High Performance CMOS Range Imaging

Diese Arbeit fokussiert sich auf die Modellierung, Charakterisierung und Optimierung von Rauschen um den Entwurf von hochperformanten CMOS-Bildsensoren im Allgemeinen und von distanzgebenden Bildsensoren im Speziellen zu unterstützen. CMOS Bildsensorik ist bekannt dafür, den CCD-Sensoren bezüglich Flexibilität überlegen zu sein, aber modifizierter Prozesse zu bedürfen um vergleichbare Leistung in Parametern wie Rauschen, Dynamik oder Empfindlichkeit zu erreichen. Rauschen wird als einer der wichtigsten Parameter erachtet, da es die erreichbare Genauigkeit maßgeblich limitiert und nicht korrigiert werden kann. Diese Thesis präsentiert einen Überblick über die weit gefächerte Theorie des Rauschens und fügt ihr eine Methodik hinzu die Rauschperformance von zeitlich abgetasteten Systemen zu schätzen. Eine Charakterisierung der verfügbaren Bauelemente des verwendeten 0:35 µm 2P4M CMOS-Prozesses wurde durchgeführt und anhand heuristischer Betrachtungen und dem Kenntnisstand der Rausch-Theorie evaluiert. Diese fundamentalen Untersuchungen werden als Grundlage erachtet, die Vorhersagbarkeit der Rauschperformance von z.B. Bildsensoren zu verbessern. Rauschquellen von Fotodetektoren wurden in der Vergangenheit erforscht, wobei viele mit der Einführung der PPD minimiert werden konnten. Üblicherweise sind die verbleibenden dominanten Rauschquellen das Resetrauschen und das Rauschen der Ausleseschaltung. Um Letzteres zu verbessern, wurde eine neuartige JFET-basierte Auslesestruktur entwickelt, welche im Vergleich zu verfügbaren Standard-MOSFETs eine um ca. Faktor 100 verbesserte Rauschperformance für niedrige Frequenzen aufweist. ToF wird als eine Schlüssel-Technologie erachtet, die neue Applikationen z.B. in Machine Vision, Automobil, Surveillance und Unterhaltungselektronik ermöglicht. Das konkurrierende CW-Verfahren ist bekannt dafür, anfällig bzgl. Störungen z.B. durch Hintergrundbestrahlung zu sein. Das PM-ToF-Prinzip wird als eine vielversprechende Methode für widrige Bedingungen erachtet, die allerdings eines schnellen Fotodetektors bedarf. Diese Arbeit trug zu zwei Generationen von LDPD basierten ToF-Bildsensoren bei und präsentiert eine alternative Implementierung des MSI-PM-ToF Verfahrens. Es wurde nachgewiesen, dass diese eine wesentlich bessere Performance bzgl. Geschwindigkeit, Linearität, Dunkelstrom und Matching bietet. Ferner bietet diese Arbeit ein nichtlineares und zeitvariantes Modell des realisierten Sensorprinzips, welches ungewünschte Phänomene wie die endliche Ladungsträgergeschwindigkeit und eine parasitäre Fotoempfindlichkeit der Speicherknoten berücksichtigt, um Großsignal-, Sensitivitäts- und Rauschperformance erforschen zu können. Es wurde gezeigt, dass das Modell gegen ein "Standard"-Modell konvergiert und die Messungen gut nachbildet. Letztlich wurde die Auswirkung dieser ungewünschten Phänomene auf die Performance der Distanzmessung präsentiert.This work is dedicated to CMOS based imaging with the emphasis on the noise modeling, characterization and optimization in order to contribute to the design of high performance imagers in general and range imagers in particular. CMOS is known to be superior to CCD due to its flexibility in terms of integration capabilities, but typically has to be enhanced to compete at parameters as for instance noise, dynamic range or spectral response. Temporal noise is an important topic, since it is one of the most crucial parameters that ultimately limits the performance and cannot be corrected. This thesis gathers the widespread theory on noise and extends the theory by a non-rigorous but potentially computing efficient algorithm to estimate noise in time sampled systems. The available devices of the 0:35 µm 2P4M CMOS process were characterized for their low-frequency noise performance and mutually compared by heuristic observations and a comparison to the state of research. These investigations set the foundation for a more rigorous treatment of noise exhibition and are thus believed to improve the predictability of the performance of e.g. image sensors. Many noise sources of CMOS APS have been investigated in the past and most of them can be minimized by usage of a PPD as a photodetector. Remaining dominant noise sources typically are the reset noise and the noise from the readout circuitry. In order to improve the latter, an alternative JFET based readout structure is proposed that was designed, manufactured and measured, proving the superior low-frequency noise performance of approximately a factor of 100 compared to standard MOSFETs. ToF is one key technology to enable new applications in e.g. machine vision, automotive, surveillance or entertainment. The competing CW principle is known to be prone to errors introduced by e.g. high ambient illuminance levels. The PM ToF principle is considered to be a promising method to supply the need for depth-map perception in harsh environmental conditions, but requires a high-speed photodetector. This work contributed to two generations of LDPD based ToF range image sensors and proposed a new approach to implement the MSI PM ToF principle. This was verified to yield a significantly faster charge transfer, better linearity, dark current and matching performance. A non-linear and time-variant model is provided that takes into account undesired phenomena such as finite charge transfer speed and a parasitic sensitivity to light when the shutters should remain OFF, to allow for investigations of large-signal characteristics, sensitivity and precision. It was demonstrated that the model converges to a standard photodetector model and properly resembles the measurements. Finally the impact of these undesired phenomena on the range measurement performance is demonstrated

