deposició del PbSe sensor a nivell d'oblia, la recerca s'amplia també al desenvolupament de noves estratègies d'emulació del detector d'IR i plataformes de test integrades especialment orientades a circuits integrats de lectura d'imatge. Cel·les DPS, dispositius d'imatge i xips de test s'han fabricat i caracteritzat, respectivament, en tecnologies CMOS estàndard 0.15 micres 1P6M, 0.35 micres 2P4M i 2.5 micres 2P1M, tots dins el marc de projectes de recerca amb socis industrials. Aquest treball ha conduït a la fabricació del primer dispositiu quàntic d'imatgeria IR d'alta velocitat, no refrigerat, basat en frames, i monolíticament fabricat en tecnologia VLSI CMOS estàndard, i ha donat lloc a Tachyon, una nova línia de càmeres IR comercials emprades en sistemes de control industrial, mediambiental i de transport en temps real.Postprint (published version

Advances on CMOS image sensors

This paper offers an introduction to the technological advances of image sensors designed using complementary metal–oxide–semiconductor (CMOS) processes along the last decades. We review some of those technological advances and examine potential disruptive growth directions for CMOS image sensors and proposed ways to achieve them. Those advances include breakthroughs on image quality such as resolution, capture speed, light sensitivity and color detection and advances on the computational imaging. The current trend is to push the innovation efforts even further as the market requires higher resolution, higher speed, lower power consumption and, mainly, lower cost sensors. Although CMOS image sensors are currently used in several different applications from consumer to defense to medical diagnosis, product differentiation is becoming both a requirement and a difficult goal for any image sensor manufacturer. The unique properties of CMOS process allows the integration of several signal processing techniques and are driving the impressive advancement of the computational imaging. With this paper, we offer a very comprehensive review of methods, techniques, designs and fabrication of CMOS image sensors that have impacted or might will impact the images sensor applications and markets

Polarization Imaging Sensors in Advanced Feature CMOS Technologies

The scaling of CMOS technology, as predicted by Moore\u27s law, has allowed for realization of high resolution imaging sensors and for the emergence of multi-mega-pixel imagers. Designing imaging sensors in advanced feature technologies poses many challenges especially since transistor models do not accurately portray their performance in these technologies. Furthermore, transistors fabricated in advanced feature technologies operate in a non-conventional mode known as velocity saturation. Traditionally, analog designers have been discouraged from designing circuits in this mode of operation due to the low gain properties in single transistor amplifiers. Nevertheless, velocity saturation will become even more prominent mode of operation as transistors continue to shrink and warrants careful design of circuits that can exploit this mode of operation. In this research endeavor, I have utilized velocity saturation mode of operation in order to realize low noise imaging sensors. These imaging sensors incorporate low noise analog circuits at the focal plane in order to improve the signal to noise ratio and are fabricated in 0.18 micron technology. Furthermore, I have explored nanofabrication techniques for realizing metallic nanowires acting as polarization filters. These nanoscopic metallic wires are deposited on the surface of the CMOS imaging sensor in order to add polarization sensitivity to the CMOS imaging sensor. This hybrid sensor will serve as a test bed for exploring the next generation of low noise and highly sensitive polarization imaging sensors

Image Sensors in Security and Medical Applications

This paper briefly reviews CMOS image sensor technology and its utilization in security and medical applications. The role and future trends of image sensors in each of the applications are discussed. To provide the reader deeper understanding of the technology aspects the paper concentrates on the selected applications such as surveillance, biometrics, capsule endoscopy and artificial retina. The reasons for concentrating on these applications are due to their importance in our daily life and because they present leading-edge applications for imaging systems research and development. In addition, review of image sensors implementation in these applications allows the reader to investigate image sensor technology from the technical and from other views as well

On evolution of CMOS image sensors

CMOS Image Sensors have become the principal technology in majority of digital cameras. They started replacing the film and Charge Coupled Devices in the last decade with the promise of lower cost, lower power requirement, higher integration and the potential of focal plane processing. However, the principal factor behind their success has been the ability to utilise the shrinkage in CMOS technology to make smaller pixels, and thereby have more resolution without increasing the cost. With the market of image sensors exploding courtesy their inte- gration with communication and computation devices, technology developers improved the CMOS processes to have better optical performance. Nevertheless, the promises of focal plane processing as well as on-chip integration have not been fulfilled. The market is still being pushed by the desire of having higher number of pixels and better image quality, however, differentiation is being difficult for any image sensor manufacturer. In the paper, we will explore potential disruptive growth directions for CMOS Image sensors and ways to achieve the same

The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing

The Sun Watcher with Active Pixels and Image Processing (SWAP) is an EUV solar telescope on board ESA's Project for Onboard Autonomy 2 (PROBA2) mission launched on 2 November 2009. SWAP has a spectral bandpass centered on 17.4 nm and provides images of the low solar corona over a 54x54 arcmin field-of-view with 3.2 arcsec pixels and an imaging cadence of about two minutes. SWAP is designed to monitor all space-weather-relevant events and features in the low solar corona. Given the limited resources of the PROBA2 microsatellite, the SWAP telescope is designed with various innovative technologies, including an off-axis optical design and a CMOS-APS detector. This article provides reference documentation for users of the SWAP image data.Comment: 26 pages, 9 figures, 1 movi

