R&D Paths of Pixel Detectors for Vertex Tracking and Radiation Imaging

This report reviews current trends in the R&D of semiconductor pixellated sensors for vertex tracking and radiation imaging. It identifies requirements of future HEP experiments at colliders, needed technological breakthroughs and highlights the relation to radiation detection and imaging applications in other fields of science.Comment: 17 pages, 2 figures, submitted to the European Strategy Preparatory Grou

Correction of Errors in Time of Flight Cameras

En esta tesis se aborda la corrección de errores en cámaras de profundidad basadas en tiempo de vuelo (Time of Flight - ToF). De entre las más recientes tecnologías, las cámaras ToF de modulación continua (Continuous Wave Modulation - CWM) son una alternativa prometedora para la creación de sensores compactos y rápidos. Sin embargo, existen gran variedad de errores que afectan notablemente la medida de profundidad, poniendo en compromiso posibles aplicaciones. La corrección de dichos errores propone un reto desafiante. Actualmente, se consideran dos fuentes principales de error: i) sistemático y ii) no sistemático. Mientras que el primero admite calibración, el último depende de la geometría y el movimiento relativo de la escena. Esta tesis propone métodos que abordan i) la distorsión sistemática de profundidad y dos de las fuentes de error no sistemático más relevantes: ii.a) la interferencia por multicamino (Multipath Interference - MpI) y ii.b) los artefactos de movimiento. La distorsión sistemática de profundidad en cámaras ToF surge principalmente debido al uso de señales sinusoidales no perfectas para modular. Como resultado, las medidas de profundidad aparecen distorsionadas, pudiendo ser reducidas con una etapa de calibración. Esta tesis propone un método de calibración basado en mostrar a la cámara un plano en diferentes posiciones y orientaciones. Este método no requiere de patrones de calibración y, por tanto, puede emplear los planos, que de manera natural, aparecen en la escena. El método propuesto encuentra una función que obtiene la corrección de profundidad correspondiente a cada píxel. Esta tesis mejora los métodos existentes en cuanto a precisión, eficiencia e idoneidad. La interferencia por multicamino surge debido a la superposición de la señal reflejada por diferentes caminos con la reflexión directa, produciendo distorsiones que se hacen más notables en superficies convexas. La MpI es la causa de importantes errores en la estimación de profundidad en cámaras CWM ToF. Esta tesis propone un método que elimina la MpI a partir de un solo mapa de profundidad. El enfoque propuesto no requiere más información acerca de la escena que las medidas ToF. El método se fundamenta en un modelo radio-métrico de las medidas que se emplea para estimar de manera muy precisa el mapa de profundidad sin distorsión. Una de las tecnologías líderes para la obtención de profundidad en imagen ToF está basada en Photonic Mixer Device (PMD), la cual obtiene la profundidad mediante el muestreado secuencial de la correlación entre la señal de modulación y la señal proveniente de la escena en diferentes desplazamientos de fase. Con movimiento, los píxeles PMD capturan profundidades diferentes en cada etapa de muestreo, produciendo artefactos de movimiento. El método propuesto en esta tesis para la corrección de dichos artefactos destaca por su velocidad y sencillez, pudiendo ser incluido fácilmente en el hardware de la cámara. La profundidad de cada píxel se recupera gracias a la consistencia entre las muestras de correlación en el píxel PMD y de la vecindad local. Este método obtiene correcciones precisas, reduciendo los artefactos de movimiento enormemente. Además, como resultado de este método, puede obtenerse el flujo óptico en los contornos en movimiento a partir de una sola captura. A pesar de ser una alternativa muy prometedora para la obtención de profundidad, las cámaras ToF todavía tienen que resolver problemas desafiantes en relación a la corrección de errores sistemáticos y no sistemáticos. Esta tesis propone métodos eficaces para enfrentarse con estos errores