Time-of-Flight Sensors in standard CMSO technologies

The goal of this PhD thesis is the design of time-of-flight sensors in standard CMOS technologies. For this, device level and circuit level task will be addressed. In the first case we will model and characterize the sensory structure. In the second case we will design the necessary circuitry to read the information captured by the sensors. The thesis will begin with the study of non-conventional photosensor structures in standard CMOS technologies, and will continue with the design of a specific circuitry in this technology. Finally, the selected design will be fabricated and tested

CMOS Sensors for Time-Resolved Active Imaging

In the past decades, time-resolved imaging such as fluorescence lifetime or time-of-flight depth imaging has been extensively explored in biomedical and industrial fields because of its non-invasive characterization of material properties and remote sensing capability. Many studies have shown its potential and effectiveness in applications such as cancer detection and tissue diagnoses from fluorescence lifetime imaging, and gesture/motion sensing and geometry sensing from time-of-flight imaging. Nonetheless, time-resolved imaging has not been widely adopted due to the high cost of the system and performance limits. The research presented in this thesis focuses on the implementation of low-cost real-time time-resolved imaging systems. Two image sensing schemes are proposed and implemented to address the major limitations. First, we propose a single-shot fluorescence lifetime image sensors for high speed and high accuracy imaging. To achieve high accuracy, previous approaches repeat the measurement for multiple sampling, resulting in long measurement time. On the other hand, the proposed method achieves both high speed and accuracy at the same time by employing a pixel-level processor that takes and compresses the multiple samples within a single measurement time. The pixels in the sensor take multiple samples from the fluorescent optical signal in sub-nanosecond resolution and compute the average photon arrival time of the optical signal. Thanks to the multiple sampling of the signal, the measurement is insensitive to the shape or the pulse-width of excitation, providing better accuracy and pixel uniformity than conventional rapid lifetime determination (RLD) methods. The proposed single-shot image sensor also improves the imaging speed by orders of magnitude compared to other conventional center-of-mass methods (CMM). Second, we propose a 3-D camera with a background light suppression scheme which is adaptable to various lighting conditions. Previous 3-D cameras are not operable in outdoor conditions because they suffer from measurement errors and saturation problems under high background light illumination. We propose a reconfigurable architecture with column-parallel discrete-time background light cancellation circuit. Implementing the processor at the column level allows an order of magnitude reduction in pixel size as compared to existing pixel-level processors. The column-level approach also provides reconfigurable operation modes for optimal performance in all lighting conditions. For example, the sensor can operate at the best frame-rate and resolution without the presence of background light. If the background light saturates the sensor or increases the shot noise, the sensor can adjust the resolution and frame-rate by pixel binning and superresolution techniques. This effectively enhances the well capacity of the pixel to compensate for the increase shot noise, and speeds up the frame processing to handle the excessive background light. A fabricated prototype sensor can suppress the background light more than 100-klx while achieving a very small pixel size of 5.9μm.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/136950/1/eecho_1.pd

