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PhD : selection by topics

Technological challenges >> Photonics, Imaging and displays
16 proposition(s).

Improvement of CdZnTe based gamma imager CdZnTe using machine learning

Département d'Optronique (LETI)

Laboratoire Architecture Systèmes Photoniques

01-11-2020

SL-DRT-20-0522

gmontemont@cea.fr

Photonics, Imaging and displays (.pdf)

Gamma imaging is a technique widely used in medical imaging (molecular imaging, nuclear medicine) and security (transportation, industry). CdZnTe semiconducting detectors usage is currently emerging for SPECT (Single Photon Emission Computed Tomography, using gamma-cameras) and portable gamma imaging. Indeed, they enable performance improvements in speed, sensitivity and image quality. These detectors operate at room temperature and are sensitive to five physical parameters of the interaction: deposited energy E, interaction time T and the 3-dimensional position XYZ. These parameters are estimated by real-time analysis of anode electronics signals. However, the link between electrical signals and physical parameters is not fully known, as material physical properties are not uniform inside detector. The goal of this Ph.D. internship is to overcome these limits by using machine learning techniques to model actual detector response. Recent multi-layered deep learning technique enable to build and train complex and flexible system models, and to overcome our lack of knowledge about detector physics. The identification of internal physical parameters of the detector would allow to optimize estimation of interaction location, time and energy. This will lead to a better image quality and then capability to detect small and weak objects, enabling better diagnoses and lower false alarm rate. The student may have a background in applied mathematics (machine learning) and/or instrumentation physics. He/she need to have taste for multi-disciplinary research, mixing experimental physics and data science.

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Characterizations of electronic defects in perovskite crystals used for medical X-ray imaging

Département d'Optronique (LETI)

Laboratoire Architecture Systèmes Photoniques

01-09-2020

SL-DRT-20-0690

eric.grosdaillon@cea.fr

Photonics, Imaging and displays (.pdf)

The photonic systems architecture laboratory is part of the CEA LETI optronics department. We have a solid expertise in the development of new detection modules including a semiconductor or scintillator detector combined with readout electronics for X-ray or gamma imaging in the fields of medical imaging or security control. The objective of this thesis is to study the traps levels and densities in the bandgap of a new perovskite-based semiconductor material for direct X-ray detection developed for medical radiography. Its use as photoconductive devices in matrix imagers should improve the spatial resolution of images and increase the signal, thus reducing the dose given to the patient, or even providing access to new information on tissue composition. To reach this goal, the student, physicist and experimenter, will develop specific test bench to identify and characterize these electronic traps in the volume of crystals and at the interfaces of the devices. He will determine the nature of the defects of the thick crystalline layers developed by a doctoral student at CEA LITEN. The student will model the effect of these trap levels on the performance of the devices. In parallel, the student will study the origin of the current of darkness in perovskite devices. These results will be correlated with experimental measurements made by a doctoral student from CEA LETI. Finally, he will provide feedback on the development of crystals and devices in order to minimize the traps density and improve their overall performance.

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Design and fabrication of GeSn based components for environmental detection

Département d'Optronique (LETI)

Laboratoire des Capteurs Optiques

01-10-2020

SL-DRT-20-0776

vincent.reboud@cea.fr

Photonics, Imaging and displays (.pdf)

Integrated laser sources compatible with microelectronic technologies is currently one of the main challenges for silicon photonics. CEA is part of the few laboratory that demonstrated mid-infrared optically pumped lasing in GeSn micro-cavities. Our aim is to go towards lasing at room temperature in fully relaxed or tensile-strained heterostructures and quantum wells made of germanium tin alloys. Defect reduction in the gain zone and carrier confinement optimisation in order to reach high gain is the major issue of this study. We would indeed like to minimize the lasing threshold and obtain continuous emission lasers. We also target a decrease the concentration of tin in germanium by focusing strain to further increase the crystalline quality of quantum wells and heterostructures and still reach direct band gap in the structures. Objectives of the research will be (i) to reduce crystalline defects in the gain zone, (ii) to find efficient geometries to confine electrons and holes, (iii) to apply tensile strain to germanium tin crystals, (iv) to evaluate the electrical gain dependence with different strains and doping levels, (v) to characterise the optoelectronic properties of epitaxial materials, (vi) to design and fabricate laser cavities with strong optical confinement in order to reach tunable continuous germanium lasers compatible with the current microelectronic technologies for environmental detection.

