Topologically Isolated Mode Acoustic Resonators
Timing is a key function in electronic circuits. Beyond on-chip signals synchronization, it also allows the synchronization of wireless data transmissions. Accurate time references require stable frequency sources, which also benefit to sensor applications. The gold standard for time or frequency generation is still quartz resonators, which are however bulky and difficult to miniaturize. Research is therefore still ongoing to provide high quality factor (> 10,000) resonators, ideally capable of operating at frequencies of several GHz. A key to reach such high quality factors is to confine strongly the mechanical vibration of micro-size structures in order to make them insensitive to external perturbations. Recently, the field of topological acoustics has demonstrated the capability to confine elastic waves in very small volumes concentrated at the interface between periodic structure, and to provide extremely high quality factor resonances.
This PhD position focuses on exploiting topologically protected modes in piezoelectric microstructures to provide next generations of high quality factor resonators, which may be used in oscillators or even filter circuits. Leveraging the know-how of CEA Leti in the design and fabrication of such components, the PhD will be part of an international collaboration with well established academic laboratories (Politecnico di Milano, Imperial College FEMTO-ST Institute) and industrial partners.
The candidate will model and design structures supporting topologically protected modes, combinining finite element simulations with simplified numerical approaches which reduce computation times. He will follow the fabrication of demonstrators in collaboration with the process integration teams in the CEA Leti clean rooms, and carry on measurements of the proposed resonators.
SiGe HBT LNA for cryogenic applications: design, characterization and optimization
The global race to build a quantum computer is heating up! These cutting-edge systems operate at temperatures below 4 K to preserve the delicate quantum states essential for computation. To achieve efficient control and detection, conventional electronic circuits must perform reliably at cryogenic temperatures, in close proximity to the quantum processor, thereby reducing wiring complexity and boosting performance. Beyond quantum computing, other domains—such as space exploration, high-performance computing, or high-energy physics—also require transistors capable of operating below 100 K.
During this phD, you will perform radiofrequency (RF) electrical characterization and modeling of Silicon-Germanium Heterojunction Bipolar Transistors in cryogenic environment, contributing to a deeper understanding of their behavior and optimizing their potential for extreme-condition applications. The objectives are twofold:
1.RF Electrical Characterization and Modeling:
•Conduct RF electrical measurements of SiGe HBTs at cryogenic temperatures.
•Develop accurate models to describe their behavior in cryogenic environments.
2.Optimization of Low-Noise Amplifiers (LNAs):
•Study the low-temperature behavior of individual passive and active devices composing an LNA.
•Optimize the design of low-noise amplifiers (LNAs) for cryogenic applications.
Study of mechanical stress on Solid State Micro-batteries
CEA-Leti provides integrated microstorage solutions, including solid state (or solid electrolyte) microbatteries. Solid-state micro-batteries are among the most promising microstorage technologies for applications in several fields such as the internet of things and implantable devices for medical use. The objective of this thesis is to study the impact of mechanical stresses on microbatteries, particularly during microbattery charge/discharge cycles. To this end, two approaches will be considered: experimental study with the development of mechanical test benches and numerical simulation.
The PhD student's work will begin with the development of test benches, the first of which will apply variable pressure to the surface of a microbattery during charge/discharge cycles. He/she will be required to develop the pressure measurement equipment. Once the mechanical test bench is operational, other characterizations, such as measuring anode deformations, will be considered. In parallel with this experimental work, a mechanical model will be developed. This model will be progressively refined using the experimental results obtained with the mechanical test bench, and new characterizations may be implemented in order to obtain the mechanical properties of the different materials used. Ultimately, the objective will be to propose the integration of new layers to improve the mechanical performance of microbatteries during cycling.
Study of Failure Modes and Mechanisms in RF Switches Based on Phase-Change Materials
Switches based on phase change materials (PCM) demonstrate excellent RF performance (FOM <10fs) and can be co-integrated into the BEOL of CMOS processes. However, their reliability is still very little studied today. Failure modes such as heater breakage, segregation, or the appearance of cavities in the material are shown during endurance tests, but the mechanisms of these failures are not discussed. The objective of this thesis will therefore be to study the failure modes and mechanisms for different operating conditions (endurance, hold, power). The analysis will be carried out through electrical and physical characterizations and accelerated aging methods will be implemented.
Superconducting Silicon and detection in the far Infrared Universe
Silicon technologies occupy a central position in today’s digital landscape, both for the fabrication of semiconductor devices and for the development of advanced sensors. In 2006, the discovery of superconductivity in silicon heavily doped with boron opened a new field of research. Since then, several laboratories, including CEA, have been investigating its electronic properties and potential applications. This emerging material exhibits particularly attractive characteristics for systems operating at sub-Kelvin cryogenic temperatures, especially in the fields of quantum electronics and ultra-sensitive detectors used in fundamental physics and astrophysics.
