Development of CMOS active pixel sensors

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This thesis describes an investigation into the suitability of complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) devices for scientific imaging applications. CMOS APS offer a number of advantages over the established charge-coupled device (CCD) technology, primarily in the areas of low power consumption, high-speed parallel readout and random (X-Y) addressing, increased system integration and improved radiation hardness. The investigation used a range of newly designed Test Structures in conjunction with a range of custom developed test equipment to characterise device performance. Initial experimental work highlighted the significant non-linearity in the charge conversion gain (responsivity) and found the read noise to be limited by the kTC component due to resetting of the pixel capacitance. The major experimental study investigated the contribution to dark signal due to hot-carrier injection effects from the in-pixel transistors during read-out and highlighted the importance of the contribution at low signal levels. The quantum efficiency (QE) and cross-talk were also investigated and found to be limited by the pixel fill factor and shallow depletion depth of the photodiode. The work has highlighted the need to design devices to explore the effects of individual components rather than stand-alone imaging devices and indicated further developments are required for APS technology to compete with the CCD for high-end scientific imaging applications. The main areas requiring development are in achieving backside illuminated, deep depletion devices with low dark signal and low noise sampling techniques.Engineering and Physical Sciences Research Council; e2v Technologie

Development of CMOS active pixel sensors

This thesis describes an investigation into the suitability of complementary metal oxide semiconductor (CMOS) active pixel sensor (APS) devices for scientific imaging applications. CMOS APS offer a number of advantages over the established charge-coupled device (CCD) technology, primarily in the areas of low power consumption, high-speed parallel readout and random (X-Y) addressing, increased system integration and improved radiation hardness. The investigation used a range of newly designed Test Structures in conjunction with a range of custom developed test equipment to characterise device performance. Initial experimental work highlighted the significant non-linearity in the charge conversion gain (responsivity) and found the read noise to be limited by the kTC component due to resetting of the pixel capacitance. The major experimental study investigated the contribution to dark signal due to hot-carrier injection effects from the in-pixel transistors during read-out and highlighted the importance of the contribution at low signal levels. The quantum efficiency (QE) and cross-talk were also investigated and found to be limited by the pixel fill factor and shallow depletion depth of the photodiode. The work has highlighted the need to design devices to explore the effects of individual components rather than stand-alone imaging devices and indicated further developments are required for APS technology to compete with the CCD for high-end scientific imaging applications. The main areas requiring development are in achieving backside illuminated, deep depletion devices with low dark signal and low noise sampling techniques.EThOS - Electronic Theses Online ServiceEngineering and Physical Sciences Research Councile2v TechnologiesGBUnited Kingdo

MOSFET Modulated Dual Conversion Gain CMOS Image Sensors

In recent years, vision systems based on CMOS image sensors have acquired significant ground over those based on charge-coupled devices (CCD). The main advantages of CMOS image sensors are their high level of integration, random accessibility, and low-voltage, low-power operation. Previously proposed high dynamic range enhancement schemes focused mainly on extending the sensor dynamic range at the high illumination end. Sensor dynamic range extension at the low illumination end has not been addressed. Since most applications require low-noise, high-sensitivity, characteristics for imaging of the dark region as well as dynamic range expansion to the bright region, the availability of a low-noise, high-sensitivity pixel device is particularly important. In this dissertation, a dual-conversion-gain (DCG) pixel architecture was proposed; this architecture increases the signal to noise ratio (SNR) and the dynamic range of CMOS image sensors at both the low and high illumination ends. The dual conversion gain pixel improves the dynamic range by changing the conversion gain based on the illumination level without increasing artifacts or increasing the imaging readout noise floor. A MOSFET is used to modulate the capacitance of the charge sensing node. Under high light illumination conditions, a low conversion gain is used to achieve higher full well capacity and wider dynamic range. Under low light conditions, a high conversion gain is enabled to lower the readout noise and achieve excellent low light performance. A sensor prototype using the new pixel architecture with 5.6μm pixel pitch was designed and fabricated using Micron Technology’s 130nm 3-metal and 2-poly silicon process. The periphery circuitries were designed to readout the pixel and support the pixel characterization needs. The pixel design, readout timing, and operation voltage were optimized. A detail sensor characterization was performed; a 127μV/e was achieved for the high conversion gain mode and 30.8μV/e for the low conversion gain mode. Characterization results confirm that a 42ke linear full well was achieved for the low conversion gain mode and 10.5ke for the high conversion gain mode. An average 2.1e readout noise was measured for the high conversion gain mode and 8.6e for the low conversion gain mode. The total sensor dynamic range was extended to 86dB by combining the two modes of operation with a 46.2dB maximum SNR. Several images were taken by the prototype sensor under different illumination levels. The simple processed color images show the clear advantage of the high conversion gain mode for the low light imaging