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Pure phase optical modulation based on Pockels effect in strained silicon

Département d'Optronique (LETI)

Laboratoire d'Intégration Photonique sur Silicium

01-09-2020

SL-DRT-20-0798

leopold.virot@cea.fr

Photonics, Imaging and displays (.pdf)

The use of silicon photonics has been identified as a mean to overcome interconnect limitations and efficiency, but also as a versatile platform able to address the new problematics encountered in Lidar and quantum photonics applications. However, the possibility to have high-speed pure phase optical modulation has not been addressed yet on this platform. Silicon, as a centrosymmetric material does not exhibits second order non-linearities. Nevertheless, it has been theoretically and experimentally demonstrated that by applying a mechanical strain, its centrosymmetric can be broken, leading to the exhibition of second order non-linearities. Recent proofs of concept have been demonstrated with a modulation at 20GHz based on the use of silicon nitride stress layers deposited by PECVD on top of silicon. The objectives of the PhD will be to enhance the Pockels effect in silicon waveguides by a factor of 10 to 100, in order to reach performances close to LiNbO3. This research activity will include : Fine theoretical study of the involved processes and how to control them, and also electro-optic simulations in order to evaluate the performances of such devices and optimize the overlap between the strain field and the optical mode in the waveguide; The design and fabrication of optical phase modulators optimized to maximize the Pockels effect in the waveguide; DC and RF characterization of optoelectronics devices bas on second order non-linearities.

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µ-LEDs based on nitride semiconductors in semi-polar orientation

Département d'Optronique (LETI)

Laboratoire des Composants Emissifs

01-09-2020

SL-DRT-20-0813

fabian.rol@cea.fr

Photonics, Imaging and displays (.pdf)

GaN-based microLEDs are on the verge to revolutionize the display world, on one hand providing ultra-high brightness microdisplays for augmented reality applications, on the other hand paving the way for large area displays with unrivaled image quality. Blue-emitting LEDs based on nitride semiconductors exhibit good efficiency, however it is not the case for green and red ones, for which external quantum efficiency does not exceed a few percent. The main reasons are related to the existing growth techniques, which induce high polarization field and high level of crystalline defects. We propose a novel GaN growth technique which will allow to fabricate microleds with improved efficiency both in blue, green and red. The objective of the thesis is first to investigate and improve the growth conditions in order to obtain GaN Led epilayers for blue, green and red emission with better crystalline quality. The objective is also to fabricate and characterize GaN microleds in order to verify the improvement at the device level.

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Waveguide adressing architecture for retinal projection display integration

Département d'Optronique (LETI)

Laboratoire Architecture Systèmes Photoniques

01-10-2020

SL-DRT-20-0837

christophe.martinez@cea.fr

Photonics, Imaging and displays (.pdf)

CEA Tech Leti is involved for several years in the development of an original concept of optical device for Augmented Reality applications. This retinal projection display concept is based on advanced technological process: SiN waveguide photonics and holographic printers. The PhD is dedicated to the first technology and concern the design of addressing waveguide architecture. It will be done in continuity of a former ending PhD on the design of dense waveguide networks in the visible range. This network, that has to interact with pixelated holograms, has to be addressed by an array of optical emitters. The PhD student will simulate and develop the waveguide multi-level architecture needed to link the emitters (LED, VCESL, laser array) to the waveguides network. He will also follow the technological steps in the clean room and bring the device characterization. The Phd will end by the conception and realization of a prototype demonstrating the interaction between an optical emitter array and a digital hologram through a waveguide network.

