Electric field and ab initio simulations, application to RRAM
Since several years, LETI/DCOS is engaged in a simulation effort of microscopic phenomena at the heart of oxide-based RRAM operation (made of HfO2, Ta2O5, Al2O3). The correct description of an external electric field applied to a MIM device (Metal-Insulator-Metal) is now possible thanks to two methods one by an orbital separation approach [1] the other by using the non equilibrium green function formalism [2]. In this work, we propose to develop and to handle these methods by combining already existing simulation approaches. The main goal is to study the degradation mechanisms of an oxide by following the oxygen atoms movements coupled directly to the applied external electric field. These mechanisms are not known and this study will support the optimization and characterization efforts already engaged at LETI on RRAM functional prototypes. The targeted simulations tools are SIESTA for the DFT part, and TB_SIM for the electronic transport part.
[1] S. Kasamatsu et al., « First principle calculation of charged capacitors under open-circuit using the orbital separation approach, PRB 92, 115124 (2015)
[2] M. Brandbyge et al., « Density functional method for nonequilibrium electron transport », PRB 65, 165401 (2002)
Aging study of silicon nanowires used as piezoresistive detection gauges for achieving inertial MEMS sensors.
Today’s sensors are present in all areas: housing, automotive... Thanks to recent developments in microelectronics, new generations of sensors combine high performance, small size and low cost. In this context, CEA-LETI has proposed an innovative concept called M&NEMS for the realization of inertial sensors such as accelerometers, magnetometers and gyroscopes. The M&Nems concept combines MEMS and NEMS to take advantage of the great inertia generated by a MEMS mass and the high detection sensitivity of piezoresistive silicon nanowires. Demonstrators have already been carried out and have shown the good potential of the M&Nems concept. One of the main challenges which remain to overcome is the reliability of sensors based on this concept and specifically the reliability of the piezoresistive nanowires. The research work will be mainly focused on the study of the failure modes of these piezoresistive nanowires gauges i.e. the identification of physical phenomena and the development of failure models. In order to do this study, a first preliminary work will be focused on the physical mechanisms which manage the electrical conduction in the nanowires: piezoresistivity, charge trapping, relaxation field effect ... The work will then continue by the study of the failure modes of nanowires, the goal will be to understand and model the physical aging of these nanowires: it will be possible to rely on the knowledge of the physics of nanowires conduction but also play with the physical parameters of these nanowires such as silicon doping, the process fabrication, the packaging technique, the thermomechanical stresses, the scale effect due to surface / volume ratio, or the surface condition. Finally, models of aging will allow proposing and validating technological choices to ensure the nanowires lifetime depending on operating conditions of the sensors.
Study of cooling solutions for compact electronic systems
3D technologies (i.e. electronic components vertically stacked) constitute an axis of global research, both at the architectural and manufacturing level. The Grenoble area is at the heart of these technological breakthroughs with world first prototypes that make Cea-Leti one of the leaders in these advanced technologies.
One of the critical points of this innovative technology is to control the thermal management in such 3D components regardless of the final application. Nowadays conventional solutions like adding a fan cannot fit all the thermal requirements, and may be of limited effectiveness. More integrated solutions are now unavoidable and can be considered from two points of view: heat can be managed directly at the component-level in silicon chips that make up the 3D-stack, or it can be managed at package level. Ideally, the two approaches should be combined.
The first objective of this study is to achieve an exhaustive state of the art and evaluate the potential of the different solutions for the components developed at Leti. This evaluation will be based on thermal simulations and a critical analysis based on technological feasibility, consumption, efficiency, cost,… and lead to choose the most appropriate solution.
The second part of the work will be dedicated to the implementation of this solution. Relying on experts of silicon and packaging technologies, the candidate will be responsible for contributing to the design of the component (design and implementation) and its characterization.
This position is for a researcher with a strong background in the areas of thermal and microelectronic components. This position requires analysis skills, a large autonomy and unifying skills.
Dual layer transfer of piezoelectric films for advanced RF devices
The aim of these workds is to study and develop an innovating concept of piezoelectric thin films multilayer transfer for RF applications.The applicant will be responsible for the development of the entire fabrication sequence of these multilayer structures and of the 3D RF components. To this end, he or she must master the physical mechanisms involved in the film transfer technology and design the complete architecture through simulation of the expected RF filters properties. Once the structure is defined and the technology backbone is mastered, the candidate will collaborate with Leti technology experts to identify the necessary process developments. He or she will then ensure their implementation in the fabrication technology platform and support the achievement of the most critical steps.
The development of this fabrication sequence will allow the generation of substrates whose features meet device specifications. The functionality of the substrates will then be demonstrated through the fabrication and characterization of RF devices that are relevant to the target applications.