Time-of-flight CMOS イメージセンサによる高精度・高速距離イメージングに関する研究

Tohoku University博士（工学）thesi

CMOS Sensors for Precision Astronomy

Thanks to rapid development in recent years, CMOS sensors are quickly approaching the performance levels achieved by scientific CCDs. They are now at a point where they are being considered for precision astronomy measurements, such as gravitational microlensing. CMOS sensors offer a number of inherent advantages over CCDs, such as higher frame rate and radiation hardness. In this work, a novel monolithic CMOS sensor capable of full depletion through an applied reverse bias is characterised and tested. Baseline characterisation of basic metrics is undertaken to ensure the device is fully operational. Image lag is measured in the device to determine optimal operating parameters. A novel method for reducing image lag is described and tested, with results indicating a successful reduction. Inter-pixel non-uniformity is investigated to examine the different photo-response from pixel to pixel, as well as intra-pixel non-uniformity to determine the areas of a pixel which are more sensitive to incoming photons than others. The point spread function of the sensor is then tested at multiple reverse biases to ensure that full depletion has been achieved and compared to results taken from a CCD

Novel Developments in Scientific EMCCDs

This thesis presents a complete characterisation and an assessment of the technology readiness of a new Electron Multiplying Charge Coupled Devices (EMCCD) technology. Several factors of interest are studied here including, charge transfer efficiency, gain ageing and radiation effects from protons. Many light-starved and high-speed image applications (e.g. observation from space and automated visual inspection) can benefit from Time Delay Integration (\acrshort{tdi}) as it allows photoelectrons from multiple exposures to be summed in the charge domain with no added noise. Electron multiplication (EM) can be used to further increase the signal to noise ratio for extremely faint light signals. There is a growing demand for Complementary metal–oxide–semiconductor (\acrshort{cmos}) sensors with the same or greater functionality and even better performance. The research presented here analyses the functionality of a recently designed EMCCD in a CMOS process. This device (EMTC1) incorporates two novel EM pixel structures which enable high gain at relatively low voltages. The theory and architecture of Charge Coupled Devices (CCDs) and EMCCDs are discussed, providing a technical background for the results. Furthermore, the practical methods, including experimental techniques developed for this device's testing, are presented here. Ageing within the device is a primary focus within this thesis, as is the effect of proton irradiation. The effects of the radiation damage on parameters such as dark current and Charge Transfer Inefficiency (CTI) have been documented along with its effect on EM gain. These results have been corroborated with simulations of device operation in TCAD

