Scientific direction Development of key enabling technologies
Transfer of knowledge to industry

PostDocs : selection by topics

AlGaN/GaN HEMTs transfert for enhanced electrical and thermal performances

Département Composants Silicium (LETI)

Laboratoire Intégration et Transfert de Film



Due to their large critical electric field and high electron mobility, gallium nitride (GaN) based devices emerge as credible candidates for power electronic applications. In order to face the large market needs and benefit from available silicon manufacturing facilities, the current trend is to fabricate those devices, such as aluminum gallium nitride (AlGaN)/GaN high electron mobility transistors (HEMTs), directly on (111) silicon substrates. However, this pursuit of economic sustainability negatively affects device performances mainly because of self-heating effect inherent to silicon substrate use. New substrates with better thermal properties than silicon are desirable to improve thermal dissipation and enlarge the operating range at high performance. A Ph.D. student in the lab. has developed a method to replace the original silicon material with copper, starting from AlGaN/GaN HEMTs fabricated on silicon substrates. He has demonstrated the interest of the postponement of a GaN power HEMT on a copper metal base with respect to self heating without degrading the voltage resistance of the component. But there are still many points to study to improve the power components. Post-doc objectives : We propose to understand what is the best integration to eliminate self-heating and increase the voltage resistance of the initial AlGaN/GaN HEMT. The impact of the component transfer on the quality of the 2D gas will be analyzed. The same approach can be made if necessary on RF components. Different stacks will be made by the post-doc and he will be in charge of the electrical and thermal characterizations. Understanding the role of each part of the structure will be critical in choosing the final stack. This process will also be brought in larger dimensions. This post-doc will work if necessary in collaboration with different thesis students on power components.

Development of flexible solar panels for space applications

Département des Technologies Solaires (LITEN)

Laboratoire Photovoltaïque à Concentration



Traditional solar panels used to power satellites can be bulky with heavy panels folded together using mechanical hinges. Smaller and lighter than traditional solar panels, flexible solar array consists of a flexible material containing photovoltaic cells to convert light into electricity. Being flexible, the solar array could roll or snap using carbon fiber composite booms to deploy solar panels without the aid of motors, making it lighter and less expensive than current solar array designs. On the other hand, satellite trends are shifting away from one-time stints and moving towards more regular use in a constellation setting. In the last years, the desire increased to mass-produce low-weight satellites. Photovoltaic arrays companies are challenged on their capacity to face these new needs in terms of production capacity and versatility. And this is exactly where space photovoltaics can learn from terrestrial photovoltaics where this mass production and low-cost shift occurred years ago. To tackle these new challenges, the Liten institute started to work on these topics two years ago. In the frame of this post-doc, we propose the candidate to work on the development of an innovative flexible solar panel architecture, using high throughput assembly processes. We are looking for a candidate with a strong experience in polymers and polymers processing, along with an experience in mechanics. A previous experience in photovoltaic will be greatly appreciated.

FDSOI technology scaling beyond 10nm node

Département Composants Silicium (LETI)

Laboratoire d'Intégration des Composants pour la Logique



FDSOI (Fully-Depleted Silicon On Insulator) is acknowledged as a promising technology to meet the requirements of emerging mobile, Internet Of Things (IOT), and RF applications for scaled technological nodes [1]. Leti is a pioneer in FDSOI technology, enabling innovative solutions to support industrial partners. Scaling of FDSOI technology beyond 10nm node offers solid perspectives in terms of SoC and RF technologies improvement. Though from a technological point of view, it becomes challenging because of thin channel thickness scaling limitation around 5nm to maintain both good mobility and variability. Thus, introduction of innovative technological boosters such as strain modules, alternative gate process, parasitics optimization, according to design rules and applications, become mandatory [2]. The viability of these new concepts should be validated first by TCAD simulations and then implemented on our 300mm FDSOI platform. This subject is in line with the recent LETI strategy announcement and investments to develop new technological prototypes for innovative technology beyond 28nm [3]. The candidate will be in charge to perform TCAD simulations, to define experiment and to manage them until the electrical characterization. The TCAD simulations will be performed in close collaboration with the TCAD team. The integration will be done in the LETI clean room in collaboration with the process and integration team. Candidate with out-of-the-BOX thinking, autonomy, and ability to work in team is mandatory. [1] 22nm FDSOI technology for emerging mobile, Internet-of-Things, and RF applications, R. Carter et al, IEEE IEDM 2016. [2] UTBB FDSOI scaling enablers for the 10nm node, L. Grenouillet et al, IEEE S3S 2013. [3]

