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

PostDocs : selection by topics

Engineering science >> Materials and applications
5 proposition(s).

Compressed Sensing Electron Tomography: Quantitative Multi-dimensional Characterization of Nanomaterials

Département technologies silicium (LETI)

Autre laboratoire

01-01-2019

PsD-DRT-19-0015

zineb.saghi@cea.fr

Electron tomography (ET) is a well-established technique for the 3D morphological characterization at the nanoscale. ET applied to spectroscopic modes for 3D structural and chemical analysis has become a hot topic but necessitates long exposure times and high beam currents. In this project, we will explore advanced compressed sensing (CS) approaches in order to improve the resolution of spectroscopic ET and reduce significantly the dose. More precisely, we will focus on the following two tasks: 1. Comparison of total variation minimization, orthogonal or undecimated wavelets, 3D curvelets or ridgelets and shearlets for nano-objects with different structures/textures; 2. Comparison of PCA and novel CS-inspired methods such as sparse PCA for dimensionality reduction and spectral un-mixing. The code will be written in Python, using Hyperspy (hyperspy.org) and PySAP (https://github.com/CEA-COSMIC/pysap) libraries. The project follows a multidisciplinary approach that involves the strong expertise of the coordinator in ET and the input of two collaborators with complementary skills: Philippe Ciuciu with expertise in MRI (DRF/Joliot/NEUROSPIN/Parietal) and Jean-Luc Starck with expertise in cosmology, signal processing and applied maths (DRF/IRFU/DAP/CosmoStat). The three communities share a strong interest in compressed sensing algorithms.

Development of lead free piezoelectric actuator

Département Composants Silicium (LETI)

Labo Composants Micro-actuateurs

01-02-2018

PsD-DRT-18-0033

gwenael.le-rhun@cea.fr

At CEA-Tech, the LETI Institute creates innovation and transfers it to industry. The micro-actuator component laboratory (LCMA) is working on the integration of piezoelectric materials into microsystems that allow electromechanical transduction. Lead zirconate titanate (PZT) is today the most powerful piezoelectric material for micro-actuator applications. However, the introduction in the near future of a new standard regarding the lead amount allowed in chips (European RoHS directive) leads us to evaluate alternative lead-free materials to PZT for piezoelectric actuator applications. The development of lead-free materials has thus become a major focus of piezoelectric research. This research led to revisit and modify some classical piezoelectric such as KNbO3 and BaTiO3. In particular, the KNaxNb1-xO3 (KNN) family has been identified as promising. The objective of the postdoc is therefore to evaluate some lead-free piezoelectric materials and to compare their properties with that of the reference material, PZT. Suitable test vehicles will be fabricated in LETI's clean rooms for electrical and piezoelectric characterizations by mean of dedicated tools already available at lab. For this work the candidate will lean on a solid experience developed at LETI for more than 20 years on piezoelectric thin films.

Ge-on-Insulator (GeOI) substrates for photonics

Département Composants Silicium (LETI)

Laboratoire Intégration et Transfert de Film

01-02-2018

PsD-DRT-18-0045

julie.widiez@cea.fr

The induction of tensile strain in intrinsic and doped Germanium (Ge) is one approach currently explored to transform the Ge indirect bandgap into a direct one. To take full advantage of Ge, we study the Ge CMOS photonics platform with Ge-on-Insulator (GeOI) structure, which enables strong 2D optical confinement in the Ge photonic-wire devices. One recent study in our lab showed the interest of a method of incorporation of mechanical stress into Ge, one of the essential ingredients of the laser. In particular, the method could be applied to the massive Ge, making compatible gap direct and crystalline quality. Post-doc objectives : Development of GeOI substrates from massive Ge donors with tensile strain inside the Ge film. These developments will be realized from the existing Smart Cut / thinning processes, combined with technological steps to overcome their current limits (SAB bonding). The substrates obtained will be characterized to determine their state of deformation as well as their damage (Raman / XRD) and final GeOI substrates will be provided to the application laboratories for the production of photonic components.

AlGaN/GaN HEMTs transfert for enhanced electrical and thermal performances

Département Composants Silicium (LETI)

Laboratoire Intégration et Transfert de Film

01-04-2018

PsD-DRT-18-0060

julie.widiez@cea.fr

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

01-04-2018

PsD-DRT-18-0066

philippe.voarino@cea.fr

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.

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