Correction of Errors in Time of Flight Cameras

En esta tesis se aborda la corrección de errores en cámaras de profundidad basadas en tiempo de vuelo (Time of Flight - ToF). De entre las más recientes tecnologías, las cámaras ToF de modulación continua (Continuous Wave Modulation - CWM) son una alternativa prometedora para la creación de sensores compactos y rápidos. Sin embargo, existen gran variedad de errores que afectan notablemente la medida de profundidad, poniendo en compromiso posibles aplicaciones. La corrección de dichos errores propone un reto desafiante. Actualmente, se consideran dos fuentes principales de error: i) sistemático y ii) no sistemático. Mientras que el primero admite calibración, el último depende de la geometría y el movimiento relativo de la escena. Esta tesis propone métodos que abordan i) la distorsión sistemática de profundidad y dos de las fuentes de error no sistemático más relevantes: ii.a) la interferencia por multicamino (Multipath Interference - MpI) y ii.b) los artefactos de movimiento. La distorsión sistemática de profundidad en cámaras ToF surge principalmente debido al uso de señales sinusoidales no perfectas para modular. Como resultado, las medidas de profundidad aparecen distorsionadas, pudiendo ser reducidas con una etapa de calibración. Esta tesis propone un método de calibración basado en mostrar a la cámara un plano en diferentes posiciones y orientaciones. Este método no requiere de patrones de calibración y, por tanto, puede emplear los planos, que de manera natural, aparecen en la escena. El método propuesto encuentra una función que obtiene la corrección de profundidad correspondiente a cada píxel. Esta tesis mejora los métodos existentes en cuanto a precisión, eficiencia e idoneidad. La interferencia por multicamino surge debido a la superposición de la señal reflejada por diferentes caminos con la reflexión directa, produciendo distorsiones que se hacen más notables en superficies convexas. La MpI es la causa de importantes errores en la estimación de profundidad en cámaras CWM ToF. Esta tesis propone un método que elimina la MpI a partir de un solo mapa de profundidad. El enfoque propuesto no requiere más información acerca de la escena que las medidas ToF. El método se fundamenta en un modelo radio-métrico de las medidas que se emplea para estimar de manera muy precisa el mapa de profundidad sin distorsión. Una de las tecnologías líderes para la obtención de profundidad en imagen ToF está basada en Photonic Mixer Device (PMD), la cual obtiene la profundidad mediante el muestreado secuencial de la correlación entre la señal de modulación y la señal proveniente de la escena en diferentes desplazamientos de fase. Con movimiento, los píxeles PMD capturan profundidades diferentes en cada etapa de muestreo, produciendo artefactos de movimiento. El método propuesto en esta tesis para la corrección de dichos artefactos destaca por su velocidad y sencillez, pudiendo ser incluido fácilmente en el hardware de la cámara. La profundidad de cada píxel se recupera gracias a la consistencia entre las muestras de correlación en el píxel PMD y de la vecindad local. Este método obtiene correcciones precisas, reduciendo los artefactos de movimiento enormemente. Además, como resultado de este método, puede obtenerse el flujo óptico en los contornos en movimiento a partir de una sola captura. A pesar de ser una alternativa muy prometedora para la obtención de profundidad, las cámaras ToF todavía tienen que resolver problemas desafiantes en relación a la corrección de errores sistemáticos y no sistemáticos. Esta tesis propone métodos eficaces para enfrentarse con estos errores

Kinect Range Sensing: Structured-Light versus Time-of-Flight Kinect

Recently, the new Kinect One has been issued by Microsoft, providing the next generation of real-time range sensing devices based on the Time-of-Flight (ToF) principle. As the first Kinect version was using a structured light approach, one would expect various differences in the characteristics of the range data delivered by both devices. This paper presents a detailed and in-depth comparison between both devices. In order to conduct the comparison, we propose a framework of seven different experimental setups, which is a generic basis for evaluating range cameras such as Kinect. The experiments have been designed with the goal to capture individual effects of the Kinect devices as isolatedly as possible and in a way, that they can also be adopted, in order to apply them to any other range sensing device. The overall goal of this paper is to provide a solid insight into the pros and cons of either device. Thus, scientists that are interested in using Kinect range sensing cameras in their specific application scenario can directly assess the expected, specific benefits and potential problem of either device.Comment: 58 pages, 23 figures. Accepted for publication in Computer Vision and Image Understanding (CVIU

