Liquid-based electrostatic energy harvesters

Mechanical energy harvesting is a growing technology aimed at developing innovative devices able to turn ambient mechanical energies (shocks, vibrations...) into electricity. This thesis will be aimed at developing mechanical energy harvesters exploiting state, shape or permittivity changes?that appear in some liquids when submitted to external effects such as vibrations, pressures, shocks?and to couple these effects with an electrostatic converter: the state change of the liquid induces a variation of capacitance that is then turned into electric energy. Because of their small output powers, these systems are firstly aimed at powering wireless sensor networks for industry, cars, habitat?in order to replace/recharge batteries. Yet, today, researches are targeted on more consumptive applications such as mobile devices recharging (phones, MP3 players?). And in fact, liquid-based energy harvesters seem to be promising for these applications. For more information: S. Boisseau, G. Despesse, B. Ahmed Seddik. Electrostatic conversion for vibration energy harvesting, Small Scale Energy Harvesting, Intech, 2012, http://dx.doi.org/10.5772/51360

Embedded system for obstacle perception in dynamic environments

The objective of this PhD position is to propose a mixed hardware and software solution for an embedded perception system designed for mobile vehicles (buses, cars, etc?). This embedded system is dedicated to avoid potential collisions of vehicles in dynamic environments. In this context, a set of different type of sensors are fixed on a mobile vehicle. The extracted information is processed in real-time by a Bayesian algorithm called Bayesian Occupancy Filter (BOF). The processing of the BOF algorithm is particularly adapted to parallel architectures due to its matrix representation. Nowadays, this processing is performed by a work-station integrating a powerful GPGPU. The PhD candidate will propose an integration solution of this type of algorithm taking advantage of novel multicore embedded architectures. The algorithm optimisation as well as the hardware/software partitioning will be studied in order to achieve the needed real-time performances at a minimum energy cost. This work will take place at the LIALP laboratory of the DACLE division of LETI in collaboration with INRIA Rhone-Alpes.

Hybrid integration of quantum cascade lasers on Silicon for gaz detection applications

Gas sensor technology based on optical detection has already grown to be indispensable for various aspects in our modern society (chemical emission monitoring, air pollution measuring, high sensitivity trace detection, biological sensing applications). However, available gas sensors are bulky, complex, and have a very high cost of ownership. The consequence is that they are not suitable for mass deployment. The objective of the thesis is to realize a miniaturized and low-cost gas sensor, bringing optical gas spectroscopy towards laboratory-on-a-chip size, by hybrid integration of Quantum Cascade Lasers (QCL) on Silicon photonic integrated circuits(PIC). QCL, based on III-V materials, cover indeed a broad portion of the mid-infrared spectral range (MIR, 3-12 µm), where many chemicals of interest for Safety & Security have their strongest absorption lines. The work will consist in the design and modelling of optical coupling between QCLs and Si PIC, taking into account technological constraints for a viable and suitable process flow to merge-and-match III-V and Si technology.

Organosilicate materials like SiOCH are an original way for the realization of light sources for applications in the field of lighting or Si photonics. These materials present the advantage of being harmless because these compounds are based on chemical elements such as silicon, carbon, oxygen or nitrogen present in large quantities on earth. PECVD SiOCH or SiOCNH thin films developed at CEA-LETI are new and original materials with light emission properties still poorly understood. A deep investigation of their optical properties as a function of elaboration parameters and their structural/physico-chemical properties is essential to consider their future use as light sources for applications. The objective of this thesis is to study their fundamental properties regarding their potential applications, in particular the emission of light in the visible range or the realization of integrated silicon-based light sources or microlasers emitting at the telecom wavelength of 1.5 microns by Er doping.

Hybrid memory hierarchy and dynamic data handling for embedded multicore architectures

Due to technological limitations on CMOS operating frequency, the race for ever increasing processing performance in embedded systems today translates to a rapid increase of the number of cores per device. But the over-proportional raise of power consumption is increasingly hindering this performance race. Regarding the processing cores, recent proposals target to limit the average power consumption of the system by adding smaller cores specifically optimized for low power and dynamically activate the most appropriate ones depending on the system load. The most known concept of this type is the ?big.LITTLE? proposal from ARM. It is admitted that a large part of the total power consumption is coming from the ?memory hierarchy? needed to supply data to the processors. Today's memory configurations are mainly optimized for compute performance and dimensioned to handle the most complex access types. Several studies in literature are addressing optimized usage of the existing memory resources [1], [2]. The work of this PhD thesis will focus on read-only data and propose a power consumption optimized memory hierarchy using specific extensions to manage and store this type of data. A coherent implementation approach will be elaborated, covering all steps from compilation down to the dynamic handling of data allocation, to enable an easy real-life implementation of this optimization. [1] A.Badawy, A.Aggarwal, D.Yeung and C.Tseng, "The Efficacy of Software Prefetching and Locality Optimizations on Future Memory Systems", J. Instruction-Level Parallelism, 2004 [2] Pfrimmer, J.; Li, K.F.; Rakhmatov, D., "Balancing scratchpad and cache in embedded systems for power and speed performance", IEEE-NEWCAS Conference, 2005. The 3rd International, vol., no., pp. 107- 110, 19-22 June 2005

