Papier électronique | EPFL Graph Search

Le papier électronique (en e-paper), également appelé papiel ou encore encre électronique (en e-ink), est une technique d'affichage sur support souple (papier, plastique), modifiable électroniquement, cherchant à imiter l'apparence d'une feuille imprimée et qui, comme le papier, ne nécessite pas d'énergie pour laisser un texte ou une image affiché. Contrairement aux techniques d'affichage classiques qui nécessitent un rétroéclairage ou l'émission de photons, le papier électronique est purement réflectif et utilise la lumière ambiante de la même manière que le papier classique. Un papier électronique doit pouvoir afficher du texte et des images indéfiniment, sans consommer d'énergie, que ce soit pour l'affichage ou pour un éventuel système de traitement de données, et doit permettre le changement de ce qu'il affiche. La plupart des papiers électroniques consomment de l'énergie uniquement lorsque le contenu affiché est modifié. Les pixels d'un tel système doive

Organic thin-film transistors

Frédéric Zanella

Organic molecules (i.e. carbon-based) have opened a new and rapidly-growing industrial field in the optoelectronic market bringing to this field a new dimension of thinness and flexibility. In this context, this thesis has focused on one particular building block of the vast and emerging field of organic electronics: the organic thin-film transistor (OTFT) which uses organic compounds as semiconductor. Whereas the OTFT-based circuits are not meant to compete with the silicon-based high-end industry (micro-processors...), their performance have already reached levels enabling their use in potential applications such as displays (e-paper, LCD, OLED) or radiofrequency identification (RFID) tags. The continuously growing number of available organic molecules exhibiting conductive, semi-conductive or insulating properties combined with the number of available deposition/patterning methods (e.g. gravure printing) gives more flexibility to the technology. These additional degrees of freedom raise two main questions: How to identify the most suitable OTFT platform for a given application and how to estimate its potential, as for instance in, of digital circuits? This thesis targets to answer to those questions. For this purpose, several OTFT platforms have been screened and their performance have been discussed and compared through standard figures of merit. The self-aligned nano-imprinted technology has demonstrated state-of-the-art sub-micrometer OTFTs on 4-inch flexible substrates. This made this platform the most suitable candidate for developing the potential evaluation framework. For that purpose, a static model suitable for the sub-micrometer OTFTs has been developed which embeds almost all known electrical aspects of OTFTs. Then the device-to-device discrepancy often observed in OTFTs has been studied and statistical modeling methods introduced. This allowed the simulation of sub-micrometer inverters performed with commercially available tools. Next, a statistical method has been developed to evaluate the potential of the sub-micrometer OTFTs for digital applications. Whereas the method concludes that these sub-micrometer OTFTs are not mature enough to make complex digital circuits, this methodology is technology-independent and may thus serve as a basis to characterize unipolar-logic printed electronics and be further extended to complementary-logic circuits. Last but not least, an automation effort has been undergone all along this thesis in order to increase the throughput for such demanding data analysis. The main outcome of this task is a user-friendly multi-analysis and parameter extraction platform.

EPFL2014

Probing Entangled States of the Nuclear-Electronic Quantum Magnet LiHoF₄

Ivan Kovacevic

Two objects are entangled when their quantum mechanical wavefunctions cannot be written in a separable product form. Entangling dissimilar quantum objects, or hybridization, has been suggested as a promising route to efficient quantum information processors, but mostly realized on a limited scale. Hybrid nuclear-electronic many-body systems remain a largely unexplored challenge to both experiments and theories. The prototypical transverse-field Ising ferromagnet LiHoF4 is an ideal platform to address this issue. The Ising model is considered as an archetype both for the investigation of quantum criticality and for the evaluation of quantum simulators. The hyperfine coupling strength of a Ho ion is exceptionally large, promoting a strong hybridization or entanglement between the nuclear and electronic moments. The magnetic coupling between the Ho ions that leads to ferromagnetic ordering is predominantly through long-range dipole interactions, while nearest-neighbor exchange interaction is negligibly weak. Applying a transverse field induces a zero temperature quantum phase transition driven by quantum fluctuations. Altogether LiHoF4 represents a unique nuclear-electronic quantum magnet, whose wavefunctions can be readily obtained by diagonalizing the Hamiltonian using the mean-field approximation. In this thesis we develop an experimental setup to probe the entangled nuclear-electronic states in a model transverse-field Ising system LiHoF4. Using magnetic resonance the field and temperature evolution of the nuclear-electronic states are successfully traced across the whole phase diagram. We develop a theoretical framework based on mean-field calculations which provides close agreement with the experimental observations. Having established experimentally that the mean-field wavefunctions are an excellent approximation of the actual wavefunction, we used them to calculate the ground-state entanglement entropy between the electronic and nuclear magnetic moments. We find that the entanglement entropy between the nuclear and electronic moments exhibits a peak at the quantum phase transition. This suggests that the electronic entanglement is encoded onto each nuclear-electronic state. Our results pave the way for new theoretical and experimental investigations of quantum entanglement.

EPFL2016

Dielectrophoresis-based continuous-flow particle microreactor

Raphaël Tornay

This thesis mainly deals with the integration of a microfluidic system for the extraction of micrometric and submicrometric particles from a solution. Traditional methods take from several minutes to hours to separate particles from a solution. Microfluidics allow for a more rapid separation, and in addition provide a way to control the duration of the exposition of the particles to a specific reagent. In the first device proposed in this dissertation (called simple exchanger) a microchannel carrying the particle solution overlaps over a short distance with a channel carrying the reagent. In this region the particles are pushed from one solution to the other by dielectrophoretic forces. They are created by an array of microelectrodes patterned on the side of the channel. Diffusion across the interface between the solutions causes molecules from the reagent stream to pollute the particle solution (and inversely). This effect is minimized by increasing the flow velocity in the overlap region. The maximum velocity applicable as well as diffusive mixing and a biochemical application of the device are presented in a first part. In a second part, new designs for the exchanger are proposed in order to prevent diffusive mixing. The first design relies on a massive enlargement of the channel as well as an intermediate buffer flow to keep the destination solution clean. The enlargement diminishes the relative effect of diffusion; the buffer flow "collects" the diffused molecules and is discarded. A second scheme relies on electrophoretic forces to pull charged reagents against diffusion, thereby decreasing diffusive mixing. In a final chapter a microfluidic device based on simple exchangers is used to probe the aggregation of nanoparticles to a biological target. Thanks to a well-controlled flow velocity in the channel and the given channel length the duration a single target is exposed to a nanoparticle solution is known. By exposing targets for different durations it is possible to follow the aggregation kinetics of the nanoparticles. This measurement is carried out for yeast cells and carboxylated nanoparticles. A Brownian dynamics simulation is finally used to outline a promotion of the aggregation due to the microchannel format. In the future, these devices could be used for various applications in the biotechnological domain, where a well-controlled, short duration of exposure of a small particle to a chemical is required.

EPFL2009