Numerical quality analysis of simulation codes with CADNA, Verificarlo and Verrou
Numerical codes rely on floating-point arithmetic to represent real numbers and the operations applied to them. However, in general, real numbers cannot be exactly represented by floating-point numbers. The finite precision of the floating-point arithmetic may lead to round-off errors that may accumulate. With the increasing computational power, the algorithm complexification and the coupling of numerical codes, it is crucial to quantify the numerical robustness of an application or an algorithm.
CADNA [1], Verificarlo [2] and Verrou [3] are dedicated tools that allow estimating the round-off errors propagation and measuring the numerical accuracy of the obtained results. The objective of this work is to use these three tools on GYSELA [4, 5], a simulation code used to characterize the plasma dynamics in Tokamak, and PATMOS [6], a mini-app representative of a Monte Carlo neutron transport code. This analysis will be aimed at assessing the numerical robustness of these two applications or some of their algorithms. In addition to the analysis of the numerical quality, these tools will also be used to see whether it is possible to lower the precision (simple or even half precision instead of double) of some algorithms, thus improving the memory footprint and/or performances (vectorization, communications). Beyond the lessons learnt on the two analyzed codes, a second objective will be the elaboration of a methodology that could be more generic and be applied more broadly to other codes.
Developpment of a control quality method for radiotherapy treatments based on dosimetric gels
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.
Development of lead free piezoelectric actuator
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.
Development of multiphysics tools dedicated to the modeling of FSR and associated studies.
The sodium group of DM2S (department of CEA Saclay) develops numerical coupling tools in order to realize accidental case studies (fast transient). The physical domains concerned are neutronics, thermo-hydraulics and mechanics. The subject of this post-doc deals within this framework.
The aim is to carry out several studies: the integration of a coupling within the CORPUS platform, to carry out studies in order to test (and introduce) in the coupling the impact of the deformation of the assemblies by the Temperature on the flow of liquid sodium, the use of the neutronic cross sections generated by the code APOLLO3, the study of other accidental cases, and extend the modeling to the subchannel and pin scales.
Study of substrate coupling in millimeter wireless circuits
The candidate will study substrate coupling in millimeter wireless circuit. He will demonstrate the influence of silicon substrate on millimeter circuit design
The first task will consist in establishing the state of the art of substrate reduction technics on millimeter chip. The influence between building blocks at layout level will be analyzed. Parasitic noise effects, frequency and power spurious will be studied with coupling substrate tool. Specifications for layout design in order to reduce spurious will be done, especially for power, analog and digital applications. A design methodology will be proposed with this results.
Development of a mechanical energy harvester based on a rotating machine architecture with permanent magnets
This Post-doc offer will be aimed at developing energy harvesters, and more especially electromagnetic energy harvesters with an operation mode close to the one of rotating machines with permanent magnets. The post-doc applicant will have a background in electrical engineering and an experience in rotating machines design, ideally, with permanent magnets.
The missions of the Post-doc applicant will be to:
1) Imagine and design small-scale innovative energy harvesters by exploiting the techniques used in rotating machines.
2) Model and optimize the devices
3) Characterize the systems
4) Participate to the industrialization process
Bio-compatible, bio-resorbable microbatteries for medical applications
In the framework of its activities dedicated to embedded micro-batteries, LETI initiates prospective research in the field of micro-batteries for medical applications, and in particular as energy power sources for implantable micro-devices. In this context, a collaborative project, including LETI labs and an academic Partner (ICMCB, Bordeaux), is aiming at designing, manufacturing and studying prototypes of bio-resorbable primary microbatteries.
The main tasks will include (i) a contribution to the design of the thin film electrochemical cell by the selection of adequate biocompatible materials (able to generate the targeted electrical power, corrodible and able to solubilize in the body), (ii) the manufacture of the cell constituents (electrodes, electrolyte, substrate) as thin films (sputtering, electrochemical plating, doctor blade coating) and their characterization,(iii) the achievement of full prototype cells and the study of their in vitro behaviour.
The work will be carried out at ICMCB (Bordeaux) in a joint CEA/ICMCB team, in collaboration with LETI labs in Grenoble.
Design / Technology Co-Optimization of SRAM and standard cells on stacked nanowires at the 5nm technology node
The post-doctoral position will focus on the layout of SRAM and standard cells dedicated to the 5nm node on stacked nanowires integrating a Direct Self-Assembly solution (DSA). He/she will use the SPICE model developed at LETI and interact with both model and process/integration teams to find the best layout for a set of cells.
Optimisation of the monolithic cascode device based on GaN/Si MOS-Channel HEMT technology
In order to adress the requirements of power conversion in the field of electrical vehicule or photovoltaics, high performance GaN on Silicon power devices need to be developped. Such power devices must fulfill agressive specifications in terms of threshold voltage (> 2V), nominal current (100-200A), breakdown voltage (650 and 1200V) and stability (low "current collapse", low hysteresis). Discrete cascode configuration, consisting in a combination of a low voltage E-mode Silicon die and a hihg voltage D-mode GaN/Si die in a single package, has been developped by different laboratories and companies to adress this need (Transphorm, On-Semi, NXP, IR…). However, this approach has some drawbacks like parasitic inductances, device pairing, need of additionnal protection devices, cost, temperature limitation due to the Si die...
The monolithic cascode is a very compact version of the cascode configuration that will allow to avoid those problems but also to improve the performance of E-mode devices developped at Leti (MOS-channel HEMT). Indeed, some actors in the field of GaN power devices already use this configuration with another E-mode technology (p-GaN gate).
Monolithic cascode device has been demonstrated recently by CEA-Leti in the frame of a PhD thesis (2014-2016) on the basis of the 200mm GaN/Si, CMOS compatible, MOS-channel HEMT technology. The aim of this post-doc is to optimize the monolithic cascode structure in terms of On-state resistance, Figure Of Merit, switching losses and high switching frequency capability in order to meet the specifications of our industrial partners.
Frequency tunable elastic plate wave resonators and filters
The increasing number of frequency bands having to be dealt with in mobile phone systems require a huge number of band pass filters in such systems. In this context, the capability to provide frequency tunable resonators and filters is seen as a key enabling element in future wireless transmission systems.
CEA-LETI has been working for more than 10 years on the development of resonators and filters exploiting the propagation of guided elastic waves in piezoelectric thin films. It has also proposed several concepts for frequency agile resonators and filters.
The purpose of this post-doc will be to further develop these ideas and to apply them to the design of demonstrators matching realistic specifications. In collaboration with the other member of the project team, more focused on fabrication in clean rooms, the candidate will propose innovative structures demonstrating frequency tuning of reconfigurability, and will take in charge their electrical characterization.