Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PhD : selection by topics

Design and integration of active EMC filters for power converter

Département de l'Electricité et de l'Hydrogène pour les Transports (LITEN)

Laboratoire Electronique avancée, Energie et Puissance

01-10-2019

SL-DRT-19-0935

xavier.maynard@cea.fr

The specifications of power converters for embedded applications have high constraints (efficiency, weight / power ratio, etc.) while respecting normative EMC constraints. A converter may be upset by its own disturbances (self-immunity) or disturb its environment, usually due to common-mode (CM) currents. Converters (even low-power ones) may also radiate high-frequency electromagnetic energy that can upset nearby equipment (near-field coupling) or radio receivers (far-field coupling). The conventional way of satisfying the EMC requirements is the use of shielding and filtering techniques based on large and heavy passive components (inductors and capacitors) which degrade the specific power of the converter. Passive EMC filters would represent approximately 20% of the cost, weight and volume of a power converter. With the adoption of GaN components allowing higher and higher switching frequencies, active CEM filters appear as a worthy alternative to the classic passive filtering approach. Similar attenuations are possible with reduced mass and bulk. The aim of the thesis is to study the different types of active CEM filters with: - The realization of a state of the art. - The realization of a common mode (CM) and differential mode (DM) noise estimator of switching cells and transformers. - Simulation and comparison of the most relevant solutions (active and passive). - EMC measurement of standard filters and converters. - The design of a model of an active filter for a given converter. - The test of the model with its associated converter. The PhD student will have a background in analog and digital electronics as well as knowledge of electronic simulation software (LTspice, Pspice, PSIM or others), routing software (KiCad, Altium for example) and embedded programming for a programmable digital circuit ( µC, DSP or FPGA).

Development of a transmissive phase modulator (SLM) based on Liquid Crystal (LCD) for Virtual and Augmented reality applications (AR/VR)

Département d'Optronique (LETI)

Laboratoire des Composants Emissifs

01-11-2019

SL-DRT-19-0941

benoit.racine@cea.fr

Today, the field of display is increasingly oriented towards applications such as augmented reality headphones (HMD) or head-up vision (HUD. In general, these devices use a micro-screen combined with an optical system for projecting an image on a specific surface in the case of an HUD, or directly on the eye in the case of an HMD. These devices have to provide an image with a very high resolution, all on a very wide angle of view. To meet these two issues, the optics needed is expensive and take too much place which increases the difficulty of integration for a mobile system such as the helmet. To solve this problem an intermediate solution exists, it is to use a system composed of an SLM (phase modulation) integrated into a so-called adaptive optical system. Furthermore, the transmissive feature of the SLM is mandatory and only the transmissive LCD microstructures, by acting on the phase and / or the polarization of the light, can find a wavefront corrector function for adaptive optics. Adaptive optics projects include, for example, compact, high-resolution, high-resolution lenses based on the concept of eye function (Foveation), where only the part of the useful field is highly defined by acting on the correction of the wavefront via the integrated SLM in the optics. Previous work has shown that this kind of object requires a technology using complex micro-electronics bricks based on the CMOS report on transparent substrate to obtain transmissive screens. Our last theoretical study on the subject showed that the LCD screen configuration called IPS for In-Plane Switching, could be adapted to meet our needs. This configuration offers a lot of advantages including that of being easier to implement. The proposed work is part of a new project in which the first phase will consist of simulating, with specific software, the evolution of the liquid crystal according to the different pixel design and electrode design to define the optimal geometry of the crystal liquid cell. If possible, preference will be given to structures where the liquid crystal does not twist. At the end of this study, the second phase of the project will include the complete realization of a screen with a passive matrix while taking into account the concept of the optimised cell. Finally, to measure the performance of the test cells and the final SLM obtained, the development and implementation of an optical and addressing bench for electro-optical characterization will also be requested.

Design and fabrication of miniaturized wireless-powered sensors on flexible substrate

Département Composants Silicium (LETI)

Laboratoire de Caractérisation et Fiabilité des Composants

01-10-2019

SL-DRT-19-0959

alexandra.koumela@cea.fr

The goal of this thesis is to develop a Wireless-powered sensors on flexible substrate. The measured quantity can be the pressure, the temperature, the acceleration, the strain, the magnetic field etc. The M&NEMS technology developed by the CEA-LETI could meet the demands of extreme miniaturization, ultra-low consumption, high performances and low cost. In order to identify the more suitable M&NEMS sensors a comparative study of the available sensors will be performed. The criteria will include the pairing with an RF antenna for circuit alimentation and information transmission. The fabrication of the sensor, the antenna and its electronics will be performed on a flexible substrate which will be chosen in function of the application. This work will rely on the Systems Department (DSYS) at CEA-LETI for the design of the antenna and on the packaging 3D laboratory (LP3D) for the fabrication on the flexible substrate. An innovative actuation principle based on the thermopiezoresistive back-action effect will also be examined in function of the integrated sensor.