CMOS SPAD-based image sensor for single photon counting and time of flight imaging

The facility to capture the arrival of a single photon, is the fundamental limit to the detection of quantised electromagnetic radiation. An image sensor capable of capturing a picture with this ultimate optical and temporal precision is the pinnacle of photo-sensing. The creation of high spatial resolution, single photon sensitive, and time-resolved image sensors in complementary metal oxide semiconductor (CMOS) technology offers numerous benefits in a wide field of applications. These CMOS devices will be suitable to replace high sensitivity charge-coupled device (CCD) technology (electron-multiplied or electron bombarded) with significantly lower cost and comparable performance in low light or high speed scenarios. For example, with temporal resolution in the order of nano and picoseconds, detailed three-dimensional (3D) pictures can be formed by measuring the time of flight (TOF) of a light pulse. High frame rate imaging of single photons can yield new capabilities in super-resolution microscopy. Also, the imaging of quantum effects such as the entanglement of photons may be realised. The goal of this research project is the development of such an image sensor by exploiting single photon avalanche diodes (SPAD) in advanced imaging-specific 130nm front side illuminated (FSI) CMOS technology. SPADs have three key combined advantages over other imaging technologies: single photon sensitivity, picosecond temporal resolution and the facility to be integrated in standard CMOS technology. Analogue techniques are employed to create an efficient and compact imager that is scalable to mega-pixel arrays. A SPAD-based image sensor is described with 320 by 240 pixels at a pitch of 8μm and an optical efficiency or fill-factor of 26.8%. Each pixel comprises a SPAD with a hybrid analogue counting and memory circuit that makes novel use of a low-power charge transfer amplifier. Global shutter single photon counting images are captured. These exhibit photon shot noise limited statistics with unprecedented low input-referred noise at an equivalent of 0.06 electrons. The CMOS image sensor (CIS) trends of shrinking pixels, increasing array sizes, decreasing read noise, fast readout and oversampled image formation are projected towards the formation of binary single photon imagers or quanta image sensors (QIS). In a binary digital image capture mode, the image sensor offers a look-ahead to the properties and performance of future QISs with 20,000 binary frames per second readout with a bit error rate of 1.7 x 10-3. The bit density, or cumulative binary intensity, against exposure performance of this image sensor is in the shape of the famous Hurter and Driffield densitometry curves of photographic film. Oversampled time-gated binary image capture is demonstrated, capturing 3D TOF images with 3.8cm precision in a 60cm range

Exploring the application of ultrasonic phased arrays for industrial process analysis