A review of advances in pixel detectors for experiments with high rate and radiation

The Large Hadron Collider (LHC) experiments ATLAS and CMS have established hybrid pixel detectors as the instrument of choice for particle tracking and vertexing in high rate and radiation environments, as they operate close to the LHC interaction points. With the High Luminosity-LHC upgrade now in sight, for which the tracking detectors will be completely replaced, new generations of pixel detectors are being devised. They have to address enormous challenges in terms of data throughput and radiation levels, ionizing and non-ionizing, that harm the sensing and readout parts of pixel detectors alike. Advances in microelectronics and microprocessing technologies now enable large scale detector designs with unprecedented performance in measurement precision (space and time), radiation hard sensors and readout chips, hybridization techniques, lightweight supports, and fully monolithic approaches to meet these challenges. This paper reviews the world-wide effort on these developments.Comment: 84 pages with 46 figures. Review article.For submission to Rep. Prog. Phy

A micromirror array with annular partitioning for high-speed random-access axial focusing

Dynamic axial focusing functionality has recently experienced widespread incorporation in microscopy, augmented/virtual reality (AR/VR), adaptive optics, and material processing. However, the limitations of existing varifocal tools continue to beset the performance capabilities and operating overhead of the optical systems that mobilize such functionality. The varifocal tools that are the least burdensome to drive (ex: liquid crystal, elastomeric or optofluidic lenses) suffer from low (~ 100 Hz) refresh rates. Conversely, the fastest devices sacrifice either critical capabilities such as their dwelling capacity (ex: acoustic gradient lenses or monolithic micromechanical mirrors) or low operating overhead (e.g., deformable mirrors). Here, we present a general-purpose random-access axial focusing device that bridges these previously conflicting features of high speed, dwelling capacity and lightweight drive by employing low-rigidity micromirrors that exploit the robustness of defocusing phase profiles. Geometrically, the device consists of an 8.2 mm diameter array of piston-motion and 48 um-pitch micromirror pixels that provide 2pi phase shifting for wavelengths shorter than 1 100 nm with 10-90 % settling in 64.8 us (i.e., 15.44 kHz refresh rate). The pixels are electrically partitioned into 32 rings for a driving scheme that enables phase-wrapped operation with circular symmetry and requires less than 30 V per channel. Optical experiments demonstrated the array's wide focusing range with a measured ability to target 29 distinct, resolvable depth planes. Overall, the features of the proposed array offer the potential for compact, straightforward methods of tackling bottlenecked applications including high-throughput single-cell targeting in neurobiology and the delivery of dense 3D visual information in AR/VR.Comment: 38 pages, 8 figure

Nano-Illumination Microscopy: a technique based on scanning with an array of individually addressable nanoLEDs

In lensless microscopy, spatial resolution is usually provided by the pixel density of current digital cameras, which are reaching a hard-to-surpass pixel size / resolution limit over 1 μm. As an alternative, the dependence of the resolving power can be moved from the detector to the light sources, offering a new kind of lensless microscopy setups. The use of continuously scaled-down Light-Emitting Diode (LED) arrays to scan the sample allows resolutions on order of the LED size, giving rise to compact and low-cost microscopes without mechanical scanners or optical accessories. In this paper, we present the operation principle of this new approach to lensless microscopy, with simulations that demonstrate the possibility to use it for super-resolution, as well as a first prototype. This proof-of-concept setup integrates an 8 x 8 array of LEDs, each 5 x 5 um2 pixel size and 10 um pitch, and an optical detector. We characterize the system using Electron-Beam Lithography (EBL) pattern. Our prototype validates the imaging principle and opens the way to improve resolution by further miniaturizing the light sources

