Scientific direction Development of key enabling technologies
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PhD : selection by topics

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Département Systèmes (LETI)

Laboratoire Sans fils Haut Débit

01-10-2020

SL-DRT-20-1008

valentin.savin@cea.fr

Communication networks, IOT, radiofrequencies and antennas (.pdf)

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Design, fabrication and characterization of microlasers for data communications

Département d'Optronique (LETI)

Laboratoire de Photonique pour les Communications et le Calcul

01-10-2019

SL-DRT-20-1013

karim.hassan@cea.fr

Photonics, Imaging and displays (.pdf)

Needs for high-speed datacommunications has increased tremendously these last years. Optical links, usually used for long distance communications, are now used for shorter distances in data centers, for instance between racks or within a rack. Silicon photonics components are excellent candidates for these short distances communications since they are low cost and highly performant. Moreover, CMOS fabrication environment brings excellent fabrication yield, and reliable testing/packaging capabilities. Nevertheless, the silicon being an indirect bandgap material, cannot emit light efficiently, thus, semiconductor lasers are generally fabricated using a III-V material (direct bandgap material, i.e. InP, GaAs), eventually added to the Si-photonics circuit. CEA-Leti expertise in transfer layer technologies by direct bonding is used to realize hybrid III-V on Si photonics circuits leading to fully integrated devices. This PhD work aims at developing new solutions for the design and fabrication of micro lasers adapted to very short communications (inter or intra chips) with high compactness and high modulation speed. These new devices rely on a CMOS compatible fabrication process flow and original design. The PhD student will be in charge of (i) microlasers design using the available software in the laboratory, (ii) microlasers fabrication relying on CEA-Leti technological platform and (iii) electro-optically characterization of these new components.

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Digital-to-Light Communications on micro-(O)LED matrices

Département Systèmes (LETI)

Laboratoire Sans fils Haut Débit

01-10-2020

SL-DRT-20-1017

luc.maret@cea.fr

Communication networks, IOT, radiofrequencies and antennas (.pdf)

In Optical Wireless Communications (OWC) with LED or OLED, increasing the data rate will probably imply the use of microLEDs that show bandwidths approaching the GHz (Organic or GaN technologies). However these micro(O)LED will be limited in terms of optical power and thus communication range. The development of microLED matrices will allow recovering enough optical power to open access to mid-range applications. An hybridization of these matrices onto another CMOS matrices of pixelated current drives will preserve the bandwidth. But it will also offer an independent access to a huge number of optical micro-sources. This type of design has recently yielded to the implementation of the so-called « Digital-to-Light » (D2L) modulations where the quantized digital signal is directly used to pilot the matrix by thermometric codes, removing the digital-to-analogue converters used in classical OWC. But this new ?Digital-to-Optical Converter? (DOC) will face new challenges due to disparities in the behavior of microLEDs when designed within a same matrix, leading to e.g. non-linearities in the emitted optical signal. This thesis must tackle these new challenges, understand the new sources of impairments and try to mitigate them by specific system architectures designs and signal processing techniques such as the implementation of efficient D2L modulations, non-uniform quantization, compensation of time constants,? The final objective is to provide an optical wireless transmission of more than 10Gb/s at ranges around one meter. Eventually, hardware implementation will be possible using micro(O)LED matrices fabricated at Leti.

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Interaction mechanisms of hydrogen with defects of silicon bulk and at the interfaces of passivated contacts in PV cells

Département des Technologies Solaires (LITEN)

Laboratoire HoMoJonction

01-10-2020

SL-DRT-20-1018

raphael.cabal@cea.fr

Solar energy for energy transition (.pdf)

Although fluctuating, the photovoltaic market is still dominated by silicon technologies occupying ~94%. The most promising homo-junction cell architectures systematically integrate a so-called "passivated" contact through a stack of polycrystalline silicon on tunnel oxide. The hydrogenation of such structures makes it possible to achieve very efficient yields >25%. However, the introduction of hydrogen can also lead to layer delamination or resistive losses through accumulation effects at the interfaces, significantly degrading the efficiency of the final device. To avoid its effects and develop this type of structure with associated yields, it is essential to understand the interactions of hydrogen involved and to understand its role in passivation phenomena. However, hydrogen is an extremely difficult element to characterize by its very nature. Its characterization therefore represents a real challenge, to which are added the difficulties related to the textured surface state of solar silicon and the configuration of poly-Si/Si/SiOx/Si interfaces. To meet this challenge, the work proposed here will be to implement and correlate characterization techniques, allowing both to locate and quantify hydrogen in the volume of silicon and at the interfaces of passivated contact structures. The implementation of a characterization methodology will lead to the main objective of the thesis, which is to propose mechanisms of hydrogen interaction with defects and its role in the quality of passivated contacts. This will open up opportunities for the development and optimization of passivated contact structures. This study will benefit from the infrastructure for the realization of samples from CEA-LITEN in INES and the means of characterization of the nano-characterization platform with its expert environment.