Modélisation/caractérisation mécanique et triboélectrique du procédé de nanoimpression en interfaces souples

Département technologies silicium (LETI)

Laboratoire

01-10-2019

SL-DRT-19-0977

hubert.teyssedre@cea.fr

The flexible molds used in nanoimprint lithography allow to reduce the impact of a particle on the defectivity of a patterning step: its flexibility is used to conform the shape of the defects without impacting the surrounding structures. This flexibility is usually obtained by using single-material or composite polymer materials that have the ability to reproduce patterns having critical dimensions of a few tens of nanometers. The state of the art materials can be transformed from a viscous state (and thus able to flow in nanostructures) at room temperature to a state of elastic solid by photo-polymerization at 365 nm while having an anti-adhesive free surface. This elastic state is fundamental for the performance of replications: the material must have sufficient stiffness to prevent buckling or irreversible deformation during the process, but it must have enough flexibility to be demolded from the resin to be printed without damaging the patterns created in the latter. Nevertheless the use of these flexible molds reinforces the appearance of electrostatic charges during the separation of the mold and the substrate. These charges are usually dissipated macroscopically by means of antistatic bars or ionized air jets, but they can persist on the extreme surface of the flexible stamp and cause deformation of the structures. The objective of this thesis is to study through AFM measurements the behavior of these interfaces.

Spike based processing chain for signal classification

Département Architectures Conception et Logiciels Embarqués (LIST-LETI)

Laboratoire Architectures Intégrées Radiofréquences

01-09-2019

SL-DRT-19-0990

dominique.morche@cea.fr

The expansion of the internet of things is conditioned by our ability to develop innovative systems able to apprehend and understand the environment while having an ultra low power consumption, compatible with energy harvesting. To reach such a goal, one of the solution which is knowing a considerable renewed interest is the use of acoustic signals. Their low frequencies undoubtedly induces a low power consumption in the circuit interface and their low cost eases the dissemination of this solution. There's a huge applicative potential: wake-up by key words (the well known ?ok google?), choc detection, source localization, event classification, surveillance, and machine health monitoring. In order to implement such complex functions in an energy efficient manner, the potential of neural networks is more and more considered. However today, these solutions are too power consuming. To reduce this power, several alternatives are considered. One of the most promising is the coding of the signal in spike, coherently with neuromorphic architecture. Recently, CEA-LETI has developed a new ADC architecture which directly generate some spike and the best power efficiency in the state of the art has been reached. The aim of this PhD is to follow up this work by implementing in the analog domain some feature extraction in order to reduce the complexity of the neural network processing. To reach the best energy efficiency, a joint optimization between the analog, digital and algorithmic part is mandatory. In the scope of this PhD, CEA-LETI and EPDFL are collaborating to develop this new analog processing interface, adapted to neural networks based on spike processing. The main objective is ti setup a methodology to reduce the power consumption in all the sensing systems. The automotive applications will be particularly considered. Other application areas and different kind of signal might be also studied.

Optimization of metal oxides for the realization of electrode in adequacy with the photosensitive material in the near infrared

Département technologies silicium (LETI)

Laboratoire

01-09-2019

SL-DRT-19-1000

serge.blonkowski@cea.fr

The thesis is part of a partnership between CEA-Léti and the Process Development Department of STMicroelectronics Crolles. The study will focus on the development of electrodes for image sensor applications. The next generations of image sensors will use chalcogenide, perovskite or 'quantum dots' photosensitive materials. These materials are inserted between electrodes to collect electrons and generated photo holes. Band engineering is necessary to promote the transfer of charges to the electrodes when the photosensitive material is illuminated, whereas when the detector is in the dark it is necessary to block the continuous flow of thermally activated charges through the structure, this flux may lead to a dark current level too high. The electrodes must also be stable in contact with these new materials, that is to say that it is necessary to limit the interface chemical reactions which can lead to the trapping of charges, or to an undesired shift of the levels of energy of the valence or conduction bands. The upper electrode must be deposited by a technique that does not degrade the photosensitive materials that are known to be fragile and easily degrade under an oxidizing atmosphere, under UV radiation or under bombardment during deposition using a plasma. Finally, these electrodes must be conductive, and the upper electrode must be transparent for the photons that pass through it. The objective of the thesis is to develop and optimize a new upper electrode adapted to image sensors operating in the field of near IR (1-1.5µm)

108 Results found (Page 16 of 18)
first   previous  14 - 15 - 16 - 17 - 18  next   last

Voir toutes nos offres