Large area CMOS photosensors for time-resolved measurements

Viele Industrieanwendungen benötigen lineare Photosensoren, die eine hohe Empfindlichkeit besitzen und geringes Rauschen verursachen. Die Atom-Emissionsspektroskopie ist eine dieser Anwendungen. Dieses spektroskopische Verfahren ergibt Informationen über die qualitative und quantitative Zusammensetzung eines Analyten. Seit 1960 sind Photoelektronenverfielfacher (photomultiplier tubes, PMT) als Standarddetektoren im Bereich der Spektrometrie im Einsatz, da sie eine kurze Reaktionszeit und niedrigen Dunkelstrom aufweisen. In der jüngeren Zeit sind Feststoffliniensensoren als vielversprechende Alternative zu den Photoelektronenverfielfachern ins Augenmerk gerückt. Neuerdings auch in hybriden Emissionspektrometern im Einsatz, sind CCD-Liniensensoren in der Lage, im Ultraviolett gelegene (für Wellenlängen über ca. 250 nm), sichtbare und nah-infrarote Spektralbereiche zu registrieren, die von einem Lichtgitter mit geringer Bandbreite an diese gesendet werden. Jedoch gibt es mit der CCD-Technologie keine Möglichkeit, zufällige Pixel zu adressieren, nichtlöschend auszulesen und Daten nach der Zeit aufgelöst erfassen, was zur Notwendigkeit führt, den gesamten Sensor mehrere Male auszulesen, um die erforderliche Ladungssammelzeit einzustellen, welche dafür benötigt wird, um zwischen benachbarten Zeilen im Spektrographen zu unterscheiden. Das braucht sehr viel Messzeit, fügt überdies Reset-Rauschen hinzu und vermindert das Signal-Rausch-Verhältnis. Der Einsatz von CMOS kann eine gute Alternative zu CCD darstellen. Ein in dieser Arbeit entwickelter und optimierter, auf einem Lateral Drift-Field Photodetector (LDPD) basierender CMOS-Zeilensensor eröffnet die Möglichkeit eines sogenannten Time-Gating und die Besonderheit eines nichtlöschenden Auslesens und einer Ladungssammlung über mehrere Zyklen, ohne, dass dabei eine Reset-Phase vonnöten ist. Große fotoaktive Bereiche von bis zu 1 mm sind, gleich wie schneller Ladungstransfer und niedriger Dunkelstrom, entscheidende Anforderungen an Sensoren, die in der optischen Emissionspektroskopie eingesetzt werden. Dies sind damit auch die Hauptziele, die mit den in dieser Arbeit eingebrachten Strukturen zu erreichen sein müssten. Der Transfer der Pixelladung vom fotoaktiven Bereich in den Sensorknoten wird in dieser Arbeit im Detail analysiert. Es werden verschiedene Mechanismen des Ladungstransports studiert. Der Dunkelstrom im LDPD-Pixel wird durch die Verwendung verschiedener Pixelstrukturen analysiert. Außerdem wird ein neuartiges Pixeldesign präsentiert, durch welches der Tranfer von Pixelladungen effizienter erfolgt. Es werden verschiedene Pixeltypen vorgeschlagen und eingehend charakterisiert. Schließlich wird die am besten geeignete Pixelstruktur herangezogen, um den Prototypen eines Zeilensensors herzustellen, dessen Arbeitscharakteristika ebenso im Detail untersucht werden.Many industrial applications require linear photosensors, which exhibit high sensitivity and low noise. The atomic emission spectroscopy is one of such applications. This spectroscopic method delivers the information about the qualitative and quantitative composition of an analyte. Since 1960 photomultiplier tubes (PMT) were used as standard detectors in the field of spectrometry due to their high speed of response and low dark current. Recently, solid-state line sensors have established themselves as a promising alternative to the photomultiplier tubes. Newly used in hybrid emission spectrometers, CCD line sensors are able to detect the part of the spectra in the ultra-violet (for wavelengths longer than some 250 nm), visible, and near infra-red ranges sent to them by a narrow bandwidth optical grid. However, CCD technology does not have the ability of random pixel addressing, non-destructive readout and time-resolved measurements, which causes the necessity of reading out the complete sensor several times to adjust the necessary charge collection period required to be able to distinguish between neighbouring lines in the spectrograph. This consumes a lot of measuring time and also adds additional reset noise and diminishes the signal-to-noise ratio after each readout. A CMOS approach can be a good alternative to CCD. Developed and optimized in this thesis, a lateral drift-field photodetector (LDPD) based CMOS line sensor offers the possibility for the so called time-gating together with the feature of non-destructive readout and charge accumulation over several cycles without the need for the reset phase. Large photoactive areas of up to 1 mm as well as fast charge transfer and low dark currents are all dominant requirements for the sensors used in optical emission spectroscopy. These are the main goals that should be achievable with the structures proposed in this thesis. Pixel charge transfer from the photoactive area into the sense node is examined in detail in this work. Different mechanisms of the charge transport are studied. Dark current in the LDPD pixel is analysed on using varied pixel structures. A novel pixel design to enhance the charge transfer efficiency is presented. Different pixel types are proposed and thoroughly characterized. Finally, the best pixel structure is used to fabricate a prototype line sensor, the operating characteristics of which are also examined in detail

Detector Technologies for CLIC

The Compact Linear Collider (CLIC) is a high-energy high-luminosity linear electron-positron collider under development. It is foreseen to be built and operated in three stages, at centre-of-mass energies of 380 GeV, 1.5 TeV and 3 TeV, respectively. It offers a rich physics program including direct searches as well as the probing of new physics through a broad set of precision measurements of Standard Model processes, particularly in the Higgs-boson and top-quark sectors. The precision required for such measurements and the specific conditions imposed by the beam dimensions and time structure put strict requirements on the detector design and technology. This includes low-mass vertexing and tracking systems with small cells, highly granular imaging calorimeters, as well as a precise hit-time resolution and power-pulsed operation for all subsystems. A conceptual design for the CLIC detector system was published in 2012. Since then, ambitious R&D programmes for silicon vertex and tracking detectors, as well as for calorimeters have been pursued within the CLICdp, CALICE and FCAL collaborations, addressing the challenging detector requirements with innovative technologies. This report introduces the experimental environment and detector requirements at CLIC and reviews the current status and future plans for detector technology R&D.Comment: 152 pages, 116 figures; published as CERN Yellow Report Monograph Vol. 1/2019; corresponding editors: Dominik Dannheim, Katja Kr\"uger, Aharon Levy, Andreas N\"urnberg, Eva Sickin

Analysis and comparison of resistive, ferroelectric and pyroelectric uncooled bolometers for electronic imaging systems

The performance parameters (responsivity (Rv). detectivity (D*), total noise and response time) of resistive, pyroelectric and ferroelectric bolometer detectors are dependent on a large number of key variables including chopping frequercy, the input impedance and voltage noise of the readout circuitry, the structure dependent parameters (particularly thermal conductance and thermal capacitance), and material properties such as dielectric constant, pyroelectric coefficient, loss tangent and thin film thickness. The interrelationship between the key variables and their influence on performance is often complex and not easily discerned for the three major types of thermal detectors: resistive, pyroelectric and ferroelectric bolometers. In this thesis research, the dependence of Rv, D* and total noise on these key parameters were analyzed and written as equations from which computer calculations could easily be made. The analyzed results were used to compare the pertbrmance of the three types of sensors for present-day structure and material characteristics and also for material characteristics and structures that night be developed in the future