This thesis was previously held under moratorium from 25/11/19 to 25/11/21Typical industrial process analysis techniques require an optical path to exist between the measurement sensor and the process to acquire data used to optimise and control an industrial process. Ultrasonic sensing is a well-established method to measure into optically opaque structures and highly focussed images can be generated using multiple element transducer arrays. In this Thesis, such arrays are explored as a real-time imaging tool for industrial process analysis. A novel methodology is proposed to characterise the variation between consecutive ultrasonic data sets deriving from the ultrasonic hardware. The pulse-echo response corresponding to a planar back wall acoustic interface is used to infer the bandwidth, pulse length and sensitivity of each array element. This led to the development of a calibration methodology to enhance the accuracy of experimentally generated ultrasonic images. An algorithm enabling non-invasive through-steel imaging of an industrial process is demonstrated using a simulated data set. Using principal component analysis, signals corresponding to reverberations in the steel vessel wall are identified and deselected from the ultrasonic data set prior to image construction. This facilitates the quantification of process information from the image. An image processing and object tracking algorithm are presented to quantify the bubble size distribution (BSD) and bubble velocity from ultrasonic images. When tested under controlled dynamic conditions, the mean value of the BSD was predicted within 50% at 100 mms-1 and the velocity could be predicted within 30% at 100 mms-1. However, these algorithms were sensitive to the quality of the input image to represent the true bubble shape. The consolidation of these techniques demonstrates successful application of ultrasonic phased array imaging, both invasively and noninvasively, to a dynamic process stream. Key to industrial uptake of the technology are data throughput and processing, which currently limit its applicability to real-time process analysis, and low sensitivity for some non-invasive applications.Typical industrial process analysis techniques require an optical path to exist between the measurement sensor and the process to acquire data used to optimise and control an industrial process. Ultrasonic sensing is a well-established method to measure into optically opaque structures and highly focussed images can be generated using multiple element transducer arrays. In this Thesis, such arrays are explored as a real-time imaging tool for industrial process analysis. A novel methodology is proposed to characterise the variation between consecutive ultrasonic data sets deriving from the ultrasonic hardware. The pulse-echo response corresponding to a planar back wall acoustic interface is used to infer the bandwidth, pulse length and sensitivity of each array element. This led to the development of a calibration methodology to enhance the accuracy of experimentally generated ultrasonic images. An algorithm enabling non-invasive through-steel imaging of an industrial process is demonstrated using a simulated data set. Using principal component analysis, signals corresponding to reverberations in the steel vessel wall are identified and deselected from the ultrasonic data set prior to image construction. This facilitates the quantification of process information from the image. An image processing and object tracking algorithm are presented to quantify the bubble size distribution (BSD) and bubble velocity from ultrasonic images. When tested under controlled dynamic conditions, the mean value of the BSD was predicted within 50% at 100 mms-1 and the velocity could be predicted within 30% at 100 mms-1. However, these algorithms were sensitive to the quality of the input image to represent the true bubble shape. The consolidation of these techniques demonstrates successful application of ultrasonic phased array imaging, both invasively and noninvasively, to a dynamic process stream. Key to industrial uptake of the technology are data throughput and processing, which currently limit its applicability to real-time process analysis, and low sensitivity for some non-invasive applications

