Électrotechnique

Résumé

L’électrotechnique se rapporte . Elle concerne par exemple la production, le transport, la distribution, le traitement, la transformation, la gestion et l’utilisation de l’énergie électrique. Parfois appelée « génie électrique », elle remonte à l'invention, en 1600, par William Gilbert, d'un électromètre permettant de déterminer la présence des charges électriques, et à l'invention, en 1672, par Otto von Guericke, d'un générateur électrostatique permettant de séparer des charges électriques à l'aide d'une machine. Principaux domaines et métiers L'une des propriétés de l'électricité est son utilité pour la transmission non seulement de l'énergie mais aussi des données. Ce sont également les premiers domaines dans lesquels l'électrotechnique s'est développée remarquablement. Aujourd'hui, en électrotechnique, les étudiants et les professionnels peuvent se spécialiser et devenir experts dans les grands domaines classiques que sont la technologie de l'énergie électrique, les té

Source officielle

https://fr.wikipedia.org/wiki/%C3%89lectrotechnique

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Semiconductor nanowires are an emerging class of materials with great potential for applications in future electronic devices. The small footprint and the large charge-carrier mobilities of nanowires make them potentially useful for applications with high-integration density, but also to replace thin-film transistors in large-area electronics. This thesis investigates the use of wet-chemically grown ZnO nanowires for the fabrication of high-performance, low-voltage field-effect transistors (FETs). The first part of this thesis addresses the electrical characteristics of the wet-chemically grown ZnO nanowires. The as-grown ZnO nanowires are highly conductive due to a large charge-carrier concentration caused by dopants unintentionally incorporated into the ZnO nanowires during the synthesis. This large charge-carrier concentration makes it difficult to modulate the conductivity of the nanowires by an external electric field, so that the as-grown wires are not suitable for FETs. A post-growth annealing step is employed to dramatically reduce the charge-carrier concentration of the nanowires which makes it possible to fabricate FETs with useful characteristics. ZnO-nanowire FETs in a global back-gate geometry based on annealed ZnO nanowires have a transconductance of 300 nS, an on/off current ratio of 107 and a subthrehold slope of 500 mV/decade. The maximum field-effect mobility of the annealed ZnO nanowires is around 50 cm2/Vs. An important requirement to obtain good FET characterisitcs is to minimize the influence of the source and drain contact resistance on the total device resistance. The material used for the source and drain contacts in this thesis is aluminum. It is demonstrated that the use of a plasma treatment in the contact regions prior to the evaporation of the aluminum contacts can greatly influence the contact properties between ZnO and aluminum. An argon-plasma treatment locally increases the charge-carrier concentration in the ZnO. It is shown that the doping effect of the argon-plasma treatment can be exploited to reduce the contact resistance between alumiunm and ZnO and improve the electrical performance of the FETs. In the second part of this thesis, the influence of the ambient air on the electrical characteristics of the ZnO-nanowire FETs is investigated. The electrical conductivity of the FETs is strongly affected by the distinct atmospheric conditions, which makes it difficult to obtain reliable FET characteristics. The potential of a self-assembled monolayer (SAM) based on fluoroalkylphosphonic acid molecules to passivate the ZnO nanowires against the undesirable effects of the ambient and to stabilize the electrical performance of ZnO-nanowire FETs is demonstrated. The stabilizing effect is attributed to the formation of a densely packed, hydrophobic SAM on the surface of ZnO and aluminum oxide. The quality of the hydrophobic SAMs is confirmed by means of water-contact-angle measurements on SAM-covered ZnO single crystals that show a contact angle of more than 110°. The third part of this thesis is dedicated to the fabrication of high-performance ZnO-nanowire FETs with patterned metal top-gate electrodes. A top-gate fabrication process is developed that uses a very thin gate dielectric consisting only of an alkylphosphonic acid SAM that can be deposited from solution. The insulating quality of the SAM is investigated for top-gate FETs that utilize either gold or aluminum for the top-gate electrode. Gold top-gate FETs show a transconductance of 1 µS, an on/off current ratio of 107, and a steep subthreshold slope of 90 mV/decade. The thin gate dielectric makes it possible to operate the gold top-gate FETs at low voltages of 1 V and simultaneously reduces the undesired gate current by more than three orders of magnitude compared to gold top-gate FETs that have been fabricated without a gate dielectric (MESFETs). The gate current of the gold top-gate FETs with SAM gate dielectric is as low as 1 pA for gate-source voltages between -1 V and 0.5 V. When aluminum is used for the top-gate electrode, a hybrid dielectric is formed at the interface between the SAM and the aluminum, consisting of the SAM and a spontaneously formed aluminum oxide layer. Owing to the hybrid gate dielectric, the aluminum top-gate FETs are operated with gate currents below 1 pA for voltages up to 3 V. The top-gate fabrication process does not require temperatures above 160 °C, which makes it possible to fabricate FETs on unconventional substrates that cannot tolerate high temperatures, such as glass or flexible plastics. Integrated circuits on single ZnO nanowires that are fabricated on glass and plastic substrates are demonstrated. The maximum switching frequency of the inverters is 1 MHz.

EPFL2011

Chargement

The service sector is the most dominant sector in every developed economy today. The ability to develop and successfully launch new services is crucial for service organizations to stay competitive and to adapt to the ever-changing conditions of the environment. However, up until now, a mismatch remains between the importance of service innovation for society and the attention given to it in both academia and practice. Existing research has compared the innovative output of service firms with manufacturing firms and found that the difference is one of degree rather than of substance. Studies which focus on the process instead of the output of service innovation, however, are still relatively scarce. This dissertation aims to help close this research gap by examining three service innovation processes in different contexts. First, it offers a theoretical illumination of service innovation with the help of knowledge creation theory. This is beneficial for defining service innovation more precisely. The second study is concerned with the influence of emotional factors on the development of dynamic capabilities in new ventures. It shows that young ventures which are able to deliberately switch between emotional and analytical modes of operation have a higher likelihood of success. The study compares the development of two service-oriented ventures with two product-oriented ones that are part of an accelerator program at the School of Design Thinking at Stanford University. The third paper is concerned with product-service strategies, or Servitization, and the relation to vertical integration and the coordination of innovation in downstream markets. The study shows that the Servitization development, i.e. the vertical integration of manufacturing firms into its users' operation, is a response to the failure of architectural innovation in more flexible buyer-supplier relationships. The study finds four different strategies for the service business of manufacturing firms based on case studies in the mechanical engineering, electrical engineering, and chemical industries. Overall, I am able to show that firms need to be able to build three distinct capabilities to master their service innovation efforts. First, they need to build up a capacity for innovation to gain economies from partial repetition of solutions. Second, firms need to have skills in place to create and manage boundary objects, especially at the client interface. Finally, they need to have capabilities to build up complementarities which help protect revenues from their service innovation initiatives.

EPFL2015

Chargement

Conformable neural interfaces : from engineering stretchability at the micro-scale to translational applications

Florent-Valéry Coen

Recently, flexible and soft bioelectronic interfaces have been proposed as a solution to improve existing neural interfaces that currently present mechanical mismatch with the soft tissue. These are devices fabricated with thin polymeric or elastomeric backbones to enable an optimal contact to the target tissue as well as reduced mechanical mismatch. For this the electrical interconnects that carry the electrical information from the tissue or deliver the stimulation charges need to be elastic to accommodate the stresses and remain conductive. Several strategies for creating stretchable tracks have been proposed in the past but are not compatible with high-density low-profile electrode arrays for chronic implantation in vivo.A method of patterning thin material stacks of flexible polymers and platinum layers embedded in silicone membranes was proposed in the Laboratory for Soft Bioelectronic Interfaces at EPFL. By creating specific microscopic cuts in the materials permits the out-of-plane deformation of the film and enables stretchability above 50% strain while remaining conductive. However, the previous fabrication method was not optimal, was not hermetically encapsulated and not reliable. In this thesis, novel soft electrode arrays were designed and fabricated using an improved manufacturing process named core-shell micropatterning. This enables fully encapsulated electrical tracks that can be micropatterned with superior electromechanical performances and notable increase in hermetic barrier lifetimes. Additionally, this method was applied to other material systems enabling new functions such as completely transparent devices to enable concurrent optical stimulation and microscopy through the implanted electrodes.These fabricated devices were applied to several device concepts in multiple animal models. First, microelectrode arrays for electrocorticography (ECoG) recordings were designed to be implanted over the auditory cortex of rat and non-human primate (NHP) models to capture evoked potentials from acoustic stimulation. This enabled the precise tonotopic mapping and the spatial representation of the auditory cortex. Next, auditory brainstem implants (ABI), targeting the cochlear nucleus (CN) after the auditory nerve were designed. This implant needs to conform to the curved surface of the CN and stimulate the auditory pathway. In non-human primates, the placement of this device is challenging and new tools were developed for the insertion of the device. Finally, the combination of soft ABI and ECoG was implanted in chronic settings in a NHP to evoke auditory percepts from brainstem stimulation that could be monitored using the cortical evoked potentials. This will enable the fine-tuning of stimulation protocols for hearing restoration and verify the stability of the implants over time.Overall, this work represents a framework to design and fabricate soft electrode arrays that can be applied for recording and stimulation in small to large animal models in a reliable way. The careful design of the system around the implant such as fine-tuning of microfabrication parameters, the characterization in vitro, device geometry, connection scheme, experimental setup and tracking of the device properties in vivo enables reliable long-term implantations in new experimental paradigms.

EPFL2022

Chargement

EPFL2015

EPFL2011

Conformable neural interfaces : from engineering stretchability at the micro-scale to translational applications

Florent-Valéry Coen

EPFL2022