Development of an hermetic thin flim packaging for RF MEMS switches
Leti has developed for many years a RF MEMS switch process which have demonstrated RF performances at the state-of-the-art as well as a process maturity level closed to industrial standards. To finalize its component and especially to ensure long-terms reliability level for space applications, Leti is today developing an innovative hermetic thin film packaging process.
The applicant will join a project team working on the development of this new technological brick. In a first step, the applicant will be in charge of the design of the process test vehicles, of the follow-up of their silicon batches fabrication in clean room and of their characterization during the process. In a second step, the applicant will perform a modeling study to optimize the design of the switches integrating this new packaging. In particular, he will propose new designs for mid RF power applications. Finally, the applicant will be in charge of the follow-up of the realization of silicon batches for the RF MEMS switches demonstrators. He will then supervise and participate to all the characterization studies on packaged components.
Outgassing studies for advanced lithography
This work address a "post doc" person. The frame work of this subject is a advanced lithography multifaisceaux Ebeam development project. Within this project framework, an multiEbeam tool is developed in a international partnership context.
Strong contamination constraints of the projection optic are identified due to resists outgassing during theirs activations by electronic expositions. Layers contamination due to resists outgassing will be studied. The candidate will be in charge to carry out outgassing studies on various resist samples in support to the existing team and using Leti outgassing studies tool and characterization tools available on Leti (BEM, XPS, interferometer,...).
Candidate will implement methodologies already developed in Leti (pumping speed, outgassed elements identification,...) and will make contribution to improvement all of these methods. It will also supervise realization of objects useful for outgassing studies(Ebeam projection optics simulator) which will be carried on Leti. The candidate will carry out electron beam characterization on the outgassing tool and could be force of proposal for improvement. He will also take charges characterization of contaminants layers. The candidate will evolved in advanced lithography context and will be in close collaboration with international teams. English is needed.
Micro-energy sources for biomedical applications
There is a growing interest towards wireless implantable systems for in vivo biomedical applications. However, such implantable systems have a limited lifetime determined by the battery capacity. CEA LITEN is working on innovative miniaturized systems integrating an energy harvesting component with a rechargeable battery. This type of micro-systems will be used for powering sensors or other implantable medical devices. The post-doctoral researcher will work on the design, the fabrication and the characterization of demonstrators consisting of the energy harvesting component, the battery and a power management circuit. Numerical simulations could also be performed, with the help of specialized engineers. The characterization of the demonstrators and the numerical simulation results will allow the post-doctoral researcher to propose innovative solutions for optimizing the system. The post-doctoral researcher will work in a multi-disciplinary team, which requires strong abilities for team working and communication.
Design of a new generation of MEMS flow or viscosity sensors
This Post-doc is defined to answer to various industrial requests for flow sensors and viscosity sensors working on a large range, low cost and able to measure different kind of fluids (liquid or gas).
The objective of this post-doc is to consider the design of a new generation of MEMS sensor for measuring flow or viscosity of any fluid that meets the specifications provided by the industry.
In particular, the possibilities of using a 3-axis micro-force sensor developed in the laboratory will be explored by exploiting the drag force or the tangential stresses near the walls of the pipes. Different cases will have to be evaluated depending on the flow dynamics of the different fluids.
A modeling and sizing of the sensor will have to be developed to determine the interactions with the fluids and the characteristics of the forces in the different flow rates.
The candidate should possess strong knowledge on fluidic and microsystems.
Study and evaluation of a micro resonator based thermal sensor for uncooled infrared imagery
The project aims at establishing the feasibility of a novel infrared microbolometer sensor exploiting the thermal sensitivity of a free oscillating micro-nano-mechanical system (M & NEMS), whose resonant frequency changes with the infrared flux it absorbs. This is a concept out who was the subject of three patents.
The project addresses the needs of high resolution uncooled infrared imaging sensors (spectral band ranging from 8µm to 12µm) which is presently in expansion but whose next generation of products is still waiting for a breakthrough to reduce the pixel size, a key factor to improve performance and reduce the cost.
The objective of this post doctoral study is to achieve a proof of concept of this new architecture. In this outlook, the study will cover first the sizing of the device, then its design, implementation and validation at a single pixel level.
Design of integrated photonics modules
Design of next generation optoelectronic transceivers (particularly on-board modules) requires the merging of two advanced technologies: Silicon Photonics and 3D Silicon Packaging, both being developed at Leti.
In order to meet the requirements in term of technical specifications, cost and density, it is needed to achieve a codesign involving mechanical, thermal, optical and mainly RF aspects.
The aim of the work consists in designing such integrated modules by optimizing the RF interconnections of the module (internal and external), and the proper setup of the integrated circuits (ASICs). Modelling of several architectures will be led under HFSS and ADS softwares.
Finally, the integration of the module into its system environnement will be taken in charge, so as its characterization (involving testboard and testbench design).