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High-performance TeraHertz detectors for passive imaging

Département d'Optronique (LETI)

Laboratoire d'Imagerie thermique et THz

01-10-2020

SL-DRT-20-0845

abdelkader.aliane@cea.fr

Photonics, Imaging and displays (.pdf)

The Terahertz (THz, 300 GHz-3 THz) frequency band triggers a high interest in numerous application domains (imaging, spectrometry, industrial inspection and test, surveillance, instrumentation) thanks to the good propagation properties through non-conductive materials, the presence of resonance frequencies typical of numerous molecules, the potential for high spatial resolution, and their non-ionizing properties. CEA-LETI is a world-leading research laboratory in THz technologies and developed several THz detectors and imaging circuits, both cooled and uncooled, for imaging applications. Since 2018, a THz imager developed and manufactured at CEA-LETI is available commercially in the THz camera from i2S (www.i2s.fr/en). The objective of this PhD thesis is to investigate and develop a new THz detector technology with a significant breakthrough in terms of sensitivity enabling passive imaging applications. The PhD student will work in a team gathering all the expertise, instrumentation and facilities required in this project. He/she will take part in all the activities involved in the development of these new detectors, in particular system studies, design and simulation (thermal, mechanical, electromechanical), fabrication, and characterization.

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Suspended vertical diodes for LWIR detection

Département d'Optronique (LETI)

Laboratoire d'Imagerie thermique et THz

01-09-2020

SL-DRT-20-0856

patrick.leduc@cea.fr

Photonics, Imaging and displays (.pdf)

Uncooled thermal detectors absorb the infrared flux for wavelengths from 7µm to 14µm. This corresponds to an atmospheric transmission window and to the maximum emission of a blackbody at 300K, which enables the detection of temperature variations of less than 100mK. The operating principle of microbolometers is based on the temperature measurement of a suspended membrane absorbing the infrared flux. The thermal transducer is the sensitive element of the microbolomètre, which determines its signal-to-noise ratio and therefore the performance of the bolometric pixel. In recent years, the miniaturization of microbolometer technologies has led to pixel size reduction down to 12 µm and has been accompanied by a reduction of manufacturing costs. However the current technology reaches its limits in a way that it becomes extremely difficult to pursue the pixel size reduction. The thesis topic is the study of a breakthrough technology for microbolometers. Unlike conventional detectors, which use thermistor for the thermal transduction, the proposed research topic will examine an original technology based on vertical diodes. The subject will focus on characterizing and modeling the performance of such a device.

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Development of superconducting single photon detectors and receiver circuits for quantum communications

Département d'Optronique (LETI)

Laboratoire d'Intégration Photonique sur Silicium

01-10-2020

SL-DRT-20-0859

segolene.olivier@cea.fr

Photonics, Imaging and displays (.pdf)

Quantum information processing turns out to be a major challenge for our society with the development of quantum computers, able to solve complex problems much more rapidly than a classical computer, and of quantum communications providing absolute security for information transfer. The development of integrated technologies is essential for the future large-scale deployment of compact and low-cost quantum information systems. CEA-Leti has been developing for several years a silicon photonics platform, providing integrated components and circuits for various applications such as telecom/datacom, lidars and more recently quantum communications. The objective of this PhD is in a first step to design, fabricate in the Leti clean room and characterize a new generation of advanced superconducting quantum detectors on Silicon able to detect single photons with above 90% efficiency. In a second step, these detectors will be integrated into secure quantum communication circuits. This PhD will benefit from collaborations with academic laboratories in France and in Europe.

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3D imaging module with integrated optics

Département d'Optronique (LETI)

Laboratoire Architecture Systèmes Photoniques

01-10-2020

SL-DRT-20-0876

laurent.frey@cea.fr

Photonics, Imaging and displays (.pdf)

3D sensing by capturing depth images, is a key function in numerous emerging applications such as facial recognition, augmented reality, robotics or drones. CEA targets the development of an innovative 3D sensing module, inspired from Lidar, and including various innovative components, from the coherent optical source to the photo-detector. The proposed PhD will focus on the definition of an integrated optics architecture coupled to an optical imaging system, optical simulation with internal code or commercial software, fabrication in micro-electronic clean-room, electro-optical characterization of individual components, computing of algorithms for signal or image processing, and demonstration of the whole system, for its miniaturization and integration for example in mobile devices such as a smartphone. The work will be performed in close collaboration with a research team that will develop in parallel a first version of the system in free space. A transfer to the industry is targeted in the end.

