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

PhD : selection by topics

Technological challenges >> Numerical simulation
4 proposition(s).

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Multiscale simulation for engineering and characterization of materials and quantum devices

Département Composants Silicium (LETI)

Laboratoire de Simulation et Modélisation



Numerical simulation (.pdf)

Quantum devices open up new perspectives for information processing. The CEA is developing, in particular, silicon quantum bits. In this innovative field, the systematic exploration of the many possible options is prohibitive. The challenges posed by quantum technologies cannot therefore be met without advanced numerical simulation. The CEA has developped a multi-physics code, TB_Sim, for the modeling of quantum devices from the nano- to mesoscopic scales. However, a few obstacles prevent simulation from being sufficiently predictive on these devices. One of the most important issues is the description of surfaces, interfaces and defects, which play an essential role in the physics of spin-orbit coupling and "valleys" in silicon. This thesis aims, therefore, to introduce atomistic "ab initio" approaches in the chain of multiscale simulations of quantum devices. The candidate will focus on the interfaces of silicon with its encapsulation materials (SiGe, SiO2 ...) and on the defects at these interfaces (amorphization, Pb defects, ...). He / She will in particular address the connexion between the atomistic ab initio and the nano- and mesoscopic scales. The ambitious objective of this thesis is to integrate numerical simulation at all stages of the design, manufacture and characterization of the devices, and to make it sufficiently predictive even on uncharted grounds. Numerical experiments will be carried out for this purpose both upstream and during the characterization in order to confront the simulation with reality, to support the analysis of the data by providing the ?missing pieces of the puzzle? which cannot be measured directly, and to provide feedback to the design. This work will be carried out in close collaboration between CEA-Leti (ab initio methods) and IRIG (TB_Sim code).

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Dynamic Mesh Reordering by Cache-aware Heuristics for scientific computing

Département Systèmes et Circuits Intégrés Numériques

Laboratoire pour la Confiance des sYstèmes de calcuL



Numerical simulation (.pdf)

In the context of simulation codes on unstructured grids, two elements appears: the traversal of the mesh on a CPU appear as random, and the "unstructured" aspect of the mesh makes accelerators problematic. However, such meshes allow the simulation at multiple scales, replacing multiple nested regular grids by a single structure, for example in tsunami simulations, resulting in a more compact structure and decreasing the computational power needed. Additionally, in some contexts the mesh will evolve in time, making partionning for multiple compute units difficult with their associated caches. This thesis focuses on the development of cache-aware heuristics of traversal of unstructured meshes, so as to allow on-the-fly reordering, in particular when sending compute kernels and mesh data on accelerators, so as to start computing before the mesh transfert has ended. This thesis will rely on existing results on mesh partitionning with tools such as SCOTCH and Metis, on models of memory / cache hierarchies and transfert capabilities (accelerators), and space filling curves related work (Hilbert-Peano, Sierpinski). The focus will be on the TsunAWI and FESOM (Finite Element/volume Sea-Ocean Model) codes from AWI and OpenFOAM. The student may have the opportunity to spend time at AWI (Germany) during the PhD.

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Modelisation and optimization of 3D micro-fabrication processes for optical applications

Département des Plateformes Technologiques (LETI)




Numerical simulation (.pdf)

The realization of 3D micro-structures is needed to build key functional microelectronics elements such as micro-lenses for optical imagers. These lenses can be done in particular by resist reflow or grey levels (grayscale) lithography. Grayscale lithography has the advantage of building structures of different topographies within one single process step. Its success will depend on the process modelling accuracy and on the lithography mask optimization strategy. Grayscale lithography was developed and pushed these past three years at CEA-LETI by a CIFRE PhD thesis in collaboration with ST-Microelectronics. The objective is to pursue 3D fabrication opportunities opened towards optical applications (Imagers, diffractive components) but also augmented reality. The thesis work will focus on different methodologies of design and data preparation for the optical mask realization. Especially, in order to maximize the lithography fidelity, non regular pixelization on mask or neural-network based inverse problems will be investigated. The resist process modelization during the 300 mm grayscale lithography will be also crucial and essential for the thesis.

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Qualitative reasonning and design of complex systems

Département Ingénierie Logiciels et Systèmes (LIST)

Labo. ingénierie des langages exécutables et optimisation



Numerical simulation (.pdf)

The design of complex systems is an activity that affects many industrial and research fields. This implies difficulties in modeling and simulating by the heterogeneous nature of the data involved, with discrete and continuous aspects. Two approaches are possible. Quantitative methods, whose analyzes are numerical, are the most used: their results are precise but they consume a lot of time and resources. Qualitative methods are based on a symbolic interpretation of the models, and can be used without knowing all the numerical parameters, by relying on dependency relationships between variables. They are less precise but they can be applied very early in the design phase and can be used to plan numerical simulations according to the objectives and to improve the results of analyzes (proofs, optimization, etc.). The work already carried out at the LIDEO laboratory of CEA LIST on modeling and qualitative simulation will be extended by the integration of concepts from naive physics and common sense reasoning to lead to an approach closer to engineering concepts. The results will be used for modeling, simulation but also for optimization on case studies representative of industrial examples.

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