A New electronic image array: The Active pixel charge injection device

This is a Ph.D. thesis dissertation in which a new type of image sensor is investigated as possible successor to the charge coupled device (CCD) for scientific applications. As a result of the work described in this dissertation, the active pixel charge injection device (AP-CID) has been developed. This device retains most of the positive features of both the charge injection device (CJD) imager (random readout, non destructive readout, antiblooming, increased UV sensitivity, radiation tolerance, low power consumption, low manufacturing price) and the CCD imager (low noise, high dynamic range). The device lacks most of the drawbacks of the aforementioned devices. A functional array architecture was created. Based on this architecture several devices were fabricated. One of the arrays was fully measured, characterized and suggestions for improvement were formulated. Most of the characterizationalysis work described in this dissertation was centered on the following issues: temporal noise, linearity and FPN. The measured noise performance of the new device is excellent and comparable to the noise performance of the scientific CCD. The newly developed sensor is necessary for scientific imaging applications in space based operation. However due to its qualities, this device could be used in a much wider range of applications including commercial digital cameras, spectroscopy, biological, nuclear and other scientific applications

Design of a Time-of-Flight Sensor with Standard Pinned-Photodiode Devices Towards 100 MHz Modulation Frequency

We present an indirect Time-of-Flight (ToF) sensor based on standard pinned-photodiode (PPD) devices and design guides to pave the way for the development of a ToF pixel operating at 100 MHz modulation frequency. The standard PPDs are established well as predominant devices for 2-D color imagers in these days because of their low noise characteristic, but slow transfer speed of photo-generated electrons still prevents them from being employed to 3-D depth imagers. Optimized PPD structure with no process modifications is introduced to create a lateral electric field for enhancing charge transfer speed inside the PPD, and essential design parameters for achieving high operating frequency such as the epitaxial layer thickness, the pinning voltage, and the threshold voltage of the transfer gates are discussed with TCAD simulation results in this paper. Prototype indirect ToF sensors with various structures and parameters were fabricated using a 0.11-??m standard CIS process and characterized fully. We successfully evaluated the demodulation contrast of each pixel at 10 to 75 MHz frequencies, figuring out the suitable conditions of the PPD-based pixel. The best pixel operating at 50 MHz frequency demonstrated a depth resolution of less than 13 mm and a linearity error of about 3.7% between 1 and 3 m distance with a zeroorder calibration. We believe further optimization of the ToF pixel incorporated with the PPD devices is possible to improve the performance, operating it towards 100 MHz modulation frequency

The Cosmic Infrared Background ExpeRiments: Probing Large-Scale Structure Formation using Near-Infrared Sounding Rocket Payloads

The ensemble emission from all sources outside of the Milky Way is known as the extragalactic background light (EBL). At optical and near-infrared (NIR) wavelengths, the EBL is primarily stellar emission tracing back to the Epoch of Reionization (EOR) at redshifts z \u3e 6 when the first luminous structures formed. Given the large uncertainties in our understanding of the EOR, measurements of the EBL provide an important probe of the galaxies that were responsible for reionization. Direct observations of the EBL are challenging due to contamination from bright local foregrounds. In recent years, intensity mapping has emerged as a successful technique in which EBL fluctuations are measured on large angular scales where the known foreground contributions are minimal or well-modeled. To isolate the signals from EOR structures, intensity mapping can be applied to optical and NIR data to probe rest-frame UV emission in galaxies at z \u3e 6. Multiple intensity mapping studies including the first Cosmic Infrared Background ExpeRiment (CIBER-1) have found that the optical/NIR EBL intensity and its large-scale fluctuations exceed predictions from galaxy models. The excess is above EOR level and also persists at wavelengths \u3c 1 μm where we do not expect to see reionization signals. To explain the excess, a number of astrophysical sources have been proposed including intra-halo light (IHL) from low-mass stars at the outskirts of galaxies. Observations at 1.1 and 1.8 μm from CIBER-1 second and third flights suggest that the excess can be best described by a level of IHL comparable to the integrated light from known galaxy populations. While this result is intriguing, given CIBER-1 spectral coverage, the IHL and EOR components could not be distinguished, prompting interest in a new mission, CIBER-2. CIBER-2 is designed to disentangle the IHL and EOR signals using broader spectral coverage from 0.5 - 2.0 μm in six wavebands and larger light-gathering power. The wavebands are selected to provide 21 auto- and cross-spectra to probe the Lyman break that can distinguish EOR contributions from low-redshift foregrounds. CIBER-2 comprises a 28.5-cm telescope cooled to \u3c 100K using liquid nitrogen, and three HAWAII-2RG detectors coupled with dual- band filters to obtain data in six wavebands simultaneously. CIBER-2 is planned for four flights on the Black Brant IX sounding rocket, with the first flight in mid-2021. In this dissertation, I present my work on the CIBER-2 design, characterization and payload integration, as well as constructing the EBL fluctuation power spectra from the data taken from CIBER-1’s final flight. This analysis relies on a previously developed pipeline for use with earlier flights, but has been revised to capture the hardware changes in the final flight and the corresponding systematic uncertainties. I will also outline the expected development of CIBER-2 post-flight analysis and highlight the advantage of CIBER-2 data for EOR studies