Investigation of dipole blockade inultracold atomic ensembles

Owing to new available technologies, new research fields become available to scientists. Within the area of atomic physics, the ultracold gas technologies open new perspectives in the investigation of the regimes with strong interactions between atoms. A wide range of applications is associated with the manipulation in different configurations of ultracold atoms excited to highly excited states. Rydberg atoms have been intensively studies since nineteen seventy and due the merge of this field with ultracold atomic physics, cold Rydberg atoms brought several concepts to a new light. Rydberg atoms are known to exhibit strong dipolar moments hence flexible investigations of strong interactions between excited atoms become an interesting subject. For example it becomes possible to investigate interactions between individual particles. One of the implications of the strong interactions between Rydberg atoms is the phenomenon denominated as dipole blockade, that has been recently studied both theoretically, for instances, and experimentally for different atomic ensembles. This concept is presented in the context of atomic clocks, quantum computation, quantum cryptography and quantum information. Further research on the Rydberg-Rydberg interactions has produced collective coherent excitations and a non-linear dependence on the number of excited atoms as a function of intensity of the irradiation lasers and atomic density. In order to achieve the quantum computation targets, the implementation of quantum protocols consisting of a sequence of quantum gates requires an experimental realization of a quantum bit. As Rydberg atoms exhibit long range interactions they were proposed to be suitable candidates for realization of controllable quantum system. Yet, the implementation of a quantum gate is an ambitious task where a coherent manipulation of a great number of coupled states is needed. For this reason it was proposed that Rydberg excitations should be performed in samples with a precise spatial order. As a solution atoms in optical lattices were proposed. Already a strong interest in optical lattices as a tool of investigation of ultracold atoms or as a tool of addressing the atoms has been showed. The combination of the strong interactions between Rydberg atoms with the possibility of implementing a spatial order that will simplify coherent manipulation of a large number of coupled states provide us with exciting applications for the quantum information. The main goal of my thesis is to present new results on the excitation of Rydberg atoms from ultracold atomic samples obtained during my work as. The dipole blockade and its experimental implications without and with the presence of optical lattices are presented. This thesis shows results on Rydberg excitations of rubidium Bose condensates in one-dimensional periodic potentials. The coherent excitation dynamics of up to 30 Rydberg states in a condensate occupying around 100 sites of an optical lattice was observed. The zero-dimensional character of the system, in which at most one Rydberg excitation is present per lattice site, is ensured by expanding the condensate in a cylindrical trap in which the radial size of the atomic cloud is much less than the blockade radius of the Rydberg states with 55 < n < 80. This thesis encompasses six chapters and is organized as follows: - Chapter 2 is an introduction to general ideas of atomic physics. It introduces basic theoretical concepts such as the light shift or the three level atom. These concepts have applications while performing our experiments. Moreover, a short characterization of Rydberg atoms and their properties is included. The most important topic of this thesis the Rydberg dipole blockade is also described. - Chapter 3 describes the theoretical background of Bose Einstein condensation. The first part presents the trapping and cooling methods used in experimental realization of ultracold atoms. The second part of the chapter gives an overview of cold atoms in periodic potentials. It presents also how to realize a periodic potential by light interference. - Chapter 4 is devoted to experimental setup. The experimental apparatus of the Pisa BEC laboratory is described. An accurate description of the experimental procedure applied to reach the BEC quantum phase in dilute gases is included. This chapter also includes information about excitation of Rydberg atoms and the implementation of periodic potentials. The setup used in this thesis to prepare cold atomic samples was build at the end of last century and described in detail in the PhD thesis of Donatella Ciampini. The part of the setup used to create optical lattices was implemented and presented in the PhD thesis’s of Alessandro Zenesini and Carlo Sias . Therefore those setups will be not described with full details. The part of setup dedicated to Rydberg excitations was mainly build during my PhD work and is first described in details in the present thesis and also reported in Viteau et al. - Chapter 5 describes the characterization of experimental parameters such as the Rabi frequencies and the efficiency of the ion detection. The first results obtained on the photoionization of Bose Einstein condensates and cold atoms in magneto-optical traps are also shown. Moreover, the effects of excitation lasers and electric fields on the atomic ensembles are mentioned. All the material contained in this chapter, and in the following ones, is the result of my original research work, in collaboration with other members of the BEC team. -Chapter 6 presents our results on the excitations of Rydberg atoms from both BEC samples and cold atoms trapped in a MOT. The experiments exploring different BEC density regimes and their influence on the ion production are presented. A new method of estimating the dipole blockade radius is examined. The further part of chapter 5 reports the temporal dependence of the detected ions on the duration of the irradiating laser pulse. Results for different atomic density regimes and different quantum number n are shown. Clear signatures of sub-Poissonian counting statistics in the regime of strong interactions have been measured. -Chapter 7 is devoted to description of the cold Rydberg atoms experiments performed within the periodic potential of optical lattices. The influence of the Rydberg excitations in optical lattices on the phase coherence of a Bose Einstein condensate is examined. The coherent excitations of the ultracold atomic samples are described. The influence of atomic distributions is also taken into account. A new method of spatial distribution cleaning is presented