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Design and assessment of FD-SOI devices specially functionalized for uncooled IR imaging

Département d'Optronique (LETI)

Laboratoire d'Imagerie thermique et THz

01-10-2020

SL-DRT-20-0893

jyon@cea.fr

Photonics, Imaging and displays (.pdf)

Uncooled infrared focal plane array (U-IRFPA) microbolometer technology has opened the field of thermal imaging to various novel applications, such as automotive driving assistance, building automation, leisure, smartphone. These new applications are expected to grow rapidly to reach a large volume market. Firstly developed at CEA-LETI, microbolometer technology was then transferred to LYNRED (LYNRED by SOFRADIR & ULIS, www.lynred.com) in charge of its industrialization. However, the freshly expressed new commercial needs require an improvement of the technology based on some breakthrough developments, in particular to reduce the pixel pitch to 5µm, i.e. the ultimate size sets by the IR radiation diffraction. It is the framework of this doctoral study, which aims at developing a novel class of microbolometers, by the mean of a thermal micro-transducer based on a MOS technology on FD-SOI silicon thin film, whose performance is expected as a breakthrough with respect to thermistor-based current technology. Research work will cover both the architectural design of a new integrated IR sensor on silicon, its technological prototyping (on the Leti's 200mm silicon platform) and the finale evaluation of its performance. Basically, it means both design and achievement of a disruptive sensor which differs from a classical unitary MOS-FET transistor as it could features for example an active sensor made of several different devices, or even a smart sensor adjusting itself its sensor properties in standalone. At the end of the 3 years, the student will have led to an in-depth evaluation of the feasibility of this technology for uncooled IR imaging.

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Mid-IR digital holography

Département d'Optronique (LETI)

Laboratoire des Capteurs Optiques

01-10-2020

SL-DRT-20-0900

mathieu.dupoy@cea.fr

Photonics, Imaging and displays (.pdf)

Currently the challenge is to develop automation and non-invasive measurements to enhance early identification or diagnosis. The optical technologies are the label free methods to detect and identify the chemical composition of sample. Infrared spectroscopy is a widespread and reliable method to obtain a spectral fingerprint of sample based on absorption of mir-IR light. An optical platform has been developed to measure the absorption of light through the sample, combining quantum cascade laser (QCL) and bolometer matrix. The objective of the thesis is to explore the potential of Mid-IR digital holography in order to obtain information on the phase of the sample. The thesis will aim to choose the best optical configuration of interferometer and the implement it in conventional optics. After processing the images and extracting the information, a second task will be perform this function on an integrated optical component

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Phase Field Models and Undestanding Interface Evolution at Crystal Growth Initial States

Département d'Optronique (LETI)

Laboratoire des Matériaux pour la photonique

01-10-2020

SL-DRT-20-0924

marc.parent@cea.fr

Photonics, Imaging and displays (.pdf)

The proposed research concerns modeling the physics of crystal growth involved in Vertical Gradient Freeze (VGF), a method that allows the manufacturing of large ingots for the semi-conductor industry. In this process, the material is molten then solidifies as the temperature is slowly decreased with spatially controlled temperature profiles, in order to favor the orientation and the low defect density of the resulting crystal. One of the main objectives of this project is to design numerical models that could provide an accurate description of the evolution of the liquid-solid interface in a II-VI alloy at the early stages of a crystal growth, so as to gain understanding of how one could control the system thermal state evolution and improve the quality of the crystallization. In particular, an approach based on phase field approximations of the solidification front will be developed. From the numerical point of view, such representation of the front should allow a more robust modeling of topology and phase changes, while also providing insight on the relevant relationships between the mesoscopic and macroscopic scales. Underlying experimental and industrial goals are also to help scientists analyze the process observable signals and determine the optimal conditions that need to be setup in order to achieve desired material properties.

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Nanostructured plastic scintillators for the development of high performance contaminameters (sensitivity and discrimination capabilities).