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Innovative Mixed RF and low power devices integration in view of advanced fdsoi SOC

Département Composants Silicium (LETI)

Laboratoire d'Intégration des Composants pour la Logique

01-10-2020

SL-DRT-20-1027

claire.fenouillet-beranger@cea.fr

Emerging materials and processes for nanotechnologies and microelectronics (.pdf)

Connected mobile devices are becoming a strategic imperative in order to remain attractive, improve efficiency and competitive for advanced electronic applications. The wireless revolution where Laptops, Smartphone's, tablets, TVs, vehicles and enterprises are connected in a cloud style environment makes possible communication anywhere at any time. Recent developments in wireless communications with the emergence of advanced radio-frequency standard such as LTE, LTE-A and 5 G have brought numerous challenges. The most critical challenge is to provide higher levels of integration with more power efficiency and cost-effective solutions on the same-chip. In parallel to the development of nanometer CMOS as well as beyond-CMOS device technologies for switching, memory and analog functions, the increasing need to integrate various (heterogeneous) technologies (e.g. RF communication, power control, passive components, sensors, actuators) helps to migrate from the system board-level into the system-in- package (SiP) or to the system-on- chip (SoC). In fact, mobile System-on-Chip (SoC) with heterogeneous integration of multiple technologies has truly revolutionized the semiconductor industry. Thanks to the trap-rich Silicon-on-Insulator (SOI) substrate invented at UCL and developed in collaboration with SOITEC, RF SOI presents outstanding RF performance. In addition, the presence of the buried oxide layer not only reduces the junction capacitance but also offers the opportunity of using high resistivity substrate to reduce substrate related RF losses and coupling. However in case of SoC integration the trap-rich is not suitable all across the wafer and localized solutions should be envisaged. Fabrication on a 28FDSOI 300mm platform of specific RF stuctures Characterization of the substrate impact (HR, trap rich, etc ?) on the RF figure of merit Imagine and integrate new technological process schemes to implement localized ?trap-rich like' area before or after FDSOI device realization. Integrate some technological modules on new designed structures and electrical caracterization

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Detection and classification of emotional state change using machine learning.

Département Systèmes (LETI)

Laboratoire Signaux et Systèmes de Capteurs

01-10-2020

SL-DRT-20-1028

vincent.heiries@cea.fr

Artificial intelligence & Data intelligence (.pdf)

This PhD work focuses on the analysis of human stress by sensor data fusion and statistical methods. There are several types of stress affecting humans, including chronic stress and acute stress. In this study, we will focus on acute stress or peak stress (panic attack) which is problematic because it can be traumatic, and especially disabling / inhibiting during a crucial task to be performed. Acute stress occurs when the stressor appears suddenly and provokes a rapid adaptation response. The issue raised by this subject is therefore the detection or even anticipation of the occurrence of a stress peak which can be considered as an unusual, relatively rare event of variable amplitude. In terms of signal processing methods, this work may use specific event-driven processing methods. Moreover, the detection and classification of these events leading to a stress peak will be obtained through a fusion of multi-sensor multi-physical data. These sensors may be signal sensors worn by the person (ECG, PPG, EDA, breathing sensor, accelerometer, etc.) or sensors monitoring the individual remotely (video facial analysis, semantic field of speech, prosody). Algorithms allowing the classification of peak stress events from the signals obtained by this set of sensors will be developed from the family of machine learning methods (for example, non-limiting: CNN, RNN, or Deep Q-learning type learning algorithms). The applications of this stress detection and classification system are broad, ranging for example from the surgeon to the industrial operator subjected to a high mental load, from the air traffic controller to the firefighter, or in general to any person subjected to a crucial task to be performed and for which any loss of capacity could be critical. This system will pave the way for the implementation of appropriate stress management adapted to each individual.

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