A DETECTION AND DATA ACQUISITION SYSTEM FOR PRECISION BETA DECAY SPECTROSCOPY

Free neutron and nuclear beta decay spectroscopy serves as a robust laboratory for investigations of the Standard Model of Particle Physics. Observables such as decay product angular correlations and energy spectra overconstrain the Standard Model and serve as a sensitive probe for Beyond the Standard Model physics. Improved measurement of these quantities is necessary to complement the TeV scale physics being conducted at the Large Hadron Collider. The UCNB, 45Ca, and Nab experiments aim to improve upon existing measurements of free neutron decay angular correlations and set new limits in the search for exotic couplings in beta decay. To achieve these experimental goals, a highly-pixelated, thick silicon detector with a 100 nm entrance window has been developed for precision beta spectroscopy and the direct detection of 30 keV beta decay protons. The detector has been characterized for its performance in energy reconstruction and particle arrival time determination. A Monte Carlo simulation of signal formation in the silicon detector and propagation through the electronics chain has been written to develop optimal signal analysis algorithms for minimally biased energy and timing extraction. A tagged-electron timing test has been proposed and investigated as a means to assess the validity of these Monte Carlo efforts. A universal platform for data acquisition (DAQ) has been designed and implemented in National Instrument\u27s PXIe-5171R digitizer/FPGA hardware. The DAQ retains a ring buffer of the most recent 400 ms of data in all 256 channels, so that a waveform trace can be returned from any combination of pixels and resolution for complete energy reconstruction. Low-threshold triggers on individual channels were implemented in FPGA as a generic piecewise-polynomial filter for universal, real-time digital signal processing, which allows for arbitrary filter implementation on a pixel-by-pixel basis. This system is universal in the sense that it has complete flexible, complex, and debuggable triggering at both the pixel and global level without recompiling the firmware. The culmination of this work is a system capable of a 10 keV trigger threshold, 3 keV resolution, and maximum 300 ps arrival time systematic, even in the presence of large amplitude noise components

Lux junior 2023: 16. Internationales Forum für den lichttechnischen Nachwuchs, 23. – 25. Juni 2023, Ilmenau : Tagungsband

Während des 16. Internationales Forums für den lichttechnischen Nachwuchs präsentieren Studenten, Doktoranden und junge Absolventen ihre Forschungs- und Entwicklungsergebnisse aus allen Bereichen der Lichttechnik. Die Themen bewegen sich dabei von Beleuchtungsanwendungen in verschiedensten Bereichen über Lichtmesstechnik, Kraftfahrzeugbeleuchung, LED-Anwendung bis zu nichtvisuellen Lichtwirkungen. Das Forum ist speziell für Studierende und junge Absolventen des Lichtbereiches konzipiert. Es bietet neben den Vorträgen und Postern die Möglichkeit zu Diskussionen und individuellem Austausch. In den 30 Jahren ihres Bestehens entwickelte sich die zweijährig stattfindende Tagung zu eine Traditionsveranstaltung, die das Fachgebiet Lichttechnik der TU Ilmenau gemeinsam mit der Bezirksgruppe Thüringen-Nordhessen der Deutschen Lichttechnischen Gesellschaft LiTG e. V. durchführt

Sympathetic cooling of a membrane oscillator in a hybrid mechanical-atomic system

The quantum behaviour of macroscopic mechanical oscillators is currently being investigated using a variety of mechanical systems and techniques such as optomechanical cooling and cold damping. As mechanical systems are also very versatile transducers between different physical systems, it is possible to build hybrid systems that combine the advantages of their constituents. This opens up new possibilities for fundamental studies of quantum physics, precision sensing and quantum information processing. Ultra-cold atoms represent one of the best-controlled systems available, thus making a well-developed toolbox for quantum manipulation available to mechanical oscillators in a hybrid system. In this thesis, I report on the realization of a hybrid mechanical-atomic system consisting of a Si3N4 membrane inside an optical cavity coupled to an ensemble of atoms. The coupling is mediated by a light field that couples the atomic motion to the membrane motion over a large distance. By laser cooling the atomic motion, the membrane is sympathetically cooled via its interaction with the atoms to a temperature of 0.7 K starting from room temperature, despite the enormous mass ratio of 10^10 between the membrane and the atomic ensemble. Up to now, sympathetic cooling had only been used to cool microscopic particles with much lower masses. The system reported in this thesis is the first hybrid system where the back-action of the atoms onto the mechanical oscillator is sufficiently large for practical applications. It represents a significant improvement over a previous experiment in our laboratory, where the atom’s influence onto the mechanical oscillator was barely detectable. An atom-membrane cooperativity C > 1 is achieved, thus enabling the study of effects such as a mechanical analog of electromagnetically induced transparency in the system, which will be investigated in the future. The quantitative analysis of the coupling mechanism also allows to predict experimental requirements for future ground state cooling of the mechanical oscillator, which are within reach. Interestingly, hybrid systems such as ours can provide ground-state cooling of low-frequency mechanical oscillators in a regime, where neither cavity optomechanical cooling nor cold damping can reach the ground state