Compact integration of optical sources and detectors on SOI for optical interconnects fabricated in a 200 mm CMOS pilot line

As the demand for bandwidth increases, optical interconnects are coming closer and closer to the chip. Optical interconnects on silicon-on-insulator (SOI) are desirable as this allows for integration with CMOS and the mature processing can be used for photonic integrated circuits. A heterogeneous integration process can be used to include III-V active optical components on SOI. For dense integration compact sources and detectors are required, but they typically need different epitaxial structures to be efficient which limits the integration density. We propose to use an epitaxial structure, which contains both the layers for a laser and for a detector, hereby enabling very compact integration of sources and detectors. Microdisk lasers and waveguide detectors using this epi were completely fabricated in a 200 mm CMOS pilot line and the results are discussed here

Etude et réalisation de liens optiques hétérogènes à base de semiconducteurs III-V reportés du Silicium

To follow the evolution imposed by Moore's law, digital circuits are becoming more and more parallelized with a large number of independent computational units. Optics may be used to provide them the necessary very high bandwidth, as traditional electrical links begin to suffer from their high consumption per transferred bit. In such cases, developing CMOS compatible optical interconnects can be necessary. If light transport around wavelength 1.55 μm is quite easily obtained thanks to the Silicon/Silica couple, obtaining laser sources is much more difficult because silicon (indirect gap) can not be used to provide optical gain. An alternate solution consists in using molecular bonding of III-V semiconductor based dies onto silicon wafers. In this thesis, we only focus on a very specific source based on Whispering Galery Modes (WGM) inresonators with circular symmetry, with a few micrometers radius. We will see how to take advantage of perturbative elements such as the electrical contacts (necessary absorbing) to decrease the lasing threshold. The use of a semi analytical model provides ultra fast design of these monolithic source, optimizing the the geometry and position of the contacting electrodes. Light collection in an optical waveguide by evanescent coupling to the source leads to complexinteractions. Modelling them from Coupled Mode Theory demonstrates how it works, and how to take advantage of them to control the lasing wavelength. The optical waveguide itself can then be used to promote a single wavelength emission. Laying out active elements around the collecting waveguide, one can get modulated and ultra-compact sources for wavelength tuning or mode hoping applications, with an external active control. The last part of this thesis provides experimental results obtained with a 200 mm pilot line at CEALETI, using CMOS compatible processes. Feasibility of the sources suggested in the previous chapters is demonstrated with their integration in a complete optical link (source, routing and detection).Afin de poursuivre la croissance imposée par la loi de Moore, les circuits numériques deviennent de plus en plus parallèles, avec un nombre important d'unités de calcul distinctes. L'utilisation de l'optique peut s'avérer intéressante pour leur assurer une bande passante élevée. Au contraire, les liens traditionnels (électriques) commencent à montrer leurs limites en terme de consommation par unité d'information échangée. Dans un tel contexte, il est alors nécessaire de développer des interconnexions optiques dont les procédés de fabrication restent compatibles avec le standard CMOS. Si le transport de la lumière est aisé à obtenir au voisinage de 1.55 μm avec le couple Silicium/Silice, l'obtention de sources LASER est nettement plus difficile puisque le silicium (gap indirect) ne permet pas de réaliser le gain optique requis. Une solution consiste alors à reporter par collage moléculaire des vignettes de composés à base de semi-conducteurs III-V.Dans cette thèse, nous nous intéresserons uniquement à une source bien particulière, basée sur les modes de galerie (WGM) dans les résonateurs à symétrie circulaire, de quelques micromètres de rayon. Nous verrons comment tirer profit des éléments a priori perturbateurs que sont les contacts électriques (absorbants) de sorte à diminuer le seuil LASER. La mise en place d'un modèle semianalytique permet d'obtenir un dimensionnement ultra-rapide de la source monolithique obtenue, en optimisant la géométrie et la position des électrodes de contact. La collection de la lumière dans un guide par couplage évanescent donne lieu à de complexes interactions. Là encore, une modélisation à partir de la théorie des modes couplés a permis d'en comprendre les rouages, et d'en tirer profit. Le guide lui-même peut alors servir à favoriser une seule et unique longueur d'onde d'émission. Avec des éléments actifs situés à proximité de ces guides, on peut même obtenir une source ultra-compacte et modulable dont on contrôle la longueur d'onde d'émission par un élément extérieur au LASER. La dernière partie de cette thèse fournit des résultats expérimentaux, obtenus avec une chaine "pilote" sur des wafers 200 mm (CEA LETI) en se limitant à des procédés CMOS. On démontre donc la faisabilité des sources proposées dans les chapitres précédents ainsi que la possibilité de les intégrer un lien optique complet (source, routage et détection)

