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

PhD : selection by topics

Machine learning methods using uncertain labels, human stress estimation application

Département Systèmes

Laboratoire Signaux et Systèmes de Capteurs



With wearable sensors development, it is now possible to monitor physiological parameters and activity. Many studies show that stress level assessment can be done by using those measurements. Supervised machine learning methods used for it are flourishing. They suppose that for each measurement, a ?ground truth? stress level is available. However, while doing experiments for database construction it is not possible to attribute an exact stress label to each event but subjective values are easily available. The goal of the PhD is to take into account data with uncertain, fuzzy, redundant, contradictory or missing values in order to obtain a better stress estimator. This kind of approach should be useful for a lot of applications including other mental state estimation like drowsiness detection, mental disease diagnosis, emotion estimation.

Innovative polymer thin films for power electronics

Département Technologies Silicium (LETI)




Power electronics require the development of smaller and smaller devices that can withstand high currents and high voltages (> 500 V). In particular, the production of high-voltage thin capacitors (300 µm thick) requires the use of dielectric materials with a high breakdown field. This field has been explored for more than 10 years within the passive components laboratory at LETI. The main approach is the reduction of the capacitor sizes by increasing the dielectric constant of the materials, this often being done to the detriment of the breakdown field. The emergence of new markets, such as batteries for electric vehicles, is now pushing developments towards the use of dielectrics with lower dielectric constants but high breakdown field. Ceramics capacitors already exist and meet the specifications for high voltage applications but their size remains a disadvantage for their integration in high-performance circuits. A promising alternative is the use of polymers that can answer to the main challenges: reduction of the thickness by thin film deposition and resistance to high voltages. The objective of this thesis is to develop, with techniques compatible with the semiconductor industry, polymer thin films capable of withstanding voltages of several hundred volts, to characterize them and to correlate their properties (including breakdown field and permittivity) to the composition and structure of the materials. Chemical Vapor Deposition (CVD) techniques will be favored because they allow conformal deposition of thin insulating layers in 3D structures. This work will take advantages of the solid expertise already acquired by CEA-LETI on the development of thin polymer films by innovative filament-assisted CVD techniques (such as iCVD). The thesis work will include the definition and selection of precursors compatible with the thin film deposition technique and the optimization of the deposition process to obtain materials that can sustain high voltages. The materials will be characterized using a wide range of physico-chemical characterization techniques (ellipsometry, FTIR, AFM, ToF-SIMS, XPS, ...). A second part of the work will include the integration of materials in electronic devices and electrical tests of these components in order to highlight the relationships between the characteristics of dielectrics (including the breakdown field) and the microstructure of the polymers. This thesis may also lead to the identification of failure mechanisms in these materials. This work will be carried out as part of a collaboration between the department of technology platforms and the RF components laboratory of the devices department. Thin film deposition and some characterizations will be carried out in a clean room. The fine characterizations will be carried out in collaboration with experts in materials characterization (nano-characterization platform) and with specialists in the electrical characterization of passive components.

Electromagnetic Wideband Vibration Energy Harvesters

Département Systèmes

Laboratoire Autonomie et Intégration des Capteurs



The purpose of energy harvesting is to exploit the ambient energy present in the environment of an electronic system (communicating sensors, actuator...) to make it energy autonomous, eliminating cables, batteries and associated maintenance (recharge, replacement). Vibration energy harvesting makes it possible to exploit the mechanical energy of a vibrating environment (motor, transport, etc.) and convert it into electricity in order to supply these electronic systems. The thesis will focus on the use of the electromagnetic principles to convert ambient vibration energy into electricity. One of the major limitations of these energy harvesters is their frequency selectivity: the use of mechanical resonators makes it possible to amplify ambient vibrations at the operating frequency, but the harvested power drops drastically when the harvester and the environment are no longer tuned in frequency, which degrades the operability of the system, its versatility and more generally its reliability (frequency drift due to the effects of mechanical fatigue). This frequency selectivity therefore remains the major barrier to vibration energy harvesting, limiting its adoption. However, this challenge can be lifted by means of so-called "broadband" harvesters and/or with the capacity to be dynamically tuned by an electronic system. Indeed, coupled with intelligent electronics, a vibration energy harvester can see its mechanical behaviour modified (change in its stiffness for example) which makes it possible (i) to follow the evolution of the input frequency (e.g. a motor whose rotation frequency decreases) and/or (ii) to compensate for a modification of its own behaviour (a resonance frequency that decreases with temperature, an ageing...). The core of this thesis focuses on (i) the development of electromagnetic conversion vibration energy harvesters whose resonance frequency can be adjusted in real time (highly coupled system, piezoelectric/electromagnetic coupling, non-linear systems) and (ii) the development of very low consumption power management electronics capable of driving these devices. The objective of the thesis is to propose, dimension, simulate, realize and test innovative energy harvesters and electronic architectures allowing automatic frequency tuning and the search for the maximum power point. After a state of the art on frequency adjustment means and techniques, a system study and electromechanical simulations will have to be carried out, which will make it possible to select the most relevant implementations. Particular care will be taken to ensure low consumption of the control electronics since the ultimate goal is to create an energy autonomous circuit that consumes a negligible part of the harvested electrical energy. A complete demonstrator (vibration energy harvester + tuning technique + adjustment circuit) is targeted for the end of the thesis.

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



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



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



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.

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