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.
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.
New generation of 3D ferroelectric memories (FeRAM) with fully BEOL-integrated 1T-1C bitcells
Ferroelectric memories of the FeRAM 1T-1C type based on HZO have the potential to replace the last levels of Cache. CEA-Leti is at the state of the art in this field at the 22nm node [1], with 1T-1C bitcells already denser than those of SRAM. In this approach, the selection transistor (1T) is a front-end transistor, and the three-dimensional ferroelectric capacitor (1C) is integrated in the back-end.
It has been shown by Micron [2] that the use of a three-dimensional back-end transistor made of polycrystalline silicon allows 1/ to densify the bitcell, 2/ to stack several levels of FeRAM, and 3/ to use the CMOS under the arrays for control logic (CMOS Under Array - CuA).
The objective of this thesis is to evaluate other types of selectors, in particular vertical amorphous oxide semiconductor field-effect transistors (AOSFETs) integrated in the back-end, for the new generations of FeRAM memories. The characteristics of these back-end transistors [3] (low Ioff, low Ion, low Vth) should offer significant advantages for the operation of FeRAM memory arrays at very low voltages (< 1V) while allowing the integration of very dense 1T-1C bitcells entirely in the back-end.
The thesis will primarily be oriented towards DTCO (Design Technology Co-Optimization) to propose dense bitcells using realistic integration schemes. It will also be able to rely on recent experimental results obtained at CEA, both on AOSFETs and on 3D ferroelectric capacitors [1], with a view to first silicon demonstrations.
[1] S. Martin et al., IEDM 2024; [2] N. Ramaswamy et al., IEDM 2023; [3] S. Deng et al., VLSI 2025
Physics-Informed Learning for Acoustic Inverse Problems: Field Reconstruction, Detection, and Detectability Analysis in Complex Environments
This PhD project aims to develop a mathematical and algorithmic framework for solving acoustic inverse problems in complex environments, based on physics-informed learning. By explicitly incorporating the wave equation into artificial intelligence architectures, the objective is to improve acoustic field reconstruction from partial measurements, the localization of mobile sources, and the quantitative analysis of their detectability. The project combines partial differential equation modeling, constrained optimization, and hybrid deep learning. Applications include distributed acoustic sensing systems and the detection of mobile platforms.
Reliability and dynamic properties of GaN high electron mobility transistors : backbarrier and substrate type impact
The rapid expansion of AI and cloud computing has placed unprecedented demands on data center infrastructure, where energy efficiency is now a defining constraint. Despite their potential, many power systems still rely on silicon-based devices, which suffer from inherent efficiency limitations that result in significant energy losses. GaN HEMTs, with their superior electron mobility and high breakdown voltage, represent a compelling alternative, capable of achieving far higher efficiencies in power conversion. However, their broader adoption is constrained by reliability challenges, particularly those arising from charge trapping mechanisms that degrade device performance over time.
In this PhD project, you will delve into the fundamental dynamics of charge carriers in GaN HEMTs, focusing on the physical origins of on-resistance and threshold voltage drifts—key indicators of device instability. By systematically analyzing the electrical behavior of these transistors under various operating conditions, you will uncover the mechanisms behind their degradation and identify pathways to enhance their robustness. Your findings will directly inform the optimization of device architectures, enabling the development of more efficient and reliable power electronics that can meet the demands of modern data centers and beyond.
You will be part of a multidisciplinary research team at CEA-Leti, collaborating with experts in semiconductor material engineering, device simulation, and electrical characterization. This environment will provide you with a comprehensive skill set, spanning process engineering, advanced electrical testing, and TCAD simulations, This position will not only expand your expertise but also position you at the forefront of a field with global impact. By contributing to the advancement of GaN HEMTs, you will play a key role in shaping the future of power electronics—where innovation directly translates into sustainable technological solutions.
Development of a bifunctionnal zwitterionic nano-coating for aptasensors - a new linker for biological probes that hinders non-specific adsorptions
The field of biosensor development frequently encounters the issue of non-specific signals. These signals often limits the performance of biosensors and complicates industrial transfers. The functionalization steps for biosensors design generally include three steps: i) functionalization of the transducer with a linker molecule, ii) immobilization of a biological probe (antibodies, aptamers, oligonucleotides...) using the linker, iii) treatment with an entity to block non-specific interactions. The literature is full of solutions that highlight the blocking of these non-specific interactions with different types of chemical or biological entities: proteins (BSA, casein...), polymers (PEG, PVP) or small molecules (ethanolamine, hexylamine...).
However, an alternative functionalization approach with a linker that offers both the ability to immobilize biological probes while ensuring the blocking of non-specific interactions represents an innovative path for the development of biosensors.
This PhD project aims to explore the design and surface functionalization with a bifunctional nano-coating responding to this approach. Regarding the blocking, zwitterionic polymers will be at the heart of the development. Indeed, numerous studies demonstrate their ability to drastically reduce the interactions of complex biological environments with surfaces that are functionalized with them. Furthermore, it is possible to exploit the chemical functions of certain types of zwitterions to immobilize biological probes on demand. After optimizing their activity in homogeneous phase, aptamers will be immobilized on silicon transducers (QCM-d and photonic chip) via the bifunctional zwitterionic nano-coating. The objective of the thesis is to obtain a proof of concept of a biosensor functionalized with this new linker that ensures the reduction of non-specific signals while ensuring the specific detection of the target considered (Tyrosinamide model) in model and complex environments derived from biomedical sector, such as serum or plasma.
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.
Advancing All-Solid-State Microbatteries: Interface Stabilization and Degradation Mitigation for Long-Term Reliability
This PhD project focuses on advancing all-solid-state microbatteries for miniaturized energy storage applications, such as wearable electronics, IoT systems, and implantable medical technologies. The research aims to stabilize and mitigate degradation at the electrode/electrolyte interfaces, which are critical bottlenecks in solid-state microbattery performance. The project involves two main research axes: (1) the study and optimization of ultrathin films (sub-nanometer to nanometer scale deposited by ALD) for engineering the interfaces in LiCoO2/LiPON/Li stacks, and (2) a fundamental investigation of the mechanisms responsible for interface degradation. The study will involve the fabrication and characterization of partial and complete stacks using techniques like cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The incorporation of alloying metals (e.g., Ag, Au) between the buffer layer and lithium will also be explored to enhance lithium-metal interface stability. The expected outcomes include an optimized microbattery stack capable of exceeding 1,000 cycles with minimal increase in interfacial resistance and a comprehensive framework describing degradation mechanisms and buffer layer effects.
Advanced SOI technologies: Design, Integration & Electrical characterization
Join CEA-Leti to develop a technological module (localized ground plane) for various applications (EU FDSOI, RF devices, ultra-miniaturized pixels, cryo-RF and quantum).
This PhD topic is challenging since you will design step by step a specific module and test it electrically. Our team will support you technically and scientifically to conduct this work. Some data are already available and waiting for your analysis.
During this PhD, you will have the opportunity to learn how a module/device is designed step by steps:
From the idea (simulation, bibliography)
Material & Processes understanding (bonding, CMP)
Integration & cleanroom fabrication management
Characterization (physical & electrical: mobility, interface traps)
Valorization (presentations, article)