Influence de surfaces structurées sur les performances de cellules en couche mince de silicium cristallin

2014International audienceno abstrac

Etude et réalisation de liens optiques hétérogènes à base de semiconducteurs III-V reportés du Silicium

Afin de poursuivre la croissance imposée par la loi de Moore, les circuits numériques deviennent de plus en plus parallèles, avec un nombre important d unités de calcul distinctes. L utilisation de l optique peut s avérer intéressante pour leur assurer une bande passante élevée. Au contraire, les liens traditionnels (électriques) commencent à montrer leurs limites en terme de consommation par unité d information échangée. Dans un tel contexte, il est alors nécessaire de développer des interconnexions optiques dont les procédés de fabrication restent compatibles avec le standard CMOS. Si le transport de la lumière est aisé à obtenir au voisinage de 1.55 m avec le couple Silicium/Silice, l obtention de sources LASER est nettement plus difficile puisque le silicium (gap indirect) ne permet pas de réaliser le gain optique requis. Une solution consiste alors à reporter par collage moléculaire des vignettes de composés à base de semi-conducteurs III-V.Dans cette thèse, nous nous intéresserons uniquement à une source bien particulière, basée sur les modes de galerie (WGM) dans les résonateurs à symétrie circulaire, de quelques micromètres de rayon. Nous verrons comment tirer profit des éléments a priori perturbateurs que sont les contacts électriques (absorbants) de sorte à diminuer le seuil LASER. La mise en place d un modèle semianalytique permet d obtenir un dimensionnement ultra-rapide de la source monolithique obtenue, en optimisant la géométrie et la position des électrodes de contact. La collection de la lumière dans un guide par couplage évanescent donne lieu à de complexes interactions. Là encore, une modélisation à partir de la théorie des modes couplés a permis d en comprendre les rouages, et d en tirer profit. Le guide lui-même peut alors servir à favoriser une seule et unique longueur d onde d émission. Avec des éléments actifs situés à proximité de ces guides, on peut même obtenir une source ultra-compacte et modulable dont on contrôle la longueur d onde d émission par un élément extérieur au LASER. La dernière partie de cette thèse fournit des résultats expérimentaux, obtenus avec une chaine "pilote" sur des wafers 200 mm (CEA LETI) en se limitant à des procédés CMOS. On démontre donc la faisabilité des sources proposées dans les chapitres précédents ainsi que la possibilité de les intégrer un lien optique complet (source, routage et détection).To follow the evolution imposed by Moore s law, digital circuits are becoming more and more parallelized with a large number of independent computational units. Optics may be used to provide them the necessary very high bandwidth, as traditional electrical links begin to suffer from their high consumption per transferred bit. In such cases, developing CMOS compatible optical interconnects can be necessary. If light transport around wavelength 1.55 m is quite easily obtained thanks to the Silicon/Silica couple, obtaining laser sources is much more difficult because silicon (indirect gap) can not be used to provide optical gain. An alternate solution consists in using molecular bonding of III-V semiconductor based dies onto silicon wafers. In this thesis, we only focus on a very specific source based on Whispering Galery Modes (WGM) inresonators with circular symmetry, with a few micrometers radius. We will see how to take advantage of perturbative elements such as the electrical contacts (necessary absorbing) to decrease the lasing threshold. The use of a semi analytical model provides ultra fast design of these monolithic source, optimizing the the geometry and position of the contacting electrodes. Light collection in an optical waveguide by evanescent coupling to the source leads to complexinteractions. Modelling them from Coupled Mode Theory demonstrates how it works, and how to take advantage of them to control the lasing wavelength. The optical waveguide itself can then be used to promote a single wavelength emission. Laying out active elements around the collecting waveguide, one can get modulated and ultra-compact sources for wavelength tuning or mode hoping applications, with an external active control. The last part of this thesis provides experimental results obtained with a 200 mm pilot line at CEALETI, using CMOS compatible processes. Feasibility of the sources suggested in the previous chapters is demonstrated with their integration in a complete optical link (source, routing and detection).LYON-Ecole Centrale (690812301) / SudocSudocFranceF