Amorphous silicon e 3D sensors applied to object detection

Nowadays, existing 3D scanning cameras and microscopes in the market use digital or discrete sensors, such as CCDs or CMOS for object detection applications. However, these combined systems are not fast enough for some application scenarios since they require large data processing resources and can be cumbersome. Thereby, there is a clear interest in exploring the possibilities and performances of analogue sensors such as arrays of position sensitive detectors with the final goal of integrating them in 3D scanning cameras or microscopes for object detection purposes. The work performed in this thesis deals with the implementation of prototype systems in order to explore the application of object detection using amorphous silicon position sensors of 32 and 128 lines which were produced in the clean room at CENIMAT-CEMOP. During the first phase of this work, the fabrication and the study of the static and dynamic specifications of the sensors as well as their conditioning in relation to the existing scientific and technological knowledge became a starting point. Subsequently, relevant data acquisition and suitable signal processing electronics were assembled. Various prototypes were developed for the 32 and 128 array PSD sensors. Appropriate optical solutions were integrated to work together with the constructed prototypes, allowing the required experiments to be carried out and allowing the achievement of the results presented in this thesis. All control, data acquisition and 3D rendering platform software was implemented for the existing systems. All these components were combined together to form several integrated systems for the 32 and 128 line PSD 3D sensors. The performance of the 32 PSD array sensor and system was evaluated for machine vision applications such as for example 3D object rendering as well as for microscopy applications such as for example micro object movement detection. Trials were also performed involving the 128 array PSD sensor systems. Sensor channel non-linearities of approximately 4 to 7% were obtained. Overall results obtained show the possibility of using a linear array of 32/128 1D line sensors based on the amorphous silicon technology to render 3D profiles of objects. The system and setup presented allows 3D rendering at high speeds and at high frame rates. The minimum detail or gap that can be detected by the sensor system is approximately 350 μm when using this current setup. It is also possible to render an object in 3D within a scanning angle range of 15º to 85º and identify its real height as a function of the scanning angle and the image displacement distance on the sensor. Simple and not so simple objects, such as a rubber and a plastic fork, can be rendered in 3D properly and accurately also at high resolution, using this sensor and system platform. The nip structure sensor system can detect primary and even derived colors of objects by a proper adjustment of the integration time of the system and by combining white, red, green and blue (RGB) light sources. A mean colorimetric error of 25.7 was obtained. It is also possible to detect the movement of micrometer objects using the 32 PSD sensor system. This kind of setup offers the possibility to detect if a micro object is moving, what are its dimensions and what is its position in two dimensions, even at high speeds. Results show a non-linearity of about 3% and a spatial resolution of < 2µm

Local Epitaxial Overgrowth for Stacked Complementary MOS Transistor Pairs

A three-dimensional silicon processing technology for CMOS circuits was developed and characterized. The first fully depleted SOI devices with individually biasable gates on both sides of the silicon film were realized. A vertically stacked CMOS Inverter built by lateral overgrowth was reported for the first time. Nucleation-free epitaxial lateral overgrowth of silicon over thin oxides was developed for both a pancake and a barrel-type epitaxy reactor: This process was optimized to limit damage to gate oxides and minimize dopant diffusion within the Substrate. Autodoping from impurities of the MOS transistors built in the substrate was greatly reduced. A planarisation technique was developed to reduce the silicon film thickness from 13μm to below 0.5μm for full depletion. Chemo-mechanical polishing was modified to yield an automatic etch stop with the corresponding control and uniformity of the silicon film. The resulting wafer topography is more planar than in a conventional substrate CMOS process. PMOS transistors which match the current drive of bulk NM0S devices of equal geometry were characterized, despite the three-times lower hole mobility. Devices realized in the substrate, at the bottom and on top of the SOI film were essentially indistinguishable from bulk devices. A novel device with two insulated gates controlling the same channel was characterized. Inverters were realized both as joint-gate configuration and with symmetric performance of n- and p-channel. These circuits were realized in the area of a single NMOS transistor