AlGaN/GaN HEMTs transfert for enhanced electrical and thermal performances
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.
Design for reliability for digital circuits
Flash memories are a key enabler for high-temperature applications such as data acquisition and engine control in aerospace, automotive and drilling industries. Unfortunately, the retention time of flash memories is very sensitive to high temperatures. Even at relatively moderated temperatures, flash memories may be affected by retention-related problems especially if they are set to store more than one bit per cell. This impact can be mitigated by periodically refreshing the stored data. The problem is that, in the presence of a variable operating temperature that could be due to variable environmental and workload conditions, a fixed data-refresh frequency may become disproportionately large with a subsequent impact on response time and cycling endurance.
The first objective of this project is to implement a data-refresh method based on a specially designed counter that is able to (a) track the evolution of the temperature and its impact on the data retention time of Flash memory blocks, (b) trigger warnings against potential retention time hazards and (c) provide timestamps.
The second objective is to find the distribution law that gives the evolution of the number of data retention errors in time. The goal is to implement a methodology able to infer the remaining retention time of flash memory pages based on their data retention age, i.e., the elapsed time since data was stored, and the number of retention and non-retention errors.
The publication of the scientific results in high-ranked conferences and journals is major project objective.
Physisorption of chemical species on sensitive surfaces during transfer in controlled mini-environment in microelectronics industry
A characterization platform based on the connection concept between process and characterization tools through the use of a transfer box under vacuum was implemented allowing a quasi in-situ characterization of substrates (wafers) of the microelectronics. Currently, this transfer concept based simply on static vacuum inside a carrier box is satisfactory regarding the residual O or C on the surface of especially sensitive materials (Ge, Ta, Sb, Ti…) and the MOCVD layers growth on GST or III/V surfaces. Its optimization for more stringent applications (molecular bonding, epitaxy…) in terms of contamination surface prevention requires studies the understanding of the physico-chemical evolution of the surfaces.
The proposed work will be focused on physico chemical studies of the evolution and molecular contamination of surfaces during transfers and will take place in clean room. XPS, TD-GCMS and MS coupled to the carrier itself (to be implemented) will be used to address the sources (wall, seals, gaseous environment…) of the adsorbed chemical species implied and to determine the physisorption mechanisms on the substrates. The studied surfaces will be sensitive to the contaminants in such a way than the box environment impact will be extracted and studied parameters will be the nature of polymer seal used, the carrier box thermal conditioning, the vacuum level, the use of low pressure gaseous environment in the carrier (gas nature, pressure level…).
Simulation of thermal exchange between fluid and structure in turbulent channels
There is presently a huge effort in Europe for the Development of high power (PW range), high repetition rate (1-10 Hz) lasers: the ELI project in three countries of Eastern Europe , the Apollon program in France have the objective to install multipetawatt high repetition rate lasers for scientific research and applications in various fields of physics. These large projects result in – and demand – an increased mastering of most challenging issues in laser technology; at high repetition rate one of the greatest issues consists in the cooling of the laser amplifiers for the highest repetition rates. In order to master this technology, CEA (Grenoble and Saclay, with a collaboration with Grenoble/LEGI) has decided to start an R&D program, with the following tasks to perform: (i) simulation of the cooling of amplifiers; (ii) validation of the calculations; (iii) design of an appropriate cooling system dedicated to future high power high repetition rate lasers: for this, cryogenic helium gas is a very interesting fluid, as working at low temperature for laser amplification allows a better thermal conductivity of the amplifiers (consequently a better uniformity of their temperature), and an increased efficiency of the laser amplification.
This postdoc position is associated with the first (simulation) task.
Development of a bimodal Brillouin-Raman microscope for biological tissue characterization
The Laboratory of Physics of Cytoskeleton and Morphogenesis (LPCV) at CEA Grenoble has an opening for setting up and characterizing a novel bioimaging modality combining Brillouin and Raman Spectroscopy. This is an interdisciplinary project between LPCV and the Laboratory of Imaging and Acquisition Systems (LISA) of CEA Grenoble. Brillouin microscopy allows non-invasive measurements of the visco-elastic properties of cells and tissue on the micrometer scale, while Raman microscopy gives complementary biochemical information. Such measurements have applications in the study of cytoskeleton organization, and for novel diagnostic tools based on following early mechanical and biochemical tissue alterations.
The postdoctoral scholar will be responsible for developing and coupling a Brillouin spectrometer to the Raman micro-spectrometer of LISA. This includes optical system development, instrument control and numerical data processing. He/She will characterize the instrument on model systems prepared at LPCV, and move forward to first in-cellulo experiments. The successful candidate is expected to coordinate the interaction between LPCV and LISA.
Development of femtosecond Fiber Bragg Grating acoustic receivers for the Structural Health Monitoring using passive acoustic tomography
The proposed post-doctoral fellowship is part of a transverse project initiated by the CEA and which consists in developing a prototype of a continuous monitoring system of a metallic structure (pipe for example) using fiber Bragg gratings acoustic receivers and passive imaging (or passive tomography). It aims to demonstrate the relevance of the SHM (Structural Health Monitoring) concept for nuclear facilities using optical fiber sensors operating in continuous and in extreme environment. This project is based on two recent developments: new generation of fiber Bragg gratings developed for severe environments and defect imaging algorithms based on ambient noise analysis. A demonstration of elastic wave reconstruction from passive algorithm applied to fiber Bragg gratings was carried out at the CEA in 2015, which is a world first, patented. The project aims more particularly to produce a demonstrator and to equip a pipeline on a test loop. It will provide input data relating to the ability of a moving fluid to generate elastic waves that can be analyzed in passive tomography.
Development of flexible solar panel for space application
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.
Simulation of supercritical helium flows in the cooling circuits of tokamaks
Future fusion reactors such as tokamaks (ITER, DEMO) will have to demonstrate the safety of their systems, validated by thermal hydraulic codes. To meet this requirement, the CATHARE code has been chosen as scientific computing tool. The work will consist in adapting the CATHARE code to helium at low temperatures and then to benchmark it with other thermal hydraulic codes used by the DRF (Direction de la Recherche Fondamentale), as well as with experimental data available at CEA Grenoble.
The study will be threefold. The first phase will be dedicated to a literature survey on the thermal hydraulics of helium, featured by closing equations for monophasic helium (friction and heat transfer coefficients). In a second step, the engineer will implement these laws in the code and perform some validations tests. The last part will focus a benchmark based on three applications: the study of a cryo-pump, the study of a supercritical helium discharge and the study of a superconducting cable.
Hardening energy efficient security features for the IoT in FDSOI 28nm technology
The security of the IoT connected objects must be energy efficient. But most of the work
around hardening by design show an additional cost, a multiplying factor of 2 to 5, on the
surface, performance, power and energy, which does not meet the constraints of the IoT.
Last 5 years research efforts on hardening have been guided by reducing silicon area or
power, which do not always imply a decrease in energy, predominant criterion in autonomous
connected objects. The postdoc topic addresses the hardening and energy consumption
optimization of the implementation of security functions (attack detection sensors,
cryptographic accelerator, random number generator, etc.) in 28nm FDSOI technology.
From the selection of existing security bricks, unhardened in FPGA technology, the postdoc
will explore hardening solutions at each step of the design flow in order to propose and
to validate, into a silicon demonstrator, the most energy efficient countermeasures that
guarantee a targeted security level.
To achieve those goals, the postdoc can rely on existing methodologies of design and of
security evaluation thanks to test benches and attack tools.