Polycrystalline silicon localised rear contacts in a PERL type silicon solar cell

2014International audienceno abstrac

Critical material reduction in PV interconnection

International audienceGiven the exponential growth of deployed photovoltaic (PV) energy sources, we have to question how to make such growth sustainable. Transition at global scale from fossil fuels to mineral-based renewable energies will indeed induce a sharp turn in materials supply chains. The concept of critical materials covers various sources of supply tensions. More precisely in PV sector, concerns grow for the last few years about Silver price volatility, relative to its scarcity, or about Indium related to its availability.Raw material criticity definition is open to question. No consensus seems to arise yet from literature in order to define influencing factors on criticity. For this study, five supply hazard criteria are selected in order to represent accurately each material supply situation: geological, logistical, geopolitical, industrial and commercial. With those criteria, the materials (and their substitutes) used in PV modules interconnection are listed and for each one, criticity is assessed. List of those elements is the following: Aluminum, Bismuth, Copper, Indium, Nickel, Silver and Tin.Although different dynamics may be observed depending on the concerned material, the main conclusion is that, except Aluminum, all listed elements supplies should face supply tensions by 2050, or even 2030 for the most critical ones [1]. It is important to note that for most of these materials, PV sector has not triggered its critical status.Two material groups should be distinguished. In the first hand, high production and consumption volumes materials (Aluminum and Copper) should not restrict PV energy production capacity expansion projections in the short term but could adversely affect growth in the mid term: by 2050, Copper demand to electrify the whole society should deplete global reserves so its supply is unreliable; it is then compulsory to deeply rethink energy networks, as well as implement a circular approach (reduce, repair, reuse and finally recycle). Moreover, aluminum needed volume for PV on TW scale would induce huge CO2 emissions [2]. On the other hand, other materials (Bismuth, Indium, Silver, and Tin) are used in PV interconnection in dispersive ways: even though PV sector requires a limited amount, they are difficult to recover. These applications must evolve otherwise the known reserves will end around 2040.It draws one main conclusion in the specific case of PV sector: conception has to evolve from dispersive cells interconnection processes, such as low temperature soldering or conductive adhesive bonding. In general, conception step has to focus on end-of-life step to introduce more circular methodologies. Change may happen at three levels: process, material or architecture. Changing or optimizing the deposition process is largely covered in literature over the last 15 years and Silver consumption reduction potential seems to reach its limit [3]. Alternative materials have been rising for the last 5 years and could have a great impact on metallization criticity. In the meantime, critical materials consumption in interconnection could further shrink with a disruptive innovation in module architecture. A few innovation examples, from NICE concept to non-uniform metallization, will be presented

Indoor Optical Wireless Communication Coverage Optimization Using a SiPM Photoreceiver

International audienceAlthough optical wireless communication (OWC) is seen as a promising complementary technology to radio frequency systems, its deployment is currently hampered by its limited communication range and the lack of compactness of its transceivers. A partial solution lies in using more sensitive photoreceivers, such as arrays of single photon avalanche diodes (SPAD). Despite their limited bandwidth and non-linearity, such devices have been shown to support Gbps data transmission while providing greatly enhanced sensitivity compared to conventional photodiodes (PD). However, their potential to increase the communication coverage of an indoor OWC system has never been studied. In this paper, a simulation framework for evaluating this metric using a SPAD-based indoor OWC system is thus detailed and implemented. Results show that an array of SPADs in the order of a mm 2 is enough to ensure connectivity over a whole 16 m 2 room, whereas similar performance with a PD requires a sensitive area of several hundreds of mm 2 , hence demonstrating the interest of SPADs for coverage as well as compactness optimization in OWC. Index Terms-single photon avalanche diode (SPAD), optical wireless communications (OWC), LiF

5 Contacts arrière localisés en silicium polycrystallin dans une architecture de cellule silicium de type •PERL

2014International audienceno abstrac

Motifs géométriques de contacts localisés en face arrière pour cellules solaires en silicium

2-5 déc. 2014,International audienceno abstrac