Département Métrologie Instrumentation et Information (LIST)

Laboratoire Capteurs et Architectures Electroniques

01-10-2020

SL-DRT-20-1006

vesna.simic@cea.fr

Photonics, Imaging and displays (.pdf)

The proposed subject deals with the development of ionizing radiation detectors, in technological rupture with existing devices. It takes advantage of recent progresses in nanostructuration and nanophotonics to control and amplify the spontaneous emission of radioluminescent materials commonly used in such devices. This will pave the way to more efficient detectors showing a better signal-to-noise ratio, with improved sensitivity at low energies and better discrimination performances. However, this original approach requires deep patterning of the material, typically to a depth of the order of the penetration length of the ionizing radiation in the material. The typical resonant structures are 2D arrays of nano-pillars and nano-holes, of about 200 nm spacing and 200 nm diameter. These nanostructures are now achievable, thanks to recent advances in polymer nanostructuring, with a barrier to be overcome, that of etching to a sufficient depth and over large surfaces. An additional area for improvement concerns the optical index of materials , which remains too low to obtain the targeted effects. The incorporation of nanomaterials with a higher optical index is a highly promising and already proven approach. Among the nanoparticles being considered for this purpose, we are particularly interested in nanodiamonds that have a high refractive index (2.4), a good transparency in the visible region, and a surface chemistry that allows many functionalization pathways. Thus, the purpose of this thesis concerns the synthesis of these new carbon-carbon hybrid materials, their nanostructuration and their photophysical and radiophysical characterizations in order to integrate them in a new functional contaminameter prototype with improved performances in terms of sensitivity and selectivity. This research work will be based on the results of an ANR project called DECISIoN (AAP ANR 2017 funding) which brings together complementary partners with recognized skills in their field of expertise: CEA-LIST, expert in the development of ionizing radiation detectors, L2n, specialist in nanophotonics and nanofabrication, Napa technologies, a French SME specialised in large scale nanostructuring of polymers for different applicative markets, and SDIS91, an end-user, first responder in case of radiological threats. This project proposes in fine the realization of a functional prototype for the detection and measurement of beta contamination in an large and fluctuating gamma environment.

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Design, fabrication and characterization of microlasers for data communications

Département d'Optronique (LETI)

Laboratoire de Photonique pour les Communications et le Calcul

01-10-2019

SL-DRT-20-1013

karim.hassan@cea.fr

Photonics, Imaging and displays (.pdf)

Needs for high speed datacommunications has increased tremendously these last years. Optical links, usually used for long distance communications, are now used for shorter distances in data centers, for instance between racks or within a rack. Components for Si photonics are excellent candidates for these short distances communications has there are low cost and highly performant. Moreover, CMOS fabrication environment brings excellent fabrication yield, and test/packaging capabilities. Nevertheless, Si, being an indirect bandgap material, cannot emit light, thus, laser are generally fabricated using a IIIV material (direct bandgap material, i. e. InP) added to the Si photonics circuit. CEA/Leti expertise in transfer layer technologies is used to bond IIIV material on Si photonics circuits leading to fully integrated devices. This phD work aims at developing new solutions for the design and fabrication of micro lasers adapted to very short communications (inter or intra dies). These new devices relie on a CMOS compatible fabrication process flow and original design. The phD student will be in charge of (i) microlasers design using the available softwares in the laboratory, (ii) microlasers fabrication relying on CEA/Leti technological platform and (iii) electro-optically characterization of these new components.

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Design, fabrication and characterization of subwavelength nanostructured Si photonics devices enabled by advanced immersion lithography

Département d'Optronique (LETI)

Laboratoire d'Intégration Photonique sur Silicium

01-10-2020

SL-DRT-20-1042

cecilia.dupre@cea.fr

Photonics, Imaging and displays (.pdf)

The demand for telecommunications capacity has increased rapidly in recent years. To satisfy this demand, optical transceivers, previously used only for long distance data transfer, are now used for the shorter distances found in datacenters. Photonic integrated circuits based on silicon are particularly relevant for this application as they use establish CMOS technology to achieve high performance and yield at a low cost. Previous work has shown that integrated components based on sub-wavelength structures allow the possibility of new optical functionalities and improved performance, such as reduced insertion losses and significantly increased spectral bandwidth. The CEA-LETI has its own Si photonics platform including an immersion lithography tool that allows reproducible and precise patterning with dimensions as low as 50nm. The objective of this PhD are to design new high spectral bandwidth/low-loss photonic components using sub-wavelength structures, to develop the fabrication technology for this type of component on the CEA-LETI Si photonics platform and to characterise their optical properties. This PhD, based at CEA-LETI (Grenoble), will be in close collaboration with the C2N-CNRS (Paris-Saclay).

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