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

PhD : selection by topics

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.

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

Département Technologies Silicium (LETI)




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



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.

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