Despite these advances, the understanding of superconducting silicon remains incomplete, particularly regarding its thermal, mechanical, and optical properties at the micrometric scale. The proposed PhD aims to address these gaps by combining modelling, design, technological fabrication, and cryogenic characterization of prototype devices, within a close collaboration between CEA-Léti and CEA-Irfu. The main objective will be to develop a new generation of detectors based on this superconducting material and to demonstrate their relevance for the detection of electromagnetic radiation in the terahertz and far-infrared ranges.
Reinventing Microspeakers: From Planar Limits to 3D Designs for Ultrasonic Modulation Loudspeakers
Are you looking for a PhD at the intersection of acoustics, microsystems, and innovation? This project may be for you.This PhD focuses on the design, fabrication, and experimental validation of an innovative MEMS microspeaker concept based on ultrasound demodulation. Conventional micro transducers face a major limitation: they require large planar surfaces to displace sufficient air at low frequencies, leading to increased device size and manufacturing cost. This project explores an alternative architecture using vertical blade structures, exploiting the third dimension together with ultrasound demodulation to improve electro acoustic efficiency while reducing device footprint.
Building on preliminary exploratory work, the objective of the PhD is to develop a complete MEMS loudspeaker demonstrator. The work will include physical modeling, multi-physics simulation, device design optimization, microfabrication process development, and experimental electro acoustic characterization. Particular attention will be given to identifying and overcoming the physical and technological limitations governing device performance.
The candidate will design and simulate the device architecture and contribute to the definition of the fabrication process in close interaction with microfabrication specialists. The PhD work will also include acoustic and electrical characterization of the fabricated devices in order to validate the proposed concepts and compare experimental results with modeling predictions. The PhD will take place in a multidisciplinary environment, providing access to expertise in acoustics, MEMS design, microfabrication processes, and electro acoustic measurement.
Dies to wafer direct bonding: from physical mechanisms to the development of thin stackable dies
Direct dies-to-wafer bonding has become, in recent years, a major development axis in microelectronics and at the heart of many LETI projects, both in silicon photonics and for 3D applications involving hybrid bonding.
Due to their small size, die bonding allows the study of direct bonding edge effects and the implementation of new direct bonding processes that can shed original light on the mechanisms of direct bonding, which are already well studied at LETI. From a more technological perspective, the development of thin stackable chips will also be a very interesting technological key for many applications. This approach is a clever alternative to classical damascene processes to address the challenges related to the planarization of surfaces with low density of high topographies.
Selective deposition of oxides by ALD
For next-generation microelectronics, Area Selective Deposition (ASD)is a promising approach to simplify integration schemes for the most advanced technology nodes. These ASD approaches need to be adapted according to a trio comprising the material to be deposited, the growth surface, and the inhibited surface.
This PhD focuses on the area selective deposition of oxides (such as SiO2, Al2O3, …) on Si or SiO2 and not on silicon nitride (SiN), which is one of the most complex topics in ASD, and aims to evaluate the relevance of this type of process for simplifying the integration and the fabrication of advanced FDSOI transistors.
To develop this selective oxide deposition process, various approaches aiming at making SiN an inhibitor of the Atomic Layer Deposition (ALD) will be explored (plasma treatments, Small Molecular Inhibitors, combination of both, etc.). Dedicated surface characterizations will be carried out in order to better understand the mechanisms of inhibition at the origin of the selective deposition and allowing to achieve high selectivity for oxide thicknesses of 10 nm and above.
This PhD project will take place at CEA-LETI, within the advanced materials deposition department, in collaboration with LMI UMR 5615 CNRS/UCBLyon. The student will have access to the CEA-LETI 300 mm cleanroom fabrication platforms for thin film deposition by PEALD, the CEA nanocharacterization platform and gas-phase surface functionalization at LMI. Surface analyses and thin film characterizations (ellipsometry, XRR, AFM, FTIR, contact angle, SEM, XPS, ToF-SIMS) will be used to determine the best selectivity and understand the physico-chemical mechanisms.
Acoustic and Ultrasound-based Predictive Maintenance Systems for Industrial Equipment
Power converters are essential in numerous applications such as industry, photovoltaic systems, electric vehicles, and data centers. Their conventional maintenance is often based on fixed schedules, leading to premature replacement of components and significant electronic waste.
This PhD project aims to develop a novel non-invasive and low-cost ultrasound-based monitoring approach to assess the state of health and remaining useful life (RUL) of power converters deployed across various industries.
The research will focus on identifying and characterizing ultrasonic signatures emitted by aging electronic components, and on developing physics-informed neural networks (PINNs) to model their degradation mechanisms. The project will combine experimental studies with advanced signal processing and AI techniques (compressed sensing), aiming to detect early signs of failure and enable predictive maintenance strategies executed locally (edge deployment).
The research will be carried out within a Marie Sklodowska-Curie Actions (MSCA) Doctoral Network, offering international training, interdisciplinary collaboration, and secondments at leading academic and industrial partners across Europe (Italy and Netherlands for this PhD offer).