Conformal deposition of polymer thin-films in high aspect ratio 3D structures

Département Technologies Silicium (LETI)




The deposition of thin films on challenging high aspect ratio structures are of key importance in many different areas of microelectronics and nano-technologies. For polymer thin films, filament-assisted CVD techniques (such as iCVD) have emerged recently as promising method for the conformal deposition of insulating thin films in 3D structures. However, it is still not clear if this CVD method can allow conformal coating inside porous and 3D substrates with acceptable growth rates and what are the limits of utilization. The work proposed here aims to study polymer thin film deposition by iCVD in high aspect ratio 3D structures in order to identify the parameters governing the deposition speed and the accessible degree of conformality. The works will be performed on high aspect ratio Through Silicon Vias and on various porous substrates. The candidate will be in charge of thin films deposition on a 200 mm tool and of the material characterization. The thin films will be characterized using physicochemical analyses (FTIR, X-Ray Reflectometry, Ellipsometry, Porosimetry, Contact angle, AFM). More in depth characterizations (using Electronic Microscopy, ToF-SIMS) will be carried out to study the deposition in 3D structures. The main objective of the work will be to identify the key parameters that play a role in the conformal deposition inside 3D structures and porous substrates as a function of the feature shape and size. The work will be done in the LETI/DTSi division. The material deposition and characterizations will be performed in the LETI clean room in close collaboration with an industrial partner. Part of the work will be done in collaboration with experts of materials characterization (CEA nanocharacterization platform), and specialists in charge of 3D integration.

In situ analytical device based on the LIBS technique for the characterization of hard environment liquid media

Département des Technologies Solaires (LITEN)

Laboratoire Matériaux et Procédés Silicium



The proposed research project aims at developing an in situ analytical device based on the LIBS technique for the characterization of hard environment liquid media such as high temperature melting materials or highly volatile liquid metals used for development of low carbon energy production. The project involves two CEA teams specialized in LIBS instrumentation, analytical developments and high temperature environments. At high temperature, the molten metals have a high surface reactivity leading to processes of oxidation, slagging ? Non-intrusive analysis of this surface by traditional LIBS tools leads to a non-representative results of the molten metal chemical composition. In this project, a new-patented concept based on a mechanical stirring coupled to the LIBS device is developed in order to have a renewable and stable surface of the liquid metal. The aim is to have an on-line representative composition of the metal during the treatment process. The developed demonstrator will be validated for the analysis of impurities (at ppmw ranges) in liquid silicon (T> 1450 °C) during the purification process and the crystallization one for photovoltaic applications. At the end of the project, recommendations for in-situ analysis of liquid sodium (used as cooling fluid in nuclear reactors) will be given.

Developpment of a control quality method for radiotherapy treatments based on dosimetric gels


Laboratoire de Métrologie de la Dose



In the field of dosimetry for radiotherapy, chemical dosimetry, and in particular gel dosimeters, are good candidates for dose distribution measurements for the quality control of treatment plans. Actually, these gels are radiosensitive and, thus, enable measurements of the dose in 3 dimensions when read by adapted imaging methods. This post-doctoral project deals with the development of gel dosimetry methods, using two types of reading devices: Optical tomography and Magnetic Reading Imaging. For gel-MRI dosimetry, the aim will be to adapt and validate the method used at LNHB (Laboratoire National Henri Becquerel) for quality control applications for MR-guided-radiotherapy devices. For this purpose, specific phantoms will have to be designed and produced using 3D printing. The reading method will also have to be optimized and transposed on partnering hospital devices. Concerning the gel-optical CT dosimetry method, the whole method will have to be developed. This involves an adaptation of the composition for the gel, a characterization of the reading device and a validation of the method established.

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