Understanding of the mechanisms of thermoelectric assemblies interfaces

In the current context of energy savings, the CEA-LITEN works on the research and development of components using thermoelectric materials for energy harvesting. The principle is to convert a part of a heat flow crossing a component in electric power using the Seebeck effect. A component is a series of pairs of thermoelectric material legs connected by metallic tracks, the quite clamped between two electrically isolated patches working as thermal heat exchanger. The subject of this thesis is the fine characterization of the interfaces between the thermoelectric material and the electric tracks to accurately measure the physical phenomena acting there, to model them and to propose technology solutions to decrease their contact resistances which penalize the efficiency of the heat flow conversion into electricity. Several materials for legs and tracks will be to study. The purpose of the thesis is, for each leg-track couple, to find a solution of specific assembly and to validate it thanks to these measurements of the interface quality. This thesis will allow the candidate to acquire an expertise on a wide range of measurement techniques including several fields of the physics: thermics, electricity, chemistry and physics.

Back contact silicon heterojunction solar cells optimization for high efficiency PV modules

The enhancement of solar cells efficiency is one way to reduce the cost of PV (photovoltaic) electricity. This may be achieved through an innovative solar cell design which combines the strength of the two highest efficiency c-Si solar cells (?24%) commercially available (SunPower MaxeonTM and Sanyo HITTM). Several labs and companies worlwide are interested in this new technology called IBC (Interdigitated Back Contact) Si-HJ (Silicon Heterojunction). The Laboratory of PV Components (LCP) at CEA-LITEN study IBC Si-HJ solar cells since a few years and this led to several publications and the fabrication of demonstrators with up to 20% efficiency. To fill the gap between this result and the theoretical efficiency above 25%, the devices has to combine perfect light trapping, surface passivation schemes and reduced resistive losses. These optimizations have to be be evaluated in this PhD, supported by device modelling as well as thin layers and interface characterizations. There will be a collaboration within this work with the Laboratory of PV Modules (LMPV) of CEA-LITEN.

Healthmonitoring for photovoltaic power converter

PV power plants are developing as important power sources that need to be improved, especially for operation and maintenance phases. Today several parameters are available to power producers in order to schedule preventive maintenance and identify the cause of failures. Inverter reliability is a major issue since inverter has the highest failure rate among the solar plant components and its failure is not predictable. The aim of this PhD proposal is to identify a set of parameters to monitor the inverter state of health in real time. Two major failure mechanisms are known: bond wire lift-off and degradation of the chip substrate. Nowadays it is possible to observe the evolution of these failures when the defaulting module is outside the inverter, ie you need to take the module out of the inverter in order to evaluate its state of health. Conversely we aim to conceive a method to determine the state of health of the inverter during operation, without arresting it, in order to ensure preventive maintenance and avoid abrupt loss of safety functions.

Epitaxial growth of AlGaN alloys on silicon substrates for LEDs in the UV-C domain

For water and air purification applications, UV LEDs are gradually replacing mercury based lamps, because of their high prices and low energy efficiency. The mùaterials involved in such LEDs are semiconducting alloys of the Ga1-xAlxN family. However, for the considered wavelength (around 270 nm), the UV LEDs have not yet reached the required performances because of their low conversion efficiencies. This limit is mainly due to the very high dislocation density present in the epitaxial layer, that act as non radiative recombination centers. We propose to investigate new epitaxial growth processes to try and circumvent the problem. These will rely on using either patterned silicon surfaces or localised growth through a mask on the silicon substrate surface, in order to limit the dislocation density as much as possible. We will work on the definition/optimisation of the pattern on the silicon surface and on the mask definition, together with the optimisation of the growth processes in both cases. Once this is achieved, we will then turn to epitaxial growth of the whole LED structure and characterize its electrooptical properties. The work mainly concerns epitaxial growth, but will also deal with optical and structural characterization(photoluminescence, cathodoluminescence, electrooptical spectra and efficiency, X-ray diffraction). The work will take place in the Lighting Component Laboratory from CEA/LETI in close collaboration with CNRS labs, CRHEA in Sophia Antipolis and GES in Montpellier.

Ultra wideBand power amplifier spectrum calibration method and architecture

In the context of smart environment, Ultra-WideBand (UWB) technology receives a great interest as a promising technology capable of both very accurate localization and high-rate short range communication network. Nowadays the Federal Communication Commission (FCC) has specified the emission mask of UWB devices within the 3.1-10.6GHz. In order to enable the worldwide dissemination of UWB devices the need of transmitter able to guarantee the output signal spectral occupation is mandatory. Most of test probers are not intrinsically able to verify this specification because of the impulse nature of the signal and because of the time, and therefore the cost, needed for spectral analysis. This PhD aims to address this specific problem in order to reduce the time, coat and complexity of the UWB transmitter test. In addition, like pre-distortion loop already existing for continuous time power amplifier (PA) the PhD aims to provide a mean to control the output spectrum of the UWB PA. In literature a few PA using different techniques to provide UWB pulse can be found. Most of them are versatile and provide different control to manually modify the signal spectrum. But none of them enable an automatic control. As UWB PA always works in transient nonlinear regime, the first part of the PhD will focus on the output signal theory in this specific regime. Then, some metrics will be identified in order to provide, using correlation techniques, a mean to estimate and servo-control the output spectrum. after this theoretic and control part of the PhD, a design part will produce probe circuits as less invasive as possible to provide identified metrics